Effects of apomorphine and amphetamine on patterns of locomotor and investigatory behavior in rats.

Rats were tested in a Behavioral Pattern Monitor after various doses of either amphetamine or apomorphine in order to characterize their behavioral profiles, including patterns and sequences of holepokes, rearings and locomotor movements. To enable direct comparisons between the behavioral effects of the two stimulants, doses and times for each drug were selected with which locomotor hyperactivity was the predominant behavioral response. Although both drugs increased the total amount of locomotor activity, amphetamine induced a relatively varied behavioral profile while apomorphine induced repetitive behavior with a restricted range of responses. These contrasting effects of the stimulants were interpreted as reflective of their differing modes of action with regard to central dopaminergic systems. It is suggested that, in the dose range used, the release of dopamine by amphetamine is coupled to neuronal firing and therefore this release increases behavioral activity without altering the normal response repertoire of the animal. Conversely, the direct agonist action of apomorphine results in a restricted and perseverative behavioral pattern because its activation of forebrain dopamine receptors is independent of the normal physiological pattern of dopaminergic neuronal firing.