1
|
Gambino G, Gallo D, Covelo A, Ferraro G, Sardo P, Giglia G. TRPV1 channels in nitric oxide-mediated signalling: insight on excitatory transmission in rat CA1 pyramidal neurons. Free Radic Biol Med 2022; 191:128-136. [PMID: 36029909 DOI: 10.1016/j.freeradbiomed.2022.08.025] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Revised: 08/13/2022] [Accepted: 08/15/2022] [Indexed: 11/18/2022]
Abstract
Nitric oxide (NO) is a fascinating signalling molecule implicated in a plethora of biological functions, especially at the synaptic level. Exploring neurotransmission in the hippocampus could be instrumental in the individuation of putative targets for nitric-oxide mediated neuromodulation, especially in terms of the potential repercussions on fundamental processes i.e. synaptic plasticity and excitability-related phenomena. Among these targets, endovanilloid signalling constitutes an object of study since Transient Receptors Vanilloid type 1 (TRPV1) channels possess a NO-sensitive gate modulating its activation. Also, NO has been referred to as a mediator for numerous endocannabinoid effects. Notwithstanding, the linkage between TRPV1 and NO systems in neuromodulation still remains elusive. To this end, we aim at investigating the involvement of TRPV1 in nitric oxide-mediated influence on hippocampal processes. Electrophysiological whole-cell recordings in CA1 pyramidal neurons were applied to evaluate excitatory neurotransmission in rat brain slices. Indeed, miniature excitatory postsynaptic currents (mEPSCs) were analysed upon pharmacological manipulation of TRPV1 and NO signalling pathways. In detail, only the administration of the specific TRPV1 exogenous agonist - capsaicin - reduced the frequency and amplitude of mEPSC similarly to the inhibitor of neuronal nitric oxide synthase (nNOS), 7-nitroindazole (7NI). In contrast, capsazepine, TRPV1 antagonist, does not influence excitatory transmission. The combined TRPV1 activation and nNOS blockade confirm the presence of a putative common mechanism. When we administered the endovanilloid-endocannabinoid ligand, i.e. anandamide, we unveiled a potentiation of neurotransmission that was selectively reverted by 7NI. Our data suggest that nitric oxide influences TRPV1 hippocampal signalling since these channels are not constitutively active, but can be "on-demand" activated to modulate excitation in CA1 pyramidal neurons, and that this effect is linked to nitric oxide production.
Collapse
Affiliation(s)
- Giuditta Gambino
- Department of Biomedicine, Neuroscience and Advanced Diagnostics (BIND), University of Palermo, Italy.
| | - Daniele Gallo
- Department of Biomedicine, Neuroscience and Advanced Diagnostics (BIND), University of Palermo, Italy
| | - Ana Covelo
- Institut National de la Santé et de la Recherche Médicale (INSERM), U1215 NeuroCentre Magendie, Bordeaux, France
| | - Giuseppe Ferraro
- Department of Biomedicine, Neuroscience and Advanced Diagnostics (BIND), University of Palermo, Italy
| | - Pierangelo Sardo
- Department of Biomedicine, Neuroscience and Advanced Diagnostics (BIND), University of Palermo, Italy
| | - Giuseppe Giglia
- Department of Biomedicine, Neuroscience and Advanced Diagnostics (BIND), University of Palermo, Italy
| |
Collapse
|
2
|
Meza RC, Ancatén-González C, Chiu CQ, Chávez AE. Transient Receptor Potential Vanilloid 1 Function at Central Synapses in Health and Disease. Front Cell Neurosci 2022; 16:864828. [PMID: 35518644 PMCID: PMC9062234 DOI: 10.3389/fncel.2022.864828] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Accepted: 03/29/2022] [Indexed: 12/11/2022] Open
Abstract
The transient receptor potential vanilloid 1 (TRPV1), a ligand-gated nonselective cation channel, is well known for mediating heat and pain sensation in the periphery. Increasing evidence suggests that TRPV1 is also expressed at various central synapses, where it plays a role in different types of activity-dependent synaptic changes. Although its precise localizations remain a matter of debate, TRPV1 has been shown to modulate both neurotransmitter release at presynaptic terminals and synaptic efficacy in postsynaptic compartments. In addition to being required in these forms of synaptic plasticity, TRPV1 can also modify the inducibility of other types of plasticity. Here, we highlight current evidence of the potential roles for TRPV1 in regulating synaptic function in various brain regions, with an emphasis on principal mechanisms underlying TRPV1-mediated synaptic plasticity and metaplasticity. Finally, we discuss the putative contributions of TRPV1 in diverse brain disorders in order to expedite the development of next-generation therapeutic treatments.
