CP-101,606, an NR2B subunit selective NMDA receptor antagonist, inhibits NMDA and injury induced c-fos expression and cortical spreading depression in rodents

Spontaneous spreading depolarizations originate subcortically in a novel mouse model of familial hemiplegic migraine type 2

The mechanisms of initiation of spreading depolarization (SD) are understudied due to a paucity of disease models with spontaneously occurring events. We here present a novel mouse model of familial hemiplegic migraine type 2 (FHM2), expressing the missense T345A-mutated α2 subunit of the Na+/K+ adenosine triphosphatase pump (Atp1a2T345A). Homozygous Atp1a2T345A mice showed regular spontaneous SDs that exhibit a diurnal rhythm and typically originate from the hippocampus. Heterozygous Atp1a2T345A mice rarely exhibited spontaneous SDs and, for electrically induced SDs, only showed an increased propagation speed, whereas homozygotes showed both increased propagation and decreased threshold. Remarkably, despite hippocampal hyperexcitability, spontaneous SDs in Atp1a2T345A mice were only rarely associated with epileptic behavior, and seizure expression during kindling was decreased. Spontaneous SDs could be prevented by modulation of persistent sodium currents. Hippocampal SDs occurred in the presence of an NMDA-receptor antagonist, but these events did not reach the cortex, suggesting that initiation and propagation of SD depend on different mechanisms in this model.

A cross talk on the role of contemporary biomarkers in depression

Introduction: Biomarkers can be used to identify determinants of response to various treatments of mental disorders. Evidence to date demonstrates that markers of inflammatory, neurotransmitter, neurotrophic, neuroendocrine, and metabolic function can predict the psychological and physical consequences of depression in individuals, allowing for the development of new therapeutic targets with fewer side effects. Extensive research has included hundreds of potential biomarkers of depression, but their roles in depression, abnormal patients, and how bioinformatics can be used to improve diagnosis, treatment, and prognosis have not been determined or defined. To determine which biomarkers can and cannot be used to predict treatment response, classify patients for specific treatments, and develop targets for new interventions, proprietary strategies, and current research projects need to be tailored.Material and Methods: This review article focuses on - biomarker systems that would help in the further development and expansion of newer targets - which holds great promise for reducing the burden of depression.Results and Discussion: Further, this review point to the inflammatory response, metabolic marker, and microribonucleic acids, long non-coding RNAs, HPA axis which are - related to depression and can serve as future targets.

Antidepressant-like effect of CP-101,606: Evidence of mTOR pathway activation

BACKGROUND

As a non-competitive N-methyl d-aspartate receptor antagonist, ketamine exerts rapid-onset and long-lasting antidepressant effects on depression, but some side effects limit its use. To identify a safer compound that may provide similar antidepressant effects, here we investigated whether CP-101,606, a selective NR2B receptor inhibitor, provides similar antidepressant effects and explored its underlying mechanisms.

METHODS

To mimic depressive-like behavior, mice were subjected to chronic unpredictable mild stress (CUMS) for 21 days. Mice were treated with CP-101,606 at 10, 20, and 40 mg/kg doses for 7, 14, and 21 days, respectively, followed by a sucrose preference test (SPT), tail suspension test (TST), and forced swimming test (FST). Western blot analysis was performed on several targets (mTOR, p-mTOR, p70S6K, p-p70S6K, PSD-95, and GluA1), along with immunohistochemistry (GluA1) and immunofluorescence (p-mTOR) assays, using hippocampal tissue.

RESULTS

CP-101,606 at 20 and 40 mg/kg doses for 7 and 14 days and fluoxetine 10 mg/kg and CP-101606 20 mg/kg for 21 days ameliorated depression-like behaviors in the SPT, TST, and FST. The effects of CP-101,606 were associated with a reversal of the CUMS-induced decrease in mTOR (Ser2448) and p70S6K (Thr389) phosphorylation and increasing PSD95 and GluA1 synthesis in the hippocampus.

CONCLUSIONS

Our results demonstrate that CP-101,606 produces antidepressant effects in CUMS mice, which may be mediated by mTOR signaling cascade upregulation. Our findings suggest the possible utility of CP-101,606 as a treatment for depression.

Specific activation of GluN1-N2B NMDA receptors underlies facilitation of cortical spreading depression in a genetic mouse model of migraine with reduced astrocytic glutamate clearance

Migraine is a common but poorly understood sensory circuit disorder. Mouse models of familial hemiplegic migraine (FHM, a rare monogenic form of migraine with aura) show increased susceptibility to cortical spreading depression (CSD, the phenomenon that underlies migraine aura and can activate migraine headache mechanisms), allowing an opportunity to investigate the mechanisms of CSD and migraine onset. In FHM type 2 (FHM2) knock-in mice with reduced expression of astrocytic Na⁺, K⁺-ATPases, the reduced rate of glutamate uptake into astrocytes can account for the facilitation of CSD initiation. Here, we investigated the underlying mechanisms and show that the reduced rate of glutamate clearance in FHM2 mice results in increased amplitude and slowing of rise time and decay of the NMDA receptor (NMDAR) excitatory postsynaptic current (EPSC) elicited in layer 2/3 pyramidal cells by stimulation of neuronal afferents in somatosensory cortex slices. The relative increase in NMDAR activation in FHM2 mice is activity-dependent, being larger after high-frequency compared to low-frequency afferent activity. Inhibition of GluN1-N2B NMDARs, which hardly affected the NMDAR EPSC in wild-type mice, rescued the increased and prolonged activation of NMDARs as well as the facilitation of CSD induction and propagation in FHM2 mice. Our data suggest that the enhanced susceptibility to CSD in FHM2 is mainly due to specific activation of extrasynaptic GluN1-N2B NMDARs and point to these receptors as possible therapeutic targets for prevention of CSD and migraine.

