What is Orexin?

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  • Written By: Mary McMahon
  • Edited By: C. Wilborn
  • Last Modified Date: 11 August 2019
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Orexin is a hormone in the brain named after its role in the appetite. The word is derived from the Greek term for "appetite." There are two types of orexin found in the brain, known as orexin-A and orexin-B; these compounds may also be referred to as hypocretins. Researchers are studying the role of these hormones in the body to learn more about them and to determine whether or not they have potential clinical and medical applications.

Researchers first began to identify these hormones in the 1990s, starting with finding the gene involved in their production in the brains of rats. Over time, they were able to find the hormone itself, along with receptors in the brain that are sensitized to it. This laid the groundwork for research that could be used to learn more about how it functions, how the body regulates production of the hormone, and what is involved in metabolizing this hormone to clear it from the body when it is no longer needed.

One key role of orexin in the brain involves the regulation of appetite. This hormone also determines wakefulness levels. Studies with monkeys showed that animals deprived of sleep and exposed to orexin could perform much like monkeys that had been well rested, establishing the possibility of using the drug to treat sleep disorders and as a supplement for people who do not sleep enough.


Other studies with rats have demonstrated that those with more orexin receptors in their brains tend to be slimmer. This suggests that the hormone also plays a role not just in regulating appetite, but in regulating weight and overall metabolism. It does so in conjunction with other hormones as part of a complex system that keeps the body functioning; thus, orexin should not be viewed as a potential quick fix for people who are attempting to lose weight and keep it off.

Like other hormones, orexin is chemically complex, and because it works in concert with other hormones, it can be difficult to tease out its precise functions and to study the way it interacts with other hormones in the body. Extensive research can provide scientists with tools for understanding which hormones orexin interacts with and how. This in turn can be used to learn more about what this hormone does in the body and how it could potentially be synthesized and used to treat specific medical issues such as narcolepsy and sleep deprivation.


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Post 4

I found myself wondering how orexin might be linked to depression. I know a couple of the symptoms are loss of appetite and having trouble sleeping. I think part of the way depression works is that neurotransmitters in the brain don't function properly, and the right signals are not always sent. It seems like a lack of orexin could potentially end up with the same results.

Does anyone have any idea how hormones are involved in depression, and whether this might be a reasonable idea?

Post 3

@kentuckycat - I read a little bit about orexin, and I'm wondering what would happen if you did take it on a regular basis. From what I understand, the way it works is by fooling your brain into thinking you are rested. Since sleep reorganizes our memories and gives our body a chance to rest, using orexin to feel awake should theoretically lead to sleep deprevation symptoms in the end.

Post 2

I am really interested in orexin's effect on sleep. After I finished reading the article, I wondered if maybe orexin was behind narcoleptics falling asleep. I don't know anything about the condition, though, so that is just a thought.

Also, even though the hormone might be able to help people perform okay in certain situations, there is no way that it could be a substitute for getting enough sleep. Even if there was a way to buy orexin as a supplement, I don't think you can underestimate the usefulness of sleep. Depending on the real effects of orexin, I could see a lot of people abusing it and having the lack of real sleep hurt them.

Post 1

What gland in the body is responsible for producing orexin? I don't know if this is linked at all, but the article says orexin has some involvement in regulating our weight and metabolism. A lot of the hormones produced by the thyroid gland in the next do the same thing, so that would be my guess about where it is produced.

What does orexin do in the brain to control our appetite and help keep us focused? Does the hormone affect a certain lobe of the brain? Are there various receptors that handle orexin?

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