Distribution of nerve growth factor in chick embryo sympathetic neurons in vitro

The distribution of nerve growth factor (NGF) in chick embryo sympathetic neurons has been followed by two distinct procedures, that is, indirect immunofluorescence microscopy employing purified NGF antibodies and autoradiography after exposure of cells to [125I]NGF. This study shows that NGF bound to sympathetic neurons is not uniformly distributed but appears in spots over the surface of perikarya and along processes. If the same cells, after incubation with NGF and fixation, are treated with methanol-acetone to allow permeation of immunoglobulins across the plasma membrane, NGF antibody immunoreactive material is also found within the cytoplasm and notably in the paranuclear area only in sympathetic neurons. Analogous findings are obtained when sympathetic neurons are incubated in the presence of [125I]NGF, fixed, sectioned and processed for autoradiography. Also with this technique NGF appears to be localized in the cytoplasmic compartment and is found around the nucleus. These studies are discussed in connection with the results of similar experiments performed on a clonal line of NGF target cells known as PC12.