Strain and locomotor speed affect over-ground locomotion in intact rats

A variety of animal models for neurological disease and injury exist and locomotor performance is an important outcome parameter in studies employing these models. The CatWalk, an automated quantitative gait analysis method is a method to study over-ground locomotor performance in large groups of animals. In the present study, we used the CatWalk which allowed us to investigate strain differences in over-ground locomotion in three commonly used strains of laboratory rat (i.e. Lewis, Wistar and Sprague-Dawley rats) based on objective data-analysis in a large number of animals. The present results revealed marked strain differences on the static paw parameters; base-of-support, and the relative paw position. Furthermore, strain differences were noted on the static parameter stride length and the dynamic parameters stance-, swing- and stepcycle duration, which are due logically to morphological differences between strains. The parameters related to coordination did not reveal any differences between the strains. Furthermore, the swing duration and the cruciate and alternate patterns i.e. regular step patterns Ca ("cruciate" pattern type a) and Ab ("alternate" pattern type b) were shown to be differentially affected by the locomotor speed. We conclude that differences in gait traits exist between the three laboratory rat strains investigated and several of the examined gait parameters showed strain dependent interdependency with locomotor speed.     

Videoanalysis of chemokinesis: characterization of speed, persistence and orientation in an agarose assay

Time-lapse video recording and off-line computer analysis were used to characterize the chemokinetic behavior of individual human neutrophils migrating in an agarose assay. When neutrophils were stimulated with an isotropic concentration of formyl-methionyl-leucyl-phenylalanine (fMLP), they migrated with a mean speed of 9.6 micron per min and oriented at random. The ratio of net displacement to total distance travelled (persistence of locomotion) was 0.66, indicating that neutrophils maintained some directional persistence even in the absence of a gradient of fMLP. The speed and persistence of locomotion index were correlated because both faster and slower cells had high persistence, while only slower cells had low persistence. The orientation angle was independent of both speed and persistence of locomotion. These are the first reported direct measurements of the chemokinetic locomotion of neutrophils using the agarose assay.     

Relating appendicular skeletal variation of sigmodontine rodents to locomotion modes in a phylogenetic context

Sigmodontinae rodents constitute the second‐largest subfamily among mammals. Alongside the taxonomic diversity, they are also ecologically diverse, exhibiting a wide array of locomotion modes, with semifossorial, terrestrial, semiaquatic, scansorial, arboreal, and saltatorial forms. To understand the ecomorphologic aspects that allow these rodents to display such locomotion diversity, we analyzed 35 qualitative characters of the appendicular skeleton (humerus, ulna, radius, scapula, femur, tibia, ilium, ischium and pubis) in 795 specimens belonging to 64 species, 34 genera and 10 tribes, representing all locomotion modes assigned to this subfamily. We performed a statistical analysis based upon the coefficient of trait differentiation to test the congruence of character states and the different locomotion modes. We also mapped characters states in a molecular phylogeny in order to reconstruct ancestral states and to evaluate how appendicular characters evolved within main lineages of Sigmodontinae radiation under a phylogenetic framework. The statistical analyses revealed six characters related to specific locomotion modes, except terrestrial. The mapping and parsimony ancestral states reconstruction identified two characters with phylogenetical signal and eight characters that are exclusively or more frequently recorded in certain modes of locomotion, four of them also detected by the statistical analysis. Notwithstanding the documented morphological variation, few changes characterize the transition to each of the locomotion modes, at least regarding the appendicular skeleton. This finding corroborates previous results that showed that sigmodontines exhibit an all‐purpose appendicular morphology that allows them to use and explore a great variety of habitats.     

