A model of perinatal hypoxic-ischemic brain damage

Pathological consequences of intermittent hypoxia in the central nervous system

Intermittent hypoxia (IH) is a frequent occurrence in clinical settings. In the last decades, evidence has emerged implicating the gas exchange alterations and sleep disruption associated with those disorders in the high prevalence of cognitive and behavioral deficits afflicting these patients. In an effort to better characterize the role of IH, and to identify potential mechanisms of IH-induced central nervous system (CNS) dysfunction, a large number of rodent models have been recently developed. The cumulative evidence confirms that IH indeed induces a heterotopic pattern of injury in the brain, particularly affecting cortical, subcortical, and hippocampal regions, ultimately leading to neuronal apoptosis and activation of microglia. These IH-induced deleterious processes exhibit substantial variability across the lifespan, are under substantial modulatory influences of diet, physical or intellectual activity, and genetic factors, and preferentially recruit oxidative stress and inflammatory pathways.

Use of an eight-arm radial water maze to assess working and reference memory following neonatal brain injury

Working and reference memory are commonly assessed using the land based radial arm maze. However, this paradigm requires pretraining, food deprivation, and may introduce scent cue confounds. The eight-arm radial water maze is designed to evaluate reference and working memory performance simultaneously by requiring subjects to use extra-maze cues to locate escape platforms and remedies the limitations observed in land based radial arm maze designs. Specifically, subjects are required to avoid the arms previously used for escape during each testing day (working memory) as well as avoid the fixed arms, which never contain escape platforms (reference memory). Re-entries into arms that have already been used for escape during a testing session (and thus the escape platform has been removed) and re-entries into reference memory arms are indicative of working memory deficits. Alternatively, first entries into reference memory arms are indicative of reference memory deficits. We used this maze to compare performance of rats with neonatal brain injury and sham controls following induction of hypoxia-ischemia and show significant deficits in both working and reference memory after eleven days of testing. This protocol could be easily modified to examine many other models of learning impairment.

Cortical region-specific engraftment of embryonic stem cell-derived neural progenitor cells restores axonal sprouting to a subcortical target and achieves motor functional recovery in a mouse model of neonatal hypoxic-ischemic brain injury

Hypoxic-ischemic encephalopathy (HIE) at birth could cause cerebral palsy (CP), mental retardation, and epilepsy, which last throughout the individual's lifetime. However, few restorative treatments for ischemic tissue are currently available. Cell replacement therapy offers the potential to rescue brain damage caused by HI and to restore motor function. In the present study, we evaluated the ability of embryonic stem cell-derived neural progenitor cells (ES-NPCs) to become cortical deep layer neurons, to restore the neural network, and to repair brain damage in an HIE mouse model. ES cells stably expressing the reporter gene GFP are induced to a neural precursor state by stromal cell co-culture. Forty-hours after the induction of HIE, animals were grafted with ES-NPCs targeting the deep layer of the motor cortex in the ischemic brain. Motor function was evaluated 3 weeks after transplantation. Immunohistochemistry and neuroanatomical tracing with GFP were used to analyze neuronal differentiation and axonal sprouting. ES-NPCs could differentiate to cortical neurons with pyramidal morphology and expressed the deep layer-specific marker, Ctip2. The graft showed good survival and an appropriate innervation pattern via axonal sprouting from engrafted cells in the ischemic brain. The motor functions of the transplanted HIE mice also improved significantly compared to the sham-transplanted group. These findings suggest that cortical region specific engraftment of preconditioned cortical precursor cells could support motor functional recovery in the HIE model. It is not clear whether this is a direct effect of the engrafted cells or due to neurotrophic factors produced by these cells. These results suggest that cortical region-specific NPC engraftment is a promising therapeutic approach for brain repair.

Pathophysiology of an hypoxic–ischemic insult during the perinatal period

Hypoxia-ischemia is a leading cause of morbidity and mortality in the perinatal period with an incidence of 1/4000 live births. Biochemical events such as energy failure, membrane depolarization, brain edema, an increase of neurotransmitter release and inhibition of uptake, an increase of intracellular Ca(2+), production of oxygen-free radicals, lipid peroxidation, and a decrease of blood flow are triggered by hypoxia-ischemia and may lead to brain dysfunction and neuronal death. These abnormalities can result in mental impairments, seizures, and permanent motor deficits, such as cerebral palsy. The physical and emotional strain that is placed on the children affected and their families is enormous. The care that these individuals need is not only confined to childhood, but rather extends throughout their entire life span, so it is very important to understand the pathophysiology that follows a hypoxic-ischemic insult. This review will highlight many of the mechanisms that lead to neuronal death and include the emerging area of white matter injury as well as the role of inflammation and will provide a summary of therapeutic strategies. Hypothermia and oxygen will also be discussed as treatments that currently lack a specific target in the hypoxic/ischemic cascade.

Evidence for therapeutic intervention in the prevention of cerebral palsy: hope from animal model research

Knowledge translation, as defined by the Canadian Institute of Health Research, is defined as the exchange, synthesis, and ethically sound application of knowledge--within a complex system of interactions among researchers and users--to accelerate the capture of the benefits of research through improved health, more effective services and products, and a strengthened healthcare system. The requirement for this to occur lies in the ability to continue to determine mechanistic actions at the molecular level, to understand how they fit at the in vitro and in vivo levels, and for disease states, to determine their safety, efficacy, and long-term potential at the preclinical animal model level. In this regard, particularly as it relates to long-term disabilities such as cerebral palsy that begin in utero, but only express their full effect in adulthood, animal models must be used to understand and rapidly evaluate mechanisms of injury and therapeutic interventions. In this review, we hope to provide the reader with a background of animal data upon which therapeutic interventions for the prevention and treatment of cerebral palsy, benefit this community, and increasingly do so in the future.

Temporal expression of cytokines and signal transducer and activator of transcription factor 3 activation after neonatal hypoxia/ischemia in mice

Hypoxia/ischemia (HI) is a prevalent reason for neonatal brain injury with inflammation being an inevitable phenomenon following such injury; but there is a scarcity of data regarding the signaling pathway involved and the effector molecules. The signal transducer and activator of transcription factor 3 (STAT3) is known to modulate injury following imbalance between pro- and anti-inflammatory cytokines in peripheral and central nervous system injury making it a potential molecule for study. The current study investigates the temporal expression of interleukin (IL)-6, IL-1β, tumor necrosis factor-α, IL-1ra, IL-4, IL-10, IL-13 and phosphorylated STAT3 (pSTAT3) after carotid occlusion and hypoxia (8% O2, 55 min) in postnatal day 7 C57BL/6 mice from 3 h to 21 days after hypoxia. Protein array illustrated notable changes in cytokines expressed in both hemispheres in a time-dependent manner. The major pro-inflammatory cytokines showing immediate changes between ipsi- and contralateral hemispheres were IL-6 and IL-1β. The anti-inflammatory cytokines IL-4 and IL-13 demonstrated a delayed augmentation with no prominent differences between hemispheres, while IL-1ra showed two distinct peaks of expression spread over time. We also illustrate for the first time the spatiotemporal activation of pSTAT3 (Y705 phosphorylation) after a neonatal HI in mice brain. The main regions expressing pSTAT3 were the hippocampus and the corpus callosum. pSTAT3+ cells were mostly a subpopulation of activated astrocytes (GFAP+) and microglia/macrophages (F4/80+) seen only in the ipsilateral hemisphere at most time points studied (till 7 days after hypoxia). The highest expression of pSTAT3+ cells was observed to be around 24-48 h, where the presence of pSTAT3+ astrocytes and pSTAT3+ microglia/macrophages was seen by confocal micrographs. In conclusion, our study highlights a synchronized expression of some pro- and anti-inflammatory cytokines, especially in the long term not previously defined. It also points towards a significant role of STAT3 signaling following micro- and astrogliosis in the pathophysiology of neonatal HI-related brain injury. In the study, a shift from pro-inflammatory to anti-inflammatory cytokine profile was also noted as the injury progressed. We suggest that while designing efficient neuroprotective therapies using inflammatory molecules, the time of intervention and balance between the pro- and anti-inflammatory cytokines must be considered.

