Ingrowth of sensory axons into an end-to-side coapted nerve stump after donor nerve crush in the rat

Abstract

Target innervation through an end-to-side (ETS) nerve coaptation depends on axonal sprouting from the donor nerve. Terminal axonal sprouting in a partially denervated target tissue is more extensive from a crushed donor nerve than from an intact donor nerve. We hypothesized that axonal sprouting into an ETS coapted recipient nerve could be stimulated by crushing the donor nerve. Twenty-seven rats were randomised into 3 groups. In all, the distal stump of the transected peroneal nerve was sutured to the side of the sural nerve in place of the epineural window. The control group received no additional treatment. In the experimental groups, the sural donor nerve was crushed either 8 mm proximal (proximal crush group) or 8 mm distal to the coaptation site (distal crush group). Sixteen weeks after the surgery, histomorphometric analysis of the recipient peroneal nerve stump 4 mm distal to the coaptation site was performed. The number of myelinated axons in the recipient peroneal nerve stump was 758 +/- 247 in the control group, 503 +/- 246 in the distal crush group and 211 +/- 96 in the proximal crush group. The differences between the groups were statistically significant (p < 0.05). The majority of myelinated axons were thin myelinated axons and the frequency distribution of their cross-sectional areas was similar in all groups. Contrary to our expectations, a significantly lower number of myelinated axons were present in recipient nerves in the proximal and distal crush groups than in the control group. This suggests that sensory axon ingrowth into an ETS coapted nerve cannot be enhanced by crushing the donor nerve.