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Biomedical subjects

C A Mason

Publications and source records attributed to C A Mason.

At least 91 records · Page 5Linked to original sources
PubMed1984

Two forms of cerebellar glial cells interact differently with neurons in vitro.

Specific interactions between neurons and glia dissociated from early postnatal mouse cerebellar tissue were studied in vitro by indirect immunocytochemical staining with antisera raised against purified glial filament protein, galactocerebroside, and the NILE glycoprotein. Two forms of cells were stained with antisera raised against purified glial filament protein. The first, characterized by a cell body 9 microns diam and processes 130-150 microns long, usually had two to three neurons associated with them and resembled Bergmann glia. The second had a slightly larger cell body with markedly shorter arms among which were nestled several dozen neuronal cells, and resembled astrocytes of the granular layer. Staining with monoclonal antisera raised against purified galactocerebroside revealed the presence of immature oligodendroglia in the cultures. These glial cells constituted approximately 2% of the total cell population in the cultures and, in contrast to astroglia, did not form specific contacts with neurons. Staining with two neuronal markers, antisera raised against purified NILE glycoprotein and tetanus toxin, revealed that most cells associated with presumed astroglia were small neurons (5-8 microns). After 1-2 d in culture, some stained neurons had very fine, short processes. Nearly all of the processes greater than 10-20 micron long were glial in origin. Electron microscopy also demonstrated the presence of two forms of astroglia in the cultures, each with a different organizing influence on cerebellar neurons. Most neurons associated with astroglia were granule neurons, although a few larger neurons sometimes associated with them. Time-lapse video microscopy revealed extensive cell migration (approximately 10 microns/h) along the arms of Bergmann-like astroglia. In contrast, cells did not migrate along the arms of astrocyte-like astroglia, but remained stationary at or near branch points. Growth cone activity, pulsating movements of cell perikarya, and ruffling of the membranes of glial and neuronal processes were also seen.

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PubMed1984

Neuron-astroglial interactions in vitro and their implications for repair of CNS injury.

To study neuron-glial interactions, our laboratory has developed an in vitro model system that, when used with cell type-specific antisera, allows visualization of contacts between cerebellar granule neurons and astroglia. When cells were dissociated from early postnatal mouse cerebellum and plated in microcultures, the neurons aligned along glial filament protein (GFP)-containing astroglial processes. The behavior of the neurons depended on the shape of the particular astroglial cell that they contacted. Neuronal migration commonly occurred along highly elongated astroglial processes of Bergmann-like glia but was inhibited when neurons nestled among the arms of stellate astroglia. To analyze the influence of neurons on the astroglial shapes associated with neuronal migration, cerebellar granule neurons and astroglia were purified and recombined. In the absence of neurons, cerebellar astroglia assumed a flattened shape and proliferated rapidly. In the absence of astroglia, neurite outgrowth was severely impaired. When neurons were recombined with purified astroglia, astroglial proliferation slowed markedly, the shape of the astroglia transformed into complex forms, and neuron-glial interactions were seen. In tissue sections, immature forms of glia were found in the developing cerebellar axon tracts, but no obvious relationship could be discerned between the growing axonal tips and the glia. At P7, a period when the growth of cerebellar axons slows markedly, a transient natural gliosis was seen in the putative white matter. These studies underscore the interdependence of neurons and astroglia during periods of neuron differentiation and neurite outgrowth. In addition, they raise the possibility that the disruption of normal neuronal-astroglial contacts suffered during CNS injury could lead to defects in astroglial form and surface properties that, in turn, might impair axon regrowth.

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PubMed1984

Defects in specific associations between astroglia and neurons occur in microcultures of weaver mouse cerebellar cells.

