Effects of estrogen on striatal dopamine receptor function in male and female rats

The present study compares, biochemically and behaviorally, the effect of estrogen on central dopamine (DA) function in male and female rats. Estrogen has no direct effect in vitro on DA receptors from striatal tissue of male or female rats. In vivo administration of 17β-estradiol valerate to male or long-term ovariectomized female rats significantly increases the density of the striatal DA receptors by about 20 percent. Behaviorally, normal female rats have more intense stereotypy produced by apomorphine (APO stereotypy), regardless of the phase of their estrous cycle, than normal male rats, while the density of striatal DA receptors is equal. Estrogen administration to male rats increases their APO stereotypy. Normal intact female rats have no changes in APO stereotypy after the administration of estrogen. However, ovariectomy of female rats increases APO stereotypy, and estrogen administration decreases APO stereotypy back to the levels observed in normal intact female rats. In the male rat there is a good correlation between the increased striatal DA receptor density and the increased APO stereotypy, but in the female rat factors other than striatal DA receptor density appear to the important in the regulation of APO stereotypy.