Behavioral studies on rats with transient cerebral ischemia induced by occlusion of the middle cerebral artery

Novel arylidene malonate derivative, KM-34, showed neuroprotective effects on in vitro and in vivo models of ischemia/reperfusion

Cerebral ischemia constitutes the most frequent type of cerebrovascular disease. The reduction of blood supply to the brain initiates the ischemic cascade starting from ionic imbalance to subsequent glutamate excitotoxicity, neuroinflammation and oxidative stress, eventually causing neuronal death. Previously, the authors have demonstrated the in vitro cytoprotective and antioxidant effects of a new arylidene malonate derivative, KM-34, against oxidizing agents like hydrogen peroxide, glutamate or Fe3+/ascorbate. Here, we examined for the first time the neuroprotective effect of KM-34 on ischemia/reperfusion models. In vitro, treatment with 10 and 50 μM KM-34 reduced the cellular death (propidium iodide incorporation) induced by oxygen glucose deprivation (OGD) in rat organotypic hippocampal slices cultures. In vivo, stroke was induced in male Wistar rats through middle cerebral artery occlusion (MCAO), followed by 23 h of reperfusion. KM-34 was orally administered 105 min after MCAO onset. We noticed that 1 mg/kg KM-34 reduced infarct volume and neurological score, and increased the latency to fall in the Hanging Wire test compared to vehicle-treated ischemic animals. While ischemic and sham-operated groups showed similar horizontal locomotor activity, vertical counts decreased after MCAO, suggesting that vertical movements are more sensitive to the ischemic injury. Treatment with KM-34 also alleviated the mitochondrial impairment (ROS generation, swelling and membrane potential dissipation) induced by transient MCAO but not significant alterations were found in oxidative stress parameters. Overall, the study provides preclinical evidences confirming the neuroprotective effects of a novel synthetic molecule and paved the way for future investigations regarding its therapeutic potential against brain ischemia/reperfusion injury.

MicroRNA-182 exacerbates blood-brain barrier (BBB) disruption by downregulating the mTOR/FOXO1 pathway in cerebral ischemia

Cerebral ischemia causes damage to the structure and function of the blood-brain barrier (BBB) and alleviating BBB destruction will be of great significance for the treatment and prognosis of ischemic stroke. Recently, microRNAs have been shown to play a critical role in BBB integrity. However, the potential mechanism by which microRNA-182 (miR-182) affects the BBB in ischemic stroke remains unclear. We demonstrated for the first time that cerebral ischemia leads to a significant progressive increase in miR-182 after pMCAO, and bEnd.3 cells are the primary target cells of miR-182. In miR-182 KD transgenic mice, infarct volume, and BBB permeability were attenuated, and tight junction (TJ) proteins increased. Inhibition of miR-182 with an antagomir reduced OGD-induced apoptosis of bEnd.3 cells and the loss of ZO-1 and Occludin. To further explore the mechanism by which miR-182 regulates BBB integrity, we detected the apoptotic proteins Bcl-2/Bax and demonstrated that mTOR and FOXO1 were the targets of miR-182. Inhibition of mTOR/FOXO1 by rapamycin/AS1842856 decreased the ratio of Bcl-2/Bax and exacerbated TJ protein loss. Taken together, inhibition of miR-182 protects BBB integrity by reducing endothelial cell apoptosis through the mTOR/FOXO1 pathway. Thus, miR-182 may be a potential target for the treatment of BBB disruption during cerebral ischemia.

Sirt1 mediates improvement in cognitive defects induced by focal cerebral ischemia following hyperbaric oxygen preconditioning in rats

Hyperbaric oxygen preconditioning (HBO-PC) has been proposed as a safe and practical approach for neuroprotection in ischemic stroke. However, it is not known whether HPO-PC can improve cognitive deficits induced by cerebral ischemia, and the mechanistic basis for any beneficial effects remains unclear. We addressed this in the present study using rats subjected to middle cerebral artery occlusion (MCAO) as an ischemic stroke model following HBO-PC. Cognitive function and expression of phosphorylated neurofilament heavy polypeptide (pNF-H) and doublecortin (DCX) in the hippocampus were evaluated 14 days after reperfusion and after short interfering RNA-mediated knockdown of sirtuin1 (Sirt1). HBO-PC increased pNF-H and DCX expression and mitigated cognitive deficits in MCAO rats. However, these effects were abolished by Sirt1 knockdown. Our results suggest that HBO-PC can protect the brain from injury caused by ischemia-reperfusion and that Sirt1 is a potential molecular target for therapeutic approaches designed to minimize cognitive deficits caused by cerebral ischemia.

Animal Models of Vascular Cognitive Impairment and Dementia (VCID)

Vascular cognitive impairment and dementia (VCID) is the most common etiology of dementia in the elderly. Both, vascular and Alzheimer's disease, pathologies work synergistically to create neurodegeneration and cognitive impairments. The main causes of VCID include hemorrhage/microbleed (i.e., hyperhomocysteinemia), cerebral small vessel disease, multi-infarct dementia, severe hypoperfusion (i.e., bilateral common carotid artery stenosis), strategic infarct, angiopathy (i.e., cerebral angiopathy), and hereditary vasculopathy (i.e., cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy). In this review, we will discuss the experimental animal models that have been developed to study these pathologies. We will discuss the limitations and strengths of these models and the important research findings that have advanced the field through the use of the models.

