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 [95].

Vasopressin docking and transmembrane topology of the human V₁ vascular receptor (V₁R). A model of arginine vasopressin (AVP), as bound to the human V₁R, is depicted. Vasopressin is shown in ball-and-stick representation and the receptor is shown in ribbons. The intracellular loops of the receptor are labeled il1, il2, and il3, and the extracellular loops are labeled el1, el2, and el3. The transmembrane segments are labeled H1–H7. Reprinted from Thibonnier M, Coles P, Thibonnier A, Shoham M: Molecular pharmacology and modeling of vasopressin receptors. Prog Brain Res 2002, 139:179–196. © 2002, with permission from Elsevier [96].