The results of cross-fostering studies with the offspring of low- and high-LG mothers provide evidence for a nongenomic transmission of individual differences in stress reactivity and maternal behavior.40 The critical groups of interest are the biological offspring of low-LG mothers fostered onto high-LG dams, and vice versa. The limited cross-fostering design did not result in any effect on group differences in maternal behavior. Hence, the frequency of pup LG across all groups of high-LG mothers was significantly higher than that for any of the low-LG dams, regardless of litter composition. The biological offspring of low-LG dams reared by high-LG mothers were significantly less fearful under conditions of novelty than were the offspring reared by low-LG mothers, including the biological offspring of high-LG mothers.40 Subsequent studies reveal similar findings for hippocampal GR expression and for the differences in both the α1 and γ2-GABAA receptor subunit expression in the amygdala.41 These findings suggest that individual differences in patterns of gene expression and behavior can be directly linked to maternal care over the first week of life.
