Med Sci Monit. 2005 Apr;11(4):RA136-45

Testosterone and aggressiveness.

Giammanco M, Tabacchi G, Giammanco S, Di Majo D, La Guardia M.

Institute of Physiology and Human Nutrition, University of Palermo, 90127
Palermo, Italy

Aggressiveness is an ancestral behavior common to all animal species. Its
neurophysiological mechanisms are similar in all vertebrates. Males are
generally more aggressive than females. In this review, aggressive behavior
in rodents, monkeys, and man and the role of testosterone and brain
serotonin levels have been considered. Interspecific aggressiveness in rats
has been studied considering the mouse-killing behavior; the neonatal
androgenization of females increases adult mouse-killing as does the
administration of testosterone in adults. Intraspecific aggressiveness was
studied by putting two or more male rats (or mice) in the same cage; the
condition of subjection or dominance is influenced by testosterone. In
monkeys, testosterone is related to aggressiveness and dominance and,
during the mating season, increases in testosterone levels and aggressive
attitude are observed. In men, higher testosterone levels were obtained in
perpetrators of violent crimes, in men from the army with antisocial
behaviors, in subjects with impulsive behaviors, alcoholics and suicidals,
in athletes using steroids, and during competitions. Aggressive and
dominant behavior are distinguished. Testosterone influences both of these,
even if man is usually inclined to affirm his power without causing
physical damage. Testosterone receptors are mainly in some hypothalamic
neurons, where it is aromatized into estrogens, which determine the
increase in aggressiveness. A relation between testosterone levels and
diencephalic serotonin has been shown: in fact, the lack of serotonin
increases aggressive behaviors both in animals and man. Testosterone also
increases ADH levels in the medial amygdala, lateral hypothalamus, and
preoptical medial area, involved in aggressive behaviors.