Disrupted synaptic development in the hypoxic newborn brain

Early versus late caffeine and/or non-steroidal anti-inflammatory drugs (NSAIDS) for prevention of intermittent hypoxia-induced neuroinflammation in the neonatal rat

Preterm infants often experience frequent intermittent hypoxia (IH) episodes which are associated with neuroinflammation. We tested the hypotheses that early caffeine and/or non-steroidal inflammatory drugs (NSAIDs) confer superior therapeutic benefits for protection against IH-induced neuroinflammation than late treatment. Newborn rats were exposed to IH or hyperoxia (50% O2) from birth (P0) to P14. For early treatment, the pups were administered: 1) daily caffeine (Caff) citrate (Cafcit, 20 mg/kg IP loading on P0, followed by 5 mg/kg from P1-P14); 2) ketorolac (Keto) topical ocular solution in both eyes from P0 to P14; 3) ibuprofen (Ibu, Neoprofen, 10 mg/kg loading dose on P0 followed by 5 mg/kg/day on P1 and P2); 4) Caff+Keto co-treatment; 5) Caff+Ibu co-treatment; or 6) equivalent volume saline (Sal). On P14, animals were placed in room air (RA) with no further treatment until P21. For late treatment, pups were exposed from P0 to P14, then placed in RA during which they received similar treatments from P15-P21 (Sal, Caff, and/or Keto), or P15-P17 (Ibu). RA controls were similarly treated. At P21, whole brains were assessed for histopathology, apoptosis, myelination, and biomarkers of inflammation. IH caused significant brain injury and hemorrhage, inflammation, reduced myelination, and apoptosis. Early treatment with Caff alone or in combination with NSAIDs conferred better neuroprotection against IH-induced damage than late treatment. Early postnatal treatment during a critical time of brain development, may be preferable for the prevention of IH-induced brain injury in preterm infants.

Apnea of prematurity induces short and long-term development-related transcriptional changes in the murine cerebellum

Apnea of prematurity (AOP) affects more than 50% of preterm infants and leads to perinatal intermittent hypoxia (IH) which is a major cause of morbimortality worldwide. At birth, the human cerebellar cortex is still immature, making it vulnerable to perinatal events. Additionally, studies have shown a correlation between cerebellar functions and the deficits observed in children who have experienced AOP. Yet, the cerebellar alterations underpinning this link remain poorly understood. To gain insight into the involvement of the cerebellum in perinatal hypoxia-related consequences, we developed a mouse model of AOP. Our previous research has revealed that IH induces oxidative stress in the developing cerebellum, as evidenced by the over-expression of genes involved in reactive oxygen species production and the under-expression of genes encoding antioxidant enzymes. These changes suggest a failure of the defense system against oxidative stress and could be responsible for neuronal death in the cerebellum. Building upon these findings, we conducted a transcriptomic study of the genes involved in the processes that occur during cerebellar development. Using real-time PCR, we analyzed the expression of these genes at different developmental stages and in various cell types. This enabled us to pinpoint a timeframe of vulnerability at P8, which represents the age with the highest number of downregulated genes in the cerebellum. Furthermore, we discovered that our IH protocol affects several molecular pathways, including proliferation, migration, and differentiation. This indicates that IH can impact the development of different cell types, potentially contributing to the histological and behavioral deficits observed in this model. Overall, our data strongly suggest that the cerebellum is highly sensitive to IH, and provide valuable insights into the cellular and molecular mechanisms underlying AOP. In the long term, these findings may contribute to the identification of novel therapeutic targets for improving the clinical management of this prevalent pathology.

Consequences of oxygen deprivation on myelination and sex-dependent alterations

Oxygen deprivation is one of the main causes of morbidity and mortality in newborns, occurring with a higher prevalence in preterm infants, reaching 20 % to 50 % mortality in newborns in the perinatal period. When they survive, 25 % exhibit neuropsychological pathologies, such as learning difficulties, epilepsy, and cerebral palsy. White matter injury is one of the main features found in oxygen deprivation injury, which can lead to long-term functional impairments, including cognitive delay and motor deficits. The myelin sheath accounts for much of the white matter in the brain by surrounding axons and enabling the efficient conduction of action potentials. Mature oligodendrocytes, which synthesize and maintain myelination, also comprise a significant proportion of the brain's white matter. In recent years, oligodendrocytes and the myelination process have become potential therapeutic targets to minimize the effects of oxygen deprivation on the central nervous system. Moreover, evidence indicate that neuroinflammation and apoptotic pathways activated during oxygen deprivation may be influenced by sexual dimorphism. To summarize the most recent research about the impact of sexual dimorphism on the neuroinflammatory state and white matter injury after oxygen deprivation, this review presents an overview of the oligodendrocyte lineage development and myelination, the impact of oxygen deprivation and neuroinflammation on oligodendrocytes in neurodevelopmental disorders, and recent reports about sexual dimorphism regarding the neuroinflammation and white matter injury after neonatal oxygen deprivation.

Intermittent hypoxia in a mouse model of apnea of prematurity leads to a retardation of cerebellar development and long-term functional deficits

Background

Apnea of prematurity (AOP) is caused by respiratory control immaturity and affects nearly 50% of premature newborns. This pathology induces perinatal intermittent hypoxia (IH), which leads to neurodevelopmental disorders. The impact on the brain has been well investigated. However, despite its functional importance and immaturity at birth, the involvement of the cerebellum remains poorly understood. Therefore, this study aims to identify the effects of IH on cerebellar development using a mouse model of AOP consisting of repeated 2-min cycles of hypoxia and reoxygenation over 6 h and for 10 days starting on postnatal day 2 (P2).

Results

At P12, IH-mice cerebella present higher oxidative stress associated with delayed maturation of the cerebellar cortex and decreased dendritic arborization of Purkinje cells. Moreover, mice present with growth retardation and motor disorders. In response to hypoxia, the developing cerebellum triggers compensatory mechanisms resulting in the unaltered organization of the cortical layers from P21 onwards. Nevertheless, some abnormalities remain in adult Purkinje cells, such as the dendritic densification, the increase in afferent innervation, and axon hypomyelination. Moreover, this compensation seems insufficient to allow locomotor recovery because adult mice still show motor impairment and significant disorders in spatial learning.

Conclusions

All these findings indicate that the cerebellum is a target of intermittent hypoxia through alterations of developmental mechanisms leading to long-term functional deficits. Thus, the cerebellum could contribute, like others brain structures, to explaining the pathophysiology of AOP.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00869-5.

Neonatal Oxidative Stress Impairs Cortical Synapse Formation and GABA Homeostasis in Parvalbumin-Expressing Interneurons

Neonatal brain injury is often caused by preterm birth. Brain development is vulnerable to increased environmental stress, including oxidative stress challenges. Due to a premature change of the fetal living environment from low oxygen in utero into postnatal high-oxygen room air conditions ex utero, the immature preterm brain is exposed to a relative hyperoxia, which can induce oxidative stress and impair neuronal cell development. To simulate the drastic increase of oxygen exposure in the immature brain, 5-day-old C57BL/6 mice were exposed to hyperoxia (80% oxygen) for 48 hours or kept in room air (normoxia, 21% oxygen) and mice were analyzed for maturational alterations of cortical GABAergic interneurons. As a result, oxidative stress was indicated by elevated tyrosine nitration of proteins. We found perturbation of perineuronal net formation in line with decreased density of parvalbumin-expressing (PVALB) cortical interneurons in hyperoxic mice. Moreover, maturational deficits of cortical PVALB+ interneurons were obtained by decreased glutamate decarboxylase 67 (GAD67) protein expression in Western blot analysis and lower gamma-aminobutyric acid (GABA) fluorescence intensity in immunostaining. Hyperoxia-induced oxidative stress affected cortical synaptogenesis by decreasing synapsin 1, synapsin 2, and synaptophysin expression. Developmental delay of synaptic marker expression was demonstrated together with decreased PI3K-signaling as a pathway being involved in synaptogenesis. These results elucidate that neonatal oxidative stress caused by increased oxygen exposure can lead to GABAergic interneuron damage which may serve as an explanation for the high incidence of psychiatric and behavioral alterations found in preterm infants.

