Delayed neurodegeneration in neonatal rat thalamus after hypoxia-ischemia is apoptosis

Plasma Biomarkers of Evolving Encephalopathy and Brain Injury in Neonates with Hypoxic-Ischemic Encephalopathy

OBJECTIVE

The objective of the study was to evaluate the relationship between a panel of candidate plasma biomarkers and (1) death or severe brain injury on magnetic resonance imaging (MRI) and (2) dysfunctional cerebral pressure autoregulation as a measure of evolving encephalopathy.

STUDY DESIGN

Neonates with moderate-to-severe hypoxic-ischemic encephalopathy (HIE) at 2 level IV neonatal intensive care units were enrolled into this observational study. Patients were treated with therapeutic hypothermia (TH) and monitored with continuous blood pressure monitoring and near-infrared spectroscopy. Cerebral pressure autoregulation was measured by the hemoglobin volume phase (HVP) index; a higher HVP index indicates poorer autoregulation. Serial blood samples were collected during TH and assayed for Tau, glial fibrillary acidic protein, and neurogranin. MRIs were assessed using National Institutes of Child Health and Human Development scores. The relationships between the candidate biomarkers and (1) death or severe brain injury on MRI (defined as a National Institutes of Child Health and Human Development score of ≥ 2B) and (2) autoregulation were evaluated using bivariate and adjusted logistic regression models.

RESULTS

Sixty-two patients were included. Elevated Tau levels on days 2-3 of TH were associated with death or severe injury on MRI (aOR: 1.06, 95% CI: 1.03-1.09; aOR: 1.04, 95% CI: 1.01-1.06, respectively). Higher Tau was also associated with poorer autoregulation (higher HVP index) on the same day (P = .022).

CONCLUSIONS

Elevated plasma levels of Tau are associated with death or severe brain injury by MRI and dysfunctional cerebral autoregulation in neonates with HIE. Larger-scale validation of Tau as a biomarker of brain injury in neonates with HIE is warranted.

Revealing the Impact of Mitochondrial Fitness During Early Neural Development Using Human Brain Organoids

Mitochondrial homeostasis -including function, morphology, and inter-organelle communication- provides guidance to the intrinsic developmental programs of corticogenesis, while also being responsive to environmental and intercellular signals. Two- and three-dimensional platforms have become useful tools to interrogate the capacity of cells to generate neuronal and glia progeny in a background of metabolic dysregulation, but the mechanistic underpinnings underlying the role of mitochondria during human neurogenesis remain unexplored. Here we provide a concise overview of cortical development and the use of pluripotent stem cell models that have contributed to our understanding of mitochondrial and metabolic regulation of early human brain development. We finally discuss the effects of mitochondrial fitness dysregulation seen under stress conditions such as metabolic dysregulation, absence of developmental apoptosis, and hypoxia; and the avenues of research that can be explored with the use of brain organoids.

Mitochondrial dynamics in the neonatal brain - a potential target following injury?

The impact of birth asphyxia and its sequelae, hypoxic–ischaemic (HI) brain injury, is long-lasting and significant, both for the infant and for their family. Treatment options are limited to therapeutic hypothermia, which is not universally successful and is unavailable in low resource settings. The energy deficits that accompany neuronal death following interruption of blood flow to the brain implicate mitochondrial dysfunction. Such HI insults trigger mitochondrial outer membrane permeabilisation leading to release of pro-apoptotic proteins into the cytosol and cell death. More recently, key players in mitochondrial fission and fusion have been identified as targets following HI brain injury. This review aims to provide an introduction to the molecular players and pathways driving mitochondrial dynamics, the regulation of these pathways and how they are altered following HI insult. Finally, we review progress on repurposing or repositioning drugs already approved for other indications, which may target mitochondrial dynamics and provide promising avenues for intervention following brain injury. Such repurposing may provide a mechanism to fast-track, low-cost treatment options to the clinic.

Is late prevention of cerebral palsy in extremely preterm infants plausible?

Preterm birth continues to be associated with neurodevelopmental problems including cerebral palsy. Cystic white matter injury is still the major neuropathology underlying cerebral palsy, affecting 1-3% of preterm infants. Although rates have gradually fallen over time, the pathogenesis and evolution of cystic white matter injury are still poorly understood. Hypoxia-ischemia (HI) remains an important contributor yet there is no established treatment to prevent injury. Clinically, serial ultrasound and magnetic resonance imaging studies typically show delayed development of cystic lesions 2 to 4 weeks after birth. This raises the important and unresolved question as to whether this represents slow evolution of injury occurring around the time of birth, or repeated injury over many weeks after birth. There is increasing evidence that tertiary injury after HI can contribute to impairment of white and grey matter maturation. In the present review, we discuss preclinical evidence that severe, cystic white matter injury can evolve for many weeks after acute HI and is associated with microglia activity. This suggests the intriguing hypothesis that the tertiary phase of injury is not as subtle as often thought and that there may be a window of therapeutic opportunity for one to two weeks after hypoxic-ischemic injury to prevent delayed cystic lesions and so further reduce the risk of cerebral palsy after preterm birth.

A new Hypoxic Ischemic Encephalopathy model in neonatal rats

BACKGROUND

Hypoxic-Ischemic Encephalopathy (HIE) occurs when an infant's brain does not receive adequate blood and oxygen supply, resulting in ischemic and hypoxic brain damage during delivery. Currently, supportive care and hypothermia have been the standard treatment for HIE. However, there are still a 20% mortality and most of the survivors are associated with significant neurodevelopmental disability. HIE animal model was first established by Vannucci et al., in 1981, and has been used extensively to explore the mechanisms of brain damage and its potential treatment. The Vannucci model involves the unilateral common carotid artery occlusion followed by 90 min hypoxia (8% oxygen). The purpose of this study is to define and validate a modified HIE model which mimics closely that of the human neonatal HIE.

METHOD

The classic Vannucci HIE model occludes one common carotid artery followed by 90 min hypoxia. In the new model, common carotid arteries were occluded bilaterally followed by breathing 8% oxygen in a hypoxic chamber for 90, 60 and 30 min, followed by the release of the common carotid artery ligatures, mimicking a reperfusion.

RESULT

We studied 110 neonatal rats in detail, following the modified in comparison with the classical Vannucci models. The classical Vannucci model has a consistent surgical mortality of 18% and the new modified models have a 20%-46%. While mortality depended on the duration of hypoxia, fifty-two animals survived for behavioral assessments and standard histology. The modified HIE model with 60 min of transient carotid occlusion is associated with a moderate brain damage, and has a 30% surgical mortality. This modified experimental model is regarded closer to the human situation than the classical Vannucci model.

Update on mechanisms of the pathophysiology of neonatal encephalopathy

Therapeutic hypothermia is now well established to significantly improve survival without disability after neonatal encephalopathy (NE). To further improve outcomes, we need to better understand the mechanisms of brain injury. The central finding, which offers the potential for neuroprotective and neurorestorative interventions, is that brain damage after perinatal hypoxia-ischemia evolves slowly over time. Although brain cells may die during profound hypoxia-ischemia, even after surprisingly severe insults many cells show transient recovery of oxidative metabolism during a "latent" phase characterized by actively suppressed neural metabolism and activity. Critically, after moderate to severe hypoxia-ischemia, this transient recovery is followed after ~6 h by a phase of secondary deterioration, with delayed seizures, failure of mitochondrial function, cytotoxic edema, and cell death over ~72 h. This is followed by a tertiary phase of remodeling and recovery. This review discusses the mechanisms of injury that occur during the primary, latent, secondary and tertiary phases of injury and potential treatments that target one or more of these phases. By analogy with therapeutic hypothermia, treatment as early as possible in the latent phase is likely to have the greatest potential to prevent injury ("neuroprotection"). In the secondary phase of injury, anticonvulsants can attenuate seizures, but show limited neuroprotection. Encouragingly, there is now increasing preclinical evidence that late, neurorestorative interventions have potential to improve long-term outcomes.

