Loss of visceral pain following colorectal distension in an endothelin‐3 deficient mouse model of Hirschsprung's disease

Abstract

Non-technical summary The endothelin-3 (ET-3) gene is essential for the development of the enteric nervous system in the gastrointestinal tract of mammals, including humans and mice. Loss of the ET-3 gene leads to the formation of an aganglionic colorectum and impaired bowel function. Endogenous endothelin peptides and their receptors also play a major role in nociception in a variety of organs and species, including humans. However, whether nociception is altered in the aganglionic region of the colorectum is unknown. We show that in ET-3 deficient mice, there is a loss of nociception from the aganglionic rectum, but not other visceral organs. This loss of nociception is due to a reduction in spinal afferent innervation and a selective deficiency in specific classes of rectal afferent nerve fibres, which are necessary for detection of noxious stimuli from this region.Abstract Endothelin peptides and their endogenous receptors play a major role in nociception in a variety of different organs. They also play an essential role in the development of the enteric nervous system. Mice with deletions of the endothelin-3 gene (lethal spotted mice, ls/ls) develop congenital aganglionosis. However, little is known about how nociception might be affected in the aganglionic rectum of mice deficient in endothelin-3. In this study we investigated changes in spinal afferent innervation and visceral pain transmission from the aganglionic rectum in ls/ls mice. Electromyogram recordings from anaesthetized ls/ls mice revealed a deficit in visceromotor responses arising from the aganglionic colorectum in response to noxious colorectal distension. Loss of visceromotor responses (VMRs) in ls/ls mice was selective, as no reduction in VMRs was detected after stimulation of the bladder or somatic organs. Calcitonin gene related peptide (CGRP) immunoreactivity, retrograde neuronal tracing and extracellular afferent recordings from the aganglionic rectum revealed decreased colorectal spinal innervation, combined with a reduction in mechanosensitivity of rectal afferents. The sensory defect in ls/ls mice is primarily associated with changes in low threshold wide dynamic range rectal afferents. In conclusion, disruption of endothelin 3 gene expression not only affects development and function of the enteric nervous system, but also specific classes of spinal rectal mechanoreceptors, which are required for visceral nociception from the colorectum.

Perturbation of Hoxb5 signaling in vagal and trunk neural crest cells causes apoptosis and neurocristopathies in mice

“…41 Especially for EDN3, a reduction in spinal sensory innervation of the rectum was reported in mice with disruption of Edn3 gene expression. 42 In line with this, this study also showed that perturbation of Hoxb5 function in NCC of mice causes multiple neurological phenotypes and hypopigmentation, resembling some of the phenotypes of syndromic HSCR. Nevertheless, the causal relationship between abnormal HOXB5 function and HSCR in human deserves further investigation, in particular, the identification of a dominant-negative type of HOXB5 mutation in these patients.…”

Identification of different functional types of spinal afferent neurons innervating the mouse large intestine using a novel CGRPα transgenic reporter mouse

“…This profile suggests that their peripheral terminals may be rectal IGLEs (33,34,65). They fire to small amounts of stretch and continue to encode without saturating to distensions into the noxious range (64). Consistent with HF afferents, rectal IGLEs are present in the murine colorectum (55).…”

Extrinsic primary afferent signalling in the gut

“…Electrophysiologically, they are typically silent at rest, but are powerfully activated by distension, with instantaneous firing frequencies up to 50 Hz. 42 The degree of distension at which their response saturates has not been determined, but they encode stretch over a wide dynamic range, into the noxious extremes 146 . They are activated by contraction of both the longitudinal and circular muscle layers, possibly via compressive forces acting on myenteric ganglia.…”

“…Evidence suggests that low-threshold, wide-dynamic range lumbosacral mechanoreceptors from the colorectum, which dominate pelvic nerve responses to rectal distension, are likely to be responsible for activation of pain pathways. 146 These mechanoreceptors include rIGLES and rectal muscularmucosal endings. Interestingly, sensation evoked by slow ramp distension in the human rec-tum was reduced by luminal application of the local anaesthetic, lidocaine, which suggests a possible role for muscular-mucosal afferents with endings close to the mucosal surface.…”