Current Biology: Specialized ASM4 Neurons in the Brain May Almost Completely Suppress Aggression

Scientists from the Salk Institute and the University of California, Los Angeles, have identified a small group of ASM4 neurons in fruit flies whose activation suppresses aggressive behavior. The findings were published in the journal Current Biology.

When two male fruit flies are placed in a small chamber, they begin attacking each other. Octopamine, a chemical messenger that performs functions similar to those of norepinephrine in humans and is associated with the “fight-or-flight” response, plays a role in this behavior. ASM4 neurons appear to work in the opposite direction and can effectively stop the fight.

The researchers developed a genetic tool that allows specific groups of neurons to be activated with precision. Using this tool, they identified ASM4 cells. When the neurons were activated with red light, the flies stopped attacking each other. Once the light was turned off, the attacks resumed.

The effect could not be explained simply by reduced motor activity. Moreover, ASM4 neurons suppressed aggression in both males and females, even though the two sexes display aggressive behavior differently. According to the authors, this may point to a more universal mechanism for controlling aggressive behavior.

Studying these cells had previously been difficult. Octopamine is used by several groups of neurons, while existing genetic tools did not allow individual cell types to be activated independently. To address this problem, the scientists tested 529 combinations of genetic markers and created 40 variants capable of selectively identifying no more than three types of neurons.

The new set of tools provided access to 14 cell subtypes that could not previously be studied separately. Using the same approach, the researchers also identified neurons involved in processing visual information and tracking moving objects.

However, the mechanism by which ASM4 neurons work is not yet fully understood. Scientists have not determined whether these cells release octopamine, tyramine or both neurotransmitters. In addition, the new tools do not yet allow ASM4 neurons to be completely separated from several neighboring cell types, meaning that activating a similar aggression-suppressing mechanism in humans is not currently possible.

Follow NEWS.am Medicine on Facebook and Twitter