Abstract
The costs of violence and aggression in our society have stimulated the scientific search for the predictors and causes of aggression. The majority of studies have focused on males, which are considered to be more aggressive than females in most species. However, rates of offensive behavior in girls and young women are considerable and are currently rising in Western society. The extrapolation of scientific results from males to young, non-maternal females is a priori limited, based on the profound sex differences in brain areas and functioning of neurotransmitters involved in aggression. Therefore, we established a paradigm to assess aggressive behavior in young virgin female rats, i.e. the female intruder test (FIT). We found that approximately 40% of un-manipulated adult (10–11 weeks old) female Wistar rats attack an intruder female during the FIT, independent of their estrous phase or that of their intruder. In addition, adolescent (7–8 weeks old) female rats selected for high anxiety behavior (HABs) displayed significantly more aggression than non-selected (NAB) or low-anxiety (LAB) rats. Intracerebroventricular infusion of oxytocin (OXT, 0.1 µg/5 µl) inhibited aggressive behavior in adult NAB and LAB, but not HAB females. Adolescent NAB rats that had been aggressive towards their intruder showed increased pERK immunoreactivity (IR) in the hypothalamic attack area and reduced pERK-IR in OXT neurons in the paraventricular hypothalamic nucleus compared to non-aggressive NAB rats. Taken together, aggressive behavior in young virgin female rats is partly dependent on trait anxiety, and appears to be under considerable OXT control.
Highlights
The prevalence, negative impact and costs of violence and aggression in our society have stimulated the scientific search for the predictors and causes of aggression, as well as possible treatments to reduce harmful violence
In addition to the damage done to the victims, the negative consequences of aggression extend to the perpetrators: the display of increased aggressive behavior in childhood and adolescence is associated with substance abuse, lower socio-economic status, various social problems, and impaired physical health in adulthood [8,9,10,11]
The experiments reported here confirm that aggression is an important component of the behavioral repertoire of adolescent and adult virgin female rats, and can be reliably quantified in the Female Intruder Test (FIT), i.e. during confrontation with a smaller female intruder rat following 48 h of isolation
Summary
The prevalence, negative impact and costs of violence and aggression in our society have stimulated the scientific search for the predictors and causes of aggression, as well as possible treatments to reduce harmful violence. In addition to the damage done to the victims, the negative consequences of aggression extend to the perpetrators (both male and female): the display of increased aggressive behavior in childhood and adolescence is associated with substance abuse, lower socio-economic status, various social problems, and impaired physical health in adulthood [8,9,10,11]. These findings signal the need to increase the understanding of the neurocircuitry underlying aggression in both sexes, for example by making use of animal models of aggressive behavior. These studies have provided considerable knowledge on the neurobiology of aggression in lactating or territorial females, the extrapolation to non-maternal females of gregarious species is a priori limited: maternal aggression is under strong influence of parturition-associated neuroendocrine adaptations [42] and the neurobiological control of offensive behavior in highly territorial species may differ from that of gregarious, group-living species such as rats and humans [43]
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