scholarly journals The Mechanism of Discharge Pattern Formation in Crayfish Interneurons

1965 ◽  
Vol 48 (3) ◽  
pp. 435-453 ◽  
Author(s):  
Kimihisa Takeda ◽  
Donald Kennedy
Keyword(s):  
Membrane Potential ◽  
Discharge Rate ◽  
Frequency Curve ◽  
Current Frequency ◽  
Inhibitory Processes ◽  
Optimal Current ◽  
Current Threshold ◽  
Time Courses ◽  
Repetitive Discharge

Excitatory and inhibitory processes which result in the generation of output impulses were analyzed in single crayfish interneurons by using intracellular recording and membrane polarizing techniques. Individual spikes which are initiated orthodromically in axon branches summate temporally and spatially to generate a main axon spike; temporally dispersed branch spikes often pace repetitive discharge of the main axon. Hyperpolarizing IPSP's sometimes suppress axonal discharge to most of these inputs, but in other cases may interact selectively with some of them. The IPSP's reverse their polarity at a hyperpolarized level of membrane potential; they sometimes exhibit two discrete time courses indicating two different input sources. Outward direct current at the main axon near branches causes repetitive discharges which may last, with optimal current intensities, for 1 to 15 seconds. The relation of discharge frequency to current intensity is linear for an early spike interval, but above 100 to 200 impulses/sec. it begins to show saturation. In one unit the current-frequency curve exhibited two linear portions, suggesting the presence of two spike-generating sites in the axon. Current threshold measurements, using test stimuli of different durations, showed that both accommodation and "early" or "residual" refractoriness contribute to the determination of discharge rate at different frequencies.

Effective synaptic current and motoneuron firing rate modulation

1995 ◽  
Vol 74 (2) ◽  
pp. 793-801 ◽  
Author(s):  
R. K. Powers ◽  
M. D. Binder
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Firing Rate ◽  
Discharge Rate ◽  
Reversal Potential ◽  
Repetitive Firing ◽  
Resting Membrane Potential ◽  
Synaptic Inputs ◽  
Rate Modulation ◽  
Repetitive Discharge

1. We used a modified voltage-clamp technique to measure the steady-state effective synaptic currents (I(N)) produced by activating four different input systems to cat hindlimb motoneurons: Ia afferent fibers, Ia-inhibitory interneurons, Renshaw interneurons, and contralateral rubrospinal neurons. In the same motoneurons, we measured the slope of the firing rate-injected current (f-I) relation in the primary range. We then reactivated these synaptic inputs during steady, repetitive firing to assess their effects on motoneuron discharge rate. 2. Our measurements of I(N) were derived from recordings made near the resting membrane potential, whereas the effects of the synaptic inputs on repetitive discharge were evaluated at more depolarized membrane potentials. Thus we adjusted the I(N) values for these changes in driving force based on estimates of the synaptic reversal potential and the mean membrane potential during repetitive discharge. 3. We found that changes in the steady-state discharge rate of a motoneuron produced by these synaptic inputs could be reasonably well predicted by the product of the estimated value of I(N) during repetitive firing and the slope of the motoneuron's f-I relation. Although there was a high correlation between predicted and observed changes in firing rate for our entire sample of motoneurons (r = 0.93; P < 0.001), the slope of the relation between predicted and observed firing rate modulation was significantly greater than 1. 4. The systematic difference between predicted and observed firing rate modulation observed in the overall sample was primarily due to the fact that our predictions underestimated the changes in firing rate produced by Ia excitation and Ia inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Calibration procedures for the quantitative determination of membrane potential in human cells using anionic dyes

2013 ◽  
Vol 83A (7) ◽  
pp. 612-626 ◽  
Author(s):  
Thomas Klapperstück ◽  
Dagobert Glanz ◽  
Stefan Hanitsch ◽  
Manuela Klapperstück ◽  
Fritz Markwardt ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Quantitative Determination ◽  
Human Cells ◽  
Anionic Dyes

scholarly journals The mobility of positive ions in helium. Part I.―Helium ions

1931 ◽  
Vol 134 (823) ◽  
pp. 125-136 ◽  
Keyword(s):  
Direct Action ◽  
High Mobility ◽  
Ionic Clusters ◽  
Frequency Curve ◽  
Current Frequency ◽  
Positive Ions ◽  
Mobility Of Ions ◽  
Helium Gas ◽  
A Current ◽  
Α Particles

