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Guilleminault L, Grassin-Delyle S, Mazzone SB. Drugs Targeting Cough Receptors: New Therapeutic Options in Refractory or Unexplained Chronic Cough. Drugs 2024:10.1007/s40265-024-02047-y. [PMID: 38904926 DOI: 10.1007/s40265-024-02047-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/06/2024] [Indexed: 06/22/2024]
Abstract
Refractory chronic cough is a disabling disease with very limited therapeutic options. A better understanding of cough pathophysiology has led to the development of emerging drugs targeting cough receptors. Recent strides have illuminated novel therapeutic avenues, notably centred on modulating transient receptor potential (TRP) channels, purinergic receptors, and neurokinin receptors. By modulating these receptors, the goal is to intervene in the sensory pathways that trigger cough reflexes, thereby providing relief without compromising vital protective mechanisms. These innovative pharmacotherapies hold promise for improvement of refractory chronic cough by offering improved efficacy and potentially mitigating adverse effects associated with current recommended treatments. A deeper comprehension of their precise mechanisms of action and clinical viability is imperative for optimising therapeutic interventions and elevating patient care standards in respiratory health. This review delineates the evolving landscape of drug development in this domain, emphasising the significance of these advancements in reshaping the paradigm of cough management.
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Affiliation(s)
- Laurent Guilleminault
- Toulouse Institute for Infectious and Inflammatory Diseases (Infinity), INSERM UMR1291, CNRS UMR5051, University Toulouse III, 31024, Toulouse, France.
- Department of Respiratory Medicine, Faculty of Medicine, Hôpital Larrey, Toulouse University Hospital, 24 chemin de Pouvourville, 31059, Toulouse, France.
| | - Stanislas Grassin-Delyle
- Exhalomics®, Hôpital Foch, Suresnes, France
- Département de Biotechnologie de la Santé, Université Paris-Saclay, UVSQ, INSERM, Infection et inflammation (2I), U1173, Montigny le Bretonneux, France
| | - Stuart B Mazzone
- Department of Anatomy and Physiology, University of Melbourne, Melbourne, VIC, Australia
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Ueda Y, Uta D, Furue H, Ohtubo Y. An electrophysiological method for evaluation of topical antipruritic drugs on itch-related neuronal activities in the spinal cord in hairless mice. Eur J Pharmacol 2023; 952:175798. [PMID: 37207968 DOI: 10.1016/j.ejphar.2023.175798] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Revised: 04/29/2023] [Accepted: 05/16/2023] [Indexed: 05/21/2023]
Abstract
To evaluate the effects of antipruritic drugs, it is important to determine whether the neural responses induced by physiological itch stimuli are suppressed. Although there are several behavioral assessments for topical antipruritic drugs applied to the skin, there are few established methods at neuronal levels using in vivo electrophysiological recordings for predicting local efficacy of antipruritic drugs for cutaneous application. To establish an assessment of topical antipruritic drugs applied to skin using in vivo extracellular recording from neurons in the superficial dorsal horn, we examined the relationships between itch-related biting behavior and spinal neuronal responses elicited by intradermal injection of pruritogen serotonin (5-HT) in hairless mice. The efficacy of topical occlusive application of local anesthetics was also evaluated by an in vivo electrophysiological method. 5-HT significantly increased the firing frequency in spinal neurons. The spinal firing frequency time course was similar to that of the biting behavior after the 5-HT injections. The 5-HT-induced spinal responses were significantly decreased by topical occlusive application of lidocaine or a Nav 1.7 channel blocker to the calf. The intradermal 5-HT injection-induced spinal neuronal responses appeared to be suppressed by topical occlusive application of lidocaine or a Nav1.7 channel blocker. The electrophysiological method for evaluating topical antipruritic drugs may be beneficial in assessing local effects on the skin.
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Affiliation(s)
- Yuhki Ueda
- Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Kitakyushu, Japan; Drug Development Laboratories, Kyoto R&D Center, Drug Development Research Laboratories, Maruho Co., Ltd., Kyoto, Japan.
| | - Daisuke Uta
- Department of Applied Pharmacology, Faculty of Pharmaceutical Sciences, University of Toyama, Toyama, Japan.
| | - Hidemasa Furue
- Department of Neurophysiology, Hyogo College of Medicine, Nishinomiya, Japan.
| | - Yoshitaka Ohtubo
- Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Kitakyushu, Japan.
