GLP-1 receptor signaling contributes to anorexigenic effect of centrally administered oxytocin in rats

The present study examined possible interactions between central glucagon-like peptide-1 (GLP-1) and oxytocin (OT) neural systems by determining whether blockade of GLP-1 receptors attenuates OT-induced anorexia and vice versa. Male rats were acclimated to daily 4-h food access. In the first experiment, rats were infused centrally with GLP-1 receptor antagonist or vehicle, followed by an anorexigenic dose of synthetic OT. Access to food began 20 min later. Cumulative food intake was measured every 30 min for 4 h. In the second experiment, rats were infused with OT receptor blocker or vehicle, followed by synthetic GLP-1 [(7-36) amide]. Subsequent food intake was monitored as before. The anorexigenic effect of OT was eliminated in rats pretreated with the GLP-1 receptor antagonist. Conversely, GLP-1-induced anorexia was not affected by blockade of OT receptors. In a separate immunocytochemical study, OT-positive terminals were found closely apposed to GLP-1-positive perikarya, and central infusion of OT activated c-Fos expression in GLP-1 neurons. These findings implicate endogenous GLP-1 receptor signaling as an important downstream mediator of anorexia in rats after activation of central OT neural pathways.