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Journal of the Neurological Sciences Feb 1985Freeze-fracture studies on myelinated fibres from the internodal regions of rat and mouse sciatic nerve show symmetrical particle aggregates within the adaxonal Schwann... (Comparative Study)
Comparative Study
Freeze-fracture studies on myelinated fibres from the internodal regions of rat and mouse sciatic nerve show symmetrical particle aggregates within the adaxonal Schwann cell plasmalemma and particle clusters in the axolemma. These are mainly confined to the vicinity of the internal mesaxon and the Schmidt-Lanterman incisures. The Schwann cell particle aggregates are concentrated as bands over the cytoplasmic pockets of Schmidt-Lanterman incisures and the paramesaxonal pockets. In the axolemma there are linear rows of particle aggregates along the groove related to the inner mesaxon and in bands to either side of it. The morphological features suggest the possibility of metabolic coupling between the axoplasm and the Schwann cell cytoplasm via the periaxonal space.
Topics: Animals; Axons; Cell Membrane; Freeze Fracturing; Mice; Mice, Inbred C57BL; Peripheral Nerves; Rats; Rats, Inbred Lew; Schwann Cells
PubMed: 3872344
DOI: 10.1016/0022-510x(85)90117-0 -
Journal of Neurocytology Jan 2000SNAP-25, synaptosomal associated protein of 25 kDa, is reported to be a t-SNARE (target receptor associated with the presynaptic plasma membrane) involved in the docking...
SNAP-25, synaptosomal associated protein of 25 kDa, is reported to be a t-SNARE (target receptor associated with the presynaptic plasma membrane) involved in the docking and fusion of synaptic vesicles. We present here the first ultrastructural localization of SNAP-25 in intact neurons by pre-embedding EM immunocytochemistry in rat brains, hippocampal slice cultures, and PC12 cells. In differentiated neurons, SNAP-25 labeling was clearly membrane-associated. The labeling was most prominent in the plasma membrane of axons and excluded from the plasma membranes of soma and dendrites. Furthermore, SNAP-25 did not appear to be restricted to the synaptic junctions. SNAP-25 labeling was seen in the cytoplasm of the soma and large dendrites, mostly associated with the Golgi complexes. There were also some SNAP-25 labeled tubulo-vesicular structures in the cytoplasm of the soma and the axons, but rarely in the smaller dendrites. In PC12 cells, after 5-10 minutes of high potassium (75 mM) stimulation in the presence of HRP, SNAP-25 labeling appeared, additionally, on HRP-filled early endosomes. After a longer (20-30 minutes) HRP incubation, most of the later stage endosomes and lysosomes were loaded with HRP but they were negative for SNAP-25. These results suggest that SNAP-25 is sorted out of these late endosomal compartments, and that the bulk of the SNAP-25 protein is probably recycled back to the axolemma from the early endosomes. In contrast, in those samples which were incubated with HRP for longer periods, there were still some SNAP-25-positive vesicular structures which were HRP-negative. These structures most likely represent anterograde vesicles that carry newly synthesized SNAP-25 from the soma to the axolemma by axonal transport. SNAP-25 appears to be sorted at the Golgi complex to reach the axolemma specifically. Its widespread distribution all along the axolemma does not support the view of SNAP-25 as a t-SNARE limited for synaptic exocytosis.
Topics: Animals; Axons; Cell Membrane; Cytoplasm; Dendrites; Endosomes; Hippocampus; Immunohistochemistry; Membrane Proteins; Microscopy, Immunoelectron; Nerve Tissue Proteins; Neurons; Neuropil; PC12 Cells; Potassium; Rats; Rats, Sprague-Dawley; SNARE Proteins; Synaptic Vesicles; Synaptosomal-Associated Protein 25; Vesicular Transport Proteins
PubMed: 11068335
DOI: 10.1023/a:1007168231323 -
Journal of Neuroscience Research 1984The present study examined proteins and glycoproteins from an axolemma-enriched fraction from the developing offspring of female rats that were pair-fed control or 6.6%...
