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

Modulation of neural co-firing to enhance network transmission and improve motor function after stroke

Stroke is a leading cause of disability. While neurotechnology has shown promise for improving upper limb recovery after stroke, efficacy in clinical trials has been variable. Our central thesis is that to improve clinical translation, we need to develop a common neurophysiological framework for understanding how neurotechnology alters network activity. Our perspective discusses principles for how motor networks, both healthy and those recovering from stroke, subserve reach-to-grasp movements. We focus on neural processing at the resolution of single movements, the timescale at which neurotechnologies are applied, and discuss how this activity might drive long-term plasticity. We propose that future studies should focus on cross-area communication and bridging our understanding of timescales ranging from single trials within a session to across multiple sessions. We hope that this perspective establishes a combined path forward for preclinical and clinical research with the goal of more robust clinical translation of neurotechnology.

Different training patterns at recovery stage improve cognitive function in ischemic stroke rats through regulation of the axonal growth inhibitor pathway

Running wheel exercise training (RWE) and skilled reaching training (SRT) are physical training approaches with positive effects on cognitive function. However, few studies have compared the different effects of these exercises on long-term memory, and their mechanism remains unknown. This study investigated the effects of SRT and RWE, at the recovery stage, on the cognitive function of transient middle cerebral artery occlusion (tMCAO) rats and explored their association with NgR1/Rho-A/ROCK/LOTUS/LGI1 signaling. Adult Sprague-Dawley rats (n = 55) were divided into four groups after pretraining: SRT, RWE, tMCAO, and Sham. Rats were subjected to modified neurological severity score (mNSS) measurements and forelimb grip strength and the Morris water maze tests. Using immunofluorescence and western blotting, we evaluated axonal growth inhibitor expression in the peri-infarct cortex on days 28 and 56 after tMCAO. Results showed the mNSS reduced, whereas the grip strengths improved in RWE and SRT groups. The escape latency in the Morris water maze test was shorter, whereas the number of times of crossing the platform was higher in both the SRT and RWE groups than in the tMCAO group on day 56; furthermore, the parameters in the SRT group improved compared to those in the RWE group. Physical exercise training could improve cognitive functions by reducing the expression of the NgR1/RhoA/ROCK axon growth inhibitors and increasing the expression of the endogenous antagonists LOTUS/LGI1. Exercise training beginning at the recovery stage could improve the cognitive function in tMCAO rats through a mechanism probably associated with the axonal growth inhibitor pathway.

Translational medicine of the glutamate AMPA receptor

Psychiatric and neurological disorders severely hamper patient's quality of life. Despite their high unmet needs, the development of diagnostics and therapeutics has only made slow progress. This is due to limited evidence on the biological basis of these disorders in humans. Synapses are essential structural units of neurotransmission, and neuropsychiatric disorders are considered as "synapse diseases". Thus, a translational approach with synaptic physiology is crucial to tackle these disorders. Among a variety of synapses, excitatory glutamatergic synapses play central roles in neuronal functions. The glutamate α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) is a principal component of glutamatergic neurotransmission; therefore, it is considered to be a promising translational target. Here, we review the limitations of current diagnostics and therapeutics of neuropsychiatric disorders and advocate the urgent need for the promotion of translational medicine based on the synaptic physiology of AMPAR. Furthermore, we introduce our recent translational approach to these disorders by targeting at AMPARs.

Training in a cooperative bimanual skilled reaching task, the popcorn retrieval task, improves unimanual function after motor cortical infarcts in rats

Disuse of the paretic hand after stroke is encouraged by compensatory reliance on the nonparetic hand, to exacerbate impairment and potentially constrain motor rehabilitation efficacy. Rodent stroke model findings support that learning new unimanual skills with the nonparetic forelimb diminishes functional improvements that can be driven by rehabilitative training of the paretic forelimb. The influence of learning new ways of skillfully using the two hands together on paretic side function is much less clear. To begin to explore this, we developed a new cooperative bimanual skilled reaching task for rats, the Popcorn Retrieval Task. After motor cortical infarcts impaired an established unimanual reaching skill in the paretic forelimb, rats underwent a 7 week period of de novo bimanual training (BiT) or no-training control procedures (Cont). Probes of paretic forelimb unimanual performance revealed significant improvements during and after the training period in BiT vs. Cont. We additionally observed a striking change in the bimanual task strategy over training days: a switch from the paretic to the nonparetic forelimb for initiating reach-to-grasp sequences. This motivated another study to test whether rats that established the bimanual skill prior to the infarcts would similarly switch handedness, which they did not, though paretic paw use for manipulative movements diminished. These results indicate that unimanual function of the paretic side can be improved by novel bimanual skill practice, even when it involves compensatory reliance on the nonparetic hand. They further support the suitability of the Popcorn Retrieval Task for studying bimanual skill learning effects in rats.

D-Amphetamine Exposure Differentially Disrupts Signaling Across Ontogeny in the Zebrafish

Background: Prescriptive and illicit amphetamine (AMPH) use continues to increase along with the likelihood that during an individual's lifetime, the drug deleteriously influences the growth and connectivity of behavior circuits necessary for survival. Throughout ontogeny, neural circuits underlying these behaviors grow in complexity, gradually integrating many sensory inputs that trigger higher order coordinated motor responses. In the present study, we examine how AMPH disrupts the establishment of these circuits at critical neurodevelopmental periods, as well as the communication among established survival circuits. Materials and Methods: Zebrafish embryos (from 1 hpf) were raised in AMPH solutions, growth parameters and escape behavior were assessed at 24 and 48 hpf, and spinal cord tissues analyzed for differences in excitatory-inhibitory signaling balance among treatments. Adult fish were fed an acute dosage of AMPH over an 11-day conditioned place preference (PP) paradigm during which behaviors were recorded and brain tissues analyzed for alterations in dopaminergic signaling. Results: AMPH negatively affects embryonic growth and slows the execution of escape behavior, suggesting an imbalance in locomotor signaling. Although local spinal circuits provide primary escape modulation, no differences in inhibitory glycinergic, and excitatory glutamatergic signaling were measured among spinal neurons. AMPH also influenced place preference in adult zebrafish and resulted in the increased expression of dopamine signaling proteins (DRD1) in brain areas governing survival behaviors.