Novel antiepileptic drug lacosamide exerts neuroprotective effects by decreasing glial activation in the hippocampus of a gerbil model of ischemic stroke

Lacosamide, which is a novel antiepileptic drug, has been reported to exert various additional therapeutic effects. The present study investigated the neuroprotective effects of lacosamide against transient cerebral ischemia-induced neuronal cell damage in the hippocampal cornu ammonis (CA)-1 region of a gerbil model. Neuronal Nuclei immunohistochemistry demonstrated that pre- and post-surgical treatment (5 min ischemia) with 25 mg/kg lacosamide protected CA1 pyramidal neurons in the lacosamide-treated-ischemia-operated group from ischemic injury 5 days post-ischemia, as compared with gerbils in the vehicle-treated-ischemia-operated group. Furthermore, treatment with 25 mg/kg lacosamide markedly attenuated the activation of astrocytes and microglia in the ischemic CA1 region at 5 days post-ischemia. The results of the present study suggested that pre- and post-surgical treatment of the gerbils with lacosamide was able to protect against transient cerebral ischemic injury-induced CA1 pyramidal neuronal cell death in the hippocampus. In addition, the neuroprotective effects of lacosamide may be associated with decreased activation of glial cells in the ischemic CA1 region.

A selective cannabinoid CB2 agonist attenuates damage and improves memory retention following stroke in mice

AIMS

We have recently demonstrated that treatment with a cannabinoid CB2 agonist was protective in a mouse middle cerebral artery occlusion model of cerebral ischemia/reperfusion injury. The present study aimed to determine whether these protective effects of CB2 agonism would extend to a mouse photoinjury model of permanent ischemia and determine associated alterations in cognition and infarct size.

MAIN METHODS

Mice received three injections of the CB2 selective agonist O-1966 or vehicle 1h prior to and 2 and 5days following induction of stroke. Infarct size was assessed at 1, 3, or 7days post-injury and learning and memory effects of injury and O-1966 treatment were assessed on days 6 and 7 using a novel object recognition task and an operant acquisition and retention procedure.

KEY FINDINGS

O-1966 treated mice had significantly smaller infarct volumes compared with vehicle treated mice. Photoinjury was also associated with a significant memory impairment on day 7 post-injury, and this deficit was reversed with O-1966 treatment. Surprisingly, sham-operated mice receiving O-1966 treatment showed a significant learning deficit in both the recognition and operant tasks compared with vehicle treated sham mice.

SIGNIFICANCE

We conclude that CB2 activation is protective against cognitive deficits and tissue damage following permanent ischemia, but may dysregulate glial or neuronal function of learning and memory circuits in the absence of injury and/or inflammation.

Of mice and men: modelling post-stroke depression experimentally

At least one-third of stroke survivors suffer from depression. The development of comorbid depression after stroke is clinically highly significant because post-stroke depression is associated with increased mortality, slows recovery and leads to worse functional outcomes. Here, we review the evidence that post-stroke depression can be effectively modelled in experimental rodents via a variety of approaches. This opens an exciting new window onto the neurobiology of depression and permits probing potential underlying mechanisms such as disturbed cellular plasticity, neuroendocrine dysregulation, neuroinflammation, and neurodegeneration in a novel context. From the point of view of translational stroke research, extending the scope of experimental investigations beyond the study of short-term end points and, in particular, acute lesion size, may help improve the relevance of preclinical results to human disease. Furthermore, accumulating evidence from both clinical and experimental studies offers the tantalizing prospect of 5-hydroxytryptaminergic antidepressants as the first pharmacological therapy for stroke that would be available during the subacute and chronic phases of recovery. Interdisciplinary neuropsychiatric research will be called on to dissect the mechanisms underpinning the beneficial effects of antidepressants on stroke recovery.

Melatonin ameliorates injury and specific responses of ischemic striatal neurons in rats

Studies have confirmed that middle cerebral artery occlusion (MCAO) causes striatal injury in which oxidative stress is involved in the pathological mechanism. Increasing evidence suggests that melatonin may have a neuroprotective effect on cerebral ischemic damage. This study aimed to examine the morphological changes of different striatal neuron types and the effect of melatonin on striatal injury by MCAO. The results showed that MCAO induced striatum-related dysfunctions of locomotion, coordination, and cognition, which were remarkably relieved with melatonin treatment. MCAO induced severe striatal neuronal apoptosis and loss, which was significantly decreased with melatonin treatment. Within the outer zone of the infarct, the number of Darpp-32+ projection neurons and the densities of dopamine-receptor-1 (D1)+ and dopamine-receptor-2 (D2)+ fibers were reduced; however, both parvalbumin (Parv)+ and choline acetyltransferase (ChAT)+ interneurons were not significantly decreased in number, and neuropeptide Y (NPY)+ and calretinin (Cr)+ interneurons were even increased. With melatonin treatment, the loss of projection neurons and characteristic responses of interneurons were notably attenuated. The present study demonstrates that the projection neurons are rather vulnerable to ischemic damage, whereas the interneurons display resistance and even hyperplasia against injury. In addition, melatonin alleviates striatal dysfunction, neuronal loss, and morphological transformation of interneurons resulting from cerebral ischemia.