Neuronal let-7b-5p acts through the Hippo-YAP pathway in neonatal encephalopathy

Despite increasing knowledge on microRNAs, their role in the pathogenesis of neonatal encephalopathy remains to be elucidated. Herein, we identify let-7b-5p as a significant microRNA in neonates with moderate to severe encephalopathy from dried blood spots using next generation sequencing. Validation studies using Reverse Transcription and quantitative Polymerase Chain Reaction on 45 neonates showed that let-7b-5p expression was increased on day 1 in neonates with moderate to severe encephalopathy with unfavourable outcome when compared to those with mild encephalopathy. Mechanistic studies performed on glucose deprived cell cultures and the cerebral cortex of two animal models of perinatal brain injury, namely hypoxic-ischaemic and intrauterine inflammation models confirm that let-7b-5p is associated with the apoptotic Hippo pathway. Significant reduction in neuronal let-7b-5p expression corresponded with activated Hippo pathway, with increased neuronal/nuclear ratio of Yes Associated Protein (YAP) and increased neuronal cleaved caspase-3 expression in both animal models. Similar results were noted for let-7b-5p and YAP expression in glucose-deprived cell cultures. Reduced nuclear YAP with decreased intracellular let-7b-5p correlated with neuronal apoptosis in conditions of metabolic stress. This finding of the Hippo-YAP association with let-7b needs validation in larger cohorts to further our knowledge on let-7b-5p as a biomarker for neonatal encephalopathy.

Using next generation sequencing of dried blood spots and subsequent validation, Ponnusamy et al identify let-7b-5p as an elevated microRNA in neonates with moderate to severe encephalopathy. Using cell culture and murine models of perinatal brain injury they demonstrate that the effects of let-7b-5p are elicited via the Hippo-YAP pathway, which should be validated in large neonate cohorts to expand our understanding of let-7b-5p as a biomarker for neonatal encephalopathy.

Mitochondrial dysfunction in perinatal asphyxia: role in pathogenesis and potential therapeutic interventions

Perinatal asphyxia (PA)-induced brain injury may present as hypoxic-ischemic encephalopathy in the neonatal period, and long-term sequelae such as spastic motor deficits, intellectual disability, seizure disorders and learning disabilities. The brain injury is secondary to both the hypoxic-ischemic event and oxygenation-reperfusion following resuscitation. Following PA, a time-dependent progression of neuronal insult takes place in terms of transition of cell death from necrosis to apoptosis. This transition is the result of time-dependent progression of pathomechanisms which involve excitotoxicity, oxidative stress, and ultimately mitochondrial dysfunction in developing brain. More precisely mitochondrial respiration is suppressed and calcium signalling is dysregulated. Consequently, Bax-dependent mitochondrial permeabilization occurs leading to release of cytochrome c and activation of caspases leading to transition of cell death in developing brain. The therapeutic window lies within this transition process. At present, therapeutic hypothermia (TH) is the only clinical treatment available for treating moderate as well as severe asphyxia in new-born as it attenuates secondary loss of high-energy phosphates (ATP) (Solevåg et al. in Free Radic Biol Med 142:113-122, 2019; Gunn et al. in Pediatr Res 81:202-209, 2017), improving both short- and long-term outcomes. Mitoprotective therapies can offer a new avenue of intervention alone or in combination with therapeutic hypothermia for babies with birth asphyxia. This review will explore these mitochondrial pathways, and finally will summarize past and current efforts in targeting these pathways after PA, as a means of identifying new avenues of therapeutic intervention.

Neuronal Circuit Activity during Neonatal Hypoxic-Ischemic Seizures in Mice

OBJECTIVE

To identify circuits active during neonatal hypoxic-ischemic (HI) seizures and seizure propagation using electroencephalography (EEG), behavior, and whole-brain neuronal activity mapping.

METHODS

Mice were exposed to HI on postnatal day 10 using unilateral carotid ligation and global hypoxia. EEG and video were recorded for the duration of the experiment. Using immediate early gene reporter mice, active cells expressing cfos were permanently tagged with reporter protein tdTomato during a 90-minute window. After 1 week, allowing maximal expression of the reporter protein, whole brains were processed, lipid cleared, and imaged with confocal microscopy. Whole-brain reconstruction and analysis of active neurons (colocalized tdTomato/NeuN) were performed.

RESULTS

HI resulted in seizure behaviors that were bilateral or unilateral tonic-clonic and nonconvulsive in this model. Mice exhibited characteristic EEG background patterns such as burst suppression and suppression. Neuronal activity mapping revealed bilateral motor cortex and unilateral, ischemic somatosensory cortex, lateral thalamus, and hippocampal circuit activation. Immunohistochemical analysis revealed regional differences in myelination, which coincide with these activity patterns. Astrocytes and blood vessel endothelial cells also expressed cfos during HI.

INTERPRETATION

Using a combination of EEG, seizure semiology analysis, and whole-brain neuronal activity mapping, we suggest that this rodent model of neonatal HI results in EEG patterns similar to those observed in human neonates. Activation patterns revealed in this study help explain complex seizure behaviors and EEG patterns observed in neonatal HI injury. This pattern may be, in part, secondary to regional differences in development in the neonatal brain. ANN NEUROL 2019;86:927-938.

Oscillating-gradient diffusion magnetic resonance imaging detects acute subcellular structural changes in the mouse forebrain after neonatal hypoxia-ischemia

The recently developed oscillating-gradient diffusion MRI (OG-dMRI) technique extends our ability to examine brain structures at different spatial scales. In this study, we investigated the sensitivity of OG-dMRI in detecting cellular and subcellular structural changes in a mouse model of neonatal hypoxia ischemia (HI). Neonatal mice received unilateral HI injury or sham injury at postnatal day 10, followed by in vivo T₂-weighted and diffusion MRI of the brains at 3-6 h and 24 h after HI. Apparent diffusion coefficient (ADC) maps were acquired using conventional pulsed-gradient dMRI (PG-dMRI) and OG-dMRI with oscillating frequencies from 50 to 200 Hz. Pathology at cellular and subcellular levels was evaluated using neuronal, glial, and mitochondrial markers. We found significantly higher rates of ADC increase with oscillating frequencies (Δ_fADC) in the ipsilateral edema region, compared to the contralateral side, starting as early as 3 h after HI. Even in injured regions that showed no apparent change in PG-ADC or pseudo-normalized PG-ADC measurements, Δ_fADC remained significantly elevated. Histopathology showed swelling of sub-cellular structures in these regions with no apparent whole-cell level change. These results suggest that OG-dMRI is sensitive to subcellular structural changes in the brain after HI and is less susceptible to pseudo-normalization than PG-dMRI.

Dysmaturation of Premature Brain: Importance, Cellular Mechanisms, and Potential Interventions

Prematurity, especially preterm birth (less than 32 weeks' gestation), is common and associated with high rates of both survival and neurodevelopmental disability, especially apparent in cognitive spheres. The neuropathological substrate of this disability is now recognized to be related to a variety of dysmaturational disturbances of the brain. These disturbances follow initial brain injury, particularly cerebral white matter injury, and involve many of the extraordinary array of developmental events active in cerebral white and gray matter structures during the premature period. This review delineates these developmental events and the dysmaturational disturbances that occur in premature infants. The cellular mechanisms involved in the genesis of the dysmaturation are emphasized, with particular focus on the preoligodendrocyte. A central role for the diffusely distributed activated microglia and reactive astrocytes in the dysmaturation is now apparent. As these dysmaturational cellular mechanisms appear to occur over a relatively long time window, interventions to prevent or ameliorate the dysmaturation, that is, neurorestorative interventions, seem possible. Such interventions include pharmacologic agents, especially erythropoietin, and particular attention has also been paid to such nutritional factors as quality and source of milk, breastfeeding, polyunsaturated fatty acids, iron, and zinc. Recent studies also suggest a potent role for interventions directed at various experiential factors in the neonatal period and infancy, i.e., provision of optimal auditory and visual exposures, minimization of pain and stress, and a variety of other means of environmental behavioral enrichment, in enhancing brain development.

