Dopamine's role in male aggression fades with fighting experience

Have you ever noticed how aggression plays a role in people’s personalities, with some seeking competition while others prefer to avoid confrontation?

Much like humans, mice engage in territory and mate competitions, displaying increased confidence and aggression as they accumulate victories.

A recent study has revealed the critical influence of dopamine, a potent brain chemical, in aggressive behavior.

Dopamine and male aggression

While dopamine has been associated with male aggression for many years, the influence of past experiences on this relationship has remained a mystery.

A group of researchers from NYU Langone Health decided to dig deeper, particularly focusing on the role of dopamine.

The team discovered that young, inexperienced male mice, when given a dopamine boost, fought twice as long as they would naturally fight.

Blocking the release of dopamine from certain cells made these novice fighters completely passive.

However, this was not the case for males with extensive fighting experience. Regardless of the increase or decrease of dopamine, the duration of their attacks remained the same.

Interestingly, the researchers noted that more victories bred more challenges, with victorious mice instigating more fights in the future.

Dopamine, aggression, and fighting experience

Study senior author Dr. Dayu Lin is a professor in the Departments of Psychiatry and Neuroscience at NYU Grossman School of Medicine.

“Our findings offer new insight into how both ‘nature’ and ‘nurture’ shape aggression in males,” said Dr. Lin. “While aggression is an innate behavior, dopamine – and fighting experience – is essential for its maturation during adulthood.”

The research wasn’t restricted to the relationship between dopamine and aggression. The team also explored the brain mechanisms at play during aggression learning.

They blocked dopamine release in certain brain areas related to aggression regulation and observed that novices stopped learning to fight, while experienced fighters continued their aggressive behavior.

The diminishing role of dopamine

As the mice gained experience, the initial dopamine release in the brain became less potent, suggesting dopamine’s critical role in initial aggression learning.

The research also debunked any similar role of dopamine in female aggression, as altering dopamine levels did not affect female mice’s aggressive behaviors.

Dr. Lin believes the results could potentially assist in addressing mental health conditions characterized by intense mood and behavior shifts, such as schizophrenia, bipolar disorder, and borderline personality disorder.

“Our results suggest that targeting dopamine may not be an effective tool when treating those with a long history of aggression,” noted Dr. Lin. “As a result, healthcare providers may need to consider a patient’s history, as well as their age and sex, when considering which therapy to use.”

Antipsychotic medications in humans

These findings may further explain why antipsychotic drugs have a stronger and longer-lasting effect in children than in adults, as adult aggression often resurfaces once they stop receiving medication.

However, Dr. Lin cautions that while mice share similar brain chemistry with people and the current findings echo human clinical results, further research is needed to establish the influence of past behavior on the effectiveness of antipsychotic medications in humans.

Implications for human behavior and mental health

Even though the study was focused on mice, the findings open up intriguing questions about human aggression and behavior regulation.

The experts believe that the interplay between dopamine and experience could help explain why some individuals exhibit persistent aggressive tendencies, while others learn to regulate their responses over time.

This research may have implications for understanding behavioral disorders such as conduct disorder, intermittent explosive disorder, and even workplace aggression.

Management strategies for aggression are complex. Interventions that focus exclusively on dopamine systems may not be effective, as long-standing patterns of behavior often require a more comprehensive approach.

Experts propose that a well-balanced application of behavioral therapy and medication for such conditions may result in better handling of aggression-related conditions.

While exploring the connection between brain chemicals and learned behaviors, scientists aim to develop more precise methods for treating mental health conditions, taking into account an individual’s life experiences and unique neurochemical responses.

The full study was published in the journal Nature.

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