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Title: Pinealocyte  
Author: World Heritage Encyclopedia
Language: English
Subject: Pineal gland, Chromaffin cell, Corticotropic cell, Gonadotropic cell, Prolactin cell
Collection: Endocrine System
Publisher: World Heritage Encyclopedia


Cross-section of pineal gland displaying pinealocytes and other cells
Latin Pinealocytus,
endocrinocitus pineale
System Endocrine system
Code TH H3.
Anatomical terminology

Pinealocytes are the main cells contained in the

  • Histology image: 14402loa – Histology Learning System at Boston University

External links

  1. ^ a b c d e Pandi-Perumal, S. R., V. Srinivasan, G.J. M. Maestroni, D. P. Cardinali, B. Poeggeler, and R. Hardeland (2006). "Melatonin". FEBS Journal 273 (13): 2813–838.  
  2. ^ Maronde, E., and J. Stehle (2007). "The Mammalian Pineal Gland: Known Facts, Unknown Facets". Trends in Endocrinology & Metabolism 18 (4): 142–49.  
  3. ^ a b c d Mano, Hiroaki, and Yoshitaka Fukada (2006). "A Median Third Eye: Pineal Gland Retraces Evolution of Vertebrate Photoreceptive Organs". Photochemistry and Photobiology 83 (1): 11–18.  
  4. ^ a b c d e f g h Klein, David (2006). "Evolution of The Vertebrate Pineal Gland: The Aanat Hypothesis". Chronobiology International 23 (1–2): 5–20.  
  5. ^ Polyakova, V. O., N. S. Linkova, and S. A. Pichugin (2011). "Changes in Apoptosis and Cell Proliferation in Human Pineal Gland during Aging". Bulletin of Experimental Biology and Medicine 150 (4): 468–70.  
  6. ^ a b c d e f Al-Hussain, S. M (2006). "The Pinealocytes of the Human Pineal Gland: A Light and Electron Microscopic Study". Folia Morphologica 65 (3): 181–87.  
  7. ^ a b c Boya, J., and J. Calvo (1984). "Ultrastructure of the Pineal Gland in the Adult Rat". Journal of Anatomy 138 (3): 405–09.  
  8. ^ a b c Khavinson, V. Kh, N. S. Linkova, I. M. Kvetnoy, T. V. Kvetnaia, V. O. Polyakova, and H. W. Korf (2012). "Molecular Cellular Mechanisms of Peptide Regulation of Melatonin Synthesis in Pinealocyte Culture". Bulletin of Experimental Biology and Medicine 153 (2): 255–58.  
  9. ^ a b c d e Spiwoks-Becker, I., C. Maus, S. Dieck, A. Fejtová, L. Engel, T. Wolloscheck, U. Wolfrum, L. Vollrath, and R. Spessert (2008). "Active Zone Proteins Are Dynamically Associated with Synaptic Ribbons in Rat Pinealocytes". Cell and Tissue Research 333 (2): 185–95.  


Synthesis of Melatonin

Pinealocytes synthesize the hormone melatonin by first converting the amino acid tryptophan to serotonin. The serotonin is then acetylated by the AANAT enzyme and converted into N-acetylserotonin. N-acetylserotonin is converted into melatonin by the enzyme hydroxyindole O-methyltransferase (HIOMT), also known as acetylserotonin O-methyltransferase (ASMT).[1] Activity of these enzymes is high during the night and regulated by the mechanisms previously discussed involving norepinephrine.[1]


Melatonin synthesis is also regulated by the nervous system. Nerve fibers in the retinohypothalamic tract connect the retina to the suprachiasmatic nucleus (SCN). The SCN stimulates the release of Norepinephrine from sympathetic nerve fibers from the superior cervical ganglia that synapse with the pinealocytes.[1][4] Norepinephrine causes the production of melatonin in the pinealocytes by stimulating the production of cAMP. Because the release of norepinephrine from the nerve fibers occurs at night, this system of regulation maintains the body’s circadian rhythms.[1]

