Circumventricular organs

Circumventricular organs
Diagram showing locations of the circumventricular organs
Identifiers
MeSHD066280
NeuroLex IDnlx_anat_20090312
FMA84081
Anatomical terms of neuroanatomy


Circumventricular organs (CVOs) (circum-: around ; ventricular: of ventricle) are structures in the brain characterized by their extensive and highly permeable capillaries, unlike those in the rest of the brain where there exists a blood–brain barrier (BBB) at the capillary level.[1][2][3][4] Although the term "circumventricular organs" was originally proposed in 1958 by Austrian anatomist Helmut O. Hofer concerning structures around the brain ventricular system,[5] the penetration of blood-borne dyes into small specific CVO regions was discovered in the early 20th century.[6] The permeable CVOs enabling rapid neurohumoral exchange include the subfornical organ (SFO), the area postrema (AP), the vascular organ of lamina terminalis (VOLT — also known as the organum vasculosum of the lamina terminalis (OVLT)), the median eminence, the pituitary neural lobe, and the pineal gland.[1][7]

The circumventricular organs are midline structures around the third and fourth ventricles that are in contact with blood and cerebrospinal fluid, and they facilitate special types of communication between the central nervous system and peripheral blood.[1][8][9] Additionally, they are an integral part of neuroendocrine function.[10][11] Highly permeable capillaries allow the CVOs to act as an alternative route for peptides and hormones in the neural tissue to sample from and secrete to circulating blood.[1][12][13] CVOs also have roles in body fluid regulation, cardiovascular functions, immune responses, thirst, feeding behavior and reproductive behavior.[1][7]

CVOs can be classified as either sensory or secretory organs serving homeostatic functions and body water balance.[3][7] The sensory organs include the area postrema, the subfornical organ, and the vascular organ of lamina terminalis, all having the ability to sense signals in blood, then pass that information neurally to other brain regions. Through their neural circuitry, they provide direct information to the autonomic nervous system from the systemic circulation.[1][10][14][15] The secretory organs include the subcommissural organ (SCO), the pituitary gland, the median eminence, and the pineal gland.[7][11] These organs are responsible for secreting hormones and glycoproteins into the peripheral blood using feedback from both the brain environment and external stimuli.[7]

Circumventricular organs contain capillary networks that vary between one another and within individual organs both in density and permeability, with most CVO capillaries having a permeable endothelial cell layer, except for those in the subcommissural organ.[1][16] Furthermore, all CVOs contain neural tissue, enabling a neuroendocrine role.

Although the choroid plexus also has permeable capillaries, it does not contain neural tissue; rather, its primary role is to produce cerebrospinal fluid (CSF), and therefore is typically not classified as a CVO.[1]

  1. ^ a b c d e f g h Gross PM, Weindl A (1987). "Peering through the windows of the brain (Review)". Journal of Cerebral Blood Flow and Metabolism. 7 (6): 663–72. doi:10.1038/jcbfm.1987.120. PMID 2891718.
  2. ^ Gross, P. M (1992). "Chapter 31: Circumventricular organ capillaries". Circumventricular Organs and Brain Fluid Environment - Molecular and Functional Aspects. Progress in Brain Research. Vol. 91. pp. 219–33. doi:10.1016/S0079-6123(08)62338-9. ISBN 9780444814197. PMID 1410407.
  3. ^ a b Fry, W.M.; Ferguson, A.V. (2009). "Circumventricular Organs". Encyclopedia of Neuroscience. Elsevier. pp. 997–1002. doi:10.1016/b978-008045046-9.00462-9. ISBN 978-0-08-045046-9. Neurons in the sensory CVOs are ideally positioned at the blood–brain interface to monitor major constituents of body fluids.
  4. ^ Kaur, C; Ling, EA (September 2017). "The circumventricular organs". Histology and Histopathology. 32 (9): 879–892. doi:10.14670/HH-11-881. PMID 28177105.
  5. ^ Hofer H (1958). "Zur Morphologie der circumventriculären Organe des Zwischenhirns der Säugetiere". Verhandlungen der Deutschen Zoologischen Gesellschaft. 55: 202–251.
  6. ^ Wislocki, George B.; King, Lester S. (1936). "The permeability of the hypophysis and hypothalamus to vital dyes, with a study of the hypophyseal vascular supply". American Journal of Anatomy. 58 (2): 421–472. doi:10.1002/aja.1000580206. ISSN 0002-9106.
  7. ^ a b c d e Gross PM, ed. (1987). Circumventricular Organs and Body Fluids, Volumes I-III. CRC Press, Inc. p. 688. ISBN 978-0849367984.
  8. ^ Johnson, AK; Gross, PM (May 1993). "Sensory circumventricular organs and brain homeostatic pathways". FASEB Journal. 7 (8): 678–86. doi:10.1096/fasebj.7.8.8500693. PMID 8500693. S2CID 13339562.
  9. ^ Sisó, S; Jeffrey, M; González, L (December 2010). "Sensory circumventricular organs in health and disease". Acta Neuropathologica. 120 (6): 689–705. doi:10.1007/s00401-010-0743-5. PMID 20830478. S2CID 33549996.
  10. ^ a b Fry M, Ferguson AV (2007). "The sensory circumventricular organs: Brain targets for circulating signals controlling ingestive behavior". Physiology & Behavior. 91 (4): 413–423. doi:10.1016/j.physbeh.2007.04.003. PMID 17531276. S2CID 28981416.
  11. ^ a b Cottrell G. T.; Ferguson A. V. (2004). "Sensory circumventricular organs: Central roles in integrated autonomic regulation". Regulatory Peptides. 117 (1): 11–23. doi:10.1016/j.regpep.2003.09.004. PMID 14687696. S2CID 32634974.
  12. ^ Rodríguez Esteban M.; Blázquez Juan L.; Guerra Montserrat (2010). "The design of barriers in the hypothalamus allows the median eminence and the arcuate nucleus to enjoy private milieus: The former opens to the portal blood and the latter to the cerebrospinal fluid". Peptides. 31 (4): 757–76. doi:10.1016/j.peptides.2010.01.003. PMID 20093161. S2CID 44760261.
  13. ^ Morita S.; Miyata S. (2012). "Different vascular permeability between the sensory and secretory circumventricular organs of adult mouse brain". Cell and Tissue Research. 349 (2): 589–603. doi:10.1007/s00441-012-1421-9. PMID 22584508. S2CID 15228158.
  14. ^ Ferguson A. V.; Bains J. S. (1996). "Electrophysiology of the circumventricular organs". Frontiers in Neuroendocrinology. 17 (4): 440–475. doi:10.1006/frne.1996.0012. PMID 8905349. S2CID 27242916.
  15. ^ Zimmerman, CA; Leib, DE; Knight, ZA (August 2017). "Neural circuits underlying thirst and fluid homeostasis". Nature Reviews. Neuroscience. 18 (8): 459–469. doi:10.1038/nrn.2017.71. PMC 5955721. PMID 28638120.
  16. ^ Duvernoy HM, Risold P-Y (2007). "The circumventricular organs: An atlas of comparative anatomy and vascularization". Brain Research Reviews. 56 (1): 119–147. doi:10.1016/j.brainresrev.2007.06.002. PMID 17659349. S2CID 43484965.