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Sex Differences in Androgen Receptors and Aromatase Activity in Microdissected Regions of the Rat Brain^*

Department of Physiology, Oregon Health Sciences University Portland, Oregon 97201
Division of Reproductive Biology and Behavior, Oregon Regional Primate Research Center Beaverton, Oregon 97006

Address all correspondence and requests for reprints to: Dr. Charles E. Roselli, Department of Physiology, Oregon Health Sciences University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97201-3098.

Abstract

Males are generally more responsive than females to the behavioral and neuroendocrine actions of androgens. The present experiments were performed to determine whether these differences may result from sex differences in the number of androgen receptors (AR) in specific brain areas. For this reason, AR binding was compared in both cytosol (ARc) and cell nuclear KC1 extracts (ARn) from microdissected brain regions of gonadectomized male and female rats treated with doses of testosterone (T) that produced equivalent physiological circulating androgen levels. In addition, microsomal aromatase activity was measured as a biochemical index of tissue responsiveness to T, since estrogen formation in certain brain areas is regulated by androgen. One week after exogenous T administration, males exhibited significantly higher levels of ARn than females in the bed nucleus of the stria terminalis, periventricular preoptic area, and ventromedial nucleus. Males also had significantly higher aromatase levels in these same areas plus the medial preoptic nucleus and anterior hypothalamus. There were no significant differences in ARn concentrations in eight other nuclei that were examined or significant sex differences in ARc levels observed under these experimental conditions. When ARc levels were compared in untreated gonadectomized male and female rats, males had greater levels of ARc in the bed nucleus of the stria terminalis only, indicating that new receptor synthesis may be responsible for the sex differences observed in Ttreated rats. These results suggest that sex differences in neural responsiveness to androgens may be due in part to sex differences in ARn occupation in specific brain regions. (Endocrinology 128: 1310–1316,1991)

Footnotes

^* Publication 1743 of the Oregon Regional Primate Research Center. This work was supported by NIH Grants HD-23293 and P30-HD-18185.

Received September 24, 1990.

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