Influence of Cerebral Vasodilation on Blood Reelin Levels in Growth Restricted Fetuses

Fetal growth restriction (FGR) is one of the most important obstetric pathologies. It is frequently caused by placental insufficiency. Previous studies have shown a relationship between FGR and impaired new-born neurodevelopment, although the molecular mechanisms involved in this association have not yet been completely clarified. Reelin is an extracellular matrix glycoprotein involved in development of neocortex, hippocampus, cerebellum and spinal cord. Reelin has been demonstrated to play a key role in regulating perinatal neurodevelopment and to contribute to the emergence and development of various psychiatric pathologies, and its levels are highly influenced by pathological conditions of hypoxia. The purpose of this article is to study whether reelin levels in new-borns vary as a function of severity of fetal growth restriction by gestational age and sex. We sub-grouped fetuses in: normal weight group (Group 1, n = 17), FGR group with normal umbilical artery Doppler and cerebral redistribution at middle cerebral artery Doppler (Group 2, n = 9), and FGR with abnormal umbilical artery Doppler (Group 3, n = 8). Our results show a significant association of elevated Reelin levels in FGR fetuses with cerebral blood redistribution compared to the normal weight group and the FGR with abnormal umbilical artery group. Future research should focus on further expanding the knowledge of the relationship of reelin and its regulated products with neurodevelopment impairment in new-borns with FGR and should include larger and more homogeneous samples and the combined use of different in vivo techniques in neonates with impaired growth during their different adaptive phases.

Chronic Intermittent Hypobaric Hypoxia Restores Hippocampus Function and Rescues Cognitive Impairments in Chronic Epileptic Rats via Wnt/β-catenin Signaling

Epilepsy is a complex neurological disorder with frequent psychiatric, cognitive, and social comorbidities in addition to recurrent seizures. Cognitive impairment, one of the most common comorbidities, has severe adverse effects on quality of life. Chronic intermittent hypobaric hypoxia (CIHH) has demonstrated neuroprotective efficacy in several neurological disease models. In the present study, we examined the effects of CIHH on cognition and hippocampal function in chronic epileptic rats. CIHH treatment rescued deficits in spatial and object memory, hippocampal neurogenesis, and synaptic plasticity in pilocarpine-treated epileptic rats. The Wnt/β-catenin pathway has been implicated in neural stem cell proliferation and synapse development, and Wnt/β-catenin pathway inhibition effectively blocked the neurogenic effects of CIHH. Our findings indicate that CIHH rescues cognitive deficits in epileptic rats via Wnt/β-catenin pathway activation. This study establishes CIHH and Wnt/β-catenin pathway regulators as potential treatments for epilepsy- induced cognitive impairments.

Dopaminergic Co-Regulation of Locomotor Development and Motor Neuron Synaptogenesis is Uncoupled by Hypoxia in Zebrafish

Hypoxic injury to the developing human brain is a complication of premature birth and is associated with long-term impairments of motor function. Disruptions of axon and synaptic connectivity have been linked to developmental hypoxia, but the fundamental mechanisms impacting motor function from altered connectivity are poorly understood. We investigated the effects of hypoxia on locomotor development in zebrafish. We found that developmental hypoxia resulted in decreased spontaneous swimming behavior in larva, and that this motor impairment persisted into adulthood. In evaluation of the diencephalic dopaminergic neurons, which regulate early development of locomotion and constitute an evolutionarily conserved component of the vertebrate dopaminergic system, hypoxia caused a decrease in the number of synapses from the descending dopaminergic diencephalospinal tract (DDT) to spinal cord motor neurons. Moreover, dopamine signaling from the DDT was coupled jointly to motor neuron synaptogenesis and to locomotor development. Together, these results demonstrate the developmental processes regulating early locomotor development and a requirement for dopaminergic projections and motor neuron synaptogenesis. Our findings suggest new insights for understanding the mechanisms leading to motor disability from hypoxic injury of prematurity.

Multiple pharmacological and toxicological investigations on Tanacetum parthenium and Salix alba extracts: Focus on potential application as anti-migraine agents

Migraine is one of the most common neurological disorder, which has long been related to brain serotonin (5-HT) depletion and neuro-inflammation. Despite many treatment options are available, the frequent occurrence of unacceptable adverse effects further supports the research toward nutraceuticals and herbal preparations, among which Tanacetum parthenium and Salix alba showed promising anti-inflammatory and neuro-modulatory activities. The impact of extract treatment on astrocyte viability, spontaneous migration and apoptosis was evaluated. Anti-inflammatory/anti-oxidant effects were investigated on isolated rat cortexes exposed to a neurotoxic stimulus. The lactate dehydrogenase (LDH) release, nitrite levels and 5-HT turnover were evaluated, as well. A proteomic analysis was focused on specific neuronal proteins and a fingerprint analysis was carried out on selected phenolic compounds. Both extracts appeared able to exert in vitro anti-oxidant and anti-apoptotic effects. S. alba and T. parthenium extracts reduced LDH release, nitrite levels and 5-HT turnover induced by neurotoxic stimulus. The downregulation of selected proteins suggest a neurotoxicity, which could be ascribed to an elevated content of gallic acid in both S. alba and T. parthenium extracts. Concluding, both extracts exert neuroprotective effects, although the downregulation of key proteins involved in neuron physiology suggest caution in their use as food supplements.

Perinatal Ischemia Alters Global Expression of Synaptosomal Proteins Critical for Neural Plasticity in the Developing Mouse Brain

Ischemic perinatal stroke (IPS) affects 1 in 2,300-5,000 live births. Despite a survival rate >95%, approximately 60% of IPS infants develop motor and cognitive impairments. Given the importance of axonal growth and synaptic plasticity in neurocognitive development, our objective was to identify the molecular pathways underlying IPS-associated synaptic dysfunction using a mouse model. IPS was induced by unilateral ligation of the common carotid artery of postnatal day 10 (P10) mice. Five days after ischemia, sensorimotor and motor functions were assessed by vibrissae-evoked forepaw placement and the tail suspension test respectively, showing evidence of greater impairments in male pups than in female pups. Twenty-four hours after ischemia, both hemispheres were collected and synaptosomal proteins then prepared for quantification, using isobaric tags for relative and absolute quantitation. Seventy-two of 1,498 qualified proteins were altered in the ischemic hemisphere. Ingenuity Pathway Analysis was used to map these proteins onto molecular networks indicative of reduced neuronal proliferation, survival, and synaptic plasticity, accompanied by reduced PKCα signaling in male, but not female, pups. These effects also occurred in the non-ischemic hemisphere when compared with sham controls. The altered signaling effects may contribute to the sex-specific neurodevelopmental dysfunction following IPS, highlighting potential pathways for targeting during treatment.

Dysmaturation of Somatostatin Interneurons Following Umbilical Cord Occlusion in Preterm Fetal Sheep

INTRODUCTION

Cerebral white matter injury is the most common neuropathology observed in preterm infants. However, there is increasing evidence that gray matter development also contributes to neurodevelopmental abnormalities. Fetal cerebral ischemia can lead to both neuronal and non-neuronal structural-functional abnormalities, but less is known about the specific effects on interneurons.

OBJECTIVE

In this study we used a well-established animal model of fetal asphyxia in preterm fetal sheep to study neuropathological outcome. We used comprehensive stereological methods to investigate the total number of oligodendrocytes, neurons and somatostatin (STT) positive interneurons as well as 3D morphological analysis of STT cells 14 days following umbilical cord occlusion (UCO) in fetal sheep.

MATERIALS AND METHODS

Induction of asphyxia was performed by 25 min of complete UCO in five preterm fetal sheep (98-100 days gestational age). Seven, non-occluded twins served as controls. Quantification of the number of neurons (NeuN), STT interneurons and oligodendrocytes (Olig2, CNPase) was performed on fetal brain regions by applying optical fractionator method. A 3D morphological analysis of STT interneurons was performed using IMARIS software.

