Recently, neuroscientists at Rockefeller University found a group of nerve cells in the hippocampus of mice. When faced with the existence of food, they sent a signal to make animals eat less. At the same time, activating the brain circuits where these neurons are located will also reduce the memory related to food in mice. This study was published online in the authoritative academic journal Neuron.
Professor Jeffrey Friedman, one of the scientists who led this work, has been devoted to studying the molecular mechanism of regulating food intake and weight for a long time. Not long ago, we just reported an achievement of this research team related to weight loss therapy. The new research results seem to help us to go further in the direction of keeping our mouths shut.
Our brains are good at remembering where food has appeared, especially when we are hungry, which often awakens the memory of food maps. The same is true of the mouse brain. The researchers put the mice that had fasted all night into the environment where food had been provided, and the mice would linger in the corner where food had been let go. Even if the food was provided for a very short time of 5 minutes, the amount of food was very small, which was still enough to leave unforgettable memories for mice.
The research team examined which neurons were active when food appeared in the brains of mice, and found that a group of neurons expressing dopamine receptor D2 (hD2R) in hippocampus were activated when faced with food.
Further through the experimental design, the researchers found that even if the mice didn't really eat food, they just saw the food (the food was put in a sealed glass jar by the researchers) or even smelled the food (the food was taken away by the researchers, and the aroma of the spare food in the cup), the information of food perception would excite these neurons in the hippocampus.
so, will the perception of food make this group of nerve cells have an impact on the behavior of eating? Then, the researchers used chemical genetics to regulate the electrical activity of neurons and verify whether the feeding behavior of mice has changed.
The results showed that when the electrical activity of this group of hD2R neurons was inhibited, the mice's appetite opened up and they ate more food. On the contrary, when neurons are activated to increase their electrical activity, mice will eat more restrainedly. Moreover, whether the acute treatment is as short as 24 hours or the chronic treatment is as long as several days, it shows that hD2R neurons regulate the eating of mice.
The experimental results of optogenetics regulating the activity of hD2R neurons also prove this point. Although we can't hear the inner monologue of "eat less" in mice, the active hD2R neurons seem to convey the message of stopping eating when facing food.
Dr. Azevedo, the first author of this study, believes that "these cells are helping animals avoid overeating".
In view of the fact that the hippocampus receives neural signals from multiple brain regions, the research team further identified that the information input received by hD2R neurons came from the lateral entorhinal cortex (LEC) by virus tracing. In addition, the information of hD2R neurons is not directly output to the hypothalamus of the feeding center, but projected to a region called the medial septal nucleus (SA). When this neural pathway was activated, the hungry mice who had been eating heavily obviously reduced their food intake. The neural pathway from LEC to hippocampal D2R neurons to SA is also the first time for scientists to find out the advanced regulatory loop between food perception and eating behavior.
More interestingly, this brain circuit also affects animals' memory of food location. When mice were in an environment with food, scientists turned on the switch to activate the neural circuits, which made their hD2R cells active. As a result, when the mice return to the same environment after they are hungry, they no longer return to the corner where there was food. In other words, the activation of hD2R neurons makes them lose some food-related memories!
"When we find that brain regions related to cognitive processing and memory formation also affect eating behavior, it means that we may learn to change the relationship with food through training." Dr. Azevedo said.
In the contemporary society where food is extremely abundant, the obsession with food may hinder the health and beauty pursued by some people. Although temporarily forgetting food may not be the life that mice want, for some people who want to control themselves in front of delicious food, perhaps this neural circuit discovered by scientists has some reverie significance.