Neuropathology of remote hypoxic-ischemic damage in the immature rat

Pretreatment with oleuropein protects the neonatal brain from hypoxia-ischemia by inhibiting apoptosis and neuroinflammation

Hypoxic-ischemic (HI) encephalopathy is a cerebrovascular injury caused by oxygen deprivation to the brain and remains a major cause of neonatal mortality and morbidity worldwide. Therapeutic hypothermia is the current standard of care but it does not provide complete neuroprotection. Our aim was to investigate the neuroprotective effect of oleuropein (Ole) in a neonatal (seven-day-old) mouse model of HI. Ole, a secoiridoid found in olive leaves, has previously shown to reduce damage against cerebral and other ischemia/reperfusion injuries. Here, we administered Ole as a pretreatment prior to HI induction at 20 or 100 mg/kg. A week after HI, Ole significantly reduced the infarct area and the histological damage as well as white matter injury, by preserving myelination, microglial activation and the astroglial reactive response. Twenty-four hours after HI, Ole reduced the overexpression of caspase-3 and the proinflammatory cytokines IL-6 and TNF-α. Moreover, using UPLC-MS/MS we found that maternal supplementation with Ole during pregnancy and/or lactation led to the accumulation of its metabolite hydroxytyrosol in the brains of the offspring. Overall, our results indicate that pretreatment with Ole confers neuroprotection and can prevent HI-induced brain damage by modulating apoptosis and neuroinflammation.

Calcium phosphate formation and deposition in ischemic neurons

Ischemic stroke causes acute brain calcium phosphate (CaP) deposition, a process involving primarily the injured neurons. Whereas the adverse impact of CaP deposition on the brain structure and function has been recognized, the underlying mechanisms remain poorly understood. This investigation demonstrated that the neuron-expressed, plasma membrane-associated Ca2+-binding proteins annexin (Anx) A2, AnxA5, AnxA6, and AnxA7 contributed to neuronal CaP deposition in the mouse model of ischemic stroke. These Anxs were released from the degraded plasma membrane of the ischemic neurons and were able to form Anx/CaP complexes, a nanostructure capable of binding to the β actin filaments via Anx-actin interaction to cause neuronal CaP deposition prior to brain infarction. Anx administration to the healthy mouse brain caused brain CaP deposition and infarction. Monomeric β actin was able to block competitively Anx binding to β actin filaments and prevent ischemic stroke- and Anx administration-induced brain CaP deposition and infarction. Administration of siRNAs specific to the four Anx mRNAs alleviated brain CaP deposition and infarction. These observations support the role of Anxs in CaP formation and deposition in ischemic neurons.

Azithromycin reduces inflammation-amplified hypoxic-ischemic brain injury in neonatal rats

BACKGROUND

Systemic inflammation amplifies neonatal hypoxic-ischemic (HI) brain injury. Azithromycin (AZ), an antibiotic with anti-inflammatory properties, improves sensorimotor function and reduces tissue damage after neonatal rat HI brain injury. The objective of this study was to determine if AZ is neuroprotective in two neonatal rat models of inflammation-amplified HI brain injury.

DESIGN/METHODS

Seven-day-old (P7) rats received injections of toll-like receptor agonists lipopolysaccharide (LPS) or Pam₃Cys-Ser-(Lys)₄ (PAM) prior to right carotid ligation followed by 50 min (LPS + HI) or 60 min (PAM + HI) in 8% oxygen. Outcomes included contralateral forelimb function (forepaw placing; grip strength), survival, %Intact right hemisphere (brain damage), and a composite score incorporating these measures. We compared postnatal day 35 outcomes in controls and groups treated with three or five AZ doses. Then, we compared P21 outcomes when the first (of five) AZ doses were administered 1, 2, or 4 h after HI.

RESULTS

In both LPS + HI and PAM + HI models, AZ improved sensorimotor function, survival, brain tissue preservation, and composite scores. Benefits increased with five- vs. three-dose AZ and declined with longer initiation delay.

CONCLUSIONS

Perinatal systemic infection is a common comorbidity of neonatal asphyxia brain injury and contributes to adverse outcomes. These data support further evaluation of AZ as a candidate treatment for neonatal neuroprotection.

IMPACT

AZ treatment decreases sensorimotor impairment and severity of brain injury, and improves survival, after inflammation-amplified HI brain injury, and this can be achieved even with a 2 h delay in initiation. This neuroprotective benefit is seen in models of inflammation priming by both Gram-negative and Gram-positive infections. This extends our previous findings that AZ treatment is neuroprotective after HI brain injury in neonatal rats.

Regulation of glutamate transport and neuroinflammation in a term newborn rat model of hypoxic–ischaemic brain injury

In the newborn brain, moderate-severe hypoxia–ischaemia induces glutamate excitotoxicity and inflammation, possibly via dysregulation of candidate astrocytic glutamate transporter ( Glt1) and pro-inflammatory cytokines (e.g. Tnfα, Il1β, Il6). Epigenetic mechanisms may mediate dysregulation. Hypotheses: (1) hypoxia–ischaemia dysregulates mRNA expression of these candidate genes; (2) expression changes in Glt1 are mediated by DNA methylation changes; and (3) methylation values in brain and blood are correlated. Seven-day-old rat pups ( n = 42) were assigned to nine groups based on treatment (for each timepoint: naïve ( n = 3), sham ( n = 3), hypoxia–ischaemia ( n = 8) and timepoint for tissue collection (6, 12 and 24 h post-hypoxia). Moderate hypoxic–ischemic brain injury was induced via ligation of the left common carotid artery followed by 100 min hypoxia (8% O2, 36°C). mRNA was quantified in cortex and hippocampus for the candidate genes, myelin ( Mbp), astrocytic ( Gfap) and neuronal ( Map2) markers (qPCR). DNA methylation was measured for Glt1 in cortex and blood (bisulphite pyrosequencing). Hypoxia–ischaemia induced pro-inflammatory cytokine upregulation in both brain regions at 6 h. This was accompanied by gene expression changes potentially indicating onset of astrogliosis and myelin injury. There were no significant changes in expression or promoter DNA methylation of Glt1. This pilot study supports accumulating evidence that hypoxia–ischaemia causes neuroinflammation in the newborn brain and prioritises further expression and DNA methylation analyses focusing on this pathway. Epigenetic blood biomarkers may facilitate identification of high-risk newborns at birth, maximising chances of neuroprotective interventions.

Modulation of behavioral responses and CA1 neuronal death by nitric oxide in the neonatal rat's hypoxia model

INTRODUCTION

Neonatal hypoxia leads to cognitive and movement impairments that might persist throughout life. Hypoxia impairs hippocampal blood circulation and metabolism. The exact mechanisms underlying hypoxia-induced memory impairment are not fully understood. Nitric oxide (NO) is a key neuromodulator that regulates cerebral blood flow. In this study, we aimed to evaluate the possible role of NO on behavioral and histomorphometric changes in the hippocampus following hypoxia in neonate rats.

MATERIAL AND METHODS

Neonate male rats (n = 28) were randomly divided into 4 groups: control, hypoxia, hypoxia plus L-NAME (20 mg/kg), and hypoxia plus L-arginine (200 mg/kg). Drugs were injected intraperitoneally for seven consecutive days. Hypoxia was induced by keeping rats in a hypoxic chamber (7% oxygen and 93% nitrogen intensity). Ten to 14 days after hypoxia, behavioral changes were measured using a shuttle box, a rotarod, and an open field test. The histological changes in the hippocampus were measured using H&E and Nissl staining methods.

RESULTS

Findings showed that hypoxia caused significant atrophy in the hippocampus. Furthermore, the administration of L-NAME decreased the atrophy of the hippocampus in comparison with the hypoxic group. Behavioral results showed that hypoxia impaired memory performance and motor activity responses. Additionally, the administration of L-NAME improved behavioral performance in a significant manner compared with the hypoxic group.

