Similar hand shaping in reaching-for-food (skilled reaching) in rats and humans provides evidence of homology in release, collection, and manipulation movements

A Murine Model of Robotic Training to Evaluate Skeletal Muscle Recovery after Injury

PURPOSE

In vivo studies have suggested that motor exercise can improve muscle regeneration after injury. Nevertheless, preclinical investigations still lack reliable tools to monitor motor performance over time and to deliver optimal training protocols to maximize force recovery. Here, we evaluated the utility of a murine robotic platform (i) to detect early impairment and longitudinal recovery after acute skeletal muscle injury and (ii) to administer varying intensity training protocols to enhance forelimb motor performance.

METHODS

A custom-designed robotic platform was used to train mice to perform a forelimb retraction task. After an acute injury to bilateral biceps brachii muscles, animals performed a daily training protocol in the platform at high (HL) or low (LL) loading levels over the course of 3 wk. Control animals were not trained (NT). Motor performance was assessed by quantifying force, time, submovement count, and number of movement attempts to accomplish the task. Myofiber number and cross-sectional area at the injury site were quantified histologically.

RESULTS

Two days after injury, significant differences in the time, submovement count, number of movement attempts, and exerted force were observed in all mice, as compared with baseline values. Interestingly, the recovery time of muscle force production differed significantly between intervention groups, with HL group showing a significantly accelerated recovery. Three weeks after injury, all groups showed motor performance comparable with baseline values. Accordingly, there were no differences in the number of myofibers or average cross-sectional area among groups after 3 wk.

CONCLUSION

Our findings demonstrate the utility of our custom-designed robotic device for the quantitative assessment of skeletal muscle function in preclinical murine studies. Moreover, we demonstrate that this device may be used to apply varying levels of resistance longitudinally as a means manipulate physiological muscle responses.

Pronounced species divergence in corticospinal tract reorganization and functional recovery after lateralized spinal cord injury favors primates

Experimental and clinical studies suggest that primate species exhibit greater recovery after lateralized compared to symmetrical spinal cord injuries. Although this observation has major implications for designing clinical trials and translational therapies, advantages in recovery of nonhuman primates over other species have not been shown statistically to date, nor have the associated repair mechanisms been identified. We monitored recovery in more than 400 quadriplegic patients and found that functional gains increased with the laterality of spinal cord damage. Electrophysiological analyses suggested that corticospinal tract reorganization contributes to the greater recovery after lateralized compared with symmetrical injuries. To investigate underlying mechanisms, we modeled lateralized injuries in rats and monkeys using a lateral hemisection, and compared anatomical and functional outcomes with patients who suffered similar lesions. Standardized assessments revealed that monkeys and humans showed greater recovery of locomotion and hand function than did rats. Recovery correlated with the formation of corticospinal detour circuits below the injury, which were extensive in monkeys but nearly absent in rats. Our results uncover pronounced interspecies differences in the nature and extent of spinal cord repair mechanisms, likely resulting from fundamental differences in the anatomical and functional characteristics of the motor systems in primates versus rodents. Although rodents remain essential for advancing regenerative therapies, the unique response of the primate corticospinal tract after injury reemphasizes the importance of primate models for designing clinically relevant treatments.

Motivational state, reward value, and Pavlovian cues differentially affect skilled forelimb grasping in rats

Motor skills represent high-precision movements performed at optimal speed and accuracy. Such motor skills are learned with practice over time. Besides practice, effects of motivation have also been shown to influence speed and accuracy of movements, suggesting that fast movements are performed to maximize gained reward over time as noted in previous studies. In rodents, skilled motor performance has been successfully modeled with the skilled grasping task, in which animals use their forepaw to grasp for sugar pellet rewards through a narrow window. Using sugar pellets, the skilled grasping task is inherently tied to motivation processes. In the present study, we performed three experiments modulating animals’ motivation during skilled grasping by changing the motivational state, presenting different reward value ratios, and displaying Pavlovian stimuli. We found in all three studies that motivation affected the speed of skilled grasping movements, with the strongest effects seen due to motivational state and reward value. Furthermore, accuracy of the movement, measured in success rate, showed a strong dependence on motivational state as well. Pavlovian cues had only minor effects on skilled grasping, but results indicate an inverse Pavlovian-instrumental transfer effect on movement speed. These findings have broad implications considering the increasing use of skilled grasping in studies of motor system structure, function, and recovery after injuries.

Development and use of an animal model to study post-traumatic stiffness and contracture of the elbow

Post-traumatic joint stiffness (PTJS) of the elbow is a debilitating condition that poses unique treatment challenges. While previous research has implicated capsular tissue in PTJS, much regarding the development and progression of this condition remains unknown. The objective of this study was to develop an animal model of post-traumatic elbow contracture and evaluate its potential for studying the etiology of PTJS. The Long-Evans rat was identified as the most appropriate species/breed for development due to anatomical and functional similarities to the human elbow joint. Two surgical protocols of varying severity were utilized to replicate soft tissue damage seen in elbow subluxation/dislocation injuries, including anterior capsulotomy and lateral collateral ligament transection, followed by 6 weeks of unilateral joint immobilization. Following sacrifice, flexion-extension mechanical joint testing demonstrated decreased range-of-motion and increased stiffness for injured-immobilized limbs compared to control and sham animals, where functional impact correlated with severity of injury. Histological evaluation showed increased cellularity, adhesion, and thickness of capsule tissue in injured limbs, consistent with clinical evidence. To our knowledge, this is the first animal model capable of examining challenges unique to the anatomically and biomechanically complex elbow joint. Future studies will use this animal model to investigate mechanisms responsible for PTJS.

