PRESYNAPTIC D-2 DOPAMINERGIC RECEPTORS MEDIATE INHIBITION OF EXCITATORY SYNAPTIC TRANSMISSION IN RAT NEOSTRIATUM

The effect of dopamine (DA) on excitatory synaptic transmission was st udied in rat neostriatal neurons using intracellular- and whole-cell v oltage clamp-recording methods. Depolarizing excitatory postsynaptic p otentials (EPSPs) were evoked by cortical stimulation. Superfusion of DA (0.01-10 mu M) reversibly decreases EPSP in a concentration-depende nt manner and with a estimated IC50 of 0.3 mu M. In addition, the inhi bitory effect induced by DA at a low concentration (0.1 mu M) was anta gonized by sulpiride (1-10 nM), a selective D-2 dopaminergic receptor antagonist. However, D-1 dopaminergic receptor antagonist SKF-83566 (1 -5 mu M) did not affect the blocking effect by DA 0.1 mu M. Based on t hese findings, we conclude that DA at a low concentration(less than or equal to 0.1 mu M) reduced the excitatory response of neostriatal neu rons following cortical stimulation via the activation of D-2, but not D-1 dopaminergic receptors, located on the terminals of corticostriat al neurons.