Motor skills training enhances lesion-induced structural plasticity in the motor cortex of adult rats

Training on a visual task improves the outcome of optic nerve regeneration

Optic nerve regeneration in a lizard, Ctenophorus ornatus, is dysfunctional despite survival of most retinal ganglion cells and axon regeneration to the optic tectum. The regenerated retino-tectal projection at 6 months has crude topography but by 1 year is disordered; visually-elicited behavior is absent via the experimental eye. Here, we assess the influence of training on the outcome of optic nerve regeneration. Lizards were trained to catch prey presented within the monocular field of either eye. One optic nerve was then severed and visual stimulation resumed throughout regeneration. In the trained group, presentation was restricted to the eye undergoing optic nerve regeneration; for the untrained group, the unoperated eye was stimulated. Pupil responses returned in trained but not in untrained animals. At 1 year, trained animals oriented to and captured prey; untrained animals demonstrated minimal orienting and failed to capture prey. Regenerated retino-tectal projections were topographic in the trained but not in the untrained group as assessed by in vitro electrophysiological recording and by carbocyanine dye tracing. In vitro electrophysiological recording during application of neurotransmitter antagonists to the tectum revealed that the level of GABAergic inhibition was modest in trained animals but elevated in the untrained group; responses were mainly AMPA-mediated in both groups. We conclude that training improves the behavioral outcome of regeneration, presumably by stabilizing and refining the transient retino-tectal map and preventing a build-up of tectal inhibition. The results suggest that for successful central nerve regeneration to occur in mammals, it may be necessary to introduce training to complement procedures stimulating axon regeneration.

Motor balance and coordination training enhances functional outcome in rat with transient middle cerebral artery occlusion

The goal of this study was to determine if relatively complex motor training on Rota-rod involving balance and coordination plays an essential role in improving motor function in ischemic rats, as compared with simple locomotor exercise on treadmill. Adult male Sprague-Dawley rats with (n=40) or without (n=40) ischemia were trained under each of three conditions: (1) motor balance and coordination training on Rota-rod; (2) simple exercise on treadmill; and (3) non-trained controls. Motor function was evaluated by a series of tests (foot fault placing, parallel bar crossing, rope and ladder climbing) before and at 14 or 28 days after training procedures in both ischemic and normal animals. Infarct volume in ischemic animals was determined with Nissl staining. Compared with both treadmill exercised and non-trained animals, Rota-rod-trained animals with or without ischemia significantly (P<0.01) improved motor performance of all tasks except for foot fault placing after 14 days of training, with normal rats having better performance. Animals trained for up to 28 days on the treadmill did not show significantly improved function. With regard to foot fault placing task, performance on foot placing was improved in ischemic rats across the three measurements at 0, 14 and 28 days regardless of training condition, while the normal group reached their best performance at the beginning of measurement. No significant differences in infarct volume were found in rats trained either with Rota-rod (47+/-4%; mean+/-S.E.), treadmill (45+/-5%) or non-exercised control (45+/-3%). In addition, no obvious difference could be detected in the location of the damage which included the dorso-lateral portion of the neostriatum and the frontoparietal cortex, the main regions supplied by the middle cerebral artery. The data suggest that complex motor training rather than simple exercise effectively improves functional outcome.

Behavioral and neuroplastic effects of focal endothelin-1 induced sensorimotor cortex lesions

Previous studies have established the usefulness of endothelin-1 (ET-1) for the production of focal cerebral ischemia. The present study assessed the behavioral effects of focal ET-1-induced lesions of the sensorimotor cortex (SMC) in adult rats as well as cellular and structural changes in the contralateral homotopic motor cortex at early (2 days) and later (14 days) post-lesion time points. ET-1 lesions resulted in somatosensory and postural-motor impairments in the contralateral (to the lesion) forelimb as assessed on a battery of sensitive measures of sensorimotor function. The lesions also resulted in the development of a hyper-reliance on the ipsilateral forelimb for postural-support behaviors. In comparison to sham-operated rats, in layer V of the motor cortex opposite the lesions, there were time- and laminar-dependent increases in the surface density of dendritic processes immunoreactive for microtubule-associated protein 2, in the optical density of N-methyl-D-asparate receptor (NMDA) subunit 1 immunoreactivity, and in the numerical density of cells immunolabeled for Fos, the protein product of the immediate early gene c-fos. These findings corroborate and extend previous findings of the effects of electrolytic lesions of the SMC. It is likely that compensatory forelimb behavioral changes and transcallosal degeneration play important roles in these changes in the cortex opposite the lesion, similar to previously reported effects of electrolytic SMC lesions.

Neonatal enucleation reduces the proportion of callosal boutons forming multiple synaptic contacts in rat striate cortex

Although bilateral enucleation at birth produces marked abnormalities in the overall distribution and topography of interhemispheric callosal connections in rat visual cortex, it is not known whether it also alters the morphology of callosal synapses. Here we report on the effect of neonatal enucleation on the proportion of callosal boutons making multiple postsynaptic contacts. Synapses were analyzed in adult rats after injections of the anterograde tracer biotinylated dextran amine into the opposite striate cortex. Results show that neonatal enucleation produces a significant reduction in the proportion of callosal boutons making multiple postsynaptic contacts.

Synapse replacement in the striatum of the adult rat following unilateral cortex ablation

Defining the selective pattern of synapse replacement that occurs in different areas of the damaged brain is essential for predicting the limits of functional compensation that can be achieved after various types of brain injury. Here we describe the time course of dendritic reorganization, spine loss and recovery, and synapse replacement in the striatum following a unilateral cortex ablation. We found that the time course for the transient loss and recovery of dendritic spines on medium spiny I (MSI) neurons, the primary postsynaptic target for corticostriatal axons, paralleled the time course for the removal of degenerating axon terminals from the neuropil and the formation of new synapses on MSI neurons. Reinnervation of the deafferented striatum occurred chiefly by axon terminals that formed asymmetric synapses with dendritic spines of MSI neurons, and the mean density of asymmetric synapses recovered to 86% of the sham-operated rat value by 30 days postlesion. In addition, the synaptic circuitry of the reconstructed striatum was characterized by an increase in the number of multiple synaptic boutons (MSBs), i.e., presynaptic axon terminals that make contact with more than one dendritic spine. Whether the postsynaptic contacts of MSBs are formed with the dendritic spines of the same or a different parent dendrite in the striatum is unknown. Nevertheless, these data suggest that the formation of MSBs is an essential part of the compensatory response to the loss of input from the ipsilateral cortex following the aspiration lesion and may serve to modulate activity-dependent adaptive changes in the reconstructed striatum that can lead to functional recovery.

Treadmill training effects on neurological outcome after middle cerebral artery occlusion in rats

BACKGROUND

Treadmill training is used for promoting rhythmical vigorous walking and for task-related training in patients with stroke. The neurological impact of treadmill training has not been established. The present investigation is aimed at (1) examining neurological changes over a four-week period after middle cerebral artery occlusion (MCAO) in rats and (2) assessing the impact of one-week, two-week and four-week treadmill training in MCAO rats.

METHODS

Male Sprague-Dawley rats were subjected to 60-minute right MCAO. All rats were randomly assigned to one of seven groups. Infarct volume and neurological score were measured.

RESULTS

Rats sacrificed 24 hours post MCAO had the largest infarct volumes (171.4 +/- 14.4 mm3) and the highest neurological score (median: 2, range: 1-3). We noted that without treadmill training, infarct sizes and neurological score diminished with time. Treadmill training for at least one week further reduced infarct volume and significantly improved neurologic function in MCAO rats.