A Proposal for a Rat Model of Spinal Cord Injury Featuring the Rubrospinal Tract and its Contributions to Locomotion and Skilled Hand Movement

Spinal cord injury and repair is a dynamic field of research. The development of reliable animal models of traumatic spinal cord injury has been invaluable in providing a wealth of information regarding the pathological consequences and recovery potential of this condition. A number of injury models have been instrumental in the elaboration and the validation of therapeutic interventions aimed at reversing this once thought permanent condition. In general, the study of spinal cord injury and repair is made difficult by both its anatomical complexity and the complexity of the behavior it mediates. In this perspective paper, we suggest a new model for spinal cord investigation that simplifies problems related to both the functional and anatomical complexity of the spinal cord. We begin by reviewing and contrasting some of the most common animal models used for investigating spinal cord dysfunction. We then consider two widely used models of spinal deficit-recovery, one involving the corticospinal tracts (CTS) and the other the rubrospinal tract (RST). We argue that the simplicity of the function of the RST makes it a useful model for studying the cord and its functional repair. We also reflect on two obstacles that have hindered progress in the pre-clinical field, delaying translation to the clinical setup. The first is recovery of function without reconnection of the transected descending fibers and the second is the use of behavioral paradigms that are not under the control of the descending fiber pathway under scrutiny.

Intersegmental Coordination in the Kinematics of Prehension Movements of Macaques

The most popular model to explain how prehensile movements are organized assumes that they comprise two "components", the reaching component encoding information regarding the object's spatial location and the grasping component encoding information on the object's intrinsic properties such as size and shape. Comparative kinematic studies on grasping behavior in the humans and in macaques have been carried out to investigate the similarities and differences existing across the two species. Although these studies seem to favor the hypothesis that macaques and humans share a number of kinematic features it remains unclear how the reaching and grasping components are coordinated during prehension movements in free-ranging macaque monkeys. Twelve hours of video footage was filmed of the monkeys as they snatched food items from one another (i.e., snatching) or collect them in the absence of competitors (i.e., unconstrained). The video samples were analyzed frame-by-frame using digitization techniques developed to perform two-dimensional post-hoc kinematic analyses of the two types of actions. The results indicate that only for the snatching condition when the reaching variability increased there was an increase in the amplitude of maximum grip aperture. Besides, the start of a break-point along the deceleration phase of the velocity profile correlated with the time at which maximum grip aperture occurred. These findings suggest that macaques can spatially and temporally couple the reaching and the grasping components when there is pressure to act quickly. They offer a substantial contribution to the debate about the nature of how prehensile actions are programmed.

Translational studies exploring neuroplasticity associated with motor skill learning and the regulatory role of the dopamine system

Cerebral palsy (CP) is a heterogeneous group of neurodevelopmental disorders associated with lifelong motor impairment and disability. Current intervention programmes aim to capitalize on the neuroplasticity of the undamaged part of the brain to improve motor functions, by engaging individuals in active motor learning and training. In this review, we highlight recent animal studies (1) exploring cellular and molecular mechanisms contributing to neuroplasticity during motor training, (2) assessing the functional role of the mesocortical dopaminergic system in motor skill learning, and (3) exploring the impact of naturally occurring genetic variation in dopamine-related gene expression on the acquisition and performance of fine motor skills. Finally, the potential influence of the dopamine system on the outcome of motor learning interventions in cerebral palsy is discussed.

Patterned, but not tonic, optogenetic stimulation in motor thalamus improves reaching in acute drug-induced Parkinsonian rats

High-frequency deep brain stimulation (DBS) in motor thalamus (Mthal) ameliorates tremor but not akinesia in Parkinson's disease. The aim of this study was to investigate whether there are effective methods of Mthal stimulation to treat akinesia. Glutamatergic Mthal neurons, transduced with channelrhodopsin-2 by injection of lentiviral vector (Lenti.CaMKII.hChR2(H134R).mCherry), were selectively stimulated with blue light (473 nm) via a chronically implanted fiber-optic probe. Rats performed a reach-to-grasp task in either acute drug-induced parkinsonian akinesia (0.03-0.07 mg/kg haloperidol, s.c.) or control (vehicle injection) conditions, and the number of reaches was recorded for 5 min before, during, and after stimulation. We compared the effect of DBS using complex physiological patterns previously recorded in the Mthal of a control rat during reaching or exploring behavior, with tonic DBS delivering the same number of stimuli per second (rate-control 6.2 or 1.8 Hz, respectively) and with stimulation patterns commonly used in other brain regions to treat neurological conditions (tonic 130 Hz, theta burst (TBS), and tonic 15 Hz rate-control for TBS). Control rats typically executed >150 reaches per 5 min, which was unaffected by any of the stimulation patterns. Acute parkinsonian rats executed <20 reaches, displaying marked akinesia, which was significantly improved by stimulating with the physiological reaching pattern or TBS (both p < 0.05), whereas the exploring and all tonic patterns failed to improve reaching. Data indicate that the Mthal may be an effective site to treat akinesia, but the pattern of stimulation is critical for improving reaching in parkinsonian rats.

