Biphasic edema after hypoxic-ischemic brain injury in neonatal rats reflects early neuronal and late glial damage

Distinguishing Laterality in Brain Injury in Rabbit Fetal Magnetic Resonance Imaging Using Novel Volume Rendering Techniques

INTRODUCTION

Our laboratory has been exploring the MRI detection of fetal brain injury, which previously provided a prognostic biomarker for newborn hypertonia in an animal model of cerebral palsy (CP). The biomarker relies on distinct patterns of diffusion-weighted imaging-defined apparent diffusion coefficient (ADC) in fetal brains during uterine hypoxia-ischemia (H-I). Despite the challenges posed by small brains and tissue acquisition, our objective was to differentiate between left and right brain ADC changes.

METHODS

A novel aspect involved utilizing three-dimensional rendering techniques to refine ADC measurements within spheroids encompassing fetal brain tissue. 25-day gestation age of rabbit fetuses underwent global hypoxia due to maternal uterine ischemia.

RESULTS

Successful differentiation of left and right brain regions was achieved in 28% of the fetal brains. Ordinal analysis revealed predominantly higher ADC on the left side compared to the right at baseline and across the entire time series. During H-I and reperfusion-reoxygenation, the right side exhibited a favored percentage change. Among these fetal brains, 73% exhibited the ADC pattern predictive of hypertonia. No significant differences between left and right sides were observed in patterns predicting hypertonia, except for one timepoint during H-I. This study also highlights a balance between left-sided and right-sided alterations within the population.

CONCLUSION

This study emphasizes the importance of investigating laterality and asymmetric hemispheric lesions for early diagnosis of brain injury, leading to CP. The technological limitations in obtaining a clear picture of the entire fetal brain for every fetus mirror the challenges encountered in human studies.

A Metabolomics Study of Hypoxia Ischemia during Mouse Brain Development Using Hyperpolarized 13C

BACKGROUND

Hyperpolarized 13C spectroscopic magnetic resonance spectroscopy (MRS) is an advanced imaging tool that may provide important real-time information about brain metabolism.

METHODS

Mice underwent unilateral hypoxia-ischemia (HI) on postnatal day (P)10. Injured and sham mice were scanned at P10, P17, and P31. We used hyperpolarized 13C MRS to investigate the metabolic exchange of pyruvate to lactate in real time during brain development following HI. 13C-1-labeled pyruvate was hyperpolarized and injected into the tail vein through a tail-vein catheter. Chemical-shift imaging was performed to acquire spectral-spatial information of the metabolites in the brain. A voxel placed on each of the injured and contralateral hemispheres was chosen for comparison. The difference in pyruvate delivery and lactate to pyruvate ratio was calculated for each of the voxels at each time point. The normalized lactate level of the injured hemisphere was also calculated for each mouse at each of the scanning time points.

RESULTS

There was a significant reduction in pyruvate delivery and a higher lactate to pyruvate ratio in the ipsilateral (HI) hemisphere at P10. The differences decreased at P17 and disappeared at P31. The normalized lactate level in the injured hemisphere increased from P10 to P31 in both sham and HI mice without brain injury.

CONCLUSION

We describe a method for detecting and monitoring the evolution of HI injury during brain maturation which could prove to be an excellent biomarker of injury.

Microcirculatory Changes in Experimental Models of Stroke and CNS-Injury Induced Immunodepression

Stroke is the second-leading cause of death globally and the leading cause of disability in adults. Medical complications after stroke, especially infections such as pneumonia, are the leading cause of death in stroke survivors. Systemic immunodepression is considered to contribute to increased susceptibility to infections after stroke. Different experimental models have contributed significantly to the current knowledge of stroke pathophysiology and its consequences. Each model causes different changes in the cerebral microcirculation and local inflammatory responses after ischemia. The vast majority of studies which focused on the peripheral immune response to stroke employed the middle cerebral artery occlusion method. We review various experimental stroke models with regard to microcirculatory changes and discuss the impact on local and peripheral immune response for studies of CNS-injury (central nervous system injury) induced immunodepression.

Mannitol decreases neocortical epileptiform activity during early brain development via cotransport of chloride and water

Seizures and brain injury lead to water and Cl^- accumulation in neurons. The increase in intraneuronal Cl^- concentration ([Cl^-]_i) depolarizes the GABA_A reversal potential (E_GABA) and worsens seizure activity. Neocortical neuronal membranes have a low water permeability due to the lack of aquaporins necessary to move free water. Instead, neurons use cotransport of ions including Cl^- to move water. Thus, increasing the extracellular osmolarity during seizures should result in an outward movement of water and salt, reducing [Cl^-]_i and improving GABA_A receptor-mediated inhibition. We tested the effects of hyperosmotic therapy with a clinically relevant dose of mannitol (20 mM) on epileptiform activity, spontaneous multiunit activity, spontaneous inhibitory post-synaptic currents (sIPSCs), [Cl^-]_i, and neuronal volume in layer IV/V of the developing neocortex of C57BL/6 and Clomeleon mice. Using electrophysiological techniques and multiphoton imaging in acute brain slices (post-natal day 7-12) and organotypic neocortical slice cultures (post-natal day 14), we observed that mannitol: 1) decreased epileptiform activity, 2) decreased neuronal volume and [Cl^-]_i through CCCs, 3) decreased spontaneous multi-unit activity frequency but not amplitude, and 4) restored the anticonvulsant efficacy of the GABA_A receptor modulator diazepam. Increasing extracellular osmolarity by 20 mOsm with hypertonic saline did not decrease epileptiform activity. We conclude that an increase in extracellular osmolarity by mannitol mediates the efflux of [Cl^-]_i and water through CCCs, which results in a decrease in epileptiform activity and enhances benzodiazepine actions in the developing neocortex in vitro. Novel treatments aimed to decrease neuronal volume may concomitantly decrease [Cl^-]_i and improve seizure control.

Early Detection of Hypothermic Neuroprotection Using T2-Weighted Magnetic Resonance Imaging in a Mouse Model of Hypoxic Ischemic Encephalopathy

Perinatal hypoxic-ischemic encephalopathy (HIE) can lead to neurodevelopmental disorders, including cerebral palsy. Standard care for neonatal HIE includes therapeutic hypothermia, which provides partial neuroprotection; magnetic resonance imaging (MRI) is often used to assess injury and predict outcome after HIE. Immature rodent models of HIE are used to evaluate mechanisms of injury and to examine the efficacy and mechanisms of neuroprotective interventions such as hypothermia. In this study, we first confirmed that, in the CD1 mouse model of perinatal HIE used for our research, MRI obtained 3 h after hypoxic ischemia (HI) could reliably assess initial brain injury and predict histopathological outcome. Mice were subjected to HI (unilateral carotid ligation followed by exposure to hypoxia) on postnatal day 7 and were imaged with T2-weighted MRI and diffusion-weighted MRI (DWI), 3 h after HI. Clearly defined regions of increased signal were comparable in T2 MRI and DWI, and we found a strong correlation between T2 MRI injury scores 3 h after HI and histopathological brain injury 7 days after HI, validating this method for evaluating initial injury in this model of HIE. The more efficient, higher resolution T2 MRI was used to score initial brain injury in subsequent studies. In mice treated with hypothermia, we found a significant reduction in T2 MRI injury scores 3 h after HI, compared to normothermic littermates. Early hypothermic neuroprotection was maintained 7 days after HI, in both T2 MRI injury scores and histopathology. In the normothermic group, T2 MRI injury scores 3 h after HI were comparable to those obtained 7 days after HI. However, in the hypothermic group, brain injury was significantly less 7 days after HI than at 3 h. Thus, early neuroprotective effects of hypothermia were enhanced by 7 days, which may reflect the additional 3 h of hypothermia after imaging or effects on later mechanisms of injury, such as delayed cell death and inflammation. Our results demonstrate that hypothermia has early neuroprotective effects in this model. These findings suggest that hypothermia has an impact on early mechanisms of excitotoxic injury and support initiation of hypothermic intervention as soon as possible after diagnosis of HIE.

