scholarly journals Variable amplification of synaptic input to cat spinal motoneurones by dendritic persistent inward current

2003 ◽  
Vol 552 (3) ◽  
pp. 945-952 ◽  
Author(s):  
H. Hultborn ◽  
M. Enríquez Denton ◽  
J. Wienecke ◽  
J. B. Nielsen
Keyword(s):  
Synaptic Input ◽  
Inward Current ◽  
Persistent Inward Current ◽  
Spinal Motoneurones

Voltage-Dependent Properties of Dendrites That Eliminate Location-Dependent Variability of Synaptic Input

1999 ◽  
Vol 81 (2) ◽  
pp. 535-543 ◽  
Author(s):  
Erik P. Cook ◽  
Daniel Johnston
Keyword(s):  
Synaptic Input ◽  
Outward Current ◽  
Compartment Model ◽  
Inward Current ◽  
Voltage Gated ◽  
Cable Properties ◽  
Dendritic Membrane ◽  
Voltage Dependent ◽  
Dendritic Location ◽  
Voltage Gated Channels

Voltage-dependent properties of dendrites that eliminate location-dependent variability of synaptic input. We examined the hypothesis that voltage-dependent properties of dendrites allow for the accurate transfer of synaptic information to the soma independent of synapse location. This hypothesis is motivated by experimental evidence that dendrites contain a complex array of voltage-gated channels. How these channels affect synaptic integration is unknown. One hypothesized role for dendritic voltage-gated channels is to counteract passive cable properties, rendering all synapses electrotonically equidistant from the soma. With dendrites modeled as passive cables, the effect a synapse exerts at the soma depends on dendritic location (referred to as location-dependent variability of the synaptic input). In this theoretical study we used a simplified three-compartment model of a neuron to determine the dendritic voltage-dependent properties required for accurate transfer of synaptic information to the soma independent of synapse location. A dendrite that eliminates location-dependent variability requires three components: 1) a steady-state, voltage-dependent inward current that together with the passive leak current provides a net outward current and a zero slope conductance at depolarized potentials, 2) a fast, transient, inward current that compensates for dendritic membrane capacitance, and 3) both αamino-3-hydroxy-5-methyl-4-isoxazolepropionic acid– and N-methyl-d-aspartate–like synaptic conductances that together permit synapses to behave as ideal current sources. These components are consistent with the known properties of dendrites. In addition, these results indicate that a dendrite designed to eliminate location-dependent variability also actively back-propagates somatic action potentials.

An evaluation of paired motor unit estimates of persistent inward current in human motoneurons

2014 ◽  
Vol 111 (9) ◽  
pp. 1877-1884 ◽  
Author(s):  
Michael S. Vandenberk ◽  
Jayne M. Kalmar
Keyword(s):  
Motor Unit ◽  
Reciprocal Inhibition ◽  
Primary Objective ◽  
Spike Frequency ◽  
Spike Frequency Adaptation ◽  
Plantar Flexors ◽  
Inward Current ◽  
Spike Threshold ◽  
Frequency Adaptation ◽  
Persistent Inward Current

Persistent inward current (PIC) plays an important role in setting the input-output gain of motoneurons. In humans, these currents are estimated by calculating the difference between synaptic input at motor unit recruitment and derecruitment (ΔF) derived from paired motor unit recordings. The primary objective of this study was to use the relationship between reciprocal inhibition (RI) and PIC to estimate the contribution of PIC relative to other motoneuron properties that result in nonlinear motor unit firing behavior. This study also assessed the contribution of other intrinsic properties (spike threshold accommodation and spike frequency adaptation) to ΔF estimates of PIC in human motor units by using ramps with varying rates of rise and duration. It was hypothesized that slower rates of ramp rise and longer ramp durations would inflate ΔF estimates of PIC, and RI and PIC values would only be correlated during the ramp with the fastest rate of rise and shortest duration when spike threshold accommodation and spike frequency adaptation is minimized. Fourteen university-aged participants took part in this study. Paired motor unit recordings were made from the right soleus muscle during ramp contractions of plantar flexors with three different rates of rise and durations. ΔF estimates of PIC increased with decreased rates of ramp rise ( P < 0.01) and increased ramp durations ( P < 0.01), most likely due to spike frequency adaptation. A correlation ( r = 0.41; P < 0.03) between ΔF and RI provides evidence that PIC is the primary contributor to ΔF in shorter ramps with faster rates of rise.

