Additive neuroprotective effects of dextrorphan and cycloheximide in rats subjected to transient focal cerebral ischemia

The Physio-Pathological Role of Group I Metabotropic Glutamate Receptors Expressed by Microglia in Health and Disease with a Focus on Amyotrophic Lateral Sclerosis

Microglia cells are the resident immune cells of the central nervous system. They act as the first-line immune guardians of nervous tissue and central drivers of neuroinflammation. Any homeostatic alteration that can compromise neuron and tissue integrity could activate microglia. Once activated, microglia exhibit highly diverse phenotypes and functions related to either beneficial or harmful consequences. Microglia activation is associated with the release of protective or deleterious cytokines, chemokines, and growth factors that can in turn determine defensive or pathological outcomes. This scenario is complicated by the pathology-related specific phenotypes that microglia can assume, thus leading to the so-called disease-associated microglia phenotypes. Microglia express several receptors that regulate the balance between pro- and anti-inflammatory features, sometimes exerting opposite actions on microglial functions according to specific conditions. In this context, group I metabotropic glutamate receptors (mGluRs) are molecular structures that may contribute to the modulation of the reactive phenotype of microglia cells, and this is worthy of exploration. Here, we summarize the role of group I mGluRs in shaping microglia cells' phenotype in specific physio-pathological conditions, including some neurodegenerative disorders. A significant section of the review is specifically focused on amyotrophic lateral sclerosis (ALS) since it represents an entirely unexplored topic of research in the field.

Brain vulnerability and viability after ischaemia

The susceptibility of the brain to ischaemic injury dramatically limits its viability following interruptions in blood flow. However, data from studies of dissociated cells, tissue specimens, isolated organs and whole bodies have brought into question the temporal limits within which the brain is capable of tolerating prolonged circulatory arrest. This Review assesses cell type-specific mechanisms of global cerebral ischaemia, and examines the circumstances in which the brain exhibits heightened resilience to injury. We suggest strategies for expanding such discoveries to fuel translational research into novel cytoprotective therapies, and describe emerging technologies and experimental concepts. By doing so, we propose a new multimodal framework to investigate brain resuscitation following extended periods of circulatory arrest.

Apoptotic cell death regulation in neurons

Apoptosis plays a major role in shaping the developing nervous system during embryogenesis as neuronal precursors differentiate to become post-mitotic neurons. However, once neurons are incorporated into functional circuits and become mature, they greatly restrict their capacity to die via apoptosis, thus allowing the mature nervous system to persist in a healthy and functional state throughout life. This robust restriction of the apoptotic pathway during neuronal differentiation and maturation is defined by multiple unique mechanisms that function to more precisely control and restrict the intrinsic apoptotic pathway. However, while these mechanisms are necessary for neuronal survival, mature neurons are still capable of activating the apoptotic pathway in certain pathological contexts. In this review, we highlight key mechanisms governing the survival of post-mitotic neurons, while also detailing the physiological and pathological contexts in which neurons are capable of overcoming this high apoptotic threshold.

Protective effect of melatonin on 3-NP induced striatal interneuron injury in rats

To confirm the effect of melatonin on 3-nitropropionic acid (3-NP)-induced striatal interneuron injury in rats, behavioral test, histology, immunohistochemistry and Western blotting were respectively used to characterize the behavioral changes of experimental animals in motor and cognition, the morphological changes of striatal interneurons and the expression level of protein markers induced by 3-NP. The results showed that (1) 3-NP induced dysfunction of experimental animals in movement, motor coordination and cognition could be relieved by melatonin treatment; (2) The 3-NP-induced lesion area was unvaryingly in dorsolateral striatum, with almost all neuronal loss in the lesion core, however, lots of neurons survived after melatonin treatment; (3) Immunohistochemical staining of the four interneuron types (parvalbuminergic, cholinergic, calretinergic, and neuropeptide Y-neuronal nitric oxide synthase co-containing) showed that, in the lesion core of 3-NP group, loss of the four interneuron types was obvious, but in transition zone, the processes and varicosities of calretinergic, and neuropeptide Y-neuronal nitric oxide synthase co-containing interneurons increased significantly. Melatonin treatment reduced the loss of the four interneuron types in the lesion core, and inhibited the increase of processes and varicosities in the transition zone; (4) Consistent with above results, the expression level of five interneuron protein markers were significantly increased in the striatum after melatonin treatment. Notably, in both the transition zone and the lesion core induced by 3-NP, TUNEL-positive cells were detected, but decreased significantly after melatonin treatment. The present results indicate that melatonin effectively protects the striatal neurons against the injury induced by 3-NP in rats.

Advances in stroke neuroprotection: hyperoxia and beyond

Refinements in patient selection, improved methods of drug delivery, use of more clinically relevant animal stroke models, and the use of combination therapies that target the entire neurovascular unit make stroke neuroprotection an achievable goal. This article provides an overview of the major mechanisms of neuronal injury and the status of neuroprotective drug trials and reviews emerging strategies for treatment of acute ischemic stroke. Advances in the fields of stem cell transplantation, stroke recovery, molecular neuroimaging, genomics, and proteomics will provide new therapeutic avenues in the near future. These and other developments over the past decade raise expectations that successful stroke neuroprotection is imminent.

New Goals in Ischemic Stroke Therapy: The Experimental Approach – Harmonizing Science with Practice

Undeniable advances have been made in clinical and experimental investigation into the pathophysiology, diagnosis, and treatment of cerebral ischemia. However, with the exception of intravenous thrombolysis and some neuroprotectors, such as citicoline, the majority of the drugs successfully tested in experimental studies have failed in clinical trials. Valuable lessons for the improvement of research methodology and appropriate coordination of experimental and clinical research can be learnt from the analysis of discrepancies between the laboratory and clinic, which will allow us to increase the power and cost-effectiveness of the studies. In addition, this progress has opened the way for the investigation of very promising new therapeutic strategies, such as combined pharmacological and mechanical thrombolysis, thrombolysis and neuroprotection, or the combination of various neuroprotectors, antiapoptotic therapies, and neurorestoration therapies, such as stem cell transplants.

