Dopaminergic inputs to the prefrontal cortex (PFC) are important for the integration of neuronal signals, the formation of working memory, and the establishment of memory fields. A detailed characterization of cellular mechanisms underlying the effects of dopamine on PFC is still emerging. We have examined how dopamine affects excitatory synaptic transmission in the PFC using whole-cell patch-clamp recording from visually identified layer II-III pyramidal cells in vitro. Bath application of dopamine significantly enhanced EPSC amplitudes. Pharmacologically isolated AMPA and NMDA receptor-mediated EPSCs were increased to a similar extent. Application of the specific D1-like receptor agonist SKF38393 [(±)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol hydrobromide] significantly increased EPSC amplitude, whereas the D2-like receptor agonist quinpirole had no effect. Responses to pressure-applied glutamate were also enhanced by dopamine, indicating a postsynaptic mechanism. Inclusion of the Ca2+ chelator BAPTA in the recording pipette blocked the dopamine enhancement. When the PKA inhibitory peptide PKI [5-24] was included in the recording pipette, dopamine did not affect EPSCs. Similarly, when the Ca2+/calmodulin-kinase II (CaMKII) inhibitory peptide was present in the pipette, dopamine enhancement of EPSCs was not observed in any of the cells tested. These results indicate that EPSC enhancement may be attributable to a postsynaptic signaling cascade involving Ca2+, PKA, and CaMKII.