Characterization of apoptosis in cultured rat sympathetic neurons after nerve growth factor withdrawal

Sympathetic neurons depend on nerve growth factor (NGF) for their survival both in vivo and in vitro. In culture, the neurons die after NGF withdrawal by an autonomous cell death program but whether these neurons die by apoptosis is under debate. Using vital DNA stains and in situ nick translation, we show here that extensive chromatin condensation and DNA fragmentation occur before plasma membrane breakdown during the death of NGF-deprived rat sympathetic neurons in culture. Furthermore, 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 apoptotic bodies does not occur. Apoptotic events proceed rapidly at around the time neurons become committed to die, regardless of neuronal culture age. However the duration of NGF deprivation required to commit neurons to die, and the rate at which apoptosis occurs, increase with culture age. Thus, within the first week of culture, apoptosis is the predominant form of cell death in sympathetic neurons.