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R M Devon

Publications and source records attributed to R M Devon.

17 recordsLinked to original sources
PubMed2000

Macrophages: their myelinotrophic or neurotoxic actions depend upon tissue oxidative stress.

There are still questions regarding whether macrophages found in MS lesions are agents of recovery or of destruction. To address this, we examined in aggregate cultures prepared from dissociated embryonic spinal cord tissue, with or without addition of exogenous macrophages, the effect of menadione-induced oxidative stress. Similar to findings of other laboratories, we observed that in the absence of oxidative stress macrophage enrichment promoted myelinogenesis. In macrophage-poor cultures, menadione at 5 microM had very little effect upon the status of the aggregate cultures; however, increasing this to 10 and 20 microM did result in some damage to axons and myelin. By contrast, in macrophage enriched cultures, menadione at a concentration as little as 5 microM caused the complete destruction of the aggregates. We suggest that in neural tissues that have sufficiently high macrophage numbers, oxidative stress results in a positive inflammatory feedback loop that results in massive tissue destruction. We further suggest that what we see in macrophage-enriched aggregates subjected to oxidative stress may represent what happens in the Marburg-type of MS lesion.

Animals↗
PubMed1992

Effects of dorsal column demyelination on evoked potentials in nucleus gracilis.

Intraspinal injections of lysolecithin were used to produce unilateral demyelination in the dorsal columns of the rat spinal cord. The purpose of this study was to evaluate the effects of demyelination on the conductive properties of axons belonging to a spinal pathway of known origin and site of termination. At 5 and 50 day intervals following injections, animals were prepared for acute experiments during which recordings of tibial nerve evoked potentials were made from the surface of the lumbar spinal cord (L5-L6) and nucleus gracilis (0.5-1.0 mm caudal to obex). Latency, duration, and strength of potentials were evaluated in control (uninjected) and lysolecithin-injected animals. The analysis of these potentials showed increases in latency and decreases in duration and strength of responses recorded 5 days after lysolecithin injections. Animals examined 50 days postinjection showed a decreased latency and increased duration and strength of responses compared to those recorded 5 days postinjection. Ultrastructural examination of lysolecithin injection sites showed these improvements to parallel the remyelination of axons by oligodendrocytes and Schwann cells. The improvement in physiologic characteristics of evoked potentials coupled with the remyelination of dorsal column axons supports the conclusion that remyelination of chemically demyelinated axons is an important factor in reestablishing the functional connectivity of demyelinated axons.

Animals↗
PubMed1991

Colloidal gold as a permanent marker of cells.

We have demonstrated that colloidal gold-labelled serum proteins are taken up by a number of cells in cultures established from the postnatal rodent neopallium. The colloidal gold enters and remains within secondary lysosomes over extended periods of time and, as well, persists after the subculture of these cells. The cell types that readily take up the label in our culture system are type-1 astrocytes, glial precursor cells and macrophages, whereas, only a small number of oligodendrocytes take up the label. The use of serum proteins to introduce colloidal gold into cells therefore seems to be a convenient and easy way to permanently mark cells.

Animals↗
PubMed1991

Muscle derived motoneuron trophic factors promote the survival of motoneurons in vitro only when serum is present in the growth medium.

Motoneuron cultures were established from E6 chick spinal cord. Motoneurons survived for less than 2 days in chemically defined medium. The addition of muscle extract to the medium supported the survival of only a small portion (approximately 2%) of motoneurons for 8 days in vitro. A similar low survival rate was observed when the growth medium was supplemented with serum. The addition of muscle extract to serum containing medium resulted in the survival of about 20% of the motoneurons for 8 days. No differences were seen in the ability of tissue extracts prepared from E8 hindlimb, or muscle obtained from E11, E15, E18 and P3 chicks to support motoneuron survival in the presence of serum. It is apparent that although there are trophic factors present in muscle that support motoneuron survival in vitro, the actions of such trophic factors are dependent upon the presence of yet other factors found in serum.

