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factoids

The pineal gland (also known as the pineal body or epiphysis cerebri) is a small endocrine gland in the brain of most vertebrates. In the darkness the pineal gland produces melatonin, a serotonin-derived hormone, which modulates sleep patterns following the diurnal cycles.JOURNAL, Reiter, R. J., November 1991, Neuroendocrine effects of light, International Journal of Biometeorology, 35, 3, 169–175, 10.1007/BF01049063, 0020-7128, 1778647, The shape of the gland resembles a pine cone, which gives it its name.WEB, Pineal (as an adjective),www.etymonline.com/word/pineal, Online Etymology Dictionary, Douglas Harper, 27 October 2018, 2018, The pineal gland is located in the epithalamus, near the center of the brain, between the two hemispheres, tucked in a groove where the two halves of the thalamus join.JOURNAL, Macchi MM, Bruce JN, Human pineal physiology and functional significance of melatonin, Frontiers in Neuroendocrinology, 25, 3–4, 177–195, 2004, 15589268, 10.1016/j.yfrne.2004.08.001, 26142713, JOURNAL, Arendt J, Skene DJ, Melatonin as a chronobiotic, Sleep Medicine Reviews, 9, 1, 25–39, February 2005, 15649736, 10.1016/j.smrv.2004.05.002, Exogenous melatonin has acute sleepiness-inducing and temperature-lowering effects during ‘biological daytime’, and when suitably timed (it is most effective around dusk and dawn) it will shift the phase of the human circadian clock (sleep, endogenous melatonin, cortisol) to earlier (advance phase shift) or later (delay phase shift) times., It is one of the neuroendocrine secretory circumventricular organs in which capillaries are mostly permeable to solutes in the blood.JOURNAL, Gross PM, Weindl A, Peering through the windows of the brain, Journal of Cerebral Blood Flow and Metabolism, 7, 6, 663–672, December 1987, 2891718, 10.1038/jcbfm.1987.120, 18748366, free, The pineal gland is present in almost all vertebrates, but is absent in protochordates in which there is a simple pineal homologue. The hagfish, considered as a primitive vertebrate, has a rudimentary structure regarded as the “pineal equivalent” in the dorsal diencephalon.JOURNAL, Ooka-Souda S, Kadota T, Kabasawa H, The preoptic nucleus: the probable location of the circadian pacemaker of the hagfish, Eptatretus burgeri, Neuroscience Letters, 164, 1–2, 33–36, December 1993, 8152610, 10.1016/0304-3940(93)90850-K, 40006945, In some species of amphibians and reptiles, the gland is linked to a light-sensing organ, variously called the parietal eye, the pineal eye or the third eye.BOOK, Eakin RM, The Third Eye, University of California Press, 1973, Berkeley, Richard M. Eakin, Reconstruction of the biological evolution pattern suggests that the pineal gland was originally a kind of atrophied photoreceptor that developed into a neuroendocrine organ.Ancient Greeks were the first to notice the pineal gland and believed it to be a valve, a guardian for the flow of pneuma. Galen in the 2nd century C.E. could not find any functional role and regarded the gland as a structural support for the brain tissue. He gave the name konario, meaning cone or pinecone, which during Renaissance was translated to Latin as pinealis. The 17th century philosopher René Descartes regarded the gland as having a mystical purpose, describing it as the “principal seat of the soul”. In the mid-20th century, the real biological role as a neuroendocrine organ was established.WEB, Lokhorst GJ, Descartes and the Pineal Gland; In: The Stanford Encyclopedia of Philosophy, 2018,plato.stanford.edu/archives/win2018/entries/pineal-gland/, Zalta EN, Winter 2018, Metaphysics Research Lab, Stanford University, 2019-12-17,

Etymology

The word pineal, from Latin pinea (pine-cone) in reference to the gland’s similar shape, was first used in the late 17th century.

Structure

The pineal gland is a pine cone-shaped (hence the name), unpaired midline brain structure.WEB, Bowen R, The Pineal Gland and Melatonin,www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/pineal.html, 14 October 2011, live,www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/pineal.html," title="web.archive.org/web/20111124190231www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/pineal.html,">web.archive.org/web/20111124190231www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/pineal.html, 24 November 2011, dmy-all, It is reddish-gray in colour and about the size of a grain of rice (5–8 mm) in humans. It forms part of the epithalamus. It is attached to the rest of the brain by a pineal stalk.BOOK, Waxman SG, Clinical Neuroanatomy, McGraw-Hill Medical, 2009, 978-0-07-160399-7, 26th, New York, 127, The ventral lamina of the pineal stalk is continuous with the posterior commissure, and its dorsal lamina with the habenular commissure.