High frequency stimulation of the subthalamic nucleus improves speed of locomotion but impairs forelimb movement in Parkinsonian rats

The subthalamic nucleus (STN) plays an important role in motor and non-motor behavior in Parkinson's disease, but its involvement in gait functions is largely unknown. In this study, we investigated the role of the STN on gait in a rat model of PD using the CatWalk method. Parkinsonian rats received bilateral high frequency stimulation (HFS) with different stimulation amplitudes of the STN. Rats were rendered parkinsonian by bilateral injections of 6-hydroxydopamine (6-OHDA) into the striatum. One group of 6-OHDA animals was implanted bilaterally with stimulation electrodes at the level of the STN. Stimulations were performed at 130 Hz (frequency), 60 micros (pulse width) and varying amplitudes of 0, 3, 30 and 150 microA. Rats were evaluated in an automated quantitative gait analysis method (CatWalk method). After behavioral evaluations, rats were killed and the brains processed for histological stainings to determine the impact of the dopaminergic lesion (tyrosine hydroxylase immunohistochemistry) and the localization of the electrode tip (hematoxylin-eosin histochemistry). Results show that bilateral 6-OHDA infusion significantly decreased (70%) the number of dopaminergic cells in the substantia nigra pars compacta (SNc). Due to 6-OHDA treatment, the gait parameters changed considerably. There was a general slowness. The most pronounced effects were seen at the level of the hind paws. Due to implantation of STN electrodes the step pattern changed. STN electrical stimulation improved the general slowness but induced slowing of the forelimb movement. Furthermore, we found that HFS with a medium amplitude significantly changed speed, the so-called dynamic aspect of gait. The static features of gait were only significantly influenced with low amplitude. Remarkably, STN stimulation affected predominantly the forepaws/limbs.     

Analysis of the National Toxicology Program data on in vitro genetic toxicity tests using multivariate statistical methods

A series of multivariate statistical methods have been usedto explore the results of a set of four in vitro short-termtests (STT) on 73 chemicals reported by the US National ToxicologyProgram (NTP). Cluster analysis showed that the mouse lymphomamutation (MLY) and sister-chromatid exchange (SCE) were similarin performance, as were the Salmonella (STY) and chromosomalaberration test (CHA). The lack of association between testsusing the same genetic end-point or at the same phylogeneticlevel found in previous analyses was confirmed in this study.Factor analysis was used to derive a scale of genetic damage.This measure was contrasted with rodent carcinogenicity; onlya limited association was found (rank correlation coefficient,rs = 0.32). Linear discriminant analysis was used to study whetherthe STTs could be used to complement one another. The combinationof STY with the other STTs did not improve significantly theprediction of rodent carcinogenicity of STY alone. In the entireset of chemicals, 33% were negative in STY and positive in atleast two other STT, and 11% was negative in STY and positivein the three other tests. SCE and MLY were complementary toSTY for identifying the most genotoxic chemicals, but CHA wasnot a useful complement. The presence of potential electrophilicsites in the chemicals was highly correlated with the STY results,but did not improve the ability of STY to identify genotoxicchemicals or predict rodent carcinogens. In conclusion, theother in vitro STTs did not complement STY for predicting carcinogenicity,but were an important complement for describing the potentialgenotoxicity of chemicals.     

Locomotion through apertures when wider space for locomotion is necessary: adaptation to artificially altered bodily states

The objective of this study is to describe the adaptability of the central nervous system to safely cross a narrow aperture when the space required for passage is transiently extended with external objects under different locomotor constraints. In one of four locomotion forms (normal walking, walking while holding a 63-cm horizontal bar with or without rotating the shoulders to cross a door opening, and wheelchair use), nine participants were asked to pass through an aperture created by two doors (the relative aperture widths were 1.02, 1.10, and 1.20 times their maximum horizontal dimension under each form of locomotion) without a collision. The kinematic analyses showed that, when the participants rotated their shoulders while walking and holding a bar, virtually the same locomotor patterns as those during normal walking were observed: shoulder rotation was regulated well in response to the width of an aperture, and no collisions occurred. When shoulder rotations were restricted while walking and holding a bar or using a wheelchair, a large reduction in the speed of movement was observed as the participants approached the door, and, furthermore, the modulation in speed was dependent on the width of the aperture. In addition, the participants crossed at the center of aperture more accurately; nevertheless, collision sometimes occurred (more frequently, during wheelchair use). These findings reveal that movement constraints on shoulder rotation are likely to be a critical factor in determining whether quick and successful adaptation takes place.     

