Maternal Style Selectively Shapes Amygdalar Development and Social Behavior in Rats Genetically Prone to High Anxiety

The early-life environment critically influences neurodevelopment and later psychological health. To elucidate neural and environmental elements that shape emotional behavior, we developed a rat model of individual differences in temperament and environmental reactivity. We selectively bred rats for high versus low behavioral response to novelty and found that high-reactive (bred high-responder, bHR) rats displayed greater risk-taking, impulsivity and aggression relative to low-reactive (bred low-responder, bLR) rats, which showed high levels of anxiety/depression-like behavior and certain stress vulnerability. The bHR/bLR traits are heritable, but prior work revealed bHR/bLR maternal style differences, with bLR dams showing more maternal attention than bHRs. The present study implemented a cross-fostering paradigm to examine the contribution of maternal behavior to the brain development and emotional behavior of bLR offspring. bLR offspring were reared by biological bLR mothers or fostered to a bLR or bHR mother and then evaluated to determine the effects on the developmental gene expression in the hippocampus and amygdala. Genome-wide expression profiling showed that cross-fostering bLR rats to bHR mothers shifted developmental gene expression in the amygdala (but not hippocampus). All samples were generated from Sprague-Dawley male rats selectively bred for high novelty response (HRs), low novelty response (LRs) or LRs that were crossfostered to either a LR dame or HR dame. Within each age and brain regions, the sample size of each group is 5 samples.