A locomotor neural circuit persists and functions similarly in larvae and adult Drosophila

Abstract

Individual neurons can undergo drastic structural changes, known as neuronal remodeling or structural plasticity. One example of this is in response to hormones, such as during puberty in mammals or metamorphosis in insects. However, in each of these examples it remains unclear whether the remodeled neuron resumes prior patterns of connectivity, and if so, whether the persistent circuits drive similar behaviors. Here, we utilize a well-characterized neural circuit in the Drosophila larva: the Moonwalking Descending Neuron (MDN) circuit. We previously showed that larval MDN induces backward crawling, and synapses onto the Pair1 interneuron to inhibit forward crawling (Carreira-Rosario et al., 2018). MDN is remodeled during metamorphosis and regulates backward walking in the adult fly. We investigated whether Pair1 is remodeled during metamorphosis and functions within the MDN circuit during adulthood. We assayed morphology and molecular markers to demonstrate that Pair1 is remodeled during metamorphosis and persists in the adult fly. In the adult, optogenetic activation of Pair1 resulted in arrest of forward locomotion, similar to what is observed in larvae. MDN and Pair1 are also synaptic partners in the adult, showing that the MDN-Pair1 interneuron circuit is retained in the adult following hormone-driven pupal remodeling. Thus, the MDN-Pair1 neurons are an interneuronal circuit - i.e. a pair of synaptically connected interneurons - that persists through metamorphosis, taking on new input/output neurons, yet generating similar locomotor behavior at both stages.