Comparison between hypothermia and glutamate antagonism treatments on the immediate outcome of perinatal asphyxia

Sustained Energy Deficit Following Perinatal Asphyxia: A Shift towards the Fructose-2,6-bisphosphatase (TIGAR)-Dependent Pentose Phosphate Pathway and Postnatal Development

Labor and delivery entail a complex and sequential metabolic and physiologic cascade, culminating in most circumstances in successful childbirth, although delivery can be a risky episode if oxygen supply is interrupted, resulting in perinatal asphyxia (PA). PA causes an energy failure, leading to cell dysfunction and death if re-oxygenation is not promptly restored. PA is associated with long-term effects, challenging the ability of the brain to cope with stressors occurring along with life. We review here relevant targets responsible for metabolic cascades linked to neurodevelopmental impairments, that we have identified with a model of global PA in rats. Severe PA induces a sustained effect on redox homeostasis, increasing oxidative stress, decreasing metabolic and tissue antioxidant capacity in vulnerable brain regions, which remains weeks after the insult. Catalase activity is decreased in mesencephalon and hippocampus from PA-exposed (AS), compared to control neonates (CS), in parallel with increased cleaved caspase-3 levels, associated with decreased glutathione reductase and glutathione peroxidase activity, a shift towards the TIGAR-dependent pentose phosphate pathway, and delayed calpain-dependent cell death. The brain damage continues long after the re-oxygenation period, extending for weeks after PA, affecting neurons and glial cells, including myelination in grey and white matter. The resulting vulnerability was investigated with organotypic cultures built from AS and CS rat newborns, showing that substantia nigra TH-dopamine-positive cells from AS were more vulnerable to 1 mM of H2O2 than those from CS animals. Several therapeutic strategies are discussed, including hypothermia; N-acetylcysteine; memantine; nicotinamide, and intranasally administered mesenchymal stem cell secretomes, promising clinical translation.

Pregnancy as a valuable period for preventing hypoxia-ischemia brain damage

Neonatal brain Hypoxia-Ischemia (HI) is one of the major causes of infant mortality and lifelong neurological disabilities. The knowledge about the physiopathological mechanisms involved in HI lesion have increased in recent years, however these findings have not been translated into clinical practice. Current therapeutic approaches remain limited; hypothermia, used only in term or near-term infants, is the golden standard. Epidemiological evidence shows a link between adverse prenatal conditions and increased risk for diseases, health problems, and psychological outcomes later in life, what makes pregnancy a relevant period for preventing future brain injury. Here, we review experimental literature regarding preventive interventions used during pregnancy, i.e., previous to the HI injury, encompassing pharmacological, nutritional and/or behavioral strategies. Literature review used PubMed database. A total of forty one studies reported protective properties of maternal treatments preventing perinatal hypoxia-ischemia injury in rodents. Pharmacological agents and dietary supplementation showed mainly anti-excitotoxicity, anti-oxidant or anti-apoptotic properties. Interestingly, maternal preconditioning, physical exercise and environmental enrichment seem to engage the same referred mechanisms in order to protect neonatal brain against injury. This construct must be challenged by further studies to clearly define the main mechanisms responsible for neuroprotection to be explored in experimental context, as well as to test their potential in clinical settings.

A working model for hypothermic neuroprotection

Therapeutic hypothermia significantly improves survival without disability in near-term and full-term newborns with moderate to severe hypoxic-ischaemic encephalopathy. However, hypothermic neuroprotection is incomplete. The challenge now is to find ways to further improve outcomes. One major limitation to progress is that the specific mechanisms of hypothermia are only partly understood. Evidence supports the concept that therapeutic cooling suppresses multiple extracellular death signals, including intracellular pathways of apoptotic and necrotic cell death and inappropriate microglial activation. Thus, the optimal depth of induced hypothermia is that which effectively suppresses the cell death pathways after hypoxia-ischaemia, but without inhibiting recovery of the cellular environment. Thus mild hypothermia needs to be continued until the cell environment has recovered until it can actively support cell survival. This review highlights that key survival cues likely include the inter-related restoration of neuronal activity and growth factor release. This working model suggests that interventions that target overlapping mechanisms, such as anticonvulsants, are unlikely to materially augment hypothermic neuroprotection. We suggest that further improvements are most likely to be achieved with late interventions that maximise restoration of the normal cell environment after therapeutic hypothermia, such as recombinant human erythropoietin or stem cell therapy.

