Centrally administered MTII affects feeding, drinking, temperature, and activity in the Sprague-Dawley rat

MTII, an agonist of melanocortinergic receptors, is a well-documented anore dgenic agent in rats. Many investigators have reported its effects on feedi ng without considering concurrent alterations in other behaviors. According ly, we performed studies to simultaneously measure nocturnal feeding, drink ing, activity, and temperature of rats after intracerebroventricular (third ventricle) administration of a wide dose range of MTII (0.05-500 ng). We o bserved that MTII modulates these physiological parameters in a dose-depend ent manner. Low doses of MTII (0.05 ng) caused reductions in feeding withou t alterations in body temperature, drinking, or activity. In contrast, hype rthermia and disrupted drinking patterns, along with food intake reductions , were evident at doses exceeding 50 ng. The fact that low doses altered on ly feeding, whereas higher doses affected a range of parameters, suggests t hat certain melanocortin-induced behavioral changes may be mediated by dist inct populations of melanocortin receptors with varying affinities or that those changes seen at higher doses may be nonspecific in nature.