Editing Neuron (section)

====Neurotransmitter====
[[File:Neurotransmitters.jpg|thumb|Synaptic vesicles containing neurotransmitters]]
{{Main|Neurotransmitter}}
[[Neurotransmitter]]s are chemical messengers passed from one neuron to another neuron or to a [[muscle cell]] or [[Gland|gland cell]].
* Cholinergic neurons – acetylcholine. [[Acetylcholine]] is released from presynaptic neurons into the synaptic cleft. It acts as a [[ligand]] for both ligand-gated ion channels and [[Metabotropic receptor|metabotropic]] (GPCRs) [[Muscarinic acetylcholine receptor|muscarinic receptors]]. [[Nicotinic receptors]] are pentameric ligand-gated ion channels composed of alpha and beta subunits that bind [[nicotine]]. Ligand binding opens the channel causing the influx of [[Sodium|Na<sup>+</sup>]] depolarization and increases the probability of presynaptic neurotransmitter release. Acetylcholine is synthesized from [[choline]] and [[acetyl coenzyme A]].
* Adrenergic neurons – noradrenaline. [[Noradrenaline]] (norepinephrine) is released from most [[postganglionic]] neurons in the [[sympathetic nervous system]] onto two sets of GPCRs: [[Adrenergic receptor|alpha adrenoceptor]]s and [[beta adrenoceptor]]s. Noradrenaline is one of the three common [[catecholamine]] neurotransmitters, and the most prevalent of them in the [[peripheral nervous system]]; as with other catecholamines, it is synthesized from [[tyrosine]].
* GABAergic neurons – [[gamma aminobutyric acid]]. GABA is one of two neuroinhibitors in the [[central nervous system]] (CNS), along with glycine. GABA has a homologous function to [[Acetylcholine|ACh]], gating anion channels that allow [[Chlorine|Cl<sup>−</sup>]] ions to enter the post synaptic neuron. Cl<sup>−</sup> causes hyperpolarization within the neuron, decreasing the probability of an action potential firing as the voltage becomes more negative (for an action potential to fire, a positive voltage threshold must be reached). GABA is synthesized from glutamate neurotransmitters by the enzyme [[glutamate decarboxylase]].
* Glutamatergic neurons – glutamate. [[Glutamate]] is one of two primary excitatory amino acid neurotransmitters, along with [[Aspartic acid|aspartate]]. Glutamate receptors are one of four categories, three of which are ligand-gated ion channels and one of which is a [[G protein|G-protein]] coupled receptor (often referred to as GPCR).

:#[[AMPA]] and [[Kainic acid|Kainate]] receptors function as [[Ion|cation]] channels permeable to Na<sup>+</sup> cation channels mediating fast excitatory synaptic transmission.
:#[[N-Methyl-D-aspartic acid|NMDA]] receptors are another cation channel that is more permeable to [[Calcium in biology|Ca<sup>2+</sup>]]. The function of NMDA receptors depends on glycine receptor binding as a co-[[agonist]] within the channel pore. NMDA receptors do not function without both ligands present.
:#Metabotropic receptors, GPCRs modulate synaptic transmission and postsynaptic excitability.
:: Glutamate can cause excitotoxicity when blood flow to the brain is interrupted, resulting in [[brain damage]]. When blood flow is suppressed, glutamate is released from presynaptic neurons, causing greater NMDA and AMPA receptor activation than normal outside of stress conditions, leading to elevated Ca<sup>2+</sup> and Na<sup>+</sup> entering the post synaptic neuron and cell damage. Glutamate is synthesized from the amino acid glutamine by the enzyme [[Glutamine oxoglutarate aminotransferase|glutamate synthase]].
* Dopaminergic neurons—[[dopamine]]. [[Dopamine]] is a neurotransmitter that acts on D1 type (D1 and D5) Gs-coupled receptors, which increase cAMP and PKA, and D2 type (D2, D3, and D4) receptors, which activate Gi-coupled receptors that decrease cAMP and PKA. Dopamine is connected to mood and behavior and modulates both pre- and post-synaptic neurotransmission. Loss of dopamine neurons in the [[substantia nigra]] has been linked to [[Parkinson's disease]]. Dopamine is synthesized from the amino acid [[tyrosine]]. Tyrosine is catalyzed into levodopa (or [[L-DOPA]]) by [[tyrosine hydroxylase]], and levodopa is then converted into dopamine by the aromatic amino acid [[Carboxy-lyases|decarboxylase]].
* Serotonergic neurons—[[serotonin]]. [[Serotonin]] (5-Hydroxytryptamine, 5-HT) can act as excitatory or inhibitory. Of its four 5-HT receptor classes, 3 are GPCR and 1 is a ligand-gated cation channel. Serotonin is synthesized from [[tryptophan]] by [[tryptophan hydroxylase]], and then further by decarboxylase. A lack of 5-HT at postsynaptic neurons has been linked to depression. Drugs that block the presynaptic [[serotonin transporter]] are used for treatment, such as [[Prozac]] and [[Zoloft]].
* Purinergic neurons—ATP. [[Adenosine triphosphate|ATP]] is a neurotransmitter acting at both ligand-gated ion channels ([[P2X]] receptors) and GPCRs ([[P2Y receptor|P2Y]]) receptors. ATP is, however, best known as a [[cotransmitter]]. Such [[purinergic signaling]] can also be mediated by other [[purine]]s like [[adenosine]], which particularly acts at P2Y receptors.
* Histaminergic neurons—[[histamine]]. [[Histamine]] is a [[monoamine neurotransmitter]] and [[neuromodulator]]. Histamine-producing neurons are found in the [[tuberomammillary nucleus]] of the [[hypothalamus]].<ref>{{cite journal | vauthors = Scammell TE, Jackson AC, Franks NP, Wisden W, Dauvilliers Y | title = Histamine: neural circuits and new medications | journal = Sleep | volume = 42 | issue = 1 | date = January 2019 | pmid = 30239935 | pmc = 6335869 | doi = 10.1093/sleep/zsy183 }}</ref> Histamine is involved in [[arousal]] and regulating sleep/wake behaviors.