Exercise improves visual deficits tested by visual evoked potentials in streptozotocin-induced diabetic rats

Visual evoked potentials (VEP) can be used as an objective non-invasive method to study the electrical activity of the visual system. Latency and amplitude measurements of VEP demonstrated that diabetes mellitus has been associated with increases in the latencies whereas the amplitude measurements revealed contradictory results. Although physical exercise has been reported to reduce the complications of diabetes mellitus, the effect of exercise on the visual system remains unknown. We investigated the effects of long-term moderate physical exercise on VEP in streptozotocin (STZ)-diabetic rats. We also measured brain thiobarbituric acid-reactive substances (TBARS) to explore the possible contribution of lipid peroxidation on the visual system. Animals were divided into four groups: control (C), control exercise (CE), diabetic (D) and diabetic exercise (DE) groups. Diabetes was induced by a single intraperitoneal injection of STZ (60 mg/kg). Three days after the confirmation of diabetes, DE and CE groups were trained by running on a motor-driven treadmill with a progressive eight-week programme. The animals began running at 10 m/min, 0 degrees slope, 10 min/day and reached a level of 28 m/min, 6 degrees slope, 60 min/day by week 8. TBARS were elevated and VEP latencies were delayed in diabetic rats, indicating diabetes-induced defects in the optic pathway. These prolonged latencies were restored by exercise training. VEP amplitudes of the DE group were found unaltered with the exception of a decrement in P(2)N(2) which represents an early component of VEP, suggesting that exercise improves visual system defects in diabetic animals at different levels of the optic pathway.