Memory Loss, Anxiety Reduction in Middle-Aged Running Mice 

Running is shown by one study to increase memory, reduce anxiety, raise stability via increased brains levels of neurotrophic factor BDNF.  

Running has been shown by several studies to increase neurogenesis (proliferation of new neurons) in the brain, specifically the dentate gyrus in the hippocampus. A decrease in neurogenesis later in life has been linked with memory loss.  

A recent study looked at the affects of 6 months of running on neurogenesis and chemistry of brain sections as well as behaviors dependent on brain function (Running throughout Middle-Age Improves Memory function, Hippocampal Neurogenesis, and BDNF Levels in Female C57BI/6J Mice, 2012; Michael W. Marlatt, et al.).

The mice were tested for behavioral changes after one month and six months of voluntary running-wheel training. Many behavioral changes were significant only after six months of training. For example, the running mice were significantly better at the Morris water maze after six months of training, but not after one month of training. How does the water maze work?  Mice were placed in a water bath with a target. After finding the target they were placed back in the water bath at a later date. The mice were tracked with a video camera and the amount of time in the target quadrant was recorded. After six months of training the running mice showed significantly more preference for the target quadrant. This suggests that these middle aged running mice had a greater memory retention.

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Time spent in quadrants in the Morris water maze.  Only the 6 month running mice spent significantly more time in the target quadrant.  

To test for anxiety, mice were placed in an open field an observed. The ratio of time spent in the center of the field to the periphery of the wall was calculated.  Mice that spent more time in the center of the field would be expected to have less anxiety, while mice that spent time hiding along the wall would have more anxiety. The running mice were found to spend more time in the center of the field than their control counterparts at both one month and six months of voluntary exercise training. This supports previous studies showing that running reduces stress and anxiety.

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Falls on a rotarod after 15 seconds in running mice (dark grey) and resting mice (light grey).

The running mice were found to be stronger and better balanced. This was tested with a rotarod. Mice spent 15 seconds on the rotarod and the number of falls were recorded.  The running mice fell about a fifth as much as the control mice as the figure above demonstrates.  

The researchers then looked at brain sections of the hippocampus to explain the behavioral differences. BrdU (an agent that gets incorporated into the DNA of new nuclei) was used to look for new neurons. Running mice had significantly higher levels of BrdU in the dentate gyrus of the hippocampus. In addition, DCX, a neural marker, was found to be slightly higher after 6 months of voluntary exercise training.  Finally, neurotrophin factor BDNF was measured. BDNF aids in keeping neurons healthy. The running mice had significantly higher levels of BDNF.

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The dentate gyrus with DCX and DAPI immunochemistry.

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A Running mice showed increased levels of neurogenesis marker BrdU B BrdU co-localized with NeuN neural marker C DCX in D neurons D DCX in type C neurons

In conclusion, this study found that six months of voluntary running raised memory retention, decreased anxiety and increased stability in middle aged mice. The hippocampus was found to have increased levels of neurogenesis, BDNF and DCX.

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