Testosterone and aggressiveness.

Abstract

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. Interspecifi c aggressiveness in rats has been studied considering the mouse-killing behavior; the neonatal androgenization of females increases adult mousekilling as does the administration of testosterone in adults. Intraspecifi c aggressiveness was studied by putting two or more male rats (or mice) in the same cage; the condition of subjection or dominance is infl uenced 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 infl uences both of these, even if man is usually inclined to affi rm 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.