Immediate early genes act in the medial hypothalamus to promote adaptation to social defeat

Territorial animals must moderate their social aggression and avoidance behaviors in a manner that maximizes their access to resources and fitness. The ventrolateral division of the ventromedial hypothalamic nucleus (VMHvl) has been shown to control both social aggression and avoidance in mice, and emerging data show that neural plasticity within VMHvl can drive the experience-dependent adaptation of these behaviors. Here, we investigated the contribution of immediate early gene (IEG) function in supporting this plasticity. In initial experiments, we found that downregulation of the IEG cFos in VMHvl did not significantly moderate the long-term increase in social avoidance seen following an experience of social defeat. However, local knockout of the IEG master regulator Serum Response Factor (SRF, Srf ) was able to blunt the impact of social defeat on social avoidance and prevented the effect of social defeat on local optogenetic-evoked social avoidance behavior, demonstrating a critical role for subcortical IEG activity in social defeat-induced behavioral plasticity. To test whether NMDA receptor dependent plasticity might be involved in this effect, we locally infused the NMDA receptor antagonist MK-801 into VMHvl and assessed the impact of social defeat. Unexpectedly, MK-801 treatment led to an increase in social defeat-induced avoidance, pointing to the existence of opposing IEG and NMDA receptor-dependent adaptive mechanisms in medial hypothalamus. These findings suggest that multiple neural plasticity mechanisms are likely to be at play in the hypothalamic nuclei supporting innate behavior adaptation and show how IEG blockade can be used as a genetic tool to systematically map neural plasticity in the brain.