Neocortical neural sprouting, synaptogenesis, and behavioral recovery after neocortical infarction in rats

Unilateral hemispherectomy at adulthood asymmetrically affects motor performance of male Swiss mice

Evidence exists indicating that cerebral lateralization is a fundamental feature of all vertebrates. In humans, a series of studies demonstrated that the left hemisphere plays a major role in controlling movement. No such asymmetries have been identified in rodents, in spite of the fact that these animals have been frequently used in studies assessing motor behavior. In this regard, here, we used unilateral hemispherectomy to study the relative importance of each hemisphere in controlling movement. Adult Swiss mice were submitted to right unilateral hemispherectomy (RH), left unilateral hemispherectomy (LH) or sham surgery. Fifteen days after surgery, motor performance was assessed in the accelerating rotarod test and in the foot-fault test (in which performance depends on skilled limb use) and in the elevated body swing test (in which performance depends on trunk movements). The surgical removal of the right hemisphere caused a more pronounced impairment in performance than the removal of the left hemisphere both in the rotarod and in the foot-fault tests. In the rotarod, the RH group presented smaller latencies to fall than both LH and sham groups. In the foot-fault test, while both the sham and the LH groups showed no differences between left and right hind limbs, the RH group showed significantly worse performance with the left hind limb than with the right one. The elevated body swing test revealed a similar impairment in the two hemispherectomized groups. Our data suggest a major role of the right hemisphere in controlling skilled limb movements in mice.

Modifying neurorepair and neuroregenerative factors with tPA and edaravone after transient middle cerebral artery occlusion in rat brain

Changes in expression of neurorepair and neuroregenerative factors were examined after transient cerebral ischemia in relation to the effects of tissue plasminogen activator (tPA) and the free radical scavenger edaravone. Physiological saline or edaravone was injected twice during 90 min of transient middle cerebral artery occlusion (tMCAO) in rats, followed by the same saline or tPA at reperfusion. Sizes of the infarct and protein factors relating to neurorepair and neuroregeneration were examined at 4d after tMCAO. The protein factors examined were: a chondroitin sulfate proteoglycan neurocan, semaphorin type 3A (Sema3A), a myelin-associated glycoprotein receptor (Nogo receptor, Nogo-R), a synaptic regenerative factor (growth associated protein-43, GAP43), and a chemotropic factor netrin receptor (deleted in colorectal cancer, DCC). Two groups treated by edaravone only or edaravone plus tPA showed a reduction in infarct volume compared to the two groups treated by vehicle only or vehicle plus tPA. Immunohistochemistry and western blot analyses indicated that protein expression of neurocan, Sema3A, Nogo-R, GAP43, and DCC was decreased with tPA, but recovered with edaravone. Additive edaravone prevented the reductions of these five proteins induced by tPA. The present study demonstrates for the first time that exogenous tPA reduced protein factors involved in inhibiting and promoting axonal growth, but that edaravone ameliorated such damage in brain repair after acute ischemia.

Functional recovery in aging mice after experimental stroke

Aging is a non-modifiable risk factor for stroke. Since not all strokes can be prevented, a major emerging area of research is the development of effective strategies to enhance functional recovery after stroke. However, in the vast majority of pre-clinical stroke studies, the behavioral tests used to assess functional recovery have only been validated for use in young animals, or are designed for rats. Mice are increasingly utilized in stroke models but well validated behavioral tests designed for rats are not necessarily reproducible in mice. We examined a battery of behavioral tests to evaluate functional recovery in an aging murine model of stroke. We found that the vertical pole, hanging wire and open field can accurately assess acute behavioral impairments after stroke in both young and aging male mice, but animals recover rapidly on these tasks. The corner test can accurately and repeatedly differentiate stroke from sham animals up to 30 days post stroke and can be performed reliably in aging mice. Aging male mice had significantly worse behavioral impairment compared to young male mice in the first two weeks after stroke but eventually recovered to the same degree as young mice. In contrast, chronic infarct size, as measured by ipsilateral cerebral atrophy, was significantly lower in aging male mice compared to young male mice. Reactive gliosis, formation of glial scar, and an enhanced innate immune response was seen in the aging brain and may contribute to the delayed behavioral recovery seen in the aging animals.

Bidirectional axonal plasticity during reorganization of adult rat primary somatosensory cortex

Cortical sensory maps contain discrete functional subregions that are separated by borders that restrict tangential activity flow. Interestingly, the functional organization of border regions remains labile in adults, changing in an activity-dependent manner. Here, we investigated if axon remodeling contributes to this reorganization. We located the border between the forepaw and lower jaw representation (forepaw/lower jaw border,(1) FP/LJ border) in SI of adult rats, and used a retrograde axonal tracer (cholera toxin subunit B(2), Ctb) to determine if horizontal axonal projections change after different durations of forelimb denervation or sham-denervation. In sham-denervated animals, neurons close to the border had axonal projections oriented away from the border (axonal bias). Forelimb denervation resulted in a sustained change in border location and a significant reduction in the axonal bias at the original border after 6 weeks of denervation, but not after 4 or 12 weeks. The change in axonal bias was due to an increase in axons that cross the border at 6 weeks, followed by an apparent loss of these axons by 12 weeks. This suggests that bidirectional axonal rearrangements are associated with relatively long durations of reorganization and could contribute transiently to the maintenance of cortical reorganization.

