Transcriptional changes in rat α-motoneurons resulting from increased physical activity

Electrophysiological properties of lumbar α-motoneurons change after chronic increases and decreases in hindlimb neuromuscular activity. Although modeling of these changes suggests that motoneurons probably alter gene expression in these situations, there is no evidence that this is the case. In this study, we measured the content of several mRNAs in lumbar motoneurons, harvested using laser capture microdissection, from rats previously subjected to normal cage activity, voluntary wheel exercise for 16 weeks, and forced treadmill training for 7 days and 16 weeks. As a result of the prolonged daily treadmill training, but not the voluntary wheel training, significant increases occurred in muscle peroxisome proliferator-activated receptor gamma, coactivator 1 alpha (PGC-1α) mRNA, and in muscle PGC-1α and cytochrome oxidase proteins, in soleus and plantaris muscles. Significant changes in mRNA contents (decreases) were evident for the receptors 5-hydroxytryptamine (serotonin) receptor 1A (5HT1a), GABA A receptor, subunit alpha 2 (GABAAα2), and for the potassium conductance calcium-activated channel protein (SK2) in the motoneurons from 16-week-trained rats, and for glutamate receptor, metabotropic 1 (mGluR1) in the voluntary wheel-trained rats. Motoneurons from 16-week treadmill-trained rats also did not demonstrate the decreases in several mRNAs that were evident after 7 days of treadmill exercise, suggesting an adaptation of motoneurons to acute stress. The mRNA changes following prolonged daily treadmill training are consistent with a reduction in inhibitory influences onto motoneurons, and a transition toward motoneurons that innervate slower contracting muscle fibers. These results demonstrate that the previously reported physiological changes in motoneurons with altered activity are accompanied by changes in gene expression.