Collapse
Affiliation(s)
- Rodrigo C Meza
- Centro Interdisciplinario de Neurociencia de Valparaíso (CINV), Instituto de Neurociencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Carlos Ancatén-González
- Centro Interdisciplinario de Neurociencia de Valparaíso (CINV), Instituto de Neurociencias, Universidad de Valparaíso, Valparaíso, Chile.,Programa de Doctorado en Ciencias, Mención Neurociencia, Universidad de Valparaíso, Valparaíso, Chile
| | - Chiayu Q Chiu
- Centro Interdisciplinario de Neurociencia de Valparaíso (CINV), Instituto de Neurociencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Andrés E Chávez
- Centro Interdisciplinario de Neurociencia de Valparaíso (CINV), Instituto de Neurociencias, Universidad de Valparaíso, Valparaíso, Chile
| |
Collapse
|
3
|
Tyagi S, Shekhar N, Thakur AK. Protective Role of Capsaicin in Neurological Disorders: An Overview. Neurochem Res 2022; 47:1513-1531. [PMID: 35150419 DOI: 10.1007/s11064-022-03549-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2021] [Revised: 02/04/2022] [Accepted: 02/05/2022] [Indexed: 11/24/2022]
Abstract
Different pathological conditions that begin with slow and progressive deformations, cause irreversible affliction by producing loss of neurons and synapses. Commonly it is referred to as 'protein misfolding' diseases or proteinopathies and comprises the latest definition of neurological disorders (ND). Protein misfolding dynamics, proteasomal dysfunction, aggregation, defective degradation, oxidative stress, free radical formation, mitochondrial dysfunctions, impaired bioenergetics, DNA damage, neuronal Golgi apparatus fragmentation, axonal transport disruption, Neurotrophins (NTFs) dysfunction, neuroinflammatory or neuroimmune processes, and neurohumoral changes are the several mechanisms that embark the pathogenesis of ND. Capsaicin (8-Methyl-N-vanillyl-6-nonenamide) one of the major phenolic components in chili peppers (Capsicum) distinctively triggers the unmyelinated C-fiber and acts on Transient Receptor Potential Vanilloid-1, which is a Ca2+ permeable, non-selective cation channel. Several studies have shown the neuroprotective role of capsaicin against oxidative damage, behavioral impairment, with 6-hydroxydopamine (6-OHDA) induced Parkinson's disease, pentylenetetrazol-induced seizures, global cerebral ischemia, and streptozotocin-induced Alzheimer's disease. Based on these lines of evidence, capsaicin can be considered as a potential constituent to develop suitable neuro-pharmacotherapeutics for the management and treatment of ND. Furthermore, exploring newer horizons and carrying out proper clinical trials would help to bring out the promising effects of capsaicin to be recommended as a neuroprotectant.
Collapse
Affiliation(s)
- Sakshi Tyagi
- Neuropharmacology Research Laboratory, School of Pharmaceutical Sciences, Delhi Pharmaceutical Sciences and Research University, New Delhi, 110 017, India
| | - Nikhila Shekhar
- Neuropharmacology Research Laboratory, School of Pharmaceutical Sciences, Delhi Pharmaceutical Sciences and Research University, New Delhi, 110 017, India
| | - Ajit Kumar Thakur
- Neuropharmacology Research Laboratory, School of Pharmaceutical Sciences, Delhi Pharmaceutical Sciences and Research University, New Delhi, 110 017, India.
