Interaction of apomorphine and haloperidol: effects on locomotion and other behaviour in the marmoset.

The behavioural effects of increasing doses of apomorphine and haloperidol were observed in a group of six marmosets. Behaviour was classified quantitatively into categories: Locomotion, inactivity, checking (small head movements), social interaction and purposeful activities. Statistical analysis revealed that apomorphine had a stimulant effect on checking and locomotion which could be antagonized by haloperidol. Activities and social contact were severly reduced by both apomorphine and haloperidol. Inactivity was increased by the lowest dose of apomorphine in otherwise untreated animals. It is suggested that haloperidol antagonizes the stimulant effects of apomorphine but is synergistic to its suppressant effects, and that the low dose effect of apomorphine on inactivity is mediated by a mechanism which may be different from that acted upon by haloperidol.