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.

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 Reinnervation of muscle fiber basal lamina after removal of myofibers. Differentiation of regenerating axons at original synaptic sites.

1978 ◽  
Vol 78 (1) ◽  
pp. 176-198 ◽  
Author(s):  
J R Sanes ◽  
L M Marshall ◽  
U J McMahan
Keyword(s):  
Skeletal Muscle ◽  
Basal Lamina ◽  
Muscle Fiber ◽  
Nerve Terminal ◽  
Synaptic Vesicles ◽  
Muscle Fibers ◽  
Nerve Terminals ◽  
Morphological Criteria ◽  
Histological Criteria ◽  
Active Zones

Axons regenerate to reinnervate denervated skeletal muscle fibers precisely at original synaptic sites, and they differentiate into nerve terminals where they contact muscle fibers. The aim of this study was to determine the location of factors that influence the growth and differentiation of the regenerating axons. We damaged and denervated frog muscles, causing myofibers and nerve terminals to degenerate, and then irradiated the animals to prevent regeneration of myofibers. The sheath of basal lamina (BL) that surrounds each myofiber survives these treatments, and original synaptic sites on BL can be recognized by several histological criteria after nerve terminals and muscle cells have been completely removed. Axons regenerate into the region of damage within 2 wk. They contact surviving BL almost exclusively at original synaptic sites; thus, factors that guide the axon's growth are present at synaptic sites and stably maintained outside of the myofiber. Portions of axons that contact the BL acquire active zones and accumulations of synaptic vesicles; thus by morphological criteria they differentiate into nerve terminals even though their postsynaptic targets, the myofibers, are absent. Within the terminals, the synaptic organelles line up opposite periodic specializations in the myofiber's BL, demonstrating that components associated with the BL play a role in organizing the differentiation of the nerve terminal.

scholarly journals Maturation of active zone assembly by Drosophila Bruchpilot

2009 ◽  
Vol 186 (1) ◽  
pp. 129-145 ◽  
Author(s):  
Wernher Fouquet ◽  
David Owald ◽  
Carolin Wichmann ◽  
Sara Mertel ◽  
Harald Depner ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Drosophila Melanogaster ◽  
High Resolution ◽  
Active Zone ◽  
Synaptic Vesicles ◽  
C Terminus ◽  
Family Protein ◽  
N Terminus ◽  
Dense Projections ◽  
Ca2 Channels

Synaptic vesicles fuse at active zone (AZ) membranes where Ca2+ channels are clustered and that are typically decorated by electron-dense projections. Recently, mutants of the Drosophila melanogaster ERC/CAST family protein Bruchpilot (BRP) were shown to lack dense projections (T-bars) and to suffer from Ca2+ channel–clustering defects. In this study, we used high resolution light microscopy, electron microscopy, and intravital imaging to analyze the function of BRP in AZ assembly. Consistent with truncated BRP variants forming shortened T-bars, we identify BRP as a direct T-bar component at the AZ center with its N terminus closer to the AZ membrane than its C terminus. In contrast, Drosophila Liprin-α, another AZ-organizing protein, precedes BRP during the assembly of newly forming AZs by several hours and surrounds the AZ center in few discrete punctae. BRP seems responsible for effectively clustering Ca2+ channels beneath the T-bar density late in a protracted AZ formation process, potentially through a direct molecular interaction with intracellular Ca2+ channel domains.

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

The Architecture of the Active Zone in the Presynaptic Nerve Terminal

Physiology ◽  
2004 ◽  
Vol 19 (5) ◽  
pp. 262-270 ◽  
Author(s):  
R. Grace Zhai ◽  
Hugo J. Bellen
Keyword(s):  
Active Zone ◽  
Synaptic Vesicles ◽  
Molecular Organization ◽  
Nerve Terminals ◽  
Presynaptic Nerve Terminal ◽  
Structural Differences ◽  
Common Principle ◽  
Active Zones ◽  
Presynaptic Nerve Terminals ◽  
Kinetics Of

Active zones are highly specialized sites for release of neurotransmitter from presynaptic nerve terminals. The architecture of the active zone is exquisitely designed to facilitate the regulated tethering, docking, and fusing of the synaptic vesicles with the plasma membrane. Here we present our view of the structural and molecular organization of active zones across species and propose that all active zones are organized according to a common principle in which the structural differences correlate with the kinetics of transmitter release.

scholarly journals Neural Organization of the Median Ocellus of the Dragonfly

1972 ◽  
Vol 60 (2) ◽  
pp. 148-165 ◽  
Author(s):  
John E. Dowling ◽  
Richard L. Chappell
Keyword(s):  
Electron Microscopy ◽  
Synaptic Vesicles ◽  
Receptor Cell ◽  
Presynaptic Membrane ◽  
Cell Axon ◽  
Axon Terminals ◽  
Neural Organization ◽  
Dense Cluster ◽  
Median Ocellus ◽  
Ocellar Nerve