Perinatal Asphyxia and Brain Development: Mitochondrial Damage Without Anatomical or Cellular Losses

Perinatal asphyxia remains a significant cause of neonatal mortality and is associated with long-term neurodegenerative disorders. In the present study, we evaluated cellular and subcellular damages to brain development in a model of mild perinatal asphyxia. Survival rate in the experimental group was 67%. One hour after the insult, intraperitoneally injected Evans blue could be detected in the fetuses' brains, indicating disruption of the blood-brain barrier. Although brain mass and absolute cell numbers (neurons and non-neurons) were not reduced after perinatal asphyxia immediately and in late brain development, subcellular alterations were detected. Cortical oxygen consumption increased immediately after asphyxia, and remained high up to 7 days, returning to normal levels after 14 days. We observed an increased resistance to mitochondrial membrane permeability transition, and calcium buffering capacity in asphyxiated animals from birth to 14 days after the insult. In contrast to ex vivo data, mitochondrial oxygen consumption in primary cell cultures of neurons and astrocytes was not altered after 1% hypoxia. Taken together, our results demonstrate that although newborns were viable and apparently healthy, brain development is subcellularly altered by perinatal asphyxia. Our findings place the neonate brain mitochondria as a potential target for therapeutic protective interventions.

Targeting Sentinel Proteins and Extrasynaptic Glutamate Receptors: a Therapeutic Strategy for Preventing the Effects Elicited by Perinatal Asphyxia?

Perinatal asphyxia (PA) is a relevant cause of death at the time of labour, and when survival is stabilised, associated with short- and long-term developmental disabilities, requiring inordinate care by health systems and families. Its prevalence is high (1 to 10/1000 live births) worldwide. At present, there are few therapeutic options, apart from hypothermia, that regrettably provides only limited protection if applied shortly after the insult.PA implies a primary and a secondary insult. The primary insult relates to the lack of oxygen, and the secondary one to the oxidative stress triggered by re-oxygenation, formation of reactive oxygen (ROS) and reactive nitrogen (RNS) species, and overactivation of glutamate receptors and mitochondrial deficiencies. PA induces overactivation of a number of sentinel proteins, including hypoxia-induced factor-1α (HIF-1α) and the genome-protecting poly(ADP-ribose) polymerase-1 (PARP-1). Upon activation, PARP-1 consumes high amounts of ATP at a time when this metabolite is scarce, worsening in turn the energy crisis elicited by asphyxia. The energy crisis also impairs ATP-dependent transport, including glutamate re-uptake by astroglia. Nicotinamide, a PARP-1 inhibitor, protects against the metabolic cascade elicited by the primary stage, avoiding NAD+ exhaustion and the energetic crisis. Upon re-oxygenation, however, oxidative stress leads to nuclear translocation of the NF-κB subunit p65, overexpression of the pro-inflammatory cytokines IL-1β and TNF-α, and glutamate-excitotoxicity, due to impairment of glial-glutamate transport, extracellular glutamate overflow, and overactivation of NMDA receptors, mainly of the extrasynaptic type. This leads to calcium influx, mitochondrial impairment, and inactivation of antioxidant enzymes, increasing further the activity of pro-oxidant enzymes, thereby making the surviving neonate vulnerable to recurrent metabolic insults whenever oxidative stress is involved. Here, we discuss evidence showing that (i) inhibition of PARP-1 overactivation by nicotinamide and (ii) inhibition of extrasynaptic NMDA receptor overactivation by memantine can prevent the short- and long-term consequences of PA. These hypotheses have been evaluated in a rat preclinical model of PA, aiming to identify the metabolic cascades responsible for the long-term consequences induced by the insult, also assessing postnatal vulnerability to recurrent oxidative insults. Thus, we present and discuss evidence demonstrating that PA induces long-term changes in metabolic pathways related to energy and oxidative stress, priming vulnerability of cells with both the neuronal and the glial phenotype. The effects induced by PA are region dependent, the substantia nigra being particularly prone to cell death. The issue of short- and long-term consequences of PA provides a framework for addressing a fundamental issue referred to plasticity of the CNS, since the perinatal insult triggers a domino-like sequence of events making the developing individual vulnerable to recurrent adverse conditions, decreasing his/her coping repertoire because of a relevant insult occurring at birth.

