Selective vulnerability in the developing central nervous system

Is cerebral palsy preventable?

PURPOSE OF REVIEW

To use evidence of good medical quality to update information on strategies for prevention of cerebral palsy, and on the success of these preventive efforts to date.

RECENT FINDINGS

Causes of cerebral palsy, and therefore promising approaches to prevention, differ by gestational age group and by clinical subtype. Neuroimaging and neuropathology indicate the importance of white matter disorders and of ischemic stroke in cerebral palsy; birth asphyxia, congenital malformations, placental pathology, and genetic variants also contribute to cerebral palsy risk. Multiplicity of risk factors markedly increases risk. Recent studies indicate that mild hypothermia lessens cerebral palsy risk in term infants with moderate neonatal encephalopathy, and the possibility that administration of magnesium sulphate to women in preterm labor may aid in primary prevention of cerebral palsy in very preterm infants.

SUMMARY

Past efforts to prevent cerebral palsy have not had the benefits sought, but recent results provide new hope and new challenges.

Postnatal age influences hypoglycemia-induced neuronal injury in the rat brain

Acute hypoglycemia is associated with neuronal injury in the mature human and rodent brains. Even though hypoglycemia is a common metabolic problem during development, its effects on the developing brain are not well understood. To characterize the severity of regional brain injury, postnatal day (P) 7, P14, P28 (N=20-30/age) and adult rats (N=8-12) were subjected to acute hypoglycemia of equivalent severity and duration (mean blood glucose concentration: 30.0+/-0.1 mg/dL for 210 min). Neuronal injury in the cerebral cortex, striatum, hippocampus and hypothalamus was assessed 24 h, 72 h and 1 wk later by determining the number of degenerating cells positive for Fluoro-Jade B (FJB+) in the region. Compared with age-matched control, greater number of FJB+ cells was present per brain section of P14, P28 and adult hypoglycemia groups (p<0.005, each). The cerebral cortex was more vulnerable than hippocampus and striatum at all three ages (p<0.01). Compared with P28 (131+/-21) and adult (171+/-21) rats, fewer FJB+ cells (39+/-6) per brain section were present in P14 hypoglycemic rats (p<0.01, each). Hypoglycemia was not associated with cell injury in P7 rats. FJB+ cells were absent in the hypothalamus in all four ages. Similar results were present 24 h post-hypoglycemia, whereas analysis at 1 wk demonstrated efficient clearing of FJB+ cells in the brain regions of developing rats. Varying the duration of fasting did not alter the severity of regional cell injury. These results suggest that postnatal age influences the regional vulnerability to hypoglycemia-induced neuronal death in the rat brain.

Hypoxic-ischemic brain injury: imaging findings from birth to adulthood

Global hypoxic-ischemic injury (HII) to the brain is a significant cause of mortality and severe neurologic disability. Imaging plays an important role in the diagnosis and treatment of HII, helping guide case management in the acute setting and providing valuable information about long-term prognosis. Appropriate radiologic diagnosis of HII requires familiarity with the many imaging manifestations of this injury. Factors such as brain maturity, duration and severity of insult, and type and timing of imaging studies all influence findings in HII. Severe hypoxia-ischemia in both preterm and term neonates preferentially damages the deep gray matter, with perirolandic involvement more frequently observed in the latter age group. Less profound insults result in intraventricular hemorrhages and periventricular white matter injury in preterm neonates and parasagittal watershed territory infarcts in term neonates. In the postnatal period, severe insults result in diffuse gray matter injury, with relative sparing of the perirolandic cortex and the structures supplied by the posterior circulation. Profound hypoxia-ischemia in older children and adults affects the deep gray matter nuclei, cortices, hippocampi, and cerebellum. Because findings at conventional imaging may be subtle or even absent in the acute setting, particularly in neonates, magnetic resonance spectroscopy can help establish the diagnosis of HII. Promising new neuroprotective strategies designed to limit the extent of brain injury caused by hypoxia-ischemia are currently under investigation.

Prenatal hypoxia down regulates the GABA pathway in newborn mice cerebral cortex; partial protection by MgSO4

The fetal and newborn brain is particularly susceptible to hypoxia, which increases the risk for neurodevelopmental deficits, seizures, epilepsy and life-span motor, behavioral and cognitive disabilities. Here, we report that prenatal hypoxia at gestation day 17 in mice caused an immediate decrease in fetal cerebral cortex levels of glutamate decarboxylase, a key proteins in the GABA pathway. While maternal MgSO4 treatment prior to hypoxia did not have an early effect, it did accelerate maturation at a later stage based on the observed protein expression profile. In addition, MgSO4 reversed the hypoxia-induced loss of a subpopulation of inhibitory neurons that express calbindin in cortex at postnatal day 14. In the hippocampus, responses to prenatal hypoxia were also evident 4 days after the hypoxia. However, in contrast to the observations in cerebral cortex, hypoxia stimulated key protein expression in the hippocampus. The hippocampal response to hypoxia was also reversed by maternal MgSO4 treatment. The data presented here suggests that decreased levels of key proteins in the GABA pathway in the cerebral cortex may lead to high susceptibility to seizures and epilepsy in newborns after prenatal or perinatal hypoxia and that maternal MgSO4 treatment can reverse the hypoxia-induced deficits in the GABA pathway.

