The pineal gland (epiphysis cerebri) has an important role in the sleep/wake daily cycle and reproductive development.
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. (More? Kennaway DJ, etal, 1996)
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.
Pineal Gland (adult hindbrain and midbrain, postero-lateral view)
The pineal gland is located at the base of the brain and cells called pinealocytes manufactures the lipophilic hormone melatonin, derivative of the amino acid tryptophan.
Melatonin synthesis and levels in the blood rises and falls on a circadian (daily) cycle, levels can be detected by the presence of a metabolite in the urine. (More? melatonin)
"This review summarizes the current knowledge about the ontogenetic development of the circadian system in mammals. The developmental changes of overt rhythms are discussed, although the main focus of the review is the underlying neuronal and molecular mechanisms."
Embryo Images Unit: Brain (Weeks 9-15)
Pineal Site of synthesis of melatonin, light sensitive in lower vertebrates (lost evolutionarily)
Embryonic appears as a diverticulum in the diencephalic roof of the third ventricle.
Birth - no melatonin cycle present.
Postnatal (8 to 15 weeks, 49 to 55 weeks postconception) - melatonin cycle present as detected by rhythmic urinary metabolite excretion.
Postnatal (3 to 5 years) - peak melatonin concentrations.
Melatonin is synthesized from the amino acid tryptophan within the pinealocytes.
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.
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.
Melatonin levels can be monitored by urinary excretion of the melatonin metabolite 6-sulfatoxymelatonin (aMT.6S).
The pineal gland has a very interesting histological structure based upon its unique anatomical position.
Pinealocytes and the astrocytes have long processes, this gives the "stringy" histological appearance.
(Image: Lutz Slomianka, UWA Blue Histology)
Now look at the slides from UNSW Virtual Slidebox BGD (B) Histology of the HP Axis.
Pineal Hypoplasia associated with retinal disease.
Pineal Tumours in children are associated with abnormal puberty development.
NIH Child Health and Human Development (USA) Pineal Gland and Chronobiology: Regulation of Pineal Function
University of Cincinnati SURVEY OF ENDOCRINE ORGANS
DARPP-32 (Dopamine- and cAMP-regulated phosphoprotein of 32 kDa) is involved in the retinal pathway transmitting photic information that resets the circadian clock.
Search Feb 2006 "pineal development" 1178 reference articles of which 167 were reviews.
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