Therapeutic effect of caffeine treatment immediately following neonatal hypoxic-ischemic injury on spatial memory in male rats

Hypoxia Ischemia (HI) refers to the disruption of blood and/or oxygen delivery to the brain. Term infants suffering perinatal complications that result in decreased blood flow and/or oxygen delivery to the brain are at risk for HI. Among a variety of developmental delays in this population, HI injured infants demonstrate subsequent memory deficits. The Rice-Vannucci rodent HI model can be used to explore behavioral deficits following early HI events, as well as possible therapeutic agents to help reduce deleterious outcomes. Caffeine is an adenosine receptor antagonist that has recently shown promising results as a therapeutic agent following HI injury. The current study sought to investigate the therapeutic benefit of caffeine following early HI injury in male rats. On post-natal day (P) 7, HI injury was induced (cauterization of the right common carotid artery, followed by two hours of 8% oxygen). Male sham animals received only a midline incision with no manipulation of the artery followed by room air exposure for two hours. Subsets of HI and sham animals then received either an intraperitoneal (i.p.) injection of caffeine (10 mg/kg), or vehicle (sterile saline) immediately following hypoxia. All animals later underwent testing on the Morris Water Maze (MWM) from P90 to P95. Results show that HI injured animals (with no caffeine treatment) displayed significant deficits on the MWM task relative to shams. These deficits were attenuated by caffeine treatment when given immediately following the induction of HI. We also found a reduction in right cortical volume (ipsilateral to injury) in HI saline animals as compared to shams, while right cortical volume in the HI caffeine treated animals was intermediate. These findings suggest that caffeine is a potential therapeutic agent that could be used in HI injured infants to reduce brain injury and preserve subsequent cognitive function.

Neuroprotective therapies after perinatal hypoxic-ischemic brain injury

Hypoxic-ischemic (HI) brain injury is one of the main causes of disabilities in term-born infants. It is the result of a deprivation of oxygen and glucose in the neural tissue. As one of the most important causes of brain damage in the newborn period, the neonatal HI event is a devastating condition that can lead to long-term neurological deficits or even death. The pattern of this injury occurs in two phases, the first one is a primary energy failure related to the HI event and the second phase is an energy failure that takes place some hours later. Injuries that occur in response to these events are often manifested as severe cognitive and motor disturbances over time. Due to difficulties regarding the early diagnosis and treatment of HI injury, there is an increasing need to find effective therapies as new opportunities for the reduction of brain damage and its long term effects. Some of these therapies are focused on prevention of the production of reactive oxygen species, anti-inflammatory effects, anti-apoptotic interventions and in a later stage, the stimulation of neurotrophic properties in the neonatal brain which could be targeted to promote neuronal and oligodendrocyte regeneration.

Neuroprotective effects of uridine in a rat model of neonatal hypoxic-ischemic encephalopathy

Neonatal hypoxic-ischemic encephalopathy (HIE) is a major cause of neurological disability requiring newer therapeutic strategies. Uridine is the principal circulating pyrimidine in humans and a substrate for nucleotides and membrane phospholipids. The objective of this study was to investigate the effects of uridine in a neonatal rat model of HIE. Rat pups subjected to hypoxic-ischemic insult on postnatal day 7 were injected intraperitoneally with either saline or uridine (100, 300 or 500mg/kg) for three consecutive days and brains were collected for evaluation of brain infarct volume and apoptosis. Compared with Control group, uridine at 300 and 500mg/kg doses significantly reduced percent infarct volume, TUNEL(+) cell ratio and active Caspase-3 immunoreactivity in the cortex, as well as in CA1 and CA3 regions of the hippocampus. Uridine (300 and 500mg/kg) also decreased active Caspase-3 expression in the ipsilateral hemisphere. These data indicate that uridine dose-dependently reduces brain injury in a rat model of neonatal HIE by decreasing apoptosis.

Fetal asphyctic preconditioning modulates the acute cytokine response thereby protecting against perinatal asphyxia in neonatal rats

Background

Perinatal asphyxia (PA) is a major cause of brain damage and neurodevelopmental impairment in infants. Recent investigations have shown that experimental sublethal fetal asphyxia (FA preconditioning) protects against a subsequent more severe asphyctic insult at birth. The molecular mechanisms of this protection have, however, not been elucidated. Evidence implicates that inflammatory cytokines play a protective role in the induction of ischemic tolerance in the adult brain. Accordingly, we hypothesize that FA preconditioning leads to changes in the fetal cytokine response, thereby protecting the newborn against a subsequent asphyctic insult.

Methods

In rats, FA preconditioning was induced at embryonic day 17 by clamping the uterine vasculature for 30 min. At term birth, global PA was induced by placing the uterine horns, containing the pups, in a saline bath for 19 min. We assessed, at different time points after FA and PA, mRNA and protein expression of several cytokines and related receptor mRNA levels in total hemispheres of fetal and neonatal brains. Additionally, we measured pSTAT3/STAT3 levels to investigate cellular responses to these cytokines.

Results

Prenatally, FA induced acute downregulation in IL-1β, TNF-α and IL-10 mRNA levels. At 96 h post FA, IL-6 mRNA and IL-10 protein expression were increased in FA brains compared with controls. Two hours after birth, all proinflammatory cytokines and pSTAT3/STAT3 levels decreased in pups that experienced FA and/or PA. Interestingly, IL-10 and IL-6 mRNA levels increased after PA. When pups were FA preconditioned, however, IL-10 and IL-6 mRNA levels were comparable to those in controls.

Conclusions

FA leads to prenatal changes in the neuroinflammatory response. This modulation of the cytokine response probably results in the protective inflammatory phenotype seen when combining FA and PA and may have significant implications for preventing post-asphyctic perinatal encephalopathy.