The neurological mutation weaver is characterized by defects in granule cell migration along Bergmann glial processes and by subsequent death and disposition of granule cells. Immunocytochemical localization of antisera raised against purified glial filament protein (AbGF) and transmission electron microscopy were used to visualize specific associations between granule neurons and astroglia in microcultures of cerebellar cells dissociated from normal (+/+), heterozygous (+/wv), and homozygous (wv/wv) B6CBA-w mouse cerebella. In microcultures of cells dissociated from normal B6CBA-Aw-J-wv (+/+) cerebella, staining with AbGF closely resembled results previously reported for cells taken from C57BL/6J (+/+) tissue. Two forms of stained astroglia were seen, one with a larger perikaryon and shorter processes, among which 12 to 20 unstained cells nestled; and another with a smaller cell soma and longer processes, along which a few unstained cells were seen. The first resembled astrocytes of the internal granular layer and white matter, the second Bergmann astroglia. In microcultures of heterozygous animals (+/wv), the number of granule cells was reduced slightly. Many stained astroglia resembled those from +/+ cerebella, but others had thickened processes and enlarged terminal "endfeet." Granule cells associated with both forms of stained astroglia. Cultures from homozygous weaver (wv/wv) cerebella contained very few, if any, granule cells and did not exhibit specific neuronal/glial interactions characteristic of +/+ cells. Both forms of stained wv/wv glial cells had enlarged cell somata giving rise to stunted processes, suggesting that both Bergmann glia and astrocytes are affected by the weaver gene. By both immunocytochemical staining and electron microscopy, accumulation and tangling of glial filaments were seen. Immunocytochemical staining of weaver cerebellar tissue with AbGF also revealed abnormalities in astrocytes of the internal granular layer and white matter in addition to previously reported defects in Bergmann glia. Agglutination with five plant lectins, each with a different carbohydrate-binding specificity, revealed that postnatal weaver cerebellar cells agglutinate with the lectins concanavalin A and the wheat germ agglutinin, suggesting the persistence postnatally of embryonic cell surface elements on postnatal weaver cells.

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PubMed1984

Postnatal maturation of cerebellar mossy and climbing fibers: transient expression of dual features on single axons.

We have studied the form and fine structure of developing afferent axons in postnatal mouse cerebellum, before and during the formation of synaptic connections. In slices of fresh brain, bundles of axons were injected with horseradish peroxidase (HRP), and individual axons were examined in the light and electron microscopes. At birth, before formation of cortical layers, axons with growing tips are rare in the peduncular tracts but instead ramify throughout the cerebellar anlage. All axons have similar structures; they branch infrequently and terminate in bud-like tips and/or small growth cones. Growth cones contain small and large vesicles in the flank and small vesicles in filopodia. Typical mossy and climbing fiber branching patterns and bouton shapes are recognizable after postnatal day (P) 5, even though fibers are still intermingled in a plexus beneath the newly formed Purkinje cell layer. Climbing fiber-like axon arbors are highly branched and covered with small foliate growing tips that contact Purkinje cells. Mossy fiber-like branches have large irregular expansions that give rise to long filopodia and resemble growth cones seen in vitro. The flanks of these growth cones contact granule cell dendrites and form glomeruli typical of mossy fibers, whereas the filopodia make primitive contacts or are associated with coated vesicles in adjacent profiles. A novel finding is the occurrence during the second postnatal week of many single axons that simultaneously have the morphology and synaptic connections of both climbing and mossy fibers. These "combination" axons have some branches that extend into the granule cell layer and others that enter the Purkinje cell layer, with the shape and synaptic connections of terminals on each branch type corresponding to the respective layer. Climbing fiber-like branches, including those on combination fibers, extend over several adjacent Purkinje cells. Combination fibers are rare in late postnatal or adult stages. These results suggest that long after arrival in the cerebellum, afferent axons have similar elementary forms and overlap in their projections. Mature axonal forms are not exhibited until cellular layers develop. During a limited period of postnatal maturation, some axons have dual morphologies and synaptic relations with appropriate and inappropriate partners. These aspects of cerebellar axonal development, particularly the transient exuberant branching onto two types of target cells, offer a valuable opportunity to examine, in developing cerebellum, the sorting out of afferents and the formation of specific synaptic connections.

