How the brain evokes deep sleep and speeds healing

How the brain evokes deep sleep and speeds healing

Written by Mariana Lenharo & Nature Magazine

Immune cells rush to the brain after a heart attack and promote deep sleep, according to a new study in both mice and humans. Studies have found that this deep sleep can reduce inflammation in the heart and aid recovery.

The findings were published on October 30th. natureThe study could help guide care for people after a heart attack, said co-author Cameron McAlpine of the Icahn School of Medicine at Mount Sinai in New York City, who studies immune function in the cardiovascular and nervous systems. “Getting enough sleep and rest after a heart attack is important for long-term healing of the heart,” he points out.

Rachel Rowe, a sleep and inflammation expert at the University of Colorado Boulder, said the study’s implications extend beyond heart attacks. “The body’s natural response to any type of injury is to help the body sleep so it can heal,” she says.

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the heart needs sleep

Scientists have long known that sleep and cardiovascular health are linked. For example, people who sleep poorly have a higher risk of developing high blood pressure than those who sleep soundly. However, how cardiovascular disease affects sleep is less well-studied.

To learn more, the authors induced heart attacks in mice and studied the animals’ brain waves. The researchers found that these mice spent more time in slow-wave sleep, a stage of deep sleep associated with healing, than mice that had not had a heart attack.

Next, the authors sought to understand what was causing that effect. One obvious place to focus is the brain, which controls sleep, McAlpine points out. After a heart attack, immune cells trigger a massive burst of inflammation in the heart, and the researchers wondered if these immune changes were also occurring in the brain, he said.

The researchers found that immune cells called monocytes flooded the brains of mice after they suffered a heart attack. These cells produced large amounts of a protein called tumor necrosis factor (TNF), which is an important regulator of inflammation and also promotes sleep.

To confirm that these cells were associated with increased sleep, the researchers prevented monocytes from accumulating in the rodent brains. As a result, “we did not see an increase in slow-wave sleep in the mice after a heart attack,” Dr. McAlpine said, supporting the theory that an influx of monocytes into the brain contributes to promoting sleep after a heart attack. are. Similar experiments confirmed the role of TNF as a messenger to brain cells that induces sleep.

Sleep towards recovery

To understand the purpose of the extra sleep, researchers repeatedly interrupted slow-wave sleep in mice that had suffered a heart attack. The researchers found that these mice had more inflammation in both their brains and hearts and had a much worse prognosis than mice that were put to rest after a heart attack.

The authors also studied humans who experienced acute coronary syndrome, a term that refers to conditions such as heart attacks caused by a sudden reduction in blood flow to the heart muscle. People who reported poor sleep in the weeks after such an episode had a higher risk of developing a heart attack or other serious cardiovascular disease over the next two years than those who slept well.

Given this study’s findings, “clinicians need to educate patients about the importance of good sleep after a heart attack,” Lowe said. This should also be considered in hospitals, where tests and procedures should ideally be carried out during the day to minimize sleep disruption.

She added that the findings highlight the bidirectional relationship between sleep and the immune system. “My grandma used to say, ‘If you don’t get enough sleep, you’ll get sick,’ and that’s very true.”

This article is reprinted with permission. first published October 30, 2024.