Axonotmesis as treatment for neurotmesis

Chronic access to endoneurial space using an arterial autograft

A technique for direct chronic infusion of compounds onto peripheral axons has been investigated in the rat sciatic nerve. A 2 cm segment of the femoral artery was removed and one end inserted into the endoneurial space of the contralateral peroneal nerve fascicle of the same animal. The other end of the artery was connected to a catheter system to allow infusion into the endoneurium, thus bypassing the barrier that the perineurium presents to hydrophilic compounds. The patency of this arterial access system was evaluated by the ability of 20 microliters of 2% lidocaine to inhibit the toe-spreading reflex. The results of the study were that the infusion system remained operational for 3-7 days after transplantation. There were histologic changes in the nerve but there were no functional deficits due to the surgery. Although a long-term endoneurial infusion was not achieved, the limited access time to the axons might be long enough for applications such as the delivery of nerve growth factors to injured nerve.

The numbers of unmyelinated and myelinated axons in normal and regenerated rat saphenous nerves

Counts have been made of the numbers of unmyelinated and myelinated axons in the proximal and distal stumps of regenerated rat saphenous nerves and from equivalent sites in normal nerves. In the proximal part of normal nerves there were averages of 1,045 myelinated axons and 4,160 unmyelinated ones. Regenerated nerves contained the same number of myelinated axons in their proximal stumps but there was a 40% reduction in the unmyelinated axon count. In the distal stumps of these nerves the myelinated axon count had increased by an average of 620; this comes about because some regenerated myelinated axons support more than one process in the distal stump. In contrast, the number of unmyelinated axons was reduced further, from a mean of 2,476 in the proximal stump to one of 2,219. The sizes of Schwann cell units in the normal and regenerated nerves were also noted. Schwann cell units in the proximal and distal stumps of the regenerated nerves were smaller than those in the normal ones. These changes associated with unmyelinated axons in regenerated nerves are likely to contribute to the sensory, vasomotor and sudomotor abnormalities that sometimes occur after peripheral nerve injury and regeneration.

Single vs multiple somatic nerve crushes in the rat

Nerve lesions modify regenerative responses to subsequent lesions. Some of the modifications might be useful. To increase our understanding of these modifications, the present study determines myelinated and unmyelinated axon numbers in the distal part of rat sciatic nerve and in 2 smaller branches, the nerve to the medial gastrocnemius muscle and the sural nerve, 8 weeks and 9 months following either single or the last of 3 crushes to the rat sciatic nerve. For myelinated axons, there is a significant and proportional increase distal to the crush in the sciatic nerve and in its smaller tributaries following both single and triple crushes. These increased axons persist. We interpret these data to indicate that some of the regenerating myelinated axons branch at the site of lesion, pass without branching into the tributary nerves, and then presumably find attachments at the periphery. If true, single or multiple crushes might be useful in conditions where it would be desirable to increase numbers of processes from surviving neurons. The major differences between single and triple crushes are that myelinated axons are increased more after triple crush and increase significantly between 8 weeks and 9 months after triple crush but not after single crush. Thus not only myelinated axon numbers, but the timing of the myelination process seems to change if regeneration following single crush is compared to similar regeneration following multiple crushes. Unmyelinated axons do not regenerate in the same way as the myelinated axons.(ABSTRACT TRUNCATED AT 250 WORDS)