Multidisciplinary approach to nitric oxide signaling: Focus on the gastrointestinal and the central nervous system.

Nitric oxide (NO), with close historical ties to cardiovascular physiology, is an important endogenous mediator, the most potent natural vasorelaxant known, involved in many biological functions . NO acts as an intra/intercellular signalling molecule and is a mediator in almost all organ systems . NO is known to occur in many cells types, including vascular endothelial cells, neurons, and epithelial cells . The transmitter of nonadrenergic, noncholinergic (NANC) inhibitory neurons has been the subject of hundreds of investigations over the past 3 decades. Recent evidence suggests that NO may serve as a NANC inhibitory signaling molecule in the gastrointestinal (GI) tract. NO serves as the primary enteric inhibitory neurotransmitter in GI muscles, and nitrergic neurons regulate gut tone, phasic contractile amplitude and frequency, and inhibitory reflexes . In the central nervous system (CNS) NO is involved in some major processes such as memory through longterm potentiation (LTP) and learning . This gasotransmitter also contributes to a pathogenesis of epilepsy. The role of NO in the generation of epilepsy is contradictory since there is evidence of its proconvulsive and anticonvulsive effects . In this review, we will discuss about the possible role of NO as neurotransmitter in the GI and CNS, with focus on the contribution of NO-mediated signaling pathways in the GI motility and CNS excitability. Physiological functions of nitric oxide