Myelin cerebrosides and proteins in the spinal cord of the pig during pre- and post-natal development

Myelin Sheath Development in the Maxillary Nerve of the Newborn Pig

Myelination, the ensheathing of neuronal axons by myelin, is important for the proper function of both central and peripheral nervous systems. Various studies have investigated the quantitative parameters of myelination in certain species. Pigs are among the species of which their use as laboratory animals in neuroscience research increased the past few decades. However, there is limited data regarding the myelination process in the pig. Moreover, the maxillary nerve is crucial for Pseudorabies Virus (PrV) neuropathogenesis. In this context, a quantitative analysis of various myelination parameters of the maxillary nerve was performed, during the first 5 weeks of porcine post-natal development, the time period, which exhibits the highest interest for PrV neuropathogenesis. The evaluation was conducted in four groups of uninfected pigs, at the time of birth (group 0w), at the age of 1 week (group 1w), 3 weeks (group 3w) and 5 weeks (group 5w), using toluidine blue staining, immunofluorescence and electron microscopy. Axon and fibre diameter, perimeter and surface, myelin sheath thickness and g-ratio were measured on histological sections transverse to the longitudinal axis of the maxillary nerve. The thickness of myelin sheath was 0.76 μm for group 0w, 0.94 μm for group 1w, 0.98 μm for group 3w and 1.03 μm for group 5w. The g-ratio was 0.529, 0.540, 0.542 and 0.531 for the respective animal groups. The results of this study contribute to the understanding of the myelination process in the pig will be used for the study of PrV effects on the myelination development of newborn piglets' maxillary nerve and may shed new light to their vulnerability to the virus.

Developmental regulation of the carbohydrate composition of glycoproteins associated with central nervous system myelin

Glycoproteins from central nervous system myelin were evaluated for developmental alterations in their carbohydrate composition by autoradiographic analysis of radioiodinated lectin binding after separation by high-resolution sodium dodecyl sulfate-pore gradient slab gel electrophoresis (SDS-PGE). Sixteen lectin-binding components were assessed in highly purified myelin preparations from 15-day, 18-day, and adult rat brains, using the lectins Triticum vulgaris (wheat germ agglutinin) and Ulex europeus (gorse agglutinin I). Developmental changes in lectin binding for individual glycoproteins were evaluated semiquantitatively by comparing densitometric scans of the autoradiographs. Both increases and decreases in lectin binding for individual components were observed as a consequence of development, as well as the appearance and disappearance of lectin binding to three low-molecular-weight components. No changes in electrophoretic mobility and hence glycoprotein molecular weight were observed in any components when using these lectins. These developmental changes in lectin binding suggest that increases in glycoprotein (receptor) density occur, as well as an elaboration of oligosaccharide branching for individual glycoproteins. In addition, the appearance of a new glycoprotein in the adult myelin membrane could imply a new functional role not present in the immature membrane. These observations suggest that dynamic alterations of myelin-associated glycoproteins occur during development. Such developmental regulation of membrane glycoproteins increases the significance of their potential role in myelination and myelin maintenance.

Factors affecting the electrophoretic analysis of myelin proteins: application to changes occurring during brain development

Several factors affecting the sodium dodecylsulfate (SDS)-electrophoretic analysis of myelin proteins were investigated. It was observed that complete solubilization of proteins with SDS-containing solutions required either that the lyophilized myelin sample was pretreated with organic solvents or that reducing agents were added to the solubilizing solution. The SDS-electrophoretic pattern of myelin proteins was strongly dependent upon the ionic strength of the resolving gel since the mobility of the large basic protein appeared to increase as the ionic strength was decreased. Attempts were made to measure ratios of the major myelin proteins as a function of pretreatment of myelin with organic solvents followed by visualization of the protein bands with different stains. These studies revealed that lowered ratios of the proteolipid to each of the basic proteins was obtained if the myelin was delipidated with ehter-ethanol mixtures followed by staining with either Fast green or naphthol blue black (amido black). The most consistent results were obtained when myelin was not delipidated, solubilized in an SDS solvent containing dithiothreitol as the reducing agent, and gels were stained with Coomassie blue. Studies on developmental changes in the protein composition of myelin using this technique revealed that as mouse myelin matured the membrane became increasingly enriched in the small basic protein with the ratios of proteolipid/large basic protein/small basic protein changing from about 2:1:1 at 8-10 days to 2:1:2 at 16-17 weeks. Furthermore, the ratios of proteolipid/large basic protein remained essentially the same at all ages examined, suggesting that these proteins may be incorporated into the membrane at about the same rate during maturation.