Initiation of self-grooming in resting rats by local PVH infusion of oxytocin but not α-MSH

The present study was designed to discriminate between factors that initiate and/or prolong self-grooming. The study of factors initiating the grooming response is complicated by the fact that rats may groom already as a consequence of the injection procedure, due to release of endogenous substances after needle insertion or just handling of the animal. Therefore we used an infusion technique that allowed the rats to settle down quietly after they had been connected to an infusion pump, before the actual infusion of the peptide took place. In a previous report, we showed that direct injections of ACTH 1–24 and α-melanocyte-stimulating hormone (α-MSH) into the paraventricular nucleus of the hypothalamus (PVH) prolong self-grooming caused by the injection procedure. Whether these peptides can also initiate grooming, however, is not yet clear. In this report, we compare the effects of α-MSH and oxytocin after infusion into the PVH in resting animals. Oxytocin is abundantly present in the PVH and is known to be involved in the regulation of grooming behavior. Slow infusions of oxytocin (0.1 μg) do initiate grooming, but α-MSH (0.1 μg) is without any behavioral effect. This suggests that oxytocin in the PVH is involved in the initiation of self-grooming, whereas α-MSH and probably ACTH do maintain grooming initiated otherwise, either by mechanical activation of the PVH and/or by the handling procedures. Infusion of substances in resting animals apparently is a way to avoid interactions between ongoing overt behavior and peptide-induced effects.