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Norepinephrine is a monoamine neurotransmitter

Monoamine neurotransmitters are neurotransmitters and neuromodulators that contain one amino group connected to an aromatic ring by a two-carbon chain (such as -CH₂-CH₂-). Examples are dopamine, serotonin and adrenaline.

All monoamines are derived from aromatic amino acids like phenylalanine, tyrosine, and tryptophan by the action of aromatic amino acid decarboxylase enzymes. They are deactivated in the body by the enzymes known as monoamine oxidases which clip off the amine group.

Monoaminergic systems, i.e., the networks of neurons that use monoamine neurotransmitters, are involved in the regulation of processes such as emotion, arousal, and certain types of memory. It has also been found that monoamine neurotransmitters play an important role in the secretion and production of neurotrophin-3 by astrocytes, a chemical which maintains neuron integrity and provides neurons with trophic support.^[1]

Drugs used to increase (or reduce) the effect of monoamine neurotransmitters are used to treat patients with psychiatric and neurological disorders, including depression, anxiety, schizophrenia and Parkinson's disease.^[2]

Examples

Biosynthetic pathways for catecholamines and trace amines in the human brain[3][4][5] L-Phenylalanine L-Tyrosine L-DOPA Epinephrine Phenethylamine p-Tyramine Dopamine Norepinephrine N-Methylphenethylamine N-Methyltyramine p-Octopamine Synephrine 3-Methoxytyramine AADC AADC AADC primary pathway PNMT PNMT PNMT PNMT AAAH AAAH brain CYP2D6 minor pathway COMT DBH DBH Phenethylaminergic trace amines and the catecholamines are derivatives of L-phenylalanine.

Classical monoamines

• 
  Imidazoleamines
  
  • 
    Histamine^[6]
    
  
  


• 
  Catecholamines:
  
  
  
  • 
    Adrenaline (Ad; Epinephrine, Epi)
  
  
  • 
    Dopamine (DA)
  
  
  • 
    Noradrenaline (NAd; Norepinephrine, NE)
  
  
  
  


• 
  Indolamines:
  
  • 
    Serotonin (5-HT)
  
  

Trace amines

• 
  Phenethylamines (related to catecholamines):
  
  
  
  • 
    Phenethylamine^[7][8][9] (PEA)
  
  
  • 
    N-Methylphenethylamine^[10][7][9] (endogenous amphetamine isomer)
  
  
  • 
    Phenylethanolamine^[11][9]
    
  
  
  • 
    m-Tyramine^[7][9]
    
  
  
  • 
    p-Tyramine^[7][9]
    
  
  
  • 
    3-Methoxytyramine^[10][9]
    
  
  
  • 
    N-Methyltyramine^[10][7][9]
    
  
  
  • 
    m-Octopamine^[7][9]
    
  
  
  • 
    p-Octopamine^[7][9]
    
  
  
  • 
    Synephrine^[10][9]
    
  
  
  
  


• 
  Tryptamine^[10][8][9]
  

Specific transporter proteins called monoamine transporters that transport monoamines in or out of a cell exist. These are the dopamine transporter (DAT), serotonin transporter (SERT), and the norepinephrine transporter (NET) in the outer cell membrane and the vesicular monoamine transporter (VMAT1 and VMAT2) in the membrane of intracellular vesicles.^{[citation needed]}

After release into the synaptic cleft, monoamine neurotransmitter action is ended by reuptake into the presynaptic terminal. There, they can be repackaged into synaptic vesicles or degraded by the enzyme monoamine oxidase (MAO), which is a target of monoamine oxidase inhibitors, a class of antidepressants.^{[citation needed]}

Evolution

A phylogenetic tree showing how a number of monoamine receptors are related to each other.

Monoamine neurotransmitter systems occur in virtually all vertebrates, where the evolvability of these systems has served to promote the adaptability of vertebrate species to different environments.^[12][13]

See also

• Monoamine receptor


• Monoamine oxidase


• Monoamine transporter


• Monoamine Hypothesis


• Biogenic amine


• Trace amine


• Monoamine nuclei

References

External links

• 
  Biogenic+monoamines at the US National Library of Medicine Medical Subject Headings (MeSH)