25 years of research on global asphyxia in the immature rat brain

Hypoxic-ischemic encephalopathy remains a common cause of brain damage in neonates. Preterm infants have additional complications, as prematurity by itself increases the risk of encephalopathy. Currently, therapy for this subset of asphyxiated infants is limited to supportive care. There is an urgent need for therapies in preterm infants - and for representative animal models for preclinical drug development. In 1991, a novel rodent model of global asphyxia in the preterm infant was developed in Sweden. This method was based on the induction of asphyxia during the birth processes itself by submerging pups, still in the uterine horns, in a water bath followed by C-section. This insult occurs at a time-point when the rodent brain maturity resembles the brain of a 22-32 week old human fetus. This model has developed over the past 25 years as an established model of perinatal global asphyxia in the early preterm brain. Here we summarize the knowledge gained on the short- and long-term neuropathological and behavioral effects of asphyxia on the immature central nervous system.

Perinatal asphyxia leads to PARP-1 overactivity, p65 translocation, IL-1β and TNF-α overexpression, and apoptotic-like cell death in mesencephalon of neonatal rats: prevention by systemic neonatal nicotinamide administration

Perinatal asphyxia (PA) is a leading cause of neuronal damage in newborns, resulting in long-term neurological and cognitive deficits, in part due to impairment of mesostriatal and mesolimbic neurocircuitries. The insult can be as severe as to menace the integrity of the genome, triggering the overactivation of sentinel proteins, including poly (ADP-ribose) polymerase-1 (PARP-1). PARP-1 overactivation implies increased energy demands, worsening the metabolic failure and depleting further NAD⁺ availability. Using a global PA rat model, we report here evidence that hypoxia increases PARP-1 activity, triggering a signalling cascade leading to nuclear translocation of the NF-κB subunit p65, modulating the expression of IL-1β and TNF-α, pro-inflammatory molecules, increasing apoptotic-like cell death in mesencephalon of neonate rats, monitored with Western blots, qPCR, TUNEL and ELISA. PARP-1 activity increased immediately after PA, reaching a maximum 1–8 h after the insult, while activation of the NF-κB signalling pathway was observed 8 h after the insult, with a >twofold increase of p65 nuclear translocation. IL-1β and TNF-α mRNA levels were increased 24 h after the insult, together with a >twofold increase in apoptotic-like cell death. A single dose of the PARP-1 inhibitor nicotinamide (0.8 mmol/kg, i.p.), 1 h post delivery, prevented the effect of PA on PARP-1 activity, p65 translocation, pro-inflammatory cytokine expression and apoptotic-like cell death. The present study demonstrates that PA leads to PARP-1 overactivation, increasing the expression of pro-inflammatory cytokines and cell death in mesencephalon, effects prevented by systemic neonatal nicotinamide administration, supporting the idea that PARP-1 inhibition represents a therapeutic target against the effects of PA.

Short- and long-term consequences of perinatal asphyxia: looking for neuroprotective strategies

Perinatal asphyxia constitutes a prototype of obstetric complications occurring when pulmonary oxygenation is delayed or interrupted. A primary insult is first produced by the length of the time without oxygenation, leading to hypoxia/ischemia and death if oxygenation is not promptly established. A second insult is produced by re-oxygenation, eliciting a cascade of biochemical events for restoring function, implying, however, improper homeostasis. The effects observed long after perinatal asphyxia can be explained by over-expression of sentinel proteins, such as poly(ADP-ribose) polymerase-1 (PARP-1), competing for oxidised nicotinamide adenine dinucleotide (NAD(+)) during re-oxygenation. Asphyxia also induces transcriptional activation of pro-inflammatory factors, including nuclear factor κB (NFκB) and its subunit p65, whose translocation to the nucleus is significantly increased in brain tissue from asphyxia-exposed animals, in tandem with PARP-1 overactivation, leading to the idea that sentinel protein inhibition constitutes a suitable therapeutic strategy. It is proposed that PARP-1 inhibition also down-regulates the expression of pro-inflammatory cytokines.Nicotinamide is a suitable PARP-1 inhibitor, whose effects have been studied in an experimental model of global perinatal asphyxia in rats, inducing the insult by immersing rat foetuses into a water bath for various periods of time. Following asphyxia, the pups are delivered, immediately treated, or given to surrogate dams for nursing, pending further experiments. Systemic administration of nicotinamide 1 h after the insult inhibited PARP-1 overactivity in peripheral and brain tissue, preventing several of the long-term consequences elicited by perinatal asphyxia, supporting the idea that it constitutes a lead for exploring compounds with similar or better pharmacological profiles.