Animals↗
PubMed1990

Macromolecular translocation--a possible function of astrocytes.

We have used dense astrocytic cultures, which display a multilamellar geometry, to determine whether translocation of macromolecules can occur across astrocytic processes. Colloidal gold-labelled transferrin and serum albumin were allowed to bind to the most superficial of the astrocytic cell membranes at 4 degrees C, the temperature was then increased to 37 degrees C and the fate of these gold-labelled macromolecules was observed using the electron microscope. The gold-labelled macromolecules appeared to undergo receptor-mediated endocytosis followed by translocation and exocytosis, with the colloidal gold-labelled macromolecules moving from the apical to the more basal processes. After 1 h of incubation at 37 degrees C, colloidal gold became accumulated within secondary lysosomes of the basal-most layer of astrocyte processes. Since the extracellular space of the central nervous system (CNS) consists of narrow tortuous channels formed to a great extent by the multitude of processes extending from fibrous and protoplasmic astrocytes, these observations suggest to us that one function of astrocytes may be to facilitate transport of macromolecules from one cell to another.

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PubMed1990

Calcitonin gene-related peptide identifies spinal motoneurons in vitro.

Cell dissociation of E6 chick spinal cord followed by isolation of larger low-density cells by using a discontinuous density metrizamide gradient resulted in the obtention of a motoneuron-enriched fraction of cells. These cells were cultured in the presence of horse serum and muscle extract for a period of 8 days and examined for the presence of calcitonin gene-related peptide. More than 90% of such cells were positive for calcitonin gene-related peptide. When E14 spinal cord was examined, calcitonin gene-related peptide was present only in the axons of primary sensory neurons and in the somas of motoneurons in the ventral horns. It is concluded that more than 90% of the neurons in our cultures are motoneurons.

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PubMed1989

Dynamic morphological responses of mouse astrocytes in primary cultures following medium changes.

Within 5 minutes of changing the medium of 3-4 week old mouse astrocyte cultures, dramatic morphological alterations were seen in the cultures at the phase microscope level. These alterations included the appearance of membrane ruffles, followed by the formation of phase light vacuolar regions. Ultrastructurally, these ruffles could be seen as phagocytic arms, and the vacuoles appeared as blisters of the superficial cell layer. These morphological responses were due to the introduction of new serum proteins. Colloidal gold-labelled serum proteins were used to visualize the dynamics of the macromolecular uptake following this medium change. Some proteins were taken up by phagocytosis, whereas others were associated with coated vesicles and endosomal vesicles. The majority of these gold-labelled proteins were concentrated in vacuoles (presumably lysosomes) and were localized in the superficial cellular sheets. Inner cellular sheets contained little colloidal gold-labelled serum proteins, but displayed prominent pinocytotic profiles. Glucose consumption in these cultures remained constant at 1.6 mumoles/mg protein/hr. Glycogen content varied among individual cells, but it remained constant in the cultures at 60 nmoles bound glucose/mg protein throughout the 48 hour examination period. These results suggest that dense cultures of primary astrocytes may act similarly to the glia limitans.

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PubMed1988

Structural complexity of primary cultures of astrocytes as revealed by transverse sections.

The tissue architecture of low-, medium-, and high-density primary mouse astroglial cultures was examined in horizontal and transverse planes using the electron microscope. It was found that the low-density (colony) cultures consisted of a true monolayer, whereas the medium- and high-density (confluent) cultures consisted of anywhere from two to seven overlapping sheets enclosing a substantial intercellular space. The presence of these multiple overlapping sheets in confluent astrocyte cultures should therefore be taken into consideration when interpreting data of cell-membrane-related phenomena such as ion fluxes.

Animals↗
PubMed1987

Comparison of oligodendrocytes grown in neocortex and spinal cord aggregate cultures.

