Balance in the cat: role of the tail and effects of sacrocaudal transection

The tail segments are required by the performance but not the accomplishment of various modes of Drosophila larval locomotion

The tail plays important roles in locomotion control in many animals. But in animals with multiple body segments, the roles of the hind body segments and corresponding innervating neurons in locomotion control are not clear. Here, using the Drosophila larva as the model animal, we investigated the roles of the posterior terminal segments in various modes of locomotion and found that they participate in all of them. In forward crawling, paralysis of the larval tail by blocking the Abdb-Gal4 labeled neurons in the posterior segments of VNC led to a slower locomotion speed but did not prevent the initiation of forward peristalsis. In backward crawling, larvae with the Abdb-Gal4 neurons inhibited were unable to generate effective displacement although waves of backward peristalsis could be initiated and persist. In head swing where the movement of the tail is not obvious, disabling the larval tail by blocking Abdb-Gal4 neurons led to increased bending amplitude upon touching the head. In the case of larval lateral rolling, larval tail paralysis by inhibition of Abdb-Gal4 neurons did not prevent the accomplishment of rolling, but resulted in slower rolling speed. Our work reveals that the contribution of Drosophila larval posterior VNC segments and corresponding body segments in the tail to locomotion is comprehensive but could be compensated at least partially by other body segments. We suggest that the decentralization in locomotion control with respect to animal body parts helps to maintain the robustness of locomotion in multi-segment animals.

The effect of tail stiffness on a sprawling quadruped locomotion

A distinctive feature of quadrupeds that is integral to their locomotion is the tail. Tails serve many purposes in biological systems, including propulsion, counterbalance, and stabilization while walking, running, climbing, or jumping. Similarly, tails in legged robots may augment the stability and maneuverability of legged robots by providing an additional point of contact with the ground. However, in the field of terrestrial bio-inspired legged robotics, the tail is often ignored because of the difficulties in design and control. In this study, we test the hypothesis that a variable stiffness robotic tail can improve the performance of a sprawling quadruped robot by enhancing its stability and maneuverability in various environments. In order to validate our hypothesis, we integrated a cable-driven, flexible tail with multiple segments into the underactuated sprawling quadruped robot, where a single servo motor working alongside a reel and cable mechanism regulates the tail's stiffness. Our results demonstrated that by controlling the stiffness of the tail, the stability of locomotion on rough terrain and the climbing ability of the robot are improved compared to the movement with a rigid tail and no tail. Our findings highlight that constant ground support provided by the flexible tail is key to maintaining stable locomotion. This ensured a predictable gait cycle, eliminating unexpected turning and slipping, resulting in an increase in locomotion speed and efficiency. Additionally, we observed the robot's enhanced climbing ability on surfaces inclined up to 20°. The flexibility of the tail enabled the robot to overcome obstacles without external sensing, exhibiting significant adaptability across various terrains.

Genomic analyses of wild argali, domestic sheep, and their hybrids provide insights into chromosome evolution, phenotypic variation, and germplasm innovation

Understanding the genetic mechanisms of phenotypic variation in hybrids between domestic animals and their wild relatives may aid germplasm innovation. Here, we report the high-quality genome assemblies of a male Pamir argali (O ammon polii, 2n = 56), a female Tibetan sheep (O aries, 2n = 54), and a male hybrid of Pamir argali and domestic sheep, and the high-throughput sequencing of 425 ovine animals, including the hybrids of argali and domestic sheep. We detected genomic synteny between Chromosome 2 of sheep and two acrocentric chromosomes of argali. We revealed consistent satellite repeats around the chromosome breakpoints, which could have resulted in chromosome fusion. We observed many more hybrids with karyotype 2n = 54 than with 2n = 55, which could be explained by the selfish centromeres, the possible decreased rate of normal/balanced sperm, and the increased incidence of early pregnancy loss in the aneuploid ewes or rams. We identified genes and variants associated with important morphological and production traits (e.g., body weight, cannon circumference, hip height, and tail length) that show significant variations. We revealed a strong selective signature at the mutation (c.334C > A, p.G112W) in TBXT and confirmed its association with tail length among sheep populations of wide geographic and genetic origins. We produced an intercross population of 110 F2 offspring with varied number of vertebrae and validated the causal mutation by whole-genome association analysis. We verified its function using CRISPR-Cas9 genome editing. Our results provide insights into chromosomal speciation and phenotypic evolution and a foundation of genetic variants for the breeding of sheep and other animals.

The Roles and Comparison of Rigid and Soft Tails in Gecko-Inspired Climbing Robots: A Mini-Review

Geckos use millions of dry bristles on their toes to adhere to and rapidly run up walls and across ceilings. This has inspired the successful development of dry adhesive materials and their application to climbing robots. The tails of geckos also help realize adaptive and robust climbing behavior. Existing climbing robots with gecko-inspired tails have demonstrated improved locomotion performance. However, few studies have focused on the role of a robot’s gecko-inspired tail when climbing a sloped surface and its effects on the overall locomotion performance. Thus, this paper reviews and analyzes the roles of the tails of geckos and robots in terms of their climbing performances and compares the advantages and disadvantages of robots’ tails made of rigid and soft materials. This review could assist roboticists decide whether a tail is required for their robots and which materials and motion types to use for the tail in order to fulfill their desired functions and even allow the robots to adapt to different environments and tasks.

