Post-trauma behavioral phenotype predicts the degree of vulnerability to fear relapse after extinction in male rats.

Current treatments for trauma-related disorders remain ineffective for many patients. Fear extinction deficiency is a prominent feature of these diseases, and many behavioral treatments rely on extinction training. However, in many patients, therapy is followed by a relapse of symptoms, and the underpinnings of such interindividual variations in vulnerability to relapse remain unknown. Here, we modeled interindividual differences in post-therapy fear relapse with an ethologically relevant trauma recovery paradigm. After fear conditioning, male rats underwent fear extinction while foraging in a large enriched arena, permitting the expression of a wide spectrum of behaviors. An automated multidimensional behavioral assessment revealed that post-conditioning fear response profiles clustered into two groups: some animals expressed fear by freezing more, whereas others darted more, as if fleeing from danger. Remarkably, the tendency of an animal to dart or to freeze after CS presentation during the first extinction session was, respectively, associated with stronger or weaker fear renewal. Moreover, genome-wide transcriptional profiling revealed that these groups differentially regulated specific sets of genes, some of which were previously implicated in anxiety and trauma-related disorders. Our results suggest that post-trauma behavioral phenotypes and the associated gene expression landscapes can serve as markers of fear relapse susceptibility and thus may be instrumental for future development of more effective treatments for psychiatric patients.