Oxytocin is a neuropeptide hormone synthesized in magnocellular neurosecretory cells of the paraventricular and supraoptic nuclei in the hypothalamus [1][2]. It is packaged into neurosecretory vesicles and transported down axons to the posterior pituitary gland, where it is released into the bloodstream [1]. Oxytocin is also released within the brain from dendrites and soma of oxytocinergic neurons [4].

The structure of oxytocin is a disulfide-linked nonapeptide containing nine amino acids: cysteine-tyrosine-isoleucine-glutamine-asparagine-cysteine-proline-leucine-glycine-amide (CYIQNCPLG-NH2) [5]. The disulfide bridge between the two cysteine amino acids gives oxytocin its characteristic cyclic structure [5].

In the bloodstream, oxytocin acts on the uterus and breasts to induce labor contractions and milk let-down [1][3]. Centrally released oxytocin acts on widespread brain regions to modulate social cognition, anxiety, memory, reward pathways and complex affiliative behaviors like maternal care, pair bonding, and sexual response [2][3][4][6].

Oxytocin receptors are found in high concentrations in the amygdala, hippocampus, striatum, and cortex [2][4]. Oxytocin is thought to dampen amygdalar reactivity, reducing anxiety and facilitating prosocial tendencies [3][6]. In the hippocampus, oxytocin may strengthen synaptic plasticity, enhancing social memory [6].

Oxytocin interacts with natural opioid systems, which mediate maternal motivation and social reward [2][4]. Oxytocin and opioid activity converge in the amygdala, influencing bonding [4]. Oxytocin also stimulates dopamine release in mesolimbic reward regions like the nucleus accumbens [4][6].