Effects of early life social experience on fear extinction and related glucocorticoid profiles - behavioral and neurochemical approaches in a rat model of PTSD.

People may agonize over an intrusive fear-inducing memory even when the traumatic event has passed, which is the principle manifestation of posttraumatic stress disorder (PTSD). However, many traumatized people do not present symptoms of PTSD, implying that certain hidden factors help those individuals to cope with the traumatic stress. Increasing evidence suggests that early life experience may serve as a predisposing factor in the development of PTSD. For example, early life social deprivation disrupts the glucocorticoid system, one of the biological abnormalities of PTSD. By employing isolation rearing (IR) with a subsequent single prolonged stress (SPS) paradigm, we examined the hypothesis that early-life social experience may change the outcome of traumatic stress in both behavioral and neurochemical profiles. Behaviorally, the performance of rats on a Pavlovian fear conditioning test was measured to evaluate their retrieval ability of fear memory extinction. Neurochemically, plasma corticosterone levels and glucocorticoid receptor (GR), FK506-binding proteins 4 and 5 (FKBP4 and FKBP5) and early growth response-1 (Egr-1) expression were measured in GR-abundant brain areas, including the hypothalamus, medial prefrontal cortex, and hippocampus. Our results demonstrated an area-dependent IR effect on the SPS outcomes. IR prevented the SPS-impaired fear extinction retrieval ability and averted the SPS-elevated expression of GR, FKBP4, and Egr-1 in the hippocampus, whereas it did not change the SPS-reduced plasma corticosterone levels and SPS-enhanced GR activity in the mPFC and hypothalamus. The present study provides some new insights to support the hypothesis that early-life experience may play a role in the occurrence of PTSD.