ABSTRACT
It is well established that melanocortic peptides, such as melanocyte-stimulating hormone (MSH) and adrenocorticotropin, induce grooming behavior. The MC3 and MC4 receptors are the MC receptors which are most abundantly expressed in the brain. gamma-MSH, a peptide with preference to the MC3 receptor, however, does not induce grooming. Recent studies have shown that MC4 receptor antagonists are very effective in inhibiting alpha-MSH induced grooming. These data have indicated that grooming behavior in rodents may be mediated by the MC4 receptor. In this study we investigated if the recently developed MC1 receptor selective agonist MS05 was able to induce grooming in comparison with alpha-MSH. The results show that MS05 is effective in inducing grooming after either intracerebroventricular or ventral tegmental area administration in rats. Central administration of either MS05 or alpha-MSH besides grooming also induced stretching, yawning, rearing and locomotion. The results indicate that the earlier hypothesis that the MC4 receptor is the main mediator of grooming behavior has to be modified. Moreover, as this behaviour does not pharmacologically correlate to the profile of any of the five cloned MC receptors, we suggest that alpha-MSH induced grooming may not primarily be mediated by any of these receptors.