Schematic of central regulation of body fluid regulation in response to acute changes in sodium and volume
Schematic of central regulation of body fluid regulation in response to acute changes in sodium and volume. The OVLT (organum vasculosum of the lamina terminalis) is a circumventricular organ located outside the blood-brain barrier (BBB), in the anteroventral part of the third ventricle that is an essential component of the osmotic thirst sensation pathway. Osmotic information from the OVLT is transmitted neurally to the hypothalamus and ultimately results in thirst, drinking, and arginine vasopressin (AVP) release. The median preoptic nucleus (NM) is responsible for initiating drinking in response to volumetric and angiotensinergic thirst stimulation. Through these mechanisms, the NM is used by both the subfornical organ (SFO) and the nucleus of the solitary tract (NTS), structures at the center of sodium appetite and thirst regulation. Changes in volume are initiated by the kidneys and stimulated by angiotensin outside the BBB. The SFO sends a message across the BBB to the NM, which then initiates volumetrically controlled thirst and drinking responses. Atrial baroreceptors also send a signal to the NTS. In addition to stimulating thirst, angiotensin stimulates the SFO and causes fluid regulating hormones to be secreted by the pituitary and adrenal glands, increases blood pressure, and eventually causes the kidney to stop secreting sodium and water, which, in turn, decreases both salt appetite and water intake. The paraventricular (PVN) and supraoptic nuclei (SON), both located in the hypothalamus, signal the release of AVP by the posterior pituitary. Thus both the PVN and SON also represent important structures involved in the control of water and sodium regulation because AVP has powerful effects upon both blood pressure and free water retention. Finally, the anterior cingulate cortex is involved in the relay of neural signals between the right and left hemispheres of the brain. This part of the brain is important for decision-making and plays an important role in sensing thirst and initiating drinking (). Figure 1 by G.W. Mack (with permission). (Reprinted from Denton, D., R. Shade, F. Zamarippa, et al .Correlation of regional cerebral blood flow and change of plasma sodium concentration during genesis and satiation of thirst. Proc. Natl. Acad. Sci. U. S. A. 96:2532–2537, 1999. Copyright © 1999 National Academy of Sciences. Used with permission.)
