Brain-specific modulation of kynurenic acid synthesis in the rat.

This study was designed to investigate modulatory mechanisms that control the synthesis of the neuroprotective endogenous excitatory amino acid receptor antagonist kynurenate. De novo kynurenate formation was examined in vitro using tissue slices from rat brain, liver, and kidney. In slices from adult cerebral cortex, veratridine, quisqualate, and L-alpha-aminoadipate decreased kynurenate synthesis substantially. Glucose removal or changes in the ionic milieu, too, influenced kynurenate formation significantly, suggesting that demands on cellular energy interfere with kynurenate production in the adult rat brain. The effects of quisqualate and L-alpha-aminoadipate were also observed in the immature brain, in the quinolinate-lesioned adult striatum, and, to a lesser extent, in peripheral organs. In contrast, the effect of veratridine was not seen in the lesioned brain or in kidney and liver tissue, indicating its dependency on intact neuron-glia interactions. Compared with the normal adult brain, ionic manipulations yielded qualitatively distinct results in the developing brain and in the periphery, but their effects remained unchanged in the lesioned striatum. Glucose deprivation was less consequential in the immature than in the adult brain and was entirely ineffective in the lesioned striatum and in the periphery. These results further link cellular, especially astrocytic, energy metabolism to kynurenate formation in the brain. More generally, the existence of brain-specific mechanisms for the regulation of kynurenate production is suggestive of a modulatory role of this metabolite in excitatory amino acid receptor function and dysfunction.