Biology subjects

Zwart, M. F.

Publications and source records attributed to Zwart, M. F..

12 recordsLinked to original sources

bioRxiv2026

A canonical excitatory-inhibitory motif embedded in the connectome underlies rhythmic locomotion in Drosophila larvae

Rhythmic locomotion is generated by central pattern generators, yet how defined neural circuits generate rhythmic motor waves remains unclear. Theoretical models, including Wilson-Cowan-type excitatory-inhibitory networks, have long proposed that reciprocal interactions between excitatory and inhibitory neuronal populations can generate oscillatory activity and travelling waves, but whether such motifs are physically embedded within biological connectomes is unknown. Here we show that Drosophila larval forward locomotion is generated by a segmentally repeated excitatory-inhibitory network centred on the excitatory A18f and inhibitory A02j neurons. Connectomic analysis revealed that A18f and A02j form reciprocally connected loops coupled across segments, receive input from forward command systems and project to premotor modules controlling muscle contraction and relaxation. Connectome-constrained firing-rate simulations, in which synaptic weights were determined by reconstructed synapse numbers, reproduced rhythmic forward-propagating motor waves with minimal parameter tuning. Physiological recordings revealed activity dynamics and phase relationships consistent with model predictions. Acute and chronic perturbations showed that A18f is required for forward locomotion, whereas optogenetic activation of posterior A18f neurons initiated forward motor waves. Perturbation of inhibitory input to A18f further supported a role for A02j-mediated inhibition. These findings identify a canonical excitatory-inhibitory motif embedded within the connectome as a biological implementation of a rhythm-generating network.

neuroscience↗

bioRxiv2026

The inferior olive transforms upstream sensorimotor errors into cerebellar teaching signals

Adaptive behavior requires evaluating whether sensory feedback matches expectations derived from motor commands. In cerebellar theories, climbing fibers arising from the inferior olive (IO) convey prediction error signals that instruct learning, yet how these signals are constructed remains unresolved. Using larval zebrafish performing visuomotor behaviors in virtual reality, we combined two-photon calcium imaging with glutamate sensors to measure excitatory input to the IO and climbing fiber output under identical conditions. IO activity scaled with discrepancies between expected and experienced optic flow across open- and closed-loop perturbations. Strikingly, excitatory drive to the IO already contained structured, motor-dependent information consistent with error-like signals. Comparison of input and output revealed selective, frequency-dependent transmission from the olive to the cerebellum. These findings suggest where error representations arise in the olivo-cerebellar pathway and support a model in which climbing fiber teaching signals reflect upstream processing combined with filtering within the IO.

neuroscience↗

bioRxiv2026

Simultaneous whole-cell recording and calcium imaging to reveal electrically coupled neurons in Xenopus tadpoles

Neuronal populations connected by gap junctions can be revealed via dye coupling of small molecules like neurobiotin and lucifer yellow. However, the extent of dye diffusion between neurons varies with connexin subtype, loading method, and neuromodulation. Due to the increasing availability of GCaMP transgenic animals, we explore the possibility of revealing gap junctional coupling using Ca2+ imaging in the Xenopus laevis tadpole motor system. Reliable axo-axonal electrical coupling was previously found in excitatory descending interneurons (dINs) using paired recordings but not with neurobiotin dye coupling. Here, we made whole-cell patch-clamp recordings with Ca2+-supplemented intracellular solution to load Ca2+ into GCaMP6s-expressing neurons, followed by Ca2+ imaging to detect potential Ca2+ diffusion across coupled neurons. Successful membrane breakthroughs led to transient fluorescence increases in the patched neuron. However, increasing the Ca2+ concentration promoted membrane resealing and rapid loss of whole-cell recordings. Regardless of recording duration, loading-triggered fluorescence only lasted up to three minutes, suggesting rapid Ca2+ clearance. Pharmacologically blocking sarcoplasmic /endoplasmic reticulum Ca2+-ATPases and plasma membrane Na+/Ca2+ exchangers did not prolong fluorescence, although sustained fluorescence was achieved with positive current injections. Counter to our expectations, fluorescence increases in Ca2+-loaded dINs did not spread to neighboring dINs. Robust intracellular Ca2+ regulation mechanisms, membrane resealing, and long dIN axons likely hindered intercellular Ca2+ diffusion. Therefore, this approach is not appropriate for revealing electrical coupling within this system.

neuroscience↗

bioRxiv2026

Tonically active interneurons gate motor output in Drosophila larvae

Tonic inhibition and its transient removal are fundamental neural mechanisms for gating activity, suppressing out-of-phase excitation, and enhancing the temporal precision of behavior. However, their roles within locomotor central pattern generators (CPGs) remain poorly understood. Here, we identify A02l neurons--segmentally repeated excitatory interneurons in the Drosophila larval ventral nerve cord (VNC)--that regulate crawling behavior through tonic inhibition. A02l neurons exhibit high baseline activity and are transiently suppressed during motor output. They provide excitatory input to inhibitory premotor networks, enabling widespread silencing of motor neurons to maintain muscle relaxation. Optogenetic activation of A02l neurons reduced crawling frequency, whereas their inhibition induced transient whole-body contractions. Together, these findings reveal a cellular-resolution mechanism for tonic inhibition within the nerve cord and highlight its importance in gating motor output and maintaining motor quiescence.