Perinatal asphyxia: CNS development and deficits with delayed onset

Perinatal asphyxia constitutes a prototype of obstetric complications occurring when pulmonary oxygenation is delayed or interrupted. The primary insult relates to the duration of the period lacking oxygenation, leading to death if not re-established. Re-oxygenation leads to a secondary insult, related to a cascade of biochemical events required for restoring proper function. Perinatal asphyxia interferes with neonatal development, resulting in long-term deficits associated to mental and neurological diseases with delayed clinical onset, by mechanisms not yet clarified. In the experimental scenario, the effects observed long after perinatal asphyxia have been explained by overexpression of sentinel proteins, such as poly(ADP-ribose) polymerase-1 (PARP-1), competing for NAD⁺ during re-oxygenation, leading to the idea that sentinel protein inhibition constitutes a suitable therapeutic strategy. Asphyxia induces transcriptional activation of pro-inflammatory factors, in tandem with PARP-1 overactivation, and pharmacologically induced PARP-1 inhibition also down-regulates the expression of proinflammatory cytokines. Nicotinamide has been proposed as a suitable PARP-1 inhibitor. Its effect has been studied in an experimental model of global hypoxia in rats. In that model, the insult is induced by immersing rat fetus into a water bath for various periods of time. Following asphyxia, the pups are delivered, treated, and nursed by surrogate dams, pending further experiments. Nicotinamide rapidly distributes into the brain following systemic administration, reaching steady state concentrations sufficient to inhibit PARP-1 activity for several hours, preventing several of the long-term consequences of perinatal asphyxia, supporting the idea that nicotinamide constitutes a lead for exploring compounds with similar or better pharmacological profiles.

The mechanisms and treatment of asphyxial encephalopathy

Acute post-asphyxial encephalopathy occurring around the time of birth remains a major cause of death and disability. The recent seminal insight that allows active neuroprotective treatment is that even after profound asphyxia (the “primary” phase), many brain cells show initial recovery from the insult during a short “latent” phase, typically lasting approximately 6 h, only to die hours to days later after a “secondary” deterioration characterized by seizures, cytotoxic edema, and progressive failure of cerebral oxidative metabolism. Although many of these secondary processes are potentially injurious, they appear to be primarily epiphenomena of the “execution” phase of cell death. Animal and human studies designed around this conceptual framework have shown that moderate cerebral hypothermia initiated as early as possible but before the onset of secondary deterioration, and continued for a sufficient duration to allow the secondary deterioration to resolve, has been associated with potent, long-lasting neuroprotection. Recent clinical trials show that while therapeutic hypothermia significantly reduces morbidity and mortality, many babies still die or survive with disabilities. The challenge for the future is to find ways of improving the effectiveness of treatment. In this review, we will dissect the known mechanisms of hypoxic-ischemic brain injury in relation to the known effects of hypothermic neuroprotection.

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.

Neuroprotective effects of hypothermia and erythropoietin after perinatal asphyxia in newborn rats

OBJECTIVE

Evaluation of neuroprotective effects of hypothermia, erythropoietin and their simultaneous use after perinatal asphyxia in newborn rats.

METHOD

Hysterectomy was performed to Wistar female rats on the last day of gestation. Perinatal asphyxia was induced by submersion of uterus containing pups in saline for 15 min. After resuscitation, pups were randomized into 4 groups, 15 animals in each: G1 - asphyxia; G2 - asphyxia + hypothermia (rectal temperature 33 °C for 1 h); G3 - asphyxia + erythropoietin (Darbepoetin-α 2.5 μg, intraperitoneally) and G4 - asphyxia + erythropoietin + hypothermia. Pups were sacrificed on 7th day of life and histopathological analysis of hippocampus was performed.

RESULTS

Measure of damage to dorsal, ventral and entire hippocampus was significantly lower in groups G2, G3 and G4 than in group G1 (p ~ 0.00; respectively). Measure of damage to hippocampus in group G4 was significantly lower than in group G2 (p = 0.029).

CONCLUSIONS

This study demonstrates that simultaneous use of hypothermia and erythropoietin has more expressed neuroprotective effects than sole use of hypothermia after perinatal asphyxia in newborn rats.

