June 10,University of Wisconsin-Madison Prominent characteristics of the syndrome include an elongated face, large or protruding ears, and low muscle tone. Wikipedia Fragile X syndrome is the most common inherited intellectual disability and the greatest single genetic contributor to autism. Unlocking the mechanisms behind fragile X could make important revelations about the brain.
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This article has been cited by other articles in PMC. Abstract The hypothalamus monitors body homeostasis and regulates various behaviors such as feeding, thermogenesis, and sleeping. Orexins also known as hypocretins were identified as endogenous ligands for two orphan G-protein-coupled receptors in the lateral hypothalamic area.
For example, orexin neurons are regulated by peripheral metabolic cues, including ghrelin, leptin, and glucose concentration.
This suggests that they may provide a link between energy homeostasis and arousal states. A link between the limbic system and orexin neurons might be important for increasing vigilance during emotional stimuli.
Orexins are also involved in reward systems 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.
Within this region, the lateral hypothalamic area LHA has been regarded as an important center for feeding and arousal because animal models with LHA lesions exhibit hypophagia and decreased arousal that frequently leads to death.
Orexin A and orexin B also known as hypocretin 1 and hypocretin 2 are neuropeptides expressed exclusively by LHA neurons. Orexin-producing neurons orexin neurons project their axons throughout the brain Peyron et al. Remarkably, dense projections of orexin neurons are observed in the serotonergic dorsal raphe nucleus DRnoradrenergic locus coeruleus LCand histaminergic tuberomammillary nucleus TMN ; and all of these nuclei are involved in promoting arousal Saper et al.
Consistently, deficiencies of orexin function were found in human narcolepsy Nishino et al. Past studies also revealed roles for orexin neurons beyond feeding and arousal, including autonomic nervous system control Sellayah et al. In this review, we first discuss the basic biological features of orexins and their receptors, and we then describe the neuronal inputs and outputs of the orexin neurons.
Finally, we discuss the various physiological roles of the orexin system, focusing on the regulation of sleep and wakefulness.
They found a novel family of neuropeptides that binds to two closely related orphan GPCRs. At the same time, de Lecea et al.
Prepro-orexin polypeptide is proteolysed to produce two orexins, orexin A and orexin B. Orexin A is a amino acid peptide of 3. The four Cys residues of orexin A form two sets of intrachain disulfide bonds.
This structure is completely conserved among several mammalian species human, rat, mouse, cow, sheep, dog, and pig. On the other hand, rat orexin B is a amino acid, C-terminally amidated, linear peptide of 2. In situ hybridization of prepro-orexin shows orexin-containing neurons are located in the LHA.
Prepro-orexin mRNA was shown to be upregulated under fasting conditions, indicating that these neurons somehow sense the animal's energy balance Sakurai et al.
Recently, the forkhead box transcription factor Foxa2, a downstream target of insulin signaling, was reported to be involved in this transcriptional regulation Silva et al.
While orexin neurons are localized within the LHA, they have widespread projections throughout the brain Peyron et al. Therefore, it is important to know the distribution pattern of orexin receptors to identify the functional neuronal network. Consistently, orexin-deficient mice display a narcolepsy-like phenotype Chemelli et al.Implanted devices send targeted electrical stimulation to the nervous system to interfere with abnormal brain activity, and it is commonly assumed that neurons are the only important brain cells that need to be stimulated by these devices.
Adult-born neurons therefore play an important role in both the identification of a sensory stimulus and the positive value associated with that sensory experience. The neurons generated shortly after birth are unable to perform this function.
HKIV (glucokinase, GK) is a minor isoform of hexokinase in the brain that has an important role in glucose-sensing neurons; it is specific for glucose and is not inhibited by GlcP. Ketogenic diet a diet that has a high fat and low carbohydrate content so that plasma levels of ketone bodies (acetoacetate and β-hydroxybutyrate) rise and serve .
It also plays an important role in the central nervous system in maintaining cognitive function. There are several dopamine pathways in the brain, and this neurotransmitter is involved in many functions, including motor control, reward and reinforcement, and motivation.
How to measure brain activity in people; What are neurotransmitters. Oct 22, · Sleep is important to a number of brain functions, including how nerve cells (neurons) communicate with each other.
In fact, your brain and body stay remarkably active while you sleep. Recent findings suggest that sleep plays a housekeeping role that removes toxins in . Mar 06, · The LHA, where orexin neurons exist, is a brain region historically implicated in reward and motivation, and orexin neurons project to many brain areas including the LC, nucleus accumbens, and VTA (Fadel and Deutch, ) that are implicated in behavioral responses to drugs of abuse.