Recruitment gain of spinal motor neuron pools in cat and human

Nielsen, Jens Bo; Morita, Hiroshi; Wenzelburger, Roland; Deuschl, Günther; Gossard, Jean‐Pierre; Hultborn, Hans

doi:10.1007/s00221-019-05628-6

Cited by 20 publications

(21 citation statements)

References 68 publications

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“…Soleus MSRs were as usual evoked by stimulating the tibial nerve, but while the participant held a small voluntary plantarflexion to activate tonic firing of a few single motor units. The size of the MSR was set to just above reflex threshold (and when the M-wave was < 5% of maximum) so that single motor units at the time of the MSR could be distinguished from the compound potential from many units that make up the MSR (Nielsen et al, 2019). For a given trial run, test MSRs were evoked every 3-5 s for the first 100 s and then MSR testing continued for a further 100s, but with a cDP-conditioning train (50 ms, 200 Hz) applied 500 ms prior to each MSR testing stimulation.…”

Section: Conditioning Of the Msrs In Humansmentioning

confidence: 99%

GABA facilitates spike propagation through branch points of sensory axons in the spinal cord

Hari

Lucas‐Osma

Metz

et al. 2021

Preprint

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SUMMARYGABA is an inhibitory neurotransmitter that produces both postsynaptic and presynaptic inhibition. We describe here an opposing excitatory action of GABA that facilitates spike transmission at nodes of Ranvier in myelinated sensory axons in the spinal cord. This nodal facilitation results from axonal GABAA receptors that depolarize nodes toward threshold, enabling spike propagation past the many branch points that otherwise fail, as observed in spinal cords isolated from mice or rats. Activation of GABAergic neurons, either directly with optogenetics or indirectly with cutaneous stimulation, caused nodal facilitation that increased sensory transmission to motoneurons without postsynaptically exciting motoneurons. This increased transmission with optogenetic or cutaneous stimulation also occurred in awake mice and humans. Optogenetic inhibition of GABAergic neurons decreased sensory transmission, implying that axonal conduction relies on GABA. The concept of nodal facilitation likely generalizes to other large axons in the CNS, enabling recruitment of selective branches and functional pathways.

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Section: Conditioning Of the Msrs In Humansmentioning

confidence: 99%

GABA facilitates spike propagation through branch points of sensory axons in the spinal cord

Hari

Lucas‐Osma

Metz

et al. 2021

Preprint

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“…Under normal conditions, Henneman's size principle suggests that Ia afferents first activate slow motor units, such that motor units producing the smallest force are recruited the earliest (Henneman, 1957;Burke & Rymer, 1976;Harrison & Taylor, 1981). However, increasing the recruitment gain of the motor pool induces a fast and synchronous activation of the entire motoneuronal pool (Nielsen et al 2019), which contributes to further increase the excitability of the H-reflex (Kernell & Hultborn, 1990). This effect can be the consequence of several factors, including: 1) homogenization of motor unit properties; 2) increased inhibition biased towards slow motor units; 3) increased excitation biased towards large faster motor units; 4) a combination of these factors (Kernell & Hultborn, 1990).…”

Section: H-reflex Hyperexcitability Is Associated With a Concurrent Imentioning

confidence: 99%

Direct evidence for decreased presynaptic inhibition evoked by PBSt group I muscle afferents after chronic SCI and recovery with step‐training in rats

Caron

Bilchak

Côté

2020

The Journal of Physiology

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Presynaptic inhibition is modulated by supraspinal centres and primary afferents in order to filter sensory information, adjust spinal reflex excitability, and ensure smooth movement. r After spinal cord injury (SCI), the supraspinal control of primary afferent depolarization (PAD) interneurons is disengaged, suggesting an increased role for sensory afferents. While increased H-reflex excitability in spastic individuals indicates a possible decrease in presynaptic inhibition, it remains unclear whether a decrease in sensory-evoked PAD contributes to this effect. r We investigated whether the PAD evoked by hindlimb afferents contributes to the change in presynaptic inhibition of the H-reflex in a decerebrated rat preparation. We found that chronic SCI decreases presynaptic inhibition of the plantar H-reflex through a reduction in PAD evoked by posterior biceps-semitendinosus (PBSt) muscle group I afferents. r We further found that step-training restored presynaptic inhibition of the plantar H-reflex evoked by PBSt, suggesting the presence of activity-dependent plasticity of PAD pathways activated by flexor muscle group I afferents.

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“…The change rate of TA and PN was also compared in affected limbs of stroke patients. 4. In order to eliminate the effect of gravity on foot inversion caused by the biomechanics characteristics of the ankle joint when both the TA and PN were paralyzed (foot drop with foot inversion), we deliberately analyzed the ability of voluntary ankle dorsiflexion stroke patients.…”

Section: Discussionmentioning

confidence: 99%

“…The reason for this phenomenon remains elusive, deserving further researches on its pathophysiological mechanism. It is well known that the recovery of motor function is closely related to the spinal neural excitability (4,5). After stroke occurs, motor neurons with relatively higher excitability tend to be excited by the residual descending impulses of the pyramidal tracts or extrapyramidal systems, causing voluntary contraction or spasticity of the corresponding muscles (6), while motor neurons with relatively lower excitability are unable to be excited and remained paralyzed.…”

Section: Introductionmentioning

confidence: 99%

Differential Changed Excitability of Spinal Motor Neurons Innervating Tibialis Anterior and Peroneus Muscles Cause Foot Inversion After Stroke

et al. 2020

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Objective: To study differential post-stroke changes of excitability of spinal motor neurons innervating a group of antagonist muscles of ankle and their effects on foot inversion.Methods: F waves in tibialis anterior (TA) and peroneus muscles (PN) were recorded. The condition of spasticity and foot inversion in stroke patients were also evaluated. The differences of F wave parameters between patients and healthy controls (HC), as well as TA and PN, were investigated.Results: There were natural differences in the persistence of the F waves (Fp) and F/M amplitude ratio (F/M) between TA and PN in HC. Stroke patients showed significantly higher F/M in TA and PN, while there was no difference in Fp comparing to HC. The natural differences in F wave parameters between TA and PN were differentially retained after stroke. The natural difference of the two muscles in Fp remained unchanged and the F/M difference disappeared in those without spasticity or foot inversion, while the Fp difference disappeared and the F/M difference remained in those with spasticity or foot inversion.Conclusion: Based on the natural difference of the number and size of spinal motor neurons innervating TA and PN, their excitability may change differently according to the severity of the stroke, which may be the reason of foot inversion.

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Recruitment gain of spinal motor neuron pools in cat and human

Cited by 20 publications

References 68 publications

GABA facilitates spike propagation through branch points of sensory axons in the spinal cord

GABA facilitates spike propagation through branch points of sensory axons in the spinal cord

Direct evidence for decreased presynaptic inhibition evoked by PBSt group I muscle afferents after chronic SCI and recovery with step‐training in rats

Differential Changed Excitability of Spinal Motor Neurons Innervating Tibialis Anterior and Peroneus Muscles Cause Foot Inversion After Stroke

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