Metabolic effects of perinatal asphyxia in the rat cerebral cortex

We reported previously that intrauterine asphyxia acutely affects the rat hippocampus. For this reason, the early effects of this injury were studied in the cerebral cortex, immediately after hysterectomy (acute condition) or following a recovery period at normoxia (recovery condition). Lactacidemia and glycemia were determined, as well as glycogen levels in the muscle, liver and cortex. Cortical tissue was also used to assay the ATP levels and glutamate uptake. Asphyxiated pups exhibited bluish coloring, loss of movement, sporadic gasping and hypertonia. However, the appearance of the controls and asphyxiated pups was similar at the end of the recovery period. Lactacidemia and glycemia were significantly increased by asphyxia in both the acute and recovery conditions. Concerning muscle and hepatic glycogen, the control group showed significantly higher levels than the asphyxic group in the acute condition and when compared with groups of the recovery period. In the recovery condition, the control and asphyxic groups showed similar glycogen levels. However, in the cortex, the control groups showed significantly higher glycogen levels than the asphyxic group, in both the acute and recovery conditions. In the cortical tissue, asphyxia reduced ATP levels by 70 % in the acute condition, but these levels increased significantly in asphyxic pups after the recovery period. Asphyxia did not affect glutamate transport in the cortex of both groups. Our results suggest that the cortex uses different energy resources to restore ATP after an asphyxia episode followed by a reperfusion period. This strategy could sustain the activity of essential energy-dependent mechanisms.

The influence of EPO and hypothermia on the kidneys of rats after perinatal asphyxia

The aim of this study was to determine the effects of erythropoietin (EPO), moderate hypothermia, and a combination thereof on the kidneys of newborn rats damaged during perinatal asphyxia. An animal model of perinatal asphyxia (Wistar rats) was used in which after birth, newborn rats were divided into four groups of 15 animals each: G1, rats exposed only to asphyxia; G2, rats exposed to asphyxia and hypothermia (rectal temperature 32°C) and which received EPO (darbepoetin alpha) intraperitoneally; G3, rats exposed to asphyxia and hypothermia; G4, rats exposed to asphyxia and which received EPO. The rats were sacrificed on the 7th day of life and histopathological evaluation of kidneys was performed. Damage to the proximal tubules was significantly higher in group G1 rats than in groups G2, G3, and G4 rats (p < 0.01). Damage to the distal tubules was found only in group G1 rats. Histological changes in the proximal tubules were more prominent than in the distal tubules (p < 0.01). The immature glomeruli zone was less expressed in group G4 rats than in groups G1, G2, and G3 rats (p < 0.01). Based on these results, we conclude that EPO and hypothermia, as well as the combination thereof, have a protective effect on rats' kidneys damaged during perinatal asphyxia.

Pathophysiology of perinatal asphyxia: can we predict and improve individual outcomes?

Perinatal asphyxia occurs still with great incidence whenever delivery is prolonged, despite improvements in perinatal care. After asphyxia, infants can suffer from short- to long-term neurological sequelae, their severity depend upon the extent of the insult, the metabolic imbalance during the re-oxygenation period and the developmental state of the affected regions. Significant progresses in understanding of perinatal asphyxia pathophysiology have achieved. However, predictive diagnostics and personalised therapeutic interventions are still under initial development. Now the emphasis is on early non-invasive diagnosis approach, as well as, in identifying new therapeutic targets to improve individual outcomes. In this review we discuss (i) specific biomarkers for early prediction of perinatal asphyxia outcome; (ii) short and long term sequelae; (iii) neurocircuitries involved; (iv) molecular pathways; (v) neuroinflammation systems; (vi) endogenous brain rescue systems, including activation of sentinel proteins and neurogenesis; and (vii) therapeutic targets for preventing or mitigating the effects produced by asphyxia.

Birth asphyxia as the major complication in newborns: moving towards improved individual outcomes by prediction, targeted prevention and tailored medical care

Perinatal Asphyxia—oxygen deficit at delivery—can lead to severe hypoxic ischaemic organ damage in newborns followed by a fatal outcome or severe life-long pathologies. The severe insults often cause neurodegenerative diseases, mental retardation and epilepsies. The mild insults lead to so-called “minimal brain-damage disorders” such as attention deficits and hyperactivity, but can also be associated with the development of schizophrenia and life-long functional psychotic syndromes. Asphyxia followed by re-oxygenation can potentially lead to development of several neurodegenerative pathologies, diabetes type 2 and cancer. The task of individual prediction, targeted prevention and personalised treatments before a manifestation of the life-long chronic pathologies usually developed by newborns with asphyxic deficits, should be given the extraordinary priority in neonatology and paediatrics. Socio-economical impacts of educational measures and advanced strategies in development of robust diagnostic approaches targeted at effected molecular pathways, biomarker-candidates and potential drug-targets for tailored treatments are reviewed in the paper.

