Background:The antagonistic actions of anticholinesterase drugs on non-depolarizing muscle relaxants are theoretically related to the activity ofacetylcholinesterase (AChE) in the neuromuscular junction (NMJ).However,till date the changes of AChE activity in the NMJ during sepsis have not been directly investigated.We aimed to investigate the effects of sepsis on the antagonistic actions ofneostigmine on rocuronium (Roc) and the underlying changes of AChE activity in the NMJ in a rat model of cecal ligation and puncture (CLP).Methods:A total of 28 male adult Sprague-Dawley rats were randomized to undergo a sham surgery (the sham group,n =12) or CLP (the septic group,n =16).After 24 h,the time-response curves of the antagonistic actions of 0.1 or 0.5 μmol/L of neostigmine on Roc (10 μmol/L)-depressed diaphragm twitch tension were measured.Meanwhile,the activity of AChE in the NMJ was detected using a modified Kovsky and Roots method.The mRNA levels of the primary transcript and the type T transcript of AChE (AChET) in the diaphragm were determined by real-time reverse transcription-polymerase chain reaction.Results:Four of 16 rats in the septic group died within 24 h.The time-response curves of both two concentrations ofneostigmine in the septic group showed significant upward shifts from those in the sham group (P ＜ 0.001 for 0.1 μmol/L;P =0.009 for 0.5 μmol/L).Meanwhile,the average optical density of AChE in the NMJ in the septic group was significantly lower than that in the sham group (0.517 ± 0.045 vs.1.047 ± 0.087,P ＜ 0.001).The AChE and AChET mRNA expression levels in the septic group were significantly lower than those in the sham group (P =0.002 for AChE;P =0.00l for AChET).Conclusions:Sepsis strengthened the antagonistic actions ofneostigmine on Roc-depressed twitch tension of the diaphragm by inhibiting the activity of AChE in the NMJ.The reduced content of AChE might be one of the possible causes of the decreased AChE activity in the NMJ.