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Kim JS, Sun H, Meeker S, Undem BJ. Role of Na V 1.9 in inflammatory mediator-induced activation of mouse airway vagal C-fibres. J Physiol 2023; 601:1139-1150. [PMID: 36750759 PMCID: PMC10023385 DOI: 10.1113/jp283751] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2022] [Accepted: 01/23/2023] [Indexed: 02/09/2023] Open
Abstract
The influence of NaV 1.9 on inflammatory mediator-induced activation of airway vagal nodose C-fibres was evaluated by comparing responses in wild-type versus NaV 1.9-/- mice. A single-cell RT-PCR analysis indicated that virtually all nodose C-fibre neurons expressed NaV 1.9 (SCN11A) mRNA. Using extracellular electrophysiological recordings in an isolated vagally innervated mouse trachea-lung preparation, it was noted that mediators acting via G protein-coupled receptors (PAR2), or ionotropic receptors (P2×3) were 70-85% less effective in evoking action potential discharge in the absence of NaV 1.9. However, there was no difference in action potential discharge between wild-type and NaV 1.9-/- when the stimulus was a rapid punctate mechanical stimulus. An analysis of the passive and active properties of isolated nodose neurons revealed no difference between neurons from wild-type and NaV 1.9-/- mice, with the exception of a modest difference in the duration of the afterhyperpolarization. There was also no difference in the amount of current required to evoke action potentials (rheobase) or the action potential voltage threshold. The inward current evoked by the chemical mediator by a P2×3 agonist was the same in wild-type versus NaV 1.9-/- neurons. However, the current was sufficient to evoke action potential only in the wild-type neurons. The data support the speculation that NaV 1.9 could be an attractive therapeutic target for inflammatory airway disease by selectively inhibiting inflammatory mediator-associated vagal C-fibre activation. KEY POINTS: Inflammatory mediators were much less effective in activating the terminals of vagal airway C-fibres in mice lacking NaV 1.9. The active and passive properties of nodose neurons were the same between wild-type neurons and NaV 1.9-/- neurons. Nerves lacking NaV 1.9 responded, normally, with action potential discharge to rapid punctate mechanical stimulation of the terminals or the rapid stimulation of the cell bodies with inward current injections. NaV 1.9 channels could be an attractive target to selectively inhibit vagal nociceptive C-fibre activation evoked by inflammatory mediators without blocking the nerves' responses to the potentially hazardous stimuli associated with aspiration.
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Affiliation(s)
- Joyce S Kim
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Hui Sun
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Sonya Meeker
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Bradley J Undem
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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Manzur-Villalobos I, Contreras-Puentes N, Díaz-Caballero A, Durán-Lengua M, Alviz-Amador A. In silico study of local anesthetics analogues on sodium channel Nav 1.7 a pharmacological target on inflamed dental pulp. INFORMATICS IN MEDICINE UNLOCKED 2022. [DOI: 10.1016/j.imu.2022.101117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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Mulpuri Y, Yamamoto T, Nishimura I, Spigelman I. Role of voltage-gated sodium channels in axonal signal propagation of trigeminal ganglion neurons after infraorbital nerve entrapment. NEUROBIOLOGY OF PAIN 2022; 11:100084. [PMID: 35128176 PMCID: PMC8803652 DOI: 10.1016/j.ynpai.2022.100084] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Revised: 01/17/2022] [Accepted: 01/17/2022] [Indexed: 11/25/2022]
Abstract
Infraorbital nerve entrapment (IoNE) induces mechanical allodynia and enhances signal propagation in primary afferent A- and C-fibers. IoNE increases sensitivity of A- and C-fibers to conduction block by tetrodotoxin (TTX) and selective voltage-gated sodium channel 1.8 (NaV1.8) inhibitor, A-803467. IoNE increases signal propagation in vibrissal pad Ad -, but not Aβ-fibers, and their sensitivity to conduction block by the selective NaV1.8 inhibitor. IoNE increases membrane excitability of dissociated small and medium sized trigeminal neurons. IoNE increases nerve, but not ganglion, levels of NaV1.3, NaV1.7, and NaV1.8 mRNAs, and NaV1.8 protein.
