Criteria for valid preclinical trials using animal stroke models

Establishment of a novel protocol for assessing the severity of subarachnoid hemorrhage in circle Willis perforation mouse model

The Circle of Willis perforation (cWp) mouse model is a key tool in subarachnoid hemorrhage (SAH) research; however, inconsistent bleeding volumes can challenge experimental reliability. To address this issue, we introduced the ROB Scoring System, a novel protocol integrating Rotarod Tests (RT), Open-field Tests (OT) video analysis, and daily Body Weight Loss (BWL) monitoring to precisely categorize SAH severity. Forty C57BL/6 mice underwent cWp SAH induction, categorized by ROB into severity subgroups (severe, moderate, mild). Validation compared ROB trends in subgroups, and ROB outcomes with autopsy results on postoperative days three and seven for acute and sub-acute evaluations. Mortality rates were analyzed via the survival log-rank test, revealing a significant difference among SAH subgroups (P < 0.05). Strong correlations between ROB grades and autopsy findings underscored its precision. Notably, the severe group exhibited 100% mortality within 4 days post SAH onset. Single parameters (RT, OT, BWL) were insufficient for distinguishing SAH severity levels. The ROB score represents a significant advancement, offering an objective method for precise categorization and addressing inherent bleeding variations in the cWp SAH model. This standardized protocol enhances the reliability and effectiveness of the SAH translational research, providing a valuable tool for future investigations into this critical area.

Environmental enrichment and cerebrolysin improve motor and cognitive performance in a rat model of stroke, in conjunction with an increase in hippocampal AMPA but not NMDA receptor subunits

Stroke is a pathology related to the vascular system in the brain and it is one of the main causes of disability, representing a burden on public health. This lesion provokes a disorganization of sensory-motor and cognitive systems, the latter associated with hippocampal activity, a structure in which α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and NMDA N-methyl-D-aspartate (NMDA) receptors are important for the integration of information. Several molecules have been studied for their capacity to enhance recovery from a stroke, including cerebrolysin that could potentially be reinforced by environmental enrichment. Here, stroke was induced in 40 male rats and 24 h later, they were administered cerebrolysin (2.5 ml/kg), put in an environmentally enriched arena or given both treatments, for 10 days. Subsequently, motor functioning was assessed with the Bederson test and the cognitive domain was assessed through novel object recognition. Hematoxylin/eosin staining was then used to assess the infarct size, and AMPA-GRIA1 and NMDA-R1 subunits in the hippocampus were measured by ELISA. In motor and cognitive performance, the administration of cerebrolysin and environmental enrichment enhanced recovery. Moreover, the infarct size decreased in all the groups that received a treatment, but an increase occurred in AMPA-GRIA1 only in experimental group regarding to control group, while NMDA-R1 had no differences. These results suggest that cerebrolysin and environmental enrichment could act in synergy to recover after a stroke, leading to a smaller infarct area and the presence of more AMPA-GRIA1 subunits in the hippocampus of experimental group. These data encourage further studies in which neurorehabilitation approaches can be combined with cerebrolysin administration to treat the motor and cognitive symptoms of stroke.

Systematic review of guidelines for internal validity in the design, conduct and analysis of preclinical biomedical experiments involving laboratory animals

Over the last two decades, awareness of the negative repercussions of flaws in the planning, conduct and reporting of preclinical research involving experimental animals has been growing. Several initiatives have set out to increase transparency and internal validity of preclinical studies, mostly publishing expert consensus and experience. While many of the points raised in these various guidelines are identical or similar, they differ in detail and rigour. Most of them focus on reporting, only few of them cover the planning and conduct of studies. The aim of this systematic review is to identify existing experimental design, conduct, analysis and reporting guidelines relating to preclinical animal research. A systematic search in PubMed, Embase and Web of Science retrieved 13 863 unique results. After screening these on title and abstract, 613 papers entered the full-text assessment stage, from which 60 papers were retained. From these, we extracted unique 58 recommendations on the planning, conduct and reporting of preclinical animal studies. Sample size calculations, adequate statistical methods, concealed and randomised allocation of animals to treatment, blinded outcome assessment and recording of animal flow through the experiment were recommended in more than half of the publications. While we consider these recommendations to be valuable, there is a striking lack of experimental evidence on their importance and relative effect on experiments and effect sizes.

