Fig. 34.Schematic drawing of the major pathways involved in regulation of vasopressin secretion. Information about osmolality is relayed to the hypothalamus largely through osmoreceptor cells in the organum vasculosum of the lamina terminalis (OVLT), subfornical organ (SFO) and medial preoptic nucleus (MnPO). Baroregulatory information is carried to magnocellular neurons in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) largely by direct afferent projections from the brainstem including the bed nucleus of the stria terminalis (NST) and ventrolateral medulla (VLM) using catecholamines as its neurotransmitter, or indirectly through the parabrachial nucleus (PBN). Vasopressin secretion can also be stimulated by activation of the chemoreceptor trigger zone in the area postrema (AP). (Adapted from Stricker and Verbalis, Fundamental Neuroscience, ch 42, pp 1111-1126, 1999.)