GABA-like immunoreactivity in different cellular populations of cerebellar cortex of rats before and after treatment with amino-oxyacetic acid

The postembedding immunogold procedure was used to detect changes in the levels of γ-aminobutyric acid (GABA)-like immunoreactivity at the ultrastructural level in the cerebellar cortex of control rats and rats treated with the GABA transaminase inhibitor, amino-oxyacetic acid (AOAA), in order to increase the levels of GABA. GABA-immunoreactive structures were labelled using an antiserum directed against GABA coupled to bovine serum albumin and a secondary antibody conjugated to colloidal gold. The density of gold particles per square micron of tissue was taken as a measure of GABA-like immunoreactivity. In separate groups of control and AOAA-treated animals, the levels of GABA were assessed biochemically in the cerebellum, the cortex, the ventral mesencephalon and the striatum. Six hours after treatment with AOAA the GABA levels in the cerebellum were 9.4-fold higher than in control rats. In the cerebellum of control animals the GABA immunoreactivity of the Golgi and basket cell terminals was significantly greater than that of mossy fibres, granule cell dendrites and perikarya and glial cells. The value obtained for Golgi terminals was the highest of all the structures examined and was twice that of their perikarya. Six hours after treatment with AOAA the GABA immunoreactivity in Golgi and basket cell terminals and in glial cells was greatly enhanced. The drug treatment slightly enhanced the immunoreactivity in mossy fibres and granule cell dendrites but induced no change in granule cell bodies. Thus, in both control and treated rats, the highest GABA immunoreactivity was present in the terminals of GABAergic cells, and the lowest in putative glutamatergic cells. The results demonstrate that there is a high degree of selectivity in the changes in GABA levels following the inhibition of GABA transaminase in the cerebellum. They also confirm the potential of the use of postembedding methods for the quantification of endogenous amino acid at cellular and subcellular levels, in relative and possibly also absolute terms. © 1991