Oxytocin and oxytocin receptors
Oxytocin (OXT, OT) is a small nine-amino acid neuropeptide/hormone, which affects social behaviour in humans and animals: intranasal application in men increases the perceived attractiveness of unfamiliar women and strengthens bonds between existing partners; OXT increases empathy, trust, and cooperation. The effects on human social processes may however be smaller than were initially assumed (Tabak et al., 2019).
Oxytocin is structurally very similar to vasopressin, and differs only by two amino acids, leading to some cross-reactions. OXT concentrations in the brain are much higher than in the peripheral tissues. Receptor for advanced glycation end-products (RAGE) on capillary endothelial cells of the blood-brain barrier (BBB) can transport oxytocin from blood into the brain (Yamamoto et al., 2019). Oxytocin pre-prohormone is produced mainly in the hypothalamus, from where it is transported to the posterior pituitary gland for storage and release. The pre-prohormone protein is cleaved during its way in pituitary stalk to oxytocin and a larger peptide, neurophysin I, which are released in the blood simultaneously in equimolar amounts, bound to each other.
Oxytocin receptor (OXTR, OTR) belongs to the family of G-protein coupled receptors (GPCRs). Receptors are expressed mainly in the central nervous system. OXTR has genetic variance which affects the individual effects of oxytocin.
PET radioligands for OXTR are being developed, but in vivo results have been disappointing so far (Wenzel et al., 2016; Vidal et al., 2017; Marzano et al., 2017; Smith et al., 2017; Beard et al., 2018), at least with intravenous administration.
The effects of OXT on dopaminergic system have been studied with [11C]raclopride (Striepens et al., 2014; Atzil et al., 2017), and on serotonergic system with [18F]MPPF and [11C]DASB (Lefevre et al., 2017a and 2017b).
Garrison JL, Macosko EZ, Bernstein S, Pokala N, Albrecht DR, Bargmann CI. Oxytocin/vasopressin-related peptides have an ancient role in reproductive behavior. Science 2012; 338(6106): 540-543. doi: 10.1126/science.1226201.
Grace SA, Rossell SL, Heinrichs M, Kordsachia C, Labuschagne I. Oxytocin and brain activity in humans: a systematic review and coordinate-based meta-analysis of functional MRI studies. Psychoneuroendocrinology 2018; 96: 6-24. doi: 10.1016/j.psyneuen.2018.05.031.
Lee HJ, Macbeth AH, Pagani JH, Young WS 3rd. Oxytocin: the great facilitator of life. Prog Neurobiol. 2009; 88(2): 127-151. doi: 10.1016/j.pneurobio.2009.04.001.
Updated at: 2019-04-29
Created at: 2018-08-18
Written by: Vesa Oikonen