Adolescent stress and neural plasticity in hamsters: a vasopressin-serotonin model of inappropriate aggressive behaviour

Animal studies show that arginine vasopressin facilitates aggression, while serotonin (5-HT) inhibits aggression by blocking the activity of the vasop ressin system. Clinical studies report that subjects with a history of 'fig hting and assault' show a significant positive correlation between cerebros pinal fluid concentrations of vasopressin and aggression in the presence of a hyporeactive 5-HT system. Thus, in animals and humans, a hyporeactive 5- HT system may result in enhanced vasopressin activity and increased aggress ion. Can the stress of emotional and physical insult, i.e. threat and attac k, during adolescence affect the development of the vasopressin and 5-HT sy stems and alter normal aggressive behaviour in early adulthood? Adolescent male golden hamsters were weaned at postnatal day 25, and stressed for 2 we eks by daily 1 h bents of threat and attack by adult hamsters. Male litterm ates were run in a parallel stress study using daily 1 h trials of isolatio n in a novel environment. During early adulthood, on postnatal day 45, 3 da ys after the cessation of stress trials, animals were tested for aggression in a resident:intruder model. The results show a context-dependent change in aggression. Animals with a history of abuse show exaggerated attack beha viour toward smaller males compared to littermates with a history of isolat ion stress. Conversely, when confronted by males of equal size, animals wit h a history of abuse show diminished aggression and increased submission co mpared to controls. It was determined that the density of vasopressin fibre s and neurones in the hypothalamus is lower in abused animals compared to c ontrols. In contrast, the number of 5-HT terminals within the hypothalamus is higher in abused animals compared to controls. These results provide evi dence in an animal model that stress in the form of threat and attack durin g adolescence can alter the balance between vasopressin and 5-HT in the bra in, resulting in inappropriate aggressive behaviour in early adulthood.