In addition, it is worth mentioning that, unlike MOR-mediated effects, KOR activity seems to be endowed with anxiogenic properties, as consistently demonstrated following its pharmacological antagonism in several unconditioned models of anxiety, such as the Elevated Plus-Maze [239,240,241], the Open-Field [242], and the Defensive Burying Test [243], in which anxiolytic effects were observed. The gene discussed is OPRM1; the disease is Anxiety.