The Intersection of Central Dopamine System and Stroke: Potential Avenues Aiming at Enhancement of Motor Recovery

Dopamine, a major neurotransmitter, plays a role in a wide range of brain sensorimotor functions. Parkinson's disease and schizophrenia are two major human neuropsychiatric disorders typically associated with dysfunctional dopamine activity levels, which can be alleviated through the druggability of the dopaminergic systems. Meanwhile, several studies suggest that optimal brain dopamine activity levels are also significantly impacted in other serious neurological conditions, notably stroke, but this has yet to be fully appreciated at both basic and clinical research levels. This is of utmost importance as there is a need for better treatments to improve recovery from stroke. Here, we discuss the state of knowledge regarding the modulation of dopaminergic systems following stroke, and the use of dopamine boosting therapies in animal stroke models to improve stroke recovery. Indeed, studies in animals and humans show stroke leads to changes in dopamine functioning. Moreover, evidence from animal stroke models suggests stimulation of dopamine receptors may be a promising therapeutic approach for enhancing motor recovery from stroke. With respect to the latter, we discuss the evidence for several possible receptor-linked mechanisms by which improved motor recovery may be mediated. One avenue of particular promise is the subtype-selective stimulation of dopamine receptors in conjunction with physical therapy. However, results from clinical trials so far have been more mixed due to a number of potential reasons including, targeting of the wrong patient populations and use of drugs which modulate a wide array of receptors. Notwithstanding these issues, it is hoped that future research endeavors will assist in the development of more refined dopaminergic therapeutic approaches to enhance stroke recovery.

Noradrenergic antagonists mitigate amphetamine-induced recovery

Brain injury, including that due to stroke, leaves individuals with cognitive deficits that can disrupt daily aspect of living. As of now there are few treatments that shown limited amounts of success in improving functional outcome. The use of stimulants such as amphetamine have shown some success in improving outcome following brain injury. While the pharmacological mechanisms for amphetamine are known; the specific processes responsible for improving behavioral outcome following injury remain unknown. Understanding these mechanisms can help to refine the use of amphetamine as a potential treatment or lead to the use of other methods that share the same pharmacological properties. One proposed mechanism is amphetamine's impact upon noradrenaline (NA). In the current, study noradrenergic antagonists were administered prior to amphetamine to pharmacologically block α- and β-adrenergic receptors. The results demonstrated that the blockade of these receptors disrupted amphetamines ability to induce recovery from hemispatial neglect using an established aspiration lesion model. This suggests that amphetamine's ability to ameliorate neglect deficits may be due in part to noradrenaline. These results further support the role of noradrenaline in functional recovery. Finally, the development of polytherapies and combined therapeutics, while promising, may need to consider the possibility that drug interactions can negate the effectiveness of treatment.

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.

Enduring Poststroke Motor Functional Improvements by a Well-Timed Combination of Motor Rehabilitative Training and Cortical Stimulation in Rats

BACKGROUND

In animal stroke models, peri-infarct cortical stimulation (CS) combined with rehabilitative reach training (RT) enhances motor functional outcome and cortical reorganization, compared with RT alone. It was unknown whether the effects of CS + RT (a) persist long after treatment, (b) can be enhanced by forcing greater use of the paretic limb, and (C) vary with treatment onset time.

OBJECTIVE

To test the endurance, time sensitivity, and the potential for augmentation by forced forelimb use of CS + RT treatment effects following ischemic stroke.

METHODS

Adult rats that were proficient in skilled reaching received unilateral ischemic motor cortical lesions. RT was delivered for 3 weeks alone or concurrently with 100-Hz cathodal epidural CS, delivered at 50% of movement thresholds. In study 1, this treatment was initiated at 14 days postinfarct, with some subgroups receiving an overlapping period of continuous constraint of the nonparetic forelimb to force use of the paretic limb. The function of the paretic limb was assessed weekly for 9 to 10 months posttreatment. In study 2, rats underwent CS, RT, and the combination during the chronic postinfarct period.

RESULTS

Early onset CS + RT resulted in greater functional improvements than RT alone. The CS-related gains persisted for 9 to 10 months posttreatment and were not significantly influenced by forced use of the paretic limb. When treatment onset was delayed until 3 months post-infarct, RT alone improved function, but CS + RT was no more effective than RT alone.

CONCLUSION

CS can enhance the persistence, as well as the magnitude of RT-driven functional improvements, but its effectiveness in doing so may vary with time postinfarct.

Amphetamine and other pharmacological agents in human and animal studies of recovery from stroke

Neuromodulation with pharmacological agents, including drugs of abuse such as amphetamine, when paired with behavioral experience, has been shown to positively modify outcomes in animal models of stroke. A number of clinical studies have tested the efficacy of a variety of drugs to enhance recovery of language deficit post-stroke. The purpose of this paper is to: (1) present pertinent animal studies supporting the use of dextro-amphetamine sulfate (AMPH) to enhance recovery after experimental lesions with emphasis on the importance of learning dependent activity for lasting recovery; (2) briefly review neuropharmacological explorations in the treatment of aphasia; (3) present a pilot study in aphasia exploring a drug combination of AMPH and donepezil hydrochloride paired with behavioral treatment to facilitate recovery; and (4) conclude with comments regarding the role of adjunctive pharmacotherapy in the rehabilitation of aphasia, particularly AMPH.

Combinatorial Motor Training Results in Functional Reorganization of Remaining Motor Cortex after Controlled Cortical Impact in Rats

Cortical reorganization subsequent to post-stroke motor rehabilitative training (RT) has been extensively examined in animal models and humans. However, similar studies focused on the effects of motor training after traumatic brain injury (TBI) are lacking. We previously reported that after a moderate/severe TBI in adult male rats, functional improvements in forelimb use were accomplished only with a combination of skilled forelimb reach training and aerobic exercise, with or without nonimpaired forelimb constraint. Thus, the current study was designed to examine the relationship between functional motor cortical map reorganization after experimental TBI and the behavioral improvements resulting from this combinatorial rehabilitative regime. Adult male rats were trained to proficiency on a skilled reaching task, received a unilateral controlled cortical impact (CCI) over the forelimb area of the caudal motor cortex (CMC). Three days post-CCI, animals began RT (n = 13) or no rehabilitative training (NoRT) control procedures (n = 13). The RT group participated in daily skilled reach training, voluntary aerobic exercise, and nonimpaired forelimb constraint. This RT regimen significantly improved impaired forelimb reaching success and normalized reaching strategies, consistent with previous findings. RT also enlarged the area of motor cortical wrist representation, derived by intracortical microstimulation, compared to NoRT. These findings indicate that sufficient RT can greatly improve motor function and improve the functional integrity of remaining motor cortex after a moderate/severe CCI. When compared with findings from stroke models, these findings also suggest that more intense RT may be needed to improve motor function and remodel the injured cortex after TBI.