Endogenous tissue plasminogen activator mediates bone marrow stromal cell-induced neurite remodeling after stroke in mice

BACKGROUND AND PURPOSE

Bone marrow stromal cells (BMSC) decrease neurological deficits in rodents after stroke and concomitantly induce extensive neurite remodeling in the brain, which highly correlates with the improvement of neurological function. We investigated the effects of endogenous tissue plasminogen activator (tPA) on neurite remodeling after BMSC treatment.

METHODS

Adult C57BL/6 wild-type (WT) mice and tPA knockout (tPA(-/-)) mice were subjected to middle cerebral artery occlusion, followed by an injection of 1×10(6) BMSC (n=18) or phosphate-buffered saline (n=18) into the tail vein 24 hours later. Behavioral tests were performed at 3, 7, and 14 days after middle cerebral artery occlusion. Animals were euthanized at 14 days after stroke.

RESULTS

The effects of BMSC on functional recovery depended on presence or absence of tPA, even after adjusting for imbalanced stroke severity. BMSC significantly improve functional recovery in WT mice compared to WT controls but show no beneficial effect in the tPA(-/-) mice compared to tPA(-/-) controls. Axonal density and synaptophysin-positive areas along the ischemic boundary zone of the cortex and striatum in WT mice are significantly higher than in the tPA(-/-) mice. BMSC treatment significantly increases tPA protein level and activity only in WT mice.

CONCLUSIONS

Our results suggest that endogenous tPA promotes BMSC-induced neurite outgrowth and may contribute to functional recovery after stroke.

Neuroplasticity in the context of motor rehabilitation after stroke

Approximately one-third of patients with stroke exhibit persistent disability after the initial cerebrovascular episode, with motor impairments accounting for most poststroke disability. Exercise and training have long been used to restore motor function after stroke. Better training strategies and therapies to enhance the effects of these rehabilitative protocols are currently being developed for poststroke disability. The advancement of our understanding of the neuroplastic changes associated with poststroke motor impairment and the innate mechanisms of repair is crucial to this endeavor. Pharmaceutical, biological and electrophysiological treatments that augment neuroplasticity are being explored to further extend the boundaries of poststroke rehabilitation. Potential motor rehabilitation therapies, such as stem cell therapy, exogenous tissue engineering and brain-computer interface technologies, could be integral in helping patients with stroke regain motor control. As the methods for providing motor rehabilitation change, the primary goals of poststroke rehabilitation will be driven by the activity and quality of life needs of individual patients. This Review aims to provide a focused overview of neuroplasticity associated with poststroke motor impairment, and the latest experimental interventions being developed to manipulate neuroplasticity to enhance motor rehabilitation.

Post-acute delivery of erythropoietin induces stroke recovery by promoting perilesional tissue remodelling and contralesional pyramidal tract plasticity

The promotion of post-ischaemic motor recovery remains a major challenge in clinical neurology. Recently, plasticity-promoting effects have been described for the growth factor erythropoietin in animal models of neurodegenerative diseases. To elucidate erythropoietin's effects in the post-acute ischaemic brain, we examined how this growth factor influences functional neurological recovery, perilesional tissue remodelling and axonal sprouting of the corticorubral and corticobulbar tracts, when administered intra-cerebroventricularly starting 3 days after 30 min of middle cerebral artery occlusion. Erythropoietin administered at 10 IU/day (but not at 1 IU/day), increased grip strength of the contralesional paretic forelimb and improved motor coordination without influencing spontaneous locomotor activity and exploration behaviour. Neurological recovery by erythropoietin was associated with structural remodelling of ischaemic brain tissue, reflected by enhanced neuronal survival, increased angiogenesis and decreased reactive astrogliosis that resulted in reduced scar formation. Enhanced axonal sprouting from the ipsilesional pyramidal tract into the brainstem was observed in vehicle-treated ischaemic compared with non-ischaemic animals, as shown by injection of dextran amines into both motor cortices. Despite successful remodelling of the perilesional tissue, erythropoietin enhanced axonal sprouting of the contralesional, but not ipsilesional pyramidal tract at the level of the red and facial nuclei. Moreover, molecular biological and histochemical studies revealed broad anti-inflammatory effects of erythropoietin in both hemispheres together with expression changes of plasticity-related molecules that facilitated contralesional axonal growth. Our study establishes a plasticity-promoting effect of erythropoietin after stroke, indicating that erythropoietin acts via recruitment of contralesional rather than of ipsilesional pyramidal tract projections.

Early motor balance and coordination training increased synaptophysin in subcortical regions of the ischemic rat brain

The aim of this study was to evaluate the effect of early motor balance and coordination training on functional recovery and brain plasticity in an ischemic rat stroke model, compared with simple locomotor exercise. Adult male Sprague-Dawley rats with cortical infarcts were trained under one of four conditions: nontrained control, treadmill training, motor training on the Rota-rod, or both Rota-rod and treadmill training. All types of training were performed from post-operation day 1 to 14. Neurological and behavioral performance was evaluated by Menzies' scale, the prehensile test, and the limb placement test, at post-operation day 1, 7, and 14. Both Rota-rod and treadmill training increased the expression of synaptophysin in subcortical regions of the ischemic hemisphere including the hippocampus, dentate gyrus, and thalamus, but did not affect levels of brain-derived neurotrophic factor or tyrosin kinase receptor B. The Rota-rod training also improved Menzies' scale and limb placement test scores, whereas the simple treadmill training did neither. The control group showed significant change only in Menzies' scale score. This study suggests that early motor balance and coordination training may induce plastic changes in subcortical regions of the ischemic hemisphere after stroke accompanied with the recovery of sensorimotor performance.

