Brief post-hypoxic-ischemic hypothermia markedly delays neonatal brain injury

Hypothermia combined with extracellular vesicles from clonally expanded immortalized mesenchymal stromal cells improves neurodevelopmental impairment in neonatal hypoxic-ischemic brain injury

BACKGROUND

Neonatal encephalopathy following hypoxia-ischemia (HI) is a leading cause of childhood death and morbidity. Hypothermia (HT), the only available but obligatory therapy is limited due to a short therapeutic window and limited efficacy. An adjuvant therapy overcoming limitations of HT is still missing. Mesenchymal stromal cell (MSC)-derived extracellular vesicles (EVs) have shown promising therapeutic effects in various brain injury models. Challenges associated with MSCs' heterogeneity and senescence can be mitigated by the use of EVs from clonally expanded immortalized MSCs (ciMSCs). In the present study, we hypothesized that intranasal ciMSC-EV delivery overcomes limitations of HT.

METHODS

Nine-day-old C57BL/6 mice were exposed to HI by occlusion of the right common carotid artery followed by 1 h hypoxia (10% oxygen). HT was initiated immediately after insult for 4 h. Control animals were kept at physiological body core temperatures. ciMSC-EVs or vehicle were administered intranasally 1, 3 and 5 days post HI/HT. Neuronal cell loss, inflammatory and regenerative responses were assessed via immunohistochemistry, western blot and real-time PCR 7 days after insult. Long-term neurodevelopmental outcome was evaluated by analyses of cognitive function, activity and anxiety-related behavior 5 weeks after HI/HT.

RESULTS

In contrast to HT monotherapy, the additional intranasal therapy with ciMSC-EVs prevented HI-induced cognitive deficits, hyperactivity and alterations of anxiety-related behavior at adolescence. This was preceded by reduction of striatal neuronal loss, decreased endothelial, microglia and astrocyte activation; reduced expression of pro-inflammatory and increased expression of anti-inflammatory cytokines. Furthermore, the combination of HT with intranasal ciMSC-EV delivery promoted regenerative and neurodevelopmental processes, including endothelial proliferation, neurotrophic growth factor expression and oligodendrocyte maturation, which were not altered by HT monotherapy.

CONCLUSION

Intranasal delivery of ciMSC-EVs represents a novel adjunct therapy, overcoming limitations of acute HT thereby offering new possibilities for improving long-term outcomes in neonates with HI-induced brain injury.

Pathophysiology of Perinatal Asphyxia in Humans and Animal Models

Perinatal asphyxia is caused by lack of oxygen delivery (hypoxia) to end organs due to an hypoxemic or ischemic insult occurring in temporal proximity to labor (peripartum) or delivery (intrapartum). Hypoxic-ischemic encephalopathy is the clinical manifestation of hypoxic injury to the brain and is usually graded as mild, moderate, or severe. The search for useful biomarkers to precisely predict the severity of lesions in perinatal asphyxia and hypoxic-ischemic encephalopathy (HIE) is a field of increasing interest. As pathophysiology is not fully comprehended, the gold standard for treatment remains an active area of research. Hypothermia has proven to be an effective neuroprotective strategy and has been implemented in clinical routine. Current studies are exploring various add-on therapies, including erythropoietin, xenon, topiramate, melatonin, and stem cells. This review aims to perform an updated integration of the pathophysiological processes after perinatal asphyxia in humans and animal models to allow us to answer some questions and provide an interim update on progress in this field.

Hypothermia modulates myeloid cell polarization in neonatal hypoxic-ischemic brain injury

Background

Neonatal encephalopathy due to hypoxia–ischemia (HI) is a leading cause of death and disability in term newborns. Therapeutic hypothermia (HT) is the only recommended therapy. However, 30% still suffer from neurological deficits. Inflammation is a major hallmark of HI pathophysiology with myeloid cells being key players, participating either in progression or in resolution of injury-induced inflammation. In the present study, we investigated the impact of HT on the temporal and spatial dynamics of microglia/macrophage polarization after neonatal HI in newborn mice.

Methods

Nine-day-old C57BL/6 mice were exposed to HI through occlusion of the right common carotid artery followed by 1 h hypoxia. Immediately after HI, animals were cooled for 4 h or kept at physiological body core temperature. Analyses were performed at 1, 3 and 7 days post HI. Brain injury, neuronal cell loss, apoptosis and microglia activation were assessed by immunohistochemistry. A broad set of typical genes associated with classical (M1) and alternative (M2) myeloid cell activation was analyzed by real time PCR in ex vivo isolated CD11b⁺ microglia/macrophages. Purity and composition of isolated cells was determined by flow cytometry.

Results

Immediate HT significantly reduced HI-induced brain injury and neuronal loss 7 days post HI, whereas only mild non-significant protection from HI-induced apoptosis and neuronal loss were observed 1 and 3 days after HI. Microglia activation, i.e., Iba-1 immunoreactivity peaked 3 days after HI and was not modulated by HT. However, ex vivo isolated CD11b⁺ cells revealed a strong upregulation of the majority of M1 but also M2 marker genes at day 1, which was significantly reduced by HT and rapidly declined at day 3. HI induced a significant increase in the frequency of peripheral macrophages in sorted CD11b⁺ cells at day 1, which deteriorated until day 7 and was significantly decreased by HT.

Conclusion

Our data demonstrate that HT-induced neuroprotection is preceded by acute suppression of HI-induced upregulation of inflammatory genes in myeloid cells and decreased infiltration of peripheral macrophages, both representing potential important effector mechanisms of HT.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02314-9.

Effects of carnosine and hypothermia combination therapy on hypoxic-ischemic brain injury in neonatal rats

BACKGROUND

Carnosine has antioxidative and neuroprotective properties against hypoxic-ischemic (HI) brain injury. Hypothermia is used as a therapeutic tool for HI encephalopathy in newborn infants with perinatal asphyxia. However, the combined effects of these therapies are unknown.

PURPOSE

Here we investigated the effects of combined carnosine and hypothermia therapy on HI brain injury in neonatal rats.

