Examining the timing of miniature endplate potential releases at the frog and mouse neuromuscular junctions for deviations from Poisson expectations

1999 ◽  
Vol 438 (5) ◽  
pp. 578 ◽  
Author(s):  
W. Van der Kloot ◽  
I. Andricioaei ◽  
O.P. Balezina
Keyword(s):  
Neuromuscular Junctions ◽  
Endplate Potential ◽  
Miniature Endplate Potential

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.

Oscillation period of MEPP frequency at frog neuromuscular junctions is inversely correlated with release efficacy and independent of acute Ca 2+ loading

1989 ◽  
Vol 237 (1289) ◽  
pp. 489-499 ◽  
Keyword(s):  
Neuromuscular Junctions ◽  
Oscillation Period ◽  
Ringer Solution ◽  
Time Interval ◽  
Frog Neuromuscular Junction ◽  
Periodic Oscillations ◽  
Endplate Potential ◽  
Intracellular Ca ◽  
Miniature Endplate Potential ◽  
Post Tetanic Potentiation

Periodic oscillations in miniature endplate potential (MEPP) frequency have been described at the frog neuromuscular junction. It is assumed that the periodic oscillations in MEPP frequency reflect cytosolic oscillations in intracellular Ca 2+ concentration. In the course of a study related to describing the differences between weak and strong neuro­muscular junctions by using the post-tetanic potentiation of MEPP fre­quency, we noted periodic oscillations in MEPP frequency in the first few minutes after a tetanus. The period of this oscillation (i. e. the time interval of one complete oscillation cycle) was inversely related to syn­aptic release efficacy, as measured by quantal content released per 100 μ m of nerve terminal length. Junctions of high release efficacy have an oscillation period of 20 s or less whereas the oscillations in weaker junc­tions have periods of up to 60 s or longer. This relation is very similar during post-tetanic recovery in either a calcium containing Ringer solution or in a zero calcium-EGTA Ringer solution, indicating that external calcium is not necessary to express the phenomenon. We also found that the oscillations are apparent in resting junctions preceding a tetanus and that they are similar in period and show the same inverse relation to synaptic strength.

scholarly journals Changes in miniature endplate potential frequency during repetitive nerve stimulation in the presence of Ca2+, Ba2+, and Sr2+ at the frog neuromuscular junction.

1981 ◽  
Vol 77 (5) ◽  
pp. 503-529 ◽  
Author(s):  
J E Zengel ◽  
K L Magleby
Keyword(s):  
Nerve Stimulation ◽  
Transmitter Release ◽  
Neuromuscular Junctions ◽  
Fourth Power ◽  
Bathing Solution ◽  
Frog Neuromuscular Junction ◽  
Repetitive Nerve Stimulation ◽  
Time Constants ◽  
Endplate Potential ◽  
Induced Changes

Miniature endplate potentials (MEPPs) were recorded from frog sartorious neuromuscular junctions under conditions of reduced quantal contents to study the effect of repetitive nerve stimulation on asynchronous (tonic) quantal transmitter release. MEPP frequency increased during repetitive stimulation and then decayed back to the control level after the conditioning trains. The decay of the increased MEPP frequency after 100-to 200-impulse conditioning trains can be described by four components that decayed exponentially with time constants of about 50 ms, 500 ms, 7 s, and 80 s. These time constants are similar to those for the decay of stimulation-induced changes in synchronous (phasic) transmitter release, as measured by endplate potential (EPP) amplitudes, corresponding, respectively, to the first and second components of facilitation, augmentation, and potentiation. The addition of small amounts of Ca2+ or Ba2+ to the Ca2+-containing bathing solution, or the replacement of Ca2+ with Sr2+, led to a greater increase in the stimulation-induced increases in MEPP frequency. The Sr-induced increase in MEPP frequency was associated with an increase in the second component of facilitation of MEPP frequency; the Ba-induced increase with an increase in augmentation. These effects of Sr2+ and Ba2+ on stimulation-induced changes in MEPP frequency are similar to the effects of these ions on stimulation-induced changes in EPP amplitude. These ionic similarities and the similar kinetics of decay suggest that stimulation induced changes in MEPP frequency and EPP amplitude have some similar underlying mechanisms. Calculations are presented which show that a fourth power residual calcium model for stimulation-induced changes in transmitter release cannot readily account for the observation that stimulation-induced changes in MEPP frequency and EPP amplitude have similar time-courses.

