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Abstract
Male sexual behavior is regulated by limbic areas like the medial preoptic nucleus
(MPN), the bed nucleus of the stria terminalis (BST), the nucleus accumbens (nAcc)
and the ventromedial hypothalamic nucleus (VMN). Neurons in these brain areas are
rich in androgen receptors (AR) and express FOS-immunoreactivity in response to mating.
In many species sexual satiation, a state of sexual behavior inhibition, is attained
after multiple ejaculations. The mechanisms underlying sexual satiation are largely
unknown. In this study we show that sexual activity reduces androgen receptor immunoreactivity
(AR-ir) in some of the brain areas associated with the control of male sexual behavior,
but not in others. Thus, one ejaculation reduced the AR-ir in the MPN and nAcc, but
not in the BST and VMN. Copulation to satiation, on the other hand, reduced AR-ir
in the MPN, nAcc and VMN, and not in the BST. The AR-ir reduction observed in the
MPN of sexually satiated rats was drastic when compared to that of animals ejaculating
once. Serum androgen levels did not vary after one ejaculation or copulation to exhaustion.
These data reveal that sexual activity reduces AR in specific brain areas and suggest
the possibility that such a reduction underlies the sexual inhibition that characterizes
sexual satiety.