1
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Sperry MM, Oskotsky TT, Marić I, Kaushal S, Takeda T, Horvath V, Powers RK, Rodas M, Furlong B, Soong M, Prabhala P, Goyal G, Carlson KE, Wong RJ, Kosti I, Le BL, Logue J, Hammond H, Frieman M, Stevenson DK, Ingber DE, Sirota M, Novak R. Target-agnostic drug prediction integrated with medical record analysis uncovers differential associations of statins with increased survival in COVID-19 patients. PLoS Comput Biol 2023; 19:e1011050. [PMID: 37146076 DOI: 10.1371/journal.pcbi.1011050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Revised: 05/17/2023] [Accepted: 03/27/2023] [Indexed: 05/07/2023] Open
Abstract
Drug repurposing requires distinguishing established drug class targets from novel molecule-specific mechanisms and rapidly derisking their therapeutic potential in a time-critical manner, particularly in a pandemic scenario. In response to the challenge to rapidly identify treatment options for COVID-19, several studies reported that statins, as a drug class, reduce mortality in these patients. However, it is unknown if different statins exhibit consistent function or may have varying therapeutic benefit. A Bayesian network tool was used to predict drugs that shift the host transcriptomic response to SARS-CoV-2 infection towards a healthy state. Drugs were predicted using 14 RNA-sequencing datasets from 72 autopsy tissues and 465 COVID-19 patient samples or from cultured human cells and organoids infected with SARS-CoV-2. Top drug predictions included statins, which were then assessed using electronic medical records containing over 4,000 COVID-19 patients on statins to determine mortality risk in patients prescribed specific statins versus untreated matched controls. The same drugs were tested in Vero E6 cells infected with SARS-CoV-2 and human endothelial cells infected with a related OC43 coronavirus. Simvastatin was among the most highly predicted compounds (14/14 datasets) and five other statins, including atorvastatin, were predicted to be active in > 50% of analyses. Analysis of the clinical database revealed that reduced mortality risk was only observed in COVID-19 patients prescribed a subset of statins, including simvastatin and atorvastatin. In vitro testing of SARS-CoV-2 infected cells revealed simvastatin to be a potent direct inhibitor whereas most other statins were less effective. Simvastatin also inhibited OC43 infection and reduced cytokine production in endothelial cells. Statins may differ in their ability to sustain the lives of COVID-19 patients despite having a shared drug target and lipid-modifying mechanism of action. These findings highlight the value of target-agnostic drug prediction coupled with patient databases to identify and clinically evaluate non-obvious mechanisms and derisk and accelerate drug repurposing opportunities.
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Affiliation(s)
- Megan M Sperry
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America
- Department of Biology, Tufts University, Medford, Massachusetts, United States of America
| | - Tomiko T Oskotsky
- Bakar Computational Health Sciences Institute, University of California San Francisco, San Francisco, California, United States of America
- Department of Pediatrics, University of California San Francisco, San Francisco, California, United States of America
| | - Ivana Marić
- Department of Pediatrics, School of Medicine, Stanford University, Stanford, California, United States of America
- Center for Academic Medicine, Stanford University School of Medicine, Stanford, California, United States of America
| | - Shruti Kaushal
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America
| | - Takako Takeda
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America
| | - Viktor Horvath
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America
| | - Rani K Powers
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America
| | - Melissa Rodas
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America
| | - Brooke Furlong
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America
| | - Mercy Soong
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America
| | - Pranav Prabhala
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America
| | - Girija Goyal
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America
| | - Kenneth E Carlson
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America
| | - Ronald J Wong
- Department of Pediatrics, School of Medicine, Stanford University, Stanford, California, United States of America
- Center for Academic Medicine, Stanford University School of Medicine, Stanford, California, United States of America
| | - Idit Kosti
- Bakar Computational Health Sciences Institute, University of California San Francisco, San Francisco, California, United States of America
- Department of Pediatrics, University of California San Francisco, San Francisco, California, United States of America
| | - Brian L Le
- Bakar Computational Health Sciences Institute, University of California San Francisco, San Francisco, California, United States of America
- Department of Pediatrics, University of California San Francisco, San Francisco, California, United States of America
| | - James Logue
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - Holly Hammond
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - Matthew Frieman
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - David K Stevenson
- Department of Pediatrics, School of Medicine, Stanford University, Stanford, California, United States of America
- Center for Academic Medicine, Stanford University School of Medicine, Stanford, California, United States of America
| | - Donald E Ingber
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America
- Vascular Biology Program and Department of Surgery, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts, United States of America
- Harvard John A. Paulson School of Engineering and Applied Sciences, Cambridge, Massachusetts, United States of America
| | - Marina Sirota
- Bakar Computational Health Sciences Institute, University of California San Francisco, San Francisco, California, United States of America
- Department of Pediatrics, University of California San Francisco, San Francisco, California, United States of America
| | - Richard Novak
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States of America
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2
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Lee AJ, Mould DL, Crawford J, Hu D, Powers RK, Doing G, Costello JC, Hogan DA, Greene CS. SOPHIE: Generative Neural Networks Separate Common and Specific Transcriptional Responses. Genomics Proteomics Bioinformatics 2022; 20:912-927. [PMID: 36216026 PMCID: PMC10025681 DOI: 10.1016/j.gpb.2022.09.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Revised: 09/09/2022] [Accepted: 09/30/2022] [Indexed: 11/06/2022]
Abstract
Genome-wide transcriptome profiling identifies genes that are prone to differential expression (DE) across contexts, as well as genes with changes specific to the experimental manipulation. Distinguishing genes that are specifically changed in a context of interest from common differentially expressed genes (DEGs) allows more efficient prediction of which genes are specific to a given biological process under scrutiny. Currently, common DEGs or pathways can only be identified through the laborious manual curation of experiments, an inordinately time-consuming endeavor. Here we pioneer an approach, Specific cOntext Pattern Highlighting In Expression data (SOPHIE), for distinguishing between common and specific transcriptional patterns using a generative neural network to create a background set of experiments from which a null distribution of gene and pathway changes can be generated. We apply SOPHIE to diverse datasets including those from human, human cancer, and bacterial pathogen Pseudomonas aeruginosa. SOPHIE identifies common DEGs in concordance with previously described, manually and systematically determined common DEGs. Further molecular validation indicates that SOPHIE detects highly specific but low-magnitude biologically relevant transcriptional changes. SOPHIE's measure of specificity can complement log2 fold change values generated from traditional DE analyses. For example, by filtering the set of DEGs, one can identify genes that are specifically relevant to the experimental condition of interest. Consequently, these results can inform future research directions. All scripts used in these analyses are available at https://github.com/greenelab/generic-expression-patterns. Users can access https://github.com/greenelab/sophie to run SOPHIE on their own data.
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Affiliation(s)
- Alexandra J Lee
- Genomics and Computational Biology Graduate Program, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Dallas L Mould
- Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA
| | - Jake Crawford
- Genomics and Computational Biology Graduate Program, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Dongbo Hu
- Department of Systems Pharmacology and Translational Therapeutics, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Rani K Powers
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA
| | - Georgia Doing
- Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA
| | - James C Costello
- Department of Pharmacology, University of Colorado School of Medicine, Denver, CO 80045, USA
| | - Deborah A Hogan
- Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA
| | - Casey S Greene
- Department of Systems Pharmacology and Translational Therapeutics, University of Pennsylvania, Philadelphia, PA 19104, USA; Center for Health AI, University of Colorado School of Medicine, Denver, CO 80045, USA; Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, Denver, CO 80045, USA.
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3
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Sperry MM, Oskotsky T, MariÄ I, Kaushal S, Takeda T, Horvath V, Powers RK, Rodas M, Furlong B, Soong M, Prabhala P, Goyal G, Carlson KE, Wong RJ, Kosti I, Le BL, Logue J, Hammond H, Frieman M, Stevenson DK, Ingber DE, Sirota M, Novak R. Target-agnostic drug prediction integrated with medical record analysis uncovers differential associations of statins with increased survival in COVID-19 patients. medRxiv 2022:2022.04.12.22273802. [PMID: 35441166 PMCID: PMC9016655 DOI: 10.1101/2022.04.12.22273802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Importance Drug repurposing requires distinguishing established drug class targets from novel molecule-specific mechanisms and rapidly derisking their therapeutic potential in a time-critical manner, particularly in a pandemic scenario. In response to the challenge to rapidly identify treatment options for COVID-19, several studies reported that statins, as a drug class, reduce mortality in these patients. However, it is unknown if different statins exhibit consistent function or may have varying therapeutic benefit. Objectives To test if different statins differ in their ability to exert protective effects based on molecular computational predictions and electronic medical record analysis. Main Outcomes and Measures A Bayesian network tool was used to predict drugs that shift the host transcriptomic response to SARS-CoV-2 infection towards a healthy state. Drugs were predicted using 14 RNA-sequencing datasets from 72 autopsy tissues and 465 COVID-19 patient samples or from cultured human cells and organoids infected with SARS-CoV-2, with a total of 2,436 drugs investigated. Top drug predictions included statins, which were then assessed using electronic medical records containing over 4,000 COVID-19 patients on statins to determine mortality risk in patients prescribed specific statins versus untreated matched controls. The same drugs were tested in Vero E6 cells infected with SARS-CoV-2 and human endothelial cells infected with a related OC43 coronavirus. Results Simvastatin was among the most highly predicted compounds (14/14 datasets) and five other statins, including atorvastatin, were predicted to be active in > 50% of analyses. Analysis of the clinical database revealed that reduced mortality risk was only observed in COVID-19 patients prescribed a subset of statins, including simvastatin and atorvastatin. In vitro testing of SARS-CoV-2 infected cells revealed simvastatin to be a potent direct inhibitor whereas most other statins were less effective. Simvastatin also inhibited OC43 infection and reduced cytokine production in endothelial cells. Conclusions and Relevance Different statins may differ in their ability to sustain the lives of COVID-19 patients despite having a shared drug target and lipid-modifying mechanism of action. These findings highlight the value of target-agnostic drug prediction coupled with patient databases to identify and clinically evaluate non-obvious mechanisms and derisk and accelerate drug repurposing opportunities.
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4
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Bein A, Fadel CW, Swenor B, Cao W, Powers RK, Camacho DM, Naziripour A, Parsons A, LoGrande N, Sharma S, Kim S, Jalili-Firoozinezhad S, Grant J, Breault DT, Iqbal J, Ali A, Denson LA, Moore SR, Prantil-Baun R, Goyal G, Ingber DE. Nutritional deficiency in an intestine-on-a-chip recapitulates injury hallmarks associated with environmental enteric dysfunction. Nat Biomed Eng 2022; 6:1236-1247. [PMID: 35739419 DOI: 10.1038/s41551-022-00899-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Accepted: 05/12/2022] [Indexed: 01/03/2023]
Abstract
Environmental enteric dysfunction (EED)-a chronic inflammatory condition of the intestine-is characterized by villus blunting, compromised intestinal barrier function and reduced nutrient absorption. Here we show that essential genotypic and phenotypic features of EED-associated intestinal injury can be reconstituted in a human intestine-on-a-chip lined by organoid-derived intestinal epithelial cells from patients with EED and cultured in nutrient-deficient medium lacking niacinamide and tryptophan. Exposure of the organ chip to such nutritional deficiencies resulted in congruent changes in six of the top ten upregulated genes that were comparable to changes seen in samples from patients with EED. Chips lined with healthy epithelium or with EED epithelium exposed to nutritional deficiencies resulted in severe villus blunting and barrier dysfunction, and in the impairment of fatty acid uptake and amino acid transport; and the chips with EED epithelium exhibited heightened secretion of inflammatory cytokines. The organ-chip model of EED-associated intestinal injury may facilitate the analysis of the molecular, genetic and nutritional bases of the disease and the testing of candidate therapeutics for it.
