Spontaneous unit discharges were recorded extracellularly from globus pallidal (GP) neurons in rat slice preparations. The firing rates of GP neurons ranged from 2.0 to 24.0 spikes/s and their firing patterns were predominantly of two types: regular and irregular. Stimulation of the neostriatum evoked two distinct types of inhibition which were dependent on GP neuronal firing patterns, a brief inhibition (about 75 ms) followed by resetting rhythmic neuronal activities and a relatively long-term inhibition (about 100 ms). These inhibitions evoked by neostriatal stimulation were attenuated or completely blocked by bath application of either bicuculline or strychnine (2 X 10(-5)-10(-4) M) but not by naloxone. Bath application of dopamine (10(-4)-10(-3) M) produced slow increases in the firing rates by 30-65% in about a half of GP neurons tested. Iontophoretic application of dopamine (10-20 nA) attenuated inhibition in GP neurons by 40-55% induced by either iontophoretically applied GABA (5-30 nA) or neostriatal stimulation without affecting their spontaneous firings. These results suggest that dopamine may produce change in the firing patterns of GP neurons by either acting directly or attenuating GABAergic inhibitory transmission from the neostriatum.