Hypoxia-Ischemia and Hypothermia Independently and Interactively Affect Neuronal Pathology in Neonatal Piglets with Short-Term Recovery

Therapeutic hypothermia is the standard of clinical care for moderate neonatal hypoxic-ischemic encephalopathy. We investigated the independent and interactive effects of hypoxia-ischemia (HI) and temperature on neuronal survival and injury in basal ganglia and cerebral cortex in neonatal piglets. Male piglets were randomized to receive HI injury or sham procedure followed by 29 h of normothermia, sustained hypothermia induced at 2 h, or hypothermia with rewarming during fentanyl-nitrous oxide anesthesia. Viable and injured neurons and apoptotic profiles were counted in the anterior putamen, posterior putamen, and motor cortex at 29 h after HI injury or sham procedure. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) identified genomic DNA fragmentation to confirm cell death. Though hypothermia after HI preserved viable neurons in the anterior and posterior putamen, hypothermia prevented neuronal injury in only the anterior putamen. Hypothermia initiated 2 h after injury did not protect against apoptotic cell death in either the putamen or motor cortex, and rewarming from hypothermia was associated with increased apoptosis in the motor cortex. In non-HI shams, sustained hypothermia during anesthesia was associated with neuronal injury and corresponding viable neuron loss in the anterior putamen and motor cortex. TUNEL confirmed increased neurodegeneration in the putamen of hypothermic shams. Anesthetized, normothermic shams did not show abnormal neuronal cytopathology in the putamen or motor cortex, thereby demonstrating minimal contribution of the anesthetic regimen to neuronal injury during normothermia. We conclude that the efficacy of hypothermic protection after HI is region specific and that hypothermia during anesthesia in the absence of HI may be associated with neuronal injury in the developing brain. Studies examining the potential interactions between hypothermia and anesthesia, as well as with longer durations of hypothermia, are needed.

Effects of hypoxia ischemia on caspase-3 expression and neuronal apoptosis in the brain of neonatal mice

Effects of hypoxia ischemia on caspase-3 expression and neuronal apoptosis in the brain of neonatal mice were investigated. Twenty-five neonatal CD1 mice aged 1 week were selected and randomly divided into sham-operation group (n=8) and newborn hypoxia ischemia encephalopathy (NHIE) model group (n=17). The messenger ribonucleic acid (mRNA) expression levels of caspase-3 and Fas ligand (FasL) in brain tissues of mice in both groups were detected via reverse transcription-polymerase chain reaction (RT-PCR). The protein expression levels of caspase-3 and FasL in mice in both groups were detected via western blotting. Moreover, apoptosis of brain tissues was detected using the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), and caspase-3 protein expression level in brain tissues was detected using immunohistochemical methods. Results of RT-PCR and western blotting revealed that compared with those in sham-operation group, caspase-3 and FasL expression levels in model group were significantly increased. Results of TUNEL showed that the number of apoptotic neurons in model group was significantly increased. Besides, results of immunohistochemical detection manifested that the caspase-3 protein expression level in model group was obviously increased. Hypoxia ischemia can lead to significant increase of caspase-3 expression and increase of neuronal apoptosis in the brain of neonatal mice.

Neuroprotective effects of inter-alpha inhibitor proteins after hypoxic-ischemic brain injury in neonatal rats

Hypoxic-ischemic (HI) brain injury is one of the most common neurological problems occurring in the perinatal period. Hypothermia is the only approved intervention for neonatal HI encephalopathy. However, this treatment is only partially protective, has a narrow therapeutic time window after birth and only can be used to treat full-term infants. Consequently, additional therapies are critically needed. Inflammation is an important contributing factor to the evolution of HI brain injury in neonates. Inter-alpha Inhibitor Proteins (IAIPs) are immunomodulatory proteins with anti-inflammatory properties. We have previously shown that IAIPs reduce neuronal cell death and improve behavioral outcomes when given after carotid artery ligation, but before hypoxia in male neonatal rats. The objective of the current study was to investigate the neuroprotective effects of treatment with IAIPs given immediately or 6 h after HI in both male and female neonatal rats. HI was induced with the Rice-Vannucci method in postnatal (P) day 7 rats. After ligation of the right common carotid artery, P7 rats were exposed to 90 min of hypoxia (8% oxygen). Human plasma-derived IAIPs or placebo (phosphate buffered saline) was given at zero, 24, and 48 h after HI. Brains were perfused, weighed and fixed 72 h after HI at P10. In a second, delayed treatment group, the same procedure was followed except that IAIPs or placebo were given at 6, 24 and 48 h after HI. Separate sham-operated, placebo-treated groups were exposed to identical protocols but were not exposed to carotid artery ligation and remained in room air. Rat sex was recorded. The effects of IAIPs on HI brain injury were examined using histopathological scoring and immunohistochemical analyses of the brain and by using infarct volume measurements on frozen tissue of the entire brain hemispheres ipsilateral and contralateral to HI injury. IAIPs given immediately after HI improved (P < 0.050) histopathological brain injury across and within the cingulate, caudate/putamen, thalamus, hippocampus and parietal cortex in males, but not in females. In contrast, IAIPs given immediately after HI reduced (P < 0.050) infarct volumes of the hemispheres ipsilateral to HI injury in similarly both the males and females. Treatment with IAIPs also resulted in higher (P < 0.050) brain weights compared with the placebo-treated HI group, reduced (P < 0.050) neuronal and non-neuronal cell death in the cortex and total hemisphere, and also increased the total area of oligodendrocytes determined by CNPase in the ipsilateral hemisphere and corpus callosum (P < 0.050) of male, but not female subjects exposed to HI. Delayed treatment with IAIPs 6 h after HI did not improve histopathological brain injury in males or females, but resulted in higher (P < 0.050) brain weights compared with the placebo-treated HI males. Therefore, treatment with IAIPs immediately after HI improved brain weights and reduced neuropathological brain injury and cell death in male rats, and reduced infarct volume in both male and female neonatal rats. We conclude that IAIPs exert neuroprotective effects after exposure to HI in neonatal rats and may exhibit some sex-related differential effects.

Chemerin reverses neurological impairments and ameliorates neuronal apoptosis through ChemR23/CAMKK2/AMPK pathway in neonatal hypoxic-ischemic encephalopathy

Hypoxic-ischemic encephalopathy (HIE) is a devastating neurological event that contributes to the prolonged neurodevelopmental consequences in infants. Therapeutic strategies focused on attenuating neuronal apoptosis in the penumbra appears to be promising. Given the increasingly recognized neuroprotective roles of adipokines in HIE, we investigated the potential anti-apoptotic roles of a novel member of adipokines, Chemerin, in an experimental model of HIE. In the present study, 10-day-old rat pups underwent right common carotid artery ligation followed by 2.5 h hypoxia. At 1 h post hypoxia, pups were intranasally administered with human recombinant chemerin (rh-chemerin). Here, we showed that rh-chemerin prevented the neuronal apoptosis and degeneration as evidenced by the decreased expression of the pro-apoptotic markers, cleaved caspase 3 and Bax, as well as the numbers of Fluoro-Jade C and TUNEL-positive neurons. Furthermore, rh-Chemerin reversed neurological and morphological impairments induced by hypoxia-ischemia in neonatal rats at 24 h and 4 weeks after HIE. In addition, chemerin-mediated neuronal survival correlated with the elevation of chemerin receptor 23 (chemR23), phosphorylated calmodulin-dependent protein kinase kinase 2 (CAMKK2), as well as phosphorylated adenosine monophosphate-activated protein kinase (AMPK). Specific inhibition of chemR23, CAMKK2, and AMPK abolished the anti-apoptotic effects of rh-chemerin at 24 h after HIE, demonstrating that rh-chemerin ameliorated neuronal apoptosis partially via activating chemR23/CAMKK2/AMPK signaling pathway. Neuronal apoptosis is a well-established contributing factor of pathological changes and the neurological impairment after HIE. These results revealed mechanisms of neuroprotection by rh-chemerin, and indicated that activation of chemR23 might be harnessed to protect from neuronal apoptosis in HIE.

Effects of ketamine on the fetal transcriptomic response to umbilical cord occlusion: comparison with hypoxic hypoxia in the cerebral cortex

KEY POINTS

The cerebral response to fetal asphyxia is characterized by an upregulation of nucleic acid and chromatin modification processes, as well as a downregulation of metabolic processes at 1 h post-umbilical cord occlusion (UCO). Twenty-four hours post UCO, there was an upregulation of metabolic processes and protein modifications. UCO did not alter bacterial gene expression levels, nor did it produce a robust inflammatory response compared to maternal hypoxia. The administration of ketamine produced minimal effects on the fetal response to UCO in the cerebral cortex.