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Affiliation(s)
- Amir Bein
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA.,Quris Technologies, Boston, MA, USA
| | - Cicely W Fadel
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA.,Department of Pediatrics, Harvard Medical School, Boston, MA, USA.,Division of Neonatology, Beth Israel Deaconess Medical Center, Boston, MA, USA
| | - Ben Swenor
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Wuji Cao
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Rani K Powers
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA.,Pluto Biosciences, Inc., Golden, CO, USA
| | - Diogo M Camacho
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA.,Rheos Medicines, Cambridge, MA, USA
| | - Arash Naziripour
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Andrew Parsons
- Department of Pediatrics, Harvard Medical School, Boston, MA, USA
| | - Nina LoGrande
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Sanjay Sharma
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Seongmin Kim
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Sasan Jalili-Firoozinezhad
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA.,Department of Bioengineering and iBB - Institute for Bioengineering and Biosciences, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
| | - Jennifer Grant
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - David T Breault
- Department of Pediatrics, Harvard Medical School, Boston, MA, USA.,Division of Endocrinology, Boston Children's Hospital, Boston, MA, USA.,Harvard Stem Cell Institute, Harvard University, Boston, MA, USA
| | - Junaid Iqbal
- Department of Paediatrics and Child Health, The Aga Khan University, Karachi, Pakistan
| | - Asad Ali
- Department of Paediatrics and Child Health, The Aga Khan University, Karachi, Pakistan
| | - Lee A Denson
- Division of Gastroenterology, Hepatology, and Nutrition, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.,Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA
| | - Sean R Moore
- Department of Pediatrics, Division of Pediatric Gastroenterology, Hepatology, and Nutrition, University of Virginia, Charlottesville, VA, USA
| | - Rachelle Prantil-Baun
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Girija Goyal
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Donald E Ingber
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA. .,Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA. .,Vascular Biology Program and Department of Surgery, Harvard Medical School and Boston Children's Hospital, Boston, MA, USA.
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5
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Bai H, Si L, Jiang A, Belgur C, Zhai Y, Plebani R, Oh CY, Rodas M, Patil A, Nurani A, Gilpin SE, Powers RK, Goyal G, Prantil-Baun R, Ingber DE. Mechanical control of innate immune responses against viral infection revealed in a human lung alveolus chip. Nat Commun 2022; 13:1928. [PMID: 35396513 PMCID: PMC8993817 DOI: 10.1038/s41467-022-29562-4] [Citation(s) in RCA: 40] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Accepted: 03/23/2022] [Indexed: 12/24/2022] Open
Abstract
Mechanical breathing motions have a fundamental function in lung development and disease, but little is known about how they contribute to host innate immunity. Here we use a human lung alveolus chip that experiences cyclic breathing-like deformations to investigate whether physical forces influence innate immune responses to viral infection. Influenza H3N2 infection of mechanically active chips induces a cascade of host responses including increased lung permeability, apoptosis, cell regeneration, cytokines production, and recruitment of circulating immune cells. Comparison with static chips reveals that breathing motions suppress viral replication by activating protective innate immune responses in epithelial and endothelial cells, which are mediated in part through activation of the mechanosensitive ion channel TRPV4 and signaling via receptor for advanced glycation end products (RAGE). RAGE inhibitors suppress cytokines induction, while TRPV4 inhibition attenuates both inflammation and viral burden, in infected chips with breathing motions. Therefore, TRPV4 and RAGE may serve as new targets for therapeutic intervention in patients infected with influenza and other potential pandemic viruses that cause life-threatening lung inflammation. Mechanical forces in lungs facilitate breathing motions. Here the authors use a microfluidic human lung alveolus chip to study influenza infection and find that mechanical forces from active chips also induce innate inflammatory responses via, at least partially, signaling from TRPV4 and RAGE, thereby implicating them as potential therapeutic targets for lung inflammation.
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Affiliation(s)
- Haiqing Bai
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA
| | - Longlong Si
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA
| | - Amanda Jiang
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA.,Vascular Biology Program and Department of Surgery, Boston Children's Hospital, Harvard Medical School, Boston, MA, 02115, USA
| | - Chaitra Belgur
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA
| | - Yunhao Zhai
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA
| | - Roberto Plebani
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA.,Center on Advanced Studies and Technology (CAST), Department of Medical, Oral and Biotechnological Sciences, "G. d'Annunzio" University of Chieti-Pescara, Chieti, 66023, Italy
| | - Crystal Yuri Oh
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA
| | - Melissa Rodas
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA
| | - Aditya Patil
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA
| | - Atiq Nurani
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA
| | - Sarah E Gilpin
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA
| | - Rani K Powers
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA
| | - Girija Goyal
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA
| | - Rachelle Prantil-Baun
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA
| | - Donald E Ingber
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, 02115, USA. .,Vascular Biology Program and Department of Surgery, Boston Children's Hospital, Harvard Medical School, Boston, MA, 02115, USA. .,Harvard John A. Paulson School of Engineering and Applied Sciences, Cambridge, MA, 02138, USA.
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6
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Si L, Bai H, Oh CY, Zhang T, Hong F, Jiang A, Ye Y, Jordan TX, Logue J, McGrath M, Belgur C, Nurani A, Cao W, Prantil-Baun R, Gygi SP, Powers RK, Frieman M, tenOever BR, Ingber DE. Self-assembling short immunostimulatory duplex RNAs with broad spectrum antiviral activity. bioRxiv 2021:2021.11.19.469183. [PMID: 34845453 PMCID: PMC8629196 DOI: 10.1101/2021.11.19.469183] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The current COVID-19 pandemic highlights the need for broad-spectrum antiviral therapeutics. Here we describe a new class of self-assembling immunostimulatory short duplex RNAs that potently induce production of type I and type III interferon (IFN-I and IFN-III), in a wide range of human cell types. These RNAs require a minimum of 20 base pairs, lack any sequence or structural characteristics of known immunostimulatory RNAs, and instead require a unique conserved sequence motif (sense strand: 5'-C, antisense strand: 3'-GGG) that mediates end-to-end dimer self-assembly of these RNAs by Hoogsteen G-G base-pairing. The presence of terminal hydroxyl or monophosphate groups, blunt or overhanging ends, or terminal RNA or DNA bases did not affect their ability to induce IFN. Unlike previously described immunostimulatory siRNAs, their activity is independent of TLR7/8, but requires the RIG-I/IRF3 pathway that induces a more restricted antiviral response with a lower proinflammatory signature compared with poly(I:C). Immune stimulation mediated by these duplex RNAs results in broad spectrum inhibition of infections by many respiratory viruses with pandemic potential, including SARS-CoV-2, SARS-CoV, MERS-CoV, and influenza A, as well as the common cold virus HCoV-NL63 in both cell lines and human Lung Chips that mimic organ-level lung pathophysiology. These short dsRNAs can be manufactured easily, and thus potentially could be harnessed to produce broad-spectrum antiviral therapeutics at low cost.
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Affiliation(s)
- Longlong Si
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA
| | - Haiqing Bai
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA
| | - Crystal Yuri Oh
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA
| | - Tian Zhang
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Fan Hong
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA
| | - Amanda Jiang
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA
- Vascular Biology Program and Department of Surgery, Boston Children’s Hospital and Harvard Medical School, Boston, MA 02115, USA
| | - Yongxin Ye
- Department of Genetics, Harvard Medical School, Boston, MA 02155, USA
| | - Tristan X. Jordan
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - James Logue
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Marisa McGrath
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Chaitra Belgur
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA
| | - Atiq Nurani
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA
| | - Wuji Cao
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA
| | - Rachelle Prantil-Baun
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA
| | - Steven P Gygi
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Rani K. Powers
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA
| | - Matthew Frieman
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Benjamin R. tenOever
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Donald E. Ingber
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA
- Harvard John A. Paulson School of Engineering and Applied Sciences, Cambridge, MA 02139, USA
- Vascular Biology Program and Department of Surgery, Boston Children’s Hospital and Harvard Medical School, Boston, MA 02115, USA
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7
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Si L, Bai H, Rodas M, Cao W, Oh CY, Jiang A, Moller R, Hoagland D, Oishi K, Horiuchi S, Uhl S, Blanco-Melo D, Albrecht RA, Liu WC, Jordan T, Nilsson-Payant BE, Golynker I, Frere J, Logue J, Haupt R, McGrath M, Weston S, Zhang T, Plebani R, Soong M, Nurani A, Kim SM, Zhu DY, Benam KH, Goyal G, Gilpin SE, Prantil-Baun R, Gygi SP, Powers RK, Carlson KE, Frieman M, tenOever BR, Ingber DE. A human-airway-on-a-chip for the rapid identification of candidate antiviral therapeutics and prophylactics. Nat Biomed Eng 2021; 5:815-829. [PMID: 33941899 PMCID: PMC8387338 DOI: 10.1038/s41551-021-00718-9] [Citation(s) in RCA: 174] [Impact Index Per Article: 58.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Accepted: 03/19/2021] [Indexed: 02/05/2023]
Abstract
The rapid repurposing of antivirals is particularly pressing during pandemics. However, rapid assays for assessing candidate drugs typically involve in vitro screens and cell lines that do not recapitulate human physiology at the tissue and organ levels. Here we show that a microfluidic bronchial-airway-on-a-chip lined by highly differentiated human bronchial-airway epithelium and pulmonary endothelium can model viral infection, strain-dependent virulence, cytokine production and the recruitment of circulating immune cells. In airway chips infected with influenza A, the co-administration of nafamostat with oseltamivir doubled the treatment-time window for oseltamivir. In chips infected with pseudotyped severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), clinically relevant doses of the antimalarial drug amodiaquine inhibited infection but clinical doses of hydroxychloroquine and other antiviral drugs that inhibit the entry of pseudotyped SARS-CoV-2 in cell lines under static conditions did not. We also show that amodiaquine showed substantial prophylactic and therapeutic activities in hamsters challenged with native SARS-CoV-2. The human airway-on-a-chip may accelerate the identification of therapeutics and prophylactics with repurposing potential.
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Affiliation(s)
- Longlong Si
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Haiqing Bai
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Melissa Rodas
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Wuji Cao
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Crystal Yuri Oh
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Amanda Jiang
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
- Vascular Biology Program and Department of Surgery, Boston Children's Hospital and Harvard Medical School, Boston, MA, USA
| | - Rasmus Moller
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Daisy Hoagland
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Kohei Oishi
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Shu Horiuchi
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Skyler Uhl
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Daniel Blanco-Melo
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Randy A Albrecht
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Wen-Chun Liu
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Tristan Jordan
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | | | - Ilona Golynker
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Justin Frere
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - James Logue
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Robert Haupt
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Marisa McGrath
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Stuart Weston
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Tian Zhang
- Department of Cell Biology, Harvard Medical School, Boston, MA, USA
| | - Roberto Plebani
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
- Center on Advanced Studies and Technology (CAST), Department of Medical, Oral and Biotechnological Sciences, "G. d'Annunzio" University of Chieti-Pescara, Chieti, Italy
| | - Mercy Soong
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Atiq Nurani
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Seong Min Kim
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Danni Y Zhu
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Kambez H Benam
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
- Division of Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA
| | - Girija Goyal
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Sarah E Gilpin
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Rachelle Prantil-Baun
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Steven P Gygi
- Department of Cell Biology, Harvard Medical School, Boston, MA, USA
| | - Rani K Powers
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Kenneth E Carlson
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
| | - Matthew Frieman
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Benjamin R tenOever
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Donald E Ingber
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA.
- Vascular Biology Program and Department of Surgery, Boston Children's Hospital and Harvard Medical School, Boston, MA, USA.
- Harvard John A. Paulson School of Engineering and Applied Sciences, Cambridge, MA, USA.
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8
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Bojar D, Powers RK, Camacho DM, Collins JJ. Deep-Learning Resources for Studying Glycan-Mediated Host-Microbe Interactions. Cell Host Microbe 2021; 29:132-144.e3. [DOI: 10.1016/j.chom.2020.10.004] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Revised: 09/09/2020] [Accepted: 10/08/2020] [Indexed: 02/07/2023]
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9
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Powers RK, Culp-Hill R, Ludwig MP, Smith KP, Waugh KA, Minter R, Tuttle KD, Lewis HC, Rachubinski AL, Granrath RE, Carmona-Iragui M, Wilkerson RB, Kahn DE, Joshi M, Lleó A, Blesa R, Fortea J, D'Alessandro A, Costello JC, Sullivan KD, Espinosa JM. Trisomy 21 activates the kynurenine pathway via increased dosage of interferon receptors. Nat Commun 2019; 10:4766. [PMID: 31628327 PMCID: PMC6800452 DOI: 10.1038/s41467-019-12739-9] [Citation(s) in RCA: 63] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Accepted: 09/23/2019] [Indexed: 12/14/2022] Open
Abstract
Trisomy 21 (T21) causes Down syndrome (DS), affecting immune and neurological function by ill-defined mechanisms. Here we report a large metabolomics study of plasma and cerebrospinal fluid, showing in independent cohorts that people with DS produce elevated levels of kynurenine and quinolinic acid, two tryptophan catabolites with potent immunosuppressive and neurotoxic properties, respectively. Immune cells of people with DS overexpress IDO1, the rate-limiting enzyme in the kynurenine pathway (KP) and a known interferon (IFN)-stimulated gene. Furthermore, the levels of IFN-inducible cytokines positively correlate with KP dysregulation. Using metabolic tracing assays, we show that overexpression of IFN receptors encoded on chromosome 21 contribute to enhanced IFN stimulation, thereby causing IDO1 overexpression and kynurenine overproduction in cells with T21. Finally, a mouse model of DS carrying triplication of IFN receptors exhibits KP dysregulation. Together, our results reveal a mechanism by which T21 could drive immunosuppression and neurotoxicity in DS.
