Development of a postnatal 3-day-old rat model of mild hypoxic-ischemic brain injury

GSK-3β inhibitor TWS119 promotes neuronal differentiation after hypoxic-ischemic brain damage in neonatal rats

Brain injury in preterm infants is a major cause of disability and mortality in children. GSK-3β is a common pathogenic factor for cognitive dysfunction and involves in neuronal proliferation and differentiation. However, GSK-3β affected neuronal differentiation and its molecular pathogenesis after hypoxic-ischemic brain damage in neonatal rats remains unclear. This study investigated the effects of GSK-3β inhibitor (TWS119) on cell cycle regulatory proteins, a neuronal differentiation factor (CEND1), maturation neurons, T-box brain transcription factor 1 (TBR1)-positive neurons to clarify the mechanisms of hypoxic-ischemic brain damage in neonatal rats. We used hypoxic-ischemic Sprague-Dawley neonatal rats with brain damage as models. These rats were used for investigating the effect of GSK-3β on cell cycle regulatory proteins, neuronal differentiation factor (CEND1), maturation neurons, TBR1-positive neurons by western blot and immunofluorescence. Cyclin D1 (a positive cell cycle regulator) expression decreased, and p21 (a negative cell cycle regulator) expression increased in the TWS119 group compared to the hypoxia-ischemia (HI) group 7 days after HI. Additionally, compared to the HI group, TWS119 treatment up-regulated CEND1 expression and promoted neuronal differentiation and cortex development based on NeuN and TBR1 expression. Our study suggests that the GSK-3β inhibitor TWS119 promotes neuronal differentiation after hypoxic-ischemic brain damage in neonatal rats by inhibiting cell cycle pathway.

Recombinant human erythropoietin protects against immature brain damage induced by hypoxic/ischemia insult

To investigate the neuroprotection of recombinant human erythropoietin (rhEPO) against hypoxic/ischemic (HI) insult in three-day-old rats. Postnatal day 3 (PD3) rats were randomly divided into three groups: Sham group, HI group and HI+rhEPO group. Ligation of the right common carotid artery and hypoxia to induce HI brain injury. After HI insult, the rats received intraperitoneal injection of rhEPO (5000 IU/Kg, qod) in HI+rhEPO group or equal saline in other groups. On PD10, damage of brain tissue was examined by hematoxylin-eosin (HE) staining, observation of neuronal apoptosis in the hippocampus and cortex using immunofluorescence assay (marker: TUNEL). Immunohistochemical staining or western blotting was performed to detect the expression of cyclooxygenase-2 (COX-2), Caspase-3 and phosphorylated Akt (p-Akt) protein. On PD28, cognitive ability of rats was assessed by Morris water maze test. HI injury causes brain pathological morphology and cognitive function damage in PD3 rats, which can be alleviated by rhEPO intervention. Compared with the HI group, the HI+rhEPO group showed an increase in platform discovery rate and cross platform frequency, while the search platform time was shortened (P < 0.05). The proportion of TUNEL positive neurons and the expression of COX-2 and Caspase-3 proteins in brain tissue in the hippocampus and cortex was decreased, while the expression of p-Akt protein was upregulated (P < 0.05). RhEPO could protect against the pathological and cognitive impairment of immature brain induced by HI insult. This neuroprotective activity may involve in inhibiting inflammatory and apoptosis by activation of PI3K/Akt signaling pathway.

Oligodendrocyte Progenitor Cell Transplantation Ameliorates Preterm Infant Cerebral White Matter Injury in Rats Model

Background

Cerebral white matter injury (WMI) is the most common brain injury in preterm infants, leading to motor and developmental deficits often accompanied by cognitive impairment. However, there is no effective treatment. One promising approach for treating preterm WMI is cell replacement therapy, in which lost cells can be replaced by exogenous oligodendrocyte progenitor cells (OPCs).

Methods

This study developed a method to differentiate human neural stem cells (hNSCs) into human OPCs (hOPCs). The preterm WMI animal model was established in rats on postnatal day 3, and OLIG2+/NG2+/PDGFRα+/O4+ hOPCs were enriched and transplanted into the corpus callosum on postnatal day 10. Then, histological analysis and electron microscopy were used to detect lesion structure; behavioral assays were performed to detect cognitive function.