Chronic pain arising from peripheral nerve injuries represents a significant clinical challenge because even the most efficacious anticonvulsant drug treatments are limited by their side effects profile. We investigated pain behavior, changes in axonal signal conduction and excitability of trigeminal neurons, and expression of voltage-gated sodium channels (NaVs) in the infraorbital nerve and trigeminal ganglion (TG) after infraorbital nerve entrapment (IoNE). Compared to Sham, IoNE rats had increased A- and C-fiber compound action potentials (CAPs) and Aδ component of A-CAP area from fibers innervating the vibrissal pad. After IoNE, A- and C-fiber CAPs were more sensitive to blockade by tetrodotoxin (TTX), and those fibers that were TTX-resistant were more sensitive to blockade by the NaV1.8 selective blocker, A-803467. Although NaV1.7 blocker, ICA-121431 alone, did not affect Aδ-fiber signal propagation, cumulative application with A-803467 and 4,9-anhydro-TTX significantly reduced the Aδ-fiber CAP in IoNE rats. In patch clamp recordings from small- and medium-sized TG neurons, IoNE resulted in reduced action potential (AP) depolarizing current threshold, hyperpolarized AP voltage threshold, increased AP duration, and a more depolarized membrane potential. While the transcripts of most NaVs were reduced in the ipsilateral TG after IoNE, NaV1.3, NaV1.7, and NaV1.8 mRNAs, and NaV1.8 protein, were significantly increased in the nerve. Altogether, our data suggest that axonal redistribution of NaV1.8, and to a lesser extent NaV1.3, and NaV1.7 contributes to enhanced nociceptive signal propagation in peripheral nerve after IoNE.
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Mauro TM. Ode to Salt: Commentary on "Skin Sodium Accumulates in Psoriasis and Reflects Disease Severity". J Invest Dermatol 2022; 142:16-17. [PMID: 34565562 PMCID: PMC8740904 DOI: 10.1016/j.jid.2021.08.401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Revised: 08/26/2021] [Accepted: 08/27/2021] [Indexed: 12/29/2022]
Abstract
"Skin Sodium Accumulates in Psoriasis and Reflects Disease Severity" (Maifeld et al., 2021) showed that skin sodium ion (Na+) is increased in patients with a PASI > 5. Na+ concentration as well as its content were increased in these patients, supporting the proposed mechanism that increased Na+ concentrations enhance IL-17 expression from CD4+ cells. These data initially were generated using a noninvasive technique, sodium (23Na) magnetic resonance imaging, and then were verified using 23Na spectroscopy and atomic absorption spectrometry in ashed-skin biopsies in humans and also using mouse models of psoriasis. These findings suggest a novel pathologic mechanism for psoriasis development and target for treatment.
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Affiliation(s)
- Theodora M Mauro
- Department of Dermatology, University of California San Francisco, San Francisco, California, USA; Dermatology Service, Veterans Affairs Health Care System, San Francisco, California, USA.
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Goodwin G, McMahon SB. The physiological function of different voltage-gated sodium channels in pain. Nat Rev Neurosci 2021; 22:263-274. [PMID: 33782571 DOI: 10.1038/s41583-021-00444-w] [Citation(s) in RCA: 59] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/12/2021] [Indexed: 02/01/2023]
Abstract
Evidence from human genetic pain disorders shows that voltage-gated sodium channel α-subtypes Nav1.7, Nav1.8 and Nav1.9 are important in the peripheral signalling of pain. Nav1.7 is of particular interest because individuals with Nav1.7 loss-of-function mutations are congenitally insensitive to acute and chronic pain, and there is considerable hope that phenocopying these effects with a pharmacological antagonist will produce a new class of analgesic drug. However, studies in these rare individuals do not reveal how and where voltage-gated sodium channels contribute to pain signalling, which is of critical importance for drug development. More than a decade of research utilizing rodent genetic models and pharmacological tools to study voltage-gated sodium channels in pain has begun to unravel the role of different subtypes. Here, we review the contribution of individual channel subtypes in three key physiological processes necessary for transmission of sensory information to the CNS: transduction of stimuli at peripheral nerve terminals, axonal transmission of action potentials and neurotransmitter release from central terminals. These data suggest that drugs seeking to recapitulate the analgesic effects of loss of function of Nav1.7 will need to be brain-penetrant - which most of those developed to date are not.
