Fourth ventricular injection of selective bombesin receptor antagonists facilitates feeding in rats

Exogenous bombesin (BN)-like peptides exert their effects on feeding through caudal brain stem BN-like peptides and their receptors. To determine if endogenous BN-like peptides are involved in the control of feeding and exert their actions on caudal brain stem neurons, nondeprived rats were administered fourth ventricular injections of either saline or BN receptor antagonists in the following doses: 5 and 25 ng [D-Phe12,Leu14]BN or 5 ng [D-Phe6]BN(6-13)methyl ester. Milk intake was measured every 5 min and each animal's behavior (eating, grooming, exploring, resting) was monitored every 1 min for 60 min. Compared with saline injections, fourth ventricular injections of 25 ng [D-Phe12,Leu14]BN and 5 ng [D-Phe6]BN(6-13)methyl ester reliably facilitated milk intake. The enhanced milk intake was evident within 5 min after the injection and persisted throughout the 1-h intake test. The behavioral sequence following fourth ventricular injections of saline and the antagonists that facilitated feeding were similar. Injections of [D-Phe12,Leu14]BN and [D-Phe6]BN(6-13)methyl ester did not produce a generalized arousal. The results indicate that food-contingent, endogenous BN-like peptides contribute to the termination of feeding and exert their behavior-controlling actions on BN-like peptide receptors in the vicinity of the fourth ventricle.