Editing Brain (section)

=== Neurotransmitters and receptors ===
[[Neurotransmitter]]s are chemicals that are released at synapses when the local membrane is depolarised and [[Calcium|Ca<sup>2+</sup>]] enters into the cell, typically when an action potential arrives at the synapse – neurotransmitters attach themselves to receptor molecules on the membrane of the synapse's target cell (or cells), and thereby alter the electrical or chemical properties of the receptor molecules. With few exceptions, each neuron in the brain releases the same chemical neurotransmitter, or combination of neurotransmitters, at all the synaptic connections it makes with other neurons; this rule is known as [[Dale's principle]].<ref name="Kandel 2000"/><!--Ch 15--> Thus, a neuron can be characterized by the neurotransmitters that it releases. The great majority of [[psychoactive drug]]s exert their effects by altering specific neurotransmitter systems. This applies to drugs such as [[cannabinoids]], [[nicotine]], [[heroin]], [[cocaine]], [[Alcohol (drug)|alcohol]], [[fluoxetine]], [[chlorpromazine]], and many others.<ref>{{cite book |last1=Cooper |first1=JR |last2=Bloom |first2=FE |last3=Roth |first3=RH |title=The Biochemical Basis of Neuropharmacology |publisher=Oxford University Press US |year=2003 |isbn=978-0-19-514008-8 |url=https://books.google.com/books?id=e5I5gOwxVMkC}}</ref>

The two neurotransmitters that are most widely found in the vertebrate brain are [[glutamic acid|glutamate]], which almost always exerts excitatory effects on target neurons, and [[gamma-aminobutyric acid]] (GABA), which is almost always inhibitory. Neurons using these transmitters can be found in nearly every part of the brain.<ref>{{cite book|last1=McGeer|first1=PL|title=Basic Neurochemistry|last2=McGeer|first2=EG|publisher=Raven Press|year=1989|isbn=978-0-88167-343-2|editor=G. Siegel|location=University of Michigan|pages=311–332|chapter=Chapter 15, ''Amino acid neurotransmitters''|display-editors=etal}}</ref> Because of their ubiquity, drugs that act on glutamate or GABA tend to have broad and powerful effects. Some [[General anaesthetic|general anesthetics]] act by reducing the effects of glutamate; most tranquilizers exert their sedative effects by enhancing the effects of GABA.<ref>{{cite journal |title=Glutamate- and GABA-based CNS therapeutics |journal=Current Opinion in Pharmacology |volume=6 |pages=7–17 |year=2006 |pmid=16377242 |doi=10.1016/j.coph.2005.11.005 |last1=Foster |first1=AC |last2=Kemp |first2=JA |issue=1}}</ref>

There are dozens of other chemical neurotransmitters that are used in more limited areas of the brain, often areas dedicated to a particular function. [[Serotonin]], for example—the primary target of many [[Antidepressant|antidepressant drugs]] and many dietary aids—comes exclusively from a small brainstem area called the [[raphe nuclei]].<ref>{{cite book |last1=Frazer |first1=A |last2=Hensler |first2=JG |editor=Siegel, GJ |title=Basic Neurochemistry |edition=Sixth |year=1999 |publisher=Lippincott Williams & Wilkins |isbn=978-0-397-51820-3 |chapter=Understanding the neuroanatomical organization of serotonergic cells in the brain provides insight into the functions of this neurotransmitter}}</ref> [[Norepinephrine]], which is involved in arousal, comes exclusively from a nearby small area called the [[locus coeruleus]].<ref name=Mehler>{{cite journal |year=2009 |title=Autism, fever, epigenetics and the locus coeruleus |journal=[[Brain Research Reviews]] |volume=59 |pages=388–392 |pmc=2668953 |doi=10.1016/j.brainresrev.2008.11.001 |last1=Mehler |first1=MF |last2=Purpura |first2=DP |issue=2 |pmid=19059284}}</ref> Other neurotransmitters such as [[acetylcholine]] and [[dopamine]] have multiple sources in the brain but are not as ubiquitously distributed as glutamate and GABA.<ref>{{cite book |last=Rang |first=HP |title=Pharmacology |publisher=Churchill Livingstone |year=2003 |pages=476–483 |isbn=978-0-443-07145-4}}</ref>