Oxytocin

Oxytocin is a nonapeptide neurohypophysial hormone, Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2 (C43H66N12O12S2, 1007.2 g/mol). A disulfide bridge between the cysteines at positions 1 and 6 forms the cyclic tocin ring, which is followed by a short C-terminal tail ending in glycinamide. Oxytocin and vasopressin differ by only two residues, and molecular dynamics work describes both as conformationally flexible cyclic peptides. In the brain, oxytocinergic projections link the paraventricular nucleus of the hypothalamus with regions including the amygdala, the bed nucleus of the stria terminalis and the medial prefrontal cortex.

Oxytocin in the research literature

Oxytocin acts through a single receptor, the oxytocin receptor (OXTR), a seven-transmembrane G protein-coupled receptor able to couple to Gαq or Gαi proteins. Downstream cascades described in the literature include the MAPK, PKC, PLC and CaMK pathways, converging on transcription factors such as CREB and MEF-2, with reported cellular responses including regulation of neurite outgrowth and cell viability.

A 2022 cryo-electron microscopy structure of the active-state receptor bound to oxytocin and a miniGq/i protein described an activation mechanism involving a Mg2+ coordination complex between the peptide and the receptor and disruption of transmembrane helix 7. The same study found that the identity of a single cation-coordinating residue determines whether receptors of the vasopressin family are cation-dependent. Circuit-level studies in rodent and prairie vole models have used genetic tools to monitor and manipulate oxytocin receptor-expressing neurons and to examine effects on neuronal spiking and synaptic plasticity.