GABAA receptor activation in the lateral septum reduces the expression of conditioned defeat and increases aggression in Syrian hamsters

Exposure to social stressors can cause profound changes in an individual's physiology andbehavior. In Syrian hamsters, even a single social defeat results in conditioned defeat, which includes an abolishment of territorial aggression and the emergence of high levels of submissive behavior. The purpose of the current study was to determine whether the lateral septum (LS) is a component of the putative neural circuit underlying conditioned defeat. Experiment 1 explored the possibility that plasticity in the LS is necessary for the induction of conditioned defeat. Infusions of the protein synthesis inhibitor, anisomycin, prior to defeat training, however, failed to alter conditioned defeat during testing on the following day, suggesting that synaptic plasticity in the LS is not critical for defeat-induced suppression of aggression. Experiment 2 tested whether the LS is necessary for the expression of conditioned defeat. Infusions of the GABAA agonist muscimol into the LS prior to testing significantly increased aggression and decreased submission in previously defeated animals suggesting that the LS is an important component of the neural circuit mediating the expression of both aggression and submission in conditioned defeat. Experiment 3 examined whether the effects of muscimol on aggression were dependent on prior social defeat. Non-defeated animals receiving muscimol infusions prior to testing with a non-aggressive intruder displayed significantly more aggression than did hamsters receiving control injections. Thus, these data suggest that the activation of GABAA receptors in the LS increases aggression regardless of whether or not a hamster has previously experienced social defeat.

► Inhibition of protein synthesis in the LS did not affect acquisition of CD.
► Infusion of muscimol in the LS impaired expression of CD and increased aggression.
► Infusion of muscimol in the LS increased aggression in non-defeated animals.
► The LS is involved in the expression of aggression regardless of social defeat experience.
► It appears that plasticity to the defeat experience does not involve the LS.