scholarly journals MORPHOLOGICAL CORRELATES OF INCREASED COUPLING RESISTANCE AT AN ELECTROTONIC SYNAPSE

1971 ◽  
Vol 49 (1) ◽  
pp. 173-188 ◽  
Author(s):  
George D. Pappas ◽  
Y. Asada ◽  
M. V. L. Bennett
Keyword(s):  
Electron Microscope ◽  
Schwann Cell ◽  
Extracellular Space ◽  
Physiological Solution ◽  
Mechanical Injury ◽  
Electrotonic Coupling ◽  
Giant Axons ◽  
Cell Processes ◽  
Coupling Resistance ◽  
Hexagonal Network

Close appositions between axonal membranes are present in the septum between adjacent axonal segments of the septate or lateral giant axons of the crayfish Procambarus. In sections the closely apposed membranes appear separated by a space or gap. The use of lanthanum indicates that there may be structures connecting the apposed membranes. The apparent gap is actually a network of channels continuous with the extracellular space. Adjacent axonal segments are electrotonically coupled at the septa. The coupling resistance is increased by mechanical injury of an axon, immersion in low Cl- solutions, and immersion in low Ca++ solutions, followed by a return to normal physiological solution. Septa at which coupling resistance had been measured were examined in the electron microscope. The induced increases in coupling resistance are associated with separation of the junctional membranes (with the exception of the moderate increases during immersion in low Ca++ solutions). Schwann cell processes are present between the separated axonal membranes. When nerve cords in low Cl- solutions are returned to normal physiological solution, coupling, i.e., electrotonic synapses. A model of an electrotonic synapse is proposed in which tween axonal membranes are again found. The association between the morphological and physiological findings provides further evidence that the junctions are the sites of electrotonic coupling, i.e., electrotonic, synapses. A model of an electrotonic synapse is proposed in which intercytoplasmic channels not open to the extracellular space are interlaced with a hexagonal network of extracellular channels between the apposed junctional membranes.

scholarly journals COEXISTENCE OF GAP AND SEPTATE JUNCTIONS IN AN INVERTEBRATE EPITHELIUM

1971 ◽  
Vol 50 (1) ◽  
pp. 92-101 ◽  
Author(s):  
A. J. Hudspeth ◽  
J. P. Revel
Keyword(s):  
Electron Microscope ◽  
Gap Junctions ◽  
Gap Junction ◽  
Extracellular Space ◽  
Intercellular Junctions ◽  
Septate Junction ◽  
High Electron ◽  
Septate Junctions ◽  
Electrotonic Coupling ◽  
Lanthanum Tracer

The intercellular junctions of the epithelium lining the hepatic caecum of Daphnia were examined. Electron microscope investigations involved both conventionally fixed material and tissue exposed to a lanthanum tracer of the extracellular space. Both septate junctions and gap junctions occur between the cells studied. The septate junctions lie apically and resemble those commonly discerned between cells of other invertebrates. They are atypical in that the high electron opacity of the extracellular space obscures septa in routine preparations. The gap junctions are characterized by a uniform 30 A space between apposed cell membranes. Lanthanum treatment of gap junctions reveals an array of particles of 95 A diameter and 120 A separation lying in the plane of the junction. As this pattern closely resembles that described previously in vertebrates, it appears that the gap junction is phylogenetically widespread. In view of evidence that the gap junction mediates intercellular electrotonic coupling, the assignment of a coupling role to other junctions, notably the septate junction, must be questioned wherever these junctions coexist.

scholarly journals Schwann cell processes guide regeneration of peripheral axons

Neuron ◽  
1995 ◽  
Vol 14 (1) ◽  
pp. 125-132 ◽  
Author(s):  
Young-Jin Son ◽  
Wesley J Thompson
Keyword(s):  
Schwann Cell ◽  
Cell Processes

scholarly journals Stimulation of corneal differentiation by interaction between cell surface and extracellular matrix. I. Morphometric analysis of transfilter "induction".

1975 ◽  
Vol 66 (2) ◽  
pp. 275-291 ◽  
Author(s):  
L Meier ◽  
E D Hay
Keyword(s):  
Extracellular Matrix ◽  
Electron Microscope ◽  
Cell Surface ◽  
Pore Size ◽  
Collagen Synthesis ◽  
Lens Capsule ◽  
Physical Contact ◽  
Corneal Epithelial ◽  
Cell Processes

