Cognitive deficits induced by global cerebral ischaemia: relationship to brain damage and reversal by transplants

Dexmedetomidine Inhibits Hippocampal Neuronal Damage Caused by Persistent Isoflurane-Induced Hypotension in Rat Model of Chronic Cerebral Hypoperfusion

Purpose The purpose of this study was to investigate the effect of dexmedetomidine (DEX) on hypotension-induced neuronal damage in a chronic cerebral hypoperfusion (CCH) model of rats, an established model of cerebral white matter lesions (WML) in humans, which is prevalent in the elderly and closely related to cognitive decline. Methods The CCH model rats were randomly assigned to one of four groups: normotension + no DEX (NN) group (n = 6), normotension + DEX (ND) group (n = 6), hypotension + no DEX (HN) group (n = 6), or hypotension + DEX (HD) group (n = 6). Under isoflurane anesthesia, mean arterial blood pressure was maintained at or above 80 mmHg (normotension) or below 60 mmHg (hypotension) for a duration of two hours. The DEX groups received 50 μg of DEX intraperitoneally. Two weeks later, the Y-maze test and, after preparing brain slices, immunohistochemical staining were performed using antibodies against neuronal nuclei (NeuN), microtubule-associated protein 2 (MAP2), glial fibrillary acidic protein (GFAP), and Ionized calcium-binding adapter molecule 1 (Iba1). Results Behavioral observations showed no significant differences among the groups. Significant reductions of both NeuN-positive cells and the MAP2-positive area were found in the hippocampal CA1 in the HN group compared with NN and ND groups, but not in the HD group. GFAP and Iba-1-positive areas were significantly increased in the HN group, but not in the HD group. Conclusion DEX significantly ameliorated hypotension-induced neuronal damage and both astroglial and microglial activation in the CA1 region of CCH rats.

Deep grey matter injury in multiple sclerosis: a NAIMS consensus statement

Although multiple sclerosis has traditionally been considered a white matter disease, extensive research documents the presence and importance of grey matter injury including cortical and deep regions. The deep grey matter exhibits a broad range of pathology and is uniquely suited to study the mechanisms and clinical relevance of tissue injury in multiple sclerosis using magnetic resonance techniques. Deep grey matter injury has been associated with clinical and cognitive disability. Recently, MRI characterization of deep grey matter properties, such as thalamic volume, have been tested as potential clinical trial end points associated with neurodegenerative aspects of multiple sclerosis. Given this emerging area of interest and its potential clinical trial relevance, the North American Imaging in Multiple Sclerosis (NAIMS) Cooperative held a workshop and reached consensus on imaging topics related to deep grey matter. Herein, we review current knowledge regarding deep grey matter injury in multiple sclerosis from an imaging perspective, including insights from histopathology, image acquisition and post-processing for deep grey matter. We discuss the clinical relevance of deep grey matter injury and specific regions of interest within the deep grey matter. We highlight unanswered questions and propose future directions, with the aim of focusing research priorities towards better methods, analysis, and interpretation of results.

Human placental mesenchymal stem cells improve stroke outcomes via extracellular vesicles-mediated preservation of cerebral blood flow

Background

Besides long-term trans-differentiation into neural cells, benefits of stem cell therapy (SCT) in ischemic stroke may include secretion of protective factors, which partly reflects extracellular vesicle (EVs) released by stem cell. However, the mechanism(s) by which stem cells/EVs limit stroke injury have yet to be fully defined.

Methods

We evaluated the protection effect of human placenta mesenchymal stem cells (hPMSC) as a potential form of SCT in experimental ischemic stroke ‘transient middle cerebral artery occusion (MCAO)/reperfusion’ mice model.

Findings

We found for the first time that intraperitoneal administration of hPMSCs or intravenous hPMSC-derived EVs, given at the time of reperfusion, significantly protected the ipsilateral hemisphere from ischemic injury. This protection was associated with significant restoration of normal blood flow to the post-MCAO brain. More importantly, EVs derived from hPMSC promote paracrine-based protection of SCT in the MCAO model in a cholesterol/lipid-dependent manner.

Interpretation

Together, our results demonstrated beneficial effects of hPMSC/EVs in experimental stroke models which could permit the rapid “translation” of these cells into clinical trials in the near-term.

Altered Neural Networks in the Papez Circuit: Implications for Cognitive Dysfunction after Cerebral Ischemia

Cerebral ischemia remains a leading cause of mortality worldwide. Although the incidence of death has decreased over the years, surviving patients may suffer from long-term cognitive impairments and have an increased risk for dementia. Unfortunately, research aimed toward developing therapies that can improve cognitive outcomes following cerebral ischemia has proved difficult given the fact that little is known about the underlying processes involved. Nevertheless, mechanisms that disrupt neural network activity may provide valuable insight, since disturbances in both local and global networks in the brain have been associated with deficits in cognition. In this review, we suggest that abnormal neural dynamics within different brain networks may arise from disruptions in synaptic plasticity processes and circuitry after ischemia. This discussion primarily concerns disruptions in local network activity within the hippocampus and other extra-hippocampal components of the Papez circuit, given their role in memory processing. However, impaired synaptic plasticity processes and disruptions in structural and functional connections within the Papez circuit have important implications for alterations within the global network, as well. Although much work is required to establish this relationship, evidence thus far suggests there is a link. If pursued further, findings may lead toward a better understanding of how deficits in cognition arise, not only in cerebral ischemia, but in other neurological diseases as well.

Grafted Neural Progenitor Cells Persist in the Injured Site and Differentiate Neuronally in a Rodent Model of Cardiac Arrest-Induced Global Brain Ischemia

Hypoxic-ischemic brain injury is the leading cause of disability and death after successful resuscitation from cardiac arrest, and, to date, no specific treatment option is available to prevent subsequent neurofunctional impairments. The hippocampal cornu ammonis segment 1 (CA1) is one of the brain areas most affected by hypoxia, and its degeneration is correlated with memory deficits in patients and corresponding animal models. The aim of this work was to evaluate the feasibility of neural progenitor cell (NPC) transplantation into the hippocampus in a refined rodent cardiac arrest model. Adult rats were subjected to 12 min of potassium-induced cardiac arrest and followed up to 6 weeks. Histological analysis showed extensive neuronal cell death specifically in the hippocampal CA1 segment, without any spontaneous regeneration. Neurofunctional assessment revealed transient memory deficits in ischemic animals compared to controls, detectable after 4 weeks, but not after 6 weeks. Using stereotactic surgery, embryonic NPCs were transplanted in a subset of animals 1 week after cardiac arrest and their survival, migration, and differentiation were assessed histologically. Transplanted cells showed a higher persistence in the CA1 segment of animals after ischemia. Glia in the damaged CA1 segment expressed the chemotactic factor stromal cell-derived factor 1 (SDF-1), while transplanted NPCs expressed its receptor CXC chemokine receptor 4 (CXCR4), suggesting that the SDF-1/CXCR4 pathway, known to be involved in the migration of neural stem cells toward injured brain regions, directs the observed retention of cells in the damaged area. Using immunostaining, we could demonstrate that transplanted cells differentiated into mature neurons. In conclusion, our data document the survival, persistence in the injured area, and neuronal differentiation of transplanted NPCs, and thus their potential to support brain regeneration after hypoxic-ischemic injury. This may represent an option worth further investigation to improve the outcome of patients after cardiac arrest.