Rapid NMDA receptor phosphorylation and oxidative stress precede striatal neurodegeneration after hypoxic ischemia in newborn piglets and are attenuated with hypothermia

The basal ganglia of newborns are extremely vulnerable to hypoxic ischemia (HI). Striatal neurons undergo prominent necrosis after HI. The mechanisms for this degeneration are not well understood. Postasphyxic hypothermia ameliorates the striatal necrosis, but the mechanisms of hypothermia-induced neuroprotection are not known. We used a newborn piglet model of hypoxic-asphyxic cardiac arrest to test the hypotheses that N-methyl-d-aspartate receptor activation and free radical damage coexist, prior to neurodegeneration, early after resuscitation, and that these changes are attenuated with hypothermia. Piglets were subjected to 30min of hypoxia followed by 7min of airway occlusion, causing asphyxic cardiac arrest, and then were resuscitated and survived normothermically for 5min, 3h, or 6h, or hypothermically for 3h. By 6h of normothermic recovery, 50% of neurons in putamen showed ischemic cytopathology. Striatal tissue was fractionated into membrane or soluble proteins and was assayed by immunoblotting for carbonyl modification, phosphorylation of the N-methyl-d-aspartate receptor subunit NR1, and neuronal nitric oxide synthase. Significant accumulation of soluble protein carbonyls was present at 3h (196% of control) and 6h (142% of control). Phosphorylation of serine-897 of NR1 was increased significantly at 5min (161% of control) and 3h (226% of control) after HI. Phosphorylation of serine-890 of NR1 was also increased after HI. Membrane-associated neuronal nitric oxide synthase was increased by 35% at 5min. Hypothermia attenuated the oxidative damage and the NR1 phosphorylation in striatum. We conclude that neuronal death signaling in newborn striatum after HI is engaged rapidly through N-methyl-d-aspartate receptor activation, neuronal nitric oxide synthase recruitment, and oxidative stress. Postasphyxic, mild whole body hypothermia provides neuroprotection by suppressing N-methyl-d-aspartate receptor phosphorylation and protein oxidation.

Genetic and pharmacologic manipulation of oxidative stress after neonatal hypoxia-ischemia

Oxidative stress is a critical component of the injury response to hypoxia-ischemia (HI) in the neonatal brain, and this response is unique and at times paradoxical to that seen in the mature brain. Previously, we showed that copper-zinc superoxide-dismutase (SOD1) over-expression is not beneficial to the neonatal mouse brain with HI injury, unlike the adult brain with ischemic injury. However, glutathione peroxidase 1 (GPx1) over-expression is protective to the neonatal mouse brain with HI injury. To further test the hypothesis that an adequate supply of GPx is critical to protection from HI injury, we crossed SOD1 over-expressing mice (hSOD-tg) with GPx1 over-expressing mice (hGPx-tg). Resulting litters contained wild-type (wt), hGPx-tg, hSOD-tg and hybrid hGPx-tg/hSOD-tg pups, which were subjected to HI at P7. Confirming previous results, the hGPx-tg mice had reduced injury compared to both Wt and hSOD-tg littermates. Neonatal mice over-expressing both GPx1 and SOD1 also had less injury compared to wt or hSOD-tg alone. A result of oxidative stress after neonatal HI is a decrease in the concentration of reduced (i.e. antioxidant-active) glutathione (GSH). In this study, we tested the effect of systemic administration of alpha-lipoic acid on levels of GSH in the cortex after HI. Although GSH levels were restored by 24h after HI, injury was not reduced compared to vehicle-treated mice. We also tested two other pharmacological approaches to reducing oxidative stress in hSOD-tg and wild-type littermates. Both the specific inhibitor of neuronal nitric oxide synthase, 7-nitroindazole (7NI), and the spin-trapping agent alpha-phenyl-tert-butyl-nitrone (PBN) did not reduce HI injury, however. Taken together, these results imply that H2O2 is a critical component of neonatal HI injury, and GPx1 plays an important role in the defense against this H2O2 and is thereby neuroprotective.

Hypoxic preconditioning reverses protection after neonatal hypoxia-ischemia in glutathione peroxidase transgenic murine brain

The effect of hypoxic preconditioning (PC) on hypoxic-ischemic (HI) injury was explored in glutathione peroxidase (GPx)-overexpressing mice (human GPx-transgenic [hGPx-tg]) mice. Six-day-old hGPx-tg mice and wild-type (Wt) littermates were pre-conditioned with hypoxia for 30 min and subjected to the Vannucci procedure of HI 24 h after the PC stimulus. Histopathological injury was determined 5 d later (P12). Additional animals were killed 2 h or 24 h after HI and ipsilateral cerebral cortices assayed for GPx activity, glutathione (GSH), and hydrogen peroxide (H2O2). In line with previous studies, hypoxic PC reduced injury in the Wt brain. Preconditioned Wt brain had increased GPx activity, but reduced GSH, relative to naive 24 h after HI. Hypoxic PC did not reduce injury to hGPx-tg brain and even reversed the protection previously reported in the hGPx-tg. GPx activity and GSH in hGPx-tg cortices did not change. Without PC, hGPx-tg cortex had less H2O2 accumulation than Wt at both 2 h and 24 h. With PC, H2O2 remained low in hGPx-tg compared with Wt at 2 h, but at 24 h, there was no longer a difference between hGPx-tg and Wt cortices. Accumulation of H2O2 may be a mediator of injury, but may also induce protective mechanisms.

Temporal and Anatomic Risk Profile of Brain Injury With Neonatal Repair of Congenital Heart Defects

BACKGROUND AND PURPOSE

Brain injury is common in newborns with congenital heart disease (CHD) requiring neonatal surgery. The purpose of this study is to define the risk factors for preoperative and postoperative brain injuries and their association with functional cardiac anatomic groups.

METHODS

Sixty-two neonates with CHD were studied with preoperative MRI, and 53 received postoperative scans. Clinical and therapeutic characteristics were compared in newborns with and without newly acquired brain injuries. A subset of 16 consecutive patients was monitored with intraoperative cerebral near-infrared spectroscopy.

RESULTS

Brain injury was observed in 56% of patients. Preoperative brain injury, seen in 39%, was most commonly stroke and was associated with balloon atrial septostomy (P=0.002). Postoperative brain injury, seen in 35%, was most commonly white matter injury and was particularly common in neonates with single-ventricle physiology and aortic arch obstruction (P=0.001). Risk factors associated with acquired postoperative brain injury included cardiopulmonary bypass (CPB) with regional cerebral perfusion (P=0.01) and lower intraoperative cerebral hemoglobin oxygen saturation during the myocardial ischemic period of CPB (P=0.008). In a multivariable model, new postoperative white matter injury was specifically associated with low mean blood pressure during the first postoperative day (P=0.04).