CONCLUSIONS

Hypoxia damaged the neurons of hippocampal CA1 region and induced memory impairment. The NOS inhibitor, L-NAME, significantly attenuated the negative effects of hypoxia on behavior and observed changes in the hippocampus.

Repression of the Glucocorticoid Receptor Increases Hypoxic-Ischemic Brain Injury in the Male Neonatal Rat

Hypoxic-ischemic encephalopathy (HIE) resulting from asphyxia is the most common cause of neonatal brain damage and results in significant neurological sequelae, including cerebral palsy. The current therapeutic interventions are extremely limited in improving neonatal outcomes. The present study tests the hypothesis that the suppression of endogenous glucocorticoid receptors (GRs) in the brain increases hypoxic-ischemic (HI) induced neonatal brain injury and worsens neurobehavioral outcomes through the promotion of increased inflammation. A mild HI treatment of P9 rat pups with ligation of the right common carotid artery followed by the treatment of 8% O₂ for 60 min produced more significant brain injury with larger infarct size in female than male pups. Intracerebroventricular injection of GR siRNAs significantly reduced GR protein and mRNA abundance in the neonatal brain. Knockdown of endogenous brain GRs significantly increased brain infarct size after HI injury in male, but not female, rat pups. Moreover, GR repression resulted in a significant increase in inflammatory cytokines TNF-α and IL-10 at 6 h after HI injury in male pups. Male pups treated with GR siRNAs showed a significantly worsened reflex response and exhibited significant gait disturbances. The present study demonstrates that endogenous brain GRs play an important role in protecting the neonatal brain from HI induced injury in male pups, and suggests a potential role of glucocorticoids in sex differential treatment of HIE in the neonate.

Sustained Release of Dexamethasone from Sulfobutyl Ether β-cyclodextrin Modified Self-Assembling Peptide Nanoscaffolds in a Perinatal Rat Model of Hypoxia-Ischemia

Inflammation plays a critical role in the development of hypoxia-ischemia (HI) induced newborn brain damage. A localized, sustained delivery of dexamethasone (Dex) through an intracerebral injection could reduce the inflammatory response in the injured perinatal brain while avoiding unnecessary side effects. Herein, investigated using anionic sulfobutyl ether β-cyclodextrin (SBE-β-CD) to load Dex in the (RADA)₄ nanofiber networks as a means of reducing the inflammatory response to HI injury is investigated. The ionic interaction between SBE-β-CD and (RADA)₄ dramatically affects nanofiber formation and the stability of the nanoscaffold is highly dependent on the SBE-β-CD/(RADA)₄ ratio. It is observed that the Dex release rate is affected by the concentration of SBE-β-CD and (RADA)₄ peptide. A higher concentration of SBE-β-CD or (RADA)₄ results in a higher drug encapsulation efficiency and slower release rate of Dex. This phenomenon may be related to the structure of fiber bundles. Animal studies show that nanoscaffold loaded with Dex inhibits both microglia activation and glial scar formation compared to controls (Dex alone or nanoscaffold alone) within 2 days of injury. It is thought that this is a step toward building a multifaceted nanoscaffold that can be used to treat HI events in perinates.

Severe Perinatal Hypoxic-Ischemic Brain Injury Induces Long-Term Sensorimotor Deficits, Anxiety-Like Behaviors and Cognitive Impairment in a Sex-, Age- and Task-Selective Manner in C57BL/6 Mice but Can Be Modulated by Neonatal Handling

Perinatal brain injury (PBI) leads to neurological disabilities throughout life, from motor deficits, cognitive limitations to severe cerebral palsy. Yet, perinatal brain damage has limited therapeutic outcomes. Besides, the immature brain of premature children is at increased risk of hypoxic/ischemic (HI) injury, with males being more susceptible to it and less responsive to protective/therapeutical interventions. Here, we model in male and female C57BL/6 mice, the impact of neonatal HI and the protective effects of neonatal handling (NH), an early life tactile and proprioceptive sensory stimulation. From postnatal day 1 (PND1, modeling pre-term) to PND21 randomized litters received either NH or left undisturbed. HI brain damage occurred by permanent left carotid occlusion followed by hypoxia at PND7 (modeling full-term) in half of the animals. The behavioral and functional screening of the pups at weaning (PND23) and their long-term outcomes (adulthood, PND70) were evaluated in a longitudinal study, as follows: somatic development (weight), sensorimotor functions (reflexes, rods and hanger tests), exploration [activity (ACT) and open-field (OF) test], emotional and anxiety-like behaviors [corner, open-field and dark-light box (DLB) tests], learning and memory [T-maze (TM) and Morris Water-Maze (MWM)]. HI induced similar brain damage in both sexes but affected motor development, sensorimotor functions, induced hyperactivity at weaning, and anxiety-like behaviors and cognitive deficits at adulthood, in a sex- and age-dependent manner. Thus, during ontogeny, HI affected equilibrium especially in females and prehensility in males, but only reflexes at adulthood. Hyperactivity of HI males was normalized at adulthood. HI increased neophobia and other anxiety-like behaviors in males but emotionality in females. Both sexes showed worse short/long-term learning, but memory was more affected in males. Striking neuroprotective effects of NH were found, with significantly lower injury scores, mostly in HI males. At the functional level, NH reversed the impaired reflex responses and improved memory performances in hippocampal-dependent spatial-learning tasks, especially in males. Finally, neuropathological correlates referred to atrophy, neuronal densities and cellularity in the affected areas [hippocampal-CA, caudate/putamen, thalamus, neocortex and corpus callosum (CC)] point out distinct neuronal substrates underlying the sex- and age- functional impacts of these risk/protection interventions on sensorimotor, behavioral and cognitive outcomes from ontogeny to adulthood.

Adverse neuropsychiatric development following perinatal brain injury: from a preclinical perspective

Perinatal brain injury is a leading cause of death and disability in young children. Recent advances in obstetrics, reproductive medicine and neonatal intensive care have resulted in significantly higher survival rates of preterm or sick born neonates, at the price of increased prevalence of neurological, behavioural and psychiatric problems in later life. Therefore, the current focus of experimental research shifts from immediate injury processes to the consequences for brain function in later life. The aetiology of perinatal brain injury is multi-factorial involving maternal and also labour-associated factors, including not only placental insufficiency and hypoxia-ischaemia but also exposure to high oxygen concentrations, maternal infection yielding excess inflammation, genetic factors and stress as important players, all of them associated with adverse long-term neurological outcome. Several animal models addressing these noxious stimuli have been established in the past to unravel the underlying molecular and cellular mechanisms of altered brain development. In spite of substantial efforts to investigate short-term consequences, preclinical evaluation of the long-term sequelae for the development of cognitive and neuropsychiatric disorders have rarely been addressed. This review will summarise and discuss not only current evidence but also requirements for experimental research providing a causal link between insults to the developing brain and long-lasting neurodevelopmental disorders.

Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges

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

Expression and localization of Inter-alpha Inhibitors in rodent brain

Inter-alpha Inhibitor Proteins (IAIPs) are a family of related serine protease inhibitors. IAIPs are important components of the systemic innate immune system. We have identified endogenous IAIPs in the central nervous system (CNS) of sheep during development and shown that treatment with IAIPs reduces neuronal cell death and improves behavioral outcomes in neonatal rats after hypoxic-ischemic brain injury. The presence of IAIPs in CNS along with their exogenous neuroprotective properties suggests that endogenous IAIPs could be part of the innate immune system in CNS. The purpose of this study was to characterize expression and localization of IAIPs in CNS. We examined cellular expressions of IAIPs in vitro in cultured cortical mouse neurons, in cultured rat neurons, microglia, and astrocytes, and in vivo on brain sections by immunohistochemistry from embryonic (E) day 18 mice and postnatal (P) day 10 rats. Cultured cortical mouse neurons expressed the light chain gene Ambp and heavy chain genes Itih-1, 2, 3, 4, and 5 mRNA transcripts and IAIP proteins. IAIP proteins were detected by immunohistochemistry in cultured cells as well as brain sections from E18 mice and P10 rats. Immunoreactivity was found in neurons, microglia, astrocytes and oligodendroglia in multiple brain regions including cortex and hippocampus, as well as within both the ependyma and choroid plexus. Our findings suggest that IAIPs are endogenous proteins expressed in a wide variety of cell types and regions both in vitro and in vivo in rodent CNS. We speculate that endogenous IAIPs may represent endogenous neuroprotective immunomodulatory proteins within the CNS.