Local hemodynamics dictate long-term dendritic plasticity in peri-infarct cortex

Changes in dendritic spine turnover are a major mechanism of experience-dependent plasticity in the adult neocortex. Dendritic spine plasticity may also contribute to functional recovery after stroke, but in that setting its expression may be complicated by alterations in local tissue perfusion, especially around the infarct. Using adult Thy-1 GFP-M mice, we simultaneously recorded long-term spine dynamics in apical dendrites from layer 5 pyramidal cells and blood flow from surrounding capillaries with in vivo two-photon microscopy in peri-infarct cortex before and after unilateral middle cerebral artery occlusion. Blood flow in peri-infarct cortex decreased significantly immediately after stroke and improved gradually over time, in a distance-dependent manner from the epicenter of the infarct. However, local tissue perfusion was never fully restored even after a 3 month recovery period. On average, surviving layer 5 pyramidal neurons experienced a ∼20% decrease in spine density acutely after stroke but eventually recovered. The dynamics of this improvement were different depending on the degree of tissue perfusion acutely after arterial occlusion. Cells in ischemic areas closer to the infarct returned to normal spine density levels slowly by retaining spines, while cells in more remote regions with preserved blood flow recovered faster by adding more spines, eventually surpassing baseline spine density by 15%. Our data suggest that maintaining tissue perfusion in the area surrounding the infarct could hasten or augment synaptic plasticity and functional recovery after stroke.

Changes in Host Blood Factors and Brain Glia Accompanying the Functional Recovery after Systemic Administration of Bone Marrow Stem Cells in Ischemic Stroke Rats

In this study, we examined the effects of systemic administration of rat or human bone marrow stromal stem cells (MSC) at early and later times following middle cerebral artery occlusion (MCAO) on blood cytokines/growth factors, brain glia, and motor behavior in rats. Rats were tail vein injected with rat (r) and human (h) MSCs at 1 or 7 days post-MCAO. In some rats ( N = 4) MSCs isolated from transgenic GFP rats were used to track the migration of cells peripherally and centrally at 2.5 and 28 days. Motor behavior was assessed using the modified Neurological Severity Score/climbing test at various time points before and after MCAO and transplantation. Prior to sacrifice at 1, 7, or 28 days post-MCAO, blood serum was collected for cytokine array analysis. Brains were analyzed for markers of activated microglia (CD11) and reactive astrocytes (GFAP). Administration of either allogeneic (rMSCs) or xenogeneic (hMSCs) stem cells produced a significant recovery of motor behavior after MCAO, with cells delivered at 1 day having greater effect than those at 7 days. Correlated with recovery was an amplification in activated microglia, reactive astrocytes, and new blood vessels in the infarct region, resulting in greater preservation in brain integrity. Concomitantly, expression of blood cytokines/chemokines (IL-13, MMP2, MIP) and growth factors/receptors (VEGF, neuropilin, EPOR, TROY, NGFR, RAGE) were modified following MSC administration. Because only rare GFP-labeled MSCs were observed in the brain, these effects did not depend on the central incorporation of stem cells. The early systemic administration of allogeneic or xenogeneic MSCs soon after experimental stroke produces a structural/functional recovery in the brain which is correlated with an increase in activated brain glia and changes in circulating cytokines and growth factors. Stem cells therefore induce an important neuroprotective and/or regenerative response in the host organism.

Lesion size-dependent synaptic and astrocytic responses in cortex contralateral to infarcts in middle-aged rats

In young adult rats, unilateral lesions of the sensorimotor cortex lead to neuronal structural plasticity and synaptogenesis in the contralateral motor cortex, which is connected to the lesion site by transcallosal fibers. The contralesional neural plasticity varies with lesion size and results from the convergence of denervation-induced reactive plasticity and behavioral asymmetries. It was unknown whether similar effects occur in older animals. Furthermore, the coordination of synaptic responses with that of perisynaptic astrocytes had not been investigated. In this study, middle-aged rats (14-16 months old) were given sham-operations or unilateral ischemic lesions of the sensorimotor cortex. Fifty days later, numerical densities of neurons and synapses and morphological characteristics of astrocytic processes in layer V of the contralesional motor cortex were measured using stereological light and electron microscopy methods. Lesions resulted in behavioral asymmetries, but no significant synapse addition in the contralesional motor cortex. Synapse number per neuron was negatively correlated with lesion size and reduced opposite larger lesions compared with smaller ones. Astrocytic changes were also lesion size-dependent. Astrocytic hypertrophy was observed only after smaller lesions and was associated with greater coverage and greater numbers of synapses. These findings are consistent with those in younger rats indicating an inverse relationship between lesion size and adaptive neuronal restructuring in denervated cortex. However, they indicate that the synaptogenic reaction to this lesion is relatively limited in older animals. Finally, the results indicate that structural plasticity of perisynaptic astrocytes parallels, and could play a role in shaping, synaptic responses to postischemic denervation.