Training Intensity Affects Motor Rehabilitation Efficacy Following Unilateral Ischemic Insult of the Sensorimotor Cortex in C57BL/6 Mice

BACKGROUND

Motor rehabilitative training improves behavioral functionality and promotes beneficial neural reorganization following stroke but is often insufficient to normalize function. Rodent studies have relied on skilled reaching tasks to model motor rehabilitation and explore factors contributing to its efficacy. It has been found that greater training intensity (sessions/day) and duration (training days) facilitates motor skill learning in intact animals. Whether rehabilitative training efficacy varies with intensity following stroke is unclear.

METHODS

Mice were trained preoperatively on a skilled reaching task. Following focal ischemic lesions, mice received rehabilitative training either twice daily (high intensity [HI]), once daily (low intensity [LI]), or not at all (control) to determine the effects of rehabilitative training intensity on skilled motor performance.

RESULTS

Within 7 days, the HI-trained mice achieved preischemic levels of performance. Mice receiving LI training eventually reached similar performance levels but required a greater quantity of training. Training intensity did not consistently affect the maintenance of performance gains, which were partially lost over time in both groups.

DISCUSSION

These data indicate that increased training intensity increases the rate of functional improvements per time and per training session following ischemic insult. Thus, training intensity is an important variable to consider in efforts to optimize rehabilitation efficacy.

Neuronal repair. Asynchronous therapy restores motor control by rewiring of the rat corticospinal tract after stroke

The brain exhibits limited capacity for spontaneous restoration of lost motor functions after stroke. Rehabilitation is the prevailing clinical approach to augment functional recovery, but the scientific basis is poorly understood. Here, we show nearly full recovery of skilled forelimb functions in rats with large strokes when a growth-promoting immunotherapy against a neurite growth-inhibitory protein was applied to boost the sprouting of new fibers, before stabilizing the newly formed circuits by intensive training. In contrast, early high-intensity training during the growth phase destroyed the effect and led to aberrant fiber patterns. Pharmacogenetic experiments identified a subset of corticospinal fibers originating in the intact half of the forebrain, side-switching in the spinal cord to newly innervate the impaired limb and restore skilled motor function.

Perilesional treatment with chondroitinase ABC and motor training promote functional recovery after stroke in rats

Ischemic stroke insults may lead to chronic functional limitations that adversely affect patient movements. Partial motor recovery is thought to be sustained by neuronal plasticity, particularly in areas close to the lesion site. It is still unknown if treatments acting exclusively on cortical plasticity of perilesional areas could result in behavioral amelioration. We tested whether enhancing plasticity in the ipsilesional cortex using local injections of chondroitinase ABC (ChABC) could promote recovery of skilled motor function in a focal cortical ischemia of forelimb motor cortex in rats. Using the skilled reaching test, we found that acute and delayed ChABC treatment induced recovery of impaired motor skills in treated rats. vGLUT1, vGLUT2, and vGAT staining indicated that functional recovery after acute ChABC treatment was associated with local plastic modification of the excitatory cortical circuitry positive for VGLUT2. ChABC effects on vGLUT2 staining were present only in rats undergoing behavioral training. Thus, the combination of treatments targeting the CSPG component of the extracellular matrix in perilesional areas and rehabilitation could be sufficient to enhance functional recovery from a focal stroke.

Vagus nerve stimulation during rehabilitative training improves forelimb strength following ischemic stroke

Upper limb impairment is a common debilitating consequence of ischemic stroke. Physical rehabilitation after stroke enhances neuroplasticity and improves limb function, but does not typically restore normal movement. We have recently developed a novel method that uses vagus nerve stimulation (VNS) paired with forelimb movements to drive specific, long-lasting map plasticity in rat primary motor cortex. Here we report that VNS paired with rehabilitative training can enhance recovery of forelimb force generation following infarction of primary motor cortex in rats. Quantitative measures of forelimb function returned to pre-lesion levels when VNS was delivered during rehab training. Intensive rehab training without VNS failed to restore function back to pre-lesion levels. Animals that received VNS during rehab improved twice as much as rats that received the same rehabilitation without VNS. VNS delivered during physical rehabilitation represents a novel method that may provide long-lasting benefits towards stroke recovery.

Amphetamine makes caudate tissue more susceptible to oxygen and glucose deprivation

Amphetamine is being investigated to reduce morbidity following stroke. However, the medicinal use of amphetamine is complicated because this drug is addictive, cardiotoxic, and can be neurotoxic. Thus, further research into the safety of giving amphetamine to stroke patients is required. Here, we examine whether prior treatment with amphetamine has any effect on oxygen-glucose deprivation (OGD)-evoked transmitter efflux and mitochondrial function. To circumvent the well-documented cardiovascular effects of amphetamine we have used rat brain slices. Brain slices were exposed to 30μM of amphetamine for 10min 1h before being exposed to OGD. Using fast cyclic voltammetry in rat caudate, dopamine efflux induced by OGD was measured. The effect of amphetamine on mitochondrial function was examined using triphenyltetrazolium chloride (TTC) staining. Prior amphetamine exposure decreased the time to onset of OGD-evoked dopamine efflux (from 460 to 220s), suggesting that the caudate was more sensitive to OGD. This increased sensitivity to OGD was attenuated by pre-treatment with the dopamine transporter blocker GBR12909 (1μM). Pre-treatment with the dopamine D2 receptor antagonist metoclopramide (1μM) had no effect on the amphetamine-evoked sensitisation to OGD. Amphetamine decreased TTC staining in the caudate suggesting that amphetamine compromised the dopamine system by disrupting mitochondrial function. Amphetamine treatment may be harmful in stroke recovery by making the brain more vulnerable to ischaemia. These data also suggest that amphetamine abusers might be more susceptible to cerebral ischaemia.

