What is Hypocretin?

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  • Written By: Misty Wiser
  • Edited By: Allegra J. Lingo
  • Last Modified Date: 28 May 2020
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Hypocretin is a neuropeptide used to transmit information between brain cells. The neurotransmitters hypocretin receptor type 1 and hypocretin receptor type 2 play an important role in the regulation of sleep cycles. Increased levels of this neurotransmitter may cause an increase in appetite. Low or nonexistent levels of these hormones are found in people with narcolepsy, a condition that causes excessive daytime sleepiness.

The peptide hypocretin is also known as orexin. Both terms may be used interchangeably in medical nomenclature. The term hypocretin is generally used when referencing sleep cycles, and orexin is more likely to be used when referring to appetite.

Less than 20,000 cells in the brain are able to produce this sleep-regulating hormone. The hypothalamus secretes molecules of this peptide neurotransmitter into the fluid around the brain and spinal cord. These molecules are not diffused into the surrounding tissues or the bloodstream. Blood tests are unable to reveal if the levels of this hormone are within normal limits.

Testing of hypocretin-1 levels is done through a lumbar spinal tap. A long needle is inserted into the spinal cord between the third and fourth vertebrae, and a small amount of cerebrospinal fluid (CSF) is aspirated into a syringe. The fluid is sent to a laboratory to analyze the concentration of the neurotransmitter. Test results may indicate a need for a sleep study to confirm a diagnosis of narcolepsy.

Side effects of the lumbar puncture are considered mild. Many people report a severe headache and lower backache within three days of the procedure. The headache pain is usually greater towards the front of the head or at the base of the skull. Over-the-counter pain relievers may be used to reduce pain. Some doctors may try to prevent the headache by flushing the aspiration site with saline after the CSF sample has been collected.

The spinal tap procedure rarely has serious complications. Nerve damage is possible from the insertion of the needle into the spinal column. This damage could result in a loss of sensation or paralysis in the lower half of the body.

Medication is usually prescribed to treat the symptoms of a hypocretin-1 deficiency. These medicines are not a synthetic form of the missing neurotransmitter. Most people with narcolepsy are prescribed modafinil to promote wakefulness. The medicine acts on the anterior portion of the hypothalamus, the same part of the brain that produces hypocretin. Modafinil prevents the reuptake of the neurotransmitter noradrenaline, resulting in an improved mood and an increased feeling of alertness.

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Post 3

@irontoenail - It's the cataplexy which I find interesting about narcolepsy, rather than the sleeping aspects. I mean, I know it would be really awful to have any of it, but how strange and inconvenient it must be to suddenly lose all muscle tone whenever you get too excited, or happy.

It doesn't affect everyone with narcolepsy though so maybe your friend doesn't have that symptom.

Post 2

@pleonasm - I had a friend who had to have a lumbar puncture in order to test whether or not she had narcolepsy.

She said that it was really painful, but not quite as bad as she had been led to believe it would be. Maybe it depends on the person, for example how fat or skinny they are.

At any rate, they found out that she did have narcolepsy, which, while not great, was actually a great relief to her.

While people think of it as a disorder that makes you fall asleep at odd times, it can also keep you awake when you really want to sleep. For a long time, she just thought she was an insomniac, but it turned out to be a real condition keeping her awake, and not just a figment of her imagination.

Post 1

Lumbar punctures are supposed to be extremely painful. I've never had to do it myself, but my sister has and she said it hurt much worse than the worse vaccination she's ever had.

Plus you have to hold quite still in order to make sure you don't do yourself any damage.

I guess they can't really numb the area since it's the spine they are tapping in to. If they did numb it, you wouldn't be able to walk for a while afterwards.

My sister had to have one because of a meningitis scare at her school. She was showing what looked like symptoms, but it turned out not to be meningitis, thank goodness.

Which made her even more annoyed about having to have a lumbar puncture. But, as I told her, it's better to be safe than sorry.

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