scholarly journals Synaptic Vesicles Having Large Contact Areas with the Presynaptic Membrane are Preferentially Hemifused at Active Zones of Frog Neuromuscular Junctions Fixed during Synaptic Activity

2019 ◽  
Vol 20 (11) ◽  
pp. 2692
Author(s):  
Jae Hoon Jung
Keyword(s):  
Synaptic Vesicles ◽  
Neuromuscular Junctions ◽  
Synaptic Activity ◽  
Membrane Thickness ◽  
Intermediate Step ◽  
Presynaptic Membrane ◽  
Vesicle Membrane ◽  
Contact Areas ◽  
Contact Sites ◽  
Active Zones

Synaptic vesicles dock on the presynaptic plasma membrane of axon terminals and become ready to fuse with the presynaptic membrane or primed. Fusion of the vesicle membrane and presynaptic membrane results in the formation of a pore between the membranes, through which the vesicle’s neurotransmitter is released into the synaptic cleft. A recent electron tomography study on frog neuromuscular junctions fixed at rest showed that there is no discernible gap between or merging of the membrane of docked synaptic vesicles with the presynaptic membrane, however, the extent of the contact area between the membrane of docked synaptic vesicles and the presynaptic membrane varies 10-fold with a normal distribution. The study also showed that when the neuromuscular junctions are fixed during repetitive electrical nerve stimulation, the portion of large contact areas in the distribution is reduced compared to the portion of small contact areas, suggesting that docked synaptic vesicles with the largest contact areas are greatly primed to fuse with the membrane. Furthermore, the finding of several hemifused synaptic vesicles among the docked vesicles was briefly reported. Here, the spatial relationship of 81 synaptic vesicles with the presynaptic membrane at active zones of the neuromuscular junctions fixed during stimulation is described in detail. For the most of the vesicles, the combined thickness of each of their contact sites was not different from the sum of the membrane thicknesses of the vesicle membrane and presynaptic membrane, similar to the docked vesicles at active zones of the resting neuromuscular junctions. However, the combined membrane thickness of a small portion of the vesicles was considerably less than the sum of the membrane thicknesses, indicating that the membranes at their contact sites were fixed in a state of hemifusion. Moreover, the hemifused vesicles were found to have large contact areas with the presynaptic membrane. These findings support the recently proposed hypothesis that, at frog neuromuscular junctions, docked synaptic vesicles with the largest contact areas are most primed for fusion with the presynaptic membrane, and that hemifusion is a fusion intermediate step of the vesicle membrane with the presynaptic membrane for synaptic transmission.

scholarly journals Freeze-fracture studies of frog neuromuscular junctions during intense release of neurotransmitter. III. A morphometric analysis of the number and diameter of intramembrane particles.

1980 ◽  
Vol 85 (2) ◽  
pp. 337-345 ◽  
Author(s):  
R Fesce ◽  
F Grohovaz ◽  
W P Hurlbut ◽  
B Ceccarelli
Keyword(s):  
Synaptic Vesicles ◽  
Neuromuscular Junctions ◽  
Freeze Fracture ◽  
Presynaptic Membrane ◽  
Small Particles ◽  
Vesicle Membrane ◽  
Intramembrane Particles ◽  
Large Particles ◽  
Black Widow Spider Venom ◽  
Indirect Stimulation

The intramembrane particles on the presynaptic membrane and on the membrane of synaptic vesicles were studied at freeze-fractured neuromuscular junctions of the frog. The particles on the P face of the presynaptic membrane belong to two major classes: small particles with diameters less than 9 nm and large particles with diameters between 9 and 13 nm. In addition, there were a few extralarge particles with diameters greater than 13 nm. Indirect stimulation of the muscle, or the application of black widow spider venom, decreased the concentration of small particles on the presynaptic membrane but did not change the concentration of large particles. Three similar classes of particles were found on the P face of the membrane of the synaptic vesicles. The concentrations of large and extralarge particles on the vesicle membrane were comparable to the concentrations of these particles on the presynaptic membrane, whereas the concentration of small particles on the vesicle membrane was less than than the concentration of small particles on the presynaptic membrane. These results are compatible with the idea that synaptic vesicles fuse with the presynaptic membrane when quanta of transmitter are released. However, neither the large nor the extralarge particles on the P face of the presynaptic membrane can be used to trace the movement of vesicle membrane that has been incorporated into the axolemma.