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PubMed1983

Postnatal maturation of neurons in the cat's lateral geniculate nucleus.

The maturation of dendrites in the cat's dorsal lateral geniculate nucleus was studied in Golgi Kopsch preparations of kittens from 3 days to 8 weeks postnatal. During the first postnatal week, more than a month after their birthdate, cells are immature and lack dendrites, bearing only multiple somatic processes or a few short thick extensions. Cells enter an active phase of dendritic extension during the second postnatal week. Growth cone-like structures and filopodia occur at the ends of dendrites and also at dendritic branch points. Assignment to general cell classes based on dendritic disposition is possible only after this period, and characteristic grapelike appendages are obvious after the third week. Mature cells in the lateral geniculate nucleus are not considered spiny, yet spines and hairs are ubiquitous on most cells once dendrites elongate and remain numerous on peripheral dendrites even after the soma and proximal dendrites become smooth, by 4-6 weeks. The decline of spine levels continues after this period. All cells go through a similar but nonsynchronous sequence of maturation. Large cells may mature first, but no correlation was noted between rate of maturation and laminar location or retinal representation. In the second and third postnatal weeks, although the terminal arbors of retinal axons presynaptic to geniculate cells have already attained their final topography and laminar placement, the shape and synaptic relations of axon terminal swellings remain immature (Mason, '82a,b) through the most active phase of dendritic outgrowth. After 3 weeks, both retinal axons and target geniculate cell dendrites finalize the shapes of characteristics appendages and synaptic relations in tandem. Potential interactions between immature axon terminal arbors and dendrite-bare geniculate cells during dendrite outgrowth and subsequent remodeling of structural details are discussed.

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PubMed1982

Studies of retinal representations within the cat's optic tract.

The manner in which each retina can be mapped onto a single cross section of the optic tract of the cat has been defined by neuroanatomical methods. It has been found that the contralateral nasal hemi-retina and both temporal hemi-retinae are represented in each tract by multiple, rough maps which partially overlap one another. All maps show the same general orientation, with area centralis represented dorsomedially, lower retina represented dorsolaterally, and upper retina represented ventromedially. The peripheral part of the horizontal meridian is represented ventrolaterally. Labeling all of the fibers from one eye by axonal degeneration or autoradiographic methods shows that the crossed map is displaced dorsally and medially relative to the uncrossed map, leaving a dorsomedial crescent of pure crossed fibers. Localized retinal lesions or injections of 3H-amino acid show the general orientation of the maps. Lesions within the dorsomedial pure crossed crescent show that fibers in this crescent arise from retinal areas close to the optic disc, near the site of the early fetal fissure. Localized injections of horseradish peroxidase into the optic tract show the relationships of the several maps in terms of the retinal distribution of retrogradely labeled retinal ganglion cells. They show that axons of large and small cells map ventrolaterally in the tract while intermediate sizes map dorsomedially. They confirm that the crossed map is displaced relative to the uncrossed maps. It is suggested that the optic tract develops by fibers taking a position in the tract in accordance with their time of arrival at the chiasm. The several maps are displaced because they develop sequentially and the optic tract can be read as a developmental record, the most dorsomedial axons being the oldest.

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PubMed1982

Development of terminal arbors of retino-geniculate axons in the kitten--I. Light microscopical observations.

