INHIBITION OF GLUTAMATE-DECARBOXYLASE ACTIVITY BY 3-MERCAPTOPROPIONICACID HAS DIFFERENT TIME-COURSE IN THE IMMATURE AND ADULT-RAT BRAINS

It has been found that the latency of epileptic seizures caused by glu tamate decarboxylase (GAD) inhibitor 3-mercaptopropionate (3-MPA) is m arkedly longer in immature rats than in the adults. Time course of rat brain GAD inhibition was studied in 12-day-old and adult (90-day-old) animals following 3-MPA (70 mg/kg i.p.). GAD activity was determined by quantification of (CO2)-C-14 liberated from [1-C-14]glutamate by su pernatant 20 000 x g of brain homogenate prepared from rats killed at different intervals after 3-MPA administration. In adult rats, the enz yme activity decreased significantly by 14.1% even 1 min after 3-MPA a dministration and was decreasing gradually till the onset of seizures. In immature rats, GAD activity decrease after 1 min was by 41.4% and further decrease was smaller. Comparison of the time profiles of GAD c hanges in both groups confirmed our findings that in spite of delayed seizure onset, GAD inhibition in immature rats is more pronounced, pro bably due to immaturity of the blood-brain barrier. (C) 1997 Elsevier Science Ireland Ltd.