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 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. 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.

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.

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.

Synaptic vesicles and microtubules in frog motor endplates

1978 ◽  
Vol 203 (1152) ◽  
pp. 219-227 ◽  
Keyword(s):  
Electron Microscopy ◽  
Skeletal Muscle ◽  
Small Proportion ◽  
Active Zone ◽  
Synaptic Vesicles ◽  
Presynaptic Membrane ◽  
Albumin Solution ◽  
Motor Endplates ◽  
Active Zones ◽  
A New Technique

Motor endplates of the cutaneous pectoris skeletal muscle of the frog have been examined by electron microscopy using a new technique. This involves pretreatment with an albumin solution, followed by fixation with 4% unbuffered tetroxide. A small proportion of the endplate axonal ramifications show microtubules clothed in synaptic vesicles and focused on the presynaptic membrane, in particular on the active zones. The microtubules run in the presynaptic cytoplasm either parallel to or across the active zones. These two sets of microtubules cross each other at the active zones, which lie opposite the dips in the post-junctional folds. The possibility that the microtubules are involved in the translocation of synaptic vesicles to the active zone is discussed.

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