CONCLUSIONS

Specific modifiable risk factors can be identified for preoperative and postoperative white matter injury and stroke associated with neonatal surgery for CHD. The high incidence of postoperative injury observed despite new methodologies of CPB indicates the need for ongoing evaluation to optimize neurological outcome.

Evidence supporting the use of melatonin in short gestation infants

Pineal melatonin regulates circadian rhythms and influences sleep. Melatonin also has protective actions against tissue damage from free-radicals and other toxins. Evidence is presented that this indoleamine is involved in pre- and postnatal brain (and ocular) development and intrauterine growth. In the absence of maternal melatonin, short gestation infants have a prolonged period of melatonin deficiency. Melatonin supplementation, which has a benign safety profile, may help reduce complications in the neonatal period that are associated with short gestation. We believe that this treatment might result in a wide range of health benefits, improved quality of life and reduced healthcare costs.

Comparison of two neonatal ischemic injury models using magnetic resonance imaging

Using an 11.7-Tesla magnetic resonance imaging (MRI) scanner in 10-d-old rat pups we report on the evolution of injury over 28 d in a model of neonatal stroke (transient filament middle cerebral artery occlusion, tfMCAO) and a model of hypoxic-ischemic injury (Rice-Vannucci model, RVM). In both models, diffusion-weighted imaging (DWI) was more sensitive in the early detection of ischemia than T2-weighted imaging (T2WI). Injury volumes in both models were greater on d 1 for DWI and d 3 for T2WI, decreased over time and by d 28 T2WI injury volumes (tfMCAO 10.3% of ipsilateral hemisphere; RVM 23.9%) were definable. The distribution of injury with tfMCAO was confined to the vascular territory of the middle cerebral artery and a definable core and penumbra evolved over time. Ischemic injury in the RVM was more generalized and greater in cortical regions. Contralateral hemispheric involvement was only observed in the RVM. Our findings demonstrate that high-field MRI over extended periods of time is possible in a small animal model of neonatal brain injury and that the tfMCAO model should be used for studies of neonatal stroke and that the RVM does not reflect the vascular distribution of injury seen with focal ischemia.

IGF-1 protects oligodendrocyte progenitors against TNFα-induced damage by activation of PI3K/Akt and interruption of the mitochondrial apoptotic pathway

Proinflammatory cytokine-mediated injury to oligodendrocyte progenitor cells (OPCs) has been proposed as a cause of periventricular leukomalacia (PVL), the most common brain injury found in preterm infants. Preventing death of OPCs is a potential strategy to prevent or treat PVL. In the current study, we utilized an in vitro cell culture system to investigate the effect of insulin-like growth factor-1 (IGF-1) on tumor necrosis factor-alpha (TNFalpha)-induced OPC injury and the possible mechanisms involved. OPCs were isolated from neonatal rat optic nerves and cultured in chemically defined medium (CDM) supplemented with platelet-derived growth factor and basic fibroblast growth factor. Exposure to TNFalpha resulted in death of OPCs. IGF-1 protected OPCs from TNFalpha cytotoxicity in a dose-dependent manner as measured by the XTT and TUNEL assays. IGF-1 activates both the PI3K/Akt and the extracellular signal-regulated kinase (ERK) pathway. However, IGF-1-enhanced cell survival signals were mediated by the PI3K/Akt, but not by the ERK pathway, as evidenced by the observation that IGF-1-enhanced cell survival was partially abrogated by Akti, the Akt inhibitor, or wortmannin, the PI3K inhibitor, but not by PD98,059, the MAPK kinase/ERK kinase inhibitor. The downstream events of IGF-1-triggered survival signals included phosphorylation of BAD, blockade of TNFalpha-induced translocation of Bax from the cytosol to the mitochondrial membrane, and suppression of caspase-9 and caspase-3 activation. These observations indicate that the protection of OPCs by IGF-1 is mediated, at least partially, by interruption of the mitochondrial apoptotic pathway via activation of PI3K/Akt.

Inflammation in adult and neonatal stroke

This chapter will discuss the current knowledge of the contribution of systemic and local inflammation in acute and sub-chronic stages of experimental stroke in both the adult and neonate. It will review the role of specific cell types and interactions among blood cells, endothelium, glia, microglia, the extracellular matrix and neurons - cumulatively called "neurovascular unit" - in stroke induction and evolution. Intracellular inflammatory signaling pathways such as nuclear factor kappa beta and mitogen-activated protein kinases, and mediators produced by inflammatory cells such as cytokines, chemokines, reactive oxygen species and arachidonic acid metabolites, as well as the modifying role of age on these mechanisms, will be reviewed as well as the potential for therapy in stroke and hypoxic-ischemic injury.

Does perinatal asphyxia impair cognitive function without cerebral palsy?

Some studies on neurodevelopmental outcomes after neonatal encephalopathy have suggested that cognitive deficits do not occur in the absence of cerebral palsy. It is increasingly apparent that childhood survivors of overt neonatal encephalopathy may have cognitive impairments, even in the absence of functional motor deficits. The risk of cognitive deficits is related to the severity of neonatal encephalopathy and the pattern of brain injury on neuroimaging, particularly the watershed pattern of injury. A better understanding of the risk factors for cognitive abnormalities after neonatal encephalopathy will ultimately lead to interventions to prevent these deficits. Identifying the full spectrum of neurodevelopmental outcomes after neonatal encephalopathy will also allow care givers to identify children requiring early intervention to maximise their potential for independent function throughout development.