Perinatal asphyxia: current status and approaches towards neuroprotective strategies, with focus on sentinel proteins

Delivery is a stressful and risky event menacing the newborn. The mother-dependent respiration has to be replaced by autonomous pulmonary breathing immediately after delivery. If delayed, it may lead to deficient oxygen supply compromising survival and development of the central nervous system. Lack of oxygen availability gives rise to depletion of NAD⁺ tissue stores, decrease of ATP formation, weakening of the electron transport pump and anaerobic metabolism and acidosis, leading necessarily to death if oxygenation is not promptly re-established. Re-oxygenation triggers a cascade of compensatory biochemical events to restore function, which may be accompanied by improper homeostasis and oxidative stress. Consequences may be incomplete recovery, or excess reactions that worsen the biological outcome by disturbed metabolism and/or imbalance produced by over-expression of alternative metabolic pathways. Perinatal asphyxia has been associated with severe neurological and psychiatric sequelae with delayed clinical onset. No specific treatments have yet been established. In the clinical setting, after resuscitation of an infant with birth asphyxia, the emphasis is on supportive therapy. Several interventions have been proposed to attenuate secondary neuronal injuries elicited by asphyxia, including hypothermia. Although promising, the clinical efficacy of hypothermia has not been fully demonstrated. It is evident that new approaches are warranted. The purpose of this review is to discuss the concept of sentinel proteins as targets for neuroprotection. Several sentinel proteins have been described to protect the integrity of the genome (e.g. PARP-1; XRCC1; DNA ligase IIIα; DNA polymerase β, ERCC2, DNA-dependent protein kinases). They act by eliciting metabolic cascades leading to (i) activation of cell survival and neurotrophic pathways; (ii) early and delayed programmed cell death, and (iii) promotion of cell proliferation, differentiation, neuritogenesis and synaptogenesis. It is proposed that sentinel proteins can be used as markers for characterising long-term effects of perinatal asphyxia, and as targets for novel therapeutic development and innovative strategies for neonatal care.

Nicotinamide prevents the long-term effects of perinatal asphyxia on apoptosis, non-spatial working memory and anxiety in rats

There is no established treatment for the long-term effects produced by perinatal asphyxia. Thus, we investigated the neuroprotection provided by nicotinamide against the effects elicited by perinatal asphyxia on hippocampus and behaviour observed at 30-90 days of age. Asphyxia was induced by immersing foetuses-containing uterine horns, removed from ready-to-deliver rats into a water bath at 37 degrees C for 20 min. Caesarean-delivered siblings were used as controls. Saline or nicotinamide (0.8 mmol/kg, i.p.) was administered to control and asphyxia-exposed animals 24, 48, and 72 h after birth. The animals were examined for morphological changes in hippocampus, focusing on delayed cell death and mossy fibre sprouting, and behaviour, focusing on cognitive behaviour and anxiety. At the age of 30-45 days, asphyxia-exposed rats displayed (1) increased apoptosis, assessed in whole hippocampus by nuclear Hoechst staining, and (2) increased mossy fibre sprouting, restricted to the stratum oriens of dorsal hippocampus, assessed by Timm's staining. Rats from the same cohorts displayed (3) deficits in non-spatial working memory, assessed by a novel object recognition task, and (4) increased anxiety, assessed by an elevated plus-maze test when examined at the age of 90 days. Nicotinamide prevented the effects elicited by perinatal asphyxia on apoptosis, working memory, and anxiety.

Protein ubiquitination in postsynaptic densities after hypoxia in rat neostriatum is blocked by hypothermia

Synaptic dysfunction has been associated with neuronal cell death following hypoxia. The lack of knowledge on the mechanisms underlying this dysfunction prompted us to investigate the morphological changes in the postsynaptic densities (PSDs) induced by hypoxia. The results presented here demonstrate that PSDs of the rat neostriatum are highly modified and ubiquitinated 6 months after induction of hypoxia in a model of perinatal asphyxia. Using both two dimensional (2D) and three dimensional (3D) electron microscopic analyses of synapses stained with ethanolic phosphotungstic acid (E-PTA), we observed an increment of PSD thickness dependent on the duration and severity of the hypoxic insult. The PSDs showed clear signs of damage and intense staining for ubiquitin. These morphological and molecular changes were effectively blocked by hypothermia treatment, one of the most effective strategies for hypoxia-induced brain injury available today. Our data suggest that synaptic dysfunction following hypoxia may be caused by long-term misfolding and aggregation of proteins in the PSD.