The bradykinesia assessment task: an automated method to measure forelimb speed in rodents

Bradykinesia in upper extremities is associated with a wide variety of motor disorders; however, there are few tasks that assay forelimb movement speed in rodent models. This study describes the bradykinesia assessment task, a novel method to quantitatively measure forelimb speed in rats. Rats were trained to reach out through a narrow slot in the cage and rapidly press a lever twice within a predefined time window to receive a food reward. The task provides measurement of multiple parameters of forelimb function, including inter-press interval, number of presses per trial, and success rate. The bradykinesia assessment task represents a significant advancement in evaluating bradykinesia in rat models because it directly measures forelimb speed. The task is fully automated, so a single experimenter can test multiple animals simultaneously with typically in excess of 300 trials each per day, resulting in high statistical power. Several parameters of the task can be modified to adjust difficulty, which permits application to a broad spectrum of motor dysfunction models. Here we show that two distinct models of brain damage, ischemic lesions of primary motor cortex and hemorrhagic lesions of the dorsolateral striatum, cause impairment in all facets of performance measured by the task. The bradykinesia assessment task provides insight into bradykinesia and motor dysfunction in multiple disease models and may be useful in assessing therapies that aim to improve forelimb function following brain damage.

The isometric pull task: a novel automated method for quantifying forelimb force generation in rats

Reach-to-grasp tasks are commonly used to assess forelimb function in rodent models. While these tasks have been useful for investigating several facets of forelimb function, they are typically labor-intensive and do not directly quantify physiological parameters. Here we describe the isometric pull task, a novel method to measure forelimb strength and function in rats. Animals were trained to reach outside the cage, grasp a handle attached to a stationary force transducer, and pull with a predetermined amount of force to receive a food reward. This task provides quantitative data on operant forelimb force generation. Multiple parameters can be measured with a high degree of accuracy, including force, success rate, pull attempts, and latency to maximal force. The task is fully automated, allowing a single experimenter to test multiple animals simultaneously with usually more than 300 trials per day, providing more statistical power than most other forelimb motor tasks. We demonstrate that an ischemic lesion in primary motor cortex yields robust deficits in all forelimb function parameters measured with this method. The isometric pull task is a significant advance in operant conditioning systems designed to automate the measurement of multiple facets of forelimb function and assess deficits in rodent models of brain damage and motor dysfunction.

Influence of constraint-induced movement therapy upon evoked potentials in rats with cerebral infarction

Constraint-induced movement therapy (CIMT) is an effective treatment promoting motor recovery of upper extremity function in stroke patients. The objective of the present study was to determine the effect of CIMT on the evoked potentials in rats with focal cerebral cortical ischemia induced by endothelin-1 (ET-1). Thirty rats were randomly assigned to the sham, infarct or CIMT groups. ET-1 was injected stereotaxically into the forelimb area of the cerebral cortex in the dominant hemisphere. Custom-made constraint jackets were applied to limit movement of the unaffected forelimb in the CIMT group. Motor and sensory function of the forelimb was evaluated by a pellet retrieval task and forearm asymmetry test. Electrophysiologic changes were evaluated by motor-evoked potentials (MEPs) and somatosensory-evoked potentials (SEPs). The location and extent of cerebral ischemia were confirmed and compared histologically. The CIMT group showed better recovery in the pellet retrieval task. Forelimb use was more symmetrical in the CIMT group. The waveform of the SEP was reversed and delayed in the infarct group, but it was preserved in the CIMT group with amplitude decrease only. The estimated volume of infarction was smaller in the CIMT group, although statistically not significant. The results demonstrate that CIMT can promote recovery of motor function in focal cerebral cortical infarcts, and that recovery may be related to reorganization of the cerebral neuronal network in the somatosensory pathway.

Amphetamine-enhanced motor training after cervical contusion injury

Individually, motor training, pharmacological interventions, and housing animals in an enriched environment (EE) following spinal cord injury (SCI) result in limited functional improvement but, when combined, may enhance motor function. Here, we tested amphetamine (AMPH)-enhanced skilled motor training following a unilateral C3-C4 contusion injury on the qualitative components of reaching and on skilled forelimb function, as assessed using single-pellet and staircase reaching tasks. Kinematic analysis evaluated the quality of the reach, and unskilled locomotor function was also tested. Animals receiving AMPH and skilled forelimb training performed better than operated control animals on qualitative reaching, but not on skilled reaching. Those that received the combination treatment and were housed in EE cages showed significantly less improvement in qualitative reaching and grasping. Kinematic analysis revealed a decrease in digit abduction during skilled reaching among all groups, with no differences among groups. Kinematics provided no evidence that improved function was related to improved quality of reach. There was no evidence of neuroprotection in the cervical spinal cord. The absence of evidence for kinematic improvement or neuroprotection suggested that AMPH-enhanced motor training is due primarily to supraspinal effects, an enhancement of attention during skilled motor training, or plasticity in supraspinal circuitry involved with motor control.

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.

Post-treatment with amphetamine enhances reinnervation of the ipsilateral side cortex in stroke rats

Amphetamine (AM) treatment has been shown to alter behavioral recovery after ischemia caused by embolism, permanent unilateral occlusion of the common carotid and middle cerebral arteries, or unilateral sensorimotor cortex ablation in rats. However, the behavioral results are inconsistent possibly due to difficulty controlling the size of the lesion before treatment. There is also evidence that AM promotes neuroregeneration in the cortex contralateral to the infarction; however, the effects of AM in the ipsilateral cortex remain unclear. The purpose of this study was to employ T2-weighted imaging (T2WI) to establish controlled criteria for AM treatment and to examine neuroregenerative effects in both cortices after stroke. Adult rats were anesthetized, and the right middle cerebral artery was ligated for 90 min to generate lesions in the ipsilateral cortex. Animals were separated into two equal treatment groups (AM or saline) according to the size of infarction, measured by T2WI at 2days after stroke. AM or saline was administered to stroke rats every third day starting on day 3 for 4weeks. AM treatment significantly reduced neurological deficits, as measured by body asymmetry and Bederson's score. T2WI and diffusion tensor imaging (DTI) were used to examine the size of infarction and axonal reinnervation, respectively, before and following treatment on days 2, 10 and 25 after stroke. AM treatment reduced the volume of tissue loss on days 10 and 25. A significant increase in fractional anisotropy ratio was found in the ipsilateral cortex after repeated AM administration, suggesting a possible increase in axonal outgrowth in the lesioned side cortex. Western analysis indicated that AM significantly increased the expression of synaptophysin ipsilaterally and neurofilament bilaterally. AM also enhanced matrix metalloproteinase (MMP) enzymatic activity, determined by MMP zymography in the lesioned side cortex. qRT-PCR was used to examine the expression of trophic factors after the 1st and 2nd doses of AM or saline injection. The expression of BDNF, but not BMP7 or CART, was significantly enhanced by AM in the lesioned side cortex. In conclusion, post-stroke treatment with AM facilitates behavioral recovery, which is associated with an increase in fractional anisotropy activity, enhanced fiber growth in tractography, synaptogenesis, upregulation of BDNF, and MMP activity mainly in the lesioned cortex. Our data suggest that the ipsilateral cortex may be the major target of action in stroke brain after AM treatment.

