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Xi Y, Schriver KE, Roe AW, Zhang X. Quantifying tissue temperature changes induced by infrared neural stimulation: numerical simulation and MR thermometry. BIOMEDICAL OPTICS EXPRESS 2024; 15:4111-4131. [PMID: 39022552 PMCID: PMC11249695 DOI: 10.1364/boe.530854] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/21/2024] [Accepted: 05/21/2024] [Indexed: 07/20/2024]
Abstract
Infrared neural stimulation (INS) delivered via short pulse trains is an innovative tool that has potential for us use for studying brain function and circuitry, brain machine interface, and clinical use. The prevailing mechanism for INS involves the conversion of light energy into thermal transients, leading to neuronal membrane depolarization. Due to the potential risks of thermal damage, it is crucial to ensure that the resulting local temperature increases are within non-damaging limits for brain tissues. Previous studies have estimated damage thresholds using histological methods and have modeled thermal effects based on peripheral nerves. However, additional quantitative measurements and modeling studies are needed for the central nervous system. Here, we performed 7 T MRI thermometry on ex vivo rat brains following the delivery of infrared pulse trains at five different intensities from 0.1-1.0 J/cm2 (each pulse train 1,875 nm, 25 us/pulse, 200 Hz, 0.5 s duration, delivered through 200 µm fiber). Additionally, we utilized the General BioHeat Transfer Model (GBHTM) to simulate local temperature changes in perfused brain tissues while delivering these laser energies to tissue (with optical parameters of human skin) via three different sizes of optical fibers at five energy intensities. The simulation results clearly demonstrate that a 0.5 second INS pulse train induces an increase followed by an immediate drop in temperature at stimulation offset. The delivery of multiple pulse trains with 2.5 s interstimulus interval (ISI) leads to rising temperatures that plateau. Both thermometry and modeling results show that, using parameters that are commonly used in biological applications (200 µm diameter fiber, 0.1-1.0 J/cm2), the final temperature increase at the end of the 60 sec stimuli duration does not exceed 1°C with stimulation values of 0.1-0.5 J/cm2 and does not exceed 2°C with stimulation values of up to 1.0 J/cm2. Thus, the maximum temperature rise is consistent with the thermal damage threshold reported in previous studies. This study provides a quantitative evaluation of the temperature changes induced by INS, suggesting that existing practices pose minimal major safety concerns for biological tissues.
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Affiliation(s)
- Yinghua Xi
- Interdisciplinary Institute of Neuroscience and Technology, Key Laboratory for Biomedical Engineering of Ministry of Education, College of Biomedical Engineering & Instrument Science, Zhejiang University , Hangzhou 310027, China
- MOE Frontier Science Center for Brain Science and Brain-machine Integration, Zhejiang University, Hangzhou 310058, China
| | - Kenneth E Schriver
- School of Brain Science and Brain Medicine, Zhejiang University, Hangzhou 310058, China
| | - Anna Wang Roe
- Interdisciplinary Institute of Neuroscience and Technology, Key Laboratory for Biomedical Engineering of Ministry of Education, College of Biomedical Engineering & Instrument Science, Zhejiang University , Hangzhou 310027, China
- MOE Frontier Science Center for Brain Science and Brain-machine Integration, Zhejiang University, Hangzhou 310058, China
- Second Affiliated Hospital of Zhejiang University School of Medicine, Zhejiang University, Hangzhou 310058, China
| | - Xiaotong Zhang
- Interdisciplinary Institute of Neuroscience and Technology, Key Laboratory for Biomedical Engineering of Ministry of Education, College of Biomedical Engineering & Instrument Science, Zhejiang University , Hangzhou 310027, China
- MOE Frontier Science Center for Brain Science and Brain-machine Integration, Zhejiang University, Hangzhou 310058, China
- Second Affiliated Hospital of Zhejiang University School of Medicine, Zhejiang University, Hangzhou 310058, China
- College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China
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Bhowmick S, Graham RD, Verma N, Trevathan JK, Franke M, Nieuwoudt S, Fisher LE, Shoffstall AJ, Weber DJ, Ludwig KA, Lempka SF. Computational modeling of dorsal root ganglion stimulation using an Injectrode. J Neural Eng 2024; 21:026039. [PMID: 38502956 PMCID: PMC11007586 DOI: 10.1088/1741-2552/ad357f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Revised: 02/23/2024] [Accepted: 03/19/2024] [Indexed: 03/21/2024]
Abstract
Objective.Minimally invasive neuromodulation therapies like the Injectrode, which is composed of a tightly wound polymer-coated Platinum/Iridium microcoil, offer a low-risk approach for administering electrical stimulation to the dorsal root ganglion (DRG). This flexible electrode is aimed to conform to the DRG. The stimulation occurs through a transcutaneous electrical stimulation (TES) patch, which subsequently transmits the stimulation to the Injectrode via a subcutaneous metal collector. However, it is important to note that the effectiveness of stimulation through TES relies on the specific geometrical configurations of the Injectrode-collector-patch system. Hence, there is a need to investigate which design parameters influence the activation of targeted neural structures.Approach.We employed a hybrid computational modeling approach to analyze the impact of Injectrode system design parameters on charge delivery and neural response to stimulation. We constructed multiple finite element method models of DRG stimulation, followed by the implementation of multi-compartment models of DRG neurons. By calculating potential distribution during monopolar stimulation, we simulated neural responses using various parameters based on prior acute experiments. Additionally, we developed a canonical monopolar stimulation and full-scale model of bipolar bilateral L5 DRG stimulation, allowing us to investigate how design parameters like Injectrode size and orientation influenced neural activation thresholds.Main results.Our findings were in accordance with acute experimental measurements and indicate that the minimally invasive Injectrode system predominantly engages large-diameter afferents (Aβ-fibers). These activation thresholds were contingent upon the surface area of the Injectrode. As the charge density decreased due to increasing surface area, there was a corresponding expansion in the stimulation amplitude range before triggering any pain-related mechanoreceptor (Aδ-fibers) activity.Significance.The Injectrode demonstrates potential as a viable technology for minimally invasive stimulation of the DRG. Our findings indicate that utilizing a larger surface area Injectrode enhances the therapeutic margin, effectively distinguishing the desired Aβactivation from the undesired Aδ-fiber activation.
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Affiliation(s)
- Sauradeep Bhowmick
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States of America
- Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States of America
| | - Robert D Graham
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States of America
- Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States of America
| | - Nishant Verma
- Department of Biomedical Engineering, University of Wisconsin–Madison, Madison, WI, United States of America
- Wisconsin Institute for Translational Neuroengineering (WITNe)–Madison, Madison, WI, United States of America
| | - James K Trevathan
- Department of Biomedical Engineering, University of Wisconsin–Madison, Madison, WI, United States of America
- Wisconsin Institute for Translational Neuroengineering (WITNe)–Madison, Madison, WI, United States of America
| | | | | | - Lee E Fisher
- Rehab Neural Engineering Labs (RNEL), Department of Physical Medicine and Rehabilitation, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Andrew J Shoffstall
- Neuronoff Inc., Cleveland, OH, United States of America
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States of America
| | - Douglas J Weber
- Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, United States of America
- Neuroscience Institute, Carnegie Mellon University, Pittsburgh, PA, United States of America
| | - Kip A Ludwig
- Department of Biomedical Engineering, University of Wisconsin–Madison, Madison, WI, United States of America
- Wisconsin Institute for Translational Neuroengineering (WITNe)–Madison, Madison, WI, United States of America
- Department of Neurosurgery, University of Wisconsin–Madison, Madison, WI, United States of America
| | - Scott F Lempka
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States of America
- Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States of America
- Department of Anesthesiology, University of Michigan, Ann Arbor, MI, United States of America
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3
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Steinemer A, Simon A, Güntürkün O, Rook N. Parallel executive pallio-motor loops in the pigeon brain. J Comp Neurol 2024; 532:e25611. [PMID: 38625816 DOI: 10.1002/cne.25611] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Revised: 03/08/2024] [Accepted: 03/24/2024] [Indexed: 04/18/2024]
Abstract
A core component of the avian pallial cognitive network is the multimodal nidopallium caudolaterale (NCL) that is considered to be analogous to the mammalian prefrontal cortex (PFC). The NCL plays a key role in a multitude of executive tasks such as working memory, decision-making during navigation, and extinction learning in complex learning environments. Like the PFC, the NCL is positioned at the transition from ascending sensory to descending motor systems. For the latter, it sends descending premotor projections to the intermediate arcopallium (AI) and the medial striatum (MSt). To gain detailed insight into the organization of these projections, we conducted several retrograde and anterograde tracing experiments. First, we tested whether NCL neurons projecting to AI (NCLarco neurons) and MSt (NCLMSt neurons) are constituted by a single neuronal population with bifurcating neurons, or whether they form two distinct populations. Here, we found two distinct projection patterns to both target areas that were associated with different morphologies. Second, we revealed a weak topographic projection toward the medial and lateral striatum and a strong topographic projection toward AI with clearly distinguishable sensory termination fields. Third, we investigated the relationship between the descending NCL pathways to the arcopallium with those from the hyperpallium apicale, which harbors a second major descending pathway of the avian pallium. We embed our findings within a system of parallel pallio-motor loops that carry information from separate sensory modalities to different subpallial systems. Our results also provide insights into the evolution of the avian motor system from which, possibly, the song system has emerged.
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Affiliation(s)
- Alina Steinemer
- Department of Biopsychology, Institute of Cognitive Neuroscience, Faculty of Psychology, Ruhr University Bochum, Bochum, Germany
| | - Annika Simon
- Department of Biopsychology, Institute of Cognitive Neuroscience, Faculty of Psychology, Ruhr University Bochum, Bochum, Germany
| | - Onur Güntürkün
- Department of Biopsychology, Institute of Cognitive Neuroscience, Faculty of Psychology, Ruhr University Bochum, Bochum, Germany
| | - Noemi Rook
- Department of Biopsychology, Institute of Cognitive Neuroscience, Faculty of Psychology, Ruhr University Bochum, Bochum, Germany
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Choudhary P, Gupta A, Gupta SK, Dwivedi S, Singh S. Comparative evaluation of divergent concoction of NGF, BDNF, EGF, and FGF growth factor's role in enhancing neuronal differentiation of adipose-derived mesenchymal stem cells. Int J Biol Macromol 2024; 260:129561. [PMID: 38246449 DOI: 10.1016/j.ijbiomac.2024.129561] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Revised: 01/13/2024] [Accepted: 01/15/2024] [Indexed: 01/23/2024]
Abstract
MSCs (Mesenchymal Stem Cells) can differentiate into various lineages, including neurons and glial cells. In the past few decades, MSCs have been well explored in the context of neuronal differentiation and have been reported to have the immense potential to form distinct kinds of neurons. The distinguishing features of MSCs make them among the most desired cell sources for stem cell therapy. This study involved the trans-differentiation of Adipose-derived human Mesenchymal Stem Cells (ADMSCs) into neurons. The protocol employs a cocktail of chemical inducers in different combinations, including Brain-derived neurotrophic factor (BDNF), epidermal growth factor (EGF), and Nerve growth factor (NGF) Fibroblastic growth factor (FGF), in induction media. Both types have been successfully differentiated into neurons, confirmed by morphological aspects and the presence of neural-specific markers through RT-PCR (Reverse transcription polymerase chain reaction) studies and immunocytochemistry assay. They have shown excellent morphology with long neurites, synaptic connections, and essential neural markers to validate their identity. The results may significantly contribute to cell replacement therapy for neurological disorders.
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Affiliation(s)
- Princy Choudhary
- Department of Applied Science, Indian Institute of Information Technology, Allahabad Devghat, Jhalwa, Prayagraj 211015, U.P., India
| | - Ayushi Gupta
- Department of Applied Science, Indian Institute of Information Technology, Allahabad Devghat, Jhalwa, Prayagraj 211015, U.P., India
| | - Saurabh Kumar Gupta
- Department of Biotechnology and Medical Engineering, National Institute of Technology, Rourkela, Odisha 769008, India
| | - Shrey Dwivedi
- Department of Applied Science, Indian Institute of Information Technology, Allahabad Devghat, Jhalwa, Prayagraj 211015, U.P., India
| | - Sangeeta Singh
- Department of Applied Science, Indian Institute of Information Technology, Allahabad Devghat, Jhalwa, Prayagraj 211015, U.P., India.
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5
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Zeng H, Mayberry JE, Wadkins D, Chen N, Summers DW, Kuehn MH. Loss of Sarm1 reduces retinal ganglion cell loss in chronic glaucoma. Acta Neuropathol Commun 2024; 12:23. [PMID: 38331947 PMCID: PMC10854189 DOI: 10.1186/s40478-024-01736-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2023] [Accepted: 01/23/2024] [Indexed: 02/10/2024] Open
Abstract
Glaucoma is one of the leading causes of irreversible blindness worldwide and vision loss in the disease results from the deterioration of retinal ganglion cells (RGC) and their axons. Metabolic dysfunction of RGC plays a significant role in the onset and progression of the disease in both human patients and rodent models, highlighting the need to better define the mechanisms regulating cellular energy metabolism in glaucoma. This study sought to determine if Sarm1, a gene involved in axonal degeneration and NAD+ metabolism, contributes to glaucomatous RGC loss in a mouse model with chronic elevated intraocular pressure (IOP). Our data demonstrate that after 16 weeks of elevated IOP, Sarm1 knockout (KO) mice retain significantly more RGC than control animals. Sarm1 KO mice also performed significantly better when compared to control mice during optomotor testing, indicating that visual function is preserved in this group. Our findings also indicate that Sarm1 KO mice display mild ocular developmental abnormalities, including reduced optic nerve axon diameter and lower visual acuity than controls. Finally, we present data to indicate that SARM1 expression in the optic nerve is most prominently associated with oligodendrocytes. Taken together, these data suggest that attenuating Sarm1 activity through gene therapy, pharmacologic inhibition, or NAD+ supplementation, may be a novel therapeutic approach for patients with glaucoma.
