Oxytocin

Oxytocin is a neuropeptide hormone composed of nine amino acids (Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2, with a cyclic disulphide bridge between the two cysteine residues), synthesised in the paraventricular and supraoptic nuclei of the hypothalamus and released by the posterior pituitary. Oxytocin is unique among neuropeptides in functioning as both a peripheral hormone and a central neurotransmitter — the same molecule acts through the oxytocin receptor (OXTR) in both the bloodstream (endocrine signalling) and the brain (neurotransmitter/neuromodulator signalling). OXTR is a class A G protein-coupled receptor that activates Galphaq/PLCbeta signalling, producing IP3-mediated calcium mobilisation and PKC activation. In peripheral tissues, oxytocin stimulates uterine smooth muscle contraction (parturition) and mammary gland myoepithelial cell contraction (lactation). In the central nervous system, oxytocin acts as a neuromodulator influencing social bonding, trust, pair bonding, maternal behaviour, and social recognition through OXTR activation in brain regions including the nucleus accumbens, amygdala, and prefrontal cortex. The dual peripheral-central signalling makes oxytocin a unique research tool for studying the neuroendocrine basis of social behaviour and the connection between peripheral hormonal signalling and central neurotransmitter pathways.