Long-term post-stroke changes include myelin loss, specific deficits in sensory and motor behaviors and complex cognitive impairment detected using active place avoidance

Persistent neurobehavioral deficits and brain changes need validation for brain restoration. Two hours middle cerebral artery occlusion (tMCAO) or sham surgery was performed in male Sprague-Dawley rats. Neurobehavioral and cognitive deficits were measured over 10 weeks included: (1) sensory, motor, beam balance, reflex/abnormal responses, hindlimb placement, forepaw foot fault and cylinder placement tests, and (2) complex active place avoidance learning (APA) and simple passive avoidance retention (PA). Electroretinogram (ERG), hemispheric loss (infarction), hippocampus CA1 neuronal loss and myelin (Luxol Fast Blue) staining in several fiber tracts were also measured. In comparison to Sham surgery, tMCAO surgery produced significant deficits in all behavioral tests except reflex/abnormal responses. Acute, short lived deficits following tMCAO were observed for forelimb foot fault and forelimb cylinder placement. Persistent, sustained deficits for the whole 10 weeks were exhibited for motor (p<0.001), sensory (p<0.001), beam balance performance (p<0.01) and hindlimb placement behavior (p<0.01). tMCAO produced much greater and prolonged cognitive deficits in APA learning (maximum on last trial of 604±83% change, p<0.05) but only a small, comparative effect on PA retention. Hemispheric loss/atrophy was measured 10 weeks after tMCAO and cross-validated by two methods (e.g., almost identical % ischemic hemispheric loss of 33.4±3.5% for H&E and of 34.2±3.5% for TTC staining). No visual dysfunction by ERG and no hippocampus neuronal loss were detected after tMCAO. Fiber tract damage measured by Luxol Fast Blue myelin staining intensity was significant (p<0.01) in the external capsule and striatum but not in corpus callosum and anterior commissure. In summary, persistent neurobehavioral deficits were validated as important endpoints for stroke restorative research in the future. Fiber myelin loss appears to contribute to these long term behavioral dysfunctions and can be important for cognitive behavioral control necessary for complex APA learning.

Experimental models of vascular dementia and vascular cognitive impairment: a systematic review

Vascular cognitive impairment (VCI) encompasses vascular dementia and is the second most common cause of dementing illness after Alzheimer's disease. The main causes of VCI are: cerebral small vessel disease; multi-infarct dementia; strategic infarct (i.e. located in a functionally-critical brain area); haemorrhage/microbleed; angiopathy (including cerebral amyloid angiopathy); severe hypoperfusion (e.g. cardiac arrhythmia); and hereditary vasculopathy (e.g. cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, CADASIL). In this systematic analysis, we aimed to relate cognitive and neuropathological features of experimental models to clinical VCI. We extracted data from 107 studies covering 16 models. These included: brief global ischaemic insults (in rats, mice or gerbils); chronic global hypoperfusion (rats, mice, gerbils); chronic hypertension (in primates or stroke-prone, spontaneously-hypertensive rats); multiple ischaemic lesions because of intra-vascular emboli (in rodents, rabbits or primates); strategic ischaemic lesions (in rats or mini-pigs); generalised vasculopathies, because of mutant Notch3, hyperhomocysteinaemia, experimental diabetes mellitus or lack of cerebral vasodilator M(5) receptors (rats or mice). Most cognitive testing showed deficits in working and reference memory. The lesions observed were microinfarcts, diffuse white matter lesions, hippocampal neuronal death, focal ischaemic lesions and micro-haemorrhages. The most-used model was bilateral carotid artery occlusion in rats, leading to chronic hypoperfusion and white matter injury.

Association between changes in weight and cerebral arteries in rats

The objective of the study was to gain a better understanding of brain artery diameters and anatomical variations for precise modification of cerebral blood supply in ischemic stroke models. Sprague-Dawley rats (n = 35) were used for the experiment. Rats were perfused and resin replicas of cerebral arteries were created using a corrosion casting technique. Resin replicas were measured and analyzed for correlation of vessel lumen with animal sex and weight. A strong correlation between root of aorta diameter and weight was observed (p < 0.0001). We also observed a significant correlation between weight, internal carotid arteries, right external carotid artery, and pterygopalatine arteries. For the common carotid artery, a significant difference between the left and right branches was observed even though there was no association with weight. There was no significant association observed between animal sex and vessel size independent of weight. A better knowledge of vessel lumen in relation to animal sex and weight is essential for adequate blockage of an intracranial artery to induce cerebral ischemia in a rat model of stroke. This study provides a viable reference for choice of rat size in relation to the size of embolic agents such as filaments, microwires, or in vitro thrombus used in ischemic stroke experiments.

