Endocrine - Pineal Development

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Introduction

Adult pineal body
Pineal gland position

The pineal gland (epiphysis cerebri) has an important role in the sleep/wake daily cycle and reproductive development. The gland is thought to evolutionarily to have been positioned as to be exposed to light, and hence remains a regulator of cyclic rhythms associated with day/night and day length. The pineal hormone (melatonin) has targets both in the nervous system and in many different peripheral tissues.


In humans, the postnatal melatonin levels in premature infants is lower and delayed, but not different when calculated from conception date. Other factors such as preeclampsia, growth restriction, and nursery lighting can cause altered rhythm development. The same study has also shown that full-term infants born at home and full-term twins born in the hospital had significantly lower metabolite excretion levels than hospital-born singleton infants at the same ages despite similar body weights.[1]


In other species, it has been shown that maternal melatonin crosses the placenta into fetal circulation and may provide photoperiodic information during fetal development that influences later postnatal circadian (daily day/night) and seasonal (day length) rhythms. The pineals of non-mammalian vertebrates are photoreceptive, whereas those of mammals do not normally respond to directly light.

In Brief

  • part of epithalmus - neurons, glia and pinealocytes
  • pinealocytes secrete melatonin - cyclic nature of activity, melatonin lowest during daylight
    • inhibit hypothalamic secretion of GnRH until puberty, pineal gland then rapidly regresses.
  • other activities - possibly gamete maturation, antioxidant effect, protect neurons?


Note that there are many clinical studies investigating the possible role of melatonin in diverse health areas, from oxygen starvation at birth through to neural effects in old age.


Endocrine Links: Introduction | BGD Lecture | Science Lecture | Lecture Movie | pineal | hypothalamus‎ | pituitary | thyroid | parathyroid | thymus | pancreas | adrenal | endocrine gonad‎ | endocrine placenta | other tissues | Stage 22 | endocrine abnormalities | Hormones | Category:Endocrine
Historic Embryology - Endocrine  
1903 Islets of Langerhans | 1903 Pig Adrenal | 1904 interstitial Cells | 1908 Pancreas Different Species | 1908 Pituitary | 1908 Pituitary histology | 1911 Rathke's pouch | 1912 Suprarenal Bodies | 1914 Suprarenal Organs | 1915 Pharynx | 1916 Thyroid | 1918 Rabbit Hypophysis | 1920 Adrenal | 1935 Mammalian Hypophysis | 1926 Human Hypophysis | 1927 Adrenal | 1927 Hypophyseal fossa | 1930 Adrenal | 1932 Pineal Gland and Cysts | 1935 Hypophysis | 1935 Pineal | 1937 Pineal | 1935 Parathyroid | 1940 Adrenal | 1941 Thyroid | 1950 Thyroid Parathyroid Thymus | 1957 Adrenal

Endocrine System Development | Lecture - Endocrine Development | Lecture - Head Development | Category:Pineal

Some Recent Findings

  • Melatonin and stable circadian rhythms optimize maternal, placental and fetal physiology[2] "A number of conclusions naturally evolve from the data summarized in this review: (i) melatonin, of both pineal and placental origin, has essential functions in fetal maturation and placenta/uterine homeostasis; (ii) circadian clock genes, which are components of all cells including those in the peripheral reproductive organs, have important roles in reproductive and organismal (fetal and maternal) physiology; (iii) due to the potent antioxidant actions of melatonin, coupled with its virtual absence of toxicity, this indoleamine may have utility in the treatment of pre-eclampsia, intrauterine growth restriction, placental and fetal ischemia/reperfusion, etc. (iv) the propensity for parturition to occur at night may relate to the synergism between the nocturnal increase in melatonin and oxytocin."
  • Melatonin as a central molecule connecting neural development and calcium signaling[3] "Melatonin (MEL) is a neuroendocrine hormone secreted by the pineal gland in association with the suprachiasmatic nucleus and peripheral tissues. MEL has been observed to play a critical role in the reproductive process and in the fetomaternal interface. Extrapineal synthesis has been reported in mammalian models during pregnancy, especially by the placenta tissue."