Changes in Brain Swelling and Infarction Volume over Four Days After Hypoxia Ischemia in Neonatal Rats

The leading cause of morbidity and mortality in infants is hypoxia-ischemia (HI). The current therapies for HI have limited success, in part due to a lack of understanding of HI pathophysiology and underlying mechanisms. Herein, a neonatal rat model of HI was used to examine the changes in brain swelling and infarct volume over 4 days after HI. Forty-four P10 rat pups were sacrificed at 2, 3, or 4 days post-HI. After sacrifice, the brains were removed, sliced, and stained with TTC (2,3,5-triphenyl-2H-tetrazolium chloride). Images of TTC-stained brains were used for measurement of the ipsilateral hemisphere brain volumes and infarct volumes, calculated using standard equations. The hemispheric brain volumes of HI animals in all groups was lower than that of sham animals and decreased as the post-HI sacrifice time increased. The infarct volume of HI animals was larger than that of sham animals. Infarct volumes tended to decrease over the days post-HI. The change in infarct volume is likely the result of a combination of brain growth and repair mechanisms. However, changes in the hemispheric brain volume may include tissue growth and repair mechanism, so also may be a limitation of the current algorithm used for calculating ipsilateral hemisphere brain volume.

New means to assess neonatal inflammatory brain injury

Preterm infants are especially vulnerable to infection-induced white matter injury, associated with cerebral palsy, cognitive and psychomotor impairment, and other adverse neurological outcomes. The etiology of such lesions is complex and multifactorial. Furthermore, timing and length of exposure to infection also influence neurodevelopmental outcomes. Different mechanisms have been posited to mediate the observed brain injury including microglial activation followed by subsequent release of pro-inflammatory species, glutamate-induced excitotoxicity, and vulnerability of developing oligodendrocytes to cerebral insults. The prevalence of such neurological impairments requires an urgent need for early detection and effective neuroprotective strategies. Accordingly, noninvasive methods of monitoring disease progression and therapy effectiveness are essential. While diagnostic tools using biomarkers from bodily fluids may provide useful information regarding potential risks of developing neurological diseases, the use of magnetic resonance imaging/spectroscopy has emerged as a promising candidate for such purpose. Various pharmacological agents have demonstrated protective effects in the immature brain in animal models; however, few studies have progressed to clinical trials with promising results.

Neuronal death after perinatal cerebral hypoxia-ischemia: Focus on autophagy-mediated cell death

Neonatal hypoxic-ischemic encephalopathy is a critical cerebral event occurring around birth with high mortality and neurological morbidity associated with long-term invalidating sequelae. In view of the great clinical importance of this condition and the lack of very efficacious neuroprotective strategies, it is urgent to better understand the different cell death mechanisms involved with the ultimate aim of developing new therapeutic approaches. The morphological features of three different cell death types can be observed in models of perinatal cerebral hypoxia-ischemia: necrotic, apoptotic and autophagic cell death. They may be combined in the same dying neuron. In the present review, we discuss the different cell death mechanisms involved in neonatal cerebral hypoxia-ischemia with a special focus on how autophagy may be involved in neuronal death, based: (1) on experimental models of perinatal hypoxia-ischemia and stroke, and (2) on the brains of human neonates who suffered from neonatal hypoxia-ischemia.

Anti-IL-6 neutralizing antibody modulates blood-brain barrier function in the ovine fetus

Impaired blood-brain barrier function represents an important component of hypoxic-ischemic brain injury in the perinatal period. Proinflammatory cytokines could contribute to ischemia-related blood-brain barrier dysfunction. IL-6 increases vascular endothelial cell monolayer permeability in vitro. However, contributions of IL-6 to blood-brain barrier abnormalities have not been examined in the immature brain in vivo. We generated pharmacologic quantities of ovine-specific neutralizing anti-IL-6 mAbs and systemically infused mAbs into fetal sheep at 126 days of gestation after exposure to brain ischemia. Anti-IL-6 mAbs were measured by ELISA in fetal plasma, cerebral cortex, and cerebrospinal fluid, blood-brain barrier permeability was quantified using the blood-to-brain transfer constant in brain regions, and IL-6, tight junction proteins, and plasmalemma vesicle protein (PLVAP) were detected by Western immunoblot. Anti-IL-6 mAb infusions resulted in increases in mAb (P < 0.05) in plasma, brain parenchyma, and cerebrospinal fluid and decreases in brain IL-6 protein. Twenty-four hours after ischemia, anti-IL-6 mAb infusions attenuated ischemia-related increases in blood-brain barrier permeability and modulated tight junction and PLVAP protein expression in fetal brain. We conclude that inhibiting the effects of IL-6 protein with systemic infusions of neutralizing antibodies attenuates ischemia-related increases in blood-brain barrier permeability by inhibiting IL-6 and modulates tight junction proteins after ischemia.

Using the endocannabinoid system as a neuroprotective strategy in perinatal hypoxic-ischemic brain injury

One of the most important causes of brain injury in the neonatal period is a perinatal hypoxic-ischemic event. This devastating condition can lead to long-term neurological deficits or even death. After hypoxic-ischemic brain injury, a variety of specific cellular mechanisms are set in motion, triggering cell damage and finally producing cell death. Effective therapeutic treatments against this phenomenon are still unavailable because of complex molecular mechanisms underlying hypoxic-ischemic brain injury. After a thorough understanding of the mechanism underlying neural plasticity following hypoxic-ischemic brain injury, various neuroprotective therapies have been developed for alleviating brain injury and improving long-term outcomes. Among them, the endocannabinoid system emerges as a natural system of neuroprotection. The endocannabinoid system modulates a wide range of physiological processes in mammals and has demonstrated neuroprotective effects in different paradigms of acute brain injury, acting as a natural neuroprotectant. The aim of this review is to study the use of different therapies to induce long-term therapeutic effects after hypoxic-ischemic brain injury, and analyze the important role of the endocannabinoid system as a new neuroprotective strategy against perinatal hypoxic-ischemic brain injury.

Vulnerability of the developing brain to hypoxic-ischemic damage: contribution of the cerebral vasculature to injury and repair?