CONCLUSION

Treadmill training after focal cerebral ischemia significantly improves neurological outcome in MCAO rats. Treadmill training may be beneficial for ischemic brain recovery.

Reorganization of remote cortical regions after ischemic brain injury: a potential substrate for stroke recovery

Although recent neurological research has shed light on the brain's mechanisms of self-repair after stroke, the role that intact tissue plays in recovery is still obscure. To explore these mechanisms further, we used microelectrode stimulation techniques to examine functional remodeling in cerebral cortex after an ischemic infarct in the hand representation of primary motor cortex in five adult squirrel monkeys. Hand preference and the motor skill of both hands were assessed periodically on a pellet retrieval task for 3 mo postinfarct. Initial postinfarct motor impairment of the contralateral hand was evident in each animal, followed by a gradual improvement in performance over 1-3 mo. Intracortical microstimulation mapping at 12 wk after infarct revealed substantial enlargements of the hand representation in a remote cortical area, the ventral premotor cortex. Increases ranged from 7.2 to 53.8% relative to the preinfarct ventral premotor hand area, with a mean increase of 36.0 +/- 20.8%. This enlargement was proportional to the amount of hand representation destroyed in primary motor cortex. That is, greater sparing of the M1 hand area resulted in less expansion of the ventral premotor cortex hand area. These results suggest that neurophysiologic reorganization of remote cortical areas occurs in response to cortical injury and that the greater the damage to reciprocal intracortical pathways, the greater the plasticity in intact areas. Reorganization in intact tissue may provide a neural substrate for adaptive motor behavior and play a critical role in postinjury recovery of function.

A squirrel monkey model of poststroke motor recovery

Nonhuman primate models of poststroke recovery have become increasingly rare primarily due to high purchase and maintenance costs and limited availability of nonhuman primate species. Despite this obstacle, nonhuman primate models may offer important advantages over rodent models for understanding many of the brain's mechanisms for self-repair due to greater similarity in cortical organization to humans. Since the mid-1990s, surgical, neurophysiological, and neuroanatomical methods have been developed to understand structural and functional remodeling of the cerebral cortex after an ischemic event, such as occurs in stroke. These methods require long surgical procedures and entail constant physiological monitoring. With careful attention to intraoperative and postsurgical monitoring, these procedures can be repeated multiple times in individual monkeys without untoward events. This model provides a statistically powerful approach for tracking brain plasticity in the ensuing weeks and months after a stroke-like injury, reducing the number of animals required for individual experiments. This methodology is described in detail, and many of the resulting findings that are relevant for understanding stroke recovery and the effects of rehabilitative and pharmacotherapeutic interventions are summarized.

Importance of behavioral manipulations and measures in rat models of brain damage and brain repair

The relevance of careful behavioral measures and manipulations in animal research on neural plasticity and brain damage has become increasingly clear. Recent research in adult rats indicates that an understanding of neural restructuring after brain damage requires an understanding of how it is influenced by postinjury behavioral experiences. Other research indicates that optimizing pharmacological and other treatments for brain damage may require their combination with rehabilitative training. Assessing the efficacy of a treatment approach in animal models requires the use of sensitive behavioral measures of functional outcome. In research on restorative plasticity after brain damage, procedures for handling and housing rats should promote the quality of behavioral measures and manipulations.

Experimental focal ischemic injury: behavior-brain interactions and issues of animal handling and housing

In experimental neurological models of brain injury, behavioral manipulations before and after the insult can have a major impact on molecular, anatomical, and functional outcome. Investigators using animals for preclinical research should keep in mind that people with brain injury have lived in, and will continue to live in, an environment that is far more complex than that of the typical laboratory rodent. To yield more reliable and relevant behavioral assessment, it may be appropriate in some cases to house animals in environments that allow for motor enrichment and to handle animals in ways that promote tameness. Experience can affect mechanisms of plasticity and degeneration beneficially or adversely. Behavioral interventions that have been found to modulate postinjury brain events are reviewed. The timing and interaction of biological and motor therapies and the potential contribution of experience-dependent and drug-induced trophic factor expression are discussed.

Constraint-induced movement therapy and rehabilitation exercises lessen motor deficits and volume of brain injury after striatal hemorrhagic stroke in rats

BACKGROUND AND PURPOSE

Constraint-induced movement therapy (CIMT) promotes motor recovery after occlusive stroke in humans, but its efficacy after intracerebral hemorrhage (ICH) has not been investigated clinically or in the laboratory. In this study we tested whether CIMT and a rehabilitation exercise program would lessen motor deficits after ICH in rats.

METHODS

Rats were subjected to striatal ICH (via infusion of collagenase) or sham stroke. Seven days later, treatment began with CIMT (8 h/d of ipsilateral forelimb restraint), rehabilitation exercises (eg, reaching, walking; 1 h/d), or both for 7 days. Some rats were not treated. Motor deficits were assessed up to the 60-day survival time, after which the volume of tissue lost was determined.

RESULTS

Untreated ICH rats made more limb slips traversing a horizontal ladder and showed an asymmetry toward less use of the contralateral paw in the cylinder test of limb use asymmetry (day 28). These rats were also significantly less successful in the Montoya staircase test (days 55 to 59) of skilled reaching. Neither therapy alone provided much benefit. However, the combination of daily exercises and CIMT substantially and persistently improved recovery. Unexpectedly, this group had a statistically smaller volume of tissue lost than untreated ICH rats.

CONCLUSIONS

The combination of focused rehabilitation exercises and CIMT effectively promotes functional recovery after ICH, while either therapy alone is less effective. This therapy may work in part by reducing the volume of tissue lost, likely through reducing atrophy while promoting remodeling.

Synaptic plasticity in thalamic nuclei enhanced by motor skill training in rat with transient middle cerebral artery occlusion

The goal of this study was to determine if synaptic plasticity in the thalamus of rats subjected to stroke could be altered by motor training. Transient occlusion of right middle cerebral artery in adult female Sprague-Dawley rats (n = 35) was induced with an intraluminal filament followed by three training conditions, 1. motor skill training on Rota-rod requiring balance and coordination skills, 2. simple exercise on treadmill, and 3. nontrained controls. Synaptic plasticity in brain was evaluated by synapotophysin immunocytochemistry at 14 or 28 days after training procedures. Infarct volume was determined in Nissl stained sections. Both at 14 and 28 days after Rota-rod training, intense synaptophysin immunoreactivity was present in the right but not the left mediodorsal and ventromedial nuclei of thalamus of ischemic rats. In treadmill-trained animals, however, similarly intense synaptic plasticity in these two thalamic nuclei was seen only at 28 days. Immunostaining was found also in other brain regions adjacent to or remote from infarct site. The data suggest that motor training, particularly motor skill training involving balance and coordination, facilitates a uniquely lateralized synaptogenesis in the thalamus.

Synaptic mitochondrial changes in the motor cortex following unilateral cortical lesions and motor skills training in adult male rats

Unilateral lesions of the forelimb sensorimotor cortex and motor skills training interact to enhance synaptic plasticity in layer V of the motor cortex contralateral to the lesion in male rats. In this study, we assessed the metabolic correlates of these synaptic changes by quantifying the number and size of mitochondria in synaptic axonal terminals with perforated or non-perforated post-synaptic densities (PSDs) and single or multiple post-synaptic contacts. The number of synaptic mitochondria per neuron was significantly greater in rats with lesions. Neither manipulation affected mitochondrial size or number of mitochondria per synapse. Independent of experimental condition, terminals with perforated PSDs had more mitochondria than those with non-perforated PSDs and, among those with non-perforated PSDs, terminals with multiple synaptic contacts had more mitochondria than those forming single synapses.

Should the injured and intact hemispheres be treated differently during the early phases of physical restorative therapy in experimental stroke or parkinsonism?

