Early nerve growth factor-induced events in developing rat septal neurons

A culture system enriched for nerve growth factor (NGF) receptor bearing cells was developed to investigate signal transduction events activated by NGF in postmitotic central nervous system neurons. Cells from the septal region of embryonic rats at 16 days of gestation were grown on glass coverslips above a glial cell layer established from postnatal rat cortex. The separation of glial and neuronal planes in this "bilaminar" system permits the diffusion of glial-derived factors required by septal neurons for survival yet allows the investigation of NGF responses in a pure neuronal population. Approximately 15% of the neurons in this culture system were immunoreactive for the low affinity NGF receptor. NGF rapidly increased MAP kinase activity (2-5 min) and transiently induced expression of c-fos in septal neurons. NGF treatment also increased choline acetyltransferase activity, while the number of cholinergic neurons remained constant. Septal neuron survival depended on the presence of glial cells, but neuronal viability in the bilaminar system was unaffected by anti-NGF antiserum, indicating that glial-derived neurotrophic support is not mediated by NGF alone. These data suggest that the bilaminar culture system is a useful system for the study of early events in NGF-activated signal transduction and the nature of glial-derived trophic support of developing basal forebrain neurons.