Neuroinflammatory response to experimental stroke is inhibited by boldine

Inflammation plays a pivotal role in the development of ischemic brain damage. Astrocyte activation promotes the production of several proinflammatory mediators, such as TNF-α and iNOS. Eventually, neuronal death occurs, leading to the development of motor and memory deficits in patients. Boldine is the main alkaloid in the leaves and bark of the Peumus boldus Molina, and has anti-inflammatory and antioxidant properties. The aim of this work was to investigate the neuroprotective effect of boldine on neuroinflammation and memory deficits induced by permanent middle cerebral artery occlusion (pMCAO) in mice. Thirty minutes before pMCAO and during the next 5 days, animals received vehicle (0.025 µmol/l HCl) or boldine (8, 16 and 25 mg/kg, intraperitoneally). The extension of the infarct area, neurological scores, and myeloperoxidase activity were evaluated 24 h after pMCAO. Locomotor activity, working, and aversive memory were evaluated 72 h after pMCAO, object recognition memory was tested 96 h after pMCAO, and spatial memory was tested 120 h after pMCAO. Cresyl violet, Fluoro-Jade C staining, and immunohistochemical for GFAP, TNF-α, and iNOS were also carried out. The treatment with boldine significantly decreased the infarct area, improved the neurological scores, and increased cell viability. The vertical exploratory activity and aversive, spatial, object recognition, and working memory deficits induced by pMCAO were prevented by boldine. Moreover, myeloperoxidase activity and GFAP, TNF-α, and iNOS immunoreactivity were decreased significantly by boldine. Although various mechanisms such as its antioxidant activity should be considered, these results suggest that the neuroprotective effect of boldine might be related in part to its anti-inflammatory properties.

Making Stem Cell Lines Suitable for Transplantation

Human stem cells, progenitor cells, and cell lines have been derived from embryonic, fetal, and adult sources in the search for graft tissue suitable for the treatment of CNS disorders. An increasing number of experimental studies have shown that grafts from several sources survive, differentiate into distinct cell types, and exert positive functional effects in experimental animal models, but little attention has been given to developing cells under conditions of good manufacturing practice (GMP) that can be scaled up for mass treatment. The capacity for continued division of stem cells in culture offers the opportunity to expand their production to meet the widespread clinical demands posed by neurodegenerative diseases. However, maintaining stem cell division in culture long term, while ensuring differentiation after transplantation, requires genetic and/or oncogenetic manipulations, which may affect the genetic stability and in vivo survival of cells. This review outlines the stages, selection criteria, problems, and ultimately the successes arising in the development of conditionally immortal clinical grade stem cell lines, which divide in vitro, differentiate in vivo, and exert positive functional effects. These processes are specifically exemplified by the murine MHP36 cell line, conditionally immortalized by a temperature-sensitive mutant of the SV40 large T antigen, and cell lines transfected with the c-myc protein fused with a mutated estrogen receptor (c-mycERTAM), regulated by a tamoxifen metabolite, but the issues raised are common to all routes for the development of effective clinical grade cells.

Human Neural Stem Cell Therapy for Chronic Ischemic Stroke: Charting Progress from Laboratory to Patients

Chronic disability after stroke represents a major unmet neurologic need. ReNeuron's development of a human neural stem cell (hNSC) therapy for chronic disability after stroke is progressing through early clinical studies. A Phase I trial has recently been published, showing no safety concerns and some promising signs of efficacy. A single-arm Phase II multicenter trial in patients with stable upper-limb paresis has recently completed recruitment. The hNSCs administrated are from a manufactured, conditionally immortalized hNSC line (ReNeuron's CTX0E03 or CTX), generated with c-mycER^TAM technology. This technology has enabled CTX to be manufactured at large scale under cGMP conditions, ensuring sufficient supply to meets the demands of research, clinical development, and, eventually, the market. CTX has key pro-angiogenic, pro-neurogenic, and immunomodulatory characteristics that are mechanistically important in functional recovery poststroke. This review covers the progress of CTX cell therapy from its laboratory origins to the clinic, concluding with a look into the late stage clinical future.

Intravenously Infused F3.Olig2 Improves Memory Deficits via Restoring Myelination in the Aged Hippocampus following Experimental Ischemic Stroke

Oligodendrocytes play a crucial role in creating the myelin sheath that is an important component in neural transmission. In an animal model of transient cerebral ischemia, application of oligodendrocyte progenitor cells (OPCs) has not yet been reported. In this study, the effects of F3.Olig2 transplantation on memory and cognitive dysfunction were investigated in the aged gerbil in which ischemic stroke was induced. To investigate the possible mechanisms underlying repair, changes in the expression of myelin basic protein (MBP), oligodendrocyte-specific protein (OSP), and brain-derived neurotrophic factor (BDNF) were examined. Experimental ischemic stroke was induced by occlusion of bilateral common carotid arteries in aged gerbils. Gerbils ( n = 31 per group) were randomly divided into three groups: (1) vehicle sham group, (2) vehicle ischemia group, and (3) F3.Olig2 ischemia group. After 1, 3, and 7 days of ischemia–reperfusion (I-R), saline or F3.Olig2 cells (1 × 10 6 cells in 100 μl) were injected into the gerbils intravenously. The gerbils were sacrificed 10 days after I-R for identification of grafted F3.Olig2 cells, and 15 and 30 days after I-R for tissue analysis after conducting passive avoidance and novel object recognition test. Injected F3.Olig2 cells and MBP, OSP, and BDNF were detected by specific antibodies using immunohistochemistry and/or Western blots. Memory and cognition were significantly increased in the F3.Olig2 ischemia group compared with the vehicle ischemia group. In the F3.Olig2 ischemia group, the neurons were not protected from ischemic damage; however, MBP, OSP, and BDNF expressions were significantly increased. Our results show that injection of F3.Olig2 cells significantly improved impaired memory and cognition, which might be related to increased MBP expression via increasing OSP and BDNF expression in the aged gerbil hippocampus following transient cerebral ischemia.