METHODS

Postnatal day 7 (P7) rats were subjected to HI brain injury and randomly assigned to 4 groups: vehicle; carnosine alone; vehicle and hypothermia; and carnosine and hypothermia. Carnosine (250 mg/kg) was intraperitoneally administered at 3 points: immediately following HI injury, 24 hours later, and 48 hours later. Hypothermia was performed by placing the rats in a chamber maintained at 27°C for 3 hours to induce whole-body cooling. Sham-treated rats were also included as a normal control. The rats were euthanized for experiments at P10, P14, and P35. Histological and morphological analyses, in situ zymography, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assays, and immunofluorescence studies were conducted to investigate the neuroprotective effects of the various interventional treatments.

RESULTS

Vehicle-treated P10 rats with HI injury showed an increased infarct volume compared to sham-treated rats during the triphenyltetrazolium chloride staining study. Hematoxylin and eosin staining revealed that vehicle-treated P35 rats with HI injury had decreased brain volume in the affected hemisphere. Compared to the vehicle group, carnosine and hypothermia alone did not result in any protective effects against HI brain injury. However, a combination of carnosine and hypothermia effectively reduced the extent of brain damage. The results of in situ zymography, TUNEL assays, and immunofluorescence studies showed that neuroprotective effects were achieved with combination therapy only.

CONCLUSION

Carnosine and hypothermia may have synergistic neuroprotective effects against brain damage following HI injury.

Neuroprotection Strategies for Term Encephalopathy

Brain injury in the full-term and near-term neonates is a significant cause of mortality and long-term morbidity, resulting in injury patterns distinct from that seen in premature infants and older patients. Therapeutic hypothermia improves long-term outcomes for many of these infants, but there is a continued search for therapies to enhance the plasticity of the newborn brain, resulting in long-term repair. It is likely that a combination strategy utilizing both early and late interventions may have the most benefit, capitalizing on endogenous mechanisms triggered by hypoxia or ischemia. Optimizing care of these critically ill newborns in the acute setting is also vital for improving both short- and long-term outcomes.

Thrombin Preconditioning Enhances Therapeutic Efficacy of Human Wharton's Jelly-Derived Mesenchymal Stem Cells in Severe Neonatal Hypoxic Ischemic Encephalopathy

We investigated whether thrombin preconditioning of human Wharton's jelly-derived mesenchymal stem cells (MSCs) improves paracrine potency and thus the therapeutic efficacy of naïve MSCs against severe hypoxic ischemic encephalopathy (HIE). Thrombin preconditioning significantly enhances the neuroprotective anti-oxidative, anti-apoptotic, and anti-cytotoxic effects of naïve MSCs against oxygen-glucose deprivation (OGD) of cortical neurons in vitro. Severe HIE was induced in vivo using unilateral carotid artery ligation and hypoxia for 2 h and confirmed using brain magnetic resonance imaging (MRI) involving >40% of ipsilateral hemisphere at postnatal day (P) 7 in newborn rats. Delayed intraventricular transplantation of 1 × 105 thrombin preconditioned but not naïve MSCs at 24 h after hypothermia significantly enhanced observed anti-inflammatory, anti-astroglial, and anti-apoptotic effects and the ensuing brain infarction; behavioral tests, such as cylinder rearing and negative geotaxis tests, were conducted at P42. In summary, thrombin preconditioning of human Wharton's jelly-derived MSCs significantly boosted the neuroprotective effects of naïve MSCs against OGD in vitro by enhancing their anti-oxidative, anti-apoptotic, and anti-cytotoxic effects, and significantly attenuated the severe HIE-induced brain infarction and improved behavioral function tests in vivo by maximizing their paracrine anti-inflammatory, anti-astroglial, and anti-apoptotic effects.

Perinatal hypoxic-ischemic brain injury in large animal models: Relevance to human neonatal encephalopathy

Perinatal hypoxia-ischemia resulting in death or lifelong disabilities remains a major clinical disorder. Neonatal models of hypoxia-ischemia in rodents have enhanced our understanding of cellular mechanisms of neural injury in developing brain, but have limitations in simulating the range, accuracy, and physiology of clinical hypoxia-ischemia and the relevant systems neuropathology that contribute to the human brain injury pattern. Large animal models of perinatal hypoxia-ischemia, such as partial or complete asphyxia at the time of delivery of fetal monkeys, umbilical cord occlusion and cerebral hypoperfusion at different stages of gestation in fetal sheep, and severe hypoxia and hypoperfusion in newborn piglets, have largely overcome these limitations. In monkey, complete asphyxia produces preferential injury to cerebellum and primary sensory nuclei in brainstem and thalamus, whereas partial asphyxia produces preferential injury to somatosensory and motor cortex, basal ganglia, and thalamus. Mid-gestational fetal sheep provide a valuable model for studying vulnerability of progenitor oligodendrocytes. Hypoxia followed by asphyxia in newborn piglets replicates the systems injury seen in term newborns. Efficacy of post-insult hypothermia in animal models led to the success of clinical trials in term human neonates. Large animal models are now being used to explore adjunct therapy to augment hypothermic neuroprotection.

The duration of hypothermia affects short-term neuroprotection in a mouse model of neonatal hypoxic ischaemic injury

Neonatal hypoxic-ischaemic encephalopathy (HIE) is major cause of neonatal mortality and morbidity. Therapeutic hypothermia is standard clinical care for moderate hypoxic-ischaemic (HI) brain injury, however it reduces the risk of death and disability only by 11% and 40% of the treated infants still develop disabilities. Thus it is necessary to develop supplementary therapies to complement therapeutic hypothermia in the treatment of neonatal HIE. The modified Rice-Vannucci model of HI in the neonatal mouse is well developed and widely applied with different periods of hypothermia used as neuroprotective strategy in combination with other agents. However, different studies use different periods, time of initiation and duration of hypothermia following HI, with subsequent varying degrees of neuroprotection. So far most rodent data is obtained using exposure to 5-6h of therapeutic hypothermia. Our aim was to compare the effect of exposure to three different short periods of hypothermia (1h, 1.5h and 2h) following HI insult in the postnatal day 7 C57/Bl6 mouse, and to determine the shortest period providing neuroprotection. Our data suggests that 1h and 1.5h of hypothermia delayed by 20min following a 60min exposure to 8%O2 do not prove neuroprotective. However, 2h of hypothermia significantly reduced tissue loss, TUNEL+ cell death and microglia and astroglia activation. We also observed improved functional outcome 7 days after HI. We suggest that the minimal period of cooling necessary to provide moderate short term neuroprotection and appropriate for the development and testing of combined treatment is 2h.

