The type IV phosphodiesterase inhibitor rolipram disturbs expression and extinction of conditioned fear in mice

Recent studies suggest that intracellular signaling pathways involving cyclic adenosine monophosphate (cAMP) may be related to fear processing and long-term memory formation. The type IV phosphodiesterase (PDE4) inhibitor rolipram prevents breakdown of cAMP, enhances long-term memory and may reduce anxiety. In the present study we investigated the role of rolipram in the expression (0, 0.2, or 1 mg/kg), acquisition (0, 0.03, 0.2 or 1 mg/kg), and extinction (0, 0.03, 0.2, 1 mg/kg) of fear using a fear-potentiated startle paradigm in mice. It was shown that rolipram reduced the expression (Experiment 1), did not influence acquisition (Experiment 2) and disturbed between-session extinction (Experiments 3 and 4) of fear responses to conditioned tones. Because within-session extinction was not impaired by rolipram and because low (i.e. 0.03 and 0.2 mg/kg) doses strongly affected extinction but not expression of fear, these findings suggest that the effect of rolipram on extinction is not directly dependent on its effect on fear expression. Taken together, these experiments indicate that preventing breakdown of cAMP interferes with the expression and extinction consolidation of conditioned fear.