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Differences in sensitivity to rocuronium among orbicularis oris muscles innervated by normal or damaged facial nerves and gastrocnemius muscle innervated by somatic nerve in rats

Authors

  • Ru-Yuan Zhou MD,

    1. Department of Anesthesiology, Eye, Ear, Nose, and Throat Hospital, Fudan University, Shanghai
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    • Ru-Yuan Zhou, MD, and Jing Xu, MD, contributed equally to this work.

  • Jing Xu MD,

    1. Department of Anesthesiology, Eye, Ear, Nose, and Throat Hospital, Fudan University, Shanghai
    2. Department of Otolaryngology, Eye, Ear, Nose, and Throat Hospital, Fudan University, Shanghai
    3. Department of Anesthesiology, Affiliated First People's Hospital, Shanghai Jiaotong University, Shanghai, China
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    • Ru-Yuan Zhou, MD, and Jing Xu, MD, contributed equally to this work.

  • Fang-Lu Chi MD, PhD,

    1. Department of Otolaryngology, Eye, Ear, Nose, and Throat Hospital, Fudan University, Shanghai
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  • Lian-Hua Chen MD, PhD,

    Corresponding author
    1. Department of Anesthesiology, Affiliated First People's Hospital, Shanghai Jiaotong University, Shanghai, China
    • Department of Anesthesiology, Haining Road 100, Affiliated First People's Hospital, Shanghai Jiaotong University, Shanghai 200080, China
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  • Shi-Tong Li MD, PhD

    1. Department of Anesthesiology, Affiliated First People's Hospital, Shanghai Jiaotong University, Shanghai, China
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  • The study was supported by the National Natural Science Foundation of China. The authors have no other funding, financial relationships, or conflicts of interest to disclose.

Abstract

Objectives/Hypothesis:

To evaluate mechanisms of discrepant responses to the nondepolarizing muscle relaxant rocuronium among normal and injured facial nerve-innervated orbicularis oris and tibial nerve-innervated gastrocnemius, and to provide information for the proper use of muscle relaxants to balance evoked electromyography (EEMG) monitoring and immobility in general anesthesia.

Study Design:

Randomized controlled study.

Methods:

Right-sided facial nerve injury was induced by crush axotomy in 18 Sprague-Dawley rats. At different rocuronium concentrations, muscular tension amplitude (MTA) was determined in vitro for normal and injured facial nerve-innervated orbicularis oris and gastrocnemius; the number of unsaturated acetylcholine receptors (AChRs) at end plates was determined by 125I-α-bungarotoxin staining followed with gamma spectroscopy. The morphological composition of muscle fibers was determined by histological examination.

Results:

Following rocuronium incubation, the percentage of MTA inhibition (MTAI%) of gastrocnemius was significantly higher than the corresponding values of orbicularis oris (P < .05), and the degree of saturation of AChR in gastrocnemius was significantly greater than that in orbicularis oris (P < .05). The baseline MTA and AChR density of injured-side orbicularis oris was significantly smaller than those of the normal side, whereas no significant difference was found regarding MTAI% and the degree of AChR saturation between the normal and injured side.

Conclusions:

The affinity of AChR at end plates and different number of AChR per unit fiber cross-sectional area may be the mechanisms for differential sensitivities to neuromuscular blockers between facial nerve-innervated muscles and somatic nerve-innervated muscles. The lower EEMG responses in the impaired facial nerve-innervated muscles may result from the lower AChR density at end plates compared with the normal facial nerve-innervated muscles.

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