Dendritic plasticity in the adult rat following middle cerebral artery occlusion and Nogo-a neutralization

Anti-Nogo-A Antibody Therapy Improves Functional Outcome Following Traumatic Brain Injury

BACKGROUND

Traumatic brain injury (TBI) can cause sensorimotor deficits, and recovery is slow and incomplete. There are no effective pharmacological treatments for recovery from TBI, but research indicates potential for anti-Nogo-A antibody (Ab) therapy. This Ab neutralizes Nogo-A, an endogenous transmembrane protein that inhibits neuronal plasticity and regeneration.

OBJECTIVE

We hypothesized that anti-Nogo-A Ab treatment following TBI results in disinhibited axonal growth from the contralesional cortex, the establishment of new compensatory neuronal connections, and improved function.

METHODS

We modeled TBI in rats using the controlled cortical impact method, resulting in focal brain damage and motor deficits like those observed in humans with a moderate cortical TBI. Rats were trained on the skilled forelimb reaching task and the horizontal ladder rung walking task. They were then given a TBI, targeting the caudal forelimb motor cortex, and randomly divided into 3 groups: TBI-only, TBI + Anti-Nogo-A Ab, and TBI + Control Ab. Testing resumed 3 days after TBI and continued for 8 weeks, when rats received an injection of the anterograde neuronal tracer, biotinylated dextran amine (BDA), into the corresponding area contralateral to the TBI.

RESULTS

We observed significant improvement in rats that received anti-Nogo-A Ab treatment post-TBI compared to controls. Analysis of BDA-positive axons revealed that anti-Nogo-A Ab treatment resulted in cortico-rubral plasticity to the deafferented red nucleus. Conclusions. Anti-Nogo-A Ab treatment may improve functional recovery via neuronal plasticity to brain areas important for skilled movements, and this treatment shows promise to improve outcomes in humans who have suffered a TBI.

Impairments and Compensation in String-pulling After Middle Cerebral Artery Occlusion in the Rat

Stroke is a leading cause of long-term disability in humans, and it is frequently associated with impairments in the skilled use of the arms and hands. Many human upper limb impairments and compensatory changes have been successfully modeled in rodent studies of neocortical stroke, especially those that evaluate single limb use in tasks, such as reaching for food. Humans also use their hands for bilaterally coordinated movements, dependent upon interhemispheric cortical projections, which are also compromised by unilateral stroke. This study describes middle cerebral artery occlusion (MCAO) dependent changes in the bilaterally dependent hand use behavior of string-pulling in the rat. The task involves making hand-over-hand movements to pull down a string that contains a food reward attached to its end. MCAO rats missed the string more often with both hands than Sham rats. When the string was missed on the contralateral to MCAO body side, rats continued to cycle through subcomponents of string-pulling behavior as if the string were grasped in the hand. Rats also failed to make a grasping motion with the contralateral to MCAO hand when the string was missed and instead, demonstrated an open-handed raking-like motions. Nevertheless, with repeated attempts, rats performed components of string-pulling well enough to obtain a reward on the end of the string. Thus, string-pulling behavior is sensitive to bilateral impairments but is achieved with compensatory adjustments following MCAO. These aspects of MCAO string-pulling provide a foundation for studies that investigate the efficacy of therapeutic intervention which might enhance neuroplasticity and recovery. DATA AVAILABILITY: The datasets generated during the current study are available upon request.

In Vivo Imaging of the Structural Plasticity of Cortical Neurons After Stroke

The comprehension of the finest mechanisms underlying experience-dependent plasticity requires the investigation of neurons and synaptic terminals in the intact brain over prolonged periods of time. Longitudinal two-photon imaging together with the expression of fluorescent proteins enables high-resolution imaging of dendritic spines and axonal varicosities of cortical neurons in vivo. Importantly, the study of the mechanisms of structural reorganization is relevant for a deeper understanding of the pathophysiological mechanisms of neurological diseases such as stroke and for the development of new therapeutic approaches. This protocol describes the principal steps for in vivo investigation of neuronal plasticity both in healthy conditions and after an ischemic lesion. First, we give a description of the surgery to perform a stable cranial window that allows optical access to the mouse brain cortex. Then we explain how to perform longitudinal two-photon imaging of dendrites, axonal branches, and synaptic terminals in the mouse brain cortex in vivo, in order to investigate the plasticity of synaptic terminals and orientation of neuronal processes. Finally, we describe how to induce an ischemic lesion in a target region of the mouse brain cortex through a cranial window by applying the photothrombotic stroke model.

Structural plasticity of motor cortices assessed by voxel-based morphometry and immunohistochemical analysis following internal capsular infarcts in macaque monkeys

Compensatory plastic changes in the remaining intact brain regions are supposedly involved in functional recovery following stroke. Previously, a compensatory increase in cortical activation occurred in the ventral premotor cortex (PMv), which contributed to the recovery of dexterous hand movement in a macaque model of unilateral internal capsular infarcts. Herein, we investigated the structural plastic changes underlying functional changes together with voxel-based morphometry (VBM) analysis of magnetic resonance imaging data and immunohistochemical analysis using SMI-32 antibody in a macaque model. Unilateral internal capsular infarcts were pharmacologically induced in 5 macaques, and another 5 macaques were used as intact controls for immunohistochemical analysis. Three months post infarcts, we observed significant increases in the gray matter volume (GMV) and the dendritic arborization of layer V pyramidal neurons in the contralesional rostral PMv (F5) as well as the primary motor cortex (M1). The histological analysis revealed shrinkage of neuronal soma and dendrites in the ipsilesional M1 and several premotor cortices, despite not always detecting GMV reduction by VBM analysis. In conclusion, compensatory structural changes occur in the contralesional F5 and M1 during motor recovery following internal capsular infarcts, and the dendritic growth of pyramidal neurons is partially correlated with GMV increase.

Astrocyte-secreted chordin-like 1 regulates spine density after ischemic injury

Ischemic injury occurs when the brain is deprived of blood flow, preventing cells from receiving essential nutrients. The injury core is the brain region directly deprived and is surrounded by the peri-infarct area, the region with recovery potential. In the peri-infarct area neurons undergo acute loss of dendritic spines, which modifies synaptic plasticity and determines neuronal survival. Astrocytes can be protective or detrimental to the ischemic injury response depending on the specific stage, yet we lack clear understanding of the underlying mechanisms. Chordin-like 1 (Chrdl1) is an astrocyte-secreted protein that promotes synaptic maturation and limits experience-dependent plasticity in the mouse visual cortex. Given this plasticity-limiting function we asked if Chrdl1 regulates the response to ischemic injury, modelled using photothrombosis (PT). We find that Chrdl1 mRNA is upregulated in astrocytes in the peri-infarct area in both acute and sub-acute phases post-PT. To determine the impact of increased Chrdl1 on the response to PT we analyzed Chrdl1 knock-out mice. We find that absence of Chrdl1 prevents ischemia-induced spine loss in the peri-infarct area and reduces cell death in the core, without impacting gliosis. These findings highlight the important role of astrocyte-secreted proteins in regulating structural plasticity in response to brain ischemic injuries.

Poststroke dendritic arbor regrowth requires the actin nucleator Cobl

Ischemic stroke is a major cause of death and long-term disability. We demonstrate that middle cerebral artery occlusion (MCAO) in mice leads to a strong decline in dendritic arborization of penumbral neurons. These defects were subsequently repaired by an ipsilateral recovery process requiring the actin nucleator Cobl. Ischemic stroke and excitotoxicity, caused by calpain-mediated proteolysis, significantly reduced Cobl levels. In an apparently unique manner among excitotoxicity-affected proteins, this Cobl decline was rapidly restored by increased mRNA expression and Cobl then played a pivotal role in poststroke dendritic arbor repair in peri-infarct areas. In Cobl knockout (KO) mice, the dendritic repair window determined to span day 2 to 4 poststroke in wild-type (WT) strikingly passed without any dendritic regrowth. Instead, Cobl KO penumbral neurons of the primary motor cortex continued to show the dendritic impairments caused by stroke. Our results thereby highlight a powerful poststroke recovery process and identified causal molecular mechanisms critical during poststroke repair.

