EFFECT OF LOCAL CHOLECYSTOKININ-8 ADMINISTRATION ON EXTRACELLULAR LEVELS OF AMINO-ACIDS AND GLYCOLYTIC PRODUCTS MONITORED BY IN-VIVO MICRODIALYSIS IN THE FRONTOPARIETAL CORTEX OF THE RAT

The effects of local cholecystokinin-8 (CCK-8) administration on corti cal extracellular levels of amino acids, catecholamines and metabolism products were studied in the halothane anaesthetized rat by in vivo m icrodialysis. CCK-8 (10 mu M), administrated via a microdialysis probe , produced a significant increase in the levels of aspartate, glutamat e and gamma-aminobutyric acid (GABA), but not of 3,4-dihydroxyphenylac etic acid (DOPAC), homovanillic acid (HVA), lactate and pyruvate, whic h were simultaneously monitored. The increase in aspartate and glutama te levels produced by CCK-8 was about 3-4-fold. The effect of CCK-8 on aspartate levels was significantly inhibited by the CCKB antagonist, L-365,260 (20 mg kg(-1), s.c.), but not by the CCKA antagonist, L-364, 718 (20 mg kg(-1) s.c.). In contrast, the increase in glutamate levels was inhibited by both L365,260 and L364,718. GABA was slightly, but s ignificantly increased (similar to 30%), by local CCK-8 and was inhibi ted by both CCK antagonists. The present results show that CCK-8 exert s a strong modulatory action on both aspartate and glutamate release i n rat cortex. While the effect of CCK-8 on aspartate is selectively me diated via CCKB receptor subtype, the effect of CCK-8 on glutamate app ears to be mediated via both CCKA and CCKB receptor subtypes.