Differences in hippocampal serotonergic activity in a mouse single prolonged stress paradigm impact discriminant fear acquisition and retention.

A mouse model of traumatic stress provided insight into a mechanism of individual differences in conditioned fear responding. Hippocampal serotonergic activity (metabolic turnover) was associated with increased behavioral freezing during fear acquisition in a portion of trauma-exposed subjects. These subjects later displayed enhanced fear to the neutral cue during retention. An inability to discriminate fear responses may underlie dysfunctional fear memories in a sub-population of individuals with Posttraumatic Stress Disorder, with contributions from the hippocampal serotonin system.