Heart rate variability in developing mice. A) Heart rate variability during development. (*P ≤ 0.05, linear mixed model). B) pNN6 throughout development (*P ≤ 0.05, logistic regression model). C) pNN12 displays the effect of altering the threshold in (B). Values are presented here as mean ± SEM. An interaction effect (P ≤ 0.01) between sex and age is present in both A and B. Arrow denotes point at which mice were weaned.