Relationship between S100β and GFAP expression in astrocytes during infarction and glial scar formation after mild transient ischemia

The expression of astrocyte marker proteins (S100beta and GFAP) during infarction and glial scar formation after transient middle cerebral artery (MCA) occlusion was examined using double immunostaining. S100beta immunoreactivity markedly decreased in the core of the injured area when observed immediately after reperfusion and did not increase again. In the periphery, however, S100beta expression increased, showing that S100beta synthesis was up-regulated. S100beta+/iNOS+ astrocytes in the periphery were observed from day 1, when small infarct areas were detectable, up to day 5, when infarct expansion had almost ended. TUNEL+ cells in the periphery were present from days 1 to 5. S100beta+/TUNEL+ cells were observed centrally and around the periphery of the injured area, predicting that cell death contributes to the increase of S100beta concentration in the injured area. Our results suggest that (1) higher concentration of S100beta in the extracellular space due to S100beta leakage from damaged astrocytes leads to up-regulation of S100beta synthesis and induction of inducible nitric oxide synthase (iNOS) synthesis in astrocytes, contributing to infarct expansion that results in DNA damage or cell death via NO and ROS production, and (2) GFAP, but not S100beta, is a main contributor to glial scar formation. On day 1 postreperfusion, the microdiascopic images of the injured areas from the unstained thick sections or the areas detected by S100beta immunoreactivity were larger than those of the infarct areas detected by hematoxylin--eosin (HE)-staining. The difference between these sizes might be useful to predict infarct expansion.

Hypoxia-induced modification of poly (ADP-ribose) polymerase and dna polymerase beta activity in cerebral cortical nuclei of newborn piglets: role of nitric oxide

Previous studies have shown that poly (ADP-ribose) polymerase (PARP) and DNA polymerase beta, nuclear enzymes, are associated with cell replication and DNA repair. The present study tests the hypothesis that hypoxia results in increased PARP and DNA polymerase activity in cerebral cortical neuronal nuclei to repair the hypoxia-induced damage to genomic DNA. Studies were conducted in 13 anesthetized and ventilated newborn piglets (age 3-5 days) divided into normoxic (n=5) and hypoxic (n=8) groups. Hypoxia was induced by decreasing inspired oxygen from 21% to 7% for 60 min. Cerebral tissue hypoxia was documented biochemically by determining the tissue levels of ATP and phosphocreatine (PCr). Following isolation of the cortical neuronal nuclei, the activity of PARP and DNA polymerase beta was determined. During hypoxia, the tissue ATP level decreased by 73% from 4.12+/-0.67 micromol/g brain to 1.12+/-0.34 micromol/g brain, and PCr decreased by 78% from 4.14+/-0.68-0.90+/-0.20 micromol/g brain. In hypoxic neuronal nuclei, PARP activity significantly increased from 5.88+/-0.51 pmol NAD/mg protein/h in normoxic nuclei to 10.04+/-2.02 (P=0.001). PARP activity inversely correlated with tissue ATP (r=0.78) and PCr levels (r=0.81). Administration of N-nitro-L-arginine prior to hypoxia decreased the hypoxia-induced increase in PARP activity by 67%. Endogenous DNA polymerase beta activity increased from 0.96+/-0.13 in normoxic nuclei to 1.39+/-0.18 nmol/mg protein/h in hypoxic nuclei (P<0.005). DNA polymerase beta activity in the presence of exogenous template increased from 1.54+/-0.14 in the normoxic to 2.42+/-0.26 nmol/mg protein/h in the hypoxic group (P<0.005). DNA polymerase beta activity in the presence or absence of template inversely correlated with the tissue ATP (r=0.95 and 0.84, respectively) and PCr levels (r=0.93 and 0.77, respectively). These results demonstrate that the activity of PARP and DNA polymerase beta enzymes increase with the increase in degree of cerebral tissue hypoxia. Furthermore, the results demonstrate a direct correlation between the PARP and the DNA polymerase beta activity. We conclude that tissue hypoxia results in increased PARP and DNA polymerase beta activities indicating activation of DNA repair mechanisms that may result in potential neuronal recovery following hypoxia and the hypoxia-induced increase in PARP activity is NO-mediated.

Expression of angiotensin type 1 and 2 receptors in brain after transient middle cerebral artery occlusion in rats

Angiotensin II (Ang II) type 2 receptors (AT2Rs) have been associated with apoptosis. We hypothesized that AT2Rs are increased in stroke and may contribute effects of stroke to the brain. To test this, we have examined the expression of Ang II type 1 receptor (AT1R), AT2R and Ang II levels in the brain 24 h after transient middle cerebral artery occlusion (MCAO). The densities of AT1R and AT2R were measured by quantitative autoradiography (n=6). The levels of Ang II were measured by radioimmunoassay (RIA) (n=6) and by immunohistochemistry (n=3). AT1R levels on autoradiography showed a significant decrease (0.87+/-0.06 to 1.39+/-0.07 fmol/mg, p<0.01) in the ventral cortex of the stroke side compared to the cortices of non-stroke (NS) rats (n=4). There was no significant difference on ATIR in the contralateral verbal cortex of the stroke rats compared to NS control. In contrast, levels of AT2R in the ventral cortex of both the stroke and the contralateral sides were significantly increased (0.77+/-0.06, p<0.05 and 0.91+/-0.05, p<0.01 compared to 0.60+/-0.03 fmol/mg tissue, respectively). RIA showed that Ang II in the ventral cortex of both the stroke and the contralateral sides were significantly increased (241.63+/-47.72, p<0.01 and 165.51+/-42.59, p<0.05 compared to 76.80+/-4.10 pg/g tissue, respectively). Also, Ang II in the hypothalamus was significantly increased (179.50+/-17.49 to 118.50+/-6.65 pg/g tissue, p<0.05). Immunohistochemistry confirmed the increase of Ang II. These results demonstrate that brain Ang II and AT2Rs are increased whereas AT1Rs are decreased after transient MCAO in rats. We conclude that in stroke, Ang II and AT2R are activated and may contribute neural effects to brain ischemia.

Neuroprotective synergy of N-methyl-D-aspartate receptor antagonist (MK801) and protein synthesis inhibitor (cycloheximide) on spinal cord ischemia-reperfusion injury in rats

Thoraco-abdominal aortic surgery requiring temporal cross clamping of the aorta results in a high incidence of paraplegia due to temporary ischemia of the spinal cord. Both excitotoxicity and apoptosis are implicated in the pathogenesis of spinal cord ischemia-reperfusion injury. We propose that the N-methyl-D-aspartate receptor antagonist dizocilpine maleate (MK801) and the protein synthesis inhibitor cycloheximide produce a synergic effect in a rodent model of spinal cord ischemia-reperfusion injury. Injury was induced by 20 min of temporal thoracic aorta occlusion and distal blood volume reduction. After injury, the animals were treated with vehicle, MK801, cycloheximide or MK801 and cycloheximide. Hind limb motor function recovery was better in the MK801 and combined therapy groups than in the control and cycloheximide groups. The mean neuronal survival rate of the control group was 45.3 +/- 3.2% on the 7(th) day after injury. In the MK801 and cycloheximide treatment groups, neuronal survival increased to 62.4 +/- 3.6% and 54.1 +/- 2.4%, respectively. For the combined therapy group, neuronal survival increased to 75.6 +/- 2.5%. The number of apoptotic cells in the control group was 211.4 +/- 8.8 per section on the 7th day after ischemic insult, while apoptosis was significantly reduced in the cycloheximide (96.8 +/- 6.7 cells) and combined (84.8 +/- 8.5 cells) groups. It was unchanged in the MK801 group (209.8 +/- 5.4 cells). These results suggest that combined treatments directed at blocking both N-methyl-D-aspartate receptor-mediated excitotoxic necrosis and caspase-mediated apoptosis might have synergic therapeutic potential in reducing spinal cord ischemia-reperfusion injury.

