Anatomy and Neural Pathways Modulating Distinct Locomotor Behaviors in Drosophila Larva

SIMPLE SUMMARY: Simple movements require the involvement of many neurons before a group of muscles receives the signal to contract and relax. The sensory system adds another layer of complexity to movement generation, as the mechanism of sensory information integration is not very well understood. Despite a large body of research in this area, our understanding of organismal behavior in the context of their natural environment remains relatively poor. Observing the brain in action to be able to build neural maps and demonstrate causality is a major challenge. Drosophila larvae provide an excellent genetic tractable model to study behavioral response to a variety of sensory modalities and underlying neural circuitries. The understanding of genetic and physiological components of movements provides directions to understand how different locomotion types are achieved. In this review, we provide details of underlying circuitry and neural pathways required by Drosophila larvae for successful movements in both normal and defensive state, with an emphasis on the role of interneurons in the regulation of these movements. ABSTRACT: The control of movements is a fundamental feature shared by all animals. At the most basic level, simple movements are generated by coordinated neural activity and muscle contraction patterns that are controlled by the central nervous system. How behavioral responses to various sensory inputs are processed and integrated by the downstream neural network to produce flexible and adaptive behaviors remains an intense area of investigation in many laboratories. Due to recent advances in experimental techniques, many fundamental neural pathways underlying animal movements have now been elucidated. For example, while the role of motor neurons in locomotion has been studied in great detail, the roles of interneurons in animal movements in both basic and noxious environments have only recently been realized. However, the genetic and transmitter identities of many of these interneurons remains unclear. In this review, we provide an overview of the underlying circuitry and neural pathways required by Drosophila larvae to produce successful movements. By improving our understanding of locomotor circuitry in model systems such as Drosophila, we will have a better understanding of how neural circuits in organisms with different bodies and brains lead to distinct locomotion types at the organism level. The understanding of genetic and physiological components of these movements types also provides directions to understand movements in higher organisms.