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Bright light arouses us. Bright light makes it easier to stayawake. Very bright light not only arouses us but is known to haveantidepressant effects. Conversely, dark rooms can make us sleepy.It's the reason some people use masks to make sure light doesn'twake them while they sleep. Now researchers at UCLA have identified the group of neurons thatmediates whether light arouses us or not. Jerome Siegel, aprofessor of psychiatry at the Semel Institute for Neuroscience andHuman Behavior at UCLA, and colleagues report in the current onlineedition of the Journal of Neuroscience that the cells necessary fora light-induced arousal response are located in the hypothalamus,an area at the base of the brain responsible for, among otherthings, control of the autonomic nervous system, body temperature,hunger, thirst, fatigue and sleep. These cells release a neurotransmitter called hypocretin, Siegelsaid. The researchers compared mice with and without hypocretin andfound that those who didn't have it were unable to stay awake inthe light, while those who had it showed intense activation ofthese cells in the light but not while they were awake in the dark. This same UCLA research group earlier determined that the loss ofhypocretin was responsible for narcolepsy and the sleepiness associated with Parkinson's disease. But the neurotransmitter's role in normal behavior was, untilnow, unclear. "This current finding explains prior work in humans that found thatnarcoleptics lack the arousing response to light, unlike otherequally sleepy individuals, and that both narcoleptics andParkinson's patients have an increased tendency to be depressedcompared to others with chronic illnesses," said Siegel, who isalso a member of the UCLA Brain Research Institute and chief ofneurobiology research at the Sepulveda Veterans Affairs MedicalCenter in Mission Hills, Calif. Prior studies of the behavioral role of hypocretin in rodents hadexamined the neurotransmitter's function during only light phases(normal sleep time for mice) or dark phases (their normal waketime), but not both. And the studies only examined the rodents whenthey were performing a single task. In the current study, researchers examined the behavioralcapabilities of mice that had their hypocretin genetically"knocked-out" (KO mice) and compared them with the activities ofnormal, wild-type mice (WT) that still had their hypocretinneurons. The researchers tested the two groups while they performeda variety of tasks during both light and dark phases. Surprisingly, they found that the KO mice were only deficient atworking for positive rewards during the light phase. During thedark phase, however, these mice learned at the same rate as theirWT littermates and were completely unimpaired in working for thesame rewards. Consistent with the data in the KO mice, the activity of hypocretinneurons in their WT littermates was maximized when working forpositive rewards during the light phase, but the cells were notactivated when performing the same tasks in the dark phase. "The findings suggest that administering hypocretin and boostingthe function of hypocretin cells will increase the light-inducedarousal response," Siegel said. "Conversely, blocking theirfunction by administering hypocretin receptor blockers will reducethis response and thereby induce sleep." Further, Siegel noted, "The administration of hypocretin may alsohave antidepressant properties, and blocking it may increasetendencies toward depression . So we feel this work has implications for treating sleepdisorders as well as depression." Other authors on the study included Ronald McGregor (first author),Ming-Fung Wu, Grace Barber and Lalini Ramanathan, all of UCLA, theVeterans Affairs Greater Los Angeles Healthcare System and the UCLABrain Research Institute. The research was supported by the National Institutes of Health andthe Medical Research Service of the Department of Veterans Affairs.The authors report no conflict of interest. Additional References Citations. I am an expert from cylindrical-rollerbearings.com, while we provides the quality product, such as Rolling Mill Bearings Manufacturer , Needle Roller Bearings Manufacturer, Rotary Table Bearings,and more.
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