The effect of long-term high-fat diet on hippocampal neurons ultrastructural and cognitive function in obese rats

Objective To investigate the effect of long-term high-fat diet on cognitive function and hippocampus neurons ultrastructure in obese rats. Methods Forty SD rats were randomly assigned to a high-fat diet (HFD) group and a common diet (CD) group.Meanwhile, HFD-induced obese rat model were established.The spatial learning and memory were measured by the Morris water maze, and the neurons ultrastructural changes in rat hippocampus CA1 region at the corresponding period were observed by transmission electron microscopy. Results The average weight of rats was 25%, 28%, and 22% higher in the HFD group than in the CD group at the 12, 16, and 20 weeks, respectively; the Lee's indexes were 6%, 4%, and 8% higher; the average swimming latency were 52%, 44%, and 40% longer; the average swimming distance were 85%, 45%, and 51% longer; the average swimming speed were 57%, 34%, and 18% higher; the duration of staying in the target quadrant were 32%, 54%, and 63% shorter; and the average times of crossing the plate-form were 30%, 34%, and 34% shorter, respectively (all P<0.001). In comparison of ultrastructure in hippocampus CA1 region of rats at corresponding time points, the amounts of degenerated and necrosis neurons, of the deformed and vacuolar mitochondria, and of the less rough endoplasmic reticulum were significantly more at 12, 16, and 20 weeks in the HFD group than in the CD group. Conclusions Long-term HFD-induced obesity damages the structure of neurons in the hippocampus, impairs spatial learning and memory function, and accelerates cognitive aging in rats. Key words: Cognition; Hippocampus; Dietary fats, unsaturated