Toward wisdom from failure: lessons from neuroprotective stroke trials and new therapeutic directions

BACKGROUND

Neuroprotective drugs for acute stroke have appeared to work in animals, only to fail when tested in humans. With the failure of so many clinical trials, the future of neuroprotective drug development is in jeopardy. Current hypotheses and methodologies must continue to be reevaluated, and new strategies need to be explored. Summary of Review- In part 1, we review key challenges and complexities in translational stroke research by focusing on the "disconnect" in the way that neuroprotective agents have traditionally been assessed in clinical trials compared with animal models. In preclinical studies, determination of neuroprotection has relied heavily on assessment of infarct volume measurements (instead of functional outcomes), short-term (instead of long-term) end points, transient (instead of permanent) ischemia models, short (instead of extended) time windows for drug administration, and protection of cerebral gray matter (instead of both gray and white matter). Clinical trials have often been limited by inappropriately long time windows, insufficient statistical power, insensitive outcome measures, inclusion of protocol violators, failure to target specific stroke subtypes, and failure to target the ischemic penumbra. In part 2, we explore new concepts in ischemic pathophysiology that should encourage us also to think beyond the hyperacute phase of ischemia and consider the design of trials that use multiagent therapy and exploit the capacity of the brain for neuroplasticity and repair.

CONCLUSIONS

By recognizing the strengths and limitations of animal models of stroke and the shortcomings of previous clinical trials, we hope to move translational research forward for the development of new therapies for the acute and subacute stages after stroke.

Troglitazone inhibits both post-glutamate neurotoxicity and low-potassium-induced apoptosis in cerebellar granule neurons

Both excitotoxicity and apoptosis contribute to neuronal loss in various neurodegenerative diseases such as Alzheimer's disease as well as stroke, and a drug inhibiting both types of cell death may lead to practical treatment for these diseases. Post-treatment with troglitazone, a potent and specific activator of peroxisome proliferator-activated receptor (PPAR)-gamma attenuated the cell death of cerebellar granule neurons, triggered by glutamate exposure. The inhibitory effect of troglitazone against glutamate excitotoxicity, in vitro, was observed even when added 2.5 h after the end of glutamate exposure, a time when glutamate antagonists are no longer neuroprotective. However, troglitazone did not block the glutamate-induced elevation of calcium influx, suggesting that troglitazone interfered with downstream consequences of excitotoxic glutamate receptor overactivation. In addition, troglitazone also suppressed low-potassium-induced apoptosis in cerebellar granule neurons in a phosphatidylinositol 3-kinase independent manner. In conclusion, although the mechanisms of troglitazone's neuroprotective effects are unknown, the post-treatment-neuroprotective effect and the dual-inhibitory-activity against both excitotoxicity and apoptosis may provide a novel therapy for various neurodegenerative diseases.

Combination therapy for ischemic stroke: potential of neuroprotectants plus thrombolytics

Thrombolysis improves clinical outcome in patients with acute ischemic stroke. However, only a small fraction of patients receive thrombolytic therapy due to the narrow therapeutic time window available for the treatment in patients with ischemic stroke. A better understanding of the mechanisms underlying ischemic injury may lead to the development of novel therapeutic strategies to reduce brain damage after stroke. Cerebral ischemia triggers a number of pathophysiological and biochemical changes in the brain that present potential targets for therapeutic intervention. Candidate pathways include those regulating cellular calcium influx, excitatory neurotransmitter uptake, and generation of reactive oxygen species, as well as activation of enzymes including kinases, proteases, and lipases. The end result of these pathophysiological pathways may be apoptosis (programmed cell death) or necrosis. The activation of inflammatory cascades following ischemia also contributes to brain injury. Several neuroprotective agents which block cell death pathways have been proposed to have therapeutic potential in patients with stroke including calcium channel antagonists, glutamate receptor antagonists, free radical scavengers, anti-inflammatory strategies, inhibitors for nitric oxide synthase, and growth factors. Although results from clinical trials to date have been disappointing, there is reason to believe that combination therapy involving both thrombolytics and neuroprotectants holds promise for stroke treatment and warrants further investigation.

Cycloheximide reduces infarct volume when administered up to 6 h after mild focal ischemia in rats

We have previously described a rodent model of brief (30 min) middle cerebral artery occlusion followed by reperfusion, in which infarction develops gradually, reaching completion more than 3 days after ischemia, accompanied by morphological, biochemical, and pharmacological evidence of apoptosis. In the present study, we tested the hypotheses that delayed administration of a protein synthesis inhibitor would be effective in reducing tissue injury in this slowly evolving ischemic infarction, and that efficacy of this treatment would wane with more prolonged ischemia. Focal cerebral ischemia was induced in Long-Evans rats by occlusion of the right middle cerebral artery. Infarction volume was analyzed using triphenyl tetrazolium chloride staining, and morphology was studied using hematoxylin and eosin stained sections. Following 30 min middle cerebral artery occlusion and reperfusion, the core ischemic region exhibited vacuolization in the neuropil by 36 h after ischemia, and infarction reached full size by 7 days after ischemia. Cycloheximide reduced infarct volume when given up to 6 h after ischemia. If the duration of ischemic insult was increased to 90 min, the therapeutic window for delayed cycloheximide was only 30 min. In permanent middle cerebral artery occlusion, cycloheximide was ineffective even when given prior to ischemia onset. After mild, but not severe, ischemic insults, cerebral infarction develops slowly and may be treatable with protein synthesis inhibitors, even when treatment is delayed for up to 6 h after the onset of ischemia.

Suppression subtraction hybridization and northern analysis reveal upregulation of heat shock, trkB, and sodium calcium exchanger genes following global cerebral ischemia in the rat

Driver (sham-operated) and tester (ischemic) hippocampal cDNAs were subtracted, and the resulting ischemia-induced upregulated gene expression was verified by northern analysis. cDNAs isolated corresponded to (1) genes known to be upregulated following ischemia, (hsc70, hsp90, hsp105 and trkB) and (2) a gene not previously implicated with cerebral ischemia, sodium calcium exchanger (ncx). Furthermore, upregulation of these genes was demonstrated following preconditioning transient global ischemia.

