Neurotransmitter 21865 224365199 2008-07-08T15:09:34Z 130.219.235.253 /* Excitatory and inhibitory */ [[Image:Aspartic Acid.png|thumb|Chemical structure of '''[[D-aspartic acid]]''', a common amino acid neurotransmitter.]] '''Neurotransmitters''' are [[chemistry|chemicals]] that are used to relay, amplify and modulate signals between a [[neuron]] and another [[cell (biology)|cell]].<ref>{{Dorlands|n_08|12571289}}</ref> According to the prevailing beliefs of the 1960s, a chemical can be classified as a neurotransmitter if it meets the following conditions: * There are precursors and/or synthesis [[enzyme]]s located in the [[presynaptic]] side of the [[synapse]]; * The chemical is present in the presynaptic element * It is available in sufficient quantity in the presynaptic neuron to affect the [[postsynaptic]] neuron; * There are postsynaptic [[biochemical receptor|receptors]] and the chemical is able to bind to them * A [[biochemical]] mechanism for inactivation is present. == Types of neurotransmitters == There are many different ways to classify neurotransmitters. Dividing them into [[amino acids]], [[peptides]], and [[monoamine]]s is sufficient for many purposes. Some more precise divisions are as follows: * Around 10 "[[small-molecule]] neurotransmitters" are known: ** [[acetylcholine]] (Ach) ** [[monoamine]]s ([[epinephrine]] (E), [[norepinephrine]] (NE), [[dopamine]] (DA), [[serotonin]] (5-HT) and [[melatonin]]) ** 3 or 4 amino acids, depending on exact definition used: (primarily [[glutamic acid]], [[gamma aminobutyric acid]] (GABA), [[aspartic acid]] & [[glycine]]) ** [[Purines]], ([[Adenosine]], [[adenosine triphosphate|ATP]], [[Guanosine triphosphate|GTP]] and their derivatives) ** Fatty acids are also receiving attention as the potential [[Cannabinoids#Endogenous Cannabinoids|endogenous cannabinoid]].{{Fact|date=February 2007}} * Over 50 neuroactive [[peptide]]s ([[vasopressin]], [[somatostatin]], [[neurotensin]], etc.) have been found, among them [[hormone]]s such as [[Luteinizing hormone]] (LH) or [[insulin]] that have specific local actions in addition to their long-range signalling properties. * [[Histamine]] * Single [[ion]]s, such as synaptically released [[zinc]], are also considered neurotransmitters by some.{{Fact|date=March 2007}} * Gaseous, including [[nitric oxide]] (NO) and [[carbon monoxide]] (CO) The major "workhorse" neurotransmitters of the [[brain]] are [[glutamic acid]] and [[GABA]].<!--what?--> ===Excitatory and inhibitory=== Release of excitatory neurotransmitters from the presynaptic membrane opens channels in the postsynaptic membrane and leads to an increase in the [[concentration]] of [[sodium ion]]s within the postsynaptic cell and a decrease in that of [[potassium]] ions. This leads to a '[[depolarisation]]' of the postsynaptic cell, which is propagated further along the cell membrane by an [[action potential]]. Inhibitory neurotransmitters encourage the [[hyperpolarization (biology)|hyperpolarization]] of the postsynaptic cell, making it less likely to generate an action potential. Whether a neurotransmitter acts in an excitatory or inhibitory manner is determined by the reaction of the receptor to its binding. Thus a given chemical can be excitatory at some receptors and inhibitory at others. <!