Evaluation of the therapeutic benefit of delayed administration of erythropoietin following early hypoxic-ischemic injury in rodents

Hypoxia-ischemia (HI) and associated brain injuries are seen in premature as well as term infants with birth complications. The resulting impairments involve deficits in many cognitive domains, including language development. Poor rapid auditory processing is hypothesized to be one possible underlying factor leading to subsequent language delays. Mild hypothermia treatment for HI injuries in term infants is widely used as an intervention but can be costly and time consuming. Data suggest that the effectiveness of hypothermia treatment following HI injury declines beyond 6 h following injury. Consequently, the availability of a therapeutic alternative without these limitations could allow doctors to treat HI-injured infants more effectively and thus reduce deleterious cognitive and language outcomes. Evidence from both human studies and animal models of neonatal HI suggests that erythropoietin (Epo), an endogenous cytokine hormone, may be a therapeutic agent that can ameliorate HI brain injury and preserve subsequent cognitive development and function. The current study sought to investigate the therapeutic effectiveness of Epo when administered immediately after HI injury, or delayed at intervals following the injury, in neonatal rodents. Rat pups received an induced HI injury on postnatal day 7, followed by an intraperitoneal injection of Epo (1,000 U/kg) immediately, 60 min, or 180 min following induction of injury. Subjects were tested on rapid auditory processing tasks in juvenile (P38-42) and adult periods (P80-85). Ventricular and cortical size was also measured from post mortem tissue. Results from the current study show a therapeutic benefit of Epo when given immediately following induction of HI injury, with diminished benefit from a 60-min-delayed injection of Epo and no protection following a 180-min-delayed injection. The current data thus show that the effectiveness of a single dose of Epo in ameliorating auditory processing deficits following HI injury decreases precipitously as treatment is delayed following injury. These data may have important implications for experimental human neonatal intervention with Epo.

Neonatal transplant in hypoxic injury

Hypoxic-ischemic encephalopathy in neonates often causes long-term disabilities. Stem cell therapy may be a successful treatment for HIE. Neurogenic astrocytes with characteristics of neural stem cells (NSCs) can be cultured as adherent monolayers. Following reintroduction into the NSC niche of both neonatal and adult hosts, these astrocytes can be induced to generate neuronal progeny in vitro and in vivo. Thus, neurogenic astrocytes represent promising candidates for cell replacement therapy in HIE. Such an approach requires optimized cell cultivation protocols as well as extensive testing of donor cells to assess their capacity for engraftment, survival, and integration in the HIE animal models. In this chapter, we describe methods of generating the HIE model, generating and culturing monolayer neurogenic astrocytes, and transplanting these cells into HIE animal models.

Neuroprotective effects of volume-regulated anion channel blocker DCPIB on neonatal hypoxic-ischemic injury

AIM

To evaluate the role of swelling-induced activation of volume-regulated anion channels (VRACs) in a neonatal hypoxic-ischemic injury model using the selective VRAC blocker 4-(2-butyl-6,7-dichloro-2-cyclopentyl-indan-1-on5-yl) oxobutyric acid (DCPIB).

METHODS

Cerebral hypoxic-ischemic injury was induced in 7-day-old mouse pups with Rice-Vannucci method. Prior to the onset of ischemia, the animals were ip administered DCPIB (10 mg/kg). The animals were sacrificed 24 h afterwards, coronal sections of the brains were cut and the areas of infarct were examined using TTC staining and an image-analysis system. Cultured PC12 cells were subjected to oxygen-glucose deprivation (OGD) for 4 h. The cellular viability was assessed using Cell Counting Kit 8. Intracellular chloride concentration [Cl(-)](i) was measured using 6-methoxy-N-ethylquinolinium iodide.

RESULTS

DCPIB-treated mice showed a significant reduction in hemispheric corrected infarct volume (26.65%±2.23%) compared to that in vehicle-treated mice (45.52%±1.45%, P<0.001). DCPIB-treated mice also showed better functional recovery as they were more active than vehicle-treated mice at 4 and 24 h post injury. In cultured PC12 cells, DCPIB (10 μmol/L) significantly reduced OGD-induced cell death. Moreover, DCPIB (20 μmol/L) blocked hypotonic-induced decrease in [Cl(-)](i) in PC12 cells of both control and OGD groups.

CONCLUSION

The results further support the pathophysiological role of VRACs in ischemic brain injury, and suggest DCPIB as a potential, easily administrable agent targeting VRACs in the context of perinatal and neonatal hypoxic-ischemic brain injury.

Granulocyte-colony stimulating factor in combination with stem cell factor confers greater neuroprotection after hypoxic-ischemic brain damage in the neonatal rats than a solitary treatment

Neonatal hypoxia-ischemia (HI) is a devastating condition resulting in neuronal cell death and often culminates in neurological deficits. Granulocyte-colony stimulating factor (G-CSF) has been shown to have neuroprotective activity via inhibition of apoptosis and inflammation in various stroke models. Stem cell factor (SCF) regulates hematopoietic stem cells in the bone marrow and has been reported to have neuroprotective properties in an experimental ischemic stroke model. In this study we aim to determine the protective effects of G-CSF in combination with SCF treatment after experimental HI. Seven-day old Sprague-Dawley rats were subjected to unilateral carotid artery ligation followed by 2.5 hours of hypoxia. Animals were randomly assigned to five groups: Sham (n=8), Vehicle (n=8), HI with G-CSF treatment (n=9), HI with SCF treatment (n=9) and HI with G-CSF+SCF treatment (coadministration group; n=10). G-CSF (50 µg/kg), SCF (50 µg/kg) and G-CSF+SCF (50 µg/kg) were administered intraperitoneally 1 hour post HI followed by daily injection for 4 consecutive days (five total injections). Animals were euthanized 14 days after HI for neurological testing. Additionally assessment of brain, heart, liver, spleen and kidney atrophy was performed. Both G-CSF and G-CSF+SCF treatments improved body growth and decreased brain atrophy at 14 days post HI. No significant differences were found in the peripheral organ weights between groups. Finally, the G-CSF+SCF coadministration group showed significant improvement in neurological function. Our data suggest that administration of G-CSF in combination with SCF not only prevented brain atrophy but also significantly improved neurological function.

Preconditioning triggered by carbon monoxide (CO) provides neuronal protection following perinatal hypoxia-ischemia

Perinatal hypoxia-ischemia is a major cause of acute mortality in newborns and cognitive and motor impairments in children. Cerebral hypoxia-ischemia leads to excitotoxicity and necrotic and apoptotic cell death, in which mitochondria play a major role. Increased resistance against major damage can be achieved by preconditioning triggered by subtle insults. CO, a toxic molecule that is also generated endogenously, may have a role in preconditioning as low doses can protect against inflammation and apoptosis. In this study, the role of CO-induced preconditioning on neurons was addressed in vitro and in vivo. The effect of 1 h of CO treatment on neuronal death (plasmatic membrane permeabilization and chromatin condensation) and bcl-2 expression was studied in cerebellar granule cells undergoing to glutamate-induced apoptosis. CO's role was studied in vivo in the Rice-Vannucci model of neonatal hypoxia-ischemia (common carotid artery ligature +75 min at 8% oxygen). Apoptotic cells, assessed by Nissl staining were counted with a stereological approach and cleaved caspase 3-positive profiles in the hippocampus were assessed. Apoptotic hallmarks were analyzed in hippocampal extracts by Western Blot. CO inhibited excitotoxicity-induced cell death and increased Bcl-2 mRNA in primary cultures of neurons. In vivo, CO prevented hypoxia-ischemia induced apoptosis in the hippocampus, limited cytochrome c released from mitochondria and reduced activation of caspase-3. Still, Bcl-2 protein levels were higher in hippocampus of CO pre-treated rat pups. Our results show that CO preconditioning elicits a molecular cascade that limits neuronal apoptosis. This could represent an innovative therapeutic strategy for high-risk cerebral hypoxia-ischemia patients, in particular neonates.