Imaging of regional metabolic activity by (18)F-FDG/PET in rats with transient cerebral ischemia

Changes in regional metabolic activities induced by middle cerebral artery occlusion (MCAO) can influence patient outcome. Our aim was to demonstrate in a rat model that (18)F-FDG with positron emission tomography (PET) imaging is a quantitative, reproducible approach for identifying acute and sub-acute metabolic variations in infarct regions. We found that imaging with (18)F-FDG/PET enabled detection and quantification of ischemia-induced metabolic deficits and provided a sensitive and reliable means of assessing cerebral ischemic lesions compared with conventional neurological scoring systems in rodents.

Assessing cognitive function after intracerebral hemorrhage in rats

Preclinical studies must rigorously assess whether putative therapies improve motor and cognitive function following brain injury. Intracerebral hemorrhage (ICH) causes significant sensory-motor and cognitive deficits in humans. However, no study has evaluated cognition in rodent ICH models. Thus, we used a battery of tests to comprehensively examine whether a striatal ICH causes cognitive impairments in rats. Bacterial collagenase (or sterile saline for SHAM surgery) was injected into the striatum to create an ICH. Two days later, functional deficits were assessed using a neurological deficit scale (NDS), which is most sensitive to ICH injury. Sensory and/or motor deficits may confound cognitive testing; thus, we waited until these had resolved before testing learning and memory. Testing was conducted 1-7 months after ICH and included spontaneous alternation, elevated plus maze, open-field, Morris water maze, T-maze (win-shift and win-stay paradigms), and the radial arm maze (eight and four arms baited protocols). Significant motor deficits at 2 days completely resolved by 1 month, at which time cognitive testing began. In contrast to persistent cognitive deficits that occur after ICH in humans, we did not detect significant learning or memory deficits after ICH in rats. Our results suggest that these tests will not likely be useful for assessing outcome in experimental ICH studies. In conclusion, animal models that better mimic clinical ICH (both motor and cognitive deficits) must be developed. This may include increasing ICH severity or injuring other functional subdivisions within the striatum that may lead to more profound cognitive deficits.

Behavioral and Histologic Neuroprotection of Aqueous Garlic Extract After Reversible Focal Cerebral Ischemia

The objective of the present study was to investigate the effects of aqueous garlic extract (AGE) on neurobehavioral activities, malondialdehyde (MDA) and reduced glutathione (GSH) levels, glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), and sodium-potassium ATPase (Na(+),K(+)-ATPase) activities, and glutamate and aspartate content in a middle cerebral artery (MCA) occlusion (MCAO) model of acute cerebral ischemia in rats. The right MCA of male Wistar rats was occluded for 2 hours using intraluminal 4-0 monofilament, and reperfusion was allowed for 22 hours. MCAO caused significant depletion in GSH and its dependent enzymes (GPx, GR, and GST) and significant elevation of MDA, glutamate, and aspartate. The activities of Na(+),K(+)- ATPase, SOD, and CAT were decreased significantly by MCAO. The neurobehavioral activities (grip strength, spontaneous motor activity, and motor coordination) were also decreased significantly in the MCAO group. All of the alterations induced by ischemia were significantly attenuated by pretreatment with AGE (500 mg/mL/kg of body weight, i.p.) 30 minutes before the induction of MCAO and correlated well with histopathology by decreasing the neuronal cell death following MCAO and reperfusion. These findings suggest that AGE effectively modulates neurobehavioral and neurochemical changes in focal ischemia, most probably by virtue of its antioxidant properties.

Long-term neuroprotective effects of carbon dioxide on neonatal rat hypoxic-ischemic brain injury: an experimental study of skilled motor tasks

OBJECTIVE

This study was undertaken to investigate the long-term effect of hypercapnia on neonatal hypoxic-ischemic brain injury, we tested its effect in a neonatal rat hypoxia-ischemia model.

STUDY DESIGN

The rats were subjected to unilateral carotid artery ligation and exposure to 8% oxygen for 30 minutes. Six percent carbon dioxide was administered to the neonatal rats during unilateral hypoxia-ischemia, and the motor function and neurologic outcomes were determined 3 months later.

RESULTS

Significant motor functional improvement was observed in the hypercapnic animals, as judged by the Montoya staircase test. The unilateral brain injury was significantly ameliorated in the hypercapnic animals, and this amelioration was well correlated with the motor functional performance. Cerebral blood flow during hypoxia-ischemia, monitored by laser Doppler flowmetry, was better preserved in the hypercapnic animals.

CONCLUSION

Our results suggest that mild hypercapnia during hypoxia-ischemia may provide long-lasting motor functional as well as neurologic protection for immature brains, possibly by increasing cerebral blood flow during hypoxia.

