How tasty is the food? A hormone and specialized brain cells regulate feeding behavior in mice

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Hunger is a powerful sensation with important biological underpinnings. It signals the body to search for food, which is crucial behavior to prevent starvation and ensure survival. When we are hungry, we crave to eat, and when we finally do eat, our bodies reward us with pleasant sensations and a general state of happiness.

A network of brain circuits and signaling pathways orchestrates eating behavior in humans and animals and elicits the associated sensations. One of the central players in this network is the hormone ghrelin. It is released by stomach cells when humans and animals are hungry or fasting, and it promotes feeding behavior.

Rüdiger Klein’s department at the Max Planck Institute for Biological Intelligence studies the brain networks underlying feeding behavior in mice. To this end, the researchers conducted a comprehensive analysis of the different cell types in a region of the brain known as the central amygdala. “Previously, the amygdala had been studied primarily in the context of feelings such as fear and reward, while regulation of eating was thought to occur in different parts of the brain, such as the hypothalamus,” says Christian Peters, a postdoctoral researcher at the Department.

nine groups of cells

Peters and his colleagues analyzed individual cells in the central amygdala, studying messenger RNA molecules, the cell’s working copies of its genes. The analysis revealed that the cells are organized into nine different cell groups. Some of these groups promote appetite, while others inhibit it, and adjust their production of messenger RNAs when the mice are fed or fasted.

“We now have a much better understanding of the diversity of cell types and the physiological processes that promote feeding in the central amygdala,” says Rüdiger Klein. “Our research discovers for the first time that the ‘hunger hormone’ ghrelin also acts on cells in the central amygdala.” There, it activates a small subset of cell groups, collectively marked by the presence of the Htr2a protein, to increase feeding.

Multiple functions for ghrelin

The scientists found that Htr2a neurons fire after an overnight fast or when stimulated by the hormone ghrelin. The cells also responded when the researchers gave the mice food. “We think that ghrelin performs multiple functions,” explains Christian Peters. “When mice are hungry, ghrelin activates appetitive brain regions to predispose the animals to eat. In addition, the hormone enhances activity in brain circuits, such as the amygdala, that grant rewards, which is likely an incentive to eat.” additional food.” In this way, ghrelin increases the palatability of food in proportion to how satisfied the mice are at the time.

After a fasting diet, when the animals were very hungry, the activity of Htr2a neurons was not required to start feeding, presumably because the taste of food is less important under these conditions. “Other brain circuits, for example the hypothalamus, which regulate the body’s metabolism, take over and tell the mice that it is important to eat to survive,” says Christian Peters.

Feeling hungry or full has a profound impact on physical but also emotional well-being, as everyone probably knows from the pleasures associated with eating tasty food. “The neural networks that convey these feelings are obviously linked to those that control eating, but exactly how they influence each other is not fully understood,” says Rüdiger Klein.

“If we discover these connections, we will better understand the neural processes that are involved in pathological eating behaviors, such as overeating,” concludes Christian Peters. “There are numerous biological factors that contribute to such complex behavior and we have to look at physiological processes to understand these factors.” Ultimately, this knowledge could lead to new therapeutic approaches to alleviate eating disorders. For now, the research lays the groundwork for future studies to investigate how specific neuron populations are involved in the neural circuitry that controls eating. It also adds another important piece to the puzzle of understanding how the brain orchestrates behavior.