Two types of presumed synaptic contacts have been recognized by electron microscopy in the synaptic plexus of the median ocellus of the dragonfly. The first type is characterized by an electron-opaque, button-like organelle in the presynaptic cytoplasm, surrounded by a cluster of synaptic vesicles. Two postsynaptic elements are associated with these junctions, which we have termed button synapses. The second synaptic type is characterized by a dense cluster of synaptic vesicles adjacent to the presumed presynaptic membrane. One postsynaptic element is observed at these junctions. The overwhelming majority of synapses seen in the plexus are button synapses. They are found most commonly in the receptor cell axons where they synaptically contact ocellar nerve dendrites and adjacent receptor cell axons. Button synapses are also seen in the ocellar nerve dendrites where they appear to make synapses back onto receptor axon terminals as well as onto adjacent ocellar nerve dendrites. Reciprocal and serial synaptic arrangements between receptor cell axon terminals, and between receptor cell axon terminals and ocellar nerve dendrites are occasionally seen. It is suggested that the lateral and feedback synapses in the median ocellus of the dragonfly play a role in enhancing transients in the postsynaptic responses.

scholarly journals Colocalization of synapsin and actin during synaptic vesicle recycling

2003 ◽  
Vol 161 (4) ◽  
pp. 737-747 ◽  
Author(s):  
Ona Bloom ◽  
Emma Evergren ◽  
Nikolay Tomilin ◽  
Ole Kjaerulff ◽  
Peter Löw ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Synaptic Vesicle ◽  
Active Zone ◽  
Synaptic Vesicles ◽  
Synaptic Activity ◽  
Immunogold Electron Microscopy ◽  
Synaptic Vesicle Recycling ◽  
Vesicle Recycling ◽  
Reserve Pool ◽  
Giant Synapse

It has been hypothesized that in the mature nerve terminal, interactions between synapsin and actin regulate the clustering of synaptic vesicles and the availability of vesicles for release during synaptic activity. Here, we have used immunogold electron microscopy to examine the subcellular localization of actin and synapsin in the giant synapse in lamprey at different states of synaptic activity. In agreement with earlier observations, in synapses at rest, synapsin immunoreactivity was preferentially localized to a portion of the vesicle cluster distal to the active zone. During synaptic activity, however, synapsin was detected in the pool of vesicles proximal to the active zone. In addition, actin and synapsin were found colocalized in a dynamic filamentous cytomatrix at the sites of synaptic vesicle recycling, endocytic zones. Synapsin immunolabeling was not associated with clathrin-coated intermediates but was found on vesicles that appeared to be recycling back to the cluster. Disruption of synapsin function by microinjection of antisynapsin antibodies resulted in a prominent reduction of the cytomatrix at endocytic zones of active synapses. Our data suggest that in addition to its known function in clustering of vesicles in the reserve pool, synapsin migrates from the synaptic vesicle cluster and participates in the organization of the actin-rich cytomatrix in the endocytic zone during synaptic activity.

A structural study of the squid synapse after intraaxonal injection of calcium

1978 ◽  
Vol 201 (1145) ◽  
pp. 317-333 ◽  
Keyword(s):  
Electron Microscopy ◽  
Nerve Terminal ◽  
Synaptic Vesicles ◽  
Presynaptic Terminal ◽  
Presynaptic Membrane ◽  
Ground Structure ◽  
Presynaptic Nerve Terminal ◽  
Dense Deposits ◽  
Membrane Bound ◽  
Giant Synapse

The giant synapse of the squid was examined by electron microscopy after ionophoretic injection of Ca 2+ ions into the pre- or postsynaptic axon. The results suggest that there are differences in the Ca-buffering mechanisms in pre- and postsynaptic axons. For instance, after injection of Ca 2+ into the postsynaptic axon, mitochondria were heavily loaded with granular inclusions. In contrast, mitochondria of injected presynaptic terminals did not contain inclusions. In the postsynaptic axon, besides inclusions in mitochondria, dense deposits were found in axoplasmic vesicles and cisterns that appeared locally at the site of injection. Injection of Ca 2+ into the presynaptic terminal produced non-membrane bound dense deposits associated with the filamentous ground structure of the axoplasm. Some calcium may also be bound to the presynaptic membrane which appears dense after injection. In both axons the alterations produced by injected Ca 2+ were confined mainly to the area of injection. After injection of Ca 2+ into the presynaptic nerve terminal, synaptic vesicles disappeared and a large number of coated vesicles appeared. In addition, membrane invaginations developed involving not only the presynaptic membrane but also that of postsynaptic processes and glial cells. After injection of large quantities of Ca 2+ into the postsynaptic axon, electron-dense precipitates were seen also in the presynaptic terminal indicating retrograde transfer of material from post- to presynaptic axons.

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.

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