Backgroulds: In this study, we tested the hypothesis that acetylcholine (ACh) release modulation by muscarinic M1 receptor in neuromuscular junction of the disused muscles may affect the tensions of the muscles during neuromuscular monitoring of rocuronium-induced neuromuscular block and compared to the normal muscles. 
Methods: A total of 20 C57BL/6 (wildtype) and 10 α7 knock out (α7KO) mice were used in this experniment. As pre-experimental procedure, knee and ankle joints of right hind limbs were fixed by needle pinning at 90° flexed position. These mice were raised for 2 wks at the environment with diurnal rhythm and food and water ad libitum. As a main experiment, both tendon of tibialis anterior (TA) muscles were obtained and muscle tensions were recored while dose-responses of rocuronium were measured three times at the same mice by serial administration of pirenzepine dose of 0, 0.001, and 0.01 μg/g. 
Results: There were no statistical differences on the body weight between wildtype and α7KO group. Weight losses were observed after 2wks of immobilization in both group and decrease of mass of TA muscles at immobilized side were observed compared with those of contralateral non-immobilized side. Tension depression of TA muscles at immobilized side of α7KO group were significantly rapid than those of wildtype group, but these differences were diminished after administration of pirenzepine. There were no statistically significant differences on Train-of-Four fade and tension depression between different pirenzepine doses at the same side in the group. 
Conclusions: Tension depression may become more rapid in the α7 nAChR-expressed disused muscles by decreased ACh release on neuronal firing by blockade of facililtatory M1 mAChR.

Effects of neuromuscular presynaptic muscarinic M1 receptor blockade on rocuronium-induced neuromuscular blockade in immobilized tibialis anterior muscles