Acetylcholine receptors in the equatorial region of intrafusal muscle fibers modulate mouse muscle spindle sensitivity

Publication Date

January 2019

Document Type


Publication Title

Journal of Physiology




Muscle spindles are complex stretch‐sensitive mechanoreceptors. They consist of specialized skeletal muscle fibres, called intrafusal fibres, which are innervated in the central (equatorial) region by afferent sensory axons and in both polar regions by efferent γ‐motoneurons. Previously it was shown that acetylcholine receptors (AChR) are concentrated in the equatorial region at the contact site between the sensory neuron and the intrafusal muscle fibre. To address the function of these AChRs, single unit sensory afferents were recorded from an isolated mouse EDL muscle in the absence of γ‐motoneuron activity. Specifically, we investigated the responses of individual sensory neurons to ramp‐and‐hold stretches and sinusoidal vibrations before and after the addition of the competitive and non‐competitive AChR blockers d‐tubocurarine or α‐bungarotoxin, respectively. The presence of either drug did not affect the frequency of the resting action potential discharge frequency. However, the action potential frequencies in response to stretch were increased. In particular, frequencies of the dynamic peak and dynamic index to ramp and hold stretches were significantly higher in the presence of either drug. Treatment of muscle spindle afferents with the high‐affinity choline transporter antagonist hemicholinium‐3 similarly increased muscle spindle afferent firing frequencies during stretch. Moreover, the firing rate during sinusoidal vibration stimuli at low amplitudes was higher in the presence of α‐bungarotoxin compared to control spindles also indicating an increased sensitivity to stretch. Collectively these data suggest a modulation of the muscle spindle afferent response to stretch by AChRs in the central region of intrafusal fibres possibly fine‐tuning muscle spindle sensitivity.This article is protected by copyright. All rights reserved


acetylcholine receptor, alpha‐bungarotoxin, d‐tubocurarine, hemicholinium‐3, intrafusal fibre, proprioception


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