Restitution of function and collateral sprouting in the cat spinal cord: The deafferented animal

Unilateral hindlimb deafferentation is followed initially by generalized loss of all reflex and useful function. As useful movement returns, certain descending reflexes recover and become hyperactive: crossed reflexes do not. Recovery of movement and reflex hyperactivity are then abolished by subsequent destruction of the ipsilateral descending systems. Although there is no sprouting from contralateral dorsal roots, bilateral degeneration of descending systems is asymmetrical, being greater in density and distribution on the previously deafferented side. Collateral sprouting to certain spinal laminae apparently took place during the recovery period from the same source which mediated reflex hyperactivity; the ipsilateral descending systems. A substantial descending projection to Clarke's nucleus was found only on the experimental side, however, suggesting that a central feedback system replaced the abolished peripheral feedback. If functional, this might subserve recovery of the ability to maintain a limb position. Chronically deafferented cats which are then transected show, for the first time, hyperreflexia of crossed responses, which develops gradually during the first week post‐transection. It may be related to sprouting of contralateral dorsal roots for contralateral ganglion injection with 3 H‐proline gives a larger than normal ipsilateral distribution of grain density over the commissural nuclei. It is suggested that recovery and hyperactivity of reflex responses underlie the recovery of useful movement and that reflex recovery may be related to collateral sprouting. It is also suggested that both the reflex and the anatomical response to a given lesion is restricted to only one of the remaining systems and is therefore a specific rather than a generalized response.