Herbie Murray
Orexins, also known as hypocretins, are neuropeptides that are exclusively expressed by neurons in the lateral hypothalamic area. They are key modulators of the sleep/wakefulness cycle and play an important role in regulating sleep. Orexin neurons strongly excite various brain nuclei with important roles in wakefulness, including the dopamine, norepinephrine, histamine, and acetylcholine systems. A lack of orexin neurons has been linked to sleep disorders such as narcolepsy and insomnia, with medications like suvorexant and lemborexant targeting the orexin system to induce sleep. Orexins also influence mood, learning, and memory, and their absence can lead to problems in these areas. Overall, orexins are crucial in maintaining the balance between sleep and wakefulness, and understanding their role has led to advancements in treating sleep disorders.
| Characteristics | Values |
|---|---|
| Orexin's role in sleep | Orexin is a neuropeptide that regulates sleep and wakefulness. |
| Orexin and sleep disorders | Lack of orexin is associated with narcolepsy and insomnia. |
| Orexin and arousal | Orexin neurons inhibit sleep to promote arousal. |
| Orexin and emotions | Orexin neurons play a role in the physiological responses associated with emotions. |
| Orexin and energy | Orexin regulates energy expenditure and may be more important in this regard than in regulating food intake. |
| Orexin and learning | Insufficient orexin can cause problems with learning and memory. |
| Orexin and treatment | Dual orexin receptor antagonists (DORAs) are a new type of prescription sleep aid that targets the body's orexin system. |
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What You'll Learn
Orexin's role in sleep/wakefulness
Orexins, also known as hypocretins, are neuropeptides that are exclusively expressed by neurons in the lateral hypothalamic area. They are key modulators of the sleep/wakefulness cycle. Orexins activate orexin neurons, monoaminergic and cholinergic neurons in the hypothalamus/brainstem regions, to maintain a long, consolidated awake period. Orexins are involved in the coordination of emotion, energy homeostasis, and the reward system. They also play a role in the physiological responses associated with emotions.
Orexins promote wakefulness and regulate energy expenditure. Central administration of orexin-A strongly promotes wakefulness, increases body temperature and locomotion, and elicits a strong increase in energy expenditure. Orexin neurons also contribute to arousal maintenance through indirect inhibition of sleep-promoting neurons of the ventrolateral preoptic nucleus. Activation of this subcortical circuit rapidly drives wakefulness from sleep by differentially modulating the activity of ventrolateral preoptic neurons. Orexin neurons also innervate the preoptic region, including the VLPO, and stimulation during NREM sleep, as compared to REM sleep, doubled the length of the evoked arousals.
Orexin-deficient people with narcolepsy have increased obesity rather than decreased BMI, indicating that orexin deficits cause narcolepsy. Orexin antagonists, such as almorexant, have clear sleep-inducing activity and are used to treat insomnia. Orexin receptor mutations cause the sleep disorder canine narcolepsy in Doberman Pinschers, and genetic knockout mice lacking the gene for orexin also exhibit narcolepsy.
Orexins also excite neurons important in regulating mood. Having too much or too little orexin activity has been linked to depression and other mental health conditions, such as anxiety, panic disorder, addictions, and post-traumatic stress disorder. Orexins encourage the creation of new neurons in the hippocampus, which is important for learning, memory, and spatial abilities.
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Orexin and narcolepsy
Orexins are neuropeptides produced in a part of the brain called the hypothalamus. They are released by projections of neurons to much of the CNS, from the cortex to the spinal cord. Orexins have many important functions in the body, including helping to regulate sleep. They do this by exciting neurons that produce neurotransmitters, such as the locus coeruleus, and by inhibiting neurons in the ventrolateral preoptic nucleus, which is a region of the brain whose neuronal activity is imperative to proper sleep function. Orexins also excite neurons important in regulating mood and encouraging the creation of new neurons in the hippocampus, which is important for learning, memory, and spatial abilities.
Orexins promote wakefulness and inhibit sleep to promote arousal. Studies indicate that a major role of the orexin system is to integrate metabolic, circadian, and sleep debt influences to determine whether an animal should be asleep or awake and active. Orexin neurons strongly excite various brain nuclei with important roles in wakefulness, including the dopamine, norepinephrine, histamine, and acetylcholine systems. They also appear to play an important role in stabilizing wakefulness and sleep.
Narcolepsy is a chronic sleep disorder that results in excessive daytime sleepiness, an inability to consolidate wakefulness during the day (and sleep at night), and cataplexy, which is the loss of muscle tone in response to strong, usually positive, emotions. Narcolepsy is caused by a highly selective and severe loss of orexin neurons, resulting in low levels of orexins in the brain and cerebrospinal fluid. This discovery has led to the recognition of two types of narcolepsy: narcolepsy type 1 (NT1) and narcolepsy type 2 (NT2). NT1 is characterized by chronic sleepiness plus cataplexy, and CSF orexin levels in this disorder are very low or undetectable. NT2 has generally less severe symptoms, and 90% of patients have normal CSF orexin levels.
Intranasal orexin is able to increase cognition in primates, especially under sleep-deprived situations, which may provide an opportunity for the treatment of excessive daytime sleepiness associated with narcolepsy. Dual orexin receptor antagonists (DORAs) are a new type of prescription sleep aid that targets the body's orexin system. These medications work by blocking the effects of orexins in the body, reducing the drive to stay awake, and facilitating sleep.