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Affiliation(s)
- Huilan Zeng
- Department of Ophthalmology, The First Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, Hunan, 421001, People's Republic of China
| | - Jordan E Mayberry
- Department of Ophthalmology and Visual Sciences, The University of Iowa, Iowa City, IA, 52242, USA
- Iowa City VA Center for the Prevention and Treatment of Visual Loss, Iowa City, IA, 52246, USA
| | - David Wadkins
- Department of Ophthalmology and Visual Sciences, The University of Iowa, Iowa City, IA, 52242, USA
- Iowa City VA Center for the Prevention and Treatment of Visual Loss, Iowa City, IA, 52246, USA
| | - Nathan Chen
- Department of Ophthalmology and Visual Sciences, The University of Iowa, Iowa City, IA, 52242, USA
- Iowa City VA Center for the Prevention and Treatment of Visual Loss, Iowa City, IA, 52246, USA
| | - Daniel W Summers
- Department of Biology, The University of Iowa, Iowa City, IA, 52242, USA
| | - Markus H Kuehn
- Department of Ophthalmology and Visual Sciences, The University of Iowa, Iowa City, IA, 52242, USA.
- Iowa City VA Center for the Prevention and Treatment of Visual Loss, Iowa City, IA, 52246, USA.
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Madden LR, Graham RD, Lempka SF, Bruns TM. Multiformity of extracellular microelectrode recordings from Aδ neurons in the dorsal root ganglia: a computational modeling study. J Neurophysiol 2024; 131:261-277. [PMID: 38169334 DOI: 10.1152/jn.00385.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2023] [Revised: 12/18/2023] [Accepted: 01/02/2024] [Indexed: 01/05/2024] Open
Abstract
Microelectrodes serve as a fundamental tool in electrophysiology research throughout the nervous system, providing a means of exploring neural function with a high resolution of neural firing information. We constructed a hybrid computational model using the finite element method and multicompartment cable models to explore factors that contribute to extracellular voltage waveforms that are produced by sensory pseudounipolar neurons, specifically smaller A-type neurons, and that are recorded by microelectrodes in dorsal root ganglia. The finite element method model included a dorsal root ganglion, surrounding tissues, and a planar microelectrode array. We built a multicompartment neuron model with multiple trajectories of the glomerular initial segment found in many A-type sensory neurons. Our model replicated both the somatic intracellular voltage profile of Aδ low-threshold mechanoreceptor neurons and the unique extracellular voltage waveform shapes that are observed in experimental settings. Results from this model indicated that tortuous glomerular initial segment geometries can introduce distinct multiphasic properties into a neuron's recorded waveform. Our model also demonstrated how recording location relative to specific microanatomical components of these neurons, and recording distance from these components, can contribute to additional changes in the multiphasic characteristics and peak-to-peak voltage amplitude of the waveform. This knowledge may provide context for research employing microelectrode recordings of pseudounipolar neurons in sensory ganglia, including functional mapping and closed-loop neuromodulation. Furthermore, our simulations gave insight into the neurophysiology of pseudounipolar neurons by demonstrating how the glomerular initial segment aids in increasing the resistance of the stem axon and mitigating rebounding somatic action potentials.NEW & NOTEWORTHY We built a computational model of sensory neurons in the dorsal root ganglia to investigate factors that influence the extracellular waveforms recorded by microelectrodes. Our model demonstrates how the unique structure of these neurons can lead to diverse and often multiphasic waveform profiles depending on the location of the recording contact relative to microanatomical neural components. Our model also provides insight into the neurophysiological function of axon glomeruli that are often present in these neurons.
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Affiliation(s)
- Lauren R Madden
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, United States
- Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan, United States
| | - Robert D Graham
- Department of Anesthesiology, Washington University, St. Louis, Missouri, United States
| | - Scott F Lempka
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, United States
- Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan, United States
- Department of Anesthesiology, University of Michigan, Ann Arbor, Michigan, United States
| | - Tim M Bruns
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, United States
- Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan, United States
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Mizumura K, Taguchi T. Neurochemical mechanism of muscular pain: Insight from the study on delayed onset muscle soreness. J Physiol Sci 2024; 74:4. [PMID: 38267849 PMCID: PMC10809664 DOI: 10.1186/s12576-023-00896-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2023] [Accepted: 12/22/2023] [Indexed: 01/26/2024]
Abstract
We reviewed fundamental studies on muscular pain, encompassing the characteristics of primary afferent fibers and neurons, spinal and thalamic projections, several muscular pain models, and possible neurochemical mechanisms of muscle pain. Most parts of this review were based on data obtained from animal experiments, and some researches on humans were also introduced. We focused on delayed-onset muscle soreness (DOMS) induced by lengthening contractions (LC), suitable for studying myofascial pain syndromes. The muscular mechanical withdrawal threshold (MMWT) decreased 1-3 days after LC in rats. Changing the speed and range of stretching showed that muscle injury seldom occurred, except in extreme conditions, and that DOMS occurred in parameters without muscle damage. The B2 bradykinin receptor-nerve growth factor (NGF) route and COX-2-glial cell line-derived neurotrophic factor (GDNF) route were involved in the development of DOMS. The interactions between these routes occurred at two levels. A repeated-bout effect was observed in MMWT and NGF upregulation, and this study showed that adaptation possibly occurred before B2 bradykinin receptor activation. We have also briefly discussed the prevention and treatment of DOMS.
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Affiliation(s)
- Kazue Mizumura
- Nagoya University, Nagoya, 464-8601, Japan.
- Department of Physiology, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo, 101-8310, Japan.
| | - Toru Taguchi
- Department of Physical Therapy, Faculty of Rehabilitation, Niigata University of Health and Welfare, Niigata, 950-3198, Japan
- Institute for Human Movement and Medical Sciences (IHMMS), Niigata University of Health and Welfare, Niigata, 950-3198, Japan
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Jang K, Garraway SM. A review of dorsal root ganglia and primary sensory neuron plasticity mediating inflammatory and chronic neuropathic pain. NEUROBIOLOGY OF PAIN (CAMBRIDGE, MASS.) 2024; 15:100151. [PMID: 38314104 PMCID: PMC10837099 DOI: 10.1016/j.ynpai.2024.100151] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 01/04/2024] [Accepted: 01/19/2024] [Indexed: 02/06/2024]
Abstract
Pain is a sensory state resulting from complex integration of peripheral nociceptive inputs and central processing. Pain consists of adaptive pain that is acute and beneficial for healing and maladaptive pain that is often persistent and pathological. Pain is indeed heterogeneous, and can be expressed as nociceptive, inflammatory, or neuropathic in nature. Neuropathic pain is an example of maladaptive pain that occurs after spinal cord injury (SCI), which triggers a wide range of neural plasticity. The nociceptive processing that underlies pain hypersensitivity is well-studied in the spinal cord. However, recent investigations show maladaptive plasticity that leads to pain, including neuropathic pain after SCI, also exists at peripheral sites, such as the dorsal root ganglia (DRG), which contains the cell bodies of sensory neurons. This review discusses the important role DRGs play in nociceptive processing that underlies inflammatory and neuropathic pain. Specifically, it highlights nociceptor hyperexcitability as critical to increased pain states. Furthermore, it reviews prior literature on glutamate and glutamate receptors, voltage-gated sodium channels (VGSC), and brain-derived neurotrophic factor (BDNF) signaling in the DRG as important contributors to inflammatory and neuropathic pain. We previously reviewed BDNF's role as a bidirectional neuromodulator of spinal plasticity. Here, we shift focus to the periphery and discuss BDNF-TrkB expression on nociceptors, non-nociceptor sensory neurons, and non-neuronal cells in the periphery as a potential contributor to induction and persistence of pain after SCI. Overall, this review presents a comprehensive evaluation of large bodies of work that individually focus on pain, DRG, BDNF, and SCI, to understand their interaction in nociceptive processing.
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Affiliation(s)
- Kyeongran Jang
- Department of Cell Biology, Emory University, School of Medicine, Atlanta, GA, 30322, USA
| | - Sandra M. Garraway
- Department of Cell Biology, Emory University, School of Medicine, Atlanta, GA, 30322, USA
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9
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Bhowmick S, Graham RD, Verma N, Trevathan JK, Franke M, Nieuwoudt S, Fisher LE, Shoffstall AJ, Weber DJ, Ludwig KA, Lempka SF. Computational modeling of dorsal root ganglion stimulation using an Injectrode. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.20.558675. [PMID: 37790562 PMCID: PMC10542492 DOI: 10.1101/2023.09.20.558675] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/05/2023]
Abstract
Objective Minimally invasive neuromodulation therapies like the Injectrode, which is composed of a tightly wound polymer-coated platinum/iridium microcoil, offer a low-risk approach for administering electrical stimulation to the dorsal root ganglion (DRG). This flexible electrode is aimed to conform to the DRG. The stimulation occurs through a transcutaneous electrical stimulation (TES) patch, which subsequently transmits the stimulation to the Injectrode via a subcutaneous metal collector. However, effectiveness of stimulation relies on the specific geometrical configurations of the Injectrode-collector-patch system. Hence, there is a need to investigate which design parameters influence the activation of targeted neural structures. Approach We employed a hybrid computational modeling approach to analyze the impact of the Injectrode system design parameters on charge delivery and the neural response to stimulation. We constructed multiple finite element method models of DRG stimulation and multi-compartment models of DRG neurons. We simulated the neural responses using parameters based on prior acute preclinical experiments. Additionally, we developed multiple human-scale computational models of DRG stimulation to investigate how design parameters like Injectrode size and orientation influenced neural activation thresholds. Main results Our findings were in accordance with acute experimental measurements and indicated that the Injectrode system predominantly engages large-diameter afferents (Aβ-fibers). These activation thresholds were contingent upon the surface area of the Injectrode. As the charge density decreased due to increasing surface area, there was a corresponding expansion in the stimulation amplitude range before triggering any pain-related mechanoreceptor (Aδ-fibers) activity. Significance The Injectrode demonstrates potential as a viable technology for minimally invasive stimulation of the DRG. Our findings indicate that utilizing a larger surface area Injectrode enhances the therapeutic margin, effectively distinguishing the desired Aβ activation from the undesired Aδ-fiber activation.
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10
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Uhelski ML, Johns ME, Horrmann A, Mohamed S, Sohail A, Khasabova IA, Simone DA, Banik RK. Adverse effects of methylene blue in peripheral neurons: An in vitro electrophysiology and cell culture study. Mol Pain 2022; 18:17448069221142523. [PMID: 36408567 PMCID: PMC9730009 DOI: 10.1177/17448069221142523] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Methylene blue (MB) is an effective treatment for methemoglobinemia, ifosfamide-induced encephalopathy, cyanide poisoning, and refractory vasoplegia. However, clinical case reports and preclinical studies indicate potentially neurotoxic activity of MB at certain concentrations. The exact mechanisms of MB neurotoxicity are not known, and while the effects of MB on neuronal tissue from different brain regions and myenteric ganglia have been examined, its effects on primary afferent neurons from dorsal root ganglia (DRG) have not been studied. Mouse DRG were exposed to MB (0.3-10 μM) in vitro to assess neurite outgrowth. Increasing concentrations of MB (0.3-10 μM) were associated with neurotoxicity as shown by a substantial loss of cells with neurite formation, particularly at 10 μM. In parallel experiments, cultured rat DRG neurons were treated with MB (100 μM) to examine how MB affects electrical membrane properties of small-diameter sensory neurons. MB decreased peak inward and outward current densities, decreased action potential amplitude, overshoot, afterhyperpolarization, increased action potential rise time, and decreased action potential firing in response to current stimulation. MB induced dose-dependent toxicity in peripheral neurons, in vitro. These findings are consistent with studies in brain and myenteric ganglion neurons showing increased neuronal loss and altered membrane electrical properties after MB application. Further research is needed to parse out the toxicity profile for MB to minimize damage to neuronal structures and reduce side effects in clinical settings.
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Affiliation(s)
- Megan L Uhelski
- Department of Pain Medicine, The University of Texas M.D. Anderson Cancer Center, Houston, TX, USA
| | - Malcolm E Johns
- Department of Anesthesiology, School of Medicine, University of Minnesota, Minneapolis, MN, USA
| | - Alec Horrmann
- Department of Anesthesiology, School of Medicine, University of Minnesota, Minneapolis, MN, USA
| | - Sadiq Mohamed
- Department of Anesthesiology, School of Medicine, University of Minnesota, Minneapolis, MN, USA
| | - Ayesha Sohail
- Department of Anesthesiology, School of Medicine, University of Minnesota, Minneapolis, MN, USA
| | - Iryna A Khasabova
- Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN, USA
| | - Donald A Simone
- Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN, USA
| | - Ratan K Banik
- Department of Anesthesiology, School of Medicine, University of Minnesota, Minneapolis, MN, USA,Ratan K Banik, Department of Anesthesiology, University of Minnesota, B515 Mayo Memorial Building, 420 Delaware Street S.E., MMC 294, Minneapolis, MN 55455, USA.
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11
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Foit NA, Yung S, Lee HM, Bernasconi A, Bernasconi N, Hong SJ. A whole-brain 3D myeloarchitectonic atlas: Mapping the Vogt-Vogt legacy to the cortical surface. Neuroimage 2022; 263:119617. [PMID: 36084859 DOI: 10.1016/j.neuroimage.2022.119617] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Revised: 09/03/2022] [Accepted: 09/05/2022] [Indexed: 11/18/2022] Open
Abstract
Building precise and detailed parcellations of anatomically and functionally distinct brain areas has been a major focus in Neuroscience. Pioneer anatomists parcellated the cortical manifold based on extensive histological studies of post-mortem brain, harnessing local variations in cortical cyto- and myeloarchitecture to define areal boundaries. Compared to the cytoarchitectonic field, where multiple neuroimaging studies have recently translated this old legacy data into useful analytical resources, myeloarchitectonics, which parcellate the cortex based on the organization of myelinated fibers, has received less attention. Here, we present the neocortical surface-based myeloarchitectonic atlas based on the histology-derived maps of the Vogt-Vogt school and its 2D translation by Nieuwenhuys. In addition to a myeloarchitectonic parcellation, our package includes intracortical laminar profiles of myelin content based on Vogt-Vogt-Hopf original publications. Histology-derived myelin density mapped on our atlas demonstrated a close overlap with in vivo quantitative MRI markers for myelin and relates to cytoarchitectural features. Complementing the existing battery of approaches for digital cartography, the whole-brain myeloarchitectonic atlas offers an opportunity to validate imaging surrogate markers of myelin in both health and disease.
