scholarly journals Damage and repair of the peripheral myelin sheath and node of Ranvier after treatment with trypsin.

1975 ◽  
Vol 64 (1) ◽  
pp. 1-14 ◽  
Author(s):  
R C Yu ◽  
R P Bunge
Keyword(s):  
Schwann Cell ◽  
Light And Electron Microscopy ◽  
Node Of Ranvier ◽  
Nerve Fibers ◽  
Myelinated Nerve ◽  
Nodal Region ◽  
Fetal Rat ◽  
The Matrix ◽  
Cell Processes

Cultures of whole fetal rat sensory ganglia which had matured and myelinated in culture were treated for 1-3 h with a pulse of 0.2% trypsin. The tissue was observed during the period of treatment and during subsequent weeks using both light and electron microscopy. Within minutes after trypsin addition the matrix of the culture was altered and the nerve fascicles loosened. Progressive changes included the retraction of Schwann cell processes from the nodal region the detachment of the myelin-related paranodal Schwann cell loops from the axon, and lengthening of the nodal region as the axon was bared. The retraction of myelin from nodal stabilized several hours after trypsin withdrawal. Breakdown of the altered myelin segments was rare. There were no discernable changes in neurons or their processes after this exposure to trypsin. The partial repair which occured over a period of several weeks included the reattachment of paranodal Schwann cell loops to the axolemma and the insertion of new myelin segments where a substantial length of axolemma had been bared. The significance of these observations to the characterization of the Schwann cell-axolemmal junctions on myelinated nerve fibers is discussed. The dramatic degree of myelin change that can occur without concomitant myelin breakdown is particularly noted, as is the observation that these altered myelin segments are, in part, repaired.

scholarly journals A LIGHT AND ELECTRON MICROSCOPE STUDY OF LONG-TERM ORGANIZED CULTURES OF RAT DORSAL ROOT GANGLIA

1967 ◽  
Vol 32 (2) ◽  
pp. 439-466 ◽  
Author(s):  
Mary Bartlett Bunge ◽  
Richard P. Bunge ◽  
Edith R. Peterson ◽  
Margaret R. Murray
Keyword(s):  
Dorsal Root Ganglia ◽  
Dorsal Root ◽  
Lamellar Spacing ◽  
Nerve Fibers ◽  
Myelinated Fiber ◽  
Myelinated Nerve ◽  
Neuronal Soma ◽  
Fetal Rat

Dorsal root ganglia from fetal rats were explanted on collagen-coated coverslips and carried in Maximow double-coverslip assemblies for periods up to 3 months. These cultured ganglia were studied in the living state, in stained whole mounts, and in sections after OsO4 fixation and Epon embedment. From the central cluster of nerve cell bodies, neurites emerge to form a rich network of fascicles which often reach the edge of the carrying coverslip. The neurons resemble their in vivo counterparts in nuclear and cytoplasmic content and organization; e.g., they appear as "light" or "dark" cells, depending on the amount of cytoplasmic neurofilaments. Satellite cells form a complete investment around the neuronal soma and are themselves everywhere covered by basement membrane. The neuron-satellite cell boundary is complicated by spinelike processes arising from the neuronal soma. Neuron size, myelinated fiber diameter, and internode length in the cultures do not reach the larger of the values known for ganglion and peripheral nerve in situ (30). Unmyelinated and myelinated nerve fibers and associated Schwann cells and endoneurial and perineurial components are organized into typical fascicles. The relationship of the Schwann cell and its single myelinated fiber or numerous unmyelinated fibers and the properties of myelin, such as lamellar spacing, mesaxons, Schmidt-Lanterman clefts, nodes of Ranvier, and protuberances, mimic the in vivo pattern. It is concluded that cultivation of fetal rat dorsal root ganglia by this technique fosters maturation and long-term maintenance of all the elements that comprise this cellular community in vivo (except vascular components) and, furthermore, allows these various components to relate faithfully to one another to produce an organotypic model of sensory ganglion tissue.

scholarly journals The Inner Quaternary Ammonium Ion Receptor in Potassium Channels of the Node of Ranvier

1972 ◽  
Vol 59 (4) ◽  
pp. 388-400 ◽  
Author(s):  
Clay M. Armstrong ◽  
Bertil Hille
Keyword(s):  
Potassium Channels ◽  
Quaternary Ammonium ◽  
Node Of Ranvier ◽  
Nerve Fibers ◽  
Ammonium Ion ◽  
Ammonium Ions ◽  
Myelinated Nerve ◽  
Quaternary Ammonium Ions ◽  
Activation Gate ◽  
Almost All

