Role of the medial amygdala glutamatergic and GABAergic neurons during social defeat

Knowing how to behave in the presence of an aggressive conspecific is essential for an individual's survival. For many rodents, olfactory cues are crucial for the animal to identify conspecifics and behave properly. An important region for the expression of social defense is the medial amygdala (MeA). This brain region receives projections from neurons in the accessory olfactory bulb (AOB) and processes olfactory cues from conspecifics. The MeA is enriched by glutamatergic (VGLUT2) and GABAergic (VGAT) neurons. Interestingly, GABAergic neurons are predominantly located in the posterodorsal part of the MeA (MeApd), while glutamatergic neurons are mainly located in the posteroventral part of the MeA (MeApv). This study aims to investigate how GABAergic and glutamatergic neurons in the MeA influence social defense behavior. To do this, we assessed the expression of Fos during social defense in VGAT+ and VGLUT2+ neurons in the MeA. We observed that VGAT+ and VGLUT2+ neurons in the medial amygdala are mobilized during social defense. However, in the MeApd, the preferentially active neurons are GABAergic neurons, while in the MeApv, there is no preference between these populations. Furthermore, by performing anterograde tracing of GABAergic neurons in the MeApd and glutamatergic neurons in the MeApv, we were able to observe that these neurons project to several common nuclei but in different ways. In conclusion, our data suggest that these neural populations contribute to the organization of social defense and possibly impact different aspects of this behavior, considering the tracing data.