Ischemic stroke is a major cause of death and long-term disability. This study reveals that, in mice, stroke-induced damage to dendritic arborization in the area around an infarct is rapidly repaired via dendritic regrowth; this plasticity requires the actin nucleator Cobl.

NEP1‑40 promotes myelin regeneration via upregulation of GAP‑43 and MAP‑2 expression after focal cerebral ischemia in rats

Axon regeneration after lesions to the central nervous system (CNS) is largely limited by the presence of growth inhibitory molecules expressed in myelin. Nogo‑A is a principal inhibitor of neurite outgrowth, and blocking the activity of Nogo‑A can induce axonal sprouting and functional recovery. However, there are limited data on the expression of Nogo‑A after CNS lesions, and the mechanism underlying its influences on myelin growth remains unknown. The aim of the present study was to observe the time course of Nogo‑A after cerebral ischemia/reperfusion in rats using immunohistochemistry and western blot techniques, and to test the effect of its inhibitor Nogo extracellular peptide 1‑40 (NEP1‑40) on neural plasticity proteins, growth‑associated binding protein 43 (GAP‑43) and microtubule associated protein 2 (MAP‑2), as a possible mechanism underlying myelin suppression. A classic model of middle cerebral artery occlusion (MCAO) was established in Sprague‑Dawley rats, which were divided into three groups: i) MCAO model group; ii) MCAO + saline group; and iii) MCAO + NEP1‑40 group. Rats of each group were divided into five subgroups by time points as follows: days 1, 3, 7, 14 and 28. Animals that only received sham operation were used as controls. The Nogo‑A immunoreactivity was located primarily in the cytoplasm of oligodendrocytes. The number of Nogo‑A immunoreactive cells significantly increased from day 1 to day 3 after MCAO, nearly returning to the control level at day 7, increased again at day 14 and decreased at day 28. Myelin basic protein (MBP) immunoreactivity in the ipsilateral striatum gradually decreased from day 1 to day 28 after ischemia, indicating myelin loss appeared at early time points and continuously advanced during ischemia. Then, intracerebroventricular infusion of NEP1‑40, which is a Nogo‑66 receptor antagonist peptide, was administered at days 1, 3 and 14 after MCAO. It was observed that GAP‑43 considerably increased from day 1 to day 7 and then decreased to a baseline level at day 28 compared with the control. MAP‑2 expression across days 1‑28 significantly decreased after MCAO. Administration of NEP1‑40 attenuated the reduction of MBP, and upregulated GAP‑43 and MAP‑2 expression at the corresponding time points after MCAO compared with the MCAO + saline group. The present results indicated that NEP1‑40 ameliorated myelin damage and promoted regeneration by upregulating the expression of GAP‑43 and MAP‑2 related to neuronal and axonal plasticity, which may aid with the identification of a novel molecular mechanism of restriction in CNS regeneration mediated by Nogo‑A after ischemia in rats.

Exercise Intervention Promotes the Growth of Synapses and Regulates Neuroplasticity in Rats With Ischemic Stroke Through Exosomes

Background: Stroke is the leading cause of death and disability. Exercise produces neuroprotection by improving neuroplasticity. Exercise can induce exosome production. According to several studies, exosomes are involved in repairing brain function, but the relationship and mechanism of exercise, exosomes, and neuroprotection have not been elucidated. This study intends to explore the relationship and potential mechanism by observing the changes in the exosome level, infarct volume, neurological function and behavioral scores, synapses, and corticospinal tract (CST).

Methods: Rats were randomly divided into four groups: a sham operation (SHAM) group, middle cerebral artery occlusion (MCAO) with sedentary intervention (SED-MCAO) group, MCAO with exercise intervention (EX-MCAO) group, and MCAO with exercise intervention and exosome injection (EX-MCAO-EXO) group. The exercise intervention was started 1 day after MCAO and lasted for 4 weeks. All rats were assessed using the modified neurological severity score (mNSS). The levels of exosomes in serum and brain, gait analysis, and magnetic resonance scan were performed 1 and 4 weeks after the intervention. After 4 weeks of intervention, the number of synapses, synaptophysin (Syn), and postsynaptic density protein 95(PSD-95) expression was detected.

Results: After 4 weeks of intervention, (1) the EX-MCAO and EX-MCAO-EXO groups showed higher serum exosome (p_EX−MCAO = 0.000, p_{EX−MCAO−EXO} = 0.000) and brain exosome (p_EX−MCAO = 0.001, p_{EX−MCAO−EXO} = 0.000) levels than the SED-MCAO group, of which the EX-MCAO group had the highest serum exosome (p = 0.000) and the EX-MCAO-EXO group had the highest brain exosome (p = 0.03) levels. (2) The number of synapses in the EX-MCAO (p = 0.032) and EX-MCAO-EXO groups (p = 0.000) was significantly higher than that in the SED-MCAO group. The EX-MCAO-EXO group exhibited a greater number of synapses than the EX-MCAO (p = 0.000) group. (3) The synaptic plasticity-associated proteins were expressed significantly higher in the EX-MCAO (p_Syn = 0.010, p_PSD−95 = 0.044) and EX-MCAO-EXO (p_Syn = 0.000, p_PSD−95 = 0.000) groups than in the SED-MCAO group, and the EX-MCAO-EXO group (p_Syn = 0.000, p_PSD−95 = 0.046) had the highest expression. (4) Compared with the SED-MCAO group, the EX-MCAO group had significantly improved infarct volume ratio (p = 0.000), rFA value (p = 0.000), and rADC (p = 0.000). Compared with the EX-MCAO group, the EX-MCAO-EXO group had a significantly improved infarct volume ratio (p = 0.000), rFA value (p = 0.000), and rADC value (p = 0.001). (5) Compared with the SED-MCAO group, the EX-MCAO group (p = 0.001) and EX-MCAO-EXO group (p = 0.000) had significantly lower mNSS scores and improved gait. (6) The brain exosome levels were negatively correlated with the mNSS score, infarct volume ratio, and rADC value and positively correlated with the rFA value, Syn, and PSD-95 expression. The serum and brain exosome levels showed a positive correlation.

Conclusions: Exercise intervention increases the serum exosome level in MCAO rats, which are recruited into the brain, leading to improved synaptic growth and CST integrity, a reduced infarct volume, and improved neurological function and gait.

Cell-to-Cell Interactions Mediating Functional Recovery after Stroke

Ischemic damage in brain tissue triggers a cascade of molecular and structural plastic changes, thus influencing a wide range of cell-to-cell interactions. Understanding and manipulating this scenario of intercellular connections is the Holy Grail for post-stroke neurorehabilitation. Here, we discuss the main findings in the literature related to post-stroke alterations in cell-to-cell interactions, which may be either detrimental or supportive for functional recovery. We consider both neural and non-neural cells, starting from astrocytes and reactive astrogliosis and moving to the roles of the oligodendrocytes in the support of vulnerable neurons and sprouting inhibition. We discuss the controversial role of microglia in neural inflammation after injury and we conclude with the description of post-stroke alterations in pyramidal and GABAergic cells interactions. For all of these sections, we review not only the spontaneous evolution in cellular interactions after ischemic injury, but also the experimental strategies which have targeted these interactions and that are inspiring novel therapeutic strategies for clinical application.