RESULTS

The number of Olig2, NeuN, and STT positive cells were reduced in IGWM, caudate and putamen in UCO animals compared to controls. There were also fewer STT interneurons in the ventral part of the hippocampus, the subiculum and the entorhinal cortex in UCO group, while other parts of cortex were virtually unaffected (p > 0.05). Morphologically, STT positive interneurons showed a markedly immature structure, with shorter dendritic length and fewer dendritic branches in cortex, caudate, putamen, and subiculum in the UCO group compared with control group (p < 0.05).

CONCLUSION

The significant reduction in the total number of neurons and oligodendrocytes in several brain regions confirm previous studies showing susceptibility of both neuronal and non-neuronal cells following fetal asphyxia. However, in the cerebral cortex significant dysmaturation of STT positive neurons occurred in the absence of cell loss. This suggests an abnormal maturation pattern of GABAergic interneurons in the cerebral cortex, which might contribute to neurodevelopmental impairment in preterm infants and could implicate a novel target for neuroprotective therapies.

Minocycline mitigates the effect of neonatal hypoxic insult on human brain organoids

Neonatal hypoxic injury (NHI) is a devastating cause of disease that affects >60% of babies born with a very low birth weight, resulting in significant morbidity and mortality, including life-long neurological consequences such as seizures, cerebral palsy, and intellectual disability. Hypoxic injury results in increased neuronal death, which disrupts normal brain development. Although animal model systems have been useful to study the effects of NHI, they do not fully represent the uniqueness and complexities of the human brain. To better understand the effects of hypoxia on human brain development, we have generated a brain organoid protocol and evaluated these cells over the course of 6 months. As anticipated, the expression of a forebrain marker, FOXG1, increased and then remained expressed over time, while there was a transition in the expression of the deep-layer (TBR1) and upper-layer (SATB2) cortical markers. In addition, ventral genes (Eng1 and Nkx2.1) as well as markers of specialized nonneuronal cells (Olig2 and GFAP) also increased at later time points. We next tested the development of our in vitro cerebral organoid model at different oxygen concentrations and found that hypoxia repressed gene markers for forebrain, oligodendrocytes, glial cells, and cortical layers, as well as genes important for the migration of cortical neurons. In contrast, ventral markers were either unaffected or even increased in expression with hypoxic insult. Interestingly, the negative effect of hypoxia on the dorsal brain genes as well as oligodendrocytes, and neuronal progenitors could be mitigated by the use of minocycline, an FDA-approved small molecule. Taken together, we have generated a unique and relevant in vitro human brain model system to study diseases such as NHI as well as their potential treatments. Using this system, we have shown the efficacy of minocycline for human NHI.

Hypoxia and connectivity in the developing vertebrate nervous system

The developing nervous system depends upon precise regulation of oxygen levels. Hypoxia, the condition of low oxygen concentration, can interrupt developmental sequences and cause a range of molecular, cellular and neuronal changes and injuries. The roles and effects of hypoxia on the central nervous system (CNS) are poorly characterized, even though hypoxia is simultaneously a normal component of development, a potentially abnormal environmental stressor in some settings, and a clinically important complication, for example of prematurity. Work over the past decade has revealed that hypoxia causes specific disruptions in the development of CNS connectivity, altering axon pathfinding and synapse development. The goals of this article are to review hypoxia's effects on the development of CNS connectivity, including its genetic and molecular mediators, and the changes it causes in CNS circuitry and function due to regulated as well as unintended mechanisms. The transcription factor HIF1α is the central mediator of the CNS response to hypoxia (as it is elsewhere in the body), but hypoxia also causes a dysregulation of gene expression. Animals appear to have evolved genetic and molecular responses to hypoxia that result in functional behavioral alterations to adapt to the changes in oxygen concentration during CNS development. Understanding the molecular pathways underlying both the normal and abnormal effects of hypoxia on CNS connectivity may reveal novel insights into common neurodevelopmental disorders. In addition, this Review explores the current gaps in knowledge, and suggests important areas for future studies.

Summary: The nervous system's exposure to hypoxia has developmental and clinical relevance. In this Review, the authors discuss the effects of hypoxia on the development of the CNS, and its long-term behavioral and neurodevelopmental consequences.

Hypoxia Delays Oligodendrocyte Progenitor Cell Migration and Myelin Formation by Suppressing Bmp2b Signaling in Larval Zebrafish

Hypoxia in newborns tends to result in developmental deficiencies in the white matter of the brain. As previous studies of the effects of hypoxia on neuronal development in rodents and human infants have been unable to use in vivo imaging, insight into the dynamic development of oligodendrocytes (OLs) in the central nervous system under hypoxia is limited. Here, we developed a visual model to study OL development using sublethal postnatal hypoxia in zebrafish larvae. We observed that hypoxia significantly suppressed OL progenitor cell migration toward the dorsum using in vivo imaging. Further, we found that hypoxia affected myelination, as indicated by thinner myelin sheaths and by a downregulation of myelin basic protein expression. Bmp2b protein expression was also significantly downregulated following hypoxia onset. Using gain of function and loss of function experiments, we demonstrated that the Bmp2b protein was associated with the regulation of OL development. Thus, our work provides a visual hypoxia model within which to observe OL development in vivo, and reveals the underlying mechanisms involved in these processes.

Endothelial cells promote excitatory synaptogenesis and improve ischemia-induced motor deficits in neonatal mice

Brain microvascular endothelial cells (BMEC) are highly complex regulatory cells that communicate with other cells in the neurovascular unit. Cerebral ischemic injury is known to produce detectable synaptic dysfunction. This study aims to investigate whether endothelial cells in the brain regulate postnatal synaptic development and to elucidate their role in functional recovery after ischemia. Here, we found that in vivo engraftment of endothelial cells increased synaptic puncta and excitatory postsynaptic currents in layers 2/3 of the motor cortex. This pro-synaptogenic effect was blocked by the depletion of VEGF in the grafted BMEC. The in vitro results showed that BMEC conditioned medium enhanced spine and synapse formation but conditioned medium without VEGF had no such effects. Moreover, under pathological conditions, transplanted endothelial cells were capable of enhancing angiogenesis and synaptogenesis and improved motor function in the ischemic injury model. Collectively, our findings suggest that endothelial cells promote excitatory synaptogenesis via the paracrine factor VEGF during postnatal development and exert repair functions in hypoxia-ischemic neonatal mice. This study highlights the importance of the endothelium-neuron interaction not only in regulating neuronal development but also in maintaining healthy brain function.

Enhancing Oligodendrocyte Myelination Rescues Synaptic Loss and Improves Functional Recovery after Chronic Hypoxia

To address the significance of enhancing myelination for functional recovery after white matter injury (WMI) in preterm infants, we characterized hypomyelination associated with chronic hypoxia and identified structural and functional deficits of excitatory cortical synapses with a prolonged motor deficit. We demonstrate that genetically delaying myelination phenocopies the synaptic and functional deficits observed in mice after hypoxia, suggesting that myelination may possibly facilitate excitatory presynaptic innervation. As a gain-of-function experiment, we specifically ablated the muscarinic receptor 1 (M1R), a negative regulator of oligodendrocyte differentiation in oligodendrocyte precursor cells. Genetically enhancing oligodendrocyte differentiation and myelination rescued the synaptic loss after chronic hypoxia and promoted functional recovery. As a proof of concept, drug-based myelination therapies also resulted in accelerated differentiation and myelination with functional recovery after chronic hypoxia. Together, our data indicate that myelination-enhancing strategies in preterm infants may represent a promising therapeutic approach for structural/functional recovery after hypoxic WMI.