Uncoupling of neurovascular communication after transient global cerebral ischemia is caused by impaired parenchymal smooth muscle Kir channel function

Transient global cerebral ischemia is often followed by delayed disturbances of cerebral blood flow, contributing to neuronal injury. The pathophysiological processes underlying such disturbances are incompletely understood. Here, using an established model of transient global cerebral ischemia, we identify dramatically impaired neurovascular coupling following ischemia. This impairment results from the loss of functional inward rectifier potassium (KIR) channels in the smooth muscle of parenchymal arterioles. Therapeutic strategies aimed at protecting or restoring cerebrovascular KIR channel function may therefore improve outcomes following ischemia.

Endocannabinoid CB1 receptor activation upon global ischemia adversely impact recovery of reward and stress signaling molecules, neuronal survival and behavioral impulsivity

Global cerebral ischemia in rodents, which mimics cardiac arrest in humans, is associated with a surge in endocannabinoids and increased transmission of dopamine and glutamate leading to excitotoxic cell death. The current study assessed the role of CB1 receptor activation at the moment of an ischemic insult on ensuing regulation of stress and reward signaling molecules, neuronal injury and anxiety-like behavior. Male Wistar rats were separated into 4 groups (n=10/group); sham and ischemic rats administered the CB1 endocannabinoid receptor antagonist AM251 (2mg/kg, i.p.) 30min prior to global cerebral ischemia, and vehicle-treated counterparts. The effects of CB1 receptor blockade on corticotropin-releasing hormone (CRH), vesicular glutamate transporter 2 (vGluT2), tyrosine hydroxylase (TH) and dopamine receptor 1 (DRD1) signaling expression, together with CA1 neuronal damage and anxiety-like behaviors were assessed. Our findings show attenuated CA1 injury and behavioral deficits in AM251-treated ischemic rats. AM251-pretreatment also partially or completely reversed ischemia-induced alterations in TH-ir expression at the hippocampus, ventral tegmental area (VTA), nucleus accumbens (NAc) and basolateral amygdala (BLA), normalized DRD1-ir at the medial forebrain bundle, and diminished BLA and PVN-CRH expression. All groups showed comparable vGluT2 expression at the BLA and PVN-parvocellular subdivision. These findings support a determinant role of CB1 receptor activation at time of ischemia on functional recovery. They also support "state-dependent" effects of endocannabinoids, raising considerations in the development of effective molecules to regulate HPA axis function and mood disorders following cardiac arrest and stroke.

Long-Term Exercise Improves Memory Deficits via Restoration of Myelin and Microvessel Damage, and Enhancement of Neurogenesis in the Aged Gerbil Hippocampus After Ischemic Stroke

BACKGROUND

The positive correlation between therapeutic exercise and memory recovery in cases of ischemia has been extensively studied; however, long-term exercise begun after ischemic neuronal death as a chronic neurorestorative strategy has not yet been thoroughly examined.

OBJECTIVE

The purpose of this study is to investigate possible mechanisms by which exercise ameliorates ischemia-induced memory impairment in the aged gerbil hippocampus after transient cerebral ischemia.

METHODS

Treadmill exercise was begun 5 days after ischemia-reperfusion (I-R) and lasted for 1 or 4 weeks. The animals were sacrificed 31 days after the induction of ischemia. Changes in short-term memory, as well as the hippocampal expression of markers of cell proliferation, neuroblast differentiation, neurogenesis, myelin and microvessel repair, and growth factors were examined by immunohistochemistry and/or western blots.

RESULTS

Four weeks of exercise facilitated memory recovery despite neuronal damage in the stratum pyramidale (SP) of the hippocampal CA1 region and in the polymorphic layer (PoL) of the dentate gyrus (DG) after I-R. Long-term exercise enhanced cell proliferation and neuroblast differentiation in a time-dependent manner, and newly generated mature cells were found in the granule cell layer of the DG, but not in the SP of the CA1 region or in the PoL of the DG. In addition, long-term exercise ameliorated ischemia-induced damage of myelin and microvessels, which was correlated with increased BDNF expression in the CA1 region and the DG.

CONCLUSIONS

These results suggest that long-term treadmill exercise after I-R can restore memory function through replacement of multiple damaged structures in the ischemic aged hippocampus.

Prolonged deficits in parvalbumin neuron stimulation-evoked network activity despite recovery of dendritic structure and excitability in the somatosensory cortex following global ischemia in mice

Relatively few studies have examined plasticity of inhibitory neuronal networks following stroke in vivo, primarily due to the inability to selectively monitor inhibition. We assessed the structure of parvalbumin (PV) interneurons during a 5 min period of global ischemia and reperfusion in mice, which mimicked cerebral ischemia during cardiac arrest or forms of transient ischemic attack. The dendritic structure of PV-neurons in cortical superficial layers was rapidly swollen and beaded during global ischemia, but recovered within 5-10 min following reperfusion. Using optogenetics and a multichannel optrode, we investigated the function of PV-neurons in mouse forelimb somatosensory cortex. We demonstrated pharmacologically that PV-channelrhodopsin-2 (ChR2) stimulation evoked activation in layer IV/V, which resulted in rapid current sinks mediated by photocurrent and action potentials (a measure of PV-neuron excitability), which was then followed by current sources mediated by network GABAergic synaptic activity. During ischemic depolarization, the PV-ChR2-evoked current sinks (excitability) were suppressed, but recovered rapidly following reperfusion concurrent with repolarization of the DC-EEG. In contrast, the current sources reflecting GABAergic synaptic network activity recovered slowly and incompletely, and was coincident with the partial recovery of the forepaw stimulation-evoked current sinks in layer IV/V 30 min post reperfusion. Our in vivo data suggest that the excitability of PV inhibitory neurons was suppressed during global ischemia and rapidly recovered during reperfusion. In contrast, PV-ChR2 stimulation-evoked GABAergic synaptic network activity exhibited a prolonged suppression even ∼1 h after reperfusion, which could contribute to the dysfunction of sensation and cognition following transient global ischemia.

Neuronal damage, central cholinergic dysfunction and oxidative damage correlate with cognitive deficits in rats with chronic cerebral hypoperfusion

Chronic cerebral hypoperfusion has been identified to be a risk factor for cognitive decline in aging, vascular dementia, and Alzheimer's disease. Substantial evidence has shown that chronic cerebral hypoperfusion may cause cognitive impairment, but the underlying neurobiological mechanism is poorly understood so far. In this study, we used a rat model of chronic cerebral hypoperfusion by permanent bilateral common carotid artery occlusion (BCCAO) to investigate the alterations of neuronal damage, glial activation oxidative stress and central cholinergic dysfunction, and their causal relationship with the cognitive deficits induced by chronic cerebral hypoperfusion. We found that BCCAO rats exhibited spatial learning and memory impairments and working memory dysfunction 12 weeks after BCCAO compared with sham-operated rats, simultaneously accompanied by significantly increased neuronal damage and glial cell activation in the cerebral cortex and hippocampus. Twelve weeks of BCCAO treatment in rats resulted in central cholinergic dysfunction and increased oxidative damage compared with sham-operated rats. Correlational analyses revealed that spatial learning and memory impairments and working memory dysfunction were significantly correlated with the measures of neuronal damage, central cholinergic dysfunction and oxidative damage in the cerebral cortex and hippocampus of rats with BCCAO. Moreover, the measures of neuronal damage and central cholinergic dysfunction were significantly correlated with the indexes of oxidative damage in rats with BCCAO. Collectively, this study provides novel evidence that neuronal damage and central cholinergic dysfunction is likely due to increased oxidative stress under the condition of chronic cerebral hypoperfusion. Furthermore, the results of the present study suggest that neuronal damage, central cholinergic dysfunction and oxidative damage in the brain following the reduction of cerebral blood flow could be involved in cognitive deficits induced by chronic cerebral hypoperfusion.

