PubMed · 7837850
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S Levander. 1995-01-18. [Aggression--a biological perspective].. https://pubmed.ncbi.nlm.nih.gov/7837850/
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In order to understand the physiological role of serotonin in regulating aggressive behaviour it is important to understand how this neuromodulator acts within the context of a naturally fluctuating social and physical environment. To accomplish this, we examined the effect of the selective serotonin reuptake inhibitor fluoxetine during the breeding season in free-living male American tree sparrows (Spizella arborea) in Northern Alaska. During this time period males are maximally aggressive towards territorial intruders. Male, territorial sparrows were injected with either vehicle or a 10 mg/kg dose of fluoxetine. One hour later, aggression was measured using a simulated territorial intrusion. Depending upon when birds were sampled, the aggression scores for vehicle and fluoxetine treatments were grouped according to the number of days after territorial behaviour was initiated. The three groups were: early, days 1-5; middle, days 6-10; and late, days 11-15. There was a significant overall difference between groups (F(5,36)=5.18, P<0.0015). Post hoc analysis demonstrated that the level of aggression did not differ between the three groups of saline injected birds. However, fluoxetine injected birds showed a time dependent decrease in aggression. When compared to control birds the middle and late fluoxetine groups had significantly less aggression. Furthermore, the late group of fluoxetine treated birds were significantly less aggressive than the early group of fluoxetine birds. This demonstrates that free-living male ATSPs show a rapid change in their behavioural response to fluoxetine across the first 2 weeks of the breeding season. The rapidity of the change in responsiveness suggests a dynamic sensitivity of the serotonergic system.
We consider a version of the Hawk-Dove game in which an animal knows its own fighting ability but not the ability of its opponent. For this game at evolutionary stability there is a critical level of ability such that animals with ability greater than the critical level play Hawk and animals with ability below the critical level play Dove. We define the level of fighting to be the probability of a Hawk-Hawk fight when two opponents meet. We show that even if an animal does not know the ability of its opponent, knowing its own ability results in a lower level of fighting at evolutionary stability than is found in the standard Hawk-Dove game in which there are no differences in ability or abilities are not known.
Repeated stress is an important risk factor for the development of depression. However, the mechanism by which stress influences depression is largely unknown, in part due to the fact that few animal models of repeated stress produce robust changes in depression-like behavior. The purpose of the present study was to characterize the effect of repeated corticosterone (CORT) injections and repeated restraint stress on anxiety and depression-like behavior in male rats. Rats received CORT injections (40 mg/kg, s.c.), vehicle injections, restraint stress (6 h/day), or handling once per day for 21 consecutive days prior to the behavioral testing. The rats were then tested for changes in fearful/anxious behavior in the open-field and social interaction tests and for depression-like behavior in the forced swim test. The repeated CORT injections had no significant effect on activity levels or anxiety in the open-field or social interaction tests. However, they did increase depression-like behaviors in the forced swim test. Repeated restraint stress had no significant effect on anxiety or depression-like behavior on any of the behavioral tests. These results suggest that repeated CORT injections warrant further investigation as an animal model to study the role of stress in depression.