Therapeutic hypothermia translates from ancient history in to practice

Acute postasphyxial encephalopathy around the time of birth remains a major cause of death and disability. The possibility that hypothermia may be able to prevent or lessen asphyxial brain injury is a "dream revisited". In this review, a historical perspective is provided from the first reported use of therapeutic hypothermia for brain injuries in antiquity, to the present day. The first uncontrolled trials of cooling for resuscitation were reported more than 50 y ago. The seminal insight that led to the modern revival of studies of neuroprotection was that after profound asphyxia, many brain cells show initial recovery from the insult during a short "latent" phase, typically lasting ~6 h, only to die hours to days later during a "secondary" deterioration phase characterized by seizures, cytotoxic edema, and progressive failure of cerebral oxidative metabolism. Studies designed around this conceptual framework showed that mild hypothermia initiated as early as possible before the onset of secondary deterioration, and continued for a sufficient duration to allow the secondary deterioration to resolve, is associated with potent, long-lasting neuroprotection. There is now compelling evidence from randomized controlled trials that mild induced hypothermia significantly improves intact survival and neurodevelopmental outcomes to midchildhood.

Prolonged exposure to isoflurane ameliorates infarction severity in the rat pup model of neonatal hypoxia-ischemia

The neonatal hypoxia-ischemia rat model referred to as the Rice-Vannucci model is extensively used to study perinatal hypoxia-ischemia and child brain injury. One of the major weaknesses of this model is its inconsistency of brain infarction among animals. We hypothesize that the inconsistency of infarction is caused by prolonged operation time and therefore isoflurane exposure. Neonatal hypoxia-ischemia was induced in postnatal days 7 and 10 rat pups by unilateral right common carotid ligation followed by 2.5 h of hypoxia (8% oxygen). The incision-to-ligation (ITL) was defined as the amount of time from initial incision (4 min after 2% isoflurane exposure) to completion of carotid ligation (at which point isoflurane exposure was also terminated). In the first part of the study, the ITL of each group was designated to be 5, 13, and 21 min. In the second part of the study, the ITL is designated to 4 min; however, continued isoflurane was used to make 5, 13, and 21 min isoflurane exposure for each group. Percentages of brain infarction were assessed at 48 h following surgery. Motor deficits were accessed by Rotarod test. Marked brain infarction was observed in the 5-min ITL group and a decrease of brain infarction observed in the 13-and 21-min groups (P<0.05). In the second part of the study, marked brain infarction was observed in the 5-min isoflurane exposure group, and a decrease of brain infarction was observed in each of the 13- and 21-min isoflurane exposure groups (P<0.05). Similar tendencies were observed in Rotarod tests than 5-min ITL and 5-min isoflurane groups showed more marked deficits (P<0.05). This study demonstrated that brain infarction inconsistency of the neonatal hypoxia-ischemia rat pup model is related to the operation time. The observed time-dependent decrease of brain infarction is correlated to the isoflurane exposure time. Shorter operation and isoflurane exposure improves this model consistency of brain infarction and motor deficits.

Pathophysiology of an hypoxic–ischemic insult during the perinatal period

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

Hypothermia and erythropoietin for neuroprotection after neonatal brain damage

BACKGROUND

Both hypothermia and erythropoietin (EPO) are reported to have neuroprotective effects after perinatal hypoxia-ischemia (HI). We investigated a possible additive effect of the use of a combination of hypothermia-EPO in a rat model of neonatal HI.

METHODS

At postnatal day 7, rats were subjected to HI and then randomized to 3 h of hypothermia, EPO, or both. Sensorimotor function was assessed by the cylinder-rearing test (CRT) at 2 and 5 wk after HI. Brain lesion volume and white matter loss were determined by hematoxylin-eosin and luxol fast blue staining, respectively.

RESULTS

Multivariable analysis using general linear modeling showed that hypothermia, EPO, and the interaction hypothermia × gender were determinants of sensorimotor function, both at 2 and 5 wk after HI. Neuroprotective effects of hypothermia at 5 wk were more pronounced in females, showing 52% improvement in the CRT. Maximal improvement in males was 26% after combined treatment with hypothermia and EPO. Histological outcome was improved by hypothermia only with no additional effect of EPO or gender.

CONCLUSION

Hypothermia after HI improved sensorimotor function in females more than in males. There was a borderline additive effect of EPO when combined with hypothermia. Histology of brain lesion volume and white matter damage was improved only by hypothermia.

Effects of combination therapy using hypothermia and erythropoietin in a rat model of neonatal hypoxia-ischemia

BACKGROUND

Hypoxic-ischemic (HI) injury to the developing brain remains a major cause of morbidity. Hypothermia is effective but does not provide complete neuroprotection, prompting a search for adjunctive therapies. Erythropoietin (Epo) has been shown to be beneficial in several models of neonatal HI. This study examines combination hypothermia and treatment with erythropoietin in neonatal rat HI.

METHODS

Rats at postnatal day 7 were subjected to HI (Vannucci model) and randomized into four groups: no treatment, hypothermia alone, Epo alone, or hypothermia and Epo. Epo (1,000 U/kg) was administered in three doses: immediately following HI, and 24 h and 1 wk later. Hypothermia consisted of whole-body cooling for 8 h. At 2 and 6 wk following HI, sensorimotor function was assessed via cylinder-rearing test and brain damage by injury scoring. Sham-treated animals not subjected to HI were also studied.

RESULTS

Differences between experimental groups, except for Epo treatment on histopathological outcome in males, were not statistically significant, and combined therapy had no adverse effects.

CONCLUSION

No significant benefit was observed from treatment with either hypothermia or combination therapy. Future studies may require older animals, a wider range of functional assays, and postinsult assessment of injury severity to identify only moderately damaged animals for targeted therapy.

Docosahexaenoic acid augments hypothermic neuroprotection in a neonatal rat asphyxia model

BACKGROUND

In neonatal rats, early post-hypoxia-ischemia (HI) administration of the omega-3 fatty acid docosahexaenoic acid (DHA) improves sensorimotor function, but does not attenuate brain damage.

OBJECTIVE

To determine if DHA administration in addition to hypothermia, now standard care for neonatal asphyxial brain injury, attenuates post-HI damage and sensorimotor deficits.

