Influence of Motor Activities on the Release of Transmitter Quanta from Motor Nerve Terminals in Mice

We investigated the effects of motor activities on transmitter release in mouse nerve-muscle preparations of the diaphragm muscle (DPH), extensor digitorum longus muscle (EDL), and soleus muscle (SOL). Mice were divided into a control group, a motor-restricted (RST) group, and a motor-compelled (CMP) group. The quantal content (m) of endplate potentials was measured intracellularly. In DPH the motor activity was unaffected. In the CMP group the m value of the EDL group increased with increases in the cooperativity of Ca2+ in transmitter release. Compared with the CMP group, the SOL of the RST group had a smaller m value with increases in the cooperativity of Ca2+ in transmitter release. These results suggest that motor activities can influence neuromuscular activity specific to different systems, however, the motor compulsion specifically activated the function of EDL and the motor restriction activated the function of SOL, and these effects might lead to altered activity of the release of transmitter quanta in motor nerve terminals of mice.