Reorganization of motor cortex after controlled cortical impact in rats and implications for functional recovery

We report the results of controlled cortical impact (CCI) centered on the caudal forelimb area (CFA) of rat motor cortex to determine the feasibility of examining cortical plasticity in a spared cortical motor area (rostral forelimb area, RFA). We compared the effects of three CCI parameter sets (groups CCI-1, CCI-2, and CCI-3) that differed in impactor surface shape, size, and location, on behavioral recovery and RFA structural and functional integrity. Forelimb deficits in the limb contralateral to the injury were evident in all three CCI groups assessed by skilled reach and footfault tasks that persisted throughout the 35-day post-CCI assessment period. Nissl-stained coronal sections revealed that the RFA was structurally intact. Intracortical microstimulation experiments conducted at 7 weeks post-CCI demonstrated that RFA was functionally viable. However, the size of the forelimb representation decreased significantly in CCI-1 compared to the control group. Subdivided into component movement categories, there was a significant group effect for proximal forelimb movements. The RFA area reduction and reorganization are discussed in relation to possible diaschisis, and to compensatory functional behavior, respectively. Also, an inverse correlation between the anterior extent of the lesion and the size of the RFA was identified and is discussed in relation to corticocortical connectivity. The results suggest that CCI can be applied to rat CFA while sparing RFA. This CCI model can contribute to our understanding of neural plasticity in premotor cortex as a substrate for functional motor recovery.

Distributed versus focal cortical stimulation to enhance motor function and motor map plasticity in a rodent model of ischemia

BACKGROUND

Motor rehabilitation after cerebral ischemia can enhance motor performance and induce motor map reorganization. Electrical stimulation of the cortex (CS) during rehabilitative training (CS/RT) augments motor map plasticity and confers gains in motor function beyond those observed with motor rehabilitation alone. However, it is unclear how the distribution of electrical stimulation across the cortex accomplishes these changes. This study examined the behavioral and neurophysiological effects of delivering CS/RT through a distributed versus focal arrangement of electrical contacts.

METHODS

Adult male rats were given rehabilitative training on a skilled forelimb reaching task following induction of focal ischemic damage within motor cortex. Intracortical microstimulation was used to derive high-resolution maps of forelimb movement representations within motor cortex contralateral to the trained/impaired paw before and after rehabilitation.

RESULTS

All animals that received rehabilitation showed greater increases in motor map area and reaching accuracy than animals that received no training. Animals with the distributed configuration performed significantly greater reaching accuracy than animals in both the CS/RT with focused contact arrangement and rehabilitative training alone (RT) conditions on days 3 to 4 and on day 6 through the remainder of the study (P < .05). However, both CS/RT groups exhibited larger motor maps than the RT condition (E1-CS/RT, 4.71 ± 0.66 mm(2); E2-CS/RT, 4.64 ± 0.46 mm(2); RT, 2.99 ± 0.28 mm(2)).

CONCLUSION

The results indicate that although both focal and distributed forms of CS/RT promote motor map reorganization only the distributed form of CS/RT enhances motor performance with rehabilitation.

Long-term motor improvement after stroke is enhanced by short-term treatment with the alpha-2 antagonist, atipamezole

Drugs that increase central noradrenergic activity have been shown to enhance the rate of recovery of motor function in pre-clinical models of brain damage. Less is known about whether noradrenergic agents can improve the extent of motor recovery and whether such improvement can be sustained over time. This study was designed to determine if increasing central noradrenergic tone using atipamezole, an alpha-2 adrenoceptor antagonist, could induce a long-term improvement in motor performance in rats subjected to ischemic brain damage caused by permanent middle cerebral artery occlusion. The importance of pairing physical "rehabilitation" with enhanced noradrenergic activity was also investigated. Atipamezole (1 mg/kg, s.c.) or vehicle (sterile saline) was administered once daily on Days 2-8 post-operatively. Half of each drug group was housed under enriched environment conditions supplemented with daily focused activity sessions while the other half received standard housing with no focused activity. Skilled motor performance in forelimb reaching and ladder rung walking was assessed for 8 weeks post-operatively. Animals receiving atipamezole plus rehabilitation exhibited significantly greater motor improvement in both behavioral tests as compared to vehicle-treated animals receiving rehabilitation. Interestingly, animals receiving atipamezole without rehabilitation exhibited a significant motor improvement in the ladder rung walk test but not the forelimb reaching test. These results suggest that a short-term increase in noradrenergic activity can lead to sustained motor improvement following stroke, especially when paired with rehabilitation.

Effects of damage to auditory cortex on the discrimination of speech sounds by rats

The intensity of a noise-induced startle response can be reduced by the presentation of an otherwise neutral stimulus immediately before the noise ("prepulse inhibition" or PPI). We used a form of PPI to study the effects of damage to auditory cortex on the discrimination of speech sounds by rats. Subjects underwent control surgery or treatment of the auditory cortex with the vasoconstrictor endothelin-1. This treatment caused damage concentrated in primary auditory cortex (A1). Both before and after lesions, subjects were tested on 5 tasks, most presenting a pair of human speech sounds (consonant-vowel syllables) so that the capacity for discrimination would be evident in the extent of PPI. Group comparisons failed to reveal any consistent lesion effect. At the same time, the analysis of individual differences in performance by multiple regression suggests that some of the temporal processing required to discriminate speech sounds is concentrated anteroventrally in the right A1. These results also confirm that PPI can be adapted to studies of the brain mechanisms involved in the processing of speech and other complex sounds.

The effects of amphetamine on recovery of function in animal models of cerebral injury: a critical appraisal

Therapeutic strategies to promote recovery from stroke are now beginning to utilize current knowledge of neural plasticity and the neuromodulatory role of physical rehabilitation. Current interests are also focused on adjuvant therapies that may enhance plasticity associated with recovery and rehabilitation. Amphetamine was one of the earliest pharmacological interventions and continues to show promising results as an adjuvant treatment for recovery of function in pre-clinical animal studies. This drug is a potent modulator of neurological function and cortical excitation, acting primarily through norepinephrine and dopamine mechanisms to enhance arousal and attention, and thus, to facilitate learning of motor skills. Although the results from the pre-clinical studies have been primarily positive, they have not translated well to clinical trials, which have yielded mixed results. This review addresses some of the conflicting evidence from pre-clinical studies conducted between 1982 and 2008 in order to better understand how to optimize the clinical application of amphetamine as an adjuvant therapy for stroke recovery. Among many of the factors that relate to differences in outcome, it is likely that both amphetamine dose and the timing of the intervention with respect to the time of injury affected the outcome.