| |
Collapse
|
4
|
Hsu SK, Hung CF, Yang HC, Weng JR, Wang SJ. TCD, a triterpenoid isolated from wild bitter gourd, reduces synaptosomal release of glutamate and protects against kainic acid-induced neuronal death. Food Funct 2021; 11:9858-9867. [PMID: 33089839 DOI: 10.1039/d0fo02039g] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
3β,7β,25-Trihydroxycucurbita-5,23(E)-dien-19-al (TCD) is a triterpenoid isolated from wild bitter gourd that is a common tropical vegetable with neuroprotective effects. Because excessive glutamate release is a major cause of neuronal damage in various neurological disorders, the aims of this study were to examine the effect of TCD on glutamate release in vitro and to examine the effect of TCD in vivo. In rat cerebrocortical synaptosomes, TCD reduced 4-aminopyridine (4-AP)-stimulated glutamate release and Ca2+ concentration elevation, but had no effect on plasma membrane potential. TCD-mediated inhibition of 4-AP-induced glutamate release was dependent on the presence of extracellular calcium; persisted in the presence of the glutamate transporter inhibitor dl-TBOA, P/Q-type Ca2+ channel blocker ω-agatoxin IVA, and intracellular Ca2+-releasing inhibitors dantrolene and CGP37157; and was blocked by the vesicular transporter inhibitor bafilomycin A1 and the N-type Ca2+ channel blocker ω-conotoxin GVIA. Molecular docking studies have demonstrated that TCD binds to N-type Ca2+ channels. TCD-mediated inhibition of 4-AP-induced glutamate release was abolished by the Ca2+-dependent protein kinase C (PKC) inhibitor Go6976, but was unaffected by the Ca2+-independent PKC inhibitor rottlerin. Furthermore, TCD considerably reduced the phosphorylation of PKC, PKCα, and myristoylated alanine-rich C kinase substrate, a major presynaptic substrate for PKC. In a rat model of kainic acid (KA)-induced excitotoxicity, TCD pretreatment substantially attenuated KA-induced neuronal death in the CA3 hippocampal region. These results suggest that TCD inhibits synaptosomal glutamate release by suppressing N-type Ca2+ channels and PKC activity and exerts protective effects against KA-induced excitotoxicity in vivo.
Collapse
Affiliation(s)
- Szu Kai Hsu
- School of Medicine, Fu Jen Catholic University, New Taipei City, Taiwan.
| | | | | | | | | |
Collapse
|
5
|
Jiang X, Yang Y, Liu P, Li M. Transcriptomics and metabolomics reveal Ca 2+ overload and osmotic imbalance-induced neurotoxicity in earthworms (Eisenia fetida) under tri-n-butyl phosphate exposure. THE SCIENCE OF THE TOTAL ENVIRONMENT 2020; 748:142169. [PMID: 33113685 DOI: 10.1016/j.scitotenv.2020.142169] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2020] [Revised: 08/28/2020] [Accepted: 09/01/2020] [Indexed: 06/11/2023]
Abstract
Tri-n-butyl phosphate (TNBP) is mass-produced and widely utilized in many products, which has increasingly drawn concern about its potential environmental risks. However, little is known about the toxic mechanism on soil-dwelling organisms caused by TNBP. In this study, earthworms (Eisenia fetida) were exposed to environmentally relevant or higher concentrations of TNBP (0, 0.1, 1, and 10 mg/kg) in artificial soil for 14 days. Our results showed that TNBP accumulated in earthworm nervous tissue (cerebral ganglions). In addition, the content of glutamate in cerebral ganglions decreased compared to the control (p < 0.05). The concentration of Ca2+ in earthworm cerebral ganglions increased. However, both Na+/K+-ATPase and Ca2+-ATPase activities were significantly reduced compared to the control (p < 0.05), which led to neurotoxicity in earthworm nervous tissue. Furthermore, the transcriptome and metabolomics revealed the toxic mechanism in earthworm nervous tissue caused by TNBP. Results indicated that the main neurotoxicity mechanisms induced by TNBP were an osmotic imbalance and Ca2+ overload in cerebral ganglions. Our findings fill a gap in the literature on neurotoxicity mechanisms of earthworm response to TNBP exposure and contribute to a better understanding of the adverse effects of TNBP on soil-dwelling organisms in terrestrial ecological systems.