Choto-san, a Kampo formula, improves chronic cerebral hypoperfusion-induced spatial learning deficit via stimulation of muscarinic M1 receptor

A recent double-blind and placebo-controlled study demonstrated a beneficial effect of Choto-san, a Kampo (traditional medicine of Japan) formula, on cognitive impairment in patients with vascular dementia. However, the neuronal mechanism underlying the therapeutic effects of this formula remains to be clarified. Using a chronic cerebral hypoperfusion model, we investigated the effect of Choto-san on cognitive dysfunction in mice to clarify its mechanism of actions. Chronic cerebral hypoperfusion was induced by permanent occlusion of both the common carotid arteries (2VO). Choto-san and Uncaria, a major constituent of Choto-san, caused an improvement in 2VO-induced learning deficits, whereas Uncaria-free Choto-san did not. The effects of Choto-san and Uncaria were blocked by pirenzepine, a selective muscarinic M1 antagonist. In a tube-dominance test, 2VO induced increased rates of assertive behavior in mice. 2VO mice administered Choto-san showed significantly reduced rates of assertive behavior compared to vehicle-treated controls, whereas Uncaria-free Choto-san and Uncaria had little effect on 2VO-induced assertive behavior. 2VO caused a significant decrease in the level of acetylcholine (ACh) contents in the brain, and the daily administration of Choto-san or Uncaria raised the ACh level to that in the sham-operated controls. These results suggest that Choto-san has an ameliorating effect on the spatial memory deficit caused by chronic hypoperfusion, and that the effect is mainly attributable to Uncaria. Moreover, it was suggested that the effects of Choto-san and Uncaria are at least partly mediated by stimulation of the muscarinic M1 receptor.

A novel behavioural registration system LABORAS™ and the social interaction paradigm detect long-term functional deficits following middle cerebral artery occlusion in the rat

Following stroke, patients suffer a wide range of disabilities including motor impairment, anxiety and depression. However, to date, characterisation of rodent stroke models has concentrated mainly on the investigation of motor deficits. The aim of the present studies was therefore to investigate home cage behaviour (as assessed by a recently developed automatic behavioural classification system, LABORAS) and social behaviour (as a measure of anxiety) in rats following transient middle cerebral artery occlusion (tMCAO). Rats subjected to tMCAO (90 min) showed deficits in general home cage behaviours including locomotion, rearing, grooming and drinking for up to 7 weeks post occlusion, as compared with sham operated controls. In addition, a significant decrease in the total duration of social interaction was also observed in occluded rats compared with shams. The data shows that in addition to motor deficits, animals display changes in home cage behaviour and decreased social behaviour which, in contrast to motor function, are prolonged over time. Transient MCAO in rats may therefore provide a pre-clinical model to investigate agents offering symptomatic relief for ischaemia-induced motor deficits and anxiety over time following injury.

The effect of voluntary exercise exposure on histological and neurobehavioral outcomes after ischemic brain injury in the rat

Physical activity can induce neuroplastic adaptations and improve outcomes after cerebral injury. To determine if these outcomes are dependent on the type and timing of physical rehabilitation and the particular outcome/endpoint being tested, we evaluated the effect of voluntary exercise exposure beginning 24 h after cerebral ischemic injury on behavioral, physiological, and histological outcomes. In an observer-blinded fashion, Sprague-Dawley (300 g) male rats were allocated to three groups [sham-exercise (SHAM), stroke-exercise (SE), stroke-no exercise (SNE)] before a 1-h right middle cerebral artery occlusion (MCAo). Running wheels were used for voluntary exercise. A significant difference was found at 1 week post-infarction between the SNE and SE, with SNE showing worst neurological scores and higher number of foot faults. In addition, nearly 20% more of the SE animals regained their pre-MCAo weight by 7 days. These differences were not as evident at 2 weeks. No differences were found between the three groups in the paw preference test, wheel activity, and body temperature, as well as between SNE and SE with regards to infarct or hemispheric volumes, body weight, synaptophysin staining, and electroencephalography (EEG) testing. Within-group comparisons showed no relationships between infarct volume and foot faults, neurological scores, or exercise level. We conclude that (1) unlike behavioral outcomes, physiological and histological outcomes may not be influenced by the introduction of voluntary exercise once lesion maturation has occurred at 24 h, and (2) repetitive outcomes testing can obscure findings in rat models of cerebral ischemic injury.

Drug-induced hypothermia reduces ischemic damage: effects of the cannabinoid HU-210

BACKGROUND AND PURPOSE

Cannabinoids confer neuroprotection in several experimental paradigms, but the responsible mechanisms remain unknown. Therefore, we sought to examine whether the synthetic CB1 agonist HU-210 is capable of reducing ischemic damage and to determine the mechanisms responsible for such protection.

METHODS

Sprague-Dawley rats underwent permanent middle cerebral artery occlusion (PMCAO). After dose-response and therapeutic time window-finding experiments, the rats were injected with HU-210 (45 microg/kg IV) or vehicle 1 hour after PMCAO. Physiological parameters and cerebral blood flow in the peri-infarct zone were monitored. The animals were examined with a motor disability scale, and the infarct volumes were measured 72 hours later. We also examined the effects of the selective CB1 antagonist SR-141716 and of controlled warming on the neuroprotection conferred by HU-210.