Are researchers moving away from animal models as a result of poor clinical translation in the field of stroke? An analysis of opinion papers

Objectives

Despite decades of research using animals to develop pharmaceutical treatments for patients who have had a stroke, few therapeutic options exist. The vast majority of interventions successful in preclinical animal studies have turned out to have no efficacy in humans or to be harmful to humans. In view of this, we explore whether there is evidence of a move away from animal models in this field.

Methods

We used an innovative methodology, the analysis of opinion papers. Although we took a systematic approach to literature searching and data extraction, this is not a systematic review because the study involves the synthesis of opinions, not research evidence. Data were extracted from retrieved papers in chronological order and analysed qualitatively and descriptively.

Results

Eighty eligible papers, published between 1979 and 2018, were identified. Most authors were from academic departments of neurology, neuroscience or stroke research. Authors agreed that translational stroke research was in crisis. They held diverse views about the causes of this crisis, most of which did not fundamentally challenge the use of animal models. Some, however, attributed the translational crisis to animal–human species differences and one to a lack of human in vitro models. Most of the proposed solutions involved fine-tuning animal models, but authors disagreed about whether such modifications would improve translation. A minority suggested using human in vitro methods alongside animal models. One proposed focusing only on human in vitro methods.

Conclusion

Despite recognising that animal models have been unsuccessful in the field of stroke, most researchers exhibited a strong resistance to relinquishing them. Nevertheless, there is an emerging challenge to the use of animal models, in the form of human-focused in vitro approaches. For the sake of stroke patients there is an urgent need to revitalise translational stroke research and explore the evidence for these new approaches.

Building Robustness into Translational Research

Nonclinical studies form the basis for the decision whether to take a therapeutic candidate into the clinic. These studies need to exhibit translational robustness for both ethical and economic reasons. Key findings confirmed in multiple species have a greater chance to also occur in humans. Given the heterogeneity of patient populations, preclinical studies or at least programs comprising multiple studies need to reflect such heterogeneity, e.g., regarding strains, sex, age, and comorbidities of experimental animals. However, introducing such heterogeneity requires larger studies/programs to maintain statistical power in the face of greater variability. In addition to classic sources of bias, e.g., related to lack of randomization and concealment, translational studies face specific sources of potential bias such as that introduced by a model that may not reflect the full spectrum of underlying pathophysiology in patients, that defined by timing of treatment, or that implied in dosing decisions and interspecies differences in pharmacokinetic profiles. The balance of all these factors needs to be considered carefully for each study and program.

Instruments for assessing risk of bias and other methodological criteria of published animal studies: a systematic review

BACKGROUND

Results from animal toxicology studies are critical to evaluating the potential harm from exposure to environmental chemicals or the safety of drugs prior to human testing. However, there is significant debate about how to evaluate the methodology and potential biases of the animal studies. There is no agreed-upon approach, and a systematic evaluation of current best practices is lacking.

OBJECTIVE

We performed a systematic review to identify and evaluate instruments for assessing the risk of bias and/or other methodological criteria of animal studies.

METHOD

We searched Medline (January 1966-November 2011) to identify all relevant articles. We extracted data on risk of bias criteria (e.g., randomization, blinding, allocation concealment) and other study design features included in each assessment instrument.

DISCUSSION

Thirty distinct instruments were identified, with the total number of assessed risk of bias, methodological, and/or reporting criteria ranging from 2 to 25. The most common criteria assessed were randomization (25/30, 83%), investigator blinding (23/30, 77%), and sample size calculation (18/30, 60%). In general, authors failed to empirically justify why these or other criteria were included. Nearly all (28/30, 93%) of the instruments have not been rigorously tested for validity or reliability.

CONCLUSION

Our review highlights a number of risk of bias assessment criteria that have been empirically tested for animal research, including randomization, concealment of allocation, blinding, and accounting for all animals. In addition, there is a need for empirically testing additional methodological criteria and assessing the validity and reliability of a standard risk of bias assessment instrument.

