Effects of hypothalamic serotonin depletion on lordosis behavior and gonadal hormone receptors

The effects of chronic depletion of serotonin on feminine sexual behavior (lordosis), cytosolic progestin receptors and estradiol nuclear receptors were investigated. Intrahypothalamic administration of 5,7-dihydroxytryptamine (5,7-DHT) markedly enhanced lordotic responding in estradiol benzoate (EB)-primed, 5,7-DHT-treated female rats and in EB-progesterone primed, 5,7-DHT-treated male rats. Cytosolic progestin receptors were measured in preoptic-hypothalamic nuclei related to reproductive function in sham and 5,7-DHT-treated rats after EB priming. In both sexes, no differences between sham and 5,7-DHT-treated subjects were noted for progestin binding in the medial preoptic nucleus, ventromedial nucleus or arcuate-median eminence area. Estrogen-nuclear complexes were measured in the same brain nuclei of female rats following EB priming, and no differences between sham and 5,7-DHT-treated rats were found. Under the conditions employed, it would appear that, despite marked elevations in lordotic responsivity, the accumulation of estrogen nuclear receptors and the levels of estrogen inducible progestin receptors remain unaltered after chronic depletion of serotonin. Thus, serotonergic influences on lordosis do not appear to involve changes in the expression of steroid receptor levels in preoptic-hypothalamic nuclei known to mediate hormone-dependent neuroendocrine processes.