Negative allosteric modulators of the GluN2B NMDA receptor with phenylethylamine structure embedded in ring-expanded and ring-contracted scaffolds

A set of GluN2B NMDA receptor antagonists with conformationally restricted phenylethylamine substructure was prepared and pharmacologically evaluated. The phenylethylamine substructure was embedded in ring expanded 3-benzazocines 4 as well as ring-contracted tetralinamines 6 and indanamines 7. The ligands 4, 6 and 7 were synthesized by reductive alkylation of secondary amine 11, reductive amination of ketones 12 and 16 and nucleophilic substitution of nosylates 14 and 17. The moderate GluN2B affinity of 3-benzazocine 4d (K_i = 32 nM) translated into moderate cytoprotective activity (IC₅₀ = 890 nM) and moderate ion channel inhibition (60% at 10 μM) in two-electrode voltage clamp experiments with GluN1a/GluN2B expressing oocytes. Although some of the tetralinamines 6 and indanamines 7 showed very high GluN2B affinity (e.g. K_i (7f) = 3.2 nM), they could not inhibit glutamate/glycine inducted cytotoxicity. The low cytoprotective activity of 3-benzazocines 4, tetralinamines 6 and indanamines 7 was attributed to the missing OH moiety at the benzene ring and/or in benzylic position. Docking studies showed that the novel GluN2B ligands adopt similar binding poses as Ro 25-6981 with the central H-bond interaction between the protonated amino moiety of the ligands and the carbamoyl moiety of Gln110. However, due to the lack of a second H-bond forming group, the ligands can adopt two binding poses within the ifenprodil binding pocket.

Impact of hydroxy moieties at the benzo[7]annulene ring system of GluN2B ligands: Design, synthesis and biological evaluation

In this study, the impact of one or two hydroxy moieties at the benzo[7]annulene scaffold on the GluN2B affinity and cytoprotective activity was analyzed. The key intermediate for the synthesis of OH-substituted benzo[7]annulenamines 11-13 and 17 was the epoxyketone 8. Reductive epoxide opening of 8 resulted with high regioselectivity in the 5-hydroxyketone 9 (Pd(OAc)₂, HCO₂H, phosphane ligand) or the 6-hydroxyketone 10 (H₂, Pd/C), whereas hydrolysis in aqueous dioxane led to the dihydroxyketone 14. Reductive amination of these ketones with primary amines and NaBH(OAc)₃ afforded the benzo[7]annulenamines 11-13 and 17. In receptor binding studies 5-OH derivatives 11 and 12 showed higher GluN2B affinity than 6-OH derivatives 13, which in turn were more active than 5,6-di-OH derivative 17a. The same order was found for the cytoprotective activity of the ligands. The tertiary amine 12a with one OH moiety in 5-position represents the most promising GluN2B negative allosteric modulator with a binding affinity of K_i = 49 nM and a cytoprotective activity of IC₅₀ = 580 nM. In the binding pocket 12a shows a crucial H-bond between the benzylic OH moiety and the backbone carbonyl O-atom of Ser132 (GluN1b). It was concluded that a 5-OH moiety is essential for the inhibition of the NMDA receptor associated ion channel, whereas a OH moiety in 6-position is detrimental for binding and inhibition. An OH or CH₂OH moiety at 2-position results in binding at the ifenprodil binding site, but very weak ion channel inhibition.

Systematic review of the pharmacological agents that have been tested against spreading depolarizations

Spreading depolarization (SD) occurs alongside brain injuries and it can lead to neuronal damage. Therefore, pharmacological modulation of SD can constitute a therapeutic approach to reduce its detrimental effects and to improve the clinical outcome of patients. The major objective of this article was to produce a systematic review of all the drugs that have been tested against SD. Of the substances that have been examined, most have been shown to modulate certain SD characteristics. Only a few have succeeded in significantly inhibiting SD. We present a variety of strategies that have been proposed to overcome the notorious harmfulness and pharmacoresistance of SD. Information on clinically used anesthetic, sedative, hypnotic agents, anti-migraine drugs, anticonvulsants and various other substances have been compiled and reviewed with respect to the efficacy against SD, in order to answer the question of whether a drug at safe doses could be of therapeutic use against SD in humans.

The Bioactive Protein-Ligand Conformation of GluN2C-Selective Positive Allosteric Modulators Bound to the NMDA Receptor

N-methyl-d-aspartate (NMDA) receptors are ligand-gated, cation-selective channels that mediate a slow component of excitatory synaptic transmission. Subunit-selective positive allosteric modulators of NMDA receptor function have therapeutically relevant effects on multiple processes in the brain. A series of pyrrolidinones, such as PYD-106, that selectively potentiate NMDA receptors that contain the GluN2C subunit have structural determinants of activity that reside between the GluN2C amino terminal domain and the GluN2C agonist binding domain, suggesting a unique site of action. Here we use molecular biology and homology modeling to identify residues that line a candidate binding pocket for GluN2C-selective pyrrolidinones. We also show that occupancy of only one site in diheteromeric receptors is required for potentiation. Both GluN2A and GluN2B can dominate the sensitivity of triheteromeric receptors to eliminate the actions of pyrrolidinones, thus rendering this series uniquely sensitive to subunit stoichiometry. We experimentally identified NMR-derived conformers in solution, which combined with molecular modeling allows the prediction of the bioactive binding pose for this series of GluN2C-selective positive allosteric modulators of NMDA receptors. These data advance our understanding of the site and nature of the ligand-protein interaction for GluN2C-selective positive allosteric modulators for NMDA receptors.

New Treatment Strategies of Depression: Based on Mechanisms Related to Neuroplasticity

Major depressive disorder is a severe and complex mental disorder. Impaired neurotransmission and disrupted signalling pathways may influence neuroplasticity, which is involved in the brain dysfunction in depression. Traditional neurobiological theories of depression, such as monoamine hypothesis, cannot fully explain the whole picture of depressive disorders. In this review, we discussed new treatment directions of depression, including modulation of glutamatergic system and noninvasive brain stimulation. Dysfunction of glutamatergic neurotransmission plays an important role in the pathophysiology of depression. Ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, has rapid and lasting antidepressive effects in previous studies. In addition to ketamine, other glutamatergic modulators, such as sarcosine, also show potential antidepressant effect in animal models or clinical trials. Noninvasive brain stimulation is another new treatment strategy beyond pharmacotherapy. Growing evidence has demonstrated that superficial brain stimulations, such as transcranial magnetic stimulation, transcranial direct current stimulation, cranial electrotherapy stimulation, and magnetic seizure therapy, can improve depressive symptoms. The antidepressive effect of these brain stimulations may be through modulating neuroplasticity. In conclusion, drugs that modulate neurotransmission via NMDA receptor and noninvasive brain stimulation may provide new directions of treatment for depression. Furthermore, exploring the underlying mechanisms will help in developing novel therapies for depression in the future.