Direction of Causation Between Shared and Non-Shared Environmental Factors

Determining the direction of causation between two related variables is an interesting and challenging problem. A simple regression model is a frequently used statistical tool to find out whether a dependent variable is significantly predicted by an independent variable; however using a simple regression model cannot determine the direction of causation, because the model fit takes no account of this direction. As an approach to this problem, non-normal structural equation modeling (nnSEM; Shimizu and Kano, J Stat Plan Inference 138:3483–3491, 2008) using higher order moments (third, fourth,…) as well as first and second order moments, can be useful. This method enables us to determine the direction of causation using goodness of fit, even for a simple regression model. In this paper, nnSEM is applied to behavior genetics, in particular, to the genetic simplex model. In this context, nnSEM enables us to determine the direction of causation between C (shared environment) factors and between E (non-shared environment) factors. The efficiency of this method is illustrated by simulation studies and the analysis of real longitudinal twin data. Edited by Stacey Cherny.     

Visually induced gait deviations during different locomotion speeds

Optic flow is essential for the perception of self motion and the control of path integration during locomotion. Inverting prisms oriented 15 degrees off vertical in the roll plane were used to experimentally distort optic flow during locomotion. Depending on the direction in which the prisms were rotated, optic flow was diagonally upward to the right or upward to the left. A reproducible deviation of gait toward the direction of perceived optic flow was found in ten healthy subjects. This deviation is explained to be a gait deviation that compensates for misleading perceived self motion induced by optic flow. The amount of deviation was dependent on locomotion speed. When walking slowly (about 1 m/s), mean deviation was 0.22+/-0.08 m/s to the right and -0.18+/-0.08 m/s to the left for right and left, respectively, diagonal prism orientation. Deviation was significantly less when running (about 3 m/s) with mean deviations of 0.05+/-0.03 m/s and -0.06+/-0.03 m/s, respectively (ANOVA, P<0.01). It is assumed that path integration during running is largely achieved by highly automated spinal programs operating independently of sensory control. In contrast, walking is more dependent on afferent and reafferent visual control. Thus, the experiments show that visual control of locomotion is direction specific and dependent on optic-flow-induced vection. It becomes less influential with increasing speed of locomotion, e.g., when walking in contrast to running.     

Computer-aided analysis of locomotion data

This paper describes a set of data reduction programs that are used to manipulate a data base derived from cine film records of cats moving on a treadmill or overground.The current system runs on a CDC 6400 computer. The programs are coded primarily in FORTRAN IV. They permit convenient searching for user-specified subclasses of data, performing statistical analyses, displaying plots of data clusters and locomotion patterns, and conditioning the data for subsequent analysis with SPSS.Some basic concepts in locomotion analysis are reviewed, and examples of the data analysis and classification capabilities of the system are presented.     

Dopamine D3 receptor knock-out mice display deficits in locomotor sensitization after chronic morphine administration

Locomotor sensitization is the progressive and enduring enhancement of locomotion induced by stimulants such as drugs, which alter rodent locomotion in a long-standing manner. The dopamine D3 receptor has been reported to play a role in morphine addiction. The aim of the present study was to investigate the role of dopamine D3 receptor in the morphine induced locomotor sensitization using dopamine D3 receptor knock-out mice. The dopamine D3 receptor knock-out mice did not display an enhanced behavioral response to acute morphine administration or develop an increased rate of locomotor sensitization to intermittent morphine administration. When 2 mg/kg naloxone was co-administered with 10 mg/kg morphine, morphine-induced locomotion sensitization in wild-type mice was significantly blocked while the locomotion in the D3 receptor knock-out mice was decreased. Then the wild-type mice were administered with dopamine D3 antagonist nafadotride. It was found that co-administration of morphine with nafadotride could effectively suppress the level of morphine induced behavioral sensitization. It was concluded that a loss of the dopamine D3 receptor gene may inhibit acute morphine induced hyperlocomotor activity and chronic morphine induced behavioral sensitization.     

