We dream and our brain works intensely: REM sleep apparently also has something to do with our eating behavior, research results on mice now suggest. During this sleep phase, certain nerve cells become active that have a lasting effect on food intake. If this function is artificially suppressed, this disturbs the rodents’ appetite. The more precise connections have yet to be clarified, but the discovery could have a bearing on research into eating disorders and addictive behavior, say the researchers.
It doesn’t work without sleep, but what functions and meanings this state has is still not fully understood. One thing is clear: while we sleep, we go through different phases that contribute in different ways to us feeling rested. Among other things, the research focuses on the sleep phase, which is characterized by rapid eye movements with closed lids. This so-called Rapid Eye Movement (REM) sleep takes up to 25 percent of the human sleep duration. In animals, too, it forms an element of sleep – as is the case with mice. REM sleep is associated not only with vivid dreams, but also with the regulation of emotions and various cognitive skills.
A special sleep phase in sight
It is known from research that different areas of the brain work intensively during REM sleep. To date, however, it is largely unclear what this electrical activity is used for. As the researchers led by Lukas Oesch from the University of Bern report, there was evidence that the so-called lateral hypothalamus also shows increased activity during REM sleep. This is a structure that occurs in the diencephalon in all mammals. It is known that the nerve cells in this brain area play a role in the regulation of appetite and food intake while awake and are important in motivation and addictive behavior. Thus, a possible connection between REM sleep and the function of this brain area emerged. As part of their study, the researchers have now followed up on this trail by investigating mice.
To this end, they recorded the activation patterns of nerve cells in the lateral hypothalamus of the test animals using modern brain research methods. In this way, the scientists were initially able to substantiate the evidence of a possible connection between REM sleep and the feeding behavior of the animals when they are awake: They discovered that certain activity patterns of the neurons that signal food intake during the awake state also occurred during REM sleep.
Manipulation makes you lose appetite
In order to investigate the possible after-effects of this activity pattern, the researchers used optogenetics. It enables the activity of nerve cells in special mouse breeding lines to be influenced by means of light pulses. Specifically, as part of their experiments, the scientists specifically switched off the neural activity of the previously observed nerve cells in the lateral hypothalamus during REM sleep. In other words, the mice lacked this aspect of REM sleep during their natural slumber. The researchers then analyzed the extent to which this manipulation had an impact on the behavior of the test animals.
As they report, it was found that switching off the signals resulted in the eating activity patterns of the cells changing in the awake mice and the animals consuming less food. “We were amazed how strong and long-lasting our intervention in the lateral hypothalamus influenced the activity of the nerve cells and the behavior of the mice. The change in the activity pattern was still noticeable after four days, ”says Oesch. “These results suggest that the hypothalamic representation of food intake is stabilized during REM sleep, which in turn influences future eating behavior,” the researchers write.
However, the findings cannot be implemented directly in a process or even in a way of influencing appetite. However, there is a fundamental potential, say the scientists: The discovered connection between the activity of cells in REM sleep and eating behavior could serve to develop new therapeutic approaches for eating disorders. In addition, they could also be of importance in researching motivation and addictive behavior. “However, this depends on the exact neural circuits, the sleep phase and other factors that still need to be researched,” says the senior author of the study Antoine Adamantidis from the University of Bern.
Source: University of Bern, specialist article, PNAS, doi: 10.1073 / pnas.1921909117