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[DSLF] Digest Number 580

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There is 1 message in this issue.

Topics in this digest:

      1. Big discovery - eye/circadian links
           From: Steve Pauley <spauley@cox-internet...>


Message: 1
   Date: Tue, 12 Feb 2002 13:47:02 -0700
   From: Steve Pauley <spauley@cox-internet...>
Subject: Big discovery - eye/circadian links

>As some have already posted, a big discovery was announced
   last week (Feb.8) in Science Magazine. Ganglion cells in mammalian
   retinas, containing a pigment called melanopsin, have nerve
   connections to our circadian clocks. The results will surely
>begin a new era in the study of circadian physiology.
>Phototransduction by Retinal Ganglion Cells That Set the Circadian Clock
>David M. Berson,* Felice A. Dunn, Motoharu Takao
>Science, 2-8-02
>*Dr Berson is a PhD (from MIT) neuroscientist at Brown, Univ.
>(Sites for Dr Berson)
>(need to subscribe to Science for this one)
>(NY Times summary article)
>(Yahoo article)
   (CBC article)

>Researchers found that some retinal ganglion cells (RGC)
>in mammal (mice-rat) retinas connect to the paired suprachiasmatic
>nuclei (SCN) of the brain -the hypothaloms =the cirdadian/clock
   center.  The RGC's regulate circadian rhythms through non visual means;
>ie  no retinal rods (cells for dark vision) or cones (cells for color vision)
>play a role at all.
>The lighting industry, utility companies, and civic
>leaders need to pay particularly close attention to these
>findings. (Am I dreaming here??)
>The big implication is: certain wave lengths of light
>(blue-green) trigger these RGC's to fire, resulting
>in a shut down of melatonin production by the pineal gland.
>The data show that blue -green (484nm) light triggers the
>response - more so than green, yellow, or red light, though those
>wave lengths can initiate a response to fire the cells.

>The paper shows that the RGC's fire when light triggers
>a retinaldehyde-based opsin inside the RGC's (most likely melanopsin,
>also present in the skin of frogs, and in the same class as rhodopsin
>& other opsins used by the rods and cones for scotopic and photopic vision).
>The protein, a light absorber, is most likely not a blue- light -sensitive,
>flavin -based, cryptochrome pigment, as previously thought.
>Melanopsin absorbs blue-green light, and is present
>in invertebrates. So this mechanism seems to be a very
>primitive, hold-over circadian system passed on to mammals
>as a selectively advantageous response to light-dark cycles.
>The system also allows totally blind people who still have
    their eyes intact, to still maintain circadian rhythms.

>The way I read the data in relation to our dark sky work:
>Blue-green light triggers (resets) our circadian clocks more
>so than green, yellow or red light.
>Therefore we ought to be most careful about using outdoor
>lights like metal halide, fluorescent, and mercury vapor.  They all
>have spikes in the blue-green wave lengths.  If bright enough,
>(with eyes open, the triggering level is low for the blue-green -
>less than .02fc), perhaps that light can even shine through
>closed eyelids, strike the newly discovered ganglion cells in
>the retina (even in blind people), and cause the RGC's to fire
>sending a message to the SCN in the hypothalamus = the
>circadian/clock center.
>Result: we can't sleep well;  the circadian disruption leads to
>improperly timed releases of hormones from the hypothalamus
>and then the pituitary gland - all connected to clock cycles which
>are linked to the light-dark cycles of day and night.
>Remedy:  no light should trespass into bedrooms, especially blue-green light.
>(throw out your flat, blue-green, "Limelite" wall-plug night light
  http://www.limelite.com/lime_frm.htm.  One is sold every 6 seconds!)
>For the sake of healthy human physiology, it would appear that hps
>(orange lighting), and lps (yellow lighting), are better choices for street
>lights than mh or mv.
>Just like color blindness (absent opsins for color vision), a person
>born with an absence of melanopsin inside the RGC's would render
>that person "clock blind", and those may be the people with severe
>sleep disorders and SAD. (my speculation)

Question of the day:
Why did nature select 484 nm to control our clocks?
Since some of our DNA matches the DNA in bacteria, I am
speculating that we simply inherited this mechanism from the
beginning of life - a circadian system that has worked
for billions of years, one that nature tells us, "if it ain't broke,
don't fix it."  We all now know that we are "breaking" it with
the advent of T. Edison followed by HID night lighting.

>Finding something new in mammalian anatomy is a big deal.
>It doesn't happen that often. The RGC's also fill in a very
>key missing link in the chain of circadian physiology and the
>understanding of biological clocks. This is great stuff.
>Steve Pauley MD

[Non-text portions of this message have been removed]


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