Properties of a persistent inward current in normal and TEA-injected motoneurons

1980 ◽  
Vol 43 (6) ◽  
pp. 1700-1724 ◽  
Author(s):  
P. C. Schwindt ◽  
W. E. Crill
Keyword(s):  
Voltage Clamp ◽  
Outward Current ◽  
Membrane Currents ◽  
Negative Slope ◽  
Activation Threshold ◽  
Inward Current ◽  
Plateau Potential ◽  
Current Voltage ◽  
Persistent Inward Current ◽  
Fast Transient

1. Membrane currents of normal and TEA-injected cat lumbar motoneurons were investigated using the technique of somatic voltage clamp. 2. The current-voltage (I-V) relation of healthy motoneurons contains a region of negative slope conductance caused by a persistent inward current component (Ii). In the most striking examples, Ii is net inward at some potentials between 10 and 30 mV positive to resting potential. 3. Near its activation threshold (greater than or equal to 10 mV positive to rest), Ii does not decrement during prolonged voltage steps and, in most cells, activates very slowly. Ii amplitude increases and time to peak Ii decreases with further small increments of depolarization, and Ii decrements during sustained voltage steps. Maximum Ii amplitude occurs 20--30 mV positive to rest in most cells. Ii is not visible at sufficiently large depolarizations. 4. Ii appears to be mixed with potassium current components at nearly every potential where it is visible. These include a slow outward current first activated near Ii activation threshold, a fast outward current additonally activated at larger depolarizing potentials, and a fast, transient outward current that obscures the true onset of Ii at nearly every potential. 5. Ii is not carried by sodium entering via the fast, transient channels and is present after pharmacological blockage of sodium currents. It is proposed that Ii is predominantly carried by calcium ions. 6. The presence of inward tail currents after repolarization from potentials that activate a steady outward current suggest that Ii remains present but hidden at large depolarizations. Ii inactivation was further investigated in TEA-injected motoneurons since Ii and the tail currents are more prominent in these cells. 7. Conventional recordings from TEA-injected motoneurons suggest that a prolonged, postspike plateau potential is maintained by a persistent inward current. Voltage-clamp data can account for the principal features of the plateau potential. 8. Voltage-clamp results in TEA-injected motoneurons suggest that Ii is subject to little or no inactivation at potentials less than or equal to 30 mV positive to rest and to partial inactivation, at most, at higher potentials during steps lasting less than or equal to 100 ms. The apparent decay of Ii during sustained depolarization is caused by the development of a larger outward current. 9. Ii is similar in several ways to a persistent calcium current observed in some molluscan neurons. Theoretical and experimental results suggest that Ii is generated predominantly in a local region under voltage control and that the observed membrane currents govern somatic membrane potential and cell behavior.

Tetrodotoxin-, dihydropyridine-, and riluzole-resistant persistent inward current: novel sodium channels in rodent spinal neurons

2011 ◽  
Vol 106 (3) ◽  
pp. 1322-1340 ◽  
Author(s):  
Yue Dai ◽  
Larry M. Jordan
Keyword(s):  
Sodium Channels ◽  
Time Constant ◽  
Reversal Potential ◽  
Flufenamic Acid ◽  
Spinal Neurons ◽  
Kinetics Parameters ◽  
Inward Current ◽  
Wide Range ◽  
Persistent Inward Current ◽  
Inward Currents

