Infarct volume varies with rat strain and vendor in focal cerebral ischemia induced by transcranial middle cerebral artery occlusion

Magnetic Resonance Imaging and Gait Analysis Indicate Similar Outcomes Between Yucatan and Landrace Porcine Ischemic Stroke Models

The Stroke Therapy Academic Industry Roundtable (STAIR) has recommended that novel therapeutics be tested in a large animal model with similar anatomy and physiology to humans. The pig is an attractive model due to similarities in brain size, organization, and composition relative to humans. However, multiple pig breeds have been used to study ischemic stroke with potentially differing cerebral anatomy, architecture and, consequently, ischemic stroke pathologies. The objective of this study was to characterize brain anatomy and assess spatiotemporal gait parameters in Yucatan (YC) and Landrace (LR) pigs pre- and post-stroke using magnetic resonance imaging (MRI) and gait analysis, respectively. Ischemic stroke was induced via permanent middle cerebral artery occlusion (MCAO). MRI was performed pre-stroke and 1-day post-stroke. Structural and diffusion-tensor sequences were performed at both timepoints and analyzed for cerebral characteristics, lesion diffusivity, and white matter changes. Spatiotemporal and relative pressure gait measurements were collected pre- and 2-days post-stroke to characterize and compare acute functional deficits. The results from this study demonstrated that YC and LR pigs exhibit differences in gross brain anatomy and gait patterns pre-stroke with MRI and gait analysis showing statistical differences in the majority of parameters. However, stroke pathologies in YC and LR pigs were highly comparable post-stroke for most evaluated MRI parameters, including lesion volume and diffusivity, hemisphere swelling, ventricle compression, caudal transtentorial and foramen magnum herniation, showing no statistical difference between the breeds. In addition, post-stroke changes in velocity, cycle time, swing percent, cadence, and mean hoof pressure showed no statistical difference between the breeds. These results indicate significant differences between pig breeds in brain size, anatomy, and motor function pre-stroke, yet both demonstrate comparable brain pathophysiology and motor outcomes post-stroke. The conclusions of this study suggest pigs of these different breeds generally show a similar ischemic stroke response and findings can be compared across porcine stroke studies that use different breeds.

Hypothermia revisited: Impact of ischaemic duration and between experiment variability

To assess the true effect of novel therapies for ischaemic stroke, a positive control that can validate the experimental model and design is vital. Hypothermia may be a good candidate for such a positive control, given the convincing body of evidence from animal models of ischaemic stroke. Taking conditions under which substantial efficacy had been seen in a meta-analysis of hypothermia for focal ischaemia in animal models, we undertook three randomised and blinded studies examining the effect of hypothermia induced immediately following the onset of middle cerebral artery occlusion on infarct volume in rats (n = 15, 23, 264). Hypothermia to a depth of 33℃ and maintained for 130 min significantly reduced infarct volume compared to normothermia treatment (by 27-63%) and depended on ischaemic duration (F(3,244) = 21.242, p < 0.05). However, the protective effect varied across experiments with differences in both the size of the infarct observed in normothermic controls and the time to reach target temperature. Our results highlight the need for sample size and power calculations to take into account variations between individual experiments requiring induction of focal ischaemia.

Strain-Related Differences in the Immune Response: Relevance to Human Stroke

There are significant differences in the immune response and in the susceptibility to autoimmune diseases among rodent strains. It would thus be expected that the contribution of the immune response to cerebral ischemic injury would also differ among rodent strains. More importantly, there are significant differences between the immune responses of rodents and humans. All of these factors are likely to impact the successful translation of immunomodulatory therapies from experimental rodent models to patients with stroke.

