Nitric oxide in health and disease of the nervous system.

Nitric oxide (NO) is a widespread and multifunctional biological messenger molecule. It mediates vasodilation of blood vessels, host defence against infectious agents and tumors, and neurotransmission of the central and peripheral nervous systems. In the nervous system, NO is generated by three nitric oxide synthase (NOS) isoforms (neuronal, endothelial and immunologic NOS). Endothelial NOS and neuronal NOS are constitutively expressed and activated by elevated intracellular calcium, whereas immunologic NOS is inducible with new RNA and protein synthesis upon immune stimulation. Neuronal NOS can be transcriptionally induced under conditions such as neuronal development and injury. NO may play a role not only in physiologic neuronal functions such as neurotransmitter release, neural development, regeneration, synaptic plasticity and regulation of gene expression but also in a variety of neurological disorders in which excessive production of NO leads to neural injury.