Striatal D1 dopamine receptor density fluctuates during the rat estrous cycle

Striatal D1 dopamine (DA) antagonist binding sites were investigated in intact female and male rats, ovariectomized (OVX) animals and during the 4-day estrous cycle. The affinity of the striatal D1 receptor as labelled with [3H]SCH 23390 remains unchanged in intact male, female rats during the estrous cycle and OVX animals. By contrast, ovariectomy decreased striatal D1 receptor density by 17% (P less than 0.01) compared to intact female rats while a small but significant higher density was observed in intact male compared to female rats (10% higher, P less than 0.05). The density of striatal D1 DA receptor was higher on the day of diestrus I (DI) and diestrus II (DII) (P less than 0.01 vs OVX) and fluctuates throughout the estrous cycle with a maximum on the day of DII (P less than 0.05 vs proestrus PM). Our results show for the first time that striatal D1 DA receptors fluctuate during the estrous cycle and can be modulated by gonadal steroids.