The fine structure of nerve cells and fibers, neuroglia, and sheaths of the ganglion chain in the cockroach (Periplaneta americana)

The abdominal nerve cord of Periplaneta americana was studied utilizing light and electron microscopes. In the nerve cells, delicate granules, similar to those probably responsible for cytoplasmic basophilia, are evenly distributed in "dark" cells and clumped in "light" cells. Neuroglial cells are stained metachromatically by cresyl violet. The neuroglial cells have many processes which ramify extensively and are enmeshed to form overlapping layers. These imbricated processes ensheath the nerve cells; the inner layer of the sheath penetrates into the neuron and is responsible for the appearance of the trophospongium of Holmgren. Nerve fibers are embedded within glial cells and surrounded by extensions of the plasma membrane similar to mesaxons. Depending on their size, two or several nerve fibers may share a single glial cell. Nerve fibers near their terminations on other nerve fibers contain particles and numerous, large mitochondria. The ganglion is ensheathed by a thick feltwork of connective tissue and perilemmal cells. The abdominal connective has a thinner connective tissue sheath which is without perilemmal cells. The nerve fibers and sheaths in the connective become thinner as they pass through ganglia.

Concentric lamination of glial processes in oligodendrogliomas

Tissues were obtained by open biopsy of a series of human intracranial neoplasms, fixed in Veronal-buffered osmium tetroxide, and embedded in Vestopal-W. In two instances in which specimens were obtained from oligodendrogliomas in regions where the tumor had infiltrated but not entirely destroyed cortical tissues, glial processes were found to be arranged in a highly organized laminar fashion. This feature was not observed in two additional oligodendrogliomas nor in other types of intracerebral neoplasms. Three types of laminar structures were recognized: (a) perikaryal sheaths composed of several layers of overlapping or concentrically orientated glial processes, (b) layers of longitudinally orientated glial processes along the outer aspect of myelinated axons, and (c) small laminated figures composed of several concentrically disposed glial processes. Spirally constituted lamellar systems were not demonstrated. These findings indicate that under certain circumstances glial cells have the capacity to form sheaths and sheath-like structures by concentric lamination of several processes, rather than by spiraling of a single process.

OBSERVATIONS ON PRISMATIC-TYPE MITOCHONDRIA WITHIN ASTROCYTES OF THE SYRIAN HAMSTER BRAIN

This paper describes a special form of mitochondria which has been observed using the electron microscope in certain astrocytes of the Syrian hamster brain. The interior structural pattern of these mitochondria is characterized by the presence of numerous equilateral prismatic tubules in a highly regular hexagonal arrangement, instead of the customary foliate cristae. Such mitochondria have been designated as "prismatic type," in contradistinction to the more usually encountered crista and tubular types. The findings are compared with the occasional similar findings reported in the literature, and their possible functional meaning is briefly discussed.

HELICAL FILAMENTS IN ASTROCYTIC MITOCHONDRIA OF THE CORPUS STRIATUM IN THE RAT

Astrocytic mitochondria have been studied in serial electron micrographs of the corpus striatum. Special filaments have been found inside several of these mitochondria located in both the cell body and the processes. They were particularly frequently observed in the pericapillary end-feet. The filaments occur within dilated intracristal spaces provided with several communications with the outer chamber, and form helices which are oriented approximately in the same direction. Each filament is about 30 A thick, the diameter of the helix is 140 A, and the pitch is 120 A. Their possible nature and significance are briefly discussed. There is no clear relationship between these mitochondria and other unusual forms of mitochondria previously described in astrocytes from other regions.

AN ELECTRON MICROSCOPE STUDY OF CULTURED RAT SPINAL CORD

Explants prepared from 17- to 18-day fetal rat spinal cord were allowed to mature in culture; such preparations have been shown to differentiate and myelinate in vitro (61) and to be capable of complex bioelectric activity (14–16). At 23, 35, or 76 days, the cultures were fixed (without removal from the coverslip) in buffered OsO₄, embedded in Epon, sectioned, and stained for light and electron microscopy. These mature explants generally are composed of several strata of neurons with an overlying zone of neuropil. The remarkable cytological similarity between in vivo and in vitro nervous tissues is established by the following observations. Cells and processes in the central culture mass are generally closely packed together with little intervening space. Neurons exhibit well developed Nissl bodies, elaborate Golgi regions, and subsurface cisternae. Axosomatic and axodendritic synapses, including synaptic junctions between axons and dendritic spines, are present. Typical synaptic vesicles and increased membrane densities are seen at the terminals. Variations in synaptic fine structure (Type 1 and Type 2 synapses of Gray) are visible. Some characteristics of the cultured spinal cord resemble infrequently observed specializations of in vivo central nervous tissue. Neuronal somas may display minute synapse-bearing projections. Occasionally, synaptic vesicles are grouped in a crystal-like array. A variety of glial cells, many apparently at intermediate stages of differentiation, are found throughout the otherwise mature explant. There is ultrastructural evidence of extensive glycogen deposits in some glial processes and scattered glycogen particles in neuronal terminals. This is the first description of the ultrastructure of cultured spinal cord. Where possible, correlation is made between the ultrastructural data and the known physiological properties of these cultures.

