Aim: In addition to learning and memory impairments, diabetes may also brings about neuronal loss in different regions of the brain specially hippocampus. In this line, the present study was conducted to investigate the effects of type I (T1D) and type II (T2D) diabetes on cognitive function and hippocampal neuronal density in rat. Methods: Three groups of male Wistar rats (N.=6) were regarded as control, T1D and T2D. T1D was induced by 60 mg/kg body weight of STZ injection and T2D by 10% fructose treatment through drinking water. Two months after the induction of both types of diabetes, learning abilities and memory retention of animals were measured using Morris Water Maze and shuttle box. All animals were perfused afterwards and their brains processed for stereological examination of hippocampal neuronal density. Results: In parallel to significant decrease in learning and memory scores, T1D showed a meaningful reduction in hippocampal neuronal density, when compared to control group. In T2D, the reductions of cognitive scores as well as hippocampal neuronal density were not significant, when compared to control and T1D. Conclusion: Although both types of diabetes led to neuronal loss and spatial learning and memory dysfunction, these abnormalities were more obvious in T1D, while they are probably age-related and duration-dependent in T2D.

Keywords