Neurotransmitter release mechanisms and microtubules

1983 ◽  
Vol 218 (1211) ◽  
pp. 253-258 ◽  
Keyword(s):  
Neurotransmitter Release ◽  
Synaptic Vesicles ◽  
Ordered Structure ◽  
Presynaptic Membrane ◽  
Vesicle Membrane ◽  
Ordered Arrays ◽  
The Central Nervous System ◽  
Active Zones ◽  
Dense Projections ◽  
Regular Arrays

The morphological mechanisms involved in translocation of the synaptic vesicle to the presynaptic membrane, release of transmitter from the vesicle and recycling of the vesicle membrane are still far from understood. However, there is strong evidence that vesicles move along the surfaces of a specific set of highly labile presynaptic microtubules that direct the vesicles to the active zones. These microtubules are focused in a precise geometrical array, which is in register with and in contact with presynaptic dense projections of the central nervous system synapse or presynaptic dense bars of the motor endplate. These dense complexes constitute the presynaptic grid or active zones. The regular arrays of dense projections or bars are in turn coincident with rings or chains of synaptic vesicles mobilized at release sites on the presynaptic membrane (having arrived at these precise points by microtubule translocation). Thus it is suggested that the presynaptic microtubules not only translocate synaptic vesicles, but because of their ordered arrays determine, in ontogeny, the ordered structure of the presynaptic grid.

scholarly journals The structure and function of ‘active zone material’ at synapses

2015 ◽  
Vol 370 (1672) ◽  
pp. 20140189 ◽  
Author(s):  
Joseph A. Szule ◽  
Jae Hoon Jung ◽  
Uel J. McMahan
Keyword(s):  
Spatial Resolution ◽  
Active Zone ◽  
Synaptic Vesicles ◽  
Neuromuscular Junctions ◽  
Electron Tomography ◽  
Structure And Function ◽  
Presynaptic Membrane ◽  
Axon Terminals ◽  
Active Zones ◽  
And Function

The docking of synaptic vesicles on the presynaptic membrane and their priming for fusion with it to mediate synaptic transmission of nerve impulses typically occur at structurally specialized regions on the membrane called active zones. Stable components of active zones include aggregates of macromolecules, ‘active zone material’ (AZM), attached to the presynaptic membrane, and aggregates of Ca 2+ -channels in the membrane, through which Ca 2+ enters the cytosol to trigger impulse-evoked vesicle fusion with the presynaptic membrane by interacting with Ca 2+ -sensors on the vesicles. This laboratory has used electron tomography to study, at macromolecular spatial resolution, the structure and function of AZM at the simply arranged active zones of axon terminals at frog neuromuscular junctions. The results support the conclusion that AZM directs the docking and priming of synaptic vesicles and essential positioning of Ca 2+ -channels relative to the vesicles' Ca 2+ -sensors. Here we review the findings and comment on their applicability to understanding mechanisms of docking, priming and Ca 2+ -triggering at other synapses, where the arrangement of active zone components differs.

scholarly journals Freeze-fracture studies of frog neuromuscular junctions during intense release of neurotransmitter. I. Effects of black widow spider venom and Ca2+-free solutions on the structure of the active zone.