Hibernation, a model of neuroprotection

Hibernation, a natural model of tolerance to cerebral ischemia, represents a state of pronounced fluctuation in cerebral blood flow where no brain damage occurs. Numerous neuroprotective aspects may contribute in concert to such tolerance. The purpose of this study was to determine whether hibernating brain tissue is tolerant to penetrating brain injury modeled by insertion of microdialysis probes. Guide cannulae were surgically implanted in striatum of Arctic ground squirrels before any of the animals began to hibernate. Microdialysis probes were then inserted in some animals after they entered hibernation and in others while they remained euthermic. The brain tissue from hibernating and euthermic animals was examined 3 days after implantation of microdialysis probes. Tissue response, indicated by examination of hematoxylin and eosin-stained tissue sections and immunocytochemical identification of activated microglia, astrocytes, and hemeoxygenase-1 immunoreactivity, was dramatically attenuated around probe tracks in hibernating animals compared to euthermic controls. No difference in tissue response around guide cannulae was observed between groups. Further study of the mechanisms underlying neuroprotective aspects of hibernation may lead to novel therapeutic strategies for stroke and traumatic brain injury.

ORP150 protects against hypoxia/ischemia-induced neuronal death

Oxygen-regulated protein 150 kD (ORP150) is a novel endoplasmic-reticulum-associated chaperone induced by hypoxia/ischemia. Although ORP150 was sparingly upregulated in neurons from human brain undergoing ischemic stress, there was robust induction in astrocytes. Cultured neurons overexpressing ORP150 were resistant to hypoxemic stress, whereas astrocytes with inhibited ORP150 expression were more vulnerable. Mice with targeted neuronal overexpression of ORP150 had smaller strokes compared with controls. Neurons with increased ORP150 demonstrated suppressed caspase-3-like activity and enhanced brain-derived neurotrophic factor (BDNF) under hypoxia signaling. These data indicate that ORP150 is an integral participant in ischemic cytoprotective pathways.

Intravenous basic fibroblast growth factor (bFGF) decreases DNA fragmentation and prevents downregulation of Bcl-2 expression in the ischemic brain following middle cerebral artery occlusion in rats

In previous studies, we showed that basic fibroblast growth factor (bFGF) reduced infarct volume when infused intravenously in animal models of focal cerebral ischemia. In the current study, we examined the potential mechanism of infarct reduction by bFGF, especially effects on apoptosis within the ischemic brain. We found that bFGF decreased DNA fragmentation in the ischemic hemisphere, as assessed by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) histochemical methods combined with morphological criteria. bFGF also prevented reduction of immunoreactivity of the anti-apoptotic protein Bcl-2 in the ischemic hemisphere, but did not alter immunoreactivity of the pro-apoptotic proteins Bax, Caspase-1, or Caspase-3. These changes in TUNEL histochemistry and Bcl-2 immunoreactivity were especially prominent in cortex at the borders ('penumbra') of infarcts, spared by bFGF treatment. We conclude that the infarct-reducing effects of bFGF may be due, in part, to prevention of downregulation of Bcl-2 expression and decreased apoptosis in the ischemic brain.

Biological plasticity: the future of science in neurosurgery

THE FUTURE OF neurosurgery is intimately related to the future of neuroscientific research. Although the field of neuroscience is immense and not subject to brief review, it is clear that certain trends have become critical to future thinking regarding neurosurgery. An important theme that recurs in much of the current research and that will become more prominent in the future is the concept of plasticity. This refers not only to the changes in cortical representation that can occur after a variety of perturbations but also to a wide variety of neurologically relevant biological processes. In this review, we describe three areas of plasticity, i.e., the response of the brain to ischemia, cortical representational changes, and the potential for stem cell biological processes to allow us to manipulate plasticity. We posit that these trends will be crucial to the future of our specialty.

Effects of neuroprotective cocktails on hippocampal neuron death in an in vitro model of cerebral ischemia

Cocktails of neuroprotectants acting at different parts of the ischemic injury cascade may have advantages over single agents. This study investigated, singly and in combination, the neuroprotective efficacy of an energy substrate (3.5 mM fructose 1,6-bisphosphate, FBP), an antagonist of NMDA receptors (1 and 10 microM MK-801), a free-radical scavenger (100 microM ascorbate), an adenosine A1 receptor agonist (10 microM 2-chloroadenosine), and an inhibitor of neurotransmission (2% isoflurane). These agents were evaluated for their ability to prevent loss and morphologic damage of CA1 neurons in rat hippocampal slices when these agents were administered during 30 minutes in vitro ischemia (combined oxygen/glucose deprivation at 37 degrees C) followed by 5 hours of recovery. Ten microM MK-801, alone or in combination with the other compounds, prevented loss of CA1 neurons and preserved their histologic appearance. Isoflurane, which prevents glutamate receptor-dependent cell death in this model, was also protective. Protection against neuron loss was also found when a subtherapeutic concentration of MK-801 (1 microM) was combined with 2-chloroadenosine (which indirectly causes NMDA receptor suppression), but not FBP or ascorbate. The authors conclude that in this model, the strategy of antagonizing NMDA receptors appears more protective than fructose-1,6-bisphosphate, 2-chloroadenosine or ascorbate.

Neuronal apoptosis after CNS injury: the roles of glutamate and calcium

While a role has been well established for excitotoxic necrosis in the pathogenesis of traumatic or ischemic damage to the CNS, accumulating evidence now suggests that apoptosis may also be a prominent contributor. In this review we focus on the role of glutamate and attendant intracellular calcium influx in triggering or modifying excitotoxic necrosis and apoptosis, raising the possibility that calcium influx may affect these two death pathways in opposite directions. Incorporating consideration of both pathways will probably be needed to develop the most effective neuroprotective treatments for CNS injury.

Synergetic activation of p38 mitogen-activated protein kinase and caspase-3-like proteases for execution of calyculin A-induced apoptosis but not N-methyl-d-aspartate-induced necrosis in mouse cortical neurons

We examined the possibility that p38 mitogen-activated protein kinase and caspase-3 would be activated for execution of apoptosis and excitotoxicity, the two major types of neuronal death underlying hypoxicischemic and neurodegenerative diseases. Mouse cortical cell cultures underwent widespread neuronal apoptosis 24 h following exposure to 10-30 nM calyculin A, a selective inhibitor of Ser/Thr phosphatase I and IIA. Activity of p38 was increased 2-4 h following exposure to 30 nM calyculin A. Addition of 3-10 microM PD169316, a selective p38 inhibitor, partially attenuated calyculin A neurotoxicity. Activity of caspase-3-like proteases was increased in cortical cell cultures exposed to 30 nM calyculin A for 8-16 h as shown by cleavage of DEVD-p-nitroanilide and phosphorylated tau. Proteolysis of tau was completely blocked by addition of 100 microM N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (z-VAD-fmk), a broad-spectrum inhibitor of caspases, but incompletely by 10 microM PD169316. Calyculin A neurotoxicity was partially sensitive to 100 microM z-VAD-fmk. Cotreatment with 10 microM PD169316 and 100 microM z-VAD-fmk showed additive neuroprotection against calyculin A. Neither PD169316 nor z-VAD-fmk showed a beneficial effect against excitotoxic neuronal necrosis induced by exposure to 20 microM NMDA. Thus, caspase-3-like proteases and p38 likely contribute to calyculin A-induced neuronal apoptosis but not NMDA-induced neuronal necrosis.

