Endogenous brain-derived neurotrophic factor is anterogradely transported in primary sensory neurons

Neurotrophins are a family of proteins which act as survival and differentiative factors in the developing and mature nervous system. Extensive evidence has been provided for their retrograde action following incorporation into nerve terminals and transport to the cell body. In contrast, we now demonstrate that one neurotrophin, brain-derived neurotrophic factor, is transported anterogradely via both peripheral and central processes of spinal sensory neurons. Using newly generated antisera, we have examined the distribution of brain-derived neurotrophic factor immunoreactivity and found it to be present within a subpopulation of sensory somata, primarily those with a small-to-medium diameter. The immunoreactivity was accumulated on both the distal and proximal sides of a ligature on the sciatic nerve. The accumulation on the distal side, but not on the proximal side, was substantially reduced by pretreatment with brain-derived neurotrophic factor antibodies in vivo. In contrast to the periphery, the immunoreactivity only accumulated on the proximal side of a lesion of the dorsal root. In the spinal cord, most nerve terminals immunoreactive for brain-derived neurotrophic factor were identified in lamina II. Lesion of the dorsal root led to a reduction of these nerve terminals. These studies indicate that the factor is transported not only retrogradely to, but also anterogradely from, the spinal ganglia to terminals in the periphery and spinal cord. The findings add a new dimension to the role of neuronal growth factors, since anterograde transport has not been observed previously for any endogenous survival factor.