ABSTRACT

Umbilical cord occlusion (UCO) is known to cause neurological disorders in the neonate. Previously, we have reported that hypoxic hypoxia (HH) stimulates the appearance of bacteria in the fetal brain and upregulates the expression of inflammatory markers in fetal cerebral cortex (CTX) and also that ketamine attenuates these responses. In the present study, we aimed to test the hypothesis that UCO, similar to HH, produces an inflammatory response in the fetal CTX and also that treatment with ketamine reduces these effects. In chronically instrumented fetal sheep (∼125 days), 30 min of partial UCO decreased fetal P a O 2 levels by ∼50%. Half of the fetuses received ketamine (3 mg kg^-1 ) 10 min prior to UCO (n = 4 per group). Fetal brains were collected 1 and 24 h after the experiment and mRNA was extracted and hybridized for microarray analyses. Differentially-expressed genes were analysed for significant association with gene ontologies and pathways. After 1 h, UCO upregulated nucleic acid processing and chromatin modification and downregulated metabolic processes compared to control. After 24 h, UCO upregulated metabolic and protein modification processes. Ketamine produced minimal effects. UCO did not alter the abundance of bacterial DNA in fetal brain, nor did it upregulate inflammation pathways compared to HH. We conclude that UCO produced time-dependent responses that did not include bacterial invasion or upregulation of inflammation pathways in fetal CTX. This contrasts with the response to HH, which resulted in the appearance of bacteria in the CTX and upregulated inflammation pathways. These responses in fetal CTX to oxygen deprivation are therefore modified by the maternal or placental response to the stimulus.

Mitochondrial dynamics, mitophagy and biogenesis in neonatal hypoxic-ischaemic brain injury

Hypoxic-ischaemic encephalopathy, resulting from asphyxia during birth, affects 2-3 in every 1000 term infants and depending on severity, brings about life-changing neurological consequences or death. This hypoxic-ischaemia (HI) results in a delayed neural energy failure during which the majority of brain injury occurs. Currently, there are limited treatment options and additional therapies are urgently required. Mitochondrial dysfunction acts as a focal point in injury development in the immature brain. Not only do mitochondria become permeabilised, but recent findings implicate perturbations in mitochondrial dynamics (fission, fusion), mitophagy and biogenesis. Mitoprotective therapies may therefore offer a new avenue of intervention for babies who suffer lifelong disabilities due to birth asphyxia.

Cell Death in the Developing Brain after Hypoxia-Ischemia

Perinatal insults such as hypoxia–ischemia induces secondary brain injury. In order to develop the next generation of neuroprotective therapies, we urgently need to understand the underlying molecular mechanisms leading to cell death. The cell death mechanisms have been shown to be quite different in the developing brain compared to that in the adult. The aim of this review is update on what cell death mechanisms that are operating particularly in the setting of the developing CNS. In response to mild stress stimuli a number of compensatory mechanisms will be activated, most often leading to cell survival. Moderate-to-severe insults trigger regulated cell death. Depending on several factors such as the metabolic situation, cell type, nature of the stress stimulus, and which intracellular organelle(s) are affected, the cell undergoes apoptosis (caspase activation) triggered by BAX dependent mitochondrial permeabilzation, necroptosis (mixed lineage kinase domain-like activation), necrosis (via opening of the mitochondrial permeability transition pore), autophagic cell death (autophagy/Na⁺, K⁺-ATPase), or parthanatos (poly(ADP-ribose) polymerase 1, apoptosis-inducing factor). Severe insults cause accidental cell death that cannot be modulated genetically or by pharmacologic means. However, accidental cell death leads to the release of factors (damage-associated molecular patterns) that initiate systemic effects, as well as inflammation and (regulated) secondary brain injury in neighboring tissue. Furthermore, if one mode of cell death is inhibited, another route may step in at least in a scenario when upstream damaging factors predominate over protective responses. The provision of alternative routes through which the cell undergoes death has to be taken into account in the hunt for novel brain protective strategies.

Children born at 32 to 35 weeks with birth asphyxia and later cerebral palsy are different from those born after 35 weeks

OBJECTIVE

The objectives of this study were to (1) establish the proportion of cerebral palsy (CP) that occurs with a history suggestive of birth asphyxia in children born at 32 to 35 weeks and (2) evaluate their characteristics in comparison with children with CP born at ⩾36 weeks with such a history.

STUDY DESIGN

Using the Canadian CP Registry, children born at 32 to 35 weeks of gestation with CP with a history suggestive of birth asphyxia were compared with corresponding ⩾36 weeks of gestation children.

RESULTS

Of the 163 children with CP born at 32 to 35 weeks and 738 born at ⩾36 weeks, 26 (16%) and 105 (14%) had a history suggestive of birth asphyxia, respectively. The children born at 32 to 35 weeks had more frequent abruptio placenta (35% vs 12%; odds ratio (OR) 4.1, 95% confidence interval (CI) 1.5 to 11.2), less frequent neonatal seizures (35% vs 72%; OR 0.20, 95% CI 0.08 to 0.52), more frequent white matter injury (47% vs 17%; OR 4.3, 95% CI 1.3 to 14.0), more frequent intraventricular hemorrhage (IVH) (40% vs 6%; OR 11.2, 95% CI 3.4 to 37.4) and more frequent spastic diplegia (24% vs 8%; OR 1.8, 95% CI 1.2 to 12.2) than the corresponding ⩾36 weeks of gestation children.

CONCLUSIONS

Approximately 1 in 7 children with CP born at 32 to 35 weeks had a history suggestive of birth asphyxia. They had different magnetic resonance imaging patterns of injury from those born at ⩾36 weeks and a higher frequency of IVH. Importantly, when considering hypothermia in preterm neonates with suspected birth asphyxia, prospective surveillance for IVH will be essential.

Impaired autophagosome clearance contributes to neuronal death in a piglet model of neonatal hypoxic-ischemic encephalopathy

To examine the temporal relationship of cortical autophagic flux with delayed neuronal cell death after hypoxia-ischemia (HI) in neonatal piglets. HI was produced with 45-min hypoxia and 7-min airway occlusion in 3-5-day-old piglets. Markers of autophagic, lysosomal and cell death signaling were studied via immunohistochemistry, immunoblotting, and histochemistry in piglet brains. In vitro, autophagy was impaired in cultured mouse cortical neurons treated with chloroquine with or without rapamycin for 1 d in the presence of Z-VAD-fmk, cyclosporine A, or vehicle control, and cell viability was assessed with the MTT assay. In vivo, neuronal cell death of sensorimotor cortex was delayed by 1-2 days after HI, whereas LC3-II, Beclin-1, PI3KC3, ATG12-ATG-5, and p-ULK1 increased by 1.5-6 h. Autophagosomes accumulated in cortical neurons by 1 d owing to enhanced autophagy and later to decreased autophagosome clearance, as indicated by LC3, Beclin-1, and p62 accumulation. Autophagy flux impairment was attributable to lysosomal dysfunction, as indicated by low lysosomal-associated membrane protein 2, cathepsin B, and cathepsin D levels at 1 d. Ubiquitin levels increased at 1 d. Autophagosome and p62 accumulated predominantly in neurons at 1 d, with p62 puncta occurring in affected cells. Beclin-1 colocalized with markers of caspase-dependent and caspase-independent apoptosis and necrosis in neurons. In vitro, mouse neonatal cortical neurons treated with rapamycin and chloroquine showed increased autophagosomes, but not autolysosomes, and increased cell death that was attenuated by cyclosporine A. Neonatal HI initially increases autophagy but later impairs autophagosome clearance, coinciding with delayed cortical neuronal death.

Nasopharynx is well-suited for core temperature measurement during hypothermia therapy

BACKGROUND

Rectal temperature is commonly used as the core temperature during therapeutic hypothermia therapy in neonates with hypoxic-ischemic encephalopathy (HIE). The purpose of this study was to examine whether nasopharyngeal temperature could serve as a substitute for rectal temperature.

METHODS

We prospectively investigated 40 neonates with HIE who underwent therapeutic hypothermia by selective head cooling, which involved cooling the body to 34°C for 72 h. During this period, nasopharyngeal temperature was measured and compared with rectal temperature every hour.

RESULTS

For 40 neonates included in this study, the mean rectal and nasopharyngeal temperatures were 34.3 ± 0.4°C (n = 2920) and 34.3 ± 0.4°C (n = 2920), respectively. Nasopharyngeal temperature strongly correlated with rectal temperature (R² = 0.623, P < 0.0001) and magnitude of the mean difference between nasopharyngeal and rectal temperature varied little during the 72 h of therapeutic hypothermia.

