A COMPARISON OF LH-SECRETION AND BRAIN ESTRADIOL RECEPTORS IN HETEROSEXUAL AND HOMOSEXUAL RAMS AND FEMALE SHEEP

This study examined endocrine components of sexual orientation of male sheep. Sexual orientation of adult rams was identified through standa rdized sexual performance tests. Four rams that copulated with ewes, f our rams that never mounted females and copulated with males, and eigh t ewes were used in the experiments. Exogenous estradiol benzoate (50 mu g, i.m.) stimulated (P < .05) a preovulatory-like LH surge 16-22 hr after administration to females. Estradiol did not (P > .05) affect L H release of heterosexual or homosexual rams. Thirty days after the es tradiol challenge, sheep were euthanized and areas of the amygdala (AM Y), hypothalamus (HYP), anterior pituitary (AP), and preoptic area (PO A) of the hypothalamus were collected. Occupied and unoccupied content of estradiol receptors (ER) was determined. The content of ER in the amygdala of both homesexual rams and ewes was similar, but less than ( P <.05) the content of ER in heterosexual rams. The ER content measure d in other brain regions did not differ by sex or orientation. In summ ary, results from these data show that the preovulatory LH surge mecha nism that is a characteristic of the female does not occur in either h omosexual or heterosexual rams. Conversely, the ER content of the AMY of homosexual rams is similar to that of ewes and differs from the het erosexual male. Differences in ER content between heterosexual and hom osexual rams imply that the amygdala serves as a link for input from p otential mates. These data suggest that the amygdala not only plays a role in sexual behavior but may be involved in sexual orientation of r ams. (C) 1995 Academic Press, Inc.