Results

Transplanted hOPCs survived and migrated throughout the major white matter tracts. Morphological differentiation of transplanted hOPCs was observed. Histological analysis revealed structural repair of lesioned areas. Re-myelination of the axons in the corpus callosum was confirmed by electron microscopy. The Morris water maze test revealed cognitive function recovery.

Conclusion

Our study showed that exogenous hOPCs could differentiate into CC1+ OLS in the brain of WMI rats, improving their cognitive functions.

miR-200b-3p antagomir inhibits neuronal apoptosis in oxygen-glucose deprivation (OGD) model through regulating β-TrCP

BACKGROUND

Hypoxia-ischemic brain damage (HIBD) is a primary cause of morbidity and disability in survivors of preterm infants. We previously discovered that miR-200b-3p plays an important role in HIBD via targeting Slit2. This study was designed to identify novel targets of miR-200b-3p and investigate the relationship between miR-200b-3p and its downstream effectors.

METHODS AND RESULTS

Cultured primary rat hippocampal neurons were used in the model of oxygen-glucose deprivation (OGD) and RT-qPCR was utilized to detect the alterations of miR-200b-3p in these cells following the OGD. Our study found that the expression of miR-200b-3p was up-regulated in neurons post OGD. Bioinformatics analysis identified that β transducin repeat-containing protein (β-TrCP) is a target gene of miR-200b-3p, and our luciferase reporter gene assay confirmed that miR-200b-3p can interact with β-TrCP mRNA. Hypoxia-ischemic brain damage was induced in three-day-old SD rats and inhibition of miR-200b-3p by injection of antagomir into bilateral lateral ventricles enhanced β-TrCP expression at both the mRNA and protein levels in rats' brains. TUNEL staining and CCK-8 assays found that the survival of hippocampal neurons in the miR-200b-3p antagomir group was improved significantly (p＜0.05), whereas apoptosis of neurons in the miR-200b-3p antagomir group was significantly decreased (p＜0.05), as compared with the OGD group. However, silencing of β-TrCP by β-TrCP siRNA impaired the neuroprotective effect of miR-200b-3p antagomir. H&E staining showed that miR-200b-3p attenuated the pathological changes in the hippocampal region of rats with HIBD.

CONCLUSION

Our study has demonstrated that β-TrCP is a target gene of miR-200b-3p and that inhibition of miR-200b-3p by antagomir attenuates hypoxia-ischemic brain damage via β-TrCP.

T0901317, a liver X receptor agonist, ameliorates perinatal white matter injury induced by ischemia and hypoxia in neonatal rats

Perinatal white matter injury (PWMI) can lead to permanent neurological damage in preterm infants and bring a huge economic burden to their families and society. Liver X receptors (LXRs) are transcription factors that have been confirmed to mediate the myelination process under physiological conditions and are involved in regulating neurogenesis in adult animal models of acute and chronic cerebral ischemia. However, the role of LXRs in PWMI induced by both ischemic and hypoxic stimulation in the immature brain has not been reported. Herein, we investigated the role of LXRs in a neonatal rat model of white matter loss after hypoxia-ischemia (HI) injury through intraperitoneal injection of the LXR agonist T0901317 (T09) 1 day before and 15 min postinjury. The in vivo data showed that T09 treatment significantly facilitated myelination and ameliorated neurological behavior after PWMI. Moreover, T09 enhanced the proliferation of oligodendrocyte lineage cells and reduced microgliosis and astrogliosis in the microenvironment for oligodendrocytes (OLs), maintaining a healthy microenvironment for myelinating OLs. In vitro data suggested that the expression of the myelin-related genes Plp and Cnpase was increased in OLN-93 cells after T09 intervention compared with OLN-93 cells injured by oxygen and glucose deprivation (OGD). In primary mixed astrocytes/microglia cells, T09 also reduced the expression of Il6, Cox2, Tnfa and Il10 that was induced by OGD. Mechanistically, the mRNA expression level and the protein level of ATP binding cassette subfamily A member 1 (Abca1) decreased after HI injury, and the protective effect of T09 might be related to the activation of the LXRβ-ABCA1 signaling pathway. Our study revealed the protective role of LXRs in myelination and white matter homeostasis, providing a potential therapeutic option for PWMI.

