A sexually dimorphic effect of cholera toxin: rapid changes in colonic motility mediated via a 5‐HT₃ receptor‐dependent pathway in female C57Bl/6 mice

Abstract

Key pointsr Cholera causes more than 100,000 deaths each year as a result of severe diarrhoea, vomiting and dehydration due to the actions of cholera toxin; more females than males are affected.r Cholera toxin induces hypersecretion via release of mucosal serotonin and over-activation of enteric neurons, but its effects on gastrointestinal motility are not well characterized.r We found that cholera toxin rapidly and reversibly reduces colonic motility in female mice in oestrus, but not in males or females in prooestrus, an effect mediated by 5-HT in the colonic mucosa and by 5-HT 3 receptors.r We show that the number of mucosal enterochromaffin cells containing 5-HT changes with the oestrous cycle in mice.r These findings indicate that cholera toxin's effects on motility are rapid and depend on the oestrous cycle and therefore can help us better understand differences in responses in males and female patients.Abstract Extensive studies of the mechanisms responsible for the hypersecretion produced by cholera toxin (CT) have shown that this toxin produces a massive over-activation of enteric neural secretomotor circuits. The effects of CT on gastrointestinal motility, however, have not been adequately characterized. We investigated effects of luminal CT on neurally mediated motor activity in ex vivo male and female mouse full length colon preparations. We used video recording and spatiotemporal maps of contractile activity to quantify colonic migrating motor complexes (CMMCs) and resting colonic diameter. We compared effects of CT in female colon from wild-type and mice lacking tryptophan hydroxylase (TPH1KO). We also compared CMMCs in colons of female mice in oestrus with those in prooestrus. In female (but not male) colon, CT rapidly, reversibly and concentration-dependently inhibits CMMC frequency and induces a tonic constriction. These effects were blocked by granisetron (5-HT 3 antagonist) and were absent from TPH1KO females. CT effects were prominent at oestrus but absent at prooestrus. The number of EC cells containing immunohistochemically demonstrable serotonin (5-HT) was 30% greater in female mice during oestrus than during prooestrus or in males. We conclude that CT inhibits CMMCs via release of mucosal 5-HT, which activates an inhibitory pathway involving 5-HT 3 receptors. This effect is sex-and oestrous cycle-dependent and is probably due to an oestrous cycle-dependent change in the number of 5-HT-containing EC cells in the colonic mucosa.

Gastrointestinal dysfunction in patients and mice expressing the autism‐associated R451C mutation in neuroligin‐3

“…Whether gut function is changed due to altered neural function involving GABA neurotransmission as reported in the brain of these mice [Etherton et al, 2011;Tabuchi et al, 2007] is unknown. The use of the video-imaging assay to quantify changes in colonic motility is well established for examining ENS function [Balasuriya, Hill-Yardin, Gershon, & Bornstein, 2016;Roberts et al, 2008;Swaminathan et al, 2016]. This approach takes advantage of the fact that when mouse colon is isolated from the CNS and maintained ex vivo, enteric neural activity drives a stereotyped repetitive motor pattern, the CMMC (Fig.…”

Enteric Glia Regulate Gastrointestinal Motility but Are Not Required for Maintenance of the Epithelium in Mice

“…When measured separately, enteric glial elimination did not alter the rates of gastric emptying or small intestinal transit (Figure 6D–E), suggesting that the effects of enteric glial elimination are most prominent in the colon. We therefore examined colonic motility in more detail and excluded the effects of extrinsic nerves by studying the propagation of colonic migrating motor complexes (CMMCs; an ENS-dependent manifestation of the peristaltic reflex) in an ex vivo preparation 15, 26 . Colons were isolated from Cre − and Cre + mice, suspended in oxygenated Krebs solution and perfused through the lumen at an intraluminal pressure sufficient to induce CMMCs.…”

“…The sex-dependent defect in gastrointestinal motility observed upon glial elimination could be a direct effect resulting from sex differences in enteric glia themselves, or an indirect effect arising from sexual dimorphism in any of the other cell types that interact with glia. Enterochromaffin cells vary in number over the course of the estrus cycle 26 and enteric glia closely appose enteroendocrine cells 3 . Although glial elimination in Plp1 CreER ;Rosa26 DTA mice did not affect enterochromaffin cell density in either sex, it remains possible that glia modulate 5-HT release or other aspects of enterochromaffin cell function that are sex-dependent.…”

Serotonergic Mechanisms Regulating the GI Tract: Experimental Evidence and Therapeutic Relevance

“…Although initial studies did not support evidence of an essential role for enteric mucosal 5-HT in GI motility (Margolis et al 2014; Bian et al 2011), more recent data has provided evidence for a subtle, yet distinct, role for mucosal 5-HT in GI peristalsis; contracting migrating motor complexes (CMMCs), the motor complexes that trigger peristaltic waves, that are elicited in isolated TPH1KO colons of male and female mice are poorly disseminated and tend to move in the retrograde direction (Heredia et al 2013; Smith et al 2014; Balasuriya et al 2016). …”