Stagewise estimation for regression analysis when independent variables are latent variables

Psychological research often deals with psychological constructs that cannot be directly measured. Thus independent variables of regression analysis for an observable dependent variable are sometimes latent variables (factors) that are defined independently of the dependent variable. In this study we pointed out the problem associated with the use of factor analysis for the combined set of dependent variable and independent variables in such a cases; that is, the derived factors are different from those originally intended, and the true regression parameters cannot be reproduced. We proposed a stagewise estimation method to solve the problem. This method estimates parameters of measurement equation in the first stage, and then estimates parameters of structural equation in the second stage. Our proposed method enables calculation of standard errors of estimators using Bootstrapping method. Numerical studies showed that the proposed method improves the estimation efficiency over the conventional methods, and provides estimates which are robust with respect to misspecification of model.     

Optical modulation of locomotion and energy expenditure at preferred transition speed

The effect of optical flow on locomotion stability and efficiency was evaluated at preferred walk-run transition speed (PTS). Seven participants were instructed to locomote (walk or run) at PTS, while looking at the end of a three-dimensional virtual corridor projected on a large screen. Three experimental conditions of optical flow were tested: optical flow velocity consistent with locomotion speed (C), optical flow velocity twice faster (F) or slower (S) than locomotion speed. They were contrasted with a control static flow condition. Transitions between patterns were more frequent in (C) than in the other conditions, suggesting that optical flow influenced the stability of locomotion. Moreover, kinematic analyses revealed a stronger destabilization of gait in (F), accompanied by a decrease in energy expenditure in that condition. These results suggest that optical flow influenced both energetic and gait components at PTS, encouraging the exploration and stabilization of the most economic behavior. The mutual dependency of the visual system, the locomotor system and the cardio-respiratory system is emphasized.

The role of inhibitory neurotransmission in locomotor circuits of the developing mammalian spinal cord

Neuronal circuits generating the basic coordinated limb movements during walking of terrestrial mammals are localized in the spinal cord. In these neuronal circuits, called central pattern generators (CPGs), inhibitory synaptic transmission plays a crucial part. Inhibitory synaptic transmission mediated by glycine and GABA is thought to be essential in coordinated activation of muscles during locomotion, in particular, controlling temporal and spatial activation patterns of muscles of each joint of each limb on the left and right side of the body. Inhibition is involved in other aspects of locomotion such as control of speed and stability of the rhythm. However, the precise roles of neurotransmitters and their receptors mediating inhibitory synaptic transmission in mammalian spinal CPGs remain unclear. Moreover, many of the inhibitory interneurones essential for output pattern of the CPG are yet to be identified. In this review, recent advances on these issues, mainly from studies in the developing rodent spinal cord utilizing electrophysiology, molecular and genetic approaches are discussed.     

An analysis of performance in human locomotion

This paper reports an analysis of the principles underlying human performances on the basis of the work initiated by Pietro Enrico di Prampero. Starting from the concept that the maximal speed that can be attained over a given distance with a given locomotion mode is directly proportional to the maximal sustainable power and inversely proportional to the energy cost of locomotion, we discuss the maximal powers (and capacities) of anaerobic (lactic and alactic) and aerobic metabolisms and the factors that limit them, and the factors affecting the energy cost of various locomotion modes. Special attention is given to the role of air resistance and frictional forces. Finally, computation of performance speed is discussed along the approach originally developed by di Prampero.     