The maturation of terminal arbors of retino-geniculate axons was studied in normal kittens from 1 to 8 postnatal weeks. Horseradish peroxidase injected into the optic tract rostral to the lateral geniculate nucleus gave a dense fill of cut axons and their terminals, resembling results obtained by the Golgi methods. At 1 and 2 weeks postnatal, the overall size and extent of axon arbors is not significantly different than in the adult. However, terminal branches of axon arbors at this age give rise to high variable endings. They terminate in finely divided sprays of finger-like extensions and filopodia bearing small spikes rather than the characteristic clusters and strands of crenulated terminals of adult axons. The bases of these sprays are broad and irregular in contour, with foliate growth-cone-like structures occurring at the ends of some branches. At 3 weeks postnatal, terminal swellings become thicker and more crenulated in contour. By 5 to 6 weeks, axon arbors have adult-like terminals with respect to their size, shape and arrangement, although entire branches may still be immature with irregular terminal swellings. Small slightly indented terminals are also seen for the first time. By 8 weeks, axon arbors are generally mature, but occasionally have a bizarre and immature arrangement of fine extensions or growth-cone-like tips. Although these observations do not establish whether reduction of branches or of terminals takes place during postnatal maturation, they demonstrate that kitten retino-geniculate axon terminal arbors are highly immature and undergo considerable changes during the period optimal for induction of sprouting by eye enucleation. The morphogenetic maturation of terminal branches that begins at 3 weeks also marks a decline in their sprouting capacity, even though remodeling of terminals is not complete until after 8 weeks of age.

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PubMed1982

Development of terminal arbors of retino-geniculate axons in the kitten--II. Electron microscopical observations.

Individual retino-geniculate axon arbors from kittens of 1 to 8 postnatal weeks were densely filled with horseradish peroxidase. The light-microscopical appearance of various types of immature growing tips was correlated with their synaptic relations as seen in the electron-microscope. During the first 2 postnatal weeks, the broad irregular bases of spray-like terminal extensions as well as foliate growth-cone-like terminals contain the round synaptic vesicles and pale mitochondria characteristic of adult retinal terminals. They form elementary glomerular arrangements in which they are the central profile synapsing with dendritic profiles. Many postsynaptic profiles contain large electron-lucent vesicles characteristic of growing neurites, whereas the immature retinal terminations do not. The more numerous finger-like growing tips also contain round synaptic vesicles and make short en passage contacts onto dendrites and outgrowths of perikarya of geniculate cells. The latter type of contact is not seen in the adult. After 3 weeks, retinal terminals are larger and make contacts in distinctly glomerular arrangements. Glial sheaths are evident for the first time. By 6-8 weeks, the terminals which appear crenulated in the light-microscope are always the central profile in a mature glomerulus. Smaller rounder terminals make simple axo-dendritic contacts as in the adult. The few immature terminal structures seen at 8 weeks also contain synaptic vesicles, but their contacts are not adult-like, nor are their synaptic arrangements entirely surrounded by glia. These findings, along with those of the previous paper, demonstrate that (a) many retino-geniculate terminals establish synaptic contacts long before attaining their adult form; (b) during the period optimal for induction of translaminar axon sprouting (1-2 weeks postnatal), only a few immature terminal forms participate in elementary glomeruli; (c) the decreasing malleability of these axons after 3 weeks is accompanied by an increase in crenulated terminals that enter glomeruli surrounded by glial sheaths. It is suggested that ensheathing of synaptic arrangements by astrocytic glia may be one factor which subsequently impedes axon sprouting in older animals.

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PubMed1981

A demonstration of several independent, partially overlapping, retinotopic maps in the optic tract of the cat.

We show here that the retina in the cat's optic tract by several separate, retino-topically organized maps. Fibers in different diameter classes form independent maps, and both hemi-retinae of the opposite side, as well as the temporal retina of the same side, are mapped in the tract. These several maps form rough topographic representations significantly out of register with each other.

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PubMed1980

An analysis of the retinal afferents to the cat's medial interlaminar nucleus and to its rostral thalamic extension, the "geniculate wing".

