THE MEDIAL AMYGDALOID NUCLEUS AND MEDIAL PREOPTIC AREA MEDIATE STEROIDAL CONTROL OF SEXUAL-BEHAVIOR IN THE MALE SYRIAN-HAMSTER

An important goal of studies on steroid receptors in the brain is to u nderstand the functions of specific populations of steroid receptor-co ntaining neurons, particularly in the control of sexual behavior. The present study compared the ability of testosterone implants directed t oward the medial amygdaloid nucleus (Me) or the bed nucleus of the str ia terminalis (BNST) and medial preoptic area (MPOA) to stimulate mati ng in castrated males. Twenty adult male hamsters were selected for vi gorous sexual behavior, and baseline measures of copulatory behavior d uring the first 10 min of a 30-min mating behavior test were recorded on two occasions. Twelve weeks after castration, sexual behavior was r ecorded as before, and each male received a single intracranial implan t constructed of 23-gauge tubing packed with crystalline testosterone placed stereotaxically into Me or BNST/MPOA (n = 10 each). Behavior wa s assessed on two occasions after surgery to determine if implants in Me or BNST/MPOA could stimulate sexual behavior above that observed af ter castration. In half of the males from each group, testosterone inc reased the males' interaction with the female, anogenital investigatio n, mounting, and reduced the latency to the first mount. After complet ion of behavioral testing, males were perfused and the brains processe d for androgen receptor immunocytochemistry to determine the extent of brain regions influenced by the testosterone-filled cannula. In tissu es stained rapidly in diaminobenzidine, androgen receptor-containing n eurons were visible only in steroid responsive brain regions adjacent to the testosterone implant. This approach revealed that steroid recep tors in both the posterior subdivision of Me and in the medial subregi ons of BNST/MPOA can mediate hormonal control of mating behavior in th e male Syrian hamster. Implants placed outside these regions failed to stimulate mating. These results suggest that maintenance of copulator y behavior by gonadal steroids is not transduced by a single brain reg ion, but that steroid effects can be elicited at multiple points along the mating behavior pathway. (C) 1995 Academic Press, Inc.