Signal transduction mechanisms involved in ischemic preconditioning in the rat retina in vivo

Ischemic preconditioning (IPC) protects the rat retina against the injury that ordinarily follows severe ischemia. We showed previously that release of adenosine and de novo protein synthesis were required for IPC protection. The mechanisms of IPC were studied in the rat retina by examining the signal transduction mediators responsible, in particular, those theorized to be downstream of adenosine receptors. In addition, we examined the hypothesis that nitric oxide and hydroxyl radicals were involved in the IPC protective phenomenon. Retinal ischemia was produced for 60 min in ketamine/xylazine-anesthetized Sprague-Dawley rats, and recovery was measured using electroretinography. We tested the effects on the protective effect of IPC resulting from antagonism of protein kinase C, potassium ATP channels, nitric oxide synthase, or hydroxyl radicals. The effects of the inhibition of de novo protein synthesis or of protein kinase C, and blockade of potassium ATP channels on the mimicking of IPC by adenosine receptor agonists was examined.IPC protection was strongly attenuated by inhibition of protein kinase C and by blockade of potassium ATP channels, but unaffected by the inhibition of hydroxyl radicals. Blockade of nitric oxide synthase produced a trend toward enhancement of IPC protection. Mimicking of IPC protection by adenosine receptor agonists was inhibited by blockade of protein synthesis or of protein kinase C, as well as by potassium ATP channel antagonism. These results demonstrate that protein kinase C and potassium ATP channels are mediators of the protective effect produced by IPC. In addition, the results show that stimulation of adenosine receptor subtypes A1 and A2a is responsible for IPC protection via downstream stimulation of protein kinase C, the opening of potassium ATP channels, and de novo protein synthesis.

The future of stroke treatment

The concept of the therapeutic window of opportunity in ischemic neuronal injury and understanding the necessity of well organized stroke services revolutionized the management of acute ischemic stroke during the last years of the second millennium. Thrombolysis with IV rt-PA within 3 hours from the onset of symptoms is an established therapy for selected patients. The challenge of stroke therapy at the outset of this millennium is how to translate basic pathophysiologic evidence of ischemic neuronal injury into novel neuroprotective therapies either independently or combined with thrombolysis. Great hopes are placed in identification of pivotal molecular events in ischemic brain tissue and design of effective pharmacological interventions to target them. Aggressive, invasive procedures are also being developed and therapies such as intra-arterial clot lysis, hemicraniectomy and mild hypothermia may improve the bleakest outcomes associated with the most severe forms of ischemic stroke, but their role must be rigorously evaluated. There is, however, no need to wait for future breakthroughs. The existing evidence strongly implies that good care of patients with stroke starts with organization of the entire stroke chain; from the prehospital scene, through the emergency room, to the stroke unit. Without structured stroke services no pharmacological or intervening therapy is likely to improve the outcome of the patient with a stroke.

Apoptosis and necrosis in cerebrovascular disease

Neuronal death following ischemic insults has been thought to reflect necrosis. However, recent evidence from several labs suggests that programmed cell death, leading to apoptosis, might additionally contribute to this death. We have used both in vitro and in vivo models to study the role of apoptosis in ischemic cell death. Some features of apoptosis (TUNEL staining, internucleosomal DNA fragmentation, sensitivity to cycloheximide) were observed following transient focal ischemia in rats. Brief transient focal ischemia was followed by delayed infarction more than 3 days later; this delayed infarction was sensitive to cycloheximide. A cycloheximide-sensitive component of neuronal cell death was also observed in cultured murine neocortical neurons deprived of oxygen-glucose in the presence of glutamate receptor antagonists. This presumed ischemic apoptosis was attenuated by caspase inhibitors, or by homozygous deletion of the bax gene. Neurons may undergo both apoptosis and necrosis after ischemic insults, and thus it may be therapeutically desirable to block both processes.

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.

The effects of N-methyl-N-nitrosourea and azoxymethane on focal cerebral infarction and the expression of p53, p21 proteins

If the activity of pro-apoptotic genes can be down-regulated by certain chemicals, cells may be protected from apoptosis. To test this hypothesis in a cerebral infarction model, we used N-methyl-N-nitrosourea (MNU) and azoxymethane (AOM), which were approved gene-modulating chemicals. A focal cerebral infarction was created by coagulation of the right middle cerebral artery and ipsilateral common carotid artery (CCA) and simultaneous transient occlusion of the contralateral CCA for 30 min in 25 adult Sprague-Dawley rats that were sacrificed 24 h later. In one group (n=7), MNU (5 mg/kg) was injected intravenously 30 min before initiation of ischemia. In another group (n=7), AOM (15 mg/kg) was administered intraperitoneally before 24 h of ischemia. The infarction volumes were checked and the brains were stained for p53 and p21 proteins. The width in micrometers of the peri-infarct area containing p53 or p21 protein-positive cells, and the number of p53 or p21 protein-positive cells (cells/HPF) were measured at an adjacent peri-infarct area. The AOM-treated group showed a significantly reduced infarction volume (by 42.5%, p<0.001), a significantly greater number of p53 positive cells (by 12.0%, p<0. 05), and a significantly wider p53 protein-positive area (by 15.6%, p<0.01) than the untreated group. AOM did not show any influence on the expression pattern of the p21 protein. MNU had no effect in the expression of p53 or p21 proteins. As a result, we concluded that AOM revealed a protective effect in ischemia by suppressing the pro-apoptotic activity of the p53 gene. Safer chemicals that can modulate apoptotic genes, if any, will provide a new therapeutic modality for cerebral infarction.

Selective activation of group II mGluRs with LY354740 does not prevent neuronal excitotoxicity

Recent reports have suggested a role for group II metabotropic glutamate receptors (mGluRs) in the attenuation of excitotoxicity. Here we examined the effects of the recently available group II agonist (+)-2-Aminobicyclo[3.1.0]hexane-2-6-dicarboxylic acid (LY354740) on N-methyl-D-aspartate (NMDA)-induced excitotoxic neuronal death, as well as on hypoxic-ischemic neuronal death both in vitro and in vivo. At concentrations shown to be selective for group II mGluRs expressed in cell lines (0.1-100 nM), LY354740 did not attenuate NMDA-mediated neuronal death in vitro or in vivo. Furthermore, LY354740 did not attenuate oxygen-glucose deprivation-induced neuronal death in vitro or ischemic infarction after transient middle cerebral artery occlusion in rats. In addition, the neuroprotective effect of another group II agonist, (S)-4-carboxy-3-phenylglycine (4C3HPG), which has shown injury attenuating effects both in vitro and in vivo, was not blocked by the group II antagonists (2 S)-alpha-ethylglutamic acid (EGLU), (RS)-alpha-methyl-4-sulphonophenylglycine (MSPG), or the group III antagonist (S)-alpha-methyl-3-carboxyphenylalanine (MCPA), suggesting that this neuroprotection may be mediated by other effects such as upon group I mGluRs.

