Effects of red nucleus ablation and exogenous neurotrophin-3 on corticospinal axon terminal distribution in the adult rat

Collateral sprouting of undamaged descending axons is one potential mechani sm for recovery of function after incomplete spinal cord injury. In this st udy, we have investigated whether terminals of the intact corticospinal tra ct in the rat would sprout following ablation of a parallel descending path way, the rubrospinal tract. No sprouting was detected after this injury alo ne. However, the combination of rubrospinal tract ablation with administrat ion of 100 ng neurotrophin-3 to neurons of the corticospinal tract resulted in marked increased density of corticospinal innervation in the superficia l dorsal horn. There was no effect of administration of neurotrophin-3 alon e and increase in axon density was not detected in the deep dorsal horn. These results imply that spontaneous sprouting of undamaged corticospinal a xons does not occur following ablation of a parallel tract system, although collateral sprouting can be induced through a combination of the lesion pl us exogenous growth factor. Induced change in corticospinal terminal densit y is detected in the superficial dorsal horn only, supporting the hypothesi s that this is an area particularly supportive of circuit reorganisation. ( C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.