Age-related changes in occurrence of Marchi-positive granules and Marchi-positive myelinoid bodies in postnatally developing feline white matter.

The occurrence of clusters of Marchi-positive granules and of Marchi-positive myelinoid bodies at different postnatal developmental stages was examined lightmicroscopically in Vibratome sections from the cervical lateral funiculus of the cat, after perfusion-fixation with glutaraldehyde. The findings show that clusters of Marchi-positive granules are most common at birth and rapidly decrease in number with development, being largely absent in animals older than 1 month. The pattern of change resembles the postnatal changes in content of esterified cholesterol in the cervical lateral funiculus and is compatible with the view that the clusters of Marchi-positive granules may result from spontaneous myelin sheath disintegration occurring early postnatally. The incidence of Marchi-positive myelinoid bodies increases 7 times during the first 4 months after birth to a peak and declines about 40% during late maturation. The size spectrum of the Marchi-positve bodies shifts markedly towards larger sizes with development and presents a close to mature picture from 120 days on. Comparisons between the Marchi-positive myelinoid bodies and the myelin sheaths in the same region, with respect to postnatal change in occurrence and size spectrum, suggest that the Marchi-positive bodies are related to myelin sheaths of large fibres or fibres destined to become large.