Hypoxia and myelination deficits in the developing brain

Myelination is a complex and orderly process during brain development that is essential for normal motor, cognitive and sensory functions. Cellular and molecular interactions between myelin-forming oligodendrocytes and axons are required for normal myelination in the developing brain. Oligodendrocyte progenitor cells (OPCs) proliferate and differentiate into mature myelin-forming oligodendrocytes. In this connection, astrocytes and microglia are also involved in survival and proliferation of OPCs. Hypoxic insults during the perinatal period affect the normal development, differentiation and maturation of the OPCs or cause their death resulting in impaired myelination. Several factors such as augmented release of proinflammatory cytokines by activated microglia and astrocytes, extracellular accumulation of excess glutamate and increased levels of nitric oxide are some of the underlying factors for hypoxia induced damage to the OPCs. Additionally, hypoxia also leads to down-regulation of several genes involved in oligodendrocyte differentiation encoding proteolipid protein, platelet-derived growth factor receptor and myelin-associated glycoprotein in the developing brain. Furthermore, oligodendrocytes may also accumulate increased amounts of iron in hypoxic conditions that triggers endoplasmic reticulum stress, misfolding of proteins and generation of reactive oxygen species that ultimately would lead to myelination deficits. More in-depth studies to elucidate the pathophysiological mechanisms underlying the inability of oligodendrocytes to myelinate the developing brain in hypoxic insults are desirable to develop new therapeutic options or strategies for myelination deficits.

Transcriptomic analysis reveals transgenerational effect of hypoxia on the neural control of testicular functions

There are over 400 hypoxic zones in the ocean worldwide. Both laboratory and field studies have shown that hypoxia causes endocrine disruption and reproductive impairments in vertebrates. More importantly, our recent study discovered that parental (F0) hypoxia exposure resulted in the transgenerational impairment of sperm quality in the F2 generation through the epigenetic regulation of germ cells. In the present study, we aim to test the hypothesis that the brain, as the major regulator of the brain-pituitary-gonad (BPG) axis, is also involved in the observed transgenerational effect. Using comparative transcriptomic analysis on brain tissues of marine medaka Oryzias melastigma, 45 common differentially expressed genes caused by parental hypoxia exposure were found in the hypoxic group of the F0 and F2 generations, and the transgenerational groups of the F2 generation. The bioinformatic analysis on this deregulated gene cluster further highlighted the possible involvement of the brain in the transgenerational effect of hypoxia on testicular structure, including abnormal morphologies of the epididymis and the seminal vesicle, and degeneration of the seminiferous tubule. This finding is concordant to the result of hematoxylin and eosin staining, which showed the reduction of testicular lobular diameter in the F0 and F2 generations. Our study demonstrated for the first time the involvement of the brain in the transgenerational effect of hypoxia.

Pathophysiological and behavioral deficits in developing mice following rotational acceleration-deceleration traumatic brain injury

Abusive head trauma (AHT) is the leading cause of death from trauma in infants and young children. An AHT animal model was developed on 12-day-old mice subjected to 90° head extension-flexion sagittal shaking repeated 30, 60, 80 and 100 times. The mortality and time until return of consciousness were dependent on the number of repeats and severity of the injury. Following 60 episodes of repeated head shakings, the pups demonstrated apnea and/or bradycardia immediately after injury. Acute oxygen desaturation was observed by pulse oximetry during respiratory and cardiac suppression. The cerebral blood perfusion was assessed by laser speckle contrast analysis (LASCA) using a PeriCam PSI system. There was a severe reduction in cerebral blood perfusion immediately after the trauma that did not significantly improve within 24 h. The injured mice began to experience reversible sensorimotor function at 9 days postinjury (dpi), which had completely recovered at 28 dpi. However, cognitive deficits and anxiety-like behavior remained. Subdural/subarachnoid hemorrhage, damage to the brain-blood barrier and parenchymal edema were found in all pups subjected to 60 insults. Proinflammatory response and reactive gliosis were upregulated at 3 dpi. Degenerated neurons were found in the cerebral cortex and olfactory tubercles at 30 dpi. This mouse model of repetitive brain injury by rotational head acceleration-deceleration partially mimics the major pathophysiological and behavioral events that occur in children with AHT. The resultant hypoxia/ischemia suggests a potential mechanism underlying the secondary rotational acceleration-deceleration-induced brain injury in developing mice.

Transient Hypoxemia Chronically Disrupts Maturation of Preterm Fetal Ovine Subplate Neuron Arborization and Activity

Preterm infants are at risk for a broad spectrum of neurobehavioral disabilities associated with diffuse disturbances in cortical growth and development. During brain development, subplate neurons (SPNs) are a largely transient population that serves a critical role to establish functional cortical circuits. By dynamically integrating into developing cortical circuits, they assist in consolidation of intracortical and extracortical circuits. Although SPNs reside in close proximity to cerebral white matter, which is particularly vulnerable to oxidative stress, the susceptibility of SPNs remains controversial. We determined SPN responses to two common insults to the preterm brain: hypoxia-ischemia and hypoxia. We used a preterm fetal sheep model using both sexes that reproduces the spectrum of human cerebral injury and abnormal cortical growth. Unlike oligodendrocyte progenitors, SPNs displayed pronounced resistance to early or delayed cell death from hypoxia or hypoxia-ischemia. We thus explored an alternative hypothesis that these insults alter the maturational trajectory of SPNs. We used DiOlistic labeling to visualize the dendrites of SPNs selectively labeled for complexin-3. SPNs displayed reduced basal dendritic arbor complexity that was accompanied by chronic disturbances in SPN excitability and synaptic activity. SPN dysmaturation was significantly associated with the level of fetal hypoxemia and metabolic stress. Hence, despite the resistance of SPNs to insults that trigger white matter injury, transient hypoxemia disrupted SPN arborization and functional maturation during a critical window in cortical development. Strategies directed at limiting the duration or severity of hypoxemia during brain development may mitigate disturbances in cerebral growth and maturation related to SPN dysmaturation.SIGNIFICANCE STATEMENT The human preterm brain commonly sustains blood flow and oxygenation disturbances that impair cerebral cortex growth and cause life-long cognitive and learning disabilities. We investigated the fate of subplate neurons (SPNs), which are a master regulator of brain development that plays critical roles in establishing cortical connections to other brain regions. We used a preterm fetal sheep model that reproduces key features of brain injury in human preterm survivors. We analyzed the responses of fetal SPNs to transient disturbances in fetal oxygenation. We discovered that SPNs are surprisingly resistant to cell death from low oxygen states but acquire chronic structural and functional changes that suggest new strategies to prevent learning problems in children and adults that survive preterm birth.

The role of endothelial HIF-1 αin the response to sublethal hypoxia in C57BL/6 mouse pups

Chronic sublethal hypoxia, a complication of premature birth, is associated with cognitive and motor handicaps. Responsiveness to and recovery from this hypoxic environment is dependent on induction of HIF-1 α in the cells affected. Microvascular endothelial-glial and microvascular endothelial-neuronal precursor interactions have been found to be dynamic and reciprocal, involving autocrine and paracrine signaling, with response and recovery correlated with baseline levels and levels of induction of HIF-1 α.To ascertain the roles of endothelial HIF-1 α in the responses of brain microvascular endothelial cells (EC) and neuronal precursors to hypoxia, we examined the effects of the presence and absence of endothelial HIF-1 α expression in culture and in cells comprising the subventricular zone (SVZ) and dentate gyrus under normoxic and hypoxic conditions. We used C57BL/6 WT and EC HIF-1 α -deficient mice and brain microvascular ECs isolated from these mice in western blots, immunofluorescence, and behavioral studies to examine the roles of EC HIF-1 α behaviors of endothelial and neuronal precursor cells (NPCs) in SVZ and hippocampal tissues under normoxic and hypoxic conditions and behaviors of these mice in open field activity tests. Analyses of ECs and SVZ and dentate gyrus tissues revealed effects of the absence of endothelial HIF-1 α on proliferation and apoptosis as well as open field activity, with both ECs and neuronal cells exhibiting decreased proliferation, increased apoptosis, and pups exhibiting gender-specific differences in open field activities. Our studies demonstrate the autocrine and paracrine effects of EC HIF-1 α-modulating proliferative and apoptotic behaviors of EC and NPC in neurogenic regions of the brain and gender-specific behaviors in normoxic and hypoxic settings.