Mechanically dissociated cells of mouse central nervous system (CNS) (neocortex and spinal cord) form spherical aggregates in rotation culture and develop into populations of mature neurons and glial cells. Synapses and myelination of axons are evident in these aggregates although onset of these processes differs between aggregate types. In this study neocortex aggregates display synapses at 2 weeks in culture but do not demonstrate myelination of axons until 8 weeks. Spinal cord aggregates demonstrate myelinated axons at 2 weeks in culture although there are few synapses evident. The difference in myelination onset is due in part to the development of predominantly perineuronal oligodendrocytes in neocortex aggregates compared to the development of interfascicular oligodendrocytes in spinal cord aggregates. Both types of oligodendrocytes exhibit light, medium and dark categories and both cell types are capable of myelinating axons in culture.

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PubMed1987

Procedure for establishing oligodendroglial cells in primary cultures based on developmental parameters.

We have established cultures using dissociated cells obtained from the neopallium of mouse pups at several different stages of development. The cellular composition of these cultures changed from more than 95% astrocytes when cultures were established from the neopallium of neonates to more than 90% oligodendrocytes when cultures were established from the neopallium of 2-week-old pups. The oligodendrocytic nature of the cells was established on morphological bases as well as the presence of an oligodendrocytic marker, galactocerebroside.

Age Factors↗
PubMed1984

Astrocyte cell lineage. V. Similarity of astrocytes that form in the presence of dBcAMP in cultures to reactive astrocytes in vivo.

The relationship between astrocytes forming in the presence of dibutyryl cyclic AMP (dBcAMP) in culture and reactive astrocytes responding to a cerebral cortex stab wound was investigated using computerized image analysis (Zeiss IBAS 1) and immunocytochemical staining. The diameters of the nuclei of astrocytes in primary cultures of newborn mouse neopallial cells were compared to those of the nuclei of normal and reactive astrocytes in histological sections of mouse cerebral cortex. We found that the nuclei of astrocytes that formed in the presence of dBcAMP in cultures are significantly larger than those of spontaneously occurring small stellate astrocytes in culture and of normal astrocytes of the cerebral cortex in vivo but corresponded more closely to the nuclei of reactive astrocytes in the area surrounding a stab wound in the cerebral cortex. Large stellate cells formed in the presence of dBcAMP had vimentin and an increase in GFP-containing intermediate filaments. Formation of reactive astrocytes in vivo is also associated with an increase in both vimentin and GFP-containing intermediate filaments. These observations indicate a closer relationship of astrocytes formed in the presence of dBcAMP in cultures to the reactive astrocytes in the cerebral cortex than to normal astrocytes. We propose, therefore, that the large stellate astrocytes that form in the presence of dBcAMP be referred to as reactive astrocytes in culture.

Animals↗
PubMed1983

Fibrous astrocytes and reactive astrocyte-like cells in transplants of cultured astrocyte precursor cells.

Mouse neopallium was disaggregated at 3 developmental stages (E15, E18, PO) and grown in colony cultures for 7 days. On the seventh day of culturing the colonies of cells were transplanted into the cerebellums of neonatal mice. After 3 weeks the astrocytes within the transplants were identified with GFAP immunoperoxidase staining and by morphometric nuclear measurements of the GFAP positive cells. Cultures of E15 and E18 disaggregated neopallium gave rise to typical fibrous astrocytes in the transplants which were similar to fibrous astrocytes in the cerebral white matter of adult mice. Cultures of PO disaggregated neopallium gave rise to reactive astrocyte-like cells in the transplants which stained intensely for GFAP and had nuclei significantly larger than the astrocytes in the cerebral white matter of adult mice and in transplants of the E15 and E18 cultures.

Animals↗
PubMed1981

Synaptic parameters in developing rat cerebral cortex: comparison of anaesthetized and unanaesthetized states.

