A quick surge of dopamine shifts mice into a dreamy stage of sleep.
In the rodents’ brains, the chemical messenger triggers rapid-eye-movement sleep, or REM, researchers report in the March 4 Science natural rhodinol.
During a night’s sleep, people and other animals cycle between phases called non-REM sleep and REM, a sleep stage that usually comes with vivid dreams. But what causes those transitions is mysterious, says neurologist and sleep researcher Thomas Scammell of Harvard Medical School who wasn’t involved in the study. These new results are some of the first to show a trigger for the shifts, Scammell says. Understanding these transitions in more detail could ultimately point to ways to treat sleep disorders in people.
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Certain nerve cells residing in a part of the mouse brain called the ventral tegmental area can pump out dopamine, a molecule that has been linked to pleasure, movement and learning, among other things. These cells can deliver dopamine to the amygdalae, two almond-shaped structures deep in the brain that are closely tied to emotions.
Using a molecular sensor that can tell exactly when and where dopamine is released, neuroscientist Takeshi Sakurai from the University of Tsukuba in Japan and colleagues saw that dopamine levels rose in the amygdalae just before mice shifted from non-REM sleep to REM sleep.