Quantitative assessment of neuroprotection against NMDA-induced brain injury

Neuroprotective Effects of AG490 in Neonatal Hypoxic-Ischemic Brain Injury

In infants and children, neonatal hypoxic-ischemic (HI) brain injury represents a major cause of chronic neurological morbidity. The transient receptor potential melastatin 2 (TRPM2), a non-selective cation channel that conducts calcium, can mediate neuronal death following HI brain injury. An important endogenous activator of TRPM2 is H₂O₂, which has previously been reported to be upregulated in the neonatal brain after hypoxic ischemic injury. Here, incorporating both in vitro (H₂O₂-induced neuronal cell death model) and in vivo (mouse HI brain injury model) approaches, we examined the effects of AG490, which can inhibit the H₂O₂-induced TRPM2 channel. We found that AG490 elicited neuroprotective effects. We confirmed that AG490 reduced H₂O₂-induced TRPM2 currents. Specifically, application of AG490 to neurons ameliorated H₂O₂-induced cell injury in vitro. In addition, AG490 administration reduced brain damage and improved neurobehavioral performance following HI brain injury in vivo. The neuroprotective benefits of AG490 suggest that pharmacological inhibition of H₂O₂-activated TRPM2 currents can be exploited as a potential therapeutic strategy to treat HI-induced neurological complications.

Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges

Neonatal hypoxia-ischaemia (HI) is the most common cause of death and disability in human neonates, and is often associated with persistent motor, sensory, and cognitive impairment. Improved intensive care technology has increased survival without preventing neurological disorder, increasing morbidity throughout the adult population. Early preventative or neuroprotective interventions have the potential to rescue brain development in neonates, yet only one therapeutic intervention is currently licensed for use in developed countries. Recent investigations of the transient cortical layer known as subplate, especially regarding subplate's secretory role, opens up a novel set of potential molecular modulators of neonatal HI injury. This review examines the biological mechanisms of human neonatal HI, discusses evidence for the relevance of subplate-secreted molecules to this condition, and evaluates available animal models. Neuroserpin, a neuronally released neuroprotective factor, is discussed as a case study for developing new potential pharmacological interventions for use post-ischaemic injury.

The Controlled Cortical Impact Model: Applications, Considerations for Researchers, and Future Directions

Controlled cortical impact (CCI) is a mechanical model of traumatic brain injury (TBI) that was developed nearly 30 years ago with the goal of creating a testing platform to determine the biomechanical properties of brain tissue exposed to direct mechanical deformation. Initially used to model TBIs produced by automotive crashes, the CCI model rapidly transformed into a standardized technique to study TBI mechanisms and evaluate therapies. CCI is most commonly produced using a device that rapidly accelerates a rod to impact the surgically exposed cortical dural surface. The tip of the rod can be varied in size and geometry to accommodate scalability to difference species. Typically, the rod is actuated by a pneumatic piston or electromagnetic actuator. With some limits, CCI devices can control the velocity, depth, duration, and site of impact. The CCI model produces morphologic and cerebrovascular injury responses that resemble certain aspects of human TBI. Commonly observed are graded histologic and axonal derangements, disruption of the blood-brain barrier, subdural and intra-parenchymal hematoma, edema, inflammation, and alterations in cerebral blood flow. The CCI model also produces neurobehavioral and cognitive impairments similar to those observed clinically. In contrast to other TBI models, the CCI device induces a significantly pronounced cortical contusion, but is limited in the extent to which it models the diffuse effects of TBI; a related limitation is that not all clinical TBI cases are characterized by a contusion. Another perceived limitation is that a non-clinically relevant craniotomy is performed. Biomechanically, this is irrelevant at the tissue level. However, craniotomies are not atraumatic and the effects of surgery should be controlled by including surgical sham control groups. CCI devices have also been successfully used to impact closed skulls to study mild and repetitive TBI. Future directions for CCI research surround continued refinements to the model through technical improvements in the devices (e.g., minimizing mechanical sources of variation). Like all TBI models, publications should report key injury parameters as outlined in the NIH common data elements (CDEs) for pre-clinical TBI.

The Controlled Cortical Impact Model of Experimental Brain Trauma: Overview, Research Applications, and Protocol

Controlled cortical impact (CCI) is a commonly used and highly regarded model of brain trauma that uses a pneumatically or electromagnetically controlled piston to induce reproducible and well-controlled injury. The CCI model was originally used in ferrets and it has since been scaled for use in many other species. This chapter will describe the historical development of the CCI model, compare and contrast the pneumatic and electromagnetic models, and summarize key short- and long-term consequences of TBI that have been gleaned using this model. In accordance with the recent efforts to promote high-quality evidence through the reporting of common data elements (CDEs), relevant study details-that should be reported in CCI studies-will be noted.

Ketamine does not increase intracranial pressure compared with opioids: meta-analysis of randomized controlled trials

BACKGROUND

Ketamine is traditionally avoided in sedation management of patients with risk of intracranial hypertension. However, results from many clinical trials contradict this concern. We critically analyzed the published data of the effects of ketamine on intracranial pressure (ICP) and other cerebral hemodynamics to determine whether ketamine was safe for patients with hemodynamic instability and brain injuries.

METHODS

We systematically searched the online databases of PubMed, Medline, Embase, Current Controlled Trials, and Cochrane Central (last search performed on January 15, 2014). Trial characteristics and outcomes were independently extracted by two assessors (Xin Wang, Xibing Ding). For continuous data, mean differences (MD) were formulated. If the P value of the chi-square test was >0.10 or I(2) <50%, a fixed-effects model was used; otherwise, the random effects model was adopted.

RESULTS

Five trials (n = 198) met the inclusion criteria. Using ICP levels within the first 24 h of ketamine administration as the main outcome, the use of ketamine leads to the same ICP levels as opioids [MD = 1.94; 95% confidence interval (95% CI), -2.35, 6.23; P = 0.38]. There were no significant differences in mean arterial pressure values between the two groups (MD = 0.99; 95% CI, -2.24, 4.22; P = 0.55). Ketamine administration was also comparable with opioids in the maintenance of cerebral perfusion pressure (MD = -1.07; 95% CI, -7.95, 5.8; P = 0.76).

CONCLUSIONS

The results of this study suggest that ketamine does not increase ICP compared with opioids. Ketamine provides good maintenance of hemodynamic status. Clinical application of ketamine should not be discouraged on the basis of ICP-related concerns.

Sevoflurane postconditioning provides neuroprotection against brain hypoxia-ischemia in neonatal rats

Application of volatile anesthetics after brain ischemia provides neuroprotection in adult animals (anesthetic postconditioning). We tested whether postconditioning with sevoflurane, the most commonly used general anesthetic in pediatric anesthesia, reduced neonatal brain injury in rats. Seven-day-old Sprague-Dawley rats were subjected to brain hypoxia-ischemia (HI). They were postconditioned with sevoflurane in the presence or absence of 5-hydroxydecanoic acid, a mitochondrial KATP channel inhibitor. Sevoflurane postconditioning dose-dependently reduced brain tissue loss observed 7 days after brain HI. This effect was induced by clinically relevant concentrations and abolished by 5-hydroxydecanoic acid. These results suggest that sevoflurane postconditioning protects neonatal brain against brain HI via mitochondrial KATP channels.

Magnesium for newborns with hypoxic-ischemic encephalopathy: a systematic review and meta-analysis

OBJECTIVE

Magnesium may have a role in neuroprotection in neonatal hypoxic-ischemic encephalopathy (HIE). The objective of this study was to systematically review the efficacy and safety of postnatal magnesium therapy in newborns with HIE.

STUDY DESIGN

MEDLINE, EMBASE, CINAHL and CCRCT were searched for studies of magnesium for HIE. Randomized controlled trials that compared magnesium to control in newborns with HIE were selected. The primary outcome was a composite outcome of death or moderate-to-severe neurodevelopmental disability at 18 months. When appropriate, meta-analyses were conducted using random effects model and risk ratios (RRs) and 95% confidence intervals (CIs) were calculated.

RESULT

Five studies with sufficient quality were included. There was no difference in the primary outcome between the magnesium and the control groups (RR 0.81, 95% CI 0.36 to 1.84). There was significant reduction in the unfavorable short-term composite outcome (RR 0.48, 95% CI 0.30 to 0.77) but no difference in mortality (RR 1.39, 95% CI 0.85 to 2.27), seizures (RR 0.84, 95% CI 0.59 to 1.19) or hypotension (RR 1.28, 95% CI 0.69 to 2.38) between the magnesium and the control groups.