1979 ◽  
Vol 81 (1) ◽  
pp. 163-177 ◽  
Author(s):  
B Ceccarelli ◽  
F Grohovaz ◽  
W P Hurlbut
Keyword(s):  
Neuromuscular Junctions ◽  
Freeze Fracture ◽  
Spider Venom ◽  
Presynaptic Membrane ◽  
Black Widow ◽  
Black Widow Spider ◽  
Intramembrane Particles ◽  
Black Widow Spider Venom ◽  
Active Zones ◽  
Widow Spider

Black widow spider venom (BWSV) was applied to frog nerve-muscle preparations bathed in Ca2+-containing, or Ca2+-free, solutions and the neuromuscular junctions were studied by the freeze-fracture technique. When BWSV was applied for short periods (10-15 min) in the presence of Ca2+, numerous dimples (P face) or protuberances (E face) appeared on the presynaptive membrane and approximately 86% were located immediately adjacent to the double rows of large intramembrane particles that line the active zones. When BWSV was applied for 1 h in the presence of Ca2+, the nerve terminals were depleted of vesicles, few dimples or protuberances were seen, and the active zones were almost completely disorganized. The P face of the presynaptic membrane still contained large intramembrane particles. When muscles were soaked for 2-3 h in Ca2+-free solutions, the active zones became disorganized, and isolated remnants of the double rows of particles were found scattered over the P face of the presynaptic membrane. When BWSV was applied to these preparations, dimples or protuberances occurred almost exclusively alongside disorganized active zones or alongside dispersed fragments of the active zones. The loss of synaptic vesicles from terminals treated with BWSV probably occurs because BWSV interferes with the endocytosis of vesicle membrane. Therefore, we assume that the dimples or protuberances seen on these terminals identify the sites of exocytosis, and we conclude that exocytosis can occur mostly in the immediate vicinity of the large intramembrane particles. Extracellular Ca2+ seems to be required to maintain the grouping of the large particles into double rows at the active zones, but is not required for these particles to specify the sites of exocytosis.

scholarly journals Freeze-fracture studies of frog neuromuscular junctions during intense release of neurotransmitter. II. Effects of electrical stimulation and high potassium.

1979 ◽  
Vol 81 (1) ◽  
pp. 178-192 ◽  
Author(s):  
B Ceccarelli ◽  
F Grohovaz ◽  
W P Hurlbut
Keyword(s):  
Nerve Terminal ◽  
Neuromuscular Junctions ◽  
Freeze Fracture ◽  
Presynaptic Membrane ◽  
High Potassium ◽  
Unique Distribution ◽  
Active Zones ◽  
Nerve Muscle ◽  
Indirect Stimulation ◽  
Quantal Release Of Neurotransmitter

Frog cutaneous pectoris nerve muscle preparations were studied by the freeze-fracture technique under the following conditions: (a) during repetitive indirect stimulation for 20 min, 10/s; (b) during recovery from this stimulation; and (c) during treatment with 20 mM K+. Indirect stimulation causes numerous dimples or protuberances to appear on the presynaptic membrane of nerve terminal, and most are located near the active zones. Deep infoldings of the axolemma often develop between the active zones. Neither the number nor the distribution of dimples, protuberances, of infoldings changes markedly during the first minute of recovery. The number of dimples, protuberances, and infoldings is greatly reduced after 10 min of recovery. Since endocytosis proceeds vigorously during the recovery periods, we conclude that endocytosis occurs mostly at the active zones, close to the sites of exocytosis. 20 mM K+ also causes many dimples or protuberances to appear on the axolemma of the nerve terminal but they are distributed almost uniformly along the presynaptic membrane. Experiments with horseradish peroxidase (HRP) show that recycling of synaptic vesicles occurs in 20 mM K+. This recycling is not accompanied by changes in the number of coated vesicles. Since both exocytosis and endocytosis occur in 20 mM K+, it is difficult to account for this unique distribution. However, we suggest that K+ causes dimples or protuberances to appear between the active zones because it activates latent sites of exocytosis specified by small numbers of large intramembrane particles located between active zones. The activation of latent release sites may be related to the complex effects that K+ has on the quantal release of neurotransmitter.

scholarly journals Macromolecular connections of active zone material to docked synaptic vesicles and presynaptic membrane at neuromuscular junctions of mouse