Oxygen consumption and usage during physical exercise: the balance between oxidative stress and ROS-dependent adaptive signaling

The complexity of human DNA has been affected by aerobic metabolism, including endurance exercise and oxygen toxicity. Aerobic endurance exercise could play an important role in the evolution of Homo sapiens, and oxygen was not important just for survival, but it was crucial to redox-mediated adaptation. The metabolic challenge during physical exercise results in an elevated generation of reactive oxygen species (ROS) that are important modulators of muscle contraction, antioxidant protection, and oxidative damage repair, which at moderate levels generate physiological responses. Several factors of mitochondrial biogenesis, such as peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α), mitogen-activated protein kinase, and SIRT1, are modulated by exercise-associated changes in the redox milieu. PGC-1α activation could result in decreased oxidative challenge, either by upregulation of antioxidant enzymes and/or by an increased number of mitochondria that allows lower levels of respiratory activity for the same degree of ATP generation. Endogenous thiol antioxidants glutathione and thioredoxin are modulated with high oxygen consumption and ROS generation during physical exercise, controlling cellular function through redox-sensitive signaling and protein-protein interactions. Endurance exercise-related angiogenesis, up to a significant degree, is regulated by ROS-mediated activation of hypoxia-inducible factor 1α. Moreover, the exercise-associated ROS production could be important to DNA methylation and post-translation modifications of histone residues, which create heritable adaptive conditions based on epigenetic features of chromosomes. Accumulating data indicate that exercise with moderate intensity has systemic and complex health-promoting effects, which undoubtedly involve regulation of redox homeostasis and signaling.

Animal models of focal brain ischemia

Stroke is a leading cause of disability and death in many countries. Understanding the pathophysiology of ischemic injury and developing therapies is an important endeavor that requires much additional research. Animal stroke models provide an important mechanism for these activities. A large number of stroke models have been developed and are currently used in laboratories around the world. These models are overviewed as are approaches for measuring infarct size and functional outcome.

The role of endothelin in the cerebrovascular response following intracerebral haemorrhage: experimental studies using the endothelin antagonist SB209670

Primary intracerebral haemorrhage (ICH) is associated with considerable morbidity and mortality. Local endothelin release following ICH may contribute to the pathophysiology of perilesional ischaemia. In diabetics, endothelin release can be enhanced by hyperglycaemia and cerebrovascular dilation may be inhibited by vascular endothelial dysfunction. To examine the effects of endothelin-mediated vasoconstriction after spontaneous ICH in the normal and diabetic brain, regional cerebral blood flow (rCBF) was examined in insulin dependent BB-rats and non-diabetic BB control rats. These experiments were performed 24 h following experimental ICH in both groups of animals that were either given the endothelin antagonist SB209670 or saline. Perilesional oligaemia was similar in control and SB209670 treated diabetic rats, but SB209670 reduced perilesional oligaemia in normal rats. In brain contralateral to the experimental ICH, rCBF was increased by SB209670 in diabetic rats, but not in non-diabetic rats. These studies show that there are differences in the cerebrovascular effects of endothelin in perilesional and contralateral brain in non-diabetic and diabetic rats following ICH.

Acute ischemic stroke: overview of major experimental rodent models, pathophysiology, and therapy of focal cerebral ischemia

Ischemic stroke is a devastating disease with a complex pathophysiology. Animal modeling of ischemic stroke serves as an indispensable tool first to investigate mechanisms of ischemic cerebral injury, secondly to develop novel antiischemic regimens. Most of the stroke models are carried on rodents. Each model has its particular strengths and weaknesses. Mimicking all aspects of human stroke in one animal model is not possible since ischemic stroke is itself a very heterogeneous disorder. Experimental ischemic stroke models contribute to our understanding of the events occurring in ischemic and reperfused brain. Major approaches developed to treat acute ischemic stroke fall into two categories, thrombolysis and neuroprotection. Trials aimed to evaluate effectiveness of recombinant tissue-type plasminogen activator in longer time windows with finer selection of patients based on magnetic resonance imaging tools and trials of novel recanalization methods are ongoing. Despite the failure of most neuroprotective drugs during the last two decades, there are good chances to soon have effective neuroprotectives with the help of improved preclinical testing and clinical trial design. In this article, we focus on various rodent animal models, pathogenic mechanisms, and promising therapeutic approaches of ischemic stroke.

