The competitive NMDA antagonist CGP 40116 permanently reduces brain damage after middle cerebral artery occlusion in rats

Topiramate mitigates 3-nitropropionic acid-induced striatal neurotoxicity via modulation of AMPA receptors

Prevalence of glutamate receptor subunit 2 (GluR2)-lacking alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors is a hallmark of excitotoxicity-related neurodegenerative diseases. Topiramate (TPM) is a structurally novel anticonvulsant with a well-known modulatory effects on AMPA/kainate subtypes of glutamate receptors. The present study aimed at investigating the neuroprotective potential of TPM on 3-nitropropionic acid (3-NP)-induced striatal neurodegeneration and Huntington's disease-like symptoms. Rats were injected with 3-NP (10 mg/kg/i.p.) for 14 days. TPM (50 mg/kg/p.o.) was given once a day, 1 h before 3-NP. TPM amended 3-NP induced changes in neurobehavioral performance, striatal neurotransmitters levels and histopathological injury. 3-NP control rats showed a significant ablation in the mRNA expression of Ca²⁺-impermeable Glu2R subunit along with an elevation in its regulatory protein (protein interacting with C kinase-1) PICK1, an effect that was largely reversed by TPM. TPM in addition, enhanced the phosphorylation of the protein kinase B/glycogen synthase kinase-3β/cAMP response element binding protein (Akt/GSK-3β/CREB) cue. Moreover, improvement in oxidative status, suppression of caspase-3 activity and restoration of striatal BDNF were noticed following treatment with TPM. The current study revealed that TPM boosted the neuroprotective (Akt/GSK-3β/CREB) pathway by its negative modulatory effect on AMPA glutamate receptors as well as its direct antioxidant property.

Ion channels involved in stroke

Ion channels are membrane proteins that flicker open and shut to regulate the flow of ions down their electrochemical gradient across the membrane and consequently regulate cellular excitability. Every living cell expresses ion channels, as they are critical life-sustaining proteins. Ion channels are generally either activated by voltage or by ligand interaction. For each group of ion channels the channels' molecular biology and biophysics will be introduced and the pharmacology of that group of channels will be reviewed. The in vitro and in vivo literature will be reviewed and, for ion channel groups in which clinical trials have been conducted, the efficacy and therapeutic potential of the neuroprotective compounds will be reviewed. A large part of this article will deal with glutamate receptors, focusing specifically on N-methyl-D-aspartate (NMDA) receptors. Although the outcome of clinical trials for NMDA receptor antagonists as therapeutics for acute stroke is disappointing, the culmination of these failed trials was preceded by a decade of efforts to develop these agents. Sodium and calcium channel antagonists will be reviewed and the newly emerging efforts to develop therapeutics targeting potassium channels will be discussed. The future development of stroke therapeutics targeting ion channels will be discussed in the context of the failures of the last decade in hopes that this decade will yield successful stroke therapeutics.

MRI analysis of the changes in apparent water diffusion coefficient, T(2) relaxation time, and cerebral blood flow and volume in the temporal evolution of cerebral infarction following permanent middle cerebral artery occlusion in rats

Detailed knowledge of similarities and differences between animal models and human stroke is decisive for selecting clinically effective drugs based on efficacy data obtained preclinically. Differences in the temporal evolution of stroke pathologies between animal models and man have been reported. In view of the importance of this issue for the development of neuroprotective treatments, the temporal evolution of stroke pathologies in the rat permanent middle cerebral artery occlusion (pMCAO) model has been evaluated with magnetic resonance imaging modalities under experimental conditions matching as close as possible those used in humans. Changes in the ipsilateral and contralateral cortex and striatum of cerebral blood flow (CBF) and volume (CBV), apparent diffusion coefficient (ADC), and spin-spin relaxation time (T(2)), as well as total cortical and striatal infarct volumes, calculated from CBF, ADC, and T(2) maps, were determined starting 1 h up to 216 h post-pMCAO. The temporal evolution of the MRI parameters in this rat model was similar to that observed in humans. In particular, the ADC values were decreased for more than 3 days and returned back to baseline between 4 to 8 days, to increase by day 9 only. Thus the stroke pathology in this rat model develops at a similar pace as in stroke patients arguing against a fundamental difference in the mechanisms involved. The infarct volumes however develop differently in this rat model as they invariably increase over the first 48 h, while in humans the evolution of infarct volume is slower and more heterogeneous.

