Experimental study of the functional reserve of median nerve in rats.

OBJECTIVE: To study the functional changes of median nerve after removing a certain bundle of it and to explore the functional reserve of median nerves. METHODS: 220 three-month old SD rats were randomly divided into experimental groups and sham groups. And the experimental group was further divided as 1/8 group, 1/4 group, 1/3 group, 1/2 group, and 2/3 group according to ratio of the resection portion, with 22 rats in each group. The section of the lowest level on median nerve trunks were exposed, and a certain portion of it were separated and resected in experimental group, while in sham groups, the nerve was only separated without resection. The general state of health of all rats were observed, and the α motor neurons in cornu anterior medullae spinalis were studied 1 week, 2 weeks and 2 months postoperatively. Neuro-electrophysiology and function of dominated muscles were studied 2 weeks, 2 months, 3 months, and 4 months postoperatively. RESULTS: All rats survived without infection and obvious ulcer. The number of the α motor neurons in cornuanterior medullae spinalis didn't change (P>0.05), and obvious superstructure changes were observed in early stage in 1/2 and 2/3 group, but restored after 2 months. There was no significant changes in latencies of motor neuron evoked potentials between experimental groups and sham group (P>0.05), however, there is significant difference if the 2 week group was compared with 2 month, 3 month and 4 month group (P<0.05). Moreover, there is also significant difference in terms of the wave amplitude of evoked potential of motor neurons, the maximum wave amplitude and the persistence time of its innervated muscle if the 2 week group was compared with those in 2 month, 3 month and 4 month group (P<0.05), and there is significant difference between different proportion resection groups (P<0.05). CONCLUSIONS: Median nerve has a certain amount of functional reserve, and the quantity of the functional reserve of median nerve without compromise is the 1/3 of the whole trunk.