Graft repair of the peroneal nerve restores histochemical profile after long-term reinnervation of the rat extensor digitorum longus muscle in contrast to end-to-end repair

Declining motor function is a prominent feature of ageing physiology. One reason for this is a reduction in plasticity that normally compensates for ongoing reorganization of motor units under physiological conditions. Previous work from our laboratory has shown that microsurgical repair of the transected peroneal nerve is followed by considerable changes in the histochemical profile of the reinnervated extensor digitorum longus (EDL) muscle and that these changes are dependent on both the time and the type of nerve repair. At 6 months postoperatively, a trend toward reversibility could be discerned. In the present work, we analysed the long-term reorganization of histochemical motor unit distribution patterns 15 months after performing either end-to-end repair or grafting of the peroneal nerve in 3-month-old rats. In addition, the EDL muscles of an age-matched control group (age 18 months) were analysed for age-dependent changes. We observed a loss of histochemical organization of motor units leading to an additional fibre type (SDH-INT) in the control group. Fifteen months after end-to-end repair, the histochemical profile showed a decrease in fibre type IIA and an increase in fibre type SDH-INT ( P < 0.05), indicating a profound histochemical disorganization of motor units. In contrast, nerve grafting largely restored the histochemical profile of reinnervated EDL muscles. Fibre type grouping was present after both types of nerve repair. These findings show that reorganization of the histochemical profile in reinnervated muscles is dependent on the time and type of nerve repair and is long lasting. In this study, grafting provided superior results compared with end-to-end repair. These long-term results after peripheral nerve repair are influenced by age-dependent changes. Accordingly, nerve repair reduces the normal functional plasticity of motor unit organization. This reduction is enhanced by increasing age.