Location

It normally lies in a depression between the two superior colliculi. It is situated between the laterally positioned thalamic bodies, and posterior to the habenular commissure. It is located in the quadrigeminal cistern.JOURNAL, Chen CY, Chen FH, Lee CC, Lee KW, Hsiao HS, Sonographic characteristics of the cavum velum interpositum, AJNR. American Journal of Neuroradiology, 19, 9, 1631–1635, October 1998, 9802483, 8337493,www.ajnr.org/content/19/9/1631.full.pdf, It is located posterior to the third ventricle and encloses the small, cerebrospinal fluid-filled pineal recess of the third ventricle which projects into the stalk of the gland.BOOK, Dorland’s, Illustrated Medical Dictionary, 2 May 2011, Elsevier Saunders, 978-1-4160-6257-8, 1607,

Blood supply

Unlike most of the mammalian brain, the pineal gland is not isolated from the body by the blood–brain barrier system;BOOK, Pritchard TC, Alloway KD, Medical Neuroscience,books.google.com/books?id=m7Y80PcFHtsC, Google books preview, 2009-02-08, 1999, Hayes Barton Press, 978-1-889325-29-3, 76–77, it has profuse blood flow, second only to the kidney,Arendt J: Melatonin and the Mammalian Pineal Gland, ed 1. London. Chapman & Hall, 1995, p 17 supplied from the choroidal branches of the posterior cerebral artery.

Afferents

The afferent nerve suppy of pineal gland is by the nervus conarii which receives postganglionic sympathetic afferents from the superior cervical ganglion, and parasympathetic afferents from the pterygopalatine ganglia and otic ganglia.JOURNAL, Møller M, Baeres FM, The anatomy and innervation of the mammalian pineal gland, Cell and Tissue Research, 309, 1, 139–150, July 2002, 12111544, 10.1007/s00441-002-0580-5, 25719864, JOURNAL, Møller M, Baeres FM, PACAP-containing intrapineal nerve fibers originate predominantly in the trigeminal ganglion: a combined retrograde tracing- and immunohistochemical study of the rat, Brain Research, 984, 1–2, 160–169, September 2003, 12932850, 10.1016/s0006-8993(03)03127-5, 40328108, According to research on animals, neurons of the trigeminal ganglion that are involved in pituitary adenylate cyclase-activating peptide neuropeptide signaling project the gland.JOURNAL, Liu W, Møller M, Innervation of the rat pineal gland by PACAP-immunoreactive nerve fibers originating in the trigeminal ganglion: a degeneration study, Cell and Tissue Research, 301, 3, 369–373, September 2000, 10994782, 10.1007/s004410000251, 5763932,

Neural pathway for melatonin production

The canonical neural pathway regulating pineal melatonin production begins in the eye with the intrinsically photosensitive ganglion cells of the retina which project inhibitory GABAergic efferents to the paraventricular nucleus of hypothalamus via the retinohypothalamic tract. The paraventricular nucleus in turn projects to the superior cervical ganglia, which finally projects to the pineal gland. Darkness thus leads to disinhibition of the paraventricular nucleus, leading it to activate pineal gland melatonin production by way of the superior cervical ganglia.JOURNAL, Tonon AC, Pilz LK, Markus RP, Hidalgo MP, Elisabetsky E, Melatonin and Depression: A Translational Perspective From Animal Models to Clinical Studies, Frontiers in Psychiatry, 12, 638981, 2021-04-08, 33897495, 8060443, 10.3389/fpsyt.2021.638981, free,

Microanatomy

(File:Pineal.jpg|thumb|Pineal gland parenchyma with calcifications)File:Pineal gland - very high mag.jpg|thumb|150px|MicrographMicrographFile:Pineal gland - intermed mag.jpg|thumb|150px|MicrographMicrographThe pineal body in humans consists of a lobular parenchyma of pinealocytes surrounded by connective tissue spaces. The gland’s surface is covered by a pial capsule.The pineal gland consists mainly of pinealocytes, but four other cell types have been identified. As it is quite cellular (in relation to the cortex and white matter), it may be mistaken for a neoplasm.JOURNAL, Kleinschmidt-DeMasters BK, Prayson RA, An algorithmic approach to the brain biopsy--part I, Archives of Pathology & Laboratory Medicine, 130, 11, 1630–1638, November 2006, 17076524, 10.5858/2006-130-1630-AAATTB, {| class=“wikitable”! Cell type !! Description

Development

The human pineal gland grows in size until about 1–2 years of age, remaining stable thereafter,JOURNAL, Schmidt F, Penka B, Trauner M, Reinsperger L, Ranner G, Ebner F, Waldhauser F, Lack of pineal growth during childhood, The Journal of Clinical Endocrinology and Metabolism, 80, 4, 1221–1225, April 1995, 7536203, 10.1210/jcem.80.4.7536203, JOURNAL, Sumida M, Barkovich AJ, Newton TH, Development of the pineal gland: measurement with MR, AJNR. American Journal of Neuroradiology, 17, 2, 233–236, February 1996, 8938291, 8338352, although its weight increases gradually from puberty onwards.JOURNAL, Tapp E, Huxley M, The weight and degree of calcification of the pineal gland, The Journal of Pathology, 105, 1, 31–39, September 1971, 4943068, 10.1002/path.1711050105, 38346296, JOURNAL, Tapp E, Huxley M, The histological appearance of the human pineal gland from puberty to old age, The Journal of Pathology, 108, 2, 137–144, October 1972, 4647506, 10.1002/path.1711080207, 28529644, The abundant melatonin levels in children are believed to inhibit sexual development, and pineal tumors have been linked with precocious puberty. When puberty arrives, melatonin production is reduced.WEB,www.chronobiology.com/melatonin-chronobiology/melatonin-production-age/, Melatonin Production and Age, Chronobiology, Medichron Publications,