Traxoprodil, a selective antagonist of the NR2B subunit of the NMDA receptor, potentiates the antidepressant-like effects of certain antidepressant drugs in the forced swim test in mice

One of the newest substances, whose antidepressant activity was shown is traxoprodil, which is a selective antagonist of the NR2B subunit of the NMDA receptor. The main goal of the present study was to evaluate the effect of traxoprodil on animals' behavior using the forced swim test (FST), as well as the effect of traxoprodil (10 mg/kg) on the activity of antidepressants, such as imipramine (15 mg/kg), fluoxetine (5 mg/kg), escitalopram (2 mg/kg) and reboxetine (2.5 mg/kg). Serotonergic lesion and experiment using the selective agonists of serotonin receptors 5-HT1A and 5-HT2 was conducted to evaluate the role of the serotonergic system in the antidepressant action of traxoprodil. Brain concentrations of tested agents were determined using HPLC. The results showed that traxoprodil at a dose of 20 and 40 mg/kg exhibited antidepressant activity in the FST and it was not related to changes in animals' locomotor activity. Co-administration of traxoprodil with imipramine, fluoxetine or escitalopram, each in subtherapeutic doses, significantly affected the animals' behavior in the FST and, what is important, these changes were not due to the severity of locomotor activity. The observed effect of traxoprodil is only partially associated with serotonergic system and is independent of the effect on the 5-HT1A and 5-HT2 serotonin receptors. The results of an attempt to assess the nature of the interaction between traxoprodil and the tested drugs show that in the case of joint administration of traxoprodil and fluoxetine, imipramine or escitalopram, there were interactions in the pharmacokinetic phase.

NR2B antagonist CP-101,606 inhibits NR2B phosphorylation at tyrosine-1472 and its interactions with Fyn in levodopa-induced dyskinesia rat model

The augmented tyrosine phosphorylation of NR2B subunit of N-methyl-d-aspartate receptors (NMDAR) dependent on Fyn kinase has been associated with levodopa (l-dopa)-induced dyskinesia (LID). CP-101,606, one selective NR2B subunit antagonist, can improve dyskinesia. Yet, the accurate action mechanism is less well understood. In the present study, the evidences were investigated. Valid 6-hydroxydopamine-lesioned parkinsonian rats were treated with l-dopa intraperitoneally for 22 days to induce LID rat model. On day 23, rats received either CP-101,606 (0.5mg/kg) or vehicle with each l-dopa dose. On the day of 1, 8, 15, 22, and 23 during l-dopa treatment, we determined abnormal involuntary movements (AIMs) in rats. The levels of NR2B phosphorylation at tyrosine-1472 (pNR2B-Tyr1472) and interactions of NR2B with Fyn in LID rat model were detected by immunoblotting and immunoprecipitation. Results showed that CP-101,606 attenuated l-dopa-induced AIMs. In agreement with behavioral analysis, CP-101,606 reduced the augmented pNR2B-Tyr1472 and its interactions with Fyn triggered during the l-dopa administration in the lesioned striatum of parkinsonian rats. Moreover, CP-101,606 also decreased the level of Ca(2+)/calmodulin-dependent protein kinase II at threonine-286 hyperphosphorylation (pCaMKII-Thr286), which was the downstream signaling amplification molecule of NMDAR overactivation and closely associated with LID. However, the protein level of NR2B and Fyn had no difference under the above conditions. These data indicate that the inhibition of the interactions of NR2B with Fyn and NR2B tyrosine phosphorylation may contribute to the CP-101,606-induced downregulation of NMDAR function and provide benefit for the therapy of LID.

Long-Term Consequences of Traumatic Brain Injury: Current Status of Potential Mechanisms of Injury and Neurological Outcomes

Traumatic brain injury (TBI) is a significant clinical problem with few therapeutic interventions successfully translated to the clinic. Increased importance on the progressive, long-term consequences of TBI have been emphasized, both in the experimental and clinical literature. Thus, there is a need for a better understanding of the chronic consequences of TBI, with the ultimate goal of developing novel therapeutic interventions to treat the devastating consequences of brain injury. In models of mild, moderate, and severe TBI, histopathological and behavioral studies have emphasized the progressive nature of the initial traumatic insult and the involvement of multiple pathophysiological mechanisms, including sustained injury cascades leading to prolonged motor and cognitive deficits. Recently, the increased incidence in age-dependent neurodegenerative diseases in this patient population has also been emphasized. Pathomechanisms felt to be active in the acute and long-term consequences of TBI include excitotoxicity, apoptosis, inflammatory events, seizures, demyelination, white matter pathology, as well as decreased neurogenesis. The current article will review many of these pathophysiological mechanisms that may be important targets for limiting the chronic consequences of TBI.

Chaos and commotion in the wake of cortical spreading depression and spreading depolarizations

Punctuated episodes of spreading depolarizations erupt in the brain, encumbering tissue structure and function, and raising fascinating unanswered questions concerning their initiation and propagation. Linked to migraine aura and headache, cortical spreading depression contributes to the morbidity in the world's migraine with aura population. Even more ominously, erupting spreading depolarizations accelerate tissue damage during brain injury. The once-held view that spreading depolarizations may not exist in the human brain has changed, largely because of the discovery of migraine genes that confer cortical spreading depression susceptibility, the application of sophisticated imaging tools and efforts to interrogate their impact in the acutely injured human brain.

GluN2B-selective N-methyl-D-aspartate (NMDA) receptor antagonists derived from 3-benzazepines: synthesis and pharmacological evaluation of benzo[7]annulen-7-amines

Given their high neuroprotective potential, ligands that block GluN2B-containing N-methyl-D-aspartate (NMDA) receptors by interacting with the ifenprodil binding site located on the GluN2B subunit are of great interest for the treatment of various neuronal disorders. In this study, a novel class of GluN2B-selective NMDA receptor antagonists with the benzo[7]annulene scaffold was prepared and pharmacologically evaluated. The key intermediate, N-(2-methoxy-5-oxo-6,7,8,9-tetrahydro-5H-benzo[7]annulen-7-yl)acetamide (11), was obtained by cyclization of 3-acetamido-5-(3-methoxyphenyl)pentanoic acid (10 b). The final reaction steps comprise hydrolysis of the amide, reduction of the ketone, and reductive alkylation, leading to cis- and trans-configured 7-(ω-phenylalkylamino)benzo[7]annulen-5-ols. High GluN2B affinity was observed with cis-configured γ-amino alcohols substituted with a 3-phenylpropyl moiety at the amino group. Removal of the benzylic hydroxy moiety led to the most potent GluN2B antagonists of this series: 2-methoxy-N-(3-phenylpropyl)-6,7,8,9-tetrahydro-5H-benzo[7]annulen-7-amine (20 a, Ki =10 nM) and 2-methoxy-N-methyl-N-(3-phenylpropyl)-6,7,8,9-tetrahydro-5H-benzo[7]annulen-7-amine (23 a, Ki =7.9 nM). The selectivity over related receptors (phencyclidine binding site of the NMDA receptor, σ1 and σ2 receptors) was recorded. In a functional assay measuring the cytoprotective activity of the benzo[7]annulenamines, all tested compounds showed potent NMDA receptor antagonistic activity. Cytotoxicity induced via GluN2A subunit-containing NMDA receptors was not inhibited by the new ligands.

