THE MC3 RECEPTOR MEDIATES THE EFFECT OF MELANOCORTINS ON SEXUAL BEHAVIOR IN PREOPTIC AREA, PARTICIPATION OF NITRIC OXIDE

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

OREGON, ESTADOS UNIDOS

Congreso; International Melanocortin Meeting; 2002

Alpha-MSH is involved in reproductive processes and can regulate the expression of lordosis, an important component of female reproductive e behavior in rats and many other species. In this study we investigated the effects of MSH peptides on lordosisi behavior when injected in medialpreoptic area (MPOA) of ovariectomised rats primed with estradiol. The results show an increase in lordotic activity after bilateral administration of a-MSH and g-MSH. Interestingly, the treatment with the MC4 receptor antagonist HS014 did not block the stimulatory effect of a-MSH. Morover, the injection of HS014 did not itself modify the lordosis quotient.  Nitric oxide has been suggested to play a crucial role in the regulation of lordosis behavior via stimulation of guanylyl cyclase to synthesize cyclic GMP. In order to determine the participation of NO for 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 did not modify significantly the lordosis quotient at the two dosis examined. The treatment with L-NAME at the lowest dose completely abolished the simulatory 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 areas are mediated through specific MC receptor, that could be the MC3 receptor and that NO may mediate the effect of the melanocortins.