CONCLUSIONS

Nasopharyngeal temperature in neonates with perinatal HIE undergoing therapeutic hypothermia may be a suitable substitute for rectal temperature.

Mechanisms of acupuncture on vascular dementia-A review of animal studies

Vascular dementia (VaD) is the second leading type of dementia after Alzheimer's disease plaguing the aging population. Acupuncture has served as alternative and complementary medicine in the world for a long time and its use for VaD is based on a large body of preclinical and clinical researches. The mechanisms that underlie the protective effects of acupuncture are slowly beginning to be understood. Acupuncture influences multiple aspects of the pathological process of VaD. It improves cognitive function through protecting cerebral neurons from oxidative stress, apoptosis, and neuroinflammation, regulating glucose metabolism and neurotransmitters. Acupuncture may also improve synaptic plasticity and blood vessel function. It is likely that no single factor can explain the protection provided by acupuncture. This review provides a comprehensive overview of established and recent findings in animal-based researches aiming to elucidate the complex mechanisms of acupuncture on VaD.

Ketamine decreases inflammatory and immune pathways after transient hypoxia in late gestation fetal cerebral cortex

Transient hypoxia in pregnancy stimulates a physiological reflex response that redistributes blood flow and defends oxygen delivery to the fetal brain. We designed the present experiment to test the hypotheses that transient hypoxia produces damage of the cerebral cortex and that ketamine, an antagonist of NMDA receptors and a known anti‐inflammatory agent, reduces the damage. Late gestation, chronically catheterized fetal sheep were subjected to a 30‐min period of ventilatory hypoxia that decreased fetal PaO₂ from 17 ± 1 to 10 ± 1 mmHg, or normoxia (PaO₂ 17 ± 1 mmHg), with or without pretreatment (10 min before hypoxia/normoxia) with ketamine (3 mg/kg, i.v.). One day (24 h) after hypoxia/normoxia, fetal cerebral cortex was removed and mRNA extracted for transcriptomics and systems biology analysis (n = 3–5 per group). Hypoxia stimulated a transcriptomic response consistent with a reduction in cellular metabolism and an increase in inflammation. Ketamine pretreatment reduced both of these responses. The inflammation response modeled with transcriptomic systems biology was validated by immunohistochemistry and showed increased abundance of microglia/macrophages after hypoxia in the cerebral cortical tissue that ketamine significantly reduced. We conclude that transient hypoxia produces inflammation of the fetal cerebral cortex and that ketamine, in a standard clinical dose, reduces the inflammation response.

Plasticity in the Neonatal Brain following Hypoxic-Ischaemic Injury

Hypoxic-ischaemic damage to the developing brain is a leading cause of child death, with high mortality and morbidity, including cerebral palsy, epilepsy, and cognitive disabilities. The developmental stage of the brain and the severity of the insult influence the selective regional vulnerability and the subsequent clinical manifestations. The increased susceptibility to hypoxia-ischaemia (HI) of periventricular white matter in preterm infants predisposes the immature brain to motor, cognitive, and sensory deficits, with cognitive impairment associated with earlier gestational age. In term infants HI causes selective damage to sensorimotor cortex, basal ganglia, thalamus, and brain stem. Even though the immature brain is more malleable to external stimuli compared to the adult one, a hypoxic-ischaemic event to the neonate interrupts the shaping of central motor pathways and can affect normal developmental plasticity through altering neurotransmission, changes in cellular signalling, neural connectivity and function, wrong targeted innervation, and interruption of developmental apoptosis. Models of neonatal HI demonstrate three morphologically different types of cell death, that is, apoptosis, necrosis, and autophagy, which crosstalk and can exist as a continuum in the same cell. In the present review we discuss the mechanisms of HI injury to the immature brain and the way they affect plasticity.

Apoptotic neurons induce proliferative responses of progenitor cells in the postnatal neocortex

Apoptotic cell death is the leading cause of neuronal loss after neonatal brain injury. Little is known about the intrinsic capacity of the immature cerebral cortex for replacing dead cells. Here we test the hypothesis that neuronal apoptosis is able to trigger compensatory proliferation in surrounding cells. In order to establish a "pure" apoptotic cell death model and to avoid the confounding effects of broken blood-brain barrier and inflammatory reactions, we used a diphtheria toxin (DT) and diphtheria toxin receptor (DTR) system to induce ablation of layer IV neurons in the rodent somatosensory cortex during the early postnatal period. We found that DT-triggered apoptosis is a slowly progressing event lasting about for 7 days. While dying cells expressed the morphological features of apoptosis, we could not detect immunoreactivity for activated caspase-3 in these cells. Microglia activation and proliferation represented the earliest cellular responses to apoptotic cell death. In addition, we found that induced apoptosis triggered a massive proliferation of undifferentiated progenitor cell pool including Sox2 as well as NG2 cells. The default differentiation pattern of proliferating progenitors appears to be the glial phenotype; we could not find evidence for newly generated neurons in response to apoptotic neuronal death. These results suggest that mitotically active progenitor populations are intrinsically capable to contribute to the repair process of injured cortical tissue and may represent a potential target for neuronal replacement strategies.

Models of hypoxia and ischemia-induced seizures

Despite greater understanding and improved management, seizures continue to be a major problem in childhood. Neonatal seizures are often refractory to conventional antiepileptic drugs, and can result in later life epilepsy and cognitive deficits, conditions for which there are no specific treatments. Hypoxic and/or ischemic encephalopathy (HIE) is the most common cause for neonatal seizures, and accounts for more than two-thirds of neonatal seizure cases. A better understanding of the cellular and molecular mechanisms is essential for identifying new therapeutic strategies that control the neonatal seizures and its cognitive consequences. This heavily relies on animal models that play a critical role in discovering novel mechanisms underlying both epileptogenesis and associated cognitive impairments. To date, a number of animal models have provided a tremendous amount of information regarding the pathophysiology of HIE-induced neonatal seizures. This review provides an overview on the most important features of the main animal models of HIE-induced seizures. In particular, we focus on the methodology of seizure induction and the characterizations of post-HIE injury consequences. These aspects of HIE-induced seizure models are discussed in the light of the suitability of these models in studying human HIE-induced seizures.

Upregulation of HIF-1α protects neuroblastoma cells from hypoxia-induced apoptosis in a RhoA-dependent manner

Hypoxic conditions regulate several metabolic enzymes and transcription factors that are involved in cancer, ischemia and pulmonary diseases. The Ras homolog (Rho) family, including Rho member A (RhoA), is involved in reorganization of the actin cytoskeleton, cell migration and in the regulation of apoptosis and gene transcription. The aim of the present study was to investigate the expression of hypoxia‑inducible factor (HIF)‑α and the activity of RhoA in PC12 neuroblastoma cells under hypoxic conditions. The upregulation of HIF‑α and RhoA by hypoxia was determined using reverse transcription‑quantitative polymerase chain reaction and western blot assays, cell apoptosis was analyzed using flow cytometry, and the activity of caspase 3 was examined using a western blot assay and caspase 3 activity assay kit. The PC12 cells were induced to apoptosis following exposure to hypoxia, and exhibited increased expression of HIF‑α and increased mRNA and protein expression levels of RhoA. The overexpression of HIF‑α attenuated the hypoxia‑induced apoptosis of the PC12 cells. In addition, RhoA knockdown using small interfering RNA abrogated the antagonism of HIF‑1α towards hypoxia‑induced apoptosis. The results of the present study confirmed the protective role of HIF‑1α and RhoA in hypoxia‑induced PC12 cell apoptosis, and that the upregulation of HIF‑1α by hypoxia is RhoA‑dependent.

Upregulation of HIF-1α by hypoxia protect neuroblastoma cells from apoptosis by promoting survivin expression

Apoptosis is one of main types of neural cell death and is reversible and is a major target of therapeutic interventions. However, detailed apoptotic cascades still need to be recognized. In present study, we determined the promotion of HIF-1α and survivin in brain samples of a mouse model of hypoxic-ischemia and in neuroblastoma SH-SY5Y cells post hypoxia treatment. Then gain-of-function and loss-of-function strategies were adopted to manipulate the HIF-1α in SH-SY5Y cells, and hypoxia-induced survivin upregulation and cell apoptosis were determined. Results demonstrated that the HIF-1α and survivin were significantly promoted in a mouse model of hypoxic-ischemia or in SH-SY5Y cells post hypoxia in vitro. Manually upregulated HIF-1α could promote the hypoxia-induced survivin upregulation and improve the hypoxia-induced SH-SY5Y cell apoptosis. On the other hand, the HIF-1α knockdown by RNAi reduced the hypoxia-induced survivin upregulation and cell apoptosis. Therefore, the present study confirmed the protective role of HIF-1α and survivin in the hypoxia-induced SH- SY5Y cell apoptosis, and the survivin upregulation by hypoxia is HIF-1α-dependent. Promotion of HIF-1α and survivin might be a valuable stragegy for therapeutic intervention for hypoxic-ischemic encephalopathy.

