If you are interested in the background and recent history of the research on mammalian SCN in line of Erik Herzog's work I described in VIP synchronizes mammalian circadian pacemaker neurons and A Huge New Circadian Pacemaker Found In The Mammalian Brain, you may want to look at these old Circadiana posts as well:
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Cutting Edge: Circadian Rhythm of Astrocytes (February 02, 2005):
Erik has done it again. He is not one to publish 30 papers per year, but whenever he publishes one, it always gives me the chills and thrills! What beautiful science:
Circadian Rhythm Generation and Entrainment in Astrocytes
Laura M. Prolo,1 Joseph S. Takahashi,2 and Erik D. Herzog1
1Department of Biology, Washington University, St. Louis, Missouri 63130-4899, and 2Howard Hughes Medical Institute and Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208
In mammals, the master circadian pacemaker is
considered the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN
consists of a heterogeneous population of neurons and relatively understudied
glia. We investigated whether glia, like neurons, rhythmically express circadian
genes. We generated pure cultures of cortical astrocytes from
Period2::luciferase (Per2::luc) knock-in mice and Period1::luciferase
(Per1::luc) transgenic rats and recorded bioluminescence as a real-time reporter
of gene activity. We found that rat Per1::luc and mouse Per2::luc astroglia
express circadian rhythms with a genetically determined period. These rhythms
damped out after several days but were reinitiated by a variety of treatments,
including a full volume exchange of the medium. If cultures were treated before
damping out, the phase of Per1::luc rhythmicity was shifted, depending on the
time of the pulse relative to the peak of Per1 expression. Glial rhythms
entrained to daily 1.5°C temperature cycles and were significantly sustained
when cocultured with explants of the adult SCN but not with cortical explants.
Thus, multiple signals, including a diffusible factor(s) from the SCN, are
sufficient to either entrain or restart circadian oscillations in cortical glia.
J Neurosci., 25:404-8. http://www.jneurosci.org/cgi/content/abstract/25/2/404
More and more complexity in the SCN (March 07, 2005):
Erik has done it again!
Vasoactive intestinal polypeptide needed by the brain's biological clock to coordinate daily rhythms
http://www.news-medical.net/?id=8229
Erik Herzog, Ph.D., Washington University assistant professor of Biology in Arts & Sciences, has discovered that VIP is needed by the brain's biological clock to coordinate daily rhythms in behavior and physiology. Neurons in the biological clock, an area called the suprachiasmatic nucleus (SCN), keep 24-hour time and are normally synchronized as a well-oiled marching band coming onto the field at half time. Herzog and graduate student, Sara Aton, found that mice lacking the gene that makes VIP or lacking the receptor molecule for VIP suffer from internal de-synchrony. When they recorded the electrical activity of SCN neurons from these mice, they found that many had lost their beat while others were cycling but unable to synch to each other.
That VIP is the signal between pacemaker cells is exciting discovery in itself, but the fact that in VIP-less mice, many SCN cells stop cycling altogether is really a novel and disturbing finding.
And that there are a number of subsets of pacemaker cells, each with a different period and different function adds to the complexity:
The circadian clock: Understanding nature's timepiece
http://www.eurekalert.org/pub_releases/2005-03/uoc-tcc030405.php
Dr. Michael Antle, a neuroscientist in the U of C's Department of Psychology, has conclusively shown that the 20,000 cells are organized in a complex network of groups that perform different functions - contrary to the previously held belief that each cell did the same thing. Antle, an emerging leader in the field, has two new papers on the subject: one is featured on the March cover of the prestigious Trends in Neurosciences, and another is due out in a forthcoming issue of the Journal of Neurosciences.
Sleepiness May Be Associated With Visual Impairment
http://www.medindia.net/news/view_news_detail.asp?x=3343&t=gn
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