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Herrera-Arcos G, Song H, Yeon SH, Ghenand O, Gutierrez-Arango S, Sinha S, Herr H. Closed-loop optogenetic neuromodulation enables high-fidelity fatigue-resistant muscle control. Sci Robot 2024; 9:eadi8995. [PMID: 38776378 DOI: 10.1126/scirobotics.adi8995] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2023] [Accepted: 04/25/2024] [Indexed: 05/25/2024]
Abstract
Closed-loop neuroprostheses show promise in restoring motion in individuals with neurological conditions. However, conventional activation strategies based on functional electrical stimulation (FES) fail to accurately modulate muscle force and exhibit rapid fatigue because of their unphysiological recruitment mechanism. Here, we present a closed-loop control framework that leverages physiological force modulation under functional optogenetic stimulation (FOS) to enable high-fidelity muscle control for extended periods of time (>60 minutes) in vivo. We first uncovered the force modulation characteristic of FOS, showing more physiological recruitment and significantly higher modulation ranges (>320%) compared with FES. Second, we developed a neuromuscular model that accurately describes the highly nonlinear dynamics of optogenetically stimulated muscle. Third, on the basis of the optogenetic model, we demonstrated real-time control of muscle force with improved performance and fatigue resistance compared with FES. This work lays the foundation for fatigue-resistant neuroprostheses and optogenetically controlled biohybrid robots with high-fidelity force modulation.
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Affiliation(s)
- Guillermo Herrera-Arcos
- K. Lisa Yang Center for Bionics, MIT, Cambridge, MA, USA
- Program in Media Arts and Sciences, MIT Media Lab, Cambridge, MA, USA
- McGovern Institute for Brain Research, MIT, Cambridge, MA, USA
| | - Hyungeun Song
- K. Lisa Yang Center for Bionics, MIT, Cambridge, MA, USA
- Harvard-MIT Division of Health Sciences and Technology (HST), MIT, Cambridge, MA, USA
| | - Seong Ho Yeon
- K. Lisa Yang Center for Bionics, MIT, Cambridge, MA, USA
- Program in Media Arts and Sciences, MIT Media Lab, Cambridge, MA, USA
| | - Omkar Ghenand
- K. Lisa Yang Center for Bionics, MIT, Cambridge, MA, USA
- Department of Biological Engineering, MIT, Cambridge, MA, USA
| | - Samantha Gutierrez-Arango
- K. Lisa Yang Center for Bionics, MIT, Cambridge, MA, USA
- Program in Media Arts and Sciences, MIT Media Lab, Cambridge, MA, USA
| | - Sapna Sinha
- K. Lisa Yang Center for Bionics, MIT, Cambridge, MA, USA
- McGovern Institute for Brain Research, MIT, Cambridge, MA, USA
| | - Hugh Herr
- K. Lisa Yang Center for Bionics, MIT, Cambridge, MA, USA
- McGovern Institute for Brain Research, MIT, Cambridge, MA, USA
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Liu J, Zhang S, Emadi S, Guo T, Chen L, Feng B. Morphological, molecular, and functional characterization of mouse glutamatergic myenteric neurons. Am J Physiol Gastrointest Liver Physiol 2024; 326:G279-G290. [PMID: 38193160 PMCID: PMC11211033 DOI: 10.1152/ajpgi.00200.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Revised: 12/26/2023] [Accepted: 01/02/2024] [Indexed: 01/10/2024]
Abstract
The enteric nervous system (ENS) functions largely independently of the central nervous system (CNS). Glutamate, the dominant neurotransmitter in the CNS and sensory afferents, is not a primary neurotransmitter in the ENS. Only a fraction (∼2%) of myenteric neurons in the mouse distal colon and rectum (colorectum) are positive for vesicular glutamate transporter type 2 (VGLUT2), the structure and function of which remain undetermined. Here, we systematically characterized VGLUT2-positive enteric neurons (VGLUT2-ENs) through sparse labeling with adeno-associated virus, single-cell mRNA sequencing (scRNA-seq), and GCaMP6f calcium imaging. Our results reveal that the majority of VGLUT2-ENs (29 of 31, 93.5%) exhibited Dogiel type I morphology with a single aborally projecting axon; most axons (26 of 29, 89.7%) are between 4 and 10 mm long, each traversing 19 to 34 myenteric ganglia. These anatomical features exclude the VGLUT2-ENs from being intrinsic primary afferent or motor neurons. The scRNA-seq conducted on 52 VGLUT2-ENs suggests different expression profiles from conventional descending interneurons. Ex vivo GCaMP6f recordings from flattened colorectum