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Affiliation(s)
- Niels A Foit
- Neuroimaging of Epilepsy Laboratory, McConnell Brain Imaging Center, Montreal Neurological Institute, Montreal, QC, Canada; Department of Neurosurgery, Medical Center - University of Freiburg, Freiburg, Germany
| | - Seles Yung
- Neuroimaging of Epilepsy Laboratory, McConnell Brain Imaging Center, Montreal Neurological Institute, Montreal, QC, Canada
| | - Hyo Min Lee
- Neuroimaging of Epilepsy Laboratory, McConnell Brain Imaging Center, Montreal Neurological Institute, Montreal, QC, Canada
| | - Andrea Bernasconi
- Neuroimaging of Epilepsy Laboratory, McConnell Brain Imaging Center, Montreal Neurological Institute, Montreal, QC, Canada
| | - Neda Bernasconi
- Neuroimaging of Epilepsy Laboratory, McConnell Brain Imaging Center, Montreal Neurological Institute, Montreal, QC, Canada
| | - Seok-Jun Hong
- Neuroimaging of Epilepsy Laboratory, McConnell Brain Imaging Center, Montreal Neurological Institute, Montreal, QC, Canada; Center for the Developing Brain, Child Mind Institute, NY, USA; Center for Neuroscience Imaging Research, Institute for Basic Science, Suwon, South Korea; Department of Biomedical Engineering, Sungkyunkwan University, Suwon, South Korea.
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12
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Graham RD, Sankarasubramanian V, Lempka SF. Dorsal Root Ganglion Stimulation for Chronic Pain: Hypothesized Mechanisms of Action. THE JOURNAL OF PAIN 2022; 23:196-211. [PMID: 34425252 PMCID: PMC8943693 DOI: 10.1016/j.jpain.2021.07.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 06/28/2021] [Accepted: 07/20/2021] [Indexed: 02/03/2023]
Abstract
Dorsal root ganglion stimulation (DRGS) is a neuromodulation therapy for chronic pain that is refractory to conventional medical management. Currently, the mechanisms of action of DRGS-induced pain relief are unknown, precluding both our understanding of why DRGS fails to provide pain relief to some patients and the design of neurostimulation technologies that directly target these mechanisms to maximize pain relief in all patients. Due to the heterogeneity of sensory neurons in the dorsal root ganglion (DRG), the analgesic mechanisms could be attributed to the modulation of one or many cell types within the DRG and the numerous brain regions that process sensory information. Here, we summarize the leading hypotheses of the mechanisms of DRGS-induced analgesia, and propose areas of future study that will be vital to improving the clinical implementation of DRGS. PERSPECTIVE: This article synthesizes the evidence supporting the current hypotheses of the mechanisms of action of DRGS for chronic pain and suggests avenues for future interdisciplinary research which will be critical to fully elucidate the analgesic mechanisms of the therapy.
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Affiliation(s)
- Robert D. Graham
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109, United States,Biointerfaces Institute, University of Michigan, Ann Arbor, MI 48109, United States
| | - Vishwanath Sankarasubramanian
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109, United States,Biointerfaces Institute, University of Michigan, Ann Arbor, MI 48109, United States
| | - Scott F. Lempka
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109, United States,Biointerfaces Institute, University of Michigan, Ann Arbor, MI 48109, United States,Department of Anesthesiology, University of Michigan, Ann Arbor, MI 48109, United States,Corresponding author: Scott F. Lempka, PhD, Department of Biomedical Engineering, University of Michigan, 2800 Plymouth Road, NCRC 14-184, Ann Arbor, MI 48109-2800,
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13
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Graham RD, Jhand AS, Lempka SF. Dorsal root ganglion stimulation produces differential effects on action potential propagation across a population of biophysically distinct C-neurons. FRONTIERS IN PAIN RESEARCH 2022; 3:1017344. [PMID: 36387415 PMCID: PMC9643723 DOI: 10.3389/fpain.2022.1017344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Accepted: 10/03/2022] [Indexed: 11/05/2022] Open
Abstract
Dorsal root ganglion stimulation (DRGS) is a neurostimulation therapy used to manage chronic pain that does not respond to conventional therapies. Unfortunately, not all patients receive sufficient pain relief from DRGS, leaving them with few other treatment options. Presently, our understanding of the mechanisms of action of DRGS is incomplete, preventing us from determining why some patients do not receive analgesia from the therapy. One hypothesis suggests that DRGS augments the filtering of action potentials (APs) at the T-junction of nociceptive C-neurons. To test this hypothesis, we utilized a computational modeling approach in which we developed a population of one thousand biophysically distinct C-neuron models which each produced electrophysiological characteristics (e.g., AP height, AP duration) reported in previous experimental studies. We used this population of model C-neurons to study how morphological and electrophysiological characteristics affected the propagation of APs through the T-junction. We found that trains of APs can propagate through the T-junction in the orthodromic direction at a higher frequency than in the antidromic direction due to the decrease in axonal diameter from the peripheral to spinal axon. Including slow outward conductances in the axonal compartments near the T-junction reduced following frequencies to ranges measured experimentally. We next used the population of C-neuron models to investigate how DRGS affected the orthodromic propagation of APs through the T-junction. Our data suggest that suprathreshold DRGS augmented the filtering of APs at the T-junction of some model C-neurons while increasing the activity of other model C-neurons. However, the stimulus pulse amplitudes required to induce activity in C-neurons (i.e., several mA) fell outside the range of stimulation pulse amplitudes used clinically (i.e., typically ≤1 mA). Furthermore, our data suggest that somatic GABA currents activated directly or indirectly by the DRGS pulse may produce diverse effects on orthodromic AP propagation in C-neurons. These data suggest DRGS may produce differential effects across a population of C-neurons and indicate that understanding how inherent biological variability affects a neuron's response to therapeutic electrical stimulation may be helpful in understanding its mechanisms of action.
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Affiliation(s)
- Robert D Graham
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States.,Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States
| | - Amolak S Jhand
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States.,Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States
| | - Scott F Lempka
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States.,Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States.,Department of Anesthesiology, University of Michigan, Ann Arbor, MI, United States
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14
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Murase S, Kobayashi K, Nasu T, Kihara C, Taguchi T, Mizumura K. Reply from Shiori Murase, Kimiko Kobayashi, Teruaki Nasu, Chiaki Kihara, Toru Taguchi and Kazue Mizumura. J Physiol 2021; 599:4227-4229. [PMID: 34258768 DOI: 10.1113/jp281903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- Shiori Murase
- Department of Physical Therapy, College of Life Sciences, Chubu University, Matsumoto-cho, Kasugai, 487-8501, Japan.,Department of Neuroscience II, Research Institute of Environmental Medicine, Nagoya University, Nagoya, 464-8601, Japan
| | - Kimiko Kobayashi
- Department of Anatomy and Neuroscience, Hyogo College of Medicine, Mukogawa-cho, Nishinomiya, 663-8501, Japan
| | - Teruaki Nasu
- Department of Physical Therapy, College of Life Sciences, Chubu University, Matsumoto-cho, Kasugai, 487-8501, Japan.,Department of Neuroscience II, Research Institute of Environmental Medicine, Nagoya University, Nagoya, 464-8601, Japan
| | - Chiaki Kihara
- Department of Physical Therapy, College of Life Sciences, Chubu University, Matsumoto-cho, Kasugai, 487-8501, Japan
| | - Toru Taguchi
- Department of Neuroscience II, Research Institute of Environmental Medicine, Nagoya University, Nagoya, 464-8601, Japan.,Department of Physical Therapy, Faculty of Rehabilitation, Niigata University of Health and Welfare, 1398 Shimami-cho, Kita-ku, Niigata, 950-3198, Japan.,Institute for Human Movement and Medical Sciences, Niigata University of Health and Welfare, 1398 Shimami-cho, Kita-ku, Niigata, 950-3198, Japan
| | - Kazue Mizumura
- Department of Physical Therapy, College of Life Sciences, Chubu University, Matsumoto-cho, Kasugai, 487-8501, Japan.,Department of Neuroscience II, Research Institute of Environmental Medicine, Nagoya University, Nagoya, 464-8601, Japan.,Department of Physiology, Nihon University School of Dentistry, 1-8-13 Kandasurugadai, Chiyoda-ku, Tokyo, 101-8310, Japan
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15
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Houben AM. Frequency Selectivity of Neural Circuits With Heterogeneous Discrete Transmission Delays. Neural Comput 2021; 33:2068-2086. [PMID: 34310671 DOI: 10.1162/neco_a_01404] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2020] [Accepted: 02/24/2021] [Indexed: 11/04/2022]
Abstract
Neurons are connected to other neurons by axons and dendrites that conduct signals with finite velocities, resulting in delays between the firing of a neuron and the arrival of the resultant impulse at other neurons. Since delays greatly complicate the analytical treatment and interpretation of models, they are usually neglected or taken to be uniform, leading to a lack in the comprehension of the effects of delays in neural systems. This letter shows that heterogeneous transmission delays make small groups of neurons respond selectively to inputs with differing frequency spectra. By studying a single integrate-and-fire neuron receiving correlated time-shifted inputs, it is shown how the frequency response is linked to both the strengths and delay times of the afferent connections. The results show that incorporating delays alters the functioning of neural networks, and changes the effect that neural connections and synaptic strengths have.
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16
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Franken G, Douven P, Debets J, Joosten EAJ. Conventional Dorsal Root Ganglion Stimulation in an Experimental Model of Painful Diabetic Peripheral Neuropathy: A Quantitative Immunocytochemical Analysis of Intracellular γ-Aminobutyric Acid in Dorsal Root Ganglion Neurons. Neuromodulation 2021; 24:639-645. [PMID: 33942947 PMCID: PMC8360133 DOI: 10.1111/ner.13398] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 02/26/2021] [Accepted: 03/15/2021] [Indexed: 11/26/2022]
Abstract
Background and Objective The sensory cell somata in the DRG contain all equipment necessary for extensive GABAergic signaling and are able to release GABA upon depolarization. With this study, we hypothesize that pain relief induced by conventional dorsal root ganglion stimulation (Con‐DRGS) in animals with experimental painful diabetic peripheral neuropathy is related to the release of GABA from DRG neurons. With use of quantitative immunocytochemistry, we hypothesize DRGS to result in a decreased intensity of intracellular GABA‐immunostaining in DRG somata. Materials and Methods Female Sprague‐Dawley rats (n = 31) were injected with streptozotocin (STZ) in order to induce Diabetes Mellitus. Animals that developed neuropathic pain after four weeks (Von Frey) were implanted with a unilateral DRGS device at L4 (n = 14). Animals were then stimulated for 30 min with Con‐DRGS (20 Hz, pulse width = 0.2 msec, amplitude = 67% of motor threshold, n = 8) or Sham‐DRGS (n = 6), while pain behavior (von Frey) was measured. DRGs were then collected and immunostained for GABA, and a relation to size of sensory cell soma diameter (small: 12–26 μm, assumed to be C‐fiber related sensory neurons; medium: 26–40 μm, assumed to be Aδ related sensory neurons; and large: 40–54 μm, assumed to be Aβ related sensory neurons) was made. Results DRGS treated animals showed significant reductions in STZ‐induced mechanical hypersensitivity. No significant differences in GABA immunostaining intensity per sensory neuron cell soma type (small‐, medium‐, or large‐sized) were noted in DRGs of stimulated (Con‐DRGS) animals versus Sham animals. No differences in GABA immunostaining intensity per sensory cell soma type in ipsi‐ as compared to contralateral DRGs were observed. Conclusion Con‐DRGS does not affect the average intracellular GABA immunofluorescence staining intensity in DRG sensory neurons of those animals which showed significant pain reduction. Similarly, no soma size related changes in intracellular GABA immunofluorescence were observed following Con‐DRGS.