Short and long-term analysis and comparison of neurodegeneration and inflammatory cell response in the ipsilateral and contralateral hemisphere of the neonatal mouse brain after hypoxia/ischemia

Understanding the evolution of neonatal hypoxic/ischemic is essential for novel neuroprotective approaches. We describe the neuropathology and glial/inflammatory response, from 3 hours to 100 days, after carotid occlusion and hypoxia (8% O₂, 55 minutes) to the C57/BL6 P7 mouse. Massive tissue injury and atrophy in the ipsilateral (IL) hippocampus, corpus callosum, and caudate-putamen are consistently shown. Astrogliosis peaks at 14 days, but glial scar is still evident at day 100. Microgliosis peaks at 3–7 days and decreases by day 14. Both glial responses start at 3 hours in the corpus callosum and hippocampal fissure, to progressively cover the degenerating CA field. Neutrophils increase in the ventricles and hippocampal vasculature, showing also parenchymal extravasation at 7 days. Remarkably, delayed milder atrophy is also seen in the contralateral (CL) hippocampus and corpus callosum, areas showing astrogliosis and microgliosis during the first 72 hours. This detailed and long-term cellular response characterization of the ipsilateral and contralateral hemisphere after H/I may help in the design of better therapeutic strategies.

Neuroprotective effects of lithium treatment following hypoxic-ischemic brain injury in neonatal rats

PURPOSE

Increasing evidence indicates that lithium is a neuroprotective agent against transient focal and global ischemic injury in the adult animal. In the developing brain, lithium has shown protective effects against neuroapoptosis induced by drugs. This study was designed to investigate the neuroprotective effects of lithium on hypoxic-ischemic brain injury in the neonatal rat.

METHODS

Seven-day-old Sprague-Dawley rats underwent hypoxic-ischemic injury (HII) induced by ligation of the common carotid artery followed by exposure to ~2.5 h of hypoxia (~7% oxygen). After HII, rat pups were randomly assigned into two groups: a control group (n = 21), which received a daily subcutaneous injection of 0.9% normal saline for 14 days following HII; and a lithium group (n = 32), treated with daily injection of lithium chloride. N-acetylaspartate/creatinine, choline/creatinine, lipid/creatinine ratios at 1.3 ppm (Lip(1.3)/Cr) and 0.9 ppm (Lip(0.9)/Cr) lipid peaks were evaluated by proton magnetic resonance spectroscopy on the day of HII and on days 7 and 14 after HII. Infarct ratios based on magnetic resonance images were also determined at the same time points.

RESULTS

Seven days after HII, the Lip(1.3)/Cr and Lip(0.9)/Cr ratios as well as the infarct ratio were significantly lower in the lithium group than in the control group. The Lip(1.3)/Cr and Lip(0.9)/Cr ratios were significantly correlated with infarct ratio.

CONCLUSION

This study showed that post-HII treatment with lithium may have a neuroprotective effect in the immature brain. Further studies are needed to elucidate the mechanism of neuroprotective properties of lithium against HII-induced neonatal brain damage.

Experimental models of seizures and epilepsies

Epilepsy is one of the most common neurological conditions that affect people of all ages. Epilepsy is characterized by occurrence of spontaneous recurrent seizures. Currently available drugs are ineffective in controlling seizures in approximately one-third of patients with epilepsy. Moreover, these drugs are associated with adverse effects, and none of them are effective in preventing development of epilepsy following an insult or injury. To develop an effective therapeutic strategy that can interfere with the process of development of epilepsy (epileptogenesis), it is crucial to study the changes that occur in the brain after an injury and before epilepsy develops. It is not possible to determine these changes in human tissue for obvious ethical reasons. Over the years, experimental models of epilepsies have contributed immensely in improving our understanding of mechanism of epileptogenesis as well as of seizure generation. There are many models that replicate at least some of the characteristics of human epilepsy. Each model has its advantages and disadvantages, and the investigator should be aware of this before selecting a specific model for his/her studies. Availability of a good animal model is a key to the development of an effective treatment. Unfortunately, there are many epilepsy syndromes, specifically pediatric, which still lack a valid animal model. It is vital that more research is done to develop animal models for such syndromes.

Neuronal death and oxidative stress in the developing brain

The developing brain is particularly vulnerable to reactive oxygen and reactive nitrogen species-mediated damage because of its high concentrations of unsaturated fatty acids, high rate of oxygen consumption, low concentrations of antioxidants, high content of metals catalyzing free radical formation, and large proportion of sensitive immature cells. In this review, we outline the dynamic changes of energy resources, metabolic requirements, and endogenous free radical scavenging systems during physiologic brain development. We further discuss the involvement of oxidative stress in the pathogenesis of neuronal death after exposure of the infant brain to hyperoxia, hypoxia/ischemia, sedative drugs, ethanol, and mechanical trauma. Several approaches have been developed to combat oxidative stress, but neuroprotective treatment strategies are limited in the clinical setting.

Chronic fetal hypoxia produces selective brain injury associated with altered nitric oxide synthases

OBJECTIVE

The purpose of this study was to investigate the impact of chronic hypoxia on the nitric oxide synthase isoenzymes in specific brain structures.

STUDY DESIGN

Time-mated pregnant guinea pigs were exposed to 10.5% molecular oxygen for 14 days (animals with chronic fetal hypoxia; HPX) or room air (control animals; NMX); L-N6-(1-iminoethyl)-lysine (L-NIL; an inducible nitric oxide synthase inhibitor, 1 mg/kg/d) was administered to HPX group for 14 days (L-NIL + HPX). Fetal brains were harvested at term. Multilabeled immunofluorescence was used to generate a brain injury map. Laser capture microdissection and quantitative polymerase chain reaction were applied; cell injury markers, apoptosis activation, neuron loss, total nitric oxide, and the levels of individual nitric oxide synthase isoenzymes were quantified.

RESULTS

Chronic hypoxia causes selective fetal brain injury rather than global. Injury is associated with differentially affected nitric oxide synthases in both neurons and glial cells, with inducible macrophage-type nitric oxide synthase up-regulated at all injury sites. L-NIL attenuated the injury, despite continued hypoxia.

CONCLUSION

These studies demonstrate that chronic hypoxia selectively injures the fetal brain in part by the differential regulation of nitric oxide synthase isoenzymes in an anatomic- and cell-specific manner.