Symmetry

In the zebrafish the pineal gland does not straddle the midline, but shows a left-sided bias. In humans, functional cerebral dominance is accompanied by subtle anatomical asymmetry.JOURNAL, Snelson CD, Santhakumar K, Halpern ME, Gamse JT, Tbx2b is required for the development of the parapineal organ, Development, 135, 9, 1693–1702, May 2008, 18385257, 2810831, 10.1242/dev.016576, JOURNAL, Snelson CD, Burkart JT, Gamse JT, Formation of the asymmetric pineal complex in zebrafish requires two independently acting transcription factors, Developmental Dynamics, 237, 12, 3538–3544, December 2008, 18629869, 2810829, 10.1002/dvdy.21607, JOURNAL, Snelson CD, Gamse JT, Building an asymmetric brain: development of the zebrafish epithalamus, Seminars in Cell & Developmental Biology, 20, 4, 491–497, June 2009, 19084075, 2729063, 10.1016/j.semcdb.2008.11.008,

Function

One function of the pineal gland is to produce melatonin. Melatonin has various functions in the central nervous system, the most important of which is to help modulate sleep patterns. Melatonin production is stimulated by darkness and inhibited by light.JOURNAL, Axelrod J, The pineal gland, Endeavour, 29, 108, 144–148, September 1970, 4195878, JOURNAL, Lowrey PL, Takahashi JS, Genetics of the mammalian circadian system: Photic entrainment, circadian pacemaker mechanisms, and posttranslational regulation, Annual Review of Genetics, 34, 1, 533–562, 2000, 11092838, 10.1146/annurev.genet.34.1.533, Light sensitive nerve cells in the retina detect light and send this signal to the suprachiasmatic nucleus (SCN), synchronizing the SCN to the day-night cycle. Nerve fibers then relay the daylight information from the SCN to the paraventricular nuclei (PVN), then to the spinal cord and via the sympathetic system to superior cervical ganglia (SCG), and from there into the pineal gland.The compound pinoline is also claimed to be produced in the pineal gland; it is one of the beta-carbolines.JOURNAL, 10.1002/jhet.5570310231, The pictet-spengler reaction and biogenic tryptamines: Formation of tetrahydro-β-carbolines at physiologicalpH, 1994, Callaway JC, Gyntber J, Poso A, Airaksinen MM, Vepsäläinen J, Journal of Heterocyclic Chemistry, 31, 2, 431–435, This claim is subject to some controversy.{{citation needed|date=March 2023}}

Regulation of the pituitary gland

Studies on rodents suggest that the pineal gland influences the pituitary gland’s secretion of the sex hormones, follicle-stimulating hormone (FSH), and luteinizing hormone (LH). Pinealectomy performed on rodents produced no change in pituitary weight, but caused an increase in the concentration of FSH and LH within the gland.JOURNAL, Motta M, Fraschini F, Martini L, Endocrine effects of pineal gland and of melatonin, Proceedings of the Society for Experimental Biology and Medicine, 126, 2, 431–435, November 1967, 6079917, 10.3181/00379727-126-32468, 28964258, Administration of melatonin did not return the concentrations of FSH to normal levels, suggesting that the pineal gland influences pituitary gland secretion of FSH and LH through an undescribed transmitting molecule.The pineal gland contains receptors for the regulatory neuropeptide, endothelin-1,JOURNAL, Naidoo V, Naidoo S, Mahabeer R, Raidoo DM, Cellular distribution of the endothelin system in the human brain, Journal of Chemical Neuroanatomy, 27, 2, 87–98, May 2004, 15121213, 10.1016/j.jchemneu.2003.12.002, 39053816, which, when injected in picomolar quantities into the lateral cerebral ventricle, causes a calcium-mediated increase in pineal glucose metabolism.JOURNAL, Gross PM, Wainman DS, Chew BH, Espinosa FJ, Weaver DF, Calcium-mediated metabolic stimulation of neuroendocrine structures by intraventricular endothelin-1 in conscious rats, Brain Research, 606, 1, 135–142, March 1993, 8461995, 10.1016/0006-8993(93)91581-C, 12713010,

Regulation of bone metabolism

Studies in mice suggest that the pineal-derived melatonin regulates new bone deposition. Pineal-derived melatonin mediates its action on the bone cells through MT2 receptors. This pathway could be a potential new target for osteoporosis treatment as the study shows the curative effect of oral melatonin treatment in a postmenopausal osteoporosis mouse model.JOURNAL, Sharan K, Lewis K, Furukawa T, Yadav VK, Regulation of bone mass through pineal-derived melatonin-MT2 receptor pathway, Journal of Pineal Research, 63, 2, e12423, September 2017, 28512916, 5575491, 10.1111/jpi.12423,