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Affiliation(s)
- Glenn Franken
- Department of Anesthesiology and Pain Management, Maastricht University Medical Centre (MUMC+), Maastricht, The Netherlands.,School for Mental Health and Neuroscience (MHeNS), Faculty of Health, Medicine and Life Sciences, Maastricht University, Maastricht, The Netherlands
| | - Perla Douven
- Department of Anesthesiology and Pain Management, Maastricht University Medical Centre (MUMC+), Maastricht, The Netherlands.,School for Mental Health and Neuroscience (MHeNS), Faculty of Health, Medicine and Life Sciences, Maastricht University, Maastricht, The Netherlands.,Department of Urology, Maastricht University Medical Centre (MUMC+), Maastricht, The Netherlands.,Department of Surgery, Maastricht University Medical Centre (MUMC+), Maastricht, The Netherlands
| | - Jacques Debets
- School for Mental Health and Neuroscience (MHeNS), Faculty of Health, Medicine and Life Sciences, Maastricht University, Maastricht, The Netherlands.,Muroidean Facility, School of Cardiovascular Diseases (CARIM), Maastricht, The Netherlands
| | - Elbert A J Joosten
- Department of Anesthesiology and Pain Management, Maastricht University Medical Centre (MUMC+), Maastricht, The Netherlands.,School for Mental Health and Neuroscience (MHeNS), Faculty of Health, Medicine and Life Sciences, Maastricht University, Maastricht, The Netherlands
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17
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Murase S, Kobayashi K, Nasu T, Kihara C, Taguchi T, Mizumura K. Synergistic interaction of nerve growth factor and glial cell‐line derived neurotrophic factor in muscular mechanical hyperalgesia in rats. J Physiol 2021; 599:1783-1798. [DOI: 10.1113/jp280683] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Accepted: 01/18/2021] [Indexed: 11/08/2022] Open
Affiliation(s)
- Shiori Murase
- Department of Physical Therapy College of Life Sciences Chubu University Kasugai 487–8501 Japan
- Department of Neuroscience II Research Institute of Environmental Medicine Nagoya University Nagoya 464–8601 Japan
| | - Kimiko Kobayashi
- Department of Anatomy and Neuroscience Hyogo College of Medicine Nishinomiya 663–8501 Japan
| | - Teruaki Nasu
- Department of Physical Therapy College of Life Sciences Chubu University Kasugai 487–8501 Japan
- Department of Neuroscience II Research Institute of Environmental Medicine Nagoya University Nagoya 464–8601 Japan
| | - Chiaki Kihara
- Department of Physical Therapy College of Life Sciences Chubu University Kasugai 487–8501 Japan
| | - Toru Taguchi
- Department of Neuroscience II Research Institute of Environmental Medicine Nagoya University Nagoya 464–8601 Japan
- Department of Physical Therapy Faculty of Rehabilitation Niigata University of Health and Welfare Niigata 950–3198 Japan
- Institute for Human Movement and Medical Sciences Niigata University of Health and Welfare Niigata 950–3198 Japan
| | - Kazue Mizumura
- Department of Physical Therapy College of Life Sciences Chubu University Kasugai 487–8501 Japan
- Department of Neuroscience II Research Institute of Environmental Medicine Nagoya University Nagoya 464–8601 Japan
- Department of Physiology Nihon University School of Dentistry Tokyo 101–8310 Japan
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18
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Santi S, Corridori I, Pugno NM, Motta A, Migliaresi C. Injectable Scaffold-Systems for the Regeneration of Spinal Cord: Advances of the Past Decade. ACS Biomater Sci Eng 2021; 7:983-999. [PMID: 33523634 DOI: 10.1021/acsbiomaterials.0c01779] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Nowadays, whenever is possible and as an alternative to open spine surgery, minimally invasive procedures are preferred to treat spinal cord injuries (SCI), with percutaneous injections or small incisions, that are faster, less traumatic, and require less recovery time. Injectable repair systems are based on materials that can be injected in the lesion site, can eventually be loaded with drugs or even cells, and act as scaffolds for the lesion repair. The review analyzes papers written from 2010 onward on injectable materials/systems used/proposed for the regenerative and combinatorial therapies of SCI and discusses the in vivo models that have been used to validate them.
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Affiliation(s)
- Sofia Santi
- BIOTech Research Center and European Institute of Excellence on Tissue Engineering and Regenerative Medicine, University of Trento, Via delle Regole 101, 38123 Trento, Italy.,Department of Industrial Engineering, University of Trento, Via Sommarive 9, 38123 Trento, Italy
| | - Ilaria Corridori
- Laboratory of Bio-inspired, Bionic, Nano, Meta Materials & Mechanics, Department of Civil, Environmental and Mechanical Engineering, University of Trento, Via Mesiano 77, 38123 Trento, Italy
| | - Nicola M Pugno
- Laboratory of Bio-inspired, Bionic, Nano, Meta Materials & Mechanics, Department of Civil, Environmental and Mechanical Engineering, University of Trento, Via Mesiano 77, 38123 Trento, Italy.,School of Engineering and Material Science, Queen Mary University of London, Mile End Road, E1 4NS London, United Kingdom
| | - Antonella Motta
- BIOTech Research Center and European Institute of Excellence on Tissue Engineering and Regenerative Medicine, University of Trento, Via delle Regole 101, 38123 Trento, Italy.,Department of Industrial Engineering, University of Trento, Via Sommarive 9, 38123 Trento, Italy
| | - Claudio Migliaresi
- BIOTech Research Center and European Institute of Excellence on Tissue Engineering and Regenerative Medicine, University of Trento, Via delle Regole 101, 38123 Trento, Italy.,Department of Industrial Engineering, University of Trento, Via Sommarive 9, 38123 Trento, Italy
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19
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Roh J, Hwang SM, Lee SH, Lee K, Kim YH, Park CK. Functional Expression of Piezo1 in Dorsal Root Ganglion (DRG) Neurons. Int J Mol Sci 2020; 21:ijms21113834. [PMID: 32481599 PMCID: PMC7313462 DOI: 10.3390/ijms21113834] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2020] [Revised: 05/25/2020] [Accepted: 05/27/2020] [Indexed: 12/13/2022] Open
Abstract
Piezo channels are mechanosensitive ion channels. Piezo1 is primarily expressed in nonsensory tissues, whereas Piezo2 is predominantly found in sensory tissues, including dorsal root ganglion (DRG) neurons. However, a recent study demonstrated the intracellular calcium response to Yoda1, a selective Piezo1 agonist, in trigeminal ganglion (TG) neurons. Herein, we investigate the expression of Piezo1 mRNA and protein in mouse and human DRG neurons and the activation of Piezo1 via calcium influx by Yoda1. Yoda1 induces inward currents mainly in small- (< 25 μm) and medium-sized (25-35 μm) mouse DRG neurons. The Yoda1-induced Ca2+ response is inhibited by cationic channel blocker, ruthenium red and cationic mechanosensitive channel blocker, GsMTx4. To confirm the specific inhibition of Piezo1, we performed an adeno-associated virus serotype 2/5 (AAV2/5)-mediated delivery of short hairpin RNA (shRNA) into mouse DRG neurons. AAV2/5 transfection downregulates piezo1 mRNA expression and reduces Ca2+ response by Yoda1. Piezo1 also shows physiological functions with transient receptor potential vanilloid 1 (TRPV1) in the same DRG neurons and is regulated by the activation of TRPV1 in mouse DRG sensory neurons. Overall, we found that Piezo1 has physiological functions in DRG neurons and that TRPV1 activation inhibits an inward current induced by Yoda1.
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Affiliation(s)
- Jueun Roh
- Gachon Pain Center and Department of Physiology, College of Medicine, Gachon University, Incheon 21999, Korea; (J.R.); (S.-M.H.); (K.L.)
| | - Sung-Min Hwang
- Gachon Pain Center and Department of Physiology, College of Medicine, Gachon University, Incheon 21999, Korea; (J.R.); (S.-M.H.); (K.L.)
| | - Sun-Ho Lee
- Department of Neurosurgery, Spine tumor center, Samsung Medical Center, Sungkyunkwan University School of Medicine, 81 Irwon-ro, Gangnam-gu, Seoul 06351, Korea;
| | - Kihwan Lee
- Gachon Pain Center and Department of Physiology, College of Medicine, Gachon University, Incheon 21999, Korea; (J.R.); (S.-M.H.); (K.L.)
| | - Yong Ho Kim
- Gachon Pain Center and Department of Physiology, College of Medicine, Gachon University, Incheon 21999, Korea; (J.R.); (S.-M.H.); (K.L.)
- Correspondence: (Y.H.K.); (C.-K.P.); Tel.: +82-32-899-6691 (Y.H.K.); +82-32-899-6692 (C.-K.P.)
| | - Chul-Kyu Park
- Gachon Pain Center and Department of Physiology, College of Medicine, Gachon University, Incheon 21999, Korea; (J.R.); (S.-M.H.); (K.L.)
- Correspondence: (Y.H.K.); (C.-K.P.); Tel.: +82-32-899-6691 (Y.H.K.); +82-32-899-6692 (C.-K.P.)
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20
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Liu Y, Schwartz AG, Hong Y, Peng X, Xu F, Thomopoulos S, Genin GM. Correction of bias in the estimation of cell volume fraction from histology sections. J Biomech 2020; 104:109705. [PMID: 32247525 DOI: 10.1016/j.jbiomech.2020.109705] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2019] [Revised: 01/10/2020] [Accepted: 02/20/2020] [Indexed: 10/24/2022]
Abstract
Accurate determination of the fraction of a tissue's volume occupied by cells is critical for studying tissue development, pathology, and biomechanics. For example, homogenization methods that predict the function and responses of tissues based upon the properties of the tissue's constituents require estimates of cell volume fractions. A common way to estimate cellular volume fraction is to image cells in thin, planar histologic sections, and then invoke either the Delesse or the Glagolev principle to estimate the volume fraction from the measured area fraction. The Delesse principle relies upon the observation that for randomly aligned, identical features, the expected value of the observed area fraction of a phase equals the volume fraction of that phase, and the Glagolev principle relies on a similar observation for random rather than planar sampling. These methods are rigorous for analysis of a polished, opaque rock sections and for histologic sections that are thin compared to the characteristic length scale of the cells. However, when histologic slices cannot be cut sufficiently thin, a bias will be introduced. Although this bias - known as the Holmes effect in petrography - has been resolved for opaque spheres in a transparent matrix, it has not been addressed for histologic sections presenting the opposite problem, namely transparent cells in an opaque matrix. In this note, we present a scheme for correcting the bias in volume fraction estimates for transparent components in a relatively opaque matrix.
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Affiliation(s)
- Yanxin Liu
- Department of Mechanical Engineering & Materials Science, Washington University in St. Louis, United States
| | - Andrea G Schwartz
- Department of Orthopaedic Surgery, Washington University School of Medicine, United States
| | - Yuan Hong
- Department of Mechanical Engineering & Materials Science, Washington University in St. Louis, United States; NSF Science and Technology Center for Engineering Mechanobiology, Washington University in St. Louis, United States; Bioinspired Engineering and Biomechanics Center, School of Life Sciences and Technology, Xi'an Jiaotong University, China
| | - Xiangjun Peng
- Department of Mechanical Engineering & Materials Science, Washington University in St. Louis, United States; NSF Science and Technology Center for Engineering Mechanobiology, Washington University in St. Louis, United States; Bioinspired Engineering and Biomechanics Center, School of Life Sciences and Technology, Xi'an Jiaotong University, China
| | - Feng Xu
- Bioinspired Engineering and Biomechanics Center, School of Life Sciences and Technology, Xi'an Jiaotong University, China
| | - Stavros Thomopoulos
- Department of Orthopedic Surgery, Department of Biomedical Engineering, Columbia University, United States
| | - Guy M Genin
- Department of Mechanical Engineering & Materials Science, Washington University in St. Louis, United States; NSF Science and Technology Center for Engineering Mechanobiology, Washington University in St. Louis, United States; Bioinspired Engineering and Biomechanics Center, School of Life Sciences and Technology, Xi'an Jiaotong University, China.
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21
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Ford JB, Ganguly M, Poorman ME, Grissom WA, Jenkins MW, Chiel HJ, Jansen ED. Identifying the Role of Block Length in Neural Heat Block to Reduce Temperatures During Infrared Neural Inhibition. Lasers Surg Med 2020; 52:259-275. [PMID: 31347188 PMCID: PMC6981060 DOI: 10.1002/lsm.23139] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/30/2019] [Indexed: 01/01/2023]
Abstract
BACKGROUND AND OBJECTIVES The objective of this study is to assess the hypothesis that the length of axon heated, defined here as block length (BL), affects the temperature required for thermal inhibition of action potential propagation applied using laser heating. The presence of such a phenomenon has implications for how this technique, called infrared neural inhibition (INI), may be applied in a clinically safe manner since it suggests that temperatures required for therapy may be reduced through the proper spatial application of light. Here, we validate the presence of this phenomenon by assessing how the peak temperatures during INI are reduced when two different BLs are applied using irradiation from either one or two adjacent optical fibers. STUDY DESIGN/MATERIALS AND METHODS Assessment of the role of BL was carried out over two phases. First, a computational proof of concept was performed in the neural conduction simulation environment, NEURON, simulating the response of action potentials to increased temperatures applied at different full-width at half-maxima (FWHM) along axons. Second, ex vivo validation of these predictions was performed by measuring the radiant exposure, peak temperature rise, and FWHM of heat distributions associated with INI from one or two adjacent optical fibers. Electrophysiological assessment of radiant exposures at inhibition threshold were carried out in ex vivo Aplysia californica (sea slug) pleural abdominal nerves ( n = 6), an invertebrate with unmyelinated axons. Measurement of the maximum temperature rise required for induced heat block was performed in a water bath using a fine wire thermocouple. Finally, magnetic resonance thermometry (MRT) was performed on a nerve immersed in saline to assess the elevated temperature distribution at these radiant exposures. RESULTS Computational modeling in NEURON provided a theoretical proof of concept that the BL is an important factor contributing to the peak temperature required during neural heat block, predicting a 11.7% reduction in temperature rise when the FWHM along an axon is increased by 42.9%. Experimental validation showed that, when using two adjacent fibers instead of one, a 38.5 ± 2.2% (mean ± standard error of the mean) reduction in radiant exposure per pulse per fiber threshold at the fiber output (P = 7.3E-6) is measured, resulting in a reduction in peak temperature rise under each fiber of 23.5 ± 2.1% ( P = 9.3E-5) and 15.0 ± 2.4% ( P = 1.4E-3) and an increase in the FWHM of heating by 37.7 ± 6.4% ( P = 1E-3), 68.4 ± 5.2% ( P = 2.4E-5), and 51.9 ± 9.9% ( P = 1.7E-3) in three MRT slices. CONCLUSIONS This study provides the first experimental evidence for a phenomenon during the heat block in which the temperature for inhibition is dependent on the BL. While more work is needed to further reduce the temperature during INI, the results highlight that spatial application of the temperature rise during INI must be considered. Optimized implementation of INI may leverage this cellular response to provide optical modulation of neural signals with lower temperatures over greater time periods, which may increase the utility of the technique for laboratory and clinical use. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.
