Protective Effect of Intranasal Insulin Administration on Cognitive Functions and Neurogenesis in a Rat Model of Alzheimer\'s Disease

Background and Objective: Alzheimer's disease is the most common destructive brain disease which is associated with cognitive disorders. Considering the protective role of insulin in the functions of the nervous system, the present study was conducted to investigate the effect of intranasal insulin administration on cognitive disorders and neurogenesis in rats treated with streptozotocin (STZ). Methods: In this experimental study, 32 male Wistar rats were divided into 4 groups of 8: control, STZ, STZ + insulin and insulin. The model of Alzheimer's disease was induced by intraventricular injection of STZ (3 mg/kg; 3 μl in each ventricle). Two weeks after STZ injection, cognitive functions were evaluated using Elevated Plus Maze (EPM) and Passive Avoidance (PA) tests. Insulin treatment (2 IU daily; 10 μl in each nasal passage) was performed after STZ injection for 14 consecutive days. The change in the expression of genes involved in neurogenesis (Nestin, DCX and Ki67) in the hippocampus area was investigated by Real-time PCR technique. Findings: STZ caused longer animal stay in open arms in acquisition phase (64.5±5.24) and recall phase (60.25±5.55) compared to the control group (33±2.17 and 26.38±2.06) in the EPM test (p