GENETIC DEPLETION OF HISTAMINE FROM THE NERVOUS-SYSTEM OF DROSOPHILA ELIMINATES SPECIFIC VISUAL AND MECHANOSENSORY BEHAVIOR

The role of histamine as a fast neurotransmitter of imaginal insect ph otoreceptors is firmly established. In adult Drosophila, histamine is also found in mechanosensory receptors of cuticular hair sensilla and in a small number of nonreceptor neurons in head and body ganglia. Her e we investigate the function of histamine by immunohistochemical and behavioral analysis of mutants deficient in the hdc gene that codes fo r histidine decarboxylase. The allele hdc(JK910) appears to be a null mutation, as histamine immunoreactivity is almost entirely eliminated. Homozygous flies are blind in various behavioral paradigms. Mutant la rvae, on the other hand, show normal photokinetic responses. Thus, adu lt Drosophila photoreceptors most likely utilize only a single substan ce, histamine, as a neurotransmitter, whereas larval photoreceptors ap parently employ a different transmitter. With the alleles hdc(P211), h dc(P217) and hdC(P218), variable amounts of histamine are found in pho toreceptors and mechanoreceptors, but no histamine could be detected i n any of the nonreceptor neurons. These mutants show various degrees o f visual and mechanosensory impairment, as determined by quantitative behavioral assays. We conclude that histamine is required for normal f unction of cuticular hair sensilla and for efficient grooming of the b ody surface. Thus, in Drosophila, histamine represents a major functio nal neurotransmitter for mechanosensory receptors.