“Strong” and “weak” synaptic differentiation in the crayfish opener muscle: Structural correlates

Govind, C. K.; Pearce, Joanne; Wojtowicz, J. Martin; Atwood, Harold L.

doi:10.1002/syn.890160106

Cited by 53 publications

(67 citation statements)

References 50 publications

(68 reference statements)

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“…In long-term stimulation and LTF experiments, structural alterations were more likely to be found in "complex" synapses. Also, in other studies (Govind et al, 1994) "high-output" terminals differ from "low-output" terminals ofthe crayfish opener muscle mainly in possessing a higher proportion of "complex" synapses. This is also true in other crustacean nerve terminals that have been studied (Govind and Meiss, 1979;Atwood and Marin, 1983).…”

Section: Discussionmentioning

confidence: 79%

Activity-induced changes in synaptic release sites at the crayfish neuromuscular junction

1994

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Crustacean motor axons provide a model in which activity-dependent changes in synaptic physiology and synaptic structure can be concurrently observed in single identifiable neurons. In response to a train of stimulation, crustacean neuromuscular junctions undergo pronounced facilitation of transmitter release. The effects of maintained high-frequency stimulation may persist for at least several hours (“long-term facilitation”). Electrophysiological studies suggest that the number of “active” synapses contributing transmitter quanta at low frequencies of stimulation increases during and after a train of high-frequency stimulation. However, at different terminal recording sites the effect of stimulation varies, and it was observed that not all released quanta produce a voltage change in the postsynaptic muscle cell. Electron microscopic examinations of serial sections from nerve terminals subjected to stimulation were made to determine whether changes in synaptic structure could be correlated with activity-induced long-lasting enhancement of transmission. A procedure was introduced for marking a recorded terminal with fluorescent polystyrene microspheres, which are visible in electron micrographs of the recording site. Crustacean nerve terminals possess a large number of discrete synapses, a small fraction of which have multiple presynaptic “active zones” (dense bodies with clustered synaptic vesicles, thought to represent sites of evoked transmitter release). In terminals previously stimulated, the proportion of synapses with multiple “active zones” is greater than in control unstimulated terminals. Total synaptic vesicle counts and readily releasable vesicles at synapses are not significantly different in previously stimulated terminals and controls. In terminals fixed during stimulation a few synapses show evidence of division in “active zones,” and synaptic vesicle counts are lower than in controls.(ABSTRACT TRUNCATED AT 250 WORDS)

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Section: Discussionmentioning

confidence: 79%

Activity-induced changes in synaptic release sites at the crayfish neuromuscular junction

1994

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“…Ultrastructural analysis of nerve terminals suggest that there is great deal of heterogeneity in the number of vesicles that can encircle the active zones of the synapses (Govind et al 1994). This suggests that various number of vesicles could be primed for release in each active zone; however, the conformational constraints of the active zone suggest that there may be a limit to the total number of primed/docked vesicles possible.…”

Section: Discussionmentioning

confidence: 99%

Role of α-SNAP in Promoting Efficient Neurotransmission at the Crayfish Neuromuscular Junction

