Monosynaptic facilitation of group I afferents between brachioradialis and extensor carpi radialis in humans

Shinozaki, Katsuhiro; Nito, Mitsuhiro; Kobayashi, Shinji; Hayashi, Masahiro; Miyasaka, Takuji; Hashizume, Wataru; Shindo, Masaomi; Naito, Akira

doi:10.1016/j.neures.2016.08.002

Cited by 8 publications

(7 citation statements)

References 23 publications

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“…To estimate the central synaptic delay of the process, the latencies of the facilitation and the monosynaptic peak in the PSTH following stimulation of the respective ECR and homonymous FDS afferents were compared for motor units receiving facilitation (Cavallari & Katz, 1989;Cavallari et al, 1992;Katz et al, 1991;Kobayashi et al, 2016;Marchand-Pauvert et al, 2000;Miyasaka et al, 2007;Naito et al, 1996Naito et al, , 1998Nakano et al, 2014;Nito, Hashizume, Jimenji, et al, 2018;Nito et al, 2016;Sato et al, 2018;Shinozaki et al, 2017). The homonymous FDS afferents were stimulated at the proximal part of the medial intermuscular septum of the arm (axilla) with bipolar surface electrodes.…”

Section: Psth Studymentioning

confidence: 99%

Monosynaptic facilitation of flexor digitorum superficialis motoneurons mediated by Group Ia afferents from the extensor carpi radialis in humans

Nito

Yoshimoto

Hashizume

et al. 2022

Eur J of Neuroscience

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Wrist position is known to affect the grip strength. We focused on the spinal reflex arc, which would support the movement, and investigated the effects of low‐threshold afferents from the extensor carpi radialis (ECR) on the excitability of the flexor digitorum superficialis (FDS) motoneurons using the post‐stimulus time‐histogram (PSTH) and electromyogram‐averaging (EMG‐A) methods. Electrical conditioning stimulation of an intensity below the motor threshold was applied to the radial nerve branch innervating the ECR. In the PSTH study, changes in the firing probability of single motor units after electrical conditioning stimulation were investigated in seven subjects. An early and significant peak (increase in the firing probability: facilitation) was recorded for 36/60 FDS motor units. The remaining 24 motor units did not show any effects. Weak mechanical conditioning stimulation of the ECR muscle belly induced a similar peak. The central latency of the facilitation was equivalent to that of the homonymous monosynaptic facilitation. In the EMG‐A study, changes in the rectified and averaged electromyograms of FDS induced by conditioning stimulation were examined in 12 subjects. An early and significant peak (facilitation) was induced by both electrical and mechanical conditioning stimulations. The facilitation decreased after withdrawal of the vibration to the ECR muscle belly. The facilitation was never induced by cutaneous nerve stimulation in the PSTH and EMG‐A studies. These findings suggest that Group Ia afferents from the ECR increase the excitability of FDS motoneurons through a monosynaptic path in the spinal cord. These reflex arcs likely facilitate hand grasping movements.

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Section: Psth Studymentioning

confidence: 99%

Monosynaptic facilitation of flexor digitorum superficialis motoneurons mediated by Group Ia afferents from the extensor carpi radialis in humans

Nito

Yoshimoto

Hashizume

et al. 2022

Eur J of Neuroscience

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“…Next, we analyzed the facilitation of motor units induced by ECR afferents. To estimate the central synaptic delay of the process, the latencies of the facilitation and the monosynaptic peak in PSTH following stimuli of the respective ECR and homonymous afferents from intrinsic hand muscles (APB, FDI, ADM) were compared (Cavallari et al, 1992 ; Cavallari & Katz, 1989 ; Katz et al, 1991 ; Kobayashi et al, 2016 ; Marchand‐Pauvert et al, 2000 ; Miyasaka et al, 2007 ; Naito et al, 1996 , 1998 ; Nakano et al, 2014 ; Nito et al, 2016 ; Nito, Hashizume, Jimenji, et al, 2018 ; Sato et al, 2018 ; Shinozaki et al, 2017 ) (Figure 1 ). To investigate the effect on APB motor units, APB homonymous afferents were stimulated at the proximal part of the medial intermuscular septum of the arm (axilla) with bipolar surface electrodes (0.8 cm diameter, 1.5 cm interelectrode distance).…”

Section: Methodsmentioning

confidence: 99%

Monosynaptic facilitation of motoneurons innervating intrinsic hand muscles mediated by group Ia afferents from the extensor carpi radialis in humans

Nito

Yoshimoto

Hashizume

et al. 2022

Physiological Reports

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The projection pattern of low‐threshold afferents from the extensor carpi radialis (ECR) to motoneurons supplying intrinsic hand muscles was investigated using the post‐stimulus time‐histogram (PSTH) and electromyogram‐averaging (EMG‐A) methods. Electrical conditioning stimulation was applied to the radial nerve branch innervating the ECR. In the PSTH study, changes in the firing probability of single motor units following the stimulation were examined. An early and significant peak (facilitation) was induced in the motoneurons innervating the muscles, but the facilitation was induced infrequently. The central latency of the facilitation was equivalent to that of homonymous facilitation through monosynaptic path in the spinal cord. In the EMG‐A study, changes in the rectified and averaged electromyograms following the conditioning stimulation were examined. An early and significant peak (facilitation) was also induced. The facilitation disappeared after withdrawal of the vibration to the ECR muscle belly. Cutaneous nerve stimulation overlaying ECR never induced such facilitation in the PSTH and EMG‐A studies. These findings suggest that monosynaptic facilitation mediated by group Ia afferents of ECR to the motoneurons supplying intrinsic hand muscles exists in humans, but the connection seems to be weak. This weakness might allow manipulatory movements of the hand.

