Distribution of metabotropic glutamate receptor DmGlu-A in Drosophila melanogaster central nervous system.

L-glutamate is the excitatory neurotransmitter at neuromuscular junctions in insects. It may also be involved in neurotransmission within the central nervous system (CNS), but its function therein remains elusive. The roles of glutamatergic synapses in the Drosophila melanogaster CNS were investigated, with focus on the study of DmGluRA, a G-protein-coupled glutamate receptor. In a first attempt to determine the function of this receptor, we describe its distribution in the larval and adult Drosophila CNS, using a polyclonal antibody raised against the C-terminal sequence of the protein. DmGluRA is expressed in a reproducible pattern both in the larva and in the adult. In particular, DmGluRA can be found in the antennal lobes, the optic lobes, the central complex, and the median bundle in the adult CNS. However, DmGluRA-containing neurons represented only a small fraction of all CNS neurons. DmGluRA immunoreactivity was not detected at the larval neuromuscular junction nor in the body wall muscles. The correlations between DmGluRA distribution and previously described glutamate-like immunoreactivity patterns, as well as the implications of these observations concerning the possible functions of DmGluRA in the Drosophila CNS, are discussed.

The leg of Drosophila as a model system for the analysis of neuronal diversity.

The neurons innervating insect sense organs vary in number, shape, dendritic morphology, axonal projections and connectivity, providing abundant material for the genetic analysis of neuronal diversity. Here we describe the leg of Drosophila as a potential model system for this analysis. The leg of Drosophila comprises a variety of sense organs arranged in a precise and reproducible pattern. The cell bodies of the sensory neurons are located near the organ they innervate, which greatly facilitates their identification and accessibility. The development of the leg from its progenitor structure, the imaginal disc, is known in good detail. In particular, the time of appearance and of divisions of the sense organ precursors is known. The origin and mode of formation of the leg nerve (through which all sensory axons project into the central nervous system) has been described. The central projections of some of the sensory neurons have been examined by horseradish peroxidase backfill or DiI labelling. Finally, the expression of several genes that control the differentiation of various types of sensory neurons can be manipulated at will. We illustrate these different aspects, and discuss the potentials and shortcomings of this system.