neuroscience↗

bioRxiv2025

Dopamine promotes motor programs underlying substrate tunneling in larval Drosophila

Dopamine is a conserved biogenic amine with diverse neuromodulatory roles. Here we examine the role of dopamine in modulating larval Drosophila melanogaster motor programs underlying movement over and through substrates. First, we performed dual-color calcium imaging in tyrosine hydroxylase (TH)-expressing dopaminergic neurons and motor neurons to reveal cell-type specific recruitment patterns during fictive motor programs. Activity of select TH-neurons correlated strongly with fictive headsweeps as well as forward and backward locomotion. Next, bath applications of dopamine biased the isolated central nervous system towards fictive forward locomotion and inhibited fictive headsweeps. To probe whether these effects are recapitulated in intact animals, we optogenetically manipulated TH-neuron activity during surface crawling and tunneling. Optogenetic activation of TH-neurons with CsChrimson during crawling had no effect on headsweeps and slowed locomotor rhythms by increasing wave duration and decreasing wave frequency. Furthermore, posterior asymmetries, motor sequences characteristic of tunneling, were triggered. On the other hand, optogenetically inhibiting TH-neurons with GtACR1 had little effect on surface crawling. Underground, TH-neuron activation enhanced tunneling activity by increasing wave frequency, instead of duration, which increased overall time spent tunnelling, whereas inhibition decreased time spent tunneling. These results suggest that dopaminergic modulation of larval forward locomotion is dependent on sensorimotor context. We propose dopamine mediates a coordinated network effort to shift central pattern generators to promote tunneling-specific motor programs. New & NoteworthyHere, we find Drosophila larval dopaminergic neurons exhibit cell-type-specific activity in relation to fictive motor patterns. Furthermore, pharmacological and optogenetic manipulations of dopaminergic signaling acutely modifies locomotor output. Specifically, dopamine application promotes forward locomotion and inhibits headsweeps in isolated preparations, while optogenetically activating TH-neurons in freely behaving larvae mediates a shift from crawling to tunneling motor programs. This provides new insights into context-dependent dopaminergic modulation of locomotion in a genetically tractable invertebrate.

neuroscience↗

bioRxiv2024

Sidelobe suppressed Bessel beams for one-photon light-sheet microscopy

Bessel beams (BB) have found widespread adoption in various forms of light-sheet microscopy. However, for one-photon fluorescence, the transverse profile of the beam poses challenges due to the detrimental effect of the sidelobes. Here, we mitigate this issue by using a computer generated phase element for generating a sidelobe suppressed Bessel beam (SSBB). We then progress to perform a comparison of biological imaging using SSBB to standard BB in a light-sheet geometry. The SSBB peak intensity is more than an order of magnitude higher than the first sidelobe. In contrast to a standard BB light-sheet, SSBB does not need deconvolution and propagates to depths exceeding 400m in phantom samples maintaining a transverse size of 5 m. Finally, we demonstrate the advantage of using a SSBB light-sheet for biological applications by imaging fixed early-stage zebrafish larvae. In comparison to the standard BB, we observe a two-fold increase in contrast-to-noise ratio (CNR) when imaging the labelled cellular eye structures and the notochords. Our results provide an effective approach to generating and using SSBB light-sheets to enhance contrast for one-photon light-sheet microscopy.

biophysics↗

bioRxiv2024

Steering From the Rear: Coordination of Central Pattern Generators Underlying Navigation by Ascending Interneurons

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.

neuroscience↗

bioRxiv2024

Context-dependent coordination of movement in Tribolium castaneum larvae

Insect pests, like the red flour beetle Tribolium castaneum, destroy up to 20% of stored grain products worldwide, making them a significant threat to food security. Their success hinges upon adapting their movements to unpredictable, heterogeneous environments like flour. Tribolium is well developed as a genetic model system; however, little is known about their natural locomotion and how their nervous systems coordinate adaptive movement. Here, we employed videographic whole-animal and leg tracking to assess how Tribolium larvae locomote over different substrates and analyze their gait kinematics across speeds. Unlike many hexapods, larvae employed a bilaterally symmetric, posterior-to-anterior wave gait during fast locomotion. At slower speeds, coordination within thoracic segments was disrupted, although intersegmental coordination remained intact. Moreover, larvae used terminal abdominal structures (pygopods) to support challenging movements, such as climbing overhangs. Pygopod placement coincided with leg swing initiation, suggesting a stabilizing role as adaptive anchoring devices. Surgically lesioning the connective between thoracic and abdominal ganglia impaired pygopod engagement and led to escalating impairments in flat-terrain locomotion, climbing and tunnelling. These results suggest that effective movement in Tribolium larvae requires thoracic-abdominal coordination, and that larval gait and limb recruitment is context-dependent. Our work provides the first kinematic analysis of Tribolium larval locomotion and gives insights into its neural control, creating a foundation for future motor control research in a genetically tractable beetle that jeopardizes global food security. Summary statementRed flour beetle larvae walk with a legged wave gait and use their tails as anchors to climb inclines and tunnel into flour.