Circulating Pro-Inflammatory Exosomes Worsen Stroke Outcomes in Aging

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Effects of Nogo-A and its receptor on the repair of sciatic nerve injury in rats

Regeneration of injured peripheral nerves is an extremely complex process. Nogo-A (neurite outgrowth inhibitor-A) inhibits axonal regeneration by interacting with Nogo receptor in the myelin sheath of the central nervous system (CNS). The aim of this study was to investigate the effects of Nogo-A and its receptor on the repair of sciatic nerve injury in rats. Sprague-Dawley rats (n=96) were randomly divided into 4 groups: control group (control), sciatic nerve transection group (model), immediate repair group (immediate repair), and delayed repair group (delayed repair). The rats were euthanized 1 week and 6 weeks after operation. The injured end tissues of the spinal cord and sciatic nerve were obtained. The protein expressions of Nogo-A and Nogo-66 receptor (NgR) were detected by immunohistochemistry. The protein expressions of Nogo-A, NgR, and Ras homolog family member A (RhoA) were detected by western blot. At 1 week after operation, the pathological changes in the immediate repaired group were less, and the protein expressions of Nogo-A, NgR, and RhoA in the spinal cord and sciatic nerve tissues were decreased (P<0.05) compared with the model group. After 6 weeks, the pathological changes in the immediate repair group and the delayed repair group were alleviated and the protein expressions decreased (P<0.05). The situation of the immediate repair group was better than that of the delayed repair group. Our data suggest that the expression of Nogo-A and its receptor increased after sciatic nerve injury, indicating that Nogo-A and its receptor play an inhibitory role in the repair process of sciatic nerve injury in rats.

Skilled movement and posture deficits in rat string-pulling behavior following low dose space radiation (28Si) exposure

Deep space flight missions beyond the Van Allen belt have the potential to expose astronauts to space radiation which may damage the central nervous system and impair function. The proposed mission to Mars will be the longest mission-to-date and identifying mission critical tasks that are sensitive to space radiation is important for developing and evaluating the efficacy of counter measures. Fine motor control has been assessed in humans, rats, and many other species using string-pulling behavior. For example, focal cortical damage has been previously shown to disrupt the topographic (i.e., path circuity) and kinematic (i.e., moment-to-moment speed) organization of rat string-pulling behavior count to compromise task accuracy. In the current study, rats were exposed to a ground-based model of simulated space radiation (5 cGy ²⁸Silicon), and string-pulling behavior was used to assess fine motor control. Irradiated rats initially took longer to pull an unweighted string into a cage, exhibited impaired accuracy in grasping the string, and displayed postural deficits. Once rats were switched to a weighted string, some deficits lessened but postural instability remained. These results demonstrate that a single exposure to a low dose of space radiation disrupts skilled hand movements and posture, suggestive of neural impairment. This work establishes a foundation for future studies to investigate the neural structures and circuits involved in fine motor control and to examine the effectiveness of counter measures to attenuate the effects of space radiation on fine motor control.

MicroRNA-130a regulates neurological deficit and angiogenesis in rats with ischaemic stroke by targeting XIAP

MicroRNAs (miRNAs) have already been proposed to be implicated in the development of ischaemic stroke. We aim to investigate the role of miR-130a in the neurological deficit and angiogenesis in rats with ischaemic stroke by regulating X-linked inhibitor of apoptosis protein (XIAP). Middle cerebral artery occlusion (MCAO) models were established by suture-occluded method, and MCAO rats were then treated with miR-130a mimics/inhibitors or/and altered XIAP for detection of changes of rats' neurological function, nerve damage and angiogenesis in MCAO rats. The oxygen-glucose deprivation (OGD) cellular models were established and respectively treated to determine the roles of miR-130a and XIAP in neuronal viability and apoptosis. The expression levels of miR-130a and XIAP in brain tissues of MCAO rats and OGD-treated neurons were detected. The binding site between miR-130a and XIAP was verified by luciferase activity assay. MiR-130a was overexpressed while XIAP was down-regulated in MCAO rats and OGD-treated neurons. In animal models, suppressed miR-130a improved neurological function, alleviated nerve damage and increased new vessels in brain tissues of rats with MCAO. In cellular models, miR-130a inhibition promoted neuronal viability and suppressed apoptosis. Inhibited XIAP reversed the effect of inhibited miR-130a in both MCAO rats and OGD-treated neurons. XIAP was identified as a target of miR-130a. Our study reveals that miR-130a regulates neurological deficit and angiogenesis in rats with MCAO by targeting XIAP.

Constraint-induced movement therapy improves functional recovery after ischemic stroke and its impacts on synaptic plasticity in sensorimotor cortex and hippocampus

Constraint-induced movement therapy (CIMT) has proven to be an effective way to restore functional deficits following stroke in human and animal studies, but its underlying neural plasticity mechanism remains unknown. Accumulating evidence indicates that rehabilitation after stroke is closely associated with synaptic plasticity. We therefore investigated the impact of CIMT on synaptic plasticity in ipsilateral and contralateral brain of rats following stroke. Rats were subjected to 90 minutes of transient middle cerebral artery occlusion (MCAO). CIMT was performed from 7 days after stroke and lasted for two weeks. Modified Neurology Severity Score (mNSS) and the ladder rung walking task tests were conducted at 7,14 and 21 days after stroke. Golgi-Cox staining was used to observe the plasticity changes of dendrites and dendritic spines. The expression of glutamate receptors (GluR1, GluR2 and NR1) were examined by western blot. Our data suggest that the dendrites and dendritic spines are damaged to varying degrees in bilateral sensorimotor cortex and hippocampus after acute stroke. CIMT treatment enhances the plasticity of dendrites and dendritic spines in the ipsilateral and contralateral sensorimotor cortex, increases the expression of synaptic GluR2 in ipsilateral sensorimotor cortex, which may be mechanisms for CIMT to improve functional recovery after ischemic stroke.

Direct myosin-2 inhibition enhances cerebral perfusion resulting in functional improvement after ischemic stroke

Acute ischemic stroke treatment faces an unresolved obstacle as capillary reperfusion remains insufficient after thrombolysis and thrombectomy causing neuronal damage and poor prognosis. Hypoxia-induced capillary constriction is mediated by actomyosin contraction in precapillary smooth muscle cells (SMCs) therefore smooth muscle myosin-2 could be an ideal target with potentially high impact on reperfusion of capillaries. Methods: The myosin-2 inhibitor para-aminoblebbistatin (AmBleb) was tested on isolated human and rat arterioles to assess the effect of AmBleb on vasodilatation. Transient middle cerebral artery occlusion (MCAO) was performed on 38 male Wistar rats followed by local administration of AmBleb into the ischemic brain area. Development of brain edema and changes in cerebrovascular blood flow were assessed using MRI and SPECT. We also tested the neurological deficit scores and locomotor asymmetry of the animals for 3 weeks after the MCAO operation. Results: Our results demonstrate that AmBleb could achieve full relaxation of isolated cerebral arterioles. In living animals AmBleb recovered cerebral blood flow in 32 out of the 65 affected functional brain areas in MCAO operated rats, whereas only 8 out of the 67 affected areas were recovered in the control animals. Animals treated with AmBleb also showed significantly improved general and focal deficit scores in neurological functional tests and showed significantly ameliorated locomotor asymmetry. Conclusion: Direct inhibition of smooth muscle myosin by AmBleb in pre-capillary SMCs significantly contribute to the improvement of cerebral blood reperfusion and brain functions suggesting that smooth muscle myosin inhibition may have promising potential in stroke therapies as a follow-up treatment of physical or chemical removal of the occluding thrombus.

