Sex differences in the rapid and acute effects of estrogen on striatal D2 dopamine receptor binding

Regional changes in striatal D2 dopamine (DA) receptor binding in castrated (CAST) or ovariectomized (OVX) rats were investigated following administration of a low dose of estradiol benzoate (EB), repeated treatment with EB followed by progesterone, or vehicle. In two separate experiments, there was a significant decrease in striatal D2 DA receptor binding in caudal striatum from OVX, but not CAST rats 30 min after a single injection of EB. In CAST rats, there was a significant increase in striatal D2 DA receptor binding in rostral striatum 4 h after injection of EB. There was no effect of EB plus progesterone treatment in either OVX or CAST rats. In addition, CAST rats had significantly lower D2 DA receptor binding in the lateral region of the rostral striatum than did OVX rats. These results show sexually dimorphic and regionally specific effects of estrogen on striatal D2 DA receptor binding, and a significant sex difference in striatal D2 DA receptor binding in the absence of circulating gonadal hormones. The present findings are discussed in light of previous reports of sex differences in gonadal hormone influences on striatal DA mediated behaviors.