Three-Dimensional Ultrastructure of the Crayfish Neuromuscular Apparatus

Jahromi, S. S.; Atwood, Harold L.

doi:10.1083/jcb.63.2.599

Cited by 160 publications

(130 citation statements)

References 27 publications

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“…1B). The results are generally similar to those of previous serial sectioning studies of the crayfish opener muscle (Jahromi and Atwood, 1974;Atwood and Kwan, 1976;Wojtowicz et al, 1989a).…”

Section: Resultssupporting

confidence: 81%

“…Individual synapses were defined on morphological grounds as regions of densely staining pre-and postsynaptic membranes with uniform separation of 20 nm (see Jahromi and Atwood, 1974;Wojtowicz et al, 1989a). An active site (or zone) within the synapse is characterized as a dense bar or projection associated with the presynaptic membrane and closely associated with a cluster of synaptic vesicles (Jahromi and Atwood, 1974). The information from all sections was combined for each terminal to provide values of surface area for each synapse, and total surface area of the terminal.…”

Section: Methodsmentioning

confidence: 99%

“…Electron microscopy ofnerve terminals from "control," "stimulated," and "long-term facilitated" specimens was conducted using well-established procedures (Jahromi and Atwood, 1974;Govind et al, 1982 after the beginning of 20 Hz stimulation of the excitatory axon. (LTF is not induced by this period of stimulation.)…”

Section: Methodsmentioning

confidence: 99%

“…The present study was undertaken to test further the hypothesis that structural changes in synapses of crustacean motoneurons are associated with changes in neuronal activity. The neuron chosen for these experiments is the motor neuron of the "opener" muscle of the crayfish walking leg, since long-term facilitation can be reliably induced in this neuron, and the general ultrastructure of the synapses is well known from previous investigations (Jahromi and Atwood, 1974;Florey and Cahill, 1982).…”

Section: Crustaceanmentioning

confidence: 99%

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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: Resultssupporting

confidence: 81%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Crustaceanmentioning

confidence: 99%

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

1994

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“…is the osmotic permeability co-efficient (cm4 S-i Osmo1-2), A is the surface area (cm2), c, is the initial osmolarity of the axoplasm (Osmol cm-3), and c0 is the extracellular osmolarity. A cylindrical region of nerve terminal under the focal electrode has a length of 10-3 cm and a radius of 10-4 cm or less (Jahromi & Atwood, 1974;Smith, 1978). If P, is assumed to be 9 x 10-3 cm4 s-1 Osmol-1, as for squid axon (Villegas & Villegas, 1960), and if all of the axoplasmic water is assumed to be osmotically exchangeable, then the maximum Jw is 2-4x 10-12 cm3 $-1 from a volume of 3-14 x 10-11 cm3 for an osmotic gradient of 4-3 x 10-4 Osmol cm-3.…”

Section: Discussionmentioning

confidence: 99%

Effects of hypertonic solutions on quantal transmitter release at the crayfish neuromuscular junction

Niles

Smith

1982

The Journal of Physiology

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SUMMARY1. The effects ofa hypertonic bathing medium, containing either NaCl or melezitose, on the average number (m) and the time course of quantal release following an action potential were studied using focal extracellular recording methods at synaptic sites on the opener muscle of the crayfish leg.2. After the application of hypertonic saline, the rate of spontaneous quantal release increased but m decreased to a new level within 1 min; the extent of depression depended on the magnitude of the increase in tonicity until the osmolarity was 50 % greater than the normal value of 0 43 osmol/l (Osm), but greater increases in tonicity exerted little further effect. 3. The synaptic delays were increased and distributed over a longer range of time in hypertonic solutions; also, the latency between the first and second quantal releases in a multiple response to a single nerve impulse was also increased.4. Hypertonicity had no significant effect on the conduction velocity of the action potential, the independence of successive quantal releases in the same response, or the uniformity of the rise and fall of the probability of quanta release following an action potential, a(t).5. The time course of a(t) is prolonged in hypertonic solutions; this was manifested as an increase in the time constant of the exponential decline in a(t) from its peak value following the nerve impulse.5. When the potentiating agent 5-hydroxytryptamine (5-HT) was added to the hypertonic saline, m was increased, and the time course of a(t) was prolonged further than in the hypertonic solution alone; 5-HT produced no change in the time course of a(t) when it was added to normal saline, although m was increased.6. It is concluded that in this preparation hypertonicity decreases the rate of release of each quantum from the nerve terminal following a nerve impulse.

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Structural features of crayfish phasic and tonic neuromuscular terminals

1996

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We examined the fine structure of terminals of the phasic and tonic excitatory axon to the crayfish limb extensor muscle. The phasic terminals are known to release 50-100 times more transmitter for a small length of terminal for a single impulse. Phasic terminals labeled with horseradish peroxidase (HRP) were relatively thin and contained a single unbranched mitochondrion; tonic terminals were much thicker, and their varicosities contained several multibranched mitochondria. Tonic terminals devoted a larger proportion of their total volume to mitochondria. The percentage volume of clear synaptic vesicles was slightly higher in phasic axon terminals, but as the tonic axon terminals were fivefold larger in volume, the total synaptic volume is much greater in tonic than phasic terminals. The number of synapses per length of terminal, and the total number of active zones per length of terminal, were greater for tonic terminals, and individual synapses were, on average, slightly larger in surface contact area for tonic terminals. In contrast, individual active zones were, on average, longer in phasic synapses. A higher proportion (50%) of phasic synapses had multiple active zones than was the case for tonic synapses (16%), and pairs of closely spaced active zones were more frequently found on phasic synapses. These findings clearly rule out synapse and active zone number as a factor contributing to higher transmitter output, but suggest that active zone size and synaptic complexity, as evidenced by multiple closely spaced active zones in a single synapse, are likely to play a causal role in the greater transmitter release of the phasic terminal. Even synapse complexity would not be enough to account fully for the large difference in terminal transmitter output, and additional factors may include electrical and biochemical differences.

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Three-Dimensional Ultrastructure of the Crayfish Neuromuscular Apparatus

Abstract: The synapse-bearing nerve terminals of the opener muscle of the crayfish Procambarus were reconstructed using electron micrographs of regions which had

Cited by 160 publications

References 27 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

Effects of hypertonic solutions on quantal transmitter release at the crayfish neuromuscular junction

Structural features of crayfish phasic and tonic neuromuscular terminals

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