Early biochemical effects after unilateral hypoxia-ischemia in the immature rat brain

Perinatal hypoxia-ischemia (HI) gives rise to inadequate substrate supply to the brain tissue, resulting in damage to neural cells. Previous studies at different time points of development, and with different animal species, suggest that the HI insult causes oxidative damage and changes Na+, K+-ATPase activity, which is known to be very susceptible to free radical-related lipid peroxidation. The aim of the present study was to establish the onset of the oxidative damage response in neonatal Wistar rats subjected to brain HI, evaluating parameters of oxidative stress, namely nitric oxide production, lipoperoxidation by thiobarbituric acid reactive substances (TBA-RS) production and malondialdehyde (MDA) levels, reactive species production by DCFH oxidation, antioxidant enzymatic activities of catalase, glutathione peroxidase, superoxide dismutase as well as Na+, K+-ATPase activity in hippocampus and cerebral cortex. Rat pups were subjected to right common carotid ligation followed by exposure to a hypoxic atmosphere (8% oxygen and 92% nitrogen) for 90 min. Animals were sacrificed by decapitation 0, 1 and 2 h after HI and both hippocampus and cerebral cortex from the right hemisphere (ipsilateral to the carotid occlusion) were dissected out for further experimentation. Results show an early decrease of Na+, K+-ATPase activity (at 0 and 1 h), as well as a late increase in MDA levels (2 h) and superoxide dismutase activity (1 and 2 h after HI) in the hippocampus. There was a late increase in both MDA levels and DCFH oxidation (1 and 2 h) and an increase in superoxide dismutase activity (2 h after HI) in cortex; however Na+, K+-ATPase activity remained unchanged. We suggest that neonatal HI induces oxidative damage to both hippocampus and cortex, in addition to a decrease in Na+, K+-ATPase activity in hippocampus early after the insult. These events might contribute to the later morphological damage in the brain and indicate that it would be essential to pursue neuroprotective strategies, aimed to counteract oxidative stress, as early as possible after the HI insult.

Systemic G-CSF treatment does not improve long-term outcomes after neonatal hypoxic-ischaemic brain injury

Hypoxia-ischaemia (HI) is a major factor in the pathogenesis of developmental brain injury, leading to cognitive deficits and motor disabilities in preterm infants. The haematopoietic growth factor granulocyte colony-stimulating factor (G-CSF) has been shown to exert a neuroprotective activity in rodent models of ischaemic stroke and is currently subject to phase I/II clinical trials in adults. Results of studies examining the effect of G-CSF in perinatal brain damage have been contradictory. We have previously shown that G-CSF increases NMDAR-mediated excitotoxic brain injury in the neonatal mouse brain. In this study, we evaluated the effect of G-CSF on long-term outcomes after HI. On postnatal day 5, mice pubs were first randomly assigned to a sham operation or HI and then divided into four treatment groups: i) G-CSF; ii) phosphate buffered saline (PBS) 1h after injury; iii) G-CSF and iv) PBS 60 h after injury. G-CSF (200 μg/kg BW) was administered five times within a 24h interval. Neuromotor and cognitive outcomes were assessed by open-field, novel object recognition tests and rotarod tests starting on P90, with subsequent histological analyses of brain injury. G-CSF treatment did not improve either neurobehavioural outcomes or brain injuries. Interestingly, the application of PBS and G-CSF in the acute phase increased brain damage in the hippocampus. We could not confirm the neuroprotective properties of G-CSF in neonatal HI brain damage. The exacerbation of injury by the administration of substances in the acute phase might indicate a heightened state of neurological sensitivity that is specific to mechanisms of secondary neurodegeneration and influenced by unidentified external factors possibly associated with the treatment protocol during the acute phase. This article is part of a Special Issue entitled "Interaction between repair, disease, & inflammation."

Apotransferrin-induced recovery after hypoxic/ischaemic injury on myelination

We have previously demonstrated that aTf (apotransferrin) accelerates maturation of OLs (oligodendrocytes) in vitro as well as in vivo. The purpose of this study is to determine whether aTf plays a functional role in a model of H/I (hypoxia/ischaemia) in the neonatal brain. Twenty-four hours after H/I insult, neonatal rats were intracranially injected with aTf and the effects of this treatment were evaluated in the CC (corpus callosum) as well as the SVZ (subventricular zone) at different time points. Similar to previous studies, the H/I event produced severe demyelination in the CC. Demyelination was accompanied by microglial activation, astrogliosis and iron deposition. Ferritin levels increased together with lipid peroxidation and apoptotic cell death. Histological examination after the H/I event in brain tissue of aTf-treated animals (H/I aTF) revealed a great number of mature OLs repopulating the CC compared with saline-treated animals (H/I S). ApoTf treatment induced a gradual increase in MBP (myelin basic protein) and myelin lipid staining in the CC reaching normal levels after 15 days. Furthermore, significant increase in the number of OPCs (oligodendroglial progenitor cells) was found in the SVZ of aTf-treated brains compared with H/I S. Specifically, there was a rise in cells positive for OPC markers, i.e. PDGFRα and SHH⁺ cells, with a decrease in cleaved-caspase-3⁺ cells compared with H/I S. Additionally, neurospheres from aTf-treated rats were bigger in size and produced more O4/MBP⁺ cells. Our findings indicate a role for aTf as a potential inducer of OLs in neonatal rat brain in acute demyelination caused by H/I and a contribution to the differentiation/maturation of OLs and survival/migration of SVZ progenitors after demyelination in vivo.

Brain injury caused by chronic fetal hypoxemia is mediated by inflammatory cascade activation

The prevalence of cerebral palsy (CP) shows little temporal or geographic variation and is associated with preterm birth, maternal/fetal infection/inflammation, and fetal growth restriction (IUGR), a potential surrogate for chronic fetal hypoxemia (CHX). We previously demonstrated CHX causes a fetal inflammatory response syndrome (FIRS). Herein, we test the hypothesis that CHX may cause fetal brain injury by upregulating inflammatory cytokine cascades, culminating in apoptosis pathway activation. Time-mated guinea pigs were housed in 12% or 10.5% O(2) for the last 21% of gestation. Chronic fetal hypoxemia increased the lactate/pyruvate and decreased the glutathione (GSH)/oxidized glutathione (GSSH) ratios, confirming a shift to a prooxidant state. The end result was a >30% decrease in hippocampal neuron density. Based on a microarray spotted with 113 cytokines and receptors, 22 genes were upregulated by CHX in proportion to the degree of hypoxia; the findings were confirmed by quantitative polymerase chain reaction (PCR). Thus, CHX triggers fetal brain inflammation inversely proportional to its severity characterized by increased apoptosis and neuronal loss. We suggest CHX fetal brain injury is not directly caused by oxygen deprivation but rather is an adaptive response that becomes maladaptive.

Magnesium sulfate treatment alters fetal cerebellar gene expression responses to hypoxia

Prenatal perturbation of brain circulation and oxygenation is a leading cause of perinatal brain damage affecting about 0.3-0.9% of births. Hypoxia-ischemia (HI) in preterm human infants at gestational week 23-32 results in neurodevelopmental abnormalities in childhood, presenting as learning disability, seizure activity, motor impairment and in the most severe cases, death. Here, we examined the potential of MgSO4 treatment, prior to foetal hypoxia, to attenuate hypoxia induced damage in a murine model of maternal hypoxia. We studied the time course of maternal hypoxia and MgSO4 pre-treatment effects on cerebellar tissue by means of DNA microarray analyses. Mild hypoxia induced minor expression changes in most genes. However, there were 5 gene sets which were down-regulated by maternal hypoxia. MgSO4 pre-treatment abrogated these decreases in gene. A cell cycle gene set which responded immediately (2 h) to hypoxia, showed a delayed response (24 h) when MgSO4 pre-treatment was given. Similar proportions of cell death were observed in all groups before P7, where combined hypoxia and MgSO4 treatment increased cell death in the internal granule layer. There were a higher number of BrdU positive cells at the end of hypoxic episodes and a down-regulation of Reelin signaling, compared to control. MgSO4 pre-treatment prevented the enhancement of cell proliferation due to hypoxia and increased Reelin levels. Altogether, MgSO4 pre-treatment both reduced the number of genes differentially affected by hypoxia and delayed the responses to hypoxia. In addition, MgSO4 pre-treatment modified the nature of the transcriptional response; while hypoxia induced down-regulation of gene sets, MgSO4 pre-treatment mostly up-regulated them. The dual reaction to the MgSO4 treatment may be the source of the ambiguity in observations reported for affected newborns.

