scholarly journals SOME FEATURES OF THE SUBMICROSCOPIC MORPHOLOGY OF SYNAPSES IN FROG AND EARTHWORM

1955 ◽  
Vol 1 (1) ◽  
pp. 47-58 ◽  
Author(s):  
Eduardo D. P. De Robertis ◽  
H. Stanley Bennett
Keyword(s):  
Electron Micrographs ◽  
Nerve Cord ◽  
Synaptic Vesicles ◽  
Sympathetic Ganglia ◽  
Synaptic Membrane ◽  
Presynaptic Membrane ◽  
Close Relationship

Electron micrographs are presented of synaptic regions encountered in sections of frog sympathetic ganglia and earthworm nerve cord neuropile. Pre- and postsynaptic neuronal elements each appear to have a membrane 70 to 100 A thick, separated from each other over the synaptic area by an intermembranal space 100 to 150 A across. A granular or vesicular component, here designated the synaptic vesicles, is encountered on the presynaptic side of the synapse and consists of numerous oval or spherical bodies 200 to 500 A in diameter, with dense circumferences and lighter centers. Synaptic vesicles are encountered in close relationship to the synaptic membrane. In the earthworm neuropile elongated vesicles are found extending through perforations or gaps in the presynaptic membrane, with portions of vesicles appearing in the intermembranal space. Mitochondria are encountered in the vicinity of the synapse, and in the frog, a submicroscopic filamentary component can be seen in the presynaptic member extending up to the region where the vesicles are found, but terminating short of the synapse itself.

scholarly journals ELECTRON MICROSCOPE OBSERVATIONS ON SYNAPTIC VESICLES IN SYNAPSES OF THE RETINAL RODS AND CONES

1956 ◽  
Vol 2 (3) ◽  
pp. 307-318 ◽  
Author(s):  
Eduardo De Robertis ◽  
Carlos M. Franchi
Keyword(s):  
Electron Microscope ◽  
Synaptic Vesicles ◽  
Sharp Decrease ◽  
Albino Rabbit ◽  
Synaptic Membrane ◽  
Complete Darkness ◽  
Rods And Cones ◽  
Retinal Rods ◽  
Filamentous Material ◽  
Rod Cell

The submicroscopic organization of the rod and cone synapses of the albino rabbit has been investigated with the use of the electron microscope. The most common rod synapse consists of an enlarged expansion of the rod fiber (the so called spherule) into which the dendritic postsynaptic fiber of the bipolar cell penetrates and digitates. The membrane surrounding the terminal consists of a double layer, the external of which is interpreted as belonging to the intervening glial cells. The synaptic membrane has a pre- and a postsynaptic layer with a total thickness of 180 to 300 A. The presynaptic layer is frequently denser and is intimately associated with the adjacent synaptic vesicles. The synaptic membrane shows processes constituted by foldings of the presynaptic layer. The entire spherule is filled with synaptic vesicles varying in diameter between 200 and 650 A with a mean of 386 A. In addition, the spherule contains a few large vacuoles near the rod fiber, interpreted as endoplasmic reticulum, and a matrix in which with high resolution a fine filamentous material can be observed. The postsynaptic fiber is homogeneous and usually does not show synaptic vesicles. In animals maintained in complete darkness for 24 hours vesicles appear to accumulate near the synaptic membrane and its processes. After 9 days there is a sharp decrease in size of the synaptic vesicles. A special rod synapse in which the dendritic postsynaptic expansion penetrates directly into the rod cell body has been identified. In line with Cajal's classification this type of synapse could be considered as a somatodendritic one. The cone synapse has a much larger terminal with a more complex relationship with the postsynaptic fiber. However, the same components recognized in the rod synapse can be observed. In animals maintained for 9 days in complete darkness there is also a considerable diminution in size of the synaptic vesicles.

Neurotransmitter Release

2017 ◽  
Author(s):  
Peggy Mason
Keyword(s):  
Plasma Membrane ◽  
Synaptic Vesicle ◽  
Active Zone ◽  
Neurotransmitter Release ◽  
Synaptic Vesicles ◽  
Synaptic Cleft ◽  
Fusion Pore ◽  
Synaptic Membrane ◽  
Specialized Region ◽  
Synaptic Vesicle Fusion

The biochemical and physiological processes of neurotransmitter release from an active zone, a specialized region of synaptic membrane, are examined. Synaptic vesicles containing neurotransmitters are docked at the active zone and then primed for release by SNARE complexes that bring them into extreme proximity to the plasma membrane. Entry of calcium ions through voltage-gated calcium channels triggers synaptic vesicle fusion with the synaptic terminal membrane and the consequent diffusion of neurotransmitter into the synaptic cleft. Release results when the fusion pore bridging the synaptic vesicle and plasma membrane widens and neurotransmitter from the inside of the synaptic vesicle diffuses into the synaptic cleft. Membrane from the active zone membrane is endocytosed, and synaptic vesicle proteins are then reassembled into recycled synaptic vesicles, allowing for more rounds of neurotransmitter release.

