Figure 5.

Comparison of (1) the exponential decline in numbers of motoneurons that reinnervated TA muscle (motor unit number), (2) mean motor unit numbers after immediate, early, and late periods of chronic axotomy (•) (A, E), CP graft denervation (○) (B, D, F), and nerve stump and muscle denervation (•) (C, D, G), and (3) exponential increase in the numbers of muscle fibers reinnervated by each motoneuron, the innervations ratio (H). The progressive decline in regenerative success for all three experimental conditions was fitted by exponential regression lines. The progressive decline after prolonged axotomy (A) was slow (time constant of 323 d) relative to the declines after chronic CP graft (B) and TA muscle denervation (C) that were both rapid, the time constants of the exponential decline being the same (49 and 45 d). The smaller asymptotic value of 19 motor units after chronic TA muscle denervation compared with the asymptotic values of 42 motor units after chronic CP graft denervation (D) argues that the chronic muscle denervation is an important contributing factor, in addition to chronic denervation of Schwann cells in reducing the success of delayed nerve repair after injury.