Quantitative studies on the regeneration of myelinated nerve fibers. I. Variations in the number and the size of myelinated fibers in the nerves of normal rats]

The number and size of myelinated nerve fibers have been determined at standard levels in the nerve to medial head of right and left gastrocnemius muscles of 24 normal rats (11 males and 13 females). The mean values of all results were comparable on right and left sides. Thus, 271 +/- 5 myelinated nerve fibers were found in the right nerve and 272 +/- 4 in the left; their mean diameter were respectively 8.1 +/- 0.1 and 8.0 +/- 0.1 micron. There were 60.1% of large nerve fibers on the right side and 59,9% on the left, their mean diameters being 10.5 and 10.6 micron. Some variations occured in all these values, depending of the weight and sex of the animals. Nevertheless, the differences between both sides of a same rat were negligible and the histograms of both nerves could be superposed. Accordingly, in the operated animals, the contralateral nerve may be used as control.