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Concept
Area postrema
Résumé
The area postrema, a paired structure in the medulla oblongata of the brainstem, is a circumventricular organ having permeable capillaries and sensory neurons that enable its dual role to detect circulating chemical messengers in the blood and transduce them into neural signals and networks. Its position adjacent to the bilateral nuclei of the solitary tract and role as a sensory transducer allow it to integrate blood-to-brain autonomic functions. Such roles of the area postrema include its detection of circulating hormones involved in vomiting, thirst, hunger, and blood pressure control.
The area postrema is a paired protuberance found at the inferoposterior limit of the fourth ventricle. Specialized ependymal cells are found within the area postrema. These cells differ slightly from the majority of ependymal cells (ependymocytes), forming a unicellular epithelial lining of the ventricles and central canal. The area postrema is separated from the vagal trigone by the funiculus separans, a thin semitransparent ridge. The vagal trigone overlies the dorsal vagal nucleus and is situated on the caudal end of the rhomboid fossa or 'floor' of the fourth ventricle. The area postrema is situated just before the obex, the inferior apex of the caudal ventricular floor. Both the funiculus separans and area postrema have a similar thick ependyma-containing tanycyte covering. Ependyma and tanycytes can participate in the transport of neurochemicals into and out of the cerebrospinal fluid from its cells or adjacent neurons, glia or vessels. Ependyma and tanycytes may also participate in chemoreception.
The area postrema is considered a circumventricular organ because of its proximity to the ventricular system. In a morphological study, area postrema capillaries in the ventral subregion of area postrema were shown to be relatively impermeable like those of the brain, whereas medial and dorsal area postrema capillaries had microscopic characteristics of high permeability, a characteristic called sinusoidal.
Source officielle
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