Quantification of Histamine and Carcinine in Drosophila melanogaster Tissues

Histamine is a neurotransmitter crucial to the visual processing of Drosophila melanogaster. It is inactivated by metabolism to carcinine, a β-alanyl derivative, and the same enzyme that controls that process also converts dopamine to N-β-alanyl-dopamine. Direct detection of histamine and carcinine has not been reported in single Drosophila brains. Here, we quantify histamine, carcinine, dopamine, and N-β-alanyl-dopamine in Drosophila tissues by capillary electrophoresis coupled to fast-scan cyclic voltammetry (CE-FSCV). Limits of detection were low, 4 ± 1 pg for histamine, 10 ± 4 pg for carcinine, 2.8 ± 0.3 pg for dopamine, and 9 ± 3 pg for N-β-alanyl-dopamine. Tissue content was compared in the brain, eyes, and cuticle from wild-type (Canton S) and mutant (tan(3) and ebony(1)) strains. In tan(3) mutants, the enzyme that produces histamine from carcinine is nonfunctional, whereas in ebony(1) mutants, the enzyme that produces carcinine from histamine is nonfunctional. In all fly strains, the neurotransmitter content was highest in the eyes and there were no strain differences for tissue content in the cuticle. The main finding was that carcinine levels changed significantly in the mutant flies, whereas histamine levels did not. In particular, tan(3) flies had significantly higher carcinine levels in the eyes and brain than Canton S or ebony(1) flies. N-β-Alanyl-dopamine was detected in tan(3) mutants but not in other strains. These results show the utility of CE-FSCV for sensitive detection of histamine and carcinine, which allows a better understanding of their content and metabolism in different types of tissues to be obtained.