Turtling the Salamander: Tail Movements Mitigate Need for Kinematic Limb Changes during Walking in Tiger Salamanders (Ambystoma tigrinum) with Restricted Lateral Movement

Lateral undulation and trunk flexibility offer performance benefits to maneuverability, stability, and stride length (via speed and distance traveled). These benefits make them key characteristics of the locomotion of tetrapods with sprawling posture, with the exception of turtles. Despite their bony carapace preventing lateral undulations, turtles are able to improve their locomotor performance by increasing stride length via greater limb protraction. The goal of this study was to quantify the effect of reduced lateral flexibility in a generalized sprawling tetrapod, the tiger salamander (Ambystoma tigrinum). We had two potential predictions: (1) either salamanders completely compensate by changing their limb kinematics, or (2) their performance (i.e., speed) will suffer due to the reduced lateral flexibility. This reduction was performed by artificially limiting trunk flexibility by attaching a 2-piece shell around the body between the pectoral and pelvic girdles. Adult tiger salamanders (n = 3; SVL = 9–14.5 cm) walked on a 1-m trackway under three different conditions: unrestricted, flexible shell (Tygon tubing), and rigid shell (PVC tubing). Trials were filmed in a single, dorsal view, and kinematics of entire midline and specific body regions (head, trunk, tail), as well as the fore and hind limbs, were calculated. Tygon individuals had significantly higher curvature than both PVC and unrestricted individuals for the body, but this trend was primarily driven by changes in tail movements. PVC individuals had significantly lower curvature in the trunk region compared with unrestricted individuals or Tygon; however, there was no difference between unrestricted and Tygon individuals suggesting the shells performed as expected. PVC and Tygon individuals had significantly higher curvature in the tails compared with unrestricted individuals. There were no significant differences for any limb kinematic variables among treatments including average, minimum, and maximum angles. Thus, salamanders respond to decreased lateral movement in their trunk by increasing movements in their tail, without changes in limb kinematics. These results suggest that tail undulations may be a more critical component to sprawling-postured tetrapod locomotion than previously recognized.

The squirrel is in the detail: Anatomy and morphometry of the tail in Sciuromorpha (Rodentia, Mammalia)

In mammals, the caudal vertebrae are certainly among the least studied elements of their skeleton. However, the tail plays an important role in locomotion (e.g., balance, prehensility) and behavior (e.g., signaling). Previous studies largely focused on prehensile tails in Primates and Carnivora, in which certain osteological features were selected and used to define tail regions (proximal, transitional, distal). Interestingly, the distribution pattern of these anatomical characters and the relative proportions of the tail regions were similar in both orders. In order to test if such tail regionalization can be applied to Rodentia, we investigated the caudal vertebrae of 20 Sciuridae and six Gliridae species. Furthermore, we examined relationships between tail anatomy/morphometry and locomotion. The position of selected characters along the tail was recorded and their distribution was compared statistically using Spearman rank correlation. Vertebral body length (VBL) was measured to calculate the proportions of each tail region and to perform procrustes analysis on the shape of relative vertebral body length (rVBL) progressions. Our results show that tail regionalization, as defined for Primates and Carnivora, can be applied to almost all investigated squirrels, regardless of their locomotor category. Moreover, major locomotor categories can be distinguished by rVBL progression and tail region proportions. In particular, the small flying squirrels Glaucomys volans and Hylopetes sagitta show an extremely short transitional region. Likewise, several semifossorial taxa can be distinguished by their short distal region. Moreover, among flying squirrels, Petaurista petaurista shows differences with the small flying squirrels, mirroring previous observations on locomotory adaptations based on their inner ear morphometry. Our results show furthermore that the tail region proportions of P. petaurista, phylogenetically more basal than the small flying squirrels, are similar to those of bauplan-conservative arboreal squirrels.

The Stabilizing Function of the Tail During Arboreal Quadrupedalism

Locomotion on the narrow and compliant supports of the arboreal environment is inherently precarious. Previous studies have identified a host of morphological and behavioral specializations in arboreal animals broadly thought to promote stability when on precarious substrates. Less well-studied is the role of the tail in maintaining balance. However, prior anatomical studies have found that arboreal taxa frequently have longer tails for their body size than their terrestrial counterparts, and prior laboratory studies of tail kinematics and the effects of tail reduction in focal taxa have broadly supported the hypothesis that the tail is functionally important for maintaining balance on narrow and mobile substrates. In this set of studies, we extend this work in two ways. First, we used a laboratory dataset on three-dimensional segmental kinematics and tail inertial properties in squirrel monkeys (Saimiri boliviensis) to investigate how tail angular momentum is modulated during steady-state locomotion on narrow supports. In the second study, we used a quantitative dataset on quadrupedal locomotion in wild platyrrhine monkeys to investigate how free-ranging arboreal animals adjust tail movements in response to substrate variation, focusing on kinematic measures validated in prior laboratory studies of tail mechanics (including the laboratory data presented). Our laboratory results show that S. boliviensis significantly increase average tail angular momentum magnitudes and amplitudes on narrow supports, and primarily regulate that momentum by adjusting the linear and angular velocity of the tail (rather than via changes in tail posture per se). We build on these findings in our second study by showing that wild platyrrhines responded to the precarity of narrow and mobile substrates by extending the tail and exaggerating tail displacements, providing ecological validity to the laboratory studies of tail mechanics presented here and elsewhere. In conclusion, our data support the hypothesis that the long and mobile tails of arboreal animals serve a biological role of enhancing stability when moving quadrupedally over narrow and mobile substrates. Tail angular momentum could be used to cancel out the angular momentum generated by other parts of the body during steady-state locomotion, thereby reducing whole-body angular momentum and promoting stability, and could also be used to mitigate the effects of destabilizing torques about the support should the animals encounter large, unexpected perturbations. Overall, these studies suggest that long and mobile tails should be considered among the fundamental suite of adaptations promoting safe and efficient arboreal locomotion.

Tails, Flails, and Sails: How Appendages Improve Terrestrial Maneuverability by Improving Stability

Trade-offs in maneuverability and stability are essential in ecologically relevant situations with respect to robustness of locomotion, with multiple strategies apparent in animal model systems depending on their habitat and ecology. Free appendages such as tails and ungrounded limbs may assist in navigating this trade-off by assisting with balance, thereby increasing the acceleration that can be achieved without destabilizing the body. This comparative analysis explores the inertial mechanisms and, in some cases, fluid dynamic mechanisms by which appendages contribute to the stabilization of gait and perturbation response behaviors in a wide variety of animals. Following a broad review of examples from nature and bio-inspired robotics that illustrate the importance of appendages to the control of body orientation, two specific cases are examined through preliminary experiments: the role of arm motion in bipedal gait termination is explored using trajectory optimization, and the role of the cheetah’s tail during a deceleration maneuver is analyzed based on motion capture data. In both these examples, forward rotation of the appendage in question is found to counteract the unwanted forward pitch caused by the braking forces. It is theorized that this stabilizing action may facilitate more rapid deceleration by allowing larger or longer-acting braking forces to be applied safely.

