DECREASE OF GLUTAMATE-DECARBOXYLASE ACTIVITY AFTER IN-VIVO CORTICAL INFUSION OF GAMMA-AMINOBUTYRIC-ACID

gamma-Aminobutyric acid (GABA) levels and the activity of glutamate de carboxylase were measured in homogenates of rat brain cortical tissue, at different times after chronic intracortical infusion of GABA in vi vo during 2, 6 or 24 h. Cortical electrical activity was also recorded . As previously described, about 1 h after cessation of the infusion e pileptic discharges were observed (GABA-withdrawal syndrome), which la sted for several days. At zero time after cessation of the infusion, b efore the appearance of seizures, GABA levels were increased 3-6-fold and glutamate decarboxylase activity was decreased 27-48% in the infus ed cortex, as compared to the contralateral cortex or to tissue from c ontrol intact rats. During epileptic discharges GABA levels gradually returned to normal values. In contrast, glutamate decarboxylase activi ty remained decreased during seizures and returned to normal only afte r recovery from the GABA-withdrawal syndrome. These results suggest th at the persistent decrease in the activity of the decarboxylase is due probably to a lowered amount of the enzymatic protein, occurring as a consequence of a temporarily elevated intracellular GABA concentratio n. The decreased rate of GABA synthesis might be involved in the patho physiology of the GABA-withdrawal syndrome.