[Modulation of Renshaw cell activity during scratching]

The activity of the Renshaw cells was recorded during fictitious scratching in 7 decerebrated and 1 spinal curarized cats. The flexor and extensor Renshaw cells were identified according to the responses induced by orthodromic stimulation of muscle nerves. Before the beginning of rhythmical oscillations, the background activity of the flexor Renshaw cells was inhibited. When the rhythmical generation began, both flexor and and extensor cells generated short bursts of spikes at the end of the flexor phase and at the extensor phase of the cycle. The activity of flexor cells began and terminated earlier in the cycle than that of the extensor cells. The results show that the flexor Renshaw cells are active reciprocally with flexor motoneurons, while the extensor cells are coactivated with extensor motoneurons.