Motor recovery and axonal plasticity with short-term amphetamine after stroke

BACKGROUND AND PURPOSE

There is considerable debate regarding the efficacy of amphetamine to facilitate motor recovery after stroke or experimental brain injury. Different drug dosing and timing schedules and differing physical rehabilitation strategies may contribute to outcome variability. The present study was designed to ascertain (1) whether short-term amphetamine could induce long-term functional motor recovery in rats after an ischemic lesion modeling stroke in humans; (2) how different levels of physical rehabilitation interact with amphetamine to enhance forelimb-related functional outcome; and (3) whether motor improvement was associated with axonal sprouting from intact corticoefferent pathways originating in the contralesional forelimb motor cortex.

METHODS

After permanent middle cerebral artery occlusion, rats received vehicle or amphetamine during the first postoperative week (2 mg/kg, subcutaneously on Postoperative Days 2, 5, and 8). In both treatment groups, separate cohorts of rats were exposed to different levels of "physical rehabilitation" represented by a control environment, enriched environment, or enriched environment with additional sessions of focused activity. Skilled forelimb performance was assessed using the forelimb reaching task and ladder rung walk test. Anterograde tracing with biotinylated dextran amine was used to assess new fiber outgrowth to denervated motor areas.

RESULTS

All treatment groups showed significant motor improvement as compared with control-housed, vehicle-treated animals. However, animals housed in an enriched environment that received amphetamine paired with focused activity sessions performed significantly better than any other treatment group and was the only group to achieve complete motor recovery (ie, reached preoperative performance) by 8 weeks. This recovery was associated with axonal sprouting into deafferentated subcortical areas from contralesional projection neurons.

CONCLUSIONS

This study suggests that, after stroke, short-term pairing of amphetamine with sufficiently focused activity is an effective means of inducing long-term improvement in forelimb motor function. The anatomic data suggests that corticoefferent plasticity in the form of axonal sprouting contributes to the maintenance of motor recovery.

Voluntary exercise or amphetamine treatment, but not the combination, increases hippocampal brain-derived neurotrophic factor and synapsin I following cortical contusion injury in rats

Prior work has shown that d-amphetamine (AMPH) treatment or voluntary exercise improves cognitive functions after traumatic brain injury (TBI). In addition, voluntary exercise increases levels of brain-derived neurotrophic factor (BDNF). The current study was conducted to determine how AMPH and exercise treatments, either alone or in combination, affect molecular events that may underlie recovery following controlled cortical impact (CCI) injury in rats. We also determined if these treatments reduced injury-induced oxidative stress. Following a CCI or sham injury, rats received AMPH (1 mg/kg/day) or saline treatment via an ALZET pump and were housed with or without access to a running wheel for 7 days. CCI rats ran significantly less than sham controls, but exercise level was not altered by drug treatment. On day 7 the hippocampus ipsilateral to injury was harvested and BDNF, synapsin I and phosphorylated (P) -synapsin I proteins were quantified. Exercise or AMPH alone significantly increased BDNF protein in sham and CCI rats, but this effect was lost with the combined treatment. In sham-injured rats synapsin I increased significantly after AMPH or exercise, but did not increase after combined treatment. Synapsin levels, including the P-synapsin/total synapsin ratio, were reduced from sham controls in the saline-treated CCI groups, with or without exercise. AMPH treatment significantly increased the P-synapsin/total synapsin ratio after CCI, an effect that was attenuated by combining AMPH with exercise. Exercise or AMPH treatment alone significantly decreased hippocampal carbonyl groups on oxidized proteins in the CCI rats, compared with saline-treated sedentary counterparts, but this reduction in a marker of oxidative stress was not found with the combination of exercise and AMPH treatment. These results indicate that, whereas exercise or AMPH treatment alone may induce plasticity and reduce oxidative stress after TBI, combining these treatments may cancel each other's therapeutic effects.

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.

Long-term monitoring of post-stroke plasticity after transient cerebral ischemia in mice using in vivo and ex vivo diffusion tensor MRI

WE USED A MURINE MODEL OF TRANSIENT FOCAL CEREBRAL ISCHEMIA TO STUDY: 1) in vivo DTI long-term temporal evolution of the apparent diffusion coefficient (ADC) and diffusion fractional anisotropy (FA) at days 4, 10, 15 and 21 after stroke 2) ex vivo distribution of a plasticity-related protein (GAP-43) and its relationship with the ex vivo DTI characteristics of the striato-thalamic pathway (21 days). All animals recovered motor function. In vivo ADC within the infarct was significantly increased after stroke. In the stroke group, GAP-43 expression and FA values were significantly higher in the ipsilateral (IL) striatum and contralateral (CL) hippocampus compared to the shams. DTI tractography showed fiber trajectories connecting the CL striatum to the stroke region, where increased GAP43 and FA were observed and fiber tracts from the CL striatum terminating in the IL hippocampus.Our data demonstrate that DTI changes parallel histological remodeling and recovery of function.

No improvement by amphetamine on learned non-use, attempts, success or movement in skilled reaching by the rat after motor cortex stroke

Amphetamine (AMPH) has been proposed as a treatment for post-stroke motor deficits when coupled with symptom-relevant physical rehabilitation. Whereas a number of experimental studies report improvements in endpoint measures of skilled reaching for food by rats, there has been no assessment of whether beneficial effects extend to overcoming learned non-use of the limb in the acute post-stroke period or to the qualitative deficits in movement in the chronic post-stroke period. In addition to evaluating the effects of AMPH on success, these were the objectives of the present study. In three different reaching experiments, groups of rats were pre-trained in skilled reaching for food prior to receiving a motor cortex stroke via pial removal. Postoperatively the rats received periodic AMPH treatment and daily rehabilitation. In the acute post-stroke period, AMPH failed to prevent the development of learned non-use of the limb, and in the acute and chronic period failed to improve recovery of reaching success, and also failed to improve the qualitative aspects of reaching movements. Nevertheless, AMPH did enhance adjunct non-reaching movements of locomotion, rearing and turning. The results are discussed in relation to the idea that the beneficial effects of post-stroke AMPH treatment do not extend to all movements, especially the movements of a forelimb in retrieving and consuming food.