The Effects of Exercise on Cognitive Recovery after Acquired Brain Injury in Animal Models: A Systematic Review

The objective of the present paper is to review the current status of exercise as a tool to promote cognitive rehabilitation after acquired brain injury (ABI) in animal model-based research. Searches were conducted on the PubMed, Scopus, and psycINFO databases in February 2014. Search strings used were: exercise (and) animal model (or) rodent (or) rat (and) traumatic brain injury (or) cerebral ischemia (or) brain irradiation. Studies were selected if they were (1) in English, (2) used adult animals subjected to acquired brain injury, (3) used exercise as an intervention tool after inflicted injury, (4) used exercise paradigms demanding movement of all extremities, (5) had exercise intervention effects that could be distinguished from other potential intervention effects, and (6) contained at least one measure of cognitive and/or emotional function. Out of 2308 hits, 22 publications fulfilled the criteria. The studies were examined relative to cognitive effects associated with three themes: exercise type (forced or voluntary), timing of exercise (early or late), and dose-related factors (intensity, duration, etc.). The studies indicate that exercise in many cases can promote cognitive recovery after brain injury. However, the optimal parameters to ensure cognitive rehabilitation efficacy still elude us, due to considerable methodological variations between studies.

Animal models of ischemic stroke and their application in clinical research

This review outlines the most frequently used rodent stroke models and discusses their strengths and shortcomings. Mimicking all aspects of human stroke in one animal model is not feasible because ischemic stroke in humans is a heterogeneous disorder with a complex pathophysiology. The transient or permanent middle cerebral artery occlusion (MCAo) model is one of the models that most closely simulate human ischemic stroke. Furthermore, this model is characterized by reliable and well-reproducible infarcts. Therefore, the MCAo model has been involved in the majority of studies that address pathophysiological processes or neuroprotective agents. Another model uses thromboembolic clots and thus is more convenient for investigating thrombolytic agents and pathophysiological processes after thrombolysis. However, for many reasons, preclinical stroke research has a low translational success rate. One factor might be the choice of stroke model. Whereas the therapeutic responsiveness of permanent focal stroke in humans declines significantly within 3 hours after stroke onset, the therapeutic window in animal models with prompt reperfusion is up to 12 hours, resulting in a much longer action time of the investigated agent. Another major problem of animal stroke models is that studies are mostly conducted in young animals without any comorbidity. These models differ from human stroke, which particularly affects elderly people who have various cerebrovascular risk factors. Choosing the most appropriate stroke model and optimizing the study design of preclinical trials might increase the translational potential of animal stroke models.

Variation in behavioral deficits and patterns of recovery after stroke among different rat strains

Pre-clinical models of stroke therapeutics depend upon the ability to detect differences in infarct volume as well as in the short- and long-term outcomes of treated animals. Little attention has been paid to interstrain differences in these outcomes and the importance of defining the most appropriate behavioral tests. In this study, we evaluate long-term outcome from stroke in three different rat strains. Lewis, Wistar, and Sprague Dawley (SD) rats were subjected to 2-h middle cerebral artery occlusion and survived for up to 49 days. Behavioral tests were performed weekly. There was continuous assessment of rotational/circling activity in the home cage by use of an automated software program. A separate group of animals was sacrificed at 24 h to determine infarct volume. Infarct volume was similar in all three strains. Mortality was significantly higher in SD rats (P < 0.001). Rotational/circling activity at 24 h was correlated with cortical infarct volume in Wistar and SD rats (ρ = 0.67, P = 0.04 and ρ = 0.72, P = 0.01, respectively). Wistar and SD rats displayed more rotational/circling activity following stroke than Lewis rats, but Lewis rats evidenced more impairment on complex motor tasks like the rotarod. Further, computer automated analysis of rotational activity was more sensitive than subjective assessment, with SD rats showing a preference for clockwise rotations to 49 days after stroke despite normalization of the neurological score after 21 days. There are significant interstrain differences in survival and in the patterns of neurological impairment and recovery after stroke. These differences must be taken into account in pre-clinical studies, but may also be capitalized upon to understand genetic contributions to injury. Finally, computerized assessment of behavior is more sensitive than subjective assessment for detecting behavioral changes.

