CCIPE, UPR 9023, 141 rue de la Cardonille 34094 Montpellier cedex 05 France,
In Drosophila, glutamate is the excitatory neurotransmitter at the neuromuscular junction. Although it is also recognized as being a neurotransmitter in the central nervous system of arthropods, little is known about its function. Glutamate is also the major excitatory neurotransmitter of the mammalian central nervous system. Its actions are mediated by glutamate-gated channels known as NMDA, AMPA and kainate receptors, and G protein-coupled receptors known as metabotropic receptors. Among these different glutamate receptors, the NMDA and the metabotropic glutamate receptors are thought to play key roles in important neuronal processes, ranging from developmental plasticity to memory. Several subunits of glutamate gated channel-receptors expressed in the central nervous system have already been characterized in Drosophila, suggesting roles for glutamate in insects brain. We therefore decided to search for the existence of G protein-coupled glutamate receptors. We report the isolation and characterization of a metabotropic glutamate receptor from Drosophila. This receptor is homologous to the family of mammalian metabotropic glutamate receptors. In contrast to previous glutamate-gated channels cloned in drosophila, this receptor shows a high affinity for glutamate and a remarkable conservation of the pharmacological profile. We show that the transduction mechanism is conserved with one group of mammalian metabotropic receptors. This receptor is expressed in the brain and the ventral nervous system, from the embryo to the adult. Its expression is found clustered in a suprisingly high number of cells in the embryonic ventral nerve cord at a period of neuronal differentiation and synaptogenesis. We are presently trying to define the function of DmGluRA. As typical features of the mammalian glutamate receptors system are present in the central nervous system of Drosophila, we propose that important elements of the glutamate induced plasticity and memory cascades are common to Drosophila and mammals.