title: 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: OBJECTIVE
  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.
  
  
  METHODS
  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.affiliation: Department of Anesthesiology, Eye, Ear, Nose, and Throat Hospital, Fudan University, Shanghai, China.
authors.forename: Ru-Yuan
authors.initials: RY
authors.lastname: Zhou
authors.forename: Jing
authors.initials: J
authors.lastname: Xu
authors.forename: Fang-Lu
authors.initials: FL
authors.lastname: Chi
authors.forename: Lian-Hua
authors.initials: LH
authors.lastname: Chen
authors.forename: Shi-Tong
authors.initials: ST
authors.lastname: Li
mesh_terms: D000732:Androstanols / Q000494:pharmacology*; D000818:Animals; D019771:Axotomy; D002038:Bungarotoxins; D004576:Electromyography / Q000187:drug effects; D005152:Facial Muscles / Q000294:innervation* / Q000473:pathology; D020220:Facial Nerve Injuries / Q000473:pathology* / Q000503:physiopathology*; D008297:Male; D009045:Motor Endplate / Q000187:drug effects*; D009129:Muscle Tonus / Q000187:drug effects; D018482:Muscle, Skeletal / Q000294:innervation* / Q000473:pathology; D009433:Neural Inhibition / Q000187:drug effects; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011950:Receptors, Cholinergic / Q000187:drug effects*; D000077123:Rocuronium; D013051:Spectrometry, Gamma; D013979:Tibial Nerve / Q000187:drug effects / Q000293:injuries* / Q000473:pathology
chemical_list: D000732:Androstanols; D002038:Bungarotoxins; D003473:Neuromuscular Nondepolarizing Agents; D011950:Receptors, Cholinergic; D000077123:Rocuronium