indicate that almost all VGLUT2-EN (181 of 215, 84.2%) are indirectly activated by colorectal stretch via nicotinic cholinergic neural transmission. In conclusion, VGLUT2-ENs are a functionally unique group of enteric neurons with single aborally projecting long axons that traverse multiple myenteric ganglia and are activated indirectly by colorectal mechanical stretch. This knowledge will provide a solid foundation for subsequent studies on the potential interactions of VGLUT2-EN with extrinsic colorectal afferents via glutamatergic neurotransmission.NEW & NOTEWORTHY We reveal that VGLUT2-positive enteric neurons (EN), although constituting a small fraction of total EN, are homogeneously expressed in the myenteric ganglia, with a slight concentration at the intermediate region between the colon and rectum. Through anatomic, molecular, and functional analyses, we demonstrated that VGLUT2-ENs are activated indirectly by noxious circumferential colorectal stretch via nicotinic cholinergic transmission, suggesting their participation in mechanical visceral nociception.
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Affiliation(s)
- Jia Liu
- Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut, United States
| | - Shaopeng Zhang
- Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut, United States
| | - Sharareh Emadi
- Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut, United States
| | - Tiantian Guo
- Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut, United States
| | - Longtu Chen
- Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut, United States
| | - Bin Feng
- Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut, United States
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Liu J, Zhang S, Emadi S, Guo T, Chen L, Feng B. Morphological, molecular, and functional characterization of mouse glutamatergic myenteric neurons. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.18.558146. [PMID: 37781576 PMCID: PMC10541117 DOI: 10.1101/2023.09.18.558146] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/03/2023]
Abstract
The enteric nervous system (ENS) functions largely independently of the central nervous system (CNS). Correspondingly, glutamate, the dominant neurotransmitter in the CNS and sensory afferents, is not a primary neurotransmitter in the ENS. Only a fraction (approximately 2%) of myenteric neurons in the mouse distal colon and rectum (colorectum) are positive for vesicular glutamate transporter type 2 (VGLUT2), the structure and function of which remain undetermined. Here, we systematically characterized VGLUT2-positive enteric neurons (VGLUT2-ENs) through sparse labeling with adeno-associated virus, single-cell mRNA sequencing (scRNA-seq), and GCaMP6f calcium imaging. Our results reveal that the majority of VGLUT2-ENs (29 out of 31, 93.5%) exhibited Dogiel type I morphology with a single aborally projecting axon; most axons (26 out of 29, 89.7%) are between 4 and 10 mm long, each traversing 19 to 34 myenteric ganglia. These anatomical features exclude the VGLUT2-ENs from being intrinsic primary afferent or motor neurons. The scRNA-seq conducted on 52 VGLUT2-ENs suggests different expression profiles from conventional descending interneurons. Ex vivo GCaMP6f recordings from flattened colorectum indicate that almost all VGLUT2-EN (181 out of 215, 84.2%) are indirectly activated by colorectal stretch via nicotinic cholinergic neural transmission. In conclusion, VGLUT2-ENs are a functionally unique group of enteric neurons with single aborally projecting long axons that traverse multiple myenteric ganglia and are activated indirectly by colorectal mechanical stretch. This knowledge will provide a solid foundation for subsequent studies on the potential interactions of VGLUT2-EN with extrinsic colorectal afferents via glutamatergic neurotransmission. New & Noteworthy We reveal that VGLUT2-positive enteric neurons (EN), although constituting a small fraction of total EN, are homogeneously expressed in the myenteric ganglia, with a slight concentration at the intermediate region between the colon and rectum. This concentration coincides with the entry zone of extrinsic afferents into the colorectum. Given that VGLUT2-ENs are indirectly activated by colorectal mechanical stretch, they are likely to participate in visceral nociception through glutamatergic neural transmission with extrinsic afferents.
