Changes in GABA metabolism in streptozotocin-induced diabetic rat retinas

Accumulation of gamma-aminobutyric acid in diabetic rat retinal Müller cells evidenced by electron microscopic immunocytochemistry

PURPOSE

To evaluate possible changes in the distribution of gamma-aminobutyric acid (GABA) in diabetic rat retinas.

METHODS

GABA distributions in the normal control and diabetic rat retinas were determined by a quantitative immunogold electron microscopic immunocytochemistry with anti-GABA antibody. GABA immunoreactivities (GABA-IR) in the retinas were visualized as bound gold colloidal particles in electron microscopy, and the average densities were calculated in each layer or in each kind of cells. The amounts of GABA-IR were statistically compared between normal control and diabetic rat retinas.

RESULTS

In the normal control rat retinas, the amounts of GABA-IR was most abundant in the inner portion of the inner nuclear layer, followed by the inner plexiform layer. GABA-IR in amacrine cells ranged from the background level to the highest throughout the retina. Although the distribution pattern of GABA-IR in the diabetic rat retinas was similar to that of the normal control, GABA-IR increased significantly in the inner segment, the outer nuclear layer, and the outer plexiform layer (P < 0.05, by the analysis of variance), and in Müller cells (P < 0.001, by Mann-Whitney's U-test) of the diabetic rat retinas. However, pathologic accumulation of GABA-IR was not demonstrated in amacrine cells of the diabetic rat retinas.

CONCLUSIONS

These results supported the accumulation of GABA in diabetic rat retinal Müller cells evidenced by light microscopic immunocytochemistry previously. It was suggested that GABA accumulation represents one of the functional deterioration of Müller cells in diabetic rat retinas.