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Scientists Find Brain Chemical That Determines Whether To Fight Or Flee

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Engaging in fights can be dangerous and potentially deadly that animals tend to flee when they realize that the cost of fighting outweighs the benefits.

The mechanism behind the decision to fight or flee, however, is unclear so researchers conducted a study involving crickets to determine where the behavior comes from.

For the new study published in the journal Science Advances on March 13, Paul Stevenson, from the Leipzig University, and Jan Rillich, from the Free University of Berlin in Germany, treated Mediterranean field crickets (Gryllus bimaculatus) with nitric oxide, a chemical-signalling molecule in the brain that influences a number of physiological processes.

The researchers then had the crickets fight in order to observe how the drug could affect their behavior. They found that nitric oxide induces a flight response, which tells the losing cricket when enough is enough and it is time to run away from its aggressor.

Stevenson and Rillich found that compared with the crickets treated with nitric oxide suppressing drugs which tend to fight longer and have escalated aggression, the crickets treated with nitric oxide did not fight as long nor do they have escalated violence.

The observations suggest that deciding to flee from a conflict is influenced by nitric oxide that involuntarily acts on the nervous system. These also indicate that insects can make what seem to be complex decisions on whether to fight or flee from a physical conflict even without higher cognitive capacity.

"If you block nitric oxide they recover quickly, and if you give them nitric oxide they don't," Stevenson said. "It's a very simple algorithm for controlling a very complicated social situation."

Based on their observations of a series of cricket fights, the researchers said that getting bitten, bumped, or visually threatened activates the sensory receptors and thus cause the neurons to release nitric oxide and this promotes the tendency among crickets to flee from dangers.

The researchers said that the crickets that showed spectacular fighting behavior get away from fight once their aggressor's aversive actions exceeds a critical amount.

"The decision to flee in crickets is based entirely on the opponent's agonistic signals perceived during fighting, which act to suppress aggression, so that individuals accumulating relatively more "punishment" will be the first to flee once a critical threshold is reached," the researchers wrote in their study.

Stevenson and Rillich also said that the same observed mechanism could be governing the flight or free response in mammals.

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