Effects of NMDA receptor antagonists with different subtype selectivities on retinal spreading depression

BACKGROUND AND PURPOSE

Spreading depression (SD) is a local, temporary disruption of cellular ionic homeostasis that propagates slowly across the cerebral cortex and other neural tissues such as the retina. Spreading depolarization associated with SD occurs in different types of stroke, and this phenomenon correlates also with the initiation of classical migraine aura. The aim of this study was to investigate how NMDA receptor antagonists with different subtype selectivity alter SD.

EXPERIMENTAL APPROACH

Immunoblotting was applied to the chick retina for NMDA receptor subunit protein analysis, and an efficient in vitro chick retinal model used with SD imaging for NMDA receptor pharmacology.

KEY RESULTS

The prominent NMDA receptor subtypes GluN1, GluN2A and GluN2B were found highly expressed in the chick retina. Nanomolar concentrations of NVP-AAM077 (GluN2A-preferring receptor antagonist) markedly suppressed high K(+) -induced SD; that is, ∼30 times more effectively than MK801. At sub-micromolar concentrations, Ro 25-6981 (GluN2B-preferring receptor antagonist) produced a moderate SD inhibition, whereas CP-101,606 (also GluN2B-preferring receptor antagonist) and UBP141 (GluN2C/2D-preferring receptor antagonist) had no effect.

CONCLUSIONS AND IMPLICATIONS

The expression of major NMDA receptor subtypes, GluN1, GluN2A and GluN2B in the chick retina makes them pertinent targets for pharmacological inhibition of SD. The high efficacy of NVP-AAM077 on SD inhibition suggests a critical role of GluN2A-containing receptors in SD genesis. Such high anti-SD potency suggests that NVP-AAM077, and other GluN2A-selective drug-like candidates, could be potential anti-migraine agents.

Brain-specific Phgdh deletion reveals a pivotal role for L-serine biosynthesis in controlling the level of D-serine, an N-methyl-D-aspartate receptor co-agonist, in adult brain

In mammalian brain, D-serine is synthesized from L-serine by serine racemase, and it functions as an obligatory co-agonist at the glycine modulatory site of N-methyl-D-aspartate (NMDA)-selective glutamate receptors. Although diminution in D-serine level has been implicated in NMDA receptor hypofunction, which is thought to occur in schizophrenia, the source of the precursor L-serine and its role in D-serine metabolism in adult brain have yet to be determined. We investigated whether L-serine synthesized in brain via the phosphorylated pathway is essential for D-serine synthesis by generating mice with a conditional deletion of D-3-phosphoglycerate dehydrogenase (Phgdh; EC 1.1.1.95). This enzyme catalyzes the first step in L-serine synthesis via the phosphorylated pathway. HPLC analysis of serine enantiomers demonstrated that both L- and D-serine levels were markedly decreased in the cerebral cortex and hippocampus of conditional knock-out mice, whereas the serine deficiency did not alter protein expression levels of serine racemase and NMDA receptor subunits in these regions. The present study provides definitive proof that L-serine-synthesized endogenously via the phosphorylated pathway is a key rate-limiting factor for maintaining steady-state levels of D-serine in adult brain. Furthermore, NMDA-evoked transcription of Arc, an immediate early gene, was diminished in the hippocampus of conditional knock-out mice. Thus, this study demonstrates that in mature neuronal circuits L-serine availability determines the rate of D-serine synthesis in the forebrain and controls NMDA receptor function at least in the hippocampus.

Lack of efficacy of NMDA receptor-NR2B selective antagonists in the R6/2 model of Huntington disease

N-methyl-D-aspartate receptor (NMDAR) mediated excitotoxicity is a probable proximate mechanism of neurodegeneration in Huntington disease (HD). Striatal neurons express the NR2B-NMDAR subunit at high levels, and this subunit is thought to be instrumental in causing excitotoxic striatal neuron injury. We evaluated the efficacy of 3 NR2B-selective antagonists in the R6/2 transgenic fragment model of HD. We evaluated ifenprodil (10 mg/kg; 100 mg/kg), RO25,6981 (10 mg/kg), and CP101,606 (30 mg/kg). Doses were chosen on the basis of pilot acute maximally tolerated dose studies. Mice were treated with subcutaneous injections twice daily. Outcomes included survival; motor performance declines assessed with the rotarod, balance beam task, and activity measurements; and post-mortem striatal volumes. No outcome measure demonstrated any benefit of treatments. Lack of efficacy of NR2B antagonists in the R6/2 model has several possible explanations including blockade of beneficial NMDAR mediated effects, inadequacy of the R6/2 model, and the existence of multiple proximate mechanisms of neurodegeneration in HD.

The effect of repetitive spreading depression on neuronal damage in juvenile rat brain

Spreading depression (SD) is pronounced depolarization of neurons and glia that travels slowly across brain tissue followed by massive redistribution of ions between intra- and extracellular compartments. There is a relationship between SD and some neurological disorders. In the present study the effects of repetitive SD on neuronal damage in cortical and subcortical regions of juvenile rat brain were investigated. The animals were anesthetized and the electrodes as well as cannula were implanted over the brain. SD-like event was induced by KCl injection. The brains were removed after 2 or 4 weeks after induction of 2 or 4 SD-like waves (with interval of 1 week), respectively. Normal saline was injected instead of KCl in sham group. For stereological study, paraffin-embedded brains were cut in 5 microm sections. The sections were stained with Toluidine Blue to measure the volume-weighted mean volume of normal neurons and the numerical density of dark neurons. The volume-weighted mean volume of normal neurons in the granular layer of the dentate gyrus and layer V of the temporal cortex in SD group were significantly decreased after four repetitive SD. Furthermore, densities of dark neurons in the granular layer of the dentate gyrus (after 2 weeks), the caudate-putamen, and layer V of the temporal cortex (after 4 weeks) were significantly increased in SD group. Repetitive cortical SD in juvenile rats may cause neuronal damage in cortical and subcortical areas of the brain. This may important in pathophysiology of SD-related neurological disorders.

