Fear extinction results in the suppression of the fear response once the conditional stimulus does not predict the threatening event anymore. Different anxiety disorders (e.g.: PTSD) have typical deficits in the formation and expression of extinction memory. It is known that stress affects the emergence of extinction memory. Thus, we planned to define whether acute stress may affect synaptic remodelling in the dorsal hippocampus (DH), possibly accounting for some of the effects of stress on extinction memory. Stressed animals were fear conditioned to context and later on trained in an extinction paradigm (repeated context re-exposures without footshock). Animals were sacrificed for preparation1 day after conditioning (before extinction) or 1 day after extinction. We confirmed that stress exposure induced a delay in extinction learning. Remarkably, a higher density of dendritic spines and particularly mature ones, was observed in the DH of non-stressed conditioned animals at pre-extinction, reaching control values after the end of the extinction sessions. In contrast, stressed animals did not show such spines boost. Moreover, animals with intra-BLA Midazolam administration prior to stress showed structural changes similar to non-stressed animals. In sum, here we show that stress impairs the structural plasticity in DH potentially associated with extinction memory. We are currently extending our studies to other areas involved in extinction memories processing
