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Re: Pineal (was new aspects..)



alan brush wrote:
> 
> 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
> message (hormone).
>       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.
>           Cheers,
> 
>                        Alan

This is great stuff!  I think as science progresses we will find that
photoperiod affects virtually all life on earth to one degree or
another.  I feel that in the case of the Cretaceous extinction, those
plants and animals that were committed to photoperiod dependancy
suffered mass extinction (assuming that they could not adapt to the new
light cycles that occurred directly after the catastrophe).
-- 
 Dave Pelley

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