Perception of task duration influences metabolic cost during split-belt adaptation and biomechanics during both adaptation and post-adaptation.

Humans continuously adapt locomotor patterns. In laboratory settings, split-belt treadmills have been used to study locomotor adaptation. Whether metabolic cost reduction is the primary objective or a by-product of the observed biomechanical changes during adaptation is not known. The main goal of our study is to determine if perception of task duration affects the adaptation of locomotor patterns to reduce energetic cost. We tested the hypothesis that individuals who believe they will sustain a split-belt adaptation task for a prolonged time will adapt toward a walking pattern associated with lower cost. N=14 participants adapted for 10 minutes with knowledge of time remaining (group K), while N=15 participants adapted under the assumption that they would walk for 30 minutes with no knowledge of time elapsed or time remaining (group U). Both groups adapted for 10 minutes. We observed a significant main effect of Time (p<0.001, observed power 1.0) and the interaction of Time×Group (p=0.004, observed power 0.84) on metabolic cost. The K group did not reduce metabolic cost during adaptation. The U group reduced metabolic cost during adaptation to a cost 12% lower than the K group. We observed a significant effect of Time×Group (p<0.050) on step lengths and work by the right/slow leg during adaptation and post-adaptation. Our results indicate that metabolic cost reduction has a primary role in tasks that need to be sustained for a prolonged time, and this reduction occurs through a combination of biomechanical changes small in magnitude and a marked influence of non-biomechanical factors.

Zebrafish and nematodes as whole organism models to measure developmental neurotoxicity.

Despite the growing epidemiological evidence of an association between toxin exposure and developmental neurotoxicity (DNT), systematic testing of DNT is not mandatory in international regulations for admission of pharmaceuticals or industrial chemicals. However, to date around 200 compounds, ranging from pesticides, pharmaceuticals and industrial chemicals, have been tested for DNT in the current OECD test guidelines (TG-443 or TG-426). There are calls for the development of new approach methodologies (NAMs) for DNT, which has resulted in a DNT testing battery using in vitro human cell-based assays. These assays provide a means to elucidate the molecular mechanisms of toxicity in humans which is lacking in animal-based toxicity tests. However, cell-based assays do not represent all steps of the complex process leading to DNT. Validated models with a multi-organ network of pathways that interact at the molecular, cellular and tissue level at very specific timepoints in a life cycle are currently missing. Consequently, whole model organisms are being developed to screen for, and causally link, new molecular targets of DNT compounds and how they affect whole brain development and neurobehavioral endpoints. Given the practical and ethical restraints associated with vertebrate testing, lower animal models that qualify as 3 R (reduce, refine and replace) models, including the nematode (Caenorhabditis elegans) and the zebrafish (Danio rerio) will prove particularly valuable for unravelling toxicity pathways leading to DNT. Although not as complex as the human brain, these 3 R-models develop a complete functioning brain with numerous neurodevelopmental processes overlapping with human brain development. Importantly, the main signalling pathways relating to (neuro)development, metabolism and growth are highly conserved in these models. We propose the use of whole model organisms specifically zebrafish and C. elegans for DNT relevant endpoints.

Representation of rhythmic chunking in striatum of mice executing complex continuous movement sequences.

We used a step-wheel system to examine the activity of striatal projection neurons as mice practiced stepping on complexly arranged foothold pegs in this Ferris-wheel-like device to receive reward. Sets of dorsolateral striatal projection neurons were sensitive to specific parameters of repetitive motor coordination during the runs. They responded to combinations of the parameters of continuous movements (interval, phase, and repetition), forming "chunking responses"-some for combinations of these parameters across multiple body parts. Recordings in sensorimotor cortical areas exhibited notably fewer such responses but were documented for smaller neuron sets whose heterogeneity was significant. Striatal movement encoding via chunking responsivity could provide insight into neural strategies governing effective motor control by the striatum. It is possible that the striking need for external rhythmic cuing to allow movement sequences by Parkinson's patients could, at least in part, reflect dysfunction in such striatal coding.

Geometric phase predicts locomotion performance in undulating living systems across scales.