Electroacupuncture-Induced Neuroprotection against Cerebral Ischemia in Rats: Role of the Dopamine D2 Receptor

Background. Cerebral ischemia is known to produce brain damage and related behavioural deficits, including memory deficits and motor disorders. Evidence shows that EA significantly promotes recovery of neurological function and thus improves quality of life. Objective. Evidence exists for the involvement of catecholamines in human neuroplasticity. A better understanding of dopaminergic (DAergic) modulation in this process will be important. Methods. A total of 72 adult male Sprague-Dawley (SD) rats were divided into 6 groups: normal, model, EA, spiperone group, EA + spiperone group, and pergolide. The middle cerebral artery occlusion (MCAO) model was used in all 6 groups except the normal group. A behavioural assessment was conducted at 1, 3, 5, and 7 days after MCAO. The percent of brain infarct area was also determined 7 days after MCAO. Tyrosine hydroxylase (TH) and growth-associated protein 43 (GAP-43) fluorescence double labeling was performed in the striatum. Results. In this study, we found that EA at Fengchi (GB20) acupoints resulted in marked improvements based on a behavioural assessment. Both TTC staining and GAP-43 immunofluorescence labeling results showed that EA treatment reduced ischemia injury and promoted neuroplasticity compared with the model group. The D2R-selective agonist, pergolide, showed similar results, but these results were reversed by the D2R-selective antagonist, spiperone. We also found that there were more colocalization and expression of GAP-43 and TH in the EA and pergolide groups than those in the other groups. Conclusion. These results suggest that the neuroplasticity induced by EA was mediated by D2 autoreceptors in DAergic neurons.

Cognitive dysfunction after cardiac surgery: Pathophysiological mechanisms and preventive strategies

Despite improvements in surgical techniques and the implementation of effective brain protection strategies, the incidence of brain injury after cardiac surgery has remained relatively constant over the years as patients have become older and sicker. Cognitive dysfunction is the most common clinical manifestation of brain injury after cardiac surgery. Its occurrence is related to a combination of three factors that are often associated with cardiopulmonary bypass (CPB): embolism, hypoperfusion, and the inflammatory response. However, such factors and their potential cerebral consequences are not exclusive to CPB. Postoperative cognitive dysfunction also afflicts patients who undergo cardiac surgery without CPB as well as nonsurgery patients who undergo transcatheter interventions. There is growing evidence that patient-related factors such as the presence of (cerebro)vascular risk factors play an important role in both early and late postoperative cognitive dysfunction.

Ziprasidone attenuates brain injury after focal cerebral ischemia induced by middle cerebral artery occlusion in rats

Ziprasidone is an atypical antipsychotic drug used for the treatment of schizophrenia. Recent studies have reported that atypical antipsychotics have neuroprotective effects against brain injury. In the present study, the effect of ziprasidone on ischemic brain injury was investigated. Focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) in rats. All the animals experienced ischemia for 1h and then underwent reperfusion. The infarct size induced by MCAO was significantly reduced in the animals that received acute treatment with 5mg/kg ziprasidone and subchronic treatment with 2.5mg/kg ziprasidone for 7 days compared with that in the vehicle-treated animals. The acute treatment with ziprasidone significantly improved neurological functions, as measured by the modified neurological severity score, in a dose-dependent manner. The subchronic treatment produced more rapid recovery from functional deficits than the vehicle treatment. The immunohistochemical investigation revealed that the subchronic treatment prevented severe loss of neuronal marker intensity and attenuated the increased in microglial marker intensity in the infarcted cortical area. These results suggest that ziprasidone has neuroprotective effects in a rat model of ischemic stroke and provide new insight for its clinical applications.

Mild cognitive impairment: animal models

Mild cognitive impairment (MCI) is an aspect of cognitive aging that is considered to be a transitional state between normal aging and the dementia into which it may convert. Appropriate animal models are necessary in order to understand the pathogenic mechanisms of MCI and develop drugs for its treatment. In this review, we identify the features that should characterize an animal model of MCI, namely old age, subtle memory impairment, mild neuropathological changes, and changes in the cholinergic system, and the age at which these features can be detected in laboratory animals. These features should occur in aging animals with normal motor activity and feeding behavior. The animal models may be middle-aged rats and mice, rats with brain ischemia, transgenic mice overexpressing amyloid precursor protein and presenilin 1 (tested at an early stage), or aging monkeys. Memory deficits can be detected by selecting appropriately difficult behavioral tasks, and the deficits can be associated with neuropathological alterations. The reviewed literature demonstrates that, under certain conditions, these animal species can be considered to be MCI models, and that cognitive impairment in these models responds to drug treatment.

Expressional changes in cerebrovascular receptors after experimental transient forebrain ischemia

BACKGROUND

Global ischemic stroke is one of the most prominent consequences of cardiac arrest, since the diminished blood flow to the brain results in cell damage and sometimes permanently impaired neurological function. The post-arrest period is often characterised by cerebral hypoperfusion due to subacute hemodynamic disturbances, the pathophysiology of which are poorly understood. In two other types of stroke, focal ischemic stroke and subarachnoid hemorrhage, it has earlier been demonstrated that the expression of certain vasoconstrictor receptors is increased in cerebral arteries several days after the insult, a phenomenon that leads to increased contraction of cerebral arteries, reduced perfusion of the affected area and worsened ischemic damage. Based on these findings, the aim of the present study was to investigate if transient global cerebral ischemia is associated with upregulation of vasoconstrictive endothelin and 5-hydroxytryptamine receptors in cerebral arteries. Experimental transient forebrain ischemia of varying durations was induced in male wistar rats, followed by reperfusion for 48 hours. Neurological function was assessed daily by three different tests and cerebrovascular expression and contractile function of endothelin and 5-hydroxytryptamine receptors were evaluated by wire myography, immunohistochemistry and western blotting.

RESULTS

Transient forebrain ischemia induced neurological deficits as well as functional upregulation of vasoconstrictive ET(B) and 5-HT(1B) receptors in cerebral arteries supplying mid- and forebrain regions. No receptor upregulation was seen in arteries supplying the hindbrain. Immunohistochemical stainings and western blotting demonstrated expressional upregulation of these receptor subtypes in the mid- and forebrain arteries and confirmed that the receptors were located in the smooth muscle layer of the cerebral arteries.