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.

Synergistic neuroprotective effects by combining an NMDA or AMPA receptor antagonist with nitric oxide synthase inhibitors in global cerebral ischaemia

We have investigated the neuroprotective effects of combining an NMDA or AMPA receptor antagonist with a nitric oxide synthase (NOS) inhibitor in the gerbil model of global cerebral ischaemia. Ischaemia was induced by occlusion of the common carotid arteries for 5 min. (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,1 0-imine (MK-801, 2.5 mg/kg i.p.) or (3S,4aR,6R,8aR)-6-[2-(1(2)H-tetrazole-5-yl)]decahydroisoq uinoline-3-carboxylic acid (LY293558, 20 mg/kg i.p.) and 7-nitroindazole (25 mg/kg i.p.) or N-[4-(2-[[(3-chlorophenyl)methyl]amino]ethyl) phenyl]-2-thiophenecarboximidamide dihydrochloride (ARL17477, 25 mg/kg i.p.) were administered alone or in combination (i.e., MK-801 with 7-nitroindazole or ARL17477 or LY293558 with 7-nitroindazole or ARL17477). In the present studies, both MK-801 and LY293558 provided significant degree of neuroprotection, while 7-nitroindazole and ARL17477 also provided some neuroprotection, which failed to reach significance in every case. However, the combination of MK-801 with 7-nitroindazole or ARL17477 provided 21% or 44% greater protection than the total protection or either alone. Likewise, the combination of LY293558 with 7-nitroindazole or ARL17477 provided 14.5% and 35% greater protection than total protection of either compound alone. These results indicate that several pathways contribute to ischaemic cell death and combining excitatory amino antagonists and NOS inhibitors provides greater protection than either alone. Therefore, combination therapy should be considered as an approach for treating ischaemic conditions.

Phenidone attenuates oxygen/glucose deprivation-induced neurotoxicity by antioxidant and antiapoptotic action in mouse cortical cultures

The abrupt elevation in the levels of cyclooxygenase or lipoxygenase metabolites of arachidonic acid during cerebral ischemia contributes to neuronal injury. Recently, evidence has accumulated that both excitotoxic and apoptotic features can coexist in ischemia models in vitro and in vivo. In this study, we evaluated whether phenidone, an inhibitor of both cyclooxygenase and lipoxygenase, can provide protection against excitotoxin- or ischemia-induced neurotoxicity, including the staurosporine apoptosis model, in mouse cortical cultures. We examined the protective effect of phenidone against free radical injuries induced by arachidonic acid, hydrogen peroxide, xanthine/xanthine oxidase, Fe2+/ascorbic acid. Pre- and post-treatment with phenidone (300 microM for 24 h) moderately attenuated the neuronal injury induced by 50 microM kainate and oxygen/glucose deprivation (45 min) by 33% and 50%, respectively. It had no effect on NMDA induced injury (150 microM for 5 min). The maximum dose of phenidone (300 microM) reduced the oxidative injury induced by arachidonic acid (71% inhibition), hydrogen peroxide (95% inhibition), xanthine/xanthine oxidase (57% inhibition), and Fe2+/ascorbic acid (99% inhibition) neurotoxicity. Phenidone (300 microM) decreased staurosporine (100 nM)-induced apoptosis to 30%. These results suggest that phenidone may contribute to neuronal survival by modulating oxidative stress, which is involved in the excitotoxic and apoptotic processes occurring under ischemic conditions.

Spreading depression induces expression of calcium-independent protein kinase C subspecies in ischaemia-sensitive cortical layers: regulation by N-methyl-D-aspartate receptors and glucocorticoids

Spreading depression is a wave of sustained depolarization challenging the energy metabolism of the cells without causing irreversible damage. In the ischaemic brain, sreading depression-like depolarization contributes to the evolution of ischaemia to infarction. The depolarization is propagated by activation of N-methyl-D-aspartate receptors, but changes in signal transduction downstream of the receptors are not known. Because protein phosphorylation is a general mechanism whereby most cellular processes are regulated, and inhibition of N-methyl-D-aspartate receptors or protein kinase C is neuroprotective, the expression of protein kinase C subspecies in spreading depression was examined. Cortical treatment with KCl induced an upregulation of protein kinase Cdelta and zeta messenger RNA at 4 and 8 h, whereas protein kinase Calpha, beta, gamma and epsilon did not show significant changes. The gene induction was the strongest in layers 2 and 3, and was followed by an increased number of protein kinase Cdelta-immunoreactive neurons. Protein kinase Cdelta and zeta inductions were inhibited by pretreatment with an N-methyl-D-aspartate receptor antagonist, dizocilpine maleate, which also blocked spreading depression propagation, and with dexamethasone, which acted without blocking the propagation. Quinacrine, a phospholipase A2 inhibitor, reduced only protein kinase C5 induction. In addition, N(G)(-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor, did not influence protein kinase Cdelta or zeta induction, whereas 6-nitro-7-sulphamoylbenzo[f]quinoxaline-2,3-dione, an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate/kainate receptor antagonist, and the cyclo-oxygenase inhibitors indomethacin and diclophenac tended to increase gene expression. The data show that cortical spreading depression induces Ca2(+)-independent protein kinase C subspecies delta and zeta, but not Ca(2+)-dependent subspecies, through activation of N-methyl-D-aspartate receptors and phospholipase A2. Even though the signal pathway is similar to the induction described previously in ischaemia for genes implicated in delayed neuronal death, the gene inductions observed here are not necessarily pathogenetic, but may represent a general reaction to metabolic stress.

Increase in p53 protein expression following cortical infarction in the spontaneously hypertensive rat

Using stroke-prone spontaneously hypertensive (SH-SP) rats with permanent occlusion of the middle cerebral artery (MCA), we investigated the expression of wild type p53 (wt-p53) protein and the occurrence of DNA fragmentation in cerebral neurons after ischemia. Three days following MCA occlusion, terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL staining) revealed a distinct pattern of nuclear staining in many neurons around the ischemic core. On the lesioned side of the cerebral cortex one day after MCA occlusion, wt-p53 immunoreactivity was observed specifically in the cortical neurons, in the same regions as the TUNEL staining. Mutant type p53 (mt-p53) immunoreactivity was not observed at any time following MCA occlusion. These findings suggest that wt-p53 dependent cell death of cortical neurons occurred in the ischemic periphery following cerebral ischemia and that this pathway for the induction of cell death may play an important role in the exaggeration of cerebral ischemic injury.

