SMALLER NUMBER OF LARGE MYELINATED FIBERS AND FOCAL MYELIN THICKENINGIN MUTANT QUAILS DEFICIENT IN NEUROFILAMENTS

The peripheral nervous system of a mutant of a Japanese quail deficien t in neurofilaments (mutant) and of a normal Japanese quail (control) was morphometrically evaluated to characterize the morphological findi ngs, especially those of the myelinated fibers of the mutant. In the p roximal peroneal nerves, the frequency of the teased myelinated fibers showing the focal myelin thickening was higher in mutant than in cont rol (P < 0.001) without obvious ongoing axonal degeneration and segmen tal demyelination.The total numbers of the myelinated fibers in the pr oximal and distal peroneal nerve, and in the tibial nerve branch to ga strocnemius muscle (pars medialis) were similar between control and mu tant, although the number of the large myelinated fibers was less (P < 0.01) and the number of the small myelinated fibers was greater (P < 0.01) in mutant compared with control. The median diameters of neurona l cell bodies of the sacral dorsal root ganglia were similar in contro l and mutant. The percentages of light, dark and unclassified cells ev aluated based on the histologic cytoplasmic features were also similar in control and mutant. Therefore, morphometric alterations were more pronounced in the peripheral myelinated nerve fibers compared with tho se in the cell bodies of the spinal dorsal root ganglia. We concluded that a smaller number of large myelinated fibers with a greater number of small myelinated fibers and the presence of focal myelin thickenin g are the main morphologic findings in this mutant, probably due to th e arrest of radial growth or maturation of the axons of the myelinated fibers in the absence of ongoing myelinated fiber degeneration.