Reduced reach-related modulation of motor thalamus neural activity in a rat model of Parkinson's disease

Motor thalamus (Mthal) is a key node in the corticobasal ganglia (BG) loop that controls complex, cognitive aspects of movement. In Parkinson's disease (PD), profound alterations in neuronal activity occur in BG nuclei and cortex. Because Mthal is located between these two structures, altered Mthal activity has been assumed to underlie the pathogenesis of PD motor deficits. However, to date, inconsistent changes in neuronal firing rate and pattern have been reported in parkinsonian animals. Moreover, although a distinct firing pattern of Mthal neurons, called low-threshold calcium spike bursts (LTS bursts), is observed in reduced preparations, it remains unknown whether they occur or what their role might be in behaving animals. We recorded Mthal spiking activity in control and unilateral 6-hydroxydopamine lesioned rats performing a skilled forelimb-reaching task. We show for the first time that Mthal firing rate in control rats is modulated in a temporally precise pattern during reach-to-grasp movements, with a peak at the time of the reach-end and troughs just before and after it. We identified LTS-like events on the basis of LTS burst characteristics. These were rare, but also modulated, decreasing in incidence just after reach-end. The inhibitory modulations in firing rate and LTS-like events were abolished in parkinsonian rats. These data confirm that nigrostriatal dopamine depletion is accompanied by profound and specific deficits in movement-related Mthal activity. These changes would severely impair Mthal contributions to motor program development in motor cortex and are likely to be an important factor underlying the movement deficits of PD.

An experimental task to examine the mirror system in rats

The mirror system in the brain is considered to be a neural basis of sociality, but previous studies have been limited to primates. Here we report an experimental task to examine the mirror system in rats. We show that a rat could reach to a pellet and grasp and eat it in front of another rat that was observing the reaching, which indicates that the task will enable us to start exploring the rat mirror system.

Rearing conditions differently affect the motor performance and cerebellar morphology of prenatally stressed juvenile rats

The cerebellum is one of the most vulnerable parts of the brain to environmental changes. In this study, the effect of diverse environmental rearing conditions on the motor performances of prenatally stressed juvenile rats and its reflection to the cerebellar morphology were investigated. Prenatally stressed Wistar rats were grouped according to different rearing conditions (Enriched=EC, Standard=SC and Isolated=IC) after weaning. Six weeks later, male and female offspring from different litters were tested behaviorally. In rotarod and string suspension tests, females gained better scores than males. Significant gender and housing effects were observed especially on the motor functions requiring fine skills with the best performance by enriched females, but the worst by enriched males. The susceptibility of cerebellar macro- and micro-neurons to environmental conditions was compared using stereological methods. In female groups, no differences were observed in the volume proportions of cerebellar layers, soma sizes and the numerical densities of granule or Purkinje cells. However, a significant interaction between housing and gender was observed in the granule to Purkinje cell ratio of males, due to the increased numerical densities of the granule cells in enriched males. These data imply that proper functioning of the cerebellum relies on its well organized and evolutionarily conserved structure and circuitry. Although early life stress leads to long term behavioral and neurobiological consequences in the offspring, diverse rearing conditions can alter the motor skills of animals and synaptic connectivity between Purkinje and granular cells in a gender dependent manner.

Laminar-specific distribution of zinc: evidence for presence of layer IV in forelimb motor cortex in the rat

The rat is the most widely studied pre-clinical model system of various neurological and neurodegenerative disorders affecting hand function. Although brain injury to the forelimb region of the motor cortex in rats mostly induces behavioral abnormalities in motor control of hand movements, behavioral deficits in the sensory-motor domain are also observed. This questions the prevailing view that cortical layer IV, a recipient of sensory information from the thalamus, is absent in rat motor cortex. Because zinc-containing neurons are generally not found in pathways that run from the thalamus, an absence of zinc (Zn) in a cortical layer would be suggestive of sensory input from the thalamus. To test this hypothesis, we used synchrotron micro X-ray fluorescence imaging to measure Zn distribution across cortical layers. Zn maps revealed a heterogeneous layered Zn distribution in primary and secondary motor cortices of the forelimb region in the adult rat. Two wider bands with elevated Zn content were separated by a narrow band having reduced Zn content, and this was evident in two rat strains. The Zn distribution pattern was comparable to that in sensorimotor cortex, which is known to contain a well demarcated layer IV. Juxtaposition of Zn maps and the images of brain stained for Nissl bodies revealed a "Zn valley" in primary motor cortex, apparently starting at the ventral border of pyramidal layer III and ending at the close vicinity of layer V. This finding indicates the presence of a conspicuous cortical layer between layers III and V, i.e. layer IV, the presence of which previously has been disputed. The results have implications for the use of rat models to investigate human brain function and neuropathology, such as after stroke. The presence of layer IV in the forelimb region of the motor cortex suggests that therapeutic interventions used in rat models of motor cortex injury should target functional abnormalities in both motor and sensory domains. The finding is also critical for future investigation of the biochemical mechanisms through which therapeutic interventions can enhance neural plasticity, particularly through Zn dependent pathways.