Functional assessments in the rodent stroke model

Stroke is a common cause of permanent disability accompanied by devastating impairments for which there is a pressing need for effective treatment. Motor, sensory and cognitive deficits are common following stroke, yet treatment is limited. Along with histological measures, functional outcome in animal models has provided valuable insight to the biological basis and potential rehabilitation efforts of experimental stroke. Developing and using tests that have the ability to identify behavioral deficits is essential to expanding the development of translational therapies. The present aim of this paper is to review many of the current behavioral tests that assess functional outcome after stoke in rodent models. While there is no perfect test, there are many assessments that are sensitive to detecting the array of impairments, from global to modality specific, after stroke.

Diverse interneuron populations have highly specific interconnectivity in the rat piriform cortex

Previous studies have suggested that the patterns of innervation and high interconnectivity of the piriform cortex (PC) provide for strong olfactory hippocampal memory; however, these same attributes may create high seizurogenic tendencies. Thus, understanding this wiring is important from a physiological and pathophysiological perspective. Distinct interneurons expressing differing calcium binding proteins (CBPs), parvalbumin (PV), calbindin (CB), and calretinin (CR), have been shown to exist in PC. However, a comprehensive examination of the distribution and innervation patterns of these neurons has not been done. Thus the purpose of this study was to combine the analysis of the CBP cell localization with analysis of their innervation patterns. Each type was differentially localized in the three layers of the PC. Only CR-positive neurons were found in layer 1. PV and CB are coexpressed in layers 2-3, most expressing both PV and CB. A morphological estimate of the dendritic extent for each subtype showed that PV and PV/CB cells demonstrated equally wide, horizontal and vertical arborizations, whereas CB cells had wide horizontal and restricted vertical arborizations. CR cells had restricted horizontal and very long vertical arborizations. Postsynaptic morphological targeting was also found to be specific, namely, PV(+) and PV/CB(+) nerve terminals (NTs) innervate perisomatic regions of principal cells. CR(+) NTs innervate only dendrites of principal cells, and CB(+) NTs innervate both somata and dendrites of principal cells. These data show highly complex innervation patterns for all of the CBP interneurons of the PC and form a basis for further studies in the plasticity of this region.

Transplantation of human neural precursor cells in Matrigel scaffolding improves outcome from focal cerebral ischemia after delayed postischemic treatment in rats

Transplantation of neural cells is a potential approach for stroke treatment, but disruption of tissue architecture may limit transplant efficacy. One strategy for enhancing the ability of transplants to restore brain structure and function is to administer cells together with biomaterial scaffolding. We electrocoagulated the distal middle cerebral artery in adult rats and, 3 weeks later, injected one of the following into the infarct cavity: artificial cerebrospinal fluid, Matrigel scaffolding, human embryonic stem cell-derived neuronal precursor cells, scaffolding plus cells, or cells cultured in and administered together with scaffolding. Five weeks after transplantation, the latter two groups showed approximately 50% and approximately 60% reductions, respectively, in infarct cavity volume. Rats given cells cultured in and administered together with scaffolding also showed (1) survival and neuronal differentiation of transplanted cells shown by immunostaining for neuronal marker proteins and cleaved caspase-3, and by patch-clamp recording, 8 weeks after transplantation and (2) improved outcome on tests of sensorimotor and cognitive functions, 4 to 9 weeks after transplantation. These results indicate that transplantation of human neural cells together with biomaterial scaffolding has the potential to improve the outcome from stroke, even when treatment is delayed for several weeks after the ischemic event.

Cortical excitability and post-stroke recovery

Stroke is the leading cause of adult disability. Recent studies show that the brain can engage in a limited process of neural repair after stroke: re-mapping of sensory and motor function and sprouting of new connections in peri-infarct cortex surrounding the stroke. Changes in cortical sensory and motor maps and alterations in axonal structure are dependent on patterned neuronal activity. The central cellular process in these events is alteration in neuronal response to incoming inputs--manipulations that increase neuronal firing to a given input are likely to induce changes in neuronal structure and alterations in cortical maps. Because post-stroke neural repair and recovery also involves neuronal sprouting and re-mapping of cortical sensory and motor representations, it has been assumed that changes in neuronal excitability underlie neural repair.

Biological approaches to aphasia treatment

In this review, we discuss the basic mechanisms of neural regeneration and repair and attempt to correlate findings from animal models of stroke recovery with clinical trials for aphasia. Several randomized controlled clinical trials involving manipulation of different neurotransmitter systems, including noradrenergic, dopaminergic, cholinergic, and glutamatergic systems, have shown signals of efficacy. Biological approaches such as anti-Nogo and cell replacement therapy have shown efficacy in preclinical models but have yet to reach proof of concept in the clinic. Finally, noninvasive cortical stimulation techniques have been used in a few small trials and have shown promising results. It appears that the efficacy of all these platforms can be potentiated through coupling with concomitant behavioral intervention. Given this array of potential mechanisms that exist to augment and/or stimulate neural reorganization after stroke, we are optimistic that approaches to aphasia therapy will transition from compensatory models to models in which brain reorganization is the goal.

