The determination of histamine in the Drosophila head.

Histamine is a neurotransmitter at arthropod photoreceptors. Even though the fruit fly, Drosophila melanogaster, is a widely used model in neuroscience research, the histamine content of its nervous system has not so far been reported. We have developed a high performance liquid chromatography (HPLC) method with pre-column o-phtaldialdehyde-mercaptoethanol (OPA-ME) derivatization and electrochemical detection, to determine this amine in Drosophila. The histamine content of the fly's head averages about 2.0 ng per head. In heads of the mutant hdc(JK910), a presumed null for the gene encoding the enzyme that synthesizes histamine, histamine was not detected in measurable amounts. In heads of the mutant sine oculis, which lacks compound eyes, only 28% of this amine was found compared with wild type flies, so histamine is mainly present in the compound eye photoreceptors. Also observed in histamine-deficient mutants was a decrease in the peak which contains a substance having the same retention time as carcinine (beta-alanyl-histamine). Our method was not able to detect compounds previously reported as histamine metabolites in insects. In spite of this, the method we have developed enables the fast and accurate measurement of histamine in the heads of Drosophila, suitable for screening mutants.