CNS effects of circulating CCK8: involvement of brainstem neurones responding to gastric distension.

Cholecystokinin octapeptide (CCK8) given i.v. or i.p. produces a variety of behavioural and CNS effects; these actions are probably exerted at a peripheral site but the neuronal pathways involved are uncertain. We show here that i.v. CCK8 acts on neurones in the n. tractus solitarius with an input from the stomach; cells are either excited or depressed by CCK8 and gastric distension, and responses to the two stimuli are always in the same direction. The responses to close arterial injection of CCK8 indicate a site of action within the splanchnic bed, and most probably a direct action on the vagal afferents mediating gastric mechanoreceptor discharge.