Aggressive Behavior In Boys And Men May Not Be A Learned Behavior; Reduced Levels Of A Vascoconstrictor Triggers Physiological Processes Leading To Fighting, Biting, And Scratching

Poets and writers of great literature may be disappointed to learn that the aggressive male passions that have caused duels, skirmishes, and wars are the result of reduced levels of serotonin in the brain. Why men? A group of researchers from the University of Akron state the Y chromosome that determines "maleness" (as opposed to the XX in females) governs serotonin levels. When stimulated, serotonin decreases, testosterone increases, and aggression results.

The authors of the study, "Sex Differences in Brain Monamines and Aggression," are Jonathon Toot, Gail Dunphry, and Daniel Ely, from the Department of Biology, The University of Akron, Akron, Ohio. Their findings are being presented in detail at the conference, Genomes and Hormones: An Integrative Approach to Gender Differences in Physiology, an American Physiological Society (APS) conference being held October 17-20, 2001, at the Westin Convention Center, Pittsburgh, Pa.

Methodology and Results

"Resident intruder" tests were used to measure the aggression and stress of male and female rats. In a colony of male and female rats a hierarchy is established, with male rats assuming a dominant role over the female rats.

Different male and female rats were then introduced into the established colony. Male intruders were attacked 2.6 times and received 1.8 scars over 15 minutes. Female intruders were not the perpetuators or recipients of any attack.

Norepinephrine, dopamine and serotonin were measured by high performance liquid chromatography (HPLC) in various regions of the brain including hypothalamus (VMH), media amygdala AME), lateral amygdala (ABL) and hippocampus (HPC). Norepinephrine content of VMH, AME, ABL, and HPC was not statistically different between the two sexes. However, values of dopamine in ABL of males were significantly less than corresponding female rats; levels of serotonin in the AME and ABL were also less in males compared to females.

Conclusion

In males, decreased serotonin in the amygdala was associated with increases in aggressive behavior. Whether this relates only to the presence of the Y chromosome or to a combination of the Y chromosome and male hormone testosterone, remains to be determined.

The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.