Nicotinamide prevents the effect of perinatal asphyxia on dopamine release evaluated with in vivo microdialysis 3 months after birth

The present study shows that nicotinamide prevents the long-term effect of perinatal asphyxia on dopamine release monitored with in vivo microdialysis in the neostriatum of 3-month-old rats. Perinatal asphyxia was induced by immersing foetuses-containing uterine horns removed from ready-to-deliver rats into a water bath for 16 or 20 min. Sibling, spontaneous, and caesarean-delivered pups were used as controls. Saline or nicotinamide (0.8 mmol/kg, i.p.) was administered to control and asphyxia-exposed animals 24, 48, and 72 h after birth. After weaning, the rats were randomly distributed in laboratory cages for animal care under standard ad libitum laboratory conditions. Approximately 3 months after birth, control and asphyxia-exposed animals were implanted with microdialysis probes into the lateral neostriatum for measuring extracellular monoamine and metabolite levels with HPLC-coupled to an electrochemical detection system under basal, D-amphetamine, and K(+)-depolarising conditions. There was an asphyxia-dependent decrease of extracellular dopamine levels, mainly observed during the periods when D-amphetamine (100 microM) or KCl (100 mM) was added into the perfusion medium. Compared to that observed in caesarean-delivered controls, the effect of D-amphetamine on dopamine levels was decreased by approximately 30 and 70% in animals exposed to 16 and 20 min of perinatal asphyxia, respectively. The effect of K(+)-depolarisation was decreased by 45 and 83% in animals exposed to the same periods of asphyxia, respectively. Both effects were prevented by nicotinamide, even if the treatment started 24 h after the insult. The present results support the idea of nicotinamide as an interesting molecule, useful for protecting against anoxia/ischemia occurring at neonatal stages. Nicotinamide can help to restore NADH/NAD+ depletion, but also to inhibit PARP-1 overactivation, a mechanism of action that has attracted attention, representing a novel target for neuroprotection following insults involving energy failure.

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.

Effects of perinatal asphyxia on cell proliferation and neuronal phenotype evaluated with organotypic hippocampal cultures

The present report summarizes studies combining an in vivo and in vitro approach, where asphyxia is induced in vivo at delivery time of Wistar rats, and the long term effects on hippocampus neurocircuitry are investigated in vitro with organotypic cultures plated at postnatal day seven. The cultures preserved hippocampus layering and regional subdivisions shown in vivo, and only few dying cells were observed when assayed with a viability test at day in vitro 27. When properly fixed, cultures from asphyxia-exposed animals showed a decreased amount of microtubule-associated protein-2 immunocytochemically positive cells (approximately 30%), as compared with that from controls. The decrease in microtubule-associated protein-2 immunocytochemistry was particularly prominent in Ammon's horn 1 and dentate gyrus regions (approximately 40%). 5-Bromo-2'deoxyuridine labeling revealed a two-fold increase in cellular proliferation in cultures from asphyxia-exposed, compared with that from control animals. Furthermore, confocal microscopy and quantification using the optical disector technique demonstrated that in cultures from asphyxia-exposed animals approximately 30% of 5-bromo-2'deoxyuridine-positive cells were also positive to microtubule-associated protein-2, a marker for neuronal phenotype. That proportion was approximately 20% in cultures from control animals. Glial fibrillary acidic protein-immunocytochemistry and Fast Red nuclear staining revealed that the core of the hippocampus culture was surrounded by a well-developed network of glial fibrillary acidic protein-positive cells and glial fibrillary acidic protein-processes providing an apparent protective shield around the hippocampus. That shield was less developed in cultures from asphyxia-exposed animals. The increased mitotic activity observed in this study suggests a compensatory mechanism for the long-term impairment induced by perinatal asphyxia, although it is not clear yet if that mechanism leads to neurogenesis, astrogliogenesis, or to further apoptosis.

Suppression of post-hypoxic-ischemic EEG transients with dizocilpine is associated with partial striatal protection in the preterm fetal sheep

In vitro studies suggest that glutamate receptor activation is important in the genesis of post-hypoxic preterm brain injury, but there are limited data on post-hypoxic N-methyl-D-aspartate (NMDA) receptor activation. We therefore examined an infusion of the specific, non-competitive NMDA receptor antagonist dizocilpine (2 mg kg(-1) bolus plus 0.07 mg kg(-1) h(-1) i.v.) from 15 min to 4 h after severe hypoxia-ischemia induced by umbilical cord occlusion for 25 min in fetal sheep at 70% of gestation. Dizocilpine suppressed evolving epileptiform transient activity in the first 6 h after reperfusion (2.3 +/- 0.9 versus 9.3 +/- 2.3 maximal counts min(-1), P < 0.05) and mean EEG intensity up to 11 h after occlusion (P < 0.05). Fetal extradural temperature transiently increased during the dizocilpine infusion (40.1 +/- 0.2 versus 39.3 +/- 0.1 degrees C, P < 0.05). After 3 days recovery, treatment was associated with a significant reduction in neuronal loss in the striatum (31 +/- 7 versus 58 +/- 2%, P < 0.05), expression of cleaved caspase-3 (111+/-7 versus 159 +/- 10 counts area(-1), P < 0.05) and numbers of activated microglia (57 +/- 9 versus 92 +/- 16 counts area(-1), P < 0.05); there was no significant effect in other regions or on loss of immature O4-positive oligodendrocytes. In conclusion, abnormal NMDA receptor activation in the first few hours of recovery from hypoxia-ischemia seems to contribute to post-hypoxic striatal damage in the very immature brain.

