Rodent early experience studies demonstrate how early parental care profoundly influences brain development, regulates gene expression, and shapes the neural systems involved in reactivity and regulation of the HPA system to subsequent stressors (Levine, 2005). In the rat, the L-HPA system is relatively hyporesponsive to stressors during the first few weeks of life (stress hyporesponsive period [SHRP]; Brunson et al., 2001). Specific maternal stimuli of licking/grooming and nursing maintain this SHRP. While brief separations from these maternal stimuli result in a more adaptive animal, perhaps due to the subsequent increases in licking and grooming upon return, removing these stimuli for longer periods of time produces HPA axis hypereactivity (Levine, 2005). These stimuli also regulate CRH activity in extrahypothalamic sites (Brunson et al., 2001). Critically, parental care not only buffers the pup from many stressors and regulates basal activity of the axis, but also influences the development of the stress- and threat-response systems. Inadequate or disorganized parental care influences stress system hyperreactivity to stressors that might persist throughout life and influences hyper-defensive behavior. These parenting effects are produced, at least in