Therapeutic exercise accompanied by neuronal modulation to enhance neurotrophic factors in the brain with central nervous system disorders

Exercise is a primary therapeutic regimen in physical therapy to rehabilitate the motor function of patients with central nervous system (CNS) disorders such as cerebrovascular accident (CVA). Furthermore, exercise positively contributes to cognitive function related to neuroplasticity and neuroprotection in the hippocampus. Neurotrophins play a crucial role in neuroplasticity, neurogenesis, and neuroprotection in the CNS. Exercise enhances the expression of neurotrophins in the brain. Thus, novel regimens for kinesiotherapy in CNS disorders to further enhance exercise-induced expression are expected. In this review, we described three novel regimens for kinesiotherapy in CNS disorders based on the interaction between exercise and pharmacological treatment with the idea of "inhibition of inhibition" in the CNS.

Retardation of Axonal and Dendritic Outgrowth Is Associated with the MAPK Signaling Pathway in Offspring Mice Following Maternal Exposure to Nanosized Titanium Dioxide

Exposure to nanosized titanium oxide (nano-TiO₂) has been proven to suppress brain growth in mouse offspring; however, whether retardation of axonal or dendritic outgrowth is associated with activation of the mitogen-activated protein kinase (MAPK) pathway remains unclear. In the present study, pregnant mice were exposed to nano-TiO₂ at 1.25, 2.5, and 5 mg/kg body weight, and the molecular mechanism of axonal or dendritic outgrowth retardation was investigated. The results suggested that nano-TiO₂ crossed the blood-fetal barrier and blood-brain barrier and deposited in the brain of offspring, which retarded axonal and dendritic outgrowth, including the absence of axonal outgrowth, and decreased dendritic filament length, dendritic branching number, and dendritic spine density. Importantly, maternal exposure to nano-TiO₂ increased phosphorylated (p)-extracellular signal-regulated kinase1/2 (ERK1/2, +24.35% to +59.4%), p-p38 (+60.82% to 181.85%), and p-c-jun N-terminal kinase (JNK, +28.28% to 97.28%) expression in the hippocampus of the offspring. These findings suggested that retardation of axonal and dendritic outgrowth in mouse offspring caused by maternal exposure to nano-TiO₂ may be related to excessive activation of the ERK1/2/MAPK signaling pathway. Therefore, the potential toxicity of nano-TiO₂ is a concern, especially in pregnant woman or children who are exposed to nano-TiO₂.

Improved functional outcome after chronic stroke with delayed anti-Nogo-A therapy: A clinically relevant intention-to-treat analysis

Many preclinical treatment strategies for stroke have failed when tested in human trials. Although the reasons for these translation failures are multifactorial, one potential concern is the statistical analysis of the preclinical data. One way to rigorously evaluate new therapies is to use an intention-to-treat analysis in preclinical studies. Therefore, in this study, we set out to evaluate the treatment efficacy of a potential clinically relevant therapeutic agent for stroke, i.e., anti-Nogo-A immunotherapy, using an intention-to-treat analysis. Adult rats were trained on the skilled forelimb reaching task and subsequently underwent an ischemic stroke. Nine weeks later, the rats either received intracerebroventricular anti-Nogo-A antibody, control antibody, or no treatment. Skilled reaching performance was assessed by a non-linear model using both an intention-to-treat and per-protocol analysis. Following testing, dendritic complexity was evaluated in the contralesional and perilesional sensorimotor cortex. Both intention-to-treat and per-protocol analysis showed that anti-Nogo-A immunotherapy resulted in statistically significant improved recovery on the skilled forelimb reaching task, although treatment effect was less (though statistically significant) in the intention-to-treat group. Improved functional performance was not shown to be associated with dendritic changes. In conclusion, this study provides evidence for the importance of using intention-to-treat paradigms in testing preclinical therapeutic strategies.

Is Environmental Enrichment Ready for Clinical Application in Human Post-stroke Rehabilitation?

Environmental enrichment (EE) has been widely used as a means to enhance brain plasticity mechanisms (e.g., increased dendritic branching, synaptogenesis, etc.) and improve behavioral function in both normal and brain-damaged animals. In spite of the demonstrated efficacy of EE for enhancing brain plasticity, it has largely remained a laboratory phenomenon with little translation to the clinical setting. Impediments to the implementation of enrichment as an intervention for human stroke rehabilitation and a lack of clinical translation can be attributed to a number of factors not limited to: (i) concerns that EE is actually the "normal state" for animals, whereas standard housing is a form of impoverishment; (ii) difficulty in standardizing EE conditions across clinical sites; (iii) the exact mechanisms underlying the beneficial actions of enrichment are largely correlative in nature; (iv) a lack of knowledge concerning what aspects of enrichment (e.g., exercise, socialization, cognitive stimulation) represent the critical or active ingredients for enhancing brain plasticity; and (v) the required "dose" of enrichment is unknown, since most laboratory studies employ continuous periods of enrichment, a condition that most clinicians view as impractical. In this review article, we summarize preclinical stroke recovery studies that have successfully utilized EE to promote functional recovery and highlight the potential underlying mechanisms. Subsequently, we discuss how EE is being applied in a clinical setting and address differences in preclinical and clinical EE work to date. It is argued that the best way forward is through the careful alignment of preclinical and clinical rehabilitation research. A combination of both approaches will allow research to fully address gaps in knowledge and facilitate the implementation of EE to the clinical setting.

The Extracellular Environment of the CNS: Influence on Plasticity, Sprouting, and Axonal Regeneration after Spinal Cord Injury

The extracellular environment of the central nervous system (CNS) becomes highly structured and organized as the nervous system matures. The extracellular space of the CNS along with its subdomains plays a crucial role in the function and stability of the CNS. In this review, we have focused on two components of the neuronal extracellular environment, which are important in regulating CNS plasticity including the extracellular matrix (ECM) and myelin. The ECM consists of chondroitin sulfate proteoglycans (CSPGs) and tenascins, which are organized into unique structures called perineuronal nets (PNNs). PNNs associate with the neuronal cell body and proximal dendrites of predominantly parvalbumin-positive interneurons, forming a robust lattice-like structure. These developmentally regulated structures are maintained in the adult CNS and enhance synaptic stability. After injury, however, CSPGs and tenascins contribute to the structure of the inhibitory glial scar, which actively prevents axonal regeneration. Myelin sheaths and mature adult oligodendrocytes, despite their important role in signal conduction in mature CNS axons, contribute to the inhibitory environment existing after injury. As such, unlike the peripheral nervous system, the CNS is unable to revert to a “developmental state” to aid neuronal repair. Modulation of these external factors, however, has been shown to promote growth, regeneration, and functional plasticity after injury. This review will highlight some of the factors that contribute to or prevent plasticity, sprouting, and axonal regeneration after spinal cord injury.

Motor Improvement of Skilled Forelimb Use Induced by Treatment with Growth Hormone and Rehabilitation Is Dependent on the Onset of the Treatment after Cortical Ablation

We previously demonstrated that the administration of GH immediately after severe motor cortex injury, in rats, followed by rehabilitation, improved the functionality of the affected limb and reexpressed nestin in the contralateral motor cortex. Here, we analyze whether these GH effects depend on a time window after the injury and on the reexpression of nestin and actin. Injured animals were treated with GH (0.15 mg/kg/day) or vehicle, at days 7, 14, and 35 after cortical ablation. Rehabilitation was applied at short and long term (LTR) after the lesion and then sacrificed. Nestin and actin were analyzed by immunoblotting in the contralateral motor cortex. Giving GH at days 7 or 35 after the lesion, but not 14 days after it, led to a remarkable improvement in the functionality of the affected paw. Contralateral nestin and actin reexpression was clearly higher in GH-treated animals, probably because compensatory brain plasticity was established. GH and immediate rehabilitation are key for repairing brain injuries, with the exception of a critical time period: GH treatment starting 14 days after the lesion. Our data also indicate that there is not a clear plateau in the recovery from a brain injury in agreement with our data in human patients.

