Monday, March 07, 2005

ClockNews #29: More and more complexity in the SCN

Erik has done it again!

Vasoactive intestinal polypeptide needed by the brain's biological clock to coordinate daily rhythms

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 thet 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
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

Latest research shows that people who have optic nerve damage might be at anincreased risk of a sleep disorder. For the study researchers involved 25 people with visual impairment. The participants had their sleep-wakefulness cycles followed for 14 days, and their results were compared with those of 12 young subjects with normal sight. It was discovered that those with optic nerve disease were 20-times more likely to have daytime sleepiness than those with normal sight and people with optic nerve damage were nine-times more likely to suffer sleepiness than even those were blind due to non-optic nerve disease. Recent work has indicated that the retina contains non-visual photoreceptors that communicate with the area of the brain involved in circadian rhythms. Thus researchers say, physicians and other health care professionals should be sensitive to the possibility of daytime sleepiness or insomnia, particularly in patients with severe optic nerve disease. Researchers also add that these findings suggest the need to try to maintain any remaining vision in people with optic nerve damage as it plays a crucial role in health and longevity.

Bill Seeks to Ban Nurses' Overtime

"Instead of hiring more nurses, understaffed hospitals typically . . . order nurses to work back-to-back eight-hour shifts or four extra hours on top of a 12-hour shift, even though it is dangerous for patients and nurses," Kennedy said.
A recent report by Circadian concurs. Focusing on the effects of shiftwork on nurses, the Circadian report found that nearly 20 percent of nurses cited fatigue as one of the top three job-related health and safety risks in their profession. The report also noted that fatigue and short staffing can affect the quality of patient care.


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