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Affiliation(s)
- Jeremy B. Ford
- Department of Biomedical Engineering, Vanderbilt University, 5824 Stevenson Center, Nashville, Tennessee 37232
- Department of Biomedical Engineering, Vanderbilt University, 5824 Stevenson Center, Nashville, Tennessee 37232
| | - Mohit Ganguly
- Department of Biomedical Engineering, Vanderbilt University, 5824 Stevenson Center, Nashville, Tennessee 37232
- Department of Biomedical Engineering, Vanderbilt University, 5824 Stevenson Center, Nashville, Tennessee 37232
| | - Megan E. Poorman
- Department of Biomedical Engineering, Vanderbilt University, 5824 Stevenson Center, Nashville, Tennessee 37232
- Vanderbilt University Institute of Imaging Sciences, Vanderbilt University, 1161 21st Ave S, Nashville, Tennessee 37232
| | - William A. Grissom
- Department of Biomedical Engineering, Vanderbilt University, 5824 Stevenson Center, Nashville, Tennessee 37232
- Vanderbilt University Institute of Imaging Sciences, Vanderbilt University, 1161 21st Ave S, Nashville, Tennessee 37232
| | - Michael W. Jenkins
- Department of Biomedical Engineering, Case Western Reserve University, 10900 Euclid Ave, Cleveland, Ohio 44106
- Department of Pediatrics, Case Western Reserve University, 2109 Adelbert Rd, Cleveland, Ohio 44106
| | - Hillel J. Chiel
- Department of Biomedical Engineering, Case Western Reserve University, 10900 Euclid Ave, Cleveland, Ohio 44106
- Department of Biology, Case Western Reserve University, 2080 Adelbert Rd, Cleveland, Ohio 44106
- Department of Neurosciences, Case Western Reserve University, 2210 Circle Drive, Cleveland, Ohio 44106
| | - E. Duco Jansen
- Department of Biomedical Engineering, Vanderbilt University, 5824 Stevenson Center, Nashville, Tennessee 37232
- Department of Biomedical Engineering, Vanderbilt University, 5824 Stevenson Center, Nashville, Tennessee 37232
- Department of Neurological Surgery, Vanderbilt University, 1161 21st Ave S, Nashville, Tennessee 37232
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22
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Sperry ZJ, Graham RD, Peck-Dimit N, Lempka SF, Bruns TM. Spatial models of cell distribution in human lumbar dorsal root ganglia. J Comp Neurol 2020; 528:1644-1659. [PMID: 31872433 DOI: 10.1002/cne.24848] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Revised: 12/18/2019] [Accepted: 12/19/2019] [Indexed: 12/15/2022]
Abstract
Dorsal root ganglia (DRG), which contain the somata of primary sensory neurons, have increasingly been considered as novel targets for clinical neural interfaces, both for neuroprosthetic and pain applications. Effective use of either neural recording or stimulation technologies requires an appropriate spatial position relative to the target neural element, whether axon or cell body. However, the internal three-dimensional spatial organization of human DRG neural fibers and somata has not been quantitatively described. In this study, we analyzed 202 cross-sectional images across the length of 31 human L4 and L5 DRG from 10 donors. We used a custom semi-automated graphical user interface to identify the locations of neural elements in the images and normalize the output to a consistent spatial reference for direct comparison by spinal level. By applying a recursive partitioning algorithm, we found that the highest density of cell bodies at both spinal levels could be found in the inner 85% of DRG length, the outer-most 25-30% radially, and the dorsal-most 69-76%. While axonal density was fairly homogeneous across the DRG length, there was a distinct low density region in the outer 7-11% radially. These findings are consistent with previous qualitative reports of neural distribution in DRG. The quantitative measurements we provide will enable improved targeting of future neural interface technologies and DRG-focused pharmaceutical therapies, and provide a rigorous anatomical description of the bridge between the central and peripheral nervous systems.
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Affiliation(s)
- Zachariah J Sperry
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan.,Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan
| | - Robert D Graham
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan.,Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan
| | - Nicholas Peck-Dimit
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan.,Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan
| | - Scott F Lempka
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan.,Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan.,Department of Anesthesiology, University of Michigan, Ann Arbor, Michigan
| | - Tim M Bruns
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan.,Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan
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23
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Nanivadekar AC, Ayers CA, Gaunt RA, Weber DJ, Fisher LE. Selectivity of afferent microstimulation at the DRG using epineural and penetrating electrode arrays. J Neural Eng 2019; 17:016011. [PMID: 31577993 PMCID: PMC9131467 DOI: 10.1088/1741-2552/ab4a24] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
OBJECTIVE We have shown previously that microstimulation of the lumbar dorsal root ganglia (L5-L7 DRG) using penetrating microelectrodes, selectively recruits distal branches of the sciatic and femoral nerves in an acute preparation. However, a variety of challenges limit the clinical translatability of DRG microstimulation via penetrating electrodes. For clinical translation of a DRG somatosensory neural interface, electrodes placed on the epineural surface of the DRG may be a viable path forward. The goal of this study was to evaluate the recruitment properties of epineural electrodes and compare their performance with that of penetrating electrodes. Here, we compare the number of selectively recruited distal nerve branches and the threshold stimulus intensities between penetrating and epineural electrode arrays. APPROACH Antidromically propagating action potentials were recorded from multiple distal branches of the femoral and sciatic nerves in response to epineural stimulation on 11 ganglia in four cats to quantify the selectivity of DRG stimulation. Compound action potentials (CAPs) were recorded using nerve cuff electrodes implanted around up to nine distal branches of the femoral and sciatic nerve trunks. We also tested stimulation selectivity with penetrating microelectrode arrays implanted into ten ganglia in four cats. A binary search was carried out to identify the minimum stimulus intensity that evoked a response at any of the distal cuffs, as well as whether the threshold response selectively occurred in only a single distal nerve branch. MAIN RESULTS Stimulation evoked activity in just a single peripheral nerve through 67% of epineural electrodes (35/52) and through 79% of the penetrating microelectrodes (240/308). The recruitment threshold (median = 9.67 nC/phase) and dynamic range of epineural stimulation (median = 1.01 nC/phase) were significantly higher than penetrating stimulation (0.90 nC/phase and 0.36 nC/phase, respectively). However, the pattern of peripheral nerves recruited for each DRG were similar for stimulation through epineural and penetrating electrodes. SIGNIFICANCE Despite higher recruitment thresholds, epineural stimulation provides comparable selectivity and superior dynamic range to penetrating electrodes. These results suggest that it may be possible to achieve a highly selective neural interface with the DRG without penetrating the epineurium.
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Affiliation(s)
- Ameya C Nanivadekar
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15213, United States of America. Rehabilitation Neural Engineering Laboratories, 3520 Fifth Avenue, Suite 300, Pittsburgh, PA 15213, United States of America. Center for Neural Basis of Cognition, Pittsburgh, PA 15213, United States of America
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24
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Transient Receptor Potential vanilloid 4 ion channel in C-fibres is involved in mechanonociception of the normal and inflamed joint. Sci Rep 2019; 9:10928. [PMID: 31358810 PMCID: PMC6662841 DOI: 10.1038/s41598-019-47342-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2019] [Accepted: 07/16/2019] [Indexed: 12/12/2022] Open
Abstract
The Transient Receptor Potential vanilloid 4 ion channel (TRPV4) is an important sensor for osmotic and mechanical stimuli in the musculoskeletal system, and it is also involved in processes of nociception. In this study we investigated the putative role of TRPV4 ion channels in joint pain. In anesthetized rats we recorded from mechanosensitive nociceptive A∂- and C-fibres supplying the medial aspect of the knee joint. The intraarticular injection of the TRPV4 antagonist RN-1734 into the knee joint reduced the responses of C-fibres of the normal joint to noxious mechanical stimulation and the responses of the sensitized C-fibres of the acutely inflamed joint to innocuous and noxious mechanical stimulation. The responses of nociceptive A∂-fibres were not significantly altered by RN-1734. The intraarticular application of the TRPV4 agonists 4αPDD, GSK 1016790 A, and RN-1747 did not consistently alter the responses of A∂- and C-fibres to mechanical stimulation of the joint nor did they induce ongoing activity. We conclude that TRPV4 ion channels are involved in the responses of C-fibres to noxious mechanical stimulation of the normal joint, and in the enhanced sensitivity of C-fibres to mechanical stimulation of the joint during inflammation of the joint.
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25
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Wang J, La JH, Hamill OP. PIEZO1 Is Selectively Expressed in Small Diameter Mouse DRG Neurons Distinct From Neurons Strongly Expressing TRPV1. Front Mol Neurosci 2019; 12:178. [PMID: 31379500 PMCID: PMC6659173 DOI: 10.3389/fnmol.2019.00178] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2019] [Accepted: 07/04/2019] [Indexed: 11/13/2022] Open
Abstract
Using a high resolution in situ hybridization technique we have measured PIEZO1, PIEZO2, and TRPV1 transcripts in mouse dorsal root ganglion (DRG) neurons. Consistent with previous studies, PIEZO2 transcripts were highly expressed in DRG neurons of all sizes, including most notably the largest diameter neurons implicated in mediating touch and proprioception. In contrast, PIEZO1 transcripts were selectively expressed in smaller DRG neurons, which are implicated in mediating nociception. Moreover, the small neurons expressing PIEZO1 were mostly distinct from those neurons that strongly expressed TRPV1, one of the channels implicated in heat-nociception. Interestingly, while PIEZO1- and TRPV1- expressing neurons form essentially non-overlapping populations, PIEZO2 showed co-expression in both populations. Using an in vivo functional test for the selective expression, we found that Yoda1, a PIEZO1-specific agonist, induced a mechanical hyperalgesia that displayed a significantly prolonged time course compared with that induced by capsaicin, a TRPV1-specific agonist. Taken together, our results indicate that PIEZO1 should be considered a potential candidate in forming the long sought channel mediating mechano-nociception.
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Affiliation(s)
- Jigong Wang
- Department of Neuroscience, Cell Biology and Anatomy, The University of Texas Medical Branch, Galveston, TX, United States
| | - Jun-Ho La
- Department of Neuroscience, Cell Biology and Anatomy, The University of Texas Medical Branch, Galveston, TX, United States
| | - Owen P Hamill
- Department of Neuroscience, Cell Biology and Anatomy, The University of Texas Medical Branch, Galveston, TX, United States
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26
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Graham RD, Bruns TM, Duan B, Lempka SF. Dorsal root ganglion stimulation for chronic pain modulates Aβ-fiber activity but not C-fiber activity: A computational modeling study. Clin Neurophysiol 2019; 130:941-951. [PMID: 30981900 DOI: 10.1016/j.clinph.2019.02.016] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2018] [Revised: 01/23/2019] [Accepted: 02/16/2019] [Indexed: 02/07/2023]
Abstract
OBJECTIVE The goal of this project was to use computational models to investigate which types of primary sensory neurons are modulated by dorsal root ganglion stimulation (DRGS) to provide pain relief. METHODS We modeled DRGS by coupling an anatomical finite element model of a human L5 dorsal root ganglion to biophysical models of primary sensory neurons. We calculated the stimulation amplitude needed to elicit an action potential in each neuron, and examined how DRGS affected sensory neuron activity. RESULTS We showed that within clinical ranges of stimulation parameters, DRGS drives the activity of large myelinated Aβ-fibers but does not directly activate small nonmyelinated C-fibers. We also showed that the position of the active and return electrodes and the polarity of the stimulus pulse influence neural activation. CONCLUSIONS Our results indicate that DRGS may provide pain relief by activating pain-gating mechanisms in the dorsal horn via repeated activation of large myelinated afferents. SIGNIFICANCE Understanding the mechanisms of action of DRGS-induced pain relief may lead to innovations in stimulation technologies that improve patient outcomes.
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Affiliation(s)
- Robert D Graham
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA; Biointerfaces Institute, University of Michigan, Ann Arbor, MI, USA
| | - Tim M Bruns
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA; Biointerfaces Institute, University of Michigan, Ann Arbor, MI, USA
| | - Bo Duan
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
| | - Scott F Lempka
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA; Biointerfaces Institute, University of Michigan, Ann Arbor, MI, USA; Department of Anesthesiology, University of Michigan, Ann Arbor, MI, USA.
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27
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Ito T, Furuyama T, Hase K, Kobayasi KI, Hiryu S, Riquimaroux H. Organization of subcortical auditory nuclei of Japanese house bat (Pipistrellus abramus) identified with cytoarchitecture and molecular expression. J Comp Neurol 2018; 526:2824-2844. [PMID: 30168138 DOI: 10.1002/cne.24529] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2018] [Revised: 08/23/2018] [Accepted: 08/25/2018] [Indexed: 11/09/2022]
Abstract
The auditory system of echolocating bats shows remarkable specialization likely related to analyzing echoes of sonar pulses. However, significant interspecies differences have been observed in the organization of auditory pathways among echolocating bats, and the homology of auditory nuclei with those of non-echolocating species has not been established. Here, in order to establish the homology and specialization of auditory pathways in echolocating bats, the expression of markers for glutamatergic, GABAergic, and glycinergic phenotypes in the subcortical auditory nuclei of Japanese house bat (Pipistrellus abramus) was evaluated. In the superior olivary complex, we identified the medial superior olive and superior paraolivary nuclei as expressing glutamatergic and GABAergic phenotypes, respectively, suggesting these nuclei are homologous with those of rodents. In the nuclei of the lateral lemniscus (NLL), the dorsal nucleus was found to be purely GABAergic, the intermediate nucleus was a mixture of glutamatergic and inhibitory neurons, the compact part of the ventral nucleus was purely glycinergic, and the multipolar part of the ventral nucleus expressed both GABA and glycine. In the inferior colliculus (IC), the central nucleus was found to be further subdivided into dorsal and ventral parts according to differences in the density of terminals and the morphology of large GABAergic neurons, suggesting specialization to sonar pulse structure. Medial geniculate virtually lacked GABAergic neurons, suggesting that the organization of the tectothalamic pathway is similar with that of rodents. Taken together, our findings revealed that specialization primarily occurs with regard to nuclei size and organization of the NLL and IC.