CONCLUSIONS

This study reveals a new pathophysiological aspect of global ischemic stroke, namely expressional upregulation of vasoconstrictor receptors in cerebral arteries two days after the insult, which might contribute to cerebral hypoperfusion and delayed neuronal damage after cardiac arrest.

Neuroprotection and Enhancement of Spatial Memory by Herbal Mixture HT008-1 in Rat Global Brain Ischemia Model

To investigate whether HT008-1, a prescription used in traditional Korean medicine to treat mental and physical weakness, has a neuroprotective effect on a rat model of global brain ischemia and an enhancing effect against memory deficit following ischemia. Global brain ischemia was induced for 10 min by using 4-vessel occlusion (4-VO). HT008-1 was orally administered at doses of 30, 100, and 300 mg/kg respectively twice at 0 and 90 min after ischemia. The effect on memory deficit was investigated by using a Y-maze neurobehavioral test 4 days after brain ischemia, and the effect on neuronal damage was measured 7 days after ischemia. The mechanism of action was studied immunohistochemically using an anti-CD11b (OX-42) antibody. The oral administration of HT008-1 at 100 and 300 mg/kg significantly reduced hippocampal neuronal cell death by 49% and 53%, respectively, compared with a vehicle-treated group, and also improved spatial memory function in the Y-maze test. Immunohistochemically, HT008-1 inhibited OX-42 expression in the hippocampus. The effects of HT008-1 were more pronounced than those of its individual herb components. The herbal mixture HT008-1 protects the most vulnerable CA1 pyramidal cells of the hippocampus and enhances spatial memory function against global brain ischemia; an anti-inflammatory effect may be one of the mechanisms of action.

Chronic brain hypoperfusion causes early glial activation and neuronal death, and subsequent long-term memory impairment

Reduction of cerebral blood flow is an important risk factor for dementia states and other brain dysfunctions. In present study, the effects of permanent occlusion of common carotid arteries (2VO), a well established experimental model of brain ischemia, on memory function were investigated, as assessed by reference and working spatial memory protocols and the object recognition task; cell damage to the hippocampus, as measured through changes in immunoreactivity for GFAP and the neuronal marker NeuN was also studied. The working hypothesis is that metabolic impairment following hypoperfusion will affect neuron and glial function and result in functional damage. Adult male Wistar rats were submitted to the modified 2VO method, with the right common carotid artery being occluded first and the left one week later, and tested seven days, three and six months after the ischemic event. A significant cognitive deficit was found in both reference and working spatial memory, as well as in the object recognition task, three and six months after surgery. Neuronal death and reactive astrogliosis were already present at 7 days and continued for up to 3 months after the occlusion; interestingly, there was no significant reduction in hippocampal volume. Present data suggests that cognitive impairment caused by brain hypoperfusion is long - lasting and persists beyond the time point of recovery from glial activation and neuronal loss.

Middle-aged, but not young, rats develop cognitive impairment and cortical neurodegeneration following the four-vessel occlusion/internal carotid artery model of chronic cerebral hypoperfusion

Permanent, stepwise occlusion of the vertebral arteries (VAs) and internal carotid arteries (ICAs) following the sequence VA→ICA→ICA, with an interstage interval (ISI, →) of 7 days, has been investigated as a four-vessel occlusion (4-VO)/ICA model of chronic cerebral hypoperfusion. This model has the advantage of not causing retinal damage. In young rats, however, 4-VO/ICA with an ISI of 7 days fails to cause behavioral sequelae. We hypothesized that such a long ISI would allow the brain to efficiently compensate for cerebral hypoperfusion, preventing the occurrence of cognitive impairment and neurodegeneration. The present study evaluated whether brain neurodegeneration and learning/memory deficits can be expressed by reducing the length of the ISI and whether aging influences the outcome. Young, male Wistar rats were subjected to 4-VO/ICA with different ISIs (5, 4, 3 or 2 days). An ISI of 4 days was used in middle-aged rats. Ninety days after 4-VO/ICA, the rats were tested for learning/memory impairment in a modified radial maze and then examined for neurodegeneration of the hippocampus and cerebral cortex. Regardless of the ISI, young rats were not cognitively impaired, although hippocampal damage was evident. Learning/memory deficits and hippocampal and cortical neurodegeneration occurred in middle-aged rats. The data indicate that 4-VO/ICA has no impact on the capacity of young rats to learn the radial maze task, despite 51% hippocampal cell death. Such resistance is lost in middle-aged animals, for which the most extensive neurodegeneration observed in both the hippocampus and cerebral cortex may be responsible.

Zingiber officinale Mitigates Brain Damage and Improves Memory Impairment in Focal Cerebral Ischemic Rat

Cerebral ischemia is known to produce brain damage and related behavioral deficits including memory. Recently, accumulating lines of evidence showed that dietary enrichment with nutritional antioxidants could reduce brain damage and improve cognitive function. In this study, possible protective effect of Zingiber officinale, a medicinal plant reputed for neuroprotective effect against oxidative stress-related brain damage, on brain damage and memory deficit induced by focal cerebral ischemia was elucidated. Male adult Wistar rats were administrated an alcoholic extract of ginger rhizome orally 14 days before and 21 days after the permanent occlusion of right middle cerebral artery (MCAO). Cognitive function assessment was performed at 7, 14, and 21 days after MCAO using the Morris water maze test. The brain infarct volume and density of neurons in hippocampus were also determined. Furthermore, the level of malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) in cerebral cortex, striatum, and hippocampus was also quantified at the end of experiment. The results showed that cognitive function and neurons density in hippocampus of rats receiving ginger rhizome extract were improved while the brain infarct volume was decreased. The cognitive enhancing effect and neuroprotective effect occurred partly via the antioxidant activity of the extract. In conclusion, our study demonstrated the beneficial effect of ginger rhizome to protect against focal cerebral ischemia.

