Regeneration of myelinated fiber after crush injury is retarded in sciatic nerves of mutant Japanese quails deficient in neurofilaments

Abstract

Regeneration of myelinated fibers in the sciatic nerve 2 weeks after crush injury was studied morphometrically in mutant Japanese quails deficient in neurofilaments and in normal quails (controls). There were fewer regenerated myelinated fibers per nerve at 10 mm (R₁) and 20 mm (R₂) distal to the crush site in mutants than in controls (P < 0.05). Both median and maximum diameters were smaller (P < 0.01) in mutants than in controls. On electron microscopy, transverse axonal area and axonal circumference were smaller (P < 0.001) at both R₁ and R₂ in mutants than in controls. The number of myelin lamellae was less (P < 0.01) in mutants than in controls at R₁, but was similar at R₂. There were fewer myelin lamellae in relation to axonal area in mutants than in controls at R₁ (P < 0.0001) and R₂ (P = 0.0032). The results indicate a retardation of both radial growth of axons and myelination around axons of the same size in mutants compared with controls. Such retardation may be explained by the deficiency of neurofilaments and the altered relationship between Schwann cell and axon in the mutant.