New patterns of intracortical projections after focal cortical stroke

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.

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.

Neurogenesis and angiogenesis within the ipsilateral thalamus with secondary damage after focal cortical infarction in hypertensive rats

Neurogenesis and angiogenesis in the subventricular zone and peri-infarct region have been confirmed. However, newly formed neuronal cells and blood vessels that appear in the nonischemic ipsilateral ventroposterior nucleus (VPN) of the thalamus with secondary damage after stroke has not been previously studied. Twenty-four stroke-prone renovascular hypertensive rats were subjected to distal right middle cerebral artery occlusion (MCAO) or sham operation. 5'-Bromo-2'-deoxyuridine (BrdU) was used to label cell proliferation. Rats were killed at 7 or 14 days after the operation. Neuronal nuclei (NeuN), OX-42, BrdU, nestin, laminin(+), BrdU(+)/nestin(+), BrdU(+)/NeuN(+), nestin(+)/GFAP(+)(glial fibrillary acidic protein), and BrdU(+)/laminin(+) immunoreactive cells were detected within the ipsilateral VPN. The primary infarction was confined to the right somatosensory cortex. Within the ipsilateral VPN of the ischemic rats, the number of NeuN(+) neurons decreased, the OX-42(+) microglia cells were activated, and BrdU(+) and nestin(+) cells were detected at day 7 after MCAO and increased in number at day 14. Moreover, BrdU(+)/nestin(+) cells and BrdU(+)/NeuN(+) cells were detected at day 14 after MCAO. In addition, the ischemic rats showed a significant increase in vascular density in the ipsilateral VPN compared with the sham-operated rats. These results suggest that secondary damage with neurogenesis and angiogenesis of the ipsilateral VPN of the thalamus occurs after focal cortical infarction.

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.

Inosine alters gene expression and axonal projections in neurons contralateral to a cortical infarct and improves skilled use of the impaired limb

Recovery after stroke and other types of brain injury is restricted in part by the limited ability of undamaged neurons to form compensatory connections. Inosine, a naturally occurring purine nucleoside, stimulates neurons to extend axons in culture and, in vivo, enhances the ability of undamaged neurons to form axon collaterals after brain damage. The molecular changes induced by inosine are unknown, as is the ability of inosine to restore complex functions associated with a specific cortical area. Using a unilateral injury model limited to the sensorimotor cortex, we show that inosine triples the number of corticospinal tract axons that project from the unaffected hemisphere and form synaptic bouton-like structures in the denervated half of the spinal cord. These changes correlate with improved recovery in animals' ability to grasp and consume food pellets with the affected forepaw. Studies using laser-capture microdissection and microarray analysis show that inosine profoundly affects gene expression in corticospinal neurons contralateral to the injury. Inosine attenuates transcriptional changes caused by the stroke, while upregulating the expression of genes associated with axon growth and the complement cascade. Thus, inosine alters gene expression in neurons contralateral to a stroke, enhances the ability of these neurons to form connections on the denervated side of the spinal cord, and improves performance with the impaired limb.

Functional engraftment of the medial ganglionic eminence cells in experimental stroke model

Currently there are no effective treatments targeting residual anatomical and behavioral deficits resulting from stroke. Evidence suggests that cell transplantation therapy may enhance functional recovery after stroke through multiple mechanisms. We used a syngeneic model of neural transplantation to explore graft-host communications that enhance cellular engraftment.The medial ganglionic eminence (MGE) cells were derived from 15-day-old transgenic rat embryos carrying green fluorescent protein (GFP), a marker, to easily track the transplanted cells. Adult rats were subjected to transient intraluminal occlusion of the medial cerebral artery. Two weeks after stroke, the grafts were deposited into four sites, along the rostro-caudal axis and medially to the stroke in the penumbra zone. Control groups included vehicle and fibroblast transplants. Animals were subjected to motor behavioral tests at 4 week posttransplant survival time. Morphological analysis demonstrated that the grafted MGE cells differentiated into multiple neuronal subtypes, established synaptic contact with host cells, increased the expression of synaptic markers, and enhanced axonal reorganization in the injured area. Initial patch-clamp recording demonstrated that the MGE cells received postsynaptic currents from host cells. Behavioral analysis showed reduced motor deficits in the rotarod and elevated body swing tests. These findings suggest that graft-host interactions influence the fate of grafted neural precursors and that functional recovery could be mediated by neurotrophic support, new synaptic circuit elaboration, and enhancement of the stroke-induced neuroplasticity.

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.

Experience-dependent plasticity mechanisms for neural rehabilitation in somatosensory cortex

Functional rehabilitation of the cortex following peripheral or central nervous system damage is likely to be improved by a combination of behavioural training and natural or therapeutically enhanced synaptic plasticity mechanisms. Experience-dependent plasticity studies in the somatosensory cortex have begun to reveal those synaptic plasticity mechanisms that are driven by sensory experience and might therefore be active during behavioural training. In this review the anatomical pathways, synaptic plasticity mechanisms and structural plasticity substrates involved in cortical plasticity are explored, focusing on work in the somatosensory cortex and the barrel cortex in particular.

Inverse relationship between adult hippocampal cell proliferation and synaptic rewiring in the dentate gyrus

Adult neurogenesis is a key feature of the hippocampal dentate gyrus (DG). Neurogenesis is accompanied by synaptogenesis as new cells become integrated into the circuitry of the hippocampus. However, little is known to what extent the embedding of new neurons rewires the pre-existing network. Here we investigate synaptic rewiring in the DG of gerbils (Meriones unguiculatus) under different rates of adult cell proliferation caused by different rearing conditions as well as juvenile methamphetamine treatment. Surprisingly, we found that an increased cell proliferation reduced the amount of synaptic rewiring. To help explain this unexpected finding, we developed a novel model of dentate network formation incorporating neurogenesis and activity-dependent synapse formation and remodelling. In the model, we show that homeostasis of neuronal activity can account for the inverse relationship between cell proliferation and synaptic rewiring.