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Orexin antagonists and insomnia treatment
Orexins are neuropeptides that play a crucial role in regulating sleep. They promote wakefulness and arousal by stimulating specific neurons in the brain. However, an imbalance in orexin activity can lead to sleep disorders, such as narcolepsy, and other mental health conditions. To address these issues, researchers have developed dual orexin receptor antagonists (DORAs), which are a new class of medications designed to block the effects of orexins and facilitate sleep.
DORAs are a novel approach to treating insomnia, a common condition that can negatively impact an individual's cognition, productivity, and quality of life. By targeting the orexin system, DORAs help reduce the drive to stay awake and induce sleep. Cognitive-behavioral therapy (CBT) is typically the first-line treatment for insomnia, but DORAs offer an additional pharmaceutical option for those who cannot participate in CBT or as a complementary treatment.
Currently, three orexin receptor antagonists have been approved by the Food and Drug Administration (FDA) for the treatment of insomnia: suvorexant, lemborexant, and daridorexant. These medications work by blocking both orexin receptors, OX1R and OX2R, which are responsible for maintaining arousal and wakefulness. By antagonizing these receptors, DORAs promote sleepiness and help individuals with insomnia fall asleep and remain asleep.
The discovery of the role of orexins in sleep regulation has opened up new possibilities for treating sleep disorders. While DORAs are a promising treatment option, more clinical trials are needed to comprehensively evaluate their safety and effectiveness across different subclasses of insomnia patients. Additionally, it is important to consider the specific requirements of each patient, as an agent with too short of a half-life may not promote sleep throughout the entire sleep period, while an agent with too long of a half-life may cause residual sleepiness beyond the necessary sleep period.
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Orexin's impact on mood and mental health
Orexins are neuropeptides that are exclusively expressed by neurons in the lateral hypothalamic area of the brain. They are key modulators of the sleep/wakefulness cycle and play a role in regulating sleep. Orexin neurons strongly excite various brain nuclei with important roles in wakefulness, including the dopamine, norepinephrine, histamine, and acetylcholine systems. They also promote the creation of new neurons in the hippocampus, which is important for learning, memory, and spatial abilities.
The impact of orexins on mood and mental health is an area of active research. Orexins excite neurons that are important for regulating mood. Studies have shown that having too much or too little orexin activity can be linked to depression and other mental health conditions such as anxiety, panic disorder, addictions, and post-traumatic stress disorder.
Orexins also play a role in the reward system and the mechanisms of drug addiction. Research has shown that orexin neurons sense the outer and inner environment of the body and maintain the proper wakefulness level of animals for survival. This suggests that orexins may be involved in increasing vigilance during emotional stimuli, which could have implications for mood and mental health.
Additionally, orexin antagonists have been found to cause signs of sleep both subjectively and according to electrophysiological measures, providing a potential new approach to treating insomnia by targeting wakefulness. Orexin-based treatments for insomnia include suvorexant, lemborexant, and daridorexant, which are approved by the US Food and Drug Administration (FDA). These medications work by blocking the effects of orexins in the body, reducing the drive to stay awake, and facilitating sleep.
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Orexin's role in arousal
Orexins, also known as hypocretins, are neuropeptides that are exclusively expressed by neurons in the lateral hypothalamic area. Orexins have many important functions in the body, including helping to regulate our sleep. Orexin neurons strongly excite various brain nuclei with important roles in wakefulness, including the dopamine, norepinephrine, histamine and acetylcholine systems, and appear to play an important role in stabilizing wakefulness and sleep. Orexin neurons also contribute to arousal maintenance through the indirect inhibition of sleep-promoting neurons in the ventrolateral preoptic nucleus. Activation of this subcortical circuit rapidly drives wakefulness from sleep by differentially modulating the activity of ventrolateral preoptic neurons.
Orexins are involved in the reward system and the mechanisms of drug addiction. These findings suggest that orexin neurons sense the outer and inner environment of the body and maintain the proper wakefulness level of animals for survival. Orexins also excite neurons that are important in regulating mood. A link between the limbic system and orexin neurons might be important for increasing vigilance during emotional stimuli. Orexins also encourage the creation of new neurons in the hippocampus, which is important for learning, memory, and spatial abilities.
Orexins were initially suggested to be primarily involved in the stimulation of food intake, based on the finding that central administration of orexin-A and -B increased food intake. However, it is now understood that they are involved in a wide range of functions beyond feeding and arousal, including autonomic nervous system control, reward and stress systems, and the coordination of emotion, energy homeostasis, and the reward system. Orexin neurons are regulated by peripheral metabolic cues, including ghrelin, leptin, and glucose concentration.
Orexin-based medications are a new type of prescription sleep aid that targets the body's orexin system. These medications work by acting as orexin receptor antagonists, meaning that they block the effects of orexins in the body, reduce the drive to stay awake, and facilitate sleep.
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Frequently asked questions
Orexins, also known as hypocretins, are neuropeptides that are exclusively expressed by neurons in the lateral hypothalamic area. They are key modulators of the sleep/wakefulness cycle.
Orexins activate orexin neurons, monoaminergic and cholinergic neurons in the hypothalamus/brainstem regions, to maintain a long, consolidated awake period. They also inhibit neurons in the ventrolateral preoptic nucleus, which is a region of the brain whose neuronal activity is imperative to proper sleep function.
Orexin antagonists like suvorexant, lemborexant, and daridorexant are used to treat insomnia by blocking the effects of orexins in the body, reducing the drive to stay awake, and facilitating sleep.