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Affiliation(s)
- Rani K Powers
- Linda Crnic Institute for Down Syndrome, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.,Computational Bioscience Program, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.,Department of Pharmacology, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Rachel Culp-Hill
- Department of Biochemistry and Molecular Genetics, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Michael P Ludwig
- Linda Crnic Institute for Down Syndrome, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.,Department of Pharmacology, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Keith P Smith
- Linda Crnic Institute for Down Syndrome, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Katherine A Waugh
- Linda Crnic Institute for Down Syndrome, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Ross Minter
- Linda Crnic Institute for Down Syndrome, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Kathryn D Tuttle
- Linda Crnic Institute for Down Syndrome, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Hannah C Lewis
- Linda Crnic Institute for Down Syndrome, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Angela L Rachubinski
- Linda Crnic Institute for Down Syndrome, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.,Department of Pediatrics, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Ross E Granrath
- Linda Crnic Institute for Down Syndrome, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - María Carmona-Iragui
- Department of Neurology, Hospital de la Santa Creu i Sant Pau, Biomedical Research Institute Sant Pau, Universitat Autonoma de Barcelona, CIBERNED, Barcelona, Spain.,Barcelona Down Medical Center, Catalan Down Syndrome Foundation, Barcelona, Spain
| | - Rebecca B Wilkerson
- Department of Biochemistry and Molecular Genetics, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Darcy E Kahn
- Linda Crnic Institute for Down Syndrome, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Molishree Joshi
- Functional Genomics Facility, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Alberto Lleó
- Department of Neurology, Hospital de la Santa Creu i Sant Pau, Biomedical Research Institute Sant Pau, Universitat Autonoma de Barcelona, CIBERNED, Barcelona, Spain
| | - Rafael Blesa
- Department of Neurology, Hospital de la Santa Creu i Sant Pau, Biomedical Research Institute Sant Pau, Universitat Autonoma de Barcelona, CIBERNED, Barcelona, Spain
| | - Juan Fortea
- Department of Neurology, Hospital de la Santa Creu i Sant Pau, Biomedical Research Institute Sant Pau, Universitat Autonoma de Barcelona, CIBERNED, Barcelona, Spain.,Barcelona Down Medical Center, Catalan Down Syndrome Foundation, Barcelona, Spain
| | - Angelo D'Alessandro
- Linda Crnic Institute for Down Syndrome, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.,Department of Biochemistry and Molecular Genetics, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - James C Costello
- Computational Bioscience Program, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.,Department of Pharmacology, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Kelly D Sullivan
- Linda Crnic Institute for Down Syndrome, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA. .,Department of Pharmacology, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA. .,Department of Pediatrics, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA. .,Functional Genomics Facility, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.
| | - Joaquin M Espinosa
- Linda Crnic Institute for Down Syndrome, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA. .,Department of Pharmacology, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA. .,Functional Genomics Facility, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA. .,Department of Molecular, Cellular and Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA.
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10
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Abstract
Motivation Gene Set Enrichment Analysis (GSEA) is routinely used to analyze and interpret coordinate pathway-level changes in transcriptomics experiments. For an experiment where less than seven samples per condition are compared, GSEA employs a competitive null hypothesis to test significance. A gene set enrichment score is tested against a null distribution of enrichment scores generated from permuted gene sets, where genes are randomly selected from the input experiment. Looking across a variety of biological conditions, however, genes are not randomly distributed with many showing consistent patterns of up- or down-regulation. As a result, common patterns of positively and negatively enriched gene sets are observed across experiments. Placing a single experiment into the context of a relevant set of background experiments allows us to identify both the common and experiment-specific patterns of gene set enrichment. Results We compiled a compendium of 442 small molecule transcriptomic experiments and used GSEA to characterize common patterns of positively and negatively enriched gene sets. To identify experiment-specific gene set enrichment, we developed the GSEA-InContext method that accounts for gene expression patterns within a background set of experiments to identify statistically significantly enriched gene sets. We evaluated GSEA-InContext on experiments using small molecules with known targets to show that it successfully prioritizes gene sets that are specific to each experiment, thus providing valuable insights that complement standard GSEA analysis. Availability and implementation GSEA-InContext implemented in Python, Supplementary results and the background expression compendium are available at: https://github.com/CostelloLab/GSEA-InContext.
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Affiliation(s)
- Rani K Powers
- Computational Bioscience Program, University of Colorado Anschutz Medical Campus, Aurora, CO, USA.,Department of Pharmacology, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Andrew Goodspeed
- Department of Pharmacology, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Harrison Pielke-Lombardo
- Computational Bioscience Program, University of Colorado Anschutz Medical Campus, Aurora, CO, USA.,Department of Pharmacology, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Aik-Choon Tan
- Department of Medical Oncology, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - James C Costello
- Computational Bioscience Program, University of Colorado Anschutz Medical Campus, Aurora, CO, USA.,Department of Pharmacology, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
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11
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Ravanelli AM, Kearns CA, Powers RK, Wang Y, Hines JH, Donaldson MJ, Appel B. Sequential specification of oligodendrocyte lineage cells by distinct levels of Hedgehog and Notch signaling. Dev Biol 2018; 444:93-106. [PMID: 30347186 DOI: 10.1016/j.ydbio.2018.10.004] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Revised: 10/11/2018] [Accepted: 10/11/2018] [Indexed: 01/18/2023]
Abstract
During development of the central nervous system oligodendrocyte precursor cells (OPCs) give rise to both myelinating oligodendrocytes and NG2 glia, which are the most proliferative cells in the adult mammalian brain. NG2 glia retain characteristics of OPCs, and some NG2 glia produce oligodendrocytes, but many others persist throughout adulthood. Why some OPCs differentiate as oligodendrocytes during development whereas others persist as OPCs and acquire characteristics of NG2 glia is not known. Using zebrafish spinal cord as a model, we found that OPCs that differentiate rapidly as oligodendrocytes and others that remain as OPCs arise in sequential waves from distinct neural progenitors. Additionally, oligodendrocyte and persistent OPC fates are specified during a defined critical period by small differences in Shh signaling and Notch activity, which modulates Shh signaling response. Thus, our data indicate that OPCs fated to produce oligodendrocytes or remain as OPCs during development are specified as distinct cell types, raising the possibility that the myelinating potential of OPCs is set by graded Shh signaling activity.
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Affiliation(s)
- Andrew M Ravanelli
- Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Christina A Kearns
- Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Rani K Powers
- Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Yuying Wang
- Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Jacob H Hines
- Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Maranda J Donaldson
- Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Bruce Appel
- Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO 80045, USA.
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12
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Morgan MJ, Fitzwalter BE, Owens CR, Powers RK, Sottnik JL, Gamez G, Costello JC, Theodorescu D, Thorburn A. Metastatic cells are preferentially vulnerable to lysosomal inhibition. Proc Natl Acad Sci U S A 2018; 115:E8479-E8488. [PMID: 30127018 PMCID: PMC6130375 DOI: 10.1073/pnas.1706526115] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Molecular alterations that confer phenotypic advantages to tumors can also expose specific therapeutic vulnerabilities. To search for potential treatments that would selectively affect metastatic cells, we examined the sensitivity of lineage-related human bladder cancer cell lines with different lung colonization abilities to chloroquine (CQ) or bafilomycin A1, which are inhibitors of lysosome function and autophagy. Both CQ and bafilomycin A1 were more cytotoxic in vitro to highly metastatic cells compared with their less metastatic counterparts. Genetic inactivation of macroautophagy regulators and lysosomal proteins indicated that this was due to greater reliance on the lysosome but not upon macroautophagy. To identify the mechanism underlying these effects, we generated cells resistant to CQ in vitro. Surprisingly, selection for in vitro CQ resistance was sufficient to alter gene expression patterns such that unsupervised cluster analysis of whole-transcriptome data indicated that selection for CQ resistance alone created tumor cells that were more similar to the poorly metastatic parental cells from which the metastatic cells were derived; importantly, these tumor cells also had diminished metastatic ability in vivo. These effects were mediated in part by differential expression of the transcriptional regulator ID4 (inhibitor of DNA binding 4); depletion of ID4 both promoted in vitro CQ sensitivity and restored lung colonization and metastasis of CQ-resistant cells. These data demonstrate that selection for metastasis ability confers selective vulnerability to lysosomal inhibitors and identify ID4 as a potential biomarker for the use of lysosomal inhibitors to reduce metastasis in patients.
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Affiliation(s)
- Michael J Morgan
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO 80045;
- University of Colorado Comprehensive Cancer Center, Aurora, CO 80045
| | - Brent E Fitzwalter
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO 80045
| | - Charles R Owens
- University of Colorado Comprehensive Cancer Center, Aurora, CO 80045
| | - Rani K Powers
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO 80045
- Computational Bioscience Program, University of Colorado School of Medicine, Aurora, CO 80045
| | - Joseph L Sottnik
- University of Colorado Comprehensive Cancer Center, Aurora, CO 80045
| | - Graciela Gamez
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO 80045
| | - James C Costello
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO 80045
- University of Colorado Comprehensive Cancer Center, Aurora, CO 80045
- Computational Bioscience Program, University of Colorado School of Medicine, Aurora, CO 80045
| | - Dan Theodorescu
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO 80045;
- University of Colorado Comprehensive Cancer Center, Aurora, CO 80045
| | - Andrew Thorburn
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO 80045
- University of Colorado Comprehensive Cancer Center, Aurora, CO 80045
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13
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Camacho DM, Collins KM, Powers RK, Costello JC, Collins JJ. Next-Generation Machine Learning for Biological Networks. Cell 2018; 173:1581-1592. [PMID: 29887378 DOI: 10.1016/j.cell.2018.05.015] [Citation(s) in RCA: 444] [Impact Index Per Article: 74.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Revised: 03/10/2018] [Accepted: 05/07/2018] [Indexed: 02/07/2023]
Abstract
Machine learning, a collection of data-analytical techniques aimed at building predictive models from multi-dimensional datasets, is becoming integral to modern biological research. By enabling one to generate models that learn from large datasets and make predictions on likely outcomes, machine learning can be used to study complex cellular systems such as biological networks. Here, we provide a primer on machine learning for life scientists, including an introduction to deep learning. We discuss opportunities and challenges at the intersection of machine learning and network biology, which could impact disease biology, drug discovery, microbiome research, and synthetic biology.
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Affiliation(s)
- Diogo M Camacho
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA
| | - Katherine M Collins
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA; Department of Brain & Cognitive Sciences and Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Rani K Powers
- Computational Bioscience Program, Department of Pharmacology, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA
| | - James C Costello
- Computational Bioscience Program, Department of Pharmacology, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA.
| | - James J Collins
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA; Department of Biological Engineering and Institute for Medical Engineering & Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA.
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14
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Vartuli RL, Zhou H, Zhang L, Powers RK, Klarquist J, Rudra P, Vincent MY, Ghosh D, Costello JC, Kedl RM, Slansky JE, Zhao R, Ford HL. Eya3 promotes breast tumor-associated immune suppression via threonine phosphatase-mediated PD-L1 upregulation. J Clin Invest 2018; 128:2535-2550. [PMID: 29757193 DOI: 10.1172/jci96784] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 03/22/2018] [Indexed: 12/12/2022] Open
Abstract
Eya proteins are critical developmental regulators that are highly expressed in embryogenesis but downregulated after development. Amplification and/or re-expression of Eyas occurs in many tumor types. In breast cancer, Eyas regulate tumor progression by acting as transcriptional cofactors and tyrosine phosphatases. Intriguingly, Eyas harbor a separate threonine (Thr) phosphatase activity, which was previously implicated in innate immunity. Here we describe what we believe to be a novel role for Eya3 in mediating triple-negative breast cancer-associated immune suppression. Eya3 loss decreases tumor growth in immune-competent mice and is associated with increased numbers of infiltrated CD8+ T cells, which, when depleted, reverse the effects of Eya3 knockdown. Mechanistically, Eya3 utilizes its Thr phosphatase activity to dephosphorylate Myc at pT58, resulting in a stabilized form. We show that Myc is required for Eya3-mediated increases in PD-L1, and that rescue of PD-L1 in Eya3-knockdown cells restores tumor progression. Finally, we demonstrate that Eya3 significantly correlates with PD-L1 in human breast tumors, and that tumors expressing high levels of Eya3 have a decreased CD8+ T cell signature. Our data uncover a role for Eya3 in mediating tumor-associated immune suppression, and suggest that its inhibition may enhance checkpoint therapies.