Clinical significance

Calcification

Calcification of the pineal gland is typical in young adults, and has been observed in children as young as two years of age.JOURNAL, Zimmerman RA, Bilaniuk LT, Age-related incidence of pineal calcification detected by computed tomography, Radiology, 142, 3, 659–662, March 1982, 7063680, 10.1148/radiology.142.3.7063680,radiology.rsna.org/content/142/3/659.full.pdf, 21 June 2012, Radiological Society of North America, dead, vanc, dmy-all,radiology.rsna.org/content/142/3/659.full.pdf," title="web.archive.org/web/20120324050246radiology.rsna.org/content/142/3/659.full.pdf,">web.archive.org/web/20120324050246radiology.rsna.org/content/142/3/659.full.pdf, 24 March 2012, The internal secretions of the pineal gland are known to inhibit the development of the reproductive glands because when it is severely damaged in children, development of the sexual organs and the skeleton are accelerated.WEB,www.theodora.com/anatomy/the_pineal_body.html, The Pineal Body, Human Anatomy (Gray’s Anatomy), 2011-09-07, live,www.theodora.com/anatomy/the_pineal_body.html," title="web.archive.org/web/20110826052347www.theodora.com/anatomy/the_pineal_body.html,">web.archive.org/web/20110826052347www.theodora.com/anatomy/the_pineal_body.html, 26 August 2011, dmy-all, Pineal gland calcification is detrimental to its ability to synthesize melatoninJOURNAL, Kunz D, Schmitz S, Mahlberg R, Mohr A, Stöter C, Wolf KJ, Herrmann WM, A new concept for melatonin deficit: on pineal calcification and melatonin excretion, Neuropsychopharmacology, 21, 6, 765–772, December 1999, 10633482, 10.1016/S0893-133X(99)00069-X, 20184373, free, JOURNAL, Tan DX, Xu B, Zhou X, Reiter RJ, Pineal Calcification, Melatonin Production, Aging, Associated Health Consequences and Rejuvenation of the Pineal Gland, Molecules, 23, 2, 301, January 2018, 29385085, 6017004, 10.3390/molecules23020301, free, and scientific literature presents inconclusive findings on whether it causes sleep problems.JOURNAL, Del Brutto OH, Mera RM, Lama J, Zambrano M, Castillo PR, Pineal gland calcification is not associated with sleep-related symptoms. A population-based study in community-dwelling elders living in Atahualpa (rural coastal Ecuador), Sleep Medicine, 15, 11, 1426–1427, November 2014, 25277665, 10.1016/j.sleep.2014.07.008, JOURNAL, Mahlberg R, Kienast T, Hädel S, Heidenreich JO, Schmitz S, Kunz D, Degree of pineal calcification (DOC) is associated with polysomnographic sleep measures in primary insomnia patients, Sleep Medicine, 10, 4, 439–445, April 2009, 18755628, 10.1016/j.sleep.2008.05.003, The calcified gland is often seen in skull X-rays. Calcification rates vary widely by country and correlate with an increase in age, with calcification occurring in an estimated 40% of Americans by age seventeen. Calcification of the pineal gland is associated with corpora arenacea, also known as “brain sand”.

Tumors

Tumors of the pineal gland are called pinealomas. These tumors are rare and 50% to 70% are germinomas that arise from sequestered embryonic germ cells. Histologically they are similar to testicular seminomas and ovarian dysgerminomas.BOOK, Robbins & Cotran Pathologic Basis of Disease, 9780323296359, 1137, Kumar V, Abbas AK, Aster JC, 2014-09-05, Elsevier Health Sciences, A pineal tumor can compress the superior colliculi and pretectal area of the dorsal midbrain, producing Parinaud’s syndrome. Pineal tumors also can cause compression of the cerebral aqueduct, resulting in a noncommunicating hydrocephalus. Other manifestations are the consequence of their pressure effects and consist of visual disturbances, headache, mental deterioration, and sometimes dementia-like behaviour.WEB, Bruce J, Pineal Tumours,emedicine.medscape.com/article/249945-overview#a10, eMedicine, 25 September 2015, live,emedicine.medscape.com/article/249945-overview#a10," title="web.archive.org/web/20150905101936emedicine.medscape.com/article/249945-overview#a10,">web.archive.org/web/20150905101936emedicine.medscape.com/article/249945-overview#a10, 5 September 2015, dmy-all, These neoplasms are divided into three categories: pineoblastomas, pineocytomas, and mixed tumors, based on their level of differentiation, which, in turn, correlates with their neoplastic aggressiveness.WEB, Pineal Tumours,www.abta.org/brain-tumor-information/types-of-tumors/pineal.html, American Brain Tumour Association, 25 September 2015, live,www.abta.org/brain-tumor-information/types-of-tumors/pineal.html," title="web.archive.org/web/20150926092531www.abta.org/brain-tumor-information/types-of-tumors/pineal.html,">web.archive.org/web/20150926092531www.abta.org/brain-tumor-information/types-of-tumors/pineal.html, 26 September 2015, dmy-all, The clinical course of patients with pineocytomas is prolonged, averaging up to several years.JOURNAL, Clark AJ, Sughrue ME, Ivan ME, Aranda D, Rutkowski MJ, Kane AJ, Chang S, Parsa AT, 6, Factors influencing overall survival rates for patients with pineocytoma, Journal of Neuro-Oncology, 100, 2, 255–260, November 2010, 20461445, 2995321, 10.1007/s11060-010-0189-6, The position of these tumors makes them difficult to remove surgically.

