Estrogen and haloperidol-induced versus handling-related catalepsy in male rats

A single injection of 17 beta-estradiol valerate produces, 6-7 days later, potentiation of neuroleptic catalepsy. Multiple behavioral measures demonstrate that this effect occurs with an acute dose of haloperidol of 0.25 mg/kg IP. An even lower dose of haloperidol (0.10 mg/kg), which fails to make control rats cataleptic, produces catalepsy in estrogen-treated animals. Thus, estrogen lowers the threshold of haloperidol-induced catalepsy. Repeated testing alone induces cataleptic reactions in control rats. Estrogen suppresses such handling-related catalepsy in animals that subsequently show potentiation of catalepsy at a dose of haloperidol (0.10 mg/kg), which has virtually no effect on control rats. Thus, in these behavioral paradigms, estrogen by itself does not produce cataleptic effects, and estrogen-induced potentiation of haloperidol catalepsy is not merely additive to an antecedent, neuroleptic-like effect of this hormone. We interpret our results in terms of (1) the relationship of cataleptic reactions in normal rats to drug-induced cataleptic states; (2) the possible relevance of our behavioral results to basal ganglia disorders; and (3) the relationship of neuroleptic catalepsy to striatal DA receptors and their modulation by estrogen.