METHODS

Seven-day-old (P7) rats underwent right carotid ligation followed by 90 min of 8% O2 exposure. Fifteen minutes later, pups received injections of DHA 2.5 mg/kg (complexed to 25% albumin) or equal volumes of albumin. After a 1-hour recovery, pups were cooled (3 h, 30°C). Sensorimotor and pathology outcomes were initially evaluated on P14. In subsequent experiments, sensorimotor function was evaluated on P14, P21, and P28; histopathology was assessed on P28.

RESULTS

At P14, left forepaw function scores (normal: 20/20) were near normal in DHA + hypothermia-treated animals (mean ± SD 19.7 ± 0.7 DHA + hypothermia vs. 12.7 ± 3.5 albumin + hypothermia, p < 0.0001) and brain damage was reduced (mean ± SD right hemisphere damage 38 ± 17% with DHA + hypothermia vs. 56 ± 15% with albumin + hypothermia, p = 0.003). Substantial improvements on three sensorimotor function measures and reduced brain damage were evident up to P28.

CONCLUSION

Unlike post-HI treatment with DHA alone, treatment with DHA + hypothermia produced both sustained functional improvement and reduced brain damage after neonatal HI.

Effect of vagus nerve stimulation during transient focal cerebral ischemia on chronic outcome in rats

The aim of this study was to investigate the effect of vagus nerve stimulation (VNS) on infarct volume and neurological recovery up to 3 weeks following transient focal cerebral ischemia. Transient ischemia was produced by filament occlusion of the proximal middle cerebral artery (MCA) in rats. The right vagus nerve was stimulated starting 30 min after MCA occlusion and consisted of 30-sec pulse trains (20 Hz) delivered to the animal's right vagus nerve every 5 min for a total period of 60 min (n = 10). All the procedures were duplicated, but no stimulus was delivered, in a control group (n = 10). Neurological evaluations were performed in all animals at 24 hr, 48 hr, 1 week, 2 weeks, and 3 weeks after MCA occlusion; animals were euthanized; and neuronal damage was evaluated in hematoxylin-eosin-stained sections. The ischemic lesion volume was smaller in the VNS-treated animals in comparison with the nonstimulated group (P < 0.02). Although the functional score in both treated and untreated groups improved over the 3-week observation period (P < 0.001), there was still a statistically significant improvement reszulting from VNS treatment compared with control animals (P < 0.05). Cerebral blood flow changes in the MCA territory during ischemia did not differ between the VNS-treated animals (31.9% ± 10.4% of baseline) and control animals (29.9% ± 9.1%; P = 0.6). Stimulation of the vagus nerve for only a brief period early in ischemia provides neuroprotection in transient ischemia, with neuroprotection persisting for at least 3 weeks.

Combined effect of hypothermia and caspase-2 gene deficiency on neonatal hypoxic-ischemic brain injury

INTRODUCTION

[corrected] Hypoxia-ischemia (HI) injury in term infants develops with a delay during the recovery phase, opening up a therapeutic window after the insult. Hypothermia is currently an established neuroprotective treatment in newborns with neonatal encephalopathy (NE), saving one in nine infants from developing neurological deficits. Caspase-2 is an initiator caspase, a key enzyme in the route to destruction and, therefore, theoretically a potential target for a pharmaceutical strategy to prevent HI brain damage.

METHODS

The aim of this study was to explore the neuroprotective efficacy of hypothermia in combination with caspase-2 gene deficiency using the neonatal Rice-Vannucci model of HI injury in mice.

RESULTS

HI brain injury was moderately reduced in caspase-2(-/-) mice as compared with wild-type (WT) mice. Five hours of hypothermia (33 °C ) vs. normothermia (36 °C) directly after HI provided additive protection overall (temperature P = 0.0004, caspase-2 genotype P = 0.0029), in the hippocampus and thalamus, but not in other gray matter regions or white matter. Delayed hypothermia initiated 2 h after HI in combination with caspase-2 gene deficiency reduced injury in the hippocampus, but not in other brain areas.

DISCUSSION

In conclusion, caspase-2 gene deficiency combined with hypothermia provided enhanced neuroprotection as compared with hypothermia alone.

Resuscitation with 100% oxygen increases injury and counteracts the neuroprotective effect of therapeutic hypothermia in the neonatal rat

INTRODUCTION

Mild therapeutic hypothermia (HT) reduces brain injury in survivors after perinatal asphyxia. Recent guidelines suggest that resuscitation of term infants should be started with air, but supplemental oxygen is still in use. It is not known whether supplemental oxygen during resuscitation affects the protection offered by subsequent HT.

RESULTS

Wilcoxon median (95% confidence interval) hippocampal injury scores (range 0.0-4.0; 0 to ≥90% injury) were 21% O(2) normothermia (NT): 2.00 (1.25-2.50), 21% O(2) HT: 1.00 (0.50-1.50), 100% O(2) NT: 2.50 (1.50-3.25), and 100% O(2) HT: 2.00 (1.25-2.50). Although HT significantly reduced hippocampal injury (B = -0.721, SEM = 0.297, P = 0.018), reoxygenation with 100% O(2) increased injury (B = +0.647, SEM = 0.297, P = 0.033). Regression constant B = 1.896, SEM = 0.257 and normally distributed residuals.

DISCUSSION

We confirm an ~50% neuroprotective effect of therapeutic HT in the neonatal rat. Reoxygenation with 100% O(2) increased injury and worsened reflex performance. HT was neuroprotective whether applied after reoxygenation with air or 100% O(2). However, HT after 100% O(2) gave no net neuroprotection.

METHODS

In an established neonatal rat model, hypoxia-ischemia (HI) was followed by 30-min reoxygenation in either 21% O(2) or 100% O(2) before 5 h of NT (37 °C) or HT (32 °C). The effects of HT and 100% O(2) on histopathologic injury in the hippocampus, basal ganglia, and cortex, and on postural reflex performance 7 d after the insult, were estimated by linear regression.

The effect of postischemic hypothermia on apoptotic cell death in the neonatal rat brain

BACKGROUND AND OBJECTIVE

Hypothermia is the most effective neuroprotective therapy against ischemic injury in the developing brain. However, the mechanism of hypothermic neuroprotection is not well understood. We sought to investigate whether hypothermia mediates neuroprotection by modulating ischemia-induced apoptosis.

