Circumventricular organs

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Circumventricular organs (CVO) are specialised sites in the brain, positioned at sites around the margin of the ventricular system, which have an incomplete blood-brain barrier. [1]

Two of these sites, the median eminence and the posterior pituitary gland, are sites of neurosecretion: neuroendocrine neurons whose cell bodies are within the hypothalamus project axons to these sites to secrete their hormonal products directly into the blood. Three other sites, the subfornical organ, and the organum vasculosum of the lamina terminalis (OVLT) adjacent to the third ventricle and the area postrema at the base of the fourth ventricle contain neurons specialised to detect blood-borne substances [2]. The subfornical organ and OVLT contain some osmosensitive neurons, and other neurons that detect a wide range of blood-borne peptides whose actions influence body fluid and electrolyte homeostasis in particular. These peptides include angiotensin, endothelin, atrial natriuretic factor, and relaxin. [3] The pineal gland \- secretes the hormone melatonin and is associated with circadian rhythms.[4] The area postrema is intimately connected with the underlying nucleus tractus solitarii and senses, amongst other things, peptides and hormones related to energy intake and utilisation. [5]

The choroid plexuses are structures specialised to import blood-borne factors such as leptin across the blood-brain barrier.[6]

The subcommissural organ is a phylogenetically ancient and conserved glandular structure formed by ependymal and hypendymal cells highly specialized in the secretion of proteins. The ependymal cells secrete various proteins into the cerebrospinal fluid; its physiological function is still unknown. [7]

## References[edit]

1. ↑ Ganong WF (2000) Circumventricular organs: definition and role in the regulation of endocrine and autonomic function. Clin Exp Pharmacol Physiol 27:422-7. PMID 10831247
2. ↑ Ferguson AV, Bains JS (1996) Electrophysiology of the circumventricular organs. Front Neuroendocrinol 17:440-75. PMID 8905349
3. ↑ Fry M, Ferguson AV (2007) The sensory circumventricular organs: brain targets for circulating signals controlling ingestive behavior. Physiol Behav 91:413-23. PMID 17531276
4. ↑ Maronde E, Stehle JH (2007) The mammalian pineal gland: known facts, unknown facets. Trends Endocrinol Metab 18:142-9. PMID 17374488
5. ↑ Wren AM (2008) Gut and hormones and obesity.  Front Horm Res 36:165-81. PMID 18230902
6. ↑ Redzic ZB et al. (2005) The choroid plexus-cerebrospinal fluid system: from development to aging. Curr Top Dev Biol 71:1-52. PMID 16344101
7. ↑ Rodríguez EM et al. (1998) The subcommissural organ. Microsc Res Tech 41:98-123. PMID 9579598