Brain-computer interfaces in neurological rehabilitation

Recent advances in analysis of brain signals, training patients to control these signals, and improved computing capabilities have enabled people with severe motor disabilities to use their brain signals for communication and control of objects in their environment, thereby bypassing their impaired neuromuscular system. Non-invasive, electroencephalogram (EEG)-based brain-computer interface (BCI) technologies can be used to control a computer cursor or a limb orthosis, for word processing and accessing the internet, and for other functions such as environmental control or entertainment. By re-establishing some independence, BCI technologies can substantially improve the lives of people with devastating neurological disorders such as advanced amyotrophic lateral sclerosis. BCI technology might also restore more effective motor control to people after stroke or other traumatic brain disorders by helping to guide activity-dependent brain plasticity by use of EEG brain signals to indicate to the patient the current state of brain activity and to enable the user to subsequently lower abnormal activity. Alternatively, by use of brain signals to supplement impaired muscle control, BCIs might increase the efficacy of a rehabilitation protocol and thus improve muscle control for the patient.

In vivo calcium imaging reveals functional rewiring of single somatosensory neurons after stroke

Functional mapping and microstimulation studies suggest that recovery after stroke damage can be attributed to surviving brain regions taking on the functional roles of lost tissues. Although this model is well supported by data, it is not clear how activity in single neurons is altered in relation to cortical functional maps. It is conceivable that individual surviving neurons could adopt new roles at the expense of their usual function. Alternatively, neurons that contribute to recovery may take on multiple functions and exhibit a wider repertoire of neuronal processing. In vivo two-photon calcium imaging was used in adult mice within reorganized forelimb and hindlimb somatosensory functional maps to determine how the response properties of individual neurons and glia were altered during recovery from ischemic damage over a period of 2-8 weeks. Single-cell calcium imaging revealed that the limb selectivity of individual neurons was altered during recovery from ischemia, such that neurons normally selective for a single contralateral limb processed information from multiple limbs. Altered limb selectivity was most prominent in border regions between stroke-altered forelimb and hindlimb macroscopic map representations, and peaked 1 month after the targeted insult. Two months after stroke, individual neurons near the center of reorganized functional areas became more selective for a preferred limb. These previously unreported forms of plasticity indicate that in adult animals, seemingly hardwired cortical neurons first adopt wider functional roles as they develop strategies to compensate for loss of specific sensory modalities after forms of brain damage such as stroke.

Manganese-enhanced MRI of brain plasticity in relation to functional recovery after experimental stroke

Restoration of function after stroke may be associated with structural remodeling of neuronal connections outside the infarcted area. However, the spatiotemporal profile of poststroke alterations in neuroanatomical connectivity in relation to functional recovery is still largely unknown. We performed in vivo magnetic resonance imaging (MRI)-based neuronal tract tracing with manganese in combination with immunohistochemical detection of the neuronal tracer wheat-germ agglutinin horseradish peroxidase (WGA-HRP), to assess changes in intra- and interhemispheric sensorimotor network connections from 2 to 10 weeks after unilateral stroke in rats. In addition, functional recovery was measured by repetitive behavioral testing. Four days after tracer injection in perilesional sensorimotor cortex, manganese enhancement and WGA-HRP staining were decreased in subcortical areas of the ipsilateral sensorimotor network at 2 weeks after stroke, which was restored at later time points. At 4 to 10 weeks after stroke, we detected significantly increased manganese enhancement in the contralateral hemisphere. Behaviorally, sensorimotor functions were initially disturbed but subsequently recovered and plateaued 17 days after stroke. This study shows that manganese-enhanced MRI can provide unique in vivo information on the spatiotemporal pattern of neuroanatomical plasticity after stroke. Our data suggest that the plateau stage of functional recovery is associated with restoration of ipsilateral sensorimotor pathways and enhanced interhemispheric connectivity.

Themes and strategies for studying the biology of stroke recovery in the poststroke epoch

BACKGROUND AND PURPOSE

This review will focus on the emerging principles of neural repair after stroke, and on the overlap between cellular mechanisms of neural repair in stroke and clinical principles of recovery and rehabilitation.

SUMMARY OF REVIEW

Stroke induces axonal sprouting and neurogenesis. Axonal sprouting occurs in tissue adjacent to the stroke and its connected cortical areas, and from sites that are contralateral to the infarct. Neurogenesis produces newly born immature neurons in peri-infarct striatum and cortex. Stimulation of both axonal sprouting and neurogenesis is associated with improved recovery in animal models of stroke. A unique cellular environment in the poststroke brain supports neural repair: an association of angiogenic and remodeling blood vessels with newly born immature neurons in a neurovasclar niche. Controversies in the field of neural repair after stroke persist, and relate to the locations of axonal sprouting in animal models of stroke and how these correlate to patterns of human remapping and recovery, and to the different models of stroke used in studies of neurogenesis.

CONCLUSIONS

On a cellular level, the phenomenology of neural repair after stroke has been defined and unique regenerative environments in the poststroke brain identified. As the field moves toward specific studies of causal mechanisms in poststroke repair, it will need to maintain a perspective of the animal models suited to the study of neural repair after stroke as they relate to the patterns of recovery in humans in this disease.

Molecular physiology of preconditioning-induced brain tolerance to ischemia

Ischemic tolerance describes the adaptive biological response of cells and organs that is initiated by preconditioning (i.e., exposure to stressor of mild severity) and the associated period during which their resistance to ischemia is markedly increased. This topic is attracting much attention because preconditioning-induced ischemic tolerance is an effective experimental probe to understand how the brain protects itself. This review is focused on the molecular and related functional changes that are associated with, and may contribute to, brain ischemic tolerance. When the tolerant brain is subjected to ischemia, the resulting insult severity (i.e., residual blood flow, disruption of cellular transmembrane gradients) appears to be the same as in the naive brain, but the ensuing lesion is substantially reduced. This suggests that the adaptive changes in the tolerant brain may be primarily directed against postischemic and delayed processes that contribute to ischemic damage, but adaptive changes that are beneficial during the subsequent test insult cannot be ruled out. It has become clear that multiple effectors contribute to ischemic tolerance, including: 1) activation of fundamental cellular defense mechanisms such as antioxidant systems, heat shock proteins, and cell death/survival determinants; 2) responses at tissue level, especially reduced inflammatory responsiveness; and 3) a shift of the neuronal excitatory/inhibitory balance toward inhibition. Accordingly, an improved knowledge of preconditioning/ischemic tolerance should help us to identify neuroprotective strategies that are similar in nature to combination therapy, hence potentially capable of suppressing the multiple, parallel pathophysiological events that cause ischemic brain damage.

