Figure 6.
Effects of chronic motoneuron axotomy (B–D), nerve graft denervation (E–G), and distal nerve and muscle denervation (H–J) on the frequency distributions of motor unit tetanic force in the reinnervated TA muscle after nerve repair and axon regeneration. Axotomized TIB motoneurons regenerated axons via an autologous 15 mm CP nerve graft and distal CP nerve stump to reinnervate denervated TA muscle after either immediate or delayed TIBp–CPg–CPd nerve surgery that chronically axotomized TIB motoneurons, denervated the CP nerve graft, or denervated the TA muscle (A). Frequency distributions of reinnervated TA muscles are plotted after immediate nerve repair (A), early reinnervation (<50 d after chronic axotomy) (B, E, H), and late reinnervation (>300 d of chronic axotomy) (C, F, I) and in the comparative cumulative frequency distributions (D, G, J). Note that the frequency and cumulative distributions are plotted on semilogarithmic scales because of the skewed distributions of motor unit forces typical of normal skeletal muscles. The frequency distributions shifted significantly to the right to larger values. **p < 0.01. The mean value (±SE) after immediate TIBp–CPg–CPd nerve surgery was 25.6 ± 1.8 mN (A) and after delayed surgery 31.2 ± 2.7 mN (B) and 44.9 ± 2.0 mN (C) for chronic TIB axotomy; 44.1 ± 3.2 mN (E) and 38.7 ± 1.5 mN (F) after chronic CP graft denervation; and 36.8 + 2.4 mN (H) and 37.2 ± 2.7 mN (I) after for chronic distal nerve stump and TA muscle denervation. The corresponding cumulative frequency histograms are shown in D, G, and J where significant (Kolmogorov–Smirnov test) and progressive rightward shifts in the cumulative force distributions to the right were seen after chronic axotomy (D) and a significant shift to the right was also seen within 50 d after chronic CP nerve graft denervation (G) and TA muscle denervation (J). There was no additional significant increase in motor unit forces (and hence no additional rightward shift) after late reinnervation.