Alcohol consumption of histidine decarboxylase knock-out (HDC KO) and wild-type (WT) mice in two-bottle choice and in the drinking in the dark experiments. In the two-bottle choice test, no differences were observed between male HDC KO and WT mice (in 129/Sv background strain) in total alcohol consumption (A) or water-alcohol preference ratio (B). P > 0.05, two-way repeated measures (RM) anova. n = 13–15 per genotype. In the drinking in the dark no differences were observed between male HDC KO and WT mice (in C57BL/6J background strain) in total alcohol (20%, v v-1, n = 7–8) (C) or sucrose (3%, w v-1, n = 5–7) (D) consumption. In female mice, no difference was observed in alcohol (20%, v v-1, n = 4–5) consumption (E) but HDC KO mice consumed less sucrose (3%, w v-1).P = 0.017, two-way RM anova, n = 4–6. (F). All data are expressed as mean ± SEM.