Cognitive function and metabolic features in male Sprague-Dawley rats receiving high-fat and low-calorie diets

Abstract

Background: Obesity is a risk factor for cognitive disorders. However, it is still unknown whether low-calorie diet will improve cognitive function in obese patients.
 Aim: To evaluate cognitive function and metabolic features in male Sprague-Dawley rats receiving high-fat and low-calorie diets.
 Materials and methods: The work was carried out on Sprague Dawley male rats (n = 32), which were divided into 2 groups with 16 animals in each group: Control (normal / low-calorie diet) and Obesity (high-fat diet). In 90 days the rats of the Control group were transferred to a low-calorie diet, the rats of the Obesity group continued to receive high-fat diet. To assess motor activity and cognitive functions at the end of the study (180 days), following behavioral tests were conducted: "open field", "tapering beam", "elevated plus-maze" (EPM) and "passive avoidance reaction". During the study glucose tolerance test were performed: at baseline (GTT 1) and in 30 days (GTT 2).
 Results: Obesity group rats gained weight significantly faster than the control animals (547.69 11.32 g against 442.8 19.8 g at study end, p = 0.0001). GTT 2 showed normal carbohydrate metabolism in control group, postprandial hyperglycemia in obesity group. Testing in the open field showed that the rats of the obesity group moved more actively across the installation area than the control ones: the total distance covered was 9.352 0.932 m against 6.781 0.951 m, p = 0.046.
 The results of a tapering beam test showed that the number of hind limb extrusions in obese rats significantly exceeded this parameter in control group (33.7 3 vs. 15.7 2.7, p = 0.0001), test time in both groups did not differ.
 When testing in EPM, there was no significant difference in any of the key test parameters between the groups. However, the number of looking out from the closed arms in animals of the obesity group was significantly higher than in the control group (4.19 0.6 vs. 2.30 0.58, p = 0.044). When testing the reproduction of conditional reactions of passive avoidance it was shown that after day 1 of the pain stimulation application the latent period of transition to the dark compartment in the obesity group was significantly higher than that of the control group (180.0 0.0 vs. 128 86 21.45, p = 0.008). This indicates a better preservation of the memorial trail compared to the "control" rats. By the end of the study 30% of animals in the control group died.
 Conclusions: Rats on high-fat diet were more active, less anxious and showed better results in training tests comparing to animals on low-calorie diet. Adherence to low-calorie diet may be harmful for cognitive functions.