Electron cytochemical localization of gamma-aminobutyric acid catabolism in rat cerebellar cortex.

An electron cytochemical technique is described for the localization of GABA-T, the enzyme which degrades the neurotransmitter GABA, in rat cerebellar cortex. The technique allows ultrastructural demonstration of GABA-T activity by the final deposition of an electron dense formazan precipitate at reaction sites, whilst maintaining adequate ultrastructural preservation for recognition of cellular and subcellular structures. Numerous electron dense precipitates are evident as discrete punctate deposits situated mainly in mitochondria of stellate cells, basket cells and astrocytic glial cells; they are also seen in axonal or dendritic profiles at some synaptic junctions. The technique enables the first cytochemical demonstration of the mitochondrial localization of GABA-T activity in nervous tissue to be presented. It establishes that GABA-T is present in supposed GABA neurones, in pre- or post-synaptic endings, or both, of presumed inhibitory synapses and in glial cells which may be associated with these synapses. From this seemingly ubiquitous distribution, functional aspects of GABA-T in these cells is considered.