Regional differences in the ontogenetic pattern of kynurenine aminotransferase in the rat brain.

The ontogenetic pattern of kynurenine aminotransferase (KAT), the biosynthetic enzyme of the neuroprotective excitatory amino acid receptor antagonist, kynurenic acid, was examined in the rat in six brain regions and in the liver. KAT activity increased in all brain areas (but not in the liver) between 3 days and 3 months post-natum, and substantial differences were observed in the rates of the increase. For example, KAT activity in the parietal cortex increased 34-fold during the observation period, whereas enzyme activity in the cerebellum and substantia nigra increased only 3-5 fold over the same interval. Intermediate developmental changes were found in striatum, hippocampus and olfactory bulb. The differential increases in KAT activity became particularly pronounced after the second postnatal week. Since N-methyl-D-aspartate (NMDA) receptors, which are preferential targets of kynurenic acid, play an important role in brain development, the regional heterogeneity of KAT's ontogenetic profile may have a bearing on the function and dysfunction of the young central nervous system.