Long-term functional recovery and compensation after cerebral ischemia in rats

Cerebral ischemia is one of the most common causes of disabilities in adults and leads to long-term motor and cognitive impairments with limited therapeutic possibilities. Treatment options have proven efficient in preclinical models of cerebral ischemia but have failed in the clinical setting. This limited translation may be due to the suitability of models used and outcomes measured as most studies have focused on the early period after injury with gross motor scales, which have limited correlation to the clinical situation. The aim of this study was to determine long-term functional outcomes after cerebral ischemia in rats, focusing on fine motor function, social and depressive behavior as clinically relevant measures. A secondary objective was to evaluate the effects of an anti-inflammatory treatment (interleukin-1 receptor antagonist (IL-1Ra)) on functional recovery and compensation. Infarct volume was correlated with long-term (25 days) impairments in fine motor skills, but not with emotional components of behavior. Motor impairments could not be detected using conventional neurological tests and only detailed analysis allowed differentiation between recovery and compensation. Acute systemic administration of IL-1Ra (at reperfusion) led to a faster and more complete recovery, but delayed (24h) IL-1Ra treatment had no effect. In summary functional assessment after brain injury requires detailed motor tests in order to address long-term impairments and compensation processes that are mediated by intact tissues. Functional deficits in skilled movement after brain injury represent ideal predictors of long-term outcomes and should become standard measures in the assessment of preclinical animal models.

Monkey see, monkey reach: action selection of reaching movements in the macaque monkey

Highly efficient systems are needed to link perception with action in the context of the highly complex environments in which primates move and interact. Another important component is, nonetheless, needed for action: selection. When one piece of fruit from a branch is being chosen by a monkey, many other pieces are within reach and visible: do the perceptual features of the objects surrounding a target determine interference effects? In humans, reaching to grasp a desired object appears to integrate the motor features of the objects which might become potential targets - a process which seems to be driven by inhibitory attention mechanisms. Here we show that non-human primates use similar mechanisms when carrying out goal-directed actions. The data indicate that the volumetric features of distractors are internally represented, implying that the basic cognitive operations allowing for action selection have deep evolutionary roots.

Low dose of valproate improves motor function after traumatic brain injury

BACKGROUND

Traumatic brain injuries (TBIs) are a major health care problem worldwide. Approximately 1.5 million new TBI cases occur annually in the United States, with mortality rates ranging between 35% and 40% in severe patients. Despite the incidence of these injuries and their substantial socioeconomic implications, no specific pharmacological intervention is available for clinical use. Several studies have indicated that 300 mg/kg or 400 mg/kg of valproate (VPA) exhibits neuroprotective effects in animal models. However, humans cannot tolerate high doses of VPA. This study aims to investigate whether 30 mg/kg of VPA administered to rats affects TBIs.

METHODS

We used a rat model to test the effects of 30 mg/kg of VPA on TBIs. Molecular identifications for histone acetylation and phosphorylation of cAMP response element-binding protein (CREB) and phosphorylated extracellular signal regulated kinase (ERK) were performed.

RESULTS

The results indicated that treating adult rats with VPA after TBIs significantly decreased the contusion volume and recovery of contusion-related skilled forelimb reaching deficits. Applying VPA also increased histone acetylation, p-ERK, and p-CREB expression in the brain. Furthermore, applying VPA reduced inflammation, glial fibrillary acidic protein activation, and apoptosis. Conclusion. This study found that 30 mg/kg of VPA assists in treating TBIs in rat models.

Different evolutionary origins for the reach and the grasp: an explanation for dual visuomotor channels in primate parietofrontal cortex

The Dual Visuomotor Channel Theory proposes that manual prehension consists of two temporally integrated movements, each subserved by distinct visuomotor pathways in occipitoparietofrontal cortex. The Reach is mediated by a dorsomedial pathway and transports the hand in relation to the target's extrinsic properties (i.e., location and orientation). The Grasp is mediated by a dorsolateral pathway and opens, preshapes, and closes the hand in relation to the target's intrinsic properties (i.e., size and shape). Here, neuropsychological, developmental, and comparative evidence is reviewed to show that the Reach and the Grasp have different evolutionary origins. First, the removal or degradation of vision causes prehension to decompose into its constituent Reach and Grasp components, which are then executed in sequence or isolation. Similar decomposition occurs in optic ataxic patients following cortical injury to the Reach and the Grasp pathways and after corticospinal tract lesions in non-human primates. Second, early non-visual PreReach and PreGrasp movements develop into mature Reach and Grasp movements but are only integrated under visual control after a prolonged developmental period. Third, comparative studies reveal many similarities between stepping movements and the Reach and between food handling movements and the Grasp, suggesting that the Reach and the Grasp are derived from different evolutionary antecedents. The evidence is discussed in relation to the ideas that dual visuomotor channels in primate parietofrontal cortex emerged as a result of distinct evolutionary origins for the Reach and the Grasp; that foveated vision in primates serves to integrate the Reach and the Grasp into a single prehensile act; and, that flexible recombination of discrete Reach and Grasp movements under various forms of sensory and cognitive control can produce adaptive behavior.