Nogo-A interacts with TrkA to alter nerve growth factor signaling in Nogo-A-overexpressing PC12 cells

The Nogo-A protein, originally discovered as a potent myelin-associated inhibitor of neurite outgrowth, is also expressed by certain neurons, especially during development and after injury, but its role in neuronal function is not completely known. In this report, we overexpressed Nogo-A in PC12 cells to use as a model to identify potential neuronal signaling pathways affected by endogenously expressed Nogo-A. Unexpectedly, our results show that viability of Nogo-A-overexpressing cells was reduced progressively due to apoptotic cell death following NGF treatment, but only after 24 h. Inhibitors of neutral sphingomyelinase prevented this loss of viability, suggesting that NGF induced the activation of a ceramide-dependent cell death pathway. Nogo-A over-expression also changed NGF-induced phosphorylation of TrkA at tyrosines 490 and 674/675 from sustained to transient, and prevented the regulated intramembrane proteolysis of p75^NTR, indicating that Nogo-A was altering the function of the two neurotrophin receptors. Co-immunoprecipitation studies revealed that there was a physical association between TrkA and Nogo-A which appeared to be dependent on interactions in the Nogo-A-specific region of the protein. Taken together, our results indicate that Nogo-A influences NGF-mediated mechanisms involving the activation of TrkA and its interaction with p75^NTR.

NogoA Neutralization Promotes Axonal Restoration After White Matter Injury In Subcortical Stroke

Blocking axonal growth inhibitor NogoA has been of great interest for promoting axonal recovery from neurological diseases. The present study investigates the therapeutic effects of blocking NogoA, inducing functional recovery and promoting white matter repair in an experimental animal model of stroke. Adult male rats were subjected to white matter injury by subcortical ischemic stroke. Twenty-four hours after surgery, 250 ug of anti-NogoA or anti-IgG-1 were administered through the tail vein. The quantity of NogoA protein was determined by immunohistochemistry in the brain and peripheral organs. In addition, functional status, lesion size, fiber tract integrity, axonal sprouting and white matter repair markers were analyzed. Moreover, an in vitro study was performed in order to strengthen the results obtained in vivo. A lower quantity of NogoA protein was found in the brain and peripheral organs of the animals that received anti-NogoA treatment. The animals receiving anti-NogoA treatment showed significantly better results in terms of functional recovery, fiber tract integrity, axonal sprouting and white matter repair markers compared with the control group at 28 days. White matter integrity was in part restored by antibody-mediated inhibition of NogoA administration in those animals that were subjected to an axonal injury by subcortical stroke. This white matter restoration triggered functional recovery.

Neural Stem Cell Transplantation Induces Stroke Recovery by Upregulating Glutamate Transporter GLT-1 in Astrocytes

Ischemic stroke is the leading cause of disability, but effective therapies are currently widely lacking. Recovery from stroke is very much dependent on the possibility to develop treatments able to both halt the neurodegenerative process as well as to foster adaptive tissue plasticity. Here we show that ischemic mice treated with neural precursor cell (NPC) transplantation had on neurophysiological analysis, early after treatment, reduced presynaptic release of glutamate within the ipsilesional corticospinal tract (CST), and an enhanced NMDA-mediated excitatory transmission in the contralesional CST. Concurrently, NPC-treated mice displayed a reduced CST degeneration, increased axonal rewiring, and augmented dendritic arborization, resulting in long-term functional amelioration persisting up to 60 d after ischemia. The enhanced functional and structural plasticity relied on the capacity of transplanted NPCs to localize in the peri-ischemic and ischemic area, to promote the upregulation of the glial glutamate transporter 1 (GLT-1) on astrocytes and to reduce peri-ischemic extracellular glutamate. The upregulation of GLT-1 induced by transplanted NPCs was found to rely on the secretion of VEGF by NPCs. Blocking VEGF during the first week after stroke reduced GLT-1 upregulation as well as long-term behavioral recovery in NPC-treated mice. Our results show that NPC transplantation, by modulating the excitatory-inhibitory balance and stroke microenvironment, is a promising therapy to ameliorate disability, to promote tissue recovery and plasticity processes after stroke.

SIGNIFICANCE STATEMENT

Tissue damage and loss of function occurring after stroke can be constrained by fostering plasticity processes of the brain. Over the past years, stem cell transplantation for repair of the CNS has received increasing interest, although underlying mechanism remain elusive. We here show that neural stem/precursor cell transplantation after ischemic stroke is able to foster axonal rewiring and dendritic plasticity and to induce long-term functional recovery. The observed therapeutic effect of neural precursor cells seems to underlie their capacity to upregulate the glial glutamate transporter on astrocytes through the vascular endothelial growth factor inducing favorable changes in the electrical and molecular stroke microenvironment. Cell-based approaches able to influence plasticity seem particularly suited to favor poststroke recovery.

Neuroplastic Changes Following Brain Ischemia and their Contribution to Stroke Recovery: Novel Approaches in Neurorehabilitation

Ischemic damage to the brain triggers substantial reorganization of spared areas and pathways, which is associated with limited, spontaneous restoration of function. A better understanding of this plastic remodeling is crucial to develop more effective strategies for stroke rehabilitation. In this review article, we discuss advances in the comprehension of post-stroke network reorganization in patients and animal models. We first focus on rodent studies that have shed light on the mechanisms underlying neuronal remodeling in the perilesional area and contralesional hemisphere after motor cortex infarcts. Analysis of electrophysiological data has demonstrated brain-wide alterations in functional connectivity in both hemispheres, well beyond the infarcted area. We then illustrate the potential use of non-invasive brain stimulation (NIBS) techniques to boost recovery. We finally discuss rehabilitative protocols based on robotic devices as a tool to promote endogenous plasticity and functional restoration.

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

OBJECTIVE

Using a new microelectrode array implanted into the cranial window employing a new stimulation protocol, we investigated the effects of the implanted electrode arrays on both motor map plasticity and neural regeneration in a rodent model of stroke.

MATERIALS AND METHODS

Rats were pretrained on single-pellet retrieval task, then received focal ischemic infarction and microelectrode arrays implantation. Rats in the cortical stimulation (CS) group received daily electrical stimulation (1 hour each day) for 14 days whereas animals in the no stimulation (NS) group did not receive electrical stimulation and only underwent motor mapping. Behavior data and residual electrophysiological mapping on stimulation days 2, 5, 8, 11, and 14 were statistically compared. Neural reorganization in pathological with glial fibrillary acidic protein and microtubule-associated protein-2 was performed.

RESULTS

Rats in CS group showed greater increases in reaching accuracy and significantly decreased in motor threshold than rats in NS group. Immunohistochemical study has shown that array focal CS suppressed inflammatory response, and enhanced dendritic sprouting in the peri-infarction cortex.

CONCLUSION

The present findings support the viability of epidural CS with microelectrode arrays for enhancing motor function after stroke and monitoring the neural reorganization of residual electrophysiological mapping after motor cortex injury.

Neurodegeneration and Glial Response after Acute Striatal Stroke: Histological Basis for Neuroprotective Studies

Stroke is a leading cause of death and neurological disability worldwide and striatal ischemic stroke is frequent in humans due to obstruction of middle cerebral artery. Several pathological events underlie damage progression and a comprehensive description of the pathological features following experimental stroke in both acute and chronic survival times is a necessary step for further functional studies. Here, we explored the patterns of microglial activation, astrocytosis, oligodendrocyte damage, myelin impairment, and Nogo-A immunoreactivity between 3 and 30 postlesion days (PLDs) after experimental striatal stroke in adult rats induced by microinjections of endothelin-1 (ET-1). The focal ischemia induced tissue loss concomitant with intense microglia activation between 3 and 14 PLDs (maximum at 7 PLDs), decreasing afterward. Astrocytosis was maximum around 7 PLDs. Oligodendrocyte damage and Nogo-A upregulation were higher at 3 PLDs. Myelin impairment was maximum between 7 and 14 PLDs. Nogo-A expression was higher in the first week in comparison to control. The results add important histopathological features of ET-1 induced stroke in subacute and chronic survival times. In addition, the establishment of the temporal evolution of these neuropathological events is an important step for future studies seeking suitable neuroprotective drugs targeting neuroinflammation and white matter damage.