As clinicians attempt to understand the underlying reasons for the vulnerability of different regions of the developing brain to injury, it is apparent that little is known as to how hypoxia-ischemia may affect the cerebrovasculature in the developing infant. Most of the research investigating the pathogenesis of perinatal brain injury following hypoxia-ischemia has focused on excitotoxicity, oxidative stress and an inflammatory response, with the response of the developing cerebrovasculature receiving less attention. This is surprising as the presentation of devastating and permanent injury such as germinal matrix-intraventricular haemorrhage (GM-IVH) and perinatal stroke are of vascular origin, and the origin of periventricular leukomalacia (PVL) may also arise from poor perfusion of the white matter. This highlights that cerebrovasculature injury following hypoxia could primarily be responsible for the injury seen in the brain of many infants diagnosed with hypoxic-ischemic encephalopathy (HIE). Interestingly the highly dynamic nature of the cerebral blood vessels in the fetus, and the fluctuations of cerebral blood flow and metabolic demand that occur following hypoxia suggest that the response of blood vessels could explain both regional protection and vulnerability in the developing brain. However, research into how blood vessels respond following hypoxia-ischemia have mostly been conducted in adult models of ischemia or stroke, further highlighting the need to investigate how the developing cerebrovasculature responds and the possible contribution to perinatal brain injury following hypoxia. This review discusses the current concepts on the pathogenesis of perinatal brain injury, the development of the fetal cerebrovasculature and the blood brain barrier (BBB), and key mediators involved with the response of cerebral blood vessels to hypoxia.

The correlation between DTI parameters and levels of AQP-4 in the early phases of cerebral edema after hypoxic-ischemic/reperfusion injury in piglets

BACKGROUND

Brain edema during the early stages of hypoxic-ischemic/reperfusion (HI/R) injury can be determined using diffusion tensor imaging (DTI). The change in ADC values has been correlated with the change in expression of AQP-4.

OBJECTIVE

To determine cerebral edema at specific time intervals after HI/R injury using DTI modalities and discuss its relationship to the expression of aquaporin-4 (AQP-4).

MATERIALS AND METHODS

Thirty newborn piglets were divided into six groups (2, 6, 12, 24, 48 and 72 h) after HI/R injury. The control group subjected to sham surgery included five piglets. DTI scans and immunohistochemistry of AQP-4 expression were performed on piglet brain. The relationship between DTI parameters (FA and ADC values) and the optical density (OD) of AQP-4 expression was determined.

RESULTS

In the striatum, ADC values dropped and reached their lowest level at 24 h (F = 27.42, P < 0.05). In the subcortical border region, ADC values increased after a transient decrease and peaked at 48 h, demonstrating a significant difference from the control group (F = 50.25, P < 0.05). FA values in the internal capsules and subcortical white matter in HI/R models decreased continuously after HI/R, although no statistically significant difference from the control group was achieved. ADC and OD values of AQP-4 expression were positively correlated (r = 0.875, P < 0.05).

CONCLUSIONS

The change in ADC value after HI/R injury correlates with the expression of AQP-4.

Near-term fetal hypoxia-ischemia in rabbits: MRI can predict muscle tone abnormalities and deep brain injury

BACKGROUND AND PURPOSE

The pattern of antenatal brain injury varies with gestational age at the time of insult. Deep brain nuclei are often injured at older gestational ages. Having previously shown postnatal hypertonia after preterm fetal rabbit hypoxia-ischemia, the objective of this study was to investigate the causal relationship between the dynamic regional pattern of brain injury on MRI and the evolution of muscle tone in the near-term rabbit fetus.

METHODS

Serial MRI was performed on New Zealand white rabbit fetuses to determine equipotency of fetal hypoxia-ischemia during uterine ischemia comparing 29 days gestation (E29, 92% gestation) with E22 and E25. E29 postnatal kits at 4, 24, and 72 hours after hypoxia-ischemia underwent T2- and diffusion-weighted imaging. Quantitative assessments of tone were made serially using a torque apparatus in addition to clinical assessments.

RESULTS

Based on the brain apparent diffusion coefficient, 32 minutes of uterine ischemia was selected for E29 fetuses. At E30, 58% of the survivors manifested hind limb hypotonia. By E32, 71% of the hypotonic kits developed dystonic hypertonia. Marked and persistent apparent diffusion coefficient reduction in the basal ganglia, thalamus, and brain stem was predictive of these motor deficits.

CONCLUSIONS

MRI observation of deep brain injury 6 to 24 hours after near-term hypoxia-ischemia predicts dystonic hypertonia postnatally. Torque-displacement measurements indicate that motor deficits in rabbits progressed from initial hypotonia to hypertonia, similar to human cerebral palsy, but in a compressed timeframe. The presence of deep brain injury and quantitative shift from hypo- to hypertonia may identify patients at risk for developing cerebral palsy.

Motor deficits are triggered by reperfusion-reoxygenation injury as diagnosed by MRI and by a mechanism involving oxidants

The early antecedents of cerebral palsy (CP) are unknown but are suspected to be due to hypoxia-ischemia (H-I). In our rabbit model of CP, the MRI biomarker, apparent diffusion coefficient (ADC) on diffusion-weighted imaging, predicted which fetuses will develop postnatal hypertonia. Surviving H-I fetuses experience reperfusion-reoxygenation but a subpopulation manifested a continued decline of ADC during early reperfusion-reoxygenation, which possibly represented greater brain injury (RepReOx). We hypothesized that oxidative stress in reperfusion-reoxygenation is a critical trigger for postnatal hypertonia. We investigated whether RepReOx predicted postnatal neurobehavior, indicated oxidative stress, and whether targeting antioxidants at RepReOx ameliorated motor deficits, which included testing of a new superoxide dismutase mimic (MnTnHex-2-PyP). Rabbit dams, 79% gestation (E25), were subjected to 40 min uterine ischemia. Fetal brain ADC was followed during H-I, immediate reperfusion-reoxygenation, and 4-72 h after H-I. Endpoints were postnatal neurological outcome at E32, ADC at end of H-I, ADC nadir during H-I and reperfusion-reoxygenation, and area under ADC curve during the first 20 min of reperfusion-reoxygenation. Antioxidants targeting RepReOx were administered before and/or after uterine ischemia. The new MRI-ADC biomarker for RepReOx improved prediction of postnatal hypertonia. Greater superoxide production, mitochondrial injury, and oligodendroglial loss occurred in fetal brains exhibiting RepReOx than in those without. The antioxidants, MnTnHex-2-PyP and Ascorbate and Trolox combination, significantly decreased postnatal motor deficits and extent of RepReOx. The etiological link between early injury and later motor deficits can thus be investigated by MRI, and allows us to distinguish between critical oxidative stress that causes motor deficits and noncritical oxidative stress that does not.

Diffusion MR imaging for monitoring treatment response

The objective of this article was to emphasize the use of diffusion-weighted imaging in the diagnosis and follow-up of several major disease contexts, as established in recent literature. In some of these diseases the diffusion changes are correlated with the clinical deficit and are potentially useful for early diagnosis and longitudinal evaluation, as well as in the context of pharmacologic trials. Diffusion magnetic resonance is a major advance in the continuing evolution of MR imaging. It provides contrasts and characterization between tissues at a cellular level that may imply differences in function as well as framework and have contributed to a better understanding of the pathophysiological mechanisms of several diseases.

