ACTH- and alpha-MSH-induced grooming, stretching, yawning and penile erection in male rats: Site of action in the brain and role of melanocortin receptors

The effect of adrenocorticotropin (ACTH)(1-24) and alpha-melanocyte stimula ting hormone (alpha-MSH) on grooming, stretching, yawning and penile erecti on was studied after injection into different brain areas. Both peptides in duce the above responses when injected into the hypothalamic periventricula r region of the third ventricle. This region includes the paraventricular n ucleus, the dorsomedial nucleus, the ventromedial nucleus and the anterior hypothalamic area. The minimal effective dose of both peptides was 0.5 mu g and the maximal effect was seen with 2 mu g, the highest dose tested. Irre spective of the injection site, grooming started 5-7 min after injection of either peptide, while stretching, yawning and penile erection started only after 15-25 min and lasted for 90-120 min. In contrast both peptides were ineffective when injected into the preoptic area, the caudate nucleus or th e CA1 field of the hippocampus. Grooming, stretching and yawning, but not p enile erection, were prevented by cyclic[AcCys(11), D-Nal(14), Cys(18), Asp NH(2)(22)]-beta-MSH (11-22) (HS014), a selective melanocortin 4 receptor an tagonist, injected into the same periventricular area 10 min before of ACTH (1-24) or a-MSH. The results show that ACTH(1-24) and alpha-MSH act in the hypothalamic periventricular region to induce the above responses and that grooming, stretching and yawning, but not penile erection, are mediated by melanocortin 4 receptors. (C) 2000 Elsevier Science Inc.