Quaternary ammonium ions were applied to the inside of single myelinated nerve fibers by diffusion from a cut end. The resulting block of potassium channels in the node of Ranvier was studied under voltage-clamp conditions. The results agree in almost all respects with similar studies by Armstrong of squid giant axons. With tetraethylammonium ion (TEA), pentyltriethylammonium ion (C5), or nonyltriethylammonium ion (C9) inside the node, potassium current during a depolarization begins to rise at the normal rate, reaches a peak, and then falls again. This unusual inactivation is more complete with C9 than with TEA. Larger depolarizations give more block. Thus the block of potassium channels grows with time and voltage during a depolarization. The block reverses with repolarization, but for C9 full reversal takes seconds at -75 mv. The reversal is faster in 120 mM KCl Ringer's and slower during a hyperpolarization to -125 mv. All of these effects contrast with the time and voltage-independent block of potassium, channels seen with external quaternary ammonium ions on the node of Ranvier. External TEA, C5, and C9 block without inactivation. The external quaternary ammonium ion receptor appears to be distinct from the inner one. Apparently the inner quaternary ammonium ion receptor can be reached only when the activation gate for potassium channels is open. We suggest that the inner receptor lies within the channel and that the channel is a pore with its activation gate near the axoplasmic end.

scholarly journals CHOLINESTERASE ACTIVITY OF NODAL AND INTERNODAL REGIONS OF MYELINATED NERVE FIBERS OF FROG

1967 ◽  
Vol 32 (3) ◽  
pp. 577-583 ◽  
Author(s):  
Miro Brzin ◽  
Wolf-D. Dettbarn
Keyword(s):  
Enzyme Activity ◽  
Esterase Activity ◽  
Cholinesterase Activity ◽  
Node Of Ranvier ◽  
Nerve Fibers ◽  
Selective Inhibitors ◽  
Myelinated Nerve ◽  
Myelinated Nerve Fibers ◽  
Significant Difference ◽  
Saltatory Conduction

The distribution of cholinesterase (Ch-esterase) in isolated myelinated fibers of the frog has been investigated. Quantitative microgasometric measurements have confirmed the previous histochemical observations. Both approaches indicate that in frog nerve fibers acetylcholinesterase (ACh-esterase) is the only or the predominant enzyme when selective inhibitors and different substrates are used: acetylcholine (ACh), butyrylcholine, and acetyl-B-methylcholine (Mecholyl). By means of the microgasometric technique, a significant difference in ACh-esterase activity between axons isolated from ventral (37.2 ± 1.7 µmole x 10-5 ACh/mm2/hr) and dorsal roots (2.0 ± 0.9 µmole x 10-5 ACh/mm2/hr) was found. In the region of the node of Ranvier the enzyme activity (50.4 ± 4.4 µmole x 10-5 ACh/mm2/hr) appears to be considerably higher than in the internodal area (36.6 ± 2.1 µmole x 10-5 ACh/mm2/hr). The findings are discussed in relation to the theory of saltatory conduction and the ACh system.

scholarly journals The mechanosensitive ion channel TRAAK is localized to the mammalian node of Ranvier

2019 ◽  
Author(s):  
Stephen G. Brohawn ◽  
Weiwei Wang ◽  
Jürgen R. Schwarz ◽  
Annie Handler ◽  
Ernest B. Campbell ◽  
...  
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Polyclonal Antibodies ◽  
Node Of Ranvier ◽  
Nerve Fibers ◽  
Resting Membrane Potential ◽  
Myelinated Nerve ◽  
Myelinated Nerve Fibers ◽  
Behavioral Studies ◽  
Mechanosensitive Ion Channel

ABSTRACTTRAAK is a membrane tension-activated K+ channel that has been associated through behavioral studies to mechanical nociception. We used specific monoclonal antibodies in mice to show that TRAAK is localized exclusively to nodes of Ranvier, the action potential propagating elements of myelinated nerve fibers. Approximately 80 percent of myelinated nerve fibers throughout the central and peripheral nervous system contain TRAAK in an all-nodes or no-nodes per axon fashion. TRAAK is not observed at the axon initial segment where action potentials are first generated. We used polyclonal antibodies, the TRAAK inhibitor RU2 and node clamp amplifiers to demonstrate the presence and functional properties of TRAAK in rat nerve fibers. TRAAK contributes to the ‘leak’ K+ current in mammalian nerve fiber conduction by hyperpolarizing the resting membrane potential, thereby increasing Na+ channel availability for action potential propagation. Mechanical gating in TRAAK might serve a neuroprotective role by counteracting mechanically-induced ectopic action potentials. Alternatively, TRAAK may open in response to mechanical forces in the nodal membrane associated with depolarization during saltatory conduction and thereby contribute to repolarization of the node for subsequent spikes.

scholarly journals THE ULTRASTRUCTURE OF ADULT VERTEBRATE PERIPHERAL MYELINATED NERVE FIBERS IN RELATION TO MYELINOGENESIS