Temporal Dysynchrony in brain connectivity gene expression following hypoxia

Background

Despite the fundamental biological importance and clinical relevance of characterizing the effects of chronic hypoxia exposure on central nervous system (CNS) development, the changes in gene expression from hypoxia are unknown. It is not known if there are unifying principles, properties, or logic in the response of the developing CNS to hypoxic exposure. Here, we use the small vertebrate zebrafish (Danio rerio) to study the effects of hypoxia on connectivity gene expression across development. We perform transcriptional profiling at high temporal resolution to systematically determine and then experimentally validate the response of CNS connectivity genes to hypoxia exposure.

Results

We characterized mRNA changes during development, comparing the effects of chronic hypoxia exposure at different time-points. We focused on changes in expression levels of a subset of 1270 genes selected for their roles in development of CNS connectivity, including axon pathfinding and synapse formation. We found that the majority of CNS connectivity genes were unaffected by hypoxia. However, for a small subset of genes hypoxia significantly affected their gene expression profiles. In particular, hypoxia appeared to affect both the timing and levels of expression, including altering expression of interacting gene pairs in a fashion that would potentially disrupt normal function.

Conclusions

Overall, our study identifies the response of CNS connectivity genes to hypoxia exposure during development. While for most genes hypoxia did not significantly affect expression, for a subset of genes hypoxia changed both levels and timing of expression. Importantly, we identified that some genes with interacting proteins, for example receptor/ligand pairs, had dissimilar responses to hypoxia that would be expected to interfere with their function. The observed dysynchrony of gene expression could impair the development of normal CNS connectivity maps.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2638-x) contains supplementary material, which is available to authorized users.

Transgenic FingRs for Live Mapping of Synaptic Dynamics in Genetically-Defined Neurons

Tools for genetically-determined visualization of synaptic circuits and interactions are necessary to build connectomics of the vertebrate brain and to screen synaptic properties in neurological disease models. Here we develop a transgenic FingR (fibronectin intrabodies generated by mRNA display) technology for monitoring synapses in live zebrafish. We demonstrate FingR labeling of defined excitatory and inhibitory synapses, and show FingR applicability for dissecting synapse dynamics in normal and disease states. Using our system we show that chronic hypoxia, associated with neurological defects in preterm birth, affects dopaminergic neuron synapse number depending on the developmental timing of hypoxia.

Impaired oligodendrocyte maturation in preterm infants: Potential therapeutic targets

Preterm birth is an evolving challenge in neonatal health care. Despite declining mortality rates among extremely premature neonates, morbidity rates remain very high. Currently, perinatal diffuse white matter injury (WMI) is the most commonly observed type of brain injury in preterm infants and has become an important research area. Diffuse WMI is associated with impaired cognitive, sensory and psychological functioning and is increasingly being recognized as a risk factor for autism-spectrum disorders, ADHD, and other psychological disturbances. No treatment options are currently available for diffuse WMI and the underlying pathophysiological mechanisms are far from being completely understood. Preterm birth is associated with maternal inflammation, perinatal infections and disrupted oxygen supply which can affect the cerebral microenvironment by causing activation of microglia, astrogliosis, excitotoxicity, and oxidative stress. This intricate interplay of events negatively influences oligodendrocyte development, causing arrested oligodendrocyte maturation or oligodendrocyte cell death, which ultimately results in myelination failure in the developing white matter. This review discusses the current state in perinatal WMI research, ranging from a clinical perspective to basic molecular pathophysiology. The complex regulation of oligodendrocyte development in healthy and pathological conditions is described, with a specific focus on signaling cascades that may play a role in WMI. Furthermore, emerging concepts in the field of WMI and issues regarding currently available animal models are put forward. Novel insights into the molecular mechanisms underlying impeded oligodendrocyte maturation in diffuse WMI may aid the development of novel treatment options which are desperately needed to improve the quality-of-life of preterm neonates.

Controversies in preterm brain injury

In this review, we highlight critical unresolved questions in the etiology and mechanisms causing preterm brain injury. Involvement of neurons, glia, endogenous factors and exogenous exposures is considered. The structural and functional correlates of interrupted development and injury in the premature brain are under active investigation, with the hope that the cellular and molecular mechanisms underlying developmental abnormalities in the human preterm brain can be understood, prevented or repaired.

Modulation of Sox10, HIF-1α, Survivin, and YAP by Minocycline in the Treatment of Neurodevelopmental Handicaps following Hypoxic Insult

Premature infants are at an increased risk of developing cognitive and motor handicaps due to chronic hypoxia. Although the current therapies have reduced the incidence of these handicaps, untoward side effects abound. Using a murine model of sublethal hypoxia, we demonstrated reduction in several transcription factors that modulate expression of genes known to be involved in several neural functions. We demonstrate the induction of these genes by minocycline, a tetracycline antibiotic with noncanonical functions, in both in vitro and in vivo studies. Specifically, there was induction of genes, including Sox10, Hif1a, Hif2a, Birc5, Yap1, Epo, Bdnf, Notch1 (cleaved), Pcna, Mag, Mobp, Plp1, synapsin, Adgra2, Pecam1, and reduction in activation of caspase 3, all known to affect proliferation, apoptosis, synaptic transmission, and nerve transmission. Minocycline treatment of mouse pups reared under sublethal hypoxic conditions resulted in improvement in open field testing parameters. These studies demonstrate beneficial effects of minocycline treatment following hypoxic insult, document up-regulation of several genes associated with improved cognitive function, and support the possibility of minocycline as a potential therapeutic target in the treatment of neurodevelopmental handicaps observed in the very premature newborn population. Additionally, these studies may aid in further interpretation of the effects of minocycline in the treatment trials and animal model studies of fragile X syndrome and multiple sclerosis.

Some of the experimental and clinical aspects of the effects of the maternal diabetes on developing hippocampus

Diabetes mellitus during pregnancy is associated with an increased risk of multiple congenital anomalies in progeny. There are sufficient evidence suggesting that the children of diabetic women exhibit intellectual and behavioral abnormalities accompanied by modification of hippocampus structure and function. Although, the exact mechanism by which maternal diabetes affects the developing hippocampus remains to be defined. Multiple biological alterations, including hyperglycemia, hyperinsulinemia, oxidative stress, hypoxia, and iron deficiency occur in pregnancies with diabetes and affect the development of central nervous system (CNS) of the fetus. The conclusion from several studies is that disturbance in glucose and insulin homeostasis in mothers and infants are major teratogenic factor in the development of CNS. Insulin and Insulin-like growth factor-1 (IGF-1) are two key regulators of CNS function and development. Insulin and IGF-1 receptors (IR and IGF1R, respectively) are distributed in a highly specific pattern with the high density in some brain regions such as hippocampus. Recent researches have clearly established that maternal diabetes disrupts the regulation of both IR and IGF1R in the hippocampus of rat newborn. Dissecting out the mechanisms responsible for maternal diabetes-related changes in the development of hippocampus is helping to prevent from impaired cognitive and memory functions in offspring.

The role of inflammation in perinatal brain injury

Inflammation is increasingly recognized as being a critical contributor to both normal development and injury outcome in the immature brain. The focus of this Review is to highlight important differences in innate and adaptive immunity in immature versus adult brain, which support the notion that the consequences of inflammation will be entirely different depending on context and stage of CNS development. Perinatal brain injury can result from neonatal encephalopathy and perinatal arterial ischaemic stroke, usually at term, but also in preterm infants. Inflammation occurs before, during and after brain injury at term, and modulates vulnerability to and development of brain injury. Preterm birth, on the other hand, is often a result of exposure to inflammation at a very early developmental phase, which affects the brain not only during fetal life, but also over a protracted period of postnatal life in a neonatal intensive care setting, influencing critical phases of myelination and cortical plasticity. Neuroinflammation during the perinatal period can increase the risk of neurological and neuropsychiatric disease throughout childhood and adulthood, and is, therefore, of concern to the broader group of physicians who care for these individuals.

Pharmacologic stabilization of hypoxia-inducible transcription factors protects developing mouse brain from hypoxia-induced apoptotic cell death

OBJECTIVE

Accumulation of hypoxia-inducible transcription factors (HIFs) by prolyl-4-hydroxylase inhibitors (PHI) has been suggested to induce neuroprotection in the ischemic rodent brain. We aimed to investigate in vivo effects of a novel PHI on HIF-regulated neurotrophic and pro-apoptotic factors in the developing normoxic and hypoxic mouse brain.

