Androgen implants in medial amygdala briefly maintain noncontact erection in castrated male rats

Abstract

Castration of male rats causes a rapid loss of their normal erectile response to inaccessible estrous females. Previous studies had demonstrated that these noncontact erections (NCEs), a putative sign of sexual arousal, could be restored by systemic treatment with testosterone (T) or dihydrotestosterone (DHT), but not estradiol (E). We examined whether androgen delivered to the medial amygdala (MeA) of castrated rats would maintain NCE. In Experiment 1, males received bilateral cannulae filled with T, DHT, or E directed at the MeA. Control males had the same hormone-filled cannulae implanted subcutaneously and blank cannulae in the MeA, or they received T in the anterior forebrain. During the 2 weeks after surgery, males were tested twice for NCE and copulation. About half the males with androgens in the MeA had NCEs 1 week after castration, but few responded a week later. Closer proximity of androgen implants to the posterodorsal MeA (MeApd) predicted shorter NCE latencies. No males with subcutaneous androgen had NCEs in either test, and few anterior forebrain-implanted males did. Some males receiving E in MeA or subcutaneously had NCE in each test. In copulation tests, the type of steroid treatment did not affect the incidence of ejaculation or most measures of copulation, and the proximity of cannulae to MeApd predicted only the time from ejaculation to the occurrence of NCE during the postejaculatory interval. Experiment 2 showed that NCEs displayed by males with androgen in MeA occurred in response to estrous females, not spontaneously. The results suggest that androgens, perhaps augmented by estrogen, act in the posterodorsal MeA to facilitate NCE and its associated arousal.