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

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

Imaging the impact of cortical microcirculation on synaptic structure and sensory-evoked hemodynamic responses in vivo

In vivo two-photon microscopy was used to image in real time dendrites and their spines in a mouse photothrombotic stroke model that reduced somatosensory cortex blood flow in discrete regions of cortical functional maps. This approach allowed us to define relationships between blood flow, cortical structure, and function on scales not previously achieved with macroscopic imaging techniques. Acute ischemic damage to dendrites was triggered within 30 min when blood flow over >0.2 mm² of cortical surface was blocked. Rapid damage was not attributed to a subset of clotted or even leaking vessels (extravasation) alone. Assessment of stroke borders revealed a remarkably sharp transition between intact and damaged synaptic circuitry that occurred over tens of μm and was defined by a transition between flowing and blocked vessels. Although dendritic spines were normally ~13 μm from small flowing vessels, we show that intact dendritic structure can be maintained (in areas without flowing vessels) by blood flow from vessels that are on average 80 μm away. Functional imaging of intrinsic optical signals associated with activity-evoked hemodynamic responses in somatosensory cortex indicated that sensory-induced changes in signal were blocked in areas with damaged dendrites, but were present ~400 μm away from the border of dendritic damage. These results define the range of influence that blood flow can have on local cortical fine structure and function, as well as to demonstrate that peri-infarct tissues can be functional within the first few hours after stroke and well positioned to aid in poststroke recovery.

The brain is critically dependent on an adequate supply of energy as it consumes up to 20% of the oxygen we breathe. Here we determine the distance scale over which interruptions in blood flow affect synaptic hard wiring and brain function. High-resolution microscopy of live mice was used to image cerebral cortex synapses (the sites of connections between neurons) in real time during targeted interruptions of cortical blood flow that model small survivable strokes. Under normal conditions, synapses were tightly coupled to small brain blood vessels, on average only 13 μm away. During targeted strokes, we find that normal synaptic structure can be maintained by flowing blood vessels at a much greater distance of 80 μm. In contrast to structure, brain function was more sensitive to interruption in blood flow and was only present 400 μm from the border of synaptic structural damage. The identification of intact brain structure in regions lacking function defines brain tissue in which restoration of normal blood flow restores function. Our results define the range of influence that blood flow has on cortical fine structure and function and are important for understanding both the pathology of stroke and how changes in blood flow alter the normal brain.

High-resolution structural and functional imaging of the effects of targeted strokes on individual synapses in somatosensory cortex reveals that blood flow from surrounding intact tissue can aid in the immediate post-stroke recovery.

Studies of stimulus parameters for seizure disruption using neural network simulations

A large scale neural network simulation with realistic cortical architecture has been undertaken to investigate the effects of external electrical stimulation on the propagation and evolution of ongoing seizure activity. This is an effort to explore the parameter space of stimulation variables to uncover promising avenues of research for this therapeutic modality. The model consists of an approximately 800 mum x 800 mum region of simulated cortex, and includes seven neuron classes organized by cortical layer, inhibitory or excitatory properties, and electrophysiological characteristics. The cell dynamics are governed by a modified version of the Hodgkin-Huxley equations in single compartment format. Axonal connections are patterned after histological data and published models of local cortical wiring. Stimulation induced action potentials take place at the axon initial segments, according to threshold requirements on the applied electric field distribution. Stimulation induced action potentials in horizontal axonal branches are also separately simulated. The calculations are performed on a 16 node distributed 32-bit processor system. Clear differences in seizure evolution are presented for stimulated versus the undisturbed rhythmic activity. Data is provided for frequency dependent stimulation effects demonstrating a plateau effect of stimulation efficacy as the applied frequency is increased from 60 to 200 Hz. Timing of the stimulation with respect to the underlying rhythmic activity demonstrates a phase dependent sensitivity. Electrode height and position effects are also presented. Using a dipole stimulation electrode arrangement, clear orientation effects of the dipole with respect to the model connectivity is also demonstrated. A sensitivity analysis of these results as a function of the stimulation threshold is also provided.

Rewiring the injured CNS: lessons from the optic nerve

The optic nerve offers a number of advantages for investigating mechanisms that govern axon regeneration in the CNS. Although mature retinal ganglion cells (RGCs) normally show no ability to regenerate injured axons through the optic nerve, this situation can be partially reversed by inducing an inflammatory response in the eye. The secretion of a previously unknown growth factor, oncomodulin, along with co-factors, causes RGCs to undergo dramatic changes in gene expression and regenerate lengthy axons into the highly myelinated optic nerve. By themselves, strategies that counteract inhibitory signals associated with myelin and the glial scar are insufficient to promote extensive regeneration in this system. However, combinatorial treatments that activate neurons' intrinsic growth state and overcome inhibitory signals result in dramatic axon regeneration in vivo. Because of the ease of introducing trophic factors, soluble receptors, drugs, or viruses expressing any gene or small interfering RNA of interest into RGCs, this system is ideal for identifying intracellular signaling pathways, transcriptional cascades, and ligand-receptor interactions that enable axon regeneration to occur in the CNS.

Fine mapping of the spatial relationship between acute ischemia and dendritic structure indicates selective vulnerability of layer V neuron dendritic tufts within single neurons in vivo

We have evaluated the spatial relationship between clotted vasculature and the structural integrity of layer V cortical neurons in YFP (yellow fluorescent protein)-H transgenic mice 2 to 10 h after photothrombotic stroke. Fortuitously, ischemic zones could be finely mapped about dysmorphic YFP labeled axons and dendrites using histology since Texas-red dextran used to assess blood flow in vivo was trapped within fixed clotted vessels. Ischemic damage to layer V neurons located at the border of ischemia was contained within apical tuft spiny dendritic structures and did not propagate to spines on the more proximal region of the apical dendrite. The lateral spread of dendritic damage decayed sharply with distance from the edge of ischemia (50% reduction in beaded dendrites within approximately 100 microm) and increased with time up to 6 h after stroke but not thereafter. Axonal damage also increased with time but extended further laterally than dendritic damage, up to 500 microm from the stroke core. Apoptotic and necrotic cell death cascades were activated 6 h after stroke; however, only within 300 microm of the ischemic core. These data suggest that the axonal and dendritic circuitry of neurons located 300 microm outside of an ischemic zone can be relatively free of damage or commitment to cell death suggesting that they may be in an ideal position to contribute to functional recovery. Given that ischemic damage may have a larger effect on circuitry involving superficial dendrites and projecting axons, it is conceivable that surviving peri-infarct neurons may have unique structural and functional properties.

