Relationship between soma diameter and oxidative enzyme activity of alpha-motoneurons

In order to determine whether there is a relationship between soma diameter and oxidative enzyme activity of alpha-motoneurons, we investigated the alpha-motoneurons innervating the different portions within a rat gluteus medius muscle. Two fluorescent neuronal tracers, Nuclear yellow and Fast blue, were used for labeling motoneurons innervating the deep (predominance of oxidative fibers) and superficial (predominance of non-oxidative fibers) portions of the muscle. An inverse relationship between soma diameter and oxidative enzyme activity was not seen in the motoneuron pool innervating either the deep or superficial portions. When the two portions were taken together, however, the inverse relationship was seen. The inverse relationship seemed to be demonstrated in a motoneuron pool which intermingled motoneurons innervating oxidative fibers and motoneurons innervating non-oxidative fibers. These results suggest that the oxidative enzyme activity of alpha-motoneurons is not correlated strictly with their soma size. We consider that the oxidative enzyme activity of alpha-motoneurons is correlated with oxidative enzyme activity of the muscle unit.