Other conditions

The morphology of the pineal gland differs markedly in different pathological conditions. For instance, it is known that its volume is reduced both in obese patients as well as patients with primary insomnia.JOURNAL, Tan DX, Xu B, Zhou X, Reiter RJ, Pineal Calcification, Melatonin Production, Aging, Associated Health Consequences and Rejuvenation of the Pineal Gland, Molecules, 23, 2, 301, January 2018, 29385085, 6017004, 10.3390/molecules23020301, 25611663, free,

Other animals

Nearly all vertebrate species possess a pineal gland. The most important exception is a primitive vertebrate, the hagfish. Even in the hagfish, however, there may be a “pineal equivalent” structure in the dorsal diencephalon. A few more complex vertebrates have lost pineal glands over the course of their evolution.JOURNAL, Erlich SS, Apuzzo ML, The pineal gland: anatomy, physiology, and clinical significance, Journal of Neurosurgery, 63, 3, 321–341, September 1985, 2862230, 10.3171/jns.1985.63.3.0321, 29929205, The lamprey (another primitive vertebrate), however, does possess one. The lancelet Branchiostoma lanceolatum, an early chordate which is a close relative to vertebrates, also lacks a recognizable pineal gland.JOURNAL, Vernadakis AJ, Bemis WE, Bittman EL, Localization and partial characterization of melatonin receptors in amphioxus, hagfish, lamprey, and skate, General and Comparative Endocrinology, 110, 1, 67–78, April 1998, 9514841, 10.1006/gcen.1997.7042, Protochordates in general do not have the distinct structure as an organ, but they have a mass of photoreceptor cells called lamellar body, which is regarded as a pineal homologue.JOURNAL, Lacalli TC, Basic features of the ancestral chordate brain: a protochordate perspective, Brain Research Bulletin, 75, 2–4, 319–323, March 2008, 18331892, 10.1016/j.brainresbull.2007.10.038, 25837046, JOURNAL, Ivashkin E, Adameyko I, Progenitors of the protochordate ocellus as an evolutionary origin of the neural crest, EvoDevo, 4, 1, 12, April 2013, 23575111, 3626940, 10.1186/2041-9139-4-12, free, The results of various scientific research in evolutionary biology, comparative neuroanatomy and neurophysiology have explained the evolutionary history (phylogeny) of the pineal gland in different vertebrate species. From the point of view of biological evolution, the pineal gland is a kind of atrophied photoreceptor. In the epithalamus of some species of amphibians and reptiles, it is linked to a light-sensing organ, known as the parietal eye, which is also called the pineal eye or third eye. It is likely that the common ancestor of all vertebrates had a pair of photosensory organs on the top of its head, similar to the arrangement in modern lampreys.JOURNAL, Cole WC, Youson JH, Morphology of the pineal complex of the anadromous sea lamprey, Petromyzon marinus L, The American Journal of Anatomy, 165, 2, 131–163, October 1982, 7148728, 10.1002/aja.1001650205, In many lower vertebrates (such as species of fish, amphibians and lizards), the pineal gland is associated with parietal or pineal eye. In these animals, the parietal eye acts as a photoreceptor, and hence are also known as the third eye, and they can be seen on top of the head in some species.{{Citation | vauthors = Dodt E |title=The Parietal Eye (Pineal and Parietal Organs) of Lower Vertebrates |date=1973 |url=https://link.springer.com/10.1007/978-3-642-65495-4_4 |work=Visual Centers in the Brain |series=Handbook of Sensory Physiology |volume=7 / 3 / 3 B |pages=113–140 | veditors = Jung R |access-date=2023-03-28 |place=Berlin, Heidelberg |publisher=Springer Berlin Heidelberg |language=en |doi=10.1007/978-3-642-65495-4_4 |isbn=978-3-642-65497-8}} Some extinct Devonian fishes have two parietal foramina in their skulls,JOURNAL, Cope ED, 85280810, The pineal eye in extinct vertebrates, American Naturalist, 1888, 22, 262, 914–917, 10.1086/274797, BOOK, Schultze HP, Hanken J, Hall BK, The Skull, 2: Patterns of Structural and Systematic Diversity, 1993, University of Chicago Press, Chicago, Illinois, 189–254,books.google.com/books?id=mTpJm8MaIF4C&pg=PA189, 2 February 2017, Patterns of diversity in the skulls of jawed fishes, 9780226315683, suggesting an ancestral bilaterality of parietal eyes. The parietal eye and the pineal gland of living tetrapods are probably the descendants of the left and right parts of this organ, respectively.BOOK, Dodt E, Visual Centers in the Brain, 1973, Springer, 113–140, The parietal eye (pineal and parietal organs) of lower vertebrates, During embryonic development, the parietal eye and the pineal organ of modern lizardsJOURNAL, Tosini G, The pineal complex of reptiles: physiological and behavioral roles, Ethology Ecology & Evolution, 1997, 9, 4, 313–333, 10.1080/08927014.1997.9522875, and tuatarasJOURNAL, Dendy A, On the structure, development and morphological interpretation of the