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Affiliation(s)
- Rebecca L Vartuli
- Department of Pharmacology, University of Colorado Denver, Aurora, Colorado, USA.,Molecular Biology Program
| | - Hengbo Zhou
- Department of Pharmacology, University of Colorado Denver, Aurora, Colorado, USA.,Cancer Biology Program
| | - Lingdi Zhang
- Department of Biochemistry and Molecular Genetics
| | - Rani K Powers
- Department of Pharmacology, University of Colorado Denver, Aurora, Colorado, USA.,Computational Bioscience Graduate Program
| | | | - Pratyaydipta Rudra
- Department of Biostatistics and Informatics, Colorado School of Public Health, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Melanie Y Vincent
- Department of Pharmacology, University of Colorado Denver, Aurora, Colorado, USA
| | - Debashis Ghosh
- Department of Biostatistics and Informatics, Colorado School of Public Health, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - James C Costello
- Department of Pharmacology, University of Colorado Denver, Aurora, Colorado, USA.,Cancer Biology Program.,Computational Bioscience Graduate Program
| | - Ross M Kedl
- Department of Immunology and Microbiology, and
| | - Jill E Slansky
- Cancer Biology Program.,Department of Immunology and Microbiology, and
| | - Rui Zhao
- Molecular Biology Program.,Department of Biochemistry and Molecular Genetics
| | - Heide L Ford
- Department of Pharmacology, University of Colorado Denver, Aurora, Colorado, USA.,Molecular Biology Program.,Cancer Biology Program.,Department of Biochemistry and Molecular Genetics
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15
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Mottram CJ, Heckman CJ, Powers RK, Rymer WZ, Suresh NL. Disturbances of motor unit rate modulation are prevalent in muscles of spastic-paretic stroke survivors. J Neurophysiol 2014; 111:2017-28. [PMID: 24572092 DOI: 10.1152/jn.00389.2013] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Stroke survivors often exhibit abnormally low motor unit firing rates during voluntary muscle activation. Our purpose was to assess the prevalence of saturation in motor unit firing rates in the spastic-paretic biceps brachii muscle of stroke survivors. To achieve this objective, we recorded the incidence and duration of impaired lower- and higher-threshold motor unit firing rate modulation in spastic-paretic, contralateral, and healthy control muscle during increases in isometric force generated by the elbow flexor muscles. Impaired firing was considered to have occurred when firing rate became constant (i.e., saturated), despite increasing force. The duration of impaired firing rate modulation in the lower-threshold unit was longer for spastic-paretic (3.9 ± 2.2 s) than for contralateral (1.4 ± 0.9 s; P < 0.001) and control (1.1 ± 1.0 s; P = 0.005) muscles. The duration of impaired firing rate modulation in the higher-threshold unit was also longer for the spastic-paretic (1.7 ± 1.6 s) than contralateral (0.3 ± 0.3 s; P = 0.007) and control (0.1 ± 0.2 s; P = 0.009) muscles. This impaired firing rate of the lower-threshold unit arose, despite an increase in the overall descending command, as shown by the recruitment of the higher-threshold unit during the time that the lower-threshold unit was saturating, and by the continuous increase in averages of the rectified EMG of the biceps brachii muscle throughout the rising phase of the contraction. These results suggest that impairments in firing rate modulation are prevalent in motor units of spastic-paretic muscle, even when the overall descending command to the muscle is increasing.
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Affiliation(s)
- C J Mottram
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois;
| | - C J Heckman
- Departments of Physiology, Physical Medicine and Rehabilitation, and Physical Therapy and Human Movement Sciences, Northwestern University Feinberg School of Medicine, Chicago, Illinois
| | - R K Powers
- Department of Physiology & Biophysics, University of Washington, Seattle, Washington; and
| | - W Z Rymer
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois; Department of Physical Medicine and Rehabilitation, Northwestern University, Feinberg School of Medicine, Chicago, Illinois
| | - N L Suresh
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois
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16
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Türker KS, Powers RK. Black box revisited: a technique for estimating postsynaptic potentials in neurons. Trends Neurosci 2005; 28:379-86. [PMID: 15927277 DOI: 10.1016/j.tins.2005.05.007] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2005] [Revised: 04/21/2005] [Accepted: 05/18/2005] [Indexed: 11/20/2022]
Abstract
Our understanding of the operation of the brain depends on knowledge of its wiring. Currently, the wiring of the human brain is estimated by counting the number of neuron discharges that occur at specific times following a stimulus. There is now strong evidence that this approach generates significant errors. Recently, the accuracy of this 'count' method has been compared directly with an alternative 'rate' method in rat brain slices. The results confirmed that the count method generates significant errors that are minimized by the rate method, because the rate of discharge of a neuron accurately displays its excitability at the time of discharge. Therefore, it is now crucial that the rate method be used to reassess previous estimates of the characteristics of wiring in the brain.
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Affiliation(s)
- K S Türker
- Discipline of Physiology, School of Molecular and Biomedical Sciences, University of Adelaide, SA 5005, Australia.
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17
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Powers RK, Dai Y, Bell BM, Percival DB, Binder MD. Contributions of the input signal and prior activation history to the discharge behaviour of rat motoneurones. J Physiol 2004; 562:707-24. [PMID: 15611038 PMCID: PMC1665549 DOI: 10.1113/jphysiol.2004.069039] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The principal computational operation of neurones is the transformation of synaptic inputs into spike train outputs. The probability of spike occurrence in neurones is determined by the time course and magnitude of the total current reaching the spike initiation zone. The features of this current that are most effective in evoking spikes can be determined by injecting a Gaussian current waveform into a neurone and using spike-triggered reverse correlation to calculate the average current trajectory (ACT) preceding spikes. The time course of this ACT (and the related first-order Wiener kernel) provides a general description of a neurone's response to dynamic stimuli. In many different neurones, the ACT is characterized by a shallow hyperpolarizing trough followed by a more rapid depolarizing peak immediately preceding the spike. The hyperpolarizing phase is thought to reflect an enhancement of excitability by partial removal of sodium inactivation. Alternatively, this feature could simply reflect the fact that interspike intervals that are longer than average can only occur when the current is lower than average toward the end of the interspike interval. Thus, the ACT calculated for the entire spike train displays an attenuated version of the hyperpolarizing trough associated with the long interspike intervals. This alternative explanation for the characteristic shape of the ACT implies that it depends upon the time since the previous spike, i.e. the ACT reflects both previous stimulus history and previous discharge history. The present study presents results based on recordings of noise-driven discharge in rat hypoglossal motoneurones that support this alternative explanation. First, we show that the hyperpolarizing trough is larger in ACTs calculated from spikes preceded by long interspike intervals, and minimal or absent in those based on short interspike intervals. Second, we show that the trough is present for ACTs calculated from the discharge of a threshold-crossing neurone model with a postspike afterhyperpolarization (AHP), but absent from those calculated from the discharge of a model without an AHP. We show that it is possible to represent noise-driven discharge using a two-component linear model that predicts discharge probability based on the sum of a feedback kernel and a stimulus kernel. The feedback kernel reflects the influence of prior discharge mediated by the AHP, and it increases in amplitude when AHP amplitude is increased by pharmacological manipulations. Finally, we show that the predictions of this model are virtually identical to those based on the first-order Wiener kernel. This suggests that the Wiener kernels derived from standard white-noise analysis of noise-driven discharge in neurones actually reflect the effects of both stimulus and discharge history.
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Affiliation(s)
- R K Powers
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, WA 98195-7290, USA.
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Abstract
Classical techniques for estimating postsynaptic potentials in motoneurones include spike-triggered averages of rectified surface and multiunit electromyographic recordings (SEMG and MU-EMG), as well as the compilation of peristimulus time histograms (PSTH) based on the discharge of single motor units (SMU). These techniques rely on the probability of spike occurrence in relation to the stimulus and can be contaminated by count- and synchronization-related errors, arising from post-spike refractoriness and the discharge statistics of motoneurones. On the other hand, since these probability-based techniques are easy to use and require only inexpensive equipment, it is very likely that they will continue to be used in clinical and laboratory settings for the foreseeable future. One aim of the present study was to develop a modification of these probability-based analyses in order to provide a better estimate of the initial phase of postsynaptic potentials. An additional aim was to combine probability-based analyses with frequency-based analyses to provide a more reliable estimate of later phases of postsynaptic potentials. To achieve these aims, we have injected simple as well as complex current transients into regularly discharging hypoglossal motoneurones recorded in vitro from rat brainstem slices. We examined the discharge output of these cells using both probability- and frequency-based analyses to identify which of the two represented the profile of the postsynaptic potential more closely. This protocol was designed to obtain PSTHs of the responses of single motor units to repeated application of the same afferent input. We have also simulated multiunit responses to afferent input by replacing the times of spike occurrence in individual trials with a representation of either an intramuscular or surface-recording single motor unit waveform and summing many of these trials to obtain either a simulated SEMG or MU-EMG. We found that in a regularly discharging motoneurone, the rising phase of an EPSP moves the occurrence of spikes forward and hence induces a substantial peak in all probability-based records. This peak is followed immediately by a period of reduced activity ('silent period') due to the phase advancement of spikes that were to occur at this period. Similarly, the falling phase of an IPSP delays spikes so that they occur during the rising phase of the IPSP. During the delay, the probability-based analyses display gaps and during the occurrence of the delayed spikes they generate peaks. We found that all the probability-based analyses (SEMG, MU-EMG and PSTH) can be made useful for illustrating the underlying initial PSP by a special use of the cumulative sum (CUSUM) calculation. We have illustrated that, in most cases, the CUSUM of probability-based analyses can overcome the delay- or advance-related (i.e. the count-related) errors of the classical methods associated with the first PSP only. The probability-based records also induce secondary and tertiary peaks and troughs due to synchronization of the spikes in relation to the stimulus (i.e. the synchronization-related errors) by the first PSP to occur at fixed times from the stimulus. Special CUSUM analyses cannot overcome these synchronization-related errors. Frequency-based analysis (PSFreq) of individual and summed trials gave comparable and often better indications of the underlying PSPs than the probability-based analyses. When used in combination, these analyses compliment each other so that a more accurate estimation of the underlying PSP is possible. Since the correct identification of the connections in the central nervous system is of utmost importance in order to understand the operation of the system, we suggest that as well as the using the special CUSUM approach on probability-based records, researchers should seriously consider the use of frequency-based analyses in their indirect estimation of stimulus-induced compound synaptic potentials in human motoneurones.
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Affiliation(s)
- K S Türker
- Discipline of Physiology, School of Molecular and Biomedical Sciences, University of Adelaide, SA 5005, Australia.
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Abstract
Synchronous discharges between a pair of concurrently active motoneurones are thought to arise from the spike-triggering effects of synaptic inputs shared by the pair. Although there are a number of quantitative indices that have been developed to estimate the strength of this common input, there is still some debate as to whether motoneurone discharge rate affects the values of these indices. The aim of the present study was to test the effects of motoneurone discharge rate on these synchronization indices using known common inputs. To achieve this aim we elicited repetitive discharge in rat hypoglossal motoneurones by combining a suprathreshold injected current step with superimposed noise to mimic the synaptic drive likely to occur during physiological activation. The amplitude of the current step was varied in different trials to achieve discharge rates from 5 to 22 Hz. We first examined the effect of discharge rate on the spike-triggering efficacy of individual EPSPs. Motoneurones were more responsive to large EPSPs delivered at a low rate when their background discharge rate was relatively low and the probability of the EPSPs evoking an extra spike decreased with increasing discharge rate. However, the opposite dependence was found for small, high-frequency EPSPs. We then compared the discharge records obtained in several trials in which the same EPSP train was applied repeatedly to the same cell firing at different background discharge rates. The effect of this 'common input' on motoneurone discharge probability was determined by compiling cross-correlation histograms (CCHists) between the discharges of the same cell at different times. The common inputs induced synchronous discharge that gave rise to large central peaks in the CCHists. The relationship between the discharge rate and the level of synchronization changed depending on the synchronization indices used and the amplitude of the common EPSPs. When large EPSPs were used as the common input, the normalized probability of synchronous spikes declined as the discharge rate increased, regardless of the method of normalization used. In contrast, when the common input was composed of a large number of small EPSPs, similar to that likely to occur during physiological activation of motoneurones, different synchronization indices exhibited a positive, a negative or no dependence on the background discharge rate. Indices based on normalizing the number of synchronous spikes by either the number of discharges in the lower frequency train (E), or by the total number of discharges in both trains (S) showed no dependence on background discharge rate and therefore may be the most suitable for quantifying motoneurone synchrony over a range of background discharge rates.
