Apomorphine increases the activity of rat globus pallidus neurons

Systemic administration of apomorphine, 0.08–1.0 mg/kg, caused a haloperidol-reversible increase in the unit activity of spontaneously firing neurons in the rat globus pallidus. Low doses of apomorphine (50, 20 μg/kg), which are thought to produce a net decrease in the stimulation of postsynaptic dopamine receptors, did not cause effects opposite to those observed with larger doses in 96% of the cells monitored. Blockade of dopamine receptors by administration of haloperidol did cause a moderate reduction in neuronal activity but only after administration of fairly high doses.