Myelin process

The myelination process is especially vulnerable during the late gestational development in humans and postnatal in rats and exposure to chemicals such as ethanol [103], tellurium [104], or lead [53] might affect the myelination process and cause persistent adverse outcomes [105]. In vitro myelination is less studied in toxicology as only few cell models can capture this complex process, often with long term culturing for cell lines [16], primary cultures [106], and stem cells [21],... 

Takikita, S., Fukuda, T., Mohri, I., Yagi, T., and Suzuki, K., Perturbed myelination process of premyelinating oligodendrocyte in Niemann-Pick type C mouse, J Neuropathol Exp Neurol 63 (2004) 660-673. 

In a comparative study of the ganglioside fraction of normal and quaking mice, an increase in the gangliosides Gt and Gq was found in the quaking mice but a 50% decrease in Gmi was noted. It was suggested that the decreased concentration of Gmi could be linked to an enzymic deficiency in the latter stages of the myelination process. A novel ganglioside, ALG, was also found... 

Although LPAj was originally believed to be involved in the myelination process, no significant abnormality in locomotion was evident in LPAj knockout mice, indicating that the myelination process was relatively normal (Yang et al, 2002). However, LPAj mice have a reduced survival rate, decreased size, impaired olfaction and altered craniofacial stmcture. LPA knockout mice have no obvious phenotype, whereas a knockout mouse for LPAj has not been reported to date (Yang et al., 2002). The LPA receptor subtypes are not redundant since LPAj present in the embryonic brain fails to rescue LPAj mice from their observed abnormalities. 

Over 20 infectious agents have been incriminated as etiologic agents for many the causal relationship has been disproved, and for others there is conflicting evidence. Human herpesvirus 6 (HHV-6) is currently the most likely causative virus. HHV-6 may initiate the autoimmune processes of MS in one of two ways. First, HHV-6 is structurally similar to myelin basic protein. When T cells become sensitive to HHV-6, the cells may attack myelin basic protein. Second, HHV-6 may directly stimulate the complement cascade, activating autoimmune processes.5 Infection with HHV-6 alone cannot fully explain MS, because HHV-6 is found in 75% of all people, but MS is much more rare. 

FIGURE 1-14 Transverse sections of a myelinated axon (left) and the process of a fibrous astrocyte (right) in dog spinal cord. The axon contains scattered neurotubules and loosely packed neurofilaments interconnected by side-arm material. The astrocytic process contains a bundle of closely packed filaments with no cross-bridges, flanked by several microtubules. Sometimes, a lumen can be seen within a filament. X60,000. 

FIGURE 1-15 A myelinating oligodendrocyte, nucleus (N), from the spinal cord of a 2-day-old kitten extends cytoplasmic connections to at least two myelin sheaths arrows). Other myelinated and unmyelinated fibers at various stages of development, as well as glial processes, are seen in the surrounding neuropil. Xl2,750. 

FIGURE 1-19 A myelinated PNS axon (A) is surrounded by a Schwann cell nucleus (N). Note the fuzzy basal lamina around the cell, the rich cytoplasm, the inner and outer mesaxons (arrows), the close proximity of the cell to its myelin sheath and the 1 1 (celhmyelin internode) relationship. A process of an endoneurial cell is seen (lower left), and unstained collagen (c) lies in the endoneurial space (white dots). X20,000. 

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