[Experimental study on the functional reserve of ulnar nerve in rats]

To study the functional change of nerve trunk after removing the partial bundles of ulnar nerve, to propose the concept of functional reserve of peripheral nerves and to investigate the functional reserve quantity of peripheral nerves.

Two hundred and twenty SD rats (male or female), aging 3 months and weighing 300-350 g, were randomized into the experimental group and the control group (n=110 per group). And the experimental group was subdivided into group 1/8, group 1/4, group 1/3, group 1/2 and group 2/3 according to the resection portion (n=22 per group). In the experimental group, the section of the lowest level on ulnar nerve trunks was exposed, and a certain portion of its bundles was separated and cut, while in the control group the bundles were only separated without resection. The general condition of all rats was observed, and the motoneurons in cornu anterius medullae spinalis were detected at 1 week, 2 weeks and 2 months after operation. The neuro-electrophysiology and the function of dominated muscles were detected at 2 weeks, 2 months, 3 months, and 4 months after operation.

All the rats survived without infection and obvious ulcer in the limbs. The number of motoneurons in cornu anterius medullae spinalis in various experimental subgroups witnessed no obvious changes (P > 0.05). The superstructure changed obviously at the early postoperative stage in group 1/2 and group 2/3, but restored well at 2 months after operation. For the latent period of evoked potential, there was no significant difference between the various experimental subgroups and the control group at each time point (P > 0.05), but there was a significant difference among the various experimental subgroups when compared the time points of 2, 3 and 4 months to that of 2 weeks (P < 0.05) and no statistically significant difference at other time points (P > 0.05). For the wave amplitude of evoked potential of motor nerves, the maximum wave amplitude and the persistence time of the dominate muscle, there were significant differences between the various experimental subgroups and the control group at each time point (P < 0.05), and there were significant differences among the various experimental subgroups when comparing the time points of 2, 3 and 4 months to that of 2 weeks (P < 0.05) and no statistical significance at other time points (P > 0.05).

The functional reserve of the ulnar nerve without compromise accounts the 1/3 of the whole trunk diameter.