The modulation of brain dopamine and GABAA receptors by estradiol: a clue for CNS changes occurring at menopause

Abstract

1. Tardive dyskinesia is more important in postmenopausal women than men of comparable age and a peak of first episodes of schizophrenia is observed in postmenopausal women. The effect of ovariectomy (2 weeks or 3 months) in rats was investigated as a model of decreased gonadal function associated with menopause. 2. Frontal cortex D1 receptor density and affinity were similar in intact male compared to intact female rats and progressively decreased in density with time after ovariectomy, with no change of affinity. Striatal D1 and D2 receptors also decreased in density after ovariectomy for both receptor subtypes, with no change of affinity. Striatal D1 receptor density and affinity were similar in intact male and female rats, whereas the density of D2 receptors was higher in females. Treatment with estradiol for 2 weeks restored the D2 but not the D1 receptor changes. 3. In the substantia nigra pars reticulata, striatum, nucleus accumbens, and entopeduncular nucleus, a progressive increase in [3H]flunitrazepam specific binding associated with GABAA receptors was observed as a function of time following ovariectomy; this was corrected with estradiol treatment. In contrast, the opposite was observed for [3H] flunitrazepam binding in the globus pallidus, where ovariectomy decreased binding, which was corrected with estradiol replacement therapy. 4. Low prefrontal cortex dopamine activity with implications of D1 receptors in negative symptoms of schizophrenia is hypothesized. Furthermore, GABAergic overactivity in the internal globus pallidus-substantia nigra pars reticulata complex is hypothesized in tardive dyskinesia. 5. The present data suggest that gonadal hormone withdrawal by reducing brain dopamine receptors and producing an imbalance of GABAA receptors in the output pathways of the striatum may predispose to schizophrenia and dyskinesia.