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Summation of Basic Endocrine Data
Published in George H. Gass, Harold M. Kaplan, Handbook of Endocrinology, 2020
Their importance is that they lack a blood-brain barrier and contain fenestrated capillaries which permit neurons to receive substances, including certain hormones, to pass directly between the blood and the brain. Thus, the subfornical organ monitors angiotensin-II levels and projects into the hypothalamus. The area postrema monitors cholecystokinin and projects by lower nuclei to the hypothalamus. The organum vasculosum of the lamina terminalis monitors cytokines in the blood and projects to the brain stem and hypothalamus. The median eminence, pineal gland, and pituitary gland, all of which lack a blood-brain barrier, secrete their own hormones from the central nervous system into the general circulation. Some brain circumventricular organs recognize cytokines in the blood, and if the cytokines are transmitted to the brain, they contribute to the production of fever.2
Neural Control of Adenohypophysis
Published in Paul V. Malven, Mammalian Neuroendocrinology, 2019
The median eminence is just one of several unique structures in the brain known as circumventricular organs (CVO). These organs, which are also called neurohemal structures, share a common vascular and ependymal organization, which is different from the rest of the brain. As the name denotes, these organs are all located adjacent to some part of a cerebral ventricle. The capillaries in circumventricular organs have a characteristic fenestrated endothelium that probably accounts for the blood-brain barrier being less restrictive in these organs than in most brain tissue. Circumventricular organs are also unique in that their ependymal cells are non-ciliated, whereas ependymal cells in most other regions are ciliated. The diagram in Figure 4-4 shows the location of four different circumventricular organs including the median eminence. The organum vasculosum of the lamina terminalis (OVLT) is located around the rostral projection of the third ventricle above the optic chiasma. The subfornical organ is located on the midline beneath the descending fornix and in contact with the choroid plexus of the third ventricle. The subcommissural organ lines the roof of the third ventricle beneath the posterior commissure and habenula. The three circumventricular organs not illustrated in Figure 4-4 are pars nervosa, pineal gland, and area postrema. The first two of these are covered in detail in Chapters 3 and 10, respectively. The area postrema is located in the roof of the fourth ventricle caudal to the cerebellum.
Cardiovascular responses in pathological situations
Published in Neil Herring, David J. Paterson, Levick's Introduction to Cardiovascular Physiology, 2018
Neil Herring, David J. Paterson
The above responses preserve cardiac and cerebral perfusion over the short term in compensated shock. Over the following days to weeks the lost water, salts, plasma proteins and red cells are gradually made good. First, the water and salt deficits are corrected through increased fluid intake and reduced renal excretion. Glomerular filtration rate is reduced by a sympa- thetic-mediated contraction of the afferent arterioles. Salt and water reabsorption are stimulated by circulating aldosterone and vasopressin. Circulating angiotensin II stimulates not only aldosterone secretion but also thirst, by activating the subfornical organ of the brain. The increase in water intake, coupled with oliguria, quickly replenishes body water mass. The normal dietary intake of 2-10 g salt per day, along with renal salt retention, restores body salt mass in a few days.
Salt-induced phosphoproteomic changes in the subfornical organ in rats with chronic kidney disease
Published in Renal Failure, 2023
Xin Wang, Huizhen Wang, Jiawen Li, Lanying Li, Yifan Wang, Aiqing Li
As a circumventricular organ, subfornical organ (SFO) locates at the caudal of the foramen of Monroe at the confluence of lateral ventricles to the third ventricle. It has a highly vascularized core lacking a blood-brain barrier and possesses a dense population of ion channels and hormone receptors. These properties allow SFO to directly detect the factors in cerebrospinal fluid (CSF) and blood, such as Na+, Ang II, and aldosterone [6–8]. For example, Nax channel expressed explicitly in the glial cells of SFO and organum vasculosum lamina terminalis (OVLT) as the most characterized brain [Na+] sensor [9,10]. SFO detects changes in [Na+] within physiological ranges and relays this information to other brain loci to control body fluid homeostasis [11,12]. Nomura et al. recently discovered that Nax signals activated by high salt in OVLT are transmitted via OVLT-paraventricular nucleus(PVN)-rostral ventral lateral medulla(RVLM) neural pathway to enhance sympathetic nerve activity(SNA) and blood pressure(BP) [13]. Thus, in salt-induced hypertension, Nax-positive glial cells in SFO are likely to detect [Na+] and relay the signal to other nuclei. Of course, more research is required to test this speculation.
Basic physiology of the blood-brain barrier in health and disease: a brief overview
Published in Tissue Barriers, 2021
In contrast to the capillaries located in the brain parenchyma, blood microvessels in the circumventricular organs do not display barrier properties. The endothelial cells of these microvessels have fenestrae, which allow the free diffusion of substances between the blood and CNS.37,213,214 These organs consist of secretory structures like pineal gland, subcommisural organ, median eminence, and choroid plexuses and sensory regions, including area postrema, subfornical organ, and organum vasculosum of the lamina terminalis.215 The exchange of hormones and other molecules between the circulation and CNS is accomplished mainly in circumventricular organs in which increased vascularization facilitates the sensory and secretory roles to mediate the communication between the brain and the periphery.215,216
Mechanisms involved in the cardiovascular effects caused by acute osmotic stimulation in conscious rats
Published in Stress, 2020
Eduardo Albino Trindade Fortaleza, Cristiane Busnardo, Aline Fassini, Ivaldo Jesus Almeida Belém-Filho, Gislaine Almeida-Pereira, José Antunes-Rodrigues, Fernando Morgan Aguiar Corrêa
Hypertonic stimulus evokes activation of magnocellular neurons in the SON and PVN nuclei that receive projections from areas involved in the osmoreceptor pathway that regulates body fluid balance, such as the subfornical organ, the organum vasculosum of the lamina terminalis and median preoptic nucleus, as well as limbic structures such as the medial nucleus of the amygdala that sends and receives projections from SON and PVN (Fortaleza, Scopinho, & Correa, 2012b; Fortaleza, Tavares, & Correa, 2009; Kremarik, Freund-Mercier, & Stoeckel, 1993; Larsen & Mikkelsen, 1995; Xiong & Hatton, 1996). Notably, the hypertonic stimulus is a potent releaser of AVP from the posterior pituitary (Dunn et al., 1973; Larsen & Mikkelsen, 1995; Onaka & Yagi, 2001; Shoji et al., 1994; Verney, 1947; Zemo & McCabe, 2002).