![]() ![]() In addition to revealing the normal role of orexin neurons in the brain, research has provided many insights into how a loss of orexin signaling causes sleepiness and cataplexy. (See Key discoveries below for more on some of the studies that have shed light on the role of orexins in narcolepsy.) The number of hypocretin (orexin)-producing neurons in the brain is markedly reduced in the brains of people with narcolepsy. Most likely, it is caused by less severe injury to the orexin neurons, resulting in fewer and less severe symptoms. Though much has been learned about narcolepsy with cataplexy, considerably less is known about the cause of narcolepsy without cataplexy. Thomas Scammell recalls the discovery of hypocretin and how it is lost in narcolepsy. In fact, REM sleep can become so poorly regulated that the paralysis or dreaming that normally occurs only in REM sleep can mix into wakefulness, causing cataplexy and dreamlike hallucinations.ĭr. The consequent lack of orexins results in lasting sleepiness and poor control of REM sleep. In people who have narcolepsy with cataplexy, most of the orexin-producing neurons die off. In individuals without narcolepsy and whose sleep is well regulated, orexins are released during wakefulness and increase activity in target neurons that promote wakefulness and suppress rapid-eye-movement (REM) sleep. (This website uses the term “orexins,” as this name is preferred by clinicians.) Orexins and brain function 1, 2 One group named them hypocretin-1 and -2, and the other group named them orexin-A and -B. Orexins were first discovered in 1998 when two research groups independently identified them in the brain. Orexins are released from these neurons during wakefulness and bind to specific orexin receptors on target neurons, which increases the activity of these neurons. Of the billions of neurons in the brain, only about 100,000–200,000 produce orexins. Orexins are only produced by a small cluster of neurons in the hypothalamus, a brain region located roughly behind the eyes and between the ears. Orexins are neurotransmitters, chemicals that transmit signals from a neuron to a target neuron. ![]() It regulates arousal, sleep, hunger, body temperature, and other fundamental behaviors. The hypothalamus is a deep brain region just in front of the brainstem. Recent research has revealed that narcolepsy with cataplexy is caused by a lack of orexins, also known as hypocretins, key brain chemicals that help sustain alertness and prevent REM sleep from occurring at the wrong times. ![]() Harvard Extension School, Psych E-1440, "Sleep and Mental Health".Undergraduate Sleep Education: GenEd 1038 at Harvard College.Undergraduate Opportunities to Perform Scientific Research.Treating Narcolepsy: Developing New Treatments.Treating Narcolepsy: Changes Across the Lifespan.Diagnosing Narcolepsy: Testing for Narcolepsy.Diagnosing Narcolepsy: Getting a Diagnosis of Narcolepsy.Diagnosing Narcolepsy: Finding a Doctor.Diagnosing Narcolepsy: Epworth Sleepiness Scale.What is Narcolepsy: The Science of Narcolepsy.What is Narcolepsy: Symptoms of Narcolepsy.What is Narcolepsy: Understanding Narcolepsy.Editorial Ethics and Compliance Standards. ![]()
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