CONCLUSION

The improvement in short-term outcomes without significant increase in side effects indicate the need for further trials to determine if there are long-term benefits of magnesium and to confirm its safety. Mortality was statistically insignificant between the magnesium and the control groups. However, the trend toward increase in mortality in the magnesium group is a major clinical concern and should be monitored closely in future trials.

The emerging use of ketamine for anesthesia and sedation in traumatic brain injuries

Traditionally, the use of ketamine for patients with traumatic brain injuries is contraindicated due to the concern of increasing intracranial pressure (ICP). These concerns, however, originated from early studies and case reports that were inadequately controlled and designed. Recently, the concern of using ketamine in these patients has been challenged by a number of published studies demonstrating that the use of ketamine was safe in these patients. This article reviews the current literature in regards to using ketamine in patients with traumatic brain injuries in different clinical settings associated with anesthesia, as well as reviews the potential mechanisms underlying the neuroprotective effects of ketamine. Studies examining the use of ketamine for induction, maintenance, and sedation in patients with TBI have had promising results. The use of ketamine in a controlled ventilation setting and in combination with other sedative agents has demonstrated no increase in ICP. The role of ketamine as a neuroprotective agent in humans remains inconclusive and adequately powered; randomized controlled trials performed in patients undergoing surgery for traumatic brain injury are necessary.

Neuroprotective effect of human placental extract on hypoxic-ischemic brain injury in neonatal rats

We investigated the neuroprotective effects of human placental extracts (HPE) and the effects of HPE on recovery of cognitive and behavioral function on hypoxic-ischemic brain injury in the newborn rat. The right common carotid arteries of 7-day-old rats were coagulated, and rats were then exposed to 8% oxygen. Immediately before and again at three times after the hypoxia-ischemia (pre-treatment group), and immediately after and three times again after hypoxia-ischemia (post-treatment group), the rats were intraperitoneally injected with HPE (0.1, 0.25, or 0.5 mL/10 g/dose). No-treatment rats received saline only. On postnatal day 12, brains were removed and gross morphological damage was evaluated. To quantify the severity of brain injury, bilateral cross-sectional areas of the anterior commissural and posterior hippocampal levels were analyzed with NIH Image. Assessments of the open field activity levels at 2, 4, 6 and 8 week and, the Morris water maze test at 8 weeks after hypoxia-ischemia were carried out according to standard methods. HPE pre-treatment decreased the incidence of liquefactive cerebral infarction, at an optimally neuroprotective dose of 0.5 mL/10 g/dose (P<0.05). In the Morris water maze test, the group injected with HPE at 0.5 mL/10 g/dose concentration showed shorter escape latencies than the no-treatment group (P<0.05). These findings support a protective effect of the HPE treatment on neuronal integrity and cognitive function following hypoxic-ischemic brain injury. Injected at an appropriate dose prior to exposure, HPE may significantly reduce or prevent hypoxic-ischemic injury in the immature brain.

Magnesium for neuroprotection in birth asphyxia

Background:

Magnesium ion gates the N-methyl-D-aspartate (NMDA) receptor and may protect the brain from NMDA receptor-mediated asphyxial injury. The present study evaluated the neuroprotective role of magnesium in birth asphyxia.

Material and Methods:

Forty term neonates with severe birth asphyxia were randomized to either the study group or the control group. Neonates in the study group received magnesium sulfate in a dose of 250 mg/kg initially within half an hour of birth followed by 125 mg/kg at 24 and 48 h of birth. Cranial computed tomography (CT) scan and electroencephalography (EEG) were performed for all the babies. Denver II was used for developmental assessment at the age of 6 months.

Results:

Two babies in each group died of severe hypoxic ischemic encephalopathy. EEG abnormalities occurred in 43.75% of the cases in the control group compared with 31.25% in the study group. CT scan abnormalities were present in 62.5% of the control group compared with 37.5% of the cases in the study group. The Denver II assessment at 6 months revealed that there were five babies that were either abnormal or suspect in the control group compared with three in the study group.

Conclusion:

Magnesium is well tolerated and does appear to have beneficial effects in babies with severe asphyxia. More data is however needed and a large multicenter trial should be conducted.

Translational neuroprotection research in glaucoma: a review of definitions and principles

The maintenance of vision, through prevention and attenuation of neuronal injury in glaucoma, forms the basis of current clinical practice. Currently, the reduction of intraocular pressure is the only proven method to achieve these goals. Although this strategy enjoys considerable success, some patients progress to blindness; hence, additional management options are highly desirable. Several terms describing treatment modalities of neuronal diseases with potential applicability to glaucoma are used in the literature, including neuroprotection, neurorecovery, neurorescue and neuroregeneration. These phenomena have not been defined within a coherent framework. Here, we suggest a set of definitions, postulates and principles to form a foundation for the successful translation of novel glaucoma therapies from the laboratory to the clinic.

Hypoxic-ischemic encephalopathy in the term infant

Hypoxia-ischemia in the perinatal period is an important cause of cerebral palsy and associated disabilities in children. There has been significant research progress in hypoxic-ischemic encephalopathy over the last 2 decades, and many new molecular mechanisms have been identified. Despite all these advances, therapeutic interventions are still limited. In this article the authors discuss several molecular pathways involved in hypoxia-ischemia, and potential therapeutic targets.

Neuroprotective effect of memantine combined with topiramate in hypoxic-ischemic brain injury

Glutamate receptor-mediated neurotoxicity is a major mechanism contributing to hypoxic-ischemic brain injury (HIBI). Memantine is a safe non-competitive NMDA receptor blocker characterized by its low affinity and fast unblocking kinetics. Topiramate is an AMPA/KA receptor blocker and use-dependent sodium channel blocker with several other neuroprotective actions and little neurotoxicity. We hypothesized that the coadministration of memantine and topiramate would be highly effective to attenuate HIBI in neonatal rats. Seven-day-old Sprague-Dawley rat pups were subjected to right common carotid artery ligation and hypoxia for 2 h, and then were randomly and blindly assigned to one of four groups: vehicle, memantine, topiramate and combination group. Brain injury was evaluated by gross damage and weight deficit of the right hemisphere at 22d after hypoxic-ischemia (HI) and by neurofunctional assessment (foot-fault test) at 21d post-HI. Acute neuronal injury was also evaluated by microscopic damage grading at 72 h post-HI. Results showed the combination of memantine and topiramate improved both pathological outcome and performance significantly. The drug-induced apoptotic neurodegeneration was assessed by TUNEL staining at 48 h post-HI and the result showed no elevated apoptosis in all observed areas. The result of the experiment indicates the combination therapy is safe and highly effective to reduce brain damage after HIBI.

Protease-activated receptor 1-dependent neuronal damage involves NMDA receptor function

Protease-activated receptor 1 (PAR1) is a G-protein coupled receptor that is expressed throughout the central nervous system. PAR1 activation by brain-derived as well as blood-derived proteases has been shown to have variable and complex effects in a variety of animal models of neuronal injury and inflammation. In this study, we have evaluated the effects of PAR1 on lesion volume in wild-type or PAR1-/- C57Bl/6 mice subjected to transient occlusion of the middle cerebral artery or injected with NMDA in the striatum. We found that removal of PAR1 reduced infarct volume following transient focal ischemia to 57% of control. Removal of PAR1 or application of a PAR1 antagonist also reduced the neuronal injury associated with intrastriatal injection of NMDA to 60% of control. To explore whether NMDA receptor potentiation by PAR1 activation contributes to the harmful effects of PAR1, we investigated the effect of NMDA receptor antagonists on the neuroprotective phenotype of PAR1-/- mice. We found that MK801 reduced penumbral but not core neuronal injury in mice subjected to transient middle cerebral artery occlusion or intrastriatal NMDA injection. Lesion volumes in both models were not significantly different between PAR1-/- mice treated with and without MK801. Use of the NMDA receptor antagonist and dissociative anesthetic ketamine also renders NMDA-induced lesion volumes identical in PAR1-/- mice and wild-type mice. These data suggest that the ability of PAR1 activation to potentiate NMDA receptor function may underlie its harmful actions during injury.

