<Originals>Higher c-fos Gene Expression in Alpha Motoneurons of Slow-twitch Muscle than those of Fast-twitch Muscle in Freely Moving Rats

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We have proposed the possible usefulness of a quantification of c-fos gene expression levels in spinal alpha motoneurons as an indicator of activity levels of spinal alpha motoneurons in locomotive rats. Here we further examined whether the method could be applied in freely moving rats. The motor pools of the soleus (SOL) and plantaris muscles (PL), mainly composed of slow-and fast-twitch fibers, respectively, were used because of their different muscular activities during free movement, with higher activity seen in the SOL than in the PL. It can thus be hypothesized that the c-fos expression level in the alpha motoneurons would be higher in the motor pool of the SOL than that of the PL. We first labeled motoneurons with a retrograde tracer, Nuclear Yellow (NY), and then quantified the c-fos mRNA expression level in the NY-labeled alpha motoneurons by means of in situ hybridization. The average c-fos expression levels in the alpha motoneurons were higher in the motor pool of the SOL than that of the PL. These results support the hypothesis that the c-fos expression in alpha motoneurons is higher in the motor pool of more active muscle than that of less active muscle. Therefore these results, together with previous findings, suggest that c-fos expression levels in alpha motoneurons are associated with corresponding muscle activity.
日本運動生理学会の論文