Anti-Nogo-A Immunotherapy Does Not Alter Hippocampal Neurogenesis after Stroke in Adult Rats

Ischemic stroke is a leading cause of adult disability, including cognitive impairment. Our laboratory has previously shown that treatment with function-blocking antibodies against the neurite growth inhibitory protein Nogo-A promotes functional recovery after stroke in adult and aged rats, including enhancing spatial memory performance, for which the hippocampus is critically important. Since spatial memory has been linked to hippocampal neurogenesis, we investigated whether anti-Nogo-A treatment increases hippocampal neurogenesis after stroke. Adult rats were subject to permanent middle cerebral artery occlusion followed 1 week later by 2 weeks of antibody treatment. Cellular proliferation in the dentate gyrus was quantified at the end of treatment, and the number of newborn neurons was determined at 8 weeks post-stroke. Treatment with both anti-Nogo-A and control antibodies stimulated the accumulation of new microglia/macrophages in the dentate granule cell layer, but neither treatment increased cellular proliferation or the number of newborn neurons above stroke-only levels. These results suggest that anti-Nogo-A immunotherapy does not increase post-stroke hippocampal neurogenesis.

Critical role of astrocytic interleukin-17 A in post-stroke survival and neuronal differentiation of neural precursor cells in adult mice

The brain and the immune system interact in complex ways after ischemic stroke, and the long-term effects of immune response associated with stroke remain controversial. As a linkage between innate and adaptive immunity, interleukin-17 A (IL-17 A) secreted from gamma delta (γδ) T cells has detrimental roles in the pathogenesis of acute ischemic stroke. However, to date, the long-term actions of IL-17 A after stroke have not been investigated. Here, we found that IL-17 A showed two distinct peaks of expression in the ischemic hemisphere: the first occurring within 3 days and the second on day 28 after stroke. Our data also showed that astrocyte was the major cellular source of IL-17 A that maintained and augmented subventricular zone (SVZ) neural precursor cells (NPCs) survival, neuronal differentiation, and subsequent synaptogenesis and functional recovery after stroke. IL-17 A also promoted neuronal differentiation in cultured NPCs from the ischemic SVZ. Furthermore, our in vitro data revealed that in primary astrocyte cultures activated astrocytes released IL-17 A via p38 mitogen-activated protein kinase (MAPK). Culture media from reactive astrocytes increased neuronal differentiation of NSCs in vitro. Blockade of IL-17 A with neutralizing antibody prevented this effect. In addition, after screening for multiple signaling pathways, we revealed that the p38 MAPK/calpain 1 signaling pathway was involved in IL-17 A-mediated neurogenesis in vivo and in vitro. Thus, our results reveal a previously uncharacterized property of astrocytic IL-17 A in the maintenance and augment of survival and neuronal differentiation of NPCs, and subsequent synaptogenesis and spontaneous recovery after ischemic stroke.

NgR1: A Tunable Sensor Regulating Memory Formation, Synaptic, and Dendritic Plasticity

Nogo receptor 1 (NgR1) is expressed in forebrain neurons and mediates nerve growth inhibition in response to Nogo and other ligands. Neuronal activity downregulates NgR1 and the inability to downregulate NgR1 impairs long-term memory. We investigated behavior in a serial behavioral paradigm in mice that overexpress or lack NgR1, finding impaired locomotor behavior and recognition memory in mice lacking NgR1 and impaired sequential spatial learning in NgR1 overexpressing mice. We also investigated a role for NgR1 in drug-mediated sensitization and found that repeated cocaine exposure caused stronger locomotor responses but limited development of stereotypies in NgR1 overexpressing mice. This suggests that NgR1-regulated synaptic plasticity is needed to develop stereotypies. Ex vivo magnetic resonance imaging and diffusion tensor imaging analyses of NgR1 overexpressing brains did not reveal any major alterations. NgR1 overexpression resulted in significantly reduced density of mature spines and dendritic complexity. NgR1 overexpression also altered cocaine-induced effects on spine plasticity. Our results show that NgR1 is a negative regulator of both structural synaptic plasticity and dendritic complexity in a brain region-specific manner, and highlight anterior cingulate cortex as a key area for memory-related plasticity.

Promoting recovery from ischemic stroke

Over recent decades, experimental and clinical stroke studies have identified a number of neurorestorative treatments that stimulate neural plasticity and promote functional recovery. In contrast to the acute stroke treatments thrombolysis and endovascular thrombectomy, neurorestorative treatments are still effective when initiated days after stroke onset, which makes them applicable to virtually all stroke patients. In this article, selected physical, pharmacological and cell-based neurorestorative therapies are discussed, with special emphasis on interventions that have already been transferred from the laboratory to the clinical setting. We explain molecular and structural processes that promote neural plasticity, discuss potential limitations of neurorestorative treatments, and offer a speculative viewpoint on how neurorestorative treatments will evolve.

Functional Improvement after Photothrombotic Stroke in Rats Is Associated with Different Patterns of Dendritic Plasticity after G-CSF Treatment and G-CSF Treatment Combined with Concomitant or Sequential Constraint-Induced Movement Therapy

We have previously shown that granulocyte-colony stimulating factor (G-CSF) treatment alone, or in combination with constraint movement therapy (CIMT) either sequentially or concomitantly, results in significantly improved sensorimotor recovery after photothrombotic stroke in rats in comparison to untreated control animals. CIMT alone did not result in any significant differences compared to the control group (Diederich et al., Stroke, 2012;43:185-192). Using a subset of rat brains from this former experiment the present study was designed to evaluate whether dendritic plasticity would parallel improved functional outcomes. Five treatment groups were analyzed (n = 6 each) (i) ischemic control (saline); (ii) CIMT (CIMT between post-stroke days 2 and 11); (iii) G-CSF (10 μg/kg G-CSF daily between post-stroke days 2 and 11); (iv) combined concurrent group (CIMT plus G-CSF) and (v) combined sequential group (CIMT between post-stroke days 2 and 11; 10 μg/kg G-CSF daily between post-stroke days 12 and 21, respectively). After impregnation of rat brains with a modified Golgi-Cox protocol layer V pyramidal neurons in the peri-infarct cortex as well as the corresponding contralateral cortex were analyzed. Surprisingly, animals with a similar degree of behavioral recovery exhibited quite different patterns of dendritic plasticity in both peri-lesional and contralesional areas. The cause for these patterns is not easily to explain but puts the simple assumption that increased dendritic complexity after stroke necessarily results in increased functional outcome into perspective.

Running exercise enhances motor functional recovery with inhibition of dendritic regression in the motor cortex after collagenase-induced intracerebral hemorrhage in rats

Rehabilitative approaches benefit motor functional recovery after stroke and relate to neuronal plasticity. We investigated the effects of a treadmill running exercise on the motor functional recovery and neuronal plasticity after collagenase-induced striatal intracerebral hemorrhage (ICH) in rats. Male Wistar rats were injected with type IV collagenase into the left striatum to induce ICH. Sham-operated animals were injected with saline instead of collagenase. The animals were randomly assigned to the sham control (SC), the sham exercise (SE), the ICH control (IC), or the ICH exercise (IE) group. The exercise groups were forced to run on a treadmill at a speed of 9 m/min for 30 min/day between days 4 and 14 after surgery. Behavioral tests were performed using a motor deficit score, a beam-walking test and a cylinder test. At fifteen days after surgery, the animals were sacrificed, and their brains were removed. The motor function of the IE group significantly improved compared with the motor function of the IC group. No significant differences in cortical thickness were found between the groups. The IC group had fewer branches and shorter dendrite lengths compared with the sham groups. However, dendritic branches and lengths were not significantly different between the IE and the other groups. Tropomyosin-related kinase B (TrkB) expression levels increased in the IE compared with IC group, but no significant differences in other protein (brain-derived neurotrophic factor, BDNF; Nogo-A; Rho-A/Rho-associated protein kinase 2, ROCK2) expression levels were found between the groups. These results suggest that improved motor function after a treadmill running exercise after ICH may be related to the prevention of dendritic regression due to TrkB upregulation.

