Effects of ethanol on murine aggression assessed by biting of an inanimate target

Changes in attack behavior and activity in EphA5 knockout mice

During development, Eph tyrosine kinase receptors and their ephrin ligands function as axon guidance molecules while, in adults, these molecules appear to be involved in the regulation of neural plasticity and emotion. The absence of EphA5 receptor mediated forward signaling may cause alterations in connectivity of neural networks and boundary formation during development, including central monoaminergic systems. In the present studies, we demonstrated altered aggressive responses by animals lacking functional EphA5 receptors. These behavioral changes were accompanied by altered concentrations of serotonin (5-HT) and the metabolite, 5-HIAA, in the hypothalamus. The changes of serotonin activity in hypothalamus also result in increase of body weight in EphA5 knockout mice. Furthermore, EphA5 knockout mice exhibited a significant decrease in activity levels following exposure to naïve intruders in their home cages. We conclude that the EphA5 receptor may be involved in mediation of aggressive behavior regulated, in part, by hypothalamic serotonin.

Differential effect of Fyn tyrosine kinase deletion on offensive and defensive aggression

Fyn tyrosine kinase is highly expressed in the limbic system and mice lacking Fyn tyrosine kinase showed increased fearfulness in a variety of tests for anxiety-related behaviors. To investigate the possible role of Fyn tyrosine kinase in aggression, we assessed the aggressive behaviors of the mice lacking the Fyn tyrosine kinase using the resident-intruder and restraint-induced target biting paradigms. The percentage of Fyn-deficient mice that attacked an inanimate target in a restraint tube was higher than that of the control mice. On the contrary, in the resident-intruder paradigm, the percentage of Fyn-deficient mice that attacked the intruder was lower and the Fyn-deficient mice showed a longer latency to attack an intruder. These results suggest a distinct role of Fyn tyrosine kinase in enhancing the offensive aggression and decreasing the defensive aggression. A possible influence of anxiety-phenotype of the Fyn-deficient mice on their abnormal aggressive behavior was discussed.

Voluntary ethanol consumption in male adolescent hamsters increases testosterone and aggression

The immediate and long-term biologic and behavioral consequences of voluntary ethanol (EtOH) exposure during male adolescence are unknown. In the present study, male golden hamsters voluntarily drank from a 15% EtOH solution in addition to consuming dry laboratory chow and water ad lib from Postnatal Day 25 to Postnatal Day 43. Over this adolescent period, they drank an average of 13 g/kg/day of EtOH, resulting in a mean blood EtOH concentration of ca. 53 mg %. On Postnatal Day 35, a period of enhanced sensitization and activation of the gonadal axis, testosterone levels were twice as high in EtOH animals than in sucrose-yoked controls. However, this difference disappeared by Postnatal Day 53, as EtOH and control animals showed comparable adult levels of plasma testosterone. When tested for aggression several days after the cessation of EtOH exposure, hamsters showed enhanced attack behavior toward smaller intruders placed into their home cage. These results suggest that voluntary EtOH exposure during male adolescence has specific neuroendocrine effects with lasting behavioral consequences.

Alcohol, GABAA-benzodiazepine receptor complex, and aggression

Neurobiological investigations have become productive since experimental protocols were developed that engender large increases in aggressive behavior after acute alcohol challenges in individual experimental animals. Recent developments extended the heightened aggressive behavior to rats that self-administered alcohol shortly before the social confrontation. Quantitative ethological analysis revealed that alcohol prolongs "bursts" of aggressive acts and displays and disrupts communication between the aggressive animal and the opponent who defends, submits, or flees. Pharmacological modulation of the GABAA receptor with benzodiazepine agonists and neuroactive steroids results in dose-dependent biphasic changes in aggressive behavior that mimic the dose-effect function of alcohol; benzodiazepines potentiate the aggression-heightening effects of alcohol as well as the behaviorally suppressive effects; and antagonists at benzodiazepine receptors prevented the aggression-heightening effects of alcohol. The maturational and experiential origins for potentially distinctive GABAA receptor characteristics in individuals who exhibit heightened aggressive behavior await identification.