The effects of acupuncture on serotonin metabolism

IntroductionThe release of the neurotransmitter, serotonin is associated with different diseases and symptoms and is thought to enhance mood. As acupuncture may effect serotonin metabolism. This paper aimed to review the evidence for changes in serotonin associated with the use of acupuncture.MethodsPubMed, Scopus, RISS, and Web of Science were searched, together with manual searches for articles published between 1974-2015 using the key words “acupuncture” with “5-hydroxytryptamine (5-HT),” “tryptophan,” “5-hydroxytryptophan (5-HTP)," or “5-hydroxyindole acetaldehyde (5-HIAA).”ResultsOf the 61 studies identified, 37 (n = 27 animal and n = 10 human studies) were included in which investigators used serotonin or serotonin antagonists/agonists to examine the mechanisms of acupuncture for various symptoms. Investigators in 32 studies concluded that acupuncture improved symptoms, and of the 24 studies measuring serotonin, it was concluded that acupuncture changed the serotonergic mechanism. Acupuncture improves pain, which might be associated with increased levels of serum or plasma serotonin or tissue serotonin in the colon or the trigeminal nucleus caudalis, and decreased levels of platelet serotonin. Receptors 5-HT1, 5-HT2, and 5HT3 and subtypes 5-HT1A and 5-HT2A are related to the mechanisms of acupuncture on pain. Acupuncture improves anxiety/depression, but the evidence for change in the serotonergic mechanism is conflicting. Acupuncture improves diarrhoea, which might be associated with reduced 5-HT expression in the colon and appeared to improve obesity, which might be associated with increased levels of tissue serotonin at the raphe nuclei.ConclusionAcupuncture appears to improve symptoms and conditions such as pain, obesity, and depression. Those symptoms might be associated with changes in 5-HT.