Abstract
To elucidate the mechanism of functional recovery after gradual nerve-stretch injury, we used rats in which the femur length was increased by 15 mm at 1.5 mm/day. We performed electrophysiology, mRNA analysis of tetrodotoxin-resistant voltage-gated sodium channels (TTX-R VGSCs) in dorsal root ganglia, and histology of unmyelinated sciatic nerve fibers and examined pain thresholds at 1, 10, 20, and 30 days after cessation of lengthening. Electrophysiology revealed conduction block after cessation that recovered after 30 days. TTX-R VGSC levels decreased immediately after cessation but were restored after 10 (Nav1.9) or 20 (Nav1.8) days. Histology revealed that injured unmyelinated nerve fibers regenerate 30 days after cessation. Pain threshold decreased gradually during lengthening but had not recovered to the control group level after 30 days. Early restoration of TTX-R VGSC mRNA in dorsal root ganglia preceded functional recovery of stretched nerves before regeneration of injured unmyelinated nerve fibers.
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