Mitsuo Ochi

The regeneration of sensory neurones in the reconstruction of the anterior cruciate ligament

We examined whether somatosensory evoked potentials (SEPs) were detectable after direct electrical stimulation of injured, reconstructed and normal anterior cruciate ligaments (ACL) during arthroscopy under general anaesthesia. We investigated the position sense of the knee before and after reconstruction and the correlation between the SEP and instability. We found detectable SEPs in all ligaments which had been reconstructed with autogenous semitendinosus and gracilis tendons over the past 18 months as well as in all cases of the normal group. The SEP was detectable in only 15 out of 32 cases in the injured group, although the voltages in the injured group were significantly lower than those of the controls. This was not the case in the reconstructed group. The postoperative position sense in 17 knees improved significantly, but there was no correlation between it and the voltage. The voltage of stable knees was significantly higher than that of the unstable joints. Our findings showed that sensory reinnervation occurred in the reconstructed human ACL and was closely related to the function of the knee.

Unilateral sciatic nerve injury stimulates contralateral nerve regeneration.

Axonal outgrowth in tissue cultures was measured to determine whether unilateral peripheral nerve injuries affect contralateral nerve regeneration. The right sciatic nerves of young male Wistar rats were cut at mid-thigh level. Sham operation as a control was limited to the exposure of the nerve without cutting. At day 6 post-surgery, bilateral L5 dorsal root ganglia (DRG) with attached nerve stumps were resected and cultured. Axonal outgrowth from the nerve stump was measured in situ. The contralateral preparations showed longer outgrowths than controls. Therefore the conditioning effect was not merely restricted to the ipsilateral neurons but also affected undamaged sensory neurons of the contralaretal DRG.

Sensory neurons regenerate more dominantly than motoneurons during the initial stage of the regenerating process after peripheral axotomy.

This study was designed to determine whether sensory neurons or motoneurons were dominant during the earlier stage of the regeneration process after peripheral axotomy. After transection of the right sciatic nerves of rats, epineurial end neurorrhaphy was performed. At 5, 7 and 14 days postoperatively, the nerves were re-transected at the positive pinch site, and their proximal stumps were exposed to the retrograde neurotracer, Fluoro-Gold (F-G). Seventy-two hours later, the lumbar spinal cords and the L4 and L5 dorsal root ganglia (DRG) were harvested and evaluated. The incidence and the intensity of F-G labelling in DRG were significantly higher than in anterior horns (AH). These results demonstrated that sensory neurons were more dominant than motoneurons in nerve regeneration.

Influence of Distal Nerve Segment Volume on Nerve Regeneration in Silicone Tubes

The influence of a volume of a distal nerve segment upon nerve regeneration in an 8-mm gap created within a silicone tube was examined. The rats were randomly divided into four groups. Each group had 5 mm, 1 mm, or a half volume of 1-mm nerve segment (a nerve piece of 1 mm transected longitudinally) inserted into the distal end of a silicone tube of 11 mm. The empty group without a nerve segment was used as control. Diameters of regenerated cylindrical structure between the nerve ends in the silicone tube were measured under an operation microscope and myelinated axon diameter, myelinated axon density, myelin sheath width, and ratio of myelinated axon area to total cross sectional area were measured using the transverse sections at the midpoint of the silicone tube at 6 weeks after surgery. Although there was a significant difference in all of those parameters between the control group and any of the remaining three groups, no significant difference was found between any pair of these three groups. The results of this study indicated that the degree of nerve regeneration does not correlate with the volume of a distal nerve segment and even a very small piece can play an important role in supporting regenerating nerve beyond a definitive gap.

The time-dependent difference of GAP-43 expression between sensory neurons and motoneurons after peripheral nerve transection.

The L5 dorsal root ganglion (DRG) cells and L5 anterior horn (AH) cells of rats were studied and examined immunocytochemically after transection of the sciatic nerve to find out whether there would be time-dependent differences in the increase of growth-associated protein (GAP-43) expression between sensory neurons and motoneurons. On the seventh day after transection at mid-thigh level, the levels of GAP-43 in the DRG cells significantly increased, while those in the AH cells began to increase gradually from the 14th day onward. Transection at the piriform muscle level induced a significant increase in immunoreactivity of GAP-43 on the third day in the DRG cells, and on the seventh day in the AH cells. These results showed that sensory neurons expressed GAP-43 immunoreactivity earlier than motoneurons after peripheral nerve transection regardless of the site, suggesting that sensory neurons might start to produce cytoskeletons for axonal elongation earlier than motoneurons after nerve transection.

EXPRESSION OF CYTOKINES IN THE DORSAL ROOT GANGLION CELL BODY IN AN EXPERIMENTAL MODEL OF ENTRAPMENT NEUROPATHY

An experimental entrapment neuropathy model was produced by wrapping the sciatic nerve with a silicone tube using 54 adult male Wistar rats. We observed the changes in expression of IL-1 and TGF-β1 in the dorsal root ganglion during the formation as well as recovery process after removal of the tube, together with electrophysiological changes. Expression of IL-1 reached its peak 2 months after tubing, while expression of TGF-β1 peaked at 6 months and thereafter slowly decreased. Motor nerve conduction velocity (MNCV) significantly decreased 8 months after tubing. Removal of the silicone tube at 8 months after tubing, induced a significant increase in the level of IL-1 expression at 1 month after the removal, and that in the level of TGF-β1 expression at 2 months after the removal, at which time MNCV began to show a significant recovery. We have concluded from these results that IL-1 and TGF-β1 are deeply involved in the formation as well as the recovery process of entrapment neuropathy.

Increase of nerve regeneration capacity by new neurotrophic pyrimidine derivative MS-430.

1. We studied whether a new neurotrophic pyrimidine compound, MS-430, can increase the regeneration length of the transected sciatic nerve in a silicone chamber gap of 14 mm. 2. The average length of regenerated myelinated axons in ten cases was 9.0+/-0 mm in the control group, 2.8+/-1.9 mm in the 1 mg/kg/day of the MS-430 group and 5.0+/-5.1 mm in the 3 mg/kg/day of the MS-430 group, indicating that the average length was significantly larger in the 3-mg group than that in the control group (P<0.05). 3. The results clearly showed that the MS-430 has promoting effects on nerve regeneration.

Improvement in nerve regeneration by monoclonal antibodies to ICAM-1 and LFA-1 in allogeneic mice.

We examined whether giving monoclonal antibodies (MoAb) to intercellular adhesion molecule 1 (ICAM-1) and leucocyte function associated antigen (LFA-1), which have important roles in the initial stage of rejection after allografts, can improve nerve regeneration in allogeneic mice. Fresh sciatic nerves were grafted using BALB/c mice as donors and C3H/He mice as recipients. Nerve regeneration at six weeks was significantly better in the mice given MoAbs at one and five days than in those given none (n = 5 in each group), although nerve regeneration even in the five-day group was significantly inferior to that in the syngeneic nerve graft group (n = 5). The survival time of the nerve donor skin graft at 12 weeks was not prolonged by treatment with MoAbs, indicating a failure to induce immunological tolerance. However, at 10 months after nerve grafting there were fewer Mac-1, Lyt-1, and Thy-1 positive cells in the five-day group and they showed less immunoreactivity than the untreated group. We conclude that giving MoAbs could effectively improve nerve regeneration in grafted allogeneic nerve segments, although it did not induce immunological tolerance.