Treatment of focal cerebral ischemia with liposomal nerve growth factor

Liposomal nerve growth factor (NGF) was used for the treatment of focal cerebral ischemia in a rat model. Positive charge inducing agents of sphingosine (SP) and stearylamine (S) were formulated in the liposomal NGF. Dose-response of intraventricular injection of liposomal NGF showed significant reduction in infarct volume at the dose of 5 and 10 microg/rat of NGF. The liposomal NGF formulated with SP or S demonstrated similar results in the reduction of total infarct volume in rats. When we increased the molar ratio of SP and S from 0.15 to 0.3, the infarct volume from rats showed a similar value as that of the control treated with NGF solution. Liposomal NGF was given prior to the development of ischemia. We found that NGF was effective in prevention of neuronal death. The NGF concentrations in brain for liposomal NGF were maintained in a level significantly higher than those for NGF solution. This was attributed to the positively charged liposomal NGF bound effectively in brain ventricle and caused longer retention time than free NGF for localization in brain. Therefore, the effect of liposomal NGF on reduction of infarct volume was significant. We assumed that the transportation of NGF might go through the cerebrospinal fluid pathway throughout the ventricular system and subarachnoid system to cerebral cortex to produce a therapeutic effect on ischemia.

Molecular changes in nNOS protein expression within the ventrolateral medulla following transient focal ischemia affect cardiovascular functions

The majority of human strokes involve an occlusion of the middle cerebral artery and subsequent damage to the brain tissues it perfuses. We have previously reported that reflex cardiovascular changes during a static muscle contraction are attenuated following transient middle cerebral artery occlusion (MCAO) and reperfusion [A. Ally, S.M. Nauli, T.J. Maher, Cardiovascular responses and neurotransmission in the ventrolateral medulla during skeletal muscle contraction following transient middle cerebral artery occlusion and reperfusion, Brain Res. 952 (2002) 176-187]. We hypothesized that the attenuation is a result of altered expression of neuronal nitric oxide synthase (nNOS) within the rostral (RVLM) and caudal ventrolateral medulla (CVLM). In this study, we have compared cardiovascular responses and nNOS protein expression within the four quadrants, i.e., left and right sides of both RVLM and CVLM in sham-operated rats (n = 10) and in rats with a temporary 90-min left-sided MCAO followed by 24 h reperfusion (n = 10). Increases in mean arterial pressure during a static muscle contraction were significantly attenuated in MCAO rats when compared to sham rats. The transient ischemia reduced nNOS expression within the ipsilateral RVLM quadrant compared to the contralateral RVLM or RVLM quadrants of control rats. In contrast, compared to sham rats and the right CVLM quadrant of MCAO rats, nNOS expression was significantly augmented in the ipsilateral CVLM in left-sided MCAO rats. These data suggest that the attenuation of cardiovascular responses during static muscle contraction in MCAO rats is partly due to a reduction in nNOS expression within the ipsilateral RVLM and an overexpression of nNOS abundance within the ipsilateral CVLM. Results demonstrate that nNOS expression within the medulla plays a significant role in mediating cardiovascular responses during static exercise in intact and pathophysiological conditions.

Effect of dexamethasone on the expression of brain-derived neurotrophic factor and neurotrophin-3 messenger ribonucleic acids after forebrain ischemia in the rat

OBJECTIVE

To determine whether a large dose of dexamethasone affected brain damage induced by concurrent cerebral ischemia, we used in situ hybridization to examine the expression of brain-derived neurotrophic factor and neurotrophin-3 messenger ribonucleic acids (mRNAs) in rats with and without dexamethasone administration after transient forebrain ischemia.

DESIGN

Prospective experimental study in rats.

SETTING

Experimental laboratory in a teaching hospital and university.

SUBJECTS

Eighty adult rats.

INTERVENTIONS

Twenty minutes of transient forebrain ischemia was induced by occlusion of four vessels in lightly anesthetized rats. Thirty-six animals received dexamethasone (15 mg/kg, intraperitoneally) after initial reperfusion. Thirty-six dexamethasone-control rats were injected with saline, and the remaining animals underwent sham surgery but no ischemia or dexamethasone.

