Larval multidendrite neurons survive metamorphosis and participate in the formation of imaginal sensory axonal pathways in the notum of Drosophila.
In each hemimesothorax of Drosophila, a cluster of five larval multidendrite neurons that survives metamorphosis is described. The cell bodies of these neurons, initially grouped together, spread out over the medial heminotum during early pupal stages and extend new dendrites. Growing axons from sensory bristle neurons first appear in a defined orientation specific for each macrochaete. They subsequently contact processes from the larval multidendrite neurons and then appear to follow the preestablished axon trajectories of the latter. Ablation of the multidendrite neurons during the larval stage causes bristle axons to adopt abnormal trajectories. We suggest that the persistent larval neurons participate in guiding axons of the bristles on the medial half of the notum to the posterior dorsal mesothoracic nerve leading to the central nervous system.