Long-term neuroprotective effect of postischemic hypothermia in a neonatal rat model of severe hypoxic ischemic encephalopathy: a comparative study on the duration and depth of hypothermia

It is not known whether deeper or longer hypothermia (HT) can achieve better neuroprotection against hypoxic ischemic encephalopathy (HIE) in neonates. To compare the neuroprotective effects of different durations and temperatures of postischemic HT in neonatal rats with severe HIE, 7-d-old rats were subjected to the Rice-Vannucci model for 150 min hypoxia. Only the rats with identified brain lesions in diffusion-weighted MRI were assigned to normothermia (NT, 36° C/48 h) or four HT (HT-30° C/48 h; HT-30° C/24 h; HT-33° C/48 h; and HT-33° C/24 h) groups. H-magnetic resonance spectroscopy (H-MRS) and T2-weighted MRI were obtained serially, and functional studies were performed. HT groups showed significantly greater residual hemispheric volume and better rotarod and cylinder tests than did the NT group at 5 wk postischemia. HT groups also showed lower lactate-plus-lipid level in H-MRS than did the NT group at 7 d postischemia. All of these outcome variables, however, did not differ among the 4 HT subgroups, despite a trend toward greater residual brain volume in the 48-h HT versus 24-h HT subgroups. In conclusion, neither reducing the target temperature from 33 to 30° C nor prolonging the duration from 24 to 48 h produced further improvements in neurologic outcomes in neonatal rat with HIE.

In vivo MRI analysis of an inflammatory injury in the developing brain

Cerebral periventricular white matter injury stands as a leading cause of cognitive, behavioral and motor impairment in preterm infants. There is epidemiological and histopathological evidence demonstrating the role of prenatal or neonatal inflammation in brain injury in preterm infants. In order to define the effect of an inflammatory insult in the developing brain on magnetic resonance (MR) imaging, we obtained high resolution conventional and diffusion MR images of the brain of rat pups after an inflammatory injury. Rat pups were subjected on postnatal day 5 (P5) to a stereotaxic injection of lipopolysaccharide in the corpus callosum and then imaged at 11.7 T on days 0, 2 and 4 following the injury. They were subsequently sacrificed for immunohistochemistry. Diffusion tensor imaging (DTI) acquired at high spatial resolution showed an initial reduction of the apparent diffusion coefficient (ADC) in the white matter. This was followed by an increase in ADC value and in T2 relaxation time constant in the white matter, with an associated increase of radial diffusivity of the corpus callosum, and a 10-fold increase in ventricular size. On histology, these MR changes corresponded to widespread astrogliosis, and decreased proportion of the section areas containing cresyl violet positive stain. The increase in radial diffusivity, typically attributed to myelin loss, occurred in this case despite the absence of myelin at this developmental stage.

O-GlcNAc modification of proteins affects volume regulation in Jurkat cells

An increasing amount of recent research has demonstrated that the hexosamine biosynthesis pathway (HBP) plays a significant role in the modulation of intracellular signaling transduction pathways, and affects cellular processes via modification of protein by O-linked beta-N-acetylglucosamine (O-GlcNAc). Besides the many known and postulated effects of protein O-GlcNAc modifications, there is little available data on the role of O-GlcNAc in cellular volume regulation. Our objective was to test the effect of increased O-GlcNAc levels on hypotonia-induced volume changes in Jurkat cells. We pretreated Jurkat cells for 1 h with glucosamine (GlcN), PUGNAc (O-(2-acetamido-2-deoxy-D-glucopyranosylidene)-amino-N-phenylcarbamate) an inhibitor of O-GlcNAcase, or a high level of glucose to induce elevated levels of O-GlcNAc. We found that the response of Jurkat cells to hypotonic stress was significantly altered. The hypotonia induced cell-swelling was augmented in both GlcN and PUGNAc-treated cells and, to a lesser extent, in high glucose concentration-treated cells. Evaluated by NMR measurements, GlcN and PUGNAc treatment also significantly reduced intracellular water diffusion. Taken together, increased cell swelling and reduced water diffusion caused by elevated O-GlcNAc show notable analogy to the regulatory volume changes seen by magnetic resonance methods in nervous and other tissues in different pathological states. In conclusion, we demonstrate for the first time that protein O-GlcNAc could modulate cell volume regulation.

Neuroprotective interventions: is it too late?

In most cases of neonatal hypoxic-ischemic encephalopathy, the exact timing of the hypoxic-ischemic event is unknown, and we have few reliable biomarkers to precisely identify the phase of injury or recovery in an individual patient. However, it is becoming increasingly clear that for neuroprotection in neonates to succeed, an understanding of the phase of injury is important to ascertain. In addition, in utero antecedents of chronic hypoxia, hypoxic preconditioning, intrauterine infection, and fetal gender may change the expected time course of injury. Neuroprotective interventions, such as hypothermia and N-acetylcysteine, currently have efficacy in human and animal studies only if instituted early in the inflammatory cascade. Although these cascades are currently being investigated, molecular mechanisms of recovery have received little attention and may ultimately reveal a window for therapeutic intervention that is much longer than current paradigms.

Hypothermia for hypoxic-ischemic encephalopathy

We are entering an era in which hypothermia will be used in combination with other novel neuroprotective interventions. The targeting of multiple sites in the cascade leading to brain injury may prove to be a more effective treatment strategy after hypoxic-ischemic encephalopathy in newborn infants than hypothermia alone.

Imaging the brain's highways-diffusion tensor imaging in epilepsy

Diffusion tensor imaging evaluates the motion of water at the voxel level and can provide data on the structural integrity of brain tissue, with quantitative measures of diffusion and fractional anisotropy. Imaging of the orientation of preferential diffusion of water in the brain can visualize major white matter pathways and infer the structural basis of cerebral networks. Thus, how these pathways and networks may be altered in specific epilepsy syndromes and in consequence to therapies can be assessed with the aid of these images.

Diffusion-weighted magnetic resonance imaging demonstrates parenchymal pathophysiological changes in epilepsy

Diffusion-weighted magnetic resonance imaging (DW-MRI) is a novel noninvasive technique probing the Brownian motion of water molecules. It has already proved very useful in the early identification of cerebral ischemia in human patients. Although a wide spectrum of peri-ictal, postictal or interictal DW-MRI abnormalities are recently being increasingly identified, clinicians are often in a dilemma about their significance in epilepsy. This article briefly reviews the whole dynamic ADC fluctuations and the implications of hypothetical pathophysiological evolution of effected zones in prolonged seizures or status epilepticus (SE) and their potential clinical applications in epilepsy.

Diffusion-based magnetic resonance imaging and tractography in epilepsy

Diffusion-based imaging is an advanced MRI technique that is sensitive to the movement of water molecules, providing additional information on the micro-structural arrangement of tissue. Qualitative and quantitative analysis of peri, post and interictal diffusion images can aid the localization of seizure foci. Diffusion tensor tractography is an extension of diffusion-based imaging, and can provide additional information about white matter pathways. Both techniques are able to increase understanding of the effects of epilepsy on the structural organization of the brain, and can be used to optimize presurgical planning of patients with epilepsy. This review focuses on the basis, applications, limitations, and future directions of diffusion imaging in epilepsy. Literature search strategy: We searched Pubmed using the terms "diffusion MRI or diffusion tensor MRI or tractography and epilepsy."

Application of magnetic resonance imaging in animal models of perinatal hypoxic-ischemic cerebral injury

Brain injury occurring in the perinatal period is an important etiology of subsequent neurodevelopmental disabilities. Magnetic resonance imaging (MRI) is a tool that is used to evaluate the nature of brain injury in the human infant. MRI techniques have also been applied to various animal models of perinatal injury. The most commonly used model is the immature rat, but there have also been imaging studies in mice, rabbit kits and piglets. The studies have been carried out using MR systems of various magnetic field strengths, ranging from 1.5 to 11.7tesla (T), with applications for quantification of infarct volume, T1 measurements, T2 measurements, proton and phosphorus spectroscopy and diffusion imaging. The MR findings are then related to histopathology and, in a few cases, behavioral evaluations. There is also a growing number of studies utilizing MRI in evaluating the efficacy of neuroprotective treatments, such as hypothermia.