2009 ◽  
Vol 513 (5) ◽  
pp. 457-468 ◽  
Author(s):  
Sharuna Nagwaney ◽  
Mark Lee Harlow ◽  
Jae Hoon Jung ◽  
Joseph A. Szule ◽  
David Ress ◽  
...  
Keyword(s):  
Active Zone ◽  
Synaptic Vesicles ◽  
Neuromuscular Junctions ◽  
Presynaptic Membrane

scholarly journals Ultrastructural heterogeneity of human layer 4 excitatory synaptic boutons in the adult temporal lobe neocortex

2019 ◽  
Author(s):  
Rachida Yakoubi ◽  
Astrid Rollenhagen ◽  
Marec von Lehe ◽  
Dorothea Miller ◽  
Bernd Walkenfort ◽  
...  
Keyword(s):  
Temporal Lobe ◽  
Synaptic Vesicles ◽  
Building Blocks ◽  
Synaptic Activity ◽  
Quantitative Morphology ◽  
Layer 4 ◽  
Total Pool ◽  
Synaptic Boutons ◽  
Active Zones ◽  
Computational Properties

AbstractSynapses are fundamental building blocks that control and modulate the ‘behavior’ of brain networks. How their structural composition, most notably their quantitative morphology underlies their computational properties remains rather unclear, particularly in humans. Here, excitatory synaptic boutons (SBs) in layer 4 (L4) of the temporal lobe neocortex (TLN) were quantitatively investigated.Biopsies from epilepsy surgery were used for fine-scale and tomographic electron microscopy to generate 3D-reconstructions of SBs. Particularly, the size of active zones (AZs) and of the three functionally defined pools of synaptic vesicles (SVs) were quantified.SBs were comparably small (∼2.50 μm2), with a single AZ (∼0.13 µm2) and preferentially established on spines. SBs had a total pool of ∼1800SVs with strikingly large readily releasable (∼ 20), recycling (∼ 80) and resting pools (∼850).Thus, human L4 SBs may act as ‘amplifiers’ of signals from the sensory periphery and integrate, synchronize and modulate intra- and extra-cortical synaptic activity.

Expression of synaptotagmin in Drosophila reveals transport and localization of synaptic vesicles to the synapse

Development ◽  
1993 ◽  
Vol 118 (4) ◽  
pp. 1077-1088 ◽  
Author(s):  
J.T. Littleton ◽  
H.J. Bellen ◽  
M.S. Perin
Keyword(s):  
Nervous System ◽  
Synaptic Vesicle ◽  
Synaptic Vesicles ◽  
Synapse Formation ◽  
Neuromuscular Junctions ◽  
Synaptic Contact ◽  
Immunocytochemical Staining ◽  
Intense Staining ◽  
General Role ◽  
Contact Sites

Synaptotagmin is a synaptic vesicle-specific integral membrane protein that has been suggested to play a key role in synaptic vesicle docking and fusion. By monitoring Synaptotagmin's cellular and subcellular distribution during development, it is possible to study synaptic vesicle localization and transport, and synapse formation. We have initiated the study of Synaptotagmin's expression during Drosophila neurogenesis in order to follow synaptic vesicle movement prior to and during synapse formation, as well as to localize synaptic sites in Drosophila. In situ hybridizations to whole-mount embryos show that synaptotagmin (syt) message is present in the cell bodies of all peripheral nervous system neurons and many, if not all, central nervous system neurons during neurite outgrowth and synapse formation, and in mature neurons. Immunocytochemical staining with antisera specific to Synaptotagmin indicates that the protein is present at all stages of the Drosophila life cycle following germ band retraction. In embryos, Synaptotagmin is only transiently localized to the cell body of neurons and is transported rapidly along axons during axonogenesis. After synapse formation, Synaptotagmin accumulates in a punctate pattern at all identifiable synaptic contact sites, suggesting a general role for Synaptotagmin in synapse function. In embryos and larvae, the most intense staining is found along two broad longitudinal tracts on the dorsal side of the ventral nerve cord and the brain, and at neuromuscular junctions in the periphery. In the adult head, Synaptotagmin localizes the discrete regions of the neurophil where synapses are predicted to occur. These data indicate that synaptic vesicles are present in axons before synapse formation, and become restricted to synaptic contact sites after synapses are formed. Since a similar expression pattern of Synaptotagmin has been reported in mammals, we propose that the function of Synaptotagmin and the mechanisms governing localization of the synaptic vesicle before and after synapse formation are conserved in invertebrate and vertebrate species. The ability to mark synapses in Drosophila should facilitate the study of synapse formation and function, providing a new tool to dissect the molecular mechanisms underlying these processes.

