The impact of the frequency of moderate exercise on memory and brain-derived neurotrophic factor signaling in young adult and middle-aged rats

The participation of the brain-derived neurotrophic factor (BDNF) in the benefits of physical exercise on cognitive functions has been widely investigated. Different from voluntary exercise, the effects of treadmill running on memory and BDNF are still controversial. Importantly, the impact of the frequency of physical exercise on memory remains still unknown. In this study, young adult and middle-aged rats were submitted to 8 weeks of treadmill running at moderate intensity and divided into 4 groups of frequency: 0, 1, 3 and 7 days/week. Aversive and recognition memory were assessed as well as the immunocontent of proBDNF, BDNF and tyrosine kinase receptor type B (TrkB) in the hippocampus. Frequencies did not modify memory in young adult animals. The frequency of 1 day/week increased proBDNF and BDNF. All frequencies decreased TrkB immunocontent. Middle-aged animals presented memory impairment along with increased BDNF and downregulation of TrkB receptor. The frequency of 1day/week reversed age-related recognition memory impairment, but worsened the performance in the inhibitory avoidance task. The other frequencies rescued aversive memory, but not recognition memory. None of frequencies altered the age-related increase in the BDNF. Seven days/week decreased proBDNF and there was a trend toward increase in the TrkB by the frequency of 1 day/week. These results support that the frequency and intensity of exercise have a profound impact on cognitive functions mainly in elderly. Thus, the effects of physical exercise on behavior and brain functions should take into account the frequency and intensity.