Innervation patterns in the cat tibialis anterior six months after self-reinnervation

The spatial distribution of fibers belonging to a single motor unit was analyzed in 10 motor units from the tibialis anterior of the cat 6 months after denervation and self-reinnervation of the anterior (superficial) compartment of the muscle. After self-reinnervation, the distribution patterns of the fibers in the fast motor units were significantly different than control, whereas the fiber distribution in the slow unit was similar to control. Reinnervated fast units had a significant increase in the number of adjacencies among motor unit fibers, and there were often distinct "clusters or groups" of fibers distributed within the motor unit territory. Clustering or grouping of fibers was evident within the motor unit, even though fiber type grouping was not evident within the muscle. The differences in distribution patterns between control and reinnervated units may be related to variations in the branching pattern of axons during reinnervation compared to the process that occurs during development.