How do adult neurons survive?

Extract: Apoptotic cell death, also known as cell suicide or programmed cell death, is a series of intracellular biochemical steps that lead to a cell's controlled but inevitable death. Apoptosis plays a crucial role in the normal development of the embryonic nervous system. Many developing neurons are destined to die by apoptosis unless they are "rescued" by their exposure to growth factors that shut off the cell suicide program, enabling their survival. Naturally too many neurons are generated, forcing them to compete for a limited supply of critical growth factors. Only the "fittest" survive -- those that make the right connections at the right time. This enables the survival of only those neurons needed for the appropriate formation and function of the nervous system; surplus neurons are discarded, creating order by cleaning out what is not needed. This is a seemingly wasteful, but effective strategy for setting up the complex and intricate circuits of the nervous system. In stark contrast, the neurons in the adult do not divide and are irreplaceably lost once they are dead, so they need to survive for the entire lifetime of the organism. Their premature death can lead to irreversible functional deficits that underlie many neurodegenerative diseases. Mature neurons possess, through multiple inherent or intrinsic molecular mechanisms, the ability to control or repress inadvertent activation of the cell suicide program that lies dormant within every cell.