Neurotransmitter

A neurotransmitter is a type of molecule that carries signals between neurons (nerve cells) at synapses in the nervous system.

Neurotransmitters may be either excitatory (EPSPs) or inhibitory (IPSPs). That is, they may foster the initiation of a nerve impulse in the receiving neuron, or they may inhibit such an impulse. Glutamate is the most prominent of excitatory transmitters; GABA and glycine are well-known inhibitory neurotransmitters.

Within the cells, neurotransmitter molecules are packaged in vesicles and released into the synaptic cleft (the space between nerve cells) by rapid exocytosis upon the arrival of an action potential (nerve impulse). Then they diffuse across the synaptic cleft to bind to neurotransmitter receptors or other ligand-gated ion channels on the postsynaptic neuron extracellular membrane, and stimulate or inhibit the firing of an action potential by the post-synaptic neuron.

Many neurotransmitters are removed from the synaptic cleft by transport proteins residing in neuronal and glial plasma membranes. This process is called reuptake (or often simply uptake). Without reuptake, the molecules might (counterproductively) continue to stimulate or inhibit the firing of the postsynaptic neuron. Another mechanism for removal of a neurotransmitter is digestion by an enzyme. For example, at cholinergic synapses (where acetylcholine is the neurotransmitter) the enzyme acetylcholinesterase breaks down the acetylcholine.

Drugs may alter the way neurotransmitters function. Cocaine, for example, blocks the reuptake of serotonin and dopamine, leaving these neurotransmitters in the synaptic gap longer. AMPT prevents the conversion of tyrosine to L-DOPA; reserpine prevents dopamine storage within vesicles; and deprenyl inhibits monoamine oxidase B and thus increases dopamine levels.

Common neurotransmitters

• Derived from amino acids:
  • aspartate
  • glutamate
  • GABA
  • glycine

• Monoamines (in the order of their synthesis):
  • from phenylalanine and tyrosine:
    • dopamine (da)
      • norepinephrine (ne/noradrenaline)
        • epinephrine (epi/adrenaline)
  • from tryptophan:
    • serotonin (5ht/5-hydroxytryptamine)
  • from histidine:
    • histamine (?)

• Polypeptides (neuropeptides):
  • Bombesin/GRP:
    • bombesin
    • gastrin releasing peptide (GRP)
  • Gastrins:
    • gastrin
    • cholecystokinin (CCK)
  • Insulins:
    • insulin
  • Neurohypophyseals:
    • vasopressin
    • oxytocin
    • neurophysin I
    • neurophysin II
  • Neuropeptide Y:
    • neuropeptide Y (NY)
    • pancreatic polypeptide (PP)
    • peptide YY (PYY)
  • Opioids:
    • corticotropin (ACTH)
    • Beta-lipotropin
    • dynorphin
    • endorphin
    • enkephaline
    • leumorphin
  • Secretins:
    • secretin
    • motilin
    • glucagon
    • vasoactive intestinal peptide (VIP)
    • growth hormone-releasing factor (GRF)
  • Somatostatins:
    • somatostatin
  • Tachykinins:
    • neurokinin A
    • neurokinin B
    • neuropeptide A
    • neuropeptide gamma
    • substance P

• Biogenic amines:
  • acetylcholine (ACh)

• Other:
  • nitric oxide (NO)
  • carbon monoxide (CO)
  • anandamide

See also

• nervous system

External links

• Molecular Expressions Photo Gallery: The Neurotransmitter Collection (http://micro.magnet.fsu.edu/micro/gallery/neurotrans/neurotrans.html)
• Brain Neurotransmitters (http://www.benbest.com/science/anatmind/anatmd10.html)
• Endogenous Neuroactive Extracellular Signal Transducers (http://www.neurotransmitter.net/neurosignaling.html)

da:Neurotransmitter de:Neurotransmitter es:Neurotransmisor fr:Neurotransmetteur nl:Neurotransmitter