RESULTS

HU-210 reduced blood pressure and heart rate but did not alter the cerebral blood flow in the infarct border zone. Motor disability and infarct volumes were significantly reduced (by up to 77%; P<0.05) in animals treated with HU-210. A single injection of HU-210 significantly lowered the body temperature compared with vehicle as measured both at 1 hour (32.3+/-1.3 degrees C versus 35+/-1.6 degrees C; P=0.0024) and at 24 hours (31.5+/-2.5 degrees C versus 37.25+/-0.3 degrees C; P=0.0031) after PMCAO. The protective effects of HU-210 were partially reversed by pretreatment with SR-141716 but were completely abolished by warming of the animals to the levels observed in controls.

CONCLUSIONS

HU-210 confers robust protection against ischemic damage. This protection is mediated at least in part by binding to CB1 receptors and is also associated with the indirect protective effects of hypothermia.

Experimental models in focal cerebral ischemia: are we there yet?

Therapeutic options available for acute stroke management are sparse and inadequate. Therefore, new insights into stroke pathophysiology leading to new therapeutic targets are needed. In order to attain these goals, adequate animal models for cerebral ischemia are needed. In the following paper the authors will review the various animal models for stroke and emphasize their potential strengths and weaknesses.

Pathological lesions in vascular dementia

According to current diagnostic criteria, a definite diagnosis of vascular dementia (VaD) can be reached on pathological grounds by showing the presence of vascular lesions and the absence of degenerative changes exceeding those expected for age. However, while it is commonly accepted that VaD is a group of heterogeneous entities rather than a process with a unique pathological substrate, the spectrum of vessel and parenchyma changes etiologically associated with the clinical syndrome remains basically unidentified. The review of some recent clinical-pathological series shows that different studies have assessed the presence of dissimilar vascular lesions and that, in many cases, no pathological definition was given. This has hindered the clarification of clinical-pathological correlations in the field of VaD. In this scenario, the use of animal models of cerebrovascular diseases may help to elucidate the type of lesions possibly linked with cognitive impairment in humans and might provide insight into some of the pathophysiological mechanisms of vascular cognitive impairment. A consensus is today needed in order to harmonize the pathological examination of vascular lesions in cases of dementia. An ongoing survey aimed at collecting information about the procedures used in different pathological laboratories in the assessment of lesions possibly associated with dementia is finally presented.

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

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

Effects of neonatal hypoxic-ischemic brain injury on skilled motor tasks and brainstem function in adult rats

In an attempt to establish more sensitive long-term neurofunctional measurements for neonatal hypoxic-ischemic brain injury, we examined skilled motor task and brainstem functions in adult rats after neonatal cerebral hypoxia-ischemia (H-I), using a staircase test and auditory brainstem response (ABR), respectively. Seven-day-old rats underwent a combination of left common carotid artery ligation and exposure to 8% O(2) for 1 h (n=16). The control animals only received sham operation (n=16). At 3 months of age, the staircase test and ABR were performed. In the staircase test, H-I animals showed marked impairment of skilled forelimb use in the side contralateral to the occluded artery, and the degree of brain damage correlated significantly to skilled forelimb use. In the ABR, H-I animals showed brainstem dysfunction assessed by measuring interpeak latencies for waves III-V and I-V. We also examined the brainstem with antibodies specific for activated caspase-3, a protein involved in initiation of apoptosis, and observed that caspase-3 was activated in the ipsilateral inferior colliculus at 24 h after H-I. The present study shows that both the staircase test and ABR are sensitive and objective long-term neurofunctional measurements that can be used in future studies to assess therapeutic intervention in this neonatal cerebral H-I model.

Cognitive and behavioral assessment in experimental stroke research: will it prove useful?

Stroke in humans is associated with deficits in sensorimotor and cognitive function. Consequently, many stroke researchers recently have expanded their techniques to assess cognitive and behavioral correlates of histologically-determined stroke damage in animal models. Although the incorporation of functional outcome assessment represents an important step forward in stroke research, reports of middle cerebral artery occlusion (MCAO) induced behavioral deficits often conflict, and a significant correlation between post-stroke histology and behavior has been reported in few stroke studies. Discrepancies in behavioral outcomes among studies may be due to several factors, such as method of MCAO, duration of occlusion, strain, the timing and method of the behavioral testing and the laboratory environment. Furthermore, proper experimental and control groups, necessary to rule out potential confounding factors during cognitive testing, often are not incorporated. The goal of this review is: (1) to provide a description of the techniques most commonly employed to assess functional outcome after (MCAO) in rodents and (2) to identify potential confounding factors that may interfere with a clear interpretation of the behavioral data.