METHODS

Neonatal mice (P7) were treated with PHI FG-4497 (30-100mg/kg, i.p.) followed by exposure to systemic hypoxia (8% O2, 6h) 4h later. Cerebral expression of HIFα-subunits, specific neurotrophic and vasoactive target genes (vascular endothelial growth factor (VEGF), adrenomedullin (ADM), erythropoietin (EPO), inducible nitric oxide synthase (iNOS)) as well as pro-apoptotic (BCL2/adenovirus E1B 19-kDa protein-interacting protein 3 gene (BNIP3), immediate early response 3 (IER3)) and migratory factors (chemokine receptor 4 (CXCR4), stromal cell-derived factor 1 (SDF-1)) was determined (quantitative real-time (RT)., Western blot analysis) in comparison to controls. Apoptotic cell death was analyzed by terminal desoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) and cleaved caspase 3 (CC3) staining.

RESULTS

Under normoxic conditions, FG-4497 treatment significantly induced the accumulation of both HIF-1α and HIF-2α isoforms in developing mouse brain. In addition, there was a significant up-regulation of HIF target genes (VEGF, ADM, EPO, CXCR4, p<0.01) with FG-4497 treatment compared to controls supporting functional activation of the HIF proteins. Under hypoxia, differential target gene activation was observed in the developing brain including additive effects of FG-4497 and hypoxia on mRNA expression of VEGF and ADM as well as a dose-dependent down-regulation of iNOS. BNIP3 but not IER3 mRNA levels significantly increased in hypoxic brains pre-treated with high-dose FG-4497 compared to controls. Of special interest, FG-4497 treatment significantly diminished apoptotic cell death, quantified by TUNEL and CC3-positive cells, in hypoxic developing brains compared to controls.

CONCLUSIONS

PHI treatment modulates neurotrophic factors known to be crucially involved in hypoxia-induced cerebral adaptive mechanisms as well as early brain maturation. Pre-treatment with FG-4497 seems to protect the developing brain from hypoxia-induced apoptosis. Present observations provide basic information for further evaluation of neuroprotective properties of PHI treatment in hypoxic injury of the developing brain. However, potential effects on maturational processes need special attention in experimental research targeting HIF-dependent neuroprotective interventions during the very early stage of brain development.

Long-lasting changes in DNA methylation following short-term hypoxic exposure in primary hippocampal neuronal cultures

While the effects of hypoxia on gene expression have been investigated in the CNS to some extent, we currently do not know what role epigenetics plays in the transcription of many genes during such hypoxic stress. To start understanding the role of epigenetic changes during hypoxia, we investigated the long-term effect of hypoxia on gene expression and DNA methylation in hippocampal neuronal cells. Primary murine hippocampal neuronal cells were cultured for 7 days. Hypoxic stress of 1% O2, 5% CO2 for 24 hours was applied on Day 3, conditions we found to maximize cellular hypoxic stress response without inducing cell death. Cells were returned to normoxia for 4 days following the period of hypoxic stress. On Day 7, Methyl-Sensitive Cut Counting (MSCC) was used to identify a genome-wide methylation profile of the hippocampal cell lines to assess methylation changes resulting from hypoxia. RNA-Seq was also done on Day 7 to analyze changes in gene transcription. Phenotypic analysis showed that neuronal processes were significantly shorter after 1 day of hypoxia, but there was a catch-up growth of these processes after return to normoxia. Transcriptome profiling using RNA-Seq revealed 369 differentially expressed genes with 225 being upregulated, many of which form networks shown to affect CNS development and function. Importantly, the expression level of 59 genes could be correlated to the changes in DNA methylation in their promoter regions. CpG islands, in particular, had a strong tendency to remain hypomethylated long after hypoxic stress was removed. From this study, we conclude that short-term, sub-lethal hypoxia results in long-lasting changes to genome wide DNA methylation status and that some of these changes can be highly correlated with transcriptional modulation in a number of genes involved in functional pathways that have been previously implicated in neural growth and development.

Hypoxia-induced developmental delays of inhibitory interneurons are reversed by environmental enrichment in the postnatal mouse forebrain

Infants born premature experience hypoxic episodes due to immaturity of their respiratory and central nervous systems. This profoundly affects brain development and results in cognitive impairments. We used a mouse model to examine the impact of hypoxic rearing (9.5-10.5% O2) from postnatal day 3 to 11 (P3-P11) on GABAergic interneurons and the potential for environmental enrichment to ameliorate these developmental abnormalities. At P15 the numbers of cortical interneurons expressing immunohistochemically detectable levels of parvalbumin (PV), somatostatin (SST), and vasoactive intestinal peptide were decreased in hypoxic-reared mice by 59%, 32%, and 38%, respectively, compared with normoxic controls. Hypoxia also decreased total GABA content in frontal neocortex by 31%. However, GAD67-EGFP knock-in mice reared under hypoxic conditions showed no changes in total number of GAD67-EGFP(+) cells and no evidence of increased interneuron death, suggesting that the total number of interneurons was not decreased, but rather, that hypoxic-rearing decreased interneuron marker expression in these cells. In adulthood, PV and SST expression levels were decreased in hypoxic-reared mice. In contrast, intensity of reelin (RLN) expression was significantly increased in adult hypoxic-reared mice compared with normoxic controls. Housing mice in an enriched environment from P21 until adulthood normalized phenotypic interneuron marker expression without affecting total interneuron numbers or leading to increased neurogenesis. Our data show that (1) hypoxia decreases PV and SST and increases RLN expression in cortical interneurons during postnatal cortical development and (2) enriched environment has the capacity to normalize the interneuron abnormalities in cortex.

Modeling the neurovascular niche: unbiased transcriptome analysis of the murine subventricular zone in response to hypoxic insult

Premature infants often experience chronic hypoxia, resulting in cognitive & motor neurodevelopmental handicaps. These sometimes devastating handicaps are thought to be caused by compromised neural precursor cell (NPC) repair/recovery resulting in variable central nervous system (CNS) repair/recovery. We have identified differential responses of two mouse strains (C57BL/6 & CD1) to chronic hypoxia that span the range of responsiveness noted in the premature human population. We previously correlated several CNS tissue and cellular behaviors with the different behavioral parameters manifested by these two strains. In this report, we use unbiased array technology to interrogate the transcriptome of the subventricular zone (SVZ) in these strains. Our results illustrate differences in mRNA expression in the SVZ of both C57BL/6 and CD1 mice following hypoxia as well as differences between C57BL/6 and CD1 SVZ under both normoxic and hypoxic conditions. Differences in expression were found in gene sets associated with Sox10-mediated neural functions that explain, in part, the differential cognitive and motor responsiveness to hypoxic insult. This may shed additional light on our understanding of the variable responses noted in the human premature infant population and facilitate early intervention approaches. Further interrogation of the differentially expressed gene sets will provide a more complete understanding of the differential responses to, and recovery from, hypoxic insult allowing for more informed modeling of the ranges of disease severity observed in the very premature human population.

Autism risk factors: genes, environment, and gene-environment interactions

The aim of this review is to summarize the key findings from genetic and epidemiological research, which show that autism is a complex disorder resulting from the combination of genetic and environmental factors. Remarkable advances in the knowledge of genetic causes of autism have resulted from the great efforts made in the field of genetics. The identification of specific alleles contributing to the autism spectrum has supplied important pieces for the autism puzzle. However, many questions remain unanswered, and new questions are raised by recent results. Moreover, given the amount of evidence supporting a significant contribution of environmental factors to autism risk, it is now clear that the search for environmental factors should be reinforced. One aspect of this search that has been neglected so far is the study of interactions between genes and environmental factors.