Habitual exercise enhances neuromuscular transmission efficacy of rat soleus muscle in situ

2001 ◽  
Vol 90 (3) ◽  
pp. 1041-1048 ◽  
Author(s):  
Patrice Desaulniers ◽  
Pierre-André Lavoie ◽  
Phillip F. Gardiner
Keyword(s):  
Soleus Muscle ◽  
Neuromuscular Transmission ◽  
Motor Nerve ◽  
Resting Membrane Potential ◽  
Potential Amplitude ◽  
Endplate Potential ◽  
Habitual Exercise ◽  
Rat Soleus Muscle ◽  
Miniature Endplate Potential

Rat motor nerve terminals and the endplates they interact with exhibit changes to varying patterns of use, as when exposed to increased activation in the form of endurance exercise training. The extent to which these changes affect neuromuscular transmission efficacy is uncertain. In this study, the effects of habitual exercise on the electrophysiological properties of neuromuscular transmission in rat soleus muscle were investigated using a novel in situ approach. Consistent with previous reports, miniature endplate potential frequency was enhanced by habitual exercise. Other passive properties, such as resting membrane potential, miniature endplate potential amplitude, and “giant” miniature endplate potential characteristics were unaltered by the training program. Full-size endplate potentials were obtained by blocking soleus muscle action potentials with μ-conotoxin GIIIb. Quantal content values were 91.5 and 119.9 for control and active groups, respectively ( P < 0.01). We also measured the rate and extent of endplate potential amplitude rundown during 3-s trains of continuous stimulation at 25, 50, and 75 Hz; at 50 and 75 Hz, we found both the rate and extent of rundown to be significantly attenuated (10–20%) in a specific population of cells from active rats ( P < 0.05). The results establish the degree of activity-dependent plasticity as it pertains to neuromuscular transmission in a mammalian slow-twitch muscle.

Incomplete recovery of endplate potential amplitude while intermittently activating rat soleus neuromuscular junctions in situ

2002 ◽  
Vol 26 (6) ◽  
pp. 810-816 ◽  
Author(s):  
Patrice Desaulniers ◽  
Pierre-Andr� Lavoie ◽  
Phillip F. Gardiner
Keyword(s):  
Neuromuscular Junctions ◽  
Potential Amplitude ◽  
Endplate Potential

Presynaptic Action of Central Depressant Drugs: Inhibition of Depolarization–Secretion Coupling

1972 ◽  
Vol 50 (3) ◽  
pp. 279-284 ◽  
Author(s):  
D. M. J. Quastel ◽  
J. T. Hackett ◽  
K. Okamoto
Keyword(s):  
Osmotic Pressure ◽  
Chloral Hydrate ◽  
Locust Muscle ◽  
Endplate Potential ◽  
Mouse Diaphragm ◽  
Miniature Endplate Potential ◽  
Diaphragm In Vitro ◽  
Potential Frequency ◽  
Central Depressant

Chlorpromazine, like raised osmotic pressure, not only increases spontaneous miniature endplate potential frequency (F) in mouse diaphragm (in vitro) but also depresses the slope of log F versus focal presynaptic depolarization. It also depresses the slope of log F versus [Ca], in raised K+ (constant depolarization). Similar effects are seen with pentobarbital, chloral hydrate, chloroform, and lowered pH. The drugs have similar actions in locust muscle, where the transmitter is not acetylcholine.

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