Recently, we reported the tetrodotoxin (TTX)- and dihydropyridine (DHP)-resistant (TDR) inward currents in neonatal mouse spinal neurons. In this study, we further characterized these currents in the presence of 1–5 μM TTX and 20–30 μM DHP (nifedipine, nimodipine, or isradipine). TDR inward currents were recorded by voltage ramp (persistent inward current, TDR-PIC) and step (TDR- Ip) protocols. TDR-PIC and TDR- Ip were found in 80.2% of recorded neurons (101/126) crossing laminae I to X from T12 to L6. TDR-PIC activated at −28.6 ± 13 mV with an amplitude of 80.6 ± 75 pA and time constant of 470.6 ± 240 ms ( n = 75). TDR- Ip had an amplitude of 151.2 ± 151 pA and a voltage threshold of −17.0 ± 9 mV ( n = 54) with a wide range of kinetics parameters. The half-maximal activation was −21.5 ± 8 mV (−37 to −12 mV, n = 29) with a time constant of 5.2 ± 2 ms (1.2–11.2 ms, n = 19), whereas the half-maximal inactivation was −26.9 ± 9 mV (−39 to −18 mV, n = 14) with a time constant of 1.4 ± 0.4 s (0.5–2.2 s, n = 19). TDR-PIC and TDR- Ip could be reduced by 60% in zero calcium and completely removed in zero sodium solutions, suggesting that they were mediated by sodium ions. Furthermore, the reversal potential of TDR- Ip was estimated as 56.6 ± 3 mV ( n = 10). TDR-PIC and TDR- Ip persisted in 1–205 μM TTX, 20–100 μM DHP, 3–30 μM riluzole, 50–300 μM flufenamic acid, and 2–30 mM intracellular BAPTA. They also persisted with T-, N-, P/Q-, and R-type calcium channel blockers. In conclusion, we demonstrated novel TTX-, DHP-, and riluzole-resistant sodium channels in neonatal rodent spinal neurons. The unique pharmacological and electrophysiological properties would allow these channels to play a functional role in spinal motor system.

T48. Hypersensitivity of the persistent inward current

2018 ◽  
Vol 129 ◽  
pp. e20
Author(s):  
Hanna R. Lajunen ◽  
Juhani V. Partanen
Keyword(s):  
Inward Current ◽  
Persistent Inward Current

scholarly journals Essential Role of a Fast Persistent Inward Current in Action Potential Initiation and Control of Rhythmic Firing

2001 ◽  
Vol 85 (1) ◽  
pp. 472-475 ◽  
Author(s):  
R. H. Lee ◽  
C. J. Heckman
Keyword(s):  
Persistent Current ◽  
Current Gain ◽  
Inward Current ◽  
Persistent Inward Current ◽  
Action Potential Initiation ◽  
Rhythmic Firing ◽  
And Control ◽  
Frequency Current

In spinal motoneurons in an in vivo preparation, we investigated the relationship between a fast persistent inward current located in or near the soma and the capacity of these cells to fire rhythmically. The fast persistent current could be markedly reduced by prolonged depolarization. Modest reductions resulted in profound changes in the slope of the frequency-current relationship. At greater reduction levels, rhythmic firing failed and could not be restored by increasing injected current. However, fully formed spikes still occurred in a slow, uncoordinated fashion, suggesting that the fast inactivating Na+ currents that generate the spike itself remained unchanged. Consequently, the fast persistent inward current, which may be primarily generated by persistent Na+ channels, appears to be essential for initiation of spikes during rhythmic firing. Additionally, it appears that the fast persistent current plays a major role in setting the frequency-current gain.

scholarly journals Estimates of persistent inward current in human motor neurons during postural sway

2019 ◽  
Vol 122 (5) ◽  
pp. 2095-2110 ◽  
Author(s):  
Ryan C. A. Foley ◽  
Jayne M. Kalmar
Keyword(s):  
Motor Unit ◽  
Motor Neurons ◽  
Postural Sway ◽  
Critical Role ◽  
Motor Units ◽  
Reciprocal Inhibition ◽  
Firing Frequency ◽  
Inward Current ◽  
Persistent Inward Current ◽  
Seated Posture