New perspectives for the treatment options in spinal cord injury

Spinal cord injury (SCI) is a serious clinical disorder that leads to lifetime disability for which no suitable therapeutic agents are available so far. Further research is needed to understand the basic mechanisms of spinal cord pathology that results in permanent disability and poses a heavy burden on our society. In the past, a lot of effort was placed on improving functional outcome with the help of various therapeutic agents, however less attention has been paid on the development and propagation of spinal cord pathology over time. Thus, it is still unclear whether improvement of functional outcome is related to spinal cord pathology or vice versa. Few drugs are able to influence functional outcome without having any improvement on cord pathology. Some drugs, however, can lessen cord pathology but fail to influence the functional outcome. The goal of future treatment options for SCI is therefore to find suitable new drugs or a combination of existing drugs and to use various cellular transplants, neurotrophic factors, myelin-inhibiting factors, tissue engineering and nano-drug delivery to improve both the functional and the pathological outcome in the inured patient. This review deals with the key aspects of the latest treatments for SCI and suggests some possible future therapeutic measures to enhance healthcare in clinical situations.

Neuroprotective effect of nipradilol, an NO donor, on hypoxic-ischemic brain injury of neonatal rats

Hypoxia-ischemia is a common cause of neonatal brain injuries. Nitric oxide (NO) is upregulated in the brain after hypoxia-ischemia and generally believed to exert a paradoxical effect on neurons, neurodestruction and neuroprotection, but it has not been demonstrated that NO is actually neuroprotective in neonatal hypoxic-ischemic encephalopathy. We evaluated the effect of intracerebroventricular administration of nipradilol (3,4-dihydro-8-(2-hydroxy-3-isopropylamino)-propoxy-3-nitroxy-2H-1-benzopyran), a potent NO donor, at various concentrations (0.1 muM to 1 mM in 5 mul PBS/brain) to neonatal rats with hypoxic-ischemic treatment. The extent of the infarct area in the brain was significantly reduced by injection of the 1 muM nipradilol solution. However, denitro-nipradilol (3,4-dihydro-8-(2-hydroxy-3-isopropylamino)-propoxy-3-hydroxy-2H-1-benzopyran), that does not release NO, did not show the neuroprotective effect, suggesting that NO released from nipradilol exerts a neuroprotective effect on neonatal neurons.

p21ras activation following hypoxia-ischemia in the newborn rat brain is dependent on nitric oxide synthase activity but p21ras does not contribute to neurologic injury

Hypoxia-ischemia (HI) in the perinatal period is associated with significant infant mortality and neurologic morbidity. Increase in the activity of nitric oxide synthase (NOS) and increased release of nitric oxide (NO) are cardinal events in the pathophysiology of stroke and perinatal asphyxia. Cell culture studies suggest that the GTP-binding protein p21ras (Ras) is activated by NO in an NMDA-receptor-dependent pathway. These findings imply that Ras may be activated in vivo by NO released in response to glutamate stimulation during HI. The contribution of downstream Ras activation to neurologic injury after perinatal HI is unknown. We used a postnatal day 7 rat model of perinatal hypoxia-ischemia to determine the response of Ras to HI, the role of NO in Ras activation and the effect of Ras inhibition on neurologic injury in vivo. Ras is activated in both hippocampus and cortex within 2 h after HI. This increase is prevented by treatment with the NOS inhibitor, aminoguanidine (AG) and by a farnesyl/protein transferase inhibitor, manumycin (MAN). Inhibition of NOS, but not Ras, significantly reduces neurologic injury after a 7-day recovery period. This data suggests that Ras is activated during the initiation of the cellular response to HI in both hippocampus and cortex and that this activation is NO-dependent. Ras does not, however, contribute to the pathophysiologic NO-dependent mechanisms of neurologic injury in this model.

L-carnitine reduces brain injury after hypoxia-ischemia in newborn rats

Perinatal hypoxia-ischemia remains a significant cause of neonatal mortality and neurodevelopmental disability. Numerous lines of evidence indicate that cerebral ischemic insults disrupt normal respiratory activity in mitochondria. Carnitine (3-hydroxy-4-N-trimethylammonium-butyrate) has an essential role in fatty acid transport in the mitochondrion and in modulating potentially toxic acyl-CoA levels in the mitochondrial matrix. There are no naturally occurring esterases available to reduce the accumulation of acyl-CoA but this process can be overcome by exogenous carnitine. We used a newborn rat model of perinatal hypoxia-ischemia to test the hypothesis that treatment with l-carnitine would reduce the neuropathologic injury resulting from hypoxia-ischemia in the developing brain. We found that treatment with l-carnitine during hypoxia-ischemia reduces neurologic injury in the immature rat after both a 7- and 28-d recovery period. We saw no neuroprotective effect when l-carnitine was administered after hypoxia-ischemia. Treatment with d-carnitine resulted in an increase in mortality during hypoxia-ischemia. Carnitine is easy to administer, has low toxicity, and is routinely used in neonates as well as children with epilepsy, cardiomyopathy, and inborn errors of metabolism. l-Carnitine merits further investigation as a treatment modality for the asphyxiated newborn or as prophylaxis for the at-risk fetus or newborn.

An aminopyridazine-based inhibitor of a pro-apoptotic protein kinase attenuates hypoxia-ischemia induced acute brain injury

Death associated protein kinase (DAPK) is a calcium and calmodulin regulated enzyme that functions early in eukaryotic programmed cell death, or apoptosis. To validate DAPK as a potential drug discovery target for acute brain injury, the first small molecule DAPK inhibitor was synthesized and tested in vivo. A single injection of the aminopyridazine-based inhibitor administered 6 h after injury attenuated brain tissue or neuronal biomarker loss measured, respectively, 1 week and 3 days later. Because aminopyridazine is a privileged structure in neuropharmacology, we determined the high-resolution crystal structure of a binary complex between the kinase domain and a molecular fragment of the DAPK inhibitor. The co-crystal structure describes a structural basis for interaction and provides a firm foundation for structure-assisted design of lead compounds with appropriate molecular properties for future drug development.

Neurotrophin potentiation of iron-induced spinal cord injury

Previous studies have shown that pretreatment with neurotrophins can potentiate the vulnerability of cultured neurons to excitotoxic and free radical-induced necrosis, in contrast to their well known neuroprotective effects against apoptosis. Here we tested the hypothesis that this unexpected injury-potentiating effect of neurotrophins would also take place in the adult rat spinal cord. Fe(3+)-citrate was injected stereotaxically into spinal cord gray matter in adult rats in amounts sufficient to produce minimal tissue injury 24 h later. Twenty-four-hour pretreatment with brain-derived neurotrophic factor, neurotrophin-3, or neurotrophin-4/5, but not nerve growth factor, markedly enhanced tissue injury in the gray matter as evidenced by an increase in the damaged area, as well as the loss of neurons and oligodendrocytes. Consistent with maintained free radical mediation, the neurotrophin-potentiated iron-induced spinal cord damage was blocked by co-application of the antioxidant N-tert-butyl-(2-sulfophenyl)-nitrone. These data support the hypothesis that the overall neuroprotective properties of neurotrophins in models of acute injury to the spinal cord may be limited by an underlying potentiation of free radical-mediated necrosis.

In vivo excitotoxicity induced by ouabain, a Na+/K+-ATPase inhibitor

The susceptibility of immature rat brain to neurotoxicity of N-methyl-D-aspartate (NMDA) has provided a widely used paradigm to study excitotoxicity relevant to acute neurodegenerative diseases such as cerebral ischemia. In this study, excitotoxicity was induced via injection of ouabain (1 mM/0.5 microL), a Na+/K+ -ATPase-inhibitor, into neonatal rat brain and compared with NMDA injection. The aim of the study was to induce excitotoxicity secondary to cellular membrane depolarization, thereby more closely mimicking the pathophysiologic processes of ischemia-induced brain injury where NMDA-receptor overstimulation by glutamate follows, not precedes, membrane depolarization. Na+/K+ -ATPase-inhibition caused an acute, 40% +/- 8% decrease of the apparent diffusion coefficient (ADC) of water, as measured using diffusion-weighted magnetic resonance imaging (MRI), and resulted in infarctlike lesions as measured using T2-weighted MRI and histology up to 2 weeks later. Localized one- and two-dimensional 1H-magnetic resonance spectroscopy (MRS) demonstrated that the early excitotoxic diffusion changes were not accompanied by an overall metabolic disturbance. Furthermore, 31P-MRS demonstrated that energy depletion is not a prerequisite for ADC decrease or excitotoxic cell death. Treatment with the NMDA-antagonist MK-801 (1 mg/kg) attenuated the volume of tissue exhibiting a decreased ADC (P < 0.005), demonstrating that the ouabain-induced injury is indeed excitotoxic in nature. The authors argue that, compared with NMDA-injection, ouabain-induced excitotoxicity elicits more appropriate glutamate-receptor overstimulation and is better suited to detect relevant neuroprotection in that it is more sensitive to attenuation of synaptic glutamate levels.