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Keshmiri Neghab H, Soheilifar MH, Grusch M, Ortega MM, Esmaeeli Djavid G, Saboury AA, Goliaei B. The state of the art of biomedical applications of optogenetics. Lasers Surg Med 2021; 54:202-216. [PMID: 34363230 DOI: 10.1002/lsm.23463] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Revised: 07/08/2021] [Accepted: 07/23/2021] [Indexed: 12/31/2022]
Abstract
BACKGROUND AND OBJECTIVE Optogenetics has opened new insights into biomedical research with the ability to manipulate and control cellular activity using light in combination with genetically engineered photosensitive proteins. By stimulating with light, this method provides high spatiotemporal and high specificity resolution, which is in contrast to conventional pharmacological or electrical stimulation. Optogenetics was initially introduced to control neural activities but was gradually extended to other biomedical fields. STUDY DESIGN In this paper, firstly, we summarize the current optogenetic tools stimulated by different light sources, including lasers, light-emitting diodes, and laser diodes. Second, we outline the variety of biomedical applications of optogenetics not only for neuronal circuits but also for various kinds of cells and tissues from cardiomyocytes to ganglion cells. Furthermore, we highlight the potential of this technique for treating neurological disorders, cardiac arrhythmia, visual impairment, hearing loss, and urinary bladder diseases as well as clarify the mechanisms underlying cancer progression and control of stem cell differentiation. CONCLUSION We sought to summarize the various types of promising applications of optogenetics to treat a broad spectrum of disorders. It is conceivable to expect that optogenetics profits a growing number of patients suffering from a range of different diseases in the near future.
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Affiliation(s)
- Hoda Keshmiri Neghab
- Department of Photo Healing and Regeneration, Medical Laser Research Center, Yara Institute, ACECR, Tehran, Iran
| | | | - Michael Grusch
- Department of Medicine I, Institute of Cancer Research, Medical University of Vienna, Vienna, Austria
| | - Manoela Marques Ortega
- Laboratory of Cell and Molecular Tumor Biology and Bioactive Compounds, São Francisco University, Bragança Paulista, São Paulo, Brazil
| | - Gholamreza Esmaeeli Djavid
- Department of Photo Healing and Regeneration, Medical Laser Research Center, Yara Institute, ACECR, Tehran, Iran
| | - Ali Akbar Saboury
- Department of Biophysics, Institute of Biochemistry and Biophysics, University of Tehran, Tehran, Iran
| | - Bahram Goliaei
- Department of Biophysics, Institute of Biochemistry and Biophysics, University of Tehran, Tehran, Iran
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Guo T, Patel S, Shah D, Chi L, Emadi S, Pierce DM, Han M, Brumovsky PR, Feng B. Optical clearing reveals TNBS-induced morphological changes of VGLUT2-positive nerve fibers in mouse colorectum. Am J Physiol Gastrointest Liver Physiol 2021; 320:G644-G657. [PMID: 33533318 PMCID: PMC8238166 DOI: 10.1152/ajpgi.00363.2020] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Revised: 01/12/2021] [Accepted: 01/27/2021] [Indexed: 01/31/2023]
Abstract
Colorectal hypersensitivity and sensitization of both mechanosensitive and mechanically insensitive afferents develop after intracolonic instillation of 2,4,6-trinitrobenzenesulfonic acid (TNBS) in the mouse, a model of postinfectious irritable bowel syndrome. In mice in which ∼80% of extrinsic colorectal afferents were labeled genetically using the promotor for vesicular glutamate transporter type 2 (VGLUT2), we systematically quantified the morphology of VGLUT2-positive axons in mouse colorectum 7-28 days following intracolonic TNBS treatment. After removal, the colorectum was distended (20 mmHg), fixed with paraformaldehyde, and optically cleared to image VGLUT2-positive axons throughout the colorectal wall thickness. We conducted vector path tracing of individual axons to allow systematic quantification of nerve fiber density and shape. Abundant VGLUT2-positive nerve fibers were present in most layers of the colorectum, except the serosal and longitudinal muscular layers. A small percentage of VGLUT2-positive myenteric plexus neurons was also detected. Intracolonic TNBS treatment significantly reduced the number of VGLUT2-positive nerve fibers in submucosal, myenteric plexus, and mucosal layers at day 7 post-TNBS, which mostly recovered by day 28. We also found that almost all fibers in the submucosa were meandering and curvy, with ∼10% showing pronounced curviness (quantified by the linearity index). TNBS treatment resulted in a significant reduction of the proportions of pronounced curvy fibers in the rectal region at 28 days post-TNBS. Altogether, the present morphological study reveals profound changes in the distribution of VGLUT2-positive fibers in mouse colorectum undergoing TNBS-induced colitis and draws attention to curvy fibers in the submucosa with potential roles in visceral nociception.NEW & NOTEWORTHY We conducted genetic labeling and optical clearing to visualize extrinsic sensory nerve fibers in whole-mount colorectum, which revealed widespread presence of axons in the submucosal layer. Remarkably, axons in the submucosa were meandering and curvy, in contrast to axons in other layers generally aligned with the basal tissues. Intracolonic TNBS treatment led to pronounced changes of nerve fiber density and curviness, suggesting nerve fiber morphologies as potentially contributing factors to sensory sensitization.