Spreading depression: from serendipity to targeted therapy in migraine prophylaxis

Despite the relatively well-characterized headache mechanisms in migraine, upstream events triggering individual attacks are poorly understood. This lack of mechanistic insight has hampered a rational approach to prophylactic drug discovery. Unlike targeted abortive and analgesic interventions, mainstream migraine prophylaxis has been largely based on serendipitous observations (e.g. propranolol) and presumed class effects (e.g. anticonvulsants). Recent studies suggest that spreading depression is the final common pathophysiological target for several established or investigational migraine prophylactic drugs. Building on these observations, spreading depression can now be explored for its predictive utility as a preclinical drug screening paradigm in migraine prophylaxis.

Pharmacology of traumatic brain injury: where is the "golden bullet"?

Traumatic brain injury (TBI) represents a major health care problem and a significant socioeconomic challenge worldwide. In the United States alone, approximately 1.5 million patients are affected each year, and the mortality of severe TBI remains as high as 35%-40%. These statistics underline the urgent need for efficient treatment modalities to improve posttraumatic morbidity and mortality. Despite advances in basic and clinical research as well as improved neurological intensive care in recent years, no specific pharmacological therapy for TBI is available that would improve the outcome of these patients. Understanding of the cellular and molecular mechanisms underlying the pathophysiological events after TBI has resulted in the identification of new potential therapeutic targets. Nevertheless, the extrapolation from basic research data to clinical application in TBI patients has invariably failed, and results from prospective clinical trials are disappointing. We review the published prospective clinical trials on pharmacological treatment modalities for TBI patients and outline future promising therapeutic avenues in the field.

Metabolism, Distribution and Excretion of a Selective N-Methyl-d-Aspartate Receptor Antagonist, Traxoprodil, in Rats and Dogs

Disposition of traxoprodil ({1-[2-hydroxy-2-(4-hydroxy-phenyl)-1-methyl-ethyl]-4-phenyl-piperidin-4-ol}mesylate; TRX), a selective antagonist of the N-methyl-d-aspartate class of glutamate receptors, was investigated in rats and dogs after administration of a single i.v. bolus dose of [(14)C]TRX. Total mean recoveries of the radiocarbon were 92.5 and 88.2% from rats and dogs, respectively. Excretion of radioactivity was rapid and nearly complete within 48 h after dosing in both species. Whole-body autoradioluminography study suggested that TRX radioactivity was retained more by uveal tissues, kidney, and liver than by other tissues. TRX is extensively metabolized in rats and dogs since only 8 to 15% of the administered radioactivity was excreted as unchanged drug in the urine of these species. The metabolic pathways included aromatic hydroxylation at the phenylpiperidinol moiety, hydroxylation at the hydroxyphenyl ring, and O-glucuronidation. There were notable species-related qualitative and quantitative differences in the metabolism of TRX in rats and dogs. The hydroxylation at the 3-position of the phenol ring followed by methylation of the resulting catechol intermediate and subsequent conjugation were identified as the main metabolic pathways in dogs. In contrast, formation of the major metabolites in rats was due to oxidation at the 4'-position of the phenylpiperidinol moiety followed by further oxidation and phase II conjugation. TRX glucuronide conjugate was identified as the major circulating component in rats, whereas the glucuronide and sulfate conjugates of O-methyl catechol metabolite were the major metabolites in dog plasma. The site of conjugation of regioisomeric glucuronides was established from the differences in the collision-induced dissociation product ion spectra of their methylated products.

Effects of pan- and subtype-selective N-methyl-D-aspartate receptor antagonists on cortical spreading depression in the rat: therapeutic potential for migraine

Spreading depression (SD) has long been associated with the underlying pathophysiology of migraine. Evidence that the N-methyl-D-aspartate (NMDA) glutamate receptor (NMDA-R) is implicated in the generation and propagation of SD has itself been available for more than 15 years. However, to date, there are no reports of NMDA-R antagonists being developed for migraine therapy. In this study, an uncompetitive, pan-NMDA-R blocker, memantine, approved for clinical use, and two antagonists with selectivity for NMDA-R containing the NR2B subunit, (1S,2S)-1-(4-hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propanol (CP-101,606) and (+/-)-(R*,S*)-alpha-(4-hydroxyphenyl)-beta-methyl-4-(phenylmethyl)-1-piperidine propanol (Ro 25-6981), were investigated to assess their protective effects against SD in the rat. Under isoflurane anesthesia, d.c. potential and the related cortical blood flow and partial pressure of O2 (pO2) were recorded simultaneously at separate cortical sites. Drugs (1, 3, and 10 mg/kg i.p.) were given 1 h or 30 min before KCl application to the brain surface. Core temperature and arterial pCO2,pO2, and pH measurements confirmed physiological stability. KCl induced 7.7+/-1.8 (mean+/-S.D.) SD events with d.c. amplitude of 14.9+/-2.8 mV. Memantine and CP-101,606 dose-dependently decreased SD event number (to 2.0+/-1.8 and 2.3+/-2.9, respectively) and SD amplitude at doses relevant for therapeutic use. Ro 25-6981 also decreased SD events significantly, but less effectively (to 4.5+/-1.6), without affecting amplitude. These results indicate that NR2B-containing NMDA receptors are key mediators of SD, and as such, memantine- and NR2B-selective antagonists may be useful new therapeutic agents for the treatment of migraine and other SD-related disorders (e.g., stroke and brain injury). Whether chronic, rather than acute, treatment may improve their efficacy remains to be determined.

The effect of the selective NMDA receptor antagonist traxoprodil in the treatment of traumatic brain injury

Traumatic brain injury (TBI) remains a major public health problem, and there is a great medical need for a pharmacological treatment that could improve long-term outcome. The excitatory neurotransmitter, glutamate, has been implicated in processes leading to neurodegeneration. Traxoprodil (CP-101,606) is a novel and potent glutamate receptor antagonist that is highly selective for the NR2B subunit of the NMDA receptor; it has been shown to be neuroprotective in animal models of brain injury and ischemia. A randomized, double-blind, placebo-controlled study was therefore conducted to assess the efficacy and safety of a 72-h infusion of traxoprodil compared to placebo in subjects with computed tomography scan evidence of severe TBI (GCS 4-8). A total of 404 males and non-pregnant females, aged 16-70, were treated within 8 h of injury. At baseline, subjects were stratified by motor score severity. The results showed that a greater proportion of the traxoprodil-treated subjects had a favorable outcome on the dichotomized Glasgow Outcome Scale (dGOS) at 6 months (delta 5.5%, OR 1.3, p = 0.21, 95% CI:[0.85, 2.06]) and at last visit (delta 7.5%, OR 1.47, p = 0.07, 95% CI:[0.97, 2.25]). The mortality rate with traxoprodil treatment was 7% less than with placebo treatment (OR 1.45, p = 0.08, 95% CI:[0.96, 2.18]). Differences between treatment groups were more pronounced in the severest subset (delta 11.8% for the dGOS at last visit and delta 16.6% for mortality). Traxoprodil was well tolerated. Although these results are intriguing, no definitive claim of efficacy can be made for traxoprodil for the treatment of severe TBI.

