Abstract
Cell body sizes and oxidative enzyme activities of spinal motoneurons innervating the soleus muscle were determined in male rats ranging in postnatal age from 3 to 13 weeks. The mean cell body sizes of motoneurons increased from 3 to 7 weeks of age, while the mean oxidative enzyme activities of motoneurons decreased from 3 to 7 weeks of age. There were no changes in mean cell body size or oxidative enzyme activity of motoneurons from 7 to 13 weeks of age. These results indicate that motoneurons innervating the rat soleus muscle show the adult pattern of cell body size and oxidative enzyme activity at an earlier stage of postnatal growth, 7 weeks of age. Male rats were hindlimb-unloaded from postnatal day 4 to month 3. The rats were sacrificed immediately, 1, 2, and 3 months after hindlimb reloading. Numbers, cell body sizes, and oxidative enzyme activities of the soleus motoneurons were determined. A smaller mean cell body size of alpha motoneurons, but not gamma motoneurons, was observed after hindlimb unloading, but this was recovered 3 months after hindlimb reloading. The mean number or oxidative enzyme activity of gamma or alpha motoneurons did not change by hindlimb unloading. It is suggested that hindlimb unloading inhibits a growth-related increase in the cell body size of soleus alpha motoneurons and that the effects of hindlimb unloading on the cell body size of alpha motoneurons are reversible at an early postnatal stage. [Jpn J Physiol 54 Suppl:S55 (2004)]
