Nitric oxide neurotransmitter functions

In the central nervous system (CNS) nitric oxide (NO) functions as a neurotransmitter (Bredt and Synder, 1992). NO has been implicated as a mediator of long-term potentiation (Haley et al., 1992 Schuman and Madison, 1994) and as a cellular correlate of memory, and it may also mediate synaptic plasticity and remodeling (Hess et al., 1993 Wu et al., 1994). Unlike conventional neurotransmitters, NO is not packaged into synaptic vesicles and then released in quantal packets. Indeed, its chemical instability in solution (Ignarro, 1990) and its membrane permeability would appear... 

After an overview of neurotransmitter systems and function and a consideration of which substances can be classified as neurotransmitters, section A deals with their release, effects on neuronal excitability and receptor interaction. The synaptic physiology and pharmacology and possible brain function of each neurotransmitter is then covered in some detail (section B). Special attention is given to acetylcholine, glutamate, GABA, noradrenaline, dopamine, 5-hydroxytryptamine and the peptides but the purines, histamine, steroids and nitric oxide are not forgotten and there is a brief overview of appropriate basic pharmacology. 

Popoli M, Zanotti S, RadaeUi R, Gaggianesi C, Verona M, Brunello N, Racagni G (1997b) The neurotransmitter release machinery as a site of action for psychotropic drugs effect of typical and atypical antidepressants. Soc Neurosci Abstr 2325 Prast H, Philippu A (2001) Nitric oxide as modulator of neuronal function. Prog Neurobiol 64 51-68... 

Synaptic communication between neurons does not only involve the classical neurotransmitter systems reviewed in this chapter. Two other classes of neurotransmitters are also known to affect brain function neuropeptides and atypical neurotransmitters, such as nitric oxide and carbon monoxide. These neurotransmitters are not stored in vesicles, are not released by exocytosis, and do not bind to postsynaptic receptors. We have chosen not to review these neurotransmitters here, since they do not yet have implications for the current practice of neuropsychopharmacology. They are, however, promising targets for the development of new treatment strategies, and the interested reader is referred to other articles for review (Hokfelt, 1991 Snyder and Ferris, 2000). 

Functions of nitric oxide NADPH is required for the synthesis of nitric oxide (NO), an important molecule that causes vasodilation by relaxing vascular smooth muscle, acts as a kind of neurotransmitter, prevents platelet aggregation, and helps mediate macrophage bactericidal activity. 

Only the first type of neurotransmitter release mediates the fast point-to-point synaptic transmission process at classical synapses (sometimes referred to as wiring transmission). All of the other types of neurotransmitter release effect one or another form of volume transmission whereby the neurotransmitter signal acts diffusely over more prolonged time periods (Agnati et al., 1995). Of these volume transmitter pathways, the time constants and volumes involved differ considerably. For example, diffusible neurotransmitters such as nitric oxide act relatively briefly in a localized manner, whereas at least some neuropeptides act on the whole brain, and can additionally act outside of it (i.e., function as hormones). There is an overlap between wiring and volume neurotransmission in that all classical neurotransmitters act as wiring transmitters via ionotropic receptors, and also act as volume transmitters via G-protein-coupled receptors. Moreover, neuromodulators in turn feed back onto classical synaptic transmission. 

The ENS is connected to the central nervous system by extrinsic parasympathetic and sympathetic motor neurons, and by extrinsic spinal and vagal sensory neurons. Through these bidirectional connections, the ENS can be monitored and modified. Despite the presence of these extrinsic nerve connections, the ENS can also function autonomously in some intestinal regions. Neural transmission within the ENS is controlled by a large variety of neurotransmitters and neuromodulatory peptides, such as serotonin, norepinephrine, acetylcholine, ATP, and nitric oxide. Most of these... 

About ten years ago scientists studying muscle relaxation discovered that our bodies produce nitric oxide for use as a neurotransmitter. (A neurofransmitter is a small molecule that serves to facilitate cell-to-cell communications.) Since then, it has been detected in at least a dozen cell types in various parts of the body. Cells in the brain, the liver, the pancreas, the gastrointestinal tract, and the blood vessels can synthesize nitric oxide. This molecule also functions as a cellular toxin to kill harmful bacteria. And that s not all In 1996 it was reported that NO binds to hemoglobin, the oxygen-carrying protein in the blood. No doubt it helps to regulate blood pressure. 

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