Pathophysiology and neuroprotection of global and focal perinatal brain injury: lessons from animal models

BACKGROUND

Arterial ischemic stroke occurs more frequently in term newborns than in the elderly, and brain immaturity affects mechanisms of ischemic injury and recovery. The susceptibility to injury of the brain was assumed to be lower in the perinatal period as compared with childhood. This concept was recently challenged by clinical studies showing marked motor disabilities after stroke in neonates, with the severity of motor and cortical sensory deficits similar in both perinatal and childhood ischemic stroke. Our understanding of the triggers and the pathophysiological mechanisms of perinatal stroke has greatly improved in recent years, but many factors remain incompletely understood.

METHODS

In this review, we focus on the pathophysiology of perinatal stroke and on therapeutic strategies that can protect the immature brain from the consequences of stroke by targeting inflammation and brain microenvironment.

RESULTS

Studies in neonatal rodent models of cerebral ischemia have suggested a potential role for soluble inflammatory molecules as important modulators of injury and recovery. A great effort is underway to investigate neuroprotective molecules based on our increasing understanding of the pathophysiology.

CONCLUSION

In this review, we provide a comprehensive summary of new insights concerning pathophysiology of focal and global perinatal brain injury and their implications for new therapeutic approaches.

Rewarming from therapeutic hypothermia induces cortical neuron apoptosis in a swine model of neonatal hypoxic-ischemic encephalopathy

The consequences of therapeutic hypothermia for neonatal hypoxic-ischemic encephalopathy are poorly understood. Adverse effects from suboptimal rewarming could diminish neuroprotection from hypothermia. Therefore, we tested whether rewarming is associated with apoptosis. Piglets underwent hypoxia-asphyxia followed by normothermic or hypothermic recovery at 2 hours. Hypothermic groups were divided into those with no rewarming, rewarming at 0.5 °C/hour, or rewarming at 4 °C/hour. Neurodegeneration at 29 hours was assessed by hematoxylin and eosin staining, TUNEL assay, and immunoblotting for cleaved caspase-3. Rewarmed piglets had more apoptosis in motor cortex than did those that remained hypothermic after hypoxia-asphyxia. Apoptosis in piriform cortex was greater in hypoxic-asphyxic, rewarmed piglets than in naive/sham piglets. Caspase-3 inhibitor suppressed apoptosis with rewarming. Rapidly rewarmed piglets had more caspase-3 cleavage in cerebral cortex than did piglets that remained hypothermic or piglets that were rewarmed slowly. We conclude that rewarming from therapeutic hypothermia can adversely affect the newborn brain by inducing apoptosis through caspase mechanisms.

The non-human primate striatum undergoes marked prolonged remodeling during postnatal development

We examined the postnatal ontogeny of the striatum in rhesus monkeys (Macaca mulatta) to identify temporal and spatial patterns of histological and chemical maturation. Our goal was to determine whether this forebrain structure is developmentally static or dynamic in postnatal life. Brains from monkeys at 1 day, 1, 4, 6, 9, and 12 months of age (N = 12) and adult monkeys (N = 4) were analyzed. Nissl staining was used to assess striatal volume, cytoarchitecture, and apoptosis. Immunohistochemistry was used to localize and measure substance P (SP), leucine-enkephalin (LENK), tyrosine hydroxylase (TH), and calbindin D28 (CAL) immunoreactivities. Mature brain to body weight ratio was achieved at 4 months of age, and striatal volume increased from ∼1.2 to ∼1.4 cm(3) during the first postnatal year. Nissl staining identified, prominently in the caudate nucleus, developmentally persistent discrete cell islands with neuronal densities greater than the surrounding striatal parenchyma (matrix). Losses in neuronal density were observed in island and matrix regions during maturation, and differential developmental programmed cell death was observed in islands and matrix regions. Immunohistochemistry revealed striking changes occurring postnatally in striatal chemical neuroanatomy. At birth, the immature dopaminergic nigrostriatal innervation was characterized by islands enriched in TH-immunoreactive puncta (putative terminals) in the neuropil; TH-enriched islands aligned completely with areas enriched in SP immunoreactivity but low in LENK immunoreactivity. These areas enriched in SP immunoreactivity but low in LENK immunoreactivity were identified as striosome and matrix areas, respectively, because CAL immunoreactivity clearly delineated these territories. SP, LENK, and CAL immunoreactivities appeared as positive neuronal cell bodies, processes, and puncta. The matrix compartment at birth contained relatively low TH-immunoreactive processes and few SP-positive neurons but was densely populated with LENK-immunoreactive neurons. The nucleus accumbens part of the ventral striatum also showed prominent differences in SP, LENK, and CAL immunoreactivities in shell and core territories. During 12 months of postnatal maturation salient changes occurred in neurotransmitter marker localization: TH-positive afferents densely innervated the matrix to exceed levels of immunoreactivity in the striosomes; SP immunoreactivity levels increased in the matrix; and LENK-immunoreactivity levels decreased in the matrix and increased in the striosomes. At 12 months of age, striatal chemoarchitecture was similar qualitatively to adult patterns, but quantitatively different in LENK and SP in caudate, putamen, and nucleus accumbens. This study shows for the first time that the rhesus monkey striatum requires more than 12 months after birth to develop an adult-like pattern of chemical neuroanatomy and that principal neurons within striosomes and matrix have different developmental programs for neuropeptide expression. We conclude that postnatal maturation of the striatal mosaic in primates is not static but, rather, is a protracted and dynamic process that requires many synchronous and compartment-selective changes in afferent innervation and in the expression of genes that regulate neuronal phenotypes.

The potential for cell-based therapy in perinatal brain injuries

Perinatal brain injuries are a leading cause of cerebral palsy worldwide. The potential of stem cell therapy to prevent or reduce these impairments has been widely discussed within the medical and scientific communities and an increasing amount of research is being conducted in this field. Animal studies support the idea that a number of stem cells types, including cord blood and mesenchymal stem cells have a neuroprotective effect in neonatal hypoxia-ischemia. Both these cell types are readily available in a clinical setting. The mechanisms of action appear to be diverse, including immunomodulation, activation of endogenous stem cells, release of growth factors, and anti-apoptotic effects. Here, we review the different types of stem cells and progenitor cells that are potential candidates for therapeutic strategies in perinatal brain injuries, and summarize recent preclinical and clinical studies.

Brain injury in premature neonates: A primary cerebral dysmaturation disorder?

With advances in neonatal care, preterm neonates are surviving with an evolving constellation of motor and cognitive disabilities that appear to be related to widespread cellular maturational disturbances that target cerebral gray and white matter. Whereas preterm infants were previously at high risk for destructive brain lesions that resulted in cystic white matter injury and secondary cortical and subcortical gray matter degeneration, contemporary cohorts of preterm survivors commonly display less severe injury that does not appear to involve pronounced glial or neuronal loss. Nevertheless, these milder forms of injury are also associated with reduced cerebral growth. Recent human and experimental studies support that impaired cerebral growth is related to disparate responses in gray and white matter. Myelination disturbances in cerebral white matter are related to aberrant regeneration and repair responses to acute death of premyelinating late oligodendrocyte progenitors (preOLs). In response to preOL death, early oligodendrocyte progenitors rapidly proliferate and differentiate, but the regenerated preOLs fail to normally mature to myelinating cells required for white matter growth. Although immature neurons appear to be more resistant to cell death from hypoxia-ischemia than glia, they display widespread disturbances in maturation of their dendritic arbors, which further contribute to impaired cerebral growth. These complex and disparate responses of neurons and preOLs thus result in large numbers of cells that fail to fully mature during a critical window in development of neural circuitry. These recently recognized forms of cerebral gray and white matter dysmaturation raise new diagnostic challenges and suggest new therapeutic directions centered on reversal of the processes that promote dysmaturation.