Diffusion-weighted MRI of infarct growth in a rat photochemical stroke model: effect of lubeluzole

We studied the neuroprotective effect of lubeluzole, a NOS (nitric oxide synthase) pathway modulator, on the development of ischemic damage within the first six hours after a photochemically induced neocortical infarct in rats using diffusion-weighted MRI and Apparent Diffusion Coefficient (ADC) maps. A unilateral photochemical infarct was induced in the hindlimb sensorimotor neocortex of Wistar rats. One hour after infarction, rats received either vehicle (n=10) or lubeluzole (n=11; a 0.31 mg/kg i.v. bolus followed by a one-hour 0.31 mg/kg i.v. infusion). During the first six hours after infarct induction, multislice T2- and Diffusion-Weighted magnetic resonance images (MRI) were obtained to measure percent change of volume of ischemic damage, whereas regional ADC maps were used to measure time-dependent density of ischemic damage. Lubeluzole reduced the percent increase of volume of ischemic damage relative to baseline (at 1 h after infarct induction just before drug treatment), by 18% at 5 and 6 hrs after infarct induction. Lubeluzole attenuated the ADC decreases in the peripheral rim of the infarct, but left the ADC values in the core unaffected. In conclusion, the neuroprotectant lubeluzole attenuates growth of ischemic damage as well as its density in the periphery of a photochemically induced neocortical infarct in rats.

3-Hydroxykynurenine potentiates quinolinate but not NMDA toxicity in the rat striatum

L-3-Hydroxykynurenine (L-3-HK) and quinolinate (QUIN) are two metabolites of the kynurenine pathway, the major route of tryptophan degradation in mammals. L-3-HK is a known generator of highly reactive free radicals, whereas QUIN is an endogenous excitotoxin acting specifically at N-methyl-D-aspartate (NMDA) receptors. This study was designed to examine possible synergistic interactions between L-3-HK and QUIN in the rat brain in vivo. Intrastriatal coinjection of 5 nmol L-3-HK and 15 nmol QUIN, i.e. doses which caused no or minimal neurodegeneration on their own, resulted in substantial neuronal loss, determined both behaviourally (apomorphine-induced rotations) and histologically (quantitative assessment of lesion size). The excitotoxic nature of the lesion was verified by tyrosine hydroxylase immunohistochemistry, showing the survival of dopaminergic striatal afferents. There was also a relative sparing of large striatal neurons, and neurodegeneration was prevented both by NMDA receptor blockade (using CGP 40116) and free radical scavenging [using N-tert-butyl-alpha-(2-sulphophenyl)-nitrone, S-PBN]. The pro-excitotoxic features of L-3-HK were especially pronounced at low QUIN doses and were not observed when QUIN was substituted by NMDA. Notably, the effect of L-3-HK was not due to its intracerebral conversion to QUIN and was duplicated by equimolar D,L-3-HK. These data indicate that an elevation of L-3-HK levels constitutes a significant hazard in situations of excitotoxic injury. Pharmacological interventions aimed at decreasing L-3-HK formation may therefore be particularly useful for the treatment of neurological diseases which are associated with an abnormally enhanced flux through the kynurenine pathway.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

In vivo magnetic resonance methods in pharmaceutical research: current status and perspectives