Over a century ago the intact cortex was proposed to contribute to recovery from unilateral brain injury, but its possible role in functional outcome has become more appreciated in recent years as a result of anatomic, metabolic and behavioral studies. Although use of the contralesional limb is naturally impaired after sensorimotor cortex injury, neural and astrocytic events in the intact hemisphere may give rise to, and may be influenced by, an enhanced ability to compensate for lost motor function. The debate is still open as to whether the neural changes are generally compensatory in nature, with activity in the homotopic cortex leading to greater capability in the nonimpaired limb, or whether they are actually a matter of reorganization in the homotopic cortex leading to connections to denervated targets in the opposite hemisphere, thus allowing the homotopic cortex to control motor programs there. Although both phenomena may occur to some degree, there is mounting evidence in support of the former view. Careful behavioral techniques have been developed that can expose compensatory tricks, and the time course of these behaviors correlates well with anatomic data. Moreover, if the intact cortex sustains a second lesion after recovery from the first, forelimb sensorimotor function specific to the first-impaired side of the body is not worsened. Partial denervation of callosal fibers coming from the injured hemisphere, plus preferential use of the good forelimb caused by a cortical injury, may increase trophic factors in the intact hemisphere. These and related events seem to provide a growth-favorable environment there that permits motor learning in the intact forelimb at a level of skill exceeding that which a normal animal can attain in the same period of time. There are anecdotal cases in human neurologic patients that are consistent with these findings. For example, a colleague of the authors who sustained a unilateral infarction that rendered his dominant right hand severely impaired noticed that soon after the stroke he was able to use his left hand for writing and computers as well as he had ever used his right hand. Cross-midline placing tests also indicate that the structural events observed in the intact cortex may potentiate projections to the damaged hemisphere. These changes may help restore the capacity of tactile information projecting to the intact hemisphere to control limb placing in the impaired forelimb. Neural events in the injured hemisphere can be affected by behavior differently than the neural events in the intact hemisphere. Different therapeutic strategies might well be used on opposing limbs at different times after unilateral sensorimotor cortex injury to optimize recovery (and, indeed, to avoid exaggerating the insult). Finally, the details of reorganization in both hemispheres differ greatly depending on the type of brain injury sustained (eg, in stroke versus Parkinson's disease), suggesting that an approach that considers the role of both hemispheres is likely to be beneficial in research on a broad variety of brain pathologies.

Functional and structural plasticity in motor cortex: implications for stroke recovery

Several studies have now demonstrated that the motor cortical representations are dynamically maintained in both normal and brain-injured animals. Functional plasticity in the motor cortex of normal animals is accompanied by changes in synaptic morphology; these changes are skill-dependent rather than simply use-dependent. Finally, motor cortical areas undergo substantial functional alterations after focal ischemic infarcts; motor experience is a potent and adaptive modulator of injury-related plasticity. These recent neuroscientific advances set the stage for the development of new, more effective interventions in chronic stroke populations that are based on the basic mechanisms underlying neuroplasticity.

Transplants and neurotrophic factors increase regeneration and recovery of function after spinal cord injury

Earlier studies suggested that while after spinal cord lesions and transplants at birth, the transplants serve both as a bridge and as a relay to restore supraspinal input caudal to the injury (Bregman, 1994), after injury in the adult the spinal cord transplants serve as a relay, but not as a bridge. We show here, that after complete spinal cord transection in adult rats, delayed spinal cord transplants and exogenous neurotrophic factors, the transplants can also serve as a bridge to restore supraspinal input (Fig. 9). We demonstrate here that when the delivery of transplants and neurotrophins are delayed until 2 weeks after spinal cord transection, the amount of axonal growth and the amount of recovery of function are dramatically increased. Under these conditions, both supraspinal and propriospinal projections to the host spinal cord caudal to the transection are reestablished. The growth of supraspinal axons across the transplant and back into the host spinal cord caudal to the lesion was dependent upon the presence of exogenous neurotrophic support. Without the neurotrophins, only propriospinal axons were able to re-establish connections across the transplant. Studies using peripheral nerve or Schwann cell grafts have shown that some anatomical connectivity can be restored across the injury site, particularly under the influence of neurotrophins (Xu et al., 1995a,b; Cheng et al., 1996; Ye and Houle, 1997). Without neurotrophin treatment, brainstem axons do not enter [figure: see text] the graft (Xu et al., 1995a,b; Cheng et al., 1996; Ye and Houle, 1997). Similarly, cells genetically modified to secrete neurotrophins and transplanted into the spinal cord influence the axonal growth of specific populations of spinally projecting neurons (Tuszynski et al., 1996, 1997; Grill et al., 1997; Blesch and Tuszynski, 1997). Taken together, these studies support a role for neurotrophic factors in the repair of the mature CNS. The regrowth of supraspinal and propriospinal input across the transection site was associated with consistent improvements in hindlimb locomotor function. Animals performed alternating and reciprocal hindlimb stepping with plantar foot contact to the treadmill or stair during ascension. Furthermore, they acquired hindlimb weight support and demonstrated appropriate postural control for balance and equilibrium of all four limbs. After spinal cord injury in the adult, the circuitry underlying rhythmic alternating stepping movements is still present within the spinal cord caudal to the lesion, but is now devoid of supraspinal control. We show here that restoring even relatively small amounts of input allows supraspinal neurons to access the spinal cord circuitry. Removing the re-established supraspinal input after recovery (by retransection rostral to the transplant) abolished the recovery and abolished the serotonergic fibers within the transplant and spinal cord caudal to the transplant. This suggests that at least some of the recovery observed is due to re-establishing supraspinal input across the transplant, rather than a diffuse influence of the transplant on motor recovery. It is unlikely, however, that the greater recovery of function in animals that received delayed transplant and neurotrophins is due solely to the restoration of supraspinal input. Recent work by Ribotta et al. (2000) suggests that segmental plasticity within the spinal cord contributes to weight support and bilateral foot placement after spinal cord transection. This recovery of function occurs after transplants of fetal raphe cells into the adult spinal cord transected at T11. Recovery of function appears to require innervation of the L1-L2 segments with serotonergic fibers, and importantly, animals require external stimulation (tail pinch) to elicit the behavior. In the current study, animals with transection only did not develop stepping overground or on the treadmill without tail pinch, although the transplant and neurotrophin-treated groups did so without external stimuli. Therefore both reorganization of the segmental circuitry and partial restoration of supraspinal input presumably interact to yield the improvements in motor function observed. It is unlikely that the recovery of skilled forelimb movement observed can be mediated solely by reorganization of segmental spinal cord circuitry. We suggest that the restoration of supraspinal input contributes to the recovery observed. It is likely that after CNS injury, reorganization occurs both within the spinal cord and at supraspinal levels, and together contribute to the recovery of automatic and skilled forelimb function and of locomotion. In summary, the therapeutic intervention of tissue transplantation and exogenous neurotrophin support leads to improvements in supraspinal and propriospinal input across the transplant into the host caudal cord and a concomitant improvement in locomotor function. Paradoxically, delaying these interventions for several weeks after a spinal cord transection leads to dramatic improvements in recovery of function and a concomitant restoration of supraspinal input into the host caudal spinal cord. These findings suggest that opportunity for intervention after spinal cord injury may be far greater than originally envisioned, and that CNS neurons with long-standing injuries may be able to re-initiate growth leading to improvement in motor function.

A brain adaptation view of plasticity: is synaptic plasticity an overly limited concept?