Regulation of melatonin synthesis is important to melatonin’s main function in circadian rhythms. The main molecular control mechanism that exists for melatonin secretion in vertebrates is the enzyme AANAT (arylalkylamine N-acetyltransferase). The expression of the AANAT gene is controlled by the transcription factor pCREB, and this is evident when cells treated with epithalone, a peptide which affects pCREB transcription, have a resulting increase in melatonin synthesis.[8] AANAT is activated through a protein kinase A system in which cyclic AMP (cAMP) is involved.[4] The activation of AANAT leads to an increase in melatonin production.[4] Though there are some differences specific to certain species of vertebrates, the effect of cAMP on AANAT and AANAT on melatonin synthesis remains fairly consistent.[4]


Structure of Melatonin


More evidence for the evolution of pinealocytes from photoreceptor cells is the similarities between the ribbon complexes in the two types of cells. The presence of the protein RIBEYE and other proteins in both pinealocytes and sensory cells (both photoreceptors and hair cells) suggests that the two cells are related to one another evolutionarily.[9] Differences between the two synaptic ribbons exist in the presence of certain proteins, such as ERC2/CAST1, and the distribution of proteins within the complexes of each cell.[9]

A common theory on the evolution of pinealocytes is that they evolved from photoreceptor cells. It is speculated that in ancestral vertebrates, the pinealocytes served the same function as photoreceptor cells, such as retinal cells. Structural, functional, and genetic similarities exist between the two cell types. Structurally, both develop from the area of the brain designated the diencephalon, also the area containing the thalamus and hypothalamus, during embryological development.[3] Both types of cells have similar features, including cilia, folded membranes, and polarity.[4] Functional evidence for this theory of evolution can be seen in lower vertebrates. The retention of photosensitivity of the pinealocytes of lampreys, fish, amphibians, reptiles, and birds and the secretion of melatonin by some of these lower vertebrates suggests that pinealocytes may have once served as photoreceptor cells.[3][4] Researchers have also indicated the presence of several proteins found in the retina in the pinealocytes in chicken and fish.[3] Genetic evidence demonstrates that phototransduction genes present in the DNA of the retina are also present in the DNA of pinealocytes.[4]

Evolution of pinealocytes

Synaptic ribbons are secretory functions within the cell. The presence of proteins such as Munc13-1 indicates that they are important in neurotransmitter release.[9] At night, synaptic ribbons of rats appear larger and slightly curved, but during the day, they appear smaller and rod-like.[9]

Synaptic ribbons

Type 2 pinealocytes are also known as dark pinealocytes because they stain at a high density when viewed under a light microscope and appear darker to the human eye. As indicated by research and microscopy, they are round, oval, or elongated cells with a diameter of about 7–11.2 micrometers.[6] The nucleus of a Type 2 pinealocyte contains many infoldings which contain large amounts of rough endoplasmic reticulum and ribosomes.[6] An abundance of cilia and centrioles has also been found in these Type 2 cells of the pineal gland.[7] Unique to the Type 2 is the presence of vacuoles containing 2 layers of membrane.[7] As Type 1 cells contain serotonin, Type 2 cells contain melatonin and are thought to have similar characteristics as endocrine and neuronal cells.[8]

Type 2 pinealocytes

Type 1 pinealocytes are also known as light pinealocytes because they stain at a low density when viewed under a autophagocytosis in these cells.[6] Research has also shown that Type 1 pinealocytes contain the neurotransmitter serotonin, which later is converted to melatonin, the main hormone secreted by the pineal gland.[8]

Type 1 pinealocytes

Types of pinealocytes


  • Types of pinealocytes 1
    • Type 1 pinealocytes 1.1
    • Type 2 pinealocytes 1.2
  • Synaptic ribbons 2
  • Evolution of pinealocytes 3
  • Melatonin 4
    • Regulation 4.1
    • Synthesis 4.2
  • References 5
  • External links 6

. cytoplasm There are two different types of pinealocytes, type I and type II, which have been classified based on certain properties including shape, presence or absence of infolding of the nuclear envelope, and composition of the [5]

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