Summation of Basic Endocrine Data
George H. Gass, Harold M. Kaplan in 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
Paul V. Malven in 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.
ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
Neural mechanisms. There are three essential signals to brain that stimulate drinking. Volumetric thirst is signalled (1) via atrial baroreceptors (which transmit via the VAGUS NERVE to the NUCLEUS OF THE SOLITARY TRACT in the MEDULLA) and (2) by angiotensin II (which has an action on the AREA POSTREMA [which is intimately connected to the nucleus of the solitary tract] and SUBFORNICAL ORGAN, two CIRCUMVENTRICULAR ORGANS); osmometric thirst is be signaled by (3) OSMORECEPTORS. Osmoreceptors are neurons in the brain whose firing rate is affected by their level of hydration. Their precise location is still uncertain: osmoreceptors were not identified and named, but were predicted by theories of osmoregulation. It seems likely that the circumventricular organs (in this case the ORGANUM VASCULOSUM OF THE LAMINA TERMINALIS) are critically involved.
Genetic identification of preoptic neurons that regulate body temperature in mice
Published in Temperature, 2022
Natalia L. S. Machado, Clifford B. Saper
A second clue came from the literature on fever caused by either lipopolysaccharide or prostaglandin E2. Studies in mice reported that these fever responses were critically dependent upon the expression of the prostaglandin E type 3 (EP3R) receptor by neurons in the preoptic area [12]. These neurons cluster in the MnPO along the along the midline of the ventral part of the preoptic area; as the 3rd ventricle begins to open, they invade the organum vasculosum of the lamina terminalis (OVLT) at the rostral tip of the third ventricle and spill over the lateral margins of the 3rd ventricle at this level (Figure 1). This population also includes neurons along the dorsal surface of the optic chiasm and extending as far as the ventrolateral part of the preoptic area (VLPO). The location of this population of neurons coincides almost precisely with the projection from the parabrachial prodynorophin population [10,13,14].
Tetraventricular hydrocephalus with aqueductal flow void: an overlooked entity having consistent improvement following endoscopic third ventriculostomy
Published in British Journal of Neurosurgery, 2023
Sushanta K. Sahoo, Sivashanmugam Dhandapani, Chirag K. Ahuja
The CT scan showed dilatation of lateral, third and fourth ventricle in all the patients. MR images showed features of hydrocephalus, rounded frontal horn, enlarged third ventricular recess, Evan’s ratio >3 in all patients (Figure 1(A–C)). Heavily T2W sagittal image showed grade 4 flow void across the cerebral aqueduct in 9 and grade 3 flow void in 2 patients (Figures 1(C) and 2(C)). There was ballooning of the fourth ventricle with cerebellar tonsillar herniation in four patients (Figures 1(C) and 2(C)). In two a membrane out pouching through the fourth ventricular outlet into the spinal subarachnoid space could be appreciated (Figure 3(A)). Additionally, outward bulging of floor of third ventricle, pineal recess and lamina terminalis were detected in eight patients suggestive of intra-extra ventricular pressure gradient. Three of them showed bulging of prepontine membrane on T2 sagittal MRI. Quantitative CSF flow study performed in two patients (cases 2,3) showed hyperdynamic flow at the level of cerebral aqueduct. None of these patients had any features of Dandy walker malformation or Blake’s pouch cyst on radiology.
Effect of Chronic Intermittent Hypoxia on Angiotensin II Receptors in the Central Nervous System
Published in Clinical and Experimental Hypertension, 2019
Barbara J. Morgan, Nicole Schrimpf, Morgan Rothman, Ann Mitzey, Mark S. Brownfield, Robert C. Speth, John M. Dopp
In rodent models of sleep apnea, intermittent hypoxia applied for several hours per day evokes increases in basal sympathetic outflow, sympathetic and ventilatory responsiveness to chemoreceptor stimulation, and blood pressure that are evident not only during exposures but also during the intervening normoxic periods (8,13,37,38). Several lines of evidence indicate that central AT1R and AT2R play important roles in producing these “carryover” effects. First, CIH-induced hypertension can be attenuated by intracerebroventricular administration of the AT1R antagonist losartan, an intervention that also reduced expression of FosB/ΔFosB in the organum vasculosum of the lamina terminalis, subfornical organ, median preoptic nucleus, nucleus of the solitary tract, RVLM, and dorsal and medial parvocellular subnuclei of the PVN (5). In addition, viral-mediated delivery of short hairpin RNA to knockdown angiotensin converting enzyme-1 in the median pre-optic nucleus of the hypothalamus (6) and AT1R in the subfornical organ (7) greatly attenuates the hypertensive response to CIH. Finally, systemic administration of losartan prevented CIH-induced increases in basal sympathetic nerve activity, chemoreflex-induced sympathoexcitation and hyperventilation, and blood pressure (3,8,38).
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