Endogenous neurotrophin-3 is retrogradely transported in the rat sciatic nerve

To address the active transport of neurotrophins, nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3 in the peripheral nerves, we examined the levels of proteins and messenger RNAs in the sciatic nerve of adult rats following transection, using enzyme immunoassays and reverse transcription polymerase chain reaction method, respectively. Neurotrophin-3 protein increased one day after transection only in the distal segment next to the transection site and returned to the original level two days later. This was considered to reflect accumulation of neurotrophin-3 transported from the periphery toward the neuronal cell bodies, because the neurotrophin-3 messenger RNA level was not changed in any sciatic segments during this experimental period. An increase in brain-derived neurotrophic factor protein was observed simultaneously in both the distal and proximal stumps three days after transection. Brain-derived neurotrophic factor messenger RNA was elevated in the same stumps two days after transection, suggesting that brain-derived neurotrophic factor was produced within the transected stumps. These observations demonstrate that neurotrophin-3, like nerve growth factor, is retrogradely transported in the sciatic nerve but that brain-derived neurotrophic factor is not. This suggests that neurotrophin-3 plays a role in the conveyance of trophic signals from target organs to neurons.