The nitric oxide donor LA 419 decreases brain damage in a focal ischemia model

Stroke affects a large number of people, especially in developed countries, but treatment options are limited. Over the years, it has become clear that nitric oxide (NO) plays a major role in this pathology and that treatments that either reduce or increase NO presence may provide an alternative route for reducing the sequelae of brain ischemia. The NO donor LA 419 previously has been shown to protect the brain tissue from ischemic damage in an experimental model of global brain ischemia. Here we study whether this holds true for focal ischemia, a condition closer to the more common form of human stroke. Ischemia was induced in rats by a stereotaxic injection of endothelin-1, a potent vasoconstrictor, in the striatum. Seven days after the injection, magnetic resonance imaging (MRI) found a significant elevation in apparent diffusion coefficient (ADC) in the injected striatum of untreated rats, due to ischemia-induced vascular edema. Animals that received LA 419 prior to injection with endothelin-1 showed an ADC undistinguishable from the contralateral striatum or from the striatum of rats not treated with LA 419. In addition, immunohistochemistry with antibodies against neuronal nitric oxide synthase (nNOS), inducible NOS (iNOS), and nitrotyrosine showed a marked increase in the expression of these markers of NO production following ischemic treatment that was dampened by treatment with LA 419. In summary, our results clearly show that the NO donor LA 419 may be a useful compound for the prevention and/or treatment of focal brain ischemia.

Changes in the kinematic structure and non-kinematic features of movements during skilled reaching after stroke: a Laban Movement Analysis in two case studies

The purpose of this study was to adapt a universal language for human movement, Laban Movement Analysis (LMA), to capture the kinematic and non-kinematic aspects of movement in a reach-for-food task by subjects whose movements had been affected by stroke. Two control subjects, one stroke subject with internal capsule damage, and one subject with right posterior parietal stroke were video recorded while performing the reaching task. The movements of limb advancement, grasping the food, and limb withdrawal to place the food in the mouth, were notated using LMA. A scale, the Expressive Reaching Scale (ERS), was derived from the notation. All subjects completed the task; however, the stroke subjects displayed abnormalities in both the kinematic and non-kinematic aspects of movements during reaching with either limb. The most extensive impairments were in the contralateral-to-stroke limb and were most severe in the subject with internal capsule damage. The ERS rating scale may be a useful diagnosis and assessment tool.

Amphetamines for improving recovery after stroke

BACKGROUND

Animal research shows that treatment with amphetamines improves recovery after focal cerebral ischaemia. If the effects are similar in humans, amphetamine treatment could have a major impact on recovery from stroke.

OBJECTIVES

To assess the effects of amphetamine treatment in patients with stroke.

SEARCH STRATEGY

We searched the Cochrane Stroke Group Trials Register (last searched January 2006), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 1, 2006), MEDLINE (1966 to January 2006), EMBASE (1980 to January 2006), CINAHL (1982 to January 2006), CINAHL (1982 to January 2006), Science Citation Index (1992 to March 2005) and registers of ongoing trials. We also checked the reference lists of all relevant articles and reviews, and contacted researchers in the field.

SELECTION CRITERIA

Randomized unconfounded trials comparing amphetamine with placebo.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion and assessed trial quality; one extracted the data.

MAIN RESULTS

Ten studies involving 287 patients were included, but not all trials contributed data to each outcome examined in this review. The quality of the trials varied but was generally high. Based on three trials (106 patients) there was no evidence that amphetamine treatment reduced death or dependence (Peto's odds ratio (Peto OR) 1.5, 95% confidence interval (CI) 0.6 to 3.3). Imbalances at baseline with more serious stroke allocated to amphetamine may account for the trend for more deaths at the end of follow up among amphetamine-allocated patients (Peto OR 2.8, 95% CI 0.9 to 8.6). Based on two trials (73 patients) systolic (weighted mean difference (WMD) 8.4 mm Hg, 95% CI 1.6 to 15.2) and diastolic (WMD 4.9 mm Hg, 95% CI 1.1 to 8.8) blood pressure, as well as heart rate, increased (WMD 10.6 bpm, 95% CI 3.3 to 17.8) in amphetamine-allocated patients. Based on six studies (176 patients) there was evidence of a better relative change from baseline to last follow up in motor function (WMD -6.1 points; 95% CI -10.4 to -1.9) Different results with different analysis approaches emphasize caution in the interpretation of the results.

AUTHORS' CONCLUSIONS

At present, too few patients have been studied to draw any definite conclusions about the effects of amphetamine treatment on recovery from stroke. The suggested benefits on motor function and the non-significant trend towards increased risk of death could be related to imbalances in prognostic variables or other bias in the studies. Further research is therefore justified.

A chronic treatment with CDP-choline improves functional recovery and increases neuronal plasticity after experimental stroke

Chronic impairment of forelimb and digit movement is a common problem after stroke that is resistant to therapy. Although in the last years some studies have been performed to increase the efficacy of rehabilitative experience and training, the pharmacological approaches in this context remain poorly developed. We decided to study the effect of a chronic treatment with CDP-choline, a safe and well-tolerated drug that is known to stabilize membranes, on functional outcome and neuromorphological changes after stroke. To assess the functional recovery we have performed the staircase reaching test and the elevated body swing test (EBST), for studying sensorimotor integration and asymmetrical motor function respectively. The treatment with CDP-choline, initiated 24 h after the middle cerebral artery occlusion (MCAO) and maintained during 28 days, improved the functional outcome in both the staircase test (MCAO+CDP=87.0+/-6.6% pellets eaten vs. MCAO+SAL=40.0+/-4.5%; p<0.05) and the EBST (MCAO+CDP=70.0+/-6.8% vs. MCAO+SAL=88.0+/-5.4%; contralateral swing p<0.05). In addition, to study potential neuronal substrates of the improved function, we examined the dendritic morphology of layer V pyramidal cells in the undamaged motor cortex using a Golgi-Cox procedure. The animals treated with CDP-choline showed enhanced dendritic complexity and spine density compared with saline group. Our results suggest that a chronic treatment with CDP-choline initiated 24 h after the insult is able to increase the neuronal plasticity within noninjured and functionally connected brain regions as well as to promote functional recovery.

A single injection of D-amphetamine facilitates improvements in motor training following a focal cortical infarct in squirrel monkeys

BACKGROUND

There is growing interest in the use of D-amphetamine (D-AMPH) as a pharmacological treatment to supplement rehabilitative therapy following stroke. Based on the success of earlier animal models, several clinical studies have demonstrated beneficial effects of applying physical rehabilitation while stroke patients are under the influence of D-AMPH. To begin to understand the neural mechanisms underlying this promising adjuvant therapy, the authors examined the effects of a single pairing of D-AMPH and rehabilitative training on motor performance after cortical infarct in squirrel monkeys.

