Myelin Forms Research Articles

The sensitivity of the myelin sheath, particularly the Schwann cell-axolemmal junction, to lowered calcium levels in cultured sensory ganglia

Light and electron microscopic observations were made on myelinated cultures of sensory ganglia maintained for 2–12 days on media with low calcium (0.025–0.050m M) or normal calcium (1.5–2.0m M) levels. After 18 h at low calcium levels, lengthening of the node of Ranvier and apparent fluid accumulation between the axon and the myelin sheath were observed in the light microscope. Electron microscopic observations indicated that these changes began with an accumulation of fluid between the Schwann cell terminal loops in the paranodal region, shrinkage and stretching of the terminal loops, and eventual breaking of the junction between the loops and the axolemma. Accompanying these changes was substantial fluid accumulation in the periaxonal space along much of the internode. These changes were found to be slowly reversible upon return to media with normal calcium levels. These observations are discussed in relation to the known properties of various types of intercellular junctions and the physiological properties of the myelinated nerve fiber. It is suggested that the unique structural characteristics of the Schwann cell-axolemmal junction in the paranodal region may relate to the presumed functional requirements of saltatory conduction, i.e., adhesiveness for the maintenance of myelin form and/or sealing of the periaxonal space from the general extracellular space, but without the establishment of low resistance channels between Schwann cell and axon.

Ruthenium red and violet. II. Fine structural localization in animal tissues.

AbstractThe inorganic dye, ruthenium red, stains extracellular materials in animal tissues which probably are acidic mucopolysaccharides. It complements other techniques, its advantages being fine grain, high resolution and good contrast. Localization is shown in mouse and rat muscle, heart, lung and intestine, frog cartilage and cells scraped from oral epithelium of human beings. Attention is paid to collagen bundles, the cell/collagen interface and particularly the myotendinal junction, cartilage matrix and agar gel, desmosomes, intestinal microvilli, erythrocytes and vascular endothelium, nerve fibers and the T‐system of striated muscle. Although ruthenium red generally is excluded by plasma membranes, it penetrates giving intracellular density, if the membrane is broken. Even when the cell membrane is intact, exceptions occur with selective staining of the T‐tubules or the sarcoplasmic sacs depending upon the state of contraction of the muscle cell, and with intracellular staining of certain nuclei and epithelial cells. Ruthenium red stains intracellular lipid droplets revealing lamellae, and stains myelin forms grown from crude egg lecithin but cannot penetrate deeply. It is localized in extracellular materials which have an important mechanical function. Its exclusion by cell membranes permits tracing tortuous cellular invaginations and those exceptions to its exclusion invite a comparison of the localization of the dye with the function of the cell.

Isolation, characterization, and surface chemistry of a surface-active fraction from dog lung

A procedure is described for the isolation of a surface-active fraction from dog lung. This material meets the established criteria for pulmonary surfactant. The fraction was shown to contain lipid, protein, and carbohydrate. The predominant lipid present was dipalmitoyl phosphatidylcholine. Surface chemistry studies indicated the surface properties of the fraction could not be explained solely from a consideration of the properties of dipalmitoyl phosphatidylcholine. Electron microscopic studies demonstrated the presence of intact osmiophilic bodies as well as other myelin forms in the surface-active fraction. It is speculated that, in situ, the alveolar lining layer is similar to a structured gel.

Myelin-like configurations in ochromonas malhamensis

The nuclear region of Ochromonas malhamensis is an active site for lipid organization and production of myelin-like bodies. These bodies resemble myelin forms reported in other microorganisms and mammalian tissue. Such lipid bodies may have important implications for understanding membrane biogenesis and mechanisms whereby cells synthesize complex lipid systems. We have therefore examined naturally occurring myelinics in Ochromonas and produced synthetic myelinics in our laboratory to obtain information about the structure and composition of these lipid bodies. We have found that myelin bodies in Ochromonas malhamensis resemble myelinics produced by dispersion of egg lecithin in water. Fixation with glutaraldehyde prior to osmium tetroxide treatment protects both natural myelinics in Ochromonas malhamensis and synthetic egg lecithin myelinics; both are degraded when fixed with osmium tetroxide alone.

The fine structure of stromalytic forms produced by osmotic hemolysis of red blood cells

When human red blood cells are hemolyzed by hypotonic salt solutions, many of the cells give rise to long cylindrical tubes which range from 200 A to μ in diameter and may be several microns long. Negative staining of these preparations shows that the tubes are bounded by a membrane 40–60 A in width, are relatively impermeable to PTA, and show no periodic structures in either negative staining or in thin sections. Influenza Virus (PR8) does not attach to the tubes. Reasons are given for supposing that the tubes are not strictly identical to myelin forms, but probably contain a high percentage of hemoglobin.