A view that is emerging is that the brain has multiple forms of plasticity that must be governed, at least in part, by independent mechanisms. This view is illustrated by: (1) the apparent separate governance of some non-neural changes by activity, in contrast to synaptic changes driven by learning; (2) the apparent independence of different kinds of synaptic changes that occur in response to the learning aspects of training; (3) the occurrence of separate patterns of synaptic plasticity in the same system in response to different task demands; and (4) apparent dissociations between behaviorally induced synaptogenesis and LTP. The historical focus of research and theory in areas ranging from learning and memory to experiential modulation of brain development has been heavily upon synaptic plasticity since shortly after the discovery of the synapse. Based upon available data, it could be argued that: (1) synaptic, and even neuronal, plasticity is but a small fraction of the range of changes that occur in response to experience; and (2) we are just beginning to understand the importance of these other forms of brain plasticity. Appreciation of this aspect of the brain's adaptive process may allow us to better understand the capacity of the brain to tailor a particular set of changes to the demands of the specific experiences that generated them.

Forced limb-use and recovery following brain injury

Animals subjected to exercise display significant alterations in brain function and neurochemistry, reflecting the innate plasticity of the adult brain to environmental challenges. Following injury, the brain is sensitive to reorganization and regeneration, and thus may be primed for influence by external behavioral demand such as increased use of an injured forelimb. The focus of this review is on the effects of altered use of the impaired forelimb in unilateral rodent models of brain injury. Both the benefits of increased use and the detrimental effects of decreased use following injury will be discussed.

Motor recovery and cortical reorganization after constraint-induced movement therapy in stroke patients: a preliminary study

Constraint-induced movement therapy (CIMT) is a physical rehabilitation regime that has been previously shown to improve motor function in chronic hemiparetic stroke patients. However, the neural mechanisms supporting rehabilitation-induced motor recovery are poorly understood. The goal of this study was to assess motor cortical reorganization after CIMT using functional magnetic resonance imaging (fMRI). In a repeated-measures design, 4 incompletely recovered chronic stroke patients treated with CIMT underwent motor function testing and fMRI. Five age-matched normal subjects were also imaged. A laterality index (LI) was determined from the fMRI data, reflecting the distribution of activation in motor cortices contralateral compared with ipsilateral to the moving hand. Pre-intervention fMRI showed a lower LI during affected hand movement of stroke patients (LI = 0.23+/-0.07) compared to controls (LI unaffected patient hand = 0.65+/-0.10; LI dominant normal hand = 0.65+/-0.11; LI nondominant normal hand = 0.69+/-0.11; P < 0.05) due to trends toward increased ipsilateral motor cortical activation. Motor function testing showed that patients made significant gains in functional use of the stroke-affected upper extremity (detected by the Motor Activity Log) and significant reductions in motor impairment (detected by the Fugl-Meyer Stroke Scale and the Wolf Motor Function Test) immediately after CIMT, and these effects persisted at 6-month follow-up. The behavioral effects of CIMT were associated with a trend toward a reduced LI from pre-intervention to immediately post-intervention (LI = -0.01+/-0.06, P = 0.077) and 6 months post-intervention (LI = -0.03+/-0.15). Stroke-affected hand movement was not accompanied by mirror movements during fMRI, and electromyographic measures of mirror recruitment under simulated fMRI conditions were not correlated with LI values. These data provide preliminary evidence that gains in motor function produced by CIMT in chronic stroke patients may be associated with a shift in laterality of motor cortical activation toward the undamaged hemisphere.

Functional improvement after motor training is correlated with synaptic plasticity in rat thalamus

The goals of this study were to determine whether functional outcome after motor training in rats was linked to synaptic plasticity in thalamus, and whether the Rota-rod apparatus, widely used to test motor function, could be used as an easy and quantitative motor skill training procedure. Adult female Sprague-Dawley rats (n = 39) were evaluated under three training conditions: 1. Movement requiring balance and coordination skills on Rota-rod; 2. simple exercise on treadmill; 3. nontrained controls. Motor function was evaluated by a series of motor tests (foot fault placing, parallel bar crossing, rope and ladder climbing) before and 14 or 28 days after training procedure. Synaptic strength in brain was assessed by synaptophysin immunocytochemistry. After 14 days of training, Rota-rod-trained animals significantly (p < 0.01) improved motor performance, compared to treadmill and nontrained animals. Animals with up to 28 days of simple exercises on the treadmill did not show a significantly improved performance on most motor tasks, except for an improvement in foot fault placing. Intensive synaptophysin immunoreactivity was present in the right but not the left mediodorsal and ventromedial nuclei of thalamus in Rota-rod-trained rats at 14 and 28 days, and in treadmill-trained rats at 28 days. The data suggested that functional outcome is effectively improved by motor skill training rather than by simple exercises, and this may be related, at least partially, to uniquely lateralized synaptogenesis in the thalamus. Both Rota-rod and treadmill could be quantitatively used in rats for motor training of different complexity.

Voluntary exercise induces a BDNF-mediated mechanism that promotes neuroplasticity

We have investigated potential mechanisms by which exercise can promote changes in neuronal plasticity via modulation of neurotrophins. Rodents were exposed to voluntary wheel running for 3 or 7 days, and their lumbar spinal cord and soleus muscle were assessed for changes in brain-derived neurotrophic factor (BDNF), its signal transduction receptor (trkB), and downstream effectors for the action of BDNF on synaptic plasticity. Exercise increased the expression of BDNF and its receptor, synapsin I (mRNA and phosphorylated protein), growth-associated protein (GAP-43) mRNA, and cyclic AMP response element-binding (CREB) mRNA in the lumbar spinal cord. Synapsin I, a synaptic mediator for the action of BDNF on neurotransmitter release, increased in proportion to GAP-43 and trkB mRNA levels. CREB mRNA levels increased in proportion to BDNF mRNA levels. In separate experiments, the soleus muscle was paralyzed unilaterally via intramuscular botulinum toxin type A (BTX-A) injection to determine the effects of reducing the neuromechanical output of a single muscle on the neurotrophin response to motor activity. In sedentary BTX-A-treated rats, BDNF and synapsin I mRNAs were reduced below control levels in the spinal cord and soleus muscle. Exercise did not change the BDNF mRNA levels in the spinal cord of BTX-A-treated rats but further reduced the BDNF mRNA levels in the paralyzed soleus relative to the levels in sedentary BTX-A-treated rats. Exercise also restored synapsin I to near control levels in the spinal cord. These results indicate that basal levels of neuromuscular activity are required to maintain normal levels of BDNF in the neuromuscular system and the potential for neuroplasticity.

Unilateral sensorimotor cortex lesions in adult rats facilitate motor skill learning with the "unaffected" forelimb and training-induced dendritic structural plasticity in the motor cortex

In humans and other animals, sufficient unilateral damage to the sensorimotor cortex can cause impairments in the opposite forelimb and the development of a hyper-reliance on the nonimpaired limb. This hyper-reliance is adaptive to the extent that it contributes to functional compensation for lesion-induced impairments. We have found that unilateral lesions of the forelimb region of the sensorimotor cortex (FLsmc) in rats, or callosal transections, cause neurons of the opposite motor cortex to become exceptionally responsive to changes in forelimb behavior. This enhanced responsiveness might facilitate learning of compensatory strategies with the nonimpaired forelimb after unilateral FLsmc lesions. The possibility that these lesions facilitate learning with the nonimpaired forelimb was addressed in this study. Rats were required to learn a skilled forelimb reaching task after either unilateral FLsmc lesions or sham operations. The trained limb in animals with lesions was the nonimpaired limb. Compared with shams, rats with unilateral lesions had a greater rate of acquisition and asymptotic performance level on the task, which was especially evident on more difficult trials. Quantitative measures of microtubule associated protein-2 (MAP2) immunostained dendrites indicated an enhancement of training-induced dendritic cytoskeletal changes in the motor cortex opposite lesions. Thus, unilateral FLsmc lesions facilitate learning of at least some types of motor skills using the nonimpaired forelimb as well as some of the neuronal changes associated with this learning. This facilitation could be a substrate underlying behavioral compensation for unilateral FLsmc damage and may contribute to the phenomenon of learned nonuse of the impaired limb.