Ketogenic diet improves forelimb motor function after spinal cord injury in rodents

High fat, low carbohydrate ketogenic diets (KD) are validated non-pharmacological treatments for some forms of drug-resistant epilepsy. Ketones reduce neuronal excitation and promote neuroprotection. Here, we investigated the efficacy of KD as a treatment for acute cervical spinal cord injury (SCI) in rats. Starting 4 hours following C5 hemi-contusion injury animals were fed either a standard carbohydrate based diet or a KD formulation with lipid to carbohydrate plus protein ratio of 3:1. The forelimb functional recovery was evaluated for 14 weeks, followed by quantitative histopathology. Post-injury 3:1 KD treatment resulted in increased usage and range of motion of the affected forepaw. Furthermore, KD improved pellet retrieval with recovery of wrist and digit movements. Importantly, after returning to a standard diet after 12 weeks of KD treatment, the improved forelimb function remained stable. Histologically, the spinal cords of KD treated animals displayed smaller lesion areas and more grey matter sparing. In addition, KD treatment increased the number of glucose transporter-1 positive blood vessels in the lesion penumbra and monocarboxylate transporter-1 (MCT1) expression. Pharmacological inhibition of MCTs with 4-CIN (α-cyano-4-hydroxycinnamate) prevented the KD-induced neuroprotection after SCI, In conclusion, post-injury KD effectively promotes functional recovery and is neuroprotective after cervical SCI. These beneficial effects require the function of monocarboxylate transporters responsible for ketone uptake and link the observed neuroprotection directly to the function of ketones, which are known to exert neuroprotection by multiple mechanisms. Our data suggest that current clinical nutritional guidelines, which include relatively high carbohydrate contents, should be revisited.

Axonal remodeling of the corticospinal tract in the spinal cord contributes to voluntary motor recovery after stroke in adult mice

BACKGROUND AND PURPOSE

We sought to demonstrate the contribution of axonal remodeling of the corticospinal tract (CST) in the spinal cord to functional outcome after stroke.

METHODS

Bilateral pyramidotomy (BPT) or sham-BPT was performed in mice with transgenic yellow fluorescent protein labeling in the CST subjected to middle cerebral artery occlusion (MCAo). Foot-fault and single pellet reaching tests were performed 3 days after MCAo and weekly thereafter. Mice were euthanized at day 14 or 28 after stroke. Immunofluorescent staining for growth-associated protein-43 and Synaptophysin was performed on cervical sections.

RESULTS

Functional improvements were evident during the initial 14 days in both MCAo-sham-BPT and MCAo-BPT mice (P<0.01, versus day 3). Progressive recovery was present during the subsequent 14 days in MCAo-sham-BPT mice (P<0.001, versus day 14) but not in MCAo-BPT mice. In the stroke-affected cervical gray matter of MCAo-sham-BPT mice, growth-associated protein-43-Cy3 staining on CST axons were significantly increased at day 14 after stroke compared with normal mice (P<0.001), and CST axonal density and Synaptophysin-Cy3 staining of CST-yellow fluorescent protein axonal terminals were significantly increased at day 28 compared with day 14 after MCAo (P<0.001).

CONCLUSIONS

Our data demonstrate that voluntary motor recovery is associated with CST axonal outgrowth and synaptic formation in the denervated side of the spinal gray matter during the later phase after stroke, suggesting that the CST axonal plasticity in the spinal cord contributes to neurological recovery.

Getting a grip on the evolution of grasping in musteloid carnivorans: a three-dimensional analysis of forelimb shape

The ability to grasp and manipulate is often considered a hallmark of hominins and associated with the evolution of their bipedal locomotion and tool use. Yet, many other mammals use their forelimbs to grasp and manipulate objects. Previous investigations have suggested that grasping may be derived from digging behaviour, arboreal locomotion or hunting behaviour. Here, we test the arboreal origin of grasping and investigate whether an arboreal lifestyle could confer a greater grasping ability in musteloid carnivorans. Moreover, we investigate the morphological adaptations related to grasping and the differences between arboreal species with different grasping abilities. We predict that if grasping is derived from an arboreal lifestyle, then the anatomical specializations of the forelimb for arboreality must be similar to those involved in grasping. We further predict that arboreal species with a well-developed manipulation ability will have articulations that facilitate radio-ulnar rotation. We use ancestral character state reconstructions of lifestyle and grasping ability to understand the evolution of both traits. Finally, we use a surface sliding semi-landmark approach capable of quantifying the articulations in their full complexity. Our results largely confirm our predictions, demonstrating that musteloids with greater grasping skills differ markedly from others in the shape of their forelimb bones. These analyses further suggest that the evolution of an arboreal lifestyle likely preceded the development of enhanced grasping ability.

