▎ WuXi AppTec content team editor
Every night, when you fall into deep sleep, your brain gradually moves into different stages of activity. In one stage, the brain is particularly active, often self-directed, creating all sorts of bizarre or sweet dreams. At this stage, because the eyeball moves rapidly, scientists who study sleep call it the "rapid eye movement" (REM).
Image credit: 123RF
The REM sleep phase usually occurs after several periods of shallow to deep non-REM (NREM) sleep, followed by a re-entry into the NREM sleep phase, alternating. This cycle continues until you wake up.
Recently, scientists have found the "key" to the brain's dreamland. In a new research paper published in science, a top academic journal, scientists at the University of Tsukuba in Japan found that elevated levels of dopamine, the brain's pleasure signal, in key areas, are key to initiating the REM sleep phase.
When it comes to dopamine, many people are not strangers. As a neurotransmitter, dopamine regulates the activity of nerve cells and makes us feel happy, so things that promote dopamine secretion (such as chocolate) are easily addictive, even addictive. Dopamine is also closely related to exercise and behavioral ability, Parkinson's disease patients due to reduced dopamine secretion, slow movement, tremor and other movement disorders.
In this study, through technical means such as somatic neural recording and optogenetic manipulation, scientists found that in the basolateral amygdala (BLA) of the brain region related to emotional processing, the transient increase in dopamine will act on neurons expressing the dopamine receptor Dr2, allowing mice to enter the REM sleep stage.
▲ Record the change of dopamine levels in the basolateral amygdala during the state transition of the awakening-sleep cycle in mice, and find that there is a brief peak before the transition from NREM to REM (Image source: Reference[2])
Further research found that dopamine changes in this brain region are not only responsible for the transition from the NREM sleep phase to REM sleep during "normal" sleep, but also provide new insights into a class of sleep disorders called narcoleptics. A typical symptom of narcolepsy is called a "cataplexy episode", in which the patient's brain suddenly falls into REM sleep while awake, muscle weakness, and loss of control over the posture of the movements.
The researchers conducted experiments in mice in a model of narcolepsy. These mice developed a seizure-like behavior due to a lack of orexin (a neuropeptide that regulates appetite and wakefulness). After these mice were fed chocolate, the number of seizures of their cataplexy increased. The researchers observed a significant increase in dopamine levels in the basolateral amygdala before the onset of blasmops; in contrast, there was no such change in the wild-type mice in the control group.
▲Mice with narcolepsy were fed chocolate, and a brief rise in dopamine levels in the basolateral amygdala was observed before the onset of cataplexy (Image source: Reference[1])
These results consistently suggest that dopamine signaling in the basolateral amygdala plays a key role in initiating REM sleep.
The journal Science also published a relevant review article, in which experts pointed out that this new discovery provides a direction for the treatment of various REM sleep disorders. For example, Parkinson's disease, which involves the destruction of dopamine signals, has a common early symptom in the rem sleep stage such as screaming, punching and kicking, and provides the development of new drug targets for neurons expressing DRD2 in the basolateral amygdala.
Resources:
[1] Emi Hasegawa et al., (2022) Rapid eye movement sleep is initiated by basolateral amygdala dopamine signaling in mice. Science. Doi: 10.1126/science.abl6618
[2] Elda Arrigoni & Patrick M. Fuller (2022) Addicted to dreaming. Science. Doi: 10.1126/science.abo1987
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