Motor System Reorganization After Stroke: Stimulating and Training Toward Perfection

Stroke instigates regenerative responses that reorganize connectivity patterns among surviving neurons. The new connectivity patterns can be suboptimal for behavioral function. This review summarizes current knowledge on post-stroke motor system reorganization and emerging strategies for shaping it with manipulations of behavior and cortical activity to improve functional outcome.

Baclofen facilitates sleep, neuroplasticity, and recovery after stroke in rats

OBJECTIVE

Sleep disruption in the acute phase after stroke has detrimental effects on recovery in both humans and animals. Conversely, the effect of sleep promotion remains unclear. Baclofen (Bac) is a known non-rapid eye movement (NREM) sleep-promoting drug in both humans and animals. The aim of this study was to investigate the effect of Bac on stroke recovery in a rat model of focal cerebral ischemia (isch).

METHODS

Rats, assigned to three experimental groups (Bac/isch, saline/isch, or Bac/sham), were injected twice daily for 10 consecutive days with Bac or saline, starting 24 h after induction of stroke. The sleep-wake cycle was assessed by EEG recordings and functional motor recovery by single pellet reaching test (SPR). In order to identify potential neuroplasticity mechanisms, axonal sprouting and neurogenesis were evaluated. Brain damage was assessed by Nissl staining.

RESULTS

Repeated Bac treatment after ischemia affected sleep, motor function, and neuroplasticity, but not the size of brain damage. NREM sleep amount was increased significantly during the dark phase in Bac/isch compared to the saline/isch group. SPR performance dropped to 0 immediately after stroke and was recovered slowly thereafter in both ischemic groups. However, Bac-treated ischemic rats performed significantly better than saline-treated animals. Axonal sprouting in the ipsilesional motor cortex and striatum, and neurogenesis in the peri-infarct region were significantly increased in Bac/isch group.

CONCLUSION

Delayed repeated Bac treatment after stroke increased NREM sleep and promoted both neuroplasticity and functional outcome. These data support the hypothesis of the role of sleep as a modulator of poststroke recovery.

Maintaining stable memory engrams: new roles for Nogo-A in the CNS

Nogo-A interaction with its different receptors (Nogo receptor 1 (NgR1), S1P receptor 2 (S1PR2), paired immunoglobulin-like receptor B (PirB)) restricts plasticity and growth-dependent processes leading, via the activation of different signaling pathway to the stabilization of the neuronal networks (either developmentally or during processes of memory consolation in the mature nervous system). Taking away these molecular brakes might allow for the induction of extensive structural and functional rearrangements and might promote compensatory growth processes after an injury of the CNS, in cortical structures as well as in the spinal cord. However, it is important to keep in mind that this could as well be a dangerous endeavor, since it might facilitate unwanted and unnecessary (and probably even maladaptive) neuronal connections.

Harnessing the power of neuroplasticity for intervention

A fundamental property of the brain is its capacity to change with a wide variety of experiences, including injury. Although there are spontaneous reparative changes following injury, these changes are rarely sufficient to support significant functional recovery. Research on the basic principles of brain plasticity is leading to new approaches to treating the injured brain. We review factors that affect synaptic organization in the normal brain, evidence of spontaneous neuroplasticity after injury, and the evidence that factors including postinjury experience, pharmacotherapy, and cell-based therapies, can form the basis of rehabilitation strategies after brain injuries early in life and in adulthood.

Finding an optimal rehabilitation paradigm after stroke: enhancing fiber growth and training of the brain at the right moment

After stroke the central nervous system reveals a spectrum of intrinsic capacities to react as a highly dynamic system which can change the properties of its circuits, form new contacts, erase others, and remap related cortical and spinal cord regions. This plasticity can lead to a surprising degree of spontaneous recovery. It includes the activation of neuronal molecular mechanisms of growth and of extrinsic growth promoting factors and guidance signals in the tissue. Rehabilitative training and pharmacological interventions may modify and boost these neuronal processes, but almost nothing is known on the optimal timing of the different processes and therapeutic interventions and on their detailed interactions. Finding optimal rehabilitation paradigms requires an optimal orchestration of the internal processes of re-organization and the therapeutic interventions in accordance with defined plastic time windows. In this review we summarize the mechanisms of spontaneous plasticity after stroke and experimental interventions to enhance growth and plasticity, with an emphasis on anti-Nogo-A immunotherapy. We highlight critical time windows of growth and of rehabilitative training and consider different approaches of combinatorial rehabilitative schedules. Finally, we discuss potential future strategies for designing repair and rehabilitation paradigms by introducing a “3 step model”: determination of the metabolic and plastic status of the brain, pharmacological enhancement of its plastic mechanisms, and stabilization of newly formed functional connections by rehabilitative training.

Searching for the principles of brain plasticity and behavior

An important development in behavioral neuroscience in the past 25 years has been the demonstration that the brain is far more flexible in structure and function than was previously believed. Studies of laboratory animals have provided an important tool for understanding the nature of brain plasticity and behavior at many levels ranging from detailed behavioral paradigms, electrophysiology, neuronal morphology, protein chemistry, and epigenetics. Here we seek a synthesis of the multidisciplinary work on brain plasticity and behavior to identify some general principles on how the brain changes in response to a wide range of experiences over the lifetime.

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

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

Therapeutic antibodies in stroke

Immunotherapy represents an active area of biomedical research to treat cancer, autoimmune diseases, and neurodegenerative disorders. In stroke, recanalization therapy is effective in reducing brain tissue damage after acute ischemic stroke. However, the narrow time window restricts its application for the majority of stroke patients. There is an urgent need to develop adjuvant therapies such as immunotherapy, stem cell replacement, and neuroprotective drugs. A number of molecules have been targeted for immunotherapy in stroke management, including myelin-associated proteins and their receptors, N-methyl-d-aspartic acid receptors, cytokines, and cell adhesion molecules. Both active vaccination and passive antibodies were tested in animal models of acute ischemic stroke. However, the mechanisms underlying the efficacy of immunotherapy are different for each target protein. Blocking myelin-associated proteins may enhance neuroplasticity, whereas blocking adhesion molecules may yield neuroprotection by suppressing the immune response after stroke. Although results from animal studies are encouraging, clinical trials using therapeutic antibodies failed to improve stroke outcome due to severe side effects. It remains a challenge to generate specific therapeutic antibodies with minimal side effects on other organs and systems.

