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Consider a scenario where a person's melatonin secretion gets inhibited (and that person also don't get external melatonin);

Will this person feel sleepiness and a desire to sleep? Or, since that person is not having melatonin being secreted, there will not be any sleepiness?

Searching for this, I found that "melatonin levels in the blood rise sharply and you begin to feel less alert". However, I would like to know if a person which is not have melatonin being secreted will not feel sleepiness.

Is Melatonin necessary to sleep or even to have desire for sleep?

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  • $\begingroup$ I think the article you linked to gives you the answer. After it talks of feeling less alert, it then says that sleep is more inviting. $\endgroup$ – Chris Rogers Feb 20 at 19:15
  • $\begingroup$ @ChrisRogers So, if the melatonin secretion of someone was inhibited, this person will not have a desire to sleep? $\endgroup$ – Mycroft Feb 20 at 21:04
  • $\begingroup$ That is a very good question because when you look at night shift workers melatonin secretion would have been reduced due to the fact that after their shift the daylight affects melatonin release, however the person needs to sleep in order to function the best they can in the next shift at work. In this case in my experience it was tiredness from working which made me sleepy. $\endgroup$ – Chris Rogers Feb 23 at 13:08
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I don’t have a direct or a very reputable reference to answer this question, but I work in the clinical field and have seen many insomniacs, so I’ll offer you the answers based on the references and the experiences I have for you to consider in the meantime.

Melatonin’s principal function is to convey the message of darkness or information about timing of the day and night to the central circadian clock. [1-3]

In mammals, a central circadian clock, located in the suprachiasmatic nuclei (SCN) of the hypothalamus, tunes the innate circadian physiological rhythms to the ambient 24 h light–dark cycle to invigorate and optimize the internal temporal order. … Melatonin conveys the message of darkness to the clock and induces night‐state physiological functions, for example, sleep/wake blood pressure and metabolism. [1]

and

The primary physiological function of melatonin, whose secretion adjusts to night length, is to convey information concerning the daily cycle of light and darkness to body structures. [2]

Melatonin does not have direct effects on sleep-wake cycles, which are governed by other complex neural circuits in the brainstem. It is not one of the neurotransmitters in the complex sleep-wake neural circuits, which utilize cholinergic, noradrenergic, and serotonergic neurotransmitters. Melatonin just influences the circuits by conveying the message of darkness or timing of the day and night to the SCN, the central circadian clock, which in turn, affects the sleep-wake neural circuits.

The highly organized sequence of human sleep states is actively generated by nuclei in the brainstem, most importantly the cholinergic nuclei of the pons–midbrain junction, the noradrenergic cells of the locus coeruleus, and the serotonergic neurons of the raphe nuclei. The activity of the relevant cell groups controls the degree of mental alertness on a continuum from deep sleep to waking attentiveness. These brainstem systems are in turn influenced by a circadian clocks located in the suprachiasmatic nucleus and VLPO of the hypothalamus. The clock adjusts periods of sleep and wakefulness to appropriate durations during the 24-hour cycle of light and darkness that is fundamental to life on Earth. [4]

Clinically, melatonin seems to be neither necessary nor sufficient for sleep to occur. This is evident by the fact that when melatonin is high in the night and a person is about to fall asleep or even asleep, he /she can be awakened and remain awake by some strong stimulus despite the high level of melatonin at that time. Also, if melatonin is given to awake people, they may feel like sleeping, but, unlike strong sleeping pills (which mostly affect cholinergic, noradrenergic, and/or serotonergic neurotransmissions), they may not fall asleep if other things such as surrounding circumstances do not allow them to sleep. So, melatonin alone is not sufficient for sleep to occur or be maintained.

On the other hand, when a person is deprived of sleep for one or more nights, he/she can fall asleep during daytime even if the level of melatonin is low at that time. Or, if strong sleeping pills (which mostly affect those mentioned neurotransmissions) are given to awake people during daytime, when melatonin level is low, they will fall asleep despite the low level of melatonin. So, melatonin alone is not necessary for sleep to occur or be maintained.

In summary, the principal role of melatonin regarding sleep is to convey the message of darkness or information about timing of the day and night to the central circadian clock to influence the sleep-wake neural circuits so that the animal, including human, can sleep at appropriate time; but it is not necessary or sufficient for sleep to occur or be maintained.

References.

  1. Nava Zisapel. New perspectives on the role of melatonin in human sleep, circadian rhythms and their regulation. Br J Pharmacol. 2018 Aug; 175(16): 3190–3199.

  2. Claustrat B, Leston J. Melatonin: Physiological effects in humans.. Neurochirurgie. 2015 Apr-Jun;61(2-3):77-84. doi: 10.1016/j.neuchi.2015.03.002.

  3. Pandi-Perumal SR1, Srinivasan V, Spence DW, Cardinali DP. Role of the melatonin system in the control of sleep: therapeutic implications. CNS Drugs. 2007;21(12):995-1018.

  4. Purves D. Chapter 27. Sleep and wakefulness. Neural circuits governing sleep. In Neuroscience. 3rd ed. Sunderland, Massachusetts: Sinauer Associates Inc; 2004. p 674-684.

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  • $\begingroup$ Your answer seems a little contradictory to me. You say that melatonin does not have direct effects on sleep-wake cycles, but then melatonin influences the central circadian clock which in turn affects the sleep-wake neural circuits. The arguement that melatonin is insufficient for sleep to occur seems counterintuitive too as melatonin is high when sleepy. Ok you can choose to override sleep and force yourself to stay awake as I found when working nights full time but nevertheless, you are primed for sleep in my mind. How do you reconcile this? $\endgroup$ – Chris Rogers Feb 23 at 13:01
  • $\begingroup$ In first quote: "Melatonin conveys the message of darkness to the clock and induces night‐state physiological functions, for example, sleep/wake blood pressure and metabolism. [1]" then after second quote, "Melatonin does not have direct effects on sleep-wake cycles, which are governed by other complex neural circuits in the brainstem." $\endgroup$ – Chris Rogers Feb 23 at 14:22
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    $\begingroup$ @ChrisRogers Melatonin has direct effects on SCN, the central circadian clock, which in turn regulates the sleep-wake neural circuits, but melatonin does not have direct effects on the sleep-wake neural circuits per se and is not one of the neurotransmitters the sleep-wake neural circuits utilize either. Its effects on the sleep-wake neural circuits are via SCN (which receives input from other sources too). Thus, I don’t think it’s correct to say that melatonin has direct effects on the sleep-wake cycles. It only has indirect, regulatory effects on sleep-wake cycles via SCN. $\endgroup$ – user287279 Feb 23 at 15:41
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    $\begingroup$ If the high melatonin level is SUFFICICIENT for sleep to occur, then sleep MUST occur when melatonin is high. But this is not true, as I exampled in the answer, a person cannot fall asleep even if the melatonin level is high if he/she is stimulated to be awake, such as from anxiety, pain, loudness, etc. So, a person needs other factors too to fall asleep; thus, high melatonin level alone is NOT SUFFICIENT – again, other factors are also needed for a person to fall asleep. $\endgroup$ – user287279 Feb 23 at 15:45
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    $\begingroup$ And may I repeat the conclusion again: the principal role of melatonin regarding sleep is “to convey the message of darkness or information about timing of the day and night” to the central circadian clock “to influence the sleep-wake neural circuits so that the animal, including human, can sleep at appropriate time”… $\endgroup$ – user287279 Feb 23 at 15:46

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