Prolonged hypothermia protects neonatal rat brain against hypoxic-ischemia by reducing both apoptosis and necrosis

Although hypothermia is an effective treatment for perinatal cerebral hypoxic-ischemic (HI) injury, it remains unclear how long and how deep we need to maintain hypothermia to obtain maximum neuroprotection. We examined effects of prolonged hypothermia on HI immature rat brain and its protective mechanisms using the Rice-Vannucci model. Immediately after the end of hypoxic exposure, the pups divided into a hypothermia group (30 degrees C) and a normothermia one (37 degrees C). Rectal temperature was maintained until they were sacrificed at each time point before 72h post HI. Prolonged hypothermia significantly reduced macroscopic brain injury compared with normothermia group. Quantitative analysis of cell death using H&E-stained sections revealed the number of both apoptotic and necrotic cells was significantly reduced by hypothermia after 24h post HI. Hypothermia seemed to decrease the number of TUNEL-positive cells. Immunohistochemistry and Western blot showed that prolonged hypothermia suppressed cytochrome c release from mitochondria to cytosol and activation of both caspase-3 and calpain in cortex, hippocampus, thalamus and striatum throughout the experiment. These results showed that prolonged hypothermia significantly reduced neonatal brain injury even when it was started after HI insult. Our results suggest that prolonged hypothermia protects neonatal brain after HI by reducing both apoptosis and necrosis.

Sub-neurotoxic neonatal anoxia induces subtle behavioural changes and specific abnormalities in brain group-I metabotropic glutamate receptors in rats

Anoxia in the first week of life can induce neuronal death in vulnerable brain regions usually associated with an impairment of cognitive function that can be detected later in life. We set-up a model of subneurotoxic anoxia based on repeated exposures to 100% nitrogen during the first 7 days of post-natal life. This mild post-natal exposure to anoxia specifically modified the behaviour of the male adult rats, which showed an attention deficit and an increase in anxiety, without any impairment in spatial learning and any detectable brain damage (magnetic resonance imaging and histological analysis). Post-anoxic rats showed a reduction in the expression of group-I metabotropic glutamate receptors (i.e. mGlu1 and mGlu5 receptors) in the hippocampus and cerebral cortex, whereas expression of the mGlu 2/3 receptors, the NR1 subunit of NMDA receptors, and the GluR1 subunit of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors was unchanged. mGlu1 and mGlu5 receptor signalling was also impaired in postanoxic rats, as revealed by a reduced efficacy of the agonist (1S,3R)-1-Aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) to stimulate polyphosphoinositide hydrolysis in hippocampal slices. We conclude that rats subjected to subneurotoxic doses of anoxia during the early post-natal life develop behavioural symptoms that are frequently encountered in the inattentive subtype of the attention deficit hyperactivity disorder, and that group-I mGlu receptors may be involved in the pathophysiology of these symptoms.

A delayed increase in hippocampal proliferation following global asphyxia in the neonatal rat

Adult neurogenesis has been shown to be upregulated following a wide variety of brain injury paradigms. During the first weeks of postnatal life there is around 50 fold more neurogenesis occurring than in the adult CNS, yet little is known regarding the effect of neonatal brain injury on this developmental proliferation. We have investigated the effect of a global perinatal birth asphyxia on postnatal proliferation at 2, 5, 8, 11, 15, 21 and 28 days after birth (injury) using a 3H-thymidine tracer study. We found a specific upregulation of proliferation at 5 days after the injury within the injured hippocampus only, with an associated increase in hippocampal mass and without any changes in GFAP content at any timepoint. Perinatal asphyxia did not alter proliferation within the cerebellum, sub ventricular zone, olfactory bulb, cervical or thoracic spinal cord. Similarly, no changes in corticosterone levels were induced by the injury. Since there were no changes in GFAP content we hypothesize that this increased proliferation is likely neurogenetic, similar to what is seen in the adult brain following injury. Further we show that the dramatic increase in corticosterone at the end of the stress hyporesponsive period is not responsible for the equally dramatic decrease in postnatal proliferation within the CNS.