Microglial involvement in neuroplastic changes following focal brain ischemia in rats

The pathogenesis of ischemic stroke is a complex sequence of events including inflammatory reaction, for which the microglia appears to be a major cellular contributor. However, whether post-ischemic activation of microglial cells has beneficial or detrimental effects remains to be elucidated, in particular on long term brain plasticity events. The objective of our study was to determine, through modulation of post-stroke inflammatory response, to what extent microglial cells are involved in some specific events of neuronal plasticity, neurite outgrowth and synaptogenesis. Since microglia is a source of neurotrophic factors, the identification of the brain-derived neurophic factor (BDNF) as possible molecular actor involved in these events was also attempted. As a means of down-regulating the microglial response induced by ischemia, 3-aminobenzamide (3-AB, 90 mg/kg, i.p.) was used to inhibit the poly(ADP-ribose) polymerase-1 (PARP-1). Indeed, PARP-1 contributes to the activation of the transcription factor NF-kB, which is essential to the upregulation of proinflammatory genes, in particular responsible for microglial activation/proliferation. Experiments were conducted in rats subjected to photothrombotic ischemia which leads to a strong and early microglial cells activation/proliferation followed by an infiltration of macrophages within the cortical lesion, events evaluated at serial time points up to 1 month post-ictus by immunostaining for OX-42 and ED-1. Our most striking finding was that the decrease in acute microglial activation induced by 3-AB was associated with a long term down-regulation of two neuronal plasticity proteins expression, synaptophysin (marker of synaptogenesis) and GAP-43 (marker of neuritogenesis) as well as to a significant decrease in tissue BDNF production. Thus, our data argue in favour of a supportive role for microglia in brain neuroplasticity stimulation possibly through BDNF production, suggesting that a targeted protection of microglial cells could represent an innovative approach to potentiate post-stroke neuroregeneration.

Promoting axonal rewiring to improve outcome after stroke

A limited amount of functional recovery commonly occurs in the weeks and months after stroke, and a number of studies show that such recovery is associated with changes in the brain's functional organization. Measures that augment this reorganization in a safe and effective way may therefore help improve outcome in stroke patients. Here we review some of the evidence for functional and anatomical reorganization under normal physiological conditions, along with strategies that augment these processes and improve outcome after brain injury in animal models. These strategies include counteracting inhibitors of axon growth associated with myelin, activating neurons' intrinsic growth state, enhancing physiological activity, and having behavioral therapy. These approaches represent a marked departure from the recent focus on neuroprotection and may provide a more effective way to improve outcome after stroke.

Plasticity during stroke recovery: from synapse to behaviour

Reductions in blood flow to the brain of sufficient duration and extent lead to stroke, which results in damage to neuronal networks and the impairment of sensation, movement or cognition. Evidence from animal models suggests that a time-limited window of neuroplasticity opens following a stroke, during which the greatest gains in recovery occur. Plasticity mechanisms include activity-dependent rewiring and synapse strengthening. The challenge for improving stroke recovery is to understand how to optimally engage and modify surviving neuronal networks, to provide new response strategies that compensate for tissue lost to injury.

Microstructural status of ipsilesional and contralesional corticospinal tract correlates with motor skill in chronic stroke patients

Greater loss in structural integrity of the ipsilesional corticospinal tract (CST) is associated with poorer motor outcome in patients with hemiparetic stroke. Animal models of stroke have demonstrated that structural remodeling of white matter in the ipsilesional and contralesional hemispheres is associated with improved motor recovery. Accordingly, motor recovery in patients with stroke may relate to the relative strength of CST degeneration and remodeling. This study examined the relationship between microstructural status of brain white matter tracts, indexed by the fractional anisotropy (FA) metric derived from diffusion tensor imaging (DTI) data, and motor skill of the stroke-affected hand in patients with chronic stroke. Voxelwise analysis revealed that motor skill significantly and positively correlated with FA of the ipsilesional and contralesional CST in the patients. Additional voxelwise analyses showed that patients with poorer motor skill had reduced FA of bilateral CST compared to normal control subjects, whereas patients with better motor skill had elevated FA of bilateral CST compared to controls. These findings were confirmed using a DTI-tractography method applied to the CST in both hemispheres. The results of this study suggest that the level of motor skill recovery achieved in patients with hemiparetic stroke relates to microstructural status of the CST in both the ipsilesional and contralesional hemispheres, which may reflect the net effect of degeneration and remodeling of bilateral CST.

Optimizing the success of cell transplantation therapy for stroke

Stem cell transplantation has evolved as a promising experimental treatment approach for stroke. In this review, we address the major hurdles for successful translation from basic research into clinical applications and discuss possible strategies to overcome these issues. We summarize the results from present pre-clinical and clinical studies and focus on specific areas of current controversy and research: (i) the therapeutic time window for cell transplantation; (ii) the selection of patients likely to benefit from such a therapy; (iii) the optimal route of cell delivery to the ischemic brain; (iv) the most suitable cell types and sources; (v) the potential mechanisms of functional recovery after cell transplantation; and (vi) the development of imaging techniques to monitor cell therapy.

Normalization of zinc intake enhances neurological retrieval of patients suffering from ischemic strokes

INTRODUCTION

The objective of this study was to investigate whether zinc (Zn2+) supplementation could contribute to neurological retrieval of patients suffering from strokes and low Zn2+ intake.

PATIENTS AND METHODS

Twenty-six patients with subacute stroke, having adequate daily energy (> or = 24 kcal/kg/day) and protein (> or = 0.8 g/kg/day) intake (EPI) and Zn2+ ingestion lower than two-thirds of the recommended allowance of 10 mg/day, were randomly allocated either to a control group (n = 13) or Zn2+ group (n = 13) where Zn2+ supplementation consisted of 10 mg Zn2+/day. Neurological gravity was tested with the NIH stroke scale (NIHSS) at patient admission and after 30 days of protocol commencement.