Plasticity-associated molecular and structural events in the injured brain

Injury to the brain appears to create a fertile ground for functional and structural plasticity that is, at least partly, responsible for functional recovery. Increases in dendritic arborization, spine density, and synaptogenesis in both peri-injury and intact cortical areas are the potential morphological strategies that enable the brain to reorganize its neuronal circuits. These injury-initiated alterations are time-dependent and frequently proceed in interaction with behavior-related signals. A complex concert of a variety of genes/proteins is required to tightly control these changes. Two broad categories of molecules appear to be involved. First, regulatory molecules or effector molecules with regulatory function, such as immediate early genes/transcription factors, kinase network proteins, growth factors, and neurotransmitter receptors, and second, structural proteins, such as adhesion molecules and compounds of synapses, growth cones, and cytoskeleton. A better understanding of the processes contributing to postinjury plasticity may be an advantage for developing new and more effective therapeutic approaches. This knowledge might also shed light on other forms of brain plasticity, such as those involved in learning processes or ontogeny.

Specific plasticity of parallel fiber/Purkinje cell spine synapses by motor skill learning

New synapse formation may underlie learning and memory. To examine specific synaptic plasticity by motor learning, we conducted quantitative analysis of synapses between parallel fibers and Purkinje cell dendritic spines in cerebella of rats trained to complete various obstacle courses. Synapses between parallel fibers and Purkinje cell spines were classified into single synapse boutons, multiple synapse boutons, and multiple synapse spines by their different contact features. Acrobat-trained animals had more single and multiple synaptic boutons, without change of multiple synapse spines, than motor control animals. These results may suggest that motor learning induces specific synaptogenesis and Purkinje cell spines are primary sites in motor learning-dependent cerebellar synaptic plasticity.

The behavioral and dendritic growth effects of focal sensorimotor cortical damage depend on the method of lesion induction

Using different models of focal cortical injury in adult rats, the neural structural and behavioral outcomes of unilateral lesions of the forelimb representation of the sensorimotor cortex (SMC) were assessed. Lesions were produced using either electrolytic, aspiration, or combined ('electroaspiration') techniques. Measurements of dendritic arborization in layer V of the motor cortex opposite the lesion revealed a growth of pyramidal neuron dendritic processes following electrolytic lesions in comparison to shams. This effect was not found in either the aspiration or electroaspiration lesion groups. Behaviorally, animals in all lesion groups developed a hyper-reliance on the forelimb ipsilateral to the lesion and proportionate disuse of the contralateral (impaired) forelimb for postural support behaviors. In comparison to sham-operated animals, the initial asymmetries in behaviors expressed during movement were similar between lesion groups, but were less enduring following electrolytic lesions than following aspiration and electroaspiration lesions. Furthermore, both aspiration lesion groups had more prevalent adduction of the impaired forelimb than the electrolytic-only lesion rats. Thus, cortical aspiration resulted in more severe and enduring forelimb impairments than the electrolytic lesions, despite similar lesion sizes, as assessed using cortical volume measures. These findings suggest that the aspiration lesion procedures, at least as performed in the present study, exacerbate the behavioral effects of focal cortical injury and limit compensatory plasticity in the contralateral cortex.

Laminar-dependent dendritic spine alterations in the motor cortex of adult rats following callosal transection and forced forelimb use

Previously, the authors found that partial denervation of the motor cortex in adult animals can enhance this region's neuronal growth response to relevant behavioral change. Rats with partial corpus callosum transections that were forced to rely on one forelimb for 18 days had increased dendritic arborization of layer V pyramidal neurons in the opposite motor cortex compared to controls. This was not found as a result of denervation alone or of forced forelimb use alone. However, it seemed possible that each independent manipulation (i.e., forced forelimb use alone and callosal transections alone) resulted in neural structural alterations that were simply not revealed in measurements of dendritic branch number and/or not inclusive of layer V dendrites. This possibility was assessed in the current study with a reexamination of the Golgi-Cox impregnated tissue generated in the previous study. Tissue was quantified from rats that received either partial transections of the rostral two-thirds of the corpus callosum (CCX) or sham operations (Sham) followed either by 18 days of forced use of one forelimb (Use) or unrestricted use of both forelimbs (Cont). Measurements of apical and basilar dendrites from pyramidal neurons of layer II/III and layer V were performed to detect spine addition resulting from either increased spine density or the addition of dendritic material. As hypothesized, significant spine addition was found following forced forelimb use alone (Sham+Use) and callosal transections alone (CCX+Cont). However, forced use primarily increased spines on layer II/III pyramidal neurons, whereas callosal transections primarily increased dendritic spines on layer V pyramidal neurons in comparison to Sham+Cont. A much more robust increase in layer V dendritic spines was found in animals with the combination of forced forelimb use and denervation (CCX+Use). In contrast to the effects of forced use alone, however, CCX+Use rats failed to show major net increases in spines on layer II/III neurons. These results indicate that while callosal denervation may greatly enhance the neuronal growth and synaptogenic response to behavioral change in layer V, it may also limit spine addition associated with forced forelimb use in layer II/III of the motor cortex.

Modification of brain aging and neurodegenerative disorders by genes, diet, and behavior

Multiple molecular, cellular, structural, and functional changes occur in the brain during aging. Neural cells may respond to these changes adaptively, or they may succumb to neurodegenerative cascades that result in disorders such as Alzheimer's and Parkinson's diseases. Multiple mechanisms are employed to maintain the integrity of nerve cell circuits and to facilitate responses to environmental demands and promote recovery of function after injury. The mechanisms include production of neurotrophic factors and cytokines, expression of various cell survival-promoting proteins (e.g., protein chaperones, antioxidant enzymes, Bcl-2 and inhibitor of apoptosis proteins), preservation of genomic integrity by telomerase and DNA repair proteins, and mobilization of neural stem cells to replace damaged neurons and glia. The aging process challenges such neuroprotective and neurorestorative mechanisms. Genetic and environmental factors superimposed upon the aging process can determine whether brain aging is successful or unsuccessful. Mutations in genes that cause inherited forms of Alzheimer's disease (amyloid precursor protein and presenilins), Parkinson's disease (alpha-synuclein and Parkin), and trinucleotide repeat disorders (huntingtin, androgen receptor, ataxin, and others) overwhelm endogenous neuroprotective mechanisms; other genes, such as those encoding apolipoprotein E(4), have more subtle effects on brain aging. On the other hand, neuroprotective mechanisms can be bolstered by dietary (caloric restriction and folate and antioxidant supplementation) and behavioral (intellectual and physical activities) modifications. At the cellular and molecular levels, successful brain aging can be facilitated by activating a hormesis response in which neurons increase production of neurotrophic factors and stress proteins. Neural stem cells that reside in the adult brain are also responsive to environmental demands and appear capable of replacing lost or dysfunctional neurons and glial cells, perhaps even in the aging brain. The recent application of modern methods of molecular and cellular biology to the problem of brain aging is revealing a remarkable capacity within brain cells for adaptation to aging and resistance to disease.

Step training with body weight support: effect of treadmill speed and practice paradigms on poststroke locomotor recovery

OBJECTIVE

To investigate the effect of practice paradigms that varied treadmill speed during step training with body weight support in subjects with chronic hemiparesis after stroke.