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Affiliation(s)
- Tiantian Guo
- Department of Biomedical Engineering, University of Connecticut, Mansfield, Connecticut
| | - Shivam Patel
- Department of Physiology and Neurobiology, University of Connecticut, Mansfield, Connecticut
| | - Dhruv Shah
- Department of Molecular and Cell Biology, University of Connecticut, Mansfield, Connecticut
| | - Ling Chi
- Department of Physiology and Neurobiology, University of Connecticut, Mansfield, Connecticut
| | - Sharareh Emadi
- Department of Biomedical Engineering, University of Connecticut, Mansfield, Connecticut
| | - David M Pierce
- Department of Biomedical Engineering, University of Connecticut, Mansfield, Connecticut
- Department of Mechanical Engineering, University of Connecticut, Mansfield, Connecticut
| | - Martin Han
- Department of Biomedical Engineering, University of Connecticut, Mansfield, Connecticut
| | - Pablo R Brumovsky
- Instituto de Investigaciones en Medicina Traslacional, National Scientific and Technical Research Council, Austral University, Buenos Aires, Argentina
| | - Bin Feng
- Department of Biomedical Engineering, University of Connecticut, Mansfield, Connecticut
- Department of Physiology and Neurobiology, University of Connecticut, Mansfield, Connecticut
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Johnson AC, Louwies T, Ligon CO, Greenwood-Van Meerveld B. Enlightening the frontiers of neurogastroenterology through optogenetics. Am J Physiol Gastrointest Liver Physiol 2020; 319:G391-G399. [PMID: 32755304 PMCID: PMC7717115 DOI: 10.1152/ajpgi.00384.2019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Neurogastroenterology refers to the study of the extrinsic and intrinsic nervous system circuits controlling the gastrointestinal (GI) tract. Over the past 5-10 yr there has been an explosion in novel methodologies, technologies and approaches that offer great promise to advance our understanding of the basic mechanisms underlying GI function in health and disease. This review focuses on the use of optogenetics combined with electrophysiology in the field of neurogastroenterology. We discuss how these technologies and tools are currently being used to explore the brain-gut axis and debate the future research potential and limitations of these techniques. Taken together, we consider that the use of these technologies will enable researchers to answer important questions in neurogastroenterology through fundamental research. The answers to those questions will shorten the path from basic discovery to new treatments for patient populations with disorders of the brain-gut axis affecting the GI tract such as irritable bowel syndrome (IBS), functional dyspepsia, achalasia, and delayed gastric emptying.
