Single Pellet Retrieval Task Research Articles

Hyperactivation of MEK1 in cortical glutamatergic neurons results in projection axon deficits and aberrant motor learning.

Abnormal extracellular signal-regulated kinase 1/2 (ERK1/2, encoded by Mapk3 and Mapk1, respectively) signaling is linked to multiple neurodevelopmental diseases, especially the RASopathies, which typically exhibit ERK1/2 hyperactivation in neurons and non-neuronal cells. To better understand how excitatory neuron-autonomous ERK1/2 activity regulates forebrain development, we conditionally expressed a hyperactive MEK1 (MAP2K1) mutant, MEK1S217/221E, in cortical excitatory neurons of mice. MEK1S217/221E expression led to persistent hyperactivation of ERK1/2 in cortical axons, but not in soma/nuclei. We noted reduced axonal arborization in multiple target domains in mutant mice and reduced the levels of the activity-dependent protein ARC. These changes did not lead to deficits in voluntary locomotion or accelerating rotarod performance. However, skilled motor learning in a single-pellet retrieval task was significantly diminished in these MEK1S217/221E mutants. Restriction of MEK1S217/221E expression to layer V cortical neurons recapitulated axonal outgrowth deficits but did not affect motor learning. These results suggest that cortical excitatory neuron-autonomous hyperactivation of MEK1 is sufficient to drive deficits in axon outgrowth, which coincide with reduced ARC expression, and deficits in skilled motor learning. Our data indicate that neuron-autonomous decreases in long-range axonal outgrowth may be a key aspect of neuropathogenesis in RASopathies.

Decoding Single-Pellet Retrieval Task From Local Field Potentials in Pre- and Post-Stroke Motor Areas: Insights Into Interhemispheric Connectivity Difference

Decoding Single-Pellet Retrieval Task From Local Field Potentials in Pre- and Post-Stroke Motor Areas: Insights Into Interhemispheric Connectivity Difference

Markerless tracking enables distinction between strategic compensation and functional recovery after spinal cord injury

Injuries to the cervical spinal cord represent around 60% of all spinal cord injuries (SCIs). A major priority for patients with cervical SCIs is the recovery of any hand or arm function. The similarities between human and rodent “reach-to-eat movements” indicate that analyzing mouse forelimb reaching behavior may be a method of identifying clinically relevant treatments for people with cervical SCIs. One popular behavioral measure of forelimb functional recovery comprises the Single Pellet Retrieval Task (SPRT). The most common outcome measure for this task, however (percentage of pellets successfully retrieved), cannot readily distinguish between recovery of pre-injury motor patterns and strategic compensation. Our objective was to establish outcome measures for the SPRT that are readily adopted by different investigators and capable of measuring recovery of limb function after SCI. We used a simple semi-automated approach to high-speed tracking of mouse forepaw movements during pellet retrieval. DeepLabCut™, a machine learning based computer vision software package, was used to track individual features of the mouse forepaw, allowing a more detailed assessment of reaching behavior after SCI. Interestingly, kinematic analysis of movements pre- and post-injury illuminated persistent deficits in specific features of the reaching motor patterns, namely pronation and paw trajectory, that were poorly correlated with recovery of the ability to successfully retrieve pellets. Thus, we have developed an inexpensive method for detailed analysis of mouse reach-to-eat behavior following SCI. Further, our results suggest that binary success/fail outcome measures primarily assess an animal's ability to compensate rather than a restoration of normal function in the injured pathways and networks.

Compensatory neuromuscular junction adaptations of forelimb muscles in focal cortical ischemia in rats.

