Elevated Epo levels motivates exercise

Elevated levels of erythropoietin motivates mice to exercise, according to this article.

... raising the levels of the hormone erythropoietin (Epo) in the brains of mice resulted in the rodents being more motivated to exercise. The discovery provides the possibility of developing a pill that can motivate people to want to exercise. 

The study, carried out by Max Gassmann, D.V.M. and colleagues from the Institute of Veterinary Physiology, Vetsuisse-Faculty and Zurich Center for Integrative Human Physiology at the University of Zurich in Switzerland, involved three groups of mice. One group received no treatment, the second was injected with human Epo, and the third was genetically modified to produce human Epo in the brain. 

The study showed that the second and third groups showed significantly higher running performance compared to the first group that had received no treatment...