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Affiliation(s)
- Anthony C. Johnson
- 1Oklahoma Center for Neuroscience, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma,2Oklahoma City Veterans Affairs Health Care System, Oklahoma City, Oklahoma,3Department of Neurology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma
| | - Tijs Louwies
- 1Oklahoma Center for Neuroscience, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma
| | - Casey O. Ligon
- 1Oklahoma Center for Neuroscience, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma
| | - Beverley Greenwood-Van Meerveld
- 1Oklahoma Center for Neuroscience, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma,2Oklahoma City Veterans Affairs Health Care System, Oklahoma City, Oklahoma,4Department of Physiology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma
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Intermittent Failure of Spike Propagation in Primary Afferent Neurons during Tactile Stimulation. J Neurosci 2019; 39:9927-9939. [PMID: 31672792 DOI: 10.1523/jneurosci.0975-19.2019] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 10/09/2019] [Accepted: 10/16/2019] [Indexed: 12/22/2022] Open
Abstract
Primary afferent neurons convey somatosensory information to the CNS. Low-threshold mechanoreceptors are classified as slow-adapting (SA) or rapid-adapting (RA) based on whether or not they spike repetitively during sustained tactile stimulation; the former are subclassified as Type 1 or 2 based on the regularity of their spiking. Recording in vivo from DRGs of mice, we observed irregular- and regular-spiking units consistent with SA1 and SA2 low-threshold mechanoreceptors, but some units, which we labeled "semiregular," did not fit cleanly into the existing classification scheme. Analysis of their spiking revealed integer-multiple patterning in which spike trains comprised a fundamental interspike interval and multiples thereof. Integer-multiple-patterned spiking was reproduced by randomly removing spikes from an otherwise regular spike train, suggesting that semiregular units represent SA2 units in which some spikes are "missing." We hypothesized that missing spikes arose from intermittent failure of spikes to initiate or to propagate. Intermittent failure of spike initiation was ruled out by several observations: integer-multiple-patterned spiking was not induced by intradermal lidocaine, was independent of stimulus modality (mechanical vs optogenetic), and could not be reproduced in a conductance-based model neuron given constant input. On the other hand, integer-multiple-patterned spiking was induced by application of lidocaine to the DRG, thus pinpointing intermittent failure of spike propagation as the basis for integer-multiple-patterned spiking. Indeed, half of all SA2 units exhibited some missing spikes, mostly at low rate (<5%), which suggests that axons are efficient in using the lowest safety factor capable of producing near-perfect propagation reliability.SIGNIFICANCE STATEMENT The impedance mismatch at axon branch points can impede spike propagation. Reliability of spike propagation across branch points remains an open question and is especially important for primary afferents whose spikes must cross a T-junction to reach the CNS. Past research on propagation reliability has relied almost entirely on simulations and in vitro experiments. Here, recording in vivo, we linked a distinctive pattern of spiking to the intermittent failure of spike propagation at the T-junction. The rarity of failures argues that safety factor is high under physiological conditions, yet the occurrence of such failures argues that safety factor is just high enough to ensure near-perfect reliability, consistent with a good balance between propagation reliability and energy efficiency.
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Gomez-Ramirez M, More AI, Friedman NG, Hochgeschwender U, Moore CI. The BioLuminescent-OptoGenetic in vivo response to coelenterazine is proportional, sensitive, and specific in neocortex. J Neurosci Res 2019; 98:471-480. [PMID: 31544973 DOI: 10.1002/jnr.24498] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Revised: 06/11/2019] [Accepted: 07/03/2019] [Indexed: 12/20/2022]
Abstract
BioLuminescent (BL) light production can modulate neural activity and behavior through co-expressed OptoGenetic (OG) elements, an approach termed "BL-OG." Yet, the relationship between BL-OG effects and bioluminescent photon emission has not been characterized in vivo. Further, the degree to which BL-OG effects strictly depend on optogenetic mechanisms driven by bioluminescent photons is unknown. Crucial to every neuromodulation method is whether the activator shows a dynamic concentration range driving robust, selective, and nontoxic effects. We systematically tested the effects of four key components of the BL-OG mechanism (luciferin, oxidized luciferin, luciferin vehicle, and bioluminescence), and compared these against effects induced by the Luminopsin-3 (LMO3) BL-OG molecule, a fusion of slow burn Gaussia luciferase (sbGLuc) and Volvox ChannelRhodopsin-1 (VChR1). We performed combined bioluminescence imaging and electrophysiological recordings while injecting specific doses of Coelenterazine (substrate for sbGluc), Coelenteramide (CTM, the oxidized product of CTZ), or CTZ vehicle. CTZ robustly drove activity in mice expressing LMO3, with photon production proportional to firing rate. In contrast, low and moderate doses of CTZ, CTM, or vehicle did not modulate activity in mice that did not express LMO3. We also failed to find bioluminescence effects on neural activity in mice expressing an optogenetically nonsensitive LMO3 variant. We observed weak responses to the highest dose of CTZ in control mice, but these effects were significantly smaller than those observed in the LMO3 group. These results show that in neocortex in vivo, there is a large CTZ range wherein BL-OG effects are specific to its active chemogenetic mechanism.