NR2B selective NMDA receptor antagonist CP-101,606 prevents levodopa-induced motor response alterations in hemi-parkinsonian rats

Sensitization of NMDA receptors containing the NR2B subunit has been increasingly associated with various forms of synaptic plasticity, including those implicated in the pathogenesis of extrapyramidal motor dysfunction. To determine whether activation of NR2B containing receptors contributes to the development and maintenance of levodopa-induced response changes in parkinsonian animals, we evaluated the effects of the selective NR2B antagonist CP-101,606 on these response alterations in unilateral 6-hydroxydopamine (6-OHDA) lesioned rats. Three weeks of twice-daily levodopa treatment decreased the duration of the rotational response to acute levodopa challenge. The response alteration was associated with an increase in GluR1 (S831) phosphorylation in medium spiny neurons of the dorsolateral striatum. Both the attenuated rotational response and augmented GluR1 phosphorylation were decreased by CP-101,606 treatment. These CP-101,606 effects were observed when the compound was administered either at the end of chronic levodopa treatment (ameliorative effect) or together with the twice-daily levodopa treatment for 3 weeks (preventive effect). Furthermore, concurrent administration of CP-101,606 with levodopa potentiated the ability of levodopa challenge to reverse the 6-OHDA lesion-induced contralateral forelimb movement deficit as measured in a drag test. These results suggest that activation of NR2B subunit containing NMDA receptors contributes to both the development and maintenance of levodopa-induced motor response alterations, through a mechanism that involves an increase in GluR1 phosphorylation in striatal spiny neurons.

Protective effect of ifenprodil against spreading depression in the mouse entorhinal cortex

In the brain, spreading depression (SD) is characterized by a large extracellular DC shift, a massive failure of ion homeostasis and a transient cessation of neuronal function. Clinically, SD is believed to be involved in various neurological disorders including migraine and cerebrovascular diseases. The propagation of cortical SD requires the release of glutamate, and N-methyl-D-aspartate (NMDA) receptors play a crucial role in this process. Here, we have isolated the NMDA receptor-mediated component of extracellularly recorded field excitatory postsynaptic potentials (fEPSPs) in layers 2-3 of the entorhinal cortex of murine brain slices. In the absence of GABAA and AMPA receptor-mediated synaptic transmission, stimulation of layer 6 afferents every 15-90 s elicited spontaneous SD on average within 18.5 min after the start of the stimulation. In the presence of ifenprodil, an NR2B receptor subunit-selective NMDA receptor antagonist, the occurrence of SD was nearly abolished. Our results are consistent with an important role of NR2B subunits in triggering SD in the entorhinal cortex.

Antioxidant‐Accelerated Oxidative Degradation: A Case Study of Transition Metal Ion Catalyzed Oxidation in Formulation

Oxidation presents a constant challenge for formulation scientists trying to develop stable dosage forms. Antioxidants are commonly used in formulation to alleviate the oxidation problem but they do not always achieve the desired results. In this study, a case of antioxidant-accelerated oxidation degradation in formulation is reported. The oxidation mechanism of a development drug candidate (1S,2S)-1-(4-hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propanol (1) in solution was investigated under various oxidative conditions, which include at different oxygen level, with transition metal ion spiking, and under light exposure with presence of photosensitizer. Oxidative degradation products and kinetics were monitored by high-performance liquid chromatography (HPLC). Kinetic solvent isotope effects of I oxidation in formulation, under metal ion catalysis, and upon photocatalysis were obtained. Metal ion spiking, exposure to stainless steel, as well as introduction of antioxidants such as ascorbic acid, thioglycerol, and sodium bisulfate, accelerated the oxidative degradation. Treatment of the solution with metal chelating resin inhibited oxidation. Kinetic solvent isotope effects are in agreement with a metal-catalyzed oxidation mechanism and inconsistent with a singlet oxygen pathway. On the basis of kinetic data, an oxidative fragmentation mechanism initiated by a metal ion catalyzed active oxygen species is suggested as the primary pathway for the oxidative degradation of I. Other oxidative species may be implied in the long-term oxidative degradation. Because many antioxidants act as pro-oxidants in metal-catalyzed oxidation, controlling metal ion contamination level in the excipients and limiting available molecular oxygen are recommended for formulation development.

Antagonist, CP-101,606, Enhances the Functional Recovery The NMDA NR2B Subunit-Selective Receptor and Reduces Brain Damage after Cortical Compression-Induced Brain Ischemia

Using a novel in vivo model for cerebral ischemia produced by short-lasting compression of a well-defined brain area of sensorimotor cortex we studied neuroprotective effects of the NMDA NR2B subunit selective antagonist, CP-101,606, in Sprague-Dawley rats. Cortical compression for 30 min produced a consistent and highly reproducible functional impairment, that is paresis of contralateral hind and fore limbs. The neurological deficit was accompanied by marked brain damage in cerebral cortex, hippocampus and thalamus as identified by Fluoro-Jade, a marker of general neuronal cell death. Using a daily performed beam walking test it was shown that untreated animals recovered from their functional impairment within 5-7 days following surgery. Intravenous administration of increasing doses (1, 5, 10, 20 mg/kg) of the NMDA NR2B subunit receptor specific antagonist, CP-101,606, dose-dependently improved the rate of functional recovery and protected against the ischemic brain damage in cerebral cortex, hippocampus, and thalamus as identified 2 days after the ischemic insult. Based upon these results, we conclude that NMDA NR2B receptor subunits represent potential targets to reduce not only the functional deficits, but also neuronal death in cortex and several midbrain regions produced by moderate, transient, cerebral ischemia.

