Rolipram reverses scopolamine-induced and time-dependent memory deficits in object recognition by different mechanisms of action

In this study, the effect of the selective phosphodiesterase type 4 (PDE4) inhibitor rolipram on memory performance was investigated using the object recognition task. First, three doses of rolipram (0.01, 0.03 or 0.1 mg/kg) were tested with a 24h delay between the learning (T1) and the test (T2) trial. Doses of rolipram were injected at different time points (30 min before T1, immediately after T1 or 3 h after T1). In a second experiment, the effects of rolipram (0.03, 0.1 or 0.3 mg/kg) were tested in combination with scopolamine (0.1 mg/kg) applying a 1 h delay between trials. Both substances were administered 30 min before T1. Using a 24h interval, rolipram showed an improvement in long-term memory performance when injected 3 h after T1 at a dose of 0.03 mg/kg. Further, rolipram reversed the scopolamine-induced short-term memory deficit at a dose of 0.1 mg/kg. Although the improved memory performance in both conditions is likely to be explained by elevated cAMP levels, two separate working mechanisms might explain these effects.