Open field mirror test as a tool for the assessment of visual functions in rats with streptozotocin-induced diabetes

Abstract

To evaluate the use of mirror test in an open field arena as a visual function assessment tool in a rodent model of diabetes. Male Sprague-Dawley rats were divided into diabetic rats, that received intraperitoneal streptozotocin (55 mg/kg body weight) for induction of diabetes, and control rats that similarly received citrate buffer. Rats with a blood glucose level of more than 20 mmol/L were considered diabetic. Blood glucose was monitored weekly throughout the experimental period. General behavioural assessment of the rats was done at week 12 post-induction using open field arena, followed by visual-behavioural assessment with mirror and reversed mirror added in the arena. Subsequently, rats were euthanised and subjected to haematoxylin and eosin staining (H&E) staining to assess changes in retinal morphology. In the open field test, diabetic rats showed a lesser number of zone crossings (3.73-fold, p<0.001), total distance travelled (2.02-fold, p<0.001), number of rearing episodes (2.22-fold, p<0.001) and number of grooming episodes (4.33-fold, p<0.01) but a greater number of freezing episodes (2.47-fold, p<0.001) and number of the faecal pellet (4.17-fold, p<0.01) compared to control rats. Control rats spent more time with higher zone entries toward mirrored than non-mirrored and reversed mirror zones (p<0.05 and p<0.01 respectively), whereas diabetic rats showed no preference for zones.  Normal rats also showed higher freezing episodes within the mirrored zone compared to diabetic rats (2.00-fold, p<0.05). The retinal morphometry showed significant thinning of various retinal layers in the diabetic group compared to control rats. Visual behavioural activities of diabetic rats in an open field arena with the presence of a mirror could detect the presence of visual loss. Changes in visual functions positively correlated with changes in retinal morphology. Therefore, an open field mirror test could be used as an alternative for assessing visual function in the rodent model of diabetes.