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.

Antioxidant Treatments Recover the Alteration of Auditory-Evoked Potentials and Reduce Morphological Damage in the Inferior Colliculus after Perinatal Asphyxia in Rat

Maturation of the auditory pathway is dependent on the central nervous system myelination and it can be affected by pathologies such as neonatal hypoxic ischemic (HI) encephalopathy. Our aim was to evaluate the functional integrity of the auditory pathway and to visualize, by histological and cellular methods, the damage to the brainstem using a neonatal rat model of HI brain injury. To carry out this morphofunctional evaluation, we studied the effects of the administration of the antioxidants nicotine, melatonin, resveratrol and docosahexaenoic acid after hypoxia-ischemia on the inferior colliculus and the auditory pathway. We found that the integrity of the auditory pathway in the brainstem was altered as a consequence of the HI insult. Thus, the auditory brainstem response (ABR) showed increased I-V and III-V wave latencies. At a histological level, HI altered the morphology of the inferior colliculus neurons, astrocytes and oligodendricytes, and at a molecular level, the mitochondria membrane potential and integrity was altered during the first hours after the HI and reactive oxygen species (ROS) activity is increased 12 h after the injury in the brainstem. Following antioxidant treatment, ABR interpeak latency intervals were restored and the body and brain weight was recovered as well as the morphology of the inferior colliculus that was similar to the control group. Our results support the hypothesis that antioxidant treatments have a protective effect on the functional changes of the auditory pathway and on the morphological damage which occurs after HI insult.

Spatial working memory deficits in male rats following neonatal hypoxic ischemic brain injury can be attenuated by task modifications

Hypoxia-ischemia (HI; reduction in blood/oxygen supply) is common in infants with serious birth complications, such as prolonged labor and cord prolapse, as well as in infants born prematurely (<37 weeks gestational age; GA). Most often, HI can lead to brain injury in the form of cortical and subcortical damage, as well as later cognitive/behavioral deficits. A common domain of impairment is working memory, which can be associated with heightened incidence of developmental disorders. To further characterize these clinical issues, the current investigation describes data from a rodent model of HI induced on postnatal (P)7, an age comparable to a term (GA 36–38) human. Specifically, we sought to assess working memory using an eight-arm radial water maze paradigm. Study 1 used a modified version of the paradigm, which requires a step-wise change in spatial memory via progressively more difficult tasks, as well as multiple daily trials for extra learning opportunity. Results were surprising and revealed a small HI deficit only for the final and most difficult condition, when a delay before test trial was introduced. Study 2 again used the modified radial arm maze, but presented the most difficult condition from the start, and only one daily test trial. Here, results were expected and revealed a robust and consistent HI deficit across all weeks. Combined results indicate that male HI rats can learn a difficult spatial working memory task if it is presented in a graded multi-trial format, but performance is poor and does not appear to remediate if the task is presented with high initial memory demand. Male HI rats in both studies displayed impulsive characteristics throughout testing evidenced as reduced choice latencies despite more errors. This aspect of behavioral results is consistent with impulsiveness as a core symptom of ADHD—a diagnosis common in children with HI insult. Overall findings suggest that task specific behavioral modifications are crucial to accommodating memory deficits in children suffering from cognitive impairments following neonatal HI.

Fetal hypoxia increases vulnerability of hypoxic-ischemic brain injury in neonatal rats: role of glucocorticoid receptors

Gestational hypoxia is a common stress to the fetal development and increases the risk of neonatal morbidity. The present study tested the hypothesis that fetal hypoxia results in heightened brain vulnerability to hypoxic-ischemic (HI) injury in neonatal rats via down-regulation of glucocorticoid receptor (GR) in the developing brain. Time-dated pregnant rats were exposed to hypoxia (10.5% O2) from days 15 to 21 of gestation. Brain HI injury was determined in day 10 pups. Maternal hypoxia resulted in asymmetric intrauterine growth restriction in the fetus. The brain HI injury was significantly increased in maternal hypoxia-treated pups as compared with the normoxia control in both males and females. Activation of brain GR by dexamethasone injection into the right lateral ventricle produced a concentration-dependent reduction of HI-induced brain injury in control pups. Maternal hypoxia significantly decreased GR mRNA and protein abundance in the fetal brain and neonatal hippocampus and abolished the dexamethasone-mediated neuroprotective effect in pup brains. This decreased GR expression was resulted from increased DNA methylation, decreased binding of transcription factors Egr-1 and Sp1 to GR gene exon 17 and 111 promoters, and reduced expression of GR exon 17 and 111 mRNA variants. The results demonstrate that gestational hypoxia causes epigenetic repression of GR gene expression in the developing brain resulting in the heightened brain vulnerability to HI injury in neonatal rats.

Sex differences in behavioral outcome following neonatal hypoxia ischemia: insights from a clinical meta-analysis and a rodent model of induced hypoxic ischemic brain injury

Hypoxia ischemia (HI; reduced oxygen and/or blood flow to the brain) is one of the most common injuries among preterm infants and term infants with birth complications. Both populations show cognitive/behavioral deficits, including impairments in sensory, learning/memory, and attention domains. Clinical data suggests a sex difference in HI outcomes, with males exhibiting more severe cognitive/behavioral deficits relative to matched females. Our laboratory has also reported more severe behavioral deficits among male rats with induced HI relative to females with comparable injury (Hill et al., 2011a,b). The current study initially examined published clinical studies from the past 20years where long-term IQ outcome scores for matched groups of male and female premature infants were reported separately (IQ being the most common outcome measure). A meta-analysis revealed a female "advantage," as indicated by significantly better scores on performance and full scale IQ (but not verbal IQ) for premature females. We then utilized a rodent model of neonatal HI injury to assess sham and postnatal day 7 (P7) HI male and female rats on a battery of behavioral tasks. Results showed expected deficits in HI male rats, but also showed task-dependent sex differences, with HI males having significantly larger deficits than HI females on some tasks but equivalent deficits on other tasks. In contrast to behavioral results, post mortem neuropathology associated with HI was comparable across sex. These findings suggest: 1) neonatal female "protection" in some behavioral domains, as indexed by superior outcome following early injury relative to males; and 2) female protection may entail sex-specific plasticity or compensation, rather than a reduction in gross neuropathology. Further exploration of the mechanisms underlying this sex effect could aid in neuroprotection efforts for at-risk neonates in general, and males in particular. Moreover, our current report of comparable anatomical damage coupled with differences in cognitive outcomes (by sex) provides a framework for future studies to examine neural mechanisms underlying sex differences in cognition and behavior in general.

Hypothermia is not neuroprotective after infection-sensitized neonatal hypoxic-ischemic brain injury

BACKGROUND

Therapeutic hypothermia (HT) is the standard treatment after perinatal hypoxic-ischemic (HI) injury. Infection increases vulnerability to HI injury, but the effect of HT on lipopolysaccharide (LPS) sensitized HI brain injury is unknown.

DESIGN/METHODS

P7 rat pups were injected either with vehicle or LPS, and after a 4h delay they were exposed to left carotid ligation followed by global hypoxia inducing a unilateral stroke-like HI injury. Pups were randomized to the following treatments: (1) vehicle treated HI-pups receiving normothermia treatment (NT) (Veh-NT; n=30); (2) LPS treated HI-pups receiving NT treatment (LPS-NT; n=35); (3) vehicle treated HI-pups receiving HT treatment (Veh-HT; n=29); or (4) LPS treated HI-pups receiving HT treatment (LPS-HT; n=46). Relative area loss of the left/right hemisphere and the areas of hippocampi were measured at P14.