Effect of lanthanum ions on function and structure of frog neuromuscular junctions

1971 ◽  
Vol 179 (1056) ◽  
pp. 247-260 ◽  
Keyword(s):  
Synaptic Vesicles ◽  
Neuromuscular Junctions ◽  
High Rate ◽  
Nerve Terminals ◽  
Presynaptic Membrane ◽  
Electron Microscopic ◽  
Lanthanum Ions ◽  
End Plate ◽  
Microscopic Studies ◽  
Membrane Bound

1. Electrophysiological and electron-microscopic studies were made of the effect of lan­thanum ions on frog neuromuscular junctions. 2. In the presence of 1 mM La 2+ , nerve impulses continued to invade the nerve terminals but ceased to release transmitter. 3. Lanthanum caused a rapid and large increase in the frequency of miniature end-plate potentials; presumably because La activates the mechanism of transmitter release without the usual prerequisite of presynaptic membrane depolarization. At 4 °C, La caused a 10000-fold, or even larger increase in the rate of leakage of transmitter quanta. Such high rate of trans­mitter release was not accompanied by obvious changes in electron-microscopic structure of the nerve terminals. 4. With continued La-treatment, the frequency of miniature end-plate potentials subsides slowly until they are no longer detectable at most end-plates. During this period the number of synaptic vesicles is reduced until practically all the endings become completely depleted of synaptic vesicles. In contrast, coated vesicles and membrane-bound tubes and cysternae become more numerous.

scholarly journals Changes in the structure of neuromuscular junctions caused by variations in osmotic pressure.

1976 ◽  
Vol 69 (3) ◽  
pp. 521-538 ◽  
Author(s):  
A W Clark
Keyword(s):  
Osmotic Pressure ◽  
Synaptic Vesicles ◽  
Rana Pipiens ◽  
Neuromuscular Junctions ◽  
Presynaptic Membrane ◽  
Normal Position ◽  
Structural Modifications ◽  
Endplate Potential ◽  
Miniature Endplate Potential ◽  
Potential Frequency

Neuromuscular junctions of the frog, Rana pipiens, were examined for structural modifications produced by exposure to increased and reduced osmotic pressure (pi). Preparations exposed to increased pi for varying lengths of time were fixed with either OSO4-Veronal with and without calcium, glutaraldehyde-phosphate, or glutaraldehyde-formaldehyde-phosphate as primary fixatives. The greatest difference between the fixatives was seen in preparations exposed to increased pi for 5 min, corresponding to the time when miniature endplate potential frequency is highest. The 5-min OSO4 calcium-free preparations appeared comparatively normal, while those fixed with OSO4 and 2 mM CaCl2 or aldehyde-phosphate had wide infoldings of the presynaptic membrane and a reduced number of synaptic vesicles. Aldehyde-phosphate had the same effect on mouse diaphragm. Another series of frog preparations were conditioned to elevated pi and then returned to normal Ringer's for varying times before fixation in OSO4-phosphate. Preparations fixed 2 min after their return to normal Ringer's showed marked disruption of the presynaptic membrane as well as apparently rupturing vesicles. If fixed after 10 min, terminals were depleted of vesicles although the presynaptic membrane had returned to its normal position and appearance.

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