IntroductionUpper limb movements are affected frequently by brain ischemia (BI). Mechanisms involved in recovery and compensatory movements have developed several studies. However, less attention is given to skeletal muscles, where neuromuscular junction (NMJ) has an important role on muscle tropism and functional performance.MethodsAnimals were divided into two groups: control (C) and BI. Then, animals were skilled to perform single‐pellet retrieval task, following these procedures: habituation, shaping, and single‐pellet retrieval task. BI was induced using stereotaxic surgery in order to apply endothelin‐1 in motor cortex, representative of movements of dominant paw. Reaching task performance was evaluated by single‐pellet retrieval task 1 day before BI induction, 4 and 15 days after BI induction. After that, biceps, triceps, fingers flexor, and extensor muscles were extracted. NMJ was assessed in morphometric characteristics (total area, total perimeter, and feret). Muscle fiber cross‐sectional area and connective tissue percentage were also evaluated for characterization. Student's t test was used for comparisons between C and BI groups. Tau Kendall's correlation was applied among variables from BI group.ResultsAn increase in all NMJ morphometric parameters, as well as increase of atrophy and fibrosis in BI group compared with C. There was a high level of direct correlation between mean values of NMJ morphometry with percentage of success in reaching task in BI group.ConclusionBrain ischemia‐induced NMJ compensatory expansion, muscle atrophy, and fibrosis in forelimb muscles that are related to reaching performance.

Reaching task performance is associated to neuromuscular junction adaptations in rats with induced diabetes mellitus.

Upper limb performance is affected by diabetes mellitus (DM). Neuromuscular junction (NMJ) is a key structure to understand the relationship between performance and morphology in DM. The aim of the study was to analyze NMJ plasticity due to DM in an animal model and its relationship with the function of forelimbs in rats. Twelve Wistar rats were divided into control (C) and DM groups. Animals were trained to perform a grasping task, following procedures of habituation, shaping, and reaching task. DM was induced using streptozotocin. Forelimb neuromuscular performance for dexterity was evaluated one day before DM induction and five weeks following induction. After that, biceps, triceps, and finger flexors and extensors were removed. Connective tissue and muscle fiber cross-sectional area (CSA) were measured. NMJ was assessed by its morphometric characteristics (area, perimeter, and maximum diameter), using ImageJ software. Motor performance analyses were made using single pellet retrieval task performance test. Student’s t-test was used for comparisons between groups. A significant decrease in all NMJ morphometric parameters was observed in the DM group compared with the C group. Results showed that DM generated NMJ retraction in muscles involved in a reaching task. These alterations are related to signs of muscular atrophy and to poor reaching task performance. In conclusion, induced DM caused NMJ retraction and muscular atrophy in muscles involved in reaching task performance. Induced DM caused significantly lower motor performance, especially in the final moments of evaluation, when DM compromised the tropism of the muscular tissue.

Focal Malonate Injection Into the Internal Capsule of Rats as a Model of Lacunar Stroke.

Background: Stroke is the first cause of disability in adults in western countries. Infarct of the internal capsule (IC) may be related to motor impairment and poor prognosis in stroke patients. Functional deficits due to medium-sized infarcts are difficult to predict, except if the specific site of the lesion is taken into account. None of the few pre-clinical models recapitulating this type of stroke has shown clear, reproducible, and long-lasting sensorimotor deficits. Here, we developed a rat model of lacunar infarction within the IC, key structure of the sensorimotor pathways, by precise injection of malonate.Methods: The mitochondrial toxin malonate was injected during stereotactic surgery into the IC of rat brains. Rats were divided in three groups: two groups received malonate solution at 1.5M (n = 12) or at 3M (n = 10) and a sham group (n = 5) received PBS. Three key motor functions usually evaluated following cerebral lesion in the clinic strength, target reaching, and fine dexterity were assessed in rats by a forelimb grip strength test, a skilled reaching task (staircase) for reaching and dexterity, and single pellet retrieval task. Sensorimotor functions were evaluated by a neurological scale. Live brain imaging, using magnetic resonance (MRI), and post-mortem immunohistochemistry in brain slices were performed to characterize the lesion site after malonate injection.Results: Intracerebral injection of malonate produced a 100% success rate in inducing a lesion in the IC. All rats receiving the toxin, regardless the dose injected, had similar deficits in strength and dexterity of the contralateral forepaw, and showed significant neurological impairment. Additionally, only partial recovery was observed with respect to strength, while no recovery was observed for dexterity and neurological deficit. MRI and immunostaining show volume size and precise location of the lesion in the IC, destruction of axonal structures and Wallerian degeneration of fibers in the area above the injection site.Conclusions: This pre-clinical model of lacunar stroke induces a lesion in the IC with measurable and reproducible sensorimotor deficits, and limited recovery with stabilization of performance 2 weeks post-injury. Future therapies in stroke may be successfully tested in this model.