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Affiliation(s)
- Tetsufumi Ito
- Department of Anatomy, Kanazawa Medical University, Uchinada, Ishikawa, Japan.,Research and Education Program for Life Science, University of Fukui, Fukui, Fukui, Japan
| | - Takafumi Furuyama
- Neuroethology and Bioengineering Laboratory, Faculty of Life and Medical Sciences, Doshisha University, Kyotanabe, Kyoto, Japan
| | - Kazuma Hase
- Neuroethology and Bioengineering Laboratory, Faculty of Life and Medical Sciences, Doshisha University, Kyotanabe, Kyoto, Japan
| | - Kohta I Kobayasi
- Neuroethology and Bioengineering Laboratory, Faculty of Life and Medical Sciences, Doshisha University, Kyotanabe, Kyoto, Japan
| | - Shizuko Hiryu
- Neuroethology and Bioengineering Laboratory, Faculty of Life and Medical Sciences, Doshisha University, Kyotanabe, Kyoto, Japan
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28
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Nascimento AI, Mar FM, Sousa MM. The intriguing nature of dorsal root ganglion neurons: Linking structure with polarity and function. Prog Neurobiol 2018; 168:86-103. [PMID: 29729299 DOI: 10.1016/j.pneurobio.2018.05.002] [Citation(s) in RCA: 75] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Revised: 04/26/2018] [Accepted: 05/01/2018] [Indexed: 11/26/2022]
Abstract
Dorsal root ganglion (DRG) neurons are the first neurons of the sensory pathway. They are activated by a variety of sensory stimuli that are then transmitted to the central nervous system. An important feature of DRG neurons is their unique morphology where a single process -the stem axon- bifurcates into a peripheral and a central axonal branch, with different functions and cellular properties. Distinctive structural aspects of the two DRG neuron branches may have important implications for their function in health and disease. However, the link between DRG axonal branch structure, polarity and function has been largely neglected in the field, and relevant information is rather scattered across the literature. In particular, ultrastructural differences between the two axonal branches are likely to account for the higher transport and regenerative ability of the peripheral DRG neuron axon when compared to the central one. Nevertheless, the cell intrinsic factors contributing to this central-peripheral asymmetry are still unknown. Here we critically review the factors that may underlie the functional asymmetry between the peripheral and central DRG axonal branches. Also, we discuss the hypothesis that DRG neurons may assemble a structure resembling the axon initial segment that may be responsible, at least in part, for their polarity and electrophysiological features. Ultimately, we suggest that the clarification of the axonal ultrastructure of DRG neurons using state-of-the-art techniques will be crucial to understand the physiology of this peculiar cell type.
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Affiliation(s)
- Ana Isabel Nascimento
- Nerve Regeneration Group, Instituto de Biologia Molecular e Celular-IBMC and Instituto de Inovação e Investigação em Saúde, University of Porto, Rua Alfredo Allen, 208, 4200-135 Porto, Portugal; Instituto de Ciências Biomédicas Abel Salazar-ICBAS, Rua Jorge Viterbo Ferreira 228, 4050-313 Porto, Portugal
| | - Fernando Milhazes Mar
- Nerve Regeneration Group, Instituto de Biologia Molecular e Celular-IBMC and Instituto de Inovação e Investigação em Saúde, University of Porto, Rua Alfredo Allen, 208, 4200-135 Porto, Portugal
| | - Mónica Mendes Sousa
- Nerve Regeneration Group, Instituto de Biologia Molecular e Celular-IBMC and Instituto de Inovação e Investigação em Saúde, University of Porto, Rua Alfredo Allen, 208, 4200-135 Porto, Portugal.
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29
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Kent AR, Min X, Hogan QH, Kramer JM. Mechanisms of Dorsal Root Ganglion Stimulation in Pain Suppression: A Computational Modeling Analysis. Neuromodulation 2018; 21:234-246. [PMID: 29377442 DOI: 10.1111/ner.12754] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 11/02/2017] [Accepted: 11/24/2017] [Indexed: 11/26/2022]
Abstract
OBJECTIVE The mechanisms of dorsal root ganglion (DRG) stimulation for chronic pain remain unclear. The objective of this work was to explore the neurophysiological effects of DRG stimulation using computational modeling. METHODS Electrical fields produced during DRG stimulation were calculated with finite element models, and were coupled to a validated biophysical model of a C-type primary sensory neuron. Intrinsic neuronal activity was introduced as a 4 Hz afferent signal or somatic ectopic firing. The transmembrane potential was measured along the neuron to determine the effect of stimulation on intrinsic activity across stimulation parameters, cell location/orientation, and membrane properties. RESULTS The model was validated by showing close correspondence in action potential (AP) characteristics and firing patterns when compared to experimental measurements. Subsequently, the model output demonstrated that T-junction filtering was amplified with DRG stimulation, thereby blocking afferent signaling, with cathodic stimulation at amplitudes of 2.8-5.5 × stimulation threshold and frequencies above 2 Hz. This amplified filtering was dependent on the presence of calcium and calcium-dependent small-conductance potassium channels, which produced a hyperpolarization offset in the soma, stem, and T-junction with repeated somatic APs during stimulation. Additionally, DRG stimulation suppressed somatic ectopic activity by hyperpolarizing the soma with cathodic or anodic stimulation at amplitudes of 3-11 × threshold and frequencies above 2 Hz. These effects were dependent on the stem axon being relatively close to and oriented toward a stimulating contact. CONCLUSIONS These results align with the working hypotheses on the mechanisms of DRG stimulation, and indicate the importance of stimulation amplitude, polarity, and cell location/orientation on neuronal responses.
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Affiliation(s)
| | - Xiaoyi Min
- Applied Research, Abbott, Sunnyvale, CA, USA
| | - Quinn H Hogan
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI, USA
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30
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Involvement of thromboxane A 2 in interleukin-31-induced itch-associated response in mice. Pharmacol Rep 2017; 70:251-257. [PMID: 29477033 DOI: 10.1016/j.pharep.2017.10.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2017] [Revised: 09/07/2017] [Accepted: 10/02/2017] [Indexed: 11/21/2022]
Abstract
BACKGROUND Atopic dermatitis is a chronic and severe pruritic skin disease. Interlukin-31 (IL-31) has been recently demonstrated to be one of the key pruritogens in atopic dermatitis. However, the mechanisms underlying IL-31-induced itching remains unclear. In our previous study, we have shown that thromboxane (TX) A2 is involved in itch-associated responses in mice with atopy-like skin diseases. METHODS IL-31 was given intradermally into the rostral back of ICR mice and the hind-paw scratching to the injection site were counted. Expression of TX synthase and IL-31 receptors were analyzed using immunohistochemical staining or RT-PCR in mouse skin or primary cultures of mouse keratinocytes. The concentration of TXB2, a metabolite of TXA2, in the skin and the culture medium of primary cultures of mouse keratinocytes was measured using enzyme immunoassay. The concentration of intracellular Ca2+ ions in mouse keratinocytes was measured using the calcium imaging method. RESULTS An intradermal injection of IL-31 elicited scratching, an itch-related response, in mice. The scratching was inhibited by TP TXA2 receptor antagonist DCHCH. The distribution of TX synthase and IL-31RA receptor was mainly epidermal keratinocytes in the skin. The primary cultures of keratinocytes expressed the mRNAs of TX synthase and IL-31 receptors. IL-31 increased the concentration of TXB2, which was inhibited by TX synthase inhibitor sodium ozagrel and EGTA, in the skin and the culture medium of primary cultures of keratinocytes. IL-31 increased the concentration of intracellular Ca2+ ions in mouse keratinocytes. CONCLUSION It is suggested that IL-31 elicits itch-associated responses through TXA2 produced from keratinocytes.
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31
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Quantitative models of feline lumbosacral dorsal root ganglia neuronal cell density. J Neurosci Methods 2017; 290:116-124. [PMID: 28739165 DOI: 10.1016/j.jneumeth.2017.07.018] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2017] [Revised: 07/17/2017] [Accepted: 07/19/2017] [Indexed: 01/02/2023]
Abstract
BACKGROUND Dorsal root ganglia (DRG) are spinal root components that contain the cell bodies of converging primary sensory neurons. DRG are becoming a therapeutic target for electrical neural interfaces. Our purpose was to establish methods for quantifying the non-random nature and distribution of neuronal cell bodies within DRG. NEW METHOD We identified neuronal cell body locations in 26 feline lumbosacral DRG cross-section histological images and used computational tools to quantify spatial trends. We first analyzed spatial randomness using the nearest-neighbor distance method. Next we overlaid a 6×6 grid, modeling neuronal cellular density in each grid square and comparing regions statistically. Finally we transformed DRG onto a polar map and calculated neuronal cellular density in annular sectors. We used a recursive partition model to determine regions of high and low density, and validated the model statistically. RESULTS We found that the arrangement of neuronal cell bodies at the widest point of DRG is distinctly non-random with concentration in particular regions. The grid model suggested a radial trend in density, with increasing density toward the outside of the DRG. The polar transformation model showed that the highest neuronal cellular density is in the outer 23.9% radially and the dorsal ±61.4° angularly. COMPARISON WITH EXISTING METHODS To our knowledge, DRG neuronal cell distribution has not been previously quantified. CONCLUSIONS These results confirm and expand quantitatively on the existing understanding of DRG anatomy. Our methods can be useful for analyzing the distribution of cellular components of other neural structures or expanding to three-dimensional models.
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32
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Colón-Rodríguez A, Hannon HE, Atchison WD. Effects of methylmercury on spinal cord afferents and efferents-A review. Neurotoxicology 2017; 60:308-320. [PMID: 28041893 PMCID: PMC5447474 DOI: 10.1016/j.neuro.2016.12.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Revised: 12/21/2016] [Accepted: 12/21/2016] [Indexed: 10/20/2022]
Abstract
Methylmercury (MeHg) is an environmental neurotoxicant of public health concern. It readily accumulates in exposed humans, primarily in neuronal tissue. Exposure to MeHg, either acutely or chronically, causes severe neuronal dysfunction in the central nervous system and spinal neurons; dysfunction of susceptible neuronal populations results in neurodegeneration, at least in part through Ca2+-mediated pathways. Biochemical and morphologic changes in peripheral neurons precede those in central brain regions, despite the fact that MeHg readily crosses the blood-brain barrier. Consequently, it is suggested that unique characteristics of spinal cord afferents and efferents could heighten their susceptibility to MeHg toxicity. Transient receptor potential (TRP) ion channels are a class of Ca2+-permeable cation channels that are highly expressed in spinal afferents, among other sensory and visceral organs. These channels can be activated in numerous ways, including directly via chemical irritants or indirectly via Ca2+ release from intracellular storage organelles. Early studies demonstrated that MeHg interacts with heterologous TRP channels, though definitive mechanisms of MeHg toxicity on sensory neurons may involve more complex interaction with, and among, differentially-expressed TRP populations. In spinal efferents, glutamate receptors of the N-methyl-D-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and possibly kainic acid (KA) classes are thought to play a major role in MeHg-induced neurotoxicity. Specifically, the Ca2+-permeable AMPA receptors, which are abundant in motor neurons, have been identified as being involved in MeHg-induced neurotoxicity. In this review, we will describe the mechanisms that could contribute to MeHg-induced spinal cord afferent and efferent neuronal degeneration, including the possible mediators, such as uniquely expressed Ca2+-permeable ion channels.
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Affiliation(s)
- Alexandra Colón-Rodríguez
- Department of Pharmacology and Toxicology, 1355 Bogue Street, Life Sciences Building Rm. B440, Michigan State University, East Lansing, MI, United States; Institute for Integrative Toxicology, 1129 Farm Lane, Food Safety and Toxicology Rm. 165, Michigan State University, East Lansing, MI, United States; Comparative Medicine and Integrative Biology Program, 784 Wilson Road, Veterinary Medical Center Rm. G-100, Michigan State University, East Lansing, MI, United States.
| | - Heidi E Hannon
- Department of Pharmacology and Toxicology, 1355 Bogue Street, Life Sciences Building Rm. B440, Michigan State University, East Lansing, MI, United States; Institute for Integrative Toxicology, 1129 Farm Lane, Food Safety and Toxicology Rm. 165, Michigan State University, East Lansing, MI, United States; Comparative Medicine and Integrative Biology Program, 784 Wilson Road, Veterinary Medical Center Rm. G-100, Michigan State University, East Lansing, MI, United States.
| | - William D Atchison
- Department of Pharmacology and Toxicology, 1355 Bogue Street, Life Sciences Building Rm. B440, Michigan State University, East Lansing, MI, United States; Institute for Integrative Toxicology, 1129 Farm Lane, Food Safety and Toxicology Rm. 165, Michigan State University, East Lansing, MI, United States; Comparative Medicine and Integrative Biology Program, 784 Wilson Road, Veterinary Medical Center Rm. G-100, Michigan State University, East Lansing, MI, United States.
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33
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Khurram A, Ross SE, Sperry ZJ, Ouyang A, Stephan C, Jiman AA, Bruns TM. Chronic monitoring of lower urinary tract activity via a sacral dorsal root ganglia interface. J Neural Eng 2017; 14:036027. [PMID: 28322213 DOI: 10.1088/1741-2552/aa6801] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
OBJECTIVE Our goal is to develop an interface that integrates chronic monitoring of lower urinary tract (LUT) activity with stimulation of peripheral pathways. APPROACH Penetrating microelectrodes were implanted in sacral dorsal root ganglia (DRG) of adult male felines. Peripheral electrodes were placed on or in the pudendal nerve, bladder neck and near the external urethral sphincter. Supra-pubic bladder catheters were implanted for saline infusion and pressure monitoring. Electrode and catheter leads were enclosed in an external housing on the back. Neural signals from microelectrodes and bladder pressure of sedated or awake-behaving felines were recorded under various test conditions in weekly sessions. Electrodes were also stimulated to drive activity. MAIN RESULTS LUT single- and multi-unit activity was recorded for 4-11 weeks in four felines. As many as 18 unique bladder pressure single-units were identified in each experiment. Some channels consistently recorded bladder afferent activity for up to 41 d, and we tracked individual single-units for up to 23 d continuously. Distension-evoked and stimulation-driven (DRG and pudendal) bladder emptying was observed, during which LUT sensory activity was recorded. SIGNIFICANCE This chronic implant animal model allows for behavioral studies of LUT neurophysiology and will allow for continued development of a closed-loop neuroprosthesis for bladder control.
