Effects of regular intermittent exercise on cognitive functions and İGF-1 levels during adolescent period in rats

It is known that exercise has positive effects on cognitive functions. In humans and animals regular aerobic exercise reduces anxiety via many neurotrophic factors and enhances learning and memory with increasing neurogenesis in the brain. Insuline like growth factor-1 is an important neruotrophic factor that mediates effects of exercise on the brain. Although it is known that IGF-1 dependent effects of exercise on adult brain, there is limited information in literature about the effects of exercise in developing adolescent brain. Present study examined the IGF-1 dependent effects of regular intermittent exercise on cognitive fuctions, behaviour and neurogenesis in hippocampal and prefrontal cortex region during adolescent period in rats. Wistar Albino male and female rats at 28 days of age were used. The animals divided into 5 groups: control group, 5 days/week (15 min x 3/day) intermittent exercise group, 3 days/week (15min x3/day) intermittent exercise group, 5 days/week (45 min/day) continuous exercise group, and 3 days/week (45 min/day) continuous exercise group. Rats in exercise groups were placed on a motor driven treadmill and they ran at a speed of 10 m/ min continuously (45 min/day) and intermittently (15 min x 3/day) for 6 weeks. Two days after the exercise period rats were subjected to behavioural tests (open field and elevated plus maze) and five days of learning-memory test (Morris water maze). Last day of the Morris water maze test rats were sacrified under low ether anesthesia. Blood samples were taken intraventricully to determine IGF-1 and corticosterone levels. Brain tissue is removed to assess tissue IGF-1 levels and neural cell proliferation. All data from these result were analyzed by using one-way ANOVA and post hoc Bonferroni tests in SPSS statistical analyse programme. 4 Present study showed that intermittent exercise decreased serum corticosteron levels and reduced anxiety leves assessed in open field and elevated plus maze test when compared to other grups. Intermittent exercise groups (15 min x 3/day; both 5 days/week and 3 days/ week) showed significantly better learning memory performance in Morris water maze task when compared to continuous exercise (45 min/day; 3 day/week) group and control group. Hippocampal and prefrontal cortex IGF-1 levels in intermittent (15 min x 3/day; 3 days/ week) exercise group were found significantly higher than all other groups. In adition prefrontal cortex IGF-1 levels in continuous exercise group were significantly higher than all other groups. We found that serum IGF-1 levels were significantly higher in continuous exercise (45 min/day; 5 days/week) group and that liver IGF-1 levels were significantly lower in intermittent exercise group (15 min/day; 5 days/ week) than all other groups. In this study brain tissue results showed that the number of hippocampal CA1 and prefrontal cortex neurons and IGF immunreactivity were significantly higher in intermittent exercise (15 min/day; 5 days/ week) group when compared to control group. In addition, according to the results of apopitosis that account of TUNEL positive cells, intermittent exercise groups (15 min/day; both 3 days/week and 5 days/week) showed significantly lower TUNEL positive cell number when compared to control group. As a result, this study suggests that intermittent exercise (15 min x 3/day) reduces anxiety and serum corticosterone levels; increases brain hippocampal and prefrontal cortex IGF-1 levels, induces neurogenesis and enhances learning memory performance in adolescent rats. Although there was no increase in serum IGF-1 and liver tissue IGF-1 levels in intermittent exercise groups, brain IGF-1 levels were increased. This increase in brain tissues may result from an increase in local brain IGF-1 production. Local IGF-1 increase in brain associated with intermittent exercise and induced neurogenesis may effect the learning memory performance in adolescent rats. Keywords: Intermittent exercise, treadmill running, adolescent, hippocampus, prefrontal cortex, learning memory, neurogenesis