Hypothalamic nuclei involved in vasopressin control. The hypothalamus surrounds the third ventricle ventral to the hypothalamic sulci. The main hypothalamic nuclei subserving vasopressin control are the median preoptic nucleus (MNPO), the paraventricular nuclei (PVN), and the supraoptic nuclei (SON), which project to the posterior pituitary along the supraoptic–hypophyseal tract. Afferent nerve impulses from stretch receptors in the left atrium (inhibitory), aortic arch, and carotid sinuses (excitatory) travel via the vagus nerve, and neural pathways project to the PVN and the SON. These nuclei also receive osmotic input from the lamina terminalis, which is excluded from the blood–brain barrier and is thus affected by systemic osmolality. Vasopressin is synthesized in the cell bodies of the magnocellular neurons located in the PVN and SON. The magnocellular neurons of the SON are directly depolarized by hypertonic conditions (hence releasing more vasopressin) and hyperpolarized by hypotonic conditions (hence releasing less vasopressin). Finally, vasopressin migrates (in its prohormone state) along the supraoptic–hypophyseal tract to the posterior pituitary, where it is released into the circulation. Used by permission from Chest .