Collapse
Affiliation(s)
- Xiaofeng Jiang
- State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China
| | - Yang Yang
- State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China; Soil Ecology Lab, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Peng Liu
- State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China
| | - Mei Li
- State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
| |
Collapse
|
6
|
Stensson N, Grimby-Ekman A. Altered relationship between anandamide and glutamate in circulation after 30 min of arm cycling: A comparison of chronic pain subject with healthy controls. Mol Pain 2020; 15:1744806919898360. [PMID: 31838922 PMCID: PMC6964246 DOI: 10.1177/1744806919898360] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The insufficient knowledge of biochemical mechanisms behind the emergence and
maintenance of chronic musculoskeletal pain conditions constrains the
development of diagnostic and therapeutic tools for clinical use. However,
physical activity and exercise may improve pain severity and physical function
during chronic pain conditions. Nevertheless, the biochemical consequences of
physical activity and exercise in chronic pain need to be elucidated to increase
the precision of this therapeutic tool in chronic pain treatment. The
endocannabinoid system has been suggested to play an important role in
exercise-induced reward and pain inhibition. Moreover, glutamatergic signalling
has been suggested as an important factor for sensation and transmission of
pain. In addition, a link has been established between the endocannabinoid
system and glutamatergic pathways. This study examines the effect of dynamic
load arm cycling (30 min) on levels of lipid mediators related to the
endocannabinoid system and glutamate in plasma of chronic pain subjects and
pain-free controls. Pain assessments and plasma levels of
arachidonoylethanolamide (anandamide), 2-aracidonoylglycerol,
oleoylethanolamide, palmitoylethanolamide, stearoylethanolamide and glutamate
from 21 subjects with chronic neck pain (chronic pain group) and 11 healthy
controls were analysed pre and post intervention of dynamic load arm cycling.
Pain intensity was significantly different between groups pre and post exercise.
Post exercise, anandamide levels were significantly decreased in health controls
but not in the chronic pain group. A strong positive correlation existed between
anandamide and glutamate in the control group post exercise but not in the
chronic pain group. Moreover, the glutamate/anandamide ratio increased
significantly in the control group and differed significantly with the chronic
pain group post exercise. The altered relationship between anandamide and
glutamate after the intervention in the chronic pain group might reflect
alterations in the endocannabinoid-glutamate mechanistic links in the chronic
pain group compared to the pain-free control group.
Collapse
Affiliation(s)
- Niclas Stensson
- Pain and Rehabilitation Centre, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden
| | - Anna Grimby-Ekman
- Health Metrics, Department of Medicine, School of Public Health and Community Medicine, Gothenburg University, Gothenburg, Sweden
| |
Collapse
|
7
|
Thakre PP, Bellingham MC. Capsaicin causes robust reduction in glycinergic transmission to rat hypoglossal motor neurons via a TRPV1-independent mechanism. J Neurophysiol 2019; 121:1535-1542. [PMID: 30785813 DOI: 10.1152/jn.00059.2019] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The effect of capsaicin on glycinergic synaptic transmission to juvenile rat hypoglossal motor neurons in acute brainstem slices was evaluated in the presence of TTX. Capsaicin caused a robust decrease in miniature IPSC frequency, amplitude, and half-width, showing that this effect is independent of action potential generation. In the presence of capsazepine, a classic TRPV1 antagonist, capsaicin was still able to reduce spontaneous inhibitory postsynaptic current (IPSC) amplitude and frequency. We further investigated whether the effect of capsaicin on glycinergic transmission to hypoglossal motor neurons is pre- or postsynaptic in nature by recording pairs of evoked IPSCs. Interestingly, capsaicin also reduced evoked IPSC amplitude without affecting paired-pulse ratio, indicating a postsynaptic mechanism of action. Significant reduction was also observed in evoked IPSC half-width, rise time, and decay tau. We also show that capsaicin does not have any effect on either transient (It) or sustained (Is) potassium currents. Finally, we also show that the hyperpolarization-activated cationic current (Ih) also remains unchanged after capsaicin application. NEW & NOTEWORTHY Capsaicin reduces the amplitude of quantal and evoked glycinergic inhibitory neurotransmission to brainstem motor neurons without altering activity-dependent transmitter release. This effect of capsaicin is not due to activation of TRPV1 receptors, as it is not blocked by capsazepine, a TRPV1 receptor antagonist. Capsaicin does not alter voltage-dependent potassium current or the hyperpolarization-activated cationic current in brainstem motor neurons.
