Co-sensitivity of vagal mucosal afferents to

A complex sensitivity of afferent nerves in the mesentery of the rat jejunum to systemic administration of histamine has recently been demonstrated. In the present study, we aimed to characterize subpopulations of mesenteric afferents that mediate this afferent nerve response. Multi-unit afferent discharge was recorded from mesenteric nerves supplying the proximal jejunum in anesthetized rats. The majority of mesenteric bundles (84%) exhibited biphasic responses to histamine (8 μmolkg) and these bundles also responded to 2m5HT. In contrast, monophasic responses lacked a short-latency component and these bundles failed to respond to 2m5HT. Single units analysis revealed a population of afferents that possessed co-sensitivity for 2m5HT and histamine. This population of afferents was absent in chronically vagotomized animals while mucosal anaesthesia with luminal lidocaine reversibly converted the biphasic profile to a monophasic one. Ondansetron (500 μgkg) blocked the response to 2m5HT with no effect on the profile of the histamine response while pyrilamine (5 mgkg) blocked the histamine response without affecting the response to 2m5HT. We conclude that histamine sensitive afferents exist in the rat proximal jejunum that also respond to 5-HT via the 5-HT3 receptor. These fibers appear to be vagal afferents originating in the intestinal mucosa and may be involved in the organisation of mast cell mediated responses.