Analysis of skilled forelimb movement in rats: the single pellet reaching test and staircase test

Brain damage, stroke, and neurodegenerative diseases such as Parkinson's or Huntington's disease can cause severe motor deficits in skilled forelimb use in both humans and rats. These deficits are typically analyzed in a reach-to-eat paradigm. Skilled reaching in rats has been found to be a good model of human skilled reaching. Therefore, rats serve as an excellent tool to monitor the development of deficits after neurological insults or changes after medical intervention. The following protocols comprise two different tests of rat skilled reaching. The single pellet reaching test is a paradigm that involves detailed rating and analysis of qualitative aspects of the reaching movement itself. The staircase test is an objective, high-throughput reaching task that allows reaching success (number of pellets eaten) to be investigated in multiple rats at the same time. Both tests have been used extensively to investigate motor deficits and effects of treatment.

Complex movement topography and extrinsic space representation in the rat forelimb motor cortex as defined by long-duration intracortical microstimulation

Electrical stimulation of the motor cortex in the rat can evoke complex forelimb multi-joint movements, including movement of limb and paw. In this study, these movements have been quantified in terms of 3D displacement and kinematic variables of two markers positioned on the wrist and middle digits (limb and paw movement, respectively). Electrical microstimulation was applied to the motor cortex using a pulse train of 500 ms duration. Movements were measured using a high-resolution 3D optical system. Five classes of limb movements (abduction, adduction, extension, retraction, elevation) and four classes of paw movements (opening, closure, opening/closure sequence, supination) were described according to their kinematics. A consistent topography of these classes of movements was presented across the motor cortex together with a topography of spatial locations to which the paw was directed. In about one-half of cortical sites, a specific pattern of limb-paw movement combination did exist. Four categories of limb-paw movements resembling behavioral repertoire were identified: reach-shaping, reach-grasp sequence, bring-to-body, and hold-like movement. Overall, the forelimb motor region included: (1) a large caudal forelimb area dominated by reach-shaping movement representation; (2) a small rostral area containing reach-grasp sequence and bring-to-body movement representation; and (3) a more lateral portion where hold-like movement was represented. These results support the view that, in rats, the motor cortex controls forelimb movements at a relatively complex level and suggest that the orderly representation of complex movements and their dynamics/kinematics emerge from the principles of forelimb motor cortex organization.

Reach-to-grasp movements in Macaca fascicularis monkeys: the Isochrony Principle at work

Humans show a spontaneous tendency to increase the velocity of their movements depending on the linear extent of their trajectory in order to keep execution time approximately constant. Termed the isochrony principle, this compensatory mechanism refers to the observation that the velocity of voluntary movements increases proportionally with their linear extension. Although there is a wealth of psychophysical data regarding isochrony in humans, there is none regarding non-human primates. The present study attempts to fill that gap by investigating reach-to-grasp movement kinematics in free-ranging macaques. Video footage of monkeys grasping objects located at different distances was analyzed frame-by-frame using digitalization techniques. The amplitude of arm peak velocity was found to be correlated with the distance to be covered, and total movement duration remained invariant although target distances varied. Like in humans, the "isochrony principle" seems to be operative as there is a gearing down/up of movement velocity that is proportional to the distance to be covered in order to allow for a relatively constant movement duration. Based on a centrally generated temporal template, this mode of motor programming could be functional in macaques given the high speed and great instability of posture and joint kinematics characterizing their actions. The data presented here take research in the field of comparative motor control a step forward as they are based on precise measurements of spontaneous grasping movements by animals living/acting in their natural environment.

The rocky road to translation in spinal cord repair

Over the past 2 decades, the biological understanding of the mechanisms underlying structural and functional repair of the injured central nervous system has strongly increased. This has resulted in the development of multiple experimental treatment strategies with the collective aim of enhancing and surpassing the limited spontaneous recovery occurring in animal models and ultimately humans suffering from spinal cord or brain injuries. Several of these experimental treatments have revealed beneficial effects in animal models of spinal cord injury. With the exception of neurorehabilitative therapies, however, therapeutic interventions that enhance recovery are currently absent within the clinical realm of spinal cord injury. The present review surveys the prospects and challenges in experimental and clinical spinal cord repair. Major shortcomings in experimental research center on the difficulty of closely modeling human traumatic spinal cord injury in animals, the small number of investigations done on cervical spinal injury and tetraplegia, and the differences in lesion models, species, and functional outcome parameters used between laboratories. The main challenges in the clinical field of spinal cord repair are associated with the standardization and sensitivity of functional outcome measures, the definition of the inclusion/exclusion criteria for patient recruitment in trials, and the accuracy and reliability of an early diagnosis to predict subsequent neurological outcome. Research and clinical networks were recently created with the goal of optimizing animal studies and human trials. Promising clinical trials are currently in progress. The time has come to translate the biologic-mechanistic knowledge from basic science into efficacious treatments able to improve the conditions of humans suffering from spinal cord injury.