In the last decade, in vivo MR methods have become established tools in the drug discovery and development process. In this review, several successful and potential applications of MRI and MRS in stroke, rheumatoid and osteo-arthritis, oncology and cardiovascular disorders are dealt with in detail. The versatility of the MR approach, allowing the study of various pathophysiological aspects in these disorders, is emphasized. New indication areas, for the characterization of which MR methods have hardly been used up to now, such as respiratory, gastro-intestinal and skin diseases, are outlined in a subsequent section. A strength of MRI, being a non-invasive imaging modality, is the ability to provide functional, i.e. physiological, readouts. Functional MRI examples discussed are the analysis of heart wall motion, perfusion MRI, tracer uptake and clearance studies, and neuronal activation studies. Functional information may also be derived from experiments using target-specific contrast agents, which will become important tools in future MRI applications. Finally the role of MRI and MRS for characterization of transgenic and knock-out animals, which have become a key technology in modern pharmaceutical research, is discussed. The advantages of MRI and MRS are versatility, allowing a comprehensive characterization of a diseased state and of the drug intervention, and non-invasiveness, which is of relevance from a statistical, economical and animal welfare point of view. Successful applications in drug discovery exploit one or several of these aspects. In addition, the link between preclinical and clinical studies makes in vivo MR methods highly attractive methods for pharmaceutical research.

Delayed treatment with YM90K, an AMPA receptor antagonist, protects against ischaemic damage after middle cerebral artery occlusion in rats

The neuroprotective effect of an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor antagonist YM90K [6-(1H-imidazol-1-yl)-7-nitro-2,3(1H,4H)-quinoxalinedione monohydrochloride] has been examined in a rat middle cerebral artery occlusion model. Intravenous infusion of YM90K (2.5-20mgkg(-l)h(-l) for 4h) starting immediately after occlusion of the middle cerebral artery significantly reduced the cortical infarct volume 24h after occlusion compared with the control group. The protection at the highest dose was 39% (P < 0.05). Similar protective effects were observed when YM90K (20mgkg(-1)h(-1) for 4h) was delayed up to 2h after middle cerebral artery occlusion (45% reduction, P < 0.05). CNS1102 [N-(1-naphthyl)-N'-(3-ethylphenyl)-N'-methylguanidine hydrochloride], a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, also reduced the cortical infarct volume when 1.13mgkg(-1) was administered by intravenous bolus injection immediately after middle cerebral artery occlusion, followed by intravenous infusion at 0.785mgkg(-l)h(-1) for 4h (35% reduction, P<0.05). This neuroprotective effect was not observed when administration was delayed lh after middle cerebral artery occlusion. These results suggest that AMPA receptors might play a more important role than NMDA receptors in the late development of neuronal cell damage after focal cerebral ischaemia and that AMPA receptor blockade would be one beneficial strategy in treating acute stroke.

A novel AMPA receptor antagonist, YM872, reduces infarct size after middle cerebral artery occlusion in rats

The neuroprotective effect of YM872 ([2.3-dioxo-7-(1H-imidazol-1-yl) 6-nitro-1,2,3,4-tetrahydro-1-quinoxalinyl]acetic acid monohydrate), a novel alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor antagonist with improved water solubility, was examined in a rat focal cerebral ischemia model. Rats were subjected to permanent middle cerebral artery (MCA) occlusion using the intraluminal suture occlusion method for 24 h. YM872 was intravenously infused for 4 h (20 and 40 mg/kg/h) or 24 h (10 and 20 mg/kg/h), starting 5 min after the MCA occlusion, to investigate the effect of prolonged duration of the treatment on infarct volume. In the 4 h infusion study, YM872 reduced the cortical infarct volume by 48% at a dose of 40 mg/kg/h. YM872 did not significantly reduce the infarct at 20 mg/kg/h for 4 h. In the 24 h infusion study, however, YM872 markedly reduced the cortical infarct volume by 62%, even at 20 mg/kg/h. The present study indicates that the neuroprotective effect of YM872 is enhanced by extending the duration of treatment, and demonstrates the benefit of the prolonged treatment with AMPA antagonists following focal cerebral ischemia. YM872, a highly water soluble compound, is applicable to investigate the role of AMPA receptors in ischemic models without concern about nephrotoxicity and could be useful in the treatment of human stroke.

