scholarly journals Prolonged time course of population excitatory postsynaptic potentials in motoneurons of chronic stroke survivors

2019 ◽  
Vol 122 (1) ◽  
pp. 176-183
Author(s):  
Jongsang Son ◽  
Xiaogang Hu ◽  
Nina L. Suresh ◽  
William Z. Rymer
Keyword(s):  
Time Course ◽  
Chronic Stroke ◽  
H Reflex ◽  
Reflex Response ◽  
Excitatory Postsynaptic Potential ◽  
Stroke Survivors ◽  
Potential Mechanism ◽  
Spinal Motoneurons ◽  
Hemispheric Stroke ◽  
Ia Epsp

Hyperexcitability of spinal motoneurons may contribute to muscular hypertonia after hemispheric stroke. The origins of this hyperexcitability are not clear, but we hypothesized that prolongation of the Ia excitatory postsynaptic potential (EPSP) in spastic motoneurons may be one potential mechanism, by enabling more effective temporal summation of Ia EPSPs, making action potential initiation easier. Thus, the purpose of this study is to quantify the time course of putative EPSPs in spinal motoneurons of chronic stroke survivors. To estimate the EPSP time course, a pair of low-intensity electrical stimuli was delivered sequentially to the median nerve in seven hemispheric stroke survivors and in six intact individuals, to induce an H-reflex response from the flexor carpi radialis muscle. H-reflex response probability was then used to quantify the time course of the underlying EPSPs in the motoneuron pool. A population EPSP estimate was then derived, based on the probability of evoking an H-reflex from the second test stimulus in the absence of a reflex response to the first conditioning stimulus. Our experimental results showed that in six of seven hemispheric stroke survivors, the apparent rate of decay of the population EPSP was markedly slower in spastic compared with contralateral (stroke) and intact motoneuron pools. There was no significant difference in EPSP time course between the contralateral side of stroke survivors and control subject muscles. We propose that one potential mechanism for hyperexcitability of spastic motoneurons in chronic stroke survivors may be associated with this prolongation of the Ia EPSP time course. Our subthreshold double-stimulation approach could provide a noninvasive tool for quantifying the time course of EPSPs in both healthy and pathological conditions. NEW & NOTEWORTHY Spastic motoneurons in stroke survivors showed a prolonged Ia excitatory postsynaptic potential (EPSP) time course compared with contralateral and intact motoneurons, suggesting that one potential mechanism for hyperexcitability of spastic motoneurons in chronic stroke survivors may be associated with this prolongation of the Ia EPSP time course.

scholarly journals Estimating the time course of population excitatory postsynaptic potentials in motoneurons of spastic stroke survivors

2015 ◽  
Vol 113 (6) ◽  
pp. 1952-1957 ◽  
Author(s):  
Xiaogang Hu ◽  
Nina L. Suresh ◽  
William Z. Rymer
Keyword(s):  
Time Course ◽  
Response Probability ◽  
Electrical Stimulus ◽  
H Reflex ◽  
Reflex Response ◽  
Excitatory Postsynaptic Potential ◽  
Stroke Survivors ◽  
Hemispheric Stroke ◽  
Ia Epsp ◽  
Electrical Stimuli

Hyperexcitable motoneurons are likely to contribute to muscle hypertonia after a stroke injury; however, the origins of this hyperexcitability are not clear. One possibility is that the effective duration of the Ia excitatory postsynaptic potential (EPSP) is prolonged, increasing the potential for temporal summation of EPSPs, making action potential initiation easier. Accordingly, the purpose of this study was to quantify the time course of EPSPs in motoneurons of stroke survivors. The experimental protocol, which was based on parameters derived from simulation, involved sequential subthreshold electrical stimuli delivered to the median nerve of hemispheric stroke survivors. The resulting H-reflex responses were recorded in the flexor carpi radialis muscle. H-reflex response probability was then used to quantify the time course of the underlying EPSPs in the motoneuron pool. A population EPSP was estimated based on the probability of evoking an H reflex from the second electrical stimulus in the absence of a reflex response to the first stimulus. The accuracy of this time-course estimate was quantified using a computer simulation that explored a range of feasible EPSP parameters. Our experimental results showed that in all five hemispheric stroke survivors the rate of decay of the population EPSP was consistently slower in spastic compared with the contralateral motoneuron pools. We propose that one potential mechanism for hyperexcitability of motoneurons in spastic stroke survivors may be linked to this prolongation of the Ia EPSP time course. Our subthreshold double-stimulation approach also provides a noninvasive tool for quantifying the time course of EPSPs in both healthy and pathological conditions.

scholarly journals Reduced postactivation depression of soleus H reflex and root evoked potential after transcranial magnetic stimulation

2015 ◽  
Vol 114 (1) ◽  
pp. 485-492 ◽  
Author(s):  
Jennifer C. Andrews ◽  
Richard B. Stein ◽  
François D. Roy
Keyword(s):  
Transcranial Magnetic Stimulation ◽  
Magnetic Stimulation ◽  
Time Course ◽  
Evoked Potential ◽  
Thoracolumbar Spine ◽  
Voluntary Contraction ◽  
H Reflex ◽  
Double Pulse ◽  
Reflex Response ◽  
Postactivation Depression