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Affiliation(s)
| | - Alexander I More
- Department of Neuroscience, Brown University, Providence, Rhode Island
| | - Nina G Friedman
- Department of Neuroscience, Brown University, Providence, Rhode Island
| | - Ute Hochgeschwender
- College of Medicine and Neuroscience Program, Central Michigan University, Mount Pleasant, Michigan
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Guo T, Bian Z, Trocki K, Chen L, Zheng G, Feng B. Optical recording reveals topological distribution of functionally classified colorectal afferent neurons in intact lumbosacral DRG. Physiol Rep 2019; 7:e14097. [PMID: 31087524 PMCID: PMC6513768 DOI: 10.14814/phy2.14097] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2019] [Accepted: 04/25/2019] [Indexed: 01/18/2023] Open
Abstract
Neuromodulation as a non-drug alternative for managing visceral pain in irritable bowel syndrome (IBS) may target sensitized afferents of distal colon and rectum (colorectum), especially their somata in the dorsal root ganglion (DRG). Developing selective DRG stimulation to manage visceral pain requires knowledge of the topological distribution of colorectal afferent somata which are sparsely distributed in the DRG. Here, we implemented GCaMP6f to conduct high-throughput optical recordings of colorectal afferent activities in lumbosacral DRG, that is, optical electrophysiology. Using a mouse ex vivo preparation with distal colorectum and L5-S1 DRG in continuity, we recorded 791 colorectal afferents' responses to graded colorectal distension (15, 30, 40, and 60 mmHg) and/or luminal shear flow (20-30 mL/min), then functionally classified them into four mechanosensitive classes, and determined the topological distribution of their somata in the DRG. Of the 791 colorectal afferents, 90.8% were in the L6 DRG, 8.3% in the S1 DRG, and only 0.9% in the L5 DRG. L6 afferents had all four classes: 29% mucosal, 18.4% muscular-mucosal, 34% low-threshold (LT) muscular, and 18.2% high-threshold (HT) muscular afferents. S1 afferents only had three classes: 19.7% mucosal, 34.8% LT muscular, and 45.5% HT muscular afferents. All seven L5 afferents were HT muscular. In L6 DRG, somata of HT muscular afferents were clustered in the caudal region whereas somata of the other classes did not cluster in specific regions. Outcomes of this study can directly inform the design and improvement of next-generation neuromodulation devices that target the DRG to alleviate visceral pain in IBS patients.
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Affiliation(s)
- Tiantian Guo
- Department of Biomedical EngineeringUniversity of ConnecticutStorrsConnecticut
| | - Zichao Bian
- Department of Biomedical EngineeringUniversity of ConnecticutStorrsConnecticut
| | - Kyle Trocki
- Department of Biomedical EngineeringUniversity of ConnecticutStorrsConnecticut
| | - Longtu Chen
- Department of Biomedical EngineeringUniversity of ConnecticutStorrsConnecticut
| | - Guoan Zheng
- Department of Biomedical EngineeringUniversity of ConnecticutStorrsConnecticut
| | - Bin Feng
- Department of Biomedical EngineeringUniversity of ConnecticutStorrsConnecticut
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10
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Takkala P, Zhu Y, Prescott SA. Combined Changes in Chloride Regulation and Neuronal Excitability Enable Primary Afferent Depolarization to Elicit Spiking without Compromising its Inhibitory Effects. PLoS Comput Biol 2016; 12:e1005215. [PMID: 27835641 PMCID: PMC5105942 DOI: 10.1371/journal.pcbi.1005215] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Accepted: 10/20/2016] [Indexed: 11/19/2022] Open
Abstract