Short-duration hypothermia after ischemic stroke prevents delayed intracranial pressure rise

BACKGROUND

Intracranial pressure elevation, peaking three to seven post-stroke is well recognized following large strokes. Data following small-moderate stroke are limited. Therapeutic hypothermia improves outcome after cardiac arrest, is strongly neuroprotective in experimental stroke, and is under clinical trial in stroke. Hypothermia lowers elevated intracranial pressure; however, rebound intracranial pressure elevation and neurological deterioration may occur during rewarming.

HYPOTHESES

(1) Intracranial pressure increases 24 h after moderate and small strokes. (2) Short-duration hypothermia-rewarming, instituted before intracranial pressure elevation, prevents this 24 h intracranial pressure elevation.

METHODS

Long-Evans rats with two hour middle cerebral artery occlusion or outbred Wistar rats with three hour middle cerebral artery occlusion had intracranial pressure measured at baseline and 24 h. Wistars were randomized to 2·5 h hypothermia (32·5°C) or normothermia, commencing 1 h after stroke.

RESULTS

In Long-Evans rats (n = 5), intracranial pressure increased from 10·9 ± 4·6 mmHg at baseline to 32·4 ± 11·4 mmHg at 24 h, infarct volume was 84·3 ± 15·9 mm(3) . In normothermic Wistars (n = 10), intracranial pressure increased from 6·7 ± 2·3 mmHg to 31·6 ± 9·3 mmHg, infarct volume was 31·3 ± 18·4 mm(3) . In hypothermia-treated Wistars (n = 10), 24 h intracranial pressure did not increase (7·0 ± 2·8 mmHg, P < 0·001 vs. normothermia), and infarct volume was smaller (15·4 ± 11·8 mm(3) , P < 0·05).

CONCLUSIONS

We saw major intracranial pressure elevation 24 h after stroke in two rat strains, even after small strokes. Short-duration hypothermia prevented the intracranial pressure rise, an effect sustained for at least 18 h after rewarming. The findings have potentially important implications for design of future clinical trials.

The intraluminal thread model revisited: rat strain differences in local cerebral blood flow

There are major differences in the outcome of focal cerebral ischemia between rat strains. This study aimed to investigate whether inter-strain differences exist in the local cerebral blood flow, changes produced by intraluminal middle cerebral artery occlusion (MCAO). Fifty-four male Long-Evans, Sprague-Dawley or Wistar rats were subjected to 60 minutes of transient MCAO, carried out with a silicone-coated 4-0 nylon monofilament. Local cerebral blood flow was monitored on the parietal cortex with laser-Doppler flowmetry. The decrease in local cerebral blood flow during the first 20 minutes of occlusion was significantly greater in Long-Evans (74.6 +/- 8.9%) than in Sprague-Dawley (50.7 +/- 26.8%) and Wistar (49.0 +/- 21.9%) rats. Strain differences in local cerebral blood flow reduction were maintained, or increased, throughout the occlusion period. These results show that the intraluminal model of MCAO produces a more pronounced, persistent and stable local cerebral blood flow reduction, with less interanimal variability, in Long-Evans than in Sprague-Dawley or Wistar rats.

Modified permanent middle cerebral artery occlusion rat model aiming to reduce variability in infarct size