Collapse
Affiliation(s)
- Prajwal P Thakre
- Faculty of Medicine, School of Biomedical Sciences, University of Queensland , Brisbane, Queensland , Australia
| | - Mark C Bellingham
- Faculty of Medicine, School of Biomedical Sciences, University of Queensland , Brisbane, Queensland , Australia
| |
Collapse
|
8
|
Hsieh TY, Chang Y, Wang SJ. Piperine-mediated suppression of voltage-dependent Ca2+ influx and glutamate release in rat hippocampal nerve terminals involves 5HT1A receptors and G protein βγ activation. Food Funct 2019; 10:2720-2728. [DOI: 10.1039/c8fo02189a] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Piperine is the crucial alkaloid component of black pepper (Piper nigrum Linn.) and has neuroprotective effects.
Collapse
Affiliation(s)
- Ting Yang Hsieh
- P.H.D. Program in Nutrition & Food Science
- Fu Jen Catholic University
- New Taipei City
- Taiwan
| | - Yi Chang
- Department of Anesthesiology
- Shin Kong Wu Ho-Su Memorial Hospital
- Taipei
- Taiwan
- School of Medicine
| | - Su Jane Wang
- School of Medicine
- Fu Jen Catholic University
- New Taipei City
- Taiwan
- Research Center for Chinese Herbal Medicine
| |
Collapse
|
9
|
Molinas AJR, Desmoulins LD, Hamling BV, Butcher SM, Anwar IJ, Miyata K, Enix CL, Dugas CM, Satou R, Derbenev AV, Zsombok A. Interaction between TRPV1-expressing neurons in the hypothalamus. J Neurophysiol 2019; 121:140-151. [PMID: 30461371 PMCID: PMC6383661 DOI: 10.1152/jn.00004.2018] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2018] [Revised: 10/29/2018] [Accepted: 11/14/2018] [Indexed: 02/08/2023] Open
Abstract
Transient receptor potential vanilloid type 1 (TRPV1) is a ligand-gated ion channel expressed in the peripheral and central nervous systems. TRPV1-dependent mechanisms take part in a wide range of physiological and pathophysiological pathways including the regulation of homeostatic functions. TRPV1 expression in the hypothalamus has been described as well as evidence that TRPV1-dependent excitatory inputs to hypothalamic preautonomic neurons are diminished in diabetic conditions. Here we aimed to determine the functional expression of TRPV1 in two hypothalamic nuclei known to be involved in the central control of metabolism and to test the hypothesis that TRPV1-expressing neurons receive TRPV1-expressing inputs. A mouse model (TRPV1Cre/tdTom) was generated to identify TRPV1-expressing cells and determine the cellular properties of TRPV1-expressing neurons in adult mice. Our study demonstrated the functional expression of TRPV1 in the dorsomedial hypothalamic nucleus and paraventricular nucleus in adult mice. Our findings revealed that a subset of TRPV1Cre/tdTom neurons receive TRPV1-expressing excitatory inputs, indicating direct interaction between TRPV1-expressing neurons. In addition, astrocytes likely play a role in the modulation of TRPV1-expressing neurons. In summary, this study identified specific hypothalamic regions where TRPV1 is expressed and functional in adult mice and the existence of direct connections between TRPV1Cre/tdTom neurons. NEW & NOTEWORTHY Transient receptor potential vanilloid type 1 (TRPV1) is expressed in the hypothalamus, and TRPV1-dependent regulation of preautonomic neurons is decreased in hyperglycemic conditions. Our study demonstrated functional expression of TRPV1 in two hypothalamic nuclei involved in the control of energy homeostasis. Our results also revealed that a subset of TRPV1-expressing neurons receive TRPV1-expressing excitatory inputs. These findings suggest direct interaction between TRPV1-expressing neurons.