neuroscience↗

bioRxiv2023

PoseR - A deep learning toolbox for decoding animal behavior

The actions of animals provide a window into how their minds work. Recent advances in deep learning are providing powerful approaches to recognize patterns of animal movement from video recordings using markerless pose estimation models. There is an increasingly rich field of unsupervised and supervised methods for classifying animal behavior built upon the outputs of pose estimation models. However, these methods often rely on species and task-specific feature engineering of trajectories, kinematics and task programming. Highly generalized solutions that use only pose estimations and the inherent structure of animals and their environment provide an opportunity to develop foundational, contextual and, importantly, standardized animal behavior models for efficient and reproducible behavioral analysis. Here, we present PoseRecognition (PoseR), a behavioral classifier leveraging action recognition models using spatio-temporal graph convolutional networks. We show that it can be used to classify animal behavior quickly and accurately from pose estimations, using zebrafish larvae, Drosophila melanogaster, mice, and rats as model organisms. PoseR can be accessed using a Napari plugin, which facilitates efficient behavioral extraction for bout-like behaviour, annotation, model training and deployment. Our tool simplifies the behavioral analysis workflow by transforming coordinates of animal position and pose into semantic labels with speed and precision. Furthermore, we contribute a novel method for unsupervised clustering of behaviors and provide open-source access to our zebrafish datasets and models. The design of our tool ensures scalability and versatility for use across multiple species and contexts, improving the efficiency of behavioral analysis across fields.

neuroscience↗

bioRxiv2022

Synchronous multi-segmental activity between metachronal waves controls locomotion speed in Drosophila larvae

The ability to adjust the speed of locomotion is essential for survival. In limbed animals, the frequency of locomotion is modulated primarily by changing the duration of the stance phase. The underlying neural mechanisms of this selective modulation remain an open question. Here, we report a neural circuit controlling a similarly selective adjustment of locomotion frequency in Drosophila larvae. Drosophila larvae crawl using peristaltic waves of muscle contractions. We find that larvae adjust the frequency of locomotion mostly by varying the time between consecutive contraction waves, reminiscent of limbed locomotion. A specific set of muscles, the lateral transverse (LT) muscles, co-contract in all segments during this phase, the duration of which sets the duration of the interwave phase. We identify two types of GABAergic interneurons in the LT neural network, premotor neuron A26f and its presynaptic partner A31c, which exhibit segmentally synchronized activity and control locomotor frequency by setting the amplitude and duration of LT muscle contractions. Altogether, our results reveal an inhibitory central circuit that sets the frequency of locomotion by controlling the duration of the period in between peristaltic waves. Further analysis of the descending inputs onto this circuit will help understand the higher control of this selective modulation.

neuroscience↗

bioRxiv2021

A brainstem integrator for self-localization and positional homeostasis

To accurately track self-location, animals need to integrate their movements through space. In amniotes, representations of self-location have been found in regions such as the hippocampus. It is unknown whether more ancient brain regions contain such representations and by which pathways they may drive locomotion. Fish displaced by water currents must prevent uncontrolled drift to potentially dangerous areas. We found that larval zebrafish track such movements and can later swim back to their earlier location. Whole-brain functional imaging revealed the circuit enabling this process of positional homeostasis. Position-encoding brainstem neurons integrate optic flow, then bias future swimming to correct for past displacements by modulating inferior olive and cerebellar activity. Manipulation of position-encoding or olivary neurons abolished positional homeostasis or evoked behavior as if animals had experienced positional shifts. These results reveal a multiregional hindbrain circuit in vertebrates for optic flow integration, memory of self-location, and its neural pathway to behavior.

neuroscience↗

bioRxiv2016

Reactive Oxygen Species Regulate Activity-Dependent Neuronal Structural Plasticity

Neurons are inherently plastic, adjusting their structure, connectivity and excitability in response to changes in activity. How neurons sense changes in their activity level and then transduce these to structural changes remains to be fully elucidated. Working with the Drosophila larval locomotor network, we show that neurons use reactive oxygen species (ROS), metabolic byproducts, to monitor their activity. ROS signals are both necessary and sufficient for activity-dependent structural adjustments of both pre- and postsynaptic terminals and for network output, as measured by larval crawling behavior. We find the highly conserved Parkinsons disease-linked protein DJ-1{beta} acts as a redox sensor in neurons where it regulates pre- and postsynaptic structural plasticity, in part via modulation of the PTEN-PI3Kinase pathway. Neuronal ROS thus play an important physiological role as second messengers required for neuronal and network tuning, whose dysregulation in the ageing brain and under neurodegenerative conditions may contribute to synaptic dysfunction.

neuroscience↗