Locomotory Movements of the Hind Limbs in Rabbits after Isolation of the Lumbosacral Cord.

In my earlier experiments with spinal cats (1962) I established that the isolated lumbosacral cord is able to co-ordinate walking movements of the hind limbs. In cats this part of the cord possesses a high degree of autonomy. It seemed interesting to know whether in rabbits the isolated lumbosacral cord is also able to maintain these functions. It was especially important to establish whether the spinal rabbit can carry out the typical jumping movements with hind limbs, which serve, as is well known, in the act of progression in normal conditions. According to Laughton (1924) the synchronous bilateral jumping movements of the hind limbs seen in normal rabbits should be replaced by alternate rhythmical movements in spinal rabbits. After decerebration Laughton made a transection of the spinal cord in rabbits at the limit of the thoracic cord. The dorsal cutaneous nerves, which innervate the hind limbs, were isolated and prepared for stimulation. Reflexmovements of the hind limbs were observed in response to electrical stimulation with faradic currents and mechanical stimulation by pinching one toe of the hind feet. Such reflexes consist of ipsilateral flexion and crossed extension of the hind limbs. He could not provoke any synchronous bilateral movement of the hind limbs in his rabbits after transection of the cord. Laughton concludes that in rabbits the nervous mechanism in the lumbosacral cord is so arranged that it can innervate only the alternate rhythmical movements of the hind limbs. The synchronous bilateral movements of the hind limbs are only possible when the cord is in connexion with the supraspinal centres of the brain-stem, which lies probably in the pontine region. Whereas Laughton made a transection of the spinal cord in decerebrated rabbits and then examined the reflex-movements of the hind limbs by excitation of the sensory nerves, I carried out chronic experiments in which I studied the walking movements of the spinal animal, as I had already done in my investigations of spinal pigeons and spinal cats.