The effect of aerobic exercise along with enriched environment on spatial memory and brain-derived neurotrophic factor in the Hippocampal tissue of Elderly female Wistar rats with Alzheimer's disease

Abstract:
Introduction: The effect of physical activity and enriched environment on some cognitive mechanisms in Alzheimer's disease (AD) is not yet well understood. Therefore, this study aimed to investigate the effect of aerobic training along with enriched environment on spatial memory and brain-derived neurotrophic factor in the Hippocampal tissue of elderly female Wistar rats with Alzheimer's disease. Methods: In this experimental study, 30 female Wistar rats with twenty-one-month-old and average weight of 260±20 grams were used and divided into 6 groups: control-healthy, Alzheimer's, sham group, Alzheimer's + aerobic exercise (treadmill), Alzheimer's + enriched environment, Alzheimer's + enriched environment + aerobic exercise (treadmill). rats in the first and second week trained two 15-minute sessions with 5-minute passive rest at a speed of 10 m/min, In the third week, three sessions at a speed of 15 meters per minute with a 5-minute break, and in the fourth week, four sessions at a speed of 15 meters per second with a 5-minute break per day. In the enriched environment group, the animals were kept in a plexiglass material larger than the standard cage (60x50x70 cm3). In these cages, devices such as ladders, hollow pipes, wooden blocks and plastic toys were placed. In Alzheimer's groups, rats were anesthetized by intraperitoneal injection of ketamine (80 mg/kg) and xylazine (20 mg/kg). Then, Alzheimer's Aβ was induced by intracerebroventricular injections (10μg/rat). In a pilot study in order to evaluate the spatial memory of rats, one week after beta-amyloid injection, all rats were divided into Alzheimer's and control groups. Rats were trained in the maze for four days and the mean percentage permanence in the platform area is reported.The results of the independent t test showed that there is a significant difference between the control group and Alzheimer's group (P=0.0152). Therefore, one week after the intrahippocampal injection of beta-amyloid, the spatial memory in rats is impaired.

Spatial memory was measured by Morris water maze, BDNF and Trk-B by western blot. One-way analysis of variance with Tukey's post hoc test (P<0.05) was used to analyze the data. Results: The results of the independent t-test in order to determine the memory level, showed a significant difference (P=0.0152). The results showed that BDNF (P>0.0001), Trk-B receptor (P>0.0001) and spatial memory (P=0.0034) variables were significant. The BDNF increased in all groups and it was significant except control-sham (P=0.27), Alzheimer's-Aerobic Alzheimer's (P=0.20) groups. Trk-B variable increased. except control-sham (P=0.22), aerobic Alzheimer's-Alzheimer's enriched environment (P=0.32) was significant in all groups. And memory variable only in Alzheimer's-control groups (P=0.02), And Alzheimer's-Alzheimer's enriched environment aerobic training (P<0.001), were significant. Conclusion: Based on the findings, it can be concluded that aerobic exercise and enriched environment can be effective on the spatial memory of elderly Alzheimer's rats through the increase of notrophic factors
Key words: aerobic exercise enriched environment, Alzheimer's, memory, BDNF, Elderly female Wistar rats.