How to Stick the Landing: Kangaroo Rats Use Their Tails to Reorient during Evasive Jumps Away from Predators

Tails are widespread in the animal world and play important roles in locomotor tasks, such as propulsion, maneuvering, stability, and manipulation of objects. Kangaroo rats, bipedal hopping rodents, use their tail for balancing during hopping, but the role of their tail during the vertical evasive escape jumps they perform when attacked by predators is yet to be determined. Because we observed kangaroo rats swinging their tails around their bodies while airborne following escape jumps, we hypothesized that kangaroo rats use their tails to not only stabilize their bodies while airborne, but also to perform aerial re-orientations. We collected video data from free-ranging desert kangaroo rats (Dipodomys deserti) performing escape jumps in response to a simulated predator attack and analyzed the rotation of their bodies and tails in the yaw plane (about the vertical-axis). Kangaroo rat escape responses were highly variable. The magnitude of body re-orientation in yaw was independent of jump height, jump distance, and aerial time. Kangaroo rats exhibited a stepwise re-orientation while airborne, in which slower turning periods corresponded with the tail center of mass being aligned close to the vertical rotation axis of the body. To examine the effect of tail motion on body re-orientation during a jump, we compared average rate of change in angular momentum. Rate of change in tail angular momentum was nearly proportional to that of the body, indicating that the tail reorients the body in the yaw plane during aerial escape leaps by kangaroo rats. Although kangaroo rats make dynamic 3D movements during their escape leaps, our data suggest that kangaroo rats use their tails to control orientation in the yaw plane. Additionally, we show that kangaroo rats rarely use their tail length at full potential in yaw, suggesting the importance of tail movement through multiple planes simultaneously.

A Barycenter Control Method for the Bioinspired Forest Chassis Robot on Slope

To improve the stability of forestry chassis on the slope, a chassis-installed barycenter adjustable mechanism (BAM) is designed, and the control method of the counterweight is proposed to make the chassis barycenter move suitably to achieve the design purpose. The kinematic analysis of BAM is carried out, and the relationship between the translation, rotation, and vertical displacement of counterweight and the chassis barycenter is calculated. Furthermore, the variation curves obtained in Matlab show the barycenter can translate 100 mm, rotate from 0 to 360 degrees, and lower about 180 mm in the vertical direction. Adams is adopted to complete the kinematics simulation of the chassis, indicating that the control method can effectively adjust the barycenter position. Finally, experiments are carried out under slope conditions to analyze chassis stability by testing plantar pressure. The results show that forest chassis using the barycenter control method helps keep stable on the slope of 15 degrees, much better than standard normal chassis.

Tail Length Evolution in Deer Mice: Linking Morphology, Behavior, and Function

Determining how variation in morphology affects animal performance (and ultimately fitness) is key to understanding the complete process of evolutionary adaptation. Long tails have evolved many times in arboreal and semi-arboreal rodents; in deer mice, long tails have evolved repeatedly in populations occupying forested habitat even within a single species (Peromyscus maniculatus). Here, we use a combination of functional modeling, laboratory studies, and museum records to test hypotheses about the function of tail-length variation in deer mice. First, we use computational models, informed by museum records documenting natural variation in tail length, to test whether differences in tail morphology between forest and prairie subspecies can influence performance in behavioral contexts relevant for tail use. We find that the deer- mouse tail plays little role in statically adjusting center of mass or in correcting body pitch and yaw, but rather it can affect body roll during arboreal locomotion. In this context, we find that even intraspecific tail-length variation could result in substantial differences in how much body rotation results from equivalent tail motions (i.e., tail effectiveness), but the relationship between commonly-used metrics of tail-length variation and effectiveness is non-linear. We further test whether caudal vertebra length, number, and shape are associated with differences in how much the tail can bend to curve around narrow substrates (i.e., tail curvature) and find that, as predicted, the shape of the caudal vertebrae is associated with intervertebral bending angle across taxa. However, although forest and prairie mice typically differ in both the length and number of caudal vertebrae, we do not find evidence that this pattern is the result of a functional trade-off related to tail curvature. Together, these results highlight how even simple models can both generate and exclude hypotheses about the functional consequences of trait variation for organismal-level performance.

Jumping Locomotion Strategies: From Animals to Bioinspired Robots

Jumping is a locomotion strategy widely evolved in both invertebrates and vertebrates. In addition to terrestrial animals, several aquatic animals are also able to jump in their specific environments. In this paper, the state of the art of jumping robots has been systematically analyzed, based on their biological model, including invertebrates (e.g., jumping spiders, locusts, fleas, crickets, cockroaches, froghoppers and leafhoppers), vertebrates (e.g., frogs, galagoes, kangaroos, humans, dogs), as well as aquatic animals (e.g., both invertebrates and vertebrates, such as crabs, water-striders, and dolphins). The strategies adopted by animals and robots to control the jump (e.g., take-off angle, take-off direction, take-off velocity and take-off stability), aerial righting, land buffering, and resetting are concluded and compared. Based on this, the developmental trends of bioinspired jumping robots are predicted.

Evaluation of prognostic factors for return of urinary and defecatory function in cats with sacrocaudal luxation

OBJECTIVES

The aim of this study was to evaluate outcomes and prognostic factors for cats with sacrocaudal luxation.

METHODS

Medical records and radiographs were reviewed for cats with sacrocaudal luxation. Information obtained from the clinical records included signalment, clinical presentation, concurrent traumatic injuries, treatment details, outcome and survival time. Severity of neurological signs was graded from 1 to 5, based on previous grading systems for cats with sacrocaudal luxation. Degree of vertebral displacement was calculated on survey radiographs. Outcomes were collected from serial neurological examinations and telephone interviews. Cats had to be given a minimum of 30 days to regain urinary function to be included in the study.

RESULTS

Seventy cats were included. Fifty-five of 61 cats (90%) regained voluntary urinary function. A higher neurological grade was associated with a decreased likelihood (P = 0.01) and longer duration (P = 0.0003) of regaining urinary function. No significant associations were found between urinary outcome and age, sex, anal tone, perineal sensation, tail base sensation, degree of craniocaudal or dorsoventral sacrocaudal displacement, concurrent orthopaedic injury, tail amputation, defecatory function at diagnosis and survival. Cats that regained defecatory function had longer survival times than those that did not recover defecatory function (P = 0.03). Defecatory outcome was not significantly associated with any other variables.