Axotomized Corticospinal Neurons Increase Supra-Lesional Innervation and Remain Crucial for Skilled Reaching after Bilateral Pyramidotomy

Skilled upper limb function heavily depends on the corticospinal tract. After bilateral lesions to this tract, motor control is disrupted but can be partially substituted by other motor systems to allow functional recovery. However, the remaining roles of motor cortex and especially of axotomized corticospinal neurons(CSNs) are not well understood. Using the single pellet retrieval task in adult rats, we induced significant recovery of skilled reaching after bilateral pyramidotomy by rehabilitative reaching training, and show that reach-related motor cortex activity, recorded in layer V, topographically reappeared shortly after axotomy. Using a chemogenetic neuronal silencing technique, we found that axotomized CSNs retained a crucial role for the recovered pellet retrieval success. The axotomized CSNs sprouted extensively in the red nucleus supplying new innervation to its magnocellular and parvocellular parts. Specific silencing of the rubrospinal tract(RST) also strongly abolished the recovered pellet retrieval success, suggesting a role of this cervically projecting nucleus in relaying cortical motor control. In summary, our results show that after bilateral corticospinal axotomy, motor cortex still actively engages in forelimb motor control and axotomized CSNs are crucially involved in the recovered reaching movement, potentially by relaying motor control via the RST.

Array Focal Cortical Stimulation Enhances Motor Function Recovery and Brain Remodeling in a Rat Model of Ischemia

Using a new microelectrode array implanted into the cranial window employing a new stimulation protocol, we investigated the effects of the implanted electrode arrays on both motor map plasticity and neural regeneration in a rodent model of stroke. Rats were pretrained on single-pellet retrieval task, then received focal ischemic infarction and microelectrode arrays implantation. Rats in the cortical stimulation (CS) group received daily electrical stimulation (1 hour each day) for 14 days whereas animals in the no stimulation (NS) group did not receive electrical stimulation and only underwent motor mapping. Behavior data and residual electrophysiological mapping on stimulation days 2, 5, 8, 11, and 14 were statistically compared. Neural reorganization in pathological with glial fibrillary acidic protein and microtubule-associated protein-2 was performed. Rats in CS group showed greater increases in reaching accuracy and significantly decreased in motor threshold than rats in NS group. Immunohistochemical study has shown that array focal CS suppressed inflammatory response, and enhanced dendritic sprouting in the peri-infarction cortex. The present findings support the viability of epidural CS with microelectrode arrays for enhancing motor function after stroke and monitoring the neural reorganization of residual electrophysiological mapping after motor cortex injury.

Motor cortex is functionally organized as a set of spatially distinct representations for complex movements.

There is a long-standing debate regarding the functional organization of motor cortex. Intracortical microstimulation (ICMS) studies have provided two contrasting views depending on the duration of stimulation. In the rat, short-duration ICMS reveals two spatially distributed forelimb movement representations, the rostral forelimb area (RFA) and caudal forelimb area (CFA), eliciting identical movements. In contrast, long-duration ICMS reveals spatially distributed, complex, multijoint movement areas, with grasping found exclusively in the rostral area and reach-shaping movements of the arm located in the caudal area. To provide corroboration for which interpretation is correct, we selectively inactivated the RFA/grasp area during the performance of skilled forelimb behaviors using a reversible cortical cooling deactivation technique. A significant impairment of grasping in the single-pellet retrieval task and manipulations of pasta was observed during cooling deactivation of the RFA/grasp area, but not the CFA/arm area. Our results indicate a movement-based, rather than a muscle-based, functional organization of motor cortex, and provide evidence for a conserved homology of independent grasp and reach circuitry shared between primates and rats.

