Interactions between serotonin (5-HT) and dopamine (DA) neuronal systems in the prefrontal cortex (PFC) may be important in the pathophysiology of cognitive disorders such as schizophrenia. We have examined the effect of 5-HT, applied locally through a microdialysis probe, on extracellular DA in the PFC, and compared the response to that observed in the striatum. 5-HT in concentrations of 1 to 10 microM increased extracellular DA dose-dependently to a greater extent in the PFC than in the striatum. The PFC response was pharmacologically characterized to determine the 5-HT receptor subtype mediating the increase in DA levels. The coperfusion of selective 5-HT2A and 5-HT3 antagonists MDL 100,907 ((R-(+)-(2,3-dimethoxyphenyl)-1-[2(4-flourophenylethyl)]-4- piperidine-methanol) and MDL 72222 (3-tropanyl-3,5-dichlorobenzoate), respectively, with 5-HT failed to significantly attenuate the 5-HT induced increase of extracellular DA. Furthermore, the local application of the 5-HT2A/2C agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl aminopropane did not yield an increase in extracellular DA. On the other hand, coperfusion of the selective 5-HT1B/1D antagonist GR 127935 (N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-1 ,2,4-oxadiazol-3-yl)-[1,1-biphenyl]-4-carboxamide)) with 5-HT completely blocked the effect of 5-HT alone. Infusion of the selective 5-HT1B agonists CP 93,129 (3-(1,2,5,6-tetrahydro-4-pyridyl)pyrrolo[3,2-b]pyrid-5-one) and CP 94,253 (3-(1,2,5,6-tetrahydro-4-pyridyl)-5-propoxypyrolo[3,2-b]pyridine) resulted in a significant increase in extracellular DA and the effect of CP 93,129 was attenuated by coperfusion of GR 127935. The results obtained demonstrate a functional interaction between DA and 5-HT pathways in the PFC, with evidence of potential mediation by the 5-HT1B receptor subtype.