Behavior performed at onset of drug action and apomorphine stereotypy

This study tests the hypothesis that stereotyped behavior induced by apomorphine reflects strengthening of behavior observed at the onset of drug action. Rats (n = 26) were injected with apomorphine (1.25 mg/kg) while being engaged in copulation. Contrary to the hypothesis, apomorphine did not strengthen ongoing copulation but arrested it. Instead of mating the males became engaged in behavior typically exhibited by rats injected with the drug. It is speculated that stereotyped behavior may be an expression of a drug-induced shift of attention or responsiveness to some particular range of stimuli.