Alterations in central neurotransmitter receptor binding sites following estradiol implantation in female rats

The subcutaneous implantation of an estradiol pellet (10 mg) into female rats induced a hypophyseal hyperplasia with hyperprolactinaemia. Examination of neurotransmitter receptors in the hippocampus, striatum and cerebral cortex one month after the implantation revealed that estrogenization was associated with: an increased density of (3)H-domperidone binding sites (D(2) receptors) in the striatum and reduced numbers of (3)H-serotonin high affinity sites (5-HT(1) receptors) in the hippocampus and of (3)H-muscimol binding sites (GABA receptors) in the hippocampus, striatum and cerebral cortex. In contrast, the characteristics of (3)H-spiperone binding to 5-HT(2) receptors (in the cerebral cortex) and those of (3)H-flunitrazepam binding to benzodiazepine sites (in the three brain regions examined) were not significantly different in estrogenized and in control female rats. However, the enhancing effect of GABA on (3)H-flunitrazepam binding was markedly reduced in brain membranes from estrogenized animals. The respective roles of estradiol and prolactin in mediating these changes in neurotransmitter receptors are discussed notably with regard to the regional heterogeneity of estradiol binding capacity in the rat brain.