METHODS

Seven-day-old rat pups were randomly assigned to either control or hypoxia-ischemia (HI) groups. In the HI group, the internal carotid artery was ligated and cut. This was followed by transient hypoxia at 8% oxygen for 90 min. In the control rats, the internal carotid was isolated but not ligated. Immediately after the hypoxic episode, pups in the HI group were either placed in water baths maintained at 28°C for 24 h (core temperatures at 31°C) or they remained in a normothermic environment. Animals were sacrificed at 24, 48 and 72 h and 1 week after the HI insult. Brain sections were processed for immunohistochemistry and Western blots.

RESULTS

Caspase 3 expression was significantly higher in the core compared with the peri-infarct area at all time points in normothermic rats. Hypothermia reduced caspase 3 expression in the core but had little effect in the peri-infarct area. Hypothermia reduced apoptosis-inducing factor translocation to the nucleus in the core and peri-infarct area. Concurrently, X-linked inhibitor of apoptosis (XIAP) expression was significantly potentiated in the hypothermic-ischemic core but not in the peri-infarct area.

CONCLUSION

Hypothermic modulation of caspase-dependent apoptosis may be mediated by upregulating XIAP. However, the effect of hypothermia on caspase-independent apoptosis may be mediated by XIAP-independent mechanisms. Importantly, these effects are mediated in both the core and the penumbral regions of ischemic lesion.

Treatment advances in neonatal neuroprotection and neurointensive care

Knowledge of the nature, prognosis, and ways to treat brain lesions in neonatal infants has increased remarkably. Neonatal hypoxic-ischaemic encephalopathy (HIE) in term infants, mirrors a progressive cascade of excito-oxidative events that unfold in the brain after an asphyxial insult. In the laboratory, this cascade can be blocked to protect brain tissue through the process of neuroprotection. However, proof of a clinical effect was lacking until the publication of three positive randomised controlled trials of moderate hypothermia for term infants with HIE. These results have greatly improved treatment prospects for babies with asphyxia and altered understanding of the theory of neuroprotection. The studies show that moderate hypothermia within 6 h of asphyxia improves survival without cerebral palsy or other disability by about 40% and reduces death or neurological disability by nearly 30%. The search is on to discover adjuvant treatments that can further enhance the effects of hypothermia.

Care for child development: basic science rationale and effects of interventions

The past few years have witnessed increasing interest in devising programs to enhance early childhood development. We review current understandings of brain development, recent advances in this field, and their implications for clinical interventions. An expanding body of basic science laboratory data demonstrates that several interventions, including environmental enrichment, level of parental interaction, erythropoietin, antidepressants, transcranial magnetic stimulation, transcranial direct current stimulation, hypothermia, nutritional supplements, and stem cells, can enhance cerebral plasticity. Emerging clinical data, using functional magnetic resonance imaging and clinical evaluations, also support the hypothesis that clinical interventions can increase the developmental potential of children, rather than merely allowing the child to achieve an already predetermined potential. Such interventions include early developmental enrichment programs, which have improved cognitive function; high-energy and high-protein diets, which have increased brain growth in infants with perinatal brain damage; constraint-induced movement therapy, which has improved motor function in patients with stroke, cerebral palsy, and cerebral hemispherectomy; and transcranial magnetic stimulation, which has improved motor function in stroke patients.

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.

Neuroprotection in the newborn infant

Neonatal brain injury is an important cause of death and disability, with pathways of oxidant stress, inflammation, and excitotoxicity that lead to damage that progresses over a long period of time. Therapies have classically targeted individual pathways during early phases of injury, but more recent therapies such as growth factors may also enhance cell proliferation, differentiation, and migration over time. More recent evidence suggests combined therapy may optimize repair, decreasing cell injury while increasing newly born cells.

Hypoxic-ischemic encephalopathy in the term infant

Hypoxia-ischemia in the perinatal period is an important cause of cerebral palsy and associated disabilities in children. There has been significant research progress in hypoxic-ischemic encephalopathy over the last 2 decades, and many new molecular mechanisms have been identified. Despite all these advances, therapeutic interventions are still limited. In this article the authors discuss several molecular pathways involved in hypoxia-ischemia, and potential therapeutic targets.

Isoflurane preconditioning improves short-term and long-term neurological outcome after focal brain ischemia in adult rats

Isoflurane preconditioning improved short-term neurological outcome after focal brain ischemia in adult rats. It is not known whether desflurane induces a delayed phase of preconditioning in the brain and whether isoflurane preconditioning-induced neuroprotection is long-lasting. Two months-old Sprague-Dawley male rats were exposed to or were not exposed to isoflurane or desflurane for 30 min and then subjected to a 90 min middle cerebral arterial occlusion (MCAO) at 24 h after the anesthetic exposure. Neurological outcome was evaluated at 24 h or 4 weeks after the MCAO. The density of the terminal deoxynucleotidyl transferase biotinylated UTP nick end labeling (TUNEL) positive cells in the penumbral cerebral cortex were assessed 4 weeks after the MCAO. Also, rats were pretreated with isoflurane or desflurane for 30 min. Their cerebral cortices were harvested for quantifying B-cell lymphoma-2 (Bcl-2) expression 24 h later. Here, we showed that pretreatment with 1.1% or 2.2% isoflurane, but not with 6% or 12% desflurane, increased Bcl-2 expression in the cerebral cortex, improved neurological functions and reduced infarct volumes evaluated at 24 h after the MCAO. Isoflurane preconditioning also improved neurological functions and reduced brain infarct volumes in rats evaluated 4 weeks after the MCAO. Isoflurane preconditioning also decreased the density of TUNEL-positive cells in the penumbral cerebral cortex. We conclude that isoflurane preconditioning improves short-term and long-term neurological outcome and reduces delayed cell death after transient focal brain ischemia in adult rats. Bcl-2 may be involved in the isoflurane preconditioning effect. Desflurane pretreatment did not induce a delayed phase of neuroprotection.

Hypothermia for hypoxic-ischemic brain injury

Hypoxic-ischemic brain injury and hypoxic-ischemic encephalopathy (HIE) remain a serious problem for both preterm and term neonates with the spectrum of injury ranging from neuronal injury to encephalopathy and death. Neonatal encephalopathy due to such injury occurs in 3-9 of every 1000 term infants. Of these, it is estimated that nearly a third to a half will either have severe adverse outcomes or die. Treatment of infants with HIE remains generally supportive with attention to resuscitation, fluid and electrolyte homeostasis, maintenance of acid-base balance, nutrition and feeding issues and treatment of seizures.

