A robust fear response is observed following the interaction of a trace memory induced by a weak fear conditioning procedure and the exposure to a stressful experience. Similarly, it is widely accepted that prior stressful experience promotes the formation of fear memory. This evidence highlights the importance of the emotional state previous to the encoding process or to the retrieval experience on the fear output. The question that arises is whether structural plasticity in dorsal hippocampus (DH), a key brain area for contextual fear memory, accompanies such behavioral manifestation ?. To this purpose, we assessed structural plasticity changes in the DH in animals stressed and later fear conditioned or, vice versa fear conditioned and later stressed. The behavioral and imaging analysis were performed 1 day after the last manipulation. Behaviorally, we observed that a single stressful exposure either prior or after fear encoding, induced a higher fear response. In a similar way, animals presented a higher density of total dendritic spines and particularly mature spines, in stressed animals prior or after encoding in comparison to non-stressed animals. In conclusion, the structural remodeling in DH accompanied the facilitated fear memory following a combination of fear conditioning and stressful stimulation.