Neurological sequelae and long-term behavioural assessment of rats with transient middle cerebral artery occlusion

Animal models of stroke, notably transient middle cerebral artery occlusion (MCAo), are used to assess the efficacy of pharmacological and transplant treatments. Long-term studies (>1 month) of the functional effects of treatments in animal models are required to predict treatments likely to improve dysfunctions associated with stroke damage. These pre-clinical studies require (1) optimum post-operative care to ensure long-term survival, (2) methods for assignment of rats to groups with equivalent impairments to reduce variability and enhance detection of treatment effects, and (3) behavioural tests that detect long-term stable deficits. For long-term functional assessment, a battery of behavioural tests sensitive to a range of deficits observed after MCAo was developed. The bilateral asymmetry test evaluated the time course of sensory neglect. Deficits of motor integration were examined in the footfault test, and motor bias was assessed by pharmacological stimulation of rotation. The water maze was used to detect long-term deficits in spatial information processing. Long-term differences between control and MCAo animals in this battery of tests indicate that the protocol provides an efficient assessment suitable for evaluating treatment outcomes in pre-clinical studies of stroke, and that the post-operative care procedure and method of assignment to groups were effective.

Neurological impairment in rats after transient middle cerebral artery occlusion: a comparative study under various treatment paradigms

The assessment of the functional outcome - in addition to the conventional endpoints as histomorphometry of the ischemic brain damage - for the evaluation of cerebroprotective therapies is increasingly recommended, although there is little consensus on appropriate procedures. We evaluated a battery of sensorimotor tasks in rats after transient middle cerebral artery occlusion (MCAO) to select those with the highest potential to discriminate between various degrees of neuronal damage. A total of 40 Sprague-Dawley rats were subjected to 90 min of MCAO and assigned to one of four treatment arms: (1) sham-operated controls, (2) vehicle-treated controls, (3) moderately effective neuroprotection by 2x100 mg/kg alpha-phenyl-N-tert-butyl nitrone (PBN), (4) highly effective neuroprotection by mild hypothermia (33 degrees C). Functional deficits were daily quantified using the beam balance task (1.5 cm, 2.5 cm diameter rectangular and 2.5 cm diameter cylindrical beam), the prehensile traction task, the rotarod, and a six-point neuro-score. Infarction of cerebral cortex and basal ganglia was assessed one week after ischemia. Treatment with PBN significantly reduced cortical infarction (-31%), while treatment with hypothermia resulted in a significantly smaller infarct volume of cortex (-94%) and basal ganglia (-27%). Beam balance, prehensile traction and rotarod failed to demonstrate any difference in motor performance. The six-point neuro-score showed a significant correlation with cortical infarction from day 2 and with total infarct volume from day 3. The smaller the reduction of infarct volume, the later the corresponding difference in neuro-score became apparent. Functional outcome after MCAO in rats can be assessed by a relatively simple measurement of neurological deficit. The slope of functional recovery is closely related with the degree of the morphological, particularly cortical damage. If expected treatment effects are small, an observation period of at least 3 days should be planned for the study design. The functional impairment from focal brain ischemia and its subsequent recovery could provide valuable information for future studies evaluating the neuroprotective potential of novel agents and procedures.

Quantitative measurement of motor and somatosensory impairments after mild (30 min) and severe (2 h) transient middle cerebral artery occlusion in rats

We tested the hypothesis that mild and severe ischemic cell damage are reflected in neurological and functional recovery after stroke. Rats were subjected to either 30 min or 120 min of middle cerebral artery occlusion or sham operation. Neurological and functional tests including, gross neurological score, and rotarod and adhesive removal tests were performed at various time points up to 21 days after stroke. Significant differences between groups of animals were detected using the rotarod and adhesive removal test. A significant correlation between lesion volume and adhesive removal test was detected in rats subjected to 30 min of ischemia. Our data indicate that quantitative rotarod and adhesive removal tests measure different aspects of functional recovery after stroke, and both are useful in characterizing functional recovery from an ischemic insult.

Middle cerebral artery occlusion produces secondary, remote impairment in hippocampal plasticity of rats - involvement of N-methyl-D-aspartate receptors?

There is increasing evidence that focal cerebral ischaemia produces remote functional alterations that may substantially contribute to the post-stroke neurological outcome. Changes initially limited to peri-infarct areas may evolve and spread via transneuronal connections to other structures. In the present study we investigated whether focal ischaemia produced by 2-h occlusion of the middle cerebral artery (MCAo) in SD rats may influence the physiological function of the hippocampus. Three days later in vitro long-term potentiation (LTP) was studied in hippocampal slices from ipsi- and contralateral hemispheres. In rats with MCAo LTP was not-inducible in the ipsilateral hippocampus, while the contralateral side expressed stable potentiation (6.6+/-4.1 vs. 35. 0+/-8.0%, respectively). Treatment with 6-h i.v. infusion of an uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist MRZ 2/579 starting at reperfusion not only preserved but additionally enhanced ipsilateral LTP, while a slight insignificant decrease was observed in the contralateral side (77.0+/-18.4 vs. 20.8+/-6.5%). The study demonstrates post-stroke functional changes in the hippocampus that can be modulated by NMDA receptor antagonists.