The central terminals of primary afferent fibers experience depolarization upon activation of GABAA receptors (GABAAR) because their intracellular chloride concentration is maintained above electrochemical equilibrium. Primary afferent depolarization (PAD) normally mediates inhibition via sodium channel inactivation and shunting but can evoke spikes under certain conditions. Antidromic (centrifugal) conduction of these spikes may contribute to neurogenic inflammation while orthodromic (centripetal) conduction could contribute to pain in the case of nociceptive fibers. PAD-induced spiking is assumed to override presynaptic inhibition. Using computer simulations and dynamic clamp experiments, we sought to identify which biophysical changes are required to enable PAD-induced spiking and whether those changes necessarily compromise PAD-mediated inhibition. According to computational modeling, a depolarizing shift in GABA reversal potential (EGABA) and increased intrinsic excitability (manifest as altered spike initiation properties) were necessary for PAD-induced spiking, whereas increased GABAAR conductance density (ḡGABA) had mixed effects. We tested our predictions experimentally by using dynamic clamp to insert virtual GABAAR conductances with different EGABA and kinetics into acutely dissociated dorsal root ganglion (DRG) neuron somata. Comparable experiments in central axon terminals are prohibitively difficult but the biophysical requirements for PAD-induced spiking are arguably similar in soma and axon. Neurons from naïve (i.e. uninjured) rats were compared before and after pharmacological manipulation of intrinsic excitability, and against neurons from nerve-injured rats. Experimental data confirmed that, in most neurons, both predicted changes were necessary to yield PAD-induced spiking. Importantly, such changes did not prevent PAD from inhibiting other spiking or from blocking spike propagation. In fact, since the high value of ḡGABA required for PAD-induced spiking still mediates strong inhibition, we conclude that PAD-induced spiking does not represent failure of presynaptic inhibition. Instead, diminished PAD caused by reduction of ḡGABA poses a greater risk to presynaptic inhibition and the sensory processing that relies upon it.
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Affiliation(s)
- Petri Takkala
- Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Ontario, Canada
- Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada
| | - Yi Zhu
- Center for Pain Research, Department of Anesthesiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Steven A. Prescott
- Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Ontario, Canada
- Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada
- Center for Pain Research, Department of Anesthesiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- Department of Physiology and the Institute of Biomaterials and Biomedical Engineering, University of Toronto, Ontario, Canada
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11
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Hass CA, Glickfeld LL. High-fidelity optical excitation of cortico-cortical projections at physiological frequencies. J Neurophysiol 2016; 116:2056-2066. [PMID: 27489370 DOI: 10.1152/jn.00456.2016] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Accepted: 08/02/2016] [Indexed: 11/22/2022] Open
Abstract
Optogenetic activation of axons is a powerful approach for determining the synaptic properties and impact of long-range projections both in vivo and in vitro. However, because of the difficulty of measuring activity in axons, our knowledge of the reliability of optogenetic axonal stimulation has relied on data from somatic recordings. Yet, there are many reasons why activation of axons may not be comparable to cell bodies. Thus we have developed an approach to more directly assess the fidelity of optogenetic activation of axonal projections. We expressed opsins (ChR2, Chronos, or oChIEF) in the mouse primary visual cortex (V1) and recorded extracellular, pharmacologically isolated presynaptic action potentials in response to axonal activation in the higher visual areas. Repetitive stimulation of axons with ChR2 resulted in a 70% reduction in the fiber volley amplitude and a 60% increase in the latency at all frequencies tested (10-40 Hz). Thus ChR2 cannot reliably recruit axons during repetitive stimulation, even at frequencies that are reliable for somatic stimulation, likely due to pronounced channel inactivation at the high light powers required to evoke action potentials. By comparison, oChIEF and Chronos evoked photocurrents that inactivated minimally and could produce reliable axon stimulation at frequencies up to 60 Hz. Our approach provides a more direct and accurate evaluation of the efficacy of new optogenetic tools and has identified Chronos and oChIEF as viable tools to interrogate the synaptic and circuit function of long-range projections.