In animal cerebral infarct experiments, the most important aspect is to produce consistent infarct size and localization. In an attempt to improve the conventional middle cerebral artery (MCA) coagulation technique, we developed a new animal model using a microclip to reduce variability in infarct size. Male Sprague-Dawley rats were subjected to right MCA occlusion. The animals were divided into two groups; conventional MCA occlusion group (Group 1; n = 9) and modified clip occlusion group (Group 2; n = 9). In Group 2, the proximal portion of MCA was occluded by applying a small clip just proximal to the olfactory nerve, and the MCA from the clipped position to the position just proximal to the level of the inferior cerebral vein was electrocoagulated using a bipolar diathermy in the same manner as in Group 1. In other words, the only difference between these two groups was the manner of occlusion of the most proximal portion of the MCA. Rats were killed 24 hours after the stroke-inducing surgery, and infarct volume was determined by an image analysis program following staining with 2,3,5-triphenyltetrazolium chloride. The cortical infarct volumes were 51.0 +/- 13.8% in Group 1 and 46.3 +/- 6.2% in Group 2. The scattering of cortical infarct volume was significantly small in Group 2 (p=0.0176). The differences in scattering of striatal and total infarct volumes did not reach statistical significance. The present results demonstrated that the new MCA occlusion model using a clip significantly reduces the variability in cortical infarct volume, solving the problems of the model using coagulation alone. That permanent MCA occlusion model using a clip is an excellent method that produces more consistent and reproducible infarction.

Fundamental interstrain differences in cortical activity between Wistar and Sprague-Dawley rats during global ischemia

Four-vessel occlusion (4VO), a frequently used model of global cerebral ischemia in rats, results in a dysfunction in wide brain areas, including the cerebral cortex and hippocampus. However, there are pronounced differences in response to global ischemia between the laboratory rat strains used in these studies. In the present work, the immediate acute effects of 4VO-induced global ischemia on the spontaneous electrocorticogram (ECoG) signals were analyzed in Wistar and Sprague-Dawley rats. The ECoG was isoelectric during the 10 min of global cerebral ischemia in Wistar rats and the first burst (FB) was seen 10-13 min after the start of reperfusion. In Sprague-Dawley rats, the FB was detected immediately after the start of 4VO or a few seconds later. The burst suppression ratio (BSR) in Wistar rats decreased to 45% in 5 min after FB, and after 25 min it was approximately 40%. In Sprague-Dawley rats, the BSR was 55% immediately after the FB and it decreased steeply to reach 0% by 10 min. There was also a significant difference between the two strains in the frequency composition of the ECoG pattern. The power spectral densities of the two strains differed virtually throughout the post-ischemic state. The histological results (Evans Blue, Cresyl Violet and Fluoro Jade C stainings) supplemented the electrophysiological data: the neuronal damage in the CA1 pyramids in Wistar rats was severe, whereas in the Sprague-Dawley animals it was only partial. These observations clearly demonstrate that the use of different rat strains (e.g. Wistar vs. Sprague-Dawley) can be a source of considerable variability in the results of acute experiments on global ischemia and it is important that the laboratory rats used in such experiments should be carefully chosen.

Peri-infarct flow transients predict outcome in rat focal brain ischemia

Spreading depolarizations are accompanied by transient changes in cerebral blood flow (CBF). In a post hoc analysis of previously studied control rats we analyzed CBF time courses after middle cerebral artery occlusion in the rat in order to test whether intra-ischemic flow, reperfusion, and different parameters of peri-infarct flow transients (PIFTs) (amplitude, number) can predict outcome. Sprague-Dawley rats anesthetized with either halothane (n=23) or isoflurane (n=32) underwent 90-min filament occlusion of the middle cerebral artery followed by 72 h of reperfusion. The infarct size was determined by 2,3,5-triphenyltetrazolium chloride staining. Relative CBF changes were monitored by laser Doppler flowmetry at 4-5 mm lateral, and 1-2mm posterior to Bregma. An additional filament occlusion study (n=12) was performed to validate that PIFTs were coupled to direct current shifts of spreading depolarization. The PIFT-direct current shift study revealed that every PIFT was associated with a negative direct current shift typical of spreading depolarization. Post-hoc analysis showed that the number of PIFTs, especially with the combination of intra-ischemic level of flow, can predict the development of cortical infarcts. These findings show that PIFTs can serve as an early biomarker in predicting outcome in preclinical animal studies.

