Cholera toxin-sensitive neurons in guinea pig submucosal plexus.

Cholera toxin (CT) increases intestinal secretions by direct stimulation of mucosal enterocytes; enteric neurons also may play a role. We tested the latter possibility by retrograde labeling of mucosal terminals in guinea pig small intestine with the B subunit of CT (B-CT) and by intracellular recordings from submucosal neurons during superfusion with CT. All vasoactive intestinal peptide (VIP)-positive neurons, and only VIP-positive neurons, were labeled with B-CT. Fluorogold (FG) was used to retrogradely label nerve terminals in submucosal arterioles in preparations in which B-CT labeled mucosal terminals; colocalization of B-CT with FG was observed in neurons up to 3 mm from the site of FG application. CT selectively depolarized neurons known to contain VIP. We conclude that all VIP-containing neurons, and only VIP neurons, in guinea pig submucosal plexus possess B-CT binding sites and can be activated by CT. Some of these neurons provide a dual innervation to both arterioles and mucosa. We suggest that one functional consequence of CT may be to activate vasodilator nerves, thus increasing vascular perfusion of the mucosa to further stimulate intestinal secretions.