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Affiliation(s)
- Charles A Hass
- Department of Neurobiology, Duke University, Durham, North Carolina
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Feng B, Joyce SC, Gebhart GF. Optogenetic activation of mechanically insensitive afferents in mouse colorectum reveals chemosensitivity. Am J Physiol Gastrointest Liver Physiol 2016; 310:G790-8. [PMID: 26950857 PMCID: PMC4888546 DOI: 10.1152/ajpgi.00430.2015] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2015] [Accepted: 02/18/2016] [Indexed: 01/31/2023]
Abstract
The sensory innervation of the distal colorectum includes mechanically insensitive afferents (MIAs; ∼25%), which acquire mechanosensitivity in persistent visceral hypersensitivity and thus generate de novo input to the central nervous system. We utilized an optogenetic approach to bypass the process of transduction (generator potential) and focus on transformation (spike initiation) at colorectal MIA sensory terminals, which is otherwise not possible in typical functional studies. From channelrhodopsin2-expressing mice (driven by Advillin-Cre), the distal colorectum with attached pelvic nerve was harvested for ex vivo single-fiber recordings. Afferent receptive fields (RFs) were identified by electrical stimulation and tested for response to mechanical stimuli (probing, stroking, and stretch), and afferents were classified as either MIAs or mechanosensitive afferents (MSAs). All MIA and MSA RFs were subsequently stimulated optically and MIAs were also tested for activation/sensitization with inflammatory soup (IS), acidic hypertonic solution (AHS), and/or bile salts (BS). Responses to pulsed optical stimuli (1-10 Hz) were comparable between MSAs and MIAs whereas 43% of MIAs compared with 86% of MSAs responded tonically to stepped optical stimuli. Tonic-spiking MIAs responded preferentially to AHS (an osmotic stimulus) whereas non-tonic-spiking MIAs responded to IS (an inflammatory stimulus). A significant proportion of MIAs were also sensitized by BS. These results reveal transformation as a critical factor underlying the differences between MIAs (osmosensors vs. inflammatory sensors), revealing a previously unappreciated heterogeneity of MIA endings. The current study draws attention to the sensory encoding of MIA nerve endings that likely contribute to afferent sensitization and thus have important roles in visceral pain.
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Affiliation(s)
- Bin Feng
- Center for Pain Research, Department of Anesthesiology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
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Montgomery KL, Iyer SM, Christensen AJ, Deisseroth K, Delp SL. Beyond the brain: Optogenetic control in the spinal cord and peripheral nervous system. Sci Transl Med 2016; 8:337rv5. [DOI: 10.1126/scitranslmed.aad7577] [Citation(s) in RCA: 111] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2015] [Accepted: 04/18/2016] [Indexed: 12/12/2022]
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Ratté S, Prescott SA. Afferent hyperexcitability in neuropathic pain and the inconvenient truth about its degeneracy. Curr Opin Neurobiol 2016; 36:31-7. [DOI: 10.1016/j.conb.2015.08.007] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2015] [Revised: 08/20/2015] [Accepted: 08/25/2015] [Indexed: 01/09/2023]
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Coggan JS, Bittner S, Stiefel KM, Meuth SG, Prescott SA. Physiological Dynamics in Demyelinating Diseases: Unraveling Complex Relationships through Computer Modeling. Int J Mol Sci 2015; 16:21215-36. [PMID: 26370960 PMCID: PMC4613250 DOI: 10.3390/ijms160921215] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2015] [Revised: 08/21/2015] [Accepted: 08/25/2015] [Indexed: 11/16/2022] Open
Abstract
Despite intense research, few treatments are available for most neurological disorders. Demyelinating diseases are no exception. This is perhaps not surprising considering the multifactorial nature of these diseases, which involve complex interactions between immune system cells, glia and neurons. In the case of multiple sclerosis, for example, there is no unanimity among researchers about the cause or even which system or cell type could be ground zero. This situation precludes the development and strategic application of mechanism-based therapies. We will discuss how computational modeling applied to questions at different biological levels can help link together disparate observations and decipher complex mechanisms whose solutions are not amenable to simple reductionism. By making testable predictions and revealing critical gaps in existing knowledge, such models can help direct research and will provide a rigorous framework in which to integrate new data as they are collected. Nowadays, there is no shortage of data; the challenge is to make sense of it all. In that respect, computational modeling is an invaluable tool that could, ultimately, transform how we understand, diagnose, and treat demyelinating diseases.
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Affiliation(s)
- Jay S Coggan
- NeuroLinx Research Institute, La Jolla, CA 92039, USA.
| | - Stefan Bittner
- Department of Neurology, Institute of Physiology, Universitätsklinikum Münster, 48149 Münster, Germany.
| | | | - Sven G Meuth
- Department of Neurology, Institute of Physiology, Universitätsklinikum Münster, 48149 Münster, Germany.
| | - Steven A Prescott
- Neurosciences and Mental Health, the Hospital for Sick Children, Toronto, ON M5G 1X8, Canada.
- Department of Physiology and the Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON M5G 1X8, Canada.
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