Lightfoot's interest in the issue drew him to work with strains of mice that had markedly different behaviors when given an exercise wheel. A "high-active" strain scored notably higher than other strains in speed, duration and distance achieved in running than other strains, including one that was labeled as "aggressively sedentary" because of its consistent avoidance of activity.
At first, Lightfoot suspected that the difference was due to genetic factors affecting the way energy is used by muscle tissue because early genetic studies of the strains indicated that variation was present in genes known to affect metabolism. However, studies the team conducted on muscle tissue in the different mice failed to show a genetic effect that could cause a difference in muscle performance.
"We have done some gene chips on muscle tissue and we don't see any differential expression between high-active and low-active animals in peripheral (muscle) tissue," Lightfoot said. "So the suggestion that by over-expressing a glucose transporter we can increase activity doesn't seem to be the explanatory factor."
Subsequent studies have led the team to suspect that genetic differences are having a profound affect on mouse activity levels by causing significant differences in their brains.
"More and more what we are seeing is differences in brain chemistry. We are really convinced now that the difference is in the brain," Lightfoot said. "There is a drive to be more active."
The current studies interbred active and inactive strains of mice to re-sort the genes. The resear
|Contact: James Hathaway|
University of North Carolina at Charlotte