RODENT STROKE MODEL GUIDELINES FOR PRECLINICAL STROKE TRIALS (1ST EDITION)

Translational stroke research is a challenging task that needs long term team work of the stroke research community. Highly reproducible stroke models with excellent outcome consistence are essential for obtaining useful data from preclinical stroke trials as well as for improving inter-lab comparability. However, our review of literature shows that the infarct variation coefficient of commonly performed stroke models ranges from 5% to 200%. An overall improvement of the commonly used stroke models will further improve the quality for experimental stroke research as well as inter-lab comparability. Many factors play a significant role in causing outcome variation; however, they have not yet been adequately addressed in the Stroke Therapy Academic Industry Roundtable (STAIR) recommendations and the Good Laboratory Practice (GLP). These critical factors include selection of anesthetics, maintenance of animal physiological environment, stroke outcome observation, and model specific factors that affect success rate and variation. The authors have reviewed these major factors that have been reported to influence stroke model outcome, herewith, provide the first edition of stroke model guidelines so to initiate active discussion on this topic. We hope to reach a general agreement among stroke researchers in the near future with its successive updated versions.

A re-assessment of erythropoietin as a neuroprotective agent following rat spinal cord compression or contusion injury

This study was initiated due to an NIH "Facilities of Research--Spinal Cord Injury" contract to support independent replication of published studies that appear promising for eventual clinical testing. We repeated a study reporting the beneficial effects of recombinant human erythropoietin (rhEPO) treatment after spinal cord injury (SCI). Moderate thoracic SCI was produced by two methods: 1) compression due to placement of a modified aneurysm clip (20 g, 10 s) at the T3 spinal segment (n=45) [followed by administration of rhEPO 1000 IU/kg/IP in 1 or 3 doses (treatment groups)] and 2) contusion by means of the MASCIS impactor (n = 42) at spinal T9 (height 12.5 cm, weight 10 g) [followed by the administration of rhEPO 5000 IU/kg/IP for 7d or single dose (treatment groups)]. The use of rhEPO following moderate compressive or contusive injury of the thoracic spinal cord did not improve the locomotor behavior (BBB rating scale). Also, secondary changes (i.e. necrotic changes followed by cavitation) were not significantly improved with rhEPO therapy. With these results, although we cannot conclude that there will be no beneficial effect in different SCI models, we caution researchers that the use of rhEPO requires further investigation before implementing clinical trials.

Modern anesthesia and peroperative monitoring methods reduce per- and postoperative mortality during transient occlusion of the middle cerebral artery in rats

Mortality and morbidity during and after occlusion of the middle cerebral artery in rats are important confounding factors which may be minimized by improved anesthesia and peroperative monitoring techniques. We describe state of the art techniques for inducing anesthesia, endotracheal intubation, ventilation and monitoring peroperatively in this context. Introducing the subtemporal approach of Tamura et al. in our laboratory 5 years ago, we experienced 25% peroperative and 24 h postoperative rat mortality when performing temporary clipping of the middle cerebral artery. This prompted us to abandon intraperitoneal anesthesia by chloral hydrate and ventilation by tracheotomy in favor of endotracheal intubation and isoflurane anesthesia (1% isoflurane in 30%:70% O(2)/N(2)O). These anesthetic techniques in combination with improved surgical skills have reduced our initial 25% peroperative- and 24 h postoperative mortality to 2.7% (1.8% peroperatively and 0.9% 24 h postoperatively). Furthermore, the following 14 days postoperative mortality rate was 1.8%. A total number of 203 rats have been operated with this method in different studies where a focal reperfusion stroke model combined with extended periods of observations were the cornerstone.

