A high fructose diet impairs spatial memory in male rats

Abstract

Over the past three decades there has been a substantial increase in the amount of fructose consumed by North Americans. Recent evidence from rodents indicates that hippocampal insulin signaling facilitates memory and excessive fructose consumption produces hippocampal insulin resistance. Based on this evidence, the present study tested the hypothesis that a high fructose diet would impair hippocampal-dependent memory. Adult male Sprague-Dawley rats (postnatal day 61) were fed either a control (0% fructose) or high fructose diet (60% of calories). Food intake and body mass were measured regularly. After 19 weeks, the rats were given 3 days of training (8 trials/day) in a spatial version of the water maze task, and retention performance was probed 48 h later. The high fructose diet did not affect acquisition of the task, but did impair performance on the retention test. Specifically, rats fed a high fructose diet displayed significantly longer latencies to reach the area where the platform had been located, made significantly fewer approaches to that area, and spent significantly less time in the target quadrant than did control diet rats. There was no difference in swim speed between the two groups. The retention deficits correlated significantly with fructose-induced elevations of plasma triglyceride concentrations. Consequently, the impaired spatial water maze retention performance seen with the high fructose diet may have been attributable, at least in part, to fructose-induced increases in plasma triglycerides.

Figure 1

Mean (+/-) SEM (a) kilocalories of food consumed per day and (b) percent change in body mass of rats fed a control or high fructose (60% of calories) diet for 138 days (*p < 0.05 vs. control rats).

Figure 2

The effects of eating a control or high fructose (60%) diet for 138 days on the mean (+/-) SEM latency to reach the platform during spatial water maze training.

Figure 3

The effects of eating a control or high fructose (60%) diet for 138 days on the mean (+/-) SEM (a) latency to reach the target, (b) number of target approaches, (c) amount of time spent in the target quadrant and (d) swimming speed during the spatial water maze retention test (*p < 0.05 vs. control rats).

Figure 4

Mean (+/-) SEM (a) liver mass, (b) plasma TG concentrations, (c) plasma glucose concentrations, (d) plasma leptin concentrations, (e) plasma insulin concentrations and (f) plasma FFA concentrations of rats fed a control or high fructose (60%) diet for 138 days (*p < 0.05 vs. control rats).

Figure 5

Scatterplots illustrating the association between (a) postmortem plasma TG concentrations and latency to reach the target and (b) the number of target approaches and (c) postmortem liver mass and the number of target approaches during spatial water maze retention (*p < 0.05 vs. control rats).