Kynurenine aminotransferase I (KATI) isoform gene expression in the rat brain: an in situ hybridization study

KYNURENINE. aminotransferase I (KATI) converts kynurenine into kynurenic ac id (KYNA), a broad-spectrum antagonist at ionotropic excitatory amino acid receptors. The main interest in KYNA centers on its potential neuroprotecti ve action in physiological and pathological conditions. We show here by in situ hybridization that KATI mRNA is widely expressed throughout the adult rat brain. A strong autoradiographic signal was detected in the hippocampus , piriform cortex, and choroid plexus. Microscopic evaluation suggested tha t KATI mRNA was expressed not only in astrocytes but also in hippocampal ne urons and in choroid plexus epithelial cells. Neuronal expression of KATI m RNA was further confirmed by RT-PCR and in a model of transient cerebral is chemia. The expression pattern of the mitochondrial form (mKATI) of the enz yme was almost comparable to that of KATI. The major difference was observe d in the choroid plexus where mKATI mRNA signal was very low. (C) 1999 Lipp incott Williams & Wilkins.