Long-term functional end points following middle cerebral artery occlusion in the rat

The purpose of the present study was to assess the magnitude and stability of a number of functional deficits in rats subjected to occlusion of the middle cerebral artery (MCAO). Three groups of rats, treated with 90-min, 120-min, or sham occlusion were used in functional studies for 22 weeks following surgery. The following tests were used: methamphetamine-induced rotation, the staircase test, acquisition of operant responding, running-wheel behavior, and performance of operant differential reinforcement of a low-rate responding (DRL) schedule of reinforcement. Histology performed at 23 weeks following infarct showed on average modest damage of a 19% reduction in hemispheric volume. Of the behavioral tests conducted, rotation, the staircase test, and the operant DRL were sensitive to ischemic damage, and were under some circumstances related to lesion size. These data show that long-term functional deficits following MCAO are demonstrable, and hence, assessment of long-term neuroprotection is feasible.

Transient focal cerebral ischemia induces sensorimotor deficits in mice

Rodents have been extensively used for experimental stroke research with rat and gerbil the preferred species. With the advent of transgenesis and gene targeting the number of mutant mouse strains is rapidly increasing. Thus, mouse models of stroke will be of great importance in the analysis of genetic factors affecting stroke. Demonstrating long-term functional recovery is of paramount importance for the pharmacological evaluation of putative stroke therapies. In the present paper we induce mild focal cerebral ischemia by tandem occlusion of the right middle cerebral artery (MCA), via craniotomy, together with the common carotid artery for 45 min in C57BL/6 strain of mice. The effects of ischemia were evaluated acutely by MRI and long-term (> 3 weeks) sensorimotor functional deficits were analyzed using a number of behavioral paradigms including the rotorod, wire hang, horizontal surface approach, eye-closure reflex, and T-maze tests. Although the induced brain damage is mild we show that it leads to clearly detectable and significant sensorimotor defects associated with fine motor coordination, balance, and postural and sensory reflexes. We conclude that the applied behavioral tests will be useful in the analysis of stroke in mutant mice.

To what extent have functional studies of ischaemia in animals been useful in the assessment of potential neuroprotective agents?

A general consensus is being reached on the use of a combination of mortality and functional end-points in clinical trials of neuroprotective agents. However, to date, few preclinical studies have examined the effects of putative neuroprotective agents on functional outcome after ischaemia. The data described in this review show the importance of combining both histopathological and neurobehavioural studies when evaluating the neuroprotective efficacy of anti-ischaemic agents in animal models of cerebral ischaemia. Here, Jackie Hunter, Ken Mackay and Derek Rogers argue that measures of functional improvement in models of ischaemia should be incorporated to characterize further the neuroprotection afforded by a compound that could aid the selection of doses and end-point measures in early clinical trials.

Correlation between motor impairment and infarct volume after permanent and transient middle cerebral artery occlusion in the rat

BACKGROUND AND PURPOSE

There have been a number of recent reports describing the relationship between ischemic damage and various behavioral and functional measures, although there have been few studies that have demonstrated a direct correlation between functional impairment and lesion volume. The purpose of the present study was to assess functional outcome by measurement of motor impairment and to determine whether this correlated to a range of infarct volumes induced by varying the duration of focal ischemic insult in the rat.

METHODS

Male Sprague Dawley rats were subjected to 0, 30, 60, of 120 minutes or permanent middle cerebral artery (MCA) occlusion by the intraluminal filament technique. Motor impairment was assessed by the accelerating rota-rod and grid-walking tests, and the brains were perfusion-fixed for histological determination of infarct volume and brain swelling 24 hours after MCA occlusion.

RESULTS

Marked impairment in performance of both motor tests was recorded in the 60-minute, 120-minute, and the permanent MCA occlusion groups when compared with sham-operated rats. There were significant correlations between regional infarct volume, brain swelling, and all behavioral measurements (all r2 > .5, P < .001).

CONCLUSIONS

The rota-rod and grid-walking tests of motor performance provide quantitative, objective, and reproducible measures of functional impairment of rats following an ischemic insult. These impairments correlate directly with infarct volume and provide information integral to future studies evaluating the effects of potential neuroprotective agents.

Photothrombotic lesions of the rat cortex impair acquisition of the water maze

Photochemical induction of a thrombosis produces lesions of the cortex of reproducible area and depth, and it has been suggested that this may provide a relatively noninvasive model of the human condition of stroke. The cognitive effects of photothrombotic lesions centred at two different positions were assessed in rats using the Morris water maze test for spatial learning and memory, and it was demonstrated that profound deficits in acquisition of this task were produced by bilateral lesions of the frontal cortex. These effects were in the absence of overt motor deficits, and there was no significant correlation between lesion volume and functional deficits. Flunarizine (2 mg/kg) did not attenuate this ischaemic damage and had no effect on the functional deficits. This model has distinct advantages over more invasive global models of ischaemia and may also provide greater understanding of the functional role of the mammalian neocortex.