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Biomedical subjects

M W Cohen

Publications and source records attributed to M W Cohen.

At least 55 records · Page 3Linked to original sources
PubMed1980

Development of an amphibian neuromuscular junction in vivo and in culture.

During normal development presumptive synaptic sites in the myotomes of Xenopus laevis begin to acquire a high density of ACh receptors within as little as 2 h after the arrival of the nerve fibres. Synaptic function also begins very shortly after the arrival of the nerve fibres. Initially synaptic currents are some eight times longer lasting than at maturity and are not prolonged by anticholinesterase. During the first day after nerve-muscle contact is made there is a considerable decrease in synaptic current duration, sensitivity to anticholinesterase develops, and synaptic ultrastructure becomes apparent. Schwann cells do not arrive until later. Synaptic development proceeds with a similar rapid time course in cultures of dissociated myotomes and spinal cord derived from Xenopus embryos. The cultured muscle cells also develop synaptic specializations in the absence of nerve including sites of high ACh receptor density, cholinesterase activity, and postsynaptic ultrastructure. Studies on mixed nerve and muscle cultures have further revealed that muscle impulse and contractile activity is unnecessary for the development of synaptic ultrastructure or for the localization of ACh receptors, that the localization of ACh receptors at nerve-muscle contacts is nerve-induced and involves a redistribution of surface receptors, and that the development of synaptic specializations does not occur at nerve-muscle contacts when the source of nerve is dorsal root ganglia or sympathetic ganglia rather than spinal cord.

Animals↗
PubMed1979

Development of synaptic ultrastructure at neuromuscular contacts in an amphibian cell culture system.

Cultures of dissociated myotomal muscle and spinal cord derived from embryos of Xenopus laevis were grown in the presence of curare in order to abolish neuromuscular activity and were examined by electron microscopy. In one-day-old cultures a few of the neuromuscular contacts already displayed several synaptic specializations including 500 A vesicles clustered against the axolemma, increased axolemmal densities, basal lamina in the cleft, an increased sarcolemmal density and subsarcolemmal filamentous material. Contacts with these specializations were observed more frequently in two and three-day-old cultures. Throughout the three-day culture period nerve fibres and neuromuscular contacts were devoid of Schwann cells. Isolated patches of basal lamina were relatively scarce and were usually accompanied by an increase in sarcolemmal density and subsarcolemmal filamentous material even in cultures in which spinal cord cells were not included. These observations indicate that the myotomal neuromuscular synapse differentiates in culture in much the same way as it does in vivo, that muscle contractions are not required for its differentiation, and that apparent postsynaptic specializations can develop in the absence of innervation.

Animals↗
PubMed1978

Problems with using dominance indices to evaluate family interaction patterns.

Used four well-accepted behavioral measures of dominance to document changes in dominant/submissive behaviors of marital couples as a result of videotape feedback of behavior in decision-making tasks. Dominance scores for 30 normal couples on each of the four indices were correlated, and results indicated that the measures bore little relationship to each other. Further, a review of videotaped interactions revealed little to warrant even intuitive support for three of the measures. Such data support the contention that these popular indices may be inappropriate to assess dominance across couples.

Behavior Therapy↗
PubMed1977

Denervated skeletal muscle fibers develop discrete patches of high acetylcholine receptor density.

Denervated skeletal muscle fibers of mice develop discrete patches of high acetylcholine receptor density. The patches vary in size from less than 1 micrometer up to 30 micrometers, depending on the muscle and the period of denervation. Within the patches the acetylcholine receptor density is some 20 times greater than elsewhere along the muscle fiber and probably approaches that in the subsynaptic membrane.

Acetylcholine↗
PubMed1977

Effects of innervation on the distribution of acetylcholine receptors on cultured muscle cells.

1. Myotomal muscle cells from embryos of Xenopus laevis were cultured as a monolayer either alone or together with neural tube cells from the same embryos. 2. Spontaneous twitching and contractions evoked by electrical stimulation of neural perikarya were observed only in nerve-contacted muscle cells, and could be abolished by curare or alpha-bungarotoxin. 3. Within 2 days in culture muscle cells not contacted by nerve developed one or more discrete patches of acetylcholine (ACh) receptors as revealed by staining with fluorescent conjugates of alpha-bungarotoxin. Similar patches were also seen when staining was carried out after paraformaldehyde fixation, suggesting that they were not induced by the dyetoxin conjugate. 4. Radioautography after labelling with [125I]alpha-bungarotoxin revealed patches with grain densities approximately twenty-five-old greater than over the remainder of the cell. 5. Fluorescent stain on innervated cells was restricted to the path of nerve-muscle contact and sometimes extended for greater lengths than the largest patches seen on non-contacted muscle cells. 6. Similar long bands of stain associated with nerve--muscle contacts were observed when cultures were grown in high concentrations of curare and carbachol which prevented spontaneous twitching. They were also seen in cultures in which the addition of neural tube cells was delayed for 2-3 days. 7. It is concluded that innervation caused receptors to accumulate at sites of nerve-muscle contact and that this process can operate independently of muscle activity.

Animals↗
PubMed1977

Nerve-induced and spontaneous redistribution of acetylcholine receptors on cultured muscle cells.