CONCLUSIONS AND RELEVANCE

In agreement with previous studies, neurological grade is the most important prognostic indicator for cats with sacrocaudal luxation. Determination of the severity of neurological signs can also aid in advising owners the time frame in which urinary function is expected to return. Faecal incontinence may be a more important prognostic factor than previously suspected.

The vertebrate tail: a gene playground for evolution

The tail of all vertebrates, regardless of size and anatomical detail, derive from a post-anal extension of the embryo known as the tail bud. Formation, growth and differentiation of this structure are closely associated with the activity of a group of cells that derive from the axial progenitors that build the spinal cord and the muscle-skeletal case of the trunk. Gdf11 activity switches the development of these progenitors from a trunk to a tail bud mode by changing the regulatory network that controls their growth and differentiation potential. Recent work in the mouse indicates that the tail bud regulatory network relies on the interconnected activities of the Lin28/let-7 axis and the Hox13 genes. As this network is likely to be conserved in other mammals, it is possible that the final length and anatomical composition of the adult tail result from the balance between the progenitor-promoting and -repressing activities provided by those genes. This balance might also determine the functional characteristics of the adult tail. Particularly relevant is its regeneration potential, intimately linked to the spinal cord. In mammals, known for their complete inability to regenerate the tail, the spinal cord is removed from the embryonic tail at late stages of development through a Hox13-dependent mechanism. In contrast, the tail of salamanders and lizards keep a functional spinal cord that actively guides the tail's regeneration process. I will argue that the distinct molecular networks controlling tail bud development provided a collection of readily accessible gene networks that were co-opted and combined during evolution either to end the active life of those progenitors or to make them generate the wide diversity of tail shapes and sizes observed among vertebrates.

Substrate use drives the macroevolution of mammalian tail length diversity

External length is one of the most conspicuous aspects of mammalian tail morphological diversity. Factors that influence the evolution of tail length diversity have been proposed for particular taxa, including habitat, diet, locomotion and climate. However, no study to date has investigated such factors at a large phylogenetic scale to elucidate what drives tail length evolution in and across mammalian lineages. We use phylogenetic comparative methods to test a priori hypotheses regarding proposed factors influencing tail length, explore possible interactions between factors using evolutionary best-fit models, and map evolutionary patterns of tail length for specific mammalian lineages. Across mammals, substrate use is a significant factor influencing tail length, with arboreal species maintaining selection for longer tails. Non-arboreal species instead exhibit a wider range of tail lengths, secondarily influenced by differences in locomotion, diet and climate. Tail loss events are revealed to occur in the context of both long and short tails and influential factors are clade dependent. Some mammalian groups (e.g. Macaca; primates) exhibit elevated rates of tail length evolution, indicating that morphological evolution may be accelerated in groups characterized by diverse substrate use, locomotor modes and climate.

In utero exposure to commercial artificial sweeteners affects mice development and mammary gland structure

Commercial artificial sweeteners present in the market are usually made of combination of nutritive and artificial sweeteners such as sorbitol and aspartame. The aim of this research was to study the effect of in utero exposure to commercial artificial sweeteners on the mouse development and on mammary gland in different stages (18-day embryos and 4-week-old mice). Pregnant mice of treated groups were given 50 mg/kg body weight of commercial artificial sweetener. The dose was given on day 1 of pregnancy until 3-week nursing, while the controls were given distilled water. Congenital malformations were seen in treated 18-day fetus and 4-week-old mice, such as a significant decrease in the diameter of the placenta and the weight of the fetuses, while in 4-week-old mice, a significant decrease in the length of the body, limbs, and tail was seen compared to the controls. The result of this study showed that in 18-day fetuses, clusters of mammary gland in the treated mice seemed to be more differentiated than the controls. In 4-week-old mice, the number of mammary gland ducts in the treated group was significantly more than the control group, and the lumen of the ducts in the treated sections seemed to be narrower than the controls, also many regressing terminal end buds (TEBs) were seen in the treated group. A significant increase in the mammary gland area of treated group was seen compared to the controls.

Body and tail-assisted pitch control facilitates bipedal locomotion in Australian agamid lizards

Certain lizards are known to run bipedally. Modelling studies suggest bipedalism in lizards may be a consequence of a caudal shift in the body centre of mass, combined with quick bursts of acceleration, causing a torque moment at the hip lifting the front of the body. However, some lizards appear to run bipedally sooner and for longer than expected from these models, suggesting positive selection for bipedal locomotion. While differences in morphology may contribute to bipedal locomotion, changes in kinematic variables may also contribute to extended bipedal sequences, such as changes to the body orientation, tail lifting and changes to the ground reaction force profile. We examined these mechanisms among eight Australian agamid lizards. Our analysis revealed that angular acceleration of the trunk about the hip, and of the tail about the hip were both important predictors of extended bipedal running, along with increased temporal asymmetry of the ground reaction force profile. These results highlight important dynamic movements during locomotion, which may not only stabilize bipedal strides, but also to de-stabilize quadrupedal strides in agamid lizards, in order to temporarily switch to, and extend a bipedal sequence.

Lateral movements of a massive tail influence gecko locomotion: an integrative study comparing tail restriction and autotomy

Tails are an intricate component of the locomotor system for many vertebrates. Leopard geckos (Eublepharis macularius) possess a large tail that is laterally undulated during steady locomotion. However, the tail is readily shed via autotomy, resulting in the loss of tail function, loss in body mass, and a cranial shift in the center of mass. To elucidate the function of tail undulations, we investigated changes in limb kinematics after manipulating the tail artificially by restricting tail undulations and naturally by removing the tail via autotomy. Restricting tail undulations resulted in kinematic adjustments similar to those that occur following tail autotomy, characterized by more flexed hind limb joints. These data suggest that effects of autotomy on locomotion may be linked to the loss of tail movements rather than the loss of mass or a shift in center of mass. We also provide empirical support for the link between lateral tail undulations and step length through the rotation of the pelvic girdle and retraction of the femur. Restriction and autotomy of the tail limits pelvic rotation, which reduces femur retraction and decreases step length. Our findings demonstrate a functional role for tail undulations in geckos, which likely applies to other terrestrial vertebrates.

