EFFECTS OF CASTRATION, ESTROGEN REPLACEMENT AND ESTRUS CYCLE ON MONOAMINE METABOLISM IN THE NUCLEUS-ACCUMBENS, MEASURED BY MICRODIALYSIS

Changes in monoamine concentration in the nucleus accumbens were measured by microdialysis during the estrus cycle of intact females rats as well as untreated ovariectomized rats and ovariectomized rats treated with estrogen and progesterone. Norepinephrine (NE), 3-methoxy-4-hydroxyphenylglycol (MHPG) dopamine (DA), 3,4-dihydroxyphenylacetic acid, (DOPAC), serotonin (5-HT) and 5-hydroxy-3-indoleacetic acid (5-HIAA) were measured by high performance liquid chromatography. The ratio of MHPG to NE and DOPAC to DA were significantly increased during proestrus when compared to other phases of the estrus cycle. The ratio of 5-HIAA: 5-HT, however, was significantly reduced during proestrus. Treatment of ovariectomized rats with estradiol at either 1 mug/day or 10 mug/day significantly increased the ratio of MHPG:NE and DOPAC:DA. In contrast, the ratio of 5-HIAA:5-HT decreased significantly. Progesterone had no significant effect on the concentrations of 5-HT or 5-HIAA, but attenuated the effect of estrogen on the ratio of MHPG:NE and similarly reduced the ratio of DOPAC: DA. These studies are consistent with the hypothesis that estrogens are associated with enhanced metabolism of NE and decreased metabolism of 5-HT and dopamine in the nucleus accumbens of freely moving rats.