In vivo imaging in a murine model of glioblastoma

OBJECTIVE

To use in vivo imaging methods in mice to quantify intracranial glioma growth, to correlate images and histopathological findings, to explore tumor marker specificity, to assess effects on cortical function, and to monitor effects of chemotherapy.

METHODS

Mice with DBT glioma cell tumors implanted intracranially were imaged serially with a 4.7-T small-animal magnetic resonance imaging (MRI) scanner. MRI tumor volumes were measured and correlated with postmortem histological findings. Different nonspecific and specific positron emission tomography radiopharmaceuticals, [18F]2-fluoro-2-deoxy-d-glucose, [18F]3'-deoxy-3'-fluorothymidine, or [11C]RHM-I, a sigma2-receptor ligand, were visualized with microPET (CTI-Concorde MicroSystems LLC, Knoxville, TN). Intrinsic optical signals were imaged serially during contralateral whisker stimulation to study the impact of tumor growth on cortical function. Other groups of mice were imaged serially with MRI after one or two doses of the antimitotic N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU).

RESULTS

MRI and histological tumor volumes were highly correlated (r2 = 0.85). Significant binding of [11C]RHM-I was observed in growing tumors. Over time, tumors reduced and displaced (P # 0.001) whisker-activated intrinsic optical signals but did not change intrinsic optical signals in the contralateral hemisphere. Tumor growth was delayed 7 days after a single dose of BCNU and 18 days after two doses of BCNU. Mean tumor volume 15 days after DBT implantation was significantly smaller for treated mice (1- and 2-dose BCNU) compared with controls (P = 0.0026).

CONCLUSION

Mouse MRI, positron emission tomography, and optical imaging provide quantitative and qualitative in vivo assessments of intracranial tumors that correlate directly with tumor histological findings. The combined imaging approach provides powerful multimodality assessments of tumor progression, effects on brain function, and responses to therapy.

Neurophysiological and anatomical plasticity in the adult sensorimotor cortex

Evidence supporting the plastic capacity of the adult cortex is abundant. Changes have been associated with exposure to enriched environments, learning, peripheral lesions and central lesions. The initial loss of function caused by a lesion is generally followed by a certain amount of recovery that is believed to be due, at least in part, to adaptive plasticity. In particular, the reorganization of cortical representational maps has been associated with improvement of performance. Therefore, areas undergoing such reorganization following lesions are generally assumed to participate in the recovery. We review evidence demonstrating the remodeling of representational maps of the forelimb in adult cortex and the structural plasticity that has been coupled with it. A particular emphasis is paid to non-human primate studies and stroke.

Enriched environment enhances transplanted subventricular zone stem cell migration and functional recovery after stroke

Stroke patients suffer from severe impairments and significant effort is under way to develop therapies to improve functional recovery. Stem cells provide a promising form of therapy to replace neuronal circuits lost to injury. Indeed, previous studies have shown that a variety of stem cell types can provide some functional recovery in animal models of stroke. However, it is unlikely that replacement therapy alone will be sufficient to maximize recovery. The aim of the present study was to determine if rodent stem cell transplants combined with rehabilitation resulted in enhanced functional recovery after focal ischemia in rats. Middle cerebral artery occlusion was induced by injection of the vasoconstrictive peptide endothelin-1 adjacent to the middle cerebral artery. Seven days after stroke the rats received adult neural stem cell transplants isolated from mouse subventricular zone or vehicle injection and then subsequently were housed in enriched or standard conditions. The rats in the enriched housing also had access to running wheels once a week. Enriched housing and voluntary running exercise enhanced migration of transplanted stem cells toward the region of injury after stroke and there was a trend toward increased survival of stem cells. Enrichment also increased the number of endogenous progenitor cells in the subventricular zone of transplanted animals. Finally, functional recovery measured in the cylinder test was facilitated only when the stem cell transplants were combined with enrichment and running exercise 7 days after the transplant. These results suggest that the ability of transplanted stem cells in promoting recovery can be augmented by environmental factors such as rehabilitation.

Vicarious function of remote cortex following stroke: recent evidence from human and animal studies

Following a lesion, the adult central nervous system undergoes dramatic structural and physiological reorganization in diverse subcortical and cortical areas. Our knowledge of the events that parallel recovery within the tissue surrounding the lesion and other distant cortical areas has evolved greatly in the past few years. Particularly, recent efforts have increased our understanding of the potential implication of premotor areas in recovery from lesions disturbing the primary motor cortex (M1) and its corticospinal outputs. Because these areas share extensive connections with M1 and have direct access to the spinal cord through corticospinal projections, they are particularly well positioned to take over the role of M1 in a vicarious manner and thus compensate for the neuronal loss resulting from M1 lesions. The impressive postlesional reorganization known to occur in many areas of the CNS including the premotor cortex traditionally has been assumed to play a beneficial role in recovery. However, recent experiments suggest that in some cases, reorganization of distant cortical areas correlates with poor recovery, raising the concept of maladaptive vicarious process. This concept might be particularly critical in the development of new treatment approaches favoring postlesion plasticity and even more so for interventions targeting specific area(s). Here, the author reviews human and animal studies that show the plastic potential of the adult CNS after stroke, highlighting the vicarious role of the premotor cortex in the recovery of motor control.

Behavioral, Temporal, and Spatial Targets for Cellular Transplants as Adjuncts to Rehabilitation for Stroke

Stem cell and more differentiated neural cell transplantation strategies are an intriguing approach for neural repair to augment rehabilitation interventions after stroke. In the cortex, exogenous cells could create, augment, or extend in time endogenous peri-infarct and remote molecular signals, such as those for neurogenesis, cell differentiation, axonal and dendritic sprouting, network connectivity, and long-term potentiation, as well as deliver engineered genes and provide replacement cells in a network. If demyelinated axons exist in the periphery of an infarct, they could be targets for remyelination to reestablish conductivity. Much is unknown, however, about the mechanisms by which pluripotent embryonic and multipotent neural stem cells serve as agents of therapeutic plasticity. The robustness of their effects on neuromodulation, reorganization, regeneration, and behavioral recovery is a work in progress. Invasive interventions may have adverse effects not appreciated in preclinical testing. These should initially be offered only to patients with specific profound impairments after it is clinically certain that major disabilities will not improve. If a cellular strategy is very safe, it may be offered to subjects with moderate impairments when they are no longer likely to make further functional gains. Clinical trial designs are suggested that take into account the optimal timing after stroke and specific targets for cellular therapies to foster repair, remapping, and modulation of neural circuits. Cell-mediated rehabilitation would then use task-specific therapies in an optimal dose to maximize training-induced reorganization and learning and, most important, reduce unwanted disability.