The present study examined proteins and glycoproteins from an axolemma-enriched fraction from the developing offspring of female rats that were pair-fed control or 6.6% (50 g/liter) ethanol liquid diets on a chronic basis prior to parturition. In addition, this study examined the synthesis of the major CNS myelin-associated glycoprotein (MAG) as an index of myelin maturation. The results of the latter study demonstrated normal MAG maturation in ethanol-treated rats. However, a significant decrease in the proportion of radioactivity associated with MAG was found in the developing offspring of ethanol-treated rats. The major axolemmal proteins from 32-day rats included those with molecular weights of 105 K, 81 K, 62 K, 55 K, 52 K, 36 K, and 33 K. Major peaks of radioactivity were associated with fucosylated axolemmal glycoproteins with apparent molecular weights of 150 K, 130 K, 85 K, 76 K, and 64 K. Several development-related changes in the protein composition of axolemma-enriched fractions were observed in control animals. Between 22 and 32 days of age control rats exhibited a significant (P less than .05) decrease in the proportion of axolemmal proteins that had apparent molecular weights of 150 K, 105 K, and 62 K. A development-related decrease in the 105 K axolemma-associated protein did not occur during the 22-32 day age period in the offspring of ethanol-treated animals. At 22 days the proportion of this 105 K protein in affected offspring was significantly (P less than .05) less than that in age-matched control rats and comparable to that in 32-day control rats. The relative distribution of radioactivity among fucosylated axolemmal glycoproteins also changed significantly between 22 and 32 days of age. These changes include a decrease in the proportion of radioactivity associated with the 110 K, 55 K, and 52 K fucosylated glycoproteins and an increase in the proportion of radioactivity associated with the 85 K and 67 K glycoproteins. Several small, but significant (P less than .05) alterations were found associated with glycoproteins in an axolemma-enriched fraction from 22- and 32-day ethanol-treated rats.
Topics: Animals; Brain; Electrophoresis, Polyacrylamide Gel; Female; Fetal Alcohol Spectrum Disorders; Glycoproteins; Myelin Proteins; Myelin Sheath; Organ Size; Pregnancy; Rats; Rats, Inbred Strains; Sodium Dodecyl Sulfate
PubMed: 6512892
DOI: 10.1002/jnr.490120412 -
Journal of Neurocytology Dec 1976The plasma membrane of myelinated axons in the frog brain has been examined by the freeze-fracture technique. The cytoplasmic leaflet of the axolemma contains numerous...
The plasma membrane of myelinated axons in the frog brain has been examined by the freeze-fracture technique. The cytoplasmic leaflet of the axolemma contains numerous randomly distributed particles in nodal and internodal regions but relatively fewer particles in the axoglial junctional portion of the paranodal region. Particle distribution is even less uniform in the outer leaflet of the axolemma, which contains a low concentration of particles in the internodal region and a relatively high concentration at the node of Ranvier (approximately 1200 particles mum-2). The nodal particles tend to be larger than most intramembranous particles, approaching 200 A diameter. The paranodal region of the leaflet is virtually devoid of such particles except in the narrow helical 'groove' which faces extracellular clefts between terminating glial processes. In places this pathway widens to form 'lakes' up to approximately 0.3 mum2 area which contain large numbers of large particles resembling those at the node. The concentration of particles at the node is in the same range as the concentration of sodium channels estimated to be in this region and it is suggested on the basis of their location and concentration that these particles represent ionophores. The distribution of particles in the paranodal region suggests that the large intramembranous particles do not have free access to the axoglial junctional portion of the membrane and therefore the movement of such particles along the paranodal region of the membrane may occur primarily in the membrane of the 'groove' spiraling through this portion of the axolemma. Such a restriction in surface area for particle movements on either side of the node of Ranvier could result in trapping of particles at the node and thus contribute to their concentration in the nodal axolemma.
Topics: Animals; Axons; Brain; Cell Membrane; Freeze Fracturing; Intercellular Junctions; Neuroglia; Rana pipiens; Ranvier's Nodes
PubMed: 1087339
DOI: 10.1007/BF01181584 -
Methods in Enzymology 1988
Topics: Animals; Axons; Brain; Brain Stem; Isoenzymes; Kinetics; Microsomes; Molecular Weight; Sodium-Potassium-Exchanging ATPase
PubMed: 2835628
DOI: 10.1016/0076-6879(88)56009-3 -
Journal of Neuroimmunology Jan 1985An antiserum was raised to rat central nervous system (CNS) axolemma-enriched fractions (AEF), which showed no cross-reactivity with myelin proteins or liver microsomes...