The changing landscape of ischaemic brain injury mechanisms

Thrombolysis has become established as an acute treatment for human stroke. But despite multiple clinical trials, neuroprotective strategies have yet to be proved effective in humans. Here we discuss intrinsic tissue mechanisms of ischaemic brain injury, and present a perspective that broadening of therapeutic targeting beyond excitotoxicity and neuronal calcium overload will be desirable for developing the most effective neuroprotective therapies.

Neuroprotection in relation to retinal ischemia and relevance to glaucoma

Management of glaucoma is directed at the control of intraocular pressure (IOP), yet it is recognized now that increased IOP isjust an important risk factor in glaucoma. Therapy that prevents the death of ganglion cells is the main goal of treatment, but an understanding of the causes of ganglion cell death and precisely how it occurs remains speculative. Present information supports the working hypothesis that ganglion cell death may result from a particular form of ischemia. Support for this view comes from the fact that not all types of retinal ischemia lead to the pathologic findings seen in glaucomatous retinas or to cupping in the optic disk area. Moreover, in animal experiments in which ischemia is caused by elevated IOP, a retinal abnormality similar to that seen in true glaucoma is produced, whereas after occlusion of the carotid arteries a different pattern of damage is found. In ischemia, glutamate is released, and this initiates the death of neurons that contain ionotropic glutamate (NMDA) receptors. Elevated glutamate levels exist in the vitreous humor of patients with glaucoma, and NMDA receptors exist on ganglion cells and a subset of amacrine cells. Experimental studies have shown that a variety of agents can be used to prevent the death of retinal neurons (particularly ganglion cells) induced by ischemia. These agents are generally those that block NMDA receptors to prevent the action of the released glutamate or substances that interfere with the subsequent cycle of events that lead to cell death. The major causes of cell death after activation of NMDA receptors are the influx of calcium into cells and the generation of free radicals. Substances that prevent this cascade of events are, therefore, often found to act as neuroprotective agents. For a substance to have a role as a neuroprotective agent in glaucoma, it would ideally be delivered topically to the eye and used repeatedly. It is, therefore, of interest that betaxolol, a beta-blocker presently used to reduce IOP in humans, also has calcium channel-blocking functions. Moreover, experimental studies show that betaxolol is an efficient neuro protective agent against retinal ischemia in animals, when injected directly into the eye or intraperitoneally.

Caspases as treatment targets in stroke and neurodegenerative diseases

Apoptosis is one of the most exciting and intensely investigated areas of biology and medicine today. Cysteine proteases called caspases serve as the executioners of apoptosis, a form of cell suicide. Hypoxic/ischemic cell death proceeds in part, by apoptosis, particularly within the periinfarct zone or ischemic penumbra. During ischemia, activated caspases dismantle the cell by cleaving multiple substrates including cytoskeletal proteins and enzymes essential for cell repair. Strategies that inhibit caspase activity block cell death in experimental models of mild ischemia, and preserve neurological function. The therapeutic window for caspase inhibition is substantially longer than for glutamate receptor antagonists, and treatment combinations with both classes of drugs decrease ischemic injury and expand the treatment window synergistically. Hence, the caspases are now recognized as novel therapeutic targets for central nervous system diseases in which cell death is prominent. This article will review the evidence and the potential importance of caspase inhibition to cerebral ischemia and briefly summarize an emerging body of data implicating caspases in cell death accompanying neurodegenerative disorders.

Purification of a multipotent antideath activity from bovine liver and its identification as arginase: nitric oxide-independent inhibition of neuronal apoptosis

Catalase is an antioxidant enzyme that has been shown to inhibit apoptotic or necrotic neuronal death induced by hydrogen peroxide. We report the purification of a contaminating antiapoptotic activity from a commercial bovine liver catalase preparation by following its ability to inhibit apoptosis when applied extracellularly in multiple death paradigms. The antiapoptotic activity was identified by protein microsequencing as arginase, a urea cycle and nitric oxide synthase-regulating enzyme, and confirmed by demonstrating the presence of antiapoptotic activity in a >97% pure preparation of recombinant arginase. The pluripotency of recombinant arginase was demonstrated by its ability to inhibit apoptosis in multiple paradigms including rat cortical neurons induced to die by glutathione depletion and oxidative stress, by 100 nM staurosporine treatment, or by Sindbis virus infection. The protective effects of arginase in these apoptotic paradigms, in contrast to previous studies on excitotoxic neuronal necrosis, are independent of nitric oxide synthase inhibition. Rather, arginase-induced depletion of arginine leads to inhibition of protein synthesis, resulting in cell survival. Because inhibitors of nitric oxide synthesis and of protein synthesis have been shown to decrease necrotic and apoptotic death, respectively, in animal models of stroke and spinal cord injury, arginine-depleting enzymes, capable of simultaneously inhibiting protein synthesis and nitric oxide generation, may be propitious therapeutic agents for acute neurological diseases. Furthermore, our results suggest caution in attributing the cytoprotective effects of some catalase preparations to catalase.

Synergistic effects of caspase inhibitors and MK-801 in brain injury after transient focal cerebral ischaemia in mice

1. Excitotoxic and apoptotic mechanisms have been implicated in the pathophysiology of cerebral ischaemia. Both MK-801, an NMDA receptor antagonist, or peptide inhibitors of the caspase family (z-VAD.FMK and z-DEVD.FMK), protect mouse brain from ischaemic cell damage. In this study, we examined whether these drugs which act via distinct mechanisms, afford even greater neuroprotection when given in combination following 2 h MCA occlusion (filament model) and 18 h reperfusion. 2. Given alone as pretreatment, MK-801 (1, 3 and 5 mg kg(-1), but not 0.3 mg kg(-1), i.p.) decreased infarct size by 34-75%. When injected 1 h after occlusion and before reperfusion, 3 mg kg(-1) reduced injury but not when administered I h after reperfusion. 3. Pretreatment with a subthreshold dose of MK-801 (0.3 mg kg(-1)) plus a subthreshold dose of z-VAD.FMK (27 ng) or z-DEVD (80 ng) significantly decreased infarct size by 29 and 30%, respectively, and enhanced neurological function. 4. Administering a subthreshold dose of z-VAD.FMK (27 ng) or z-DEVD.FMK (80 ng) as pretreatment extended the time window for MK-801 (3 mg kg(-1)) by 2 h from 1 h before reperfusion to at least 1 h after reperfusion. 5. Pretreating with a subthreshold dose of MK-801 (0.3 mg kg(-1)) extended the time window for z-DEVD.FMK (480 ng) from 1 h after reperfusion to at least 3 h after reperfusion. 6. We conclude that caspase inhibitors which putatively block apoptotic cell death and inhibit cytokine production and the NMDA antagonist MK-801 act synergistically and prolong their respective therapeutic windows in cerebral ischaemia.