MEASUREMENTS AND MAIN RESULTS

Using in situ hybridization, we determined hippocampal brain-derived neurotrophic factor and neurotrophin-3 mRNA expression 2, 4, 6, 12, and 24 hrs and 2, 3, 4, and 7 days after brain ischemia. Additionally, hippocampal CA1 region cell death was measured with Nissl stains. Both brain-derived neurotrophic factor and neurotrophin-3 mRNA exhibited a biphasic response after ischemia. Brain-derived neurotrophic factor mRNA showed two peaks of 4.07-fold and 2.84-fold increases relative to sham operation at 6 hrs and 2 days, respectively. Neurotrophin-3 mRNA initially decreased to 59% of sham levels at 4 hrs and then increased to 146% at 3 days before it returned to basal levels. When the ischemic rats were treated with dexamethasone, the elevation of brain-derived neurotrophic factor mRNA and the reduction of neurotrophin-3 mRNA level were prevented within the first 24 hrs, and hippocampal CA1 neurons were protected from ischemia-induced cell loss 7 days after brain ischemia. The protein levels of both brain-derived neurotrophic factor and neurotrophin-3 in general correspond to the mRNA levels in the hippocampal region.

CONCLUSIONS

Dexamethasone modulates the intriguing temporal and spatial expression of brain-derived neurotrophic factor and neurotrophin-3 that predominantly supports neuronal innervation at different times after brain ischemia and also may provide specific trophic support for various neurons in the central nervous system.

High-dose methylprednisolone treatment in experimental focal cerebral ischemia

Previous studies using steroids for experimental focal stroke have demonstrated conflicting results, possibly related to dose used or ischemic models employed. In this study we examined high-dose methylprednisolone treatment following permanent and temporary focal cerebral ischemia in the rat. Focal stroke was induced in spontaneously hypertensive rats by permanent right common carotid and either permanent or 3 h of temporary middle cerebral artery (MCA) occlusion. Methylprednisolone (105 mg/kg) was administered intra-arterially. Infarct volume was measured at 24 h after permanent and temporary MCA occlusion. Cerebral edema was determined by measuring right and left hemispheric volumes and water content 24 h after permanent MCA occlusion in one experiment. Methylprednisolone, whether administered in divided doses over 12 h (n = 15 in each group) or a single bolus (n = 9 per group), had no effect on infarct volume after permanent MCA occlusion. Methylprednisolone treatment also had no influence on cerebral edema (n = 9 per group). In two different experiments, methylprednisolone given in divided doses over 12 h (n = 11, n = 25) after temporary MCA occlusion decreased infarct volume (P < 0.05) by 20% compared with saline controls (n = 10, n = 25). High dose methylprednisolone decreased infarct volume following temporary, but not permanent, focal ischemia. The benefit suggests that high dose methylprednisolone may prove useful clinically if reperfusion can be established with thrombolytic agents. Furthermore, the differential treatment effect in the setting of comparable ischemic insults implies that different modifiable biochemical processes may be present during temporary but not permanent focal ischemia, thus providing indirect evidence for reperfusion injury.

Why do neuroprotective drugs work in animals but not humans?

Many neuroprotective agents that seemed promising in animal studies of ischemic brain injury prove to have no effect when tested in clinical trials, suggesting that fundamental elements of translational research require better definition. A number of modifications have led to improvements in preclinical and human studies since the earliest controlled trials failed to confirm hypotheses suggested by animal data. Continued re-evaluation and sharing of information derived from the laboratory bench or the patient's bedside should eventually lead to effective neuroprotection in acute stroke. Experimental data should be carefully studied to improve the quality of agents coming to clinical trials and to design trial phasing that effectively determines drug safety and efficacy. This article will examine preclinical modeling and its translation to prospective studies of acute stroke therapy and will focus on some potential solutions directed at clinical trial design.

What animal models have taught us about the treatment of acute stroke and brain protection

Stroke research has progressed in leaps and bounds in the past decades. A driving force is the increasing availability of new research tools in this field (eg, animal stroke models). Animal stroke models have been extensively applied to advance our understanding of the mechanisms of ischemic brain injury and to develop novel therapeutic strategies for reducing brain damage after a stroke. Animal stroke models have been useful in characterizing the molecular cascades of injury processes. These "injury pathways" are also the targets of therapeutic interventions. The major achievements made in the past 2 decades applying animal stroke models include 1) the identification of the mediator role of excitotoxin and oxygen free radicals in ischemic brain injury; 2) the confirmation of apoptosis as a major mechanism of ischemic cell death; 3) the characterization of postischemic gene expression; 4) the delineation of postischemic inflammatory reaction; 5) the application of transgenic mice to confirm the roles of purported mediators in ischemic brain injury; 6) development of novel magnetic resonance imaging sequences for early noninvasive detection of ischemic brain lesions; and, 7) the development of novel therapeutic strategies based on preclinical findings derived from animal stroke models.