Use of therapeutic hypothermia for term infants with hypoxic-ischemic encephalopathy

Newborn encephalopathy represents a clinical syndrome with diverse causes, many of which may result in brain injury. Hypoxic-ischemic encephalopathy represents a subset of newborns with encephalopathy and, in contrast to other causes, may have a modifiable outcome. Laboratory research has demonstrated robust neuroprotection associated with reductions of brain temperature following hypoxia-ischemia in animals. The neuroprotective effects of hypothermia reflect antagonism of multiple cascades of events that contribute to brain injury. Clinical trials have translated laboratory observations into successful interventions. Hypoxicischemic encephalopathy is often unanticipated, unavoidable, and may occur in any obstetric setting. Pediatricians and other providers based in community hospitals play a critical role in the initial assessment, recognition, and stabilization of infants who may be candidates for therapeutic hypothermia.

Cooling combined with immediate or delayed xenon inhalation provides equivalent long-term neuroprotection after neonatal hypoxia-ischemia

Hypothermia (HT) improves outcome after neonatal hypoxia-ischemia. Combination therapy may extend neuroprotection. The noble anesthetic gas xenon (Xe) has an excellent safety profile. We have shown earlier that 3 h of 50% Xe plus HT (32 degrees C) additively gives more protection (72%) than either alone (HT=31.1%, Xe=10.2%). Factors limiting clinical use include high-cost and specialist administration requirements. Thus, combinations of 1 h of 50% Xe were administered concurrently for either the first (1 h(Immediate)Xe) or last (1 h(Delayed)Xe) of 3 h of posthypoxic-ischemic HT as compared with 3 h of 50%Xe/HT to investigate how brief Xe exposure with a delay would affect efficacy. An established neonatal rat hypoxia-ischemia model was used. Serial functional neurologic testing into adulthood was performed, followed by neuropathological examination. Xenon with HT was more effective with longer Xe duration (3 h versus 1 h) (P=0.015). However, 1 h Xe/3 h HT resulted in better neuroprotection than 3 h HT alone (P=0.03), this significant effect was also present with 1 h Xe after a 2-h delay. One (immediate or with a delay) or 3 h Xe also significantly improved motor function (P=0.024). Females had significantly better motor scores than males, but no sex-dependent difference in pathology results. The neuroprotection of short, delayed Xe treatment would allow transport to specialist facilities to receive Xe.

Ascorbic acid protects the newborn rat brain from hypoxic-ischemia

Ascorbic acid (AA) is a potent antioxidant, and its neuroprotective effect has not been established yet. Using the Rice-Vannucci model, we examined the effect of AA on hypoxic-ischemic (HI) injury in the immature rat brain. Under isoflurane anesthesia, 7-day-old rat pups received 750 mg/kg of AA by intraperitoneal injection just before hypoxic exposure; 8% oxygen for 90 min. Vehicle controls received an equal volume of saline. AA decreased a macroscopic brain injury score at 48 and 168 h post-HI compared with vehicle controls (48 h post-HI, AA 1.38+/-0.45 vs. controls 2.94+/-0.24, p<0.05; 168 h post-HI, 1.13+/-0.44 vs. 2.50+/-0.25, p<0.05). AA injection significantly decreased the number of both necrotic and apoptotic cells in cortex, caudate putamen, thalamus and hippocampus, and also seemed to reduce the number of TUNEL-positive cells. Western blot analysis showed that AA significantly suppressed 150/145 kDa subunits of alpha-fodrin breakdown products (FBDP) in cortex, striatum, thalamus and hippocampus at 24 and 48 h post-HI, and also 120 kDa subunit of FBDP in all examined regions except for thalamus, which indicated that AA injection inhibited both calpain and caspase-3 activation. Western blot analysis of nitrotyrosine failed to show inhibition of free radical production by AA, however, our results show that AA inhibits both necrotic and apoptotic cell death and that AA is neuroprotective after HI in immature rat brain.

Treatment of the term newborn with brain injury: simplicity as the mother of invention

Neonatal brain injury remains a common cause of developmental disability, despite tremendously enhanced obstetrical and neonatal care. The timing of brain injury occurs throughout gestation, labor, and delivery, providing an evolving form of brain injury and a moving target for therapeutic intervention. Nonetheless, markedly improved methods are available to identify those infants injured at birth, via clinical presentation with neonatal encephalopathy and neuroimaging techniques. Postischemic hypothermia has been shown to be of tremendous clinical promise in several completed and ongoing trials. As part of this approach to the treatment of the newborn, other parameters of physiologic homeostasis can and should be attended to, with strong animal and clinical evidence that their correction will have dramatic influence on the outcome of the newborn infant. This review addresses aspects of newborn care to which we can direct our attention currently, and which should result in a safe and efficacious improvement in the prognosis of the newborn with neonatal encephalopathy.

Therapeutics for neonatal brain injury

Neonatal brain injury is an important cause of death and neurodevelopmental delay. Multiple pathways of oxidant stress, inflammation, and excitotoxicity lead to both early and late phases of cell damage and death. Therapies targeting these different pathways have shown potential in protecting the brain from ongoing injury. More recent therapies, such as growth factors, have demonstrated an ability to increase cell proliferation and repair over longer periods of time. Even though hypothermia, which decreases cerebral metabolism and possibly affects other mechanisms, may show some benefit in particular cases, no widely effective therapeutic interventions for human neonates exist. In this review, we summarize recent findings in neuroprotection and neurogenesis for the immature brain, including combination therapy to optimize repair.

Xenon and hypothermia combine additively, offering long-term functional and histopathologic neuroprotection after neonatal hypoxia/ischemia

BACKGROUND AND PURPOSE

Hypoxic/ischemic (HI) brain injury affects 1 to 6 per 1000 live human births, with a mortality of 15% to 20%. A quarter of survivors have permanent disabilities. Hypothermia is the only intervention that improves outcome; however, further improvements might be obtained by combining hypothermia with additional treatments. Xenon is a noble anesthetic gas with an excellent safety profile, showing great promise in vitro and in vivo as a neuroprotectant. We investigated combinations of 50% xenon (Xe(50%)) and hypothermia of 32 degrees C (HT(32 degrees C)) as a post-HI therapy.

METHODS

An established neonatal rat HI model was used. Serial functional neurologic testing into adulthood 10 weeks after injury was performed, followed by global and regional brain histopathology evaluation.

