STABILITY OF SYNAPTOSOMAL GABA LEVELS AND THEIR USE IN DETERMINING THE IN VIVO EFFECTS OF DRUGS: CONVULSANT AGENTS

—The stability of the GABA content of synaptosomal-enriched fractions was evaluated by two approaches. Firstly, the addition of 10^?3m -aminooxyacetic acid to the homogenizing medium totally inhibited the GABA-degrading enzyme in the fractions but did not affect the GABA levels. This indicated that GABA was not being metabolized during the normal preparation of the synaptosomal-enriched fraction. Secondly, when synaptosomal-enriched fractions were re-fractionated by discontinuous density gradient centrifugation, the GABA contents of the fractions before and after the second fractionation were very similar provided they were expressed on a per mg protein basis. It was therefore concluded that the GABA content of the organelles was not subject to change during the fractionation procedures. On the basis of these findings and others it was suggested that the synaptosomal-enriched fraction could be used as a model to evaluate drug-induced changes in GABA levels in nerve endings. In vivo experimentation indicated that the convulsant agents hydrazine, isonicotinic acid hydrazide and aminooxyacetic acid brought about similar decreases in the GABA content of the synaptosomal-enriched fractions prepared from tissue at the onset of seizures despite the fact that no correlation was observed between seizure activity and whole brain GABA levels.