We have investigated the effects of nerve growth factor (NGF), brain-derive
d neurotrophic factor (BDNF),and neurotrophin-3 (NT-3) on the intraspinal r
egeneration of anterogradely labeled axotomized ascending primary sensory f
ibers in the adult rat. These fibers were allowed to grow across a predegen
erated peripheral nerve graft and back into the thoracic spinal cord. In co
ntrol animals that had been infused with vehicle for two weeks into the dor
sal column, 3 mm rostral to the nerve graft, essentially no fibers had exte
nded from the nerve graft back into the spinal cord. The number of sensory
fibers in the rostral end of the nerve graft was not significantly differen
t between control and neurotrophin-infused animals. With infusion of NGF, 3
7 +/- 2% of the fibers at the rostral end of the graft had grown up to 0.5
mm into the dorsal column white matter, 30 +/- 2% up to 1 mm, 19 +/- 3% up
to 2 mm and 8 +/- 2% up to 3 mm, i.e., the infusion site. With infusion of
NT-3, sensory fiber outgrowth was similar to that seen with NGF, but with B
DNF fewer fibers reached farther distances into the cord. Infusion of a mix
ture of all three neurotrophins did not increase the number of regenerating
sensory fibers above that seen after infusion of the individual neurotroph
ins. These findings suggest that injured ascending sensory axons are respon
sive to all three neurotrophins and confirm our previous findings that neur
otrophic factors can promote regeneration in the adult central nervous syst
em. (C) 1999 Elsevier Science B.V. All rights reserved.