CHARACTERIZATION OF APOPTOSIS IN CULTURED RAT SYMPATHETIC NEURONS AFTER NERVE GROWTH-FACTOR WITHDRAWAL

Sympathetic neurons depend on nerve growth factor (NGF) for their surv ival both in vivo and in vitro. In culture, the neurons die after NGF withdrawal by an autonomous cell death program but whether these neuro ns die by apoptosis is under debate. Using vital DNA stains and in sit u nick translation, we show here that extensive chromatin condensation and DNA fragmentation occur before plasma membrane breakdown during t he death of NGF-deprived rat sympathetic neurons in culture. Furthermo re, kinetic analysis of chromatin condensation events within the cell population is consistent with a model which postulates that after NGF deprivation nearly all of the neurons die in this manner. Although the dying neurons display membrane blebbing, cell fragmentation into apop totic bodies does not occur. Apoptotic events proceed rapidly at aroun d the time neurons become committed to die, regardless of neuronal cul ture age. However the duration of NGF deprivation required to commit n eurons to die, and the rate at which apoptosis occurs, increase with c ulture age. Thus, within the first week of culture, apoptosis is the p redominant form of cell death in sympathetic neurons.