Enhancement of autophagic flux after neonatal cerebral hypoxia-ischemia and its region-specific relationship to apoptotic mechanisms

The multiplicity of cell death mechanisms induced by neonatal hypoxia-ischemia makes neuroprotective treatment against neonatal asphyxia more difficult to achieve. Whereas the roles of apoptosis and necrosis in such conditions have been studied intensively, the implication of autophagic cell death has only recently been considered. Here, we used the most clinically relevant rodent model of perinatal asphyxia to investigate the involvement of autophagy in hypoxic-ischemic brain injury. Seven-day-old rats underwent permanent ligation of the right common carotid artery, followed by 2 hours of hypoxia. This condition not only increased autophagosomal abundance (increase in microtubule-associated protein 1 light chain 3-11 level and punctuate labeling) but also lysosomal activities (cathepsin D, acid phosphatase, and beta-N-acetylhexosaminidase) in cortical and hippocampal CA3-damaged neurons at 6 and 24 hours, demonstrating an increase in the autophagic flux. In the cortex, this enhanced autophagy may be related to apoptosis since some neurons presenting a high level of autophagy also expressed apoptotic features, including cleaved caspase-3. On the other hand, enhanced autophagy in CA3 was associated with a more purely autophagic cell death phenotype. In striking contrast to CA3 neurons, those in CA1 presented only a minimal increase in autophagy but strong apoptotic characteristics. These results suggest a role of enhanced autophagy in delayed neuronal death after severe hypoxia-ischemia that is differentially linked to apoptosis according to the cerebral region.

Rodent neonatal bilateral carotid artery occlusion with hypoxia mimics human hypoxic-ischemic injury

We report a new clinically relevant model of neonatal hypoxic-ischemic injury in a 10-day-old rat pup. Bilateral carotid artery occlusion and 8% hypoxia (1 to 15 mins, BCAO-H) was induced with varying degrees of injury (mild, moderate, severe), which was quantified using magnetic resonance imaging including diffusion-weighted and T2-weighted imaging at 24 h and 21/28 days. We developed a magnetic resonance imaging-based rat pup severity score and compared 3D ischemic injury volumes/rat pup severity score with histology and behavioral testing. At 24 h, hypoxic-ischemic injury was observed in 17/27 animals; long-term survival was 81%. Magnetic resonance imaging lesion volumes did not correlate with hypoxia duration but correlated with rat pup severity score, which was used to classify animals into mild (n=21), moderate (n=6), and severe (n=10) groups with average brain lesion volumes of 0.9%, 33.2%, and 56.3%, respectively. Histology confirmed lesion location and histologic scoring correlated with the rat pup severity score. We also found excellent correlation between injury severity and multiple behavioral tasks. Bilateral carotid artery occlusion and hypoxia in the P10 rat pup is an excellent model of neonatal hypoxic-ischemic injury because it induces diffuse global injury similar to the term infant. This model can produce graded injury severity, similar to that seen in human neonates, but manipulation with hypoxia duration is unpredictable.

Isoflurane exerts a short-term but not a long-term preconditioning effect in neonatal rats exposed to a hypoxic-ischaemic neuronal injury

BACKGROUND

Isoflurane has been shown to induce tolerance against ischaemic injury in adult rodents. Although the delayed preconditioning effect of isoflurane has been demonstrated in neonatal rat pups, the acute preconditioning effects of isoflurane remained undetermined. The present study was therefore conducted to evaluate the acute preconditioning efficacy of isoflurane in neonatal rats subjected to a hypoxic-ischaemic (HI) injury.

METHODS

Post-natal day 7 pups were exposed to 1 or 2% isoflurane in oxygen for either 30, 60 or 90 min. Fifteen minutes after isoflurane exposure, the pups were subjected to an HI injury induced by left common carotid artery ligation and exposure to 8% oxygen for 2 h. Pups not exposed to isoflurane or not subjected to HI served as controls. Histopathologic injury to the cortex and hippocampus was evaluated 7 and 49 days after HI.

RESULTS

Isoflurane 2% exposure for 60 or 90 min before HI induced tolerance in the hippocampus and the number of normal neurons in the CA1 sector 7 days after HI was significantly greater than in non-preconditioned animals. This protective efficacy of isoflurane preconditioning was not observed 49 days after HI.

CONCLUSIONS

Exposure of 2% isoflurane for at least 60 min is required to induce tolerance against HI injury in rat pups. However, this neuroprotective efficacy results in only transient neuroprotection.

Hitting a moving target: Basic mechanisms of recovery from acquired developmental brain injury

Acquired brain injuries represent a major cause of disability in the pediatric population. Understanding responses to developmental acquired brain injuries requires knowledge of the neurobiology of normal development, age-at-injury effects and experience-dependent neuroplasticity. In the developing brain, full recovery cannot be considered as a return to the premorbid baseline, since ongoing maturation means that cerebral functioning in normal individuals will continue to advance. Thus, the recovering immature brain has to 'hit a moving target' to achieve full functional recovery, defined as parity with age-matched uninjured peers. This review will discuss the consequences of developmental injuries such as focal lesions, diffuse hypoxia and traumatic brain injury (TBI). Underlying cellular and physiological mechanisms relevant to age-at-injury effects will be described in considerable detail, including but not limited to alterations in neurotransmission, connectivity/network functioning, the extracellular matrix, response to oxidative stress and changes in cerebral metabolism. Finally, mechanisms of experience-dependent plasticity will be reviewed in conjunction with their effects on neural repair and recovery.

Neuroprotective effects of hydrogen saline in neonatal hypoxia-ischemia rat model

Cerebral hypoxia-ischemia (HI) represents a major cause of brain damage in the term newborn. This study aimed to examine the short and long-term neuroprotective effect of hydrogen saline (H(2) saline) using an established neonatal HI rat pup model. Seven-day-old rat pups were subjected to left common carotid artery ligation and then 90 min hypoxia (8% oxygen at 37 degrees C). H(2) saturated saline was administered by peritoneal injection (5 ml/kg) immediately and again at 8 h after HI insult. At 24 h after HI, the pups were decapitated and brain morphological injury was assessed by 2,3,5-triphenyltetrazolium chloride (TTC), Nissl, and TUNEL staining. Acute cell death, inflammation and oxidative stress were evaluated at 24 h by studying caspase-3 activity, MDA measurement as well as Iba-1 immunochemistry in the brain. At 5 weeks after HI, spontaneous activity test and Morris water maze test were conducted. We observed that H(2) saline treatment reduced the caspase activity, MDA, Iba-1 levels, the infarct ratio, and improved the long-term neurological and neurobehavioral functions. H(2) saline has potentials in the clinical treatment of HI and other ischemia-related cerebral diseases.

