TONIC D-2-MEDIATED ATTENUATION OF CORTICAL EXCITATION IN NUCLEUS-ACCUMBENS NEURONS RECORDED IN-VITRO

The effects of dopamine D-1 and D-2 selective drugs on the responses evoked in accumbens neurons by stimulation of cortical afferents were studied in an in vitro brain slice preparation. The D-2-specific antagonist sulpiride (1-10 mu M) increased, whereas the D-2 agonist quinpirole (1-20 mu M) occasionally attenuated the amplitude of stimulation-evoked EPSPs recorded in accumbens neurons. Administration of the D-1 agonist SKF 38393 (3-10 mu M) or the D-1 antagonist SCH 23390 (10 mu M) 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 corticoaccumbens fiber stimulation via D-2 receptors. Furthermore, these D-2 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 D-2 receptor stimulation in the accumbens slice preparation.