An antiserum was raised to rat central nervous system (CNS) axolemma-enriched fractions (AEF), which showed no cross-reactivity with myelin proteins or liver microsomes yet gave an endpoint titer of 1:51 200 to CNS AEF by the enzyme-linked immunosorbent assay (ELISA). Immunochemical staining of electroblotted proteins from rat CNS and peripheral nervous system (PNS) AEFs separated by gel electrophoresis identified a major reactive band at 38.5 kD. CNS AEF also showed major immunoreactivity at 91 kD (+/- 3 kD) and a broad band from 110 kD to 130 kD. By immunoperoxidase staining the antiserum specifically recognized the axolemma of peripheral nerve and synaptic terminals in the CNS. The significance of the specificity is discussed with respect to anti-synaptosome antisera.
Topics: Animals; Axons; Cell Membrane; Cross Reactions; Electrophoresis; Enzyme-Linked Immunosorbent Assay; Humans; Immune Sera; Ion Channels; Myelin Basic Protein; Peripheral Nerves; Rabbits; Rats; Rats, Inbred Strains; Sodium; Synaptic Membranes; Synaptosomes
PubMed: 2578136
DOI: 10.1016/s0165-5728(84)80022-3 -
Journal of Neuroscience Research 1987Neuronal membranes are unique in that they consist of several functionally distinct segments: the perikaryal plasma membrane, the axolemma, the synaptic membrane, and... (Comparative Study)
Comparative Study
Neuronal membranes are unique in that they consist of several functionally distinct segments: the perikaryal plasma membrane, the axolemma, the synaptic membrane, and the dendritic membrane. Methods are now available to isolate the first three types of membranes as well as to isolate oligodendroglial plasma membranes. The protein and glycoprotein compositions for each set of membranes were analyzed by silver staining after separation by SDS polyacrylamide gradient gel electrophoresis and by radiolabeled lectin binding to glycoproteins transferred to nitrocellulose. Analysis of the composition of each set of membranes reveals that they are all complex structures consisting of heterogeneous mixtures of proteins and glycoproteins, ranging in molecular weights from greater than 200,000 to 15,000. Each membrane fraction presents a unique pattern of staining and of lectin binding. As there were proteins and glycoproteins in common among the membranes, there were also differences. Synaptic membranes and axolemma appeared to have more proteins of higher molecular weight than the other membranes. Neuronal plasma membranes had a major concanavalin A binding glycoprotein at 79 kDa, which was not found in the other membranes. The three neuronal membrane fractions had a common wheat germ agglutinin binding glycoprotein at 82 kDa. The most interesting finding was the intense binding of neuronal plasma membrane glycoproteins to Ulex europaeus, suggesting high levels of fucose-containing glycoproteins.
Topics: Animals; Axons; Brain Chemistry; Carbohydrates; Cell Membrane; Glycoproteins; Lectins; Membrane Proteins; Nerve Tissue Proteins; Neuroglia; Neurons; Oligodendroglia; Rats; Synaptic Membranes
PubMed: 3599099
DOI: 10.1002/jnr.490170312 -
Biophysical Journal May 1999To account for the beading of myelinated fibers, and axons of unmyelinated nerve fibers as well of neurites of cultured dorsal root ganglia caused by mild stretching, a...
To account for the beading of myelinated fibers, and axons of unmyelinated nerve fibers as well of neurites of cultured dorsal root ganglia caused by mild stretching, a model is presented. In this model, membrane tension and hydrostatic pressure are the basic factors responsible for axonal constriction, which causes the movement of axonal fluid from the constricted regions into the adjoining axon, there giving rise to the beading expansions. Beading ranges from a mild undulation, with the smallest degree of stretch, to more globular expansions and narrow intervening constrictions as stretch is increased: the degree of constriction is physically limited by the compaction of the cytoskeleton within the axons. The model is a general one, encompassing the possibility that the membrane skeleton, composed mainly of spectrin and actin associated with the inner face of the axolemma, could be involved in bringing about the constrictions and beading.