Neonatal hypoxic/ischemic brain injury induces production of calretinin-expressing interneurons in the striatum

Ischemia-induced striatal neurogenesis from progenitors in the adjacent subventricular zone (SVZ) in young and adult rodents has been reported. However, it has not been established whether the precursors that reside in the SVZ retain the capacity to produce the full range of striatal neurons that has been destroyed. By using a neonatal rat model of hypoxic/ischemic brain damage, we show here that virtually all of the newly produced striatal neurons are calretinin (CR)-immunoreactive (+), but not DARPP-32(+), calbindin-D-28K(+), parvalbumin(+), somatostatin(+), or choline acetyltransferase(+). Retroviral fate-mapping studies confirm that these newly born CR(+) neurons are indeed descendants of the SVZ. Our studies indicate that, although the postnatal SVZ has the capacity to produce a range of neurons, only a subset of this repertoire is manifested in the brain after injury.

Erythropoietin attenuates brain injury, subventricular zone expansion, and sensorimotor deficits in hypoxic-ischemic neonatal rats

The aim of this study was to investigate the effect of erythropoietin (EPO) on histological brain injury, subventricular zone (SVZ) expansion, and sensorimotor function deficits induced by hypoxia-ischemia (HI) in newborn rat pups. Seven-day-old male rat pups were divided into six groups: normoxia control, normoxia EPO, hypoxia control, hypoxia EPO, HI control, and HI EPO group. Sham surgery or HI was performed in all animals. HI was induced by ligation of the right common carotid artery followed by 90 min of hypoxia with 8% oxygen. Recombinant human EPO 3 U/g or saline was administered intraperitoneally, immediately, at 24- and 48-hr after insult. At two weeks after insult, animals were challenged with cylinder-rearing test for evaluating forelimb asymmetry to determine sensorimotor function. All animals were then sacrificed for volumetric analysis of the cerebral hemispheres and the SVZ. The saline-treated HI rats showed marked asymmetry by preferential use of the non-impaired, ipsilateral paw in the cylinder-rearing test. Volumetric analysis of brains revealed significantly decreased preserved ipsilateral hemispheric volume and increased ipsilateral SVZ volume compared with the sham-operated animals. Treatment of EPO significantly improved forelimb asymmetry and preserved ipsilateral hemispheric volume along with decreased expansion of ipsilateral SVZ following HI compared to the saline-treated HI rats. These results support the use of EPO as a candidate drug for treatment of neonatal hypoxic-ischemic brain damage.

Sustained hypoxia modulates mitochondrial DNA content in the neonatal rat brain

The effects of placental insufficiency and preterm birth on neurodevelopment can be modeled in experimental settings of neonatal hypoxia in rodents. Here, rat pups were reared in reduced oxygen (9.5%) for 11 days, starting on postnatal day 3 (P3). This led to a significant reduction in brain and body weight gain in hypoxic pups compared to age-matched normoxia-reared controls, plausibly reflecting an inability to fulfill the energetic needs of normal growth and development. Adaptive processes designed to augment energetic capacity in eukaryotes include stimulation of mitochondrial biogenesis. We show that after 11 days of sustained hypoxia, the levels of nuclear respiratory factor-1 and mitochondrial transcription factor A are elevated and the content of mitochondrial DNA (mtDNA) is greater in the hypoxic P14 pup brain compared to normoxic conditions. Corresponding immunohistochemical analyses reveal increased density of mtDNA in large cortical neurons. In contrast, no changes in mtDNA content are observed in the brain of pups reared for 24 h (P3-P4) under hypoxic conditions. Together, these data suggest that prolonged inadequate oxygenation may trigger a compensatory increase in neuronal mitochondrial DNA content to partially mitigate compromised energy homeostasis and reduced energetic capacity in the developing hypoxic brain.

Stroke in the immature brain: review of pathophysiology and animal models of pediatric stroke

Pediatric stroke research presents many challenges. Relatively low incidence, need for age stratification, diverse etiologies, delays in diagnosis, lack of an established age-based stroke severity scale and outcome measures are only some of the issues that have prevented the implementation of clinical trials in infants and children with stroke. Experimental animal models of pediatric stroke, therefore, are critical to understanding the pathophysiology and management of ischemic brain damage in the immature brain, and provide the necessary platform for future clinical trials. In this review we discuss the pertinent clinical aspects of pediatric stroke, the pathophysiology of stroke in the developing brain and the animal models established to study basic mechanisms as well as translational issues in pediatric stroke.

Profile of glutamate uptake and cellular viability in hippocampal slices exposed to oxygen and glucose deprivation: developmental aspects and protection by guanosine

Stroke syndromes are a major cause of disability in middle and later life resulting in severe neuronal degeneration and loss of brain functions. In situations with energy failure, glutamate transport is impaired and high levels of this amino acid accumulate on the synaptic cleft. Our group has showed that guanosine exerts neuroprotection against neurotoxicity situations. The aim of this work is draw a post-ischemic profile of glutamate uptake and cell damage using an oxygen and glucose deprivation model (OGD) in hippocampal slices from young (P10) and adult (P60) rats, analyzing guanosine effect. OGD decreases glutamate uptake in both ages and recovery times, although decrease in cell viability was only observed 1 and 3 h after OGD in young and adult animals, respectively. Guanosine partially protected cell damage from 1 h in P10 and at 3 h in P60 rats and avoided glutamate uptake decrease from P10 rats at 3 h. The impairment of glutamate transporters since immediately after the insult observed here is probably due to an energetic failure; loss of cell viability was only observed from 1 h after OGD. The mechanism by which guanosine acts in the 'ischemic' model used here is still unknown, but evidence leads to its antiapoptotic effect.

Hypoxic-ischemic injury in neonatal brain: involvement of a novel neuronal molecule in neuronal cell death and potential target for neuroprotection

Perinatal hypoxia-ischemia (HI) is the most common cause of various neurological disabilities in children with high societal cost. Hypoxic-ischemic brain damage is an evolving process and ample evidence suggests distinct difference between the immature and mature brain in the pathology and consequences of brain injury. Therefore, it is of utmost importance to better understand the mechanisms underlying the hypoxic-ischemic injury in neonatal brain to devise effective therapeutic strategies. Nonetheless, the mechanism(s) involved in this pathology in the developing brain remain inadequately understood. Effective neuroprotective strategies will include either inhibition of the death effector pathways or induction of their regulatory and survival promoting cellular proteins. Neuronal pentraxins (NPs) define a family of novel proteins "long pentraxins" that are exclusively expressed in the central neurons, and are homologous to the C-reactive and acute-phase proteins in the immune system. NPs have been shown to be involved in the excitatory synaptic remodeling. We found that the neuronal protein 'neuronal pentraxin 1' (NP1) is induced in neonatal rat brain following HI, and NP1 induction preceded the time of actual tissue loss in brain. In demonstrating this we also found that NP1 gene silencing is neuroprotective against hypoxia-induced neuronal death. This is the first evidence for a pathophysiological function of NP1 in central neurons. Our results suggest that NP1 is part of a death program triggered by HI. Most importantly, our findings of specific interactions of NP1 with the excitatory glutamate receptors AMPA GluR1 subunit and their co-localization suggest a role for this novel neuronal protein NP1 in the excitotoxic cascade. Blockade of AMPA-induced neuronal death following inhibition of NP1 expression further implicates a regulatory interaction between NP1 and AMPA glutamate receptors. Subsequent experiments using NP1 loss-of-function strategies, we have demonstrated specific requirements of NP1 induction in HI-induced neuronal death. Together our findings clearly identify a novel role for NP1 in the coupling between HI and cerebral cell death. Thus, NP1 could be a new molecular target in the central neurons for preventing hypoxic-ischemic neuronal death in developing brain. These very novel results could lead to more effective neuroprotective strategies against hypoxic-ischemic brain injury in neonates.