RESULTS

At day 30, the improvement in NIHSS was higher in the zinc group than in the placebo (-4.7 +/- 1.3 points versus -3.3 +/- 1.1 points; P < 0.02). NIHSS and Zn2+ intake were negatively correlated (r = -0.46; P < 0.02).

CONCLUSION

The normalization of Zn2+ intake in stroke patients with low mineral intake may enhance neurological recovery.

Melatonin improves presynaptic protein, SNAP-25, expression and dendritic spine density and enhances functional and electrophysiological recovery following transient focal cerebral ischemia in rats

Synapto-dendritic dysfunction and rearrangement takes place over time at the peri-infarct brain after stroke, and the event plays an important role in post-stroke functional recovery. Here, we evaluated whether melatonin would modulate the synapto-dendritic plasticity after stroke. Adult male Sprague-Dawley rats were treated with melatonin (5 mg/kg) or vehicle at reperfusion onset after transient occlusion of the right middle cerebral artery (tMCAO) for 90 min. Local cerebral blood perfusion, somatosensory electrophysiological recordings and neurobehavioral tests were serially measured. Animals were sacrificed at 7 days after tMCAO. The brain was processed for Nissl-stained histology, Golgi-Cox-impregnated sections, or Western blotting for presynaptic proteins, synaptosomal-associated protein of 25 kDa (SNAP-25) and synaptophysin (a calcium-binding protein found on presynaptic vesicle membranes). Relative to controls, melatonin-treated animals had significantly reduced infarction volumes (P < 0.05) and improved neurobehavioral outcomes, as accessed by sensorimotor and rota-rod motor performance tests (P < 0.05, respectively). Melatonin also significantly improved the SNAP-25, but not synaptophysin, protein expression in the ischemic brain (P < 0.05). Moreover, melatonin significantly improved the dendritic spine density and the somatosensory electrophysiological field potentials both in the ischemic brain and the contralateral homotopic intact brain (P < 0.05, respectively). Together, melatonin not only effectively attenuated the loss of presynaptic protein, SANP-25, and dendritic spine density in the ischemic territory, but also improved the reductions in the dendritic spine density in the contralateral intact brain. This synapto-dendritic plasticity may partly account for the melatonin-mediated improvements in functional and electrophysiological circuitry after stroke.

Translating the frontiers of brain repair to treatments: starting not to break the rules

The field of neural repair in stroke has identified cellular systems of reorganization and possible molecular mechanisms. Conceptual barriers now limit the generation of clinically useful agents. First, it is not clear what the causal mechanisms of neural repair are in stroke. Second, adequate delivery systems for neural repair drugs need to be determined for candidate molecules. Third, ad hoc applications of existing pharmacological agents that enhance attention, mood or arousal to stroke have failed. New approaches that specifically harness the molecular systems of learning and memory provide a new avenue for stroke repair drugs. Fourth, combinatorial treatments for neural repair need to be considered for clinical therapies. Finally, neural repair therapies have as a goal altering brain connections, cognitive maps and active neural networks. These actions may trigger a unique set of "neural repair side effects" that need to be considered in planning clinical trials.

Ischaemic stroke in adults and epilepsy

Stroke is an important cause of symptomatic epilepsy especially in the elderly. Seizures in the setting of stroke will furthermore worsen the prognosis of stroke. Studies show that the frequency of seizures in stroke ranges between 2.3% and 14%. Typically early seizures are defined as those that occur within 14 days of the stroke, and later seizures those that occur after this period. A number of risk factors have been identified like cortical involvement, size of the infarct and stroke severity. Status epilepticus can be a presenting symptom of acute stroke and can lead to increased mortality. Early seizures are risks for recurrent seizures though not for the development of epilepsy but late seizures do carry a higher risk. There are no clear cut guidelines for the treatment of seizures in stroke and hence treatment needs to be initiated in the context of the patient. The presence of co morbid conditions and the use of other drugs also complicate antiepileptic therapy, and the risk of drug interactions is a particular hazard in elderly patients on multiple co medication. Although hemorrhagic and ischaemic stroke can both result in epilepsy, this review focuses primarily the association of epilepsy and ischaemic stroke.

A model for cortical rewiring following deafferentation and focal stroke

It is still unclear to what extent structural plasticity in terms of synaptic rewiring is the cause for cortical remapping after a lesion. Recent two-photon laser imaging studies demonstrate that synaptic rewiring is persistent in the adult brain and is dramatically increased following brain lesions or after a loss of sensory input (cortical deafferentation). We use a recurrent neural network model to study the time course of synaptic rewiring following a peripheral lesion. For this, we represent axonal and dendritic elements of cortical neurons to model synapse formation, pruning and synaptic rewiring. Neurons increase and decrease the number of axonal and dendritic elements in an activity-dependent fashion in order to maintain their activity in a homeostatic equilibrium. In this study we demonstrate that synaptic rewiring contributes to neuronal homeostasis during normal development as well as following lesions. We show that networks in homeostasis, which can therefore be considered as adult networks, are much less able to compensate for a loss of input. Interestingly, we found that paused stimulation of the networks are much more effective promoting reorganization than continuous stimulation. This can be explained as neurons quickly adapt to this stimulation whereas pauses prevents a saturation of the positive stimulation effect. These findings may suggest strategies for improving therapies in neurologic rehabilitation.