RESULTS

Mean brain area loss in the Veh-NT group was 11.2±14%. The brain area loss in LPS-NT pups was 29.8±17%, which was significantly higher than in the Veh-NT group (p=0.002). The Veh-HT group had a significantly smaller brain area loss (5.4±6%), when compared to Veh-NT group (p=0.043). The LPS-HT group showed a brain area loss of 32.5±16%, which was significantly higher than in the Veh-HT group (p<0.001). LPS-HT group also had significantly smaller size of the left hippocampus, which was not found in other groups. LPS-sensitization significantly decreased the sizes of the right, unligated-hemispheres, independent of post-HI treatment.

CONCLUSIONS

Therapeutic hypothermia is not neuroprotective in this LPS-sensitized unilateral stroke-like HI brain injury model in newborn rats. Lack of neuroprotection was particularly seen in the hippocampus. Pre-insult exposure to LPS also induced brain area loss in the unligated hemisphere, which is normally not affected in this model.

Evaluation of inhaled .NO in a model of rat neonate brain injury caused by hypoxia-ischaemia

OBJECTIVES

Inhaled NO (INO), at 5-40 parts per million (ppm) in the air, is indicated for treating neonatal hypoxic respiratory failure. Whether these doses of INO are protective or toxic towards brain was here evaluated in laboratory animals.

METHODS

In rat neonates (postnatal day 7), a brain injury based on permanent right carotid artery occlusion plus transient (90 min) respiratory hypoxia (8% O(2)) was challenged by two NO dosages (10 and 40 ppm) given either before, during or after transient hypoxia. Three weeks later, animal brains were studied for the loss of cerebral matter (infarct or atrophy).

RESULTS

In right hemispheres, significant increases (26-39%) in lesion sizes were induced by 40 and not 10 ppm INO, whatever the inhalation period. The two doses reduced significantly the left hemisphere volume only when NO was inhaled at the re-oxygenation period.

DISCUSSION

Our results suggest that high doses of INO, brain damaging events and inhalation at re-oxygenation might affect brain integrity when these conditions are cumulated. However, the clinical relevance of this (infarct or atrophy) and previously described (haematomas) brain toxicity associated with INO remains to be clarified in the human neonates, for instance through non-invasive cerebral imagery follow-up of patients given INO.

Cerebral heme oxygenase 1 and 2 spatial distribution is modulated following injury from hypoxia-ischemia and middle cerebral artery occlusion in rats

The regional and cellular distribution of heme oxygenase (HO)-1 and -2 following cerebral ischemia has not been ascertained. Employing the transient middle cerebral artery occlusion (MCAO) and hypoxia-ischemia (HI) models of unilateral brain injury, the aim was to elucidate immunolocalization of HO-1 and HO-2. Animals were sacrificed 3 days post-ischemia and immunohistochemistry and Western blotting were utilized to determine HO-1 and HO-2 expression. In the ipsilateral hemisphere following HI, HO-1 immunoreactivity was significantly upregulated in many neuronal and glial populations (including the cortex, hippocampus and thalamus). HO-1 was also detected in macrophages/microglia within the infarct. In addition to widespread neuronal HO-2 labelling, HO-2 was also expressed in vascular endothelial cells. Inflammatory cells within the infarct of MCAO and HI animals were surprisingly immunoreactive for HO-2, but only HI animals had significantly elevated HO-2 protein expression in the ipsilateral hemisphere. This may be due to the presence of global hypoxia in the HI model which can upregulate vascular endothelial growth factor and subsequent proliferation of endothelial cells. This report of HO-2 protein expression upregulation following HI coupled with an increase in HO-1 immunoreactivity suggests that this response may be implicated in reducing cell death or repairing damage induced by cerebral ischemia.

Animal models of perinatal hypoxic-ischemic brain damage

Animal models are often presumably the first step in determining mechanisms underlying disease, and the approach and effectiveness of therapeutic interventions. Perinatal brain damage, however, evolves over months of gestation, during the rapid maturation of the fetal and newborn brain. Despite marked advances in our understanding of these processes and technologic advances providing an improved window on the timing and duration of injury, neonatal brain injury remains a "moving target" regarding our ability to "mimic" its processes in an animal model. Moreover, interfering with normal processes of development as part of a therapeutic intervention may do "more harm than good." Hence, controversy continues over which animal model can reflect human disease states. Numerous models have provided information regarding the pathophysiology of brain damage in term and preterm infants. Our challenges consist of identifying infants at greatest risk for permanent injury, identifying the timing of injury, and adapting therapies that provide more benefit than harm. A combination of appropriately suitable animal models to conduct these studies will bring us closer to understanding human perinatal damage and the means to treat it.

Neonatal rat hypoxia-ischemia: Effect of the anti-oxidant mitoquinol, and S-PBN

BACKGROUND

The production of oxygen free radicals after perinatal hypoxia-ischemia is thought to play a critical role in the pathogenesis of the brain injury. Administration of anti-oxidants may thus be neuroprotective. The aim of the present study was to investigate the effect of a mitochondria-targeted anti-oxidant mitoquinol (mitoQ) administered in the form of the prodrug mitoquinone, and an extracellular anti-oxidant N-tert-butyl-(2-sulfophenyl)-nitrone (S-PBN; Aldrich, St Louis, MO, USA), on neuronal survival in the rat striatum after acute perinatal hypoxia-ischemia.

METHODS

Mitoquinone at 17 micromol/L (n = 6) or 51 micromol/L (n = 6), or its diluent (n = 12), was continuously infused over 3 days into the right striatum of Sprague-Dawley rats. Infusion was via an Alzet micro-osmotic pump (Alza, Los Angeles, CA, USA), stereotaxically implanted on postnatal day (PN) 7 under anesthesia. In another experiment, S-PBN (100 mg/kg) (n = 8) or its diluent (n = 8) was administered in six s.c. injections every 12 h from the evening of PN7. Hypoxia-ischemia was induced on PN8 by right common carotid artery ligation under anesthesia, followed 2.5 h later by exposure to 8% oxygen for 1.5 h. On PN14 the pups were euthanased and 40 microm serial sections were cut through the entire striatum. The total number of medium-spiny neurons within the right striatum was stereologically determined using the optical disector/Cavalieri method.

RESULTS

No significant difference was seen in the total number of striatal medium-spiny neurons between the 17 micromol/L or 51 micromol/L mitoQ-treated pups and their respective diluent-treated controls. No significant difference was seen in the total number of striatal medium-spiny neurons between the S-PBN-treated and diluent-treated pups.

CONCLUSION

Solely targeting mitochondrial oxidants with mitoQ, or extracellular oxidants with S-PBN, is not protective for striatal medium-spiny neurons after perinatal hypoxia-ischemia.

Experimental models of hypoxic-ischemic encephalopathy: hypoxia-ischemia in the immature rat

The development of experimental models to study the mechanisms of perinatal hypoxic-ischemic encephalopathy and stroke and effective therapies represents an important goal in perinatal medicine. However, due to the complexity of this pathological condition in humans, to date there is no ideal animal model that completely reproduces this condition. This unit describes the most widely used rodent animal model for the study of hypoxic-ischemic encephalopathy during development. The model consists of 7-day-old pup rats subjected to unilateral carotid artery ligation followed by timed hypoxia exposure, and incorporates both focal cerebral ischemia and reperfusion. Its strength lies in the relative ease of the surgical procedure, the low mortality rate, and the possibility of performing long-term experiments, a necessity for preclinical therapeutic trials. Over the years, this model has been extensively characterized, and most information on the mechanisms responsible for neurodegeneration and possible therapeutic approaches following hypoxia-ischemia during brain development derives from studies performed using this model.

Myelin expression is altered in the brains of neonatal rats reared in a fluctuating oxygen atmosphere

BACKGROUND

Preterm infants receiving supplemental oxygen therapy experience frequent fluctuations in their blood oxygen levels, the magnitude of which has been associated with the incidence and severity of retinopathy of prematurity in such infants.

