Quinolinic acid effects on amino acid release from the rat cerebral cortex in vitro and in vivo

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Abstract
1 The effect of quinolinic acid, N-methyl-d,l-aspartate (NMDLA) and kainate on the release of endogenous and exogenous amino acids from the rat cerebral cortex in vitro and in vivo was studied. 2 Neither quinolinic acid nor NMDLA had any effect on the basal or potassium-evoked release of [3H]-d-aspartate from slices of rat cerebral cortex either in the presence or absence of magnesium. Kainic acid failed to modify the basal efflux of [3H]-d-aspartate but significantly inhibited (by 34.4% ± 0.04%, P < 0.05) the potassium-evoked release. 3 Neither quinolinate nor NMDLA had any effect on the basal efflux of endogenous amino acids from rat cortical slices either in the presence or absence of magnesium ions at concentrations between 10 μm and 5 mm. 4 Both NMDLA (1 mm) and quinolinate (5 mm) produced an efflux of endogenous aspartate (371.4% ± 11.6%; 389.3% ± 12.1%) and glutamate (405.4% ± 13.6%; 430.1 ± 8.7%) respectively from the rat cerebral cortex in vivo (P < 0.01). The quinolinic acid-evoked efflux was abolished by the NMDLA antagonist, 2-amino-5-phosphonovaleric acid (200 μm). 5 Kainic acid also caused an efflux of endogenous amino acids from the rat cerebral cortex in vivo. However, the profile of this release was different from that produced by quinolinate and NMDLA. 6 The results add further support to the suggestion that quinolinic acid acts at the NMDLA-preferring receptor and may also explain the requirement for intact afferent projections for the neurotoxic effects of quinolinate to be manifested.