Mean Genes

Mean Genes Review René Hen Levine, 1969). In adult rats, castration reduces intermale aggression and injection of testosterone reinstates ag-Center for Neurobiology and Behavior Columbia University gressiveness. However, testosterone injections are ineffective if castration is performed neonatally (vom Saal, New York, New York 10032 1983). The secretion of testosterone early in development has therefore been suggested to stimulate the development of neural circuits that facilitate intermale Aggressive behavior is displayed by most animal spe-aggression. cies and subserves functions that are essential for the Insights into the neurochemistry of aggressive behav-survival of the species, such as defense of the territory, ior first came from animal studies which showed that defense of the progeny, and access to females (Lorenz, aggressive behavior could be markedly altered through 1966). For example, isolated male mice as well as lactat-the modification of specific neurotransmitter systems ing females will attack male intruders. Humans may dis-such as the serotonergic system, and, to some extent, play aggressive behavior in response to a threat or under the dopaminergic, noradrenergic, and GABAergic sys-the influence of alcohol. In its most extreme cases, ag-tems (Eichelman, 1990; Miczek et al., 1994). gressive behavior is considered a social ill, and the prevention of violence is a major concern of our societies. Social stressors such as poverty or a history of child The Serotonin Hypothesis abuse are likely to play a crucial role in many violent I will focus on the serotonergic system because recent behaviors (Dodge et al., 1990). Environmental factors evidence points to the involvement of specific compo-can trigger behavioral responses by influencing the ac-nents of the serotonergic system in the modulation of tivity of biological substrates. For example, in mice isola-aggressive behavior. tion results in an increase in aggressive behavior as well Early animal studies suggested an inverse relationship as changes in levels of neurotransmitters and hormones between the activity of the brain serotonergic system (Valzelli and Bernasconi, 1979). In this review, we will and aggressive behavior (Pucilowski and Kostowski, focus on the molecular mechanisms that might underlie 1983). Specifically, experimental manipulations that low-aggressive behavior, not because we believe that envi-ered brain levels of serotonin increased aggressive re-ronment plays a minor role but because recent advances sponding in some animal models of aggression (Vergnes have pointed toward specific molecules as modulators et al., 1986). Conversely, manipulations that raised sero-of aggressive behavior. tonin levels decreased aggressive responding (Molina et al., 1987). In humans, several …