Bombesin changes excitability of rat brain stem neurons sensitive to gastric distension

The responses of single neurons in the dorsal vagal complex to physiological gastric distension were investigated in anesthetized control and capsaicin-treated rats. In both groups, the responses of brain stem neurons to close arterial injection of the regulatory peptide bombesin (BBS) were studied. These experiments observed whether selective chemical deafferentation by capsaicin caused any significant change in the central representation of responses to gastric distension and peripheral BBS administration. In 43 animals a total of 49 neurons was studied, 21 of which were in rats pretreated with capsaicin. In normal animals, the majority of neurons (89%, n = 28) responded in the same manner (increase or decrease in firing rate) to gastric distension and peripheral BBS administration. Of the 21 neurons studied in capsaicin-treated rats, 76% responded in the same direction to gastric distension and BBS. Two neurons responsive to gastric distension failed to respond to BBS. There was no significant difference between the proportion of neurons responding both to gastric distension and BBS in normal and capsaicin-treated rats. Responses to both gastric distension and BBS were abolished by bilateral cervical vagotomy in both groups of rats. In these experiments, BBS apparently acted on peripheral receptors near the stomach to produce, via the vagus nerve, effects on neuronal excitability in the dorsal vagal complex. Almost all of these neurons were also responsive to activation of gastric mechanoreceptors. The responses of dorsal vagal complex neurons to gastric distension and peripheral BBS were capsaicin insensitive, which is in contrast to the action of cholecystokinin under the same conditions.