RESULTS

In the combination Xe(50%)HT(32 degrees C) group, complete restoration of long-term functional outcomes was seen. Hypothermia produced improvement on short- (P<0.001) and long- (P<0.001) term functional testing, whereas Xe(50%) alone predominantly improved long-term function (P<0.05), suggesting that short-term testing does not always predict eventual outcome. Similarly, the Xe(50%)HT(32 degrees C) combination produced the greatest (71%) improvement in global histopathology scores, a pattern mirrored in the regional scores, whereas Xe(50%) and HT(32 degrees C) individually produced smaller improvements (P<0.05 and P<0.001, respectively). The interaction between the 2 treatments was additive.

CONCLUSIONS

The xenon/hypothermia combination additively confers greater protection after HI than either treatment alone. The functional improvement is almost complete, is sustained long term, and is accompanied by greatly improved histopathology. The unique safety profile differentiates xenon as an attractive combination therapy with hypothermia to improve the otherwise bleak outcome from neonatal HI.

Effect of hypothermic post-treatment on hypoxic-ischemic striatal injury, and normal striatal development, in neonatal rats: a stereological study

Fundamental questions remain about the optimal temperature, duration, and mode of delivery that provide the best striatal neuroprotection from hypothermia after perinatal hypoxia-ischemia. This study used stereological methods to investigate whether a mild (i.e. 2 degrees C) or a moderate (5 degrees C) decrease in whole body temperature, for 6 h immediately postinsult, was neuroprotective for striatal medium-spiny neurons after perinatal hypoxia-ischemia in the rat. This study also investigated whether moderate hypothermia had any effect on normal striatal development. Hypoxia-ischemia or sham hypoxia-ischemia was induced on postnatal day (PN) 7. Pups were kept either normothermic, mildly hypothermic, or moderately hypothermic for 6 h immediately postinsult. The absolute number of striatal medium-spiny neurons was calculated using modern stereological methods. There was no significant difference in the absolute number of medium-spiny neurons in the right striatum after either mild hypothermia or moderate hypothermia. There was also no significant difference in the absolute number of medium-spiny neurons between the control normothermic and the control moderately hypothermic pups. The latter results suggest that moderate hypothermia for 6 h immediately postinsult may be a safe treatment for striatal medium-spiny neurons. Yet, neither mild nor moderate hypothermia alone for 6 h immediately posthypoxia-ischemia is neuroprotective for striatal medium-spiny neurons.

Head cooling for neonatal encephalopathy: the state of the art

The possibility that hypothermia started during or after resuscitation at birth might reduce brain damage and cerebral palsy has tantalized clinicians for a long time. The key insight was that transient severe hypoxia-ischemia can precipitate a complex biochemical cascade leading to delayed neuronal loss. There is now strong experimental and clinical evidence that mild to moderate cooling can interrupt this cascade, and improve the number of infants surviving without disability in the medium term. The key remaining issues are to finding better ways of identifying babies who are most likely to benefit, to define the optimal mode and conditions of hypothermia and to find ways to further improve the effectiveness of treatment.

Long-term histological outcome after post-hypoxic treatment with 100% or 40% oxygen in a model of perinatal hypoxic-ischemic brain injury

Hypoxic newborns have traditionally been given supplemental oxygen, and until recently, guidelines for neonatal resuscitation recommended that 100% oxygen be used. Exposure to 100% oxygen after hypoxic injury, however, may exacerbate oxidative stress. The current study evaluated the effect of exposure to 100, 40 or 21% oxygen after neonatal hypoxic-ischemic injury on the severity of brain injury after long-term survival. The severity of histological brain injury was not different in animals exposed to 100% oxygen versus room air. Male animals treated with 40% oxygen post-hypoxia had the lowest mean total histology scores, but this was not statistically significant due to the large variation in injury within each treatment group. These results support the growing number of studies in human infants and experimental animals that show no benefit of 100% oxygen over room air for neonatal resuscitation. Our results suggest that post-hypoxia treatment with 40% oxygen may be beneficial, particularly in males. Further studies of the effects of different concentrations of oxygen on brain injury are warranted and should have sufficient power to examine sex differences.

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.

Grape seed extract given three hours after injury suppresses lipid peroxidation and reduces hypoxic-ischemic brain injury in neonatal rats

We have reported that pretreatment with grape seed extract (GSE), a potent antioxidant, is neuroprotective. This study examined whether treatment after injury with GSE is protective. Seven-day-old rat pups had the right carotid artery ligated, and then 2.5 h of 8% oxygen. GSE (50 mg/kg) or vehicle was administered by i.p. initial injection at 5 min to 5 h after reoxygenation, with an additional three doses within 26 h after injury. Brain damage was evaluated by weight deficit of the right hemisphere at 22 d after hypoxia. Treatment at 3 h after reoxygenation reduced brain weight loss from 21.0 +/- 3.3% in vehicle-treated pups (n = 31) to 11.4 +/- 2.8% in treated pups (n = 31, p < 0.05). GSE lowered body temperature, but reduced brain injury even when body temperature was controlled. GSE reduced neurofunctional abnormalities caused by the hypoxia-ischemia (HI). GSE reduced a HI induced increase in 8-isoprostaglandin F2alpha (8-isoPGF2alpha) and reduced an HI-induced increase in the proapoptotic protein c-jun in the brain cortex. GSE up to 3 h after reoxygenation reduces brain injury in rat pups, probably by suppressing lipid peroxidation and the proapoptotic protein c-jun.

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

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

Long-term effect of moderate and profound hypothermia on morphology, neurological, cognitive and behavioural functions in a rat model of perinatal asphyxia

BACKGROUND

Perinatal asphyxia is a frequent cause of neurological handicap with no known therapy. However, hypothermic therapy has recently attracted attention owing to its neuroprotective property in brain of immature organisms.

OBJECTIVES

Hypothermia appears to be promising in reversing the immediate effect of perinatal asphyxia, but data on long-term neuroprotection is still lacking. We therefore intended to test the long-term effect of moderate and profound hypothermia on brain morphology and functions using a well established rat model of perinatal asphyxia.

METHODS

Rat pups delivered by caesarean section were placed into a water bath, still in patent membranes, at 37 degrees C and variable hypothermic conditions to induce asphyxia and thereafter given to surrogate mothers. Examinations were performed at the age of three months, consisting of a battery of motor, behavioural, cognition and reflex tests including rota-rod, Morris water maze, multiple T-maze, elevated plus maze and open field studies. Morphological alterations were evaluated by Nissl staining of brain areas known to be hypoxia sensitive. Neurotransmission system markers, including tyrosine hydroxylase, vesicular monoamine transporter, vesicular acetylcholine transporter and excitatory amino acid carrier1 were analyzed by immunohistochemistry.

