Both BDNF and its receptor (trkB) declines in the brain as animals age and this reduction is correlated with the reduction of new neurons (neurogenesis) in the adult brain. There is a precarious drop from age 3 month to 13 months old (middle age) where things start looking like a flat line out to 24 months. For example 13 month old animals only have 3-5% as many new immature neurons (neurogenesis) in the hippocampus (important for memory and possibly general mood) as compared to 3 month old animals (which would represent young teenagers in humans). The question the researchers asked was can 5 weeks of treadmill running reverse this downward trend in middle age animals?
The actual exercise paradigm start out with 20 minutes the first day (at 10 m/min) then 10 minutes of duration added every day until they reach 60 minutes of running per day (they are running at around 70% of their V02 max). This is interesting as most rodent running neurogenesis studies put in a running wheel and the animals run a great deal (up to 10 km per day – and think of how small they are) where in this study they restricted running to a level that is more reasonable for humans – one hour per day.
5 weeks of treadmill running increased the levels of both BDNF and trkB. What is interesting is that this short exercise period produced levels of these two proteins in 13.5 month old animals (started running at 12 months of age after a one week habituation to the treadmill – they usually live 24-30 months – hence middle age animals) to levels above sedentary younger animals (9.5 month old).
The number of neural stem cells (NSC), but also the number of immature and more mature neurons were increased with running in 13.5 month old animals – to the point it was slightly above the 9.5 month old sedentary animals (but still quite a bit below running 9.5 month old animals) . Additionally, the dendritic branch pattern of these new neurons were increased to a more mature neuronal state (their measurement for more mature neurons).
Take home message:
Most of you reading this are not young teenagers (far as I know) so your rate of neurogenesis is drastically decreased and hence you should be out there exercising. According to this paper an hour a day at roughly 70% of your Vo2 max which equates to approximately 80 % of your max heart rate.