What your parents didn't tell you about pulling an all-nighter? It might just ease depression for several days. At least, that's what researchers found happened to mice in a study published in the journal Neuron Thursday.

Most people who've stayed up all night know the "tired and wired" feeling they get the next day. The body might be exhausted, but the brain feels jittery, hyperactive or even giddy. Even after these changes wear off, sleep loss can have a strong antidepressant effect in people that lasts several days.

But researchers hadn't figured out why sleeplessness might have this effect —until this study from neurobiologists at Northwestern University.

The morning after a sleepless night

To study all of this, the team looked at the effects of sleep loss in mice. They induced sleep loss in some of the mice, while the others got a typical night's rest.

They found that after this sleepless night, the mice were more excitable, more aggressive, more sexual and less depressed than mice that got a regular amount of sleep.

Of course, researchers can't just ask mice whether they feel "less depressed." Instead, they created a depression-like state in all the mice before either disrupting their sleep or allowing them to rest by repeatedly giving them small shocks. In response to these shocks, the mice entered a depressive-like state and eventually stopped trying to escape their cages.

Then, they tested the mice's response to shocks again. The ones that had stayed up all night showed a reversed depressive state, indicated by more attempts to escape the shocks.

What causes these changes in mice?

Dopamine is responsible for the brain's reward response. Changes in the brain's dopamine system have also been implicated in conditions like depression and in sleep regulation.

And so, to see how the mice's brains responded to their sleepless night, the researchers measured dopamine neuron activity. They saw that sleep-deprived mice showed higher dopamine activity in three regions: the prefrontal cortex, nucleus accumbens and hypothalamus.

But this still didn't tell the researchers which areas were related to the antidepressant effects they saw in the mice.

To figure that out, they silenced dopamine reactions in each of these areas of the brain. The antidepressant effect persisted in the mice except when the team silenced the dopamine input in the prefrontal cortex. That's why Northwestern University neurobiologist Yevgenia Kozorovitskiy, who oversaw the study, says that this region may be important in the search for new depression treatments.

Neuroplasticity and sleep loss

Researchers think that transitions between affects — like a depressed state and a non-depressed state — are mediated by neuroplasticity, or the brain's ability to reorganize connections and structures.

Based on their findings in the prefrontal cortex, Kozorovitskiy and her team looked at individual neurons in this area for signs of growth or neuroplasticity. They saw evidence of the early stages of new connections, suggesting that dopamine had rewired neurons in the mice brains to maintain their mood for several days.

Kozorovitskiy says this work may help scientists understand how human moods transition naturally and why some drugs like ketamine have fast-acting effects on mood.

At the same time, scientists have known that chronic sleep loss in humans leads to health problems, so the researchers do not recommend that people start staying up all night to ease depression.

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Today's episode was produced by Rachel Carlson and Michael Levitt. It was edited by Amina Khan, Christopher Intagliata and Viet Le. Anil Oza checked the facts. Stu Rushfield and Josh Newell were the audio engineers.

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