The Resident-Intruder model: Evaluation of the possible factors and mechanisms that control the display of aggressive behavior in rodents
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One model that is commonly used to study aggressive behavior and its subsequent negative consequences (e.g. social stress) is the Resident-Intruder paradigm, commonly used for mice and rats. In this model, two rodents are introduced to each other in the home cage of one of the animals (the resident) and then allowed to interact for a set period of time. The aim of this thesis was to discuss the possible mechanisms that determine the display of aggressive or submissive behaviors of rodents during this social interaction. Up to date, one of the neurotransmitters that have most consistently been shown to be correlate with the display of aggressive behavior in the Resident-intruder model is serotonin. A large body of research shows a negative correlation between serotonergic activity and aggressive behavior, suggesting an inhibitory role of serotonin on the display of aggressive behavior i.e. the serotonin deficiency hypothesis. However, there are also some studies that contradict show a positive correlations between serotonergic activity and aggression. These opposing correlations can be explained by distinguishing between functional forms of aggressive behavior (which are positively correlated with serotonergic activity) and escalated/pathological forms (which are negatively correlated with serotonergic activity). A revised version of the serotonin deficiency hypothesis is proposed, which suggests that low serotonergic activity may predispose an animal towards displaying aggressive behavior but only in (1) certain regions of the rodent brain (e.g. anterior hypothalamus) and only in (2) escalated forms of aggressive behavior.