Effect of Alpha-MSH on Sexual Receptivity in Preoptic Area: Identification of the Melanocortin Receptors Involved and Participation of Nitric Oxide

NOCETTO, CARLA; CRAGNOLINI, ANDREA BEATRIZ; SCIMONELLI, TERESA NIEVES; SCHIÖTH, HELGI BIRGIR

Los Cocos, Cordoba, Argentina

Congreso; XVII Reunión de la Sociedad Argentina de Neuroquímica; 2002

Alpha-MSH is involved in reproductive processes and can regulate the expression of lordosis, an important component of female reproductive behavior in rats and many other species. In this study we investigated the melanocortin receptors involved in the effects of MSH peptides on lordosis behavior when injected in medial preoptic area (MPOA) of ovariectomised rats primed with estradiol. In addition the possibility has been investigated that the behavioral effect of MSHmay be mediated viaNO. The results show an increase in lordotic activity after bilateral administration of a-MSH and g-MSH. Interestingly, the treatment with theMC4receptor antagonist HS014 did not block the stimulatory effect of a-MSH. Moreover, the injectionof HS014 did not itself modify the lordosis quotient. In order to determine the participation of NO in the effect of the melanocortins, another group of rats were treated with L-NAME, an inhibitor of NOS, alone or 15 min before the injection of a-MSH or g-MSH. The injection of L-NAME into the MPOA of E-primed rats 15 min before the test for sexual receptivity didn’t modify significantly the lordosis quotient at the two doses examined. The treatment with L-NAME at the lowest dose completely abolished the stimulatory effect of a-MSH and g-MSH on sexual behavior. The results indicate that the effects of MSH peptides on female sexual behavior in this area are mediated through a specificMC receptor, which could be the MC3 receptor, and that NO mediates the melanocortins, effects.