Hyperbaric oxygen decreases infarct size and behavioral deficit after transient focal cerebral ischemia in rats

Cerebral hypoxia is a major component of immediate and secondary cell damage caused by ischemia. Hyperbaric oxygen (HBO) is a potent means to increase the amount of oxygen dissolved in blood plasma. The effectiveness of HBO in clinical and experimental cerebral ischemia, however, is controversial. We sought to determine whether treatment with HBO initiated early after focal cerebral ischemia-onset protects the brain when experimental conditions such as brain temperature are controlled. Male Wistar rats (n=57) underwent reversible filament occlusion of the right middle cerebral artery (MCA) for 75 min. Animals were awakened after filament introduction and assessed for presence of forelimb paresis. Rats then underwent a 60-min course of either 100% O(2) at 1.0 atmosphere absolute (ata; control group), HBO 1.5 ata, or HBO 2.5 ata in a customized HBO chamber allowing physiological monitoring and pericranial temperature control. The filament was then removed. Seven days after ischemia, rat behavior was scored from 3-18 (18=normal) and brains were removed for histological analysis of infarct volume. Rats treated with HBO 2.5 ata had better mean+/-standard deviation (S.D.) behavioral scores (14+/-2; p<0.05) than control (10+/-3) or HBO 1.5-ata-treated animals (11+/-3). Similarly, total infarct volumes (mean+/-S.D.) were smaller in animals receiving HBO at 2.5 ata (76+/-65 mm(3); p<0.05) compared to control (129+/-83 mm(3)) and HBO 1.5-ata (119+/-68 mm(3))-treated groups. Cortical infarction occurred less frequently in HBO 2. 5-ata-treated than in control animals (44% vs. 71%; p<0.05). We conclude that HBO can improve outcome after temporary focal ischemia when treatment is started early after ischemia-onset but HBO dose appears important. Potential mechanisms include enhanced oxygen supply to marginally perfused cells.

MRI study on delayed ancrod therapy of focal cerebral ischaemia in rats

The therapeutic window for efficient post-treatment of focal cerebral ischaemia with the fibrinogen lowering agent ancrod was studied by magnetic resonance imaging (MRI) in spontaneously hypertensive rats (SHR). Ancrod or vehicle solution (0.9% NaCl) were i.v. infused (0.12 IU/kg per min) via implanted mini pumps starting 0.5, 1.5, 3 or 6 h after permanent proximal middle cerebral artery occlusion and lasting until brain mapping by multislice T2-weighted magnetic resonance imaging in vivo 24 h after middle cerebral artery occlusion. Plasma fibrinogen concentrations were measured before middle cerebral artery occlusion, before pump implantation and after magnetic resonance imaging. Total brain lesion volumes as determined by magnetic resonance imaging 24 h after middle cerebral artery occlusion were 131 +/- 36 (188 +/- 28)*, 151 +/- 39 (194 +/- 39)*, 147 +/- 44 (207 +/- 33)* and 209 +/- 60 (214 +/- 42) mm3 in rats with 0.5, 1.5, 3 and 6 h, respectively, delay of ancrod treatment (means +/- S.D., 8-11 animals/group, corresponding control groups in parentheses, *P < 0.05). Continuous i.v. ancrod infusions reduced plasma fibrinogen levels significantly (P < 0.05) in all ancrod-treated groups as compared to vehicle-treated controls until the end of the experiments 24 h after middle cerebral artery occlusion. In conclusion, significant cerebroprotection was achieved even when the onset of ancrod therapy for lowering of the plasma fibrinogen level was delayed for up to 3 h. To the best of our knowledge no drug efficacy has been reported so far with a therapeutic window of 3 h after permanent middle cerebral artery occlusion in spontaneously hypertensive rats suggesting that ancrod may provide an efficient therapy of acute human stroke.