DESIGN

Randomized, repeated-measures pilot study with 1- and 3-month follow-ups.

SETTING

Outpatient locomotor laboratory.

PARTICIPANTS

Twenty-four individuals with hemiparetic gait deficits whose walking speeds were at least 50% below normal.

INTERVENTION

Participants were stratified by locomotor severity based on initial walking velocity and randomly assigned to treadmill training at slow (0.5mph), fast (2.0mph), or variable (0.5, 1.0, 1.5, 2.0mph) speeds. Participants received 20 minutes of training per session for 12 sessions over 4 weeks.

MAIN OUTCOME MEASURE

Self-selected overground walking velocity (SSV) was assessed at the onset, middle, and end of training, and 1 and 3 months later.

RESULTS

SSV improved in all groups compared with baseline (P<.001). All groups increased SSV in the 1-month follow-up (P<.01) and maintained these gains at the 3-month follow-up (P=.77). The greatest improvement in SSV across training occurred with fast training speeds compared with the slow and variable groups combined (P=.04). Effect size (ES) was large between fast compared with slow (ES=.75) and variable groups (ES=.73).

CONCLUSIONS

Training at speeds comparable with normal walking velocity was more effective in improving SSV than training at speeds at or below the patient's typical overground walking velocity.

Impaired motor activity and motor learning function in rat with middle cerebral artery occlusion

The poor quality of life after a stroke is largely attributed to deficits in cognitive-motor functioning. The goals of this study were to detect if damaged motor learning function were attributed to motor deficits in rats following a transient middle cerebral artery (MCA) occlusion. Stroke was induced by a 2-h occlusion of the MCA using an intraluminal filament. Motor functions were evaluated from 5 up to 28 days after reperfusion in ischemic and control rats. Motor function was detected by a series of motor tests (runway traversing and beam balancing, as well as foot fault placing, parallel bar crossing, rope and ladder climbing), and motor learning behavior was determined by analyzing the rate of improvement of impaired function during performance of the motor tasks. Significant (P<0.001) motor deficits were detected in the stroke group (n=10) while performing motor tasks that involve extensive coordination, in comparison to the controls (n=12). Although motor behavior was improved with repeated behavior testing, unparalleled rate of improvement of motor performance on rope and ladder climbing tests was found between the two groups, suggesting an impaired motor learning function. Brain tissue damage was detected in the ischemic animals 28 days after surgery, demonstrated by 40% infarct volume of contralateral hemisphere. Both motor learning and motor function were impaired in ischemic rats. The motor tests used in this study are sensitive, semi-quantitative, and reproducible measurements of functional impairment in rats following an ischemic stroke.

Neural adaptations to resistance training: implications for movement control

It has long been believed that resistance training is accompanied by changes within the nervous system that play an important role in the development of strength. Many elements of the nervous system exhibit the potential for adaptation in response to resistance training, including supraspinal centres, descending neural tracts, spinal circuitry and the motor end plate connections between motoneurons and muscle fibres. Yet the specific sites of adaptation along the neuraxis have seldom been identified experimentally, and much of the evidence for neural adaptations following resistance training remains indirect. As a consequence of this current lack of knowledge, there exists uncertainty regarding the manner in which resistance training impacts upon the control and execution of functional movements. We aim to demonstrate that resistance training is likely to cause adaptations to many neural elements that are involved in the control of movement, and is therefore likely to affect movement execution during a wide range of tasks. We review a small number of experiments that provide evidence that resistance training affects the way in which muscles that have been engaged during training are recruited during related movement tasks. The concepts addressed in this article represent an important new approach to research on the effects of resistance training. They are also of considerable practical importance, since most individuals perform resistance training in the expectation that it will enhance their performance in related functional tasks.

Prereperfusion flushing of ischemic territory: a therapeutic study in which histological and behavioral assessments were used to measure ischemia-reperfusion injury in rats with stroke

OBJECT

In ischemic stroke, the ischemic crisis activates a cascade of traumatic events that are potentiated by reperfusion and eventually lead to neuronal degeneration. The primary aim of this study was to investigate a procedure that could minimize this damage by interfering with the interactions between reestablished blood flow and ischemically damaged tissue, as well as by improving regional microcirculation.

METHODS

Using a novel hollow filament, the authors flushed the ischemic territory with heparinized saline before vascular reperfusion after occlusion of the middle cerebral artery (MCA). The results demonstrate a statistically significant (p < 0.001) reduction in infarct volume (75%; from 45.3 +/- 3.6% to 11.4 +/- 1.7%, determined with Nissl staining) in rats in which a 2-hour MCA occlusion was followed by a 48-hour reperfusion. Infarction and neuronal degeneration were confirmed using silver staining, which revealed a significantly larger infarct (36.3%, p < 0.05) than that detected with Nissl staining. The long-term neuroprotection of the prereperfusion flushing was also evaluated. This was determined by a series of motor behavior tasks (foot placing, parallel bar traversing, rope and ladder climbing) performed up to 28 days after reperfusion. Motor deficits were found to be significantly ameliorated in animals that underwent the flushing procedure (p < 0.001). In addition, neurological outcome was also improved significantly (p < 0.001) in the same animals.

CONCLUSIONS

These results indicate that interaction between reperfusion and the metabolically and biochemically compromised tissue could be interrupted by the prereperfusion flushing procedure, which could lead to a reduction in brain injury from stroke. Mechanical reopening of the cerebral occlusion with local flushing and isolated reperfusion of the regionally injured brain might offer new treatment options for patients with stroke.

Neuronal plasticity and dendritic spines: effect of environmental enrichment on intact and postischemic rat brain

The authors compared the influence of environmental enrichment on intact and lesioned brain, and tested the hypothesis that postischemic exposure to an enriched environment can alter dendritic spine density in pyramidal neurons contralateral to a cortical infarct. The middle cerebral artery was occluded distal to the striatal branches in spontaneously hypertensive rats postoperatively housed either in a standard or in an enriched environment. Intact rats were housed in the same environment. Three weeks later the brains were perfused in situ. The dendritic and spine morphology was studied with three-dimensional confocal laser scanning microscopy after microinjection of Lucifer yellow in pyramidal neurons in layers II/III and V/VI in the somatosensory cortex. In intact rats, the number of dendritic spines was significantly higher in the enriched group than in the standard group in all layers ( P < 0.05). Contralateral to the infarct, pyramidal neurons in layers II/III, which have extensive intracortical connections that may play a role in cortical plasticity, had significantly more spines in the enriched group than in the standard group ( P < 0.05). No difference was observed in layers V/VI. They conclude that housing rats in an enriched environment significantly increases spine density in superficial cortical layers in intact and lesioned brain, but in deeper layers of intact brain.

Motor learning-dependent synaptogenesis is localized to functionally reorganized motor cortex

The regional specificity and functional significance of learning-dependent synaptogenesis within physiologically defined regions of the adult motor cortex are described. In comparison to rats in a motor activity control group, rats trained on a skilled reaching task exhibited an areal expansion of wrist and digit movement representations within the motor cortex. No expansion of hindlimb representations was seen. This functional reorganization was restricted to the caudal forelimb area, as no differences in the topography of movement representations were observed within the rostral forelimb area. Paralleling the physiological changes, trained animals also had significantly more synapses per neuron than controls within layer V of the caudal forelimb area. No differences in the number of synapses per neuron were found in either the rostral forelimb or hindlimb areas. This is the first demonstration of the co-occurrence of functional and structural plasticity within the same cortical regions and provides strong evidence that synapse formation may play a role in supporting learning-dependent changes in cortical function.

