A fast surge of dopamine shifts mice right into a dreamy stage of sleep.
In the rodents’ brains, the chemical messenger triggers rapid-eye-movement sleep, or REM, researchers report within the March 4 Science.
During an evening’s sleep, folks and different animals cycle between phases known as non-REM sleep and REM, a sleep stage that normally comes with vivid goals. But what causes these transitions is mysterious, says neurologist and sleep researcher Thomas Scammell of Harvard Medical School who wasn’t concerned within the examine. These new outcomes are a few of the first to point out a set off for the shifts, Scammell says. Understanding these transitions in additional element might finally level to methods to deal with sleep problems in folks.
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Certain nerve cells residing in part of the mouse mind known as the ventral tegmental space can pump out dopamine, a molecule that has been linked to pleasure, motion and studying, amongst different issues. These cells can ship dopamine to the amygdalae, two almond-shaped buildings deep within the mind which might be intently tied to feelings.
Using a molecular sensor that may inform precisely when and the place dopamine is launched, neuroscientist Takeshi Sakurai from the University of Tsukuba in Japan and colleagues noticed that dopamine ranges rose within the amygdalae simply earlier than mice shifted from non-REM sleep to REM sleep.
Next, the researchers compelled the mice into the REM section by controlling these dopamine-producing nerve cells utilizing lasers and genetic strategies — a way known as optogenetics. Compelled with gentle, the nerve cells launched dopamine within the amygdalae whereas mice had been in non-REM sleep. The mice then shifted into REM sleep earlier than they usually did, after a mean of about two minutes in contrast with about eight minutes for mice that weren’t prompted to launch dopamine. Stimulating these cells each half hour elevated the mice’s complete quantity of REM sleep.
Additional experiments recommend that these dopamine-making nerve cells might also be concerned in features of narcolepsy. A sudden lack of muscle tone, known as cataplexy, shares options with REM sleep and might accompany narcolepsy (SN: 10/9/10). Stimulating these dopamine-making nerve cells whereas mice had been awake prompted the mice to cease transferring and fall instantly into REM sleep.
The outcomes assist make clear a set off for REM in mice; whether or not the same factor occurs in folks isn’t recognized, Sakurai says. Earlier research have discovered that nerve cells in folks’s amygdalae are energetic throughout REM sleep, he says, hinting at a task for the mind construction.
Many questions stay. Drugs that change dopamine ranges in folks don’t appear to have large results on REM sleep and cataplexy, Scammell says. But these medicine have an effect on the entire mind, he factors out, and it’s doable that they’re simply not selective sufficient. “My overall question about this is, ‘How can we translate this to humans?’” Scammell says.