METHODS

Microelectrode stimulation techniques were used to delineate hand movement areas in the primary motor cortex prior to delivering a unilateral infarct to the complete hand representation. Postinfarct recovery was assessed for 3 groups of monkeys: D-AMPH + training, saline + training, and spontaneous recovery (SR). Postinfarct training groups received 14 consecutive days of motor skill training on a reach and retrieval task. A single injection of D-AMPH (0.25 mg/kg) or saline was given only on the 1st day of training (postinfarct day 10). Monkeys in the SR group had only minimal exposure to the training task once per week to monitor recovery.

RESULTS

The results show that a single coupling of D-AMPH + training initiated 10 days after cortical infarct facilitated the rate of recovery and improved performance (68% improvement from 1st day of training) beyond the level achieved by the monkeys in the saline + training group (27% improved from 1st day of training).

CONCLUSIONS

D-AMPH is a potent modulator of behavioral recovery following an ischemic infarct in nonhuman primates.

Rat Models of Upper Extremity Impairment in Stroke

Stroke remains the leading cause of adult disability, with upper extremity motor impairments being the most prominent functional deficit in surviving stroke victims. The development of animal models of upper extremity dysfunction after stroke has enabled investigators to examine the neural mechanisms underlying rehabilitation-dependent motor recovery as well as the efficacy of various adjuvant therapies for enhancing recovery. Much of this research has focused on rat models of forelimb motor function after experimentally induced ischemic or hemorrhagic stroke. This article provides a review of several different methods for inducing stroke, including devascularization, photothrombosis, chemical vasoconstriction, and hemorrhagia. We also describe a battery of sensorimotor tasks for assessing forelimb motor function after stroke. The tasks range from measures of gross motor performance to fine object manipulation and kinematic movement analysis, and we offer a comparison of the sensitivity for revealing motor deficits and the amount of time required to administer each motor test. In addition, we discuss several important methodological issues, including the importance of testing on multiple tasks to characterize the nature of the impairments, establishing stable baseline prestroke motor performance measures, dissociating the effects of acute versus chronic testing, and verifying lesion location and size. Finally, we outline general considerations for conducting research using rat models of stroke and the role that these models should play in guiding clinical trials.

Mechanisms for recovery of motor function following cortical damage

Recent studies of focal injury to the cerebral cortex have demonstrated that the remaining, intact tissue undergoes structural and functional changes that could play a substantial role in neurological recovery. New information regarding the molecular and cellular environment in the adjacent, intact tissue has suggested that waves of growth promotion and inhibition modulate the self-repair processes of the brain. Furthermore, recent studies have documented widespread neurophysiological and neuroanatomical changes in regions remote from a focal cortical injury, suggesting that entire cortical networks participate in the recovery process.

Plasticity

Over the past 20 years, evidence has mounted regarding the capacity of the central nervous system to alter its structure and function throughout life. Injury to the central nervous system appears to be a particularly potent trigger for plastic mechanisms to be elicited. Following focal injury, widespread neurophysiological and neuroanatomical changes occur both in the peri-infarct region, as well as throughout the ipsi- and contralesional cortex, in a complex, time-dependent cascade. Since such post-injury plasticity can be both adaptive or maladaptive, current research is directed at understanding how plasticity may be modulated to develop more effective therapeutic interventions for neurological disorders, such as stroke. Behavioral training appears to be a significant contributor to adaptive plasticity after injury, providing a neuroscientific foundation for the development of physical therapeutic approaches. Adjuvant therapies, such as pharmacological agents and exogenous electrical stimulation, may provide a more receptive environment through which behavioral therapies may be imparted. This chapter reviews some of the recent results from animal models of injury and recovery that depict the complex time course of plasticity following cortical injury and implications for neurorehabilitation.

Axonal plasticity is associated with motor recovery following amphetamine treatment combined with rehabilitation after brain injury in the adult rat

Clinical and laboratory studies have suggested that amphetamine treatment when paired with rehabilitation results in improved recovery of function after stroke or traumatic brain injury. In the present study, we investigated whether new anatomical pathways developed in association with improved motor function after brain damage and amphetamine treatment linked with rehabilitation. Following a unilateral sensorimotor cortex lesion in the adult rat, amphetamine (2 mg/kg) was administered in conjunction with physiotherapy sessions on postoperative days two and five. Physiotherapy was continued twice daily for the first 3 weeks after injury, and then once daily until week six. Performance on skilled forelimb reaching and ladder rung walking was used to assess motor improvement. Our results show that animals with sensorimotor cortical lesions receiving amphetamine treatment linked with rehabilitation had significant improvement in both tasks. Neuroanatomical tracing of efferent pathways from the opposite, non-damaged cortex resulted in the novel finding that amphetamine treatment linked with rehabilitation, significantly increased axonal growth in the deafferented basilar pontine nuclei. These results support the notion that pharmacological interventions paired with rehabilitation can enhance neuronal plasticity and thereby improve functional recovery after CNS injury.

Epidural cortical stimulation enhances motor function after sensorimotor cortical infarcts in rats

This study examined whether epidurally delivered cortical electrical stimulation (CS) improves the efficacy of motor rehabilitative training and alters neuronal density and/or cell proliferation in perilesion cortex following ischemic sensorimotor cortex (SMC) lesions. Adult rats were pre-trained on a skilled reaching task and then received partial unilateral SMC lesions and implantation of electrodes over the remaining SMC. Ten to fourteen days later, rats received daily reach training concurrent with anodal or cathodal 100 Hz CS or no stimulation (NoCS) for 18 days. To label newly generated cells, bromodeoxyuridine (BrdU; 50 mg/kg) was administered every third day of training. Both anodal and cathodal CS robustly enhanced reaching performance compared to NoCS controls. Neuronal density in the perilesion cortex was significantly increased in the cathodal CS group compared to the NoCS group. There were no significant group differences in BrdU-labeled cell density in ipsilesional cortex. Staining with Fluoro-Jade-B indicated that neurons continue to degenerate near the infarct at the time when cortical stimulation and rehabilitation were initiated. These data indicate that epidurally delivered CS greatly improves the efficacy of rehabilitative reach training following SMC damage and raise the possibility that cathodal CS may influence neuronal survival in perilesion cortex.