• Kenji Hashimoto, Yuko Fujita, Mao Horio, Shinsui Kunitachi, Masaomi Iyo, Dana Ferraris, and Takashi Tsukamoto.
• Division of Clinical Neuroscience, Chiba University Center for Forensic Mental Health, Chiba, Japan. hashimoto@faculty.chiba-u.jp
• Biol. Psychiatry. 2009 Jun 15; 65 (12): 1103-6.

BackgroundD-Serine, an endogenous agonist of the N-methyl-D-aspartate (NMDA) receptors, is effective in the treatment of schizophrenia. However, orally administered D-serine is metabolized substantially by D-amino acid oxidase (DAAO), diminishing its oral bioavailability. In this study, we examined the effects of oral D-serine administration with or without a DAAO inhibitor, 5-chloro-benzo[d]isoxazol-3-ol (CBIO), on the prepulse inhibition (PPI) deficits after administration of the NMDA receptor antagonist dizocilpine.MethodsVehicle or D-serine (30, 300, or 900 mg/kg) with or without CBIO (30 mg/kg) was orally administered to mice 1 hour before administration of dizocilpine (.1 mg/kg), and then the PPI of the acoustic startle response was measured. We measured the extracellular levels of D-serine in the frontal cortex after oral administration of D-serine with or without CBIO.ResultsCoadministration of CBIO with D-serine (30 mg/kg), but not D-serine (30 mg/kg) alone, significantly attenuated dizocilpine-induced PPI deficits. Furthermore, coadministration of CBIO significantly increased the extracellular levels of D-serine in the frontal cortex after administration of D-serine.ConclusionsThese findings suggest that coadministration of CBIO significantly enhanced the efficacy of D-serine in attenuating PPI deficits by administration of dizocilpine. Therefore, coadministration of D-serine and a DAAO inhibitor has therapeutic potential for the treatment of schizophrenia.

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