New Study Identifies Brain Cells That Regulate Sleep Response
A new study out of UCLA found that the cells that control a person’s response to light and dark is located in the hypothalamus. The study was conducted by Jerome Siegel, a Professor of Psychiatry at the Semel Institute for Neuroscience and Human Behavior at UCLA, and his colleagues.
In the current online edition of the Journal of Neuroscience, Professor Siegel explains how the area at the base of the brain called the hypothalamus controls the autonomic nervous system, and functions such as body temperature, hunger and thirst, energy and fatigue, and we now know, wakefulness or sleepiness.
In the study, Siegel and his colleagues found that a specific group of neurons in the hypothalamus called hypocretin — scientifically known as hypothalamic orexin/hypocretin (orx/hcrt) neurons — control whether light arouses us or not, and thus whether we feel sleepy or not. Too little hypocretin inhibits a person’s ability to respond to light stimuli, and thus may inhibit their ability to fall asleep in the dark.
The results of the new study reinforce the findings of an earlier study by the same research group, which determined that the loss of hypocretin was responsible for narcolepsy and the sleepiness associated with Parkinson’s disease. But the neurotransmitter’s role in normal behavior was, until now, unclear.
How the Study Was Conducted
The researchers examined the behavior of mice that had their hypocretin genetically “knocked-out” (called KO mice), and compared them to the behavior of normal, wild-type mice (called WT mice) that still had their hypocretin neurons.
The two groups were studied while they performed a variety of tasks in both light and dark phases. The result of the mice hypocretin test was that the KO mice without hypocretin were deficient at working for positive rewards during the light phase. During the dark phase, however, the mice without hypocretin learned at the same rate as their WT littermates with hypocretin.
Implications of the Findings
As a result of the findings, Professor Siegel suggests that by administering hypocretin and boosting the function of hypocretin cells, a person’s light-induced arousal response will increase. Conversely, blocking a person’s light response function by administering hypocretin receptor blockers will reduce their light response, and thus induce sleep. Siegel also noted that the administration of hypocretin may also have antidepressant properties, and blocking hypocretin may increase a person’s tendencies toward depression.
Source: R. McGregor, M.-F. Wu, G. Barber, L. Ramanathan, J. M. Siegel. Highly Specific Role of Hypocretin (Orexin) Neurons: Differential Activation as a Function of Diurnal Phase, Operant Reinforcement versus Operant Avoidance and Light Level. Journal of Neuroscience, 2011; 31 (43): 15455 DOI: 10.1523/JNEUROSCI.4017-11.2011
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