Changes in neuronal connectivity after stroke in rats as studied by serial manganese-enhanced MRI

Loss of function and subsequent spontaneous recovery after stroke have been associated with physiological and anatomical alterations in neuronal networks in the brain. However, the spatiotemporal pattern of such changes has been incompletely characterized. Manganese-enhanced MRI (MEMRI) provides a unique tool for in vivo investigation of neuronal connectivity. In this study, we measured manganese-induced changes in longitudinal relaxation rate, R(1), to assess the spatiotemporal pattern of manganese distribution after focal injection into the intact sensorimotor cortex in control rats (n=10), and in rats at 2 weeks after 90-min unilateral occlusion of the middle cerebral artery (n=10). MEMRI data were compared with results from conventional tract tracing with wheat-germ agglutinin horseradish peroxidase (WGA-HRP). Distinct areas of the sensorimotor pathway were clearly visualized with MEMRI. At 2 weeks after stroke, manganese-induced changes in R(1) were significantly delayed and diminished in the ipsilateral caudate putamen, thalamus and substantia nigra. Loss of connectivity between areas of the sensorimotor network was also identified from reduced WGA-HRP staining in these areas on post-mortem brain sections. This study demonstrates that MEMRI enables in vivo assessment of spatiotemporal alterations in neuronal connectivity after stroke, which may lead to improved insights in mechanisms underlying functional loss and recovery after stroke.

A neurovascular niche for neurogenesis after stroke

Stroke causes cell death but also birth and migration of new neurons within sites of ischemic damage. The cellular environment that induces neuronal regeneration and migration after stroke has not been defined. We have used a model of long-distance migration of newly born neurons from the subventricular zone to cortex after stroke to define the cellular cues that induce neuronal regeneration after CNS injury. Mitotic, genetic, and viral labeling and chemokine/growth factor gain- and loss-of-function studies show that stroke induces neurogenesis from a GFAP-expressing progenitor cell in the subventricular zone and migration of newly born neurons into a unique neurovascular niche in peri-infarct cortex. Within this neurovascular niche, newly born, immature neurons closely associate with the remodeling vasculature. Neurogenesis and angiogenesis are causally linked through vascular production of stromal-derived factor 1 (SDF1) and angiopoietin 1 (Ang1). Furthermore, SDF1 and Ang1 promote post-stroke neuroblast migration and behavioral recovery. These experiments define a novel brain environment for neuronal regeneration after stroke and identify molecular mechanisms that are shared between angiogenesis and neurogenesis during functional recovery from brain injury.

Whisker stimulation enhances angiogenesis in the barrel cortex following focal ischemia in mice

Post-ischemia angiogenesis and vascular plasticity help to restore blood flow to ischemic tissue and likely benefit long-term functional recovery. Physical activity has been shown to cause morphologic and functional effects, including promoting angiogenesis in normal or injured animals. A therapeutic effect of peripheral activity on central angiogenesis after cerebral ischemia, however, has not been studied. In the present study of whisker-barrel cortex ischemia in the mouse model, we tested the hypothesis that enhancing whisker activity and sensory input to the ischemic barrel cortex might promote post-ischemia cerebral angiogenesis. Three days after focal ischemia in adult mice, the whiskers corresponding to the ischemic barrel cortex were stimulated by two methods: (1) whiskers on the right side of the mouse face were trimmed away, so the left whiskers were overused by the animals, (2) left whiskers were manually stimulated to enhance input signals to the ischemic barrel cortex. Western blot analysis showed that whisker stimulation increased expression of the angiogenic factors vascular endothelial growth factor, basic fibroblast growth factor, Tie-1, angiopoietin-2 (Ang-2), and possibly Ang-1. Co-immunostaining with markers for proliferation (5-bromo-2'-deoxyuridine (BrdU)) and vascular endothelial cells (Glut-1/CD-31) identified vessel proliferation in the penumbra region. Whisker stimulation increased BrdU-positive endothelial cells and vessels in this region 7 and 14 days after ischemia. Whisker stimulation also attenuated endothelial cell death and increased local cerebral blood flow. Our data suggest that appropriately enhanced peripheral activity and afferent signals to the ischemic cortex can promote post-ischemic angiogenesis, which may imply beneficial effects of specific physical therapy on long-term recovery from ischemic stroke.

Regulation of intrinsic neuronal properties for axon growth and regeneration

Regulation of neuritic growth is crucial for neural development, adaptation and repair. The intrinsic growth potential of nerve cells is determined by the activity of specific molecular sets, which sense environmental signals and sustain structural extension of neurites. The expression and function of these molecules are dynamically regulated by multiple mechanisms, which adjust the actual growth properties of each neuron population at different ontogenetic stages or in specific conditions. The neuronal potential for axon elongation and regeneration are restricted at the end of development by the concurrent action of several factors associated with the final maturation of neurons and of the surrounding tissue. In the adult, neuronal growth properties can be significantly modulated by injury, but they are also continuously tuned in everyday life to sustain physiological plasticity. Strict regulation of structural remodelling and neuritic elongation is thought to be required to maintain specific patterns of connectivity in the highly complex mammalian CNS. Accordingly, procedures that neutralize such mechanisms effectively boost axon growth in both intact and injured nervous system. Even in these conditions, however, aberrant connections are only formed in the presence of unusual external stimuli or experience. Therefore, growth regulatory mechanisms play an essentially permissive role by setting the responsiveness of neural circuits to environmental stimuli. The latter exert an instructive action and determine the actual shape of newly formed connections. In the light of this notion, efficient therapeutic interventions in the injured CNS should combine targeted manipulations of growth control mechanisms with task-specific training and rehabilitation paradigms.

