On the effect of chemically activated fine muscle afferents on interneurones mediating group I non-reciprocal inhibition of extensor ankle and knee muscles in humans.

In a previous paper it was shown that muscle nociceptive discharge depressed the activity of interneurones mediating group I non-reciprocal inhibition (or Ib interneurones) in humans [A. Rossi, B. Decchi, Changes in Ib heteronymous inhibition to soleus motoneurons during cutaneous and muscle nociceptive stimulation in humans, Brain Res. 774 (1997) 55-61.]. However, since nociceptive discharge depressed the size of the soleus H-reflex (by which Ib inhibition was tested) the question arises as to whether modification of motoneurone membrane conductance per se could depress the size of Ib inhibitory post-synaptic potentials. The results of the present study suggest that the contribution of motoneurone hyperpolarization to Ib disinhibition is negligible and that muscle nociceptive discharge actually depresses the activity of these pathways.