scholarly journals ON THE THICKNESS OF THE UNIT MEMBRANE

1963 ◽  
Vol 17 (2) ◽  
pp. 413-421 ◽  
Author(s):  
Toshiyuki Yamamoto
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Electron Micrographs ◽  
Synaptic Vesicles ◽  
Multivesicular Bodies ◽  
Unit Membrane ◽  
Cell Organelles ◽  
Membrane Unit ◽  
Nuclear Membranes ◽  
Golgi Vesicles

Peak-to-peak distances between two dense lines of the unit membranes of cell organelles were measured on electron micrographs. These distances were compared with corresponding measurements on the plasma membrane and assigned a percentage value. The comparison between organelle and plasma membrane was always carried out with the same negative, in order to exclude as far as possible errors due to differences in focus or other causes. It was revealed by this study that the membranous structures of the cell can be classified into two groups, one thicker and one thinner. Unit membranes of the thicker group (synaptic vesicles, vesicles and capsules of multivesicular bodies, Golgi vesicles) were not significantly different in thickness from the plasma membrane. Unit membranes of the thinner group (mitochondria, nuclear membranes, Golgi lamellae, endoplasmic reticulum), however, were between 85 and 90 per cent of the thickness of the plasma membrane.

scholarly journals Submicroscopic Changes in Visual Cells of the Rabbit Induced by Iodoacetate

1959 ◽  
Vol 5 (2) ◽  
pp. 245-250 ◽  
Author(s):  
Arnaldo Lasansky ◽  
Eduardo De Robertis
Keyword(s):  
Body Weight ◽  
Synaptic Vesicles ◽  
Single Injection ◽  
Synaptic Membrane ◽  
Visual Cells ◽  
Rod Cells ◽  
Complete Destruction ◽  
Cone Cells ◽  
The Matrix ◽  
Myelin Figures

Alterations produced by iodoacetate in visual cells have been studied under the electron microscope. Lesions of the outer segments of the rods are visible as early as 3 hours after a single injection of 20 mg. iodoacetate per kg. body weight. After 6 hours the changes are more marked and consist then of disorganization, vesiculation, and lysis of the rod sacs. The inner segments of most rod cells show swelling and vacuolization of the matrix, the endoplasmic reticulum, and the Golgi complex. The mitochondria of the ellipsoid show a tendency to disintegrate. In some inner segments the changes consist primarily in an increase in density of the matrix and deposition of a granular material. The rod synapses are also affected, showing lysis of the synaptic vesicles and alterations of the synaptic membrane. With a second injection of 20 mg. iodoacetate per kg. body weight, all these changes become more marked and lead to complete destruction of the rod cells. The cones seem more resistant than the rods. A single injection produces no visible changes in the outer or inner segments of the cones. At cone synapses, however, there are changes consisting of fusion of synaptic vesicles and other membranous material to form large concentric membranes characteristic of myelin figures. A second dose of the drug causes complete destruction of the cone cells. All these, and other submicroscopic changes, are discussed in relation to various hypotheses put forward to explain the mode of action of iodoacetate on visual cells. The pronounced alterations of submicroscopic intracellular membranes suggest that the locus of action of iodoacetate may be a component widely dispersed throughout the visual cells and related, in some way, to the maintenance of these lipoprotein structures.

Investigations of the Relationship Between Acetylcholine Synthesis and the Recycling of Synaptic Vesicles

1976 ◽  
Vol 34 ◽  
pp. 4-5
Author(s):  
Francine M. Benes ◽  
Russell J. Barrnett
Keyword(s):  
Synaptic Vesicles ◽  
Neuromuscular Junctions ◽  
Synaptic Membrane ◽  
Frog Neuromuscular Junction ◽  
Acetylcholine Synthesis ◽  
The Reformation ◽  
Key Factor ◽  
Choline Acetylase ◽  
Series Of Experiments ◽  
Biochemical Analyses

It is well established that synaptic vesicles fuse with the pre-synaptic membrane during stimulation, and are reformed during a period of rest. These events have been correlated with the depletion and resynthesis of stores of acetylcholine (Ach) in the frog neuromuscular junction. Thus, choline acetylase (ChAc) activity appears to be a key factor in the metabolism of the transmitter Ach pool. The present work inquires into the possible interrelationship of the above events; that is, whether the reformation of vesicles after depletion by stimulation is associated with the activity of ChAc. Therefore, a series of experiments on frog neuromuscular junctions were performed in which the data from biochemical analyses of acetylcholine synthesis and from the morphometric determination of vesicle numbers were compared.

