Dams exhibit natural variability in quality of maternal care exhibited towards their offspring, with some dams performing high levels of licking and grooming (LG) and others performing low levels of LG towards offspring until PD 8 (Caldji et al., 1998). Experiencing inadequate maternal care (i.e. low levels of LG in rodents) has been linked with lifelong alterations in stress responsivity. Animals that received low levels of LG in infancy reveal increased anxiety-like behavior as measured by the open field test and novelty suppressed feeding. Additionally, these same animals exhibit an enhanced corticosterone response to acute stressors. Similar to humans that experienced abuse during childhood, animals with a history of non-nurturing maternal care have reduced levels of GR expression in their hippocampus, which was found to correspond with increased methylation, decreased H3K9 acetylation, and reduced transcription factor binding at the GR promoter suggesting that epigenetic programming mediates the effects of infant caregiver experience on adult stress responsivity (Weaver et al., 2004).