Self-propelling organisms locomote via generation of patterns of self-deformation. Despite the diversity of body plans, internal actuation schemes and environments in limbless vertebrates and invertebrates, such organisms often use similar traveling waves of axial body bending for movement. Delineating how self-deformation parameters lead to locomotor performance (e.g. speed, energy, turning capabilities) remains challenging. We show that a geometric framework, replacing laborious calculation with a diagrammatic scheme, is well-suited to discovery and comparison of effective patterns of wave dynamics in diverse living systems. We focus on a regime of undulatory locomotion, that of highly damped environments, which is applicable not only to small organisms in viscous fluids, but also larger animals in frictional fluids (sand) and on frictional ground. We find that the traveling wave dynamics used by mm-scale nematode worms and cm-scale desert dwelling snakes and lizards can be described by time series of weights associated with two principal modes. The approximately circular closed path trajectories of mode weights in a self-deformation space enclose near-maximal surface integral (geometric phase) for organisms spanning two decades in body length. We hypothesize that such trajectories are targets of control (which we refer to as "serpenoid templates"). Further, the geometric approach reveals how seemingly complex behaviors such as turning in worms and sidewinding snakes can be described as modulations of templates. Thus, the use of differential geometry in the locomotion of living systems generates a common description of locomotion across taxa and provides hypotheses for neuromechanical control schemes at lower levels of organization.

The role of fatty acid-binding protein 5 and 7 on locomotor, anxiety and social behavior: Interaction with NMDA signaling.

The endocannabinoid system has been shown to be a powerful mediator of anxiety, learning and memory, as well as nociception behaviors. Exogenous cannabinoids like delta-9-tetrahydrocannabinol mimic the naturally occurring endogenous cannabinoids found in the mammalian central and peripheral nervous system. The hydrophobic properties of endocannabinoids mean that these psychoactive compounds require help with cellular transport. A family of lipid intracellular carriers called fatty acid-binding proteins (FABPs) can bind to endocannabinoids. Pharmacological inhibition or genetic deletion of FABP subtypes 5 and 7 elevates whole-brain anandamide (AEA) levels, a type of endocannabinoid. This study examined locomotor behavior, anxiety-like behavior, and social behavior in FABP5-/- and FABP7-/- mice. Furthermore, we measured N-methyl-D-aspartate (NMDA) receptor levels in the brain to help identify potential underlying mechanisms related to the behavioral findings. Results showed that both male and female FABP5-/- mice exhibited significantly lower activity when compared with both FABP5/7 +/+ (control) and FABP7-/-. For social behavior, male, but not female, FABP5-/- mice spent more time interacting with novel mice compared with controls (FABP5/7 +/+) and FABP7-/- mice. No significant difference was found for anxiety-like behavior. Results from the NMDA autoradiography revealed [3H] MK-801 binding to be significantly increased within sub-regions of the striatum in FABP7-/- compared with control. In summary, these results show that FABP5 deficiency plays a significant role in locomotion activity, exploratory behavior, as well as social interaction. Furthermore, FABP7 deficiency is shown to play an important role in NMDA receptor expression, while FABP5 does not.

Phasic stimulation of dopaminergic neurons of the lateral substantia nigra increases open field exploratory behaviour and reduces habituation over time.

Transient nigrostriatal dopaminergic signaling is well known for its role in reinforcement learning and increasingly so for its role in the initiation of voluntary movement. However, how transient bursts of dopamine modulate voluntary movement remains unclear, likely due to the heterogeneity of the nigrostriatal system, the focus of optogenetic studies on locomotion at sub-sec time intervals, and the overlapping roles of phasic dopamine in behaviour and novelty signalling. In this study we investigated how phasic activity in the lateral substantia nigra pars compacta (lateral SNc) over time affects voluntary behaviours during exploration. Using a transgenic mouse model of both sexes expressing channelrhodopsin (ChR2) in dopamine transporter-expressing cells, we stimulated the lateral SNc while mice explored an open field over two consecutive days. We found that phasic activation of the lateral SNc induced an increase in exploratory behaviours including horizontal movement activity, locomotion initiation, and rearing specifically on the first open field exposure, but not on the second day. In addition, stimulated animals did not habituate to the same extent as their ChR2-negative counterparts, as indicated by a lack of decrease in baseline activity. These findings suggest that rather than prompting voluntary movement in general, phasic nigrostriatal dopamine prompts context-appropriate behaviours. In addition, dopamine signalling that modulates movement acts over longer timescales than the transient signal, affecting behaviour even after the signal has ended.