Pathophysiology of cerebral palsy

Cerebral palsy (CP), defined as a group of nonprogressive disorders of movement and posture, is the most common cause of severe neurodisability in children. Understanding its physiopathology is crucial to developing some protective strategies. Interruption of oxygen supply to the fetus or brain asphyxia was classically considered to be the main causal factor explaining later CP. However several ante-, peri-, and postnatal factors could be involved in the origins of CP syndromes. Congenital malformations are rarely identified. CP is most often the result of environmental factors, which might interact with genetic vulnerabilities, and could be severe enough to cause the destructive injuries visible with standard imaging (i.e., ultrasonographic study or MRI), predominantly in the white matter in preterm infants and in the gray matter and the brainstem nuclei in full-term newborns. Moreover they act on an immature brain and could alter the remarkable series of developmental events. Biochemical key factors originating in cell death or cell process loss, observed in hypoxic-ischemic as well as inflammatory conditions, are excessive production of proinflammatory cytokines, oxidative stress, maternal growth factor deprivation, extracellular matrix modifications, and excessive release of glutamate, triggering the excitotoxic cascade. Only two strategies have succeeded in decreasing CP in 2-year-old children: hypothermia in full-term newborns with moderate neonatal encephalopathy and administration of magnesium sulfate to mothers in preterm labor.

Emerging roles for semaphorins and VEGFs in synaptogenesis and synaptic plasticity

Synapse formation, maintenance and plasticity are critical for the correct function of the nervous system and its target organs. During development, these processes enable the establishment of appropriate neural circuits. During adulthood, they allow adaptation to both physiological and environmental changes. In this review, we discuss emerging roles for two families of classical axon and vascular guidance cues in synaptogenesis and synaptic plasticity, the semaphorins and the vascular endothelial growth factors (VEGFs). Their contribution to synapse formation and function add a new facet to the spectrum of overlapping and complementary roles for these molecules in development, adulthood and disease.

The potential for cellular therapy combined with growth factors in spinal cord injury

Any traumatic spinal cord injury (SCI) may cause symptoms ranging from pain to complete loss of motor and sensory functions below the level of the injury. Currently, there are over 2 million SCI patients worldwide. The cost of their necessary continuing care creates a burden for the patient, their families, and society. Presently, few SCI treatments are available and none have facilitated neural regeneration and/or significant functional improvement. Research is being conducted in the following areas: pathophysiology, cellular therapies (Schwann cells, embryonic stem cells, induced pluripotent stem cells, mesenchymal stem cells, olfactory ensheathing cells), growth factors (BDNF), inhibitory molecules (NG2, myelin protein), and combination therapies (cell grafts and neurotrophins, cotransplantation). Results are often limited because of the inhibitory environment created following the injury and the limited regenerative potential of the central nervous system. Therapies that show promise in small animal models may not transfer to nonhuman primates and humans. None of the research has resulted in remarkable improvement, but many areas show promise. Studies have suggested that a combination of therapies may enhance results and may be more effective than a single therapy. This paper reviews and discusses the most promising new SCI research including combination therapies.

The Effect of Growth Factors and Soluble Nogo-66 Receptor Protein on Transplanted Neural Stem/Progenitor Survival and Axonal Regeneration after Complete Transection of Rat Spinal Cord

Adult central mammalian axons show minimal regeneration after spinal cord injury due to loss of oligodendrocytes, demyelination of surviving axons, absence of growth-promoting molecules, and inhibitors of axonal outgrowth. In the present study, we attempted to address these impediments to regeneration by using a combinatory strategy to enhance cell survival and regeneration after complete spinal cord transection (SCT) in adult rats. The strategy comprised: 1) adult rat brain-derived neural stem/progenitor cells (NSPCs) preseeded on laminin-coated chitosan channels; 2) extramedullary chitosan channels to promote axonal regrowth and reduce the barrier caused by scarring; 3) local delivery of a novel rat soluble Nogo-66 receptor protein [NgR(310)ecto-Fc, referred to as NgR] to block the inhibitory effect of myelin-based inhibitors; and 4) local delivery of basic fibroblast growth factor, epidermal growth factor, and platelet-derived growth factor to enhance survival and promote differentiation of transplanted cells. Compared with our previous studies where brain-derived NSPCs preseeded in extramedullary chitosan channels were implanted in the same SCT model but without growth factors and NgR, the present channel–growth factor combination produced greater numbers of surviving NSPCs after SCT. Also, the growth factors promoted preferential differentiation of NSPCs toward oligodendrocytes, while NgR significantly decreased astrocytic differentiation of NSPCs. NgR alone or in combination with NSPCs significantly enhanced the total number of myelinated fibers in the bridge and increased the area of the bridging tissue between the cord stumps. The combination of NgR, growth factors, and NSPCs had synergistic effect on bridge formation. However, only a small number of descending corticospinal tract axons grew into the central portions of the bridges as shown by anterograde tracing of the corticospinal tract with BDA. The majority of the regenerated axons in the channels originated from local host neurons adjacent to the tissue bridges. In conclusion, we showed that growth factors increased survival of transplanted NSPCs whereas NgR enhanced axonal regeneration, but the combination did not have additive effects on functional recovery or regeneration.

Hypoxia disruption of vertebrate CNS pathfinding through ephrinB2 Is rescued by magnesium

The mechanisms of hypoxic injury to the developing human brain are poorly understood, despite being a major cause of chronic neurodevelopmental impairments. Recent work in the invertebrate Caenorhabditis elegans has shown that hypoxia causes discrete axon pathfinding errors in certain interneurons and motorneurons. However, it is unknown whether developmental hypoxia would have similar effects in a vertebrate nervous system. We have found that developmental hypoxic injury disrupts pathfinding of forebrain neurons in zebrafish (Danio rerio), leading to errors in which commissural axons fail to cross the midline. The pathfinding defects result from activation of the hypoxia-inducible transcription factor (hif1) pathway and are mimicked by chemical inducers of the hif1 pathway or by expression of constitutively active hif1α. Further, we found that blocking transcriptional activation by hif1α helped prevent the guidance defects. We identified ephrinB2a as a target of hif1 pathway activation, showed that knock-down of ephrinB2a rescued the guidance errors, and showed that the receptor ephA4a is expressed in a pattern complementary to the misrouting axons. By targeting a constitutively active form of ephrinB2a to specific neurons, we found that ephrinB2a mediates the pathfinding errors via a reverse-signaling mechanism. Finally, magnesium sulfate, used to improve neurodevelopmental outcomes in preterm births, protects against pathfinding errors by preventing upregulation of ephrinB2a. These results demonstrate that evolutionarily conserved genetic pathways regulate connectivity changes in the CNS in response to hypoxia, and they support a potential neuroprotective role for magnesium.

How hypoxia damages the developing human brain is poorly understood, despite being a major cause of life-long neurologic and psychiatric problems. Premature infants are especially at risk for these problems, with increased rates of attention-deficit disorder, autism, cerebral palsy, epilepsy, psychiatric disorders, and cognitive impairment. It is unknown whether hypoxia can cause errors in the connections of neurons in the vertebrate nervous system. We used zebrafish, a vertebrate model animal, to answer this question. We found that hypoxic injury causes errors in how neurons connect. We went on to determine that a specific genetic pathway, the hif1 pathway, is activated by hypoxia and turns on downstream genes, which cause the connection problems. One of the genes activated by hif1, ephrinB2a, is responsible for many of the connection problems. Importantly, magnesium, used as a treatment for some preterm births, is able to help protect against the neuron connection errors. Our results show that hypoxia in vertebrates does cause errors in neuron connections and that magnesium can help prevent this.

Systemic hypoxia differentially affects neurogenesis during early mouse brain maturation

BACKGROUND

Cerebral tissue oxygen level modifies crucial processes of neurogenesis, glial and neuronal development during physiological and hypoxic conditions. Whether hypoxia-sensitive factors such as doublecortin (DCX) and hypoxia-inducible transcription factor (HIF)-regulated CXCR4 and SDF-1 modify and activate adaptation to hypoxia in developing brain is not well understood. Present study investigated maturational regulation of oxygen-sensitive developmental genes and proteins in developing mouse brain in relation to the degree of hypoxia.