Mitochondria: hub of injury responses in the developing brain

Progress in the field of mitochondrial biology in the past few years has shown that mitochondrial activities go beyond bioenergetics. These new aspects of mitochondrial physiology and pathophysiology have important implications for the immature brain. A picture emerges in which mitochondrial biogenesis, mitophagy, migration, and morphogenesis are crucial for brain development and synaptic pruning, and play a part in recovery after acute insults. Mitochondria also affect brain susceptibility to injury, and mitochondria-directed interventions can make the immature brain highly resistant to acute injury. Finally, the mitochondrion is a platform for innate immunity, contributes to inflammation in response to infection and acute damage, and participates in antiviral and antibacterial defence. Understanding of these new aspects of mitochondrial function will provide insights into brain development and neurological disease, and enable discovery and development of new strategies for treatment.

Protective effect of ginsenoside Re on acute gastric mucosal lesion induced by compound 48/80

The protective effect of ginsenoside Re, isolated from ginseng berry, against acute gastric mucosal lesions was examined in rats with a single intraperitoneal injection of compound 48/80 (C48/80). Ginsenoside Re (20 mg/kg or 100 mg/kg) was orally administered 0.5 h prior to C48/80 treatment. Ginsenoside Re dose-dependently prevented gastric mucosal lesion development 3 h after C48/80 treatment. Increases in the activities of myeloperoxidase (MPO; an index of neutrophil infiltration) and xanthine oxidase (XO) and the content of thiobarbituric acid reactive substances (TBARS; an index of lipid peroxidation) and decreases in the contents of hexosamine (a marker of gastric mucus) and adherent mucus, which occurred in gastric mucosal tissues after C48/80 treatment, were significantly attenuated by ginsenoside Re. The elevation of Bax expression and the decrease in Bcl2 expression after C48/80 treatment were also attenuated by ginsenoside Re. Ginsenoside Re significantly attenuated all these changes 3 h after C48/80 treatment. These results indicate that orally administered ginsenoside Re protects against C48/80-induced acute gastric mucosal lesions in rats, possibly through its stimulatory action on gastric mucus synthesis and secretion, its inhibitory action on neutrophil infiltration, and enhanced lipid peroxidation in the gastric mucosal tissue.

Experimental modelling of the consequences of brief late gestation asphyxia on newborn lamb behaviour and brain structure

Brief but severe asphyxia in late gestation or at the time of birth may lead to neonatal hypoxic ischemic encephalopathy and is associated with long-term neurodevelopmental impairment. We undertook this study to examine the consequences of transient in utero asphyxia in late gestation fetal sheep, on the newborn lamb after birth. Surgery was undertaken at 125 days gestation for implantation of fetal catheters and placement of a silastic cuff around the umbilical cord. At 132 days gestation (0.89 term), the cuff was inflated to induce umbilical cord occlusion (UCO), or sham (control). Fetal arterial blood samples were collected for assessment of fetal wellbeing and the pregnancy continued until birth. At birth, behavioral milestones for newborn lambs were recorded over 24 h, after which the lambs were euthanased for brain collection and histopathology assessments. After birth, UCO lambs displayed significant latencies to (i) use all four legs, (ii) attain a standing position, (iii) find the udder, and (iv) successfully suckle - compared to control lambs. Brains of UCO lambs showed widespread pathologies including cell death, white matter disruption, intra-parenchymal hemorrhage and inflammation, which were not observed in full term control brains. UCO resulted in some preterm births, but comparison with age-matched preterm non-UCO control lambs showed that prematurity per se was not responsible for the behavioral delays and brain structural abnormalities resulting from the in utero asphyxia. These results demonstrate that a single, brief fetal asphyxic episode in late gestation results in significant grey and white matter disruption in the developing brain, and causes significant behavioral delay in newborn lambs. These data are consistent with clinical observations that antenatal asphyxia is causal in the development of neonatal encephalopathy and provide an experimental model to advance our understanding of neuroprotective therapies.

Inflammatory responses in hypoxic ischemic encephalopathy

Inflammation plays a critical role in mediating brain injury induced by neonatal hypoxic ischemic encephalopathy (HIE). The mechanisms underlying inflammatory responses to ischemia may be shared by neonatal and adult brains; however, HIE exhibits a unique inflammation phenotype that results from the immaturity of the neonatal immune system. This review will discuss the current knowledge concerning systemic and local inflammatory responses in the acute and subacute stages of HIE. The key components of inflammation, including immune cells, adhesion molecules, cytokines, chemokines and oxidative stress, will be reviewed, and the differences between neonatal and adult inflammatory responses to cerebral ischemic injury will also be discussed.

Apoptosis in cerebral ischemia: executional and regulatory signaling mechanisms

Programmed cell death, often in the form of apoptosis, is an important contributing mechanism in the pathogenesis of ischemic brain injury. Depending on the severity of the insult and the stage of the injury, the executional pathways that are directly responsible for cell death and the signaling mechanisms that participate in the regulation of these death pathways may vary. It is likely that molecular or pharmacological targeting of the upstream signaling mechanisms that control the death executional pathways may offer opportunities for more complete and long-term neuroprotection. This review summarizes the recent advancements in the understanding of the executional and regulatory signaling mechanisms in ischemic brain injury.

Multiple interacting cell death mechanisms in the mediation of excitotoxicity and ischemic brain damage: a challenge for neuroprotection

There is currently no approved neuroprotective pharmacotherapy for acute conditions such as stroke and cerebral asphyxia. One of the reasons for this may be the multiplicity of cell death mechanisms, because inhibition of a particular mechanism leaves the brain vulnerable to alternative ones. It is therefore essential to understand the different cell death mechanisms and their interactions. We here review the multiple signaling pathways underlying each of the three main morphological types of cell death--apoptosis, autophagic cell death and necrosis--emphasizing their importance in the neuronal death that occurs during cerebral ischemia and hypoxia-ischemia, and we analyze the interactions between the different mechanisms. Finally, we discuss the implications of the multiplicity of cell death mechanisms for the design of neuroprotective strategies.

Neuro-protective effects of growth hormone (GH) after hypoxia-ischemia injury in embryonic chicken cerebellum

Neuroprotection is a mechanism within the central nervous system (CNS) that protects neurons from damage as a result of a severe insult. It is known that growth hormone (GH) is involved in cell survival and may inhibit apoptosis in several cell types, including those of the CNS. Both GH and GH-receptor (GHR) genes are expressed in the cerebellum. Thus, we investigated the possible neuroprotective role of GH in this organ, which is very sensitive to hypoxic/ischemic conditions. Endogenous GH levels increased in the brain and cerebellum (30% and 74%, respectively) of 15-day-old chicken embryos exposed to hypoxia during 24h compared to normoxia. In primary embryonic cerebellar neuron cultures treated under hypoxia (0.5% O(2)) and low glucose (1g/L) conditions (HLG) for 1h, GH levels increased 1.16-fold compared to the control. The addition of 1nM recombinant chicken GH (rcGH) to cultures during HLG increased cell viability (1.7-fold) and the expression of Bcl-2 (1.67-fold); in contrast the caspase-3 activity and the proportion of apoptotic cells decreased (37% and 54.2%, respectively) compared to HLG. rcGH activated the PI3K/Akt pathway both under normoxic and HLG conditions, increasing the proportion of phosphorylated Akt (1.7- and 1.4-fold, respectively). These effects were abolished by wortmannin and by immunoneutralization, indicating that GH acts through this signaling pathway. Furthermore, the 15-kDa GH variant (10nM) significantly increased cell viability and decreased caspase-3 activity during HLG condition. Thus GH may act as a paracrine/autocrine neuroprotective factor that preserves cellular viability and inhibits apoptotic cell death.

