Fig. 8. HPLC separation of head homogenates from flies that drank a 25% solution of [³H]histamine (37 MBq ml^–1 and 858.4 GBq mmol l^–1) in 4% aqueous glucose. (A) Wild-type, tan and double-mutant white, tan heads. (B) Wild-type, ebony and double-mutant white; ebony heads. Double-mutant white, tan has a significantly reduced carcinine (CA) peak compared with tan whereas double-mutant white; ebony rescues normal histamine (HA) uptake, which is otherwise significantly reduced in ebony. Both differences are indicated by arrows delimiting the magnitude of white's (w) added action. All data are plotted as 2-min bins, compiled from the emissions from two adjacent 1-min fractions. Retention time of carcinine is 12 min and retention time of histamine is 18 min. The tan peak with the shorter retention time (4 min) is an unknown metabolite. For a detailed comment see Borycz et al. (Borycz et al., 2000).