Interaction of alpha-melanotropin (alpha-MSH) and noradrenaline in the median eminence in the control of female sexual behavior

In the present study, we examined the effects of the injection of alpha-mel anotropin (alpha-MSH), noradrenaline (NA), and dopamine in the median emine nce of ovariectomized-adrenalectomized rats on female sexual behavior. The animals were primed with 10 mu g of estradiol benzoate, and 52-54 h later t hey were injected into the median eminence with either 1 mu l of artificial cerebrospinal fluid, 1 mu g/rat alpha-MSH, 200 ng/rat NA, 200 ng or 2 mu g /rat dopamine, in 1 mu l of artificial cerebrospinal fluid. Both alpha-MSH and NA significantly stimulated sexual behavior. This effect was antagonize d by two beta-adrenergic antagonists: propranolol (500 ng/rat) and metoprol ol (400 ng/rat) applied 15 min before the alpha-MSH or NA. The alpha-adrene rgic antagonist prazosine (500 ng/rat) was ineffective in reducing the effe ct of alpha-MSH. The vehicle and dopamine at both doses had no effect on se xual activity. These results indicate that alpha-MSH and NA in the median e minence stimulate female sexual behavior and that NA mediates the action of alpha-MSH via beta-receptors. (C) 2000 Elsevier Science Inc. All rights re served.