To assess the in vivo long-lasting effects on neuromuscular transmission using transcutaneous stimulation with anodal and cathodal direct currents applied over the end-plate region (epDCS).

An active DCS electrode was placed over the end-plate region of both abductor pollicis brevis and first dorsal interosseous muscles, with a reference electrode located on the forearm. Cathodal or anodal currents were applied (2.5mA during 15min). Repetitive nerve stimulation of the median and ulnar nerves at the wrist was performed before and after DCS: protocol A – 500 stimuli at 3Hz; protocol B – 30 stimuli at 30Hz. For both muscles, we measured changes in amplitude and area between the first and 4th compound muscle action potential (CMAP) and between the first and 500th CMAP (protocol A); and the change in amplitude and area between the first and 30th CMAP (protocol B).

Anodal current did not change any measurement. Using cathodal epDCS and median nerve testing, there was a larger increase in CMAP amplitude (p=0.046) and a smaller decrease in area (p=0.008) between the first and 30th response (protocol B). Using cathodal epDCS and ulnar nerve testing, there was a possible significant smaller amplitude decrease of the CMAP measured, between the first and fourth response (protocol A).

Cathodal transcutaneous direct currents over the end-plate may modulate end-plate function by increasing the release of quanta of acetylcholine (Ach) and/or the number of Ach receptors available. Future studies should address this topic.