RESULTS

Survival increased with hypothermia. The Nissl stain revealed neuronal loss in hippocampus and hypothalamus of normothermic asphyxiated group (20/37) compared to controls (0/37), but no neuroprotective patterns emerged from hypothermia. An overall inconsistent protection of the neural systems was noted by variable periods of hypothermia. Motor function was significantly impaired in 20/37 as compared to 0/37. In the Morris water maze and multiple T-maze, results were comparable between the groups. In the elevated plus maze, time spent in the closed arm was reduced and in the open field, vertical behaviour was altered in the 20/37 group with horizontal motor behaviour being unaffected. Hypothermia reversed all abnormalities seen in 20/37, with short-term moderate and profound hypothermia being superior to long-term hypothermia.

CONCLUSION

Hypothermia not only significantly increased survival, but also resulted in unimpaired motor as well as improved cognitive functions. Those findings are in contrast to altered brain morphology. As neuronal loss was present in various brain regions, we conclude that deficits may be compensated in the maturing animal. Intrahypoxic hypothermia was able to protect the rat from the devastating effect of perinatal asphyxia not in morphological, but in functional terms.

Intraventricular ascorbic acid administration decreases hypoxic-ischemic brain injury in newborn rats

Neuronal cell damage following hypoxic-ischemic (HI) brain injury is partly caused by production of free radicals and reactive oxygen species (ROS). Ascorbic acid (AA) is a potent antioxidant, which scavenges various types of ROS. Some studies have shown that it is neuroprotective, however, the issue is still controversial. In this study, we examined the effect of intraventricular AA administration on immature HI brain using the Rice-Vannucci model. After unilateral carotid artery ligation under isoflurane anesthesia, 7-day-old rat pups received varying concentrations of AA (0.04, 0.2, 1 and 5 mg/kg) by intraventricular injection and were exposed to 8% oxygen for 90 min. Vehicle controls received an equal volume of phosphate saline buffer. We assessed the neuroprotective effect of AA at 7 days post-HI. The percent brain damage measured by comparing the wet weight of the ligated side of hemisphere with that of contralateral one was reduced in both 1 and 5 mg/kg groups but not in either 0.04 or 0.2 mg/kg groups compared to vehicle controls (5 mg/kg 16.0 +/- 4.3%, 1 mg/kg 10.9 +/- 5.0%, vs. controls 36.7 +/- 3.6%, P < 0.05). Macroscopic evaluation of brain injury revealed the neuroprotective effect of AA in both 1 and 5 mg/kg groups (5 mg/kg 1.1 +/- 0.4, 1 mg/kg 0.4 +/- 0.3, vs. controls 2.9 +/- 0.3, P < 0.05). Western blots of fodrin on the ligated side also showed that AA significantly suppressed 150/145-kDa bands of fodrin breakdown products, which suggested that AA suppressed activation of calpain. Neuropathological quantitative analysis of cell death revealed that 1 mg/kg of AA injection significantly reduced the number of necrotic cells in cortex, caudate putamen, thalamus and hippocampus CA1, whereas that of apoptotic cells was only reduced in cortex. These findings show that intraventricular AA injection is neuroprotective after HI in immature rats.

Hypothermic neuroprotection

The possibility that hypothermia during or after resuscitation from asphyxia at birth, or cardiac arrest in adults, might reduce evolving damage has tantalized clinicians for a very long time. It is now known that severe hypoxia-ischemia may not necessarily cause immediate cell death, but can precipitate a complex biochemical cascade leading to the delayed neuronal loss. Clinically and experimentally, the key phases of injury include a latent phase after reperfusion, with initial recovery of cerebral energy metabolism but EEG suppression, followed by a secondary phase characterized by accumulation of cytotoxins, seizures, cytotoxic edema, and failure of cerebral oxidative metabolism starting 6 to 15 h post insult. Although many of the secondary processes can be injurious, they appear to be primarily epiphenomena of the 'execution' phase of cell death. Studies designed around this conceptual framework have shown that moderate cerebral hypothermia initiated as early as possible before the onset of secondary deterioration, and continued for a sufficient duration in relation to the severity of the cerebral injury, has been associated with potent, long-lasting neuroprotection in both adult and perinatal species. Two large controlled trials, one of head cooling with mild hypothermia, and one of moderate whole body cooling have demonstrated that post resuscitation cooling is generally safe in intensive care, and reduces death or disability at 18 months of age after neonatal encephalopathy. These studies, however, show that only a subset of babies seemed to benefit. The challenge for the future is to find ways of improving the effectiveness of treatment.

Combination of systemic hypothermia and N-acetylcysteine attenuates hypoxic-ischemic brain injury in neonatal rats

Hypoxic ischemic (HI) injury in neonates may have devastating, long-term consequences. Recently completed clinical trials in HI neonates indicate that hypothermia within 6 h of birth results in modest improvement in the combined outcome of death or severe disability. The aim of this study was to investigate the effects of combining hypothermia and N-acetylcysteine (NAC) on brain injury, neonatal reflexes and myelination after neonatal HI. Seven-day-old rats were subjected to right common carotid artery ligation and hypoxia (8% oxygen) for 2 h. Systemic hypothermia (30 + 0.5 degrees C) was induced immediately after the period of HI and was maintained for 2 h. NAC (50 mg/kg) was administered by intraperitoneal injection daily until sacrifice. Brain infarct volumes were significantly reduced at 48 h post-HI in the hypothermia plus NAC group (21.5 +/- 3.84 mm3) compared with vehicle (240.85 +/- 4.08 mm3). Neonatal reflexes were also significantly improved by combination therapy at days 1 and 7. There was a significant loss of right hemispheric brain volume in the untreated group at 2 and 4 wk after HI insult. Brain volumes were preserved in hypothermia plus NAC group and were not significantly different when compared with the sham group. Similarly, increased myelin expression was seen in brain sections from hypothermia plus NAC group, when stained for Luxol Fast Blue (LFB), Myelin Basic Protein (MBP) and Proteolipid protein (PLP). These results indicate that hypothermia plus NAC combination therapy improves infarct volume, myelin expression and functional outcomes after focal HI injury.