Immunofluorescence micrograph demonstrating fluorescence of vasopressin (antidiuretic hormone, ADH) in the paraventricular nucleus of a rat's brain. Rounded neurone cell bodies and fibres which contain the hormone are visible on either side of the third ventricle (dark area at centre; one of brain's four-fluid filled chambers). Vasopressin is released from the brain into the posterior pituitary gland and from there into the bloodstream, where it increases the reabsorption of water from the kidneys & thus prevents excessive loss of water from the body. Vasopressin also causes the constriction of blood vessels. Magnification: X 10 at 35mm size.