Magnetic resonance imaging (MRI) findings in children surviving extremely premature delivery and extremely low birthweight with cerebral palsy

To delineate the frequency, severity, and characteristics of the brain injury occurring in children surviving extremely premature birth, we reviewed brain magnetic resonance images (MRIs) of children with cerebral palsy whose birthweight was less than 1000 g and whose gestational age was less than 28 weeks. The patients were all enrolled in the state Children's Rehabilitative Services clinic, where cerebral palsy is an automatic qualifying condition. We tabulated the MRI findings with respect to the cerebellum, periventricular white matter, and corpus callosum. The inclusion criteria were met by 157 children; 94 had an MRI. The available scans were reviewed by the authors, and the findings were tabulated. Fifty scans were available for review. There were 4 totally normal scans, 18 scans had normal cerebellar imaging, and 8 scans were felt to have normal cerebral findings. The common cerebral abnormalities included decreased white-matter volume without gliosis (n = 36), periventricular leukomalacia (n = 16), and a thin corpus callosum (n = 18). Cerebellar abnormalities were found in 32. The cerebellar findings included destruction of major portions of the cerebellum (usually the inferior vermis and hemispheres) (n = 23) and focal or unilateral loss of cerebellar tissue (n = 4). The high incidence of injury to the cerebellum has not been previously appreciated. The most common cerebral injury is decreased volume of white matter in the periventricular regions without gliosis. The pattern of cerebellar injury suggests a vascular insult, and the deficient white matter without gliosis suggests immaturity of oligodendrogliocytes with limited response to injury. Both lesions are more or less unique to the age at which the insult occurred and represent an emerging, newly recognized type of cerebral palsy.

Maternal infection and white matter toxicity

Studies examining maternal infection as a risk factor for neurological disorders in the offspring have suggested that altered maternal immune status during pregnancy can be considered as an adverse event in prenatal development. Infection occurring in the mother during the gestational period has been implicated in multiple neurological effects. The current manuscript will consider the issue of immune/inflammatory conditions during prenatal development where adverse outcomes have been linked to maternal systemic infection. The discussions will focus primary on white matter and oligodendrocytes as they have been identified as target processes. This white matter damage occurs in very early preterm infants and in various other human diseases currently being examined for a linkage to maternal or early developmental immune status. The intent is to draw attention to the impact of altered immune status during pregnancy on the offspring for the consideration of such contributing factors to the general assessment of developmental neurotoxicology.

Behavioral and neurochemical effects induced by pyrethroid-based mosquito repellent exposure in rat offsprings during prenatal and early postnatal period

Synthetic pyrethroids, besides their use in agriculture, are prevalently used in our houses as mosquito repellent (MR) in the form of aerosol, mats, coils and liquid vaporizers. Inhalation of fumes of the MR/liquid vaporizers may get entry into the brain by breaching the developing blood-brain barrier, hence deleterious to developing nervous system and can lead to long-term functional deficits. In the present study the consequence of MR exposure has further been investigated at various stages of development, evaluating free radical mediated effect pertinent to neurobehavioral and neurochemical functioning. Rat pups were exposed to pyrethroid-based MR (allethrin 3.6% w/v, 8 h/day through inhalation) during prenatal (GD1-20), postnatal (PND1-30) and perinatal (GD1-PND30) period of development and assessments were made on PND31. We observed significant oxidative stress, where an increase in lipid peroxidation and a decrease in antioxidants, glutathione, superoxide dismutase and catalase in various brain areas (cerebellum, corpus striatum, frontal cortex and hippocampus) were evident at all the exposure schedules. The hippocampus was the most affected region and further exhibited altered cholinergic functioning in the form of significant decrease in cholinergic (muscarinic) receptor binding (prenatal 32%, postnatal 35%, perinatal 38%) and inhibition in acetylcholinesterase activity (prenatal 20%, postnatal 31% and perinatal 33%). The neurochemical changes were found to accompany decrease in learning and memory performance in exposed rats, the function governed by hippocampus. The result suggests that pyrethroid-based MR inhalation during early developmental period may have adverse effect on developing nervous system causing cholinergic dysfunction leading to learning and memory deficit.

White matter volume and concentration reductions in adolescents with history of very preterm birth: a voxel-based morphometry study

Very preterm birth (VPTB) is an important risk factor for white matter (WM) damage. We used voxel-based morphometry (VBM) to examine regional WM brain abnormalities in 50 adolescents with antecedents of very preterm birth (VPTB) without evidence of WM damage on T2-weighted MRI. This group was compared with a group of 50 subjects born at term and matched for age, handedness and socio-cultural status. We also examined the relationship between WM changes and gestational age (GA) and weight (GW) at birth in VPTB subjects. Both modulated and unmodulated VBM analyses showed significant abnormalities in several WM brain regions in the VPTB group, involving all the cerebral lobes. However, density analyses (unmodulated data) mainly identified periventricular damage and the involvement of the longitudinal fascicles while volume analyses (modulated data) detected WM decreases in regions distant from the ventricular system, located at the origin and end of the long fascicles. A significant correlation was found between WM decreases and both GA and GW in various brain regions: the lower the GA and GW, the lower the WM integrity. This study supports the current view that widespread white matter impairment is associated with immature birth.

Effects of oxidative challenge and calcium on ATP-levels in neuronal cells

BACKGROUND

Neurocellular overload with hydrogen peroxide (H2O2) induces oxidative stress and may initiate a cascade of intracellular toxic events leading to energy failure, increased lipid peroxidation and subsequently cell death. Studies suggest that hippocampal neurons may be more vulnerable to oxidative stress than cortical cells pointing to a differential vulnerability of neuronal cells. Since disturbed ATP- and calcium (Ca2+)-metabolism may be involved in this process, we here evaluated the effects of H2O2-induced oxidative stress and the involvement of Ca2+-regulation on neuronal energy metabolism.

METHODS

Using primary cortical and hippocampal neurons as well as immortalized hippocampal HT22 cells, we determined ATP-levels and accompanying cell death after oxidative challenge with H2O2. Additionally, the combined effects of H2O2 and alterations in Ca2+-concentrations were pharmacologically characterized in more detail.

RESULTS

H2O2-incubation decreased ATP-levels in a dose- and time-dependent manner in all neuronal cell systems tested. Such effects were most pronounced in primary hippocampal neurons. In cortical cells, increased ATP-levels were notable under low H2O2-concentrations. A dose-dependent decrease in ATP-concentrations was observed after treatment with Ca2+, which was further enhanced by additional H2O2-challenge.

CONCLUSIONS

Our data underline that both, H2O2- and Ca2+-treatment, are able to disturb intracellular energy metabolism. Out of the different systems studied, the ATP-decrease is most pronounced in hippocampal primary neurons, suggesting that this mechanism contributes to the selective neuronal vulnerability to oxidative stress in these neurons.