Prolonged suppression of brain nitric oxide synthase activity by 7-nitroindazole protects against cerebral hypoxic-ischemic injury in neonatal rat

Nitric oxide mediates glutamate-induced excitotoxicity associated with cerebral hypoxia-ischemia through production in the brain by several isoforms of nitric oxide synthase (NOS). We examined the influence of the selective neuronal NOS inhibitor, 7-nitroindazole (7-NI), on brain NOS activity and its neuroprotective effects against cerebral hypoxic-ischemic injury in the postnatal day (PND) 7 rat. In the first set of experiments, 7-NI (50 mg/kg) administered intraperitoneally (i.p.) transiently inhibited NOS activity to 40% below the vehicle control level at 1 h after injection (P<0.001, analysis of variance (ANOVA)). In contrast, 7-NI (100 mg/kg, i.p.) inhibited NOS activity to 56% below the control level at 1 h with prolonged suppression of NOS activity at 3, 6, 9 and 12 h after injection. Two-factor ANOVA revealed an overall effect on NOS activity of 7-NI treatment (P<0.001) and time after injection (P<0.001). In the second set of experiments, 7-NI (50, 100 mg/kg) or an equal volume of vehicle was administered after unilateral carotid artery ligation, but 30 min before hypoxia in PND 7 rats. 7-NI (100 mg/kg) significantly protected against cerebral hypoxic-ischemic injury (100 mg/kg of 7-NI, 1.7+/-1.0% damage; control, 8.7+/-1.6%,P<0.05). 7-NI administered 15 min after cerebral hypoxia-ischemia was not neuroprotective. The data suggest that the protective effect of 7-NI is dose dependent, and is related to the duration of suppressed NOS activity.

Platelet-activating factor antagonist BN 50730 attenuates hypoxic-ischemic brain injury in neonatal rats

Platelet-activating factor (PAF) is a lipid derived from breakdown of cell membranes that is postulated to be a mediator of cerebral ischemic injury. PAF regulates CNS gene transcription via intracellular binding sites. To test the hypothesis that PAF mediates CNS injury in part by modulating gene transcription, we evaluated the neuroprotective efficacy of the drug BN 50730, an antagonist of the intracellular (microsomal) CNS PAF binding site, in the neonatal rat model of unilateral cerebral hypoxia-ischemia. Seven-day-old rats underwent right carotid ligation followed by a 2.5-h exposure to 8% O(2), and were then treated with BN 50730 (2.5 or 25 mg/kg per dose) or vehicle, at 0 and 2 h after the end of hypoxia. Ipsilateral cortical, striatal, and hippocampal damage was quantitated either 5 d later, or at 5 wk after the insult. Treatment with BN 50730 resulted in approximately 60- 80% reduction in ipsilateral tissue loss at both times. Learning and memory were evaluated 5 wk after insult using the Morris Watermaze place navigation task. Severity of cortical and striatal damage correlated significantly with learning and memory deficits. These results support the hypothesis that PAF is a pathogenetic mediator of hypoxic-ischemic damage in the immature brain. Accumulating evidence suggests that PAF mediates its deleterious effects in the immature CNS via multiple mechanisms.

Neuronal protection with magnesium

Delayed neuronal death following hypoxic ischaemic insult is primarily mediated by the N-methyl D-aspartate (NMDA) receptor. The NMDA receptor antagonist MK 801, has been shown to limit neuronal death following hypoxic ischaemic injury but is too toxic to be used in the human neonate. Magnesium blocks the NMDA channel in a voltage dependent manner. Its administration after a simulated hypoxic ischaemic insult limits neurological damage in several animal models. The efficacy of magnesium in providing neuroprotection in the human neonate, however needs to be established in controlled clinical trials.

Monocyte chemoattractant protein-1 is a mediator of acute excitotoxic injury in neonatal rat brain

Monocyte chemoattractant protein-1 is a chemokine with potent monocyte activating and chemotactic effects. Monocyte chemoattractant protein-1 gene and protein expression is rapidly up-regulated in response to a variety of acute and chronic central nervous system disorders. The activation and recruitment of microglia and monocytes into areas of inflammation may play a critical role in the pathogenesis of acute brain injury. Monocyte chemoattractant protein-1 could be a pathophysiologically important mediator of the microglial and monocyte responses in the brain. Using a well-characterized model of acute excitotoxic brain injury in neonatal rats, experiments were designed to evaluate whether monocyte chemoattractant protein-1 plays a role in the progression of tissue damage. Direct co-administration of recombinant monocyte chemoattractant protein-1 with the excitotoxin N-methyl-D-aspartate exacerbated injury, both in the striatum and in the hippocampus, by 55% and 167%, respectively. Complementary experiments to determine the effect of functional inhibition of monocyte chemoattractant protein-1, using an anti-monocyte chemoattractant protein-1-neutralizing antibody, revealed that co-administration of the antibody with N-methyl-D-aspartate attenuated tissue injury in the striatum and hippocampus by 57% and 39%, respectively.Together, these data suggest that monocyte chemoattractant protein-1 is a mediator of acute excitotoxic brain injury in neonatal rats and that inflammatory mechanisms contribute significantly to the pathogenesis of acute neonatal brain injury. Whether chemokines are pathophysiologically relevant mediators of neuronal injury in human neonates remains to be determined.

Acute excitotoxic injury induces expression of monocyte chemoattractant protein-1 and its receptor, CCR2, in neonatal rat brain

Chemokines are a family of structurally related cytokines that activate and recruit leukocytes into areas of inflammation. The "CC" chemokine, monocyte chemoattractant protein (MCP)-1 may regulate the microglia/monocyte response to acute brain injury. Recent studies have documented increased expression of MCP-1 in diverse acute and chronic experimental brain injury models; in contrast, there is little information regarding expression of the MCP-1 receptor, CCR2, in the brain. In the neonatal rat brain, acute excitotoxic injury elicits a rapid and intense microglial response. To determine if MCP-1 could be a regulator of this response, we evaluated the impact of excitotoxic injury on MCP-1 and CCR2 expression in the neonatal rat brain. We used a reproducible model of focal excitotoxic brain injury elicited by intrahippocampal injection of NMDA (10 nmol) in 7-day-old rats, to examine injury-induced alterations in MCP-1 and CCR2 expression. RT-PCR assays demonstrated rapid stimulation of both MCP-1 and CCR2 mRNA expression. MCP-1 protein content, measured by ELISA in tissue extracts, increased >30-fold in lesioned tissue 8-12 h after lesioning. CCR2 protein was also detectable in tissue extracts. Double-immunofluorescent labeling enabled localization of CCR2 both to activated microglia/monocytes in the corpus callosum adjacent to the lesioned hippocampus and subsequently in microglia/monocytes infiltrating the pyramidal cell layer of the lesioned hippocampus. These results demonstrate that in the neonatal brain, acute excitotoxic injury stimulates expression of both MCP-1 and its receptor, CCR2, and suggests that MCP-1 regulates the microglial/monocyte response to acute brain injury.

Reduced nitric oxide is involved in prenatal ischemia-induced tolerance to neonatal hypoxic-ischemic brain injury in rats

To explore the role of nitric oxide (NO) in the hypoxic-ischemic (HI) tolerance phenomenon, NO production and brain injury following neonatal hypoxia-ischemia (induced by unilateral common carotid artery ligation followed by hypoxic exposure) were assessed in rat pups with or without HI preconditioning. A previously demonstrated prenatal HI rat model of preconditioning was used in this study. On G17, rat fetuses were subjected to either HI in utero (PreHI) for 30 min or a sham operation (SH). The PreHI treatment provided significant protection against neonatal HI-induced brain injury, as indicated by decreased ipsilateral brain weight reduction, less severe tissue damage, and decreased activation of caspase-3. Concomitant with the protective effect of prenatal HI preconditioning, elevation of nitrite/nitrate content in the ipsilateral cortex of the brain, as an indirect measure of NO production, was significantly lower in the PreHI group than in the SH group following neonatal HI. The protective effect of prenatal HI preconditioning could be reversed by sodium nitroprusside (SNP), a spontaneous NO donor, while SNP had no effect on neonatal HI-induced brain injury in the SH group. Intraperitoneal administration of SNP to pups from the PreHI group (2 mg/kg, 24 and 1.5 h before neonatal HI) increased neonatal HI-induced brain injury similar to that observed in the SH group. On the other hand, L-N(G)-nitro-arginine (2 mg/kg, i.p., 1.5 h before the hypoxic exposure), an NO synthase inhibitor, significantly attenuated neonatal HI-induced brain injury in the SH group. The overall results indicate that reduced NO production in the preconditioned rat brain contributes to prenatal HI-induced tolerance to neonatal HI brain injury.

