Area postrema, lateral parabrachial nucleus, and the antinatriorexic effect of bombesin

Bombesin (BN) injected to sodium depleted rats either centrally, particularly into the paraventricular nucleus (PVN) or peripherally by intraperitoneal (IP) route, exerts a potent inhibitory effect on the intake of 2% sodium chloride. To determine whether the area postrema (AP) and the lateral parabrachial nucleus (LPBN), which are known to be involved in the control of ingestive behavior, could be sites for the antinatiorexic activity of BN, we studied the effects of injections of this peptide into the LPBN or, by IP or fourth ventricular route, to surgically AP-lesioned rats. We observed that in sodium depleted rats: 1) injected into the LPBN at a dose of 50, but not of 25, ng per nucleus, BN significantly reduced the intake of 2% sodium chloride; 2) administered either intraperitoneally or into the fourth brain ventricle, BN induced a potent antinatriorexic effect in AP-sham lesioned animals; and 3) in the same experimental conditions, surgical ablation of the AP did not reduce the antinatriorexic effect of the peptide. These data indicate that the LPBN may be, with the PVN, a site for the BN-ergic inhibitory control of salt appetite and that the AP, which has been implicated in BN-induced anorexia, does not play a role in the antinatriorexic effect of this peptide.