Consistent with previous reports that acute in vitro exposure of brain slices to kynurenine enhances KYNA synthesis (Turski et al., 1989; Gramsbergen et al., 1997; Scharfman et al., 1999), incubation of rat hippocampal slices with 200 M kynurenine led to a continuous de novo synthesis of endogenous‚Äö√Ñ¬∂