The cannabinoid agonist WIN55212 reduces brain damage in an in vivo model of hypoxic-ischemic encephalopathy in newborn rats

Neonatal hypoxic-ischemic encephalopathy (NHIE) is a devastating condition for which effective therapeutic treatments are still unavailable. Cannabinoids emerge as neuroprotective substances in adult animal studies; therefore, we aimed herein to test whether cannabinoids might reduce brain damage induced by hypoxiaischemia (HI) in newborn rats. Thus, 7-d-old Wistar rats (P7) were exposed to 8% O2 for 120 min after left carotid artery ligature, then received s.c. vehicle (VEH) (HI+VEH), the cannabinoid agonist WIN55212 (WIN) (0.1 mg/kg), or WIN with the CB1 or CB2 receptor antagonist SR141617 (SR1) (3 mg/kg) or SR141588 (SR2) (2 mg/kg). Brain damage was assessed by magnetic resonance imaging (MRI) at 1, 3, and 7 d after the insult. At the end of the experiment, MRI findings were corroborated by histology (Nissl staining). HI+VEH showed an area of cytotoxic and vasogenic edema at 24 h after the insult, then evolving to necrosis. HI+WIN showed a similar damaged area at 24 h after the insult, but the final necrotic area was reduced by 66%. Coadministration of either SR1 or SR2 reversed the effects of WIN. In conclusion, likely by activating CB1 and CB2 receptors, WIN afforded robust neuroprotection in newborn rats after HI.

Fetal brain magnetic resonance imaging response acutely to hypoxia-ischemia predicts postnatal outcome

OBJECTIVE

Cerebral palsy (CP) is caused by either hypoxia-ischemia (H-I) or long-standing causative factors such as inflammation or genetics. Multiple pathophysiological events over time are thought to contribute eventually to cerebral palsy. Our objective was to examine whether the immediate response of the fetus to an acute H-I event determined the motor deficits associated with cerebral palsy.

METHODS

Serial diffusion-weighted imaging were performed on 79% gestation New Zealand white rabbits using a 3-Tesla magnetic resonance scanner during 40 minutes of uterine ischemia, 20 minutes of reperfusion, and at 4, 24, and 72 hours. Individual fetuses were tracked to near term, and the delivered kits were divided into hypertonic H-I (n = 18), nonhypertonic H-I (n = 9), stillbirth H-I (n = 4), and control groups (n = 16).

RESULTS

The hypertonia group had significantly less of a nadir in apparent diffusion coefficient (ADC) during H-I (71.6 +/- 23.8% vs 84.5 +/- 9.3% baseline) and slower and incomplete recovery of ADC during reperfusion compared with the nonhypertonic group. All fetuses in the hypertonic and stillbirth groups had an ADC nadir of less than 0.83 microm(2)/msec (70.3% decrease from baseline), whereas 94% of control animals had an ADC nadir greater than this value. The difference between outcome groups was the largest at 4 hours reperfusion and persisted for 24 hours.

INTERPRETATION

Serial fetal brain scans indicate that the immediate response of a fetus to H-I is crucial to the development of hypertonia. If the fetal brain can be scanned at the time of insult, ADC changes can predict which fetuses will have an unfavorable outcome.

Perinatal iron deficiency predisposes the developing rat hippocampus to greater injury from mild to moderate hypoxia-ischemia

The hippocampus is injured in both hypoxia-ischemia (HI) and perinatal iron deficiency that are co-morbidities in infants of diabetic mothers and intrauterine growth restricted infants. We hypothesized that preexisting perinatal iron deficiency predisposes the hippocampus to greater injury when exposed to a relatively mild HI injury. Iron-sufficient and iron-deficient rats (hematocrit 40% lower and brain iron concentration 55% lower) were subjected to unilateral HI injury of 15, 30, or 45 mins (n=12 to 13/HI duration) on postnatal day 14. Sixteen metabolite concentrations were measured from an 11 microL volume on the ipsilateral (HI) and contralateral (control) hippocampi 1 week later using in vivo 1H NMR spectroscopy. The concentrations of creatine, glutamate, myo-inositol, and N-acetylaspartate were lower on the control side in the iron-deficient group (P<0.02, each). Magnetic resonance imaging showed hippocampal injury in the majority of the iron-deficient rats (58% versus 11%, P<0.0001) with worsening severity with increasing durations of HI (P=0.0001). Glucose, glutamate, N-acetylaspartate, and taurine concentrations were decreased and glutamine, lactate and myo-inositol concentrations, and glutamine/glutamate ratio were increased on the HI side in the iron-deficient group (P<0.01, each), mainly in the 30 and 45 mins HI subgroups (P<0.02, each). These neurochemical changes likely reflect the histochemically detected neuronal injury and reactive astrocytosis in the iron-deficient group and suggest that perinatal iron deficiency predisposes the hippocampus to greater injury from exposure to a relatively mild HI insult.

White matter injury correlates with hypertonia in an animal model of cerebral palsy

Hypertonia and postural deficits are observed in cerebral palsy and similar abnormalities are observed in postnatal rabbits after antenatal hypoxia-ischemia. To explain why some kits become hypertonic, we hypothesized that white matter injury was responsible for the hypertonia. We compared newborn kits at postnatal day 1 (P1) with and without hypertonia after in vivo global fetal hypoxia-ischemia in pregnant rabbits at 70% gestation. The aim was to examine white matter injury by diffusion tensor magnetic resonance imaging indices, including fractional anisotropy (FA). At P1, FA and area of white matter were significantly lower in corpus callosum, internal capsule, and corona radiata of the hypertonic kits (n=32) than that of controls (n=19) while nonhypertonic kits (n=20) were not different from controls. The decrease in FA correlated with decrease in area only in hypertonia. A threshold of FA combined with area identified only hypertonic kits. A reduction in volume and loss of phosphorylated neurofilaments in corpus callosum and internal capsule were observed on immunostaining. Concomitant hypertonia with ventriculomegaly resulted in a further decrease of FA from P1 to P5 while those without ventriculomegaly had a similar increase of FA as controls. Thus, hypertonia is associated with white matter injury, and a population of hypertonia can be identified by magnetic resonance imaging variables. The white matter injury manifests as a decrease in the number and density of fiber tracts causing the decrease in FA and volume. Furthermore, the dynamic response of FA may be a good indicator of the plasticity and repair of the postnatal developing brain.

Comparing diffusion-weighted and T2-weighted MR imaging for the quantification of infarct size in a neonatal rat hypoxic-ischemic model at 24h post-injury

PURPOSE

In a neonatal rat model of hypoxic-ischemic (HI) brain injury, using T2-weighted imaging (T2WI) and diffusion-weighted imaging (DWI), we aim to determine the best MRI method of lesion quantification that reflects infarct size.

MATERIALS AND METHODS

Twenty 7-day-old rats underwent MRI 24h after HI brain injury was induced. Lesion size relative to whole brain was measured using T2WI and apparent diffusion coefficient (ADC) maps, applying thresholds of 60%, 70% and 80% contralateral control hemisphere mean ADC, and at day 10 post-HI on pathology with TTC staining. Multiple linear regression analysis was used to study the relationships between lesion size at MRI and pathology.