Cortical electrical stimulation promotes neuronal plasticity in the peri-ischemic cortex and contralesional anterior horn of cervical spinal cord in a rat model of focal cerebral ischemia

PurposeThis study evaluated the effect of cortical electrical stimulation (CES) on function recovery, dendritic plasticity, astrogliosis, and neuron recruitment in the peri-ischemic cortex (PIC) and contralesional anterior horn of cervical spinal cord (CSC) in a rat model of focal cerebral ischemia. Materials and methods: Rats were pre-trained on single pellet retrieval task, then received focal ischemic lesions and electrodes implantation. Seven days after surgery, rats received CES (CES group) or no stimulation (NS group) during 18 days of training. Behavior data on stimulation days 2, 4, 6, 8, 10, 12, 14, 16 and 18 were pooled for use. Immunohistochemical investigations for microtubule-associated protein 2 (MAP-2), glial fibrillary acidic protein (GFAP) and neuronal nuclei antigen (NeuN) were performed. Results: Rats in CES group showed greater functional recovery of the impaired forelimb compared to the NS group. Moreover, the functional improvement coincided with a significant increase in MAP-2-immunoreactive dendritic surface density in PIC and CSC (P=0.011; P=0.005, respectively). CES group had a significant decrease in GFAP-immunoreactive astrocytic surface density in PIC and CSC (P=0.039; P=0.013, respectively). In the immunoassaying of NeuN, there was no significant difference between the two groups in PIC and CSC (P=0.834, P=0.782, respectively). Conclusion: CES can promote dendritic plasticity and reduce astrogliosis in the PIC and CSC in a rat model of focal cerebral ischemia. CES is still an appealing method for post-stroke rehabilitation provided that viability of pathways is evaluated presurgically.

Breeder and batch-dependent variability in the acquisition and performance of a motor skill in adult Long–Evans rats

Reaching tasks are popular tools for investigating the neural mechanisms of motor skill learning and recovery from brain damage in rodents, but there is considerable unexplained variability across studies using these tasks. We investigated whether breeder, batch effects, experimenter, time of year, weight and other factors contribute to differences in the acquisition and performance of a skilled reaching task, the single pellet retrieval task, in adult male Long–Evans hooded rats. First, we retrospectively analyzed task acquisition and performance in rats from different breeding colonies that were used in several studies spanning a 3 year period in our laboratory. Second, we compared reaching variables in age-matched rats from different breeders that were trained together as a batch by the same experimenters. All rats had received daily training on the reaching task until they reached a criterion of successful reaches per attempt. We found significant breeder-dependent differences in learning rate and final performance level. This was found even when age-matched rats from different breeders were trained together by the same experimenters. There was also significant batch-to-batch variability within rats from the same breeder trained by the same experimenter. Other factors, including weight, paw preference and the experimenter, were not as strong or consistent in their contributions to differences across studies. The breeder and batch effects found within the same rat strain may reflect genetic and environmental influences on the neural substrates of motor skill learning. This is an important consideration when comparing baseline performance across studies and for controlling variability within studies.

Motor Skill Training, but not Voluntary Exercise, Improves Skilled Reaching After Unilateral Ischemic Lesions of the Sensorimotor Cortex in Rats

Background and Purpose . Exercise and rehabilitative training each have been implicated in the promotion of restorative neural plasticity after cerebral injury. Because motor skill training induces synaptic plasticity and exercise increases plasticity-related proteins, we asked if exercise could improve the efficacy of training on a skilled motor task after focal cortical lesions. Methods . Female young and middle-aged rats were trained on the single-pellet retrieval task and received unilateral ischemic sensorimotor cortex lesions contralateral to the trained limb. Rats then received both, either, or neither voluntary running and/or rehabilitative training for 5 weeks beginning 5 days postlesion. Motor skill training consisted of daily practice of the impaired forelimb in a tray-reaching task. Exercised rats had free access to running wheels for 6 h/day. Reaching function was periodically probed using the single-pellet retrieval task. Results. In young adults, motor skill training significantly enhanced skilled reaching recovery compared to controls. However, exercise did not significantly enhance performance when administered alone or in combination with skill training. There was also no major benefit of exercise in older rats. Additionally, there were no effects of exercise in a measure of coordinated forelimb placement (the foot-fault test) or in immunocytochemical measures of several plasticity-related proteins in the motor cortex. Conclusions. In young and middle-aged animals, exercise did not improve motor skill training efficacy following ischemic lesions. Practicing motor skills more effectively improved recovery of these skills than did exercise. It remains possible that an alternative manner of administering exercise would be more effective.

