Oxytocin · Grey Matter

Oxytocin is a small peptide hormone, nine amino acids long, that makes the uterus contract during birth and the breast release milk during suckling, and that also acts inside the brain on social behaviour and bonding.

Oxytocin. Oxytocin is a small peptide hormone, nine amino acids long, that makes the uterus contract during birth and the breast release milk during suckling, and that also acts inside the brain on social behaviour and bonding.

It is made by large neurosecretory cells in the paraventricular and supraoptic nuclei of the hypothalamus, carried down their axons and stored in their endings in the posterior pituitary gland, from where it is released into the blood when those neurons fire. Its two classic reflexes are positive feedback loops: stretching of the cervix during labour triggers more oxytocin, which strengthens contractions, and suckling triggers the milk-ejection reflex. Smaller oxytocin neurons project within the brain itself, to the amygdala and other regions.

In the brain it modulates social behaviour. In animals it supports maternal care and pair bonding; in humans the effects of nasal oxytocin on trust and empathy reported in early studies have proved small and hard to replicate.

It is the posterior pituitary's other product beside vasopressin, the two molecules differing in only two amino acids.

Its synthetic form is used in obstetrics to induce labour and to control bleeding after birth.

Questions: Why are oxytocin and vasopressin said to come from the pituitary when the hypothalamus makes them? Both hormones are made in the cell bodies of large neurons in the supraoptic and paraventricular nuclei of the hypothalamus. The neurons pack them into vesicles that travel down their axons, through the pituitary stalk, to endings in the posterior pituitary, where they are stored. When the neurons fire, the endings release the hormones into the capillaries of the posterior pituitary, so the gland is the place of release and the hypothalamus is the place of manufacture.