Most dorsal root ganglion neurons of the adult rat survive nerve crush injury

Severe crush of the rat sciatic nerve does not result in any significant cell death among motor neurons (Swett et al., 1991a). The present study reports on the survival of the dorsal root ganglion (DRG) neurons in the same experiments. From 15 to 187 days after crush of the left sciatic nerve, the common peroneal or sural nerve was cut and labeled distal to the injury with a mixture of horseradish peroxidase (HRP) and its wheatgerm agglutinin conjugate (WGA:HRP). In other cases, the crush injury was made far enough distally on a peroneal or sural branch to permit labeling several millimeters proximal to the injury. The procedures for reconstructing the regenerated DRG neuron populations were identical to those used in an earlier study describing the normal sciatic DRG neuron populations in the rat (Swett et al., 1991b). The normal peroneal nerve contains 2699 +/- 557 DRG neurons. When the peroneal nerve was crushed near its point of origin from the sciatic and labeled 10 mm distal to the injury, 2186 +/- 163 DRG neurons were counted, suggesting a decrease of about 19% (p < 0.01). However, when the entire sciatic nerve was crushed, distal labeling of the peroneal nerve revealed a mean number of 2578 +/- 291 DRG neurons, an insignificant reduction (p > 0.2). When the peroneal nerve was labeled proximal to a peroneal crush site, a similar number of DRG neurons (2563 +/- 412) was counted. Results following sural nerve crush were similar. The sural nerve normally contains 1675 +/- 316 DRG neurons. When the nerve was labeled distal to the injury, 1558 +/- 64 DRG neurons were counted - a number almost identical to that found (1529 +/- 240) when this nerve was labeled proximal to the injury. The results demonstrate that within 6 months of severe crush injury of the rat sciatic nerve, the vast majority of DRG neurons survive and regenerate new axons distally beyond the injury site, presumably to reinnervate their original targets.