SYSTEMIC DL-KYNURENINE AND PROBENECID PRETREATMENT ATTENUATES QUINOLINIC ACID-INDUCED NEUROTOXICITY IN RATS

Kynurenine (KYN) is the precursor of kynurenic acid (KYNA), an endogen ous antagonist of the glycine site of the NMDA (N-methyl-D-aspartate) receptor. Probenecid (PROB), blocks the excretion of KYNA from the ext racellular fluid. KYNA antagonizes the toxic action of quinolinic acid (QUIN), an endogenous NMDA receptor agonist. In this study, we tested the effect of the systemic administration of KYN and PROB, either alo ne or in combination, on QUIN-induced circling behavior and gamma-amin obutyric acid (GABA) depletion in rats. Circling behavior and GABA dep letion induced by QUIN were both partially prevented by PROB (200 and 300 mg/kg) and KYN (300 and 450 mg/kg) treatments. Lower doses of drug s administered separately were nonprotective. However, when administer ed in combination, doses of 150 or 300 mg/kg KYN plus 100 mg/kg PROB s ignificantly protected animals against QUIN neurotoxicity. These findi ngs suggest a role of KYN and PROB as promoters of KYNA-mediated NMDA receptor antagonism, via an increase of kynurenate in brain extracellu lar spaces.