Development Overview

  • Neuroectoderm - prosenecephalon then diencephalon
  • caudal roof, median diverticulum, epiphysis
  • Initially a hollow diverticulum, cell proliferation to solid, pinealocytes (neuroglia), cone-shaped gland innervated by epithalamus
    • epithalamus consists of the pineal gland and habenular nuclei

Melatonin

Melatonin molecular structure
  • Melatonin is synthesized from the amino acid tryptophan within the pinealocytes.
    • Serotonin is first acetylated by aryl alkylamine N-acetyltransferase (AA-NAT), then converted to melatonin by acetyl serotonin methyl transferase (ASMT also known as hydroxyindole O-methyltransferase or HIOMT).
  • Melatonin release is stimulated by darkness and inhibited by light and is said to have neurological "chronobiotic" properties for resynchronization of sleep and circadian rhythms disturbances. In the periphery, melatonin is also involved in the regulation of several complex cycles: seasonal reproduction, body weight and energy balance.
  • Melatonin levels can be monitored by urinary excretion of the melatonin metabolite 6-sulfatoxymelatonin (aMT.6S).

Melatonin Receptors

The hormone melatonin acts through receptors (high affinity G protein-coupled) embedded in the cell membrane. Three different receptor subtypes have been identified in mammals: MT1 (Mel 1a) and MT2 (Mel 1b) and a putative binding site called MT3.

  • MT1 - expressed in humans in the pars tuberalis of the pituitary gland and the suprachiasmatic nuclei of the hypothalamus.
  • MT2 - expressed in the retina.
  • MT3 - expressed in many non-mammalian vertebrates in a range of brain areas.

Innervation

Nerve fibers innervating the mammalian pineal gland originate from perikarya located in the sympathetic superior cervical ganglion, the parasympathetic sphenopalatine and otic ganglia, as well as by nerve fibers originating in the central nervous system.[4]

  • sympathetic nerves - contain norepinephrine and neuropeptide Y as neurotransmitters
  • parasympathetic nerves - contain vasoactive intestinal peptide and peptide histidine isoleucine
  • trigeminal ganglion - containing substance P, calcitonin gene-related peptide, and pituitary adenylate cyclase-activating peptide

Abnormalities

  • Pineal Hypoplasia associated with retinal disease.
  • Pineal Tumours in children are associated with abnormal puberty development.

Molecular Development

DARPP-32 (Dopamine- and cAMP-regulated phosphoprotein of 32 kDa) is involved in the retinal pathway transmitting photic information that resets the circadian clock.

Histology

Adult Pineal (sheep)

Adult Histology

  • Astrocytes - small dark nuclei
  • Pinealocytes - most nuclei present, larger lighter and round nuclei surrounded by a broad rim of light cytoplasm
  • Endothelial cells - nuclei in association with the vessels and capillaries traversing the tissue.
  • Cytoplasmic processes - "stringy" appearance from both pinealocytes and astrocytes


Links: large histology image

References

  1. <pubmed>8636362</pubmed>
  2. <pubmed>24132226</pubmed>
  3. <pubmed>21465271</pubmed>
  4. <pubmed>12111544</pubmed>


Online Textbooks

Journals

Reviews

<pubmed></pubmed> <pubmed></pubmed> <pubmed></pubmed> <pubmed>16021838</pubmed> <pubmed>15589268</pubmed> <pubmed>15352385</pubmed> <pubmed>14561326</pubmed> <pubmed>9852259</pubmed> <pubmed></pubmed>

Articles

<pubmed>19665543</pubmed> <pubmed>16182388</pubmed> <pubmed>8938291</pubmed>

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Search April 2010

  • Endocrine Development - All (14277) Review (4620) Free Full Text (3140)

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Cite this page: Hill, M.A. (2021, April 21) Embryology Endocrine - Pineal Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Endocrine_-_Pineal_Development

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© Dr Mark Hill 2021, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G