Stimulus-dependent effects in the actions of sodium channel blockers on sensory C-units.

Stimulus-dependent inhibition of discharges from cutaneous C fibers from mechanothermo-sensitive (MTS) units (nociceptive sensors) can explain the paradoxical analgesic effect of local anesthetics at low concentrations, insufficient to block axonal conduction of nerve impulses. Three types of experiments are proposed which could detect the stimulus-dependent inhibition of the terminal section of sensory C units: a method involving repeated series of stimuli, the increasing stimulus method, and the spike encounter method. The applications of these methods to assessing the magnitudes of the neuroleptic effects of local anesthetics and cardiac antiarrhythmics is discussed.