OBJECTIVE

Our objective was to investigate in a relevant animal model whether the immature brain with its poorly vascularised white matter might also be susceptible to injury when exposed to such fluctuations in blood oxygen.

METHODS

Newborn rats were reared in an atmosphere in which a computer reproduced the oxygen fluctuations derived from the transcutaneous oxygen levels of a 24-week preterm infant who had developed severe retinopathy. Following 14 days of exposure, we measured the expression of active caspase-3, myelin basic protein (MBP) and glial fibrillary acidic protein (GFAP) in the brains comparing with rat pups raised in room air.

RESULTS

Compared to room air controls, at day 14, the expression of active caspase-3 was increased by up to 162% (significant increase in 7 of 9 regions), MBP decreased by up to 70% (significant in the hypothalamus only) and GFAP increased by up to 103% (significant in 6 of 7 regions. On day 21, following 7 days of reparative recovery, GFAP levels in most areas of oxygen-exposed brains had returned to near control levels. There were no longer significant differences in caspase-3 levels apart from the cerebral cortex, cerebellum and striatum. In contrast, MBP expression was now much higher in most regions of the treated brains compared to controls.

CONCLUSION

We conclude that fluctuations in blood oxygen, observed in preterm survivors, may constitute a source of injury to the white matter and corpus striatum of the developing brain and contribute to the neurological sequelae in extremely premature infants.

Neuropathogical features of a rat model for perinatal hypoxic-ischemic encephalopathy with associated epilepsy

Hypoxic-ischemic (HI) encephalopathy is an important neurological problem of the perinatal period. Little is known of the long-term progression of HI insults or the maladaptive changes that lead to epilepsy. Using rats with unilateral carotid occlusion followed by hypoxia at postnatal day 7, this study provides an initial analysis of the epilepsy caused by a perinatal HI insult with chronic and continuous behavioral monitoring. The histopathology was investigated at postnatal day 30 and later at > or =6 months of age using cresyl violet, Timm, and rapid Golgi staining and immunocytochemistry. The resultant epilepsy showed an increase in seizure frequency over time, with a preponderance for seizure clusters and behavioral features of an ipsilateral cerebral syndrome. In addition to parasagittal infarcts and porencephalic cysts in severe lesions, columnar neuronal death was found with cytomegaly in isolated groups of dysmorphic cortical neurons. Cortical dysgenesis was seen in the form of deep laminar cell loss, microgyri, white matter hypercellularity, and blurring of the white and gray matter junction. Mossy fiber sprouting was not only detected in the atrophied ipsilateral dorsal hippocampus of HI rats with chronic epilepsy, but was also found in comparable grades in spared ipsi- and contralateral ventral hippocampi. The cortical lesions in this animal model show histological similarities with those found in humans after perinatal HI. The occurrence of cortical abnormalities that are associated with epilepsy in humans correlates with the consequent detection of spontaneous recurrent seizures.

Gap junctional intercellular communication in hypoxia-ischemia-induced neuronal injury

Brain hypoxia-ischemia is a relatively common and serious problem in neonates and in adults. Its consequences include long-term histological and behavioral changes and reduction in seizure threshold. Gap junction intercellular communication is pivotal in the spread of hypoxia-ischemia related injury and in mediating its long-term effects. This review provides a comprehensive and critical review of hypoxia-ischemia and hypoxia in the brain and the potential role of gap junctions in the spread of the neuronal injury induced by these insults. It also presents the effects of hypoxia-ischemia and of hypoxia on the state of gap junctions in vitro and in vivo. Understanding the mechanisms involved in gap junction-mediated neuronal injury due to hypoxia will lead to the development of novel therapeutic strategies.

Auditory processing and learning/memory following erythropoietin administration in neonatally hypoxic–ischemic injured rats

BACKGROUND

Hypoxia-ischemia (HI) is a common injury arising from prematurity/complications at birth and is associated with later language, auditory, and learning impairments.

OBJECTIVE

To investigate the efficacy of two doses (300 or 1000 U/kg) of Erythropoietin (Epo) in protecting against neuropathological and behavioral impairments associated with HI injury in rats.

METHODS

HI injury (right carotid artery cauterization and 120 min of 8% O(2)) was induced on postnatal day 7 (P7) and Epo or saline was administered i.p. immediately following the procedure. Auditory processing and learning/memory were assessed throughout development.

RESULTS

Both doses of Epo provided behavioral protection following HI injury. Rats given 300 or 1000 U/kg of Epo performed significantly better than HI animals on a short duration complex auditory processing procedure, on a spatial Morris water maze assessing spatial learning/reference memory, and a non-spatial water maze assessing associative learning/reference memory.

CONCLUSIONS

Given Epo's extant clinical use (FDA approved for pediatric patients with anemia secondary to prematurity), the current results add to a growing body of literature supporting the use of Epo as a potential protective agent for neurological and behavioral impairments following early HI injury in infants.

Brief update on animal models of hypoxic-ischemic encephalopathy and neonatal stroke

The discovery of safe and effective therapies for perinatal hypoxia ischemia (HI) and stroke remains an unmet goal of neonatal-perinatal medicine. Because of the many developmental and functional differences between the neonatal brain and the adult brain, the ability to extrapolate adult data to the neonatal condition is very limited. For this reason, it is incumbent on scientists in the field of neonatal brain injury to address the questions of therapeutic efficacy of an array of potential therapies in a developmentally appropriate model. Toward that end, a number of new models of neonatal HI and stroke have been introduced recently. Additionally, some of the established models have been adapted to different species and different ages, giving scientists a greater choice of models for the study of neonatal HI and stroke. Many of these models are now also being used for functional and behavioral testing, an absolute necessity for preclinical therapeutic trials. This review focuses primarily on the newly developed models, recent adaptations to established models, and the studies of functional outcome that have been published since 2000.

Rapid auditory processing and learning deficits in rats with P1 versus P7 neonatal hypoxic-ischemic injury

Hypoxia-ischemia (HI) is associated with premature birth, and injury during term birth. Many infants experiencing HI later show disruptions of language, with research suggesting that rapid auditory processing (RAP) deficits (i.e., impairment in the ability to discriminate rapidly changing acoustic signals), play a causal role in language problems. We recently bridged these lines of research by showing RAP deficits in rats with unilateral-HI injury induced on postnatal days 1, 7, or 10 (P1, P7, or P10. While robust RAP deficits were found in HI animals, it was suggested that our within-age sample size did not provide sufficient power to detect age-at-injury differences within the pooled HI group. The current study sought to examine differences in neuropathology and behavior following unilateral-HI injury on P1 versus P7 in rats. Ages chosen for HI induction reflect differential stages of neurodevelopmental maturity, and subsequent regional differences in vulnerability to reduced blood flow/oxygen (modeling age-related differences in premature/term HI injury). Results showed that during the juvenile period, both P1 and P7 HI groups exhibited significant RAP deficits, but deficits in the P1 HI group resolved with repeated testing (compared to shams), while P7 HI animals showed lasting deficits in RAP and spatial learning/memory through adulthood. The current findings are in accord with evidence that HI injury during different stages of developmental maturity (age-at-injury) leads to differential neuropathologies, and provide the novel observation that in rats, P1 versus P7 induced pathologies are associated with different patterns of auditory processing and learning/memory deficits across the lifespan.

Glial activation in white matter following ischemia in the neonatal P7 rat brain

This study examines cell death and proliferation in the white matter after neonatal stroke. In postnatal day 7 injured rat, there was a marked reduction in myelin basic protein (MBP) immunostaining mainly corresponding to numerous pyknotic immature oligodendrocytes and TUNEL-positive astrocytes in the ipsilateral external capsule. In contrast, a substantial restoration of MBP, as indicated by the MBP ratio of left-to-right, occurred in the cingulum at 48 (1.27 +/- 0.12) and 72 (1.30 +/- 0.18, P < 0.05) h of recovery as compared to age-matched controls (1.03 +/- 0.14). Ki-67 immunostaining revealed a first peak of newly generated cells in the dorsolateral hippocampal subventricular zone and cingulum at 72 h after reperfusion. Double immunofluorescence revealed that most of the Ki-67-positive cells were astrocytes at 48 h and NG2 pre-oligodendrocytes at 72 h of recovery. Microglia infiltration occurs over several days in the cingulum, and a huge quantity of macrophages reached the subcortical white matter where they engulfed immature oligodendrocytes. The overall results suggest that the persistent activation of microglia involves a chronic component of immunoinflammation, which overwhelms repair processes and contributes to cystic growth in the developing brain.