Southard

Chen

et al. 1999

Journal of Neurophysiology

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He, Ping, R. Chase Southard, Dong Chen, S. W. Whiteheart, and R. L. Cooper. Role of ␣-SNAP in promoting efficient neurotransmission at the crayfish neuromuscular junction. J. Neurophysiol. 82: 3406 -3416, 1999. In this manuscript, we address the role of the soluble N-ethylmaleimide sensitive factor attachment protein (␣-SNAP) in synaptic transmission at the neuromuscular junction of the crayfish opener muscle. Immunochemcial methods confirm the presence of ␣-SNAP in these preparations and show that it is concentrated in the synaptic areas. Microinjection and electrophysiological studies show that ␣-SNAP causes an increase in neurotransmitter release yet does not significantly affect the kinetics. More specific quantal analysis, using focal, macropatch, synaptic current recordings, shows that ␣-SNAP increases transmitter release by increasing the probability of exocytosis but not the number of potential release sites. These data demonstrate that the role of ␣-SNAP is to increase the efficiency of neurotransmission by increasing the probability that a stimulus will result in neurotransmitter release. What this suggests is that ␣-SNAP is critical for the formation and maintenance of a "ready release" pool of synaptic vesicles.The studies of neurotransmitter (NT) release have yielded a long list of molecules, proposed to play a role in neurotransmission and have suggested an outline of a molecular interactions required for synaptic vesicle (SV) exocytosis (reviewed in Bajjalieh and Scheller 1995;Martin 1997;Rothman 1994;Sudhof 1995). Membrane proteins from the synaptic vesicle [called vesicle soluble N-ethylmaleimide sensitive factor attachment protein receptors (v-SNAREs), e.g., vesicle associated membrane protein (VAMP)/synaptobrevin] and from the active zone [called target membrane SNAREs (t-SNAREs), e.g., syntaxins and synaptosome associated protein 23 or 25 (SNAP23/25)] appear to be essential for membrane fusion events (Hunt et al. 1994;Littleton et al. 1998;Weber et al. 1998). Current data suggest that the three SNARE proteins, interlocked by the interactions of their coiled-coil domains (Poirier et al. 1998;Sutton et al. 1998;Weber et al. 1998), form a bimembrane-spanning complex that is sufficient for bilayer fusion (Weber et al. 1998).The interactions of the SNARE proteins are, in part, regulated by cytosolic proteins called SNAPs and NSF (N-ethylmaleimide sensitive factor). SNAPs initially bind to the SNARE complex and serve as adapters to correctly position NSF (Clary et al. 1990;Weidman et al. 1989). SNAP is also responsible for the stimulation of NSF's ATPase activity, which in turn is needed to disassemble the SNARE complex (Barnard et al. 1997;Nagiec et al. 1995). Although SNAREs are needed for fusion (Hunt et al. 1994;Littleton et al. 1998;Weber et al. 1998), it is less obvious what role SNAP and NSF play in neurotransmission (Banerjee et al. 1996;Haas and Wickner 1996;Hay and Martin 1992;Martin et al. 1995;Mayer and Wickner 1997;Mayer et al. 1996). Injection studies using squid axons have shown tha...

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“…Ž . nm than one section thickness Govind et al, 1994 . Sometimes a transversely sectioned dense bar is observed in up to three serial sections.…”

Section: Presynaptic Dense Bodiesmentioning

confidence: 98%

“…3 . Attempts have been made in previous work to relate measurements of synaptic Ž or active zone size to synaptic strength Atwood et al, 1978;Govind and Meiss, 1979;Atwood and Marin, 1983;. Govind et al, 1994 .…”

Section: Problems In Estimating Sizes Of Small Structures In Serial Smentioning

confidence: 99%

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Assessing ultrastructure of crustacean and insect neuromuscular junctions

Atwood

Cooper

1996

Journal of Neuroscience Methods

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Motor nerve terminals of arthropods provide excellent models for study of synaptic transmission, and their ultrastructure can be investigated in the same endings from which physiological recordings have been obtained. An experimental procedure for marking a recording site for subsequent ultrastructural analysis is described. The most commonly used procedure for ultrastructural analysis has been serial sectioning and three-dimensional reconstruction. This procedure has the advantage of providing information about the entire nerve terminal, including quantitative information on number, sizes, and relative positions of individual synapses and presynaptic 'active zones'. However, several errors may be generated in the process of viewing the sections and making the reconstruction; these errors can in principle lead to overestimation of synapse and active zone size. The errors become relatively more serious for smaller structures. Procedures for alleviating some of the possible errors are outlined. It is desirable to have additional information from other methods, such as freeze-fracture replication, to guide analysis of reconstructions from serial sections. Combined physiological and ultrastructural analysis of arthropod terminals has shown that each terminal has many small synapses, differing in size and in number of active zones, and that in some terminals, many of the observed synapses have a very low probability of transmission when nerve impulses occur at low frequencies.

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“Strong” and “weak” synaptic differentiation in the crayfish opener muscle: Structural correlates

Cited by 53 publications

References 50 publications

Activity-induced changes in synaptic release sites at the crayfish neuromuscular junction

Activity-induced changes in synaptic release sites at the crayfish neuromuscular junction

Role of α-SNAP in Promoting Efficient Neurotransmission at the Crayfish Neuromuscular Junction

Assessing ultrastructure of crustacean and insect neuromuscular junctions

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