Pentoxifylline attenuates hypoxic-ischemic brain injury in immature rats

Inflammatory mediators are implicated in the pathogenesis of ischemic injury in immature brain. The phosphodiesterase inhibitor pentoxifylline inhibits production of tumor necrosis factor-alpha and platelet-activating factor. We hypothesized that pentoxifylline treatment would attenuate hypoxic-ischemic brain injury in immature rats. Seven-day-old rats (n = 79) underwent right carotid ligation, followed by hypoxia (FiO2 = 0.08). Rats received pentoxifylline immediately before and again after hypoxia (two doses, 25-150 mg/kg/dose, n = 34), or vehicle (n = 27). In separate experiments, rats received pentoxifylline treatment (40 mg/kg/dose, n = 8), or vehicle (n = 10) immediately and again 3 h after hypoxia-ischemia. Severity of injury was assessed 5 d later by visual evaluation of ipsilateral hemisphere infarction and by measurement of bilateral hemispheric cross-sectional areas. Pentoxifylline pretreatment reduced the incidence of liquefactive cerebral infarction, from 75% in controls to 10% with pentoxifylline, 40 mg/kg/dose (p<0.001, chi2 trend test). Quantification of hemispheric areas confirmed these findings. In contrast, posthypoxic-ischemic treatment with pentoxifylline resulted in only a modest reduction in cortical damage, without an overall reduction in incidence of infarction. Phosphodiesterase inhibition may be an effective strategy to use to decrease the severity of neonatal hypoxic-ischemic brain injury. Pretreatment regimens could be clinically relevant in settings in which an increased risk of cerebral ischemia can be anticipated, such as in infants undergoing surgery to correct congenital heart disease.

Tumor necrosis factor-a attenuates N-methyl-D-aspartate-mediated neurotoxicity in neonatal rat hippocampus

Tumor necrosis factor-a TNFa. has been implicated in the pathophysiology of acute neonatal brain injury. We hypothesized that acute brain injury would induce TNFa expression and that exogenous TNFa would influence the severity of N-methyl-D-aspartate-induced tissue damage. We performed two complementary groups of experiments to evaluate the potential role s. of TNFa in a neonatal rodent model of excitotoxic injury, elicited by intracerebral injection of N-methyl-D-aspartate. We used immunohistochemistry and ELISA to evaluate N-methyl-D-aspartate-induced changes in TNFa expression, and we co-injected TNFa with N-methyl-D-aspartate, to evaluate the effect of this cytokine on the severity of tissue injury. Both intra-hippocampal and intra-striatal injection of N-methyl-D-aspartate 5 nmol. stimulated TNFa expression. Increased TNFa expression was detected 3-12 h after lesioning; TNFa was localized both in glial cells in the corpus callosum, and in cells with the morphology of interneurons in the ipsilateral hippocampus, striatum, cortex and thalamus. Intra-hippocampal or intra-striatal administration of TNFa 50 ng. alone did not elicit neuropathologic damage. In the hippocampus, when co-injected with N-methyl-D-aspartate 5 or 10 nmol., TNFa 50 ng. attenuated excitotoxic injury by 35%-57%, compared to controls co-injected with heat-treated TNFa. In contrast, in the striatum, co-injection of TNFa with N-methyl-D-aspartate had no effect on the severity of the ensuing damage. The data indicate that TNFa is rapidly produced in glial cells and neurons after an excitotoxic insult in the neonatal rat brain, and that administration of exogenous TNFa results in region-specific attenuation of excitotoxic damage. We speculate that endogenous TNFa may modulate the tissue response to excitotoxic injury in the developing brain.

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.

Mice deficient in interleukin-1 converting enzyme are resistant to neonatal hypoxic-ischemic brain damage

Interleukin-1 (IL-1) converting enzyme (ICE) is a cysteine protease that cleaves inactive pro-IL-1beta to active IL-1beta. The pro-inflammatory cytokine IL-1beta is implicated as a mediator of hypoxic-ischemic (HI) brain injury, both in experimental models and in humans. ICE is a member of a family of ICE-like proteases (caspases) that mediate apoptotic cell death in diverse tissues. The authors hypothesized that in neonatal mice with a homozygous deletion of ICE (ICE-KO) the severity of brain injury elicited by a focal cerebral HI insult would be reduced, relative to wild-type mice. Paired litters of 9- to 10-day-old ICE-KO and wild-type mice underwent right carotid ligation, followed by 70 or 120 minutes of exposure to 10% O2. In this neonatal model of transient focal cerebral ischemia followed by reperfusion, the duration of hypoxia exposure determines the duration of cerebral ischemia and the severity of tissue damage. Outcome was evaluated 5 or 21 days after lesioning; severity of injury was quantified by morphometric estimation of bilateral cortical, striatal, and dorsal hippocampal volumes. In animals that underwent the moderate HI insult (70-minute hypoxia), damage was attenuated in ICE-KO mice, when evaluated at 5 or 21 days post-lesioning. In contrast, in mice that underwent the more severe HI insult (120-minute hypoxia), injury severity was the same in both groups. Reductions in intra-HI CBF, measured by laser Doppler flow-metry, and intra- and post-HI temperatures did not differ between groups. These results show that ICE activity contributes to the progression of neonatal HI brain injury in this model. Whether these deleterious effects are mediated by pro-inflammatory actions of IL-1beta and/or by pro-apoptotic mechanisms is an important question for future studies.

An international network for evaluating neuroprotective therapy after severe birth asphyxia

Animal studies have shown great promise in their applicability to potentially neuroprotective therapies for severe birth asphyxia in human babies. It is now necessary to consider a strategy to evaluate some or all of these techniques within the context of human neonatal randomized control trials (RCT). We have set up a pilot study for an international RCT of mature babies with severe asphyxia (defined by an Apgar score of 5 or less at 10 minutes) and have shown that we can recruit from 120 centers in 17 countries an average of three babies a week, which is the required number to undertake a study over a 2-year period with sufficient power to show a significant improvement in outcome. Particular attention must be given in future studies to the size of improvement in outcome required, generalizability of entry criteria, and the appropriate measure of functional outcome in treated babies.

Possible protective role of growth hormone in hypoxia-ischemia in neonatal rats

Perinatal asphyxia still constitutes a clinical hazard associated with considerable neurologic morbidity. Several growth factors, including insulin-like growth factor-I (IGF-I), have been reported to have a neuroprotective effect in experimental models of hypoxic ischemia (HI). In the present study, we have applied solution hybridization for quantification of the time course for mRNA expression of IGF-I, IGF-I receptor, and growth hormone (GH) receptor after HI in 7-d-old rats. There was a significant increase in IGF-I mRNA in the damaged hemisphere 72 h (1.19 +/- 0.28 vs 0.48 +/- 0.02 amol/microg DNA, p < 0.05) and 14 d (0.61 +/- 0.18 vs 0.19 +/- 0.05 amol/microg DNA, p < 0.05) after HI. In the contralateral hemisphere, both IGF-I and GH receptor mRNA had increased by 14 d after the insult (0.36 +/- 0.042 vs 0.13 +/- 0.011, p < 0.05, and 0.31 +/- 0.013 vs 0.11 +/- 0.004 amol/microg DNA, p < 0.001, respectively). There were no changes in IGF-I receptor mRNA throughout the study period. We have also evaluated the neuroprotective effect of GH after HI in neonatal rats. GH administered s.c. after HI in daily doses of 50 and 100 mg/kg provided a moderate neuroprotection of 20%. These results suggest a role for the GH/IGF-I axis in the neurochemical process leading to HI brain injury.

Changes in the diffusion of water and intracellular metabolites after excitotoxic injury and global ischemia in neonatal rat brain

The reduction of the apparent diffusion coefficient (ADC) of brain tissue water in acute cerebral ischemia, as measured by diffusion-weighted magnetic resonance imaging, is generally associated with the development of cytotoxic edema. However, the underlying mechanism is still unknown. Our aim was to elucidate diffusion changes in the intracellular environment in cytotoxic edematous tissue. The ADC of intracellular metabolites was measured by use of diffusion-weighted 1H-magnetic resonance spectroscopy after (1) unilateral N-methyl-D-aspartate (NMDA) injection and (2) cardiac arrest-induced global ischemia in neonatal rat brain. The distinct water ADC drop early after global ischemia was accompanied by a significant reduction of the ADC of all measured metabolites (P < 0.01, n = 8). In the first hours after excitotoxic injury, the ADC of water and the metabolites taurine and N-acetylaspartate dropped significantly (P < 0.05, n = 8). At 24 and 72 hours after NMDA injection brain metabolite levels were diminished and metabolite ADC approached contralateral values. Administration of the NMDA-antagonist MK-801 1.5 hours after NMDA injection completely normalized the water ADC but not the metabolite ADC after 1 to 2 hours (n = 8). No damage was detected 72 hours later and, water and metabolite ADC had normal values (n = 8). The contribution of brain temperature changes (calculated from the chemical shift between the water and N-acetylaspartate signals) and tissue deoxygenation to ischemia-induced intracellular ADC changes was minor. These data lend support to previous suggestions that the ischemia-induced brain water ADC drop may partly be caused by reduced diffusional displacement of intracellular water, possibly involving early alterations in intracellular tortuosity, cytoplasmic streaming, or intracellular molecular interactions.

