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Gastrointestinal (GI) discomfort is a hallmark of most gut disorders and represents an important component of chronic visceral pain1. For the growing population afflicted by irritable bowel syndrome, GI hypersensitivity and pain persist long after tissue injury has resolved2. Irritable bowel syndrome also exhibits a strong sex bias, afflicting women three times more than men1. Here, we focus on enterochromaffin (EC) cells, which are rare excitable, serotonergic neuroendocrine cells in the gut epithelium3-5. EC cells detect and transduce noxious stimuli to nearby mucosal nerve endings3,6 but involvement of this signalling pathway in visceral pain and attendant sex differences has not been assessed. By enhancing or suppressing EC cell function in vivo, we show that these cells are sufficient to elicit hypersensitivity to gut distension and necessary for the sensitizing actions of isovalerate, a bacterial short-chain fatty acid associated with GI inflammation7,8. Remarkably, prolonged EC cell activation produced persistent visceral hypersensitivity, even in the absence of an instigating inflammatory episode. Furthermore, perturbing EC cell activity promoted anxiety-like behaviours which normalized after blockade of serotonergic signalling. Sex differences were noted across a range of paradigms, indicating that the EC cell-mucosal afferent circuit is tonically engaged in females. Our findings validate a critical role for EC cell-mucosal afferent signalling in acute and persistent GI pain, in addition to highlighting genetic models for studying visceral hypersensitivity and the sex bias of gut pain.

Voltage-gated sodium (Na.sub.v) channels initiate action potentials in most neurons, including primary afferent nerve fibres of the pain pathway. Local anaesthetics block pain through non-specific actions at all Na.sub.v channels, but the discovery of selective modulators would facilitate the analysis of individual subtypes of these channels and their contributions to chemical, mechanical, or thermal pain. Here we identify and characterize spider (Heteroscodra maculata) toxins that selectively activate the Na.sub.v1.1 subtype, the role of which in nociception and pain has not been elucidated. We use these probes to show that Na.sub.v1.1-expressing fibres are modality-specific nociceptors: their activation elicits robust pain behaviours without neurogenic inflammation and produces profound hypersensitivity to mechanical, but not thermal, stimuli. In the gut, high-threshold mechanosensitive fibres also express Na.sub.v1.1 and show enhanced toxin sensitivity in a mouse model of irritable bowel syndrome. Together, these findings establish an unexpected role for Na.sub.v1.1 channels in regulating the excitability of sensory nerve fibres that mediate mechanical pain. Two spider toxins are shown to target the Na.sub.v1.1 subtype of sodium channel specifically, shedding light on the role of these channels in mechanical pain signalling. Na.sub.v1.1 channels mediate mechanical pain Mutations affecting several Na.sub.v1 subtype voltage-gated sodium channels have been shown to be associated with insensitivity to pain or persistent pain syndromes. Na.sub.v1.1 is expressed by somatosensory neurons, but no direct link has been established between this subtype and nociception. Further studies have been hampered by a paucity of pharmacological agents that discriminate between the closely related members of the Na.sub.v1 family. Now David Julius and colleagues have identified two spider toxins specifically targeting Na.sub.v1.1, and use them to show that this channel is key to the specific transduction of mechanical but not thermal pain by myelinated A[delta] sensory fibres. Previous genetic studies of Na.sub.v1.1 indicate that such selective agents may open therapeutic avenues in disorders associated with the central nervous system, such as epilepsy, autism and Alzheimer disease. The involvement of Na.sub.v1.1 channels in mediating mechanical pain reported here was unexpected., Author(s): Jeremiah D. Osteen [sup.1] , Volker Herzig [sup.2] , John Gilchrist [sup.3] , Joshua J. Emrick [sup.1] , Chuchu Zhang [sup.1] , Xidao Wang [sup.4] , Joel Castro [sup.5] [...]