Resuscitative hypothermia protects the neonatal rat brain from hypoxic-ischemic injury

The effect of 24 h of hypothermic recovery on moderate hypoxic-ischemic brain damage in P7-rats was investigated for 42 d after the insult, using magnetic resonance and histopathology. Occlusion of right common carotid artery and 90 min exposure to 8% O2 at 37 degrees C body temperature produced cytotoxic edema of 51(+/-11)% brain volume (BV) and depression of brain energy metabolism (PCr/Pi) from 1.43(+/-0.21) to 0.14(+/-0.11). During recovery, the body temperature was reduced to 30 degrees C for 24 h in 36 animals, but was kept at 37 degrees C in 34 animals. The edema waned upon reoxygenation leaving only the core lesion at 2 h, but reappeared reaching a maximal extent of 11+/-8% BV under hypothermia compared to 45(+/-10)% under normothermia at around 24 h. PCr/Pi recovered transiently within 13 h and declined again to 1.07(+/-0.19) under hypothermia and to 0.48(+/-0.22) under normothermia at around 24 h. Hypothermia led to significant long term brain protection, leaving permanent tissue damage of 12(+/-6)% BV compared to 35(+/-12)% BV under normothermia. However, animals with severe initial injury developed large infarctions, despite hypothermic treatment. Even then, the time to develop infarction was significantly prolonged, leaving the opportunity for additional therapeutic intervention.

Hypoxia/ischemia expands the regenerative capacity of progenitors in the perinatal subventricular zone

Neurons and oligodendrocyte progenitors are highly sensitive to perinatal hypoxic-ischemic injury. As accumulating evidence suggests that many insults to the human infant occur in utero, and preventing brain damage to infants in utero will prove difficult, there is strong rationale to pursue regenerative strategies to reduce the morbidity associated with developmental brain injuries. The purpose of this study was to determine whether a hypoxic-ischemic insult stimulates the neural stem/progenitor cells in the subventricular zone to generate new neurons and oligodendrocytes. Hypoxia-ischemia was induced using the Vannucci rat model on postnatal day-6 pups. Injections of 5'-bromo-2'-deoxyuridine to label cells undergoing DNA synthesis after hypoxia-ischemia revealed that there is a robust proliferative response within the subventricular zone of the injured hemisphere that continues for at least 1 week after the hypoxic-ischemic episode. Using the neurosphere assay to quantify the number of neural stem/progenitor cells in the subventricular zone, we find that there are twice as many neural stem/progenitor cells in the affected dorsolateral subventricular zone at 1 week of recovery and that these cells generate larger spheres in response to growth factors compared with controls. Precursors from the injured hemisphere generate three times as many neurons in vitro and more than twice as many oligodendroglia compared with controls. Hypoxia-ischemia also increases neurogenesis in vivo. Doublecortin positive cells with migratory profiles were observed streaming from the ipsilateral subventricular zone to the striatum and neocortex, whereas, few doublecortin positive cells were found in the contralateral hemisphere after hypoxia-ischemia. These observations provide evidence that the somatic neural progenitors of the subventricular zone participate in the production of new brain cells lost after hypoxia-ischemia.

Effect of the mitochondrial antioxidant, Mito Vitamin E, on hypoxic-ischemic striatal injury in neonatal rats: a dose-response and stereological study

A mitochondria-targeted antioxidant, Mito Vitamin E (MitoVit E), has previously been shown to prevent mitochondrial oxidative damage. The aim of this study was to investigate the effect of MitoVit E on neuronal survival in the rat striatum after acute perinatal hypoxia-ischemia. Continuous striatal infusion with 4.35 microM, 43.5 microM, or 148 microM of MitoVit E before, during, and after hypoxia-ischemia was not neuroprotective for striatal medium-spiny neurons. Pre- or posttreatment with 435 microM MitoVit E was neurotoxic. These results suggest that MitoVit E is not significantly neuroprotective for striatal medium-spiny neurons after acute perinatal hypoxic-ischemic brain injury. The results also suggest that mitochondrial oxidative damage does not contribute significantly to the death of striatal medium-spiny neurons after perinatal hypoxia-ischemia.

Evaluation of neuronal damage following hypoxic–ischaemic brain injury in acute and early chronic periods in neonatal rats

This study was undertaken to investigate the effects of neonatal cerebral hypoxic-ischaemic brain injury (HIBI) in acute and early chronic phases in the rat. HIBI was induced in 7-day-old rat pups by ligation of the right common carotid and then the pups were exposed to 1 h of hypoxia in 8% oxygen. They were divided into two groups: 1-day (acute phase, in the first 24 h) and 5-day (early chronic phase, 120 h). Neuropathological evaluation was performed using the hippocampus, cerebral cortex and basal ganglia on the coronal plane. The following values were obtained: (i) the ratio of the infarcted area; (ii) hemispheric atrophy/asymmetry; (iii) patchy lesions confined to the thalamus, caudate and putamen; (iv) the ratio of damaged neurons to all neurons; and (v) the percentage of apoptotic neurons relative to the total neurons in all brain areas. HIBI-induced global cerebral damage and cellular damage findings did not significantly differ between the two groups. However, they showed a tendency to recover/deteriorate in both acute and early chronic phases. The ratio of ipsi- and contra-lateral hemisphere infarct areas (20.7 and 15.7% vs. 40.1 and 26.7%, respectively), basal ganglia patchy lesion ratio (27.5 vs. 36.7%) and hemispheric atrophy/asymmetry (92.4 vs. 84.7%) were found to be lower in the rat pups in the chronic phase than those in the acute phase. In contrast, increases in the ratio of damaged neurons (16.7 vs. 13.3% in the cerebral and dorsal hippocampus, respectively) and in the ratio of apoptotic neurons (ipsi-lateral: 18 vs. 6%; contra lateral hemispheres: 3.5 vs. 1.7%, respectively) were recorded. It is concluded that cellular damage tends to deteriorate (damaged and apoptotic neurons) while global damage (cerebral infarct and patchy damage) improves with the progression of HIBI. However, further studies are needed in order to elucidate this process.

Apoptosis in perinatal hypoxic-ischemic brain injury: how important is it and should it be inhibited?

The discovery of safe and effective therapies for perinatal hypoxia-ischemia (HI) and stroke remains an unmet goal of perinatal medicine. Hypothermia and antioxidants such as allopurinol are currently under investigation as treatments for neonatal HI. Drugs targeting apoptotic mechanisms are currently being studied in adult diseases such as cancer, stroke, and trauma and have been proposed as potential therapies for perinatal HI and stroke. Before developing antiapoptosis therapies for perinatal brain injury, we must determine whether this form of cell death plays an important role in these injuries and if the inhibition of these pathways promotes more benefit than harm. This review summarizes current evidence for apoptotic mechanisms in perinatal brain injury and addresses issues pertinent to the development of antiapoptosis therapies for perinatal HI and stroke.

Glycolysis and perinatal hypoxic-ischemic brain damage

To ascertain the regulation of glycolysis during perinatal hypoxia-ischemia, 7-day postnatal rats were subjected to unilateral common carotid artery ligation followed by hypoxia with 8% oxygen for up to 90 min. Brain concentrations of glucose, lactate, and key glycolytic intermediates were determined at specific intervals of hypoxia. During hypoxia-ischemia, anaerobic glycolysis increased to approximately 62% of its maximal capacity, which equates to a 135% stimulation of the glycolytic flux. The key regulatory enzymes, hexokinase, phosphofructokinase and pyruvate kinase, were all stimulated during hypoxia-ischemia, and there were no enzymatic rate limitations. The major rate-limiting step for glycolysis was the transport of glucose across the blood-brain barrier into the brain.