THE FINE STRUCTURE OF THE RAT CEREBELLUM. II. THE STELLATE NEURONS, GRANULE CELLS, AND GLIA

This paper describes the fine structure of the granule cells, stellate neurons, astrocytes, Bergmann glia, oligodendrocytes, and microglia of the rat cerebellum after fixation by perfusion with buffered 1 per cent osmium tetroxide. Criteria are given for differentiating the various cell types, and the findings are correlated with previous light microscope and electron microscope studies of the cerebellum.

THE ULTRASTRUCTURE OF MAUTHNER CELL SYNAPSES AND NODES IN GOLDFISH BRAINS

An electron microscope study of goldfish Mauthner cells is reported.¹ The cell is covered by a synaptic bed ∼ 5 µ thick containing unusual amounts of extracellular matrix material in which synapses and clear glia processes are implanted. The preterminal synaptic neurites are closely invested by an interwoven layer of filament-containing satellite cell processes. The axoplasm of the club endings contains oriented mitochondria, neurofilaments, neurotubules, and relatively few synaptic vesicles. That of the boutons terminaux contains many unoriented mitochondria and is packed with synaptic vesicles and some glycogen but no neurofilaments or neurotubules. The bare axons of club endings are surrounded by a moderately abundant layer of matrix material. The synaptic membrane complex (SMC) in cross-section shows segments of closure of the synaptic cleft ∼ 0.2 to 0.5 µ long. These alternate with desmosome-like regions of about the same length in which the gap widens to ∼ 150 A and contains a condensed central stratum of dense material. Here, there are also accumulations of dense material in pre- and postsynaptic neuroplasm. The boutons show no such differentiation and the extracellular matrix is largely excluded around them. The axon cap is a dense neuropil of interwoven neural and glial elements free of myelin. It is covered by a closely packed layer of glia cells. The findings are interpreted as suggestive of electrical transmission in the club endings.

THE ENZYMATIC RESPONSE OF ASTROCYTES TO VARIOUS IONS IN VITRO

The effect of environmental ion concentration on the enzyme activity of astrocytes was investigated in tissue cultures of rat cerebral cortex. It was found that the oxidative enzymatic activity (succinic dehydrogenase, DPN-diaphorase, and several other enzymes) of astrocytes depended on the concentration of NaCl in the environment. This response was not specific for NaCl, but was also elicited by MgCl(2) and LiCl; the response was less consistent, and often questionable for KCl. However, only NaCl could elicit enzymatic changes in astrocytes at concentrations known to be present in a living organism. Astrocytes were the only cells which responded this way; it appeared that the foot-plates were particularly involved in the response since increase of enzyme activity occurred earlier in the foot-plates than in the perikarya. It was concluded that astrocytes are metabolically involved in the maintenance of the ionic and osmotic environment of the central nervous system, particularly in regard to the active transport of sodium.

A STUDY OF EXTRACELLULAR SPACE IN CENTRAL NERVOUS TISSUE BY FREEZE-SUBSTITUTION

It was attempted to preserve the water distribution in central nervous tissue by rapid freezing followed by substitution fixation at low temperature. The vermis of the cerebellum of white mice was frozen by bringing it into contact with a polished silver mirror maintained at a temperature of about -207°C. The tissue was subjected to substitution fixation in acetone containing 2 per cent OsO₄ at -85°C for 2 days, and then prepared for electron microscopy by embedding in Maraglas, sectioning, and staining with lead citrate or uranyl acetate and lead. Cerebellum frozen within 30 seconds of circulatory arrest was compared with cerebellum frozen after 8 minutes' asphyxiation. From impedance measurements under these conditions, it could be expected that in the former tissue the electrolyte and water distribution is similar to that in the normal, oxygenated cerebellum, whereas in the asphyxiated tissue a transport of water and electrolytes into the intracellular compartment has taken place. Electron micrographs of tissue frozen shortly after circulatory arrest revealed the presence of an appreciable extracellular space between the axons of granular layer cells. Between glia, dendrites, and presynaptic endings the usual narrow clefts and even tight junctions were found. Also the synaptic cleft was of the usual width (250 to 300 A). In asphyxiated tissue, the extracellular space between the axons is either completely obliterated (tight junctions) or reduced to narrow clefts between apposing cell surfaces.

GAMMA-GLOBULIN AFFINITY FOR NORMAL HUMAN TISSUE OF THE CENTRAL NERVOUS SYSTEM

Immunofluorescent staining of the serum and cerebrospinal fluid of patients with and without neurological disease demonstrates an affinity of the gamma-globulin fraction for glial cells and myelin sheaths in normal human nervous tissue. This affinity appears to be specific for the 7S gamma-globulin fraction and is not seen with the other major protein fractions of serum and cerebrospinal fluid or with the fluorescein conjugated antisera alone.

TISSUE CULTURE STUDIES OF GLIOMAS. I. INTRANUCLEAR INCLUSIONS IN GLIAL CELLS

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PARTICLES RESEMBLING PAPOVA VIRUSES IN HUMAN CEREBRAL DEMYELINATING DISEASE

Degenerated brain tissue obtained from a deceased patient who had progressive multifocal leukoencephalopathy had been fixed in formalin prior to processing for electron microscopy. In ultrathin sections virus-like particles resembling papova virions were frequently observed in glial nuclei. Correlation with light-microscopy findings suggests that demyelination resulted from the cytocidal effect of the virus on oligodendroglia.

PROGRESSIVE MULTIFOCAL LEUCOENCEPHALOPATHY

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HISTOCHEMISTRY OF THE NEUROGLIA AND MYELIN IN EXPERIMENTAL CEREBRAL OEDEMA

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