The Glutamate System in Schizophrenia and Depression

The Glutamate Systern in Schizophrenia Kynurenic Acid as a Schizophrenogenic Substance 

In contrast to microglial cells, which produce quinolinic acid, astrocytes play a key role in the production of kynurenic acid (KYNA) in the CNS. Astrocytes are the main source of KYNA (Heyes et al., 1997). The cellular localization of the kynurenine metabolism is primarily in macrophages and microglial cells, but also in astrocytes (Speciale and Schwarcz, 1993 Kiss et al., 2003). KYN-OHse, however, a critical enzyme in the 

A second key-player in the metabolizing of 3-HK are monocytic cells infiltrating the CNS. They help astrocytes in the further metabolism to quinolinic acid (Guillemin et al., 2001). However, the low levels of sICAM-1 (ICAM-1 is the molecule that mainly mediates the penetration of monocytes and lymphocytes into the CNS) in the serum and in the CSF of non-mecUcated schizophrenic patients (Schwarz et al., 2000) and the increase of adhesion molecules during antipsychotic therapy indicate that the penetration of monocytes may be reduced in non-mecUcated schizophrenic patients (Muller etal., 1999). 

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