pineal organs and adjacent parts of the brain in the tuatara (Sphenodon punctatus), Philosophical Transactions of the Royal Society of London B, 1911, 201, 274–281, 227–331, 10.1098/rstb.1911.0006,zenodo.org/record/1447470, free, form together from a pocket formed in the brain ectoderm. The loss of parietal eyes in many living tetrapods is supported by developmental formation of a paired structure that subsequently fuses into a single pineal gland in developing embryos of turtles, snakes, birds, and mammals.BOOK, Quay WB, Gans C, Northcutt RG, Ulinski P, Biology of the Reptilia. Volume 9. Neurology A, 1979, Academic Press, London, 245–406,carlgans.org/bor-view/?borv=9&borpage=245, The parietal eye–pineal complex, live,carlgans.org/bor-view/?borv=9&borpage=245," title="web.archive.org/web/20170203075058carlgans.org/bor-view/?borv=9&borpage=245,">web.archive.org/web/20170203075058carlgans.org/bor-view/?borv=9&borpage=245, 3 February 2017, dmy-all, The pineal organs of mammals fall into one of three categories based on shape. Rodents have more structurally complex pineal glands than other mammals.BOOK, Vollrath L, Comparative Morphology of the Vertebrate Pineal Complex, 52, 25–38, 1979, 398532, 10.1016/S0079-6123(08)62909-X, 9780444801142, Progress in Brain Research, Crocodilians and some tropical lineages of mammals (some xenarthrans (sloths), pangolins, sirenians (manatees and dugongs), and some marsupials (sugar gliders)) have lost both their parietal eye and their pineal organ.JOURNAL, Ralph CL, The pineal gland and geographical distribution of animals, International Journal of Biometeorology, 19, 4, 289–303, December 1975, 1232070, 10.1007/bf01451040, 30406445, 1975IJBm...19..289R, JOURNAL, Ralph C, Young S, Gettinger R, O’Shea TJ, Does the manatee have a pineal body?, Acta Zoologica, 1985, 66, 55–60, 10.1111/j.1463-6395.1985.tb00647.x, Polar mammals, such as walruses and some seals, possess unusually large pineal glands.All amphibians have a pineal organ, but some frogs and toads also have what is called a “frontal organ”, which is essentially a parietal eye.JOURNAL, Adler K, Extraocular photoreception in amphibians, Photophysiology, 23, 4, 275–298, April 1976, 775500, 10.1111/j.1751-1097.1976.tb07250.x, vanc, 33692776, Pinealocytes in many non-mammalian vertebrates have a strong resemblance to the photoreceptor cells of the eye. Evidence from morphology and developmental biology suggests that pineal cells possess a common evolutionary ancestor with retinal cells.JOURNAL, Klein DC, The 2004 Aschoff/Pittendrigh lecture: Theory of the origin of the pineal gland--a tale of conflict and resolution, Journal of Biological Rhythms, 19, 4, 264–279, August 2004, 15245646, 10.1177/0748730404267340, 17834354, free, Pineal cytostructure seems to have evolutionary similarities to the retinal cells of the lateral eyes. Modern birds and reptiles express the phototransducing pigment melanopsin in the pineal gland. Avian pineal glands are thought to act like the suprachiasmatic nucleus in mammals.JOURNAL, Natesan A, Geetha L, Zatz M, Rhythm and soul in the avian pineal, Cell and Tissue Research, 309, 1, 35–45, July 2002, 12111535, 10.1007/s00441-002-0571-6, 26023207,zenodo.org/record/1232737, The structure of the pineal eye in modern lizards and tuatara is analogous to the cornea, lens, and retina of the lateral eyes of vertebrates.In most vertebrates, exposure to light sets off a chain reaction of enzymatic events within the pineal gland that regulates circadian rhythms.JOURNAL, Moore RY, Heller A, Wurtman RJ, Axelrod J, Visual pathway mediating pineal response to environmental light, Science, 155, 3759, 220–223, January 1967, 6015532, 10.1126/science.155.3759.220, 44377291, 1967Sci...155..220M, In humans and other mammals, the light signals necessary to set circadian rhythms are sent from the eye through the retinohypothalamic system to the suprachiasmatic nuclei (SCN) and the pineal gland.The fossilized skulls of many extinct vertebrates have a pineal foramen (opening), which in some cases is larger than that of any living vertebrate.JOURNAL, Edinger T, The size of parietal foramen and organ in reptiles: a rectification, Bulletin of the Museum of Comparative Zoology, 1955, 114, 1–34,www.biodiversitylibrary.org/item/26724#page/13/mode/1up, live,web.archive.org/web/20171201154018/https://www.biodiversitylibrary.org/item/26724#page/13/mode/1up, 1 December 2017, dmy-all, Although fossils seldom preserve deep-brain soft anatomy, the brain of the Russian fossil bird Cerebavis cenomanica from Melovatka, about 90 million years old, shows a relatively large parietal eye and pineal gland.JOURNAL, Kurochkin EN, Dyke GJ, Saveliev SV, Pervushov EM, Popov EV, A fossil brain from the Cretaceous of European Russia and avian sensory evolution, Biology Letters, 3, 3, 309–313, June 2007, 17426009, 2390680, 10.1098/rsbl.2006.0617,

