The Effect Of Rocuronium On Presynaptic Quantal Release Of Acetylcholine From Normal Or Damaged Facial Nerve And Somatic Nerve Innervated Neuromuscular Junctions In Rats

Objective:To compare the amount of presynaptic quantal release of acetylcholine from normal or damaged facial nerve and somatic nerve innervated neuromuscular junctions under the effect of different concentrations of rocuronium in rat in vitro. To evaluate whether the differences in sensitivity to rocuronium among the normal or damaged facial nerve and somatic nerve innervated muscles are related to the function of presynaptic neurotransmitter release.Methods:Autologous paired controlled design was used in the study. An acute nerve trunk squeeze injury model was induced in the right facial nerves of the rats and the left facial nerves were used for control. The facial nerve trunks from both sides with the connected orbicularis oris muscle strips and the somatic nerve trunks with the connected gastrocnemius muscle strips were isolated for measuring the endplate potentials (EPP) and the miniature endplate potentials (MEPP) from the three groups of neuromuscular junctions by using intracellular microelectrode gauge. The EPPs and MEPPs were recorded at different concentrations of rocuronium(2.5,5,7.5,10μg/ml), and then, the presynaptic quantal release of acetylcholine which was calculated from the values of EPP/MEPP was compared among normal or damaged facial nerve and somatic nerve innervated neuromuscular junctions.Results:The EPPs and MEPPs from all the three groups of neuromuscular junctions exhibited a dose-dependent decreasing as the concentration of rocuronium increased. At rocuronium concentrations of2.5,5,7.5and10μg/ml, the extent of decreasing in EPPs of damaged facial nerves was significantly bigger than that of normal facial nerves, and that of somatic nerves was the biggest (P<0.05), while no significant difference was found for the comparisons of MEPPs among the three groups of neuromuscular junctions (P>0.05). EPP/MEPP of all the three kinds of neuromuscular junction exhibit a dose-dependent decrease against a concentration increase of rocuronium. In the2.5μg/ml concentration level of rocuronium, EPP/MEPP of damaged facial nerves decrease more obviously than that of normal facial nerves, and somatic nerves EPP/MEPP reduction is even more obvious, but with no statistical significance (P>0.05). Whereas in the5μg/ml、7.5μg/ml and10μg/ml concentration level of rocuronium, EPP/MEPP of damaged facial nerves decrease more obviously than that of normal facial nerves, and somatic nerves EPP/MEPP reduction is even more apparent, with statistically significant difference(P<0.05).Conclusion:Rocuronium presents different levels of inhibition on presynaptic quantal release of acetylcholine in normal or damaged facial nerve and somatic nerve innervated neuromuscular junctions, the extent of inhibition was showed as the sequence of somatic nerve> damaged facial nerve> normal facial nerve. This kind of difference may be one of the reasons causing differences in sensitivity to rocuronium among the normal or damaged facial nerve and somatic nerve innervated muscles.