Evaluation of preferential motor reinnervation by measuring choline acetyltransferase activity and by Karnovsky staining

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A hundred-eight Wister rats were used to examine whether preferential motor fiber regeneration exists. Rat femoral nerve bifurcates into motor branch (quadriceps branch) and sensory branch (saphenous nerve). Femoral nerve was sectioned just proximal to the bifurcation and both nerve stumps were inserted into silicone tube leaving 2mm gap (2mm gap group) and 4mm gap (4mm gap group) between stumps. Right femoral nerve was repaired without rotation (no rotation group) and left femoral nerve was repaired with 180 degrees rotation (rotation group). At 4,8,16,24,36,48 weeks after surgery, nerve specimens were harvested from both motor and sensory branches 5mm distal from distal nerve stumps. Choline acetyltransferase (CAT) activity of these specimens and those from normal nerves were measured. Also frozen sections of these specimens were stained with Karnovsky staining in order to see the localization of acetylcholine esterase, which is specific to motor axon, at 4,8,12,24 weeks after surgery. Regenerated motor axons were counted.At 2mm gap group, CAT activity in motor branch became significantly higher than that in sensory branch at 4,8,16,24 weeks in no rotation group and at 8 weeks in rotation group (p<0.05). At 4mm gap group, CAT activity in motor branch became significantly higher than that in sensory branch at 4,8,16,24,36 weeks in no rotation group and at 8,16,36weeks in rotation group (p<0.05). Histrogic examination showed no specific motor exon staining was seen 4 weeks after surgery. Regenerated motor axons started to show staining in both motor and sensory branches after 8 weeks in each group. Number of regenerated exons increased with time in motor and sensory branches in no rotation and rotation groups at 2mm gap group, and was not different between motor and sensory branches. This result and significant higher CAT activity in motor branch suggests that motor axons regenerated into motor branch matured more than those regenerated into sensory branch.