The ultrastructure of synapses from the molecular layer of parietal cortex was examined in male rats aged between 7 and 75 days. Two groups were compared, one group consisting of rats anaesthetized with 50 mg/kg pentobarbitone and the other consisting of those killed by stunning across the back of the neck. Various synaptic parameters were analyzed. In the anaesthetized material, the sectioned area of the pre-synaptic terminals decreases between 7 and 75 days, as does the number of terminals containing intraterminal profiles other than synaptic vesicles. Mean synaptic vesicle number per terminal increases, while the remaining parameters fluctuate over the developmental period. Comparing these data with those from the unanaesthetized material, the only parameters showing similar trends are the pre-synaptic terminal area, the mean vesicle number per terminal, and the length of the postsynaptic thickening. The remaining parameters are comparable up to 15 or 21 days postnatally, after which they diverge. The percentage of terminals containing intraterminal profiles, the terminal perimeter and the mean vesicle density in the unanaesthetized terminals all show increased values. The form factor indicates these terminals are more ellipsoidal by 75 days, while the mean synaptic curvature is more positive by 75 days. It is concluded that the synaptic organization of the early terminals differs from that of the older ones, and this may be related to different mechanisms of transmitter storage and release.

Age Factors↗
PubMed1979

Synaptic terminal parameters in unanesthetized rat cerebral cortex.

The ultrastructure of synapses from the molecular layer of parietal cortex was examined in two groups of unanesthetized rats. Rats of the first group were killed by stunning across the back of the neck, and those of the second group by the introduction of fixative through a preimplanted carotid artery cannula. Comparison of synapses from the two groups revealed that the distribution of synaptic types was the same. A larger percentage of synapses of the cannulated group has vesicle attachment sites than did those of the stunned group. The area and perimeter of the presynaptic terminals were significantly larger in synapses from the cannulated group, although the equivalent length of the postsynaptic thickening was less. The mean value for synaptic curvature was greater in the cannulated group, although over 80% of synapses in both groups had positive curvatures. No significant differences were found between the groups for the relationships between presynaptic terminal area and synaptic vesicle number, and between postsynaptic thickening length and synaptic curvature. Membrane recycling is suggested as a mechanism of accounting for the differences. The preponderance of postively-curved synapses in unanesthetized material may indicate a preponderance of functioning synapses.

Anatomy↗
PubMed1978

An ultrastructural study into the effects of pentobarbitone on synaptic organization.

A series of adult male rats was analyzed to test the effects of varying doses of pentobarbitone sodium on the ultrastructure of synapses in the molecular layer of the parietal cortex. The rats were divided into the following categories: unanaesthetized stunned, unanaesthetized cannulated and those subjected to 40, 80, 160, 300, or 400 mg/kg pentobarbitone. All material was examined both qualitatively and quantitatively after aldehyde-OsO4 or ethanolic phosphotungstic acid (E-PTA) treatment. The principal qualitative observations were: the preponderance in the unanaesthetized stunned and 160-400 mg/kg material of a variety of intraterminal profiles including synaptic vesicles, mitochondria, coated vesicles, tubular profiles, vacuoles, cisterns and double membrane profiles; the presence of exocytotic sites along the presynaptic membrane in the unanaesthetized stunned and cannulated material; the presence of endocytotic sites over the limiting membrane of the terminal away from the cleft in the unanaesthetized stunned and 160-400 mg/kg material; the prominence of the presynaptic network in the unanaesthetized and 40 mg/kg E-PTA material; discontinuity of the cleft material in the 40-160 mg/kg material. Findings to emerge from the quantitative aspect of the study show that pentobarbitone influences synaptic curvature, with a marked increase in curvature negativity over the 0-80 mg/kg dose range and a decrease in negativity at higher dose levels. The increase in curvature negativity is accompanied by an increase in synaptic length and dense projection numbers, with a consonant increase in the perimeter and area of the presynaptic terminal. Reversal of the negativity trend at higher dose levels is parallelled by reversal of these accompanying trends. Both sets of findings can be accounted for by membrane recycling within the terminal, supporting a membrane redistribution hypothesis.

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