A single dose of kainic acid elevates the levels of enkephalins and activator protein-1 transcription factors in the hippocampus for up to 1 year

Neuronal plasticity plays a very important role in brain adaptations to environmental stimuli, disease, and aging processes. The kainic acid model of temporal lobe epilepsy was used to study the long-term anatomical and biochemical changes in the hippocampus after seizures. Using Northern blot analysis, immunocytochemistry, and Western blot analysis, we have found a long-term elevation of the proconvulsive opioid peptide, enkephalin, in the rat hippocampus. We have also demonstrated that an activator protein-1 transcription factor, the 35-kDa fos-related antigen, can be induced and elevated for at least 1 year after kainate treatment. This study demonstrated that a single systemic injection of kainate produces almost permanent increases in the enkephalin and an activator protein-1 transcription factor, the 35-kDa fos-related antigen, in the rat hippocampus, and it is likely that these two events are closely associated with the molecular mechanisms of induction of long-lasting enhanced seizure susceptibility in the kainate-induced seizure model. The long-term expression of the proenkephalin mRNA and its peptides in the kainate-treated rat hippocampus also suggests an important role in the recurrent seizures of temporal lobe epilepsy.

Effect of basic fibroblast growth factor on experimental focal ischemia studied by diffusion-weighted and perfusion imaging

BACKGROUND AND PURPOSE

Basic fibroblast growth factor (bFGF) has documented neuroprotective properties. This study was performed to evaluate the effects of bFGF on infarct size when administered 30 minutes after induction of focal cerebral ischemia in rats. Diffusion-weighted and perfusion MRI were used during the drug infusion.

METHODS

We blindly randomized 20 Sprague-Dawley rats to receive either drug (n = 10) or vehicle (n = 10). The animals underwent middle cerebral artery (MCA) occlusion using the suture model. Diffusion-weighted MRI was initiated 30 minutes after induction of ischemia and repeated frequently for 3.5 hours. Drug (45 micrograms/kg per hour) or vehicle (saline) infusion began 30 minutes after MCA occlusion and continued for 3 hours. Perfusion images were made at 25, 90, and 150 minutes after MCA occlusion. The animals were killed after 24 hours of permanent MCA occlusion, and brains were stained with 2,3,5-triphenyltetrazolium chloride (TTC).

RESULTS

The TTC-derived, corrected infarct volume postmortem in the bFGF-treated group was significantly smaller than that in controls (126.6 +/- 51.9 versus 180.2 +/- 54.9 mm3, mean +/- SD, P = .038). Diffusion imaging showed essentially equal lesion volumes 3 hours after MCA occlusion (195.4 +/- 61 mm3 in the drug-treated group and 194.4 +/- 65 mm3 in controls). At 4 hours, ischemic lesion size was 182.1 +/- 56.9 mm3 in treated animals and 222.9 +/- 88.7 mm3 in the controls (P = .24, NS). Perfusion imaging did not show a change of cerebral perfusion within ischemic brain regions in the bFGF group during the infusion. No behavioral or physiological side effects were observed.

CONCLUSIONS

bFGF is a safe and effective treatment for focal cerebral ischemia in rats. We observed a modest delayed difference of ischemic lesion size in vivo with diffusion MRI. The diffusion-weighted MRI findings suggest a potential delayed therapeutic effect of bFGF, and the perfusion imaging findings imply that the effect is not due to increased blood flow to the ischemic region.

Dextrorphan reduces infarct volume, vascular injury, and brain edema after ischemic brain injury

Focal cerebral ischemia confined to the cerebral cortex in the right middle cerebral artery (MCA) territory was induced by temporary ligation of the MCA and both common carotid arteries (CCAs). Reperfusion was initiated by releasing all three arterial occlusions after 90 min of ischemia. Infarct volume was morphometrically measured after triphenyltetrazolium chloride staining 24 h postischemia. Blood-brain barrier breakdown was assessed 4 h postischemia by measuring vascular permeability to fluorescein isothiocyanate-conjugated dextran (FITC-D), a macromolecule tracer. Ischemic brain edema was measured based on percent water content, 24 h postischemia. Dextrorphan (DX) 20-10 mg/kg given ip 15 min before ischemia reduced infarct volume in a dose-dependent manner with an apparent U-shaped dose-response curve; best protection was observed at 30 mg/kg. Posttreatment at 30 min, but not 60 min, was still effective. DX (30 mg/kg, given 15 min before ischemia) also reduced the postischemic increase in vascular permeability and brain edema in the right MCA cortex. Results from this study support the idea that NMDA receptor activation contributes to blood-brain barrier breakdown and brain edema after ischemic insults

Apoptotic features of selective neuronal death in ischemia, epilepsy and gp 120 toxicity

The occurrence of physiological cell death has been known for decades, but interest in the subject was renewed in 1972 when Kerr, Wyllie and Currie described in detail the ultrastructural changes characteristic of dying cells and coined the term apoptosis to describe the process. Cells display a wide variety of morphological changes when dying during development or following a toxic insult. A binary classification scheme suggests that physiologically appropriate death is due to apoptosis and that pathological mechanisms involve necrosis. However, recent studies indicate a potential involvement of apoptotic cell death in ischemia, status epilepticus and HIV-1 infection.

