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: combined morphological and functional analyses.

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 (125) I-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.

• Authors: Ru-Yuan Zhou, Jing Xu, Fang-Lu Chi, Lian-Hua Chen, Shi-Tong Li
• Journal: The Laryngoscope (Laryngoscope) Vol. 122 Issue 8 Pg. 1831-7 (Aug 2012) ISSN: 1531-4995 [Electronic] United States
• PMID: 22522983 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2012 The American Laryngological, Rhinological, and Otological Society, Inc.

Chemical References

• Androstanols
• Bungarotoxins
• Neuromuscular Nondepolarizing Agents
• Receptors, Cholinergic
• Rocuronium

Topics

• Androstanols (pharmacology)
• Animals
• Axotomy
• Bungarotoxins
• Electromyography (drug effects)
• Facial Muscles (innervation, pathology)
• Facial Nerve Injuries (pathology, physiopathology)
• Male
• Motor Endplate (drug effects)
• Muscle Tonus (drug effects)
• Muscle, Skeletal (innervation, pathology)
• Neural Inhibition (drug effects)
• Neuromuscular Nondepolarizing Agents (pharmacology)
• Rats
• Rats, Sprague-Dawley
• Receptors, Cholinergic (drug effects)
• Rocuronium
• Spectrometry, Gamma
• Tibial Nerve (drug effects, injuries, pathology)