Microbiota influence on behavior: Integrative analysis of serotonin metabolism and behavioral profile in germ-free mice.

Previous studies on germ-free (GF) animals have described altered anxiety-like and social behaviors together with dysregulations in brain serotonin (5-HT) metabolism. Alterations in circulating 5-HT levels and gut 5-HT metabolism have also been reported in GF mice. In this study, we conducted an integrative analysis of various behaviors as well as markers of 5-HT metabolism in the brain and along the GI tract of GF male mice compared with conventional (CV) ones. We found a strong decrease in locomotor activity, accompanied by some signs of increased anxiety-like behavior in GF mice compared with CV mice. Brain gene expression analysis showed no differences in HTR1A and TPH2 genes. In the gut, we found decreased TPH1 expression in the colon of GF mice, while it was increased in the cecum. HTR1A expression was dramatically decreased in the colon, while HTR4 expression was increased both in the cecum and colon of GF mice compared with CV mice. Finally, SLC6A4 expression was increased in the ileum and colon of GF mice compared with CV mice. Our results add to the evidence that the microbiota is involved in regulation of behavior, although heterogeneity among studies suggests a strong impact of genetic and environmental factors on this microbiota-mediated regulation. While no impact of GF status on brain 5-HT was observed, substantial differences in gut 5-HT metabolism were noted, with tissue-dependent results indicating a varying role of microbiota along the GI tract.

Anatomical insights into fish terrestrial locomotion: A study of barred mudskipper (Periophthalmus argentilineatus) fins based on µCT 3D reconstructions.

Mudskippers are a group of extant ray-finned fishes with an amphibious lifestyle and serve as exemplars for understanding the evolution of amphibious capabilities in teleosts. A comprehensive anatomical profile of both the soft and hard tissues within their propulsive fins is essential for advancing our understanding of terrestrial locomotor adaptations in fish. Despite the ecological significance of mudskippers, detailed data on their musculoskeletal anatomy remains limited. In the present research, we utilized contrast-enhanced high-resolution microcomputed tomography (µCT) imaging to investigate the barred mudskipper, Periophthalmus argentilineatus. This technique enabled detailed reconstruction and quantification of the morphological details of the pectoral, pelvic, and caudal fins of this terrestrial mudskipper, facilitating comparison with its aquatic relatives. Our findings reveal that P. argentilineatus has undergone complex musculoskeletal adaptations for terrestrial movement, including an increase in muscle complexity and muscle volume, as well as the development of specialized structures like aponeuroses for pectoral fin extension. Skeletal modifications are also evident, with features such as a reinforced shoulder-pelvic joint and thickened fin rays. These evolutionary modifications suggest biomechanically advanced fins capable of overcoming the gravitational challenges of terrestrial habitats, indicating a strong selective advantage for these features in land-based environments. The unique musculoskeletal modifications in the fins of mudskippers like P. argentilineatus, compared with their aquatic counterparts, mark a critical evolutionary shift toward terrestrial adaptations. This study not only sheds light on the specific anatomical changes facilitating this transition but also offers broader insights into the early evolutionary mechanisms of terrestrial locomotion, potentially mirroring the transformative journey from aquatic to terrestrial life in the lineage leading to tetrapods.

Neural dynamics of robust legged robots.

Legged robot control has improved in recent years with the rise of deep reinforcement learning, however, much of the underlying neural mechanisms remain difficult to interpret. Our aim is to leverage bio-inspired methods from computational neuroscience to better understand the neural activity of robust robot locomotion controllers. Similar to past work, we observe that terrain-based curriculum learning improves agent stability. We study the biomechanical responses and neural activity within our neural network controller by simultaneously pairing physical disturbances with targeted neural ablations. We identify an agile hip reflex that enables the robot to regain its balance and recover from lateral perturbations. Model gradients are employed to quantify the relative degree that various sensory feedback channels drive this reflexive behavior. We also find recurrent dynamics are implicated in robust behavior, and utilize sampling-based ablation methods to identify these key neurons. Our framework combines model-based and sampling-based methods for drawing causal relationships between neural network activity and robust embodied robot behavior.

