Bitopertin (RG1678) dose-dependently increases cerebrospinal fluid and striatal levels of glycine measured bymicrodialysis in rats. Additionally Bitopertin attenuates hyperlocomotion induced by the psychostimulant D-amphetamine or the NMDA receptor glycine site antagonist L-687,414 in mice. Bitopertin also prevents the hyper-response to D-amphetamine challenge in rats treated chronically with phencyclidine, an NMDA receptor open-channel blocker. Administration of vehicle has no effect on extracellular levels of striatal glycine, which remained constant throughout the experiment. In contrast, p.o. administration of Bitopertin (1-30 mg/kg) produced a dose-dependent increase in extracellular glycine levels. Bitopertin 30 mg/kg produces glycine levels 2.5 times higher than pretreatment levels. A similar dose-dependent increase in glycine concentration is observed in the CSF of rats treated p.o. with Bitopertin (1-10 mg/kg) compared with vehicle-treated animals, 3 h after drug administration. Interestingly, the level of CSF glycine increase 3 h after Bitopertin dosing is very similar to the increase in the microdialysis experiment at the same time point^[1]. In vivo pharmacokinetic studies in rat and monkey reveals that Bitopertin (RG1678) has, in both species, a low plasma clearance, an intermediate volume of distribution, a good oral bioavailability (78% for rat, 56% for monkey), and a favorable terminal half-life (5.8 h for rat, 6.4 h for monkey). The plasma protein binding is high in the two preclinical species (97%) and in human (98%). The CNS penetration of Bitopertin in rat (brain/plasma=0.7) is better than that in mouse (brain/plasma=0.5)^[2].