Hallmarks of trauma-based anxiety disorders, such as PTSD, are exaggerated fear responses to cues associated with the trauma and difficulty suppressing fear behavior even when these cues no longer predict danger. In rats, this SE 175 behavioral phenotype can be modeled by producing elevated startle response to acoustic stimuli and impaired fear extinction. Rats, like humans, show heterogeneity in post-trauma anxiety responses and have been previously classified as those with a PTSD-like phenotype based on their lasting elevation of post-trauma acoustic startle responses and anxiety-like behavior in the elevated plus maze. Encouragingly, the percentage of rats identified with this combination of criteria was 20�C25%, similar to the incidence rate of PTSD in humans. Attempts at pre-trauma classification, however, have yielded limited success. Previous studies have shown no relationship between behavior during a traumatic event and impaired extinction ; additionally, it is not known if pre-classification based on ASR alone will predict impaired extinction, although it can predict elevated startle. One interpretation of such findings is that there is no identifiable population predisposed to impaired extinction and elevated startle, but, rather, these develop solely as a PD166326 consequence of the traumatic event. We tested an alternative hypothesis that predispositions do exist and they can be identified prior to the emotional trauma. Specifically, we tested whether predispositions to a more comprehensive PTSD-like behavioral phenotype which includes elevated ASR and impaired fear extinction, could be predicted before the trauma, based on ASR and EPM measures. The results only partially support this hypothesis: pre-classification is possible, but only after the animals have experienced a mild stressor, which by itself does not induce the PTSD-like phenotype. Our investigations also compare what aspects of post-trauma behaviors can be predicted based on either of the two classification factors alone. The main finding of the current research is that impaired extinction and prolonged elevated startle can be predicted based on a combination of anxiety and startle responses that are measured after exposure to a mild stressor, but prior to exposure to an emotionally traumatic event.