Abnormalities in skilled reaching movements are improved by peripheral anesthetization of the less-affected forelimb after sensorimotor cortical infarcts in rats

Unilateral damage to sensorimotor cortical (SMC) regions can profoundly impair skilled reaching function in the contralesional forelimb. Such damage also results in impairments and compensatory changes in the less-affected/ipsilesional forelimb, but these effects remain poorly understood. Furthermore, anesthetization of the ipsilesional hand in humans with cerebral infarcts has been reported to produce transient functional improvements in the paretic hand [Floel A, Nagorsen U, Werhahn KJ, Ravindran S, Birbaumer N, Knecht S, et al. Influence of somatosensory input on motor function in patients with chronic stroke. Ann Neurol 2004;56:206–12; Voller B, Floel A, Werhahn KJ, Ravindran S, Wu CW, Cohen LG. Contralateral hand anesthesia transiently improves poststroke sensory deficits. Ann Neurol 2006;59:385–8]. One aim of this study was to sensitively assay the bilateral effects of unilateral ischemic SMC damage on performance of a unimanual skilled reaching task (the single pellet retrieval task) that rats had acquired pre-operatively with each forelimb. The second aim was to determine whether partially recovered contralesional reaching function is influenced by anesthetization of the ipsilesional forelimb. Unilateral SMC lesions were found to result in transient ipsilesional impairments in reaching success and significant ipsilesional abnormalities in reaching movements compared with sham-operates. There were major contralesional reaching impairments which improved during a 4 week training period, but movements remained significantly abnormal. Anesthetization of the ipsilesional forelimb with lidocaine at this time attenuated the contralesional movement abnormalities. These findings indicate that unilateral ischemic SMC lesions impair skilled reaching behavior in both forelimbs. Furthermore, after partial recovery in the contralesional forelimb, additional improvements can be induced by transient anesthetization of the ipsilesional forelimb. This is consistent with the effects of unilateral anesthetization in humans which have been attributed to the modulation of competitive interhemispheric interactions. The present findings suggest that such interactions are also likely to influence skilled reaching function in rats.

D-Amphetamine enhances skilled reaching after ischemic cortical lesions in rats

Unilateral sensorimotor cortical (SMC) lesions in rats impair reaching and grasping movements of the contralateral forelimb. These impairments can be improved using motor rehabilitative training on a skilled reaching task, but the training may be far from sufficient to return animals to pre-lesion levels of performance. Because d-amphetamine (AMPH) has been found to promote neuroplastic responses to injury and to be very beneficial when combined with some (but not all) types of rehabilitative training, we asked in this experiment whether it could improve the efficacy of rehabilitative training in skilled reaching. Ten to 14 days after unilateral ischemic (endothelin-1 induced) lesions of the SMC, adult rats were given a 3-week regimen of AMPH (1 mg/kg) coupled with daily rehabilitative training on a skilled reaching task, the single pellet retrieval task. AMPH treatment not only dramatically improved reaching performance compared with saline-injected controls, the AMPH treated rats surpassed pre-lesion levels of performance by the end of the rehabilitative training period. The greater performance in AMPH compared to saline-treated rats was still evident at 1 month, but not at 2 and 3 months, after the end of rehabilitative training. Thus, AMPH treatment can greatly enhance the efficacy of rehabilitative training on a skilled reaching task after unilateral SMC lesions, but alternate injection and training regimes may be needed to produce permanent improvements.