Consequences of lost endings: caudal autotomy as a lens for focusing attention on tail function during locomotion

Autotomy has evolved in many animal lineages as a means of predator escape, and involves the voluntary shedding of body parts. In vertebrates, caudal autotomy (or tail shedding) is the most common form, and it is particularly widespread in lizards. Here, we develop a framework for thinking about how tail loss can have fitness consequences, particularly through its impacts on locomotion. Caudal autotomy is fundamentally an alteration of morphology that affects an animal's mass and mass distribution. These morphological changes affect balance and stability, along with the performance of a range of locomotor activities, from running and climbing to jumping and swimming. These locomotor effects can impact on activities critical for survival and reproduction, including escaping predators, capturing prey and acquiring mates. In this Commentary, we first review work illustrating the (mostly) negative effects of tail loss on locomotor performance, and highlight what these consequences reveal about tail function during locomotion. We also identify important areas of future study, including the exploration of new behaviors (e.g. prey capture), increased use of biomechanical measurements and the incorporation of more field-based studies to continue to build our understanding of the tail, an ancestral and nearly ubiquitous feature of the vertebrate body plan.

Effects of head and tail as swinging appendages on the dynamic walking performance of a quadruped robot

We designed a quadruped robot with a one-degree-of-freedom (1-DOF)-pitch head, a 1-DOF-roll tail, and 14 active DOFs in total, which are controlled via a central pattern generator (CPG) based on a Hopf oscillator. Head and tail movements are coupled to the leg movements with fixed phase differences. Experiments show that tail swinging in roll can equilibrate feet–ground reaction forces (GRF), reducing yaw errors and enabling the robot to maintain its direction when trotting. Head swing in pitch has the potential to increase flight time and stride length of the swinging legs and increase the robot's forward velocity when running in bounds.

The kangaroo's tail propels and powers pentapedal locomotion

When moving slowly, kangaroos plant their tail on the ground in sequence with their front and hind legs. To determine the tail's role in this 'pentapedal' gait, we measured the forces the tail exerts on the ground and calculated the mechanical power it generates. We found that the tail is responsible for as much propulsive force as the front and hind legs combined. It also generates almost exclusively positive mechanical power, performing as much mass-specific mechanical work as does a human leg during walking at the same speed. Kangaroos use their muscular tail to support, propel and power their pentapedal gait just like a leg.

Tail function during arboreal quadrupedalism in squirrel monkeys (Saimiri boliviensis) and tamarins (Saguinus oedipus)

The need to maintain stability on narrow branches is often presented as a major selective force shaping primate morphology, with adaptations to facilitate grasping receiving particular attention. The functional importance of a long and mobile tail for maintaining arboreal stability has been comparatively understudied. Tails can facilitate arboreal balance by acting as either static counterbalances or dynamic inertial appendages able to modulate whole-body angular momentum. We investigate associations between tail use and inferred grasping ability in two closely related cebid platyrrhines-cotton-top tamarins (Saguinus oedipus) and black-capped squirrel monkeys (Saimiri boliviensis). Using high-speed videography of captive monkeys moving on 3.2 cm diameter poles, we specifically test the hypothesis that squirrel monkeys (characterized by grasping extremities with long digits) will be less dependent on the tail for balance than tamarins (characterized by claw-like nails, short digits, and a reduced hallux). Tamarins have relatively longer tails than squirrel monkeys, move their tails through greater angular amplitudes, at higher angular velocities, and with greater angular accelerations, suggesting dynamic use of tail to regulate whole-body angular momentum. By contrast, squirrel monkeys generally hold their tails in a comparatively stationary posture and at more depressed angles, suggesting a static counterbalancing mechanism. This study, the first empirical test of functional tradeoffs between grasping ability and tail use in arboreal primates, suggests a critical role for the tail in maintaining stability during arboreal quadrupedalism. Our findings have the potential to inform our functional understanding of tail loss during primate evolution.

Flexibility of the axial central pattern generator network for locomotion in the salamander

In tetrapods, limb and axial movements are coordinated during locomotion. It is well established that inter- and intralimb coordination show considerable variations during ongoing locomotion. Much less is known about the flexibility of the axial musculoskeletal system during locomotion and the neural mechanisms involved. Here we examined this issue in the salamander Pleurodeles waltlii, which is capable of locomotion in both aquatic and terrestrial environments. Kinematics of the trunk and electromyograms from the mid-trunk epaxial myotomes were recorded during four locomotor behaviors in freely moving animals. A similar approach was used during rhythmic struggling movements since this would give some insight into the flexibility of the axial motor system. Our results show that each of the forms of locomotion and the struggling behavior is characterized by a distinct combination of mid-trunk motor patterns and cycle durations. Using in vitro electrophysiological recordings in isolated spinal cords, we observed that the spinal networks activated with bath-applied N-methyl-d-aspartate could generate these axial motor patterns. In these isolated spinal cord preparations, the limb motor nerve activities were coordinated with each mid-trunk motor pattern. Furthermore, isolated mid-trunk spinal cords and hemicords could generate the mid-trunk motor patterns. This indicates that each side of the cord comprises a network able to generate coordinated axial motor activity. The roles of descending and sensory inputs in the behavior-related changes in axial motor coordination are discussed.

Fictive rhythmic motor patterns produced by the tail spinal cord in salamanders

Most investigations into the role of the body axis in vertebrate locomotion have focused on the trunk, although in most tetrapods, the tail also plays an active role. In salamanders, the tail contributes to propulsion during swimming and to dynamic balance and maneuverability during terrestrial locomotion. The aim of the present study was to obtain information concerning the neural mechanisms that produce tail muscle contractions during locomotion in the salamander Pleurodeles waltlii. We recorded the ventral root activities in in vitro spinal cord preparations in which locomotor-like activity was induced via bath application of N-methyl-d-aspartate (20μM) and d-serine (10μM). Recordings showed that the tail spinal cord is capable of producing propagated waves of motor activity that alternate between the left and right sides. Lesion experiments further revealed that the tail rhythmogenic network is composed of a double chain of identical hemisegmental oscillators. Finally, using spinal cord preparations bathed in a chamber partitioned into two pools, we revealed efficient short-distance coupling between the trunk and tail networks. Together, our results demonstrate the existence of a pattern generator for rhythmic tail movements in the salamander and show that the global architecture of the tail network is similar to that previously proposed for the mid-trunk locomotor network in the salamander. Our findings further support the view that salamanders can control their trunk and tail independently during stepping movements. The relevance of our results in relation to the generation of tail muscle contractions in freely moving salamanders is discussed.