Persistent inward current (PIC) plays a critical role in setting the gain of spinal motor neurons. In humans, most estimates of PIC are made from plantarflexor or dorsiflexor motor units in a seated position. This seated and static posture negates the task-dependent nature of the monoaminergic drive and afferent inhibition that modulate PIC activation. Our purpose was to estimate PIC during both the conventional seated posture and in a more functionally relevant anterior postural sway. We hypothesized that paired motor unit estimates of PIC would be greater when during standing compared with sitting. Soleus motor neuron PIC was estimated via the paired motor unit (PMU) technique. For each motor unit pair, difference in reference unit firing frequency (ΔF) estimates of PIC were made during isometric ramps in plantarflexion force during sitting (conventional approach) and during standing anterior postural sway (new approach). Baseline reciprocal inhibition (RI) was also measured in each posture using the poststimulus time histogram technique. ΔF estimates during standing postural sway were not different [2.64 ± 0.95 pulses/s (pps), P = 0.098] from seated PIC estimates (3.15 ± 1.45 pps) measured from the same motor unit pair. Similarly, reciprocal inhibition at the onset of each task was the same in standing (−0.60 ± 0.32, P = 0.301) and seated (−0.86 ± 0.82) postures. PMU recordings made during standing postural sway met all assumptions that underlay the PMU technique, including rate modulation ≥0.5 pps (3.11 ± 1.90 pps), rate-rate correlation r ≥ 0.7 (0.84 ± 0.13), and time between reference and test unit recruitment ≥1 s (1.83 ± 0.81 s). This study presents a novel, functionally relevant standing method for investigating PIC in humans. NEW & NOTEWORTHY Paired motor unit (PMU) estimates of persistent inward current (PIC) in human soleus motor units are typically made in seated posture. Our study demonstrates that these estimates can be made during standing forward sway, a task that more accurately reflects the postural role of human soleus muscle. PMU recordings made during standing postural sway were validated using all previously published criteria used to test the assumptions of the PMU technique. Standing estimates of PIC did not differ from seated estimates made from the same motor unit pairs.

scholarly journals Concurrent Achilles tendon vibration and tibial nerve stimulation to estimate persistent inward current strength in motoneurons

2021 ◽  
Author(s):  
Denis César Leite Vieira ◽  
Amilton Vieira ◽  
Matheus Avelino Dos Santos ◽  
Rafael Rodrigues Da Cunha ◽  
Victor Lage ◽  
...  
Keyword(s):  
Electrical Stimulation ◽  
Tibial Nerve ◽  
Neuromuscular Electrical Stimulation ◽  
Current Strength ◽  
Systematic Bias ◽  
Tendon Vibration ◽  
Plantar Flexors ◽  
Muscle Belly ◽  
Inward Current ◽  
Persistent Inward Current

Vibratory (Tvib) and sustained (Tsust) torque responses to concurrent Achilles tendon vibration and neuromuscular electrical stimulation applied over the muscle belly (vib+stim) are used as indicators of motoneuron facilitation and, theoretically, persistent inward current strength. However, neuromuscular electrical stimulation (NMES) applied to the nerve trunk may potentiate motoneuronal excitability more than muscle belly NMES, yet it remains unclear whether NMES applied over the nerve evokes robust Tvib and Tsust responses when used during the vib+stim protocol. This study tested whether a nerve-targeted vib+stim protocol elicits Tvib and Tsust responses in the ankle plantar flexors with acceptable intra- and inter-session reliability. Fifteen men performed the vib+stim protocol with NMES applied over the tibial nerve three times across two sessions; twice in a single session (5-min apart) to test intrasession reliability and then again after 48 h to test intersession reliability. Intraclass correlation coefficients (ICC3,1), within-participant coefficients of variation (CV) and pairwise comparisons were used to verify relative and absolute reliability as well as systematic bias. Thirteen men presented Tvib and Tsust responses (response rate of 87%). Intrasession Tvib and Tsust ICCs were >0.73 but inter-session ICCs were <0.5. Although no systematic bias was detected (p>0.05), both intra- and inter-session CVs were large (>10%) for Tvib and Tsust. The Vib+stim protocol with NMES applied over the nerve evoked Tvib and Tsust in almost all participants, but presented a large intra- and inter-session variability. The method does not appear to be effective for assessing motoneuron facilitation in the plantar flexors.

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