Postcajalian Period

Putting together the fundamental discoveries of the previous period, it becomes evident that in addition to the already classic types of glia, fibrous and protoplasmic, there was another element different in morphology and staining properties. Although it had been seen before and given various descriptive names (see Cajalian Period), Cajal brought it to the foreground and speculated on its nature. There were indeed discrepant issues. His goldsublimate method did not reveal the existence of...

Figure 23

Schematic representation of the orientation and membrane distribution of P0 protein and MAG during conversion of mesaxon membranes to compact myelin. MAG and P0 are shown only in the inner membrane bilayers. Initial mesaxon wraps contain MAG but little P0 protein (A). The bulk of MAGs extracellular domain maintains a constant spacing of 12 to 14 nm between apposing mesaxon membranes. The spacing between the extracellular leaflets of apposing mesaxon membranes containing MAG and P0 is dictated...

Summary And Future Considerations

As illustrated in this chapter, myelinated axons form a complex structure that exemplifies functional cell-cell interactions. While our general knowledge of the molecular compos ition of myelin internodes is substantial, we know little about the molecular mechanisms responsible for spiral wrapping of myelin membranes or for axon-myelin-forming cell communication. Future research will identify additional myelin molecules that are essential to the process of myelination and to axonal function....

Contributors

Mihaela Anitei Department of Neuroscience, University of Connecticut Medical School, Farmington, Connecticut 06030-3401 Jack Antel Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, Canada H3A 2B4 D. L. Arnold Magnetic Resonance Spectroscopy Laboratory, Brain Imaging Center, Montreal Neurological Institute, Montreal, Quebec, Canada H3A 2B4 Edgardo J. Arroyo Department of Neurology, The University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104...

Noncompact Myelin

When comparing the ultrastructure of PNS (Fig. 1.3A) and CNS (Fig. 1.3B) myelinated fibers, one is struck by the similar appearances of both the compact myelin and the axon. While the periodicity of compact CNS and PNS myelin differs, they still remain difficult to distinguish without morphometric comparisons. CNS and PNS myelinated fibers can be easily distinguished by the presence of a basal lamina around PNS, but not CNS, myeli-nated fibers. They also differ by the distribution and...

Schmidtlanterman Incisures

As part of the Wrst reports on the morphology of PNS myelinated axons, Schmidt and Lanterman independently described a series of funnel-shaped clefts or incisures that interrupted the dense appearance of myelin (Figs. 1.1A and 1.10A). These clefts, called Schmidt-Lanterman incisures, traverse the thickness of the myelin internode at an average angle of 9 degrees. They are abundant between the perinuclear region and paranodes and their total number within individual internodes increases with...

Figure 311

Protein partitioning into rafts. (A) Membrane proteins can (a) partition between raft and nonraft domains (e.g., myelin oligodendrocyte glycoprotein), (b, c, d) be exclusively raft-associated (e.g., GPI-linked proteins (b) such as contactin NCAM120, certain tetraspan proteins (c) such as oligodendrocyte specific protein OSP, and transmembrane raft proteins (d)), or (e) be localized entirely outside raft microdomains (e.g., myelin associated glycoprotein). GalC galactocerebroside Chol...

Figure 11

Myelin internodes in the peripheral nervous system (PNS). Drawings by Ramon y Cajal of osmic acid-fixed (A) and silver impregnated (B, negative image) myelinated fibers from the PNS. Compact myelin membranes surround the axon (A, black) and comprise the majority of the myelin internode. To illustrate the membrane expansion that occurs during myelination, the size of a Schwann cell before myelination (C) is compared to a Schwann cell and it unrolled myelin internode (D). Cytoplasmic domains at...

Cajalian Period

Cajal came into the glia research picture with his initial attempts with the Golgi technique. After first learning about this method in 1887, he soon published a study on the nervous system of birds (Cajal, 1888a). He demonstrated clear differences between the neuroglia in the granule cell layer of the cerebellum and in the underlying white matter, thus preceding the observations of Andriezen (1893a, 1893b) and Kolliker (1896). In the same year, he also demonstrated for the first time the...

Schwann Cell Myelination

Initially, myelinating Schwann cells polarize their surface membranes into two domains. The abaxonal plasma membrane is exposed to, and interacts with, the external environment or endoneurial fluid. As part of its maturation, it directs the production of the basal lamina, which is a prerequisite for myelination (Bunge et a ., 1986 Eldridge et a ., 1987). The second domain, the adaxonal or periaxonal membrane, is in direct contact with the axon and is enriched in myelin-associated glycoprotein...

Figure

Nicolas Achucarro 1880-1918 photo circa 1910 established in a few years the basis of neuroglia histopathology and raised the category of this tissue, adducing its possible secretory role as the basis for certain mental disorders. Courtesy of La Gran Enciclopedia Vasca, Bilbao. At about the time that the neuroglia became the focus of Cajal's laboratory, a new star appeared in his laboratory. He was Nicolas AchUcarro Fig. 3 , whose background was indeed impressive. He had extensive training in...