Морфологічні структури циркумвентрикулярного комплексу (Morphological structures of the circumvetricular complex)

Abstract

Brain homeostasis requires the maintenance of barriers between the brain and the periphery, which are provided by brain microvessels in the blood-brain barrier and epithelial cells in the choroid plexus. Circumventricular complex (CVC) – structures located around the third and fourth ventricles, lining the cavity of the third ventricle (neurohypophysis, vascular organ of the end plate, epiphysis, subvault and subcommissural organs) and the fourth ventricle (posterior region), different from other structures of the brain due to the maximum vascularization and the absence of a typical blood-brain barrier. The subcommissural organ and the area postrema are located at the confluence between the ventricles, while the neurohypophysis, the vascular organ of the terminal plate, and the pineal gland line the ventricular depressions. All structures of the central nervous system are divided into sensory and secretory. Vessels in the CVC branch into a network of fenestrated capillaries with loosely connected astrocytic ends, which allows them to be considered as gates» to the brain; substances are transported by blood and freely leave the capillary lumen. Neurons and glial cells of the CVC form a unique symbiosis of receptors and ion channels, receiving chemical signals from the bloodstream. CVCs are described as the «windows of the brain» that form the blood-CSF barrier on the ventricular wall, which is composed of tanycyte-like cells that line the ventricular ependyma. Astrocytes and tanycytes form a dense barrier in the distal part of the CVC, preventing the free diffusion of the molecules obtained. from the blood to the neighboring areas of the brain. The barrier in front of the fenestrated vessels of the CVC may limit molecules carried by the blood through these «windows of the brain» and prevent their diffusion into the cerebrospinal fluid. In the central nervous system, connections between the central nervous system and peripheral blood flow serve as an alternative route for peptides and hormones of nervous tissue into the bloodstream, primarily performing neuroimmune-endocrine functions, as well as the role of an «immune watchman». Key words: circumventricular complex, cerebrospinal fluid, brain, blood-brain barrier.