Participation of ventral and dorsal tail muscles in bending movements of rat tail

The rat controls the form of its tail, from straight to curved, by contraction and relaxation of its four tail muscles. The tendons of these muscles insert on any of the cranial articular, transverse, and hemal processes of each of 24 coccygeal vertebrae (Co5-Co28). In this study, we isolated for the four coccygeal muscles each muscular fascicle segment inserting on any process of the coccygeal vertebrae. We measured the length and weight of all muscular fascicles and tendons, and then divided all muscular fascicles into four groups based on their insertion: Co5-Co10, Co11-Co16, Co17-Co22, and Co23-Co28. Moreover, we used soft X-ray imaging to investigate the geometrical relationship between neighboring coccygeal vertebrae. Additionally we carried out serial sectioning at the sacral and caudal portions, and traced the course of the tendons of coccygeal muscles from their origin to the Co4 level. We discuss which muscles and tendons play important roles when coccygeal vertebrae bend along and rotate around the longitudinal axis.

Perspectives on transgenic livestock in agriculture and biomedicine: an update

It has been 30 years since the first transgenic mouse was generated and 26 years since the first example of transferring the technology to livestock was published. While there was tremendous optimism in those initial years, with most convinced that genetically modified animals would play a significant role in agricultural production, that has not come to be. So at first sight one could conclude that this technology has, to a large extent, failed. On the contrary, it is believed that it has succeeded beyond our original expectations, and we are now at what is perhaps the most exciting time in the development and implementation of these technologies. The original goals, however, have drastically changed and it is now biomedical applications that are playing a central role in pushing both technical and scientific developments. The combination of advances in somatic cell nuclear transfer, the development of induced pluripotent stem cells and the completion of the sequencing of most livestock genomes ensures a bright and exciting future for this field, not only in livestock but also in companion animal species.

Development of a model of sacrocaudal spinal cord injury in cloned Yucatan minipigs for cellular transplantation research

Research into transplantation strategies to treat spinal cord injury (SCI) is frequently performed in rodents, but translation of results to clinical patients can be poor and a large mammalian model of severe SCI is needed. The pig has been considered an optimal model species in which to perform preclinical testing, and the Yucatan minipig can be cloned successfully utilizing somatic cell nuclear transfer (SCNT). However, induction of paralysis in pigs poses significant welfare and nursing challenges. The present study was conducted to determine whether Yucatan SCNT clones could be used to develop an SCI animal model for cellular transplantation research. First, we demonstrated that transection of the sacrocaudal spinal cord in Yucatan SCNT clones produces profound, quantifiable neurological deficits restricted to the tail. We then established that neurospheres could be isolated from brain tissue of green fluorescence protein (GFP) transfected SCNT clones. Finally, we confirmed survival of transplanted GFP-expressing neural stem cells in the SCI lesion and their differentiation into glial and neuronal lineages for up to 4 weeks without immunosuppression. We conclude that this model of sacrocaudal SCI in Yucatan SCNT clones represents a powerful research tool to investigate the effect of cellular transplantation on axonal regeneration and functional recovery.

CatWalk-Assisted Gait Analysis in the Assessment of Spinal Cord Injury

Gait analysis plays an important role in the assessment of neurological function in many disease models. In this review, we focus on the newly developed CatWalk system for gait analysis. CatWalk was originally developed as a tool to enhance assessment of functional outcome in spinal cord injury (SCI) models. Although it is also of value in models of among others (neuropathic) pain and peripheral nerve damage, we will limit ourselves to its use in SCI models in this review. The system is positioned against well-established locomotor function tests, and it is indicated how CatWalk can enhance the usefulness of such tests. Development of the system started with the idea that it should enable objective assessment of coordination, and powerful measures of coordination are nowadays included in the analysis options provided by CatWalk. Therefore, a major part of this review is devoted to the history and meaning of these coordination measures.

Alteration in axial motoneuronal morphology in the spinal cord injured spastic rat

Following spinal cord injury (SCI), exaggerated reflexes and muscle tone emerge that contribute to a general spastic syndrome in humans. At present, the underlying mechanisms involved with the development of spasticity following traumatic spinal cord injury, especially with regard to axial musculature, remains unclear. The purpose of the present study was to examine the temporal changes in sacrocaudal motoneuronal morphology following complete transection of the sacral spinal cord and to correlate these changes with the onset and progression of spasticity within the tail musculature. The spinal cords of rats were transected at the upper sacral (S(2)) level. Animals were behaviorally tested for the onset and progression of spasticity in the tail and at 1, 2, 4, or 12 weeks postinjury were sacrificed. At these time points, the animals demonstrated stage 1, 2, 3, or 4 spastic behavior, respectively. Sacrocaudal motoneurons innervating selected flexor muscles within the tail were retrogradely labeled with cholera toxin beta-subunit and neuronal morphology was analyzed using a combination of immunocytochemistry and standard microscopy. Initially over the first 2 weeks postinjury, a transient increase in the lengths of primary and secondary dendrites occurred. However, a progressive decrease in the overall number of dendritic branches was observed between 2 and 12 weeks postinjury, which parallels the time frame for the progressive increase in spastic behavior in the tail musculature. Following spinal cord injury, there is an alteration in the morphology of tail flexor motoneurons, which may be relevant to the development of spasticity within the tail.

Behavioral testing strategies in a localized animal model of multiple sclerosis

To assess neurological impairments quantitatively in an animal model of multiple sclerosis (MS), we have used a targeted model of experimental autoimmune encephalomyelitis (EAE), which leads to the formation of anatomically defined lesions in the spinal cord. Deficits in the hindlimb locomotion are therefore well defined and highly reproducible, in contrast to the situation in generalized EAE with disseminated lesions. Behavioral tests for hindlimb sensorimotor functions, originally established for traumatic spinal cord injury, revealed temporary or persistent deficits in open field locomotion, the grid walk, the narrow beam and the measurement of the foot exorotation angle. Such refined behavioral testing in EAE will be crucial for the analysis of new therapeutic approaches for MS that seek to improve or prevent neurological impairment.

