Monoamine Sythesis, Storage and Degradation
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psychology
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date published 13/11/2007
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SummaryIn addition to similarities in neuronal organization, monoaminergic systems are similar with regard to their synthesis, storage, and degradation. Monoamines are synthesized within neurons from common amino acid precursors and taken up into synaptic vesicles via a vesicular monoamine transporter. Upon stimulation, vesicles within nerve terminals release neurotransmitter into the synaptic cleft. Once released, the monoamines interact with postsynaptic receptors to alter the excitability of postsynaptic cells. Monoamines may also interact with presynaptic autoreceptors located on the nerve terminal to suppress further release. In addition, released monoamines may be taken back up from the synaptic cleft into the nerve terminal by plasma membrane transporter proteins. Reuptake plays an important role in limiting the magnitude and duration of action of synaptically released monoamines. Once monoamines are taken up, they may be subject to enzymatic degradation or they may be protected from degradation by uptake into vesicles. The processing of acetylcholine differs from this scheme, and is described below.
Table of Contents
- Serotonin The CNS contains less than 2 percent of the serotonin in the body; peripheral serotonin is located in platelets, mast cells, and enterochromaffin cells of the gastrointestinal system.
- The first step in the degradation of serotonin is mediated by monoamine oxidase (MAO) type A
- Two enzymes that play major roles in the degradation of catecholamines are monoamine oxidase and catechol O-methyltransferase
- Histamine As is the case for serotonin, the brain contains only a small portion of the histamine found in the body.
- Plasma Membrane Transporters A great deal of progress has been made in the molecular characterization of the monoamine plasma membrane transporter proteins.
- Vesicular Monoamine Transporter In addition to the reuptake of monoamines into the presynaptic nerve terminal, a second transport process serves to concentrate and store monoamines within synaptic vesicles.
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