Effects of microgram doses of haloperidol on open-field behavior in mice

This study was designed to evaluate the effects of low doses of haloperidol on the open-field behavior of mice. A three-phase effect of haloperidol on the motor activity of mice was observed (depression, no effect, depression). This three-phase action was clear-cut in three experimental approaches (amphetamine-induced hyperactivity, and apomorphine- and bromocriptine-induced hypoactivity). A differential action of haloperidol on dopamine receptors mediating motor stimulation and motor depression was proposed. The present data indicate that considerably more attention should be paid to the novel behavioral and biochemical actions of neuroleptic drugs in the microgram dose range.