Correlation of gene expression and THs in the PN14 rat. Percent change in serum T4 correlated to percent change in (A) Parv and (B) Hr in the pup neocortex. These candidate genes were also highly correlated to brain T4 (C, D), but in an exponential manner. Percent change in expression of Parv and Hr, interrogated as a function of brain T3, were best represented by quadratic equations. Expectedly, differential gene expression in the cortex was more highly predicted by brain TH status, as opposed to serum T4. Error bars represent 6 SEM for both the x and y data, and R2 values are noted on each panel.