Tat, a human immunodeficiency virus-1-derived protein, augments excitotoxic hippocampal injury in neonatal rats

To test the hypothesis that the human immunodeficiency virus-1-derived Tat protein may cause neuronal damage in the CNS, we evaluated the neurotoxicity of recombinant human immunodeficiency virus-1-derived Tat in vivo in seven-day-old rats. The intrinsic neurotoxicity of Tat (250 ng-1 microg) and the effects of direct intra-hippocampal co-infusion of Tat with N-methyl-D-aspartate were assessed. Extent of injury in the lesioned hippocampus was evaluated five days later, based on histopathology and morphometric measurements of hippocampal volume. To confirm that any observed neurotoxic effects were attributable to Tat bioactivity, all experiments included controls that received equal amounts of heat-treated (boiled) Tat. Intra-hippocampal injection of Tat, alone, elicited minimal focal tissue damage immediately adjacent to the injection track, and no hippocampal atrophy. Co-injection of Tat (500 ng) with N-methyl-D-aspartate (5 nmol, threshold excitotoxic dose) doubled the severity of hippocampal injury, quantified by comparison of bilateral hippocampal volumes, in comparison with animals that received heat-treated Tat or saline co-injections; in animals that received injections of N-methyl-D-aspartate (5 nmol) in combination with saline, heat-treated Tat, or Tat [mean(+/-S.E.M.) % volume loss values in the lesioned hippocampus were: 11(+/-3), 11(+/-3), and 26(+/-3), respectively (P<0.002, ANOVA)]. Co-injection of 100 ng Tat with 5 nmol N-methyl-D-aspartate exacerbated the severity of excitotoxic injury to a similar extent, whereas co-injection of 20 ng Tat had no effect on N-methyl-D-aspartate-mediated injury. Treatment with the N-methyl-D-aspartate antagonist 3-((RS)-2-carboxypiperazin4-yl)-propyl-1-phosphonic acid (20 mg/kg) markedly attenuated hippocampal injury resulting from co-injection of 100 ng Tat with N-methyl-D-aspartate [mean(+/-S.E.M.) % volume loss in lesioned hippocampus: 0.1(+/-2) in 3-((RS)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid-treated vs 19(+/-3) in controls, P<0.001, ANOVA]. Co-injection of Tat had no effect on N-methyl-D-aspartate-mediated striatal damage or on alpha-amino-3-hydroxy-5-methylisoxazole-4-pro hippocampal damage. These data support the hypothesis that locally released Tat could exert neurotoxic effects, mediated by N-methyl-D-aspartate receptor activation, in vivo in the immature brain.

Excitotoxic brain injury stimulates expression of the chemokine receptor CCR5 in neonatal rats

Chemokines interact with specific G-protein-coupled receptors to activate and direct recruitment of immune cells. Some chemokines are up-regulated in pathological conditions of the central nervous system, and recently several chemokine receptors, including CCR5, were identified in the brain. However, little is known about the regulation of expression of chemokine receptors in the brain. Direct intracerebral injection of N-methyl-D-aspartate (NMDA), an excitatory amino acid agonist, elicits reproducible focal excitotoxic brain injury; in neonatal rats, intrahippocampal NMDA injection stimulates expression of pro-inflammatory cytokines and elicits a robust microglia/monocyte response. We hypothesized that NMDA-induced neurotoxicity would also stimulate expression of CCR5 in the neonatal rat brain. We evaluated the impact of intrahippocampal injections of NMDA on CCR5 expression in postnatal day 7 rats. Reverse transcription polymerase chain reaction revealed an increase in hippocampal CCR5 mRNA expression 24 hours after lesioning, and in situ hybridization analysis demonstrated that CCR5 mRNA was expressed in the lesioned hippocampus and adjacent regions. Western blot analysis demonstrated increased CCR5 protein in hippocampal tissue extracts 32 hours after lesioning. Complementary immunocytochemistry studies identified both infiltrating microglia/monocytes and injured neurons as the principal CCR5-immunoreactive cells. These results provide the first evidence that acute excitotoxic injury regulates CCR5 expression in the developing rat brain.

Effect of N-methyl-D-aspartate and potassium on striatal monoamine metabolism in immature rat: an in vivo microdialysis study

Effects of N-methyl-D-aspartate (NMDA) and potassium on 5-day-old rat's brain were examined. We measured extracellular striatal monoamines such as dopamine (DA), 3,4 dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindole-3-acetic acid (5-HIAA) using intracerebral microdialysis. After 3 h stabilization, pups received varying concentrations of NMDA (1-3 mM) and potassium (200-800 mM) by intrastriatal perfusion for 32 minutes. Increasing the concentration of NMDA and potassium induced a dose related DA increase (p < 0.001), whereas DOPAC, HVA, and 5-HIAA decreased significantly. Five days later the same animals were sacrificed and the weight reduction of their cerebral hemispheres was measured. The weight of the drug perfused side was significantly reduced compared with that of the contralateral one. We examined next the relationship between the level of maximum DA and the relative hemisphere weight reduction. The DA peak was highly correlated with the hemisphere weight reduction (r = 0.70, n = 52, p < 0.001 in the NMDA group, r = 0.83, n = 30, p < 0.001 in the potassium group, respectively). These data show that each treatment alter striatal monoamine metabolism in immature rat brain and that the extracellular DA peak is a potential early indicator to estimate brain injury.

Expression of NMDA receptor subunit mRNA after MK-801 treatment in neonatal rats

Although NMDA receptor antagonists are neuroprotective when delivered in conjunction with NMDA, supersensitivity to NMDA-mediated injury follows dizocilpine (MK-801) administration in neonatal rats. An increase in NMDA-sensitive [3H]-glutamate binding accompanies the increase in vulnerability to excitotoxic injury. The present study tests the hypothesis that MK-801 may alter gene expression for the NMDA receptor subunits. Quantitative in situ hybridization histochemistry was used to evaluate the expression of NMDA receptor subunits NR1 and NR2A-D in neonatal rats, 2 to 4 h after treatment with MK-801. Increased mRNA for multiple NMDA receptor subunits was observed in cerebral cortex, striatum and hippocampus. The percent increase in NR2A mRNA was larger than the percent change in NR1, NR2B or NR2D. A small increase in mRNA for the metabotropic glutamate receptor mGluR5 was also observed after MK-801 treatment. These results indicate that gene expression for NMDA receptor subunits in the developing brain is rapidly altered after antagonist exposure. Increased expression of excitatory amino acid receptor subunit mRNA may contribute to the enhanced vulnerability to excitotoxic injury that has been observed after MK-801 treatment.

Excitotoxic injury induces monocyte chemoattractant protein-1 expression in neonatal rat brain

Intra-hippocampal injection of NMDA (12.5 nmol) in postnatal day 7 (P7) rats results in neuronal necrosis and hippocampal atrophy; injury extends into the adjacent striatum, thalamus and cortex. NMDA-induced injury is marked by an acute microglial/monocyte response; the molecular signals that control this response and the role of activated microglia/monocytes in the progression of excitotoxic injury are unknown. Monocyte chemoattractant protein-1 (MCP-1) is a well-characterized chemokine that regulates monocyte chemotaxis and activation, and contributes to the pathogenesis of monocyte-dependent tissue injury in several disease models. We hypothesized that MCP-1 could be a regulator of the microglial/monocyte response to excitotoxic injury in neonatal rat brain. To determine if intra-hippocampal NMDA injections induced MCP-1 mRNA expression, in situ hybridization assays were performed in brain samples obtained from 7-day-old rats, evaluated 0-24 h after intra-hippocampal NMDA injection. MCP-1 mRNA expression was first detected at 2 h after lesioning, in the choroid fissure, adjacent to the lesioned hippocampus; levels of expression increased markedly in the lesioned hippocampus and adjacent structures within the first 16 h after NMDA injection, and then rapidly declined. In control animals that received intra-hippocampal saline injections, only minimal MCP-1 mRNA was detected, along the injection track. These results demonstrate that excitotoxic injury transiently induces MCP-1 gene expression in neonatal rat brain. The functional role of MCP-1 in the injured brain remains to be determined.

