State-dependent performance of rats on a complex maze task

State-dependent learning occurs when information acquired in one chemical s tate fails to transfer or only partially transfers to another state. Thirty -five Long-Evans rats learned to nm the Hampton Court maze and then were te sted in an ABA design, alternating between administration of one of three d oses of morphine sulfate (6, 10, or 15 mg/kg) and saline. At the two highes t drug doses, regardless of direction of switch (saline to morphine or vice versa), the subjects' running time increased significantly after the first switch, but not at all or to a much lesser degree after the second switch, indicating possible state-dependency effects. Analysis of errors indicated that, after the first state change only, rats that had switched from morph ine to saline committed errors immediately after the change under all three dose conditions, but those that switched from saline to morphine continued to nm the maze without error. The results of this study indicate that morp hine-related state changes can create temporary disruptions in performance- independently of direct drug effects-on a task with a long learning curve s uch as this one.