Measures related to locomotor activity on the EPM following KOR activation in male and female adolescents (left) and adults (right). Animals were given an i.p. injection of KOR agonist U69593 (0.01, 0.1, or 1 mg/kg) or vehicle, and anxiety was tested 20 min following injection. There was a significant difference between adolescents and adults in closed arm time (A, B), closed arm entries (C, D), and total arm entries (E, F; difference not indicated). There was a significant sex difference in both ages on total number of arm entries (E, F; not indicated).