Topics: Animals; Biophysical Phenomena; Biophysics; Cats; Freeze Substitution; Ganglia, Spinal; In Vitro Techniques; Microscopy, Electron; Models, Neurological; Nerve Fibers; Nerve Fibers, Myelinated; Rats; Sciatic Nerve; Stress, Mechanical
PubMed: 10233101
DOI: 10.1016/S0006-3495(99)77439-4 -
Brain Research Jul 1983Axolemma-enriched fractions isolated from rat CNS stimulated cultured Schwann cells to divide without changing their morphology. Fluorescent activated cell sorter...
Axolemma-enriched fractions isolated from rat CNS stimulated cultured Schwann cells to divide without changing their morphology. Fluorescent activated cell sorter analysis of the axolemma-stimulated cells demonstrated an approximate 3-fold increase in the number of Schwann cells in the S-phase of the cell cycle. This increase correlated well with increases in the number of [3H]thymidine-labeled nuclei observed by light level radioautography. The membrane-bound mitogen was relatively heat-stable, but trypsin-sensitive, and was inactivated both by lipid extraction and sonication. Liver plasma membranes did not increase the mitotic index over that of untreated cells, indicating the axolemma-induced mitosis was not a general response to exogenous membranes. Increasing serum concentrations in the presence of a constant level of axolemma did not change the mitotic index, suggesting that the axolemma did not cause mitosis by removal of an inhibitory factor in serum. Potential mitogens such as gangliosides, myelin basic protein, heparin, an axolemmal lipid extract, and cGMP had no effect on the cultured Schwann cells. The characteristics of the axolemma-related mitogenic factor are discussed relative to other known mitogens for cultured Schwann cells.
Topics: Animals; Axons; Cell Division; Cells, Cultured; Central Nervous System; DNA; Membranes; Mitogens; Rats; Schwann Cells; Subcellular Fractions
PubMed: 6883129
DOI: 10.1016/0165-3806(83)90112-8 -
Cell and Tissue Research 1981The axolemma is associated structurally and functionally with the axoplasm, forming an axolemma-ectoplasm complex. To study the structure of this complex, a new...
The axolemma is associated structurally and functionally with the axoplasm, forming an axolemma-ectoplasm complex. To study the structure of this complex, a new technique was developed for removing the Schwann sheath from a portion of the giant nerve fiber. An isolated fiber was treated, without loss of excitability, with trypsin dissolved in natural seawater. Next, the fiber was treated with a mild fixative and then was placed in a hypertonic solution of sucrose in seawater. The elevated sheath was transected and everted, thus exposing the surface of the axon. Desheathed axons were examined by scanning and transmission electron microscopy. The surface of the axon has a ridge-and-groove pattern, reflecting an underlying helical arrangement of filaments which bundle and unbundle. Both left and right axons of the squid possess right-handed helical twists with a tilt angle of 10 degrees. Hemispherical protuberances about 1.5 microns at their base are observed along the ridges. Thin sections of the desheathed axons reveal that the desheathing procedure leaves the axolemma intact. Desheathed axons display electron-dense bodies associated with the axolemma and with the filaments of the ectoplasm similar to the dense bodies observed in whole fibers fixed in the presence of 10 mM Co(II) ions. Axons perfused for 40 min with a solution containing 2 mM Co(II) ions retain their excitability and display a smooth inner ectoplasmic face. A portion of the axolemma, together with adhering ectoplasm, was removed from desheathed axons, mounted between folding double grids, stained, and critical-point dried. Through this novel method a network of 10 nm filaments spaced 40 nm apart and cross-linked by filaments 5 to 7 nm in diameter was demonstrated.
Topics: Animals; Axons; Cobalt; Cytological Techniques; Cytoplasm; Decapodiformes; Fixatives; Intracellular Membranes; Microscopy, Electron; Microscopy, Electron, Scanning; Myelin Sheath
PubMed: 7032702
DOI: 10.1007/BF00216566