What it is

Oxytocin is a cyclic nonapeptide: nine amino acids with a sulfur bridge between the two cysteines, closing a six-amino-acid ring. It is made in the paraventricular and supraoptic nuclei of the hypothalamus. Released into the blood it acts on the body; released inside the brain it acts on mood and behaviour. It lasts only a few minutes in the blood, but its effects on the brain outlast it.