The effects of dopamine D1 and D2 selective drugs on the responses evoked in accumbens neurons by stimulation of cortical afferents were studied in an in vitro brain slice preparation. The D2-specific antagonist sulpiride (1-10 microM) increased, whereas the D2 agonist quinpirole (1-20 microM) occasionally attenuated the amplitude of stimulation-evoked EPSPs recorded in accumbens neurons. Administration of the D1 agonist SKF 38393 (3-10 microM) or the D1 antagonist SCH 23390 (10 microM) did not alter the EPSP amplitude, although an apparent change in the time course of the EPSP was often observed. In slices obtained from dopamine (DA)-depleted animals, sulpiride failed to induce changes in the amplitude of the EPSPs, whereas quinpirole produced a highly significant suppression of EPSP amplitude that was only occasionally observed in control slices. These results indicate that DA modulates the response of accumbens neurons to cortico-accumbens fiber stimulation via D2 receptors. Furthermore, these D2 receptors appear to be located presynaptically on the cortical afferent terminals, since this action of DA was not accompanied by changes in membrane potential, input resistance, or time constant, and was not modified by changes in the membrane potential. These data provide evidence for a tonic basal level of D2 receptor stimulation in the accumbens slice preparation.