Editing Dopamine (section)

=== Aging brain ===
{{Main|Aging brain}}
A number of studies have reported an age-related decline in dopamine synthesis and dopamine receptor density (i.e., the number of receptors) in the brain.<ref name="Hof 2009">{{cite book | vauthors = Mobbs CV, Hof PR |title=Handbook of the neuroscience of aging |publisher=Elsevier/Academic Press |location=Amsterdam |year=2009 |isbn=978-0-12-374898-0 |oclc= 299710911 }}</ref> This decline has been shown to occur in the striatum and [[extrastriate cortex|extrastriatal]] regions.<ref>{{cite journal | vauthors = Ota M, Yasuno F, Ito H, Seki C, Nozaki S, Asada T, Suhara T | title = Age-related decline of dopamine synthesis in the living human brain measured by positron emission tomography with L-[beta-11C]DOPA | journal = Life Sciences | volume = 79 | issue = 8 | pages = 730–36 | date = July 2006 | pmid = 16580023 | doi = 10.1016/j.lfs.2006.02.017 }}</ref> Decreases in the [[Dopamine receptor D1|D<sub>1</sub>]], [[Dopamine receptor D2|D<sub>2</sub>]], and [[Dopamine receptor D3|D<sub>3</sub>]] receptors are well documented.<ref name="Kaasinen 2000">{{cite journal | vauthors = Kaasinen V, Vilkman H, Hietala J, Någren K, Helenius H, Olsson H, Farde L, Rinne J | s2cid = 40871554 | title = Age-related dopamine D2/D3 receptor loss in extrastriatal regions of the human brain | journal = Neurobiology of Aging | volume = 21 | issue = 5 | pages = 683–68 | year = 2000 | pmid = 11016537 | doi = 10.1016/S0197-4580(00)00149-4 }}</ref><ref name="Wang 1998">{{cite journal | vauthors = Wang Y, Chan GL, Holden JE, Dobko T, Mak E, Schulzer M, Huser JM, Snow BJ, Ruth TJ, Calne DB, Stoessl AJ | title = Age-dependent decline of dopamine D1 receptors in human brain: a PET study | journal = Synapse | volume = 30 | issue = 1 | pages = 56–61 | date = September 1998 | pmid = 9704881 | doi = 10.1002/(SICI)1098-2396(199809)30:1<56::AID-SYN7>3.0.CO;2-J | s2cid = 31445572 }}</ref><ref name="Wong 1984">{{cite journal | vauthors = Wong DF, Wagner HN, Dannals RF, Links JM, Frost JJ, Ravert HT, Wilson AA, Rosenbaum AE, Gjedde A, Douglass KH | s2cid = 24278577 | title = Effects of age on dopamine and serotonin receptors measured by positron tomography in the living human brain | journal = Science | volume = 226 | issue = 4681 | pages = 1393–96 | date = December 1984 | pmid = 6334363 | doi = 10.1126/science.6334363 | bibcode = 1984Sci...226.1393W }}</ref> The reduction of dopamine with aging is thought to be responsible for many neurological symptoms that increase in frequency with age, such as decreased arm swing and increased [[Rigidity (neurology)|rigidity]].<ref name="Wang Snyder 1998">{{cite book | vauthors = Wang E, Snyder SD |year=1998 |title=Handbook of the aging brain |location=San Diego, California |publisher=Academic Press |isbn=978-0-12-734610-6 |oclc=636693117}}</ref> Changes in dopamine levels may also cause age-related changes in cognitive flexibility.<ref name="Wang Snyder 1998"/>