Characterization of N-methyl-D-aspartate receptor subunits involved in acute ammonia toxicity

Rapid administration of large doses of ammonia leads to death of animals, which is largely prevented by pretreatment with N-methyl-D-aspartate (NMDA) receptor antagonists. The present study focuses on a subunit(s) of NMDA receptor involved in ammonia-induced death by use of NMDA receptor GluRepsilon subunit-deficient (GluRepsilon(-/-)) mice and the selective GluRepsilon2 antagonist CP-101,606. Acute ammonia intoxication was induced in mice (eight per group) by a single intraperitoneal (i.p.) injection of ammonium chloride. Appearance of neurological deteriorations depended on the doses of ammonium chloride injected. While wild-type, GluRepsilon1(-/-), GluRepsilon4(-/-), and GluRepsilon1(-/-)/epsilon4(-/-) mice all died by ammonium chloride at 12 mmol/kg during the first tonic convulsions, two of eight GluRepsilon3(-/-) mice survived. Pretreatment of wild-type mice with CP-101,606 prevented two mice from ammonia-induced death. Pretreatment of GluRepsilon3(-/-) mice with CP-101,606 prevented the death of three mice and prolonged the time of death of non-survivors. Similarly, the neuronal form of nitric oxide synthase (NOS) inhibitor 7-nitroindazole (7-NI) as well as the nonselective NOS inhibitor L-NMMA, but not the inducible NOS inhibitor 1400W, partially prevented the death of mice and prolonged the period of death. Furthermore, ammonium chloride prolonged the increase in intracellular free Ca2+ concentration ([Ca2+]i) and subsequent NO production induced by NMDA in the cerebellum. These results suggest that activation of NMDA receptor containing GluRepsilon2 and GluRepsilon3 subunits and following activation of neuronal NOS are involved in acute ammonia intoxication which leads to death of animals.

Treatment with the snail peptide CGX-1007 reduces DNA damage and alters gene expression of c-fos and bcl-2 following focal ischemic brain injury in rats

Delayed cell death following ischemic brain injury has been linked to alterations in gene expression. In this study we have evaluated the upregulation of several genes associated with delayed cell death (c-fos, bax, and bcl-2) during the initial 24 h of transient middle cerebral artery occlusion (MCAo) in the rat and the effects of postinjury treatment with the NR2B subunit specific NMDA receptor antagonist CGX-1007 (Conantokin-G, Con-G). C-fos mRNA levels peaked at 1 h postinjury in both cortical and subcortical ischemic brain regions (30-fold increase), remained elevated at 4 h and returned to within normal, preinjury levels 24 h postinjury. The increase in mRNA levels correlated to increased protein expression in the entire ipsilateral hemisphere at 1 h. Regions of necrosis at 4 h were void of C-Fos immunoreactivity with continued upregulation in surrounding regions. At 24 h, loss of C-Fos staining was observed in the injured hemisphere except for sustained increases along the border of the infarct and in the cingulate cortex of vehicle treated rats. CGX-1007 treatment reduced c-fos expression throughout the infarct region by up to 50%. No significant differences were measured in either bcl-2 or bax mRNA expression between treatment groups. However, at 24 h postinjury CGX-1007 treatment was associated with an increase in Bcl-2 immunoreactivity that correlated to a reduction in DNA fragmentation. In conclusion, CGX-1007 effectively attenuated gene expression associated with delayed cell death as related to a neuroprotective relief of cerebral ischemia.

Reduced brain infarct volume and improved neurological outcome by inhibition of the NR2B subunit of NMDA receptors by using CP101,606-27 alone and in combination with rt-PA in a thromboembolic stroke model in rats

OBJECT

A novel postsynaptic antagonist of N-methyl-D-aspartate (NMDA) receptors, CP-101,606-27 may attenuate the effects of focal ischemia. In current experiments, the authors investigated its neuroprotective effect alone and in combination with recombinant tissue plasminogen activator (rt-PA) in thromboembolic focal cerebral ischemia in rats.

METHODS

Forty-eight male Wistar rats underwent embolization of the right middle cerebral artery to produce focal cerebral ischemia. After random division into six groups (eight rats in each group), animals received: vehicle; low-dose (LD) CP-101, 606-27, 14.4 mg/kg; high-dose (HD) CP- 101,606-27, 28.8 mg/kg; rt-PA, 10 mg/kg; low-dose combination (LDC) CP- 101,606-27, 14.4 mg/kg plus rt-PA, 10 mg/kg; or high-dose combination (HDC) CP- 101,606-27, 28.8 mg/kg plus rt-PA, 10 mg/kg) 2 hours after induction of embolic stroke. Animals were killed 48 hours after the onset of focal ischemia. Brain infarction volume, neurobehavioral outcome, poststroke seizure activity, poststroke mortality, and intracranial hemorrhage incidence were observed and evaluated. Compared with vehicle-treated animals (39.4 +/- 8.6%) 2 hours posttreatment with CP-101,606-27 or rt-PA or in combination a significant reduction in the percentage of brain infarct volume was seen (LD CP-101,606-27: 20.8 +/- 14.3%, p < 0.05; HD CP-101,606-27: 10.9 +/- 3.2%, p < 0.001; rt-PA: 21.1 +/- 7.3%, p < 0.05; LDC, 18.6 +/- 11.5%, p < 0.05; and HDC: 15.2 +/- 10.1%, p < 0.05; compared with control: 39.4 +/- 8.6%). Combination of CP-101,606-27 with rt-PA did not show a significantly enhanced neuroprotective effect. Except for the control and LDC treatment groups, neurobehavioral outcome was significantly improved 24 hours after embolic stroke in animals in all other active therapeutic groups receiving CP-101,606-27 or rt-PA or in combination. The authors also observed that treatment with HD CP-101,606-27 decreased poststroke seizure activity.

CONCLUSIONS

The data in this study suggested that postischemia treatment with CP-101,606-27 is neuroprotective in the current stroke model; however, the authors also note that although rt-PA may offer modest protection when used alone, combination with CP-101,606-27 did not appear to enhance its effects.

The N-methyl-D-aspartate receptor subunit NR2B: localization, functional properties, regulation, and clinical implications

The N-methyl-D-aspartate (NMDA) receptor is an example of a heteromeric ligand-gated ion channel that interacts with multiple intracellular proteins by way of different subunits. NMDA receptors are composed of seven known subunits (NR1, NR2A-D, NR3A-B). The present review focuses on the NR2B subunit of the receptor. Over the last several years, an increasing number of reports have demonstrated the importance of the NR2B subunit in a variety of synaptic signaling events and protein-protein interactions. The NR2B subunit has been implicated in modulating functions such as learning, memory processing, pain perception, and feeding behaviors, as well as being involved in a number of human disorders. The following review provides a summary of recent findings regarding the structural features, localization, functional properties, and regulation of the NR2B subunit. The review concludes with a section discussing the role of NR2B in human diseases.