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Affiliation(s)
- George Goodwin
- Pain and Neurorestoration Group, King's College London, London, UK.
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Langedijk JAGM, Beuers UH, Oude Elferink RPJ. Cholestasis-Associated Pruritus and Its Pruritogens. Front Med (Lausanne) 2021; 8:639674. [PMID: 33791327 PMCID: PMC8006388 DOI: 10.3389/fmed.2021.639674] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2020] [Accepted: 02/12/2021] [Indexed: 12/17/2022] Open
Abstract
Pruritus is a debilitating symptom of various cholestatic disorders, including primary biliary cholangitis (PBC), primary sclerosing cholangitis (PSC) and inherited progressive familial intrahepatic cholestasis (PFIC). The molecular mechanisms leading to cholestasis-associated pruritus are still unresolved and the involved pruritogens are indecisive. As a consequence of pruritus, patients suffer from sleep deprivation, loss of daytime concentration, auto-mutilation and sometimes even suicidal ideations. Current guideline-approved therapy of cholestasis-associated pruritus includes stepwise administration of several medications, which may alleviate complaints in some, but not all affected patients. Therefore, also experimental therapeutic approaches are required to improve patients' quality of life. This article reviews the current state of research on pruritogens and their receptors, and shortly discusses the most recent experimental therapies.
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Affiliation(s)
- Jacqueline A G M Langedijk
- Amsterdam University Medical Centers, Tytgat Institute for Liver and Intestinal Research, Research Institute Amsterdam Gastroenterology, Endocrinology and Metabolism (AGEM), University of Amsterdam, Amsterdam, Netherlands
| | - Ulrich H Beuers
- Amsterdam University Medical Centers, Tytgat Institute for Liver and Intestinal Research, Research Institute Amsterdam Gastroenterology, Endocrinology and Metabolism (AGEM), University of Amsterdam, Amsterdam, Netherlands
| | - Ronald P J Oude Elferink
- Amsterdam University Medical Centers, Tytgat Institute for Liver and Intestinal Research, Research Institute Amsterdam Gastroenterology, Endocrinology and Metabolism (AGEM), University of Amsterdam, Amsterdam, Netherlands
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MicroRNA-96 is required to prevent allodynia by repressing voltage-gated sodium channels in spinal cord. Prog Neurobiol 2021; 202:102024. [PMID: 33636225 DOI: 10.1016/j.pneurobio.2021.102024] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 12/18/2020] [Accepted: 02/11/2021] [Indexed: 12/20/2022]
Abstract
Voltage-gated sodium channels (Navs) 1.7, 1.8, and 1.9 are predominately expressed in peripheral sensory neurons and are critical for action potential propagation in nociceptors. Unexpectedly, we found that expression of SCN9A, SCN10A, SCN11A, and SCN2A, the alpha subunit of Nav1.7, Nav1.8, Nav1.9 and Nav1.2, respectively, are up-regulated in spinal dorsal horn (SDH) neurons of miR-96 knockout mice. These mice also have de-repression of CACNA2D1/2 in DRG and display thermal and mechanical allodynia that could be attenuated by intrathecal or intraperitoneal injection of Nav1.7 or Nav1.8 blockers or Gabapentin. Moreover, Gad2::CreERT2 conditional miR-96 knockout mice phenocopied global knockout mice, implicating inhibitory neurons; nerve injury induced significant loss of miR-96 in SDH GABAergic and Glutamatergic neurons in mice which negatively correlated to up-regulation of Nav1.7, Nav1.8, Nav1.9 and Scn2a, this dis-regulation of miR-96 and Navs in SDH neurons contributed to neuropathic pain which can be alleviated by intrathecal injection of Nav1.7 or Nav1.8 blockers. In conclusion, miR-96 is required to avoid allodynia through limiting the expression of VGCCs and Navs in DRG and Navs in SDH in naïve and nerve injury-induced neuropathic pain mice. Our findings suggest that central nervous system penetrating Nav1.7 and Nav1.8 blockers may be efficacious for pain relief.
