Induction of grooming in resting rats by intracerebroventricular oxytocin but not by adrenocorticotropic hormone-(1–24) and α-melanocyte-stimulating hormone

Abstract

Adrenocorticotropic hormone (ACTH) and α-melanocyte-stimulating hormone (α-MSH) injected i.c.v. induce so called ‘excessive grooming’. Whether these peptides play a role in the initiation of grooming is not clear, since rats will groom even as a consequence of a particular environmental stimulation, such as handling and/or novel environment. In most studies, therefore, the first 15 min after i.c.v. injection are not examined. Here we report on the effects of slow i.c.v. infusions of ACTH-(1–24), α-MSH and oxytocin in resting rats in their home cages. Interestingly, i.c.v. infusions of oxytocin did initiate grooming in a dose-related way. In contrast, i.c.v. infusions of both ACTH-(1–24) and α-MSH in resting rats were without effect on grooming. Oxytocin is apparently involved in the initiation of self-grooming in rats, whereas ACTH and α-MSH prolonged grooming initiated by other means, e.g. handling procedures and/or a novel environment. We conclude that the effects of α-MSH and ACTH on grooming are conditional, depending on the behavioural state (active or resting) of the animal.