Serotonin shown to have impact on feeding habits and lifespan of fruit flies

Sunday, September 18, 2016 - 7:21pm

New University of Michigan research is helping explain why a host of species, including fruit flies and humans, selectively crave protein-rich foods — a phenomenon that has eluded researchers for decades.  

Researchers in the study observed that the reward that fruit flies got from eating protein — based off serotonin in the brain — played a role in their longevity and lifespan, a finding that could translate to humans and other mammals.

The research team was led by Scott Pletcher, associate professor of molecular and integrative physiology at the University, and Jennifer Ro, a post-doctoral fellow at Harvard Medical School, who published the report in the journal eLife.

Pletcher said the brain releases serotonin to travel between neurons when triggered by certain neuronal actions, such as a response to eating certain foods, stimulating a feeling of reward and pleasure.

In the case of fruit flies, Pletcher and Ro discovered serotonin was regulating the fruit flies’ tendency to selectively choose protein over sugars when hungry.

“The choice process itself, of thinking about what we should eat, seems to affect the lifespan of an animal, and that is the case here with the fruit fly,” Ro said.

Researchers controlled fruit flies’ access to different types of food and manipulated genes involved in serotonin regulation for the study through a Fly Liquid-food Interaction Counter, which allowed them to observe which foods fruit flies are choosing and track when and how fruit flies were rewarded by choosing protein-rich foods.

Researchers first gave fruit flies one of three different options: a protein-focused meal, a sugar-focused meal or the ability to choose between both single-nutrient meals and a mixed diet, Ro said. They found it wasn’t the nutrients in protein, but rather the way the brain responded to craving it, that impacted longevity. In essence, when fruit flies craved protein, they tended not to live as long.

“We found that the neurological aspects associated with protein consumption, independent of the energy or nutritional value of protein, were important for modulating aging,” Pletcher said.

By blocking a single receptor for serotonin found on the surface of just 100 neurons in the brain of a fruit fly, Pletcher and Ro found that the fruit flies’ lifespan doubled. Food choices also changed, Pletcher noted. Fruit flies ate just as much food as they did before, but were less inclined to eat protein-rich foods.

Pletcher and Ro said potential implications from this study are wide-ranging. Serotonin is an evolutionarily conserved molecule, meaning it is present in many different species — including humans. If researchers find serotonin processes in fruit flies, it may translate in similar ways to humans and other organisms.

“Because serotonin is evolutionarily conserved and it’s known to have effects of similar type in different species, this brings up the possibility that it may influence aging and feeding-related behaviors in humans,” Pletcher said.

Nicholas Rabah, an LSA senior majoring in neuroscience, said he would be interested in how this research sheds light on the health effects of protein, which are generally assumed to be completely beneficial.

“I think this is an intriguing link because it contradicts the established notions behind protein’s health benefits,” Rabah said. “It will be interesting to see what further research can illustrate about the role serotonin plays in our diet choices.”

In the future, Pletcher said he aims to translate these experiments and findings to more complex biological systems, like mammals, to test evidence for neurological mechanisms underlying feeding patterns and aging in humans.

“We must investigate whether serotonin affects similar processes in mammals that we’ve identified in flies,” he said.