In rats, injecting certain ACTH/Melanotan‑I‑like peptides directly into the brain raised blood pressure at the same time they caused the animals to groom a lot. Peptides that didn’t trigger grooming barely changed blood pressure. Blocking dopamine signals or getting tolerant to the peptide stopped both effects, suggesting the two are linked.

After the i.c.v. administration of 300 pmol ACTH-(1-24) or [Nle4,D-Phe7]alpha-MSH, a long-lasting increase in blood pressure was observed synchronously with the incidence of excessive grooming. Two structurally related peptides with no grooming behavior-inducing potency, ACTH-(7-16)-NH2 and gamma 2-MSH, in doses of 300 and 500 pmol, respectively, caused a slight and short-lasting increase in blood pressure or had no effect, respectively. When the grooming behavior-inducing effect of ACTH-(1-24) was abolished, either by the prior manipulation of central dopaminergic neurotransmission by the i.c.v. administration of the dopamine receptor antagonist, haloperidol, or, due to the occurrence of single-dose tolerance to ACTH-(1-24), the pressor response was abolished as well. These data are in support of the postulate that the incidence of grooming behavior and the elevation of blood pressure are temporally associated and indicate that the two phenomena are causally related.