Effect of estrogens on apomorphine-induced circling behavior in the rat

The effect of administration of estrogens parenterally for 1 week was tested on apomorphine-induced circling in a group of castrated female rats with a lesion of the left entopednucluar nucleus. We observed a significant decrease in the number of turns per minute in estrogen-treated animals as compared with controls. Our tentative explanation is that estrogens decrease the sensitivity of dopamine receptors in the striatum.