Effects of fourth ventricle bombesin injection on meal-related parameters and grooming behavior.

Injections of bombesin (BN) into the vicinity of the caudal brainstem suppress food intake in rats. In the present study, the food intake parameters [meal size (MS), intermeal interval (IMI), satiety ratio (SR)] affected by 4th ventricle BN injections were determined. Following a 15-h food deprivation, rats were administered 4th ventricle injections of saline (0.15 M) and BN in doses of 1, 5, 10, and 20 ng BN, and were then given access to sweetened milk. The animals' behaviors (feeding, resting, grooming, exploring) were scored every one min and milk intake every five min for 60 min following the injections. Fourth ventricle injections of 5 ng BN and greater reliably suppressed milk. intake. This reduction was reflected in a significant reduction in the MS. The IMI was not affected. As a result, the SR (IMI2/MS1), which is thought to represent the satiating property of food, was reliably greater following BN than following saline administration. The reduced food intake was accompanied by a significant increase in grooming behavior and a corresponding decrease in exploring. The amount of time spent resting (inactive) was similar following saline and all but the highest dose of BN. To demonstrate that the behavioral effects of BN were mediated by specific caudal brainstem BN receptors, 4th ventricle injections of [D-Phe12,Leu14]BN, a BN receptor antagonist, or saline preceded the 4th ventricle injection of 5 ng BN. Pretreatment with [D-Phe12,Leu14]BN reliably blocked the effects of BN on food intake and grooming.