A Modified Resident‐intruder Assay for Determination of Aggressiveness in Mice

Aggression is the conduct intending to cause physical harm on another individual during situations of conflict. It will be important to understand how territorial claiming regulates the change from nonaggressive to aggressive behaviors. It is known that the medial amygdala nucleus of the brain regulates aggression, particularly the cells expressing the aromatase gene. However it is not known whether these cells are excitatory or inhibitory. Surgically castrated males were swabbed with urine from noncastrated mice and used as intruders. They were introduced for 20 minutes into resident's cages which consisted of ten adult males and were tested at 0, 1, 5 and 11 days after being individually housed. All trials were recorded and analyzed for aggressive behaviors. After five days we found that aggression increased reaching its maximum. These results are helpful to understand aggression patterns and could facilitate identification of genes and environmental cues underpinnings. We also wanted to determine the distribution of the neurotransmitters, GABA and Glutamate, in aromatase positive neurons of the medial amygdala with immunohistochemistry. These studies helped us determine the distribution of neurotransmitters (GABA and Glutamate), both neurotransmitters are involved in these synapses. Understanding these interactions could provide entry points to study brain circuits important in aggressive behaviors.