rating the negative symptoms [7] that are prominent in patients with a chronic course.l 8 ] Antipsychotics render schizophrenia manageable, but do not completely cure the disorder. Explanations other than dopaminergic hyperactivity are required for further understanding of the illness, as well as for therapeutic advancement. As reviewed below, accumulating evidence indicates that the glutamate hypothesis is one such candidate that may provide a more comprehensive view of schizophrenia, into which dopaminergic hyperactivity may be incorporated.
.2 Glutamate Levels in Schizophrenic Brains and CSFGlutamate is the major excitatory neurotransmitter in the mammalian brain. [9. 10] Its effects are mediated through binding to a number of receptors: N-methyl-D-aspartate (NMDA), kainate, aamino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and metabotropic. Glutamate is responsible for not only the classical fast synaptic transmission through non-NMDA receptors, but a long term potentiation through the NMDA receptor. This latter effect underlies neuronal plasticity.lll] Dysfunction in glutamatergic neural transmission is assumed in various neuropsychiatric disor-eNS Drugs 1997 Jan; 7 (1) Recently, Tsai et alP2] performed a postmortem study of brains from patients who had had schizophrenia that focused on N-acetylaspartyl-glutamate (NAAG), a neuropeptide that is highly concentrated in glutamatergic neurons.!22] NAAG is a partial antagonist of NMDA receptors and, more-