In a previous paper we gave an account of some experiments on the mobility of positive ions in helium gas. It was shown that minute traces of impurity profoundly affect the speed at which the charge is carried through the gas, so that very little significance can be attached to the values of the mobility of ions recorded in the literature. In particular we studied the behaviour of carefully purified helium gas when admitted at a pressure of 360 mm. of mercury into a baked-out apparatus. In our method of determining the mobility, a single group of ions gives rise to a peak in a current frequency curve, and it is easy to follow the changes produced by an impurity. Initially the ions in the helium had a high mobility and in one case we obtained a group with a mobility of the order of 17 cm./sec./volt/cm. at 760 mm. As the gas became contaminated by impurities gradually evolved from the glass walls and metal parts of the apparatus, peaks corresponding to groups of smaller mobility appeared, and eventually the charge was all carried by a group with mobility rather less than 8. The ions in these experiments were produced by means of α-particles from polonium. Traces of impurity in helium may affect the results in several ways. Firstly, they may lead to the formation of ionic clusters, particularly if the molecules of the impurity have a permanent dipole. In our experiments it seemed unlikely that molecules capable of forming clusters were present. Secondly, although with small concentrations of an impurity a negligible number of its ions will be produced by the direct action of the α-rays, they may be formed indirectly in either of the two following ways:—

Simultaneous determination of membrane potential and pH gradient by photodiode array spectroscopy

1986 ◽  
Vol 862 (2) ◽  
pp. 278-284 ◽  
Author(s):  
Tetsuya Konishi ◽  
Naoyuki Murakami ◽  
Yoshihiko Hatano ◽  
Katsuyoshi Nakazato
Keyword(s):  
Membrane Potential ◽  
Simultaneous Determination ◽  
Ph Gradient ◽  
Photodiode Array

Effects of Common Excitatory and Inhibitory Inputs on Motoneuron Synchronization

2001 ◽  
Vol 86 (6) ◽  
pp. 2807-2822 ◽  
Author(s):  
K. S. Türker ◽  
R. K. Powers
Keyword(s):  
Background Noise ◽  
Cross Correlation ◽  
Discharge Rate ◽  
Central Peak ◽  
Common Input ◽  
Synaptic Inputs ◽  
Input Waveform ◽  
The Common ◽  
Repetitive Discharge ◽  
Current Transients

We compared the effects of common excitatory and inhibitory inputs on motoneuron synchronization by simulating synaptic inputs with injected current transients. We elicited repetitive discharge in hypoglossal motoneurons recorded in slices of rat brain stem using a combination of a suprathreshold injected current step with superimposed noise to mimic the synaptic drive likely to occur during physiological activation. The effects of common inputs to motoneurons were simulated by the addition of a waveform composed of from 6 to 300 trains of current transients designed to mimic excitatory and/or inhibitory synaptic currents. We compared the discharge records obtained in several trials in which the same “common input” waveform was applied repeatedly in the presence of different background noise waveforms. The effects of the common input on motoneuron discharge probability and discharge rate were determined by compiling a cross-correlation histogram (CCHist) and a perispike frequencygram (PSFreq) between the discharges of the same cell at different times. Both excitatory and inhibitory common inputs induced synchronous discharge that was evident by a large central peak in the CCHist. The CCHists produced by common excitatory inputs were characterized by larger and narrower central peaks than those generated by common inhibitory inputs. The PSFreqs produced by common excitatory inputs indicated an increase in the discharge rate of motoneurons around time 0 that coincided with the narrow and large central peak in the CCHist. On the other hand, inhibitory inputs often generated very little, if any, change in the discharge rate around time 0 corresponding with the small and wide central peak in the CCHist. These results suggest that the CCHist indicates the effective strength of the net common input but not its sign. Although correlated changes in discharge rate are often quite different for net excitatory and inhibitory common input, except in some restricted conditions, the PSFreq analysis also cannot be used to unambiguously distinguish net excitation from net inhibition.

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