Chondroitinase enhances cortical map plasticity and increases functionally active sprouting axons after brain injury

The beneficial effect of interventions with chondroitinase ABC enzyme to reduce axon growth-inhibitory chondroitin sulphate side chains after central nervous system injuries has been mainly attributed to enhanced axonal sprouting. After traumatic brain injury (TBI), it is unknown whether newly sprouting axons that occur as a result of interventional strategies are able to functionally contribute to existing circuitry, and it is uncertain whether maladaptive sprouting occurs to increase the well-known risk for seizure activity after TBI. Here, we show that after a controlled cortical impact injury in rats, chondroitinase infusion into injured cortex at 30 min and 3 days reduced c-Fos⁺ cell staining resulting from the injury alone at 1 week postinjury, indicating that at baseline, abnormal spontaneous activity is likely to be reduced, not increased, with this type of intervention. c-Fos⁺ cell staining elicited by neural activity from stimulation of the affected forelimb 1 week after injury was significantly enhanced by chondroitinase, indicating a widespread effect on cortical map plasticity. Underlying this map plasticity was a larger contribution of neuronal, rather than glial cells and an absence of c-Fos⁺ cells surrounded by perineuronal nets that were normally present in stimulated naïve rats. After injury, chondroitin sulfate proteoglycan digestion produced the expected increase in growth-associated protein 43-positive axons and perikarya, of which a significantly greater number were double labeled for c-Fos after intervention with chondroitinase, compared to vehicle. These data indicate that chondroitinase produces significant gains in cortical map plasticity after TBI, and that either axonal sprouting and/or changes in perineuronal nets may underlie this effect. Chondroitinase dampens, rather than increases nonspecific c-Fos activity after brain injury, and induction of axonal sprouting is not maladaptive because greater numbers are functionally active and provide a significant contribution to forelimb circuitry after brain injury.

Management of patients with stroke: is it time to expand treatment options?

Approximately 700,000 people in the United States have an ischemic stroke annually. Substantial research has tested therapies for the very early treatment of ischemic stroke but, to date, only intravenous thrombolysis and intra-arterial measures to restore perfusion have shown success. Despite a 15-year effort to increase the use of these therapies, only approximately 5% of patients with stroke are currently being treated. Although most patients with stroke have some neurological recovery, more than half of stroke survivors have residual impairments that lead to disability or long-term institutionalized care. Laboratory research has demonstrated several mechanisms that help the brain to recover after a stroke. New pharmacological and cell-based approaches that are known to promote brain plasticity are emerging from laboratory studies and may soon expand the window for stroke treatment to restore function. It is time to build on this knowledge and to translate the understanding of recovery after stroke into the clinical setting. Measures that might augment recovery should become a major focus of clinical research in stroke in the 21st century.

Alpha tocopherol treatment reduces the expression of Nogo-A and NgR in rat brain after traumatic brain injury

BACKGROUND

Neurite outgrowth inhibitor-A (Nogo-A), myelin-associated glycoprotein, and oligodendrocyte myelin glycoprotein are three myelin-associated proteins that act as inhibitors to central nervous system regeneration. Neurite outgrowth inhibitor-A imposes the strongest effect on inhibiting axonal regeneration after traumatic brain injury. Alpha-tocopherol, a member of the vitamin E family, is recognized as an active antioxidative substance. Its use has not been well studied in brain injury research, especially in axonal regeneration research.

METHODS

We obtained 99 intact adult male Sprague-Dawley rats (200-250 g) from the Experimental Animal Center of Central South University. We used the modified method of Freeney to generate moderate brain injury in the rats. We injected 600 mg/kg α-tocopherol intraperitoneally daily as traumatic brain injury (TBI) treatment. Then, we performed behavioral tests in the corresponding time point, examined brain tissues after hematoxylin-eosin staining to identify changes in cell morphology, and performed immunohistochemical staining and quantitative real-time polymerase chain reaction to detect the expression of NoGo and Nogo receptor (NgR) in brain tissue.

RESULTS

For the Neurological Severity Scores of rats, there were obvious differences among the three groups at the corresponding time points. Standard hematoxylin-eosin staining showed that the brain structure of a sham-operated group of rats was clear, uniform, and compact. A TBI group exhibited hemorrhage, edema, inflammatory cell infiltration, condensed nuclei, and necrosis. We also saw glial cells and fibrous tissue proliferation. The α-tocopherol-treated TBI group had similar but less severe changes than the TBI group. Expression of Nogo-A and NgR increased after TBI compared with the sham-operated group. However, Nogo-A and NgR expression was significantly lower in the α-tocopherol-treated TBI group compared with the TBI group. Similarly, results showed that functional neurological deficits among rats in the α-tocopherol-treated TBI group were less pronounced than in the TBI group (model group).

CONCLUSIONS

Our data demonstrate that α-tocopherol-treated rats had reduced microscopic evidence of brain damage. Alpha-tocopherol reduced Nogo-A and NgR expression in brain tissue after traumatic brain injury and promoted nerve regeneration. Alpha-tocopherol treatment of TBI rats had a neuroprotective role in their recovery.

Indomethacin protects rats from neuronal damage induced by traumatic brain injury and suppresses hippocampal IL-1β release through the inhibition of Nogo-A expression

BACKGROUND

Nogo-A is a member of the reticulon family of membrane-associated proteins and plays an important role in axonal remodeling. The present study aimed to investigate alterations in Nogo-A expression following traumatic brain injury (TBI)-induced inflammation and neuronal damage.

METHODS

A weight-drop device was used to deliver a standard traumatic impact to rats. Western blot, RT-PCR and ELISA were used to analyze the expression of Nogo-A and IL-1β. Nogo-A antisense, and an irrelevant control oligonucleotide was intracerebroventricularly infused. We also performed H & E staining and luxol fast blue staining to evaluate the neuronal damage and demyelination resulting from TBI and various treatments.

RESULTS

Based on RT-PCR and western blot analyses, the expression of Nogo-A was found to be significantly upregulated in the hippocampus beginning eight hours after TBI. In addition, TBI caused an apparent elevation in IL-1β levels and severe neuronal damage and demyelination in the tested animals. All of the TBI-associated molecular and cellular consequences could be effectively reversed by treating the animals with the anti-inflammatory drug indomethacin. More importantly, the TBI-associated stimulation in the levels of both Nogo-A and IL-1β could be effectively inhibited by a specific Nogo-A antisense oligonucleotide.

CONCLUSIONS

Our findings suggest that the suppression of Nogo-A expression appears to be an early response conferred by indomethacin, which then leads to decreases in the levels of IL-1β and TBI-induced neuron damage.

Niaspan increases axonal remodeling after stroke in type 1 diabetes rats

BACKGROUND AND OBJECTIVE

We investigated axonal plasticity in the bilateral motor cortices and the long term therapeutic effect of Niaspan on axonal remodeling after stroke in type-1 diabetic (T1DM) rats.

EXPERIMENTAL APPROACHES

T1DM was induced in young adult male Wistar rats via injection of streptozotocin. T1DM rats were subjected to 2h transient middle cerebral artery occlusion (MCAo) and were treated with 40 mg/kg Niaspan or saline starting 24 h after MCAo and daily for 28 days. Anterograde tracing using biotinylated dextran amine (BDA) injected into the contralateral motor cortex was performed to assess axonal sprouting in the ipsilateral motor cortex area. Functional outcome, SMI-31 (a pan-axonal microfilament marker), Bielschowsky silver and synaptophysin expression were measured. In vitro studies using primary cortical neuron (PCN) cultures and in vivo BDA injection into the brain to anterogradely label axons and terminals were employed.

RESULTS

Niaspan treatment of stroke in T1DM-MCAo rats significantly improved functional outcome after stroke and increased SMI-31, Bielschowsky silver and synaptophysin expression in the ischemic brain compared to saline treated T1DM-MCAo rats (p<0.05). Using BDA to anterograde label axons and terminals, Niaspan treatment significantly increased axonal density in ipsilateral motor cortex in T1DM-MCAo rats (p<0.05, n=7/group). Niacin treatment of PCN significantly increased Ang1 expression under high glucose condition. Niacin and Ang1 significantly increased neurite outgrowth, and anti-Ang1 antibody marginally attenuated Niacin induced neurite outgrowth (p=0.06, n=6/group) in cultured PCN under high glucose condition.

CONCLUSION

Niaspan treatment increased ischemic brain Ang1 expression and promoted axonal remodeling in the ischemic brain as well as improved functional outcome after stroke. Ang1 may partially contribute to Niaspan-induced axonal remodeling after stroke in T1DM-rats.