Kinematic analysis of chemotaxis of fresh and stored neutrophils

When neutrophils are isolated from the circulation the first function to begin to deteriorate is chemotaxis. To characterize the loss of chemotaxis that occurs during storage, a computer-assisted video motion analysis of neutrophils responding to formyl-methionyl-leucyl-phenylalanine (FMLP) was used in an agarose assay. The chemotactic speed, velocity, and orientation angle were measured, and a persistence of locomotion index (velocity/speed) and chemotropic index (cosine of the orientation angle) were calculated for fresh neutrophils and neutrophils stored in plasma at 20 to 22 degrees C for 24 hours. The data reveal that: (1) the frequency distribution of speed for individual stored cells had a different shape than that of fresh cells owing to a subpopulation of stored cells (approximately 35 percent) which migrated at a slower mean speed; (2) the frequency distribution of orientation for fresh cells is not normally distributed and contains a subpopulation (approximately nine percent of the total) of cells which orient at random in a gradient; (3) the precision of orientation of the majority of stored cells is comparable to that of fresh cells, but approximately 35 percent of the stored cells orient at random in a chemoattractant gradient; (4) neither the persistence index nor the orientation of both fresh and stored cells were correlated with speed; (5) the chemotropic index and persistence index are correlated, and this correlation is not altered by storage suggesting that stored cells which show decreased persistence also show a decreased chemotropic index. It is proposed that neutrophils respond to a gradient of fMLP with either fast, persistent, accurately oriented locomotion or slower, less persistent, randomly oriented locomotion. In addition to those neutrophils which do not migrate in response to fMLP, it is proposed that there are two subpopulations of motile neutrophils. Storage at 20 to 22 degrees C induces shifts between these three modes of behavior.     

The developmental order of bipedal locomotion in the jerboa (Jaculus orientalis): Pivoting,creeping, quadrupedalism,and bipedalism

This is a brief report on the postnatal development of locomotor behavior in the jerboa, a bipedal kangaroo-like rodent. Observations on one litter revealed three intriguing aspects of the postnatal development of the jerboa compared to other rodent species: (a) The weaning period is extended, (b) the developmental stage in which pivoting is the main locomotor activity is extended, and (c) locomotor performance is differently related to anatomical growth. Jerboa pups are born after a long pregnancy compared to other altricial rodents, but possess typical neonate morphology: The hindlegs and forelegs are of the same length, the tail is short, skin pigmentation and fur are absent, and the eyes and ears are closed. However, the neonate jerboa differs from other rodents in posture and activity: Its hindlegs extend laterally to the same side of the pelvis and it creeps with stepping of only the forelegs that drag the trunk while the hindlegs remain passive. Pivoting and creeping are preserved in the jerboa for 4 weeks, as compared to a few days in other species. Afterwords, quadruped locomotion emerges and the jerboa pup walks while folding its long hindlegs to the same functional length as the forelegs. Bipedal locomotion is acquired only in postnatal Day 47. These observations illustrate that further studies of the development of the jerboa, as well as other bipedal rodent species, may provide new perspectives on anatomy, histology, physiology, and motor behavior during postnatal development. ©1997 John Wiley & Sons, Inc. Dev Psychobiol 31: 137–142, 1997     

Amphetamine sensitization: nonassociative and associative components

Rats, pretreated with amphetamine (AMPH, 1 mg/kg) or saline for 2 weeks, were challenged with AMPH (0.5 mg/kg) or saline following 1 week of abstinence, and locomotion was measured. In Experiments 1 and 2, the pretreatment occurred in various contexts (home cage, novel box, test box). Sensitization was observed only when pretreatment context and test context were the same; a context switch abolished sensitization. When rats anesthetized with chloral hydrate were pretreated with AMPH, sensitization was completely dependent on the pretreatment, but independent of context. This "zero context" condition isolated the basal level of excitation attributable to unconditioned neural change to determine the role of contextual input to be a modulator that enhances or inhibits sensitization.     

