Metamorphosis of an identified serotonergic neuron in the Drosophila olfactory system

In this study, we examine a wide-field serotonergic neuron in the Drosophila olfactory pathway and map the dramatic changes that it undergoes from larva to adult. We show that expression of a dominant-negative form of the ecdysterone receptor prevents remodeling. We further use different transgenic constructs to silence neuronal activity and report defects in the morphology of the adult-specific dendritic trees. The branching of the presynaptic axonal arbors is regulated by mechanisms that affect axon growth and retrograde transport. The neuron develops its normal morphology in the absence of sensory input to the antennal lobe, or of the mushroom bodies. However, ablation of its presumptive postsynaptic partners, the projection neurons and/or local interneurons, affects the growth and branching of terminal arbors.Our studies establish a cellular system for studying remodeling of a central neuromodulatory feedback neuron and also identify key elements in this process. Understanding the morphogenesis of such neurons, which have been shown in other systems to modulate the sensitivity and directionality of response to odors, links anatomy to the development of olfactory behavior.The spatial representation of olfactory stimuli in Drosophila is achieved by the highly specific connectivity between neural elements within the antennal lobe. The architecture of individual components of the olfactory pathway are well defined and mechanisms specifying their development are beginning to be understood [1]. Olfactory receptor neurons (ORNs) map, in a receptor-specific manner, from the antenna to glomeruli within the antennal lobes [2,3]. Here they synapse onto projection interneurons (PNs) that, in turn, wire to dendritic fields of the mushroom bodies and the lateral horn of the protocerebrum [4]. Local interneurons (LNs), which are either GABAergic (inhibitory) or cholinergic (excitatory), arborize extensively between glomeruli, providing a substrate for lateral interactions betw