Effects of exercise on retinal and cognitive function in Type II diabetic rats

Abstract

Purpose : Diabetes mellitus affects nearly 10% of all Americans and its prevalence is predicted to rise 35% by 2025 (CDC). Diabetic retinopathy is the leading cause of blindness in working adults. Previously, we showed that exercise reduced retinal and cognitive dysfunction in Type I diabetic animals. Because 90% of diabetic patients have Type II diabetes, in our current study we investigated exercise as a potential protective factor against retinal and cognitive deficits in the Type II Goto-Kakizaki (GK) rat.

Methods : GK rats (n=20) and non-diabetic Wistar rats (n=12) were randomly placed in cages attached to either unlocked (active) or locked (inactive) running wheels at 3 wks of age. Assessments were conducted at 2 and 4 mo. Glucose tolerance tests were performed to confirm hyperglycemia and to monitor glucose tolerance changes. Electroretinograms were performed to evaluate retinal function. Y-maze was used to assess cognitive function and exploratory behavior. Rats were euthanized at 4 mo and retinas, brains, and serum were harvested for analysis.

Results : Active GK rats showed significantly improved glucose tolerance at 2 mo compared to inactive GK rats (p<0.001), but this improvement was not significant at 4 mo. Both GK groups demonstrated increases in a-wave, b-wave, flicker, and oscillatory potential amplitudes compared to controls. While the GK inactive group was significantly different from controls at both 2 and 4 mo, the GK active group was not significantly different from controls at 2 mo (Figure). Y-maze analysis at 2 mo showed no significant difference in spatial alternation, but exploratory behavior of active animals in each group was significantly lower than that of the inactive groups (p<0.05). No significant difference in spatial alternation or exploratory behavior was present at 4 mo, despite a trend for reduced deficits in active animals (Figure). Blood serum ELISA showed lower insulin levels in active Wistar rats.

Conclusions : Exercise improved glucose tolerance in GK rats at 2 mo and reduced serum insulin in Wistar rats. Active GK rats demonstrated improved retinal function at 2 mo but not at 4 mo. All active animals showed decreased exploratory behavior. A trend for improved cognitive function was evident in active GK rats. Based on these findings, exercise may provide a protective effect against retinal and cognitive deficits characteristic of Type II diabetes.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.