Nerve growth factor supply for sensory neurons: site of origin and competition with the sympathetic nervous system

Nerve growth factor (NGF) levels in the sensory nervous system were measured by a highly sensitive two-site enzyme immunoassay for NGF. Dorsal root ganglia and the adjacent spinal nerves contained 2.8 +/- 0.3 and 1.7 +/- 0.4 ng NGF/g wet wt., respectively, whereas no NGF was detectable in dorsal roots and spinal cord (less than 0.05 ng NGF/g wet wt.). It is concluded that sensory neurons are supplied with NGF exclusively from their peripheral and not from their central field of projection. Two days after treatment with 6-hydroxydopamine, which destroys sympathetic nerve terminals and thereby prevents the removal of NGF by sympathetic neurons, the NGF content of dorsal root ganglia and trigeminal ganglia increased to 285% and 161% of control, respectively. This indicates that in peripheral target tissues sensory and sympathetic neurons compete for NGF.