Time-dependent sensitization of stress responses in zebrafish: A putative model for post-traumatic stress disorder.

Time-dependent sensitization (TDS)-the delayed increase in neurobehavioral responses to heterotypic stressors after exposure to an intense, inescapable stressor-has been proposed as an animal model for post-traumatic stress disorder (PTSD). Translationally relevant stressors used in TDS are capable of affecting more than one behavioral domain and produce interindividual variability in responsiveness. Here, conspecific alarm substance (CAS) is shown to induce TDS in zebrafish in inter- and intra-population-specific way. Exposure to CAS, an ecologically relevant stimulus which produces fear-like responses acutely, increased anxiety and arousal in zebrafish from the blue shortfin (BSF) phenotype 24h after stimulus delivery. Anxiety-like responses were differently affected immediately and 24h after stimulus delivery. Anxiety-like responses were more sensitized in zebrafish from the longfin (LOF) than in the BSF phenotype, an effect which is reminiscent of "basal" differences in anxiety-like behavior. After application of behavioral cutoff criteria, CAS was shown to produce intense TDS in ∼25% of LOF animals, while ∼20% of exposed animals showed little evidence of TDS. Overall, these results suggest that CAS induces TDS in zebrafish after a 24h "incubation" period, with inter- and intra-population variability that underlines its face and ecological validity.