History

File:Descartes_mind_and_body.gif|thumb|Diagram of the operation of the pineal gland for Descartes in the Treatise of Man (figure published in the edition of 1664)]]The secretory activity of the pineal gland is only partially understood. Its location deep in the brain suggested to philosophers throughout history that it possessed particular importance. This combination led to its being regarded as a “mystery” gland with mystical, metaphysical, and occult theories surrounding its perceived functions. The earliest recorded description of the pineal gland is from the Greek physician Galen in the 2nd century C.E.JOURNAL, Shoja MM, Hoepfner LD, Agutter PS, Singh R, Tubbs RS, History of the pineal gland, Child’s Nervous System, 32, 4, 583–586, April 2016, 25758643, 10.1007/s00381-015-2636-3, 26207380, free, According to Galen, Herophilus (325–280 B.C.E.) had already considered the structure as a kind of valve that partitioned the brain chambers, particularly for the flow of vital spirits (pneuma).JOURNAL, Choudhry O, Gupta G, Prestigiacomo CJ, On the surgery of the seat of the soul: the pineal gland and the history of its surgical approaches, Neurosurgery Clinics of North America, 22, 3, 321–33, vii, July 2011, 21801980, 10.1016/j.nec.2011.04.001, Specifically, the ancient Greeks believed that the structure maintained the movement of vital spirits from the middle (now identified as the third) ventricle to the one in the parencephalis (fourth ventricle).JOURNAL, Berhouma M, Beyond the pineal gland assumption: a neuroanatomical appraisal of dualism in Descartes’ philosophy, Clinical Neurology and Neurosurgery, 115, 9, 1661–1670, September 2013, 23562082, 10.1016/j.clineuro.2013.02.023, 9140909, BOOK, Cardinali DP, The Prescientific Stage of the Pineal Gland, 2016, Ma Vie en Noir, 9–21, Cham, Springer International Publishing, en, 10.1007/978-3-319-41679-3_2, 978-3-319-41678-6, Galen described the pineal gland in De usu partium corporis humani, libri VII (On the Usefulness of Parts of the Body, Part 8) and De anatomicis administrationibus, libri IX (On Anatomical Procedures, Part 9).BOOK, López-Muñoz F, Marín F, Álamo C, History of Pineal Gland as Neuroendocrine Organ and the Discovery of Melatonin, 2016,link.springer.com/10.1007/978-81-322-2803-5_1, Melatonin, Neuroprotective Agents and Antidepressant Therapy, 1–23, López-Muñoz F, Srinivasan V, de Berardis D, Álamo C, 2023-03-28, New Delhi, Springer India, en, 10.1007/978-81-322-2803-5_1, 978-81-322-2801-1, He introduced the name κωνάριο (konario, often Latinised as conarium) that means cone, as in pinecone,JOURNAL, Laios K, The Pineal Gland and its earliest physiological description, Hormones, 16, 3, 328–330, July 2017, 29278521, 10.14310/horm.2002.1751, free, in De usu partium corporis humani. He correctly located the gland as directly lying behind the third ventricle. He argued against the prevailing concept of it as a valve for two basic reasons: it is located outside of the brain tissue and it does not move on its own.Galen instead identified the valve as a worm-like structure in the cerebellum (later called vermiform epiphysis, known today as the vermis cerebelli or cerebellar vermis).JOURNAL, Steinsiepe KF, The ‘worm’ in our brain. An anatomical, historical, and philological study on the vermis cerebelli, Journal of the History of the Neurosciences, 265–300, January 2023, 32, 3, 36599122, 10.1080/0964704X.2022.2146515, 255470624, From his study on the blood vessels surrounding the pineal gland he discovered the great vein of the cerebellum, later called the vein of Galen.JOURNAL, Ustun C, Galen and his anatomic eponym: vein of Galen, Clinical Anatomy, 17, 6, 454–457, September 2004, 15300863, 10.1002/ca.20013, He could not establish any functional role of the pineal gland and regarded it as a structural support for the cerebral veins.NEWS, Pearce JM, 2022, The pineal: seat of the soul, en-US, Hektoen International,hekint.org/2022/04/20/the-pineal-seat-of-the-soul/, 2023-03-28, 2155-3017, Seventeenth-century philosopher and scientist René Descartes discussed the pineal gland both in his first book, the Treatise of Man (written before 1637, but only published posthumously 1662/1664), and in his last book, The Passions of the Soul (1649) and he regarded it as “the principal seat of the soul and the place in which all our thoughts are formed”. In the Treatise of Man, he described conceptual models of man, namely creatures created by God, which consist of two ingredients, a body and a soul.BOOK, Descartes R, The Passions of the Soul, Philosophy of the Mind, Chalmers D, New York, Oxford University Press, Inc., 2002, 978-0-19-514581-6, In the Passions, he split man up into a body and a soul and emphasized that the soul is joined to the whole body by “a certain very small gland situated in the middle of the brain’s substance and suspended above the passage through which the spirits in the brain’s anterior cavities communicate with those in its posterior cavities”. Descartes gave importance to the structure as it was the only unpaired component of the brain.The Latin name pinealis became popular in the 17th century. For example, English physician Thomas Willis described a glandula pinealis in his book, Cerebri anatome cui accessit nervorum descriptio et usus (1664). Willis criticised Descartes’ concept, remarking: “we can scarce[ly] believe this to be the seat of the Soul, or its chief Faculties to arise from it; because Animals, which seem to be almost quite destitute of Imagination, Memory, and other superior Powers of the Soul, have this Glandula or Kernel large and fair enough.“Walter Baldwin Spencer at the University of Oxford gave the first description of the pineal gland in lizards. In 1886, he described an eye-like structure, which he called the pineal eye or parietal eye, that was associated with the parietal foramen and the pineal stalk.BOOK, Spencer B,books.google.com/books?id=kvwXAAAAYAAJ&dq=baldwin+spencer+third+eye+1886&pg=PA1, Bartholomew Close, Quarterly Journal of Microscopy, 1885, London, 1–76, en, On the Presence and Structure of the Pineal Eye in Lacertilia, The presence of a pineal body was already discovered by German zoologist Franz Leydig in 1872, in European lizards. Leydig called them the “frontal organ” (German stirnorgan).JOURNAL, Flemming AF, 1991, A third eye,journals.co.za/doi/pdf/10.10520/AJA10162275_149, Culna, 40, 26–27, Sabinet, BOOK, Eakin RM, 3 Structure, 1973, The Third Eye, 32–84, University of California Press, 10.1525/9780520326323-004, 978-0-520-32632-3, In 1918, Swedish zoologist Nils Holmgren described the “parietal eye” in frogs and dogfish.JOURNAL, Wurtman RJ, Axelrod J, The Pineal Gland, Scientific American, 213, 50–60, July 1965, 1, 14298722, 10.1038/scientificamerican0765-50, 1965SciAm.213a..50W, He discovered that the parietal eyes were made up of sensory cells similar to the cone cells of the retina, and suggested that it was a primitive light-sensor organ (photoreceptor).The pineal gland was originally believed to be a “vestigial remnant” of a larger organ. In 1917, it was known that extract of cow pineals lightened frog skin. Dermatology professor Aaron B. Lerner and colleagues at Yale University, hoping that a hormone from the pineal gland might be useful in treating skin diseases, isolated it and named it melatonin in 1958.JOURNAL, Lerner AB, Case JD, Takahashi Y, Isolation of melatonin and 5-methoxyindole-3-acetic acid from bovine pineal glands, The Journal of Biological Chemistry, 235, 7, 1992–1997, July 1960, 14415935, 10.1016/S0021-9258(18)69351-2, free, The substance did not prove to be helpful as intended, but its discovery helped solve several mysteries, such as why removing a rat’s pineal gland accelerated its ovary growth, why keeping rats in constant light decreased the weight of their pineals, and why pinealectomy and constant light affect ovary growth to an equal extent; this knowledge gave a boost to the then-new field of chronobiology.BOOK, Coates PM, Blackman MR, Cragg GM, Levine M, Moss J, White JD,books.google.com/books?id=Sfmc-fRCj10C&q=Lerner+melatonin+history&pg=PA457, Encyclopedia of Dietary Supplements, CRC Press, 2005, 978-0-8247-5504-1, 457, 2009-03-31, Of the endocrine organs, the function of the pineal gland was the last to be discovered.JOURNAL, Sahai A, Sahai RJ, December 2013, Pineal gland: A structural and functional enigma, Journal of the Anatomical Society of India, 62, 2, 170–177, 10.1016/j.jasi.2014.01.001,