Treatment with the competitive NMDA antagonist GPI 3000 does not improve outcome after cardiac arrest in dogs

BACKGROUND AND PURPOSE

We previously showed that treatment with a competitive N-methyl-D-aspartate (NMDA) receptor antagonist GPI-3000 (GPI) improved short-term physiological recovery after incomplete global cerebral ischemia complicated by dense acidosis. We tested the hypothesis that GPI administered after resuscitation from cardiac arrest would improve a more long-term recovery as measured by neurobehavioral assessment and neuropathology 4 days after resuscitation.

METHODS

Anesthetized dogs were subjected to 7 minutes of cardiac arrest followed by vest cardiopulmonary resuscitation. Neurobehavioral outcomes were scored daily on a score ranging from 0 (normal) to 500 (worst). On the fourth day, the animals were killed, and neuropathology was evaluated in a blinded manner in the hippocampus and the neocortex by hematoxylin and eosin staining and by determination of percentage of injured neurons. Three groups of animals were treated in a randomized, blinded protocol with either saline (SAL), low-dose GPI (5 mg/kg followed by 1 mg/kg per hour for 2 hours), or high-dose GPI (25 mg/kg, followed by 5 mg/kg per hour for 2 hours).

RESULTS

The mortality rate was higher in animals receiving GPI than in saline-treated control animals (4 of 15 deaths in SAL, 6 of 15 in the low-dose GPI group, and 9 of 18 in the high-dose GPI group). Neurobehavioral scores were depressed in GPI-treated animals compared with saline-treated control animals in a dose-dependent manner, with 96-hour scores of essentially normal (9+/-2) in saline-treated animals compared with those animals with significant impairment (181+/-47) treated with high-dose GPI. Neuropathological damage in the neocortex was most severe in GPI-treated animals, with the percentage of injured neurons dependent on the dose: 8.3%+/-2.7% SAL, 13.2%+/-6.4% low-dose GPI, and 39.4%+/-10.1%, high-dose GPI. CA1 neuronal damage was severe regardless of treatment.

CONCLUSIONS

Contrary to results seen in experimental global and focal cerebral ischemia, in which NMDA receptor antagonism may improve responses to injury, receptor antagonism with GPI does not improve brain outcome after cardiac arrest and resuscitation in the dog. Behavioral and histological outcomes both were worsened by GPI treatment at two doses, and mortality was higher relative to saline control treatment. We speculate that systemic drug effects, as well as potential neurotoxicity of the drug under ischemic conditions, may be responsible for the deleterious outcomes observed in our cardiac arrest model.

Carotid artery and jugular vein ligation with and without hypoxia in the rat

A continuing concern about the use of extracorporeal membrane oxygenation (ECMO) is the cannulation of the common carotid artery or the internal jugular vein. The authors investigated the changes that might occur in the brain with neck vessel ligation in the normal and the hypoxic rat. Two groups of 60 rats each were studied. The first group was divided into three subgroups of 20 animals each. Subgroup 1 (HH) was hypoxic both 24 hours before and 24 hours after operation. Subgroup 2 (HN) (the ECMO model) was hypoxic before operation and recovered for 24 hours in room air. Subgroup 3 (NN) underwent the entire procedure in room air. For each oxygen environment, four different operations were performed: carotid artery ligation, jugular vein ligation, carotid artery and jugular vein ligation, and dissection of the vessels without ligation (sham). Thus each subgroup was further divided into four sub-subgroups based on the operation performed. Rats were again anesthetized after a 24-hour recovery period and killed using low, blunt cervical dislocation. In the first group of 60 rats, the skull was opened and the brain was carefully removed from the cranial vault and placed in a fixative. The brains were placed in a small magnetic resonance imaging (MRI) head coil in groups of five and scans were obtained to provide T1 and T2 images that correlated with histological sections. MRI scans were reviewed in random, blinded fashion by an imager unaware of how these animals had been treated. The brains were then sectioned coronally at six corresponding levels: frontal, mid and posterior cerebrum, midbrain, pons, and medulla. Histological examination was performed in blinded fashion. The number of lesions (usually ischemic as noted by a decrease in the number of neurons) was totaled for each area of the brain. There were no differences that were consistent or statistically significant in the MR images of brains removed from the head, although it would appear that rats with jugular vein and carotid artery ligation were relatively protected. In the HN group jugular vein ligation was worst, and adding carotid artery ligation was best. In the histological studies the NN group had significantly more lesions than the HH group (P < .01). The second group of 60 rats was divided and treated as the first group in all respects except that MRI was conducted immediately after death on intact heads, and no histological studies were performed. This was done to control for lesions that might have been produced by removal of the brains from the skulls. In this group all findings were right sided. One animal in the HN group showed midcerebral white matter edema after jugular and carotid ligation. Focal anterior cerebral edema was seen in another animal (HH) after isolated carotid ligation. An occipital infarct was found in one animal (HH) after both carotid and jugular ligation. The authors conclude that neck vessel ligation in the hypoxic or normoxic rat causes only occasional and sporadic brain injury much as is seen clinically in newborn ECMO patients.

