Estrogen treatment increases the oral component of apomorphine-induced stereotypy.

Twelve weeks after surgery, sham operated intact and ovariectomized (OVX) female rats were treated for 3 days with either estradiol benzoate (50 micrograms/kg per day) or the oil vehicle. They were then tested for apomorphine-induced stereotypy 24 or 72 h after the last steroid injection. The data was collected and analysed in terms of both stereotypy ratings and individual behavioural responses. Estradiol, in those animals tested 72 h after estrogen, increased the frequency of oral behaviour in intact and in OVX groups. One possible explanation for the results is that estradiol may exert an anti-dopaminergic effect in the nigrostriatal system.