Early life adversity decreases fear expression in pre-adolescence by accelerating amygdalar parvalbumin cell development

Resource insecurity (e.g., poverty) can be a significant source of stress. Decreased resources during childhood has been associated with increased risk for developing stress-related disorders, including major depressive disorder and anxiety Although the link between early life adversity and increased risk for psychopathology has been well established, the developmental mechanisms remain unclear. Using a mouse model of poverty-like rearing, limited bedding and nesting materials (LB), we tested the effects of LB on the development of fear learning and of key neuronal structures involved in emotional regulation, the medial prefrontal cortex (mPFC) and basolateral amygdala (BLA). LB delayed the ability of pre-adolescent mice to express, but not form, an auditory conditioned fear memory. LB disrupted typical fear circuit development, accelerating parvalbumin positive (PV+) inhibitory interneuron maturation in the BLA and delaying the maturation of connections between the mPFC and BLA. The decreased fear expression in LB reared mice during early development was rescued through optogenetic inactivation of PV+ cells in the BLA. Together our data demonstrate that LB has profound and deleterious effects on mPFC and BLA development, decreasing threat-associated behavior expression, but not learning, in childhood. The current results provide a model of transiently blunt emotional reactivity in childhood, with fear-associated memories emerging later in adolescence, and possibly contributing to later pathology development.