--==Mechanism of action==--> ==Actions== Some examples of neurotransmitter action: * [[Acetylcholine]] - voluntary movement of the skeletal muscles (via the [[Sympathetic nervous system|sympathetic]] pathways) and movement of the viscera (via the [[Parasympathetic nervous system|parasympathetic]] pathways) * [[Norepinephrine]] - wakefulness or arousal - via the sympathetic pathways * [[Epinephrine]] - similar to nor-epinephrine. Large amounts of it are produced and are released by the [[adrenal glands]]. Also called adrenaline. * [[Dopamine]] - voluntary movement and motivation, "wanting", pleasure, associated with addiction and love * [[Serotonin]] - [[memory]], [[emotion]], wakefulness, [[sleep]] and [[thermoregulation|temperature regulation]] * [[gamma aminobutyric acid|GABA]] - inhibition of [[motor neuron]]s * [[Glycine]] - [[spinal reflex]]es and motor behaviour * [[Neuromodulator]]s - [[sensory system|sensory]] transmission, especially [[pain]] NB: Neurotransmitters may be specific to particular target organs and have multiple roles around the body. For instance, Acetylcholine is released from both [[sympathetic]] and [[parasympathetic]] neurons. ACH can be either excitatory to skeletal muscle cells or inhibitory to both smooth muscle and cardiac muscle. ==Neurotransmitter systems== {{Main|Neuromodulation}} Neurons expressing certain types of neurotransmitters sometimes form distinct systems, where activation of the system affects large volumes of the brain, called ''volume transmission''.<!--huh?--> The major neurotransmitter systems are the [[noradrenaline]] (norepinephrine) system, the [[dopamine]] system, the [[serotonin]] system and the [[cholinergic]] system. Drugs targeting the neurotransmitter of such systems affects the whole system; this fact explains the mode of action of many drugs. [[Cocaine]], for example, blocks the reentering of [[dopamine]] back into the [[presynaptic]] neuron, leaving these neurotransmitters in the [[synapse|synaptic gap]] longer. Since the dopamine is in the synapse longer, the neurotransmitter rapidly hit the receptors on the [[postsynaptic]] neuron cell, and therefore causing happiness. Excess intake of [[cocaine]] can lead to physical addiction. The physical addiction of cocaine is when the neurotransmitters stay in the synapse so long , the body removes some receptor from the [[postsynaptic]] neuron. After the drug affect is done, the person usually feels unhappy, because now the neurotransmitters are less likely to hit the receptor since the body removed many of them during the drug intake. [[Prozac]] is a [[serotonin reuptake inhibitor|selective serotonin reuptake inhibitor]] (SSRI), hence potentiating the effect of naturally released serotonin. [[AMPT]] prevents the conversion of tyrosine to [[L-DOPA]], the precursor to dopamine; [[reserpine]] prevents dopamine storage within [[vesicles]]; and [[deprenyl]] inhibits [[monoamine oxidase]] (MAO)-B and thus increases dopamine levels. Diseases may affect specific neurotransmitter systems. For example, [[Parkinson's disease]] is at least in part related to failure of dopaminergic cells in [[deep-brain nuclei]], for example the [[substantia nigra]]. Treatments potentiating the effect of dopamine precursors have been proposed and effected, with moderate success. A brief comparison of the major neurotransmitter systems follows: {| class="wikitable" |+Neurotransmitter systems |- ! System !! Origin <ref name=Rang> {{cite book |author=Rang, H. P. |title=Pharmacology |publisher=Churchill Livingstone |location=Edinburgh |year=2003 |pages= page 474 for noradrenaline system, page 476 for dopamine system, page 480 for serotonin system and page 483 for cholinergic system. |isbn=0-443-07145-4 |oclc= |doi=}} </ref> !! Effects<ref name=Rang/> |- !rowspan=2| Noradrenaline