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Huang Z, Zhou X, Zhang J, Mai CL, Mai JZ, Liu C, Zhang H, Liu XG. Bulleyaconitine A Inhibits Itch and Itch Sensitization Induced by Histamine and Chloroquine. Neuroscience 2020; 429:68-77. [DOI: 10.1016/j.neuroscience.2019.12.048] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Revised: 12/11/2019] [Accepted: 12/31/2019] [Indexed: 02/07/2023]
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Li Q, Qin L, Li J. Enhancement by TNF-α of TTX-resistant Na V current in muscle sensory neurons after femoral artery occlusion. Am J Physiol Regul Integr Comp Physiol 2020; 318:R772-R780. [PMID: 32101460 DOI: 10.1152/ajpregu.00338.2019] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Femoral artery occlusion in rats has been used to study human peripheral artery disease (PAD). Using this animal model, a recent study suggests that increases in levels of tumor necrosis factor-α (TNF-α) and its receptor lead to exaggerated responses of sympathetic nervous activity and arterial blood pressure as metabolically sensitive muscle afferents are activated. Note that voltage-dependent Na+ subtype NaV1.8 channels (NaV1.8) are predominately present in chemically sensitive thin fiber sensory nerves. The purpose of this study was to examine the role played by TNF-α in regulating activity of NaV1.8 currents in muscle dorsal root ganglion (DRG) neurons of rats with PAD induced by femoral artery occlusion. DRG neurons from control and occluded limbs of rats were labeled by injecting the fluorescent tracer DiI into the hindlimb muscles 5 days before the experiments. A voltage patch-clamp mode was used to examine TTX-resistant (TTX-R) NaV currents. Results were as follows: 72 h of femoral artery occlusion increased peak amplitude of TTX-R [1,922 ± 139 pA in occlusion (n = 11 DRG neurons) vs. 1,178 ± 39 pA in control (n = 10), means ± SE; P < 0.001 between the 2 groups] and NaV1.8 currents [1,461 ± 116 pA in occlusion (n = 11) and 766 ± 48 pA in control (n = 10); P < 0.001 between groups] in muscle DRG neurons. TNF-α exposure amplified TTX-R and NaV1.8 currents in DRG neurons of occluded muscles in a dose-dependent manner. Notably, the amplification of TTX-R and NaV1.8 currents induced by TNF-α was attenuated in DRG neurons with preincubation with respective inhibitors of the intracellular signaling pathways p38-MAPK, JNK, and ERK. In conclusion, our data suggest that NaV1.8 is engaged in the role of TNF-α in amplifying muscle afferent inputs as the hindlimb muscles are ischemic; p38-MAPK, JNK, and ERK pathways are likely necessary to mediate the effects of TNF-α.
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Affiliation(s)
- Qin Li
- Heart and Vascular Institute, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania
| | - Lu Qin
- Heart and Vascular Institute, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania
| | - Jianhua Li
- Heart and Vascular Institute, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania
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Complementary roles of murine Na V1.7, Na V1.8 and Na V1.9 in acute itch signalling. Sci Rep 2020; 10:2326. [PMID: 32047194 PMCID: PMC7012836 DOI: 10.1038/s41598-020-59092-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2019] [Accepted: 01/17/2020] [Indexed: 12/19/2022] Open
Abstract
Acute pruritus occurs in various disorders. Despite severe repercussions on quality of life treatment options remain limited. Voltage-gated sodium channels (NaV) are indispensable for transformation and propagation of sensory signals implicating them as drug targets. Here, NaV1.7, 1.8 and 1.9 were compared for their contribution to itch by analysing NaV-specific knockout mice. Acute pruritus was induced by a comprehensive panel of pruritogens (C48/80, endothelin, 5-HT, chloroquine, histamine, lysophosphatidic acid, trypsin, SLIGRL, β-alanine, BAM8-22), and scratching was assessed using a magnet-based recording technology. We report an unexpected stimulus-dependent diversity in NaV channel-mediated itch signalling. NaV1.7−/− showed substantial scratch reduction mainly towards strong pruritogens. NaV1.8−/− impaired histamine and 5-HT-induced scratching while NaV1.9 was involved in itch signalling towards 5-HT, C48/80 and SLIGRL. Furthermore, similar microfluorimetric calcium responses of sensory neurons and expression of itch-related TRP channels suggest no change in sensory transduction but in action potential transformation and conduction. The cumulative sum of scratching over all pruritogens confirmed a leading role of NaV1.7 and indicated an overall contribution of NaV1.9. Beside the proposed general role of NaV1.7 and 1.9 in itch signalling, scrutiny of time courses suggested NaV1.8 to sustain prolonged itching. Therefore, NaV1.7 and 1.9 may represent targets in pruritus therapy.