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Affiliation(s)
- Abeer Khurram
- Biomedical Engineering Department, University of Michigan, Ann Arbor, MI, United States of America. Biointerfaces Institute, University of Michigan, Ann Arbor, MI, United States of America
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Quartu M, Serra MP, Boi M, Poddighe L, Picci C, Demontis R, Del Fiacco M. TRPV1 receptor in the human trigeminal ganglion and spinal nucleus: immunohistochemical localization and comparison with the neuropeptides CGRP and SP. J Anat 2016; 229:755-767. [PMID: 27456865 DOI: 10.1111/joa.12529] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/30/2016] [Indexed: 01/02/2023] Open
Abstract
This work presents new data concerning the immunohistochemical occurrence of the transient receptor potential vanilloid type-1 (TRPV1) receptor in the human trigeminal ganglion (TG) and spinal nucleus of subjects at different ontogenetic stages, from prenatal life to postnatal old age. Comparisons are made with the sensory neuropeptides calcitonin gene-related peptide (CGRP) and substance P (SP). TRPV1-like immunoreactive (LI) material was detected by western blot in homogenates of TG and medulla oblongata of subjects at prenatal and adult stages of life. Immunohistochemistry showed that expression of the TRPV1 receptor is mostly restricted to the small- and medium-sized TG neurons and to the caudal subdivision of the spinal trigeminal nucleus (Sp5C). The extent of the TRPV1-LI TG neuronal subpopulation was greater in subjects at early perinatal age than at late perinatal age and in postnatal life. Centrally, the TRPV1 receptor localized to fibre tracts and punctate elements, which were mainly distributed in the spinal tract, lamina I and inner lamina II of the Sp5C, whereas stained cells were rare. The TRPV1 receptor colocalized partially with CGRP and SP in the TG, and was incompletely codistributed with both neuropeptides in the spinal tract and in the superficial laminae of the Sp5C. Substantial differences were noted with respect to the distribution of the TRPV1-LI structures described in the rat Sp5C and with respect to the temporal expression of the receptor during the development of the rat spinal dorsal horn. The distinctive localization of TRPV1-LI material supports the concept of the involvement of TRPV1 receptor in the functional activity of the protopathic compartment of the human trigeminal sensory system, i.e. the processing and neurotransmission of thermal and pain stimuli.
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Affiliation(s)
- Marina Quartu
- Department of Biomedical Sciences, Cytomorphology Section, University of Cagliari, Monserrato (CA), Italy
| | - Maria Pina Serra
- Department of Biomedical Sciences, Cytomorphology Section, University of Cagliari, Monserrato (CA), Italy
| | - Marianna Boi
- Department of Biomedical Sciences, Cytomorphology Section, University of Cagliari, Monserrato (CA), Italy
| | - Laura Poddighe
- Department of Biomedical Sciences, Cytomorphology Section, University of Cagliari, Monserrato (CA), Italy
| | - Cristina Picci
- Department of Biomedical Sciences, Cytomorphology Section, University of Cagliari, Monserrato (CA), Italy
| | - Roberto Demontis
- Department of Public Health, Clinical and Molecular Medicine, University of Cagliari, Cagliari, Italy
| | - Marina Del Fiacco
- Department of Biomedical Sciences, Cytomorphology Section, University of Cagliari, Monserrato (CA), Italy
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Krames ES. The Dorsal Root Ganglion in Chronic Pain and as a Target for Neuromodulation: A Review. Neuromodulation 2014; 18:24-32; discussion 32. [DOI: 10.1111/ner.12247] [Citation(s) in RCA: 147] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2012] [Revised: 11/08/2013] [Accepted: 02/04/2014] [Indexed: 11/29/2022]
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Krames ES. The role of the dorsal root ganglion in the development of neuropathic pain. PAIN MEDICINE 2014; 15:1669-85. [PMID: 24641192 DOI: 10.1111/pme.12413] [Citation(s) in RCA: 120] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
BACKGROUND The dorsal root ganglion (DRG), in the not too distant past, had been thought of as a passive organ not involved in the development of abnormal aberrent neuropathic pain (NP), but merely metabolically "supporting" physiologic functions between the peripheral nervous system (PNS) and the central nervous system (CNS). New information regarding metabolic change within the DRG has dispelled this supportive passive role and suggests that the DRG is an active, not a passive, organ, in the process of the development of chronic pain. METHODS A review of the anatomic and physiologic literature utilizing PubMed and Google Scholar was performed to create a review of the anatomic and physiologic foundations for the development of NP after peripheral afferent fiber injury. CONCLUSIONS The DRG is as involved in the process of generating NP as is the nociceptor and the dorsal horn of the spinal cord.
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Gear RW, Bogen O, Ferrari LF, Green PG, Levine JD. NOP receptor mediates anti-analgesia induced by agonist-antagonist opioids. Neuroscience 2014; 257:139-48. [PMID: 24188792 PMCID: PMC3947912 DOI: 10.1016/j.neuroscience.2013.10.061] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2013] [Revised: 10/25/2013] [Accepted: 10/25/2013] [Indexed: 11/18/2022]
Abstract
Clinical studies have shown that agonist-antagonist opioid analgesics that produce their analgesic effect via action on the kappa-opioid receptor, produce a delayed-onset anti-analgesia in men but not women, an effect blocked by co-administration of a low dose of naloxone. We now report the same time-dependent anti-analgesia and its underlying mechanism in an animal model. Using the Randall-Selitto paw-withdrawal assay in male rats, we found that nalbuphine, pentazocine, and butorphanol each produced analgesia during the first hour followed by anti-analgesia starting at ∼90min after administration in males but not females, closely mimicking its clinical effects. As observed in humans, co-administration of nalbuphine with naloxone in a dose ratio of 12.5:1 blocked anti-analgesia but not analgesia. Administration of the highly selective kappa-opioid receptor agonist U69593 produced analgesia without subsequent anti-analgesia, and confirmed by the failure of the selective kappa antagonist nor-binaltorphimine to block nalbuphine-induced anti-analgesia, indicating that anti-analgesia is not mediated by kappa-opioid receptors. We therefore tested the role of other receptors in nalbuphine anti-analgesia. Nociceptin/orphanin FQ (NOP) and sigma-1 and sigma-2 receptors were chosen on the basis of their known anti-analgesic effects and receptor binding studies. The selective NOP receptor antagonists, JTC801, and J-113397, but not the sigma receptor antagonist, BD 1047, antagonized nalbuphine anti-analgesia. Furthermore, the NOP receptor agonist NNC 63-0532 produced anti-analgesia with the same delay in onset observed with the three agonist-antagonists, but without producing preceding analgesia and this anti-analgesia was also blocked by naloxone. These results strongly support the suggestion that clinically used agonist-antagonists act at the NOP receptor to produce anti-analgesia.
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Affiliation(s)
- R W Gear
- Department of Oral and Maxillofacial Surgery, University of California, San Francisco, CA 94143-0440, United States
| | - O Bogen
- Department of Oral and Maxillofacial Surgery, University of California, San Francisco, CA 94143-0440, United States
| | - L F Ferrari
- Department of Oral and Maxillofacial Surgery, University of California, San Francisco, CA 94143-0440, United States
| | - P G Green
- Department of Oral and Maxillofacial Surgery, University of California, San Francisco, CA 94143-0440, United States
| | - J D Levine
- Department of Oral and Maxillofacial Surgery, University of California, San Francisco, CA 94143-0440, United States; Department of Medicine, University of California at San Francisco, San Francisco, CA 94143-0120, United States.
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Abstract
The pseudounipolar sensory neurons of the dorsal root ganglia (DRG) give rise to peripheral branches that convert thermal, mechanical, and chemical stimuli into electrical signals that are transmitted via central branches to the spinal cord. These neurons express unique combinations of tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) Na(+) channels that contribute to the resting membrane potential, action potential threshold, and regulate neuronal firing frequency. The small-diameter neurons (<25 μm) isolated from the DRG represent the cell bodies of C-fiber nociceptors that express both TTX-S and TTX-R Na(+) currents. The large-diameter neurons (>35 μm) are typically low-threshold A-fibers that predominately express TTX-S Na(+) currents. Peripheral nerve damage, inflammation, and metabolic diseases alter the expression and function of these Na(+) channels leading to increases in neuronal excitability and pain. The Na(+) channels expressed in these neurons are the target of intracellular signaling cascades that regulate the trafficking, cell surface expression, and gating properties of these channels. Post-translational regulation of Na(+) channels by protein kinases (PKA, PKC, MAPK) alter the expression and function of the channels. Injury-induced changes in these signaling pathways have been linked to sensory neuron hyperexcitability and pain. This review examines the signaling pathways and regulatory mechanisms that modulate the voltage-gated Na(+) channels of sensory neurons.
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Affiliation(s)
- Mohamed Chahine
- Centre de recherche, Institut en santé mentale de Québec, Local F-6539, 2601, chemin de la Canardière, QC City, QC, Canada, G1J 2G3,
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Bosco R, Alvarado S, Quiroz D, Eblen-Zajjur A. Digital Morphometric Characterization of Lumbar Dorsal Root Ganglion Neurons in Rats. J Histotechnol 2013. [DOI: 10.1179/his.2010.33.3.113] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
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Malafoglia V, Bryant B, Raffaeli W, Giordano A, Bellipanni G. The zebrafish as a model for nociception studies. J Cell Physiol 2013; 228:1956-66. [DOI: 10.1002/jcp.24379] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2013] [Accepted: 03/26/2013] [Indexed: 12/18/2022]
Affiliation(s)
| | - Bruce Bryant
- Monell Chemical Senses Center; Philadelphia, Pennsylvania
| | - William Raffaeli
- Institute for Research on Pain; ISAL-Foundation; Torre Pedrera (RN); Italy
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Chien CH, Tsai YC, Tseng CY, Huang BM, Chang YH. The Spatial and Segmental Innervation of Somatic Acupoint — A Study of Canine Shen-Shu Point (BL-23). THE AMERICAN JOURNAL OF CHINESE MEDICINE 2012; 35:437-46. [PMID: 17597502 DOI: 10.1142/s0192415x07004953] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Although an acupuncture needle penetrates the skin, subcutaneous tissue, and underlying muscle, the most effective locus for the somatic acupoint on the needle path is not well established. We therefore investigated the sensory innervations of tissues in the needle path of the canine Shen-Shu point and evaluated their roles in initiating an acupunctural signal. Horseradish peroxidase solution was injected at all three levels within the acupoint. Only a few peroxidase-positive neurons were observed in the L1 dorsal root ganglion following intradermal injection. Following subcutaneous injection, peroxidase-labeled neurons were detected extending from spinal levels T10 to L2, with maximal labeling at T12 (46.3%). Approximately 95% of positive neurons were at spinal levels T11, T12, T13, and L1. As a result of an intramuscular injection, labeled neurons were observed at spinal levels T12 to L3, with most labeling occurring at L1 (39.9%). Approximately 95% of positive neurons were at spinal levels T13, L1, and L2. The results suggest that most afferent terminals are in the subcutaneous tissue rather than the muscular tissue, with an approximate ratio of 3.75:1. The data provide solid evidence that sensory innervation to a somatic acupoint is confined to a spinal segment and spatially organized, and we speculate that to cause a maximum effect, the centripetally transmitted signal from needling a somatic acupoint is spatio-segmental and divergently amplified.
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Affiliation(s)
- Chi-Hsien Chien
- Department of Anatomy, National Cheng-Kung University, No. 1, Tae-Shue Road, Tainan, Taiwan, 701.
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Kubo A, Koyama M, Tamura R, Takagishi Y, Murase S, Mizumura K. Absence of mechanical hyperalgesia after exercise (delayed onset muscle soreness) in neonatally capsaicin-treated rats. Neurosci Res 2012; 73:56-60. [PMID: 22381959 DOI: 10.1016/j.neures.2012.02.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2011] [Revised: 02/09/2012] [Accepted: 02/13/2012] [Indexed: 10/28/2022]
Abstract
Delayed onset muscle soreness (DOMS) appears with some delay after unaccustomed, strenuous exercise, especially after lengthening contraction (LC). It is characterized by tenderness and movement related pain, namely muscular mechanical hyperalgesia. To clarify the involvement of C-fibers in this mechanical hyperalgesia, we examined whether DOMS could be induced in rats treated neonatally with capsaicin. We confirmed that a large portion of unmyelinated afferent fibers were lost in capsaicin treated rats. In these animals, LC failed to induce muscular mechanical hyperalgesia. mRNA of nerve growth factor (NGF) in the muscle, which plays a pivotal role in maintaining mechanical hyperalgesia, was upregulated in the capsaicin treated animals similar to the vehicle treated animals. These results demonstrate that C-fiber afferents are essential in transmitting the nociceptive information from exercised muscle in DOMS.
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Affiliation(s)
- Asako Kubo
- Department of Neuroscience II, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
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Todorovic SM, Jevtovic-Todorovic V. T-type voltage-gated calcium channels as targets for the development of novel pain therapies. Br J Pharmacol 2011; 163:484-95. [PMID: 21306582 DOI: 10.1111/j.1476-5381.2011.01256.x] [Citation(s) in RCA: 111] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
It is well recognized that voltage-gated calcium (Ca(2+)) channels modulate the function of peripheral and central pain pathways by influencing fast synaptic transmission and neuronal excitability. In the past, attention focused on the modulation of different subtypes of high-voltage-activated-type Ca(2+) channels; more recently, the function of low-voltage-activated or transient (T)-type Ca(2+) channels (T-channels) in nociception has been well documented. Currently, available pain therapies remain insufficient for certain forms of pain associated with chronic disorders (e.g. neuropathic pain) and often have serious side effects. Hence, the identification of selective and potent inhibitors and modulators of neuronal T-channels may help greatly in the development of safer, more effective pain therapies. Here, we summarize the available information implicating peripheral and central T-channels in nociception. We also discuss possible future developments aimed at selective modulation of function of these channels, which are highly expressed in nociceptors.
