Recent studies have demonstrated that antagonism of somatodendritic serotonin1A (5-HT1A) autoreceptors can potentiate the increase of extracellular 5-HT concentrations induced by selective serotonin reuptake inhibitors including fluoxetine. The present study was conducted to uncover any functional difference between the 5-HT1A autoreceptors located on the cell bodies of 5-HT neurons in the dorsal (DRN) and median (MRN) raphe nuclei. The investigational approach used in the present study was to detect extracellular 5-HT concentrations in two terminal areas, prefrontal cortex (Pfc) and dorsal hippocampus (Dhp), which are mainly innervated by the 5-HT neurons located in the DRN and MRN respectively. To avoid possible variation between individual animals a dual-probe microdialysis procedure was applied to determine 5-HT concentrations in both brain areas of the same rat. Fluoxetine (10 mg/kg, s.c.) alone produced a smaller increase in the extracellular 5-HT concentration in the Pfc than Dhp of the same rat (maximal 5-HT concentrations were 183% and 223% of the baseline values in Pfc and Dhp respectively). However, an antagonist of 5-HT1A receptors, WAY100635, subsequently injected (s.c.) at 1 mg/kg brought the 5-HT concentrations to similar levels in the Pfc (332%) and Dhp (308%). Since the 5-HT concentrations immediately before the injection of WAY100635 were lower in the Pfc (102%) than Dhp (186%), WAY100635 induced a larger 5-HT net increase in the Pfc (332%-102%=230%) than Dhp (308%-186%=122%). On the other hand, WAY100635 alone did not significantly change the extracellular 5-HT concentrations in both areas. Furthermore, extracellular concentrations of dopamine (DA) and two DA metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, in both areas were not altered by the administrations of fluoxetine and WAY100635. In conclusion, the present study demonstrated that the antagonist of 5-HT1A receptors, WAY100635, produced a more robust potentiation in the fluoxetine-induced 5-HT increases in the Pfc than Dhp. Since Pfc and Dhp are predominately innervated by 5-HT neurons located in the DRN and MRN respectively, this result may indicate a functional difference between the 5-HT1A autoreceptors located on the cell bodies of 5-HT neurons in the DRN and MRN.