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Affiliation(s)
- K S Türker
- Department of Physiology, University of Adelaide, S.A.5005, Australia.
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Abstract
We compared the effects of common excitatory and inhibitory inputs on motoneuron synchronization by simulating synaptic inputs with injected current transients. We elicited repetitive discharge in hypoglossal motoneurons recorded in slices of rat brain stem using a combination of a suprathreshold injected current step with superimposed noise to mimic the synaptic drive likely to occur during physiological activation. The effects of common inputs to motoneurons were simulated by the addition of a waveform composed of from 6 to 300 trains of current transients designed to mimic excitatory and/or inhibitory synaptic currents. We compared the discharge records obtained in several trials in which the same "common input" waveform was applied repeatedly in the presence of different background noise waveforms. The effects of the common input on motoneuron discharge probability and discharge rate were determined by compiling a cross-correlation histogram (CCHist) and a perispike frequencygram (PSFreq) between the discharges of the same cell at different times. Both excitatory and inhibitory common inputs induced synchronous discharge that was evident by a large central peak in the CCHist. The CCHists produced by common excitatory inputs were characterized by larger and narrower central peaks than those generated by common inhibitory inputs. The PSFreqs produced by common excitatory inputs indicated an increase in the discharge rate of motoneurons around time 0 that coincided with the narrow and large central peak in the CCHist. On the other hand, inhibitory inputs often generated very little, if any, change in the discharge rate around time 0 corresponding with the small and wide central peak in the CCHist. These results suggest that the CCHist indicates the effective strength of the net common input but not its sign. Although correlated changes in discharge rate are often quite different for net excitatory and inhibitory common input, except in some restricted conditions, the PSFreq analysis also cannot be used to unambiguously distinguish net excitation from net inhibition.
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Affiliation(s)
- K S Türker
- Department of Physiology, University of Adelaide, SA 5005, Australia.
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Abstract
Synchronized discharge of individual motor units is commonly observed in the muscles of human subjects performing voluntary contractions. The amount of this synchronization is thought to reflect the extent to which motoneurons in the same and related pools share common synaptic input. However, the relationship between the proportion of shared synaptic input and the strength of synchronization has never been measured directly. In this study, we simulated common shared synaptic input to cat spinal motoneurons by driving their discharge with noisy, injected current waveforms. Each motoneuron was stimulated with a number of different injected current waveforms, and a given pair of waveforms were either completely different or else shared a variable percentage of common elements. Cross-correlation histograms were then compiled between the discharge of motoneurons stimulated with noise waveforms with variable degrees of similarity. The strength of synchronization increased with the amount of simulated "common" input in a nonlinear fashion. Moreover, even when motoneurons had >90% of their simulated synaptic inputs in common, only approximately 25-45% of their spikes were synchronized. We used a simple neuron model to explore how variations in neuron properties during repetitive discharge may lead to the low levels of synchronization we observed experimentally. We found that small variations in spike threshold and firing rate during repetitive discharge lead to large decreases in synchrony, particularly when neurons have a high degree of common input. Our results may aid in the interpretation of studies of motor unit synchrony in human hand muscles during voluntary contractions.
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Affiliation(s)
- M D Binder
- Department of Physiology and Biophysics, School of Medicine, University of Washington, Seattle, Washington 98195, USA.
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Abstract
Our intent in this review was to consider the relationship between the biophysical properties of motoneurons and the mechanisms by which they transduce the synaptic inputs they receive into changes in their firing rates. Our emphasis has been on experimental results obtained over the past twenty years, which have shown that motoneurons are just as complex and interesting as other central neurons. This work has shown that motoneurons are endowed with a rich complement of active dendritic conductances, and flexible control of both somatic and dendritic channels by endogenous neuromodulators. Although this new information requires some revision of the simple view of motoneuron input-output properties that was prevalent in the early 1980's (see sections 2.3 and 2.10), the basic aspects of synaptic transduction by motoneurons can still be captured by a relatively simple input-output model (see section 2.3, equations 1-3). It remains valid to describe motoneuron recruitment as a product of the total synaptic current delivered to the soma, the effective input resistance of the motoneuron and the somatic voltage threshold for spike initiation (equations 1 and 2). However, because of the presence of active channels activated in the subthreshold range, both the delivery of synaptic current and the effective input resistance depend upon membrane potential. In addition, activation of metabotropic receptors by achetylcholine, glutamate, noradrenaline, serotonin, substance P and thyrotropin releasing factor (TRH) can alter the properties of various voltage- and calcium-sensitive channels and thereby affect synaptic current delivery and input resistance. Once motoneurons are activated, their steady-state rate of repetitive discharge is linearly related to the amount of injected or synaptic current reaching the soma (equation 3). However, the slope of this relation, the minimum discharge rate and the threshold current for repetitive discharge are all subject to neuromodulatory control. There are still a number of unresolved issues concerning the control of motoneuron discharge by synaptic inputs. Under dynamic conditions, when synaptic input is rapidly changing, time- and activity-dependent changes in the state of ionic channels will alter both synaptic current delivery to the spike-generating conductances and the relation between synaptic current and discharge rate. There is at present no general quantitative expression for motoneuron input-output properties under dynamic conditions. Even under steady-state conditions, the biophysical mechanisms underlying the transfer of synaptic current from the dendrites to the soma are not well understood, due to the paucity of direct recordings from motoneuron dendrites. It seems likely that resolving these important issues will keep motoneuron afficiandoes well occupied during the next twenty years.
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Affiliation(s)
- R K Powers
- Department of Physiology & Biophysics, University of Washington School of Medicine, Box 357290, Seattle, Washington 98195-7290, USA
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Abstract
The aim of this study was to measure the effects of synaptic input on motoneuron firing rate in an unanesthetized cat preparation, where activation of voltage-sensitive dendritic conductances may influence synaptic integration and repetitive firing. In anesthetized cats, the change in firing rate produced by a steady synaptic input is approximately equal to the product of the effective synaptic current measured at the resting potential (I(N)) and the slope of the linear relation between somatically injected current and motoneuron discharge rate (f-I slope). However, previous studies in the unanesthetized decerebrate cat indicate that firing rate modulation may be strongly influenced by voltage-dependent dendritic conductances. To quantify the effects of these conductances on motoneuron firing behavior, we injected suprathreshold current steps into medial gastrocnemius motoneurons of decerebrate cats and measured the changes in firing rate produced by superimposed excitatory synaptic input. In the same cells, we measured I(N) and the f-I slope to determine the predicted change in firing rate (Delta F = I(N) * f-I slope). In contrast to previous results in anesthetized cats, synaptically induced changes in motoneuron firing rate were greater-than-predicted. This enhanced effect indicates that additional inward current was present during repetitive firing. This additional inward current amplified the effective synaptic currents produced by two different excitatory sources, group Ia muscle spindle afferents and caudal cutaneous sural nerve afferents. There was a trend toward more prevalent amplification of the Ia input (14/16 cells) than the sural input (11/16 cells). However, in those cells where both inputs were amplified (10/16 cells), amplification was similar in magnitude for each source. When these two synaptic inputs were simultaneously activated, their combined effect was generally very close to the linear sum of their amplified individual effects. Linear summation is also observed in medial gastrocnemius motoneurons of anesthetized cats, where amplification is not present. This similarity suggests that amplification does not disturb the processes of synaptic integration. Linear summation of amplified input was evident for the two segmental inputs studied here. If these phenomena also hold for other synaptic sources, then the presence of active dendritic conductances underlying amplification might enable motoneurons to integrate multiple synaptic inputs and drive motoneuron firing rates throughout the entire physiological range in a relatively simple fashion.
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Affiliation(s)
- J F Prather
- Department of Physiology, Emory University, Atlanta, Georgia 30322, USA.
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Abstract
1. We elicited repetitive discharges in cat spinal motoneurones by injecting noisy current waveforms through a microelectrode to study the relationship between the time course of the motoneurone's afterhyperpolarization (AHP) and the variability in its spike discharge. Interspike interval histograms were used to estimate the interval death rate, which is a measure of the instantaneous probability of spike occurrence as a function of the time since the preceding spike. It had been previously proposed that the death rate can be used to estimate the AHP trajectory. We tested the accuracy of this estimate by comparing the AHP trajectory predicted from discharge statistics to the measured AHP trajectory of the motoneurone. 2. The discharge statistics of noise-driven cat motoneurones shared a number of features with those previously reported for voluntarily activated human motoneurones. At low discharge rates, the interspike interval histograms were often positively skewed with an exponential tail. The standard deviation of the interspike intervals increased with the mean interval, and the plots of standard deviation versus the mean interspike interval generally showed an upward bend, the onset of which was related to the motoneurone's AHP duration. 3. The AHP trajectories predicted from the interval death rates were generally smaller in amplitude (i.e. less hyperpolarized) than the measured AHP trajectories. This discrepancy may result from the fact that spike threshold varies during the interspike interval, so that the distance to threshold at a given time depends upon both the membrane trajectory and the spike threshold trajectory. Nonetheless, since the interval death rate is likely to reflect the instantaneous distance to threshold during the interspike interval, it provides a functionally relevant measure of fluctuations in motoneurone excitability during repetitive discharge.
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Affiliation(s)
- R K Powers
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, WA 98195, USA.
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Affiliation(s)
- R K Powers
- Department of Physiology & Biophysics, University of Washington School of Medicine, Seattle 98195, USA.
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Abstract
The aim of this study was to examine how cat spinal motoneurons integrate the synaptic currents generated by the concurrent activation of large groups of presynaptic neurons. We obtained intracellular recordings from cat triceps surae motoneurons and measured the effects of repetitive activity in different sets of presynaptic neurons produced by electrical stimulation of descending fibers or peripheral nerves and by longitudinal vibration of the triceps surae muscles (to activate primary muscle spindle Ia afferent fibers). We combined synaptic activation with subthreshold injected currents to obtain estimates of effective synaptic currents at the resting potential (I(Nrest)) and at the threshold for repetitive discharge (I(Nthresh)). We then superimposed synaptic activation on suprathreshold injected current steps to measure the synaptically evoked change in firing rate. We studied eight different pairs of synaptic inputs. When any two synaptic inputs were activated concurrently, both the effective synaptic currents (I(Nrest)) and the synaptically evoked changes in firing rate generally were equal to or slightly less than the linear sum of the effects produced by activating each input alone. However, there were several instances in which the summation was substantially less than linear. In some motoneurons, we induced a partial blockade of potassium channels by adding tetraethylammonium (TEA) or cesium to the electrolyte solution in the intracellular pipette. In these cells, persistent inward currents were evoked by depolarization that led to instances of substantially greater-than linear summation of injected and synaptic currents. Overall our results indicate that the spatial distribution of synaptic boutons on motoneurons acts to minimize electrical interactions between synaptic sites permitting near linear summation of synaptic currents. However, modulation of voltage-gated conductances on the soma and dendrites of the motoneuron can lead to marked nonlinearities in synaptic integration.
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Affiliation(s)
- R K Powers
- Department of Physiology, School of Medicine, University of Washington, Seattle, Washington 98195, USA
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Abstract
We elicited repetitive discharge in hypoglossal motoneurons recorded in slices of rat brain stem using a combination of a suprathreshold injected current step with superimposed noise to mimic the synaptic drive likely to occur during physiological activation. The effects of repetitive en mass stimulation of afferent nerves were simulated by the further addition of trains of injected current transients of varying shapes and sizes. The effects of a given current transient on motoneuron discharge timing and discharge rate were measured by calculating a peristimulus time histogram (PSTH) and a peristimulus frequencygram (PSF). The amplitude and time course of the simulated postsynaptic potentials (PSPs) produced by the current transients were calculated by convolving the current transient with an estimate of the passive impulse response of the motoneuron. We then compared the shape of the injected current transient and the simulated PSP to the profiles of the PSTH and the PSF records. The PSTHs produced by excitatory PSPs (EPSPs) were characterized by a large, short-latency increase in firing probability that lasted slightly longer than the rising phase of the EPSP, followed by a reduced discharge probability during the falling phase of the EPSP. In contrast, the PSF analysis revealed a proportionate increase in discharge rate over the entire profile of the EPSP, even though relatively few spikes occurred during the falling phase. The PSTHs associated with inhibitory PSPs (IPSPs) indicated a reduction in discharge probability during the initial, hyperpolarizing phase of the IPSP, followed by an increase in the discharge probability during its subsequent repolarizing phase. Using the PSF analysis, the initial phase of the IPSP appeared as a large hole in the record where a very small number or no discharges occurred. The subsequent phase of the IPSP was associated with frequency values that were lower than the background values. The primary features of both PSTHs and PSFs can be used to estimate the relative amplitudes of the underlying EPSPs and IPSPs. However, PSTHs contain secondary peaks and troughs that are not directly related to the underlying PSP but instead reflect the regular recurrence of spikes following those affected by the PSP. The PSF analysis is more useful for indicating the total duration and the profile of the underlying PSP. The shape of the underlying PSP can be obtained directly from the PSF records because the discharge frequency of the spikes follow the PSPs very closely, especially for EPSPs.
