The Role of Itch-Mediating Receptors and Channels in the Mouse Urinary Bladder

Altered sensitivity of afferent signalling from the urinary bladder is implicated in chronic and debilitating conditions such as overactive bladder syndrome (OAB) and interstitial cystitis/bladder pain syndrome (IC/BPS). The range of receptors and ion channels expressed and functional on the afferent neurons drives overall afferent sensitivity. Receptors known to mediate ‘itch’ sensation have recently been identified in the viscera and shown to play a role in visceral hypersensitivity; where ‘itch’ signalling in the skin results in scratching, activation of similar signalling mechanisms in the bladder may stimulate removal of irritants via increased micturition. In this thesis, a combination of techniques was used to identify the expression and function of histaminergic and non-histaminergic irritant-sensing G-proteins coupled receptors (GPCRs) in bladder sensory pathways. Single cell RT-PCR was used to identify expression of mRNA encoding for histamine receptor subtype 1 (H1R; Hrh1), mas-related G-protein receptors A3 (Mrgpra3) and C11 (Mrgprc11), and bile-acid receptor TGR5 (Gpbar1) in retrogradely labelled bladder-innervating afferent neurons from the dorsal root ganglia (DRG). Co-expression of irritant-sensing GPCRs with ion channels transient receptor potential vanilloid 1 (Trpv1) and TRP ankyrin 1 (Trpa1) was also determined. Further, QRT-PCR showed Hrh3 and Gpbar1 expression in urothelial cells. Functional assays, including in vitro live cell calcium imaging and ex vivo bladder afferent nerve recordings in conjunction with a range of genetic knockout mouse models, were used to demonstrate that stimulation of H1R, MrgprA3 and MrgprC11, or TGR5 in bladder-innervating afferent neurons results in increased bladder afferent sensitivity to distension. TRPV1 expression was required for H1R-induced hypersensitivity. TGR5-induced hypersensitivity was partially mediated by TRPV1 while the absence of TRPA1 had limited impact. To further demonstrate physiological relevance of these results, in vivo instillation of compounds into the bladder with or without bladder distension was used in conjunction with pERK immunoreactivity assays in the lumbosacral spinal cord. Increased activation of lumbosacral spinal neurons (where peripheral afferent bladder signals input) indicated central transmission of bladder afferent signalling in response to peripheral activation of these itch-mediating GPCRs. This thesis has identified a novel sub-class of receptors involved in mediating bladder afferent sensitivity and begun to determine the signalling pathways involved, opening a number of avenues for future research in the area of bladder sensation. Irritant-sensing mechanisms may contribute to conditions of bladder hypersensitivity such as OAB and IC/BPS and represent potentially viable future targets for treatment.Thesis (Ph.D.) -- University of Adelaide, Adelaide Medical School, 202

Mechanisms Underlying Overactive Bladder and Interstitial Cystitis/Painful Bladder Syndrome

The bladder is innervated by extrinsic afferents that project into the dorsal horn of the spinal cord, providing sensory input to the micturition centers within the central nervous system. Under normal conditions, the continuous activation of these neurons during bladder distension goes mostly unnoticed. However, for patients with chronic urological disorders such as overactive bladder syndrome (OAB) and interstitial cystitis/painful bladder syndrome (IC/PBS), exaggerated bladder sensation and altered bladder function are common debilitating symptoms. Whilst considered to be separate pathological entities, there is now significant clinical and pre-clinical evidence that both OAB and IC/PBS are related to structural, synaptic, or intrinsic changes in the complex signaling pathways that mediate bladder sensation. This review discusses how urothelial dysfunction, bladder permeability, inflammation, and cross-organ sensitisation between visceral organs can regulate this neuroplasticity. Furthermore, we discuss how the emotional affective component of pain processing, involving dysregulation of the HPA axis and maladaptation to stress, anxiety and depression, can exacerbate aberrant bladder sensation and urological dysfunction. This review reveals the complex nature of urological disorders, highlighting numerous interconnected mechanisms in their pathogenesis. To find appropriate therapeutic treatments for these disorders, it is first essential to understand the mechanisms responsible, incorporating research from every level of the sensory pathway, from bladder to brain

Mechanisms Underlying Overactive Bladder and Interstitial Cystitis/Painful Bladder Syndrome

Copyright © 2018 Grundy, Caldwell and Brierley. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.The bladder is innervated by extrinsic afferents that project into the dorsal horn of the spinal cord, providing sensory input to the micturition centers within the central nervous system. Under normal conditions, the continuous activation of these neurons during bladder distension goes mostly unnoticed. However, for patients with chronic urological disorders such as overactive bladder syndrome (OAB) and interstitial cystitis/painful bladder syndrome (IC/PBS), exaggerated bladder sensation and altered bladder function are common debilitating symptoms. Whilst considered to be separate pathological entities, there is now significant clinical and pre-clinical evidence that both OAB and IC/PBS are related to structural, synaptic, or intrinsic changes in the complex signaling pathways that mediate bladder sensation. This review discusses how urothelial dysfunction, bladder permeability, inflammation, and cross-organ sensitisation between visceral organs can regulate this neuroplasticity. Furthermore, we discuss how the emotional affective component of pain processing, involving dysregulation of the HPA axis and maladaptation to stress, anxiety and depression, can exacerbate aberrant bladder sensation and urological dysfunction. This review reveals the complex nature of urological disorders, highlighting numerous interconnected mechanisms in their pathogenesis. To find appropriate therapeutic treatments for these disorders, it is first essential to understand the mechanisms responsible, incorporating research from every level of the sensory pathway, from bladder to brain

Multiple sodium channel isoforms mediate the pathological effects of Pacific ciguatoxin-1

This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/Human intoxication with the seafood poison ciguatoxin, a dinoflagellate polyether that activates voltage-gated sodium channels (NaV), causes ciguatera, a disease characterised by gastrointestinal and neurological disturbances. We assessed the activity of the most potent congener, Pacific ciguatoxin-1 (P-CTX-1), on NaV1.1–1.9 using imaging and electrophysiological approaches. Although P-CTX-1 is essentially a non-selective NaV toxin and shifted the voltage-dependence of activation to more hyperpolarising potentials at all NaV subtypes, an increase in the inactivation time constant was observed only at NaV1.8, while the slope factor of the conductance-voltage curves was significantly increased for NaV1.7 and peak current was significantly increased for NaV1.6. Accordingly, P-CTX-1-induced visceral and cutaneous pain behaviours were significantly decreased after pharmacological inhibition of NaV1.8 and the tetrodotoxin-sensitive isoforms NaV1.7 and NaV1.6, respectively. The contribution of these isoforms to excitability of peripheral C- and A-fibre sensory neurons, confirmed using murine skin and visceral single-fibre recordings, reflects the expression pattern of NaV isoforms in peripheral sensory neurons and their contribution to membrane depolarisation, action potential initiation and propagation