Estradiol, but not dihydrotestosterone, in the medial amygdala facilitates male hamster sex behavior.

In the male Syrian hamster, the medial amygdaloid nucleus (Me) and medial preoptic area (MPOA) are critical for expression of male mating behavior. These regions contain steroid receptor-containing neurons that transduce hormonal signals essential for copulation. In castrated males bearing an intracerebral steroid implant in the MPOA, testosterone or estradiol can facilitate sexual activity. However, DHT is without effect. Testosterone can also stimulate mating when implanted in the Me. The present study determined if estradiol or DHT had behavioral activity in the Me. Twenty adult male hamsters were selected for vigorous sexual behavior. Twelve weeks after castration, sexual behavior was assessed and each male received a single intracranial implant (23-gauge tubing packed with crystalline estradiol or DHT, n = 10 each) placed stereotaxically into posterior Me (MeP). Behavior was examined after surgery to determine if androgens or estrogens in MeP could stimulate sexual behavior above that observed after castration. Mating behavior in DHT-implanted males was not significantly different from castrates. However, males with estradiol implants displayed significantly more copulatory and noncopulatory sexual activity after surgery compared to males with DHT implants. These results suggest that testosterone facilitation of mating behavior in MeP is mediated by aromatization to estradiol, and that DHT is not behaviorally active in this nucleus.