Eating or sex? That is the question, and the answer is: sex. At least in a group of moderately hungry mice that have been stimulated with leptin, a hormone that suppresses appetite.
“We can only pursue one behavior at a time, so our brain has to somehow calculate which one will be the most rewarding or which is our most pressing need,” says lead author Tatiana Korotkova, from Cologne University Hospital, Germany. , author of the study published in «Cell Metabolism».
To elucidate the hierarchy of innate behaviors like eating, drinking, socializing, and mating, Korotkova’s team observed and stimulated mouse neurons within the lateral hypothalamus, one of the brain’s main “feeding centers.” They focused on neurons that have receptors for leptin and neurons that produce neurotensin, two hormones associated with hunger and thirst. To their surprise, they found that these neurons were also involved in guiding social behavior and helping the mice balance their nutritional and social needs.
“Activation of leptin receptor neurons causes mice to prioritize social interaction despite acute hunger or thirst. This makes sense biologically because mating partners are not something you have all the time, so one must be able to ignore hunger or thirst in order to mate», explains first author Anne Petzold
The researchers used small microscopes to visualize the activity of individual brain neurons as the mice explored and engaged in various behaviors in an enclosure.
To see how the mice’s priorities changed depending on their level of hunger, the team compared the behavior of mice that had unlimited access to food with that of “very hungry” mice (whose eating had been restricted overnight) and “chronically starved” mice (whose food had been restricted for 5 days). The researchers note that this “chronic hunger” can also occur in nature, where food is not available all the time.
They found that leptin receptor neurons were inhibited when the mice ate and activated when they interacted with mice of the opposite sex (potential mates), but not when they interacted with mice of the same sex.
The researchers then used light and chemical signals to selectively stimulate the neurons, allowing them to see if and how this activation altered the behavior of the mice.
We can only pursue one behavior at a time, so our brain has to calculate which one will be the most rewarding.
Leptin stimulation had little effect on the behavior of the sated mice, which were generally more interested in socializing than eating, but when the researchers activated the leptin-receptor neurons of the acutely hungry mice, their priorities changed: They were slower. to get closer to food, they ate less, and spent more time socializing with potential mates.
However, leptin stimulation could not abolish the stronger hunger of the chronically food-restricted mice, whose appetites were not reduced and their priorities not shifted by leptin activation.
“We have this system that can only regulate moderate hunger, but not strong hunger,” says Korotkova. “This circuit could help explain why diets don’t work: reducing food intake for a short time is not a problem, but it doesn’t work long term».