RESULTS

Lesion size measurement using all MRI methods significantly correlated with infarct size at pathology; using T2WI, r=0.808 (p<0.001), using 80% ADC, 70% ADC and 60% ADC thresholds, r=0.888 (p<0.001), 0.761, (p<0.001) and 0.569 (p=0.014), respectively. Eighty percent ADC threshold was found to be the only significant independent predictor of final infarct volume (adjusted R(2)=0.775).

CONCLUSION

At 24h post-HI, lesion size on DWI, using 80% ADC threshold is the best predictor of final infarct volume. Although T2WI performed less well, it has the advantage of superior spatial resolution and is technically less demanding. These are important considerations for experiments which utilize MRI as a surrogate method for lesion quantification in the neonatal rat HI model.

The effect of cerebral hypothermia on white and grey matter injury induced by severe hypoxia in preterm fetal sheep

Prolonged, moderate cerebral hypothermia is consistently neuroprotective after experimental hypoxia-ischaemia; however, it has not been tested in the preterm brain. Preterm (0.7 gestation) fetal sheep received complete umbilical cord occlusion for 25 min followed by cerebral hypothermia (fetal extradural temperature reduced from 39.4 +/- 0.3 to 29.5 +/- 2.6 degrees C) from 90 min to 70 h after the end of occlusion or sham cooling. Occlusion led to severe acidosis and profound hypotension, which recovered rapidly after release of occlusion. After 3 days recovery the EEG spectral frequency, but not total intensity, was increased in the hypothermia-occlusion group compared with normothermia-occlusion. Hypothermia was associated with a significant overall reduction in loss of immature oligodendrocytes in the periventricular white matter (P < 0.001), and neuronal loss in the hippocampus and basal ganglia (P < 0.001), with suppression of activated caspase-3 and microglia (isolectin-B4 positive). Proliferation was significantly reduced in periventricular white matter after occlusion (P < 0.05), but not improved after hypothermia. In conclusion, delayed, prolonged head cooling after a profound hypoxic insult in the preterm fetus was associated with a significant reduction in loss of neurons and immature oligodendroglia, with evidence of EEG and haemodynamic improvement after 3 days recovery, but also with a persisting reduction in proliferation of cells in the periventricular region. Further studies are required to evaluate the long-term impact of cooling on brain growth and maturation.

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.

Detection of wallerian degeneration in a newborn by diffusion magnetic resonance imaging (MRI)

We present the case of an infant with hypoxic-ischemic encephalopathy in whom wallerian degeneration is demonstrated in white-matter fiber tracts by diffusion magnetic resonance imaging (MRI). MRI was undertaken on days 2 and 9 and then at 9 months of age. On day 2, conventional MRI was normal, but diffusion MRI showed bioccipital abnormalities. On day 9, diffusion MRI showed marked abnormalities in the deep white matter of the occipital regions (left > right), corpus callosum, left posterior limb of the internal capsule, and left cerebral peduncle. Water apparent diffusion coefficient values showed a significant reduction in the left occipital white matter and corpus callosum between days 2 and 9 while demonstrating the expected pseudonormalization in cortical gray matter. Images at 9 months showed left occipital porencephaly and atrophy of the left cerebral peduncle, with the infant displaying right hemiplegia at 18 months of age. In this case, the time course of diffusion changes differed between white and gray matter, with diffusion MRI showing delayed wallerian degeneration of the cerebral white matter. This case characterizes this degeneration with clinical and follow-up MRI at 9 months of age.

Biphasic changes in the levels of poly(ADP-ribose) polymerase-1 and caspase 3 in the immature brain following hypoxia-ischemia

Poly(ADP-ribose) polymerase-1 (PARP-1) is a DNA repair-associated enzyme that has multiple roles in cell death. This study examined the involvement of PARP-1 in ischemic brain injury in the 7-day old rat, 0.5-48 h after unilateral carotid artery ligation and 2 h of 7.8% oxygen. This experimental paradigm produced a mild to moderate injury; 40-67% of animals in the ligated groups had histological evidence of neuronal death. Ipsilateral cortical injury was seen at all survival times, while mild contralateral cortical injury was seen only at the 1h survival time. Hippocampal injury was delayed relative to the cortex and did not show a biphasic pattern. Immunohistochemical staining for PARP showed bilateral increased staining as early as 1 h post-hypoxia. PARP staining at early time periods was most intense in layer V of cortex, but did not demonstrate a pattern of cell clusters or columns. Ipsilateral PARP-1 levels quantified by western blotting showed a biphasic pattern of elevation with peaks at 0.5 and 12 h post-hypoxia. Contralateral PARP-1 levels were also elevated at 0.5 and 24 h. PARP activity as determined by immunoreactivity for poly(ADP-ribose) (PAR) was increased ipsilaterally at 0.5, 2 and 12 h survival times. Cortical caspase 3-activity was increased ipsilaterally at 6, 12, and 24 h and contralaterally at 0.5, 1, 2 and 6 h post-hypoxia. There are three main findings in this study. First, changes in the distribution and amount of cell death correlate well with measured PARP-1 levels after hypoxia-ischemia, and both display biphasic characteristics. Second, there are significant early, transient morphological and biochemical changes in the contralateral cortex after neonatal hypoxia-ischemia due to unilateral permanent occlusion of a carotid artery followed by 2 h of systemic hypoxia. Third, variability in the responses of individual pups to hypoxia-ischemia suggests the presence of unidentified confounding factors.

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.

Perinatal Hypoxic-Ischemic Brain Damage: Evolution of an Animal Model

Early research in the Vannucci laboratory prior to 1981 focused largely on brain energy metabolism in the developing rat. At that time, there was no experimental model to study the effects of perinatal hypoxia-ischemia in the rodent, despite the tremendous need to investigate the pathophysiology of perinatal asphyxial brain damage in infants. Accordingly, we developed such a model in the postnatal day 7 rat, using a modification of the Levine preparation in the adult rat. Rat pups underwent unilateral common carotid artery ligation followed by exposure to systemic hypoxia (8% oxygen) at a constant temperature of 37 degrees C. Brain damage, seen histologically, was generally confined to the cerebral hemisphere ipsilateral to the arterial occlusion, and consisted of selective neuronal death or infarction, depending on the duration of the systemic hypoxia. Tissue injury was observed in the cerebral cortex, hippocampus, striatum, and thalamus. Subcortical and periventricular white matter injury was also observed. This model was originally described in the Annals of Neurology in 1981, and during the more than 20 years since that publication numerous investigations utilizing the model have been conducted in our laboratories as well as laboratories around the world. Cerebral blood flow and metabolic correlates have been fully characterized. Physiologic and pharmacologic manipulations have been applied to the model in search of neuroprotective strategies. More recently, molecular biologic alterations during and following the hypoxic-ischemic stress have been ascertained and the model has been adapted to the immature mouse for specific use in genetically altered animals. As predicted in the original article, the model has proven useful for the study of the short- and long-term effects of hypoxic-ischemic brain damage on motor activity, behavior, seizure incidence, and the process of maturation in the brain and other organ systems.

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.

