Immunocytochemical localization of γ-aminobutyric acid transaminase at cellular and ultrastructural levels

Abstract

.gamma.-Aminobutyric acid transaminase (GABA-Tase; 4-aminobutyrate:2-oxaglutarate aminotransferase, EC 2.6.1.19) immunoreactivity in the rat''s cerebellum was studied by EM and light microscopy with indirect immunofluorescence and peroxidase-antiperoxidase methods. Evidence is presented for neuronal and neuroglial compartments of GABA-Tase. Labeled neurons included stellate, basket, Purkinje and Golgi cells of the cortex and a few large neurons in the deep nuclei. Labeled neuroglia included those surrounding Purkinje cells, their radial fibers in the molecular layer, and astrocytes in the granular layer and deep nuclei. No evidence for sagittal microzonation was found. At the ultrastructural level, GABA-Tase immunoreactive sites were localized to cell surface membranes, intracellular organelles, and the cytoplasmic matrix. GABA-Tase immunoreactivity at synapses could be localized precisely to pre- and postsynaptic membranes in .gamma.-aminobutyric acid (GABA)-containing and non-GABA-containing neurons. Specific label was absent from tissues treated with normal rabbit preimmune sera. GABA-Tase labeling was more intense in tissues from animals anesthetized with ether than with barbiturates and after formaldehyde fixation without glutataldehyde. Increased GABA-Tase immunoreactivity was observed on treatment with colchicine, GABA with oxamic acid, GABA, harmaline, norepinephrine and glutamate, or diazepam (in order of decreasing effectiveness). Serotonin produced no detectable change and apomorphine and muscimol decreased the immunoreactivity.