Translational stroke research in the developing brain

Preclinical animal models can help guide the development of clinical pediatric and newborn stroke trials. Data obtained using currently available models of hypoxia-ischemia and focal stroke have demonstrated the need for age-appropriate models. There are age-related differences in susceptibility of the immature brain to oxidative stress and inflammation, as well as in the rate and degree of apoptotic neuronal death. These issues need to be carefully addressed in designing future clinical trials.

Reduction of Caspase-8 and -9 Cleavage Is Associated With Increased c-FLIP and Increased Binding of Apaf-1 and Hsp70 After Neonatal Hypoxic/Ischemic Injury in Mice Overexpressing Hsp70

Background and Purpose— Caspase-8 and caspase-9 are essential proteases of the extrinsic and intrinsic apoptotic pathways, respectively. We investigated whether neuroprotection associated with overexpression of heat-shock protein 70 (Hsp70), a natural cellular antiapoptotic protein, is mediated by caspase-8 and caspase-9 signaling in the neonatal mouse brain after hypoxia/ischemia (H/I) injury.

Methods— Postnatal day 7 transgenic mice overexpressing rat Hsp70 (Hsp70 Tg) and their wild-type (Wt) littermates underwent unilateral common carotid artery ligation followed by 30 minutes of exposure to 8% O 2 . The expression of apoptotic proteins was quantified by Western blot analysis, and the specific interaction between Hsp70 and apoptotic protease activating factor 1 (Apaf-1) was determined by coimmunoprecipitation.

Results— Hsp70 overexpression reduced cytosolic translocation of cytochrome c without affecting the levels of Apaf-1 and pro–caspase-9 24 hours after H/I. The expression of these apoptotic proteins in the naïve neonatal brains was also not affected by Hsp70 overexpression. Reduced caspase-9 cleavage occurred in Hsp70 Tg mice compared with Wt littermates 24 hours after H/I and correlated with increased binding of Hsp70 and Apaf-1. Increased cellular Fas-associated death domain–like interleukin-1β–converting enzyme inhibitory protein (FLIP) expression and decreased caspase-8 cleavage were also observed in Hsp70 Tg compared with Wt mice 24 hours after H/I.

Conclusions— Our results suggest that the extrinsic and intrinsic apoptotic pathways mediate the neuroprotective effects of Hsp70 overexpression in neonatal H/I, specifically by upregulating FLIP and sequestering Apaf-1, leading to reduced cleavage of caspase-8 and caspase-9.

Neuropathologic substrate of cerebral palsy

Animal models have assisted in understanding the mechanisms of brain injury underlying cerebral palsy. Nevertheless, no such models replicate every aspect of the human disease. This review summarizes the classic and more recent studies of the neuropathology of human perinatal brain injury most commonly associated with cerebral palsy, for use by researchers and clinicians alike who need to analyze published animal models with respect to their fidelity to the human disorder. The neuropathology underlying cerebral palsy includes white-matter injury, known as periventricular leukomalacia, as well as germinal matrix hemorrhage with intraventricular extension, and injury to the cortex, basal ganglia, and thalamus. Each has distinctive features while sharing some risk factors, such as prematurity and/or hypoxia-ischemia in the perinatal period. Periventricular leukomalacia consists of diffuse injury of deep cerebral white matter, with or without focal necrosis. Recent work directly in human postmortem tissue has focused on the role of free radical injury, cytokine toxicity (especially in light of the epidemiologic association of periventricular leukomalacia with maternofetal infection), and excitotoxicity in the development of periventricular leukomalacia. Premyelinating oligodendrocytes, which predominate in periventricular regions during the window of vulnerability to periventricular leukomalacia (24-34 postconceptional weeks), are the targets of free radical injury, as determined by immunocytochemical markers of lipid peroxidation and protein nitration. This maturational susceptibility can be attributed in part to a relative deficiency of superoxide dismutases in developing white matter. Microglia, which respond to cytokines and to bacterial products such as lipopolysaccharide via Toll-like receptors, are increased in periventricular leukomalacia white matter and can contribute to cellular damage. Indeed, several cytokines, including tumor necrosis factor-a and interleukins 2 and 6, as well as interferon-g, have been demonstrated in periventricular leukomalacia. Preliminary work suggests a role for glutamate receptors and glutamate transporters in periventricular leukomalacia based on expression in human developing oligodendrocytes. Germinal matrix hemorrhage, with or without intraventricular hemorrhage, occurs in premature infants and can coexist with periventricular leukomalacia. Studies in human germinal matrix tissue have focused on maturation-based vascular factors, such as morphometry and expression of molecules related to the structure of the blood-brain barrier. Gray-matter injury, seen more commonly in term infants, includes cortical infarcts and status marmoratus. Subtle cortical injury overlying periventricular leukomalacia is the subject of current interest as a possible substrate for the cognitive difficulties seen in patients with cerebral palsy. In summary, it is hoped that work in human tissue, in conjunction with experimental animal models, will lead to eventual therapeutic or preventive strategies for the perinatal brain injury underlying cerebral palsy.

Systemic prenatal insults disrupt telencephalon development: implications for potential interventions

Infants born prematurely are prone to chronic neurologic deficits including cerebral palsy, epilepsy, cognitive delay, behavioral problems, and neurosensory impairments. In affected children, imaging and neuropathological findings demonstrate significant damage to white matter. The extent of cortical damage has been less obvious. Advances in the understanding of telencephalon development provide insights into how systemic intrauterine insults affect the developing white matter, subplate, and cortex, and lead to multiple neurologic impairments. In addition to white matter oligodendrocytes and axons, other elements at risk for perinatal brain injury include subplate neurons, GABAergic neurons migrating through white matter and subplate, and afferents of maturing neurotransmitter systems. Common insults including hypoxia-ischemia and infection often affect the developing brain differently than the mature brain, and insults precipitate a cascade of damage to multiple neural lineages. Insights from development can identify potential targets for therapies to repair the damaged neonatal brain before it has matured.