The "apparent molecular weight" of myelin forms prepared from normal red cells and some of its variations.

Some of the properties of myelin forms prepared by freezing, thawing, and homogenization of ghosts of human red cells are described, among these being the "apparent molecular weight" as found by light scattering, the effect of repeated freezing and thawing on the "apparent molecular weight," the quantity of fatty acids split off at various temperatures of freezing, the effect of the anticoagulant used, and the remarkable constancy in the "apparent molecular weight" met with when myelin forms are prepared from the ghosts of the red cells of normal people. Taken together, these observations lead to the description of a "standard technique" for the preparations of myelin forms; this technique can later be extended to the myelin forms obtained from animals other than man and also to those obtained from abnormal red cells.

The Behavior, as Regards Shape and Volume, of Human Red Cell Ghosts in Fresh and in Stored Blood

Abstract(1) When human red cells are hemolyzed in very hypotonic media (NaCl of a tonicity of 0.167) and when the tonicity is restored, by adding appropriate amounts of NaCl, to tonicities such as 0.3, 0.5, 1.0, and 1.7, the mean volume of the ghosts appears to be linear with the reciprocal of the tonicity. This might lead one to conclude that the ghosts are osmometers and that their volume is governed by simple osmotic considerations such as those expressed by a modified van't Hoff-Mariotte law. Examination of the shapes and volumes of individual ghosts by a technic which combines phase optics, electronic flash (exposure time 0.001 second) and photography shows that three distinct populations of ghost coexist in any tonicity. These are spherical ghosts with a mean volume of 150 µ3, discoidal biconcave ghosts with a mean volume of 85 µ3, and crenated ghosts with a smaller volume which can be calculated. The most likely reason for this complexity is that the shape and volume of the ghost depends partly on its structure, and not altogether on the tonicity of the surrounding medium. Simple osmotic laws have no real application to systems of this kind.(2) The changes in ghost volume and shape, as they depend on the duration of storage of the blood, at 4 C, from which the ghosts are prepared, and as they reflect changes in ghost structure, can be expressed simply. Crenated and discoidal ghosts certainly have some of the elements of red cell structure; the spherical ghost, which soon fragments and gives rise to myelin forms, may also retain some of the original elements of structure, but the fragment and the myelin form have certainly lost them. The latter objects are so small and light that they are not thrown down into the ghost column in the hematocrit tube, and so, as ghost structure disappears with increasing time of storage of the red cells from which they are prepared, a discrepancy appears between the volume of the ghost column as measured by the hematocrit and the volume which one would expect. This discrepancy can be used as a measure of the extent to which ghost structure is lost, and there comes a time, as the duration of red cell storage is increased, when the ghosts prepared from these red cells begin to be replaced by breakdown products such as myelin forms, etc.(3) The less the efficiency of the conditions of red cell preservation, the shorter is this time. In human blood rendered incoagulable with heparin, structural breakdown in the preceding sense and measured by a simple expression which changes sign when the loss of structure has reached a certain point, occurs after about 26 days. In human blood preserved in ACD, structural breakdown measured in an identical manner occurs after about 55 to 60 days. In human blood preserved in ACD-inosine, structural breakdown does not occur until about 75 to 80 days.These results are based on a large amount of preliminary work of an exploratory nature and then on three runs with heparin, five runs with ACD and five runs with ACD-Inosine.

New Observations on Sickle Cells: With Special Reference to Their Agglutinability

Abstract Observations made on sickle cells with phase contrast and with the electron microscope lead to the following conclusions. 1. When the red cell sickles, its oscillatory movements cease. 2. Spherical red cells give rise to a special form of sickle cell. 3. Myelin forms, whether attached to the cell or free, become rigid when the tension of oxygen is reduced. 4. The electron microscope, combined with the technic of moulage, shows that the sickle cell contains striated rod-like structures, which give a characteristic appearance to the surface of the sickle cell. 5. Agglutination by appropriate antisera does not occur to any extent in sickled cells, because these rigid structures do not form myelin forms. This is additional evidence of the importance of the formation of viscous surface layers already described as part of the mechanism of agglutination.

Agglutination Reactions in Human Red Cells Fragmented by Heat

Murray and Clark1 have shown that, if red cells are heated to 50° C., substances can be obtained from the surrounding fluid which, even if derived from Rh-negative red cells, can give rise to anti-D agglutinins when injected into guinea pigs. Temperatures in the neighbourhood of 50°–56° produce extensive modifications of the human red-cell surface, namely, fragmentation, development of myelin forms, and, at the higher temperatures, haemolysis2. It is therefore likely that the substances found by Murray and Clark in the fluid surrounding the heated cells are the products of the fragmentation phenomena and the changes in the red-cell surface which accompany them.

