Researchers at Harvard Medical School are watching angry flies fight for the advancement of science. In a new study published last month in the Proceedings of the National Academy of the Sciences, Harvard researchers found that two pairs of dopamine-producing neurons in fruit flies may be exclusively linked with aggressive behavior.

The research team used a set of genetic tools to manipulate individual brain cells in the flies. According to Olga V. Alekseyenko, the study’s first author and Harvard Medical School postdoctoral fellow, these techniques allow researchers to “express whatever you want, wherever you want in the brain.”

The researchers isolated dopamine-producing, or dopaminergic, neurons in the brains of Drosophila, the genus of fruit flies. Then, using a genetically encoded neurotransmitter inhibitor and a temperature-sensitive neuronal activator, the researchers were able to selectively activate and deactivate these neurons. The team then measured aggression in the flies by examining the intensity of fights between males over prizes like a food cup or a female.

“By turning on the dopaminergic neurons in Drosophila we found escalated intensity of fights between socially naïve males,” Alekseyenko said.

The researchers also found that deactivating these dopaminergic neurons increased aggressive behavior. Researchers found that while activating and deactivating these dopaminergic neurons affected Drosophila’s aggression, other aspects of the fruit flies’ behavior remained undisturbed.

“Both neurons are exclusively involved in aggression and holding aggression in check,” said Neurobiology professor Edward A. Kravitz, who is lead author of the study. This discovery could have important implications for organisms more complex than fruit flies, according to Kravitz.

“Dopamine is also involved in the motivation and reward systems in humans and higher vertebrates,” said Kravitz. “We want to understand how amines like serotonin and dopamine actually function in a circuitry relating to behavior. By finding the fundamental principles of how they work in the cells of Drosophila we hope to eventually model how they work in humans."