Perinatal subplate neuron injury: implications for cortical development and plasticity

Perinatal brain injury may result in widespread deficits in visual, motor and cognitive systems suggesting disrupted brain development. Neurosensory and cognitive impairment are observed at increasing frequency with decreasing gestational ages, suggesting a unique vulnerability of the developing brain. The peak of human subplate neuron development coincides with the gestational ages of highest vulnerability to perinatal brain injury in the premature infant. At the same time, human thalamocortical connections are forming and being refined by activity-dependent mechanisms during critical periods. Subplate neurons are the first cortical neurons to mature and are selectively vulnerable to early hypoxic-ischemic brain injury in animal models. Timing of subplate neuron death determines the resulting defect in thalamocortical development: very early excitotoxic subplate neuron death results in failure of thalamocortical innervation, while later subplate neuron death interferes with the refinement of thalamocortical connections into mature circuits. We suggest that subplate neuron injury may be a central component of perinatal brain injury resulting in specific neurodevelopmental consequences.

The many faces of nitric oxide in schizophrenia. A review

Intense research has been conducted in an effort to identify specific biological markers of schizophrenia. The gas nitric oxide (NO) is one of the most important signaling molecules involved in a plethora of cellular events that take place in the cardiovascular, immune and nervous systems of animals. This survey aims to demonstrate that NO and its metabolites play important roles in schizophrenia and have a significant influence on our understanding of the development, progression and treatment of the disease. Special emphasis is given to the impact of NO metabolism on processes known to be disturbed in schizophrenia (i.e., cell migration, formation of synapses, NMDA receptor mediated neurotransmission, membrane pathology and cognitive abilities). However, when comparing data on the NO metabolism in the brain tissue and body fluids of schizophrenics with those obtained from patients with other neurological and psychiatric diseases, it becomes clear that alterations of NO metabolism are not unique to, or indicative of, schizophrenia. Thus, NO and its metabolites are not suitable diagnostic tools to distinguish schizophrenia from psychically healthy control cases or from other brain disorders.

Object working memory deficits predicted by early brain injury and development in the preterm infant

Children born preterm and of very low birth weight are at increased risk of learning difficulties and educational under-achievement. However, little is known about the specific neuropsychological problems facing these children or their neurological basis. Using prospective longitudinal data from a regional cohort of 92 preterm and 103 full-term children, this study examined relations between term MRI measures of cerebral injury and structural brain development and children's subsequent performance on an object working memory task at the age of 2 years. Results revealed clear between-group differences, with preterm children having greater difficulty encoding new information in working memory than term control children. Within the preterm group, task performance at the age of 2 years was related to both qualitative MRI measures of white matter (WM) injury and quantitative measures of total and regional brain volumes assessed at term equivalent. Bilateral reductions in total tissue volumes (%region) of the following cerebral regions were specifically related to subsequent working memory performance: dorsolateral prefrontal cortex, sensorimotor, parietooccipital and premotor. Associations between total cerebral tissue volumes at term (adjusted and unadjusted for intracranial volume) persisted even after the effects of WM injury were taken into account. This suggests that early disturbance in cerebral development may have an independent adverse impact on later working memory function in the preterm infant. These findings add to our understanding of the neuropathological pathways associated with later executive dysfunction in the very preterm infant.

Patterns of excitotoxin-induced brain lesions in the newborn rabbit: a neuropathological and MRI correlation

There is pressing need to employ new advances in structural MR brain imaging to better diagnose brain damage in newborn infants. Timely application of such technology will enable improved therapeutic interventions. Diffusion-weighted sequences are a sensitive marker of very early neuronal injury, the spatial pattern of which provides critical information regarding the underlying pathophysiology. We have modified our murine model of excitotoxic neonatal brain injury to the rabbit, an animal whose brain is larger and where the neuroanatomic organization of the subcortical white matter more closely resembles that of the human. Utilizing this rabbit model, we undertook an MRI/histopathologic correlation. We found that as with the mouse, there is a spatiotemporal selectivity to the pattern of brain injury, and that the period from postnatal day (P) 7 to P9 in rabbits corresponds to the time of maximum vulnerability of the brain to excitotoxic white matter damage, which neuropathologically simulates periventricular leukomalacia (PVL). We additionally noted that diffusion-weighted imaging provided the most sensitive means of detecting such lesions and that this method was sensitive to structural maturational changes accompanying the normal cortical ontogeny. Taken together, our findings suggest that this rabbit model of perinatal excitotoxic brain injury will be a valuable addition to experimental approaches to further our understanding of perinatal brain damage, that diffusion-weighted imaging will be an invaluable adjunct to the diagnosis of such injury, and that therapeutic strategies aimed at interrupting the evolution of PVL should include targeting the pathophysiologic cascade induced by excitotoxic neonatal brain injury.

Overexpression of glutathione peroxidase protects immature murine neurons from oxidative stress

Neuronal enzyme systems involved in free radical detoxification are developmentally regulated such that intracellular glutathione peroxidase (GPx-1) activity is low in the newborn mouse brain. We hypothesized that neurons expressing a higher level of GPx-1 will be more resistant to hydrogen peroxide (H(2)O(2)) exposure. We show a dose-dependent protection against H(2)O(2) in primary neuronal cultures from fetuses overexpressing human GPx-1 compared to wild types of the same genetic background. Exogenous antioxidants completely protected neurons, even at extremely high H(2)O(2 )concentrations and regardless of the genotype. Specific depletion of glutathione with buthionine sulfoximine increased cell death in transgenic cultures exposed to 200 microM H(2)O(2), reducing protection afforded by increased GPx-1 activity. Increased GPx-1 expression in immature cortical neurons confers protection from oxidative stress, but availability of reducing equivalents determines susceptibility to oxidative cell death.

