Distribution of Three Enzymes of γ‐Aminobutyric Acid Metabolism in Monkey Retina

Abstract

The distributions of glutamate decarboxylase (EC 4.1.1.15), gamma-aminobutyric acid transaminase (EC 2.6.1.19), and succinate semialdehyde dehydrogenase (EC 1.2.1.24) were determined in monkey retina. The decarboxylase was almost restricted to the inner plexiform layer. The transaminase was also highest in this layer, but activities were 40% as high in the adjacent third of the inner nuclear layer and in the ganglion cell and fiber layers. Succinate semialdehyde dehydrogenase was distributed very differently. Although it also showed a peak of activity in the inner plexiform layer, there was a second equal peak in the photoreceptor inner segment layer and a smaller peak in the outer plexiform layer, regions where both gamma-aminobutyric acid transaminase and glutamate decarboxylase were essentially absent.

Distribution of Glycine, γ‐Aminobutyric Acid, Glutamate Decarboxylase, and γ‐Aminobutyric Acid Transaminase in Rabbit and Mudpuppy Retinas

“…Part of the supporting evidence for GABAergic and glycinergic retinal neurons has been the finding of marked differences in the GABA/glycine content of different retinal layers (Kuriyama et al, 1968;Graham et al, 1970;Graham, 1972; Kuriyama and Kimura, 1976;Berger et al, 19776;Kennedy et al, 1977). In addition, peak retinal GABA levels have been shown to coincide with peak levels of the enzymes that synthesize and degrade GABA, for example, as reported in a companion paper to this study (Pusateri et al, 1984). The present study has pursued these lines of evidence by measuring the intraretinal distributions of GABA, glycine, glutamate decarboxylase (GAD; EC 4.1.1.15), and GABA transaminase (GABA-T; EC 2.6.1.19) in rabbit and mudpuppy (Necturus maculosus).…”

“…In support of the likelihood of GABA-and glycine-releasing amacrine cells, it was earlier found, in monkey retina, that peak GABA/glycine levels occur in the inner plexiform layer (Berger et al, 197717). Peak levels of GAD and GABA-T, the enzymes of GABA synthesis and inactivation, also occur in the inner plexiform layer of monkey retina (Pusateri et al, 1984). In the present study we add strong evidence for the existence of a subclass of GABA-releasing amacrine cells in mudpuppy retina by measuring the GABA content of individual putative amacrine cell somas in that species.…”

A Fluorescence-Coupled Assay for Gamma Aminobutyric Acid (GABA) Reveals Metabolic Stress-Induced Modulation of GABA Content in Neuroendocrine Cancer

“…The method was modified from previous protocols [26], [44]. The assay buffer contained 100 mM Tris pH 8.8, 50 mM potassium chloride, 1 mM dithiothreitol, 2.5 mM nicotinamide adenine dinucleotide (NAD), 1.25 mM SSAL, and 0.02% bovine serum albumin.…”

Changes of GABA Metabolic Enzymes in Acute Retinal Ischemia

“…In the retina, glutamate was converted to GABA by GAD. Others have reported GAD localized in GCL, IPL and INL (Pusateri et al, 1984 ;Tyler, Fite and Devries, 1995). It is well-known that GAD activity does not change during ischemia (Miller, Walters and Martin, 1977 ;Perry et al, 1981).…”