Remapping the somatosensory cortex after stroke: insight from imaging the synapse to network

Together, thousands of neurons with similar function make up topographically oriented sensory cortex maps that represent contralateral body parts. Although this is an accepted model for the adult cortex, whether these same rules hold after stroke-induced damage is unclear. After stroke, sensory representations damaged by stroke remap onto nearby surviving neurons. Here, we review the process of sensory remapping after stroke at multiple levels ranging from the initial damage to synapses, to their rewiring and function in intact sensory circuits. We introduce a new approach using in vivo 2-photon calcium imaging to determine how the response properties of individual somatosensory cortex neurons are altered during remapping. One month after forelimb-area stroke, normally highly limb-selective neurons in surviving peri-infarct areas exhibit remarkable flexibility and begin to process sensory stimuli from multiple limbs as remapping proceeds. Two months after stroke, neurons within remapped regions develop a stronger response preference. Thus, remapping is initiated by surviving neurons adopting new roles in addition to their usual function. Later in recovery, these remapped forelimb-responsive neurons become more selective, but their new topographical representation may encroach on map territories of neurons that process sensory stimuli from other body parts. Neurons responding to multiple limbs may reflect a transitory phase in the progression from their involvement in one sensorimotor function to a new function that replaces processing lost due to stroke.

Increase of neuronal sprouting and migration using 780 nm laser phototherapy as procedure for cell therapy

BACKGROUND AND OBJECTIVES

The present study focuses on the effect of 780 nm laser irradiation on the growth of embryonic rat brain cultures embedded in NVR-Gel (cross-linked hyaluronic acid with adhesive molecule laminin and several growth factors). Dissociated neuronal cells were first grown in suspension attached to cylindrical microcarriers (MCs). The formed floating cell-MC aggregates were subsequently transferred into stationary cultures in gel and then laser treated. The response of neuronal growth following laser irradiation was investigated.

MATERIALS AND METHODS

Whole brains were dissected from 16 days Sprague-Dawley rat embryos. Cells were mechanically dissociated, using narrow pipettes, and seeded on positively charged cylindrical MCs. After 4-14 days in suspension, the formed floating cell-MC aggregates were seeded as stationary cultures in NVR-Gel. Single cell-MC aggregates were either irradiated with near-infrared 780 nm laser beam for 1, 4, or 7 minutes, or cultured without irradiation. Laser powers were 10, 30, 50, 110, 160, 200, and 250 mW.

RESULTS

780 nm laser irradiation accelerated fiber sprouting and neuronal cell migration from the aggregates. Furthermore, unlike control cultures, the irradiated cultures (mainly after 1 minute irradiation of 50 mW) were already established after a short time of cultivation. They contained a much higher number of large size neurons (P<0.01), which formed dense branched interconnected networks of thick neuronal fibers.

CONCLUSIONS

780 nm laser phototherapy of embryonic rat brain cultures embedded in hyaluronic acid-laminin gel and attached to positively charged cylindrical MCs, stimulated migration and fiber sprouting of neuronal cells aggregates, developed large size neurons with dense branched interconnected network of neuronal fibers and, therefore, can be considered as potential procedure for cell therapy of neuronal injury or disease.

Enriched environment promotes efficiency of compensatory movements after cerebral ischemia in rats

Rehabilitation therapy is known to drive motor improvement in stroke patients. However, the interplay of functional recovery and compensation in postischemic motor behavior is poorly understood. This study focused on the time course of functional recovery versus motor compensation in skilled forelimb movements after cerebral ischemia in rats. Young adult male rats underwent a focal cerebral ischemia by unilateral photothrombotic lesion of the motor cortex related to the preferred forelimb. In a first set of experiments animals were exposed to small cortical lesions comprising the forelimb motor cortex (n=8) or to larger lesions additionally extending into the hind limb motor area (n=8). In a second set of experiments animals with large lesion were either housed in standard (n=10) or enriched environment (n=14). Skilled reaching was assessed for 25 to 28 days postischemia. This task allows the distinction between recovery and compensation by parallel quantitative (reaching success) and qualitative (movement pattern) analysis. The results reveal that lesion size determines the initial magnitude of motor deficits, but not the degree of chronic impairments in movement pattern in all experimental groups. Compensatory movements represent the major mechanism of functional improvement and were accompanied by a partial functional restitution. Enriched environment facilitates effective compensation in skilled reaching, while it does not promote restitution of function. In particular, rotating movements of the forelimb during reaching were permanently impaired and required functional compensation through intensified use of the upper body. We conclude an activity dependent postischemic restoration of movement success. Enriched environment provides benefit by increased motor activity mainly due to compensation. Furthermore, these findings emphasize the power of comprehensive movement analysis to gain insight into recovery processes after stroke.

Effect of prolonged cortical stimulation differs with size of infarct after sensorimotor cortical lesions in rats

Motor deficit improvement is limited in rats with a large sensorimotor cortex infarct, even with cortical stimulation during rehabilitation. However, we find prolonged stimulation that differs with the size of cortical lesion to be effective. Two weeks of prolonged epidural electrical stimulation and rehabilitative training were delivered to rats whose cortex had been subjected to photothrombotic infarct after training in a single-pellet reaching task. Continuous stimulation greatly improved recovery in animals with large infarcts (6 mm diameter), while intermittent stimulation was more effective in animals with small (4 mm) lesions. Thus, prolonged cortical stimulation is a strategy to enhance motor recovery in photothrombotic infarct model rats. However, pattern and duration of stimulation requires modification depending on the extent of infarct.

