T. Samorajski

Abstract The number of neurofilaments and microtubules present in nerve fibers was determined for sciatic nerves from adult mice and from rats of three different ages. More microtubules than neurofilaments were found in nonmyelinated fibers; the ratio of tubules/filaments was reversed in myelinated fibers and was found to change with axon caliber independent of the presence of a myelin sheath. A series of regression analyses indicated that axon caliber correlates best with the sum of the number of neurofilaments and microtubules per fiber. This correlation was only slightly better than that for neurofilaments alone. Axon caliber also correlated better with the filament‐tubular material than with the thickness of the myelin sheath. The results were similar for both rats and mice, and age differences were not apparent in the samples of nerves analyzed.

Journal Article Myelin Formation in the Sciatic Nerve of the Rat: A Quantitative Electron Microscopic, Histochemical and Radioautographic Study Get access R. L. Friede, M.D., R. L. Friede, M.D. Cleveland, Ohio Search for other works by this author on: Oxford Academic PubMed Google Scholar T. Samorajski, Ph.D. T. Samorajski, Ph.D. Cleveland, Ohio Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Neuropathology & Experimental Neurology, Volume 27, Issue 4, October 1968, Pages 546–570, https://doi.org/10.1097/00005072-196810000-00002 Published: 01 October 1968

Abstract Nerve fiber populations of the vagus and sciatic nerves of mice were classified according to the number of myelin lamellae present in the sheaths. This method for classifying fiber populations was superior to others used previously since it provided a more sensitive procedure for the analysis of individual fibers and better control over the technical factors involved in tissue processing. The relationship of the number of myelin lamellae in the sheath to axon circumference was found to be linear. In fresh tissue there was one myelin lamella for every 0.24 μ increase in axon circumference above da value of 2.32 μ (the mean circumference of an average‐sized nonmyelinated fiber). A formula was proposed which may be useful for understanding how axons control myelin development and interpreting developmental stages, as well as for evaluating pathologic conditions affecting the peripheral nervous system. The critical diameter above which fibers were found to be myelinated was about 0.8 μ for fixed nerve and 1.1 μ for fresh nerve. The ratio of axon diameter to fiber diameter ranged between 0.5 and 0.9 and was not related to fiber size.

An examination of the topographic distribution of lipofuscin pigment granules with the light and electron microscope revealed either smaller and randomly "dispersed" or larger and more complex "clustered" pigment configurations in the cytoplasm of neurons in the dorsal ganglia and ventral spinal cord of 24-month old male mice. Qualitative comparisons revealed no major differences in shape, size, complexity, density, orientation, and cytologic distribution of the pigment bodies in motor and sensory neurons. In general, when the pigment granules were quite numerous within the 2 types of cells, they were smaller in size ( approximately lmicro), had a dense homogeneous matrix with few bands or lamellae, and were uniformly distributed throughout the cytoplasm. In contrast, when the pigment configurations were less in number, they were usually larger in size ( approximately 3micro), had a more complex internal banded structure, and appeared more localized within the cell. Examination of the bands revealed a repeating pattern of approximately 70 A. The bands appeared to fuse, forming hexagonal arrays of linear densities intersecting at an angle of approximately 120 degrees in some regions of the pigment bodies. Structural similarities suggested that the striated membranous bands may be composed of phospholipids.