Complete spinal cord transection at different postnatal ages: recovery of motor coordination correlated with spinal...

The ability of rats that are cordotomized at different times between postnatal day (PN) 0-28, to recover four-limb motor coordination, varies as a function of the time of cordotomy. The rats were evaluated at 37 independent observers for four-limb coordination, scored on a scale of 10 (best) to 0 (worst). The rank order of recovery from best to worst is: PN7 greater than PN0 greater than PN14 greater than PN21 greater than PN28. The hindlimbs are active only when they receive proprioceptive sensation from contact with a surface. They appear completely paralyzed when, for example, the rats are challenged to climb an inclined surface of spaced metal bars (Fig. 4). The content of both dopamine (DA) and norepinephrine (NE) in the adult spinal cord rostral to the transection, also varied as a function of transection time. DA was present in the lumbar (that is, caudal to the transection) region of the cord in the PN0, PN7 and PN14 groups, with the highest concentration in the PN7 group. NE was not present in the lumbar region in any of the experimental groups. It is concluded that rats can recover a substantial degree of four limb motor activity after cordotomy, provided the cord is transected before the fourteenth postnatal day. Moreover, this recovery of motor coordination, apparently correlates closely with the presence of DA in the lumbar region of the cord. Whether there is a causal relationships between recovery of motor coordination and the content of DA in the lumbar cord is not known.