METHODS

Physiological expression of HIF-1, CXCR4, SDF-1 and DCX were analyzed in the brain of C57/BL6 mice (P0-P60). In addition, mice (P0, P7) were exposed to normoxia, acute (8% O(2), 6 h) or chronic hypoxia (10% O(2), 7 d) followed by reoxygenation. Gene expression was analyzed by quantitative PCR, proteins were quantified by Western blot analysis and immunohistochemistry.

RESULTS

Cerebral HIF-1α protein, CXCR4 and DCX mRNA levels showed maturational stage-related peak levels at P0/P1, whereas SDF-1 mRNA levels were highest at P17. CXCR4 and SDF-1 mRNA levels were not altered in response to hypoxia. Whereas DCX mRNA levels significantly increased during acute hypoxia, down-regulation of DCX transcripts was found in response to chronic hypoxia compared to controls, and these changes were related to specifically vulnerable brain regions.

CONCLUSIONS

Maturational stage-related dynamic changes of HIF-1α, CXCR4, SDF-1 and DCX may reflect involvement of hypoxia-regulated systems in important developmental regulatory processes of the developing brain. Extending the knowledge of differential effects of hypoxia on neurogenesis and dynamic regulatory networks present data provide a basis for future research on gestational age-specific neuroprotective options.

Mouse intermittent hypoxia mimicking apnoea of prematurity: effects on myelinogenesis and axonal maturation

Premature babies are at high risk for both infantile apnoea and long-term neurobehavioural deficits. Recent studies suggest that diffuse structural changes in brain white matter are a positive predictor of poor cognitive outcomes. Since oligodendrocyte maturation, myelination, axon development, and synapse formation mainly occur in the third trimester of gestation and first postnatal year, infantile apnoea could lead to and/or exaggerate white matter impairments in preterm neonates. Therefore, we investigated oligodendroglia and axon development in a neonatal mouse model of intermittent hypoxia between postnatal days 2 and 10. During critical phases of central nervous system development, intermittent hypoxia induced hypomyelination in the corpus callosum, striatum, fornix, and cerebellum, but not in the pons or spinal cord. Intermittent hypoxia-elicited alterations in myelin-forming processes were reflected by decreased expression of myelin proteins, including MBP, PLP, MAG, and CNPase, possibly due to arrested maturation of oligodendrocytes. Ultrastructural abnormalities were apparent in the myelin sheath and axon. Immature oligodendrocytes were more vulnerable to neonatal intermittent hypoxia exposures than developing axons, suggesting that hypomyelination may contribute, at least partially, to axonal deficits. Insufficient neurofilament synthesis with anomalous components of neurofilament subunits, β-tubulin, and MAP2 isoforms indicated immaturity of axons in intermittent hypoxia-exposed mouse brains. In addition, down-regulation of synapsin I, synaptophysin, and Gap-43 phosphorylation suggested a potential stunt in axonogenesis and synaptogenesis. The region-selective and complex impairment in brain white matter induced by intermittent hypoxia was further associated with electrophysiological changes that may underlie long-term neurobehavioural sequelae.

Hypoxia in the regulation of neural stem cells

In aerobic organisms, oxygen is a critical factor in tissue and organ morphogenesis from embryonic development throughout post-natal life, as it regulates various intracellular pathways involved in cellular metabolism, proliferation, survival and fate. In the mammalian central nervous system, oxygen plays a critical role in regulating the growth and differentiation state of neural stem cells (NSCs), multipotent neuronal precursor cells that reside in a particular microenvironment called the neural stem cell niche and that, under certain physiological and pathological conditions, differentiate into fully functional mature neurons, even in adults. In both experimental and clinical settings, oxygen is one of the main factors influencing NSCs. In particular, the physiological condition of mild hypoxia (2.5-5.0% O(2)) typical of neural tissues promotes NSC self-renewal; it also favors the success of engraftment when in vitro-expanded NSCs are transplanted into brain of experimental animals. In this review, we analyze how O(2) and specifically hypoxia impact on NSC self-renewal, differentiation, maturation, and homing in various in vitro and in vivo settings, including cerebral ischemia, so as to define the O(2) conditions for successful cell replacement therapy in the treatment of brain injury and neurodegenerative diseases.

Intrauterine growth restriction affects the maturation of myelin

Intrauterine growth-restriction (IUGR) can lead to adverse neurodevelopmental sequelae in postnatal life. Our objective was to determine whether IUGR, induced by chronic placental insufficiency (CPI) in the guinea pig results in long-term deficits in brain myelination and could therefore contribute to altered neural function. CPI was induced by unilateral ligation of the uterine artery at mid-gestation (term~67 days of gestation; dg), producing growth-restricted (GR) foetuses (60 dg), neonates (1 week) and young adults (8 week); controls were from the unligated horn or sham-operated animals. In GR foetuses (n=8) and neonates (n=7), white matter (WM) volume was reduced (p<0.05); this reduction did not persist in young adults (n=11) however the corpus callosum width was reduced (p<0.05). Immunoreactivity (IR) for myelin basic protein (MBP), myelin-associated glycoprotein (MAG) and myelin proteolipid protein (PLP), all markers of myelinating oligodendrocytes (OL), was reduced in GR foetuses compared to controls. MBP was the most markedly affected with an abnormal retention of protein in the OL soma and a reduction of its incorporation into the myelin sheath. MAG-IR OL density was reduced (p<0.05), while the density of OLs immunoreactive for Olig-2, a transcription factor expressed throughout the entire OL lineage, was increased (p<0.05). MBP-, MAG- and PLP-IR recovered to control levels postnatally. These results suggest that IUGR transiently delays OL maturation and myelination in utero but that myelination and WM volume are restored to control levels postnatally. Long-term deficits in myelination are therefore unlikely to be the major factor underlying the altered neurological function which can be associated with IUGR.

Development of smooth pursuit eye movements in very prematurely born infants: 2. The low-risk subgroup

AIM

To investigate the impact of premature birth on visual tracking in a group of 37 infants, born before the 32nd gestational weeks (mean 29 + 6 weeks) and diagnosed as being without major neonatal complications. This paper is a part of the LOVIS study (Strand Brodd, Ewald, Grönqvist, Holmström, Strömberg, Von Hofsten, et al. Acta Pediatrica, 2011).

METHODS

At 2 and 4 months corrected age, eye and head movements were measured when the infant tracked a moving object. The eye movements were analysed in terms of smooth pursuit and saccades (Vision Res, 37, 1997, 1799; Exp Brain Res, 146, 2002, 257). Accuracy of gaze, proportion of smooth pursuit, head movements and saccades were calculated.

RESULTS

  Between 2 and 4 months of age, all infants improved their ability to smoothly pursue a moving object. However, at both occasions, the preterm infants had less proportion smooth pursuit than the full-term infants. The groups did not differ with respect to gaze and head movements, but the saccade frequency was higher for the very preterms in some of the conditions.

CONCLUSION

The development of smooth pursuit in the low-risk preterm infant group was strongly delayed compared to typically developed infants. Thus, the 2 months or more extra visual experience did not have a distinguishable positive effect on visuo-motor development as expressed in smooth pursuit.

A neonatal mouse model of intermittent hypoxia associated with features of apnea in premature infants

A neonatal mouse model of intermittent hypoxia (IH) simulating the recurring hypoxia/reoxygenation episodes of apnea of prematurity (AOP) was developed. C57BL/6 P2 pups were culled for exposure to either intermittent hypoxia or intermittent air as control. The IH paradigms consisted of alternation cycles of 20.9% O2 and either 8.0% or 5.7% O2 every 120 or 140s for 6h a day during daylight hours from day 2 to day 10 postnatally, i.e., roughly equivalent to human brain development in the perinatal period. IH exposures elicited modest to severe decrease in oxygen saturation along with bradycardia in neonatal mice, which were severity-dependent. Hypomyelination in both central and peripheral nervous systems was observed despite the absence of visible growth retardation. The neonatal mouse model of IH in this study partially fulfills the current diagnostic criteria with features of AOP, and provides opportunities to reproduce in rodents some of the pathophysiological changes associated with this disorder, such as alterations in myelination.