Brain repair in a unilateral rat model of Huntington's disease: new insights into impairment and restoration of forelimb movement patterns

Huntington's disease (HD) produces severe neurodegeneration in the striatum leading to disabling motor impairments, including the loss of control of skilled reaching movements. Fetal GABAergic transplants can physically replace the lost striatal cells but with only partial success in functional recovery. Here, we aimed to determine the extent and quality of the repair produced by fetal cell transplantation through an in-depth analysis of reaching behavior in the quinolinic acid-lesioned rat model of HD. Control, quinolinic acid-lesioned plus sham graft, and quinolinic acid-lesioned plus graft groups of rats were assessed in skilled reaching performance prior to and following lesion surgery and 3 months following injection of 400,000 fetal whole ganglionic eminence-derived cells into the striatum. This was compared to their performance in two more rudimentary tests of motor function (the adjusting step and vibrissae-evoked hand-placing tests). Grafted rats demonstrated a significant improvement in reaching success rate (graft +59%, shamTX +3%). Importantly, the quality of reaching behavior, including all components of the movement, was fully restored with no identifiable differences in the normal behavior shown by control rats. Postmortem immunohistochemical examination verified the survival of large intrastriatal grafts, and Fluoro-Gold tracing indicated appropriate outgrowth to the globus pallidus. Our study illustrates for the first time the detailed analysis of qualitative improvement of motor function following brain repair in a rat model of HD. The results demonstrate significant improvements not only in gross movements but also in the skilled motor patterns lost during HD. Fetal GABAergic cell transplantation showed a demonstrable ability to restore motor function to near normal levels, such that there were few differences from intact control animals, an effect not observed in standard tests of motor function.

Closing the gap between clinic and cage: sensori-motor and cognitive behavioural testing regimens in neurotoxin-induced animal models of Parkinson's disease

Animal models that make use of chemical toxins to adversely affect the nigrostriatal dopaminergic pathway of rodents and primates have contributed significantly towards the development of symptomatic therapies for Parkinson's disease (PD) patients. Although their use in developing neuro-therapeutic and -regenerative compounds remains to be ascertained, toxin-based mammalian and a range of non-mammalian models of PD are important tools in the identification and validation of candidate biomarkers for earlier diagnosis, as well as in the development of novel treatments that are currently working their way into the clinic. Toxin models of PD have and continue to be important models to use for understanding the consequences of nigrostriatal dopamine cell loss. Functional assessment of these models is also a critical component for eventual translational success. Sensitive behavioural testing regimens for assessing the extent of dysfunction exhibited in the toxin models, the degree of protection or improvement afforded by potential treatment modalities, and the correlation of these findings with what is observed clinically in PD patients, ultimately determines whether a potential treatment moves to clinical trials. Here, we review existing published work that describes the use of such behavioural outcome measures associated with toxin models of parkinsonism. In particular, we focus on tests assessing sensorimotor and cognitive function, both of which are significantly and progressively impaired in PD.

Can motor volition be extracted from the spinal cord?

Background

Spinal cord injury (SCI) results in the partial or complete loss of movement and sensation below the level of injury. In individuals with cervical level SCI, there is a great need for voluntary command generation for environmental control, self-mobility, or computer access to improve their independence and quality of life. Brain-computer interfacing is one way of generating these voluntary command signals. As an alternative, this study investigates the feasibility of utilizing descending signals in the dorsolateral spinal cord tracts above the point of injury as a means of generating volitional motor control signals.

Methods

In this work, adult male rats were implanted with a 15-channel microelectrode array (MEA) in the dorsolateral funiculus of the cervical spinal cord to record multi-unit activity from the descending pathways while the animals performed a reach-to-grasp task. Mean signal amplitudes and signal-to-noise ratios during the behavior was monitored and quantified for recording periods up to 3 months post-implant. One-way analysis of variance (ANOVA) and Tukey’s post-hoc analysis was used to investigate signal amplitude stability during the study period. Multiple linear regression was employed to reconstruct the forelimb kinematics, i.e. the hand position, elbow angle, and hand velocity from the spinal cord signals.

Results

The percentage of electrodes with stable signal amplitudes (p-value < 0.05) were 50% in R1, 100% in R2, 72% in R3, and 85% in R4. Forelimb kinematics was reconstructed with correlations of R² > 0.7 using tap-delayed principal components of the spinal cord signals.

Conclusions

This study demonstrated that chronic recordings up to 3-months can be made from the descending tracts of the rat spinal cord with relatively small changes in signal characteristics over time and that the forelimb kinematics can be reconstructed with the recorded signals. Multi-unit recording technique may prove to be a viable alternative to single neuron recording methods for reading the information encoded by neuronal populations in the spinal cord.

The use of rodent skilled reaching as a translational model for investigating brain damage and disease

Neurological diseases, including Parkinson's disease, Huntington's disease, and brain damage caused by stroke, cause severe motor impairments. Deficits in hand use are one of the most debilitating motor symptoms and include impairments in body posture, forelimb movements, and finger shaping for manipulating objects. Hand movements can be formally studied using reaching tasks, including the skilled reaching task, or reach-to-eat task. For skilled reaching, a subject reaches for a small food item, grasps it with the fingers, and places it in the mouth for eating. The human movement and its associated deficits can be modeled by experimental lesions to the same systems in rodents which in turn provide an avenue for investigating treatments of human impairments. Skilled reaching movements are scored using three methods: (1) end point measures of attempts and success, (2) biometric measures, and (3) movement element rating scales derived from formal descriptions of movement. The striking similarities between human and rodent reaching movements allow the analysis of the reach-to-eat movement to serve as a powerful tool to generalize preclinical research to clinical conditions.

