The fine structural localization of glutamate decarboxylase in synaptic terminals of rodent cerebellum

Glutamic acid decar☐ylase (GAD), the enzyme that synthesizes the putative neurotransmitter γ-aminobutyric acid (GABA), has been localized by peroxidase labeling antibody techniques at the light and electron microscopic levels in rodent cerebellum. Specific anti-GAD peroxidase product was highly localized in certain synaptic terminals in close association with the membranes of synaptic vesicles and mitochondria but not within these organelles. GAD-positive terminals were seen on the somata and proximal dendrites of neurons in the deep cerebellar nuclei. Other positive terminals were presumed Golgi type II endings of synaptic glomeruli in the granular layer. Positive terminals were also seen in the molecular layer, including presumed basket cell endings which contained product on smooth membrane cisternae in the preterminal axon as well as around synaptic vesicles and mitochondria. These observations correlate well with a large body of evidence that certain synaptic connections in the cerebellum are inhibitory and that many, if not all, of the presynaptic components of these connections may use GABA as their neurotransmitter.