Role of glutamate receptor-mediated excitotoxicity in bilirubin-induced brain injury in the Gunn rat model

Severe hyperbilirubinemia in neonates with prematurity and/or systemic illnesses such as hemolytic disease, acidosis, and hypoxemia enhances their risk for developing cerebral palsy, paralysis of ocular upgaze, and deafness. This neurologic syndrome has been associated with selective neuronal vulnerability in the basal ganglia, certain brainstem nuclei, and Purkinje cells. However, the mechanism by which bilirubin damages neurons remains unclear. In these studies, we found that intracerebral injection of N-methyl-D-aspartate (NMDA), an excitotoxic analogue of glutamate, caused greater injury in jaundiced 7-day-old Gunn (jj) rat pups than in nonjaundiced heterozygous (Nj) littermate controls. NMDA injection caused even greater injury when protein-bound bilirubin was displaced with the sulfonamide drug sulfadimethoxine in jaundiced homozygous pups. In additional experiments, the acute signs of bilirubin-mediated neuronal injury, induced in homozygous (jj) Gunn rats by treatment with sulfonamide, were reduced by concurrent treatment with the NMDA-type glutamate channel antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohept-5,10-imine (MK-801, dizocilpine). The results suggest that bilirubin may cause encephalopathy and neuronal injury, at least in part, through an NMDA receptor-mediated excitotoxic mechanism. This conclusion is consistent with clinical observations that bilirubin encephalopathy is synergistically worsened by hypoxemia, which also shares an excitotoxic mechanism of neuronal injury.

Lamotrigine protects hippocampal CA1 neurons from ischemic damage after cardiac arrest

BACKGROUND AND PURPOSE

Lamotrigine (LTG) is an anticonvulsant drug whose mechanism of action may involve the inhibition of glutamate release by blocking voltage-dependent sodium channels. Glutamate neurotoxicity may contribute to cerebral ischemic damage after recovery from cardiac arrest. Thus, LTG may prevent the brain damage associated with global cerebral ischemia by reducing the release of glutamate from presynaptic vesicles during the ischemic insult or the early recovery period.

METHODS

LTG was studied in cardiac arrest-induced global cerebral ischemia with reperfusion in rats. In the first set of experiments, LTG (100 mg/kg, p.o.) was administered before induction of ischemia; and in the second experiment, LTG (10 mg/kg, i.v.) was given 15 minutes after ischemia and a second dose (10 mg/kg,i.v.) was given 5 hours later.

RESULTS

In both experiments LTG reduced the damage to the hippocampal CA1 cell population by greater than 50%. Neuroprotection was not associated with changes in brain temperature or plasma glucose concentration. Plasma concentrations of LTG ranged between 8 and 13 micrograms/mL. Patients taking LTG as a monotherapy for epilepsy typically have plasma levels of LTG in the 10 to 15 micrograms/mL range.

CONCLUSIONS

These data suggest that LTG may be effective in preventing brain damage after recovery from cardiac arrest. Patients on LTG monotherapy for epilepsy have plasma concentrations very similar to those found to be neuroprotective in this study. Although difficult to extrapolate, our data suggest that LTG at neuroprotective doses may be well tolerated by humans.

The non-competitive AMPA antagonist LY 300168 (GYKI 53655) attenuates AMPA-induced hippocampal injury in neonatal rodents

In contrast with the neuroprotective efficacy of competitive and non-competitive N-methyl-D-aspartate (NMDA) antagonists versus NMDA neurotoxicity, reported neuroprotective effects of non-NMDA antagonists in limiting alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) toxicity have been less robust. We tested the effect of the non-competitive AMPA receptor antagonist LY 300168 (GYKI 53655; E. Lilly) (0.25 or 2.5 mg/kg per dose i.p. x 3 doses vs. vehicle) on AMPA-induced excitotoxic injury in postnatal day 7 (P7) rats. To assess specificity, we tested the effect of LY 300168 (2.5 mg/kg per dose x 3 doses) on NMDA-induced excitotoxic injury. P7 rats received right intrahippocampal injections of either (S)-AMPA (2.5 nmol, n = 67) or NMDA (12.5 nmol, n = 11). Injection of AMPA resulted in right hippocampal atrophy with pyramidal cell loss. LY 300168 treatment produced dose-dependent attenuation of AMPA-induced right hippocampal injury; based on comparisons with left hippocampal volumes, 2.5 nmol AMPA resulted in 42 +/- 3% (mean +/- SEM) right hippocampal volume loss in controls, but only 10 +/- 5% after LY 300168 2.5 mg/kg per dose (P < 0.001; ANOVA). LY 300168 had no effect on NMDA-induced hippocampal injury. The data support the hypothesis that drugs that allosterically regulate AMPA receptor activity can modulate the response of immature brain to AMPA-mediated injury.

Neonatal cerebral hypoxia-ischemia: the effect of adenosine receptor antagonists

The effects of nonselective (theophylline), A1-(DPCPX) or A2A-selective (SCH 58261) adenosine receptor antagonists administered before or after neonatal hypoxia-ischemia (HI) were studied on the extent of brain injury in 7-day-old rats evaluated after 14 days. A possible effect of theophylline (20 mg/kg) on expression of immediate early genes was studied with in situ hybridization. Theophylline (20, 30 or 60 mg/kg) given prior to HI reduced brain damage by 48% (P < 0.001), 36% (P < 0.01) and 34% (P < 0.05), respectively, compared to control rats. This effect was not explained by changes in temperature, cerebral blood flow, blood gas/acid base status or blood glucose during the insult. Theophylline enhanced the upregulation of c-fos and NFGI-A during reperfusion but did not prevent the decrease in adenosine A1 receptor mRNA. Posttreatment with SCH 58261 (0.2 or 2 mg/kg) reduced brain damage by 19% (P < 0.05) and 14% (NS), respectively, compared to control rats which was unrelated to the core temperature. DPCPX (2 or 10 mg/kg) had no effect on the development of brain injury. In conclusion, nonselective and A2A adenosine receptor antagonists reduced brain injury in a model of HI in immature animals.

Brief post-hypoxic-ischemic hypothermia markedly delays neonatal brain injury

The influence of post-insult temperature modulation on ischemic injury in immature brain was studied in 7-day-old rats that underwent a unilateral carotid artery ligation followed by exposure to hypoxia in 8% oxygen at an ambient temperature of 36.5 degrees C. After the hypoxic exposure, the animals were separated into three groups and placed for 3 h in temperature-controlled incubators set at 32 degrees C, 35 degrees C, and 38 degrees C. In Study 1, the influence of post-insult temperature modulation was assessed after graded cerebral hypoxic-ischemic injury. Brain damage was assessed 1 week after the insult by comparison of wet weights in the cerebral hemispheres ipsilateral and contralateral to the carotid artery ligation. Rectal temperatures of the animals significantly correlated with extent of brain injury after 60 min (Spearman correlation coefficient, p = 0.44, P = 0.005) and 90 min (p = 0.46, P = 0.004) but not 120 min of hypoxia (p = 0.18, P = 0.46). In Study 2, animals were exposed to 75 min hypoxia, and injury was assessed morphometrically and histologically at 1 and 4 weeks after the injury. Rectal temperatures significantly correlated with the extent of ischemic injury in the cerebral cortex (p = 0.3, P = 0.046) and striatum (p = 0.3, P = 0.048) at 1 week, but not 4 weeks, after the insult. The findings indicate that post-insult hypothermia delayed the expression of mild to moderate brain damage by more than a week, after which the damage was as severe as in normothermic animals. The results indicate that the events that determine the final expression of a neonatal hypoxic-ischemic insult can be extended over a long interval by post-insult hypothermia.