Ischemia-induced ADC changes are larger than osmotically-induced ADC changes in a neonatal rat hippocampus model

Diffusion-weighted imaging (DWI) is frequently used to diagnose stroke. However, the origin of the observed reduction in the apparent diffusion coefficient (ADC) in the acute phase following ischemia is not well understood. Although cell swelling is considered to play an important role, it is unclear whether this can completely explain the large ADC decrease. We developed a method to induce in neonatal rat hippocampal slices both osmotic perturbations, which lead to cell swelling, and oxygen/glucose deprivation (OGD), which simulates ischemia. A perfusion system was used to provide the hippocampal slices with nutrients and oxygen to maintain slice viability, which was verified with the use of fluorescent dyes (live/dead staining). Upon induction of OGD, the ADC decreased to approximately 57% of the initial value within 2 hr. The ADC reduction cannot fully be explained by changes due to cell swelling, since these led only to a maximum decrease of approximately 83%. Therefore, in addition to cell swelling, other changes must contribute significantly to the ADC reduction.

Hypoxia/aglycemia alters expression of occludin and actin in brain endothelial cells

The blood-brain barrier (BBB) serves as a critical organ in the maintenance of central nervous system homeostasis and is disrupted in a number of neurological disorders, including stroke. We examined the effects of hypoxia/aglycemia on the expression and localization of tight junction proteins, and on the function of the BBB in an in vitro model system. A receptor-operated/store-operated calcium channel blocker, SKF 96365, was used to determine if calcium flux was important in mediating hypoxia/aglycemia effects on the BBB. Expression of the tight junction protein occludin increased after hypoxic/aglycemic stress when cells were exposed to SKF 96365; this was correlated with partial protection of membrane localization of occludin and inhibition of the hypoxia-induced increase in permeability. Actin expression was dramatically reduced by hypoxia/aglycemia. Treatment with SKF 96365 during hypoxic stress protected monolayer permeability of sucrose, but transendothelial electrical resistances decreased with exposure to hypoxic stress regardless of treatment. Therefore, the presence of occludin at the membrane is dependent in part on calcium-sensitive signaling cascades; this provides a target for therapeutic intervention to minimize BBB disruption after stroke.

MRI characterisation of a novel rat model of focal astrocyte loss

Blood-brain barrier (BBB) integrity is lost in several neurological conditions in which astrocytes are damaged. We studied 3-chloropropanediol-induced focal lesions, a toxicant that induces early astrocytic (but not neuronal) death followed by BBB leakage. T2-weighted images illustrate regional selectivity of the lesions, affected areas including the inferior colliculi and red nuclei. Gd-DTPA intensity quantified the degree of vascular leakage in the lesioned areas. MRI intensity in lesioned areas peaked at 2 days, correlating with BBB breakdown, and diminished thereafter, returning to pre-injection levels by 30 days in parallel with the return of astrocytes. T2 measurements were unchanged at 6 h, a time when astrocyte swelling is marked but the vasculature is intact, but increased at 2 days, consistent with cellular damage and BBB leakage. Gd-DTPA enhancement was also greatest at 2 days then decreased over the next 28 days, indicating a tracer-size-dependent rate of BBB repair. A simple model based on experimentally acquired data indicated that the vascular breakdown was the result of leakage of only a small percentage of blood vessels in the affected areas. Loss of astrocytes contributes to barrier loss, and restoration of astrocytes is needed for full barrier recovery.

Novel MR contrasts to reveal more about the brain

Twenty percent of patients with refractory focal epilepsy have an undetermined etiologic basis for their epilepsy despite extensive investigation, including optimal MR imaging. Surgical treatment of this group is associated with a less favorable postoperative outcome. Even with improvements in imaging techniques, a proportion of these patients will remain "MR imaging-negative." It is likely, however, that some of the discrete macroscopic focal lesions that are currently occult will be identified by imaging techniques interrogating different microstructural characteristics. Furthermore, these methods may provide pathologic specificity when used in combination. The description and application of these techniques in epilepsy are the focus of this article.

Acute diffusion abnormalities in the hippocampus of children with new-onset seizures: the development of mesial temporal sclerosis

We studied the role of early diffusion-weighted imaging DWI in the investigation of children with new-onset prolonged seizures which eventually result in unilateral hippocampal sclerosis (HS). We carried out MRI on five children aged 17 months to 7 years including conventional and diffusion-weighted sequences. We calculated apparent diffusion coefficients (ADC) for the affected and the normal opposite hippocampus. Follow-up examinations were performed, including DWI and ADC measurements in four. We studied four children within 3 days of the onset of prolonged psychomotor seizures and showed increased signal on T2-weighted images, and DWI, indicating restricted diffusion, throughout the affected hippocampus. The ADC were reduced by a mean of 14.4% in the head and by 15% in the body of the hippocampus. In one child examined 15 days after the onset of seizures, the ADC were the same on both sides. All five patients showed hippocampal atrophy on follow-up 2-18 months later. In the four patients in whom ADC were obtained on follow-up, they were increased by 19% in the head and 17% in the body. DWI may represent a useful adjunct to conventional MRI for identifying acute injury to the hippocampus which results in sclerosis.

The influence of litter size on brain damage caused by hypoxic-ischemic injury in the neonatal rat

Hypoxic ischemia is a common cause of brain injury in the human neonate. This can be mimicked in the neonatal rat, but produces variable injury. The present study investigated the influence of litter size on the severity and variability of damage caused by hypoxic-ischemic injury in neonatal rats. Groups of 7-d-old pups from birth-sized litters (13-15 pups), or from litters culled to 10 on postnatal d 2, and 8- and 9-d-old pups from birth-sized litters, were exposed to common carotid artery occlusion and then, 3 h later, hypoxia (2 h 15 min, 8% oxygen). Damage was assessed histologically 72 h after injury, and graded (I-IV) according to severity. In nonculled litters, similar numbers of animals had each grade of injury. Most pups (70%) from culled litters had grade III or IV damage, and severity was significantly greater than in nonculled litters (p < 0.001). Pups from culled litters were heavier (17.6 +/- 0.4 g) than pups from nonculled litters (14.7 +/- 0.3 g, p < 0.0001). To determine whether this indicated that culled litters were more similar to older pups in their response to hypoxic-ischemic injury, we examined injury in 8- and 9-d-old pups of similar body weight to 7-d-old pups from culled litters. The severity and distribution of damage in the older pups was different from damage in the 7-d-old pups from culled litters. These data suggest that in 7-d-old rats, litter size influences damage caused by hypoxic-ischemic injury, and that the relationship between body weight, brain development, and susceptibility to hypoxic-ischemic injury is complex.

MRI evaluation and functional assessment of brain injury after hypoxic ischemia in neonatal mice

BACKGROUND AND PURPOSE

Severe perinatal asphyxia is an important cause of brain injury in the newborn infant. We examined early events after hypoxic ischemia (HI) in the 7-day-old mouse brain by MRI and related them to long-term functional effects and histopathology in the same animals at 4 to 5 weeks of age.

METHODS

HI was induced in 7-day-old CD1 mice by exposure to 8% oxygen for 30 minutes after occlusion of the left common carotid artery. The resulting unilateral focal lesion was evaluated in vivo by MRI (T2 maps and apparent diffusion coefficient maps) at 3, 6, and 24 hours and 5 days after hypoxia. Locomotion and sensorimotor function were analyzed after 3 weeks. Four weeks after HI, the mice were killed, and cresyl violet-stained brain sections were examined morphologically.