White matter damage precedes that in gray matter despite similar magnetic resonance imaging changes following cerebral hypoxia-ischemia in neonatal rats

We hypothesized that the cerebral injury produced by hypoxia-ischemia (HI) in neonatal rats would differ in white compared with gray matter as detected histologically or with magnetic resonance (MR) imaging methods. Maps of T2 and the apparent diffusion coefficient (ADC) of water were acquired in 1-week-old rats at times prior to cerebral HI (right carotid artery occlusion plus 1.5 h of hypoxia), within the last 5-10 min of HI, and 1 h or 24 h after HI. Near the end of HI, ADC decreased and T2 increased in both cortical gray and subcortical white matter within the cingulum of the HI hemisphere. One hour after HI, ADC partially recovered, but T2 remained increased and then increased further by 24 h post-HI. In contrast to the similar MR responses in white and gray matter, histological evidence for irreversible cell damage occurred in white matter earlier than in gray matter within the HI hemisphere. At 1 h post-HI, rarefied or disrupted nerve fibers and an increase in TUNEL-positive cells were observed within white matter in the cingulum, whereas neurons within the cortical gray matter appeared normal. By 24 h post-HI, damage was apparent in both white and gray matter. Thus, MR imaging detected acute tissue edema following cerebral HI in both gray and white matter but did not distinguish between the early irreversible tissue injury detected histologically in white but not gray matter in this rather severe model of neonatal encephalopathy.

Potential for protection and repair following injury to the developing brain: a role for erythropoietin?

Perinatal brain injury is a major contributor to perinatal morbidity and mortality, and a considerable number of these children will develop long term neurodevelopmental disabilities. Despite the severe clinical and socio-economic significance and the advances in neonatal care over the past twenty years, no therapy yet exists that effectively prevents or ameliorates detrimental neurodevelopmental effects in cases of perinatal/neonatal brain injury. Our objective is to review recent evidence in relation to the pervading hypothesis for targeting time-dependent molecular and cellular repair mechanisms in the developing brain. In addition we review several potential neuroprotective strategies specific to the developing nervous system, with a focus on erythropoietin (Epo) because of its potential role in protection as well as repair.

Meconium aspiration induces oxidative injury in the hippocampus of newborn piglets

BACKGROUND

Meconium aspiration-induced hypertensive lung injury has been associated with neuronal damage in the newborn, but the mechanisms of the injury are poorly known.

AIMS

The aim of the study was to determine the contribution of oxidative stress to the brain damage after pulmonary meconium contamination.

STUDY DESIGN

Sixteen anesthetized and ventilated newborn piglets were studied for 6 h. Eight piglets were instilled with a bolus of human meconium intratracheally and eight piglets with saline instillation served as controls. Brain tissue lipid peroxidation products (TBARS), reduced glutathione (GSH), myeloperoxidase activity and oxidized DNA were analyzed as indicators of oxidative stress.

RESULTS

Meconium aspiration did not change the systemic or carotid hemodynamics, but caused a well-established pulmonary hypertensive response. Sustained increase in additional oxygen demand was also observed after meconium insult, but no actual hypoxemia or hypercarbia was evident during the whole study period. Myeloperoxidase activity was elevated in the cerebellum after pulmonary meconium instillation, whereas concentrations of peroxidation products and glutathione were similar in the cortical, cerebellar and hippocampal regions of the two groups. Still, the amount of oxidized DNA was increased in the hippocampus of the meconium-aspirated piglets when compared to controls.

CONCLUSIONS

Our data thus suggest that oxidative injury associated with pulmonary, but not systemic, hemodynamic disturbances may contribute to hippocampal damage after meconium aspiration in newborns.

Patterns of brain injury in term neonatal encephalopathy

OBJECTIVES

To determine whether the pattern of brain injury in term neonatal encephalopathy is associated with distinct prenatal and perinatal factors and to determine whether the pattern of injury is associated with 30-month neurodevelopmental outcome.

STUDY DESIGN

A total of 173 term newborns with neonatal encephalopathy from 2 centers underwent magnetic resonance imaging (MRI) at a median of 6 days of age (range, 1-24 days). Patterns of injury on MRI were defined on the basis of the predominant site of injury: watershed predominant, basal ganglia/thalamus predominant, and normal.

RESULTS

The watershed pattern of injury was seen in 78 newborns (45%), the basal ganglia/thalamus pattern was seen in 44 newborns (25%), and normal MRI studies were seen in 51 newborns (30%). Antenatal conditions such as maternal substance use, gestational diabetes, premature rupture of membranes, pre-eclampsia, and intra-uterine growth restriction did not differ across patterns. The basal ganglia/thalamus pattern was associated with more severe neonatal signs, including more intensive resuscitation at birth ( P = .001), more severe encephalopathy ( P = .0001), and more severe seizures ( P = .0001). The basal ganglia/thalamus pattern was associated with the most impaired motor and cognitive outcome at 30 months.

CONCLUSION

The patterns of brain injury in term neonatal encephalopathy are associated with different clinical presentations and neurodevelopmental outcomes. Measured prenatal risk factors did not predict the pattern of brain injury.

The influence of age on apoptotic and other mechanisms of cell death after cerebral hypoxia-ischemia

Unilateral hypoxia-ischemia (HI) was induced in C57/BL6 male mice on postnatal day (P) 5, 9, 21 and 60, corresponding developmentally to premature, term, juvenile and adult human brains, respectively. HI duration was adjusted to obtain a similar extent of brain injury at all ages. Apoptotic mechanisms (nuclear translocation of apoptosis-inducing factor, cytochrome c release and caspase-3 activation) were several-fold more pronounced in immature than in juvenile and adult brains. Necrosis-related calpain activation was similar at all ages. The CA1 subfield shifted from apoptosis-related neuronal death at P5 and P9 to necrosis-related calpain activation at P21 and P60. Oxidative stress (nitrotyrosine formation) was also similar at all ages. Autophagy, as judged by the autophagosome-related marker LC-3 II, was more pronounced in adult brains. To our knowledge, this is the first report demonstrating developmental regulation of AIF-mediated cell death as well as involvement of autophagy in a model of brain injury.