The modified 2VO ischemia protocol causes cognitive impairment similar to that induced by the standard method, but with a better survival rate

Permanent bilateral occlusion of the common carotid arteries (2VO) in the rat has been established as a valid experimental model to investigate the effects of chronic cerebral hypoperfusion on cognitive function and neurodegenerative processes. Our aim was to compare the cognitive and morphological outcomes following the standard 2VO procedure, in which there is concomitant artery ligation, with those of a modified protocol, with a 1-week interval between artery occlusions to avoid an abrupt reduction of cerebral blood flow, as assessed by animal performance in the water maze and damage extension to the hippocampus and striatum. Male Wistar rats (N = 47) aged 3 months were subjected to chronic hypoperfusion by permanent bilateral ligation of the common carotid arteries using either the standard or the modified protocol, with the right carotid being the first to be occluded. Three months after the surgical procedure, rat performance in the water maze was assessed to investigate long-term effects on spatial learning and memory and their brains were processed in order to estimate hippocampal volume and striatal area. Both groups of hypoperfused rats showed deficits in reference (F(₈,₁₇₂) = 7.0951, P < 0.00001) and working spatial memory [2nd (F(₂,₄₄) = 7.6884, P < 0.001), 3rd (F(₂,₄₄) = 21.481, P < 0.00001) and 4th trials (F(₂,₄₄) = 28.620, P < 0.0001)]; however, no evidence of tissue atrophy was found in the brain structures studied. Despite similar behavioral and morphological outcomes, the rats submitted to the modified protocol showed a significant increase in survival rate, during the 3 months of the experiment (P < 0.02).

Preconditioning-induced ischemic tolerance: a window into endogenous gearing for cerebroprotection

Ischemic tolerance defines transient resistance to lethal ischemia gained by a prior sublethal noxious stimulus (i.e., preconditioning). This adaptive response is thought to be an evolutionarily conserved defense mechanism, observed in a wide variety of species. Preconditioning confers ischemic tolerance if not in all, in most organ systems, including the heart, kidney, liver, and small intestine. Since the first landmark experimental demonstration of ischemic tolerance in the gerbil brain in early 1990's, basic scientific knowledge on the mechanisms of cerebral ischemic tolerance increased substantially. Various noxious stimuli can precondition the brain, presumably through a common mechanism, genomic reprogramming. Ischemic tolerance occurs in two temporally distinct windows. Early tolerance can be achieved within minutes, but wanes also rapidly, within hours. Delayed tolerance develops in hours and lasts for days. The main mechanism involved in early tolerance is adaptation of membrane receptors, whereas gene activation with subsequent de novo protein synthesis dominates delayed tolerance. Ischemic preconditioning is associated with robust cerebroprotection in animals. In humans, transient ischemic attacks may be the clinical correlate of preconditioning leading to ischemic tolerance. Mimicking the mechanisms of this unique endogenous protection process is therefore a potential strategy for stroke prevention. Perhaps new remedies for stroke are very close, right in our cells.

Functional differentiation and cooperation among the hippocampal subregions in rats to effect spatial memory processes

We investigated the roles of the hippocampal subregions and intrahippocampal networks in effecting spatial reference and working processes. The results showed that the dentate gyrus plays a key role in encoding both types of spatial memory. Lesions in the dentate gyrus caused severe impairment in the acquisition of the Morris water maze and delayed matching-to-place tasks as compared to those in the other hippocampal subregions (Exp. 1). Further, there was functional cooperation between CA3 and CA1 via the Schaffer collaterals and the hippocampal commissure in the performance of both types of spatial memory tasks. Among the rats with intact hippocampal commissure, those with both contralateral and ipsilateral CA1/CA3 lesions showed a similar performance (Exp. 2A); however, among the rats with transected hippocampal commissure, those with the contralateral CA1/CA3 lesions showed a more disruptive performance than the rats with the ipsilateral CA1/CA3 lesions (Exp. 2B). This study suggests that the hippocampus is the functional unit for spatial reference and working memory processes, including differential functions and functional cooperation among the hippocampal subregions.

Persistent behavioral impairments and neuroinflammation following global ischemia in the rat

Cognitive deficits associated with cardiac arrest have been well documented; however, the corresponding deficits in animal models of global ischemia have not been comprehensively assessed, particularly after long-term, clinically relevant survival times. We exposed male Sprague-Dawley rats to 10 min of bilateral carotid artery occlusion + systemic hypotension (40-45 mmHg) or sham surgery, and used histopathological assessments for short-term survival animals (16 days) and both behavioral and histopathological assessments for long-term survival animals (270 days). Analyses revealed significant long-term deficits in ischemic animals' learning, memory (T-maze, radial arm maze), working memory (radial arm maze), and reference memory (Morris water maze, radial arm maze) abilities that were not associated with a general cognitive decline. Histological results showed significant increases in glial fibrillary acidic protein, neuron glia 2, OX-42 and ED-1 staining, as well as significant decreases in microtubule-associated protein 2 staining and cornu ammonis area 1 (CA1) cell counts 16 days post-ischemia. The pattern at 270 days was similar, but notably there was a persistent elevation of ED-1 staining, suggesting recent cell death as well as significant atrophy of CA1. Whereas previous work has primarily reported transient changes in behavior after global ischemia, this study describes disturbances in several different functional domains following CA1 cell loss at clinically relevant survival times. Moreover, the histopathological outcome is suggestive of a spontaneous repopulation of CA1, but this was not sufficient to offset the behavioral impairments arising from the ischemic insult.

Benzamide protects delayed neuronal death and behavioural impairment in a mouse model of global cerebral ischemia

The present study is aimed at evaluating the functional and neuroprotective effect of benzamide, a poly-(ADP-ribose) polymerase (PARP) inhibitor on delayed neuronal death (DND) in hippocampus CA1 region and memory impairment following global cerebral ischemia (GCI) in a mouse model. GCI was induced by bilateral common carotid artery occlusion (BCAo) for 20 min followed by reperfusion for 9 days. Postischemic continuous treatment with benzamide (160 mg/kg b w i.p. for 9 days) significantly reversed the GCI-induced anterograde memory impairment in passive avoidance step through and elevated plus maze tasks. The observed memory impairment in vehicle treated ischemia group was found to be well correlated with DND and downregulation of cholinergic muscarinic receptor-1 expression, which was possibly mediated by inflammation and apoptosis, as revealed from inducible nitric oxide synthase (iNOS) expression and number of TUNEL positive neurons in hippocampus CA1 region. It is clear from the present experiment that benzamide treatment significantly decreases the iNOS expression and number of apoptotic neurons and thereby improves the neuronal survival and memory during GCI. Our present findings provide compelling evidence that multiple doses of benzamide treatment is a promising therapeutic approach for cerebrovascular and neurodegenerative diseases, which deserves further clinical evaluation.

