HETERONYMOUS RECURRENT INHIBITION FROM GASTROCNEMIUS-MUSCLE TO SOLEUSMOTONEURONS IN HUMANS

Presence of heteronymous recurrent inhibition in motoneurones (Mns) in nervating the soleus muscle (Sol) was investigated following electrica l stimulation of the nerve of gastrocnemius medialis muscle (GM). Sub- threshold electrical stimulation for alpha Mns produced short-lasting inhibition of the Sol, reflecting non-reciprocal group I inhibition. A fter increasing the intensity of stimulation above the motor threshold , a short-latency, long-lasting inhibition appeared superimposed on th e group I inhibition. Its amount increased with the size of the condit ioning motor response and after acute administration Of L-acetylcarnit ine. It is concluded that this long-lasting inhibition of the Sol Mns is due to the heteronymous activity of the GM-coupled Renshaw cells.