Neonatal cerebral hypoxia-ischemia: involvement of FAK-dependent pathway

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase thought to play a major role in transducing extracellular matrix (ECM)-derived survival signals into cells. Thus, modulation of FAK activity may affect the linkage between ECM and signaling cascade to which it is connected and may participate in a variety of pathological settings. In the present study, we investigated the effect of neonatal cerebral hypoxia-ischemia (HI) on levels and tyrosine phosphorylation of focal adhesion kinase and the interaction of this enzyme with Src protein tyrosine kinase and adapter protein p130Cas, involved in FAK-mediated signaling pathway. The total amount of focal adhesion kinase as well as its phosphorylated form declined substantially to about 50% of the control between 24 and 48 h after the insult. Concomitantly a decreased association of FAK with its investigated molecular partners, Src kinase and p130Cas protein has been observed. This early response to brain hypoxia-ischemia was attenuated during prolonged recovery with almost complete return to control values at 7 days. These data are indicative of an involvement of FAK-dependent signaling pathway in the evolution of HI-induced neuronal degeneration.

IGF-I neuroprotection in the immature brain after hypoxia-ischemia, involvement of Akt and GSK3beta?

Insulin-like growth factor I (IGF-I) is a neurotrophic factor that promotes neuronal growth, differentiation and survival. Neuroprotective effects of IGF-I have previously been shown in adult and juvenile rat models of brain injury. We wanted to investigate the neuroprotective effect of IGF-I after hypoxia-ischemia (HI) in 7-day-old neonatal rats and the mechanisms of IGF-I actions in vivo. We also wanted to study effects of HI and/or IGF-I on the serine/threonine kinases Akt and glycogen synthase kinase 3beta (GSK3beta) in the phophatidylinositol-3 kinase (PI3K) pathway. Immediately after HI, phosphorylated Akt (pAkt) and phosphorylated GSK3beta (pGSK3beta) immunoreactivity was lost in the ipsilateral and reduced in the contralateral hemisphere. After 45 min, pAkt levels were restored to control values, whereas pGSK3beta remained low 4 h after HI. Administration of IGF-I (50 microg i.c.v.) after HI resulted in a 40% reduction in brain damage (loss of microtubule-associated protein) compared with vehicle-treated animals. IGF-I treatment without HI was shown to increase pAkt whereas pGSK3beta decreased in the cytosol, but increased in the nuclear fraction. IGF-I treatment after HI increased pAkt in the cytosol and pGSK3beta in both the cytosol and the nuclear fraction in the ipsilateral hemisphere compared with vehicle-treated rats, concomitant with a reduced caspase-3- and caspase-9-like activity. In conclusion, IGF-I induces activation of Akt during recovery after HI which, in combination with inactivation of GSK3beta, may explain the attenuated activation of caspases and reduction of injury in the immature brain.

Protective effects of valproic acid against hypoxic-ischemic brain injury in neonatal rats

Although controversial, protective and therapeutic effects of valproic acid in various types of cellular injury suggest a potential role for this agent in hypoxic-ischemic brain injury. We therefore investigated the effects of valproic acid in an experimental model of neonatal hypoxic-ischemic brain injury. To examine the effect of valproic acid in this condition, hypoxic-ischemic brain injury was induced in 7-day-old rat pups by ligation of the right common carotid and then the pups were exposed to 1 hour of hypoxia in 8% oxygen. Low (200 mg/kg/day) and high (400 mg/kg/day) doses of valproic acid were administered in a 5-day regimen. Neuropathologic evaluation was performed using the hippocampus, cerebral cortex, and basal ganglia in the coronal plane. The 5-day regimen of valproic acid administration resulted in some protective and therapeutic effects on the brain damage and neuronal apoptosis in both hemispheres in a dose-dependent manner. Administration of valproic acid also decreased the percentage of apoptotic neurons in the contralateral hemisphere (P < .05). These results suggest that valproic acid can have therapeutic and protective effects in hypoxic-ischemic brain injury.

The effect of hypoxic-ischemic brain injury in perinatal rats on the abundance and proteolysis of brevican and NG2

Oligodendrocyte (OL) progenitor cells are particularly susceptible to perinatal hypoxia/ischemia (H-I) resulting in decreased myelination and attenuated development of white matter fiber tracts. Brevican is an aggregating chondroitin sulfate proteoglycan (CSPG) secreted by OLs and their progenitors prior to and during active developmental myelination whereas neuron-glia antigen 2 (NG2) is a transmembrane CSPG produced by early OL progenitors. Although both proteoglycans are associated with maturation of OLs, it is not known if they are altered by H-I brain injury in the neonate. We have therefore examined the time course of changes in brevican and NG2 abundance and proteolysis in the neonatal rat hippocampus after H-I. In a standard H-I model of unilateral carotid artery ligation and exposure to hypoxia, a cavitary infarct involving the ipsilateral parietal and temporal regions of cerebral cortex, hippocampus, and striatum of most rat pups was clearly evident 4 days after H-I. The abundance of total extractable brevican was markedly reduced in the ipsilateral hippocampus at 1 and 14 days after H-I (relative to the contralateral side). At these times, the total G1 proteolytic fragment of brevican was lower in the ipsilateral hippocampus and the level of a protease-generated brevican fragment was significantly diminished in the OL-rich hippocampal fimbria. Hippocampal NG2 levels were also lower at 1 and 4 days after H-I, but were not different from the contralateral side at 14 days. Since brevican, brevican G1 fragment, and NG2 loss occur around the time of progressive cell death and the appearance of the infarct, it may be that H-I rapidly induces a cellular response that actively depletes these proteoglycans from the hippocampal matrix. While the mechanism of this loss is unclear, it would appear to be an early event in the process that could be involved in apoptotic cell death and/or tissue injury.

Differential neuroprotective effects for three GABA-potentiating compounds in a model of hypoxia–ischemia

Clomethiazole (CMZ) is a GABA(A)-potentiating compound; however, it is unclear whether this mode of action is responsible for its neuroprotective effects in animal models of ischemia. This study compared the neuroprotective efficacies of muscimol and midazolam, two potent GABA(A)-potentiating compounds, to that of CMZ in a model of hypoxia-ischemia (H-I). To establish a neuroprotective profile for CMZ, CMZ (60, 95, or 125 mg kg-1, i.p.) was administered to post-natal day 25 male rats at numerous post-hypoxic time points and the rats were sacrificed 1 or 4 weeks later. Varying degrees of histological protection were evident when CMZ was administered 1, 2, or 3 h post-hypoxia with the 125 mg kg-1 dose producing complete histological protection if administered 3 h post-hypoxia. To determine whether midazolam or muscimol could match the protection provided by CMZ administered 3 h post-hypoxia, H-I rats received varying doses of these compounds 3 h post-hypoxia and were sacrificed 1 week later. Under identical conditions, no dose of muscimol or midazolam provided equivalent neuroprotection to that provided by CMZ. In fact, muscimol showed no neuroprotective ability whatsoever. Thus, CMZ, administered as late as 3 h post-hypoxia, was able to completely prevent H-I-induced cell death while a full dose range of other GABA-potentiating agents did not. Such direct comparison of these compounds in this model suggests the mechanism underlying the protective effects of CMZ may not rely solely on GABA(A)-potentiating properties. Elucidation of a novel mechanism of action for CMZ may expose new therapeutic targets in stroke treatment.

