Acute systemic fibroblast growth factor-2 enhances long-term extinction of fear and reduces reinstatement in rats.

Despite having made substantial advances in the treatment of anxiety disorders over the past few decades it appears that we have now reached a 'therapeutic impasse'. Further clinical progress requires a greater understanding of the neural mechanisms underlying fear inhibition. In this study, we examined, for the first time, the effects of fibroblast growth factor-2 (FGF2), a mitogen involved in the molecular cascade of memory, on extinction and relapse in rats. In all experiments, rats were first trained to fear a white noise-conditioned stimulus, and then had this learned fear extinguished the following day. Extinction is the process underlying exposure-based therapy in humans. Experiments 1 and 2 demonstrated that FGF2 facilitated the loss of learned fear (ie, extinction) when given either prior to or immediately after extinction but not when given 4 h after extinction. This suggests that FGF2 must be present during the consolidation of the extinction memory to have an effect. Experiment 3 further supported this interpretation by showing that short-term extinction must occur for FGF2 to facilitate long-term extinction, suggesting that FGF2 is facilitating the translation of memory from short-term to long-term storage. In experiment 4 rats given FGF2 immediately after extinction exhibited less shock-induced reinstatement, which is a model preparation of relapse, than did vehicle-treated rats. Together, these experiments demonstrate that FGF2 facilitates extinction and attenuates relapse. Thus, FGF2 may be a novel pharmacological adjunct to exposure therapy.