1. Theree-day-old cultures of myotomal muscle, obtained from embryos of Xenopus laevis, were stained with fluorescent conjugates of alpha-bungarotoxin and maintained in native toxin in order to ensure that ACh receptors subsequently inserted into the sarcolemma would not be stained. Neural tube cells were then added to the cultures. 2. When cultures were exmained 1-3 days later fluorescent stain was found to be associated with sites of nerve-muscle contact. In some cases the stain along the path of contact extended for greater distances than the patches of stain seen on non-contacted muscle cells. 3. The development of new areas of fluorescent stain at sites of nerve-muscle contact was confirmed by making successive observations on the same muscle cells over a period of a day. 4. Similar experiments on muscle cells not contacted by nerve revealed the formation of new receptor patches, usually in areas of cell growth. 5. The majority of fluorescent pathes on non-contacted muscle cells did not undergo changes in size or shape over the course of 1-2 days. However some examples of enlargement, shrinkage and disappearance were observed. 6. On the basis of these findings it is concluded that ACh receptors aggregate within the sarcolemma, spontaneously as well as in response to innervation. In the latter case extrajunctional receptors accumulate at the site of nerve contact thereby contributing to the development of high receptor density in the subneural muscle membrane. This process of receptors redistribution occurs in the absence of synaptic or contractile activity. 7. Possible mechanisms involved in the redistribution of ACh receptors are discussed in relation to those which appear to modulate ligand-induced changes in the distribution of lectin and immunoglobulin receptors.

Animals↗
PubMed1976

Citizen participation in the decision-making activities of formal social service agencies: an unreasonable goal?

In the past, attempts by social service agencies to include nonprofessional area residents in program planning and policy-making activities have met with little success. Such failures may be due in part to mistrust and a feeling that the agencies and their programs have little relevance to the problems faced by most people. Perhaps an alternative way of developing resident participation in community action programs would be to move the planning and decision-making process away from the trained experts associated with formal institutions to the residents within the neighborhoods themselves. The people living within a defined community would decide which problems they wish to address, and then use resources available within the community to solve them.

Community Mental Health Services↗
PubMed1976

Production of experimental toxemia in the pregnant dog.

The aortas of 14 pregnant bitches were treated 1 to 3 weeks before term, producing a stricture that reduced the lumen from an average normal of 7-11 mm to 2.1 mm in diameter. Nine animals developed hypertension, 3 had significant proteinuria, and 1 had fluid retention. Light microscopy revealed moderate or severe glomerular lesions in 9 animals characterized by endotlial cell swelling, mesangial cell proliferation, and focal basement membrane thickening; electron microscopy revealed mesangial enlargement and electron-dense deposits. Immunofluorescence with rabbit anti-dog fibrinogen showed glomerular deposition of fibrinogen or its breakdown products in 11 of 12 cases so studied. Focal necrosis was seen in the liver in 5 cases, and diffuse hemorrhagic infarction of the placenta was present in all animals. None of these changes was found in nonpregnant or in sham-operated controls.

Animals↗
PubMed1974

Fluorescent staining of acetylcholine receptors in vertebrate skeletal muscle.

1. alpha-Bungarotoxin was labelled with fluorescent dyes and used as a stain for visualizing the distribution of acetylcholine receptors in vertebrate skeletal muscle fibres.2. Dye-toxin conjugates had the same pharmacological properties as native toxin, but their potencies were lower.3. Fluorescent staining was examined in teased muscle fibres. The stain was found to be confined to the neuromuscular junction and associated with the subsynaptic membrane.4. Staining intensity was reduced by curare and even more so by carbachol, but not by atropine or neostigmine. Pre-treatment of muscles with unlabelled alpha-bungarotoxin entirely prevented staining.5. The staining at amphibian neuromuscular junctions was characterized by a pattern of intense transverse bands occurring at intervals of approximately 0.5-1 mum, with fluorescence of lower intensity between them. Fluorescent staining was not detected on adjacent, extrasynaptic, muscle membrane. In side views the staining appeared as a fine line with small protuberances occurring at the same intervals as the intense bands seen face-on. These results indicate that acetylcholine receptors are associated with the entire subsynaptic membrane, including the membrane of the junctional folds and that their density changes abruptly at the border between synaptic and extrasynaptic muscle membrane.

Animals↗
PubMed1970

The contribution by glial cells to surface recordings from the optic nerve of an amphibian.

1. The contribution by glial cells to surface recordings has been examined in the optic nerve of the amphibian Necturus maculosus. The method of current injection was employed selectively to alter the membrane potential of glial cells without affecting that of the axons. The resulting changes in potential were recorded simultaneously from the surface of the nerve using the sucrose gap method and intracellularly from a glial cell near the gap.2. The sucrose gap method recorded 40% of the changes in glial membrane potential. This percentage was not affected when the current electrode was inserted into different glial cells while maintaining the recording conditions constant.3. Following axonal degeneration, produced by removing the eye 2-3 months earlier, the percentage contribution by glia increased to 84%.4. By measuring sucrose gap responses to changes in K(o) it was possible to estimate that the sucrose gap method recorded 31-60% of changes in axonal membrane potential. It was also determined that the axons, unlike glial cells, are relatively insensitive to reductions in K(o). Surface responses to decreases in external potassium thus reflect the magnitude of the glial contribution.5. It is concluded that changes in glial membrane potential contribute about as much to surface recordings from the optic nerve of Necturus as do equivalent changes in axonal membrane potential. The contributions by the glial cells and axons are related to the relative volumes of tissue they respectively occupy. The significance of these findings to the analysis of surface recordings from the mammalian brain is discussed. Since mammalian glial cells, like those in Amphibia and the leech, become depolarized during neuronal activity and on the basis of electron microscopic evidence appear to be electrically coupled, it is likely that they contribute to the electroencephalogram.

Animals↗