Reflex control of magnocellular vasopressin and oxytocin secretion.

Reflex control of magnocellular vasopressin and oxytocin secretion has captured the curiosity and investigative imagination of neuroendocrinologists for nearly 50 years. While it may seem obvious that brisk elevations in circulating levels of vasopressin in response to hemorrhage, or of oxytocin in response to suckling, must of necessity arise from magnocellular neurosecretory neurons in the hypothalamus, the central pathways mediating these reflexes have, until quite recently, remained elusive. In this brief review, ongoing attempts to delineate these pathways are summarized. Evidence for plasticity and local modulation of magnocellular reflexes in response to prolonged stimulation, such as chronic dehydration and lactation, is also presented.