SM-31900, a novel NMDA receptor glycine-binding site antagonist, reduces infarct volume induced by permanent middle cerebral artery occlusion in spontaneously hypertensive rats

The purpose of this study was to investigate the effect of (3S)-7-chloro-3-[2-((1R)-1-carboxyethoxy)-4-aminomethylphenyl]aminocarbonylmethyl-1,3,4,5-tetrahydrobenz[c,d]indole-2-carboxylic acid hydrochloride (SM-31900), an antagonist with high selectivity and affinity for the NMDA receptor glycine-binding site, on the cerebral infarct volume in a permanent middle cerebral artery occlusion (MCAo) model, which was constructed by electrocoagulation of a unilateral middle cerebral artery distal to the olfactory tract using spontaneously hypertensive rats (SHRs). To investigate the dose-response characteristics and the therapeutic time window of SM-31900 in this MCAo model, we conducted three experiments, in which the administration of SM-31900 was started 5min (experiment I), 30min (experiment II), or 60min (experiment III) after MCAo, respectively. In all the studies, SM-31900 was administered by intravenous bolus injection followed by continuous intravenous infusion to obtain a steady-state level of this compound in blood immediately after its administration. The treatment with SM-31900 was continued until 24h after MCAo, at which time the cerebral infarct volume was measured. In experiment I, SM-31900 significantly reduced the infarct volume by 37% at a dosage of 0.38mg/kg bolus followed by 1.5mg/kg/h continuous infusion (0.38mg/kg+1.5mg/kg/h). In experiment II, the neuroprotective effect of SM-31900 was also significant, with a 25% reduction in infarct volume at a dosage of 0.38mg/kg+1.5mg/kg/h, and a 40% reduction at 1.5mg/kg+6.0mg/kg/h. Furthermore, even in experiment III, SM-31900 exerted a significant neuroprotective effect, with a 20% reduction at 1.5mg/kg+6.0mg/kg/h. These studies revealed that SM-31900 can exert a neuroprotective effect when it is administered up to at least 60min after the onset of ischemia in the MCAo model, an animal model of stroke, indicating that SM-31900 is a good candidate for treating acute brain ischemia.

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.

Confounding factors in toxicity testing

The necessity for understanding normal human functions and the mechanisms which underlie dysfunction in these processes is essential in the promotion of a healthier lifestyle. To achieve this goal utilization of a suitable animal model is necessary in order to develop new pharmaceutical agents to alleviate diseases or chemicals to enhance the quality of life. It is incumbent upon investigators to choose a species in which pharmacokinetic principles are established and it is important that these phenomena resemble those of the humans. The choice of rats has specific advantages in that these rodents possess similar pharmacodynamic parameters to humans. Other advantages include availability, low cost, ease of breeding, and an extensive literature data-base to enable comparisons to present findings. However, in the interpretation of data from animals to humans, there are factors which need to be recognized as playing important roles in chemical-induced outcomes. The confounding factors include strain, supplier, age, gender, hormonal status and dietary intake. The aim of this article is to demonstrate that there are differences in the responsiveness of rat stock/strains to chemicals and that lack of consideration of confounding factors yields inappropriate conclusions regarding risk assessment for humans.

Neuroprotection by LY341122, a novel inhibitor of lipid peroxidation, against focal ischemic brain damage in rats

