Maturation of regenerating nerve assessed by evoked potential in the rat: hyperbolic time course

Recovery of sensory fiber excitability after sciatic nerve lesion induced by freezing was assessed by the somesthesic evoked potential (SEP) in response to plantar pad electrical stimulation. SEP was recorded from the S1 area through chronically implanted cortical electrodes. The P1 wave reappeared on Day 22 or 23 postinjury, indicating that the axonal elongation rate ranged between 3.9 and 4.1 mm/day. P1 onset (P1o) latency decreased from 61.9 +/- 6.4 ms (SD) on Postoperative Day 22 to 18.8 +/- 1.13 ms on Day 50. Computation of standardized residuals showed that the best values for the regression equation as a function of time were obtained after hyperbolic transformation. Covariance analysis showed significant differences between untreated animals and after treatment with thyroxin (T4) and metformin p-chlorophenoxyacetate (MP) or after conditioning lesion (CL). This indicates that these treatments acted selectively on the components of the maturation process.