Using a microdialysis technique, we continuously infused D-kynurenine (KYN) (0, 50, and 100 microM) into the prefrontal cortices (PFCs) of male Sprague-Dawley rats. We then used column-switching high-performance liquid chromatography to assess the alterations in the concentration of kynurenic acid (KYNA)-an antagonist of N-methyl-D-aspartate and alpha7 nicotinic acetylcholine receptors-in the extracellular fluid in the PFC. Local infusion of D-KYN into the PFC remarkably increased the extracellular KYNA concentration, indicating that D-KYN is metabolized to KYNA in the PFC. The D-KYN-induced increase in KYNA levels was significantly attenuated by the co-administration of 3-methylpyrazole-5-carboxylic acid (AS057278)-a specific inhibitor of D-amino acid oxidase (DAAO). These results suggest that DAAO may be involved in the production of KYNA from D-KYN in the PFC in vivo.