Amnesia for early life stress does not preclude the adult development of posttraumatic stress disorder symptoms in rats

Background Traumatic experience can result in life-long changes in the ability to cope with future stressors and emotionally salient events. These experiences, particularly during early development, are a significant risk factor for later life anxiety disorders such as posttraumatic stress disorder (PTSD). However, because traumatic experience typically results in strong episodic memories, it is not known whether such long-term memories are necessary for particular features of PTSD, such as enhanced fear and anxiety. Here, we used a fear conditioning procedure in juvenile rats before maturation of the neural systems supporting declarative memory to assess the necessity of early memory to the later life development of PTSD-related symptoms. Methods Nineteen-day old rats were exposed to unpredictable and inescapable footshocks, and fear memory for the shock context was assessed during adulthood. Thereafter, adult animals were either exposed to single-trial fear conditioning or elevated plus maze or sacrificed for basal diurnal corticosterone and quantification of neuronal glucocorticoid and neuropeptide Y receptors. Results Early trauma exposed rats displayed stereotypic footshock reactivity, yet by adulthood, hippocampus-dependent contextual fear-related memory was absent. However, adult rats showed sensitized fear learning, aberrant basal circadian fluctuations of corticosterone, increased amygdalar glucocorticoid receptors, decreased time spent in the open arm of an elevated plus maze, and an odor aversion associated with early-life footshocks. Conclusions These results suggest that traumatic experience during developmental periods of hippocampal immaturity can promote lifelong changes in symptoms and neuropathology associated with human PTSD, even if there is no explicit memory of the early trauma. © 2014 Society of Biological Psychiatry.