CAUDAL BRAIN-STEM SYSTEMS MEDIATE EFFECTS OF BOMBESIN-LIKE PEPTIDES ON INTAKE IN RATS

Intraoral intakes of sucrose (SI; 0.1 M) and distilled water (WI) were measured in tube-fed neurologically intact and tube-fed chronic supracollicular decerebrate (CD) rats after intraperitoneal injections of saline and bombesin (BN) and gastrin-releasing peptide (GRP) in concentrations of 1, 2.5, 5, and 10-mu-g/kg. Also, to determine whether BN and GRP administration interacted with taste processing, oral motor responses during the 1st min of the intraoral infusion were videotaped and subsequently analyzed to determine the number of ingestive and aversive taste reactivity (TR) responses. Injections of greater-than-or-equal-to 2.5-mu-g/kg BN reliably suppressed SI similarly in both control and CD rats. In response to GRP, the only group difference was that injections of 1-mu-g/kg GRP reliably suppressed SI in control but not CD rats. Administration of greater-than-or-equal-to 2.5-mu-g/kg GRP suppressed SI similarly in both control and CD rats. Although SI was suppressed by peripheral administration of BN and GRP, these treatments had no effect on the TR responses elicited by sucrose in either group. To determine whether the effects of BN and GRP were selective for sweet nutritive stimuli, intraoral WI was also measured in control rats after the same treatments. Injections of 5 and 10-mu-g/kg BN and 10-mu-g/kg GRP reliably suppressed WI, but lower doses had no effect. BN and GRP had no reliable effect on the pattern of TR responses elicited by water. Intraoral WI by CD rats was minimal (< 1 ml) after injections of saline, BN, and GRP, and hence peptide effects could not be reliably assessed. These results indicate that 1) afferent signals elicited by BN-like peptides are integrated by caudal brain stem structures to control intraoral intake, 2) BN and GRP inhibit WI by non-deprived rats at doses greater than those required to suppress SI, and 3) BN-like peptides inhibit SI and WI but do not reduce the animal's gustatory responsiveness to these tastes.