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Affiliation(s)
- Slobodan M Todorovic
- Department of Anesthesiology and Neuroscience, University of Virginia School of Medicine, Charlottesville, 22908-0710, USA.
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Russo D, Bombardi C, Castellani G, Chiocchetti R. Characterization of spinal ganglion neurons in horse (Equus caballus). A morphometric, neurochemical and tracing study. Neuroscience 2011; 176:53-71. [DOI: 10.1016/j.neuroscience.2010.12.042] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2010] [Revised: 12/21/2010] [Accepted: 12/22/2010] [Indexed: 10/18/2022]
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Ho C, O'Leary ME. Single-cell analysis of sodium channel expression in dorsal root ganglion neurons. Mol Cell Neurosci 2011; 46:159-66. [PMID: 20816971 PMCID: PMC3005531 DOI: 10.1016/j.mcn.2010.08.017] [Citation(s) in RCA: 118] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2010] [Revised: 08/19/2010] [Accepted: 08/26/2010] [Indexed: 01/08/2023] Open
Abstract
Sensory neurons of the dorsal root ganglia (DRG) express multiple voltage-gated sodium (Na) channels that substantially differ in gating kinetics and pharmacology. Small-diameter (<25 μm) neurons isolated from the rat DRG express a combination of fast tetrodotoxin-sensitive (TTX-S) and slow TTX-resistant (TTX-R) Na currents while large-diameter neurons (>30 μm) predominately express fast TTX-S Na current. Na channel expression was further investigated using single-cell RT-PCR to measure the transcripts present in individually harvested DRG neurons. Consistent with cellular electrophysiology, the small neurons expressed transcripts encoding for both TTX-S (Nav1.1, Nav1.2, Nav1.6, and Nav1.7) and TTX-R (Nav1.8 and Nav1.9) Na channels. Nav1.7, Nav1.8 and Nav1.9 were the predominant Na channels expressed in the small neurons. The large neurons highly expressed TTX-S isoforms (Nav1.1, Nav1.6, and Nav1.7) while TTX-R channels were present at comparatively low levels. A unique subpopulation of the large neurons was identified that expressed TTX-R Na current and high levels of Nav1.8 transcript. DRG neurons also displayed substantial differences in the expression of neurofilaments (NF200, peripherin) and Necl-1, a neuronal adhesion molecule involved in myelination. The preferential expression of NF200 and Necl-1 suggests that large-diameter neurons give rise to thick myelinated axons. Small-diameter neurons expressed peripherin, but reduced levels of NF200 and Necl-1, a pattern more consistent with thin unmyelinated axons. Single-cell analysis of Na channel transcripts indicates that TTX-S and TTX-R Na channels are differentially expressed in large myelinated (Nav1.1, Nav1.6, and Nav1.7) and small unmyelinated (Nav1.7, Nav1.8, and Nav1.9) sensory neurons.
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Affiliation(s)
- Cojen Ho
- Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, 1020 Locust Street, JAH 265, Philadelphia, PA 19107, USA
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Ip V, Liu JJ, Mercer JFB, McKeage MJ. Differential expression of ATP7A, ATP7B and CTR1 in adult rat dorsal root ganglion tissue. Mol Pain 2010; 6:53. [PMID: 20836889 PMCID: PMC2949721 DOI: 10.1186/1744-8069-6-53] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2010] [Accepted: 09/13/2010] [Indexed: 01/17/2023] Open
Abstract
BACKGROUND ATP7A, ATP7B and CTR1 are metal transporting proteins that control the cellular disposition of copper and platinum drugs, but their expression in dorsal root ganglion (DRG) tissue and their role in platinum-induced neurotoxicity are unknown. To investigate the DRG expression of ATP7A, ATP7B and CTR1, lumbar DRG and reference tissues were collected for real time quantitative PCR, RT-PCR, immunohistochemistry and Western blot analysis from healthy control adult rats or from animals treated with intraperitoneal oxaliplatin (1.85 mg/kg) or drug vehicle twice weekly for 8 weeks. RESULTS In DRG tissue from healthy control animals, ATP7A mRNA was clearly detectable at levels similar to those found in the brain and spinal cord, and intense ATP7A immunoreactivity was localised to the cytoplasm of cell bodies of smaller DRG neurons without staining of satellite cells, nerve fibres or co-localisation with phosphorylated heavy neurofilament subunit (pNF-H). High levels of CTR1 mRNA were detected in all tissues from healthy control animals, and strong CTR1 immunoreactivity was associated with plasma membranes and vesicular cytoplasmic structures of the cell bodies of larger-sized DRG neurons without co-localization with ATP7A. DRG neurons with strong expression of ATP7A or CTR1 had distinct cell body size profiles with minimal overlap between them. Oxaliplatin treatment did not alter the size profile of strongly ATP7A-immunoreactive neurons but significantly reduced the size profile of strongly CTR1-immunoreactive neurons. ATP7B mRNA was barely detectable, and no specific immunoreactivity for ATP7B was found, in DRG tissue from healthy control animals. CONCLUSIONS In conclusion, adult rat DRG tissue exhibits a specific pattern of expression of copper transporters with distinct subsets of peripheral sensory neurons intensely expressing either ATP7A or CTR1, but not both or ATP7B. The neuron subtype-specific and largely non-overlapping distribution of ATP7A and CTR1 within rat DRG tissue may be required to support the potentially differing cuproenzyme requirements of distinct subsets of sensory neurons, and could influence the transport and neurotoxicity of oxaliplatin.
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Affiliation(s)
- Virginia Ip
- Department of Pharmacology and Clinical Pharmacology, School of Medical Sciences, Faculty of Medical and Health Sciences, The University of Auckland, Auckland, New Zealand
| | - Johnson J Liu
- Department of Pharmacology and Clinical Pharmacology, School of Medical Sciences, Faculty of Medical and Health Sciences, The University of Auckland, Auckland, New Zealand
| | - Julian FB Mercer
- Centre for Cellular and Molecular Biology, School of Life and Environmental Sciences, Deakin University, Melbourne, Australia
| | - Mark J McKeage
- Department of Pharmacology and Clinical Pharmacology, School of Medical Sciences, Faculty of Medical and Health Sciences, The University of Auckland, Auckland, New Zealand
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Russo D, Clavenzani P, Mazzoni M, Chiocchetti R, Di Guardo G, Lalatta-Costerbosa G. Immunohistochemical characterization of TH13-L2 spinal ganglia neurons in sheep (Ovis aries). Microsc Res Tech 2010; 73:128-39. [PMID: 19725058 DOI: 10.1002/jemt.20764] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Spinal ganglia (SG) neurons are commonly classified according to various specific features. The most widespread classification based on morphological and ultrastructural features subdivides SG neurons into light and small dark neurons. Using immunohistochemical, histochemical and lectin methods, it is possible to further subdivide the small dark neurons into two subpopulations: peptidergic and nonpeptidergic neurons. The majority of studies on SG neurons were carried out on mice and rats; there are few or no studies on large mammals. In this study, some of the widely used neuronal markers, neurofilament 200 kDa (NF200), substance P (SP), calcitonin gene-related peptide (CGRP) and isolectin B4 (IB4), were employed to characterize neuronal nitric oxide synthase (nNOS)-immunoreactivity (-IR) in sheep (Ovis aries) SG (Th13-L2) neurons. The majority of the SG neurons were IB4-labeled (79 +/- 10%), followed by NF200- (45 +/- 4%), NOS- (44 +/- 10%), SP- (42 +/- 5%) and CGRP-IR (35 +/- 7%) neurons. The triple staining experiments showed that a higher percentage (75 +/- 16%) of NOS-IR neurons bound both IB4 and CGRP, or both IB4 and SP (49 +/- 6%). The IB4 marker showed an unexpected staining pattern; in fact, IB4-labeled neurons largely colocalized with NF200, usually considered a marker of light SG neurons, and with CGRP and SP. For this reason, IB4 cannot be employed in sheep to differentiate between light and dark neurons, or between peptidergic and nonpeptidergic neurons. These results suggest the importance of being cautious when comparing data among different species.
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Affiliation(s)
- Domenico Russo
- Department of Veterinary Morphophysiology and Animal Productions, University of Bologna, 40064 Ozzano dell'Emilia (BO), Italy.
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Bojak I, Liley DTJ. Axonal velocity distributions in neural field equations. PLoS Comput Biol 2010; 6:e1000653. [PMID: 20126532 PMCID: PMC2813262 DOI: 10.1371/journal.pcbi.1000653] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2009] [Accepted: 12/18/2009] [Indexed: 11/19/2022] Open
Abstract
By modelling the average activity of large neuronal populations, continuum mean field models (MFMs) have become an increasingly important theoretical tool for understanding the emergent activity of cortical tissue. In order to be computationally tractable, long-range propagation of activity in MFMs is often approximated with partial differential equations (PDEs). However, PDE approximations in current use correspond to underlying axonal velocity distributions incompatible with experimental measurements. In order to rectify this deficiency, we here introduce novel propagation PDEs that give rise to smooth unimodal distributions of axonal conduction velocities. We also argue that velocities estimated from fibre diameters in slice and from latency measurements, respectively, relate quite differently to such distributions, a significant point for any phenomenological description. Our PDEs are then successfully fit to fibre diameter data from human corpus callosum and rat subcortical white matter. This allows for the first time to simulate long-range conduction in the mammalian brain with realistic, convenient PDEs. Furthermore, the obtained results suggest that the propagation of activity in rat and human differs significantly beyond mere scaling. The dynamical consequences of our new formulation are investigated in the context of a well known neural field model. On the basis of Turing instability analyses, we conclude that pattern formation is more easily initiated using our more realistic propagator. By increasing characteristic conduction velocities, a smooth transition can occur from self-sustaining bulk oscillations to travelling waves of various wavelengths, which may influence axonal growth during development. Our analytic results are also corroborated numerically using simulations on a large spatial grid. Thus we provide here a comprehensive analysis of empirically constrained activity propagation in the context of MFMs, which will allow more realistic studies of mammalian brain activity in the future.
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Affiliation(s)
- Ingo Bojak
- Donders Institute for Brain, Cognition and Behaviour, Centre for Neuroscience, Radboud University Nijmegen, Nijmegen, The Netherlands.
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Hoffman EM, Schechter R, Miller KE. Fixative composition alters distributions of immunoreactivity for glutaminase and two markers of nociceptive neurons, Nav1.8 and TRPV1, in the rat dorsal root ganglion. J Histochem Cytochem 2009; 58:329-44. [PMID: 20026672 DOI: 10.1369/jhc.2009.954008] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Most, if not all, dorsal root ganglion (DRG) neurons use the neurotransmitter glutamate. There are, however, conflicting reports of the percentages of DRG neurons that express glutaminase (GLS), the enzyme that synthesizes glutamate, ranging from 30% to 100% of DRG neurons. Defining DRG neuron populations by the expression of proteins like GLS, which indicates function, is routinely accomplished with immunolabeling techniques. Proper characterization of DRG neuron populations relies on accurate detection of such antigens. It is known intuitively that fixation can alter immunoreactivity (IR). In this study, we compared the effects of five formaldehyde concentrations between 0.25% and 4.0% (w/v) and five picric acid concentrations between 0.0% and 0.8% (w/v) on the IR of GLS, the voltage-gated sodium channel 1.8 (Na(v)1.8), and the capsaicin receptor TRPV1. We also compared the effects of five incubation time lengths from 2 to 192 hr, in primary antiserum on IR. Lowering formaldehyde concentration elevated IR for all three antigens, while raising picric acid concentration increased Na(v)1.8 and TRPV1 IR. Increasing IR improved detection sensitivity, which led to higher percentages of labeled DRG neurons. By selecting fixation conditions that optimized IR, we found that all DRG neurons express GLS, 69% of neurons express Na(v)1.8, and 77% of neurons express TRPV1, indicating that some previous studies may have underestimated the percentages of DRG neurons expressing these proteins. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.
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Affiliation(s)
- E Matthew Hoffman
- Department of Anatomy and Cell Biology, Oklahoma State University Center for Health Sciences, Tulsa, Oklahoma 74107, USA
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Abstract
The inferior colliculus (IC) is unique, having both glutamatergic and GABAergic projections ascending to the thalamus. Although subpopulations of GABAergic neurons in the IC have been proposed, criteria to distinguish them have been elusive and specific types have not been associated with specific neural circuits. Recently, the largest IC neurons were found to be recipients of somatic terminals containing vesicular glutamate transporter 2 (VGLUT2). Here, we show with electron microscopy that VGLUT2-positive (VGLUT2(+)) axonal terminals make axosomatic synapses on IC neurons. These terminals contain only VGLUT2 even though others in the IC have VGLUT1 or both VGLUT1 and 2. We demonstrate that there are two types of GABAergic neurons: larger neurons with VGLUT2(+) axosomatic endings and smaller neurons without such endings. Both types are present in all subdivisions of the IC, but larger GABAergic neurons with VGLUT2(+) axosomatic terminals are most prevalent in the central nucleus. The GABAergic tectothalamic neurons consist almost entirely of the larger cells surrounded by VGLUT2(+) axosomatic endings. Thus, two types of GABAergic neurons in the IC are defined by different synaptic organization and neuronal connections. Larger tectothalamic GABAergic neurons are covered with glutamatergic axosomatic synapses that could allow them to fire rapidly and overcome a slow membrane time constant; their axons may be the largest in the brachium of the IC. Thus, large GABAergic neurons could deliver IPSPs to the medial geniculate body before EPSPs from glutamatergic IC neurons firing simultaneously.
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