Ultrastructural localization of calcium-binding sites in the electrocyte of Electrophorus electricus (L.)

1979 ◽  
Vol 38 (1) ◽  
pp. 97-104
Author(s):  
T.C. De Araujo Jorge ◽  
W. De Souza ◽  
R.D. Machado
Keyword(s):  
Plasma Membrane ◽  
Binding Sites ◽  
Calcium Binding ◽  
Synaptic Vesicles ◽  
Ultrastructural Localization ◽  
Synaptic Membrane ◽  
Electrophorus Electricus ◽  
Calcium Binding Sites

Calcium-binding sites were detected in the electrocyte of Electrophorus electricus (L.) using the Oschman & Wall technique, in which CaCl2 was added to the fixative and washing solutions. Deposits were seen scattered along the plasma membrane of the electrocyte, inside mitochondria, associated with the post-synaptic membrane and the membrane of synaptic vesicles.

The Synaptology of the Granule Cells of the Olfactory Bulb

1970 ◽  
Vol 7 (1) ◽  
pp. 125-155
Author(s):  
J. L. PRICE ◽  
T. P. S POWELL
Keyword(s):  
Olfactory Bulb ◽  
Synaptic Vesicles ◽  
Granule Cells ◽  
Mitral Cell ◽  
Synaptic Membrane ◽  
Quantitative Evidence ◽  
Axon Terminals ◽  
Quantitative Measurements ◽  
Asymmetrical Synapse ◽  
Cell Somata

The synapses related to the granule cells of the olfactory bulb of rat brain have been studied in aldehyde-fixed material. The synapses can be divided into three classes: (1) those which have asymmetrical synaptic membrane thickenings and spheroidal synaptic vesicles; (2) those with symmetrical synaptic thickenings and flattened vesicles; and (3) the reciprocal synapses, one half of which (from mitral to granule cell) has an asymmetrical synaptic thickening associated with spheroidal vesicles, while the other half (from granule to mitral cell) has a symmetrical synaptic thickening and flattened vesicles. Qualitative observations, supported by preliminary quantitative measurements, suggest that it may be possible to divide both the spheroidal and flattened-vesicle types into two further varieties, on the basis of size, The smaller variety of spheroidal vesicles is found in most axon terminals, while the larger spheroidal vesicles are present in mitral cell dendrites and in some of the axon terminals. The flattened vesicles associated with symmetrical synapses which are oriented on to the granule cells are smaller than the spheroidal vesicles, but the flattened vesicles in the spines and gemmules of the granule cells are the same size or larger than the spheroidal vesicles. The division of flattened vesicles into two sizes is supported by statistical analysis of measurements of these vesicles, but because of difficulty in identifying the axon terminals with asymmetrical synapses there is no quantitative evidence for such a division of spheroidal vesicles. The asymmetrical synapses are found predominantly on spines, gemmules, and dendritic varicosities, although they are occasionally present on shafts of dendrites and on the cell somata. The symmetrical synapses are almost completely restricted to the shafts of the peripheral processes and the deep dendrites, and to the cell somata; only very rarely are synapses of this type found on spines, and then always in conjunction with an asymmetrical synapse.

scholarly journals Vesicle-associated membrane protein-2 (synaptobrevin-2) forms a complex with synaptophysin

1995 ◽  
Vol 305 (3) ◽  
pp. 721-724 ◽  
Author(s):  
P Washbourne ◽  
G Schiavo ◽  
C Montecucco
Keyword(s):  
Membrane Protein ◽  
Neurotransmitter Release ◽  
Synaptic Vesicles ◽  
Cross Linking ◽  
Type Ii ◽  
Presynaptic Membrane ◽  
Terminal Part ◽  
Vesicle Docking ◽  
Botulinum Neurotoxins ◽  
Type Ii Membrane Protein

Vesicle-associated membrane protein (VAMP) (or synaptobrevin), a type II membrane protein of small synaptic vesicles, is essential for neuroexocytosis because its proteolysis by tetanus and botulinum neurotoxins types B, D, F and G blocks neurotransmitter release. The addition of cross-linking reagents to isolated small synaptic vesicles induces the formation of 30 and 50 kDa complexes containing the isoform 2 of VAMP (VAMP-2). Whereas the 30 kDa band is a VAMP-2 homodimer, the 50 kDa species results from the cross-linking of VAMP-2 with synaptophysin. This heterodimer also forms in detergent-solubilized vesicles and involves the N-terminal part of VAMP-2. The implications of the existence of a synaptophysin-VAMP-2 complex in the processes of vesicle docking and fusion with the presynaptic membrane are discussed.

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