Arginine vasotocin constitutes a molecular compromise, being vasopressinlike at position #8 and oxytocin-like at position #3. This molecule is found in neurohypophysial tissue of most submammalian vertebrates, but it also occurs in the neurohypophysis of mammalian fetuses and perhaps in the pineal gland of some adult mammals. The lysine vasopressin form is present in neurohypophysial tissues only in pigs and a few related species, whereas most mammals synthesize arginine vasopressin. One particular experimental model contributed greatly to our understanding of neurohypophysial electrophysiology. It was discovered by G. A. Lincoln and J. B. Wakerley that lactating rats, which are anesthetized and exposed continuously to suckling by hungry pups, release oxytocin only in periodic bursts. The process of neurohormone release must be instantly responsive to various stimuli. The ability of this neuroendocrine system to respond very rapidly and convert transient neural signals into neurohormone release for prolonged blood-borne action is an essential element of the neuro-hypophysial system.