Effects of cyclooxygenase (COX) inhibition on memory impairment and hippocampal damage in the early period of cerebral hypoperfusion in rats

Chronic cerebral hypoperfusion is related to neurological disorders and contributes to a cognitive decline. Its experimental model in rats is permanent, bilateral common carotid artery occlusion. The cyclooxygenase (COX) system plays a pivotal role in the evolution of ischemic brain damage. Several COX inhibitors have proved to be neuroprotective in stroke models. We set out to characterize the effects of COX inhibitors in rats with permanent cerebral hypoperfusion. Some of the animals were exposed to two-vessel occlusion (n=72), while the others served as sham-operated controls (n=54). This was followed by a 3-day post-treatment with the nonselective COX inhibitor indomethacin (3 mg/kg) or with the selective COX-2 inhibitor NS-398 (15 mg/kg) or with the solvent. Some groups of the animals were sacrificed after 3 days, while the remainder were tested in the Morris watermaze for 5 days, and were sacrificed after 2 weeks. Neurons in the hippocampus were subjected to immunocytochemical labeling with cresyl violet, the dendrites with microtubule-associated protein-2, astrocytes with glial fibrillary acidic protein and microglia activation with OX-42 antibody. Two-vessel occlusion induced a learning impairment, mild neuronal damage, marked dendritic injury and moderate astrocytic reaction in the hippocampus. NS-398, but not indomethacin improved the survival rate and abolished the learning disability. However, both drugs increased the proportion of animals displaying neuronal damage. Glial markers revealed a time-dependent elevation in both the sham and the two-vessel occluded group, and were unaffected by the treatments. In summary, NS-398 prevented the hypoperfusion-induced memory impairment, but not by protecting the hippocampal neurons.

Long-lasting cognitive injury in rats with apparent full gross neurological recovery after short-term cardiac arrest

OBJECTIVE

The long-term behavioral effects of mild global ischemia have not been well described. We used short (5 min) asphyxic-cardiac arrest that resulted in no apparent gross neurological deficits to study the long-term effects of mild hypoxic ischemia on the neurobehavioral status of rats.

METHODS

Fifteen adult, male Wistar rats were studied. One group was given asphyxic-cardiac arrest (CA) for 5 min (n=10) and the other group had Sham procedure (n=5). Neurobehavioral testing was performed before and 2 weeks after CA. The neurobehavioral evaluations were: neurological deficit score (NDS), Y Maze, open field, pre-pulse inhibition (PPI) of acoustic startle reflex (ASR), wire hanging, and inclined screen.

RESULTS

At 24h post-CA, all of the rats regained normal neurological function as measured by NDS, an integral score for consciousness, brainstem reflexes, sensorimotor function and simple behavioral reflex tests. However, 1 week after CA, the rats exhibited significant activity reductions in the open field and in spontaneous alternation in the Y maze. The CA rats also showed a significant decrease in startle reaction amplitude and startle inhibition in the PPI tests. Two weeks after CA, the changes in motor activity and deficits in PPI remained significant, but the spontaneous alternation recovered. The muscle strength test of wire hanging and inclined screen tests did not exhibit significant change.

CONCLUSION

We present a rodent model of mild CA that, despite apparent full recovery of global neurological function at 24h post-resuscitation, exhibited long-term cognitive injury lasting for at least 2 weeks after CA. This model may help understand better the injury associated with CA and develop management strategies for mild brain injury.

A simplified procedure for the quantitative measurement of neurological deficits after forebrain ischemia in mice

This study describes a comprehensive method to assess neurological deficits after brain ischemia produced by sequential common carotid artery sectioning (SCAS) in aged mice, and a scale to determine the degree of functional incapacity of ischemic animals. The method involves an initial phase of undisturbed observation and a later manipulative phase during which each animal is subjected to a sequence of very simple manipulations. Sham-operated animals demonstrated 96% survival throughout the study period (72 h), whereas the 24, 48 and 72 h survival rates of SCAS-mice were 48, 38 and 36%, respectively. In the surviving SCAS-mice, we detected a total of 23 neurological alterations throughout the observation period (72 h); the most frequent alterations were: motor incoordination, abnormal body position, hypomobility, decreased body tone and muscular strength, tremor, hunched back, passivity, forelimb flexion and ataxic gait. Based on these alterations, we used a global scale that comprises 10 progressive grades beyond 0 (normal), extending to status 10 (death due to SCAS), with higher scores indicating greater deficit. The median neurological scores for sham-operated animals were 1.36, 1.48 and 1.32 at 24, 48 and 72 h, respectively, whereas total neurological scores in SCAS-mice of 6.1, 6.8 and 7.4, at 24, 48 and 72 h, respectively, were substantially greater than those observed in sham-operated animals. The simplicity of the procedure, herein described, to measure the functional neurological condition of ischemic animals, and the remarkable level of functional impairment produced by SCAS offer the possiblity to test the efficacy of putative stroke therapies and to monitor progress of deficits over time in groups of animals.

Use of a Maze to Detect Cognitive Dysfunction in a Porcine Model of Hypothermic Circulatory Arrest

BACKGROUND

Hypothermic circulatory arrest (HCA) can result in cognitive impairment not reflected by histopathology or gross neurologic observation. We tested the sensitivity of two multi-room maze tasks in detecting cerebral dysfunction after HCA in pigs.

METHODS

Twenty-seven pigs were studied, divided between two tasks. 13 underwent 90 minutes HCA at 20 degrees C and were trained from postoperative day (POD) 7; 14 were unoperated controls. The maze includes a holding area, 8 rooms, and a center hallway. One piece of apple is placed in each baited room on each of 10 days of learning evaluation. After a pig enters a room, doors to all other rooms close, and the pig must return to the holding area. In task 1, 6 of 8 rooms were baited, and each day's session ended when each baited room had been entered, or after 20 trials. In task 2, initially only the right- or left-sided rooms were baited. Pigs were evaluated each day until they entered 4 baited rooms, or for 15 trials; the process was then repeated, baiting the other side.

RESULTS

Intraoperative physiology and postoperative recovery showed no differences between task 1 or 2 pigs. Task 1 did not distinguish between control and HCA groups (p = 0.5), but task 2 revealed significantly (p = 0.04) better learning in controls.

CONCLUSIONS

The significantly poorer performance of pigs after HCA suggests that the reversal of baited rooms in task 2 provides the sensitivity to detect cognitive dysfunction. The maze is a promising tool to investigate in pigs the mild cerebral damage often seen after HCA.

Effects of vibrissae removal on search accuracy in the water maze

In two experiments, the vibrissae were clipped on either the left, the right, or both sides, and the rats were trained to find a submerged platform in the Morris water maze. In both experiments, animals without vibrissae on both sides or on the left consistently spent significantly more time in the "counter" area twice the platform diameter in size, surrounding the submerged platform, than intact controls. Counter preference was not as consistent across experiments in rats with right vibrissae removed. These results suggest that the vibrissae are required for proprioceptive location of the platform itself, but not for proximal search accuracy. Since ischemic damage to hippocampal CA1 pyramidal cells has also been reported to prolong counter search during training, the results support the suggestion that impaired hippocampal processing of proprioceptive information from the vibrissae may contribute to the increased latency to find the platform shown by ischemic rats.

