Effects of ovariectomy and of estrogen administration on some dopamine-related behaviors in the rat.

1. The effects of ovariectomy and of estrogen administration were determined on some dopamine-related behaviors. 2. Haloperidol withdrawal induced a progressive increase in locomotion and rearing frequencies of female rats observed in an open-field. This increase started earlier and was greater in ovariectomized than in sham-operated animals. 3. Repeated administration of increasing doses of 17-beta-estradiol (from 0.05 to 0.3 mg/kg once daily, for 28 days) significantly decreased apomorphine-induced stereotyped behavior in ovariectomized rats, 30 min after the last hormone injection. 4. Withdrawal from long-term 17-beta-estradiol administration increased the sensitivity of the animals to apomorphine. 5. These results suggest not only an antidopaminergic effect for estrogen but also a possible summation of estrogen and haloperidol withdrawal effects.