On the natural formation of myelin figures in the necrobiotic cells of crop plants.

Myelin figures, in general, are easily formed in the cells artificially, when they are treated by solutions of alkaline, heavy metals, tannin, etc. We have, however, observed them naturaly formed in the yellowed leaves of some crop plants. In wheat, they are about the same size and apparrently the similary structure as nucleus. But, in rice plant cells, they have protuberant or ring-like typical myelin form. Myelin formation is an important mark of pathological states of protoplasm. By the occurrence of the figure, therefore, we may be able to guess a definite physico-chemical state of crop plant cells, when they suffered injury by pilz, and other bad environments.

Myelin Forms in Acetocarmine Smear Preparation. Lecithin as a Nuclear Constituent

1. In acetocarmine smears of PMCs and tapetum cells of Papaver, Hosta, Tradescantia, and Magnolia, lipoid drops came out from the tapetal and PMC nuclei and chromosomes. The drops stained with acetocarmine showed afterwards various myelin forms in water or in acid medium, sometimes in the nuclear and cell cavity.2. The stained drops were identified as drops of lecithin. Its slow separation from the resting nucleus and chromosomes may be due to the fact that the lecithin does not exist in a free condition, but in a state of combination.3. The observations of acetocarmine smear materials as well as the case of Tradescantia PMCs fixed with the osmium containing mixture show that the lecithin drops are derived from chromosomes and nucleoli, and not from karyolymph.

Spontaneous emulsification, and reactions overshooting equilibrium

Spontaneous emulsification was discovered in 1878 by Johannes Gad (1878). He observed that when an oil containing fatty acid is placed quietly upon an alkaline solution with avoidance of stirring, streamers shoot out which at their ends disintegrate into minute droplets forming a milky emulsion. In the following year, Brücke (1879) confirmed Gad's numerous observations, showing that a higher concentration of alkali suppresses this motion, and instead gives rise to slowly swelling growths or “myelin forms”, familiar since 1852 in medical literature (see Adami and Aschoff 1906). The phenomenon of spontaneous emulsification appears to have been lost sight of during the past generation, apart from some observations recorded by Gurwitsch in connexion with petroleum technology.

CHEMISTRY OF THE LENS

The relation of lenticular lipids to cataract has been a point of interest to ophthalmologists for many years. However, in spite of numerous investigations the lenticular lipids have not been well characterized. For this reason much confusion has arisen in ophthalmologic literature in the discussion of lipids in cataracts. Lipids in myelin forms are frequently seen in cataracts. The lipids which may give rise to these forms are: (1) the phospholipids, that is, lecithin, cephalin and sphingomyelin, and (2) the cerebrosides, namely, kerasin, phrenosin, nervone and hydroxynervone. Myelin is a term often applied to birefractive substances as well as to substances with a myelin form. In addition to unmasked phospholipids and cerebrosides many organic and inorganic substances, such as calcium salts and cholesterol esters, may also be birefractive. It is unfortunate that the term myelin is so poorly defined that it causes confusion in the ophthalmologic literature. Myelin forms

ON NORRIS' THEORY FOR THE SHAPE OF THE MAMMALIAN ERYTHROCYTE

This paper is concerned with an attempt to put Norris' theory for the shape of the mammalian erythrocyte into a quantitative form. The theory supposes that the biconcave form of the cell is brought about by an expansive force enlarging the surface, and is also supposed to apply to the formation of the myelin forms of lecithn. The attempt is not successful, and is published merely because it is suggestive. Various points regarding the shape of the cell, the curvature of its surface, and the kind of system to which Norris' theory might be supposed to apply, are discussed, and an empirical formula is given for the curve which bounds the cross-section of the cell. This empirical formula describes the shape almost to perfection.

"Analogies between the phosphorized fats obtained from the brain and kidney," with exhibition of products

So much attention has been directed to the protein constituents of protoplasm that it has become usual to regard proteins as the physical basis of life. Relatively recent investigations have, however, indicated that all cells contain complex substances of a fatty or lipoid nature, in which phosphorus and nitrogen are conspicuous elements. Many of these lipoids possess remarkable physical properties. In contact with water or alkaline liquids, they pass into colloidal solution after imbibing large quantities of water with the production of “myelin forms.” They also differ from neutral fats in doubly refracting light. Such physical characters and the complex molecular constitution of these lipoids appear to justify the assumption that they, as well as proteins, are essential constituents of protoplasm and that a study of living matter must include the consideration of these compounds of the fatty acids.The phosphorized fats, or lipoids, which have been most carefully studied have been obtained from the brain...