Fear extinction results in the suppression of the fear response once theconditioned stimulus does not predict the threatening event anymore. Differentanxiety disorders have typical deficits in both extinction memory formation andexpression.

Ventral Hippocampus (VH) is critically involved in the processing of theaversive information as well as in the expression fear extinction memory. Theaim of the present work was to evaluate whether the structural plasticity ofCA1 VH accompanied the characteristic extinction memory formation and theinfluence of stress on the extinction memory.

Stressed animals were fear conditioned to context and later trained inan extinction paradigm (repeated context re-exposures without foot-shock).Animals were sacrificed for preparation 1 day after conditioning (beforeextinction) or 1 day after extinction.

Prior stress exposure induced a deficit in the formation of theextinction fear memory. With respect to structural plasticity, and on thecontrary to the higher density of dendritic spines observed in CA1 DorsalHippocampus after fear conditioning, returning to basal levels after extinctiontraining, CA1 VH presented no changes in the number or the morphology ofdendritic spines, regardless of the fear conditioning, extinction training orstress condition.  

Thus, changes in the dynamic of the extinction fear memory might not besupported by synaptic structural remodeling in VH.