Analysis and treatment of visual pathway disturbance in diabetes mellitus

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Streptozotocin (STZ) was administrated to rats to induce diabetes. Loss of body weight and significantly elevated level of serum glucose were observed. After treatment of STZ,the GABA content in retina decreased compared to that of control animals. The glutamic acid decarboxylase (GAD) activity and the GABA transaminase (GABA-T) activity of diabetic group was decreased. The GABA content in the superior colluiculus (SC) and the cerebral cortex decreased compared to the control level. The GAD and GABA-T activity of SC and conrtex in DM animals also reduced. The GAD activity of diabetic group was markedly decreased. Decreases of GAB content were dependent on the inhibition of the GAD activity.Structural impairments of optic nerve fibers in STZ-induced diabetic rat were investigated using morphometric analysis. Electron microscopic morphometry showed significantly smaller cross-sectional size of axons and myelin but no change of myelinated fiber number. Reductions of myelinated fiber size was especially remarkable in the larger fibers. ARI treatment improved structural abnormalities without any changes in body weight and blood glucose level. These findings suggest that structural impairment may contribute to the abnormalities of psychophysical and electrophysiological measurement detected in diabetes. Moreover, ARI treatment, which can improve the polyol metabolism, may have a beneficial effect on optic nerve impairment in diabetes.