In nature, confrontations between conspecifics are recurrent and related, in general, due to the lack of resources such as food and territory. Adequate defences against a conspecific aggressor are essential for the individual’s survival and the group integrity. However, repeated social defeat is a significant stressor promoting several behavioural changes including social defence per se. What would be the neural basis of these behavioural changes? To build new hypotheses about this, we here investigate the effects of repeated social stress on the neural circuitry underlying motivated social defence behaviour in male mice. We observed that animals re-exposed to the aggressor three times spent more time in passive defence during the last exposure than in the first one. These animals also show less activation of the amygdalar and hypothalamic nuclei related to the processing of conspecific cues. In turn, we found no changes in the activation of the hypothalamic dorsal pre-mammillary nucleus (PMD) that is essential for passive defence. Therefore, our data suggest that the balance between the activity of circuits related to conspecific processing and the PMD determines the pattern of social defence behaviour. Changes in this balance may be the basis of the adaptations in social defence after repeated social defeat.

Behavioural and neural activation data from each male mouse used during the experiments: "Effects of reexposure to the resident-intruder paradigm in social defence" and "Comparison of neural activity after social defeat and restraint stress".

Behaviour Analysis - Intruder - Experiment 01: Behavioural data from intruder animals during the resident-intruder paradigm of experiment 01 (analysis of the effects of re-exposure to the intruder-resident paradigm).

Behaviour Analysis - Resident - Experiment 01: Behavioural data from resident animals during the resident-intruder paradigm of experiment 01 (analysis of the effects of re-exposure to the intruder-resident paradigm).

Neural Activation - Experiment 01: Fos density from different brain regions of intruder male mice - experiment 01 (analysis of the effects of re-exposure to the resident intruder paradigm).

Neural Activation - Experiment 01: Fos density from different brain regions of male mice - experiment 02 (comparing the activation pattern under social and restraint stress).

Tracking Analysis - Intruder - Experiment 01: Tracking analyzes of intruder animals during the paradigm - experiment 01 (analysis of the effects of re-exposure to the resident intruder paradigm).

Tracking Analysis - Resident - Experiment 01: Tracking analyzes of resident animals during the paradigm - experiment 01 (analysis of the effects of re-exposure to the resident intruder paradigm).