Gait performance is not influenced by working memory when walking at a self-selected pace

Gait performance exhibits patterns within the stride-to-stride variability that can be indexed using detrended fluctuation analysis (DFA). Previous work employing DFA has shown that gait patterns can be influenced by constraints, such as natural aging or disease, and they are informative regarding a person’s functional ability. Many activities of daily living require concurrent performance in the cognitive and gait domains; specifically working memory is commonly engaged while walking, which is considered dual-tasking. It is unknown if taxing working memory while walking influences gait performance as assessed by DFA. This study used a dual-tasking paradigm to determine if performance decrements are observed in gait or working memory when performed concurrently. Healthy young participants (N = 16) performed a working memory task (automated operation span task) and a gait task (walking at a self-selected speed on a treadmill) in single- and dual-task conditions. A second dual-task condition (reading while walking) was included to control for visual attention, but also introduced a task that taxed working memory over the long term. All trials involving gait lasted at least 10 min. Performance in the working memory task was indexed using five dependent variables (absolute score, partial score, speed error, accuracy error, and math error), while gait performance was indexed by quantifying the mean, standard deviation, and DFA α of the stride interval time series. Two multivariate analyses of variance (one for gait and one for working memory) were used to examine performance in the single- and dual-task conditions. No differences were observed in any of the gait or working memory dependent variables as a function of task condition. The results suggest the locomotor system is adaptive enough to complete a working memory task without compromising gait performance when walking at a self-selected pace.     

Differential effects of absent visual feedback control on gait variability during different locomotion speeds

Healthy persons exhibit relatively small temporal and spatial gait variability when walking unimpeded. In contrast, patients with a sensory deficit (e.g., polyneuropathy) show an increased gait variability that depends on speed and is associated with an increased fall risk. The purpose of this study was to investigate the role of vision in gait stabilization by determining the effects of withdrawing visual information (eyes closed) on gait variability at different locomotion speeds. Ten healthy subjects (32.2 ± 7.9 years, 5 women) walked on a treadmill for 5-min periods at their preferred walking speed and at 20, 40, 70, and 80 % of maximal walking speed during the conditions of walking with eyes open (EO) and with eyes closed (EC). The coefficient of variation (CV) and fractal dimension (α) of the fluctuations in stride time, stride length, and base width were computed and analyzed. Withdrawing visual information increased the base width CV for all walking velocities (p < 0.001). The effects of absent visual information on CV and α of stride time and stride length were most pronounced during slow locomotion (p < 0.001) and declined during fast walking speeds. The results indicate that visual feedback control is used to stabilize the medio-lateral (i.e., base width) gait parameters at all speed sections. In contrast, sensory feedback control in the fore-aft direction (i.e., stride time and stride length) depends on speed. Sensory feedback contributes most to fore-aft gait stabilization during slow locomotion, whereas passive biomechanical mechanisms and an automated central pattern generation appear to control fast locomotion.     

Expression of emotion in the kinematics of locomotion

Here, we examine how different emotions—happiness, fear, sadness and anger—affect the kinematics of locomotion. We focus on a compact representation of locomotion properties using the intersegmental law of coordination (Borghese et al. in J Physiol 494(3):863–879, 1996), which states that, during the gait cycle of human locomotion, the elevation angles of the thigh, shank and foot do not evolve independently of each other but form a planar pattern of co-variation. This phenomenon is highly robust and has been extensively studied. The orientation of the plane has been correlated with changes in the speed of locomotion and with reduction in energy expenditure as speed increases. An analytical model explaining the conditions underlying the emergence of this plane and predicting its orientation reveals that it suffices to examine the amplitudes of the elevation angles of the different segments along with the phase shifts between them (Barliya et al. in Exp Brain Res 193:371–385, 2009). We thus investigated the influence of different emotions on the parameters directly determining the orientation of the intersegmental plane and on the angular rotation profiles of the leg segments, examining both the effect of changes in walking speed and effects independent of speed. Subjects were professional actors and naïve subjects with no training in acting. As expected, emotions were found to strongly affect the kinematics of locomotion, particularly walking speed. The intersegmental coordination patterns revealed that emotional expression caused additional modifications to the locomotion patterns that could not be explained solely by a change in speed. For all emotions except sadness, the amplitude of thigh elevation angles changed from those in neutral locomotion. The intersegmental plane was also differently oriented, especially during anger. We suggest that, while speed is the dominant variable allowing discrimination between different emotional gaits, emotion can be reliably recognized in locomotion only when speed is considered together with these kinematic changes.