Mechanisms for recovery of motor function following cortical damage

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

Time-dependent increase in Nogo-A expression after focal cerebral ischemia in marmoset monkeys

Nogo-A is a myelin-associated protein that has been shown to inhibit axonal sprouting after lesions to the CNS. Several studies have demonstrated that blocking the activity or expression of this inhibitor can induce structural and functional recovery after CNS lesions. However, there are limited and contradictory data on the expression of Nogo-A after CNS lesions. In the present study, marmoset monkeys received permanent occlusion of the middle cerebral artery (MCAo). Two, 3, or 4 months after the onset of injury brain sections were stained for Nogo-A protein. Two sham operated marmosets were included as a control. Nogo-A protein expression was quantified in white matter and grey matter in the areas adjacent to the lesion (or the equivalent areas in the intact side). At 2 months after injury, but not at 3 or 4 months, there was a significant increase in the number of oligodendrocytes that were Nogo-A immunopositive. This increase was observed in white matter structures that were adjacent to the lesion (e.g. corona radiate (CR)); but not in: white matter structures distal to the lesion (e.g. corpus callosum (CC)); cortical regions adjacent to the lesion; contralateral regions or in sham operated marmosets. These data suggest that Nogo-A levels are significantly increased within oligodendrocytes in areas adjacent to the lesion up to 2 months following cerebral ischaemia. Future studies will determine whether this offers the opportunity to promote plasticity by targeting Nogo-A weeks or months following stroke.

Growth-associated gene and protein expression in the region of axonal sprouting in the aged brain after stroke

Aged individuals exhibit reduced functional recovery after stroke. We examined the expression profile in aged animals of a recently identified group of growth-associated genes that underlies post-stroke axonal sprouting in the young adult. Basal levels of most growth-promoting genes are higher in aged cortex compared with young adult, and are further induced after stroke. Compared with the young adult, these genes are induced at later time points after stroke. For growth-inhibitory molecules, myelin-associated glycoprotein and ephrin A5 are uniquely induced in the aged brain; chondroitin sulfate proteoglycans and oligodendrocyte myelin glycoprotein are induced at earlier time points; and Nogo-A, semaphorin IIIa and NG2 decline in aged vs. young adult after stroke. The aged brain does not simply have a reduction in growth-associated molecules after stroke, but a completely unique molecular profile of post-stroke axonal sprouting.

Cellular and molecular mechanisms of neural repair after stroke: making waves

Stroke is associated with a limited degree of functional recovery. Imaging studies in humans have shown that reorganization in periinfarct and connected cortical areas most closely correlates with functional recovery after stroke. On a cellular level, two major regenerative events occur in periinfarct cortex: axons sprout new connections and establish novel projection patterns, and newly born immature neurons migrate into periinfarct cortex. Stroke induces a unique microenvironment for axonal sprouting in periinfarct cortex, in which growth-inhibitory molecules are reduced for 1 month after the infarct. During this period, neurons activate growth-promoting genes in successive waves. Neurogenesis also occurs through waves of migration of immature neurons from their origin in the subventricular zone into periinfarct cortex. This migration is mediated, in part, by the cytokine erythropoietin. These data indicate that the cellular environment after stroke is far from one of just death and destruction, but rather involves a longer evolving process of neuronal regeneration. Poststroke neuronal regeneration is characterized by waves of specific cellular and molecular events. Manipulating these waves of regeneration may provide for novel therapies that will improve recovery after stroke.

Enhanced excitatory synaptic connectivity in layer v pyramidal neurons of chronically injured epileptogenic neocortex in rats

Formation of new recurrent excitatory circuits after brain injuries has been hypothesized as a major factor contributing to epileptogenesis. Increases in total axonal length and the density of synaptic boutons are present in layer V pyramidal neurons of chronic partial isolations of rat neocortex, a model of posttraumatic epileptogenesis. To explore the functional consequences of these changes, we used laser-scanning photostimulation combined with whole-cell patch-clamp recording from neurons in layer V of somatosensory cortex to map changes in excitatory synaptic connectivity after injury. Coronal slices were submerged in artificial CSF (23 degrees C) containing 100 microM caged glutamate, APV (2-amino-5-phosphonovaleric acid), and high divalent cation concentration to block polysynaptic responses. Focal uncaging of glutamate, accomplished by switching a pulsed UV laser to give a 200-400 micros light stimulus, evoked single- or multiple-component composite EPSCs. In neurons of the partially isolated cortex, there were significant increases in the fraction of uncaging sites from which EPSCs could be evoked ("hot spots") and a decrease in the mean amplitude of individual elements in the composite EPSC. When plotted along the cortical depth, the changes in EPSCs took place mainly between 150 and 200 microm above and below the somata, suggesting a specific enhancement of recurrent excitatory connectivity among layer V pyramidal neurons of the undercut neocortex. These changes may shift the balance within cortical circuits toward increased synaptic excitation and contribute to epileptogenesis.

Necrosis, apoptosis and hybrid death in the cortex and thalamus after barrel cortex ischemia in rats

Focal ischemia in the cerebral cortex results in acute and delayed cell death in the ischemic cortex and non-ischemic thalamus. We examined the hypothesis that neurons in ischemic and non-ischemic regions died from different mechanisms; specifically, we tested whether a mixed form of cell death containing both necrotic and apoptotic changes could be identified in individual cells. Focal barrel cortex ischemia in rats was induced by occlusion of small branches of the middle cerebral artery (MCA) corresponding to the barrel cortex, local blood flow was measured by quantitative autoradiography. Cell death was visualized by 2,3,5-triphenyltetrazolium chloride (TTC) staining, hematoxylin-eosin (H&E) staining, the terminal deoxyribonucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), and caspase-3 staining 1 to 10 days after the ischemia. Electron microscopy was used for ultrastructural examination. Cell death occurred in the ipsilateral cortex 24 h after ischemia, followed by selective neuronal death in the ventrobasal (VB) thalamus 3 days later. TUNEL positive neurons were found in these two regions, but with striking morphological differences, designated as type I and type II TUNEL positive cells. The type I TUNEL positive cells in the ischemic cortex underwent necrotic changes. The type II TUNEL positive cells in the thalamus and the cortex penumbra region represented a hybrid death, featured by concurrent apoptotic and necrotic alterations in individual cells, including marked caspase-3 activation, nuclear condensation/fragmentation, but with swollen cytoplasm, damaged organelles and deteriorated membranes. Cell death in the thalamus and the cortex penumbra were attenuated by delayed administration of the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp fluoromethylketone (Z-VAD-FMK). Our data suggest that TUNEL staining should be evaluated with morphological changes, the hybrid death but not typical apoptosis occurs in the penumbra region and non-ischemic thalamus after cerebral ischemia.