A novel calpastatin-based inhibitor improves postischemic neurological recovery

Calpastatin, a naturally occurring protein, is the only inhibitor that is specific for calpain. A novel blood-brain barrier (BBB)-permeant calpastatin-based calpain inhibitor, named B27-HYD, was developed and used to assess calpain's contribution to neurological dysfunction after stroke in rats. Postischemic administration of B27-HYD reduced infarct volume and neurological deficits by 35% and 44%, respectively, compared to untreated animals. We also show that the pharmacologic intervention has engaged the intended biologic target. Our data further demonstrates the potential utility of SBDP145, a signature biomarker of acute brain injury, in evaluating possible mechanisms of calpain in the pathogenesis of stroke and as an adjunct in guiding therapeutic decision making.

In vivo voltage-sensitive dye imaging in adult mice reveals that somatosensory maps lost to stroke are replaced over weeks by new structural and functional circuits with prolonged modes of activation within both the peri-infarct zone and distant sites

After brain damage such as stroke, topographically organized sensory and motor cortical representations remap onto adjacent surviving tissues. It is conceivable that cortical remapping is accomplished by changes in the temporal precision of sensory processing and regional connectivity in the cortex. To understand how the adult cortex remaps and processes sensory signals during stroke recovery, we performed in vivo imaging of sensory-evoked changes in membrane potential, as well as multiphoton imaging of dendrite structure and tract tracing. In control mice, forelimb stimulation evoked a brief depolarization in forelimb cortex that quickly propagated to, and dissipated within, adjacent motor/hindlimb areas (<100 ms). One week after forelimb cortex stroke, the cortex was virtually unresponsive to tactile forelimb stimulation. After 8 weeks recovery, forelimb-evoked depolarizations reemerged with a characteristic pattern in which responses began within surviving portions of forelimb cortex (<20 ms after stimulation) and then spread horizontally into neighboring peri-infarct motor/hindlimb areas in which depolarization persisted 300-400% longer than controls. These uncharacteristically prolonged responses were not limited to the remapped peri-infarct zone and included distant posteromedial retrosplenial cortex, millimeters from the stroke. Structurally, the remapped peri-infarct area selectively exhibited high levels of dendritic spine turnover, shared more connections with retrosplenial cortex and striatum, and lost inputs from lateral somatosensory cortical regions. Our findings demonstrate that sensory remapping during stroke recovery is accompanied by the development of prolonged sensory responses and new structural circuits in both the peri-infarct zone as well as more distant sites.

Treatment with bone marrow mononuclear cells induces functional recovery and decreases neurodegeneration after sensorimotor cortical ischemia in rats

We evaluated the beneficial effect of treatment with bone marrow mononuclear cells(BMMC) in a rat model of focal ischemia induced by thermocoagulation of the blood vessels in the left sensorimotor cortex. BMMC were obtained from donor rats and injected into the femoral vein one day after ischemia. BMMC-treated animals received approx. 3×10⁷ cells and control animals received PBS. Animals were evaluated for functional sensorimotor recovery weekly with behavioral tests and for changes in neurodegeneration and structural plasticity with histochemical and immunostaining techniques, respectively. The BMMC-treated group showed a significant recovery of function in the cylinder test 14, 21 and 28 days after ischemia. In the beam test, both groups showed improvement, with a tendency for faster recovery in the BMMC-treated group. In the adhesive test, both groups did not show significant recovery of function. FJC+ cell counting revealed significant decrease in the neurodegeneration in the periphery of the lesion in the BMMC-treated group. The analyses by immunoblotting revealed no significant difference in the expression of GAP-43 and synaptophysin between the groups. Thus, our results showed beneficial effects of the treatment with BMMC, which promoted significant functional recovery and decreased neurodegeneration. These results suggest that the therapy with BMMC is effective and might be a protocol of treatment for stroke in humans, alternative to the therapy proposed with the bone marrow-derived mesenchymal stem cells.

Epilepsy in the elderly

BACKGROUND

Epilepsy is the third most common disease affecting the brain in the elderly. Current demographic trends will lead to an increased prevalence of epilepsy in the general population.

METHOD

A selective literature search revealed 102 relevant publications as of September 2008, 50 of which were original articles.

RESULTS

The level of evidence was found to be very low. No guidelines, systematic reviews or meta-analyses are available, and there have been only three randomized, double-blind trials of treatment for epilepsy in the elderly. The seizures often escape clinical attention, because premonitory symptoms (aura) and secondary generalization into tonic-clonic seizures are both rarer in older patients. On the other hand, sudden loss of consciousness from various causes becomes more common with increasing age, presenting a challenge in differential diagnosis. Treatment is often more complex because of comorbidities and multiple other drugs, and requires a cautious approach. Drug interactions, in particular, require special attention. On the positive side, epileptic seizures in the elderly seem to be more easily controlled by medications than they are in young adults.

CONCLUSIONS

Epilepsy is often more difficult to recognize in old age. The treatment is hampered by side effects and drug interactions. Thus, certainty about the diagnosis is indispensable, and the treatment often requires the use of newer-generation antiepileptic drugs.