Postactivation depression of the Hoffmann (H) reflex is associated with a transient period of suppression following activation of the reflex pathway. In soleus, the depression lasts for 100–200 ms during voluntary contraction and up to 10 s at rest. A reflex root evoked potential (REP), elicited after a single pulse of transcutaneous stimulation to the thoracolumbar spine, has been shown to exhibit similar suppression. The present study systematically characterized the effect of transcranial magnetic stimulation (TMS) on postactivation depression using double-pulse H reflexes and REPs. A TMS pulse reduced the period of depression to 10–15 ms for both reflexes. TMS could even produce postactivation facilitation of the H reflex, as the second reflex response was increased to 243 ± 51% of control values at the 75-ms interval. The time course was qualitatively similar for the REP, yet the overall increase was less. While recovery of the H reflex was slower in the relaxed muscle, the profile exhibited a distinct bimodal shape characterized by an early peak at the 25-ms interval, reaching 72 ± 23% of control values, followed by a trough at 50 ms, and then a gradual recovery at intervals > 50 ms. The rapid recovery of two successively depressed H reflexes, ∼25 ms apart, was also possible with double-pulse TMS. The effect of the TMS-induced corticospinal excitation on postactivation depression may be explained by a combination of pre- and postsynaptic mechanisms, although further investigation is required to distinguish between them.

Time-course investigation of postural sway variability: Does anxiety exacerbate the sensory reweighting impairment in chronic stroke survivors?

2019 ◽  
Vol 127 ◽  
pp. 185-194 ◽  
Author(s):  
Shamsi Jamali ◽  
Akram Azad ◽  
Hajar Mehdizadeh ◽  
Asgar Doostdar ◽  
Fatemeh Hoseinpour ◽  
...  
Keyword(s):  
Time Course ◽  
Postural Sway ◽  
Chronic Stroke ◽  
Stroke Survivors ◽  
Sensory Reweighting

Aerobic locomotor exercise modulates brain activation patterns in chronic stroke survivors

2005 ◽  
Vol 32 (S 4) ◽  
Author(s):  
A.R Luft ◽  
L Forrester ◽  
F Villagra ◽  
R Macko ◽  
D.F Hanley
Keyword(s):  
Brain Activation ◽  
Chronic Stroke ◽  
Stroke Survivors ◽  
Activation Patterns

scholarly journals Alterations in Muscle Networks in the Upper Extremity of Chronic Stroke Survivors

2021 ◽  
pp. 1-1
Author(s):  
Michael Houston ◽  
Xiaoyan Li ◽  
Ping Zhou ◽  
Sheng Lia ◽  
Jinsook Roh ◽  
...  
Keyword(s):  
Upper Extremity ◽  
Chronic Stroke ◽  
Stroke Survivors

Computer Simulation of the Responses of Human Motoneurons to Composite 1A EPSPS: Effects of Background Firing Rate

1997 ◽  
Vol 77 (1) ◽  
pp. 405-420 ◽  
Author(s):  
Kelvin E. Jones ◽  
Parveen Bawa
Keyword(s):  
Computer Simulation ◽  
Firing Rate ◽  
Time Course ◽  
Current Model ◽  
Response Probability ◽  
Muscle Spindles ◽  
Excitatory Postsynaptic Potential ◽  
Biophysical Properties ◽  
Rhythmic Firing ◽  
The Relationship

Jones, Kelvin E. and Parveen Bawa. Computer simulation of the responses of human motoneurons to composite 1A EPSPS: effects of background firing rate. J. Neurophysiol. 77: 405–420, 1997. Two compartmental models of spinal alpha motoneurons were constructed to explore the relationship between background firing rate and response to an excitatory input. The results of these simulations were compared with previous results obtained from human motoneurons and discussed in relation to the current model for repetitively firing human motoneurons. The morphologies and cable parameters of the models were based on two type-identified cat motoneurons previously reported in the literature. Each model included five voltage-dependent channels that were modeled using Hodgkin-Huxley formalism. These included fast Na+ and K+ channels in the initial segment and fast Na+ and K+ channels as well as a slow K+ channel in the soma compartment. The density and rate factors for the slow K+ channel were varied until the models could reproduce single spike AHP parameters for type-identified motoneurons in the cat. Excitatory synaptic conductances were distributed along the equivalent dendrites with the same density described for la synapses from muscle spindles to type-identified cat motoneurons. Simultaneous activation of all synapses on the dendrite resulted in a large compound excitatory postsynaptic potential (EPSP). Brief depolarizing pulses injected into a compartment of the equivalent dendrite resulted in pulse potentials (PPs), which resembled the compound EPSPs. The effects of compound EPSPs and PPs on firing probability of the two motoneuron models were examined during rhythmic firing. Peristimulus time histograms, constructed between the stimulus and the spikes of the model motoneuron, showed excitatory peaks whose integrated time course approximated the time course of the underlying EPSP or PP as has been shown in cat motoneurons. The excitatory peaks were quantified in terms of response probability, and the relationship between background firing rate and response probability was explored. As in real human motoneurons, the models exhibited an inverse relationship between response probability and background firing rate. The biophysical properties responsible for the relationship between response probability and firing rate included the shapes of the membrane voltage trajectories between spikes and nonlinear changes in PP amplitude during the interspike interval at different firing rates. The results from these simulations suggest that the relationship between response probability and background firing rate is an intrinsic feature of motoneurons. The similarity of the results from the models, which were based on the properties of cat motoneurons, and those from human motoneurons suggests that the biophysical properties governing rhythmic firing in human motoneurons are similar to those of the cat.

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