Permanent, 3-stage, 4-vessel occlusion as a model of chronic and progressive brain hypoperfusion in rats: a neurohistological and behavioral analysis

Permanent, 3-stage, 4-vessel occlusion (4-VO) was evaluated as a practicable model of progressive, cerebral hypoperfusion in rats, resulting in quantifiable, reproducible, neuronal damage within a time interval shorter than that described in the 2-VO model. The effect of permanent and graded 4-VO on cognition was also evaluated using the newly developed, aversive radial maze. The vertebral arteries (VA) plus the common carotid arteries (CCA) or internal carotid arteries (ICA) were progressively and permanently occluded, following different experimental sequences (CCA--> VA; VA-->CCA-->CCA or VA-->ICA-->ICA) with inter-stage intervals ranging from 1 to 4 weeks. Only two of four groups subjected to 2-stage 4-VO (CCA-->VA) showed modest reduction in the number of normal-appearing CA1 pyramidal cells, despite the significant treatment effect (p < 0.001-0.01 versus sham). A high rate of mortality (63.8%) was associated with 2-stage 4-VO. More pronounced and consistent neuronal damage occurred 8 weeks after 3-stage 4-VO, following the sequence VA --> CCA --> CCA (p < 0.001). One month after this schedule, profound, persistent cognitive impairment was demonstrated in the aversive radial maze (p < 0.01-0.0001). This behavioral effect was not manifested when the ICA, rather than the CCA, were occluded, despite the presence of significant, although less severe, hippocampal lesioning. The mortality rate was significantly reduced when 3-stage 4-VO was used (p < 0.0001). These consistent, histological and behavioral effects, combined with a low mortality rate, suggest that permanent, 3-stage 4-VO may represent a reliable animal model of chronic, progressive, cerebral hypoperfusion.

Neuroprotection of catalpol in transient global ischemia in gerbils

The neuroprotection of catalpol and its mechanism was evaluated in cerebral ischemic model in gerbils. Three groups were designed as sham-operated, ischemia-treated, respectively, with catalpol and saline. Catalpol was injected intraperitoneally immediately after reperfusion and repeatedly at 12, 24, 48 and 72 h with the dose of 5.0 mg/kg. The neuroprotection was estimated by the indexes of behavior and histology. Behavioral testing was performed in Y-maze and the survival neurons in CA1 subfield were counted under a microscope after behavioral testing. In addition, apoptosis induced by ischemia was also examined by using the terminal deoxynucleotidyl transferase-mediated UTP nick end labeling method. It was shown that catalpol significantly attenuated apoptosis, rescued hippocampal CA1 neurons and reduced cognitive impairment. In order to make clear the mechanism of catalpol's neuroprotection, the activities of endogenous antioxidants and nitric oxide synthase together with the content of lipid peroxide in cortex and hippocampus were assayed. The results proved that catalpol significantly reduced the content of lipid peroxide, increased the activity of glutathione peroxidase and decreased the activity of nitric oxide synthase. All these suggested that catalpol was a potential neuroprotective agent and its neuroprotective effects were achieved at least partly by promoting endogenous antioxidant enzymatic activities and reducing the formation of nitric oxide.

Genetic and Cellular Therapies for Cerebral Infarction

Neurosurgeons, working as surgical scientists, can have a prominent role in developing and implementing genetic and cellular therapies for cerebral ischemia. The rapid emergence of both genetic and cellular therapies for neural regeneration warrants a careful analysis before implementation of human studies to understand the pitfalls and promises of this strategy. In this article, we review the topic of genetic and cellular therapy for stroke to provide a foundation for practicing neurosurgeons and clinical scientists who may become involved in this type of work. In Part 1, we review preclinical approaches with gene transfer, such as 1) improved energy delivery, 2) reduction of intracellular calcium availability, 3) abrogation of effects of reactive oxygen species, 4) reduction of proinflammatory cytokine signaling, 5) inhibition of apoptosis mediators, and 6) restorative gene therapy, that are paving the way to develop new strategies to treat cerebral infarction. In Part 2, we discuss the results of studies that address the possibility of using cellular therapies for stroke in animal models and in human trials by reviewing 1) the basics of stem cell biology, 2) exogenous and 3) and endogenous cell sources for therapy, and 4) clinical considerations in cell therapy applications. These emerging technologies based on the advancements made in recent years in the fields of genetics, therapeutic cloning, neuroscience, stem cell biology, and gene therapy provide significant potential for new therapies for stroke.

A novel version of the 8-arm radial maze: effects of cerebral ischemia on learning and memory

A novel version of the 8-arm radial maze task was developed to quantify spatial learning and memory in rats subjected to transient cerebral ischemia (TCI) using the 4-VO model. This maze uses the rat's natural behavior of avoiding open, illuminated areas, and preference for a darkened, enclosed shelter. Ischemic rats were required to escape from the central area into the darkened goal box. Ischemia was induced before or after training to examine its influence on acquisition and retention of cognition, respectively. During the acquisition test, latency of ischemic rats to find the goal box, and working memory performance were significantly impaired (P < 0.005-0.001). The performance for retention of cognition was also disrupted by ischemia (P < 0.05-0.01). There was no correlation between the degree of CA1 pyramidal cell loss and behavioral deficits. The present data reveal that the aversive version of the 8-arm radial maze is sensitive to the cognitive effects of ischemia. Since it excludes the need for food deprivation or immersion of the animal in water, the method should provide a sensitive and more practical behavioral test with which to evaluate the effects of ischemic brain damage on cognition.

Effect of tacrolimus (FK506) on ischemia-induced brain damage and memory dysfunction in rats

The behavioral and neurohistological protective effects of tacrolimus (FK506) were examined in rats subjected to 15-min global forebrain ischemia. Learning and memory performance were evaluated in an aversive, non-food-motivated, eight-arm radial maze. In one experiment, naive rats were rendered ischemic, and 15 days later they were tested for acquisition of a spatial task (postoperative training). In a complementary experiment, rats were trained for 8 days and then subjected to ischemia (preoperative training); 15 days later (on Day 24 of testing) they were retested for retention of cognition. FK506 (1.0 mg/kg) was given intravenously at the beginning of reperfusion, followed by doses applied intraperitoneally 6, 24, 48 and 72 h postischemia. Behavioral performance was expressed by latency to find the goal box, and number of errors. Ischemia did not affect acquisition performance. In contrast, retention of cognition was markedly impaired by ischemia, particularly working memory (P<.05-.001). This ischemia-induced, retrograde amnesia was significantly reduced by FK506 compared to vehicle alone on Day 24, as measured by latency and working memory errors (P<.025). A neuroprotective effect of FK506 was also seen on working memory, when postischemic performance was compared to that prior to ischemia (P>.05, Day 24 vs. Day 8, paired samples), in contrast to the significant, retrograde amnesia found in the ischemic, vehicle-treated group (P<.01). FK506 also significantly reduced the extent of hippocampal CA1 cell loss; however, this effect did not correlate with behavior. The present results suggest that the histological, neuroprotective effect of FK506 may be accompanied by a reduction in cognitive impairment, as assessed in a novel, non-food-motivated, eight-arm radial maze after transient, global, cerebral ischemia in rats.