RESULTS

A decrease in apparent diffusion coefficient values in cortex on the affected side was found at 3 hours after HI. T2 values were significantly increased after 6 hours and remained so for 5 days. Maximal size of the lesion was attained at 3 to 6 hours after HI and declined thereafter. Animals with MRI-detected lesions had decreased forward locomotion, performed worse than controls in the beam-walking test, and showed a unilateral hypotrophy in the cresyl violet-stained brain sections 4 weeks later.

CONCLUSIONS

The temporal progression of the damage after HI in 7-day-old mice differs from that of the adult brain as judged by MRI. The early lesions detected by MRI were related to functional impairments for these mice in near-adult life.

Delayed postischemic hypothermia improves long-term behavioral outcome after cerebral hypoxia-ischemia in neonatal rats

Hypothermia may be an ideal neuroprotective intervention in hypoxic-ischemic encephalopathy after perinatal asphyxia. The present study describes the long-term effects of prolonged resuscitative whole-body hypothermia initiated 2 h after hypoxic-ischemic injury on brain morphology and neuropsychological behavior in 7-d-old rats. After right common carotid artery ligation and exposure to hypoxia of 8% O(2) for 105 min, 10 animals were kept normothermic at 37 degrees C and 10 animals were cooled to 30 degrees C rectal temperature for 26 h, starting 2 h after the hypoxic-ischemic insult. All hypoxic-ischemic animals were gavage fed to guarantee long-term survival. Neuroprotection was evaluated by magnetic resonance imaging and behavioral testing. Hypothermia significantly reduced the final size of cerebral infarction by 23% at 6 wk after the insult. The most extended tissue rescue was found in the hippocampus (21%, p = 0.031), followed by the striatum (13%, p = 0.143) and the cortex (11%, p = 0.160). Cooling salvaged spatial memory deficits verified at 5 wk of recovery with Morris Water Maze test; whereas circling abnormalities after apomorphine injection and sensory motor dysfunctions on rotating treadmill improved, yet did not reach statistical significance. When compared with controls, hypoxic-ischemic animals performed worse in all behavioral tests. Hypothermia did not influence functional outcome in controls. Significant correlations between behavioral performance and corresponding regional brain volumes were found. We conclude that 26 h of mild to moderate resuscitative hypothermia leads not only to brain tissue rescue, but most important to long-lasting behavioral improvement throughout brain maturation despite severity of injury and delayed onset of cooling.

Time course of changes in diffusion-weighted magnetic resonance imaging in a case of neonatal encephalopathy with defined onset and duration of hypoxic-ischemic insult

The onset and duration of hypoxic-ischemic (HI) insults rarely can be determined precisely in perinatal asphyxia. The need to establish the timing of HI insults will be critical for the successful application of evolving neuroprotective therapies that may be administered to the asphyxiated newborn. Diffusion-weighted magnetic resonance imaging has emerged as an imaging technique that can be used to identify HI brain injury before the detection of abnormalities by conventional magnetic resonance imaging. This case illustrates the early changes in diffusion-weighted and conventional magnetic resonance imaging studies and in quantitative values of the apparent diffusion coefficient in a unique case of neonatal asphyxia in which the onset and duration of the HI insult were known.hypoxia-ischemia, newborn brain, perinatal asphyxia, diffusion-weighted imaging, proton magnetic resonance spectroscopy.

Transcriptional regulation of the BCL-X gene by NF-kappaB is an element of hypoxic responses in the rat brain

Signal transduction pathways that mediate neuronal commitment to apoptosis involve the nuclear factor kappa B (NF-kappaB) transcription factor. The bcl-x gene is a member of the bcl-2 family of genes that regulate apoptosis, and gives rise to two proteins, Bcl-XL and Bcl-XS, via alternative mRNA splicing. BCl-XL protein, like Bcl-2, is a dominant inhibitor of apoptotic cell death, whereas Bcl-XS promotes apoptosis. While there is high expression of Bcl-XL in the developing and adult brain, few transcriptional control elements have been identified in the bcl-x promoter. There are two functional nuclear factor-kappa B (NF-kappaB) DNA binding sites clustered upstream of the brain-specific transcription start site in the upstream promoter region of murine bcl-x. Recombinant NF-kappaB proteins bind to these sites. Also NF-kappaB overexpression, coupled with bcl-x promoter/reporter assays using a series of murine bcl-x promoter and deletion mutants, has identified the downstream 1.1kb of the bcl-x promoter as necessary for basal promoter activity and induction by NF-kappaB in support of the hypothesis that NF-kappaB can act to enhance BCl-XL expression via highly selective interactions with the bcl-x promoter, where NF-kappaB binding and promoter activation are dependent on specific DNA binding site sequences and NF-kappaB protein dimer composition. Hypoxia induces apoptosis in the hippocampus where the NF-kappaB dimers c-Rel/p50 and p50/pS0 bind to the bcl-x promoter NF-kappaB site.

Insulin-like growth factor-1 reduces postischemic white matter injury in fetal sheep

Insulin-like growth factor-1 (IGF-1) is known to be important for oligodendrocyte survival and myelination. In the current study, the authors examined the hypothesis that exogenous IGF-1 could reduce postischemic white matter injury. Bilateral brain injury was induced in near-term fetal sheep by 30 minutes of reversible carotid artery occlusion. Ninety minutes after ischemia, either vehicle (n = 8) or a single dose of 3 microg IGF-1 (n = 9) was infused intracerebroventricularly over 1 hour. White matter changes were assessed after 4 days recovery in the parasagittal intragyral white matter and underlying corona radiata. Proteolipid protein (PLP) mRNA staining was used to identify bioactive oligodendrocytes. Glial fibrillary acidic protein (GFAP) and isolectin B-4 immunoreactivity were used to label astrocytes and microglia, respectively. Myelin basic protein (MBP) density and the area of the intragyral white matter tracts were determined by image analysis. Insulin-like growth factor-1 treatment was associated with significantly reduced loss of oligodendrocytes in the intragyral white matter (P < 0.05), with improved MBP density (P < 0.05), reduced tissue swelling, and increased numbers of GFAP and isolectin B-4 positive cells compared with vehicle treatment. After ischemia there was a close association of PLP mRNA labeled cells with reactive astrocytes and macrophages/microglia. In conclusion, IGF-1 can prevent delayed, postischemic oligodendrocyte cell loss and associated demyelination.

Delayed increase in neuronal nitric oxide synthase immunoreactivity in thalamus and other brain regions after hypoxic-ischemic injury in neonatal rats

We examined the response of neuronal nitric oxide synthase (nNOS)-containing CNS neurons in rats exposed to a unilateral hypoxic-ischemic insult at 7 days of age. Animals were sacrificed at several time points after the injury, up to and including 7 days (Postnatal Day 14). Brain regions ipsilateral to the injury (including cerebral cortex, caudate-putamen, and thalamus) exhibited delayed, focal increases in nNOS immunoreactivity. The increase in nNOS immunoreactive fiber staining was prominent in areas adjacent to severe neuronal damage, especially in the cortex and the thalamus, regions that are also heavily and focally injured in term human neonates with hypoxic-ischemic encephalopathy. In cerebral cortex, these increases occurred despite modest declines in nNOS catalytic activity and protein levels. Proliferation of surviving nNOS immunoreactive fibers highlights regions of selective vulnerability to hypoxic-ischemic insult in the neonatal brain and may also contribute to plasticity of neuronal circuitry during recovery.