system | ''[[locus coeruleus]]'' |rowspan=2| *arousal *reward |- | [[Lateral tegmental field]] |- ! Dopamine system || [[dopamine]] [[neural pathway|pathways]]: * [[mesocortical pathway]] * [[mesolimbic pathway]] * [[nigrostriatal pathway]] * [[tuberoinfundibular pathway]] || [[motor system]], reward, [[cognition]], [[endocrine]], [[nausea]] |- !rowspan=2| Serotonin system | caudal [[dorsal raphe nucleus]] |rowspan=2| Increase ([[extraversion and introversion|introversion]]), [[Mood (psychology)|mood]], [[satiety]], [[body temperature]] and [[sleep]], while decreasing [[nociception]]. |- | rostral [[dorsal raphe nucleus]] |- !rowspan=3| Cholinergic system | ''pontomesencephalotegmental complex'' |rowspan=3| *[[learning]] *[[Memory#Short-term|short-term memory]] *arousal *reward |- | [[basal optic nucleus of Meynert]] |- | medial [[septal nucleus]] |} == Common neurotransmitters == {| class="wikitable" class="sortable wikitable" | '''Category''' || '''Name''' || '''Abbreviation''' || '''[[Metabotropic]]''' || '''[[Ionotropic]]''' |- | Small: Amino acids || [[Aspartate]] || || - || - |- | [[Neuropeptide]]s || [[N-Acetylaspartylglutamate]] || [[NAAG]] || [[Metabotropic glutamate receptor]]s; selective agonist of [[mGluR3]] || - |- | Small: Amino acids || [[Glutamate]] (glutamic acid) || Glu || [[Metabotropic glutamate receptor]] || [[NMDA receptor]], [[Kainate receptor]], [[AMPA receptor]] |- | Small: Amino acids || [[Gamma-aminobutyric acid]] || GABA || [[GABAB receptor]] || [[GABAA receptor]], [[GABAC receptor]] |- | Small: Amino acids || [[Glycine]] || Gly || - || [[Glycine receptor]] |- | Small: Acetylcholine || [[Acetylcholine]] || Ach || [[Muscarinic acetylcholine receptor]] || [[Nicotinic acetylcholine receptor]] |- | Small: Monoamine ([[Phenylalanine|Phe]]/[[Tyrosine|Tyr]]) || [[Dopamine]] || DA || [[Dopamine receptor]] || - |- | Small: Monoamine ([[Phenylalanine|Phe]]/[[Tyrosine|Tyr]]) || [[Norepinephrine]] (noradrenaline) || NE || [[Adrenergic receptor]] || - |- | Small: Monoamine ([[Phenylalanine|Phe]]/[[Tyrosine|Tyr]]) || [[Epinephrine]] (adrenaline) || Epi || [[Adrenergic receptor]] || - |- | Small: Monoamine ([[Phenylalanine|Phe]]/[[Tyrosine|Tyr]]) || [[Octopamine]] || || - || - |- | Small: Monoamine ([[Phenylalanine|Phe]]/[[Tyrosine|Tyr]]) || [[Tyramine]] || || - |- | Small: Monoamine ([[Tryptophan|Trp]]) || [[Serotonin]] (5-hydroxytryptamine) || 5-HT || [[Serotonin receptor]], all but 5-HT3 || [[5-HT3]] |- | Small: Monoamine ([[Tryptophan|Trp]]) || [[Melatonin]] || Mel || [[Melatonin receptor]] || - |- | Small: Monoamine ([[Histamine|His]]) || [[Histamine]] || H || [[Histamine receptor]] || - |- | PP: Gastrins || [[Gastrin]] || || - || - |- | PP: Gastrins || [[Cholecystokinin]] || CCK || [[Cholecystokinin receptor]] || - |- | PP: Neurohypophyseals || [[Vasopressin]] || || [[Vasopressin receptor]] || - |- | PP: Neurohypophyseals || [[Oxytocin]] || || [[Oxytocin receptor]] || - |- | PP: Neurohypophyseals || [[Neurophysin I]] || || - || - |- | PP: Neurohypophyseals || [[Neurophysin II]] || || - || - |- | PP: Neuropeptide Y || [[Neuropeptide Y]] || NY || [[Neuropeptide Y receptor]] || - |- | PP: Neuropeptide Y || [[Pancreatic polypeptide]] || PP || - || - |- | PP: Neuropeptide Y || [[Peptide YY]] || PYY || - || - |- | PP: Opioids || [[Corticotropin]] (adrenocorticotropic hormone) || ACTH || [[Corticotropin receptor]] || - |- | PP: Opioids || [[Dynorphin]] || || - || - |- | PP: Opioids || [[Endorphin]] || || - || - |- | PP: Opioids || [[Enkephaline]] || || - || - |- | PP: Secretins || [[Secretin]] || || [[Secretin receptor]] || - |- | PP: Secretins || [[Motilin]] || || [[Motilin receptor]] || - |- | PP: Secretins || [[Glucagon]] || || [[Glucagon receptor]] || - |- | PP: Secretins || [[Vasoactive intestinal peptide]] || VIP || [[Vasoactive intestinal peptide receptor]] || - |- | PP: Secretins || [[Growth hormone-releasing factor]] || GRF || - || - |- | PP: Somtostatins || [[Somatostatin]] || || [[Somatostatin receptor]] || - |- | SS: Tachykinins || [[Neurokinin A]] || || - || - |- | SS: Tachykinins || [[Neurokinin B]] || || - || - |- | SS: Tachykinins || [[Substance P]] || || - || - |- | PP: Other || [[Bombesin]] || || - || - |- | PP: Other || [[Gastrin releasing peptide]] || GRP || - || - |- | Gas || [[Nitric oxide]] || NO || - || - |- | Gas || [[Carbon monoxide]] || CO || - || - |- | Other || [[Anandamide]] || AEA || [[Cannabinoid receptor]] || - |- | Other || [[Adenosine triphosphate]] || ATP || [[P2Y12]] || [[P2X receptor]] |} == Degradation and elimination== Neurotransmitter must be broken down once it reaches the post-synaptic cell to prevent further excitatory or inhibitory signal transduction. For example, [[acetylcholine| acetylcholine, (ACH)]] (an excitatory neurotransmitter), is broken down by [[acetylcholinesterase]] (AchE). [[Choline]] is taken up and recycled by the pre-synaptic neuron to synthesize more ACH. Other neurotransmitters such as [[dopamine]] are able to [[diffusion|diffuse]] away from their targeted synaptic junctions and are eliminated from the body via the kidneys, or destroyed in the liver. Each neurotransmitter has very specific degradation pathways at regulatory points, which may be the target of the body's own regulatory system or [[recreational drug]]s. ==Sub-Neurotransmitters== In the process of neurotransmission, certain unknown components are existent and active, though their activities are subtle. These components assist and desist procession of neurotransmission by aiding communication or stimulating the building blocks of the neurotransmitter itself. Examples are: Mesoendodextrine Mesotetradextrine == See also == * [[Neuropsychopharmacology]] * [[Nervous system]] * [[Gasotransmitters]] ==References== {{Reflist}} ==External links== {{commons|Neurotransmitter|Neurotransmitter}} * [http://micro.magnet.fsu.edu/micro/gallery/neurotrans/neurotrans.html Molecular Expressions Photo Gallery: The Neurotransmitter Collection] * [http://www.benbest.com/science/anatmind/anatmd10.html Brain Neurotransmitters] * [http://www.neurotransmitter.net/neurosignaling.html Endogenous Neuroactive Extracellular Signal Transducers] * {{MeshName|Neurotransmitter}} {{Cell signaling}} {{Neurotransmitter systems}} [[Category:Neurotransmitters]] [[Category:Neurochemistry]] [[Category:Molecular neuroscience]] [[ar:ناقل عصبي]] [[bn:নিউরোট্রান্সমিটার]] [[bg:Невротрансмитер]] [[ca:Neurotransmissor]] [[cs:Neurotransmitér]] [[da:Neurotransmitter]] [[de:Neurotransmitter]] [[el:Νευροδιαβιβαστής]] [[es:Neurotransmisor]] [[eo:Neŭrotransmisiilo]] [[fr:Neurotransmetteur]] [[ko:신경전달물질]] [[hr:Neurotransmiter]] [[it:Neurotrasmettitore]] [[he:מוליך עצבי]] [[lt:Mediatorius (biochemija)]] [[hu:Ingerületátvivő anyagok]] [[nl:Neurotransmitter]] [[ja:神経伝達物質]] [[no:Nevrotransmitter]] [[pl:Neuroprzekaźnik]] [[pt:Neurotransmissor]] [[ro:Neurotransmiţător]] [[ru:Нейромедиатор]] [[simple:Neurotransmitter]] [[sk:Neurotransmiter]] [[sr:Неуротрансмитери]] [[fi:Aivojen välittäjäaine]] [[sv:Signalsubstans]] [[th:สารสื่อประสาท]] [[tr:Nörotransmitterler]] [[uk:Нейромедіатори]] [[zh:神经递质]]