SMALLER AXON AND UNALTERED NUMBERS OF MICROTUBULES PER AXON IN RELATION TO NUMBER OF MYELIN LAMELLAE OF MYELINATED FIBERS IN THE MUTANT QUAIL DEFICIENT IN NEUROFILAMENTS

To characterize the morphological features of the myelinated fibers in the mutant quails deficient in neurofilaments (NF), caused by a nonse nse mutation in the NF-L gene, the morphological parameters of the axo n and myelin sheath, and their relationships in the peroneal nerve wer e evaluated. In the mutant, the axonal area was smaller than in the co ntrol (P > 0.01), reflecting the lack of large diameter axons. There w as no significant difference in the mean number of myelin lamellae and of their spacings between controls and mutants. Therefore, it was dec ided to analyze the alteration of axonal parameters in relation to the number of myelin lamellae. In the regression analysis, the number of microtubules (MT) per square micrometer of the axonal area was greater in the mutant than in the control (P < 0.05); however, the number of MT per axon was similar in controls and mutants with the same given nu mber of myelin lamellae. The number of MT+NF per axon was smaller in t he mutant than in the control only for myelinated fibers with more tha n 25 myelin lamellae (P > 0.05). These findings indicate that there wa s a less significant effect of NF deficiency on the smaller than on th e larger myelinated fibers. There was no compensatory increase in the numbers of MT per axon of the myelinated fibers in the mutant as found previously in the unmyelinated fibers of the mutant.