LY341122 (2-(3, 5-di-t-butyl-4-hydroxyphenyl)-4-(2-(4-methylethylaminomethyl-ph enylox y)ethyl)oxazole) is a potent inhibitor of lipid peroxidation which has been shown to protect against global ischemia and traumatic brain injury in rats. The purpose of this study was to examine the effect of LY341122 on ischemic injury in a highly reproducible model of focal cerebral ischemia in rats. Male Sprague-Dawley rats were anesthetized with halothane and subjected to 120 min of temporary middle cerebral artery occlusion by retrograde insertion of an intraluminal nylon suture coated with poly-L-lysine. The drug (LY341122, n=19) or vehicle (phosphate-buffered saline (PBS), n=10) was administered i.v. (as a 5 or 10 mg/kg bolus followed by a 5 or 10 mg/kg/h infusion for 20 h, respectively, starting 1 or 2 h after the onset of middle cerebral artery occlusion). Neurological status was evaluated during middle cerebral artery occlusion (60 min) and daily for 3 days thereafter. Three days after ischemia, brains were perfusion-fixed and infarct volumes and brain edema were determined. LY341122 significantly improved the neurological score compared to vehicle at 24, 48 and 72 h after middle cerebral artery occlusion. Treatment with LY341122 significantly reduced total infarct volume in all treated groups compared to vehicle rats. Cortical infarct volume was significantly reduced by LY341122 treatment in the 10 mg/kg (1 h) and LY341122 10 mg/kg (2 h) groups compared to vehicle rats (14.7+/-9.5 vs. 106.8+/-20.9 mm(3), and 36.9+/-20.1 vs. 106. 8+/-20.9 mm(3), respectively (mean+/-S.E.M.)). Striatal infarct volume was also significantly reduced by treatment with LY341122 in the 10 mg/kg (1 h) group compared to vehicle (23.7+/-3.4 vs. 68. 2+/-6.7 mm(3)). These results demonstrate the neuroprotective efficacy of LY341122 in focal cerebral ischemia.

Strain-related brain injury in neonatal mice subjected to hypoxia-ischemia

The development of transgenic mice has led to an increase in the use of mice as models for human disease. We hypothesized that the degree of brain damage sustained by animals in a neonatal mouse model of hypoxia-ischemia depends on the strain used. We compared three strains of mice commonly used to generate transgenic strains (C57Bl/6, 129Sv and CD1), as well as three hybrids of these strains (C57Bl/6x129Sv, CD1xC57Bl/6, and CD1x129Sv). At postnatal day 7 (P7), pups were subjected to a modified Vannucci procedure for hypoxia-ischemia as follows: permanent ligation of right common carotid artery under halothane anesthesia, 2-h recovery period, exposure to 8% oxygen at 37 degreesC for varying durations (30, 60 or 90 min). After 5 days, animals were perfused with 4% paraformaldehyde, brains were removed, postfixed and examined histologically with cresyl violet and Perl's iron stain to assess the degree of damage. Damage was assessed blindly using a score ranging from 0 (none) to 3 (infarct) in eight regions (ant-, mid-, and post- cortex, CA1, CA2, CA3 and dentate gyrus of the hippocampus, and striatum). We found significant differences in susceptibility to brain damage and mortality depending on the strain used. While determining the maximal degree of injury with the least amount of mortality for each strain, it was found that some strains (CD1) are particularly susceptible to brain damage in this model, while others (129Sv) are resistant.

Neuroprotective activity of a new class of steroidal inhibitors of the N-methyl-D-aspartate receptor

Release of the excitatory neurotransmitter glutamate and the excessive stimulation of N-methyl-D-aspartate (NMDA)-type glutamate receptors is thought to be responsible for much of the neuronal death that occurs following focal hypoxia-ischemia in the central nervous system. Our laboratory has identified endogenous sulfated steroids that potentiate or inhibit NMDA-induced currents. Here we report that 3alpha-ol-5beta-pregnan-20-one hemisuccinate (3alpha5betaHS), a synthetic homologue of naturally occurring pregnanolone sulfate, inhibits NMDA-induced currents and cell death in primary cultures of rat hippocampal neurons. 3alpha5betaHS exhibits sedative, anticonvulsant, and analgesic properties consistent with an action at NMDA-type glutamate receptors. Intravenous administration of 3alpha5betaHS to rats (at a nonsedating dose) following focal cerebral ischemia induced by middle cerebral artery occlusion significantly reduces cortical and subcortical infarct size. The in vitro and in vivo neuroprotective effects of 3alpha5betaHS demonstrate that this steroid represents a new class of potentially useful therapeutic agents for the treatment of stroke and certain neurodegenerative diseases that involve over activation of NMDA receptors.

