Chicken NGF and non-NGF trophic factor synthesis and release by sciatic nerves in vitro

The time course of production and release of nerve growth factor (NGF) and non-NGF neuronotrophic factors for sympathetic neurons by chicken and rat sciatic nerves in culture was examined. These tissues actively synthesize and release neuronotrophic activity as metabolically poisoning nerves with azide dramatically reduced the amount of trophic activity released into the culture medium. The sustained release of this activity also was shown to be dependent on the presence of low-molecular-weight dialysable molecules present in foetal calf serum and amniotic fluid from day 11 chicken embryos. Affinity-purified antimouse NGF antibodies were used to show that sciatic nerves in culture release both NGF and non-NGF trophic factors. These antibodies inhibited all bioactivity of both mouse NGF and of a partially purified preparation of chicken NGF. Immunoblot studies confirm that the antibodies recognize both rodent and avian NGF. Excess antibody inhibited only about 50% of the trophic activity in media conditioned over rat or chicken nerves for the first 24 hr. Relatively similar amounts of this non-NGF trophic activity were released throughout 6 days in culture, and this trophic activity kept sympathetic neurons alive in culture in the absence of NGF for more than 4 days. NGF levels were quantified with a two-site enzyme-linked immunoassay and found to parallel changes in NGF bioactivity. Rat nerves released increasing amounts of NGF with time in culture. Whole chicken sciatic nerves, however, released decreasing amounts of NGF with time in culture, but when these nerves were desheathed by removal of the epineurium and attached tissue, the pattern of NGF release was similar to that observed in the smaller rat sciatic nerves. These studies therefore characterize antibodies recognizing chicken NGF, demonstrate that peripheral nerve tissue synthesize trophic factors other than NGF, and identify factors that influence NGF synthesis.