Collapse
Affiliation(s)
- Adrien J R Molinas
- Department of Physiology, School of Medicine, Tulane University , New Orleans, Louisiana
| | - Lucie D Desmoulins
- Department of Physiology, School of Medicine, Tulane University , New Orleans, Louisiana
| | - Brooke V Hamling
- Department of Physiology, School of Medicine, Tulane University , New Orleans, Louisiana
- Neuroscience Program, Brain Institute, Tulane University , New Orleans, Louisiana
| | - Sierra M Butcher
- Department of Physiology, School of Medicine, Tulane University , New Orleans, Louisiana
- Neuroscience Program, Brain Institute, Tulane University , New Orleans, Louisiana
| | - Imran J Anwar
- Department of Physiology, School of Medicine, Tulane University , New Orleans, Louisiana
| | - Kayoko Miyata
- Department of Physiology, School of Medicine, Tulane University , New Orleans, Louisiana
| | - Courtney L Enix
- Department of Physiology, School of Medicine, Tulane University , New Orleans, Louisiana
| | - Courtney M Dugas
- Department of Physiology, School of Medicine, Tulane University , New Orleans, Louisiana
| | - Ryousuke Satou
- Department of Physiology, School of Medicine, Tulane University , New Orleans, Louisiana
| | - Andrei V Derbenev
- Department of Physiology, School of Medicine, Tulane University , New Orleans, Louisiana
- Neuroscience Program, Brain Institute, Tulane University , New Orleans, Louisiana
| | - Andrea Zsombok
- Department of Physiology, School of Medicine, Tulane University , New Orleans, Louisiana
- Neuroscience Program, Brain Institute, Tulane University , New Orleans, Louisiana
| |
Collapse
|
10
|
Thakre PP, Bellingham MC. Capsaicin Enhances Glutamatergic Synaptic Transmission to Neonatal Rat Hypoglossal Motor Neurons via a TRPV1-Independent Mechanism. Front Cell Neurosci 2017; 11:383. [PMID: 29259542 PMCID: PMC5723349 DOI: 10.3389/fncel.2017.00383] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Accepted: 11/17/2017] [Indexed: 01/02/2023] Open
Abstract
We investigated whether capsaicin modulated synaptic transmission to hypoglossal motor neurons (HMNs) by acting on transient receptor potential vanilloid type 1 (TRPV1) receptors. Using whole-cell patch clamp recording from neonatal rat HMNs, we found that capsaicin increased spontaneous excitatory post-synaptic current (sEPSC) frequency and amplitude. Interestingly, the only effect of capsaicin on spontaneous inhibitory post-synaptic currents (sIPSCs) was a significant decrease in sIPSC amplitude without altering frequency, indicating a post-synaptic mechanism of action. The frequency of miniature excitatory post-synaptic currents (mEPSCs), recorded in the presence of tetrodotoxin (TTX), was also increased by capsaicin, but capsaicin did not alter mEPSC amplitude, consistent with a pre-synaptic mechanism of action. A negative shift in membrane current (Iholding) was elicited by capsaicin under both recording conditions. The effect of capsaicin on excitatory synaptic transmission remained unchanged in the presence of the TRPV1 antagonists, capsazepine or SB366791, suggesting that capsaicin acts to modulate EPSCs via a mechanism which does not require TRPV1 activation. Capsaicin, however, did not alter evoked excitatory post-synaptic currents (eEPSCs) or the paired-pulse ratio (PPR) of eEPSCs. Repetitive action potential (AP) firing in HMNs was also unaltered by capsaicin, indicating that capsaicin does not change HMN intrinsic excitability. We have demonstrated that capsaicin modulates glutamatergic excitatory, as well as glycinergic inhibitory, synaptic transmission in HMNs by differing pre- and post-synaptic mechanisms. These results expand our understanding regarding the extent to which capsaicin can modulate synaptic transmission to central neurons.
Collapse
Affiliation(s)
- Prajwal P Thakre
- Faculty of Medicine, School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, Australia
| | - Mark C Bellingham
- Faculty of Medicine, School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, Australia
| |
Collapse
|