The ultrastructural characterization of macroglial cell types

Abstract

In the prelaminar region of adult cat optic nerve, silver impregnation revealed a macroglial cell population consisting solely of small fibrous astrocytes. Electron microscopically the cells were characterized by abundant processes containing closely packed filaments and occasional glycogen granules; their perikarya contained few organelles, glycogen particles were conspicuous but not abundant, and their cytoplasmic and nucleoplasmic matrices were of low density.The laminar region contained typical fibrous astrocytes. These cells were characterized by similar processes and matrices but their perikarya contained filaments and were richer i n organelles whose orientation was primarily radial.The postlaminar region contained both astrocytes and oligodendrocytes. The latter were identified as cells characterized by the absence of filaments and glycogen, the presence of canaliculi, dense cytoplasmic and nucleoplasmic matrices and perikarya very rich in organelles, whose orientation was primarily circumferential.The presence of filaments and/or glycogen on the one hand, and of dense matrices on the other hand, seemed to be mutually exclusive and provided diagnostic criteria for astrocytes and oligodendrocytes respectively. Bivalent forms were not seen. Cells usullly identified as microglia were not seen.The relationship between astrocytes and finely myelinated nerve fibers in the lamina cribrosa indicates a sheath-supporting role. Astrocytes are probably generally concerned with the isolation and insulation of neurons and their processes. Oligodendrocytes may be concerned with the energetic support of neurons and their processes.

The Glioarchitectonics of the Chicken Optic Nerve

“…Therefore, it was possible to consider that the occurrence of the connective tissue septa in the chicken optic nerve head might, for one thing, depend upon the existence of the pecten. However, the astrocytes in this portion possessed enriched gliofilaments, and revealed a more or less different shape than astrocytes of other portions of the optic nerve, were the same in the chicken as in the cat, monkey and man (Anderson 1969, Anderson et al 1967, Wendell-Smith 1966. Astrocytes had been found to be grouped to form the cytoplasmic septum between the retina and optic nerve in the monkey as well as the chicken optic nerve, as pointed out in this study.…”

“…Oligodendroglia in the chicken optic nerve possessed almost the same characteristics in ultra-fine structures as those of the rat brain (Mori and Leblond 1970), the rat optic nerve (Peters, Palay and Webster 1970), the monkey and the human optic nerve (Anderson 1969) and the cat optic nerve (Wendell-Smith 1966) ; that is, a great amount of free ribosomes and rough-surfaced endoplasmic reticulum, well-developed Golgi complex and characteristic microtubules had been pointed out to be common structures of oligodendroglia. Mori and Leblond (1970) classified the oligodendroglia in the young rat brain into three types.…”

“…The connective tissue septa, at the optic nerve head anterior to the lamina cribrosa sclerae of the cat, monkey and man, were rapidly decreased in amount, but the cytoplasmic septa of the astrocyte came to be substituted for the connective tissue septa and to circumscribe each nerve fiber bundle , Anderson 1969, Anderson et al 1967, Wendell-Smith 1966. On the other hand, at the optic nerve head of the chicken the connective tissue was found to invade from the sclera and to be contiguous with the base of the pecten, which was an organ enriched in the vascular system, and was located characteristically on the surface of the avian optic nerve head.…”

“…As another particularity of the lamina cribrosa sclerae, it should be pointed out that the lamina cribrosa sclerae was the boundary where the optic nerve fibers changed from unmyelinated fibers to myelinated ones that is, in the cat, monkey and man (Anderson 1969, Anderson et al 1967, Blunt et al 1965, Wendell-Smith 1966) from the optic nerve head to the portion of the lamina cribrosa sclerae, the optic nerve fibers were all unmyelinated, and turned rapidly into myelinated nerve fibers immediately after passing through the lamina cribrosa sclerae. On the other hand, in the chicken optic nerve, thick nerve fibers had a myelin sheath for the whole length of the optic nerve from the optic nerve head to the optic chiasm, although thin nerve fibers were unmyelinated in the optic nerve head and in the portion of the lamina cribrosa sclerae, and got myelin sheaths immediately after passing the lamina cribrosa, sclerae.…”

Guillain-Barre syndrome associated with typhoid fever.

“…Webb (1967) and many others have suggested that demyelinization seen in these chronic neurological diseases is secondary to an abnormality of the glial cells. Both astrocytes and oligodendrocytes have been shown to be able to produce myelin (Wendell-Smith et al, 1966 ;Peters, 1964). If there is a situation of increased multiplication of glial cells their increased metabolic requirements may not permit them to con-tinue to support the myelin they have produced.…”