The protective effect of MK-801 on infarct development over a period of 24 h as assessed by diffusion-weighted magnetic resonance imaging

Diffusion-weighted MRI has been used to investigate therapeutic intervention with MK-801 in an animal model of permanent focal cerebral ischaemia. The animals were imaged continuously for 4 h and again at 24 h following occlusion of the middle cerebral artery (MCA) allowing the development of the ischaemic lesion to be monitored continuously in the same animals. An increased DWI signal, seen as a region of hyperintensity, was detected 1 h after MCA-occlusion in the lateral cortex and caudate nucleus in both control and MK-801 (administered at a dose of 3 mg/kg i.p. 5 min post-ischaemia) treated animals. However, the volume of hemispheric and cortical hyperintensity was smaller in the MK-801-treated animals. The area of hyperintensity progressively increased in the control group over the 4 h imaging time and there was also an increase in the area of hyperintensity between 4 and 24 h. At these time points the area of hyperintensity encompassed the dorsolateral cortex and caudate nucleus. MK-801 treated animals also demonstrated some progressive increase in the area of hyperintensity between 1 and 3 h, but no significant increase in the area of hyperintensity was seen after this time. The hyperintense regions at 4 and 24 h were restricted to the so-called 'core areas' of the lesion in MK-801-treated animals. Thus, using DWI the tissue 'at risk' following ischaemia could be identified and the protective effect of therapeutic intervention demonstrated.

Diffusion-weighted NMR imaging: application to experimental focal cerebral ischemia

Changes in diffusion NMR imaging are believed to be based on intra/extracellular water homeostasis and will therefore reflect early disturbances of ion and water homeostasis after the onset of an ischemic event. Diffusion-weighted NMR imaging (DWI) thus has the potential to be a sensitive tool for the observation of stroke evolution. The present state of information extracted from diffusion-weighted NMR imaging for the understanding of cerebral focal ischemia in experimental research has been compiled in this review. The emphasis was set on three essential aspects of the technique in relation to focal ischemia. Firstly, the sensitivity of diffusion-weighted imaging for ischemic alterations is described. A comparison with conventional NMR imaging using relaxation time changes is included. Secondly, the comparison of the diffusion-weighted imaging with invasive techniques is discussed. Here, interpretation of the physiological, metabolic and hemodynamic alterations reflected in the observed diffusion changes is presented. The importance of regionally resolved information for a meaningful assignment of DWI changes to pathophysiological alterations is demonstrated for the differentiation between ischemic core and penumbra from DWI and quantitative diffusion coefficient data. The time dependence of correlations with physiological, biochemical and hemodynamic variables as a further important aspect is stressed. Thirdly, the potential of the technique for the assessment of development and effectiveness of new therapeutical strategies against stroke is demonstrated.