High mirror symmetry in mouse exploratory behavior.

The physicality of the world in which the animal acts-its anatomical structure, physiology, perception, emotional states, and cognitive capabilities-determines the boundaries of the behavioral space within which the animal can operate. Behavior, therefore, can be considered as the subspace that remains after secluding all actions that are not available to the animal due to constraints. The very signature of being a certain creature is reflected in these limitations that shape its behavior. A major goal of ethology is to expose those constraints that carve the intricate structure of animal behavior and reveal both uniqueness and commonalities between animals within and across taxa. Exploratory behavior in an empty arena seems to be stochastic; nevertheless, it does not mean that the moving animal is a random walker. In this study, we present how, by adding constraints to the animal's locomotion, one can gradually retain the 'mousiness' that characterizes the behaving mouse. We then introduce a novel phenomenon of high mirror symmetry along the locomotion of mice, which highlights another constraint that further compresses the complex nature of exploratory behavior in these animals. We link these findings to a known neural mechanism that could explain this phenomenon. Finally, we suggest our novel finding and derived methods to be used in the search for commonalities in the motion trajectories of various organisms across taxa.

Impacts of a Simulated Infection on the Locomotor Behavior of Invasive and Noninvasive Species of Congeneric Anurans.

AbstractLocomotion is essential for survival, but it requires resources such as energy and metabolites and therefore may conflict with other physiological processes that also demand resources, particularly expensive processes such as immunological responses. This possible trade-off may impose limits on either the magnitude of immune responses or the patterns of activity and performance. Previous studies have shown that invasive species may have a depressed immune response, allowing them to maintain locomotor function and reproduction even when sick. This may contribute to the ecological success of invasive species in colonization and dispersal. In contrast, noninvasive species tend to reduce activity as a response to infection. Here, we studied the impact of a simulated infection on locomotor performance and voluntary movement in the anurans Xenopus laevis (a globally invasive species) and Xenopus allofraseri (a noninvasive congeneric). We found that a simulated infection reduces locomotor performance in both species, with an accentuated effect on X. allofraseri. Voluntary movement was marginally different between species. Our data suggest that a simulated infection leads to behavioral depression and reduced locomotor performance in anurans and show that this effect is limited in the invasive X. laevis. Contrasting responses to an immune challenge have been reported in the few amphibian taxa analyzed to date and suggest relationships between ecology and immunology that deserve further investigation. Specifically, a depressed immune response may underlie a propension to invasion in some species. Whether this is a general trend for invasive species remains to be tested, but our data add to the growing body of work documenting depressed immune systems in invasive species.

Effects of Environmental Enrichment on Exposure to Human-Relevant Mixtures of Endocrine Disrupting Chemicals in Zebrafish.

Fish models used for chemical exposure in toxicological studies are normally kept in barren tanks without any structural environmental enrichment. Here, we tested the combined effects of environmental enrichment and exposure to two mixtures of endocrine disrupting chemicals (EDCs) in zebrafish. Firstly, we assessed whether developmental exposure to an EDC mixture (MIX G1) combined with rearing the fish in an enriched environment influenced behaviour later in life. This was evaluated using locomotion tracking one month after exposure, showing a significant interaction effect between enrichment and the MIX G1 exposure on the measured locomotion parameters. After three months, we assessed behaviour using custom-made behaviour tanks, and found that enrichment influenced swimming activity. Control fish from the enriched environment were more active than control fish from the barren environment. Secondly, we exposed adult zebrafish to a separate EDC mixture (MIX G0) after rearing them in a barren or enriched environment. Behaviour and hepatic mRNA expression for thyroid-related genes were assessed. There was a significant interaction effect between exposure and enrichment on swimming activity and an effect of environment on latency to approach the group of conspecifics, where enriched fish took more time to approach the group, possibly indicating that they were less anxious. Hepatic gene expression of a thyroid-related gene (thrb) was significantly affected by EDC exposure, while enrichment had no discernible impact on the expression of the measured genes. In conclusion, environmental enrichment is important to consider when studying the effects of EDCs in fish.

