Chemical and autoradiographic analysis of γ-aminobutyric acid transport in Purkinje cells of the cerebellum

Abstract

The transport of 3H-GABA in Purkinje cells of rat cerebellum was studied by chemical, light microscopic, and electron microscopic techniques. 3H-GABA was applied to the exposed cerebellar surface in vivo. One hour later the animals were killed and the radioactive content of the cerebellar cortex and deep cerebellar nuclei examined. In unfixed tissue most of the label corresponded chromatographically with GABA, and in fixed tissue all was in a single ninhydrin-negative peak which corresponded chromatographically to an unidentified derivative formed by treating 3H-GABA with the fixing solution. Much more radioactivity appeared in the deep cerebellar nuclei than in the liver or the caudate-putamen. Light microscopic radioautographic sections of cerebellum showed significantly higher grain counts in the deep cerebellar nuclei as compared with the surrounding white matter. These findings are consistent with 3H-GABA moving to the deep nuclei by the process of axoplasmic flow but not by diffusion or transport via the blood stream. Electron microscopic radioautograms of the deep nuclei showed that 42% of the grains were in axons and 20% in nerve endings which showed by far the highest relative grain density (relative grain density = % grains/% area) at 3.39. Dendrites had 16% of the grains (relative grain density = 1.93), while glia had 15% of the grains (relative grain density = 0.98). The labelled boutons all made symmetrical synaptic contacts with dendrites and contained elongated pleomorphic vesicles.