Society and culture

The notion of a “pineal-eye” is central to the philosophy of the French writer Georges Bataille, which is analyzed at length by literary scholar Denis Hollier in his study Against Architecture. In this work Hollier discusses how Bataille uses the concept of a “pineal-eye” as a reference to a blind-spot in Western rationality, and an organ of excess and delirium.BOOK, Hollier D, Against Architecture: The Writings of Georges Bataille, Wing B, MIT, 1989, This conceptual device is explicit in his surrealist texts, The Jesuve and The Pineal Eye.BOOK, Bataille G, Visions of excess: Selected writings 1927-1939., Manchester University Press, 1985, In the late 19th century Madame Blavatsky, founder of theosophy, identified the pineal gland with the Hindu concept of the third eye, or the Ajna chakra. This association is still popular today. The pineal gland has also featured in other religious contexts, such as in the Principia Discordia, which claims it can be used to contact the goddess of discord Eris.WEB, Principia Discordia - Page 15,principiadiscordia.com/book/22.php, 2023-09-22, principiadiscordia.com, In the short story “From Beyond” by H. P. Lovecraft, a scientist creates an electronic device that emits a resonance wave, which stimulates an affected person’s pineal gland, thereby allowing them to perceive planes of existence outside the scope of accepted reality, a translucent, alien environment that overlaps our own recognized reality. It was adapted as a film of the same name in 1986. The 2013 horror film Banshee Chapter is heavily influenced by this short story.In Season 16, episode 6 of “American Dad” Steve tries to “astral project” using his pineal gland to help him understand the meaning of life. The episode is entitled “The Wondercabinet”.

Additional images

The pineal body is labeled in these images.File:Gray715.png|Mesal aspect of a brain sectioned in the median sagittal planeFile:Gray716.png|Dissection showing the ventricles of the brainFile:Gray719.png|Hind- and mid-brains; antero-lateral viewFile:Gray720.png|Median sagittal section of brainFile:Slide4ff.JPG|Pineal glandFile:Slide2BRA.JPG|Brainstem; posterior view

See also

• Pineal gland cyst

References

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External links

{{Commons category|Pineal gland}}{{Wiktionary|pineal gland}}{{System and organs}}{{Diencephalon}}{{Authority control}}