The retinal afferents to the medial interlaminar nucleus and to its rostro-dorsal extension at the edge of the pulvinar have been studied in cats by fiber degeneration and autoradiographic methods. Fiber degeneration following section of one optic nerve shows two distinct retinal inputs: One is coarse-fibered and goes to the medial interlaminar nucleus itself; the second, which is fine-fibered, goes to the rostral and medial borders of the medial interlaminar nucleus and continues into the pulvinar. The regions in receipt of these fine fibers have been called the "geniculate wing". The topography of retinal representations and the degree of binocular overlap within the medial interlaminar nucleus and the wing have been studied by combining intraocular injections of 3H proline with local lesions of the injected eye, or with removal of the non-injected eye. In the medial interlaminar nucleus three distinct laminae are recognizable and are particularly clearly shown in horizontal sections. Rostrally and medially, lamina 1 maps the contralateral nasal retina as a mirror reversal of lamina A. Posterior and lateral to this, lamina 2 maps the ipsilateral temporal retina as a mirror reversal of lamina A1. Lamina 3 lies closest to the optic tract and receives crossed afferents from the temporal retina. In this lamina, which is the smallest, vertical retinal dimensions map as in the other layers, but we were unable to determine the mapping of the horizontal dimensions. In the geniculate wing, as in the other geniculate layers, vertical lines of the visual field are mapped as corresponding vertical diencephalic dimensions; horizontal retinal dimensions are mapped as horizontal lines in the wing, with central retinal areas represented furthest from the optic tract. In the geniculate wing the contralateral nasal and ipsilateral temporal retina are mapped with considerable binocular overlap. The crossed temporal retina has no demonstrable representation in the wing.

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PubMed1978

Terminal arbors of axons that have formed abnormal connections.

Ther terminal arbors of individual retinogeniculate axons that have been induced to grow into an inappropriate geniculate layer have been revealed for light and electron microscopic study by being filled with horseradish peroxidase. After a unilateral ocular enucleation in kittens, single axons from the surviving eye show terminal arbors not only within their own geniculate layers but also in the denervated layers. The new, abnormal arbors arise from the terminal segments of arbors that lie within the nondenervated layer and make patterns of synaptic contacts that appear normal.

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PubMed1977

The seventh cranial nerve of the rat. Visualization of efferent and afferent pathways by cobalt precipitation.

The cobalt sulphide precipitation technique, in conjunction with Timm's intensification procedure, was used to delineate the afferent and efferent intramedullary pathways of the seventh cranial nerve complex in the rat. The branchial motor nucleus with the accompanying first part, genu, and second part of the root are described. The motor branches to the superficial facial musculature do not contain fibres of geniculate ganglion origin or fibres which terminate in the spinal trigeminal nucleus. The motor branches to the deep facial muscles arise from the dorsal part of the branchial motor nucleus and traverse to the midline medial to the genu, then project under the genu into the lateral reticular formation before exiting with the facial nerve. The salivatory and lacrimal nuclei and their intramedullary pathways are described. Sensory fibres from the cutaneous auricular branch enter the spinal trigeminal tract and most of the chorda tympani gustatory fibres enter the fasciculus solitarius. A smaller number of gustatory fibres extend medially to the region of the salivatory nucleus. Fibres of greater superficial petrosal origin also enter the fasciculus solitarius as well as the medial reticular formation. These findings are discussed in relation to previous anatomical, physiological and clinical reports.

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PubMed1977

Prevalence and effects of Parelaphostrongylus tenuis in a captive wapiti population.

Prevalence of neurologic disease attributed to Parelaphostrongylus tenuis was investigated in a population of wapii (Cervus elaphus canadensis) enclosed in a 2080 ha. preserve. Brains of 44 animals harvested in 1973, 1974 and 1975 were examined grossly and microscopically. Prevalence of infection increased each year from 26.6% of the sample in 1973 to 64.3% in 1975. These data suggest that wapiti living close to white-tailed deer (Odocoileus virginianus) may have a high prevalence of infection, but many individuals may not show signs. Accordingly, routine histologic examination of natural mortality cases without supporting observations of clinical signs would be inadequate to define cause of death. While the effects of the parasite in the population studied did not produce a high herd mortality or a sudden die-off situation, the apparent greater susceptibility of the younger age-classes to the parasite would have a detrimental effect on population recruitment and might limit the growth of wapiti herds living in proximity to white-tailed deer that harbor P. tenuis.

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