Incremental responses of compound muscle action potentials in normal rats produced by repeated electrical stimulation

The purpose was to clarify the mechanism of normal incremental amplitude responses in compound muscle action potentials (CMAPs) and single fiber action potentials (SFAPs) produced by repeated high frequency electrical stimulation. Whereas the amplitude response of CMAPs and SFAPs increased during stimulation at 20 c.p.s. of the right flexor carpi ulnaris muscles of 50 rats, their durations gradually decreased. Incremental responses of the CMAPs and SFAPs evoked by repeated stimulation were suppressed in 25 rats by 30 mg/kg of magnesium sulfate and in 25 rats by 120 mg/kg of dantrolene sodium. We speculate that the incremental responses of CMAPs and SFAPs evoked by repeated stimulation were suppressed by the unchanged shape of the muscle after the injection of those chemicals.