Rescue of myocytes and locomotion through AAV2/9-2YF intracisternal gene therapy in a rat model of creatine transporter deficiency.

Creatine deficiency syndromes (CDS), caused by mutations in GATM (AGAT), GAMT, and SLC6A8, mainly affect the central nervous system (CNS). CDS show brain creatine (Cr) deficiency, intellectual disability with severe speech delay, behavioral troubles, epilepsy, and motor dysfunction. AGAT/GAMT-deficient patients lack brain Cr synthesis but express the Cr transporter SLC6A8 at the blood-brain barrier and are thus treatable by oral supplementation of Cr. In contrast, no satisfactory treatment has been identified for Cr transporter deficiency (CTD), the most frequent of CDS. We used our Slc6a8Y389C CTD rat model to develop a new AAV2/9-2YF-driven gene therapy re-establishing the functional Slc6a8 transporter in rat CNS. We show, after intra-cisterna magna AAV2/9-2YF-Slc6a8-FLAG vector injection of postnatal day 11 pups, the transduction of Slc6a8-FLAG in cerebellum, medulla oblongata, and spinal cord as well as a partial recovery of Cr in these brain regions, together with full prevention of locomotion defaults and impairment of myocyte development observed in Slc6a8Y389 C/y male rats. While more work is needed to correct those CTD phenotypes more associated with forebrain structures, this study is the first demonstrating positive effects of an AAV-driven gene therapy on CTD and thus represents a very encouraging approach to treat the so-far untreatable CTD.

Investigation of intersegmental coordination patterns in human walking.

BACKGROUND: Intersegmental coordination between thigh, shank, and foot plays a crucial role in human gait, facilitating stable and efficient human walking. Limb elevation angles during the gait cycle form a planar manifold describes the by the planar covariation law, a recognized fundamental aspect of human locomotion. RESEARCH QUESTION: How does the walking speed, age, BMI, and height, affect the size and orientation of the intersegmental coordination manifold and covariation plane? METHODS: This study introduces novel metrics for quantifying intersegmental coordination, including the mean radius of the manifold, rotation of the manifold about the origin, and the orientation of the plane with respect to the coordinate planes. A statistical investigation is conducted on a publicly available human walking dataset for subjects aged 19-67 years, walking at speeds between 0.18 and 2.3 m s-1 to determine correlations of the proposed quantities. We used two sample t-test and ANOVA to find statistical significance of changes in the metrics with respect to gender and walking speed, respectively. Regression analysis was used to establish relationships between the introduced metrics and walking speed. RESULTS: High correlations are observed between walking speed and the computed metrics, highlighting the sensitivity of these metrics to gait characteristics. Conversely, negligible correlations are found for demographic parameters like age, body mass index (BMI), and height. Male and female groups exhibit no practically significant differences in any of the considered metrics. Additionally, metrics tend to increase in magnitude as walking speed increases. SIGNIFICANCE: This study contributes numerical metrics to characterize ISC of lower limbs with respect to walking speed along with regression models to estimate these metrics and related kinematic quantities. These findings hold significance for enhancing clinical gait analysis, generating optimal walking trajectories for assistive devices, prosthetics, or rehabilitation, aiming to replicate natural gaits and improve the functionality of biomechanical devices.

Critical review of the evidence for Vojta Therapy: a systematic review and meta-analysis.