1955 ◽  
Vol 1 (4) ◽  
pp. 271-278 ◽  
Author(s):  
J. David Robertson
Keyword(s):  
Electron Microscope ◽  
Schwann Cell ◽  
Cell Surface ◽  
Peripheral Nerve ◽  
Myelin Sheath ◽  
Nerve Fibers ◽  
Myelinated Nerve ◽  
Thin Sections ◽  
Double Membrane ◽  
Myelinated Nerve Fibers

Adult chameleon myelinated peripheral nerve fibers have been studied with the electron microscope in thin sections. The outer lamella of the myelin sheath has been found to be connected as a double membrane to the surface of the Schwann cell. The inner lamella is connected as a similar double membrane with the double axon-Schwann membrane. The relations of these double connecting membranes suggest that the layered myelin structure is composed of a double membrane which is closely wound about the axon as a helix. These findings support the new theory of myelinogenesis proposed recently by Geren. The possible significance of these results with respect to cell surface membranes and cytoplasmic double membranes is discussed.

scholarly journals The mechanosensitive ion channel TRAAK is localized to the mammalian node of Ranvier

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Stephen G Brohawn ◽  
Weiwei Wang ◽  
Annie Handler ◽  
Ernest B Campbell ◽  
Jürgen R Schwarz ◽  
...  
Keyword(s):  
Action Potential ◽  
Polyclonal Antibodies ◽  
Node Of Ranvier ◽  
Nerve Fibers ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Na Channel ◽  
Nodes Of Ranvier ◽  
Myelinated Nerve ◽  
Myelinated Nerve Fibers

TRAAK is a membrane tension-activated K+ channel that has been associated through behavioral studies to mechanical nociception. We used specific monoclonal antibodies in mice to show that TRAAK is localized exclusively to nodes of Ranvier, the action potential propagating elements of myelinated nerve fibers. Approximately 80 percent of myelinated nerve fibers throughout the central and peripheral nervous system contain TRAAK in what is likely an all-nodes or no-nodes per axon fashion. TRAAK is not observed at the axon initial segment where action potentials are first generated. We used polyclonal antibodies, the TRAAK inhibitor RU2 and node clamp amplifiers to demonstrate the presence and functional properties of TRAAK in rat nerve fibers. TRAAK contributes to the ‘leak’ K+ current in mammalian nerve fiber conduction by hyperpolarizing the resting membrane potential, thereby increasing Na+ channel availability for action potential propagation. We speculate on why nodes of Ranvier contain a mechanosensitive K+ channel.

Membrane Specializations in Developing Nodes of Ranvier

1980 ◽  
Vol 38 ◽  
pp. 626-627
Author(s):  
J.H. Tao-Cheng ◽  
J. Rosenbluth
Keyword(s):  
Schwann Cell ◽  
Freeze Fracture ◽  
Structural Features ◽  
Nerve Fibers ◽  
Nodes Of Ranvier ◽  
Myelinated Nerve ◽  
Thin Sections ◽  
Frog Tadpole ◽  
Cell Layers ◽  
Mature Node

Mature myelinated nerve fibers exhibit distinctive structural features at nodes of Ranvier and the adjacent paranodal regions. In order to obtain information about the interrelationships between these specializations during development, thin sections and freeze-fracture replicas of immature peripheral nerve fibers from grass frog tadpole hind legs were examined during the period of myelinogenesis. Early in myelination axons are enwrapped individually by a few loose Schwann cell layers whose edges overhang each other forming "terminal loops" against the axolemma. Unlike those of the mature node, these loops are widely sepa-rated and irregularly spaced (Fig.l), and similarly the presumptive nodal region between successive developing myelin segments is usually much longer than adult nodes of Ranvier. The presumptive nodal axolemma may exhibit a cytoplasmic "undercoating." However, the density of this coating is highly variable. Usually it is much lower than at adult nodes, and in some cases the undercoating is not distinguishable. The outermost layers of the Schwann cell are usually the first to form axoglial junctional specializations character¬ized by the presence of "transverse bands" and ER cisternae applied to the junctional Schwann cell membrane. In some instances the outermost layer con¬tacts the axon over an extensive area and forms multiple small junctional specializations at widely separated intervals along the length of the axolemma.