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Affiliation(s)
- K S Türker
- Department of Physiology, University of Adelaide, South Australia 5005, Australia
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Abstract
Spinal motoneurones receive thousands of presynaptic excitatory and inhibitory synaptic contacts distributed throughout their dendritic trees. Despite this extensive convergence, there have been very few studies of how synaptic inputs interact in mammalian motoneurones when they are activated concurrently. In the experiments reported here, we measured the effective synaptic currents and the changes in firing rate evoked in cat spinal motoneurones by concurrent repetitive activation of two separate sets of presynaptic neurons. We compared these effects to those predicted by a linear sum of the effects produced by activating each set of presynaptic neurons separately. We generally found that when two inputs were activated concurrently, both the effective synaptic currents and the synaptically-evoked changes in firing rate they produced in motoneurones were generally linear, or slightly less than the linear sum of the effects produced by activating each input alone. The results suggest that the spatial distribution synaptic terminals on the dendritic trees of motoneurones may help isolate synapses from one another, minimizing non-linear interactions.
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Affiliation(s)
- M D Binder
- Department of Physiology & Biophysics, School of Medicine, University of Washington, Seattle 98195, USA
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Abstract
We studied the responses of rat hypoglossal and cat lumbar motoneurones to a variety of excitatory and inhibitory injected current transients during repetitive discharge. The amplitudes and time courses of the transients were comparable to those of the synaptic currents underlying postsynaptic potentials (PSPs) recorded in these cells. Poisson trains of these current transients were combined with an additional independent, high frequency random waveform to approximate band-limited white noise. The composite, white noise waveform was then superimposed on long duration suprathreshold current steps. We used the responses of the motoneurones to the white noise stimulus to derive zero-, first- and second-order Wiener kernels, which provide a quantitative description of the relation between injected current and discharge probability. The convolution integral computed for an injected current waveform and the first-order Wiener kernel provides the best linear prediction of the associated peristimulus time histogram (PSTH). This linear model provided good matches to most of the PSTHs compiled between the times of occurrence of individual current transients and motoneurone discharges. However, for the largest amplitude current transients, a significant improvement in the PSTH match was often achieved by expanding the model to include the convolution of the second-order Wiener kernel with the input. The overall transformation of current inputs into firing rate could be approximated by a second-order Wiener Model, i.e., a cascade of a dynamic, linear filter followed by a static non-linearity. At a given mean firing rate, the non-linear component of the motoneurone's response could be described by the square of the linear component multiplied by a constant coefficient. The amplitude of the response of the linear component increased with the average firing rate, whereas the value of the multiplicative coefficient in the nonlinear component decreased. As a result, the overall transform could be predicted from the mean firing rate and the linear impulse response, yielding a relatively simple, general description of the motoneurone's input-output function.
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Affiliation(s)
- M D Binder
- Department of Physiology and Biophysics, School of Medicine, University of Washington, Seattle 98195, USA
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Abstract
Spike-frequency adaptation is the continuous decline in discharge rate in response to a constant stimulus. We have described three distinct phases of adaptation in rat hypoglossal motoneurones: initial, early and late. The initial phase of adaptation is over in one or two intervals, and is primarily due to summation of the calcium-activated potassium conductance underlying the medium duration afterhyperpolarization (mAHP). The biophysical mechanisms underlying the later phases of adaptation are not well understood. Two of the previously-proposed mechanisms for adaptation are an increase in outward current flowing through calcium-activated potassium channels and increasing outward current produced by the electrogenic sodium-potassium pump. We found that neither of these mechanisms are necessary for the expression of the early and late phases of adaptation. The magnitude of the initial phase of adaptation was reduced when the calcium in the external solution was replaced with manganese, but the magnitudes of the early and late phases were consistently increased under these conditions. Partial blockade of the sodium-potassium pump with ouabain had no significant effect on any of the three phases of adaptation. Our current working hypothesis is that the magnitude of late adaptation depends upon the interplay between slow inactivation of sodium currents, that tends to decrease discharge rate, and the slow activation or facilitation of a calcium current that tends to increase discharge rate. Adaptation is often associated with a progressive decrease in the peak amplitude and rate of rise of action potentials, and a computer model that incorporated slow inactivation of sodium channels reproduced this phenomenon. However, the time course of adaptation does not always parallel changes in spike shape, indicating that the progressive activation of another inward current might oppose the decline in frequency caused by slow sodium inactivation.
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Affiliation(s)
- R K Powers
- Department of Physiology and Biophysics, School of Medicine, University of Washington, Seattle 98195, USA
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Binder MD, Robinson FR, Powers RK. Distribution of effective synaptic currents in cat triceps surae motoneurons. VI. Contralateral pyramidal tract. J Neurophysiol 1998; 80:241-8. [PMID: 9658045 DOI: 10.1152/jn.1998.80.1.241] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
We measured the effective synaptic currents (IN) produced by stimulating the contralateral pyramidal tract (PT) in triceps surae motoneurons of the cat. This is an oligosynaptic pathway in the cat that generates both excitation and inhibition in hindlimb motoneurons. We also determined the effect of the PT synaptic input on the discharge rate of some of the motoneurons by inducing repetitive firing with long, injected current pulses during which the PT stimulation was repeated. At resting potential, all but one triceps motoneuron received a net depolarizing effective synaptic current from the PT stimulation. The effective synaptic currents (IN) were much larger in putative type F motoneurons than in putative type S motoneurons [+4.6 +/- 2.9 (SD) nA for type F vs. 0.9 +/- 2.4 nA for putative type S]. When the values of IN at the threshold for repetitive firing were estimated, the distribution was markedly altered. More than 60% of the putative type S motoneurons received a net hyperpolarizing effective synaptic current from the pyramidal tract stimulation as did 33% of the putative type F motoneurons. This distribution pattern is very similar to that observed previously for the effective synaptic currents produced by stimulating the contralateral red nucleus. As would be expected from the wide range of IN values at threshold (-4.8 to +8.7 nA), the PT stimulation produced dramatically different effects on the discharge of different triceps motoneurons. The discharge rates of those motoneurons that received depolarizing effective synaptic currents at threshold were accelerated by PT stimulation (+1 to +8 imp/s), whereas the discharge rates of cells that received hyperpolarizing currents were retarded by the PT input (-2 to -7 imp/s). The change in firing rates produced by the PT stimulation was generally approximated by the product of the effective synaptic currents and the slopes of the motoneurons' frequency-current relations. Our findings indicate that the contralateral pyramidal tract may provide a powerful source of synaptic drive to some high-threshold motoneurons while concurrently inhibiting low-threshold cells. Thus this input system, like that from the contralateral red nucleus, can potentially alter the gain of the input-output function of the motoneuron pool as well as disrupt the normal hierarchy of recruitment thresholds.
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Affiliation(s)
- M D Binder
- Department of Physiology and Biophysics, University of Washington, School of Medicine, Seattle, Washington 98195, USA
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32
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Abstract
Contribution of outward currents to spike-frequency adaptation in hypoglossal motoneurons of the rat. J. Neurophysiol. 78: 2246-2253, 1997. Spike-frequency adaptation has been attributed to the actions of several different membrane currents. In this study, we assess the contributions of two of these currents: the net outward current generated by the electrogenic Na+-K+ pump and the outward current that flows through Ca2+-activated K+ channels. In recordings made from hypoglossal motoneurons in slices of rat brain stem, we found that bath application of a 4-20 microM ouabain solution produced a partial block of Na+-K+ pump activity as evidenced by a marked reduction in the postdischarge hyperpolarization that follows a period of sustained discharge. However, we observed no significant change in either the initial, early, or late phases of spike-frequency adaptation in the presence of ouabain. Adaptation also has been related to increases in the duration and magnitude of the medium-duration afterhyperpolarization (mAHP) mediated by Ca2+-activated K+ channels. When we replaced the 2 mM Ca2+ in the bathing solution with Mn2+, there was a significant decrease in the amplitude of the mAHP after a spike. The decrease in mAHP amplitude resulted in a decrease in the magnitude of the initial phase of spike-frequency adaptation as has been reported previously by others. However, quite unexpectedly we also found that reducing the mAHP resulted in a dramatic increase in the magnitude of both the early and late phases of adaptation. These changes could be reversed by restoring the normal Ca2+ concentration in the bath. Our results with ouabain indicate that the Na+-K+ pump plays little, if any, role in the three phases of adaptation in rat hypoglossal motoneurons. Our results with Ca2+ channel blockade support the hypothesis that initial adaptation is, in part, controlled by conductances underlying the mAHP. However, our failure to eliminate initial adaptation completely by blocking Ca2+ channels suggests that other membrane mechanisms also contribute. Finally, the increase in both the early and late phases of adaptation in the presence of Mn2+ block of Ca2+ channels lends further support to the hypothesis that the initial and later (i.e., early and late) phases of spike-frequency adaptation are mediated by different cellular mechanisms.
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Affiliation(s)
- A Sawczuk
- Department of Physiology and Biophysics, University of Washington, School of Medicine, Seattle, Washington 98195, USA
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33
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Abstract
1. We studied the responses of rat hypoglossal and cat lumbar motoneurones to a variety of excitatory and inhibitory injected current transients during repetitive discharge. The amplitudes and time courses of the transients were comparable to those of the synaptic currents underlying unitary and small compound postsynaptic potentials (PSPs) recorded in these cells. Poisson trains of ten of these excitatory and ten inhibitory current transients were combined with an additional independent, high-frequency random waveform to approximate band limited white noise. The white noise waveform was then superimposed on long duration (39 s) suprathreshold current steps. 2. We measured the effects of each of the current transients on motoneurone discharge by compiling peristimulus time histograms (PSTHs) between the times of occurrence of individual current transients and motoneurone discharges. We estimated the changes in membrane potential associated with each current transient by approximating the passive response of the motoneurone with a simple resistance-capacitance circuit. The relations between the features of these simulated PSPs and those of the PSTHs were similar to those reported previously for real PSPs: the short-latency PSTH peak (or trough) was generally longer than the initial phase of the PSP derivative, but shorter than the time course of the PSP itself. Linear models of the PSP to PSTH transform based on the PSP time course, the time derivative of the PSP, or a linear combination of the two parameters could not reproduce the full range of PSTH profiles observed. 3. We also used the responses of the motoneurones to the white noise stimulus to derive zero-, first- and second-order Wiener kernels, which provide a quantitative description of the relation between injected current and discharge probability. The convolution integral computed for an injected current waveform and the first-order Wiener kernel should provide the best linear prediction of the associated PSTH. This linear model provided good matches to the PSTHs associated with a wide range of current transients. However, for the largest amplitude current transients, a significant improvement in the PSTH match was often achieved by expanding the model to include the convolution of the second-order Wiener kernel with the input. 4. The overall transformation of current inputs into firing rate could be approximated by a second-order Wiener model, i.e. a cascade of a dynamic, linear filter followed by a static non-linearity. At a given mean firing rate, the non-linear component of the response of the motoneurone could be described by the square of the linear component multiplied by a constant coefficient. The amplitude of the response of the linear component increased with the average firing rate, whereas the value of the multiplicative coefficient in the non-linear component decreased. As a result, the overall transform could be predicted from the mean firing rate and the linear impulse response, yielding a relatively simple, general description of the motoneurone input-output function.