Introduction: It is essential to link the theoretical framework of any neurophysiotherapy approach with a detailed analysis of the central motor control mechanisms that influence motor behavior. Vojta therapy (VT) falls within interventions aiming to modify neuronal activity. Although it is often mistakenly perceived as exclusively pediatric, its utility spans various functional disorders by acting on central pattern modulation. This study aims to review the existing evidence on the effectiveness of VT across a wide range of conditions, both in the adult population and in pediatrics, and analyze common therapeutic mechanisms, focusing on motor control modulation. Aim: The goals of this systematic review are to delineate the existing body of evidence concerning the efficacy of Vojta therapy (VT) in treating a broad range of conditions, as well as understand the common therapeutic mechanisms underlying VT with a specific focus on the neuromodulation of motor control parameters. Methods: PubMed, Cochrane Library, SCOPUS, Web of Science, and Embase databases were searched for eligible studies. The methodological quality of the studies was assessed using the PEDro list and the Risk-Of-Bias Tool to assess the risk of bias in randomized trials. Methodological quality was evaluated using the Risk-Of-Bias Tool for randomized trials. Random-effects meta-analyses with 95% CI were used to quantify the change scores between the VT and control groups. The certainty of our findings (the closeness of the estimated effect to the true effect) was evaluated using the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE). Results: Fifty-five studies were included in the qualitative analysis and 18 in the meta-analysis. Significant differences in cortical activity (p = 0.0001) and muscle activity (p = 0.001) were observed in adults undergoing VT compared to the control, as well as in balance in those living with multiple sclerosis (p < 0.03). Non-significant differences were found in the meta-analysis when evaluating gross motor function, oxygen saturation, respiratory rate, height, and head circumference in pediatrics. Conclusion: Although current evidence supporting VT is limited in quality, there are indications suggesting its potential usefulness for the treatment of respiratory, neurological, and orthopedic pathology. This systematic review and meta-analysis show the robustness of the neurophysiological mechanisms of VT, and that it could be an effective tool for the treatment of balance in adult neurological pathology. Neuromodulation of motor control areas has been confirmed by research focusing on the neurophysiological mechanisms underlying the therapeutic efficacy of VT.Systematic Review Registration:https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=476848, CRD42023476848.

Active Adaptive Strategies of Mallard Feet in Response to Changes in Wetness and Compactness of the Sand Terrain.

Mallards (Anas platyrhynchos) exhibit exceptional locomotive abilities in diverse terrains, such as beaches, swamps, and tidal flats. This capability is primarily attributed to their unique webbed toe structure and cooperative locomotion posture of their feet. Therefore, this study aims to further delve into the active adaptive strategies of mallard feet in response to diverse external environmental conditions. Six adult male mallards were selected for this research. Their locomotion on sandy surfaces with differing wetness levels and varying degrees of compaction were captured using a high-speed camera, and analysis of instantaneous and continuous changes in the primary joint angles of the mallards' feet, including the toe-webbed opening and closing angles, the tarsometatarsal-phalangeal joint (TMTPJ), and the intertarsal joint (ITJ). It was found that on loose sandy surfaces, increasing wetness expanded the ground contact area of the mallards' feet. This led to greater flexion at the TMTPJ joint during mid-stance, accompanied by decreased flexion of the ITJ during touch-down and mid-stance. Conversely, on compacted sand, increasing wetness resulted in a reduced foot effect area and lessened ITJ flexion at both touch-down and mid-stance. Furthermore, on looser sand, the ground contact area of the mallards' feet decreased, with an increase in ITJ buckling at touch-down. During the swing phase, sand wetness and compactness effected minimally on the feet of the mallards. On dry and loose sand ground, mallards will contract their second and fourth toes with webbing upon ground contact, covering and compacting the sand beneath while increasing ITJ flexion to mitigate sinking. This adaptation reduces the energy expended on sand and enhances body stability. In wet and compacted sand conditions, mallards expand their second and fourth toes upon ground contact and reduce ITJ flexion. Therefore, this coordinated foot and ITJ locomotion offers mallards a natural advantage when moving on various environmental media.

Developmental milestones in captive Galago moholi.

Systems of the body develop in a modular manner. For example, neural development in primates is generally rapid, whereas dental development varies much more. In the present study, we examined development of the skull, teeth, and postcrania in a highly specialized leaping primate, Galago moholi. Eighteen specimens ranging from birth to adult were studied. Bones, teeth, and the cranial cavity (i.e., endocast) were reconstructed with Amira software based on microCT cross-referenced to histology. Amira was also used to compute endocast volume (as a proxy for brain size). Reconstructions of the wrist and ankle show that ossification is complete at 1 month postnatally, consistent with the onset of leaping locomotion in this species. Endocranial volume is less than 50% of adult volume at birth, ~80% by 1 month, and has reached adult volume by 2 months postnatal age. Full deciduous dentition eruption occurs by 2 weeks, and the young are known to begin capturing and consuming arthropods on their own by 4 weeks, contemporaneous with the timing of bone and ankle ossification that accompanies successful hunting. The modular pattern of development of body systems in Galago moholi provides an interesting view of a "race" to adult morphology for some joints that are critical for specialized leaping and clinging, rapid crown mineralization to begin a transitional diet, but perhaps more prolonged reliance on nursing to support brain growth.

