Links between cell survival signaling through neurotrophins and cell death signaling are beginning to be found. For example, survival effects of nerve growth factor on sympathetic neurons are mediated by Ras (96). Ras proteins are GDP/GTPregulated switches that interact with exchange proteins that facilitate cycling between an active GTP-bound state and an inactive GDP-bound state. Extracellular signal regulated kinases (ERK1 and ERK2) regulate the exchange factors. In neurons, Ras suppresses the levels or activities of c-jun, p53 and Bax through PI3-K and ERK (96). Insulin-like growth factor-I acts through similar kinases that inactivate caspase-9 and Bad by phosphorylation (97).