Increased hunger-related synapses in the brain

The yo-yo effect is well known to many dieters: following the diet, the pounds are swiftly added back on. Now, scientists from Harvard Medical School and the Max Planck Institute for Metabolism Research have demonstrated in mice that synapses in the brain communication changes during a diet: The nerve cells that mediate the feeling of hunger receive stronger signals, causing the mice to eat significantly more after the diet and gain weight more quickly. These discoveries may eventually aid in the creation of medications that stop this amplification and support the maintenance of a decreased body weight following dieting. “The short-term results of dieting have received the majority of attention. In order to determine how the brain alters over time, “explains Henning Fenselau, the study’s principal investigator and a researcher at the Max Planck Institute for Metabolic Research.

**How can we change the brain’s dietary patterns?**

In order to achieve this, the researchers fed mice different diets while monitoring how certain brain circuits changed. They focused on the AgRP neurons in the hypothalamus, a set of neurons known to regulate the sensation of hunger. They were able to demonstrate that when the mice were on a diet, the neural pathways that trigger AgRP neurons delivered more messages. Long after the diet, this dramatic shift in the brain may still be seen. Also, the scientists were able to specifically disrupt the mouse brain pathways that activate AgRP neurons. After the diet, there was a noticeably smaller weight gain as a result. According to Fenselau, this may present an opportunity to lessen the yo-yo impact. “Our long-term objective is to discover treatments for people that could support keeping off weight reduction following dieting. We are still investigating strategies to prevent the neuronal circuits in humans from becoming stronger in order to do this.”

**A direct link between the gut and the brain**

“This research deepens our understanding of how hunger is controlled by brain wiring patterns. A significant group of upstream neurons that physically synapses with and stimulates AgRP hungry neurons have already been identified by us. In the current study, we discover that dieting and weight loss significantly increase the physical neurotransmitter connection between these two neurons, a process known as synaptic plasticity, which causes persistently excessive hunger “co-author Bradford Lowell of Harvard Medical School offers his thoughts.