Glutamatergic signals in the dorsal raphe nucleus regulate maternal aggression and care in an opposing manner in mice.

Lactating female mice nurture their pups and attack intruders in their territory. When an intruder invades a dam's territory, she needs to switch her behavior from care to aggression to protect her pups and territory. Although the neuronal mechanisms underlying each distinct behavior have been studied, it is unclear how these behaviors are displayed alternatively. The dorsal raphe nucleus (DRN) regulates both nurturing and aggressive behaviors. In the present study, we examined whether the DRN is involved in regulating alternative display of maternal care and aggression. We first examined neuronal activity in the medial prefrontal cortex (mPFC) and lateral habenula (LHb), which send glutamatergic input to the DRN, in dams by injecting Fluorogold, a retrograde tracer, into the DRN. The number of c-Fos- and Fluorogold-positive neurons in the mPFC and LHb increased in the dams that displayed biting behavior in response to an intruder, but remained unchanged in the dams that displayed nurturing behavior. Injections of N-methyl-D-aspartic acid (NMDA) receptor antagonists or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptor antagonists into the DRN inhibited biting behavior but not nurturing behavior. In contrast, injections of NMDA or AMPA into the DRN inhibited nurturing behavior. These results suggest that glutamatergic signals in the DRN, which may originate from the mPFC and/or LHb, regulate the preferential display of biting behavior over nurturing behavior in dams.