Peripheral Nerve Injection Injury

Neurosurgery ◽  
1979 ◽  
Vol 4 (3) ◽  
pp. 244-253 ◽  
Author(s):  
Fred Gentili ◽  
Alan Hudson ◽  
David G. Kline ◽  
Dan Hunter
Keyword(s):  
Nerve Fiber ◽  
Nerve Injury ◽  
Light And Electron Microscopy ◽  
Nerve Fibers ◽  
Myelinated Nerve ◽  
Injection Injury ◽  
Nerve Fascicle ◽  
Minimal Damage ◽  
Sciatic Nerves ◽  
Subsequent Regeneration

Abstract In an attempt to answer questions regarding nerve injection injuries, we injected 11 agents in current use and commonly administered by intramuscular injection into the sciatic nerves of adult Wistar rats. Equal volumes of normal saline were used as control. We harvested the sciatic nerves at various times after injection and examined them by both light and electron microscopy. We performed myelinated nerve fiber counts and constructed histograms. Any impairment of motor function was also noted. We gave injections to 79 animals a total of 158 times; 116 injections were directly into the nerve fascicle (intrafascicular) and 42 were into the epineural tissue (extrafascicular). The results revealed considerable variation in the degree of nerve fiber injury according to the agent injected. Minimal damage resulted from the injection of irondextran. meperidine, and cephalothin, and maximal nerve injury followed the injection of penicillin, diazepam, and chlorpromazine. The site of injection was crucial. Intrafascicular injection was invariably associated with severe nerve injury, but, with few exceptions, extrafascicular injection resulted in minimal damage. The quantity of drug injected was also important in determining the degree of injury. Large, heavily myelinated fibers were more susceptible to injection injury than smaller, thinly myelinated nerve fibers. The effect of the injected drug seemed to be related to injury of the nerve fiber unit—both the axon and the Schwann cell with its myelin sheath. Regeneration in damaged nerves was a constant finding; even the most severely injured nerves, with total axonal degeneration, underwent subsequent regeneration.

The fine structure of the cuticle and interchordal hypodermis of the parasitic nematodes, Capillaria hepatica and Trichuris myocastoris

1968 ◽  
Vol 46 (2) ◽  
pp. 173-179 ◽  
Author(s):  
K. A. Wright
Keyword(s):  
Light And Electron Microscopy ◽  
Basal Layer ◽  
Outer Region ◽  
Parasitic Nematodes ◽  
Cortical Layers ◽  
Capillaria Hepatica ◽  
Permeability Characteristics ◽  
Matrix Layer ◽  
The Matrix ◽  
Cell Processes

The cuticle and underlying hypodermis of the parasitic nematodes, Capillaria hepatica and Trichuris myocastoris, were examined by light and electron microscopy. The cuticle in both species consists of a filamentous, collagenous, basal layer, which contains a zone of striated material in its outer region; a matrix layer; and thin cortical layers which may appear as three osmiophilic lines. It is suggested that the striated layer of the cuticle provides the tensile strength given by fiber layers in the cuticle of other species. The matrix layer of T. myocastoris contains large amounts of non-glycogen polysaccharide while the matrix layer of C. hepatica does not. It is speculated that the polysaccharide content of the cuticle may determine its permeability characteristics. The interchordal hypodermis contains little endoplasmic reticulum, very few Golgi zones, but abundant mitochondria. In C. hepatica the interchordal hypodermis is formed of cell processes from cells of the lateral and median hypodermal chords, while in T. myocastoris, it is cellular.

scholarly journals The pH-dependent rate of action of local anesthetics on the node of Ranvier.

1977 ◽  
Vol 69 (4) ◽  
pp. 475-496 ◽  
Author(s):  
B Hille
Keyword(s):  
Membrane Permeability ◽  
Local Anesthetics ◽  
Time Course ◽  
Node Of Ranvier ◽  
Nerve Fibers ◽  
Lipid Solubility ◽  
Myelinated Nerve ◽  
Degree Of Ionization ◽  
Hydrophobic Barrier ◽  
High Lipid Solubility

Local anesthetic solutions were applied suddenly to the outside of single myelinated nerve fibers to measure the time course of development of block of sodium channels. Sodium currents were measured under voltage clamp with test pulses applied several times per second during the solution change. The rate of block was studied by using drugs of different lipid solubility and of different charge type, and the external pH was varied from pH 8.3 to pH 6 to change the degree of ionization of the amine compounds. At pH 8.3 the half-time of action of amine anesthetics such as lidocaine, procaine, tetracaine, and others was always less than 2 s and usually less than 1 s. Lowering the pH to 6.0 decreased the apparent potency and slowed the rate of action of these drugs. The rate of action of neutral benzocaine was fast (1 s) and pH independent. The rate of action of cationic quaternary QX-572 was slow (greater than 200 s) and also pH independent. Other quaternary anesthetic derivatives showed no action when applied outside. The result is that neutral drug forms act much more rapidly than charged ones, suggesting that externally applied local anesthetics must cross a hydrophobic barrier to reach their receptor. A model representing diffusion of drug into the nerve fiber gives reasonable time courses of action and reasonable membrane permeability coefficients on the assumption that the hydrophobic barrier is the nodal membrane. Arguments are given that there may be a need for reinterpretation of many published experiments on the location of the anesthetic receptor and on which charge form of the drug is active to take into account the effects of unstirred layers, high membrane permeability, and high lipid solubility.

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