Auditory processing deficits in rats with neonatal hypoxic-ischemic injury

Hypoxia-ischemia (HI) refers to reduced blood oxygenation and/or a diminished amount of blood perfusing the brain, and is associated with premature birth/very low birth weight (VLBW). HI represents a common cause of injury to the perinatal brain. Indeed, a significant number of premature/VLBW infants go on to demonstrate cognitive/behavioral deficits, with particularly high incidence of disruptions in language development. Auditory processing deficits, in turn, have been suggested to play a causal role in the development of language impairments. Specifically, the inability to identify fast elements in speech is purported to exert cascading detrimental effects on phonological discrimination, processing, and identification. Based on this convergent evidence, the current studies address auditory processing evaluation in a rodent model of HI injury induced on postnatal days 1, 7, or 10 (which in turn is well accepted as modeling HI-related injury to the perinatal human). Induced injuries were followed by a battery of auditory testing, and a spatial maze assessment, performed both during juvenile and adult periods. Results indicate that rats suffering from these early HI insults performed significantly worse than shams on tasks requiring rapid auditory processing, and on a test of spatial learning (Morris water maze (MWM)), although these effects were not seen on simpler versions of auditory tasks or on a water escape assessment (thus ruling out hearing/motor impairments). Correlations were found between performance on rapid auditory and spatial behavioral tasks and neuroanatomical measures for HI animals such as: the volume of the hippocampus, cerebral cortex, ventricles, and/or the area of the corpus callosum. Cumulative findings suggest that perinatal HI injury in the rat may lead to neurodevelopmental damage associated, in turn, with auditory processing and/or learning and memory impairments. As such, the current model may have critical implications for the study of neurophysiological underpinnings of cognitive deficits in premature/VLBW infants.

Pyruvate kinase activity in cerebral hemispheres and cerebellum-brainstem of normal and hypoxic-ischemic newborn rats

Energy metabolism is affected in hypoxia-ischemia. Changes in the tissue concentrations of the high-energy phosphate reserves occur early during the course of the metabolic insult and with concurrent increases in cellular ADP and AMP leading glycolysis. It has been shown that enzymes of glycolysis tend to be regulated in hypoxia and ischemia. In this study we determined pyruvate kinase (PK) activity, one of the main enzymes in glycolysis, in brain tissues of healthy (n = 15) and hypoxic-ischemic (n = 18) 7-day-old newborn rats. Left common carotid artery was ligated in the hypoxic-ischemic group and after 2 hours rats were exposed to hypoxia in a chamber at 34-36 degrees C with 8% oxygen in nitrogen. The rats were decapitated after 2 hours of hypoxia and right and left cerebral hemispheres (CH) and cerebellum-brain stem (C-BS) were removed. Pyruvate kinase activity was significantly higher in C-BSs than CHs in both groups (p < 0.00005). There was no significant difference in enzyme activities of either CHs or C-BS of hypoxic-ischemic group compared to control healthy group (p > 0.05). In conclusion, brain pyruvate kinase activity did not change in hypoxia-ischemia and suggests that PK of brain differs from other tissues where it usually increases in hypoxiaischemia.

Epilepsy and destructive brain insults in early life: a topographical classification on the basis of MRI findings

Destructive insults of early development can lead to a wide variety of lesional patterns and are a well known cause of epilepsy. The aim of this study is to present a topographic magnetic resonance imaging (MRI) classification of these lesions in adult patients with epilepsy. Thirty-three consecutive patients were divided in three groups according to the topographic distribution of their lesion on MRI: hemispheric (H, n = 7); main arterial territory (AT, n = 18); arterial borderzone (Bdz, n = 8). We analyzed clinical, MRI and magnetic resonance angiography (MRA) data. Status epilepticus (SE) during childhood was more common in group H (7/7) than in the groups AT (1/18) and Bdz (0/8) (P < 0.001). MRA pattern of impaired flow signal in the distal segments of all three major arteries in the affected hemisphere was present in 85.7% of group H patients, and was exclusive to this group. 88.8% (16/18) of patients from group AT presented congenital motor deficit, in contrast to 37.5% (3/8) of group Bdz, and in none of group H (P < 0.001). All patients with Bdz lesions had antecedent of fetal distress, in contrast to 1/7 from group H and 5/18 of group AT (P = 0.001). The MRAs of patients with Bdz lesions were often normal except in those with larger lesions. Our data suggest that in adult patients with epilepsy due to precocious destructive brain insults, a MRI topographical classification distributes them in relatively homogenous clinical groups.

Cytotoxicity of the E(2)-isoprostane 15-E(2t)-IsoP on oligodendrocyte progenitors

Oxidant stress plays a significant role in the pathogenesis of periventricular leukomalacia (PVL). Isoprostanes (IsoPs) are bioactive products of lipid peroxidation abundantly generated during hypoxic-ischemic injuries. Because loss of oligodendrocytes (OLs) occurs early in PVL, we hypothesized that IsoPs could induce progenitor OL death. 15-E(2t)-IsoP but not 15-F(2t)-IsoP elicited a concentration-dependent death of progenitor OLs by oncosis and not by apoptosis, but exerted minimal effects on mature OLs. 15-E(2t)-IsoP-induced cytotoxicity could not be explained by its conversion into cyclopentenones, because PGA(2) was hardly cytotoxic. On the other hand, thromboxane A(2) (TxA(2)) synthase inhibitor CGS12970 and cyclooxygenase inhibitor ibuprofen attenuated 15-E(2t)-IsoP-induced cytotoxicity. Susceptibility of progenitor OLs was independent of TxA(2) receptor (TP) expression, which was far less in progenitor than in mature OLs. However, TxA(2) synthase was detected in precursor but not in mature OLs, and TxA(2) mimetic U46619 induced hydroperoxides generation and progenitor OL death. The glutathione synthesis enhancer N-acetylcysteine prevented 15-E(2t)-IsoP-induced progenitor cell death. Depletion of glutathione in mature OLs with buthionine sulfoximine rendered them susceptible to cytotoxicity of 15-E(2t)-IsoP. These novel data implicate 15-E(2t)-IsoP as a product of oxidative stress that may contribute in the genesis of PVL.

Timing of neutrophil depletion influences long-term neuroprotection in neonatal rat hypoxic-ischemic brain injury

In neonatal rats, neutrophils do not accumulate in ischemic brain parenchyma to the extent that they do in adult rodents. They are also confined to the intravascular compartment during the first few hours of recovery. However, neonatal rats rendered neutropenic have less brain swelling after a hypoxic-ischemic (HI) insult. In this study, we used the Rice-Vannucci model of HI brain injury in 7-d-old rats, and we depleted neutrophils before injury in one group and 4-8 h after injury in another group to determine 1) whether neutrophils contribute to cerebral atrophy, 2) whether neutropenia induced within 8 h after recovery from HI is neuroprotective, and 3) whether neutropenia preserved energy metabolites during the HI insult. Brain energy metabolites were measured at 0 h and 6 h of recovery. Brain atrophy was measured morphometrically on brain slices at 2 wk of recovery. In 67 rats, we found that neutropenia induced before the HI insult, but not after HI, reduced brain swelling at 42 h of recovery by about 75% (p < 0.001). In another 60 rats, we found that cerebral atrophy was reduced by 61% provided that neutropenia was induced before HI (p < 0.05). Total adenine nucleotides were better preserved in the neutropenic rats at the end of the HI insult (0 h recovery); p < 0.05. We conclude that neutrophils do contribute to vascular dysfunction either during the HI insult or early hours (<4-8 h) of recovery. Antineutrophil strategies initiated after this time are unlikely to be protective in the neonatal rat.

Animal models of hypoxic-ischemic brain damage in the newborn

Controversy continues over which animal model to use as a reflection of human disease states. With respect to perinatal brain disorders, scientists must contend with a disease in evolution. In that regard, the perinatal brain is at risk during a time of extremely rapid development and maturation, involving processes that are required for normal growth. Interfering with these processes, as part of therapeutic intervention must be efficacious and safe. To date, numerous models have provided tremendous information regarding the pathophysiology of brain damage to term and preterm infants. Our challenges will continue to be in identifying those infants at greatest risk for permanent injury, and adapting therapies that provide more benefit than harm. Using animal models to conduct these studies will bring us closer to that goal.