Extensive cortical rewiring after brain injury

Previously, we showed that the ventral premotor cortex (PMv) underwent neurophysiological remodeling after injury to the primary motor cortex (M1). In the present study, we examined cortical connections of PMv after such lesions. The neuroanatomical tract tracer biotinylated dextran amine was injected into the PMv hand area at least 5 months after ischemic injury to the M1 hand area. Comparison of labeling patterns between experimental and control animals demonstrated extensive proliferation of novel PMv terminal fields and the appearance of retrogradely labeled cell bodies within area 1/2 of the primary somatosensory cortex after M1 injury. Furthermore, evidence was found for alterations in the trajectory of PMv intracortical axons near the site of the lesion. The results suggest that M1 injury results in axonal sprouting near the ischemic injury and the establishment of novel connections within a distant target. These results support the hypothesis that, after a cortical injury, such as occurs after stroke, cortical areas distant from the injury undergo major neuroanatomical reorganization. Our results reveal an extraordinary anatomical rewiring capacity in the adult CNS after injury that may potentially play a role in recovery.

Allogeneic bone marrow stromal cells promote glial-axonal remodeling without immunologic sensitization after stroke in rats

We evaluated the effects of allogeneic bone marrow stromal cell treatment of stroke on functional outcome, glial-axonal architecture, and immune reaction. Female Wistar rats were subjected to 2 h of middle cerebral artery occlusion. Rats were injected intravenously with PBS, male allogeneic ACI--or syngeneic Wistar--bone marrow stromal cells at 24 h after ischemia and sacrificed at 28 days. Significant functional recovery was found in both cell-treated groups compared to stroke rats that did not receive BMSCs, but no difference was detected between allogeneic and syngeneic cell-treated rats. No evidence of T cell priming or humoral antibody production to marrow stromal cells was found in recipient rats after treatment with allogeneic cells. Similar numbers of Y-chromosome+ cells were detected in the female rat brains in both groups. Significantly increased thickness of individual axons and myelin, and areas of the corpus callosum and the numbers of white matter bundles in the striatum were detected in the ischemic boundary zone of cell-treated rats compared to stroked rats. The areas of the contralateral corpus callosum significantly increased after cell treatment compared to normal rats. Processes of astrocytes remodeled from hypertrophic star-like to tadpole-like shape and oriented parallel to the ischemic regions after cell treatment. Axonal projections emanating from individual parenchymal neurons exhibited an overall orientation parallel to elongated radial processes of reactive astrocytes of the cell-treated rats. Allogeneic and syngeneic bone marrow stromal cell treatment after stroke in rats improved neurological recovery and enhanced reactive oligodendrocyte and astrocyte related axonal remodeling with no indication of immunologic sensitization in adult rat brain.

Region-specific sprouting of crossed corticofugal fibers after unilateral cortical lesions in adult mice

Long considered to be limited to early development or restricted adult brain regions in mammals, axonal sprouting of spared axons into denervated brain areas now appears more widespread in the adult mammalian brain. However, its extent and mechanisms remain poorly understood. In this study, we show that robust sprouting of corticofugal axons occurs in the dorsolateral striatum but not the red nucleus of adult mice after unilateral lesions of the sensorimotor cortex induced either by mechanical removal or by thermocoagulation of pial blood vessels. These results show that local factors are critical for axonal sprouting in adult brain. They also extend previous findings in rats to a species readily amenable to genetic analysis in order to elucidate the mechanisms of this effect.

Rodent models of focal stroke: size, mechanism, and purpose

Rodent stroke models provide the experimental backbone for the in vivo determination of the mechanisms of cell death and neural repair, and for the initial testing of neuroprotective compounds. Less than 10 rodent models of focal stroke are routinely used in experimental study. These vary widely in their ability to model the human disease, and in their application to the study of cell death or neural repair. Many rodent focal stroke models produce large infarcts that more closely resemble malignant and fatal human infarction than the average sized human stroke. This review focuses on the mechanisms of ischemic damage in rat and mouse stroke models, the relative size of stroke generated in each model, and the purpose with which focal stroke models are applied to the study of ischemic cell death and to neural repair after stroke.

Enriched environment enhances recovery of motor function after focal ischemia in mice, and downregulates the transcription factor NGFI-A

The purpose of this study was to investigate the effect of enriched environment on motor function after experimental stroke in mice, and to determine whether time in enriched environment affects functional recovery. Earlier investigations have shown that rats placed in an enriched environment after focal ischemia, remarkably improve motor function, but similar observations in mice have not been reported. In this study, we show that placing mice in an enriched environment for 3 h daily for 2 weeks, after transient (50 mins) occlusion of the middle cerebral artery, enhanced neurologic outcome. Continuous postischemic housing in the enriched environment likewise improved motor function, but mortality increased. Two weeks exposure to enriched environment followed by housing the mice in standard cages for 2 weeks, resulted in a loss of the improved motor function. In contrast, 4 weeks exposure to enriched environment led to an improved motor function and to a better maintenance of neurologic recovery. The expression levels of the immediate-early gene nerve growth factor-induced gene A at 2 to 3 weeks of recovery decreased in animals housed in enriched environment, implying this transcription factor in the recovery process. We conclude that housing mice in an enriched environment after experimental stroke improves functional outcome. Also, the presented experimental procedure is useful for further studies of the genomics of functional recovery after experimental stroke.