Vascular response to hypoxic preconditioning in the immature brain

We hypothesized that hypoxic preconditioning (PC) modifies the microvasculature in the immature brain and thereby affects the cerebral blood flow (CBF) during a subsequent hypoxic-ischemic (HI) insult. On postnatal day 6 rats were exposed to hypoxia (36 degrees C, 8.0% O2) or normoxia for 3 h. Unilateral HI (unilateral carotid ligation and 8% hypoxia) was induced 24 h later. Cortical CBF was measured with the 14C-iodoantipyrine technique (at the end of HI) or with laser Doppler flowmetry (Perimed PF5001) before and during HI. At 0, 2, 8, and 24 h cerebral cortex was sampled and analyzed with gene arrays (Affymetrix 230 2.0). L-nitroarginine or vehicle was administrated before hypoxic PC or 30 mins before HI followed by CBF measurement (laser Doppler) during subsequent HI. Twenty-four hours after PC animals were perfusion-fixed and brains immunolabeled for von Willebrand factor and vascular density was determined by stereological quantification. The decrease in CBF during HI was attenuated significantly in PC versus control animals (P<0.01), as detected by both techniques. Several vascular genes (Angpt2, Adm, Apln, Vegf, Flt1, Kdr, Pdgfra, Agtrap, Adora2a, Ednra, serpine1, caveolin, Id1, Prrx1, Ero1l, Acvrl1, Egfl7, Nudt6, Angptl4, Anxa2, and NOS3) were upregulated and a few (Csrp2, Adora2b) were downregulated after PC. A significant increase in vascular density (P<0.05) was seen after PC. Nitric oxide synthase inhibition did not affect CBF during HI after PC. In conclusion, hypoxic PC upregulates vascular genes, increases vascular density and attenuates the decrease of CBF during a subsequent HI, which could contribute to tolerance.

New pediatric model of ischemic stroke in infant piglets by photothrombosis: acute changes in cerebral blood flow, microvasculature, and early histopathology

BACKGROUND AND PURPOSE

The etiology and pathophysiology of acute ischemic stroke in children differ greatly from those in adults. The purpose of this study was to establish a new pediatric model of ischemic stroke in infant piglets for use in future studies of the response of the developing brain to focal ischemic injury.

METHODS

Ischemic stroke was produced in male infant piglets (2 to 4 weeks old) by photothrombotic occlusion of the middle cerebral artery. Regional cerebral blood flow was measured with radiolabeled microspheres up to 4 hours after occlusion. Early histopathology, including caspase-3 immunohistochemistry for apoptosis, was examined 4 hours after ischemia. The nature of the thrombus and its interaction with vascular endothelium were assessed by electron microscopy.

RESULTS

Severe ischemia (0 to 15 mL/100 g per min) occurred rapidly in 1.4+/-0.2 g of tissue at 15 minutes and increased to 2.4+/-0.7 g at 4 hours. Similarly, moderate ischemia (16 to 30 mL/100 g per min) was measured in 1.2+/-0.3 g of tissue at 15 minutes and increased to 2.0+/-0.6 g at 4 hours. These regional cerebral blood flow values represent ischemic levels of blood flow in 20% to 25% of the volume of the ischemic hemisphere at 4 hours after ischemia. Ischemic infarction occurred in both gray and white matter, and cerebral microvessels in the ischemic hemisphere contained large numbers of inflammatory leukocytes. Caspase-3-positive cells were few in number and were found in the periphery of the infarct; cell death appeared to occur primarily by necrosis rather than apoptosis at 4 hours. Electron microscopy revealed a pure platelet thrombus firmly attached to the vascular endothelium, which in some areas appeared to be detached from the basement membrane.

CONCLUSIONS

Ischemic stroke can be produced in infant piglets by middle cerebral artery photothrombosis. The stroke involved both gray and white matter and exhibited a robust inflammatory component. The mean infarct volume determined histopathologically amounted to 9.6+/-2.4% of the affected (ipsilateral) hemisphere, which was correlated well with the mass equivalent of tissue (12.0+/-3.5%), in which severe declines in regional cerebral blood flow were observed at 4 hours.

Oxygen treatment restores energy status following experimental neonatal hypoxia-ischemia

OBJECTIVE

The purpose of this study was to determine whether oxygen treatment could attenuate the alterations in cerebral energy metabolism found in the brain following hypoxia-ischemia.

DESIGN

Seven-day-old rat pups were subjected to unilateral carotid artery ligation followed by 2 hrs of hypoxia (8% oxygen at 37 degrees C). The concentrations of high-energy phosphate compounds and glycolytic intermediates and the activity of Na+/K+-adenosine triphosphatase were measured at 4-72 hrs of recovery. Brain weight was used to determine the severity of the brain injury at 2 wks after insult.

SETTING

Experimental setting.

SUBJECTS

Rat pups.

INTERVENTIONS

Pups were treated with 100% oxygen 1 hr after the insult at 2.5 atmospheres absolute (hyperbaric oxygen) or at normobaric pressure for a duration of 2 hrs.

MEASUREMENTS AND MAIN RESULTS

During the initial period of recovery from hypoxia-ischemia, values of adenosine triphosphate and phosphocreatine remained at levels below normal, whereas the levels of glucose and other glycolytic intermediates were elevated. Hyperbaric oxygen and normobaric oxygen both attenuated brain injury, restored the levels of adenosine triphosphate and phosphocreatine, decreased the levels of the glycolytic intermediates, and increased the utilization of energy.

CONCLUSIONS

These results suggest that oxygen treatment during the initial period of recovery from a hypoxia-ischemic insult is able to attenuate energy deficits in the brain, which ultimately leads to a reduction in brain injury.

Glutamate-mediated excitotoxicity in neonatal hippocampal neurons is mediated by mGluR-induced release of Ca++ from intracellular stores and is prevented by estradiol

Hypoxic/ischemic (HI) brain injury in newborn full-term and premature infants is a common and pervasive source of life time disabilities in cognitive and locomotor function. In the adult, HI induces glutamate release and excitotoxic cell death dependent on NMDA receptor activation. In animal models of the premature human infant, glutamate is also released following HI, but neurons are largely insensitive to NMDA or AMPA/kainic acid (KA) receptor-mediated damage. Using primary cultured hippocampal neurons we have determined that glutamate increases intracellular calcium much more than kainic acid. Moreover, glutamate induces cell death by activating Type I metabotropic glutamate receptors (mGluRs). Pretreatment of neurons with the gonadal steroid estradiol reduces the level of the Type I metabotropic glutamate receptors and completely prevents cell death, suggesting a novel therapeutic approach to excitotoxic brain damage in the neonate.