Cocaine addiction traced to increase in number of orexin neurons

A study in cocaine-addicted rats reports long-lasting increases in the number of neurons that produce orexin—a chemical messenger important for sleep and appetite—that may be at the root of the addiction. The study, performed ...

Alzheimer's disease & dementia

Dysregulation in orexinergic system associated with Alzheimer disease

In patients with Alzheimer disease (AD), increased cerebrospinal fluid levels of orexin, which helps regulate the sleep-wake cycle, may be associated with sleep deterioration, which appears to be associated with cognitive ...

Medical research

Orexin: A hormone that fights fat with fat

The fat we typically think of as body fat is called white fat. But there's another type—known as brown fat—that does more than just store fat. It burns fat. Scientists used to think that brown fat disappeared after ...

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Orexins, also called hypocretins, are the common names given to a pair of excitatory neuropeptide hormones that were simultaneously discovered by two groups of researchers in rat brains.

The two related peptides (Orexin-A and B, or hypocretin-1 and -2), with approximately 50% sequence identity, are produced by cleavage of a single precursor protein. Orexin-A/hypocretin-1 is 33 amino acid residues long and has two intrachain disulfide bonds, while Orexin-B/hypocretin-2 is a linear 28 amino acid residue peptide. Studies suggest that orexin A/hypocretin-1 may be of greater biological importance than orexin B/hypocretin-2. Although these peptides are produced by a very small population of cells in the lateral and posterior hypothalamus, they send projections throughout the brain. The orexin peptides bind to the two G-protein coupled orexin receptors, OX1 and OX2, with Orexin-A binding to both OX1 and OX2 with approximately equal affinity while Orexin-B binds mainly to OX2 and is 5 times less potent at OX1.

The orexins/hypocretins are strongly conserved peptides, found in all major classes of vertebrates.[citation needed]

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