<unk>  (), also known as hypocretin, is a neuropeptide that regulates arousal, wakefulness, and appetite. The most common form of narcolepsy, type 1, in which the individual experiences brief losses of muscle tone (cataplexy), is caused by a lack of<unk>  in the brain due to destruction of the cells that produce it. There are only 10,000–20,000<unk> -producing neurons in the human brain, located predominantly in the perifornical area and lateral hypothalamus. They project widely throughout the central nervous system, regulating wakefulness, feeding, and other behaviours. There are two types of<unk>  peptide and two types of<unk>  receptor.<unk>  was discovered in 1998 almost simultaneously by two independent groups of researchers working on the rat brain. One group named it<unk> , from<unk> , meaning "appetite" in Greek; the other group named it hypocretin, because it is produced in the hypothalamus and bears a weak resemblance to secretin, another peptide. Officially, hypocretin (HCRT) is used to refer to the genes and transcripts, while<unk>  is used to refer to the encoded peptides. There is considerable similarity between the<unk>  system in the rat brain and that in the human brain.
Orexin
Cortisol
Thyroglobulin
Leptin
Adrenalone
Prorenin
Growth hormone
Parathyroid hormone