Electron Microscopic Observations of the Central Nervous System

Abstract

Study of the central nervous system by electron microscopyrequires identification of the neural and glial cells and of their processes. Superficial inspection. of electron micrographs reveals what first appears to be a bewildering array of components. Cells of varying sizes, shapes, and densities are recognizable by their nuclei, and in some instances, by the outline of their delimiting plasma membranes. Coursing among these cells are blood vessels, which may b e identified by the morphology of their endothelial elements and b y the presence of erythrocytes and leucocytes in their lumens. Between the cells and blood vessels, completely filling all available space, lies the neuropil. This component is a complexly interwoven meshwork of cellular processes derived from both neural and glial cells. It contains, in amounts which vary relative to one another in different locations, dendrites, axons (myelinated and unmyelinated), nerve endings, fibrous and protoplasmic processes of glial cells, and possibly~ an ill defined ground substance. By light microscopy, the relationships of: these components of the neuropil have been poorly understood, since only the larger elements could be resolved. With electron microscopy, even the smallest of the cellular processes can be visualized, but the complexity of the structures revealed makes identification of the various elements difficult.The problem of cellular identification has been approached by attempting, first, to correlate the characteristics of the neural and gilal cells as observed by light microscopy with the electron microscopic appearance of the same cells, Much information concerning the structure and interrelationships of the neural and glial cells has been obtained from use of the silver and gold chloride procedures of Ram6n y Cajal and of Del Rio-Hortega. In our interpretations, we have relied heavily on the accounts of Penfield (1) and Del Rio-Hortega (2). The nuclear differences which characterize the glial ceils can be seen both

Formation of Myelin in the Central Nervous System of Mice and Rats, as Studied With the Electron Microscope

“…Many of them, as has been illustrated here, are of oligodendroglial origin, but there is no clear indication that all of them are derived from oligocytes. And though the oligocyte is of increased prominence at the time of myelin formation, later it is the astrocytic folded membranes that closely invest all myelinated fibers centrally (14). This raises the question of functional significance of the two cell types.…”

Switching on cilia: transcriptional networks regulating ciliogenesis

“…In some rare cases, defects in ependymal motile cilia of the CNS can lead to swelling of the brain ventricles or to hydrocephalus (Afzelius, 1976) (reviewed by Boon et al, 2013). (Rhodin and Dalhamn, 1956); (B) X. laevis tracheal (Steinman, 1968) and R. pipiens pharyngeal (Fawcett and Porter, 1954) multicilia; (C) X. laevis epidermal multicilia (Steinman, 1968;Stubbs et al, 2008); (D) Human sperm flagellum and mouse oviduct multicilia (Fawcett, 1954); (E) Zebrafish (Wolenski and Hart, 1987) and Rana (Poirier and Spink, 1971) sperm flagella and R. pipiens oviduct multicilia (Fawcett and Porter, 1954); (F) Drosophila spermatocyte multiple cilia (Carvalho-Santos et al, 2012;Riparbelli et al, 2012) and sperm flagellum (Acton, 1966); (G) rat brain ependymal multicilia (Brightman and Palay, 1963) [immotile multicilia with a 9+0 configuration also exist in the choroid plexus (Narita et al, 2010)]; (H) X. laevis ependymal monocilia and multicilia (Hagenlocher et al, 2013) [these have a 9+2 configuration in R. temporaria (De Waele and Dierickx, 1979)]; (I) cilia on mouse spinal canal ependymal cells, which are normally biciliated (Luse, 1956); (J) zebrafish spinal canal ependymal cilia, which can have 9+0 or 9+2 configurations (Kramer-Zucker et al, 2005;Sarmah et al, 2007); (K) mouse nodal monocilia [most have a 9+0 configuration (Jurand, 1974;Sulik et al, 1994) but 9+2 cilia have been described (Caspary et al, 2007) with 9+4 cilia occasionally present in rabbit embryos (Feistel and Blum, 2006)]; (L) zebrafish KV monocilia (Kramer-Zucker et al, 2005); (M) rat kidney monocilia (Latta et al, 1961); (N) zebrafish pronephric multicilia and monocilia (Kramer-Zucker et al, 2005), and X. laevis pronephric multicilia (Fox and Hamilton, 1971); (O) rat signaling cilia (Sorokin, 1962); (P) zebrafish signaling cilia (S. Roy, unpublis...…”

Cellular Differentiation in the Kidneys of Newborn Mice Studied With the Electron Microscope

“…The terminal bar consists of a local thickening and increased density of the apposed cell membranes and resembles terminal bars in other epithelia (t~e adhesion plates of Palade and Porter, 1954;. Terminal bars also resemble the intercellular bridges of skin , the intercalated discs of cardiac muscle (SjSstrand and Andersson, 1954), the adhesion plates between neuroglial cells (Schultz, Berkowitz, and Pease, 1956), and synapfic membrane junctions in the nervous system (De Robertis and Franchi, 1956;Luse, 1956). Each of these sites of cellular juxtaposition is characterized by thickening and increased density of the apposed cell membranes.…”