The present study was undertaken to determine whether or not physical contact with the substratum is essential for the stimulatory effect of extracellular matrix (ECM) on corneal epithelial collagen synthesis. Previous studies showed that collagenous substrata stimulate isolated epithelia to produce three times as much collagen as they produce on noncollagenous substrate; killed collagenous substrata (e.g., lens capsule) are just as effective as living substrata (e.g., living lens) in promoting the production of new corneal stroma in vitro. In the experiments to be reported here, corneal epithelia were placed on one side of Nucleopore filters of different pore sizes and killed lens capsule on the other, with the expectation that contact of the reacting cells with the lens ECM should be limited by the number and size of the cell processes that can tranverse the pores. Transfilter cultures were grown for 24 h in [3H]proline-containing median and incorporation of isotope into hot trichloroacetic acid-soluble protein was used to measure corneal epithelial collagen production. Epithelial collagen synthesis increases directly as the size of the pores in the interposed filter increases and decreases as the thickness of the filter layer increases. Cell processes within Nucleopore filters were identified with the transmission electron microscope with difficulty; with the scanning electron microscope, however, the processes could easily be seen emerging from the undersurface of even 0.1-mum pore size filters. Morphometric techniques were used to show that cell surface area thus exposed to the underlying ECM is linearly correlated with enhancement of collagen synthesis. Epithelial cell processes did not pass through ultrathin (25-mum thick) 0.45-mum pore size Millipore filters nor did "induction" occur across them. The results are discussed in relation to current theories of embryonic tissue interaction.

Electrotonic Coupling in the Inferior Olivary Nucleus Revealed by Simultaneous Double Patch Recordings

2002 ◽  
Vol 87 (6) ◽  
pp. 3048-3058 ◽  
Author(s):  
Anna Devor ◽  
Yosef Yarom
Keyword(s):  
Coupling Coefficient ◽  
Direct Calculation ◽  
Physiological Data ◽  
Inferior Olivary Nucleus ◽  
Potential Oscillations ◽  
Electrotonic Coupling ◽  
Cell Pair ◽  
Coupling Resistance ◽  
The Difference ◽  
Inferior Olivary

Electrotonic coupling in the inferior olivary (IO) nucleus is assumed to play a crucial role in generating the subthreshold membrane potential oscillations in olivary neurons and in synchronizing climbing fiber input into the cerebellar cortex. We studied the strength and spatial distribution of the coupling by simultaneous double patch recordings from olivary neurons in the brain slice preparation. Electrotonic coupling was observed in 50% of the cell pairs. The coupling coefficient ( CC), defined as the ratio between voltage responses of the post- and the prejunctional cell, varied between 0.002 and 0.17; most of the pairs were weakly coupled. In more than 75% of the pairs, the CCwas <0.05. The coupling resistance varied between 0.7 to 19.8 GΩ, and 68% of the values fell between 0.7 to 8 GΩ. The difference between the coupling coefficient measured on stimulation of cell 1 or cell 2 of a coupled pair was 27 ± 16%. Direct calculation of the coupling resistance revealed an asymmetry of 24 ± 12%, suggesting a directional preference of coupling. The coupling was voltage independent, although depolarization of either the pre- or the postjunctional neuron reduced the CC. The chance of a cell pair being coupled was 80% in immediate neighboring cells, but dropped to about 30% at a distance of 40 μm. No coupled pairs were observed at distances larger than 70 μm. In 52% of staining experiments neurobiotin injection into an olivary neuron produced indirect labeling of 1–11 nearby cells with an average of 3.8 ± 2.9. All indirectly labeled cells were found in, or immediately adjacent, to the dendritic field of the directly stained neuron. Two distinct morphological types of olivary neurons, “curly” and “straight” cells, were found. In each case all neurons stained indirectly by dye passage through gap junctions belonged to the same type. Using the physiological data we estimated that each olivary neuron is directly coupled to about 50 neurons. Since somatic recordings may not reveal coupling through remote dendrites, we conclude that each neuron is directly connected to ≥50 neurons forming two distinct networks of curly and straight cells.

Ultrastructure of region of a low safety factor in inhomogeneous giant axon of the cockroach

1976 ◽  
Vol 39 (4) ◽  
pp. 900-908 ◽  
Author(s):  
M. Castel ◽  
M. E. Spira ◽  
I. Parnas ◽  
Y. Yarom
Keyword(s):  
Electron Microscopy ◽  
Glial Cells ◽  
Extracellular Space ◽  
Light And Electron Microscopy ◽  
Giant Axon ◽  
Serial Sections ◽  
Giant Axons ◽  
Chemical Synapses ◽  
Cytoplasmic Processes ◽  
Periaxonal Space

1. The structure of the ventral giant axons of the cockroach at the level of ganglion T3 was studied by means of light and electron microscopy. 2. From serial sections and cobalt injections, the axons diameter was found to range between 40 and 60 mum at the caudal end of ganglion T3; toward the center of T3 they narrow to 20-40 mum, and again expand to 30-45 mum anteriorly in ganglion T3. 3. Each giant axon sends off several branches, 1-15 mum in diameter, into the neuropil. The giant axons and the bases of their branches are enveloped by cytoplasmic processes of glial cells. The periaxonal space is about 100-200 A. 4. Distally the branches are devoid of glial envelopes and the extracellular space between the branches and other axonal profiles is about 200 A. Terminals with presumptive chemical synapses on the giant axon branches were found. Clear vesicles, 300-400 A in diameter, are seen clustered together. The width of the supposedly synaptic gap is about 100 A. 5. In some areas the branches and other axonal profiles form close appositions.

