Mice who keep busy playing with toys also keep their brains and bodies active, more importantly, they also have lower levels of the peptides and brain plaques associated with Alzheimer's disease, compared to mice raised in environments not "enriched" with chew toys, running wheels,and tunnels, according to a new study in the 11 March issue of the journal Cell. The levels of b-amyloid peptides, which clump together to form the brain "tangles" or plaques that are toxic to nerve cells in Alzheimer's disease, were significantly lower in the enriched mice.
The mice who played may have been better equipped than their less-stimulated counterparts to sweep these peptides out of the brain, according to the researchers' analysis of gene and enzyme expression in the animals, says Sangram Sisodia, of the University of Chicago, and colleagues, and reverts to the old idea of use it or lose it, that using your brain keeps it more active and is more common sense than science; but previously it was not appreciated that it might affect the pathology that is characteristic of Alzheimer's disease.
The experiments in mice suggest that the enriched environment acts as a protective factor, keeping peptide levels low before they can aggregate and cause problems, rather than a therapeutic factor that dissolves plaques that have already formed, Sisodia says. The researchers are also discovering interesting clues that an active body, as well as an active brain, might be a key factor in reaping the benefits of an enriched environment.
The most physically active of the mice in the elaborately furnished cages had the most dramatic reductions in amyloid peptides and deposits. At least among this small group of mouse workout devotees, "exercise appears to play a significant role in modulating amyloid deposition," Sisodia and colleagues write. More experiments with larger numbers of animals are needed to determine exactly how enriched environments benefit mice, whether through increased physical activity, a boost in visual, social, and spatial stimuli that awaken the brain, or some combination of all of these factors. Sisodia says exercise, along with any kind of mental activity from reading to doing the crossword puzzle, are probably the equivalent of chew toys and running wheels for humans. "It's all very important in keeping the mind active and potentially staving off effects of old age." The b-amyloid peptides found in Alzheimer's are snippets of a larger protein called amyloid precursor protein.