dopamine receptors in the rat prefrontal cortex were examined using whole-cell recordings from pyramidal neurons. The effects of NMDA, the D 1 agonist SKF38393, or both compounds combined were tested on measures of cell excitability. Both NMDA (10-100 µM) and SKF38393 (5-10 µM) independently increased the number of spikes and decreased the latency of the first spike evoked by intracellular depolarizing current pulses. Combining low doses of NMDA (5 µM) and SKF38393 (2 µM) resulted in a marked

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... crease of cell excitability. This synergism was blocked by SCH23390, protein kinase A (PKA) inhibitors, and the Ca 2+ chelator BAPTA, and reduced by nifedipine. These results indicate the presence of a dopamineglutamate interaction in the prefrontal cortex at the postsynaptic level, by which D 1 dopamine receptors may maintain NMDAmediated responses in prefrontal cortical pyramidal neurons through both a PKA-dependent pathway and Ca 2+ -dependent mechanisms.