Critical role of neuronal pentraxin 1 in mitochondria-mediated hypoxic-ischemic neuronal injury

Developing brain is highly susceptible to hypoxic-ischemic (HI) injury leading to severe neurological disabilities in surviving infants and children. Previously, we have reported induction of neuronal pentraxin 1 (NP1), a novel neuronal protein of long-pentraxin family, following HI neuronal injury. Here, we investigated how this specific signal is propagated to cause the HI neuronal death. We used wild-type (WT) and NP1 knockout (NP1-KO) mouse hippocampal cultures, modeled in vitro following exposure to oxygen glucose deprivation (OGD), and in vivo neonatal (P9-10) mouse model of HI brain injury. Our results show induction of NP1 in primary hippocampal neurons following OGD exposure (4-8 h) and in the ipsilateral hippocampal CA1 and CA3 regions at 24-48 h post-HI compared to the contralateral side. We also found increased PTEN activity concurrent with OGD time-dependent (4-8 h) dephosphorylation of Akt (Ser473) and GSK-3β (Ser9). OGD also caused a time-dependent decrease in the phosphorylation of Bad (Ser136), and Bax protein levels. Immunofluorescence staining and subcellular fractionation analyses revealed increased mitochondrial translocation of Bad and Bax proteins from cytoplasm following OGD (4 h) and simultaneously increased release of Cyt C from mitochondria followed by activation of caspase-3. NP1 protein was immunoprecipitated with Bad and Bax proteins; OGD caused increased interactions of NP1 with Bad and Bax, thereby, facilitating their mitochondrial translocation and dissipation of mitochondrial membrane potential (ΔΨ(m)). This NP1 induction preceded the increased mitochondrial release of cytochrome C (Cyt C) into the cytosol, activation of caspase-3 and OGD time-dependent cell death in WT primary hippocampal neurons. In contrast, in NP1-KO neurons there was no translocation of Bad and Bax from cytosol to the mitochondria, and no evidence of ΔΨ(m) loss, increased Cyt C release and caspase-3 activation following OGD; which resulted in significantly reduced neuronal death. Our results indicate a regulatory role of NP1 in Bad/Bax-dependent mitochondrial release of Cyt C and caspase-3 activation. Together our findings demonstrate a novel mechanism by which NP1 regulates mitochondria-driven hippocampal cell death; suggesting NP1 as a potential therapeutic target against HI brain injury in neonates.

Disruption of raphé serotonergic neural projections to the cortex: a potential pathway contributing to remote loss of brainstem neurons following neonatal hypoxic-ischemic brain injury

Neuronal injury is a key feature of neonatal hypoxic-ischemic (HI) brain injury. However, the mechanisms underpinning neuronal losses, such as in the brainstem, are poorly understood. One possibility is that disrupted neural connections between the cortex and brainstem may compromise the survival of neuronal cell bodies in the brainstem. We investigated whether brainstem raphé serotonergic neurons that project to the cortex are lost after HI. We also tested if neuroinflammation has a role in disrupting brainstem raphé projections. Postnatal day 3 (P3) rats underwent unilateral carotid artery ligation followed by hypoxia (6% oxygen for 30 min). A retrograde tracer, choleratoxin b, was deposited in the motor cortex on P38. On P45 we found that retrogradely labelled neurons in the dorsal raphé dorsal, ventrolateral, interfascicular, caudal and ventral nuclei were lost after P3 HI. All retrogradely labelled neurons in the raphé nuclei were serotonergic. Numbers of retrogradely labelled neurons were also reduced in the ventromedial thalamus and basolateral amygdala. Minocycline treatment (45 mg/kg 2 h post-HI, 22.5 mg/kg daily P4-P9) attenuated losses of retrogradely labelled neurons in the dorsal raphé ventrolateral, interfascicular and ventral raphé nuclei, and the ventromedial thalamus. These results indicate that raphé neurons projecting to the cortex constitute a population of serotonergic neurons that are lost after P3 HI. Furthermore, neuroinflammation has a role in the disruption of raphé and thalamic neural projections. Future studies investigating the cellular mechanisms of axonal degeneration may reveal new targets for interventions to prevent neuronal losses after neonatal HI.

Programmed Necrosis: A Prominent Mechanism of Cell Death following Neonatal Brain Injury

Despite the introduction of therapeutic hypothermia, neonatal hypoxic ischemic (HI) brain injury remains a common cause of developmental disability. Development of rational adjuvant therapies to hypothermia requires understanding of the pathways of cell death and survival modulated by HI. The conceptualization of the apoptosis-necrosis “continuum” in neonatal brain injury predicts mechanistic interactions between cell death and hydrid forms of cell death such as programmed or regulated necrosis. Many of the components of the signaling pathway regulating programmed necrosis have been studied previously in models of neonatal HI. In some of these investigations, they participate as part of the apoptotic pathways demonstrating clear overlap of programmed death pathways. Receptor interacting protein (RIP)-1 is at the crossroads between types of cellular death and survival and RIP-1 kinase activity triggers formation of the necrosome (in complex with RIP-3) leading to programmed necrosis. Neuroprotection afforded by the blockade of RIP-1 kinase following neonatal HI suggests a role for programmed necrosis in the HI injury to the developing brain. Here, we briefly review the state of the knowledge about the mechanisms behind programmed necrosis in neonatal brain injury recognizing that a significant proportion of these data derive from experiments in cultured cell and some from in vivo adult animal models. There are still more questions than answers, yet the fascinating new perspectives provided by the understanding of programmed necrosis in the developing brain may lay the foundation for new therapies for neonatal HI.

Apoptosis-inducing factor downregulation increased neuronal progenitor, but not stem cell, survival in the neonatal hippocampus after cerebral hypoxia-ischemia

BACKGROUND

A considerable proportion of all newly generated cells in the hippocampus will die before becoming fully differentiated, both under normal and pathological circumstances. The caspase-independent apoptosis-inducing factor (AIF) has not been investigated previously in this context.

RESULTS

Postnatal day 8 (P8) harlequin (Hq) mutant mice, expressing lower levels of AIF, and wild type littermates were injected with BrdU once daily for two days to label newborn cells. On P10 mice were subjected to hypoxia-ischemia (HI) and their brains were analyzed 4 h, 24 h or 4 weeks later. Overall tissue loss was 63.5% lower in Hq mice 4 weeks after HI. Short-term survival (4 h and 24 h) of labeled cells in the subgranular zone was neither affected by AIF downregulation, nor by HI. Long-term (4 weeks) survival of undifferentiated, BLBP-positive stem cells was reduced by half after HI, but this was not changed by AIF downregulation. Neurogenesis, however, as judged by BrdU/NeuN double labeling, was reduced by half after HI in wild type mice but preserved in Hq mice, indicating that primarily neural progenitors and neurons were protected. A wave of cell death started early after HI in the innermost layers of the granule cell layer (GCL) and moved outward, such that 24 h after HI dying cells could be detected in the entire GCL.

CONCLUSIONS

These findings demonstrate that AIF downregulation provides not only long-term overall neuroprotection after HI, but also protects neural progenitor cells, thereby rescuing hippocampal neurogenesis.

Disruption of the serotonergic system after neonatal hypoxia-ischemia in a rodent model

Identifying which specific neuronal phenotypes are vulnerable to neonatal hypoxia-ischemia, where in the brain they are damaged, and the mechanisms that produce neuronal losses are critical to determine the anatomical substrates responsible for neurological impairments in hypoxic-ischemic brain-injured neonates. Here we describe our current work investigating how the serotonergic network in the brain is disrupted in a rodent model of preterm hypoxia-ischemia. One week after postnatal day 3 hypoxia-ischemia, losses of serotonergic raphé neurons, reductions in serotonin levels in the brain, and reduced serotonin transporter expression are evident. These changes can be prevented using two anti-inflammatory interventions; the postinsult administration of minocycline or ibuprofen. However, each drug has its own limitations and benefits for use in neonates to stem damage to the serotonergic network after hypoxia-ischemia. By understanding the fundamental mechanisms underpinning hypoxia-ischemia-induced serotonergic damage we will hopefully move closer to developing a successful clinical intervention to treat neonatal brain injury.

Molecular mechanisms of neonatal brain injury

Fetal/neonatal brain injury is an important cause of neurological disability. Hypoxia-ischemia and excitotoxicity are considered important insults, and, in spite of their acute nature, brain injury develops over a protracted time period during the primary, secondary, and tertiary phases. The concept that most of the injury develops with a delay after the insult makes it possible to provide effective neuroprotective treatment after the insult. Indeed, hypothermia applied within 6 hours after birth in neonatal encephalopathy reduces neurological disability in clinical trials. In order to develop the next generation of treatment, we need to know more about the pathophysiological mechanism during the secondary and tertiary phases of injury. We review some of the critical molecular events related to mitochondrial dysfunction and apoptosis during the secondary phase and report some recent evidence that intervention may be feasible also days-weeks after the insult.