Cell signaling and neuronal death.

The past few decades have revealed that cell death can be precisely programmed with two principal forms, apoptosis and necrosis. Besides pathophysiological alterations, physiologic processes, such as the pruning of neurons during normal development and the involution of the thymus, involve apoptosis. This review focuses on the role of inter- and intracellular signaling systems in cell death, especially in the nervous system. Among neurotransmitters, glutamate and nitric oxide have been most extensively characterized and contribute to cell death in excitotoxic damage, especially in stroke and possibly in neurodegenerative diseases. Within cells, calcium, the most prominent of all intracellular messengers, mediates diverse forms of cell death with actions modulated by many proteins, including IP3 receptors, calcineurin, calpain, and cytochrome c.