Changes in motor cortex activation after recovery from spinal cord inflammation

Diseases of the spinal cord are associated with reactive changes in cerebral cortex organization. Many studies in this area have examined spinal cord conditions not associated with recovery, making it difficult to consider the value of these cortical events in the restoration of neurological function. We studied patients with myelitis, a syndrome of transient spinal cord inflammation, in order to probe cortical changes that might contribute to recovery after disease of the spinal cord. Seven patients, each of whom showed improvement in hand motor function after a diagnosis of myelitis involving cervical spinal cord, were clinically evaluated then studied with functional MRI. During right and left index finger tapping, activation volumes were assessed in three cortical motor regions within each hemisphere. Results were compared with findings in nine control subjects. Compared to the control group, myelitis patients had larger activation volumes within contralateral sensorimotor as well as contralateral premotor cortex. The degree of daily hand use showed a significant correlation with the volume of activation in contralateral sensorimotor cortex. Recovery from myelitis is associated with an enlarged activation volume in contralateral motor cortices. This change in motor cortex function is related to behavioral experience, and thus may contribute to motor improvement. The expanded activation in motor cortex, seen with several forms of spinal cord insult may have maximal utility when corticospinal tract axons are preserved.

Long-term neuroprotective effect of inhibiting poly(ADP-ribose) polymerase in rats with middle cerebral artery occlusion using a behavioral assessment

Poly(ADP-ribose) polymerase (PARP) can initiate an energy-consuming and inefficient repair cycle following cerebral ischemia/reperfusion by transferring ADP ribose units to nuclear proteins eventually leading to cellular dysfunction and neuronal death. 3-Aminobenzamide (3-AB) is a selective inhibitor of PARP that can significantly reduce brain damage after focal ischemia in rats and displays a low toxicity in vivo. The goals of this study were to determine if inhibiting PARP with 3-AB has a long-term neuroprotective effect and if functional outcome improves in rats following focal ischemia and treatment with 3-AB. Focal ischemia was induced by a 2-h occlusion of the middle cerebral artery (MCA), using an intraluminal filament. Motor functions were evaluated from 5 to 28 days after reperfusion in four groups of rats: stroke without treatment; stroke treated with 3-AB at doses of 15 mg/kg, stroke treated with 3-AB at doses of 55 mg/kg; and the non-ischemic control rats. Functional behaviors were tested by a series of motor function tasks (foot placing, parallel bar crossing, rope and ladder climbing), as well as a neurological examination. Infarct volume of stroke brain in the same rat was determined by Nissl staining 28 days after surgery. Comparison of the untreated stroke group (n=11) and the treated stroke groups indicates that impairment of motor function was significantly (P<0.001) reduced by administration of 3-AB at doses of 15 mg/kg (n=9) or 55 mg/kg (n=10). Neurological outcome was also improved significantly (P<0.001). Infarct volume was significantly (P<0.01) reduced in both treated groups. Long-term neuroprotection following ischemia/reperfusion injury to the brain can be obtained by administration of a PARP inhibitor. The motor tests employed in this study can be used as sensitive, objective and reproducible measurements of functional impairment in rats following an ischemic stroke.

Dysregulation of cellular calcium homeostasis in Alzheimer's disease: bad genes and bad habits

Calcium is one of the most important intracellular messengers in the brain, being essential for neuronal development, synaptic transmission and plasticity, and the regulation of various metabolic pathways. The findings reviewed in the present article suggest that calcium also plays a prominent role in the pathogenesis of Alzheimer's disease (AD). Associations between the pathological hallmarks ofAD (neurofibrillary tangles [NFT] and amyloid plaques) and perturbed cellular calcium homeostasis have been established in studies of patients, and in animal and cell culture models of AD. Studies of the effects of mutations in the beta-amyloid precursor protein (APP) and presenilins on neuronal plasticity and survival have provided insight into the molecular cascades that result in synaptic dysfunction and neuronal degeneration in AD. Central to the neurodegenerative process is the inability of neurons to properly regulate intracellular calcium levels. Increased levels of amyloid beta-peptide (Abeta) induce oxidative stress, which impairs cellular ion homeostasis and energy metabolism and renders neurons vulnerable to apoptosis and excitotoxicity. Subtoxic levels of Abeta may induce synaptic dysfunction by impairing multiple signal transduction pathways. Presenilin mutations perturb calcium homeostasis in the endoplasmic reticulum in a way that sensitizes neurons to apoptosis and excitotoxicity; links between aberrant calcium regulation and altered APP processing are emerging. Environmental risk factors for AD are being identified and may include high calorie diets, folic acid insufficiency, and a low level of intellectual activity (bad habits); in each case, the environmental factor impacts on neuronal calcium homeostasis. Low calorie diets and intellectual activity may guard against AD by stimulating production of neurotrophic factors and chaperone proteins. The emerging picture of the cell and molecular biology of AD is revealing novel preventative and therapeutic strategies for eradicating this growing epidemic of the elderly.

Role of adaptive plasticity in recovery of function after damage to motor cortex

Based upon neurophysiologic, neuroanatomic, and neuroimaging studies conducted over the past two decades, the cerebral cortex can now be viewed as functionally and structurally dynamic. More specifically, the functional topography of the motor cortex (commonly called the motor homunculus or motor map), can be modified by a variety of experimental manipulations, including peripheral or central injury, electrical stimulation, pharmacologic treatment, and behavioral experience. The specific types of behavioral experiences that induce long-term plasticity in motor maps appear to be limited to those that entail the development of new motor skills. Moreover, recent evidence demonstrates that functional alterations in motor cortex organization are accompanied by changes in dendritic and synaptic structure, as well as alterations in the regulation of cortical neurotransmitter systems. These findings have strong clinical relevance as it has recently been shown that after injury to the motor cortex, as might occur in stroke, post-injury behavioral experience may play an adaptive role in modifying the functional organization of the remaining, intact cortical tissue.

Associative learning elicits the formation of multiple-synapse boutons

The formation of new synapses has been suggested to underlie learning and memory. However, previous work from this laboratory has demonstrated that hippocampus-dependent associative learning does not induce a net gain in the total number of hippocampal synapses and, hence, a net synaptogenesis. The aim of the present work was to determine whether associative learning involves a specific synaptogenesis confined to the formation of multiple-synapse boutons (MSBs) that synapse with more than one dendritic spine. We used the behavioral paradigm of trace eyeblink conditioning, which is a hippocampus-dependent form of associative learning. Conditioned rabbits were given daily 80-trial sessions to a criterion of 80% conditioned responses in a session. During each trial, the conditioned stimulus (tone) and the unconditioned stimulus (corneal airpuff) were presented with an intervening trace interval of 500 msec. Brain tissue was taken for morphological analyses 24 hr after the last session. Unbiased stereological methods were used for obtaining estimates of the total number of MSBs in the stratum radiatum of hippocampal subfield CA1. The results showed that the total number of MSBs was significantly increased in conditioned rabbits as compared with pseudoconditioned or unstimulated controls. This conditioning-induced change, which occurs without a net synaptogenesis, reflects a specific synaptogenesis resulting in MSB formation. Models of the latter process are proposed. The models postulate that it requires spine motility and may involve the relocation of existing spines from nonactivated boutons or the outgrowth of newly formed spines for specific synaptogenesis with single-synapse boutons activated by the conditioning stimulation.