A system for automated tracking of motor components in neurophysiological research

In the study of motor systems it is often necessary to track the movements of an experimental animal in great detail to allow for interpretation of recorded brain signals corresponding to different control signals. This task becomes increasingly difficult when analyzing complex compound movements in freely moving animals. One example of a complex motor behavior that can be studied in rodents is the skilled reaching test where animals are trained to use their forepaws to grasp small food objects, in many ways similar to human hand use. To fully exploit this model in neurophysiological research it is desirable to describe the kinematics at the level of movements around individual joints in 3D space since this permits analyses of how neuronal control signals relate to complex movement patterns. To this end, we have developed an automated system that estimates the paw pose using an anatomical paw model and recorded video images from six different image planes in rats chronically implanted with recording electrodes in neuronal circuits involved in selection and execution of forelimb movements. The kinematic description provided by the system allowed for a decomposition of reaching movements into a subset of motor components. Interestingly, firing rates of individual neurons were found to be modulated in relation to the actuation of these motor components suggesting that sets of motor primitives may constitute building blocks for the encoding of movement commands in motor circuits. The designed system will, thus, enable a more detailed analytical approach in neurophysiological studies of motor systems.

Three-dimensional motion analysis of postural adjustments during over-ground locomotion in a rat model of Parkinson's disease

Postural instability, a symptom of Parkinson's disease (PD) patients, leads to frequent falls and difficulty in forward motion during gait. These motor deficits are mainly caused by neurodegenerative processes in the brain leading to reduced levels of the neurotransmitter dopamine. Postural studies involving animal models of PD are mainly based on movement scores or descriptive approaches to discerning differences in behaviour or function. Our aim was to describe postural adjustments in a rat model of PD utilising a quantitative three dimensional motion analysis technique during gait to investigate the effects of unilateral dopamine depletion on rat locomotion while walking on beams of varying widths (wide, narrow and graduated). Tail orientation, limb positions on the beam, range of motion and kinematic waveforms of the Roll, Pitch and Yaw of male Lister Hooded rats were investigated using passive markers placed in locations that were representative of their body axis. Hemiparkinsonian rats moved on the wide beam with a significantly higher Roll range of motion coupled with a positively biased Roll kinematic waveform during one gait cycle. While walking on the narrow beam they displayed an increased use of the ledge and placed their tail towards the right. These results are brought about by the rats' inability to shift body posture using the impaired limb. Our data demonstrate that marker-based motion capture can provide an effective and simple approach to quantifying postural adjustments for rat models of PD.

Feed-forward control of preshaping in the rat is mediated by the corticospinal tract

Rats are used to model human corticospinal tract (CST) injury and repair. We asked whether rats possess the ability to orient their paw to the reaching target and whether the CST mediates this skill, as it does in primates. To test this ability, called preshaping, we trained rats to reach for pieces of pasta oriented either vertically or horizontally. We measured paw angle relative to the target and asked whether rats used target information attained before contact to preshape the paw, indicating feed-forward control. We also determined whether preshaping improved with practice. We then selectively lesioned the CST in the medullary pyramid contralateral to the reaching forepaw to test whether preshaping relies on the CST. Rats significantly oriented their paw to the pasta orientation before contact, demonstrating feed-forward control. Both preshaping and reaching efficiency improved with practice, while selective CST lesion abrogated both. The loss of preshaping was greatest for pasta oriented vertically, suggesting loss of supination, as seen with human CST injury. The degree of preshaping loss strongly correlated with the amount of skill acquired at baseline, suggesting that the CST mediates the learned component of preshaping. Finally, the amount of preshaping lost after injury strongly correlated with reduced retrieval success, showing an important functional consequence for preshaping. We have thus demonstrated, for the first time, preshaping in the rat and dependence of this skill on the CST. Understanding the basis for this skill and measuring its recovery after injury will be important for studying higher-level motor control in rats.

Deficits in fine motor skills in a genetic animal model of ADHD

Background

In an attempt to model some behavioral aspects of Attention Deficit/Hyperactivity Disorder (ADHD), we examined whether an existing genetic animal model of ADHD is valid for investigating not only locomotor hyperactivity, but also more complex motor coordination problems displayed by the majority of children with ADHD.

Methods

We subjected young adolescent Spontaneously Hypertensive Rats (SHRs), the most commonly used genetic animal model of ADHD, to a battery of tests for motor activity, gross motor coordination, and skilled reaching. Wistar (WIS) rats were used as controls.

Results

Similar to children with ADHD, young adolescent SHRs displayed locomotor hyperactivity in a familiar, but not in a novel environment. They also had lower performance scores in a complex skilled reaching task when compared to WIS rats, especially in the most sensitive measure of skilled performance (i.e., single attempt success). In contrast, their gross motor performance on a Rota-Rod test was similar to that of WIS rats.

Conclusion

The results support the notion that the SHR strain is a useful animal model system to investigate potential molecular mechanisms underlying fine motor skill problems in children with ADHD.