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Understanding how animals coordinate movements to achieve goals is a fundamental pursuit in neuroscience. Here we explore how neurons that reside in posterior lower-order regions of a locomotor system project to anterior higher-order regions to influence steering and navigation. We characterized the anatomy and functional role of a population of ascending interneurons in the ventral nerve cord of Drosophila larvae. Through electron microscopy reconstructions and light microscopy, we determined that the cholinergic 19f cells receive input primarily from premotor interneurons and synapse upon a diverse array of postsynaptic targets within the anterior segments including other 19f cells. Calcium imaging of 19f activity in isolated central nervous system (CNS) preparations in relation to motor neurons revealed that 19f neurons are recruited into most larval motor programmes. 19f activity lags behind motor neuron activity and as a population, the cells encode spatio-temporal patterns of locomotor activity in the larval CNS. Optogenetic manipulations of 19f cell activity in isolated CNS preparations revealed that they coordinate the activity of central pattern generators underlying exploratory headsweeps and forward locomotion in a context and location specific manner. In behaving animals, activating 19f cells suppressed exploratory headsweeps and slowed forward locomotion, while inhibition of 19f activity potentiated headsweeps, slowing forward movement. Inhibiting activity in 19f cells ultimately affected the ability of larvae to remain in the vicinity of an odor source during an olfactory navigation task. Overall, our findings provide insights into how ascending interneurons monitor motor activity and shape interactions amongst rhythm generators underlying complex navigational tasks.

Sensory systems are dynamically adjusted according to the animal's ongoing needs by neuromodulators, such as neuropeptides. Neuropeptides are often widely-distributed throughout sensory networks, but it is unclear whether such neuropeptides uniformly modulate network activity. Here, we leverage the Drosophila antennal lobe (AL) to resolve whether myoinhibitory peptide (MIP) uniformly modulates AL processing. Despite being uniformly distributed across the AL, MIP decreases olfactory input to some glomeruli, while increasing olfactory input to other glomeruli. We reveal that a heterogeneous ensemble of local interneurons (LNs) are the sole source of AL MIP, and show that differential expression of the inhibitory MIP receptor across glomeruli allows MIP to act on distinct intraglomerular substrates. Our findings demonstrate how even a seemingly simple case of modulation can have complex consequences on network processing by acting non-uniformly within different components of the overall network., (© 2023. Springer Nature Limited.)

Mechanisms of rhythm generation have been extensively studied in motor systems that control locomotion over terrain in limbed animals; however, much less is known about rhythm generation in soft-bodied terrestrial animals. Here we explored how muscarinic acetylcholine receptor (mAChR)-modulated rhythm-generating networks are distributed in the central nervous system (CNS) of soft-bodied Drosophila larvae. We measured fictive motor patterns in isolated CNS preparations, using a combination of Ca 2+ imaging and electrophysiology while manipulating mAChR signaling pharmacologically. Bath application of the mAChR agonist oxotremorine potentiated bilaterally asymmetric activity in anterior thoracic regions and promoted bursting in posterior abdominal regions. Application of the mAChR antagonist scopolamine suppressed rhythm generation in these regions and blocked the effects of oxotremorine. Oxotremorine triggered fictive forward crawling in preparations without brain lobes. Oxotremorine also potentiated rhythmic activity in isolated posterior abdominal CNS segments as well as isolated anterior brain and thoracic regions, but it did not induce rhythmic activity in isolated anterior abdominal segments. Bath application of scopolamine to reduced preparations lowered baseline Ca 2+ levels and abolished rhythmic activity. Overall, these results suggest that mAChR signaling plays a role in enabling rhythm generation at multiple sites in the larval CNS. This work furthers our understanding of motor control in soft-bodied locomotion and provides a foundation for study of rhythm-generating networks in an emerging genetically tractable locomotor system. NEW & NOTEWORTHY Using a combination of pharmacology, electrophysiology, and Ca 2+ imaging, we find that signaling through mACh receptors plays a critical role in rhythmogenesis in different regions of the Drosophila larval CNS. mAChR-dependent rhythm generators reside in distal regions of the larval CNS and provide functional substrates for central pattern-generating networks (CPGs) underlying headsweep behavior and forward locomotion. This provides new insights into locomotor CPG operation in soft-bodied animals that navigate over terrain.

