Accelerated maturation of fear regulation systems in infant rats following early life inflammation

Early life stress is a well-established risk factor for neuropsychiatric and neurodevelopmental disorders, yet the mechanisms underlying this lifelong vulnerability remain unclear. One possibility is that early stress exposure disrupts the developmental trajectory of neural systems involved in emotion regulation, creating long-term susceptibility to psychopathology. Therefore, here we explored the impact of two forms of early-life adversity on maturation of emotional regulation in infant rats. Two forms of adversity were examined: maternal separation (MS) and to early-life inflammation (ELI) via post-natal injections of the bacterial endotoxin lipopolysaccharide. In Experiment 1, we examined the effects of these two types of early life stress in infant male rats. Based on the results of the first experiment, in Experiment 2 we replicated the procedures from Experiment 1 in females but only examined ELI as an early stressor. In both experiments, ELI infants displayed a precocious emergence of context-mediated relapse of extinguished fear, whereas standard-rearing (SR) and MS male infants did not. These findings suggest that ELI accelerates the development of infant emotion regulation, consistent with studies using other stressors (e.g., psychosocial), and point to shared mechanisms underlying the long-term adverse effects of early-life stress.