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“…The PSTH method was employed to evaluate the effects of a reflex arc on each individual motor neuron and to estimate the central synaptic delay of the reflex arc . PSTHs (bin width 0.1 ms) of the discharge of a voluntarily activated TB motor unit (firing interval: about 100 ms) were constructed for the period from 10 to 50 ms after the conditioning stimulation.…”

Section: Methodsmentioning

confidence: 99%

“…For motor units receiving inhibition, to estimate the central synaptic delay of the inhibitory process, latencies of the troughs and the monosynaptic peaks in PSTH were compared following stimuli to the respective BR and homonymous afferents (radial nerve; Fig. ) . The homonymous TB afferents were stimulated at the proximal part of the medial intermuscular septum (axilla) or the distal part of the lateral intermuscular septum of the arm with surface electrodes.…”

Section: Methodsmentioning

confidence: 99%

“…Spinal reflex arcs mediated by low‐threshold afferents (group I afferents, Ia fibers from muscle spindles and Ib fibers from Golgi tendon organs) among muscles in the human upper limb have been extensively studied . Among human elbow flexors and extensors, oligosynaptic inhibition mediated by group Ia afferents has been demonstrated between the biceps brachii (BB) and the triceps brachii (TB) muscles, which are elbow flexors and extensors, respectively, and between the BB and the brachioradialis (BR) muscles, both of which are elbow flexors .…”

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Oligosynaptic inhibition of group Ia afferents from brachioradialis to triceps brachii motor neurons in humans

et al. 2017

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Introduction: This study examines effects of lowthreshold afferents from the brachioradialis (BR) on excitability of triceps brachii (TB) motor neurons in humans. Methods: We evaluated the effects using a post stimulus time histogram (PSTH) and electromyogram averaging (EMG-A) methods in 13 healthy human participants. Electrical conditioning stimulation to the radial nerve branch innervating BR with the intensity below the motor threshold was delivered. Results: In the PSTH study, the stimulation produced a trough (inhibition) in 36/69 TB motor units for all the participants. A cutaneous stimulation never provoked such inhibition. The central latency of the inhibition was 1.5 6 0.5 ms longer than that of the homonymous facilitation. In the EMG-A study, the stimulation produced inhibition in EMG-A of TB in all participants. The inhibition diminished with a tonic vibration stimulation to BR. Discussion: These findings suggest that oligosynaptic inhibition mediated by group Ia afferents from BR to TB exists in humans. 57: 122-128, 2018 Spinal reflex arcs mediated by low-threshold afferents (group I afferents, Ia fibers from muscle spindles and Ib fibers from Golgi tendon organs) among muscles in the human upper limb have been extensively studied. 1-23 Among human elbow flexors and extensors, oligosynaptic inhibition mediated by group Ia afferents has been demonstrated between the biceps brachii (BB) and the triceps brachii (TB) muscles, which are elbow flexors and extensors, respectively, and between the BB and the brachioradialis (BR) muscles, both of which are elbow flexors. 4,9,11,16 However, no reports describe a reflex arc between BR and TB. Muscle NerveOn the other hand, Cavallari and Katz 3 demonstrated disynaptic inhibition mediated by group Ia afferents from the radial nerve branch innervating wrist extensor muscles to TB. However, their conditioning stimulation did not include the radial nerve branch innervating BR. Therefore, the reflex arc between BR and TB is still unknown. The current study explores inhibition from BR to TB motor neurons using a post stimulus time histogram (PSTH) and electromyogram averaging (EMG-A) methods. MATERIALS AND METHODS Participants.The experiments were performed with 13 healthy human participants, ages 20-42 years, all of whom gave their informed consent to the experimental procedures, which were approved by the ethics committee of Yamagata University School of Medicine. The PSTH study was carried out with 8 of the 13 participants (males, 25-42 years old) and the EMG-A study was carried out with 9 (eight males, 1 female, 20-38 years old) of the 13 participants. Each participant was seated comfortably in an armchair. The examined (right) arm lay on an armrest with the shoulder slightly flexed (about 308), the elbow semiflexed, and the forearm pronated.Conditioning Stimulation. In both the PSTH and the EMG-A studies, electrical rectangular pulses of 1.0-ms duration were delivered to the radial nerve branch innervating BR (BR nerve) with surface electrodes (1.0-c...

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Monosynaptic facilitation of group I afferents between brachioradialis and extensor carpi radialis in humans

Cited by 8 publications

References 23 publications

Monosynaptic facilitation of flexor digitorum superficialis motoneurons mediated by Group Ia afferents from the extensor carpi radialis in humans

Monosynaptic facilitation of flexor digitorum superficialis motoneurons mediated by Group Ia afferents from the extensor carpi radialis in humans

Monosynaptic facilitation of motoneurons innervating intrinsic hand muscles mediated by group Ia afferents from the extensor carpi radialis in humans

Oligosynaptic inhibition of group Ia afferents from brachioradialis to triceps brachii motor neurons in humans

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