Metabolism, pharmacokinetics, and excretion of a highly selective N-methyl-D-aspartate receptor antagonist, traxoprodil, in human cytochrome P450 2D6 extensive and poor metabolizers

The excretion, biotransformation, and pharmacokinetics of a selective N-methyl-D-aspartate receptor antagonist, traxoprodil, were investigated in six healthy male volunteers, phenotyped either as CYP2D6 extensive or poor metabolizers of dextromethorphan. Each subject received an i.v. infusion of a single 50-mg (100 microCi) dose of [(14)C]traxoprodil. Approximately 89% of the administered dose was recovered in poor metabolizers (PMs) and 61% in extensive metabolizers (EMs), with the majority of the dose being excreted in the urine (86% in PMs and 52% in EMs). The elimination of traxoprodil was more rapid in EMs than in PMs with terminal elimination half-lives of 2.8 and 26.9 h, respectively, for EMs and PMs. Area under the plasma concentration-time curve from time 0 to T (AUC((0-Tlast))) values for unchanged traxoprodil were 1.2 and 32.7% of the corresponding AUC values for total radioactivity in EMs and PMs, respectively. Traxoprodil was metabolized in both EMs and PMs, with approximately 7 and 50% of the administered radioactivity excreted as unchanged drug in the excreta of EMs and PMs, respectively. Hydroxylation at the 3-position of the hydroxyphenyl ring and methylation of the resulting catechol followed by conjugation were identified as the main metabolic pathways in EMs. In contrast, direct conjugation of traxoprodil with glucuronic or sulfuric acid was the major pathway in PMs. In vitro studies using CYP2D6-selective inhibitor and recombinant enzyme also support that the metabolism of traxoprodil is mainly mediated by CYP2D6. Taken together, these studies suggest that traxoprodil is eliminated mainly by Phase I oxidative metabolism mediated by CYP2D6 isozyme in EMs and by Phase II conjugation and renal clearance of parent in PMs.

Accumulation of Quinolinic Acid With Neuroinflammation: Does It Mean Excitotoxicity?

The quinolinic acid (QUIN) accumulation that is associated with neuroinflammation is often considered capable of promoting excitotoxic neuronal damage, but QUIN is a relatively weak agonist of N-methyl-D-aspartate (NMDA) receptors. Our study aimed to determine, in vivo, which extracellular concentrations of QUIN must be reached to initiate electrophysiological changes indicative of excitotoxic stress in the cerebral cortex of rats, under normal conditions and when superimposed to a challenge involving NMDA-receptor activation, i.e. repeated cortical spreading depression (CSD). Our experimental strategy relied on microdialysis probes incorporating an electrode, implanted in the brain of halothane-anaesthetised rats. These devices were used to apply QUIN or NMDA locally to the cortical area under study (with or without co-perfusion of high K+ for repetitive induction of CSD), and to record the associated changes in the extracellular DC potential (for information on the membrane polarisation of the cellular population surrounding the probe) and lactate (for the detection of increased local energy demand). The extracellular EC50 for induction of local depolarisation in the normal cortex was around 30 times higher than the extracellular QUIN levels measured in the immunoactivated brain of gerbils. Within the range of concentrations 0.03 to 0.3 mM in the perfusion medium, QUIN suppressed concentration-dependently the elicitation of CSD by K+, presumably because of NMDA-receptor desensitisation. Finally, on-line monitoring of changes in extracellular lactate with local application of QUIN indicated that extracellular concentration of QUIN in the low micromolar range are well tolerated by the brain parenchyma, at least in cortical regions. All these data do not support the notion that QUIN accumulation adds an excitotoxic component to neuroinflammation.

Reduced NR2A expression and prolonged decay of NMDA receptor-mediated synaptic current in rat vagal motoneurons following axotomy

To elucidate characteristic changes in the N-methyl-D-aspartate (NMDA) receptor on neurons following axotomy, subunit expressions and functional features of the NMDA receptor were examined in the dorsal motor nucleus of vagus (DMV) of rats receiving vagal axotomy at the neck. Western blotting analysis demonstrated that the expression of NR2A decreased 2-3 days after in vivo axotomy, while expression of NR1 and NR2B, NR2C and NR2D subunits did not change significantly. To examine the functional changes, patch clamp recordings in whole-cell mode were employed on the axotomized DMV neurons identified by retrograde labelling with fluorescent dye. The amplitude ratios of ifenprodil-sensitive components of NMDA response and D,L-2-amino-5-phosphovaleric acid (APV)-sensitive evoked postsynaptic current increased after axotomy. In addition, APV-sensitive postsynaptic currents exhibited a longer decay time in identified axotomized vagal motoneurons than in control neurons. No significant differences in the current density of the NMDA response and the peak amplitude of APV-sensitive synaptic currents were observed between axotomized and intact DMV neurons. In conclusion, a decrease in NR2A expression results in the appearance of functional characteristics of the NMDA receptor predominantly containing the NR2B subunit. This might lead to a long-term increase of the susceptibility of neurons to excitotoxicity.

Extradural compression of sensorimotor cortex: a useful model for studies on ischemic brain damage and neuroprotection

Behavioral and morphological changes were examined for up to 9 days after moderate cerebral ischemia caused by slow compression of a specific brain area in the sensorimotor cortex of Sprague-Dawley rats. Functional deficits after the cerebral ischemia were assessed by daily beam-walking tests, whereas morphological changes were verified using Nissl staining on day 1, 2, 3, 5, and 9, respectively. Rats exposed to cerebral ischemia displayed impaired beam walking performance. Mild hypothermia prevented both the compression-produced functional deficits and the brain damage. Younger (5 weeks) animals showed less neurological deficits than older (9 weeks) animals. Histological examination revealed a pronounced increase in the number of injured pyramidal neurons from day 1 to day 3 in the primarily damaged brain region. Between day 3 and day 5, the number of injured cells remained constant, whereafter there was a slow decline of thionin-positive neurons as examined on day 9. The noncompetitive NMDA receptor antagonist, dizocilpine (MK-801; 3 mg/kg, i.p.), did not alter the neurological impairment on day 1, but improved thereafter the rate of functional recovery and reduced the number of damaged cells. The AMPA receptor antagonist, LY326325 (15 or 30 mg/kg; i.p.), dose-dependently diminished the neurological deficits on day 1, enhanced the rate of recovery, and reduced the number of injured neurons over time. Our data suggest that short-lasting extradural compression of a well-defined brain area in the sensorimotor cortex is a highly reproducible model with a high success rate for the study of functional and morphological consequences after cerebral ischemia as well as for the evaluation of the therapeutic potential of novel, neuroprotective pharmacological agents.