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Pineal (was new aspects..)
Some of the recent postings regarding photoperiod make it sound as if the
pineal might be non-functional in the 'higher' vertebrates (birds & mammals).
This is certainly not the case.
The main product of the pineal is melatonin (an indoleamine) and is
especially important in seasonally reproducing animals (reptiles, birds,
and most mammals). Circulatory melanins are elevated at night and
probably coordinates daily and seasonal rhythms with the day/night cycle.
Physiologically, melatonin is probably an antigonadotropin.
Various experiments have demonstrated that melatonin can manipulate
seasonal rhythyms. Generally, increased plasma melatonin level are preceived
as a "super-short day" and induce reproductive activity.
Melatonin is currently popular as a treatment to prevent jet-lag. It
happens to be derived from the amino acid Tryptophan, which has enjoyed
some popularity as a natural aid to sleep!
Actually, the CNS controls synthesis in the pineal. Essentially, the
pineal is the intermediary between the external photoperiod and the animals
internal environment. It converts information on light and dark into a chemical
Turns out there is a fair sized body of information on the specific
roles of the pineal in birds. Because the daily cycle continues in blinded
birds, light may effect the pineal directly. This is a rather old idea that
has recently received strong experimental support.
BYW pineals in ALL non-mammalinan vertebrates (Sharks, teleost fish,
amphibians,reptiles...) are directly photosensitative.. They all synthesize
and release melatonin in the absence of light. Evidence supports the
idea that the pineal is not controled by the CNS (suggests it is directly
stimulated by light). Overall, the pineal glands of ALL vertebrates (presumably
including dinosaurs!!) actively produce indoleamines , regardless of how
they couple to the environment.
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