Novel molecular clues behind nocturnal behavior

Research provides new insights into sleep/awake circadian rhythm patterns

Date: August 22, 2016

Source: University of California - Irvine

Research from University of California, Irvine scientists and their colleagues offers new insights into why many animals sleep at night and are active during the day, while others do the reverse.

A team headed by Qun-Yong Zhou, UCI professor of pharmacology, examined the day/night patterns of monkeys (diurnal) and mice (nocturnal) and found that although both process light through the eyes in a similar way, the signals that determine sleep/awake modes are sent to the brain via different routes and produce completely opposite sleep/awake patterns.

"Since humans are diurnal, this has clear implications for potential novel treatment of certain sleep or mood disorders," said Zhou, the study's lead author. Results appear online in Molecular Brain.

Sleep/awake patterns are among the basic physiological functions in virtually all organisms that are governed by circadian rhythms. These fundamental time-tracking systems anticipate environmental changes and adapt to the appropriate time of day.

Zhou and his colleagues discovered that the sleep/awake switch exists in the eyes within the intrinsically photosensitive retinal ganglion cells, or ipRGC. Previously, a brain region called the suprachiasmatic nucleus, or SCN, was believed to house the master clock that keeps the body on an approximately 24-hour schedule.

The current findings give the eyes a more central role in the control of the sleep/awake cycle. In the nocturnal mice, ipRGC and SCN appear to function similarly, and either could serve as the timekeeper. But in the diurnal monkeys, the eyes' ipRGC seems to be dominant.

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