Aims: Multiple nerve repair by means of a Y-shaped nerve guide represents a good model for studying the specificity of peripheral nerve fiber regeneration. Here we have employed this model for investigating the specificity of axonal regeneration in mixed nerves of the rat forelimb model. Specificity of nerve regeneration can be defined as the ability of the nerve fibers of a peripheral nerve, after a lesion. Tree types of specificity on nerve regeneration has been postulated: “tissue specificity” (the preferential reinnervation of distal nerve tissue versus other types of tissue), topographic specificity (regenerating nerve fibers are preferentially attracted by analogous distal pathways (e.g. preferential regeneration along tibial nerve pathways by tibial nerve fibers), and end-organ specificity, which is the hypothesis that distal end-organs (muscle vs. sensory targets) specifically attracts the respective (motor vs. sensory) regenerating nerve fibers. Exists no agreement regarding the presence and features of the two last type of specificity.

Methods: The left median and ulnar nerves, in adult female rats, were transected and repaired with a 14-mm Y-shaped conduit. The proximal end of the Y-shaped conduit was sutured to the proximal stump of either the median nerve or the ulnar nerve. Ten months after surgery, rats were tested for functional recovery of each median and ulnar nerve. Quantitative morphology of regenerated myelinated nerve fibers was then carried out by the two-dimensional disector technique.

Results: Results showed that partial recovery of both median and ulnar nerve motor function was regained in all experimental groups. Performance in the grasping test was significantly lower when the ulnar nerve was used as the proximal stump. Ulnar test assessment showed no significant difference between the two Y-shaped repair groups. The number of regenerated nerve fibers was significantly higher in the median nerve irrespectively of the donor nerve, maintaining the same proportion of myelinated fibers between the two nerves (about 60% median and 40% ulnar). On the other hand, nerve fiber size and myelin thickness were significantly larger in both distal nerves when the median nerve was used as the proximal donor nerve stump. G-ratio and myelin thickness/ axon diameter ratio returned to normal values in all experimental groups.

Conlusions: These results demonstrate that combined Y-shaped-tubulization repair of median and ulnar nerves permits the functional recovery of both nerves, independently from the proximal donor nerve employed, and that tissue, and not topographic, specificity guides nerve fiber regeneration in major forelimb mixed nerves of rats.

Aims: the recent ten years have seen a growing interest in termino-lateral (end-to-side) neurorrhaphy; this interest mainly originates from the prospected possibility to recover the function of a damaged nerve without loosing the function of a donor nerve.

We investigated voluntary control recovery after termino-lateral neurorrhaphy in the upper limb of mixed rat nerves (median and ulnar nerves) to assess functional recovery and nerve fibers regeneration.

Methods: We made a termino-lateral neurorrhaphy between median (lesioned) and ulnar nerve (donor) on left upper limb of 24 Wistar female rats. After 6 months, functional recovery of the limb was investigated using grasping test and electrical stimulation; then, rats were sacrificed and we studied morphological changes in muscles and regenerated nerves with light microscopy and stereology.

Results: We observed a functional recovery up to 15 % ± 5% of the normal at grasping test, while electrostimulation was positive in all cases; muscle trophism was good (40 % > than denervated muscles).

On microscope median nerve presented the typical structure of a regenerated nerve; in ulnar nerve some slight signs of degeneration can be detected distally to the site of suture. At the point of suture, nerve fibers of ulnar nerve sprouts into median nerve (collateral sprouting).

Conclusions: Termino-lateral neurorrhaphy induces a collateral sprouting from the donor nerve (as described in the literature); fiber regeneration in the severed nerve leads to a recovery of voluntary functional control.

In the donor ulnar nerve distally to the suture site we found some slight signs of damage, but they do not impair motor function.

In conclusion, termino-lateral neurorrhaphy can be used to repair peripheral nerve lesions with large substance loss where other types of repair strategies cannot be attempted.