For both phenotypes, animals were selected to form ten High- and ten Low-response families; brother–sister mating was avoided even if it meant using an animal that was not in the highest or lowest tier. To the extent possible, animals used for acute withdrawal selection were mated to balance differences in baseline withdrawal scores. A similar selection procedure was followed for each subsequent generation. Selection was stopped at S5 and S4 for acute withdrawal and ethanol consumption, respectively. All animal care, breeding, and testing procedures were approved by the Laboratory Animal Users Committees at the Veterans Affairs Medical Center, Portland, OR, USA and Oregon Health & Science University, Portland, OR, USA.
