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

Toshiaki Sato; Mitsuhiro Nito; Katsuhiko Suzuki; Hiromi Fujii; Wataru Hashizume; Takuji Miyasaka; Masaomi Shindo; Akira Naito

doi:10.1002/mus.25664

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

Muscle Nerve. 2018 Jan;57(1):122-128. doi: 10.1002/mus.25664. Epub 2017 Jun 5.

Authors

Toshiaki Sato¹, Mitsuhiro Nito², Katsuhiko Suzuki³, Hiromi Fujii¹, Wataru Hashizume², Takuji Miyasaka⁴, Masaomi Shindo⁵, Akira Naito²

Affiliations

¹ Department of Occupational Therapy, Yamagata Prefectural University of Health Sciences, Yamagata, Japan.
² Department of Anatomy and Structural Science, Yamagata University School of Medicine, 2-2-2 Iida-nishi, Yamagata, 990-9585, Japan.
³ Department of Physical Therapy, Yamagata Prefectural University of Health Sciences, Yamagata, Japan.
⁴ Department of Judo Therapy, Teikyo University Faculty of Medical Technology, Utsunomiya, Japan.
⁵ Graduate School of Health Sciences, Matsumoto University, Matsumoto, Japan.

PMID: 28398686
DOI: 10.1002/mus.25664

Abstract

Introduction: This study examines effects of low-threshold 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 ± 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. Muscle Nerve 57: 122-128, 2018.

Keywords: brachioradialis; group Ia afferents; humans; oligosynaptic inhibition; triceps brachii.

MeSH terms

Adult
Electric Stimulation
Electromyography
Female
Healthy Volunteers
Humans
Male
Motor Neurons / physiology*
Muscle Fibers, Skeletal / physiology
Muscle, Skeletal / innervation*
Muscle, Skeletal / physiology*
Neurons, Afferent / physiology*
Synapses / physiology*
Young Adult