Alpha MSH-induced excessive grooming behavior involves a GABAergic mechanism.

It has been shown that MSH administered in the ventral tegmental area (VTA) elicits excessive grooming behavior (EGB) by stimulating an acetylcholinergic pathway. The present work was performed in order to evaluate the possible participation of the GABAergic system in this behavior. VTA injection of GABA antagonist bicuculline stimulated the EGB (55.5 +/- 2.4). In contrast, this effect disappeared if the animals were pretreated with atropine (33.1 +/- 1.5). When bicuculline was injected before a 200 ng/microliters dose of MSH, the EGB increased (87.6 +/- 4.4) in comparison to MSH-treated rats (46.5 +/- 3.2). Our results suggest that GABA, ACh, and MSH interact in the VTA in the induction of EGB; an increase in MSH levels appears to stimulate cholinergic neurons. GABAergic fibers probably modulate the cholinergic discharge at the presynaptic level.