Objective To find out effective methods to prevent the motor neurons of spinal cord from degenerating and dying caused by axon transection.
Methods Forty-eight SD rats were randomized into two groups: a nerve root transection group and a procaine blocking + nerve root transection group (procaine group). The numbers of motor neurons of spinal cord were calculated and analyzed after nerve root transection.
Results Nissl bodies of motor neurons reduced and the cells swelled postoperatively in the nerve root transection group.
Conclusion The blocking of procaine could protect the neurons of spinal cord from the degeneration and dying caused by axon transection.

Donor motor nerve must be cut when nerve transfer is used for the treatment of brachial plexus injuries, while the transection of the nerve may cause degeneration and death of the motor neurons, which will prevent the axon regeneration and affect the result of nerve transfer. Thus, it's important to find out effective methods to prevent the motor neurons from degenerating and dying caused by axon transection. We initiated this study based on a rat model.

MATERIALS AND METHODS

Forty-eight healthy, male adult Sprague-Dawley rats were randomized into two groups: a nerve root transection group and a procaine blocking + nerve root transection group (procaine group) with 24 rats in each group. Anesthesia was induced with 1% pentobarbital sodium (0.5 ml/100g ip). The left brachial plexus was used as the experimental side and the right as the control.

The incision was made along the clavicle, a layered dissection was performed and brachial plexus was exposed, 5 roots were cut at the lateral edge of intervertebral foramen by sharp microscissors, a segment of 0.5 cm was cut from each distal nerve and the distal ends were ligated with silk thread. In the procaine group, 0.2 ml of 2% procaine was injected beneath the epineurium of the roots of brachial plexus at first, 5 minutes later, the same procedure described above was proceeded. All animals were raised in different cages.

The animals were anaesthetized again, 3 days, 1 and 2 weeks and 1, 2 and 3 months after operation, and a vsilica gel tube was put into the vein, meanwhile, blood could bleed slowly from a small hole cut open in the left external jugular vein. When the liquid became colorless, 150 ml of 10% formaldehyde was given into the vein for tissue fixation. Spinal cord from C5 to T1 was obtained and put into 10% formaldehyde/alcohol solution (1∶9) and fixed for 48 hours. The fixed specimen were dehydrated, embedded and continuous cross section of 7 μm were made. One out of 20 sections was left and a total of 5 sections was obtained for each specimen. HE stained sections were observed under light microscope. The number of α-motor neurons of anterior horn of the spinal cord was counted. The diameter of anterior horn cells exceeding 20 μm with clear nucleus and nucleolar were included. The numbers of α-motor neurons of the 5 sections of each specimen were summed and the ratio of the sums of the left to the right side was calculated (L/R). The results were analyzed using statistics method of analysis of variation (ANOVA).

RESULTS

Morphological Observation In the nerve transection group, Nissl bodies of motor neurons in the left side reduced and the cells swelled 3 days postoperatively, while the control side didn't show these phenomenon. In the procaine group, no significant change could be seen.

Neuron counting The result of neuron counting showed: in the nerve transection group, the number of α-motor neuron in the experimental side (left) was less than that in the control side, the L/R ratio was 0.74, the two sides differed significantly (P<0.05), no significant difference was found between the experimental side and the control side in the procaine group (P>0.05, Table).

Table The ratio of the number of α-motor neurons of
the left to the right side (L/R, ±SD)