Mean (SEM) dose-response effects of nicotine on startle response (top) and on pre-pulse inhibition (PPI) of startle (bottom), by DRD4, DRD2 C957T, SLC6A3, and DRD2/ANKK1 genotypes and, where relevant, by sex. Larger values indicate greater startle (top) and reduced inhibition of startle (bottom). DRD4 effects on the AUC measure of startle (not shown) were virtually identical to those shown here for max startle. Similarly, SLC6A3 and DRD2/ANKK1 effects on the max measure of PPI (not shown) were virtually identical to those shown here for the AUC measure of PPI.