Amphetamine-haloperidol interactions in rat striatum: failure to correlate behavioral effects with dopaminergic and cholinergic dynamics.

Previous reports have suggested that the hyperactivity and stereotypy produced by amphetamine (AMP) and the catalepsy produced by haloperidol (HAL) are mediated by striatal dopaminergic mechanisms. In the present study, we have measured the behavioral effects of AMP and HAL, and their effects on striatal dopaminergic function, using both an index of pre-synaptic activity (synaptosomal dopamine (DA) synthesis) and a parameter which we suggest will reflect post-synaptic dopaminergic function (sodium-dependent, high affinity choline uptake). Administration of 2 mg/kg AMP produces hyperactivity and causes a decrease in DA biosynthesis, both of which are blocked by 0.75 mg/kg HAL. AMP (5 mg/kg) produces stereotypy, further decreases DA biosynthesis and causes a decrease in choline uptake, consistent with stimulation of DA receptors. However, while pretreatment with 3 mg/kg HAL completely blocked the stereotypy induced by 5 mg/kg AMP it failed to reverse the effects of this dose on either DA biosynthesis or choline uptake. These data suggest that either 5 mg/kg AMP affects straital dopaminergic and cholinergic parameters by a mechanism independent of HAL sensitive receptors, or the stereotypy produced by high doses of AMP are not related to striatal dopaminergic and cholinergic function.