Effects of estradiol benzoate on apomorphine-induced pecking behavior in the pigeon.

Clinical and laboratory observations suggested an interaction between sex hormones and dopaminergic functions. Estrogens are reported to exert dual effects on dopaminergic system(s). In the apomorphine-induced pecking behavior model in the pigeon, acute administration of estradiol benzoate (5, 10, 20 mg/kg) significantly reduced the total pecking counts, indicating an antidopaminergic effect. Other sex steroids, testosterone and progesterone were found to be ineffective. Chronic administration of low dose estradiol benzoate (20 micrograms/kg/day) resulted in an increase in total pecking counts elicited by a single dose of apomorphine administration, revealing an increased sensitivity in dopaminergic functions.