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Driessen AK. Vagal Afferent Processing by the Paratrigeminal Nucleus. Front Physiol 2019; 10:1110. [PMID: 31555145 PMCID: PMC6722180 DOI: 10.3389/fphys.2019.01110] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Accepted: 08/12/2019] [Indexed: 12/26/2022] Open
Abstract
The paratrigeminal nucleus is an obscure region in the dorsal lateral medulla, which has been best characterized as a collection of interstitial cells located in the dorsal tip of the spinal trigeminal tract. The paratrigeminal nucleus receives afferent input from the vagus, trigeminal, spinal, and glossopharyngeal nerves, which contribute to its long-known roles in the baroreceptor reflex and nociceptive processing. More recently, studies have shown that this region is also involved in the processing of airway-derived sensory information. Notably, these studies highlight an underappreciated complexity in the neuronal content and circuit connectivity of the paratrigeminal nucleus. However, much remains to be understood about how paratrigeminal processing of vagal afferents is altered in disease. The aim of the present review is to provide an update of the current understanding of vagal afferent processing in the paratrigeminal nucleus and to explore how dysregulation at this site may contribute to vagal sensory neural dysfunction during disease.
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Affiliation(s)
- Alexandria K Driessen
- School of Biomedical Science, Department of Anatomy and Neuroscience, University of Melbourne, Parkville, VIC, Australia
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Abstract
In this study, we sought to elucidate the molecular mechanism underlying human Mas-related G protein-coupled receptor X1 (MrgprX1) mediated itch sensation. We found that activation of MrgprX1 by BAM8-22 triggered robust action potential discharges in dorsal root ganglion (DRG) neurons. This neuronal excitability is not mediated by Transient receptor potential (TRP) cation channels, M-type potassium channels, or chloride channels. Instead, activation of MrgprX1 lowers the activation threshold of TTX-resistant sodium channels and induces inward sodium currents. These MrgprX1-elicited action potential discharges can be blocked by Pertussis toxin (PTX) and a Gβγ inhibitor - Gallein. Behavioral results showed that Nav1.9 knockout but not Trpa1 knockout significantly reduced BAM8-22 evoked scratching behavior. Collectively, these data suggest that activation of MrgprX1 triggers itch sensation by increasing the activity of TTX-resistant voltage-gated sodium channels.
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Jurcakova D, Ru F, Undem BJ. Allergen-induced histaminergic and non-histaminergic activation of itch C-fiber nerve terminals in mouse skin. Neuroscience 2019; 410:55-58. [PMID: 31047975 DOI: 10.1016/j.neuroscience.2019.04.039] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Revised: 03/29/2019] [Accepted: 04/22/2019] [Indexed: 11/16/2022]
Abstract
Acute cutaneous exposure to allergen often leads to itch, but seldom pain. The effect of mast cell activation on cutaneous C-fibers was studied using innervated isolated mouse skin preparation that allows for intra-arterial delivery of chemicals to the nerve terminals in the skin. Allergen (ovalbumin) injection into the isolated skin of actively sensitized mice strongly stimulated chloroquine (CQ)-sensitive C-fibers (also referred to as "itch" nerves); on the other hand, CQ-insensitive C-fibers were activated only modestly, if at all. The histamine H1 receptor antagonist pyrilamine abolished itch C-fibers response to histamine, but failed to significantly reduce the response to ovalbumin. Ovalbumin also strongly activated itch C-fibers in skin isolated from Mrgpr-cluster Δ-/- mice. When pyrilamine was studied in the Mrgpr-cluster Δ-/- mice thereby eliminating the influence of both histamine H1 and Mrgpr receptors (MrgprA3 and C11 are selectively expressed by itch nerves), the ovalbumin response was very nearly eliminated. The data indicate that the acute activation of itch C-fibers in mouse skin is largely secondary to the combined effect of activation of histamine H1 and Mrpgr receptors.
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Affiliation(s)
- Danica Jurcakova
- Johns Hopkins School of Medicine, Baltimore, MD, USA; Department of Pathophysiology, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Martin, Slovakia
| | - Fei Ru
- Johns Hopkins School of Medicine, Baltimore, MD, USA.
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