Enriched rehabilitative training promotes improved forelimb motor function and enhanced dendritic growth after focal ischemic injury

Chronic impairment of forelimb and digit movement is a common problem after stroke that is resistant to therapy. Previous studies have demonstrated that enrichment improves behavioral outcome after focal ischemia; however, postischemic enrichment alone is not capable of enhancing fine digit and forelimb function. Therefore, we combined environmental enrichment with daily skilled-reach training to assess the effect of intensive task-specific rehabilitation on long-term functional outcome. Rats were subjected to either endothelin-1-induced focal ischemia or sham surgery and subsequently designated to enriched-rehabilitation or standard-housing treatment groups starting 15 d after ischemia. Functional assessment of the affected forelimb at 4 and 9 weeks after treatment revealed that ischemic plus enrichment (IE) animals had improved approximately 30% on the staircase-reaching task and were indistinguishable from sham animals for both latency and foot faults in a beam-traversing task. In contrast, ischemic plus standard (IS) animals remained significantly impaired on both tasks. Interestingly, both ischemic groups (IE and IS) relied on the nonaffected forelimb during upright weight-bearing movements, a pattern that persisted for the duration of the experiment. Dendritic arborization of layer V pyramidal cells within the undamaged motor cortex was examined using a Golgi-Cox procedure. IE animals showed enhanced dendritic complexity and length compared with both IS and sham groups. These results suggest that enrichment combined with task-specific rehabilitative therapy is capable of augmenting intrinsic neuronal plasticity within noninjured, functionally connected brain regions, as well as promoting enhanced functional outcome.

Corticospinal responses to motor training revealed by transcranial magnetic stimulation

Transcranial magnetic stimulation was recently used to investigate the nature of adaptations that occur in the central nervous system in response to motor training. In this report, we provide a brief description of trancranial magnetic stimulation and discuss its potential as a tool for identifying corticospinal response to exercise.

Experience-dependent structural plasticity in cortex heterotopic to focal sensorimotor cortical damage

Structural plasticity following focal neocortical damage in adult rats has recently been found to be sensitive to postinjury rehabilitative training. Experience on a complex motor skills task, the acrobatic task, after unilateral lesions of the forelimb representation region of the sensorimotor cortex (FLsmc) enhanced synaptic structural changes in the cortex contralateral and homotopic to the lesions. Using tissue from this previous study, the present study examined whether a heterotopic region of the sensorimotor cortex of either hemisphere, the hindlimb representation area (HLsmc), would undergo structural changes following unilateral FLsmc lesions and whether these changes would also be sensitive to postinjury training on the acrobatic task. Stereological methods for light and electron microscopy were used to assess structural changes in lesion or sham-operated rats following 28 days of postoperative acrobatic training or simple repetitive exercise (motor controls). In the HLsmc contralateral to the lesions of rats receiving acrobatic training, there was a subtle, but significant, increase in cortical volume and in layer II/III neuropil and dendritic volume per neuron in comparison to shams. In rats receiving simple exercise after the lesions, these changes were not significantly different from shams. Acrobatic training also prevented a loss of cortical volume in the HLsmc adjacent to the lesion in comparison to shams. These data suggest that behavioral training following cortical injury facilitates structural plasticity in behaviorally relevant areas of the neocortex other than the homotopic cortex contralateral to the lesion. This structural plasticity might be relevant to the development of behavioral compensation after cortical injury.

Experience-associated structural events, subependymal cellular proliferative activity, and functional recovery after injury to the central nervous system

Considerable structural plasticity is possible in the damaged neocortex and connected brain areas, and the potential for significant functional recovery remains even during the chronic phases of the recovery process. In this article, the authors review the literature on use-dependent morphologic events, focusing on the direct interaction of behavioral experience and structural changes associated with plasticity and degeneration. Experience-associated neural changes have the potential to either hinder or enhance functional recovery; therefore, issues concerning the nature, timing, and intensity of behavior-based intervention strategies are addressed.

Functional differentiation of multiple perilesional zones after focal cerebral ischemia

Transient and permanent focal cerebral ischemia results in a series of typical pathophysiologic events. These consequences evolve in time and space and are not limited to the lesion itself, but they can be observed in perilesional (penumbra) and widespread ipsi- and sometimes contralateral remote areas (diaschisis). The extent of these areas is variable depending on factors such as the type of ischemia, the model, and the functional modality investigated. This review describes some typical alterations attributable to focal cerebral ischemia using the following classification scheme to separate different lesioned and perilesional areas: (1) The lesion core is the brain area with irreversible ischemic damage. (2) The penumbra is a brain region that suffers from ischemia, but in which the ischemic damage is potentially, or at least partially, reversible. (3) Remote brain areas are brain areas that are not directly affected by ischemia. With respect to the etiology, several broad categories of remote changes may be differentiated: (3a) remote changes caused by brain edema; (3b) remote changes caused by waves of spreading depression; (3c) remote changes in projection areas; and (3d) remote changes because of reactive plasticity and systemic effects. The various perilesional areas are not necessarily homogeneous; but a broad differentiation of separate topographic perilesional areas according to their functional state and sequelae allows segregation into several signaling cascades, and may help to understand the functional consequences and adaptive processes after focal brain ischemia.

Denervation facilitates neuronal growth in the motor cortex of rats in the presence of behavioral demand

This study tests the hypothesis that degeneration of a neocortical pathway may facilitate behaviorally-induced growth of neurons in a connected region of the cortex. Degeneration of trancallosal afferents to the motor cortex and changes in forelimb use were independently manipulated in adult rats. The combination of degeneration and behavioral change resulted in the growth of layer V pyramidal neuron dendrites which was not found as a result of either denervation or behavioral manipulation alone. These results indicate that mild degeneration in the adult brain can facilitate neuronal growth when accompanied by appropriate behavioral demand, a finding which has implications for rehabilitative therapy after brain damage.

Reactive astrocytic responses to denervation in the motor cortex of adult rats are sensitive to manipulations of behavioral experience

Recent research has suggested that mild denervation of the neocortex of adult rats may facilitate neuronal growth in response to behavioral changes. Astrocytes react to denervation, produce growth-promoting factors and are a potential mediator of this denervation-facilitated growth. The present study assessed whether astrocytic reactions to denervation vary dependent upon post-injury behavioral experience. Denervation of the transcallosal afferents to the motor cortex was induced via partial transections of the corpus callosum. Transected- or sham-operated rats were then either forced to use the opposite forelimb (via limb-restricting vests) or permitted to use both forelimbs normally for 8 days. In the motor cortex, the surface density of glial fibrillary acidic protein (GFAP)-immunoreactive (IR) astrocytic processes and the density of basic fibroblast growth factor (FGF-2)-IR glial cells was significantly increased as a result of transections alone and as a result of forced forelimb-use alone in comparison to controls. The combination of transections and forced-use significantly enhanced GFAP-IR in comparison to all other groups, but did not further enhance FGF-2-IR. These findings are consistent with behavior and denervation having interactive influences on astrocytic reactivity in the motor cortex. These results also raise the possibility that astrocyte-mediated support of neural restructuring after brain injury might be enhanced with appropriate post-injury behavioral manipulations.

Physiological consequences of morphologically detectable synaptic plasticity: potential uses for examining recovery following damage

A growing literature indicates that brain structure is modified in various ways with experience. In this paper we briefly survey evidence that the brain retains the capacity to modify its organization in response to demands, including demands resulting from learning, throughout the lifetime. We attempt to address whether these experience-induced changes are accompanied by physiological changes that indicate a functional reorganization of the brain. The kinds of morphological changes that have been observed following brain injury appear to be very similar to those seen after learning. The similarity suggests that many of the basic mechanisms of synaptic change in the brain may be utilized for both functions. This suggests that we can take advantage of some of the methods used to test the changes in physiology with behavioral manipulations to examine the damaged brain. We advocate utilizing electrophysiological techniques to measure functional recovery from brain injury as these may be useful in evaluating both spontaneous recovery from damage and the therapeutic benefits of training, or other therapies.