Short therapeutic window for MK-801 in transient focal cerebral ischemia in normotensive rats

The present study investigates the role of N-methyl-D-aspartate (NMDA) receptors in a model of transient focal cerebral ischemia in normotensive rats. The left middle cerebral artery and both common carotid arteries were occluded for 60 min. Preliminary studies indicated that this gave reproducible infarctions of the cortex and striatum. These infarctions were the result of severe ischemia followed by complete reperfusion after clamp removal, as showed by striatal tissue Po2 monitoring. Microdialysis indicated that glutamate concentration increased immediately after occlusion and returned to the baseline value 40 min after clamp removal. MK-801 (1 mg kg-1 i.v.), an antagonist of the NMDA glutamatergic receptor, reduced the cortical infarct volume by 29% (p < 0.001) and the striatal infarct volume by 14% (p < 0.05) when given just prior to ischemia, but had no neuroprotective activity when given 30 min after the onset of ischemia. This short therapeutic window for MK-801 suggests that NMDA receptors play only a transient role in reversible focal ischemia in rats.

Expression of interleukin-6, c-fos, and zif268 mRNAs in rat ischemic cortex

The expression of interleukin-6 (IL-6) mRNA in the focal ischemic rat cortex was studied by means of Northern hybridization. IL-6 mRNA was induced after permanent occlusion of the middle cerebral artery, reached a significant level at 3 h, and peaked at 12 h, i.e., approximately 10-fold increase in the ischemic zone compared with the nonischemic cortex or sham-operated controls. The increased IL-6 mRNA was elevated for at least 24 h. Low levels of IL-6 mRNA were detected in sham-operated rats or in the contralateral nonischemic cortex. The expression of c-fos and zif268 mRNAs, two early response genes, was rapid (increased by 1 h postischemia) and transient (returned to basal levels by 24 and 12 h, respectively), clearly having different kinetic patterns from that of IL-6 mRNA. The early response kinetic pattern of c-fos and zif268 mRNAs in focal ischemia suggests their transcriptional regulatory roles in response to ischemic insult, while the delayed induction pattern of IL-6 mRNA suggests a role for this pleiotropic cytokine in the inflammatory response to the focal ischemic damage of the brain.

Suppression of ischemia-induced fos expression and AP-1 activity by an antisense oligodeoxynucleotide to c-fos mRNA

Activation of c-fos, an immediate early gene, and the subsequent expression of the Fos protein have been noted following focal cerebral ischemia. Fos and Jun form a heterodimer as activator protein 1 (AP-1), which transregulates the expression of several genes. To study the postischemic events related to c-fos expression, we suppressed the expression of c-fos by intraventricular infusion of an antisense oligodeoxynucleotide (anti-rncfosr115) of c-fos mRNA. The effectiveness of anti-rncfosr115 was confirmed first by its capability to block in vitro c-fos mRNA translation. In vivo, after intraventricular infusion of 32P-labeled anti-rncfosr115, the oligodeoxynucleotide was internalized within 6 hours and detectable also in the nucleic acids fraction up to 41 hours. Treatment of the recovered nucleic acids with RNase H separated the labeled oligodeoxynucleotide from the nucleic acid fraction, indicating an association of the antisense oligodeoxynucleotide and cellular RNA after uptake. When focal cerebral ischemia was induced 16 hours after the infusion of anti-rncfosr115, the postischemic increase in Fos expression and AP-1 binding activity were suppressed. Specificity of the effect of anti-rncfosr115 was suggested by its failure to suppress the DNA binding activity of nuclear cyclic AMP response elements. These results support the hypothesis that increased AP-1 binding activity following focal cerebral ischemia is dependent on Fos expression and can be inhibited in vivo by antisense c-fos oligodeoxynucleotides.