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Affiliation(s)
- A V Poliakov
- Department of Physiology & Biophysics, School of Medicine, University of Washington, Seattle 98195, USA
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Poliakov AV, Powers RK, Sawczuk A, Binder MD. Effects of background noise on the response of rat and cat motoneurones to excitatory current transients. J Physiol 1996; 495 ( Pt 1):143-57. [PMID: 8866358 PMCID: PMC1160731 DOI: 10.1113/jphysiol.1996.sp021580] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. We studied the responses of rat hypoglossal motoneurones to excitatory current transients (ECTs) using a brainstem slice preparation. Steady, repetitive discharge at rates of 12-25 impulses s-1 was elicited from the motoneurones by injecting long (40 s) steps of constant current. Poisson trains of the ECTs were superimposed on these steps. The effects of additional synaptic noise was simulated by adding a zero-mean random process to the stimuli. 2. We measured the effects of the ECTs on motoneurone discharge probability by compiling peristimulus time histograms (PSTHs) between the times of occurrence of the ECTs and the motoneurone spikes. The ECTs produced modulation of motoneurone discharge similar to that produced by excitatory postsynaptic currents. 3. The addition of noise altered the pattern of the motoneurone response to the current transients: both the amplitude and the area of the PSTH peaks decreased as the power of the superimposed noise was increased. Noise tended to reduce the efficacy of the ECTs, particularly when the motoneurones were firing at lower frequencies. Although noise also increased the firing frequency of the motoneurones slightly, the effects of noise on ECT efficacy did not simply result from noise-induced changes in mean firing rate. 4. A modified version of the experimental protocol was performed in lumbar motoneurones of intact, pentobarbitone-anaesthetized cats. These recordings yielded results similar to those obtained in rat hypoglossal motoneurones in vitro. 5. Our results suggest that the presence of concurrent synaptic inputs reduces the efficacy of any one input. The implications of this change in efficacy and the possible underlying mechanisms are discussed.
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Affiliation(s)
- A V Poliakov
- Department of Physiology & Biophysics, School of Medicine, University of Washington, Seattle 98195, USA.
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35
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Abstract
1. We measured the modulation of the background firing rate of cat spinal motoneurons produced by simulated, repetitive excitatory postsynaptic potentials (EPSPs) to test the accuracy of several proposed motoneuron input-output functions. Rhythmic discharge was elicited in the motoneurons by injecting suprathreshold current steps 1-1.5 s in duration. On alternate trials, trains of short (0.5-5 ms) current pulses were superimposed on the current steps to stimulate the effects of trains of individual EPSPs. The increase in firing rate (delta F) due to the addition of the pulses was calculated as the difference in motoneuron discharge rate between trials with and without the superimposed pulse trains. 2. In the same motoneurons, we were able to study the effects of changes in pulse frequency, duration, and amplitude, as well as changes in the background discharge rate. A sublinear relationship between pulse rate and delta F was observed, with delta F rising relatively steeply with increasing pulse frequency at low pulse rates and saturating at high pulse rates. A similarly shaped relation was observed between delta F and pulse duration. In contrast, delta F generally increased in a greater than linear fashion with increasing pulse amplitude. 3. In previous studies we demonstrated that when a relatively constant synaptic input is produced by high-frequency synaptic activity, delta F is approximately equal to the product of the net synaptic current reaching the soma and the slope of the motoneuron's steady-state frequency-current (f-I) relation. In the present study, this input-output function consistently underestimated the observed delta F, particularly for low input rates, indicating that the transient current pulses are more effective in modulating motoneuron discharge than an equivalent amount of constant current. 4. Other investigators have proposed input-output functions derived from the relation between synaptic potential amplitude and the magnitude of the peak of a cross correlogram compiled from the discharge of the pre- and postsynaptic neurons. These functions consistently overestimated the observed delta F, particularly for high pulse rates. This overestimation may result in part from the fact that the effects of a synaptic potential (or current pulse) on postsynaptic discharge probability also include a period of decreased firing probability. Moreover, the cross correlation function may depend on the arrival rate of synaptic potentials (or current pulses). 5. Another proposed input-output function based on a simple threshold-crossing model of the motoneuron with a fixed spike threshold predicts firing rates that were often close to the observed delta F. However, the model did not reproduce the observed relations between delta F and input pulse rate or pulse duration. 6. The deficiencies of the basic threshold-crossing model may arise from the fact that it does not incorporate variations in membrane conductance and firing threshold that occur in real motoneurons. A more complete motoneuron model that incorporates both of these features was able to replicate the observed delta Fs associated with changes in input pulse frequency and duration.
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Affiliation(s)
- R K Powers
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle 98195, USA
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36
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Abstract
We applied supramaximal, repetitive stimulation to the lateral vestibular nucleus (Deiters' nucleus, DN) at 200 Hz to evoke stead-state synaptic potentials in ipsilateral triceps surae motoneurons of the cat. The effective synaptic currents underlying these potentials were measured using a modified voltage-clamp technique. The steady-state effective synaptic currents evoked by activating DN were generally small and depolarizing (mean 2.5 +/- 2.6 nA). DN stimulation generated hyperpolarizing synaptic currents in 2 of the 34 triceps motoneurons studied. The effective synaptic currents from DN tended to be larger in putative type F motoneurons than in putative type S cells (type F mean 3.0 +/- 3.1 nA; type S mean 1.8 +/- 1.0 nA). There was a statistically significant difference between the inputs to putative type FF and putative type S motoneurons (mean difference 2.8 nA, t = 2.87, P < 0.01). The synaptic input from DN to medial gastrocnemius motoneurons had approximately the same amplitude as that from homonymous Ia afferent fibers. However, the distribution of DN input with respect to putative motor unit type was the opposite of that previously reported for Ia afferent input. Thus, the synaptic input from DN might act to compress the range of recruitment thresholds within the motoneuron pool and thereby increase the gain of its input-output function.
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Affiliation(s)
- S L Westcott
- Department of Physiology and Biophysics, University of Washington, School of Medicine, Seattle 98195, USA
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37
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Abstract
1. We used a modified voltage-clamp technique to measure the steady-state effective synaptic currents (I(N)) produced by activating four different input systems to cat hindlimb motoneurons: Ia afferent fibers, Ia-inhibitory interneurons, Renshaw interneurons, and contralateral rubrospinal neurons. In the same motoneurons, we measured the slope of the firing rate-injected current (f-I) relation in the primary range. We then reactivated these synaptic inputs during steady, repetitive firing to assess their effects on motoneuron discharge rate. 2. Our measurements of I(N) were derived from recordings made near the resting membrane potential, whereas the effects of the synaptic inputs on repetitive discharge were evaluated at more depolarized membrane potentials. Thus we adjusted the I(N) values for these changes in driving force based on estimates of the synaptic reversal potential and the mean membrane potential during repetitive discharge. 3. We found that changes in the steady-state discharge rate of a motoneuron produced by these synaptic inputs could be reasonably well predicted by the product of the estimated value of I(N) during repetitive firing and the slope of the motoneuron's f-I relation. Although there was a high correlation between predicted and observed changes in firing rate for our entire sample of motoneurons (r = 0.93; P < 0.001), the slope of the relation between predicted and observed firing rate modulation was significantly greater than 1. 4. The systematic difference between predicted and observed firing rate modulation observed in the overall sample was primarily due to the fact that our predictions underestimated the changes in firing rate produced by Ia excitation and Ia inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- R K Powers
- Department of Physiology and Biophysics, University of Washington, School of Medicine, Seattle 98195, USA
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38
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Abstract
1. We studied spike frequency adaptation of motoneuron discharge in the rat hypoglossal nucleus using a brain stem slice preparation. The characteristics of adaptation in response to long (60 s) injected current steps were qualitatively similar to those observed previously in cat hindlimb motoneurons. The discharge rate typically exhibited a rapid initial decline, characterized by a linear frequency-time relation, followed by a gradual exponential decline that continued for the duration of current injection. However, a more systematic, quantitative analysis of the data revealed that there were often three distinct phases of the adaptation rather than two. 2. The three phases of adaptation (initial, early, and late) were present in at least one 60-s trial of repetitive firing in all but a small number of motoneurons. Initial adaptation was limited to the first few spikes except in a few trials (7%) in which there was no initial adaptation. The time course of the subsequent decline in rate could be adequately described by a single-exponential function in about half of the trials (48%). In the remaining trials this subsequent decline in frequency was better described as the sum of two exponential functions: an early phase, lasting < 2 s, and a late phase, which lasted for the duration of the discharge period. 3. The magnitude of initial adaptation was correlated with the initial firing frequency (i.e., the reciprocal of the 1st interspike interval). The magnitudes of the early and late phases of adaptation were correlated with the firing frequency reached at the end of initial adaptation. Neither the magnitudes nor the time courses of the three phases were correlated with other membrane properties such as input resistance, rheobase, or repetitive firing threshold. 4. The slope of the frequency-current (f-I) curve was steeper in the initial phase (first 2-5 spikes) than in either the early (< 2 s) or late (> 2 s) phases of adaptation as previously reported by other investigators. In the absence of early adaptation, a steady state for the f-I slope was reached by 0.7-1 s, the time typically reported in studies of repetitive discharge. However, when early adaptation was present (50% of the trials), a steady-state value for the f-I slope was not reached until the cell had discharged for > 1 s. 5. To characterize the time course of firing rate recovery from the adaptive processes, the current was turned off for periods of < or = 10 s during the course of a 60-s trial.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- A Sawczuk
- Department of Physiology and Biophysics, University of Washington, School of Medicine, Seattle 98195, USA
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39
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Abstract
A new method for quantifying upper motoneuron (UMN) weakness using standard EMG equipment is presented and compared to the twitch occlusion method. Control subjects and patients with stroke, spinal cord injury (SCI), and peripheral nerve injury (PNI) were evaluated. Force, EMG, and twitch force from nerve electrical stimulation were recorded during isometric contractions of the biceps and triceps. Ratios of the elicited CMAP amplitude (M)/voluntary-root-mean-square EMG activity (RMS) and of the voluntary contraction twitch force (Ti)/the resting twitch force (Tmax) were the two measures of UMN weakness studied. Both ratios are linearly correlated with force for controls, log M/RMS (r = 0.96) and Ti/Tmax (r = 0.86). Log M/RMS ratio was abnormally high (> mean + 2 SD; i.e., > 1.09) for weak muscles affected by stroke and incomplete SCI, but was normal in muscles weakened by PNI. An elevated M/RMS ratio, may aid in quantification of deficient supraspinal activation from UMN or functional weakness.
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Affiliation(s)
- J F Haughton
- Department of Rehabilitation Medicine, University of Washington, Seattle
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Little JW, Powers RK, Michelson P, Moore D, Robinson LR, Goldstein B. Electrodiagnosis of upper limb weakness in acute quadriplegia. Am J Phys Med Rehabil 1994; 73:15-22. [PMID: 8305176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Clinical and neuropathologic observations after cervical spinal cord injury suggest varying involvement of gray and white matter. The resulting upper limb weakness may reflect varying degrees of upper motoneuron (UMN) and/or lower motoneuron (LMN) involvement. This study uses electrophysiologic measures, including compound muscle action potential (M response) amplitude, root mean square (RMS) of the surface electromyographic activity during voluntary muscle contractions and the firing rate of motor units, to distinguish UMN and LMN weakness in upper extremities after acute quadriplegia. M response amplitude did not correlate with strength; many muscles had large M responses given their strength. These muscles manifest: (1) high M/RMS ratios (ratio of electrically elicited to voluntarily recruited electromyographic activity) and (2) slow firing rates of single motor units during maximal isometric contractions. For muscles with normal M amplitudes, M/RMS ratio correlates inversely with strength. For muscles with normal M/RMS ratios, M amplitude correlates positively with strength. Cluster analysis was used to distinguish UMN, LMN or Mixed types of weakness. Distinguishing these different types of weakness in acute quadriplegia may allow individualized rehabilitation for the type of weakness present.
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Affiliation(s)
- J W Little
- Spinal Cord Injury Service, VA Medical Center, Seattle, Washington 98108
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41
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Abstract
In theory, there are at least two distinct mechanisms by which afferent inputs could alter motoneuron discharge and shape the output of a motoneuron pool: either by delivering synaptic current to the motoneurons' somata ('classic' synaptic transduction); or by altering the motoneurons' voltage-sensitive conductances (neuromodulation). Recent work has confirmed the operation of both of these mechanisms. It has been shown that the effect of a 'classic' synaptic input on motoneuron firing rate is predicted by the product of the effective synaptic current and the slope of the motoneuron's frequency-current relation. It has also been shown that neuromodulators can alter both the slope of a motoneuron's frequency-current relation and its threshold for repetitive firing. It is argued here, however, that when two or more sources of synaptic input are activated concurrently, the distinction between these two mechanisms is blurred. Computer simulations of motoneuron and motor pool behavior have proved extremely useful in understanding these processes.
