Des chercheurs découvrent le circuit crucial du cycle sommeil-éveil

13 septembre 2016 par maty185

Scientists discover brain circuit crucial to sleep-wake cycle

Mice in an unfamiliar cage ordinarily explore their new surroundings energetically. And indeed, VTA-suppressed mice stayed awake for the first 45 minutes of the hour they spent in a new cage. But Eban-Rothschild noticed something: They spent that waking time building nests.

« They were really careful about it, » she noted. Once they were satisfied with what they’d built, they dozed off.

This wasn’t just some stereotyped behavior guaranteed to emerge when VTA activity was inhibited, Eban-Rothschild added. « If we put the nest they’d already built in their usual cage into the novel cage, they climbed in and went right to sleep. »

Control mice in the unfamiliar cage ran around, either ignoring the pellet of nesting materials placed inside or scattering those materials all over the cage.

Nest-making activities

Eban-Rothschild analyzed video footage of the animals’ behavior in their novel environments, and correlated 1-second video segments with recorded brain activity during the corresponding time frame. She saw that actions directly connected to building nests were marked by reduced VTA activity, while actions that weren’t were associated with higher levels of VTA activity.

« We knew stimulating the brain’s dopamine-related circuitry would increase goal-directed behaviors such as food- and sex-seeking » said Eban-Rothschild. « But the new study shows that at least one complex behavior is induced not by stimulating, but by inhibiting, this very circuit. Interestingly, this behavior — nest building — is essential to a mouse’s preparation for sleep. »

Nobody had noticed that before, said de Lecea. « This is the first finding of a sleep-preparation starter site in the brain. It’s likely we humans have one, too. If we’re disrupting this preparation by, say, reading email or playing videogames, which not only give off light but charge up our emotions and get our VTA dopaminergic circuitry going, it’s easy to see why we’re likely to have trouble falling asleep. »

Noting that this anticipatory phase is often at the root of many people’s sleeping problems, de Lecea suggested that the newly identified circuit could be a target for pharmacological intervention to help people ease into sleep.  http://www.news-medical.net/news/20160905/Scientists-discover-brain-circuit-crucial-to-sleep-wake-cycle.aspx

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