Rhythmic brain activity at rest from rolandic areas in acute mono-hemispheric stroke: a magnetoencephalographic study

In order to deepen our knowledge of the brain's ability to react to a cerebral insult, it is fundamental to obtain a "snapshot" of the acute phase, both for understanding the neural condition immediately after the insult and as a starting point for follow-up and clinical outcome prognosis. The characteristics of the brain's spontaneous neuronal activity in perirolandic cortical areas were investigated in 32 patients who had a stroke in the middle cerebral artery (MCA) territory of one hemisphere in the previous 10 days. Magnetic fields from both left and right rolandic areas were recorded at rest with open eyes. Total and band power properties, the individual alpha frequency (IAF) and the spectral entropy were analyzed and compared with a sex-age matched control group. In agreement with electroencephalographic literature, low frequency absolute powers were higher and high frequency were lower in the affected (AH) than in the unaffected hemisphere (UH), and also their values in both hemispheres differed from control values. An IAF reduction was found in AH with respect to UH. As new findings, the total power was higher in AH than in UH, after excluding 4 right-damaged patients with cortico-subcortical lesions, who showed a completely disorganized spectral pattern. Spectral entropy was lower in AH than in UH. Clinical severity correlated with the AH decrease of gamma band power, IAF and spectral entropy. Larger lesions were associated to worse clinical pictures and MEG alterations. A lesion affecting the MCA territory of one hemisphere induces a perilesional increase of the low-frequency rhythms' spectral power within the AH rolandic areas; the same effect was present also in the UH, indicating interhemispheric diaschisis. In the AH, results showed an increase of the total power and a reduction of the spectral entropy, suggesting a higher synchrony of local neuronal activity, a reduction of the intra-cortical inhibitory networks efficiency and an increase of neuronal excitability. Direct correlation linked gamma band activity preservation and less severe clinical status. Dependence of the clinical picture, and associated spectral alterations, on the lesion volume and not on the lesion level, suggests a diffuse neuronal impairment, rather than a selective structures damage, contributing to neurological status in the acute phase of stroke.

Correlations between MRI-assessed volumes of the thalamus and cortical Brodmann's areas in schizophrenia

BACKGROUND

We compared the thalamic-cortical volumetric correlational patterns in patients with schizophrenia and normal comparison subjects, and evaluated their relations to outcome.

METHODS

High-resolution MR images were acquired in patients with schizophrenia (n=106) and normal comparison subjects (n=42). Patients were divided into good-outcome (n=52) and poor-outcome (Kraepelinian, n=54) subtypes based on their ability for self-care. Correlations between the relative gray and white matter volumes of the individual cortical Brodmann's areas and five dorsoventral levels of the thalamus were assessed.

RESULTS

Compared to normal subjects, schizophrenia patients lacked significant thalamic gray matter volume correlations with the prefrontal and medial temporal cortical regions in the right hemisphere, and with frontal, cingulate, posterior parietal and occipital regions in the left hemisphere, while normal white matter volume cortical-thalamic correlations along the cingulate gyrus and in the temporal lobe were not found in schizophrenia patients in both hemispheres. In contrast to both normal comparison subjects and good-outcome group, schizophrenia patients with poor outcomes showed significant bilateral gray matter volume correlations between the dorsal thalamus and ventral prefrontal cortex, while the group differences in the white matter volume correlations were mostly restricted to the cingulate arch.

CONCLUSIONS

Whereas patients with schizophrenia exhibit deficiencies in cortical-thalamic correlational patterns, poor outcome is associated with abnormal interregional correlations not observed in either normal subjects or patients with good outcomes. This latter finding may be explained by a core neurodevelopmental disturbance that results in aberrant cortical-thalamic connectivity in poor-outcome schizophrenia.

Growth-associated gene expression after stroke: evidence for a growth-promoting region in peri-infarct cortex

Stroke induces axonal sprouting in peri-infarct cortex. A set of growth-associated genes important in axonal sprouting in peripheral nervous system regeneration and cortical development has recently been defined. The expression profiles of these growth-associated genes were defined during the post-stroke axonal sprouting response using a model of stroke in barrel field cortex. Stroke induces sequential waves of neuronal growth-promoting genes during the sprouting response: an early expression peak (SPRR1), a mid expression peak (p21, Ta1 tubulin, L1, MARCKS), a late peak (SCG10, SCLIP), and an early/sustained pattern (GAP43, CAP23, c-jun). These expression peaks correspond to specific time points in the sprouting response. The expression of the growth-inhibiting chondroitin sulfate proteoglycans aggrecan, brevican, versican, and phosphacan are induced late in the sprouting process; except neurocan, which is increased during the peak of the growth-promoting gene expression. The developmentally associated growth inhibitors ephrin-A5, ephB1, semaphorin IIIa, and neuropilin 1 are also induced in the early phases of the sprouting response. At the cellular level, chondroitin sulfate proteoglycans, in the form of peri-neuronal nets, are reduced in the region of axonal sprouting, during the peak of growth-promoting gene expression. These results identify a unique profile of growth-promoting gene expression in adult cortex after stroke, the inhibitory molecules that are present during the sprouting response, and a region in which growth-promoting genes are increased, growth-inhibitory proteins are diminished and axonal sprouting occurs. This region may be a growth-promoting zone after stroke.

Increased oxidative protein and DNA damage but decreased stress response in the aged brain following experimental stroke

Aged individuals experience the highest rate of stroke and have less functional recovery, but do not have larger infarcts. We hypothesized that aged individuals experience greater sublethal damage in peri-infarct cortex. Focal cortical stroke was produced in aged and young adult animals. After 30 min, 1, 3 and 5 days brain sections and Western blot were used to analyze markers of apoptotic cell death, oxidative DNA and protein damage, heat shock protein (HSP) 70 induction, total neuronal number and infarct size. Focal stroke produces significantly more oxidative DNA and protein damage and fewer cells with HSP70 induction in peri-infarct cortex of aged animals. There is no difference in infarct size or the number of cells undergoing apoptosis between aged and young adults. Stroke in the aged brain is associated with a greater degree of DNA and protein damage and a reduced stress response in intact, surviving tissue that surrounds the infarct.

Cortical origin of functional recovery in the somatosensory cortex of the adult mouse after thalamic lesion

To study the degree and time course of the functional recovery in the somatosensory cortex (SI) after an excitotoxic lesion in the adult mouse thalamus, metabolic activity was determined in SI at various times points post-lesion. Immediately after the lesion, metabolic activity in the thalamically deafferented part of SI was at its lowest value but increased progressively at subsequent time points. This was seen in all cortical layers; however, layers I and Vb recovered more rapidly than layers II, III, IV, Va and VI. Removal of the mystacial whiskers corresponding to the deafferented area, 5 weeks after cortical recovery, produced a subsequent 32% drop in metabolic activity, demonstrating peripheral sensory activation of this part of the cortex. Tracing experiments revealed that the deafferented cortex did not receive a novel thalamic input but that cortico-cortical and contralateral barrel cortex projections to this area were reinforced. We conclude that the cortical functional recovery after a thalamic lesion is, at least partially, due to modified cortico-cortical and callosal projections to the deafferented cortical area.