Cytokines and perinatal brain injury

A rapidly expanding body of data provides support for the hypothesis that pro-inflammatory cytokines including interleukin-1 beta (IL-1 beta), and tumor necrosis factor-alpha (TNF-alpha) are expressed acutely in injured brain and contribute to progressive neuronal damage. Little is known about the pathogenetic role of these cytokines in perinatal brain injury. Recent experimental studies have incorporated two closely related in vivo perinatal rodent brain injury models to evaluate the role(s) of pro-inflammatory cytokines in the progression of neuronal injury: a perinatal stroke model, elicited by unilateral carotid artery ligation and subsequent timed exposure to 8% oxygen in 7-day-old rats, and a model of excitotoxic injury, elicited by stereotactic intra-cerebral injection of the selective excitatory amino acid agonist NMDA. Each of these lesioning methods results in reproducible, quantifiable focal forebrain injury at this developmental stage. Acute brain injury, evoked by cerebral hypoxia-ischemia or excitotoxin lesioning, results in transient marked increases in expression of IL-1 beta, and TNF-alpha mRNA in brain regions susceptible to irreversible injury, and there is evidence that pharmacological antagonism of IL-1 receptors can attenuate injury in both models. Recent studies also suggest that complementary strategies, based on pharmacological antagonism of platelet activating factor and on neutrophil depletion can also limit the extent of irreversible injury. In summary, current data suggest that pro-inflammatory cytokines contribute to the progression of perinatal brain injury, and that these mediators are important targets for neuroprotective interventions in the acute post-injury period.

gp120, a human immunodeficiency virus-1 coat protein, augments excitotoxic hippocampal injury in perinatal rats

Recent data suggest that gp120, a human immunodeficiency virus-1 (HIV-1) coat glycoprotein that is secreted by HIV-infected cells, is neurotoxic, and that this toxicity is mediated, at least in part, by activation of N-methyl-D-aspartate-type excitatory amino acid receptors. To test this hypothesis in vivo, we examined the neurotoxicity of gp120 injected intrahippocampally, alone or co-injected with the selective excitatory amino acid agonist N-methyl-D-aspartate, in seven-day-old rats. Severity of injury in the lesioned hippocampus was assessed five days later, using three outcome measures: histopathology, hippocampal atrophy (derived from regional cross-sectional area measurements) and loss of [3H]glutamate receptor binding (based on in vitro autoradiography assays). To confirm that any observed effects were attributable to gp120 bioactivity, each group of experiments included controls that received equal amounts of heat-treated gp120. Gp120 (200 ng) elicited minimal focal pyramidal cell loss immediately adjacent to the injection track; there was no hippocampal atrophy or loss of [3H]glutamate binding. Co-injection of 50 ng gp120 with N-methyl-D-aspartate (5 nmol, threshold excitotoxic dose) increased the severity of hippocampal injury; hippocampal atrophy was greater in animals that received injections of 5 nmol N-methyl-D-aspartate in combination with 50 ng gp120 than in those that received either N-methyl-D-aspartate alone (5 nmol) or 5 nmol N-methyl-D-aspartate+50 ng heat-treated gp120 (mean+/-S.E.M. percentage reduction in injected hippocampal volume vs contralateral: N-methyl-D-aspartate, -19+/-3; N-methyl-D-aspartate+gp120, -26.8+/-2.1; N-methyl-D-aspartate+heat-treated gp120, -14.0+/-2.2; P<0.001, ANOVA). Treatment with the competitive N-methyl-D-aspartate antagonist 3-((RS)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (20mg/kg) markedly reduced the severity of injury elicited by the combination of gp120 with N-methyl-D-aspartate. These data support the hypothesis that locally secreted gp120 could exert neurotoxic effects, mediated by N-methyl-D-aspartate receptor activation, in vivo in the immature brain.

Adenovirus-mediated over-expression of interleukin-1 receptor antagonist reduces susceptibility to excitotoxic brain injury in perinatal rats

In seven-day-old rats, intracerebral injection of N-methyl-D-aspartate transiently stimulates expression of Interleukin-1 beta messenger RNA. To evaluate the role of Interleukin-1 beta in the pathogenesis of excitotoxic injury, we sought to determine if Interleukin-1 receptor antagonist, an endogenous competitive inhibitor of Interleukin-1 beta, could attenuate N-methyl-D-aspartate-induced injury. To induce sustained over-expression of Interleukin-1 receptor antagonist in the brain, a recombinant adenovirus encoding Interleukin-1 receptor antagonist was administered by intracerebroventricular injection into three-day-old rats. Increased brain concentrations of Interleukin-1 receptor antagonist two to six days later were documented by assays of tissue homogenates and by immunocytochemistry. To evaluate the impact of Interleukin-1 receptor antagonist on N-methyl-D-aspartate neurotoxicity, three-day-old animals received intracerebroventricular injections of either adenovirus encoding Interleukin-1 receptor antagonist or a control adenovirus encoding beta-galactosidase, followed four days later by right intrastriatal injections of N-methyl-D-aspartate (10 nmol/0.5 microliter), a dose that typically elicits excitotoxic injury in the ipsilateral striatum and adjacent hippocampus, or saline. Animals were killed five days later, and brain damage was quantitated by measurement of bilateral cross-sectional areas of the striatum and anterior hippocampus. In three independent experiments, in N-methyl-D-aspartate-lesioned animals, both striatal and hippocampal injuries were reduced in animals that had been infected with adenovirus that encoded Interleukin-1 receptor antagonist, in comparison with littermates infected with the control adenovirus (right striatal volume loss ranged from 16 to 24%, compared with 54-65% volume loss in control). There was no striatal atrophy in adenovirus-infected saline-injected animals. These results provide strong support for the hypothesis that Interleukin-1 beta is a mediator of excitotoxic brain injury in perinatal rats.

The platelet-activating factor antagonist BN 52021 attenuates hypoxic-ischemic brain injury in the immature rat

Platelet-activating factor (PAF) is overproduced in ischemic brain. Although postischemic PAF antagonist administration protects the mature brain in some models, little is known about the effects of PAF antagonists in the immature brain. We hypothesized that the PAF antagonist BN 52021 would attenuate perinatal cerebral hypoxic-ischemic injury. To elicit focal hypoxic-ischemic brain injury, 7-d-old (P7) rats (n = 111) underwent right carotid ligation, followed by 2.5-3.25 h of hypoxia (fractional concentration of inspired O2 = 0.08). BN 52021 neuroprotection was evaluated in three groups of experiments: 1) 25 mg/kg/dose, 0 and 2 h posthypoxia; 2), 25 mg/kg/dose immediately before and 1 h after hypoxia; and 3) posthypoxia-ischemia treatment with BN 52021 12.5, 25, or 50 mg/kg/dose in 2 doses 0 and 2 h after hypoxia. All experiments included concurrent vehicle-injected controls. To quantitate severity of injury, bilateral regional cross-sectional areas (groups 1 and 2) or hemisphere weights (group 3) were evaluated on P12. Both pre- and posthypoxic treatment with BN 52021 (25 mg/kg/dose, two serial doses) decreased the incidence of cerebral infarction from 90% to about 30% (p < 0.02, Fisher's exact test). Measurement of cross-sectional areas confirmed neuroprotection and indicated some benefit of pre- over posthypoxic-ischemic treatment in hippocampus and cortex. Over the dose range tested, the neuroprotective effect of BN 52021 administration was not dose-dependent. In contrast, BN 52021 did not attenuate N-methyl-D-aspartate-induced hippocampal excitotoxic injury in P7 rats. Either prophylactic or "rescue" administration of PAF antagonists decreases the incidence and severity of brain injury associated with an episode of perinatal cerebral hypoxia-ischemia.

Microglial response to N-methyl-D-aspartate-mediated excitotoxicity in the immature rat brain

The intracerebral injection of N-methyl-D-aspartate (NMDA) has been proposed as a model for hypoxic-ischemic insult in the immature brain. In this light, the aim of this study was to describe the time course of the microglial reaction in the areas undergoing primary degeneration at the site of intracortical NMDA injection as well as in areas undergoing secondary anterograde and/or retrograde degeneration. Fifty nanomoles of NMDA were injected in the sensorimotor cortex of 6-day-old rats. After survival times ranging from 10 hours to 28 days, cryostat sections were stained for routine histology and for the demonstration of microglial cells by means of tomato lectin histochemistry. The areas affected by primary degeneration caused by the intracortical injection of NMDA were the neocortex, the hippocampus, and the rostral thalamus. Secondary degeneration (retrograde and anterograde) was observed in the ventrobasal complex of the thalamus. The cortical lesion also caused Wallerian degeneration of the cortical descending efferents as observed in the basilar pons. Microglial reactivity in all these areas was present at 10 hours postinjection and was restricted to the areas undergoing neuronal or axonal degeneration. Reactive microglial cells were stained intensely and showed a round or pseudopodic morphology. At 3 days, an apparent increase in the number of tomato lectin-positive cells was observed in the areas undergoing neuronal death. By 7 days after the injection, the lesion became nonprogressive, and by 14 and 28 days, microglial cells showed moderate lectin binding and a more ramified morphology.