OPRM1 and Anxiety: Optogenetic stimulation of MOR-positive neurons in the mHb of rodents triggers aversive avoidance and despair-like responses with no anxiety-related effects, and stimulation at the dorsal raphe nucleus terminal of MOR-positive mHb neurons increases anxiety levels without affecting other behaviors, revealing the involvement of two separate pathways in aversive learning and its affective behavioral phenotypes [109].