Precocious movements are widely seen in embryos of various animal species. Whether such movements via proprioceptive feedback play instructive roles in motor development or are a mere reflection of activities in immature motor circuits is a long-standing question. Here we image the emerging motor activities in Drosophila embryos that lack proprioceptive feedback and show that proprioceptive experience is essential for the development of locomotor central pattern generators (CPGs). Downstream of proprioceptive inputs, we identify a pioneer premotor circuit composed of two pairs of segmental interneurons, whose gap-junctional transmission requires proprioceptive experience and plays a crucial role in CPG formation. The circuit autonomously generates rhythmic plateau potentials via IP 3 -mediated Ca 2+ release from internal stores, which contribute to muscle contractions and hence produce proprioceptive feedback. Our findings demonstrate the importance of self-generated movements in instructing motor development and identify the cells, circuit, and physiology at the core of this proprioceptive feedback., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Typical patterned movements in animals are achieved through combinations of contraction and delayed relaxation of groups of muscles. However, how intersegmentally coordinated patterns of muscular relaxation are regulated by the neural circuits remains poorly understood. Here, we identify Canon, a class of higher-order premotor interneurons, that regulates muscular relaxation during backward locomotion of Drosophila larvae. Canon neurons are cholinergic interneurons present in each abdominal neuromere and show wave-like activity during fictive backward locomotion. Optogenetic activation of Canon neurons induces relaxation of body wall muscles, whereas inhibition of these neurons disrupts timely muscle relaxation. Canon neurons provide excitatory outputs to inhibitory premotor interneurons. Canon neurons also connect with each other to form an intersegmental circuit and regulate their own wave-like activities. Thus, our results demonstrate how coordinated muscle relaxation can be realized by an intersegmental circuit that regulates its own patterned activity and sequentially terminates motor activities along the anterior-posterior axis.

Alcohol use disorder (AUD) is a major health, social and economic problem for which there are few effective treatments. The opiate antagonist naltrexone is currently prescribed clinically with mixed success. We have used naltrexone in an established behavioral assay (CAFE) in Drosophila melanogaster that measures the flies' preference for ethanol-containing food. We have confirmed that Drosophila exposed to ethanol develop a preference toward this drug and we demonstrate that naltrexone, in a dose dependant manner, reverses the ethanol-induced ethanol preference. This effect is not permanent, as preference for alcohol returns after discontinuing naltrexone. Additionally, naltrexone reduced the alcohol-induced increase in protein kinase C activity. These findings are of interest because they confirm that Drosophila is a useful model for studying human responses to addictive drugs. Additionally because of the lack of a closely conserved opiate system in insects, our results could either indicate that a functionally related system does exist in insects or that in insects, and potentially also in mammals, naltrexone binds to alternative sites. Identifying such sites could lead to improved treatment strategies for AUD.

Objectives: The purpose of this study was to evaluate the influence of leukocyte- and platelet-rich fibrin (L-PRF) on impacted mandibular third molar (IMTM) extraction wound healing, patient postoperative discomfort, and incidence of alveolar osteitis., Method and Materials: Thirty-four patients (20 female, 14 male) who met the inclusion criteria for this split-mouth randomized clinical trial were enrolled and 30 patients completed the study. Patients were randomized and underwent bilateral IMTM surgical extractions. Following extraction, one socket randomly received L-PRF, and the other socket served as a regular blood clot control. Postoperatively, the soft tissue healing index (HI), pain according to visual analog scale (VAS), facial swelling using a horizontal and vertical guide, and incidence of alveolar osteitis were evaluated 1, 3, 7, and 14 days after surgery., Results: Sites treated with L-PRF resulted in improved HI (P = .001) and lower pain VAS scores (P = .001) in the first postoperative week. Significant reduction of facial swelling was recorded on first (P = .035) and third (P = .023) postoperative days in L-PRF sites versus controls, ceasing to nonsignificant difference at day 7 (P = .224). None of the L-PRF sites and four control sites were affected by alveolar osteitis (P = .001)., Conclusion: Within the limitations of this split-mouth study, L-PRF improved soft tissue healing and reduced postoperative pain, swelling, and incidence of alveolar osteitis after IMTM surgical extractions.

Background: The aim of this study was to investigate associations between the immune component of the oral cavity, lysozyme, in gingival crevicular fluid and unstimulated saliva, and colonization dynamics of periodontopathogenic bacteria from supra- and subgingival plaque samples in patients with gingivitis or periodontitis., Material/methods: Lysozyme in crevicular fluid and unstimulated saliva, and bacteria in supra- and subgingival plaque samples were assessed in 84 samples from 28 patients with gingivitis, 96 samples from 32 patients with periodontitis, and 72 samples from 24 donors with intact periodontium and free of internal disease. Lysozyme activity was determined spectrophotometrically. The micro-IDent plus assay was used to detect 6 periodontopathogenic bacteria plaque samples., Results: Lysozyme activity in crevicular fluid in the gingivitis and periodontitis groups was significantly greater than that in the donor group, but lysozyme activity in unstimulated saliva was less than that in the donor group. Peptostreptococcus micros, Fusobacterium periodontium and Campylobacter rectus were predominant in subgingival plaque samples in the periodontitis group compared to the donor group (P<0.001), and Eubacterium nodatum and Eikenella corrodens were predominant in the gingivitis group compared to the donor group (P<0.001)., Conclusions: Lysozyme activity in crevicular fluid and in unstimulated saliva correlated with periodontal pocket depth in donors and in patients with gingivitis or periodontitis (specificity and sensitivity were both 100%). These findings indicate that infection with P. micros, F. periodontium, E. nodatum, E. corrodens, and C. rectus may be an important indicator of inflammatory periodontal disease development.