Alpha-1 Adrenoceptor Agonists Generate a “Fast” NMDA Receptor-Independent Motor Rhythm in the Neonatal Rat Spinal Cord

Noradrenaline, a potent activator of rhythmogenic networks in adult mammals has not been reported to produce functional rhythmic patterns in isolated spinal cords of newborn rats. We now show that a “fast” (cycle time: 1–4 s) transient rhythm was induced in sacrococcygeal (SC) and rostral-lumbar spinal segments of the neonatal rat by bath-applied noradrenaline. The fast rhythm was blocked by 1 μM of the α1-adrenoceptor antagonist prazosin but not by 1–20 μM of the α2-adrenoceptor blocker yohimbine, it could be initiated and maintained by α1-adrenoceptor agonists, and it was accompanied by a slow nonlocomotor rhythm. Transection at the lumbosacral junction abolished the fast-thoracolumbar (TL) rhythm while the fast-SC and slow-TL rhythms were unaffected. The N-methyl-d-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonopentanoic acid (AP5) abolished the slow- and did not interrupt the fast rhythm. Thus α1-adrenoceptor agonists induce an NMDA receptor-independent rhythm in the SC cord and modulate NMDA receptor-dependent rhythmicity in TL segments. Injection of current steps into S2 and flexor-dominated L2 motoneurons during the fast rhythm revealed a 20–30% decrease in input-resistance ( RN), coinciding with contralateral bursting. The RN of extensor-dominated L5 motoneurons did not vary with the fast rhythm. The rhythmic fluctuations of RN in L2 motoneurons were abolished, but the alternating left-right pattern of the fast rhythm was unchanged in midsagittally split TL cords. We suggest that the locomotor generators were not activated during the fast rhythm, that crossed-inhibitory pathways activated by SC projections controlled the rhythmic decrease in RN in L2 motoneurons, and that the alternating pattern of the split TL cord was maintained by excitatory SC projections.

Neural pathways between sacrocaudal afferents and lumbar pattern generators in neonatal rats

Projections of sacrocaudal afferents (SCA) onto lumbar pattern generators were studied in isolated spinal cords of neonatal rats. A locomotor-like pattern could be produced by SCA stimulation in the majority of the preparations. The SCA-induced lumbar rhythm was abolished after blocking synaptic transmission in the sacrococcygeal (SC) cord by bathing its segments in a low-calcium, high-magnesium artificial cerebrospinal fluid and restored when the synaptic block was alleviated by local application of calcium onto specific SC segments prior to SCA stimulation. Thus the SCA evoked lumbar rhythm involves synaptic activation of relay neurons in the SC cord. Functional activation of these relays depends on non-N-methyl-D-aspartate (NMDA) receptors because the lumbar rhythm was abolished when the non-NMDA receptor antagonist CNQX was added to the SC cord. By contrast, pharmacological block of the rhythmicity in the SC cord by specific antagonists of NMDA receptors and alpha1 and alpha2 adrenoceptors did not impair the SCA-induced lumbar rhythm. Midsagittal splitting experiments of parts of the SC and lumbar cord revealed that crossed and uncrossed ascending/propriospinal pathways are coactivated by SCA stimulation. We suggest that these pathways ascend onto the thoracolumbar cord through the lateral, ventrolateral, and ventral funiculi, because a complete block of the lumbar rhythm could only be obtained with a bilateral interruption of all of these funiculi. The relevance of our findings to the neural control of the rhythmogenic networks in the spinal cord is discussed.

Pattern generation in caudal-lumbar and sacrococcygeal segments of the neonatal rat spinal cord

The rhythmogenic capacity of the tail-innervating segments (L4-Co3) of the spinal cord was studied in isolated spinal cord and tail-spinal cord preparations of neonatal rats. Bath-applied serotonin/N-methyl-D-aspartate (NMDA) failed to produce a robust sacrococcygeal rhythmicity following midlumbar transection of the spinal cord. By contrast, a regular alternating left-right rhythm could be induced in the sacrococcygeal segments by application of noradrenaline (NA) or NA and NMDA before and after midlumbar transection of the cord. This rhythm was accelerated with the concentration of NMDA and was blocked by alpha1 or alpha2 adrenoceptor antagonists. The efferent bursts induced by NA/NMDA were accompanied by rhythmic tail movements produced by alternating activation of the left and right tail muscles and by coactivation of flexors, extensors, and abductors on a given side of the tail. This coactivation implies that reciprocal inhibitory pathways were not activated during the rhythm. Lesion experiments revealed that the rhythmogenic circuitry is distributed along all or most of the sacrococcygeal segments. The NA/NMDA-induced rhythm persisted in the isolated sacrococcygeal (S1-Co3), sacral (S1-S4), coccygeal (Co1-Co3), and smaller isolated regions of the sacrococcygeal cord. The rhythm also could be maintained in longitudinally split sacrococcygeal hemicords in which flexor, extensor, and abductor motoneurons are coactivated. This finding indicates that neither left/right nor flexor/extensor inhibitory interactions are required for rhythmogenesis in the sacrococcygeal cord. A slow rhythm lacking the alternating left-right pattern was induced by NA/NMDA in tail-innervating caudal lumbar segments of isolated L4-Co3 preparations. This rhythm was independent of the concurrent sacrococcygeal rhythm and the activity pattern of the tail musculature and it does not seem to contribute to rhythmic tail movements under these conditions. Comparative studies of the rhythm produced in the isolated caudal lumbar, sacrococcygeal cord, and caudal thoracic-rostral lumbar segments revealed that the S1-Co3 rhythm was faster than the L4-L6 pattern and slower than the T6-L3 rhythm. It is suggested that the caudal lumbar and sacrococcygeal segments of the cord are normally driven by the faster rostral lumbar central pattern generators. The relevance of the findings described above to pattern generation in the mammalian spinal cord is discussed.