An electron microscope study of quantitative relationships between axon and Schwann cell sheath in myelinated fibres of peripheral nerves

1987 ◽  
Vol 175 (4) ◽  
pp. 423-430 ◽  
Author(s):  
E. Pannese ◽  
L. Rigamonti ◽  
P. Procacci ◽  
M. Ledda ◽  
G. Arcidiacono ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Schwann Cell ◽  
Peripheral Nerves ◽  
Microscope Study ◽  
Electron Microscope Study ◽  
Myelinated Fibres ◽  
Cell Sheath

scholarly journals A STRUCTURAL ANALYSIS OF THE MYELIN SHEATH IN THE CENTRAL NERVOUS SYSTEM

1967 ◽  
Vol 34 (2) ◽  
pp. 555-567 ◽  
Author(s):  
Asao Hirano ◽  
Herbert M. Dembitzer
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Electron Microscope ◽  
Myelin Sheath ◽  
Cerebral White Matter ◽  
Experimental Conditions ◽  
Myelin Sheaths ◽  
Basic Theme ◽  
Cell Processes ◽  
The Central Nervous System

The cerebral white matter of rats subjected to a variety of noxious experimental conditions was examined in the electron microscope. Several unusual configurations of the myelin sheath are identified in addition to the usual configuration. These variations include the presence of (a) formed organelles within the inner and outer loops, (b) isolated islands of cytoplasm in unfused portions of the major dense lines, (c) apparently unconnected cell processes between the sheath and the axon, and (d) concentric, double myelin sheaths. A generalized model of the myelin sheath based on a hypothetical unrolling of the sheath is described. It consists of a shovel-shaped myelin sheet surrounded by a continuous thickened rim of cytoplasm. Most of the unusual myelin configurations are explained as simple variations on this basic theme. With the help of this model, an explanation of the formation of the myelin sheath is offered. This explanation involves the concept that myelin formation can occur at all cytoplasmic areas adjacent to the myelin proper and that adjacent myelin lamellae can move in relation to each other.

Three dimensional organization of glial cell processes as revealed by high voltage electron microscope stereoscopy

1978 ◽  
Vol 36 (2) ◽  
pp. 18-19
Author(s):  
Kiyoshi Hama ◽  
Toshio Kosaka
Keyword(s):  
Electron Microscope ◽  
Cerebellar Cortex ◽  
High Voltage ◽  
Three Dimensional ◽  
Angular Aperture ◽  
Neuroglial Cell ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
High Voltage Electron ◽  
Cell Processes

The stereo-observation of biological materials can effectively achieved by the high voltage electron microscope utilizing the high penetration power of electrons at high accelerating voltage which enables the observation of thick specimens, and the large depth of forcus resulted by the small angular aperture used in the electron microscope (Hama, 1972). The high voltage electron microscope was applied to the study of the neuroglial cell processes in the cerebellar cortex of monkey and rat by Chang-Palayand Palay (1972). We investigated further the three dimensional organization of the neuroglial cell processes in the cerebellum and retina of rat by means of high voltage electron microscope stereoscopy.The Golgi preparations of cerebellar cortex and retina of rat were prepared by the methods described previously (Stell and Lightfoot, 1975; Colonnier, 1964). Plastic sections 100 μm thick were used for the light microscope observation.

scholarly journals LIMITATIONS OF THE PYROANTIMONATE TECHNIQUE FOR LOCALIZATION OF SODIUM IN ISOLATED CEREBRAL TISSUES

1971 ◽  
Vol 19 (10) ◽  
pp. 605-610 ◽  
Author(s):  
S. M. SUMI ◽  
P. D. SWANSON
Keyword(s):  
Cerebral Cortex ◽  
Electron Microscope ◽  
Guinea Pig ◽  
Extracellular Space ◽  
Brain Slices ◽  
Intracellular Space ◽  
Thin Slices ◽  
Glutaraldehyde Solution ◽  
Potassium Pyroantimonate

Thin slices of guinea pig cerebral cortex incubated for 30-60 min with or without ouabain were analyzed for Na+, K+ and inulin contents. Other brain slices treated in a similar manner were fixed in potassium pyroantimonate-containing buffered glutaraldehyde solution and examined in the electron microscope. Slices incubated in the presence of ouabain contained considerably more Na+ in the non-inulin, presumably intracellular, space. However, precipitates of pyroantimonate which have been accepted by some to indicate the site of Na+ localization were almost entirely restricted to the extracellular space in both the control and experimental slices and appeared to reflect the method of fixation by immersion and not the movement of Na+. It is our conclusion that the lack of correlation between the chemical localization of Na+ and the pyroantimonate technique is due to the limitation of the latter method.

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