ABSTRACT: The chronic level of neuromuscular activity, that is, activation
and loading, strongly influences the morphological, metabolic, phenotypic,
and physiological properties of skeletal muscles. The effects on the innervating
motoneurons, however, are less established. We determined and
compared the effects of 30 days of decreased activity (induced by a complete
mid-thoracic spinal cord transection, ST) or near inactivity (induced by
spinal cord isolation, SI) on the soma size and succinate dehydrogenase
(SDH) activity of motoneurons innervating a predominantly slow ankle extensor
(soleus) and a predominantly fast ankle flexor (tibialis anterior) muscle
of adult rats. Soleus and tibialis anterior motoneuron pools were labeled
retrogradely using nuclear yellow. The - and -motoneurons were classified
based on soma size. Mean number of labeled motoneurons, and mean
soma size and SDH activity for both - and -motoneurons were similar in
control, ST, and SI rats.......
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