HISTAMINE IS A MAJOR MECHANOSENSORY NEUROTRANSMITTER CANDIDATE IN DROSOPHILA-MELANOGASTER

Histamine is known to be the neurotransmitter of insect photoreceptors . Histamine-like immunoreactivity is also found in a number of interne urons in the central nervous system of various insects. Here, we demon strate by immunohistochemical techniques that, in Drosophila melanogas ter (Acalypterae), most or all mechanosensory neurons of imaginal hair sensilla selectively bind antibodies directed against histamine. The histamine-like staining includes the cell bodies of these neurons as w ell as their axons, which form prominent fibre bundles in peripheral n erves, and their terminal projections in the central neuropil of head and thoracic ganglia. The specificity of the immunostaining is demonst rated by investigating a Drosophila mutant unable to synthesize histam ine. Other mechanosensory organs, such as campaniform sensilla or scol opidial organs, do not stain. In the calypteran flies, Musca and Calli phora, we find no comparable immunoreactivity associated with either h air sensilla or the nerves entering the central nervous system, observ ations in agreement with earlier studies on Calliphora. Thus, histamin e seems to be a major mechanosensory transmitter candidate of the adul t nervous system of Drosophila, but apparently not of Musca or Calliph ora.