Rat strain and vendor differences in collateral anastomoses

Recently we observed inter- and intrastrain differences in cortical infarct volumes after middle cerebral artery (MCA) occlusion. Variations in the anastomoses providing collateral blood supply could account for different lesion sizes. Our objectives were to compare number and internal diameters of the MCA-anterior cerebral artery (MCA-ACA) anastomoses and to determine if the lesion extended beyond branches of the MCA territory into the field of the ACA in the rat strains/lines. Sprague-Dawley rats and Wistar rats from Simonsen Laboratories (SLSD and SLWIS) and Sprague-Dawley rats from Taconic Laboratories (TLSD) and Charles River Laboratories (CRSD) were anesthetized and injected with papaverine and Vultex (white latex) for arterial visualization. Some rats were also subjected to MCA occlusion. Significantly fewer anastomoses were present in SLSD and SLWIS than in CRSD and TLSD (p < 0.05). The mean internal diameters of the anastomoses were not significantly different between the strains/lines (p < 0.05). After MCA occlusion, significantly more (p < 0.05) TLSD and CRSD than SLSD had lesions extending from the MCA field beneath the anastomoses and into the region supplied by the ACA. Neither the number, luminal diameter, nor density of MCA-ACA anastomoses appears to be the limiting factor that differentiates lesion size following MCA occlusion in these particular rat strains/lines. Therefore, factors other than anatomical variations probably account for different lesion sizes.

Sensorimotor impairments in rats with cerebral infarction, induced by unilateral occlusion of the left middle cerebral artery: strain differences and effects of the occlusion site

Enormous differences exist between rat strains with respect to the infarct volume induced by unilateral middle cerebral artery (MCA) occlusion. We performed three experiments to address the following questions. Firstly, whether the pattern of MCA-occlusion (MCA-O) induced sensorimotor impairments in rats are strain dependent; secondly, whether proximal (i.e., close to its origin) and distal occlusions (above the lenticulostriate branch) of the MCA affect infarct volume and the behavioral impairments to a different extent; and thirdly, whether there is a relationship between the infarct volume and behavioral deficits. We found that the pattern of sensorimotor malfunctions induced by proximal unilateral MCA-O were highly strain dependent. Of the eight strains tested, Winkelmann-Wistar rats, Spontaneously Hypertensive Stroke-Prone rats, and Wistar-Kyoto rats were most severely affected. By contrast, Brown-Norway rats showed only mild behavioral deficits after the MCA-O. The second experiment confirmed that proximal occlusions induced slightly more behavioral malfunctions than distal occlusions did. Histological evaluation of the brain damage caused by proximal and distal MCA-O, confirmed that distal MCA-O damaged nearly exclusively cortical areas, and spared the caudate/putamen. An exploratory analysis of the relationship between infarct volume and behavioral deficits did not indicate that the severity of sensorimotor malfunctions can be predicted from the size of the infarct.

The neuroprotective efficacy of MK-801 in focal cerebral ischemia varies with rat strain and vendor

The present study was designed to evaluate whether the neuroprotective efficacy of MK-801 in focal cerebral ischemia was dependent on strain and/or vendor differences. MK-801 (0.12 mg/kg i.v. bolus followed by 0.108 mg/kg/h infusion or 0.60 mg/kg i.v. bolus followed by 0.540 mg/kg/h infusion) or saline was administered just after intraluminal middle cerebral artery occlusion. Administration of 0.540 mg/kg/h MK-801 provided strain/line-dependent neuroprotection in the following rank order: Simonsen Laboratories Sprague-Dawley rats > Simonsen Laboratories Wistar rats > Taconic Laboratories Sprague-Dawley rats. After 0.108 mg/kg/h MK-801 treatment, Simonsen Laboratories Wistar rats were the only strain/line that were significantly neuroprotected. These results indicate that the neuroprotective effect of an experimental drug may be influenced by rat strain and vendor differences.