Modification of group I field potentials in the intermediate nucleus of the cat spinal cord after chronic axotomy of an extensor nerve.

In walking decerebrate cats the influence of group I afferents from the medial gastrocnemius (MG) and the lateral gastrocnemius/soleus (LGS) muscles on stance phase duration is altered after axotomy of the LGS nerve [Whelan, P.J., Hiebert, G.W. and Pearson, K.G., J. Neurophysiol., 74 (1995) 2782-2787]. We examined whether a site for this plasticity is the connection from group I afferents onto spinal interneurons. Group I field potentials from MG, LGS and plantaris (PL) muscle afferents were recorded in the intermediate nucleus of the L6/L7 segments. Within 5 days following the transection of the LGS nerve in one hind leg, the field potential amplitudes from LGS afferents were decreased, from MG increased and those from PL were unchanged. The changes in the field potentials parallel modifications in the influence of group I afferents from the MG and LGS muscles on stance phase duration during walking.