Carreira-Rosario, A. | bioRxiv Science

bioRxiv2021

Mechanosensory input shapes Drosophila motor behavior through Patterned Spontaneous Network Activity

Neural activity sculpts circuit wiring in many animals. In vertebrates, patterned spontaneous network activity (PaSNA) generates sensory maps and establishes local circuits 1-3. However, it remains unclear how PaSNA might shape neuronal circuits and behavior in invertebrates. Previous work in the developing Drosophila embryo discovered spontaneous muscle activity that did not require synaptic transmission, and hence was myogenic, preceding PaSNA 4-6. These studies, however, monitored muscle movement, not neural activity, and were therefore unable to observe how myogenic activity might relate to subsequent neural network engagement. Here we use calcium imaging to directly record neural activity and characterize the emergence of PaSNA. We demonstrate that the spatiotemporal properties of PaSNA are highly stereotyped across embryos, arguing for genetic programming. Consistent with previous observations, we observe neural activity well before it becomes patterned, initially emerging during the myogenic stage. Remarkably, inhibition of mechanosensory input as well as inhibition of muscle contractions results in premature and excessive PaSNA, demonstrating that muscle movement serves as a brake on this process. Finally, using an optogenetic strategy to selectively disrupt mechanosensory inputs during PaSNA, followed by quantitative modeling of larval behavior, we demonstrate that mechanosensory modulation during development is required for proper larval foraging. This work thus provides a foundation for using the Drosophila embryo to study the role of PaSNA in circuit formation, provides mechanistic insight into how PaSNA is entrained by motor activity, and demonstrates that spontaneous network activity is essential for locomotor behavior. These studies argue that sensory feedback during the earliest stages of circuit formation can sculpt locomotor behaviors through innate motor learning. HighlightsO_LIPaSNA in the Drosophila embryonic CNS is spatiotemporally stereotyped C_LIO_LIMechanosensory neurons negatively modulate PaSNA C_LIO_LIEmbryonic PaSNA is required for larval locomotor behavior C_LI

neuroscience↗

bioRxiv2018

A command-like descending neuron that coordinately activates backward and inhibits forward locomotion

Command-like descending neurons can induce many behaviors, such as backward locomotion, escape, feeding, courtship, egg-laying, or grooming. In most animals it remains unknown how neural circuits switch between these antagonistic behaviors: via top-down activation/inhibition of antagonistic circuits or via reciprocal inhibition between antagonistic circuits. Here we use genetic screens, intersectional genetics, circuit reconstruction by electron microscopy, and functional optogenetics to identify a bilateral pair of larval \"mooncrawler descending neurons\" (MDNs) with command-like ability to coordinately induce backward locomotion and block forward locomotion; the former by activating a backward-specific premotor neuron, and the latter by disynaptic inhibition of a forward-specific premotor neuron. In contrast, direct reciprocal inhibition between forward and backward circuits was not observed. Thus, MDNs coordinate a transition between antagonistic larval locomotor behaviors. Interestingly, larval MDNs persist into adulthood, where they can trigger backward walking. Thus, MDNs induce backward locomotion in both limbless and limbed animals.\n\nHighlightsO_LIMDN command-like descending neuron induces backward larval locomotion\nC_LIO_LIMDN neurons coordinately regulate antagonistic behaviors (forward/backward locomotion)\nC_LIO_LIMDN-motor circuit validated at structural (TEM) and functional (optogenetic) levels\nC_LIO_LIMDN neurons induce backward locomotion in both limbless larva and limbed adult\nC_LI

neuroscience↗