Tract orientation and the intensity of myelin staining
When frozen sections of brain are stained by the usual techniques for lipids some myelinated tracts react more intensely than others; up to 30% more in a M85 scanning microdensitometer.
The variations in staining intensity are not due to structural, phylogenetical or histochemical differences but to differences in orientation of myelin thickness in the component fibres as shown by our results from histochemistry and microdensitometry.
Both in the CNS and in the periferal nerves, the thickness of stained myelin in transverse sections of the sheath is the same thickness as the section, whereas in the longitudinal sections the depth of myelin is either interrupted by axons or reduced by tangential sampling.
In peripheral nerves, where the endoneurial material stains more heavily than myelin with basic protein techniques, the longitudinal/transverse difference is masked by the more intense extra-myelin reaction.
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