Amelioration of ischaemia-induced neuronal death in the rat striatum by NGF-secreting neural stem cells

The objective of the present study was to explore whether grafted immortalized neural stem cells, genetically modified to secrete nerve growth factor (NGF), can ameliorate neuronal death in the adult rat striatum following transient middle cerebral artery occlusion (MCAO). One week after cell implantation in the striatum, animals were subjected to 30 min of MCAO. Striatal damage was evaluated at the cellular level after 48 h of recirculation using immunocytochemical and stereological techniques. The ischaemic insult caused an extensive degeneration of projection neurons, immunoreactive for dopamine- and adenosine 3': 5'-monophosphate-regulated phosphoprotein with a molecular weight of 32 kilodaltons (DARPP-32). 3H-Thymidine autoradiography demonstrated surviving grafted cells in the lesioned striatum in all transplanted rats. The loss of striatal projection neurons was significantly reduced (by an average of 45%) in animals with NGF-secreting grafts, whereas control cells, not producing NGF, had no effect. The neuroprotective action of NGF-secreting grafts was also observed when the total number of striatal neurons immunopositive for the neuronal marker NeuN was quantified, as well as in cresyl violet-stained sections. The present findings indicate that administration of NGF by ex vivo gene transfer and grafting of neural stem cells can ameliorate death of striatal projection neurons caused by transient focal ischaemia.

Focal cerebral ischemia in rats induces expression of P75 neurotrophin receptor in resistant striatal cholinergic neurons

Expression of p75 neurotrophin receptor and survival of medium-sized spiny projection neurons and cholinergic interneurons in the rat striatum were studied using immunocytochemistry at different times after transient, unilateral middle cerebral artery occlusion. Thirty minutes of middle cerebral artery occlusion caused a major loss of projection neurons, identified by their immunoreactivity to dopamine- and adenosine 3':5'-monophosphate-regulated phosphoprotein with a molecular weight of 32,000, in the lateral part of the striatum, as observed at 48 h following the insult with no further change at one week. In contrast, no reduction of the number of choline acetyltransferase-positive, cholinergic interneurons, which also expressed TrkA, was detected at either time-point. At 48 h following middle cerebral artery occlusion, expression of p75 neurotrophin receptor was observed in striatal cells which, by the use of double-label immunostaining, were identified as the cholinergic interneurons. No p75 neurotrophin receptor immunoreactivity remained in cholinergic cells after one week of reperfusion. Based on current hypotheses regarding the function of the p75 neurotrophin receptor, the transient expression of this receptor in striatal cholinergic interneurons might contribute to their high resistance to ischemic neuronal death. However, the expression of p75 neurotrophin receptor could also be a first step in a pathway leading to apoptosis, which is inhibited after the present insult due to concomitant activation of TrkA.

Protection of rat spinal cord from ischemia with dextrorphan and cycloheximide: effects on necrosis and apoptosis

OBJECTIVE

We examined the characteristics of neuronal cell death after transient spinal cord ischemia in the rat and the effects of an N-methyl-D-aspartate antagonist, dextrorphan, and a protein synthesis inhibitor, cycloheximide.

METHODS

Spinal cord ischemia was induced for 15 minutes in Long-Evans rats with use of a 2F Fogarty catheter, which was passed through the left carotid artery and occluded the descending aorta, combined with a blood volume reduction distal to the occlusion. The rats were killed after 1, 2, and 7 days. Other groups of rats were pretreated with dextrorphan (30 mg/kg, intraperitoneally, n = 7), cycloheximide (30 mg, intrathecally, n = 7), or vehicle (saline solution, n = 12) and killed after 2 days.

RESULTS

This model reliably produced paraplegia and histopathologically distinct morphologic changes consistent with necrosis or apoptosis by light and electron microscopic criteria in different neuronal populations in the lumbar cord. Scattered necrotic neurons were seen in the intermediate gray matter (laminae 3 to 7) after 1, 2, and 7 days, whereas apoptotic neurons were seen in the dorsal horn laminae 1 to 3 after 1 and 2 days. Deoxyribonucleic acid extracted from lumbar cord showed internucleosomal fragmentation (laddering) on gel electrophoresis indicative of apoptosis. The severity of paraplegia in the rats treated with dextrorphan and cycloheximide was attenuated 1 day and 2 days after ischemia. The numbers of both necrotic and apoptotic neurons were markedly reduced in both dextrorphan- and cycloheximide-treated rats.

CONCLUSIONS

The results suggest that both N-methyl-D-aspartate receptor-mediated excitotoxicity and apoptosis contribute to spinal cord neuronal death after ischemia and that pharmacologic treatments directed at blocking both of these processes may have therapeutic utility in reducing spinal cord ischemic injury.

Neuronal and glial apoptosis after traumatic spinal cord injury

Cell death was examined by studying the spinal cords of rats subjected to traumatic insults of mild to moderate severity. Within minutes after mild weight drop impact (a 10 gm weight falling 6.25 mm), neurons in the immediate impact area showed a loss of cytoplasmic Nissl substances. Over the next 7 d, this lesion area expanded and cavitated. Terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL)-positive neurons were noted primarily restricted to the gross lesion area 4-24 hr after injury, with a maximum presence at 8 hr after injury. TUNEL-positive glia were present at all stages studied between 4 hr and 14 d, with a maximum presence within the lesion area 24 hr after injury. However 7 d after injury, a second wave of TUNEL-positive glial cells was noted in the white matter peripheral to the lesion and extending at least several millimeters away from the lesion center. The suggestion of apoptosis was supported by electron microscopy, as well as by nuclear staining with Hoechst 33342 dye, and by examination of DNA prepared from the lesion site. Furthermore, repeated intraperitoneal injections of cycloheximide, beginning immediately after a 12.5 mm weight drop insult, produced a substantial reduction in histological evidence of cord damage and in motor dysfunction assessed 4 weeks later. Present data support the hypothesis that apoptosis dependent on active protein synthesis contributes to the neuronal and glial cell death, as well as to the neurological dysfunction, induced by mild-to-moderate severity traumatic insults to the rat spinal cord.

Susceptibility to apoptosis is enhanced in immature cortical neurons

The susceptibility of cortical neurons to two forms of apoptotic death was compared with susceptibility to excitotoxic death during development in vitro (DIV 4-21). Murine cortical cultures were exposed for 48 h to the phosphatase inhibitor cyclosporine, the protein kinase inhibitor staurosporine or the excitotoxin N-methyl-D-aspartate (NMDA). Susceptibility to apoptosis induced by staurosporine or cyclosporine was maximal between DIV 4-10 and declined from DIV 10 through 18. The opposite pattern was observed with susceptibility to NMDA receptor-mediated excitotoxic necrosis, which was minimal at DIV 6 and progressively increased through DIV 21.