Biogenic amine systems in the fruit fly Drosophila melanogaster

Biogenic amines are important neuroactive molecules of the central nervous system (CNS) of several insect species. Serotonin (5HT), dopamine (DA), histamine (HA), and octopamine (OA) are the amines which have been extensively studied in Drosophila melanogaster. Each one of the four aminergic neuronal systems exhibits a stereotypic pattern of a small number of neurons that are widely distributed in the fly CNS. In this review, histochemical and immunocytochemical data on the distribution of the amine neurons in the larval and adult nervous system, are summarized. The majority of DA and 5HT neurons are interneurons, most of which are found in bilateral clusters. 5HT innervation is found in the feeding apparatus as well as in the endocrine organ of the larva, the ring gland. The octopaminergic neuronal population consists of both interneurons and efferent neurons. In the larval CNS all OA immunoreactive somata are localized in the midline of the ventral ganglion while in the adult CNS both unpaired neurons and bilateral clusters of immunoreactive cells are observed. One target of OA innervation is the abdominal muscles of the larval body wall where OA immunoreactivity is associated with the type II boutons in the axonal terminals. Histamine is mainly found in all photoreceptor cells where it is considered to be the major neurotransmitter molecule, and in specific mechanosensory neurons of the peripheral nervous system. Similarities between specific aminergic neurons and innervation sites in Drosophila and in other insect species are discussed. In addition, studies on the development and differentiation of 5HT and DA neurons are reviewed and data on the localization of 5HT, DA, and OA receptors are included as well. Finally, an overview on the isolation of the genes and the mutations in the amine biosynthetic pathways is presented and the implications of the molecular genetic approach in Drosophila are discussed.