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Affiliation(s)
- M D Binder
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle 98195
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42
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Abstract
1. We evoked steady-state synaptic potentials in triceps surae motoneurons of the cat by stimulating the hindlimb projection area of the contralateral magnocellular red nucleus at 200 Hz. We measured the effective synaptic currents (IN) underlying the synaptic potentials using a modified voltage-clamp technique. We also determined the effect of the rubrospinal input on the discharge rate of some of the motoneurons by inducing repetitive discharge with long injected current pulses during which the red nucleus stimulation was repeated. 2. At motoneuron resting potential, the distribution of IN from the red nucleus within the triceps surae pools was qualitatively similar to the distribution of synaptic potentials: 86% of the putative type F motoneurons received a net depolarizing IN from the red nucleus stimulation, whereas only 38% of the putative type S units did so. The mean values of IN were significantly different in the two groups [+4.1 +/- 5.0 nA (SD) for putative type F and -1.6 +/- 3.1 nA for putative type S]. 3. However, when the values of IN at threshold for repetitive firing were estimated, the distribution of IN from the red nucleus was quite different. At threshold, all of the putative type S units received hyperpolarizing IN but so did nearly half of the putative type F units. 4. As would be expected from the wide range of IN at threshold (-20 to +12 nA), the red nucleus input produced dramatically different effects on the discharge of different motoneurons.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- R K Powers
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle 98195
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Abstract
1. A "threshold-crossing" motoneuron model was developed to relate recently described biophysical features of cat alpha-motoneurons to motoneuron discharge behavior. This model incorporated three features not included in precedent models: 1) a low-threshold, persistent calcium current; 2) realistic voltage dependencies of the major ionic conductances; and 3) a variable spike threshold. The effects of these additional biophysical features on model behavior were investigated by successively adding them to a fixed threshold model with a single potassium conductance. 2. Fixed-threshold models with either one or two potassium conductances could not produce appropriate discharge behavior. Steady-state frequency-current (F-I) relations were characterized by a continuously increasing slope, unlike the piecewise linear relations observed in real motoneurons. These models also produced unrealistically high discharge rates at the highest levels of "injected" current. 3. The addition of a variable spike threshold, which was made to increase linearly with the magnitude of injected current, could limit maximum discharge rates to more realistic levels. However, steady-state F-I relations still did not exhibit the appropriate shape. 4. The incorporation of a low-threshold calcium current led to a good quantitative agreement between the steady-state F-I relations produced by the model and those obtained in real motoneurons. In addition, the steady-state relation between total membrane current and membrane voltage (I-V relation) of the model was very similar to those measured in real motoneurons. The model's I-V and F-I relations were both very sensitive to the exact form of the steady-state relation between the magnitude of the calcium conductance and membrane voltage. 5. Additional modifications, which included a second calcium conductance and a factor relating spike threshold to membrane voltage, helped to produce more realistic afterhyperpolarizations and first-interval F-I relations. 6. Bistable discharge behavior could be produced by reducing the slow potassium conductance and increasing the time constants governing the activation and deactivation of the low-threshold calcium conductance. 7. The final model thus reproduces a wide range of motoneuron behaviors including subthreshold rectification, piecewise linear first interval and steady-state F-I relations, and, with appropriate modifications, bistable discharge behavior. Nonetheless, by simplifying the representation of fast spike conductances as well as the kinetics of the other ionic conductances, the model remains simple enough to be incorporated into a larger neural network.
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Affiliation(s)
- R K Powers
- Department of Physiology and Biophysiology, University of Washington, Seattle 98195
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Abstract
1. The basic question of how motoneurons transform synaptic inputs into spike train outputs remains unresolved, despite detailed knowledge of their morphology, electrophysiology, and synaptic connectivity. We have approached this problem by making measurements of a synaptic input under steady-state conditions and combining them with quantitative assessments of their effects on the discharge rates of cat spinal motoneurons. 2. We used a modified voltage-clamp technique to measure the steady-state effective synaptic currents (IN) produced by rubrospinal input to cat triceps surae motoneurons. In the same motoneurons we measured the slope of the firing rate-injected current (f-i) relation in the primary range. We then reactivated the rubrospinal input during steady, repetitive firing to assess its effect on motoneuron discharge rate. 3. We found that changes in the steady-state discharge rate of a motoneuron produced by this synaptic input could be described simply as the product of the net effective synaptic current measured at the soma and the slope of the motoneuron's f-i relation. This expression essentially redefines synaptic efficacy in terms of a cell's basic input-output function. Further, measurements of effective synaptic current simplify the task of estimating synaptic efficacy, because detailed knowledge of neither the electrotonic architecture of the postsynaptic cell nor of the locations of the presynaptic boutons is required.
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Affiliation(s)
- R K Powers
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle 98195
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Powers RK, Binder MD. Summation of motor unit tensions in the tibialis posterior muscle of the cat under isometric and nonisometric conditions. J Neurophysiol 1991; 66:1838-46. [PMID: 1812220 DOI: 10.1152/jn.1991.66.6.1838] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
1. The tension produced by the combined stimulation of two to four single motor units of the cat tibialis posterior muscle was compared with the algebraic sum of the tensions produced by each individual motor unit. Comparisons were made under isometric conditions and during imposed changes in muscle length. 2. Under isometric conditions, the tension resulting from combined stimulation of units displayed marked nonlinear summation, as previously reported in other cat hindlimb muscles. On average, the measured tension was approximately 20% greater than the algebraic sum of the individual unit tensions. However, small trapezoidal movements imposed on the muscle during stimulation significantly reduced the degree of nonlinear summation both during and after the movement. This effect was seen with imposed movements as small as 50 microns. 3. The degree of nonlinear summation was not dependent on motor unit size or on stimulus frequency. The effect was also unrelated to tendon compliance because the degree of nonlinear summation of motor unit forces was unaffected by the inclusion of different amounts of the external tendon between the muscle and the force transducer. 4. Our results support previous suggestions that the force measured when individual motor units are stimulated under isometric conditions is reduced by friction between the active muscle fibers and adjacent passive fibers. These frictional effects are likely to originate in the connective tissue matrix connecting adjacent muscle fibers. However, because these effects are virtually eliminated by small movements, linear summation of motor unit tensions should occur at low force levels under nonisometric conditions.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- R K Powers
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle 98195
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Abstract
1. Tension-frequency relations were measured in single fast-twitch motor units of the cat flexor digitorum longus (FDL) muscle before and after stimulating each unit with a series of 10-s trains at 20 Hz. The 20-Hz conditioning stimulation produced a combination of potentiating and fatiguing effects, similar to those previously reported to follow higher frequency stimulation of single motor units of the cat and maximal voluntary contractions in man. 2. The conditioning stimulation left three types of after effects: 1) short-term potentiation, 2) a somewhat longer lasting depression of maximal tension, and 3) a delayed depression of low-frequency responses (low-frequency fatigue). 3. The immediate potentiating effect of the conditioning stimulation was most prominent in fatigue-resistant (FR) motor units, whereas depression of maximal tension and low-frequency fatigue were most prominent in fatigue-intermediate (FI) and highly fatigable (FF) motor units. 4. On the basis of our results and those of other investigators, we propose that potentiation, depression of maximal tension, and low-frequency fatigue are independent phenomena, acting at distinct points in the excitation-contraction coupling process. 5. Our results suggest that both potentiation and low-frequency fatigue can result from rather modest amounts of preceding activity. Thus large changes in muscle force production are not unique to maximal contractions but are likely to follow sustained, submaximal contractions as well.
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Affiliation(s)
- R K Powers
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle 98195
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Abstract
Using intracellular recording techniques, we studied the response characteristics of two separate populations of triceps surae motoneurons in unanesthetized decerebrate cats, recorded before and after low thoracic hemisection of the spinal cord. In each preparation, we studied the response properties of one group of motoneurons and the protocol was then repeated for a separate group, immediately following the dorsal hemisection. In each group, we examined both the minimum firing rates of motoneurons during intracellular current injection and a range of cellular properties, including input resistance, rheobase current and afterhyperpolarization time course and magnitude. Although earlier studies from this laboratory have shown substantial reductions in minimum firing rate in reflexively active motoneurons in the hemisected decerebrated preparation, the response of motoneurons to intracellular current injection in the current preparation proved to be quite different. Minimum firing rates were either normal or even somewhat higher in the post-lesion group, while the time course of the afterhyperpolarization was shortened. Moreover, these effects were not evenly distributed across the motoneuron pool. The rate effect was most evident in motoneurons with higher conduction velocity, while the afterhyperpolarization effect occurred predominantly in motoneurons with lower conduction velocity. Neither of these effects could be accounted for by lesion-induced changes in other cellular properties. We conclude that tonically active neurons with descending axons traversing dorsolateral white matter may influence both the discharge characteristics and membrane properties of spinal motoneurons in novel ways, presumably by modifying voltage or calcium activated motoneuronal conductances. The previously described reactions in the firing rate of motoneurons after such lesions appear to be mediated by different means, perhaps by alterations in synaptic input from segmental interneurons.
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Affiliation(s)
- J S Carp
- Department of Physiology, Northwestern University Medical School, Chicago, Il 60611
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48
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Abstract
Cross-correlation techniques were used to test for the presence of shared, direct input to motoneurons innervating different synergist elbow flexor muscles in man. Motor unit activity was recorded intramuscularly from two elbow flexor muscles during steady isometric elbow flexion in normal and paretic subjects. To increase the probability of detecting weak synchrony, one of the intramuscular needles was positioned to record multiunit activity. Significant correlogram peaks were obtained in 25/57 runs in normal subjects, and the features of the correlograms were similar to those previously reported based on cross-correlation of two single units within the same muscle. Further, the characteristics of discharge synchrony measured in paretic stroke patients are consistent with other reports on the effects of stroke on synchrony among motoneurons belonging to the same pool, i.e. narrow correlogram peaks were rare in paretic subjects and significant correlogram peaks often had longer than normal durations.
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Affiliation(s)
- R K Powers
- Sensory-Motor Performance Program, Rehabilitation Institute of Chicago, IL
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49
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Abstract
Previous studies of stretch reflexes in patients with spastic hypertonia have emphasized the dynamic character of stretch reflex output. In contrast, our own studies of stretch reflex dynamics in spastic elbow flexor muscles of 14 hemiparetic human subjects have shown that stretch-evoked torque displays a relatively weak dependence on stretch velocity, and there is generally no preferential enhancement of dynamic as compared with static reflex output. Moreover, stretch reflex dynamics are broadly similar in voluntarily activated spastic and normal elbow flexor muscles. These findings support our hypothesis that spastic hypertonia results primarily from a decrease in stretch reflex threshold. The strong velocity dependence of stretch-evoked electromyographic activity in initially inactive spastic muscles could be due to a decrease in reflex threshold with increasing stretch velocity, rather than an abnormal velocity-dependent increase in stretch reflex responsiveness.
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Affiliation(s)
- R K Powers
- Sensory-Motor Performance Program, Rehabilitation Institute of Chicago, IL 60611
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50
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Abstract
1. The discharge of single alpha-motoneuron axons was recorded from small cut filaments of the medial gastrocnemius (MG) muscle nerve in the decerebrated cat preparation before and after a dorsal hemisection of the thoracic spinal cord. The remainder of the MG muscle nerve was left intact, and muscle force and multiunit electromyographic (EMG) activity were recorded along with alpha-motoneuron discharge, while motor output was varied by manual stimulation of the contralateral hindlimb. 2. We recorded activity in 32 motoneurons before and after the spinal lesion, and pre- and postlesion recruitment forces and minimum firing rates were determined for 30 of these. Postlesion decreases in minimum firing rates were observed in 25/30 motoneurons, and decreases in recruitment force were seen in 21/30 motoneurons. The remaining motoneurons, which generally had low presection recruitment forces and minimum rates, exhibited postlesion increases in both parameters (see below). 3. The effects of the spinal lesion on the recruitment force and minimum firing rate of a motoneuron were related to the prelesion values of these parameters; the largest postlesion decreases were seen in motoneurons with the highest prelesion rates and recruitment forces. Spinal lesions thus acted to shift and compress the range of recruitment forces and minimum firing rates, so that after the lesion all motoneurons tended to exhibit discharge behavior typical of that seen only in the lowest threshold motoneurons before the lesion. In addition, motoneurons with low prelesion recruitment forces (less than 1.0 N of active force) generally showed an increase in recruitment force after the lesion, indicating that the lesion may have led to changes in the prelesion recruitment order. Direct evidence of recruitment reversals was obtained in 4/14 experiments where two or more motoneurons were followed pre- and postlesion. 4. The lesion-induced changes in motoneuron discharge characteristics were associated with changes in the relations between muscle force, rectified EMG, and motoneuron rate. Postlesion discharge rates were always significantly lower than the prelesion rates when compared over the same range of EMG levels. This postlesion drop in discharge rates was generally associated with inefficient force production, as evidenced by a significant drop in muscle force for matched EMG levels. 5. The degree of discharge synchrony in MG motoneurons was assessed by calculating a spike-triggered average (STA) between axonal discharge and multiunit rectified EMG. Significant STA peaks were rare before the lesion (4/32 motoneurons) but were quite common after the lesion (29/32 motoneurons).(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- R K Powers
- Department of Physiology, Northwestern University Medical School, Chicago, Illinois
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