The Dorsal Raphe Regulates the Duration of Attack through the Medial Orbitofrontal Cortex and Medial Amygdala.

The dorsal raphe (DR) is an evolutionarily conserved brain structure that is involved in aggressive behavior. It projects onto numerous cortical and limbic areas underlying attack behavior. The specific neurocircuit through which the DR regulates aggression, however, is largely unclear. In this study we show that DR neurons expressing CaMKIIα are activated by attack behavior in mice. These neurons project to the medial aspect of the orbitofrontal cortex (OFC; MeOC) and the medial amygdala (MeA), two key regions within the neural circuit known to control aggressive behavior. Using an optogenetic approach, we show that attack bouts are shortened by inhibiting CaMKIIα neurons in the DR and their axons at the MeOC and prolonged by stimulating the DR-MeOC axons during an attack. By contrast, stimulating the axons of CaMKIIα DR neurons at the MeA shortens attack. Notably, neither the DR-MeOC or DR-MeA pathway initiates attack when stimulated. These results indicate that the DR-MeOC and DR-MeA pathways regulate the duration of attack behavior in opposite directions, revealing a circuit mechanism for the control of attack by the DR.