Transient microcircuits formed by subplate neurons and their role in functional development of thalamocortical connections

Subplate neurons are a transient population of neurons in the brain forming one of the first functional cortical circuits. Past experiments have demonstrated their importance in growth of thalamocortical afferents into the cortical plate and later segregation of thalamocortical afferents. Recently, subplate neurons have been shown to be required for the functional maturation of both thalamocortical connections and mature visual responses in visual cortex. These findings suggest that thalamocortical afferents might not segregate properly in the absence of subplate neurons because the thalamocortical synapse does not mature. Subplate neurons are unique in that they form a circuit that appears to promote synaptic scaling and maturation. Although the precise contribution of subplate neurons within the context of cortical development is unknown, they might play an early role in providing thalamic input to cortex that then interacts with learning rules governing synaptic strengthening at the thalamocortical synapse. Because they appear to play multiple key roles at different stages of development, subplate neurons might also play a role in the pathology of developmental disorders, such as epilepsy and schizophrenia.

Transplanted human embryonic germ cell-derived neural stem cells replace neurons and oligodendrocytes in the forebrain of neonatal mice with excitotoxic brain damage

Stem cell therapy is a hope for the treatment of some childhood neurological disorders. We examined whether human neural stem cells (hNSCs) replace lost cells in a newborn mouse model of brain damage. Excitotoxic lesions were made in neonatal mouse forebrain with the N-methyl-D-aspartate (NMDA) receptor agonist quinolinic acid (QA). QA induced apoptosis in neocortex, hippocampus, striatum, white matter, and subventricular zone. This degeneration was associated with production of cleaved caspase-3. Cells immunopositive for inducible nitric oxide synthase were present in damaged white matter and subventricular zone. Three days after injury, mice received brain parenchymal or intraventricular injections of hNSCs derived from embryonic germ (EG) cells. Human cells were prelabeled in vitro with DiD for in vivo tracking. The locations of hNSCs within the mouse brain were determined through DiD fluorescence and immunodetection of human-specific nestin and nuclear antigen 7 days after transplantation. hNSCs survived transplantation into the lesioned mouse brain, as evidenced by human cell markers and DiD fluorescence. The cells migrated away from the injection site and were found at sites of injury within the striatum, hippocampus, thalamus, and white matter tracts and at remote locations in the brain. Subsets of grafted cells expressed neuronal and glial cell markers. hNSCs restored partially the complement of striatal neurons in brain-damaged mice. We conclude that human EG cell-derived NSCs can engraft successfully into injured newborn brain, where they can survive and disseminate into the lesioned areas, differentiate into neuronal and glial cells, and replace lost neurons. (c) 2005 Wiley-Liss, Inc.

Neonatal encephalopathy: association of cytokines with MR spectroscopy and outcome

In term neonatal encephalopathy, little is known about the relationship between early inflammatory markers, neonatal brain injury, and long-term neurodevelopmental outcome. Our goal was to determine whether neonatal serum cytokine levels are associated with cerebral metabolism assessed by proton magnetic resonance spectroscopy (MRS), with magnetic resonance imaging (MRI) abnormalities, and with neurodevelopmental outcome at 30 mo of age. Levels of seven cytokines [IL-1 beta, IL-6, IL-8, IL-9, IL-12, IL-13, and tumor necrosis factor (TNF)-alpha] were measured in dried neonatal blood by immunoaffinity chromatography in a prospective cohort of 62 term newborns at risk of neonatal encephalopathy. MR images (n = 61) were scored and lactate/choline and N-acetyl-aspartate (NAA)/choline were measured by MRS (n = 42) on median day of life 6 in the deep gray nuclei (DGN) and in the watershed/cortical zone (WS). Neurodevelopmental outcome (n = 54) was considered abnormal if the infant died or if cognitive delay and/or functional motor deficit were detected at 30 mo. IL-1 beta, IL-6, IL-8 and TNF-alpha were significantly associated with lactate/choline in the DGN (p = 0.03, 0.02, 0.03, and 0.01 respectively), but not in the WS (all p > 0.1). Cytokines were not associated with NAA/choline in any region or with MRI scores. Children with abnormal neurodevelopmental outcome had higher neonatal levels of IL-1 beta, IL-6, IL-8, and lower levels of IL-12 (p = 0.04, 0.03, 0.01, 0.03 respectively). Elevated inflammatory cytokines were associated with impaired cerebral oxidative metabolism, but not with detectable MRI changes in the neonatal period. Understanding the link between elevated cytokines and outcome would inform novel strategies of cerebral protection.

Mechanisms of hypoxic-ischemic injury in the term infant

The pathogenesis of hypoxic-ischemic brain injury in the term infant is multifactorial and complex. Over the past decade the investigative emphasis has turned to cellular and molecular mechanisms of injury, and it has been increasingly recognized that the neonatal brain differs vastly from the adult brain in terms of response to hypoxia-ischemia. This review will discuss the initiation and evolution of brain injury in the term neonate, and the inherent biochemical and physiologic qualities of the neonatal brain that make its response to hypoxia-ischemia unique. Attention will be given to specific areas of investigation including excitotoxicity, oxidative stress, and inflammation. The coalescence of these entities to a final common pathway of hypoxic-ischemic brain injury will be emphasized.

Magnetic resonance imaging of differential gray versus white matter injury following a mild or moderate hypoxic-ischemic insult in neonatal rats

Selective white matter injury in the pre-mature infants suggests it has a greater susceptibility to hypoxia-ischemia. To investigate whether white matter injury would predominate following a mild hypoxic-ischemic insult, 7-day-old rats underwent either mild or moderate hypoxia-ischemia and magnetic resonance imaging 24 h later. Mild and moderate hypoxia-ischemia were produced by unilateral carotid artery occlusion plus exposure to hypoxia for either 45-50 or 90 min at ambient temperatures of 34.5 or 35.5 degrees C, respectively. Following mild hypoxia-ischemia, there was a significant increase in T(1) and T(2) within periventricular white matter (e.g. corpus callosum) in the hemisphere ipsilateral to the occlusion compared to that contralaterally and less of an increase within gray matter (e.g. cortex and striatum). This corresponded to relatively selective white matter injury detected histologically. Following a moderate hypoxia-ischemia, both gray and white matter was severely injured with marked increases in T(1) and T(2) occurring in both white and gray matter regions ipsilateral to the hypoxia-ischemia. We conclude that a mild insult, consisting of a short duration of hypoxia-ischemia at a slightly lower body temperature than a moderate hypoxic-ischemic insult, produces enhanced injury in white matter and a relative sparing of gray matter.