Maternal hormones engage a dormant monomorphic aggression circuit, leading to the introduction of an innate behavior in adulthood in females

Abstract

Aggression - a sexually dimorphic behavior, is prevalent in males and typically absent in virgin females. Following parturition, however, the transient expression of aggression in adult females ensures the pups’ defense from predators and infanticide. While maternal hormones are known to elicit nursing, whether they play a role in the expression of maternal aggression remains unknown. Here we show that a molecularly defined subset of ventral premammillary (PMvᴰᴬᵀ) neurons, instrumental for intermale aggression, switch into a hyperexcitable state during lactation. We identify that the maternal hormones prolactin and oxytocin excite these cells, an effect mediated through T-type Ca²⁺ channels. Optogenetic manipulation or genetic ablation of PMvᴰᴬᵀ neurons profoundly affects maternal aggression, while activation of these neurons impairs the expression of non-aggression-related behaviors. This work identifies a monomorphic neural substrate that incorporates hormonal cues to enable the transient expression of a dormant behavioral program in adult females.