Dopamine-sensitive neurons in the mesencephalic locomotor region control locomotion initiation, stop, and turns.

The locomotor role of dopaminergic neurons is traditionally attributed to their ascending projections to the basal ganglia, which project to the mesencephalic locomotor region (MLR). In addition, descending dopaminergic projections to the MLR are present from basal vertebrates to mammals. However, the neurons targeted in the MLR and their behavioral role are unknown in mammals. Here, we identify genetically defined MLR cells that express D1 or D2 receptors and control different motor behaviors in mice. In the cuneiform nucleus, D1-expressing neurons promote locomotion, while D2-expressing neurons stop locomotion. In the pedunculopontine nucleus, D1-expressing neurons promote locomotion, while D2-expressing neurons evoke ipsilateral turns. Using RNAscope, we show that MLR dopamine-sensitive neurons comprise a combination of glutamatergic, GABAergic, and cholinergic neurons, suggesting that different neurotransmitter-based cell types work together to control distinct behavioral modules. Altogether, our study uncovers behaviorally relevant cell types in the mammalian MLR based on the expression of dopaminergic receptors.

Dynamics of centipede locomotion revealed by large-scale traction force microscopy.

We present a novel approach to traction force microscopy (TFM) for studying the locomotion of 10 cm long walking centipedes on soft substrates. Leveraging the remarkable elasticity and ductility of kudzu starch gels, we use them as a deformable gel substrate, providing resilience against the centipedes' sharp leg tips. By optimizing fiducial marker size and density and fine-tuning imaging conditions, we enhance measurement accuracy. Our TFM investigation reveals traction forces along the centipede's longitudinal axis that effectively counterbalance inertial forces within the 0-10 mN range, providing the first report of non-vanishing inertia forces in TFM studies. Interestingly, we observe waves of forces propagating from the head to the tail of the centipede, corresponding to its locomotion speed. Furthermore, we discover a characteristic cycle of leg clusters engaging with the substrate: forward force (friction) upon leg tip contact, backward force (traction) as the leg pulls the substrate while stationary, and subsequent forward force as the leg tip detaches to reposition itself in the anterior direction. This work opens perspectives for TFM applications in ethology, tribology and robotics.

The application of a single session of capacitive resistive electric transfer 24 h before exercise modifies the accelerometric pattern in standardbred racing trotters.

BACKGROUND: It has been reported that capacitive resistive electric transfer (CRET) increases blood circulation, hemoglobin oxygenation and temperature in muscles. The attributed benefits of these changes have been linked to improved athletic performance, enhanced muscle flexibility and fastening recovery from exercise-induced fatigue. For all of this, the present research aims to investigate whether the application of CRET 24 h before exercise affects the accelerometric pattern in horses during exercise. Six sound Standardbred trotters were subjected to a CRET session of 40 min of duration, applied on both sides of the neck, back and croup, 24 h before a training session. Training sessions consisted of a warming-up (WU) for 6400 m and a training bout (TB) at their maximal training speed for 1600 m. The same protocol was followed for the device off (sham protocol), also applied 24 h before the training session. CRET and sham experiments were separated by one week, the order of application of both was randomly defined for each individual and drivers were blinded for the duration of the experiment. During the training sessions, horses wore an accelerometer fixed at the sternal level. Speed, stride frequency (SF), length (SL), regularity and symmetry and accelerometric activities were measured during WU and TB. RESULTS: CRET increased speed, mediolateral and total accelerometric activities during WU and speed, SL, dorsoventral, longitudinal and total accelerometric activities during TB, but stride regularity and symmetry decreased. CONCLUSION: The application of CRET 24 h before exercise increased speed and accelerometric activities, results that highlight the need to evaluate the interaction between CRET and training in order to develop new methods to limit fatigue. However, the decrease in stride regularity and symmetry after CRET application could be negative effects, which could be attributed to the increased speed.