Effects of sacrocaudal spinal cord transection and transplantation of fetal spinal tissue on withdrawal reflexes of the tail

Reflex responses to electrocutaneous stimulation of the tail were characterized in awake cats, before and after transection of the spinal cord at sacrocaudal levels S3-Ca1. Consistent with effects of spinal transection at higher levels, postoperative cutaneous reflexes were initially depressed, and the tail was flaccid. Recovery ensued over the course of 70-90 days after sacrocaudal transection. Preoperative and chronic postlesion reflexes elicited by electrocutaneous stimulation were graded in amplitude as a function of stimulus intensity. Chronic postlesion testing of electrocutaneous reflexes revealed greater than normal peak amplitudes, peak latencies, total amplitudes (power), and durations, particularly for higher stimulus intensities. Thus, sacrocaudal transection produced effects representative of the spastic syndrome. In contrast, exaggerated reflex responsivity did not develop for a group of cats that received transplants of fetal spinal cord tissue within sacrocaudal transection cavities at the time of injury, in conjunction with long-term immunosuppression by cyclosporine. We conclude that gray matter replacement and potential neuroprotective actions of the grafts and/or immunosuppression prevent development of the spastic syndrome. This argues that the spastic syndrome does not result entirely from interruption of long spinal pathways.

Crossed and uncrossed projections to the cat sacrocaudal spinal cord: III. Axons expressing calcitonin gene-related peptide immunoreactivity

We have investigated the projection patterns of peptidergic small-diameter primary afferent fibers to the cat sacrocaudal spinal cord, a region associated with midline structures of the lower urogenital system and of the tail. Calcitonin gene-related peptide (CGRP)-immunoreactive (CGRP-IR) primary afferent fibers were observed within the superficial laminae, rostrally as the typical inverted U-shaped band that capped the separate dorsal horns (S1 to rostral S2) and caudally as a broad band that spanned the entire mediolateral extent of the fused dorsal horns (caudal S2 and caudal). Within the dorsal gray commissure, labeling was seen as a periodic vertical, midline band. CGRP-IR labeling was prevalent in an extensive mediolateral distribution at the base of the dorsal horn, originating from both lateral and medial collateral bundles that extend from the superficial dorsal horn. Some bundles, in part traveling within the dorsal commissure, conspicuously crossed the midline. In addition to the robust projection to the superficial dorsal horn, there was a more extensive distribution of CGRP-IR fibers within the deeper portions of the cat sacrocaudal dorsal horn than has been reported for other regions of the cat spinal cord. Presumably, these deep projections convey visceral information to projection or segmental neurons at the neck of the dorsal horn and in the region of the central canal. This deep distribution overlaps the reported projections of the pelvic and pudendal nerves. In addition, the contralateral projections of CGRP-IR fibers may form an anatomical substrate of the bilateral receptive fields for selective dorsal horn neurons. The density and variety of CGRP-IR projection patterns is a reflection of the functional attributes of the innervated structures.

Pattern generation in non-limb moving segments of the mammalian spinal cord

The ability of mammalian spinal cords to generate rhythmic motor patterns has been traditionally studied in hindlimb innervating segments of the spinal cord. The rhythmogenic capacity of these segments decreases substantially in the rostrocaudal direction so that the caudal lumbar segments are virtually incapable of producing the rhythm. Our recent studies of the sacrococcygeal segments of the neonatal rat spinal cord showed that these non-limb innervating segments have an intrinsic rhythmogenic capacity that is used to elicit rhythmic tail movements. The high viability of the sacrococcygeal segments, the specific behavior produced by them, and their simple functional organization, makes the isolated sacrocaudal network a new promising model for studies of neural automaticity in mammals. The present work summarizes the current knowledge on sacrococcygeal rhythmicity and discusses its functional implication.

The effect of pyramidal stimulation upon tail muscle motoneurons in the decerebrate cat

This study aimed to determine the effects of the corticospinal tract (CST) on the motoneurons innervating the tail muscles in cats. The stimulation of the pyramidal tract predominantly evoked excitatory postsynaptic potentials (EPSPs; 48/90 motoneurons: 53%). Single-pulse stimulation produced EPSPs in 18 of 48 motoneurons, but double shocks evoked postsynaptic potentials in most of the remaining cells (26/48). Monosynaptic excitatory connections between pyramidal tract fibers and tail motoneurons were confirmed in 4 motoneurons. Inhibitory postsynaptic potentials (IPSPs) were recorded from motoneurons innervating long tendinous tail muscles (7/90: 8%) and the shortest neuronal pathways of IPSPs were shown to be disynaptic pathways. Interactions between the CST and reflex pathways from low-threshold muscle and cutaneous afferents innervating the tail and hindlimbs were observed.

Sacrocaudal afferents induce rhythmic efferent bursting in isolated spinal cords of neonatal rats

The ability of mammalian spinal cords to generate rhythmic motor behavior in nonlimb moving segments was examined in isolated spinal cords of neonatal rats. Stimulation of sacrocaudal afferents (SCA) induced alternating left-right bursts in lumbosacral efferents and in tail muscles. On each side of the tail, flexors, extensors, and abductors were coactive during each cycle of activity. This rhythm originated mainly in the sacrocaudal region because it persisted in sacrocaudal segments after surgical removal of the thoracolumbar cord. Sacrocaudal commissural pathways were sufficient to maintain the left-right alternation of lumbar efferent bursts, because their timing was unaltered after a complete thoracolumbar hemisection. The lumbar rhythm originated in part from sacrocaudal activity ascending in lateral and ventrolateral funiculi, because efferent bursts in rostral lumbar segments were nearly abolished on a particular side by lesions of the lateral quadrant of the cord at the L(4)-L(5) junction. Intracellular recordings from S(2)-S(3) motoneurons, obtained during the rhythm, revealed the presence of phasic oscillations of membrane potential superimposed on a tonic depolarization. Bursts of spikes occurred on the depolarizing phases of the oscillation. Between these bursts the membrane input conductance increased, and hyperpolarizing drive potentials were revealed. The inhibitory drive and the decreased input resistance coincided with contralateral efferent bursts, suggesting that crossed pathways controlled it. Our studies indicate that pattern generators are not restricted to limb-moving spinal segments and suggest that regional specializations of pattern-generating circuitry and their associated interneurons are responsible for the different motor patterns produced by the mammalian spinal cord.