Peripheral bombesin decreases gastric vagal efferent activity in part through vagal pathways in rats

The influence of intravenous (iv) bombesin on multiunit activities recorded from the ventral gastric branch of the vagus was investigated in urethan-anesthetized rats. Consecutive injections of bombesin (0.062, 0.62, 6.2, 62, and 620 pmol iv) decreased dose dependently gastric vagal efferent discharges to 79.8 +/- 4.9, 68.3 +/- 10.2, 47.0 +/- 6.7, 41.6 +/- 4.7, and 36.5 +/- 8.9%, respectively, from preinjection levels. Saline injection had no effect. Bombesin (62 pmol iv) reduced cervical vagal efferent discharges to 25 +/- 6% before and 67 +/- 5% after bilateral cervical vagotomy distal to the recording site. Bombesin (62 and 620 pmol iv) increased gastric vagal afferent discharges by 45 and 93%, respectively. These data show that systemic injection of bombesin potently decreases gastric and cervical vagal efferent activity in part through vagal-dependent mechanisms that may involve the increase in gastric vagal afferent activity.