Longitudinal Analysis of Sleep-Wake States in Neonatal Rats Subjected to Hypoxia-Ischemia

OBJECTIVE

Sleep is necessary for brain maturation in infants. Perinatal hypoxic-ischemic encephalopathy (HIE) is a major cause of chronic neurological disease in infants. Although the developmental changes of electroencephalogram (EEG) in human newborns have been described, little is known about the EEG normal maturation characteristics in rodents and the changes in sleep-awake states caused by hypoxia-ischemia (HI). This study aimed to investigate the pathological response of sleep-wake states in neonatal rats with HIE.

METHODS

We constructed HIE and sham models on postnatal day (P) 3 rats and continuously monitored them using electroencephalography and electromyography for up to P12. The distribution of sleep-wake states was analyzed to estimate the effects of HIE.

RESULTS

Compared with the sham group, the HI group showed lower rapid eye movement (REM) sleep percentage, but wake percentage and frequency was higher during P4-P12. The frequency of REM and non-rapid eye movement (NREM) sleep increased and the duration of REM and NREM sleep decreased after HI induction. However, it gradually returned to the normal level with an increase in daytime.

CONCLUSION

HI damage alters the sleep-wake patterns during early neural development. The findings provide a comprehensive assessment of serial sleep-wake state recordings in neonatal rats from P4-P12.

Seizure Characteristics and Background Amplitude-Integrated Electroencephalography Activity in Neonatal Rats Subjected to Hypoxia-Ischemia

OBJECTIVE

Perinatal hypoxic-ischemic encephalopathy (HIE) is a major cause of epilepsy and chronic neurologic morbidity in premature infants. This study aimed to investigate the characteristics of acute seizures and the pattern of background activity on amplitude-integrated electroencephalography (aEEG) in neonatal rats with HIE.

METHODS

Hypoxia-ischemia (HI) was induced in postnatal day (P) 3 neonatal rats (n = 12) by ligation of the left carotid artery and exposure to airtight hypoxia for 2 h. Data regarding seizure type, frequency, and duration and those related to neurobehavioral development were collected, and the integrated power of background EEG was analyzed to evaluate the effect of HI.

RESULTS

All neonatal rats in the HI group experienced frequent seizures during hypoxia, and 83.3% of rats (10/12) experienced seizures immediately after hypoxia. Seizure frequency and duration gradually decreased with increasing age. The mortality rate of the HI group was 8.33% (1/12); 120 h after HI induction, only 27.3% (3/11) of pups had low-frequency and short-duration electrographic seizures, respectively. HI rats, which presented seizure activities 96 h after HI insult, exhibited an increase in righting reflex time and a decrease in forelimb grip reflex time. Background EEG was significantly inhibited during HI induction and immediately after hypoxia and gradually recovered 72 h after hypoxia.

CONCLUSION

Seizures caused by HI brain damage in premature infants can be simulated in the P3 neonatal rat model.

A novel RIP1/RIP3 dual inhibitor promoted OPC survival and myelination in a rat neonatal white matter injury model with hOPC graft

Background

The dual inhibitors of receptor interacting protein kinase-1 and -3 (RIP1 and RIP3) play an important role in cell death processes and inflammatory responses. White matter injury (WMI), a leading cause of neurodevelopmental disabilities in preterm infants, which is characterized by extensive myelination disturbances and demyelination. Neuroinflammation, leads to the loss and differentiation-inhibition of oligodendrocyte precursor cells (OPCs), represents a major barrier to myelin repair. Whether the novel RIP1/RIP3 dual inhibitor ZJU-37 can promote transplanted OPCs derived from human neural stem cells (hOPCs) survival, differentiation and myelination remains unclear. In this study, we investigated the effect of ZJU-37 on myelination and neurobehavioral function in a neonatal rat WMI model induced by hypoxia and ischemia.

Methods

In vivo, P3 rat pups were subjected to right common carotid artery ligation and hypoxia, and then treated with ZJU-37 or/and hOPCs, then OPCs apoptosis, myelination, glial cell and NLRP3 inflammasome activation together with cognitive outcome were evaluated at 12 weeks after transplantation. In vitro, the effect of ZJU-37 on NLRP3 inflammasome activation in astrocytes induced by oxygen–glucose deprivation (OGD) were examined by western blot and immunofluorescence. The effect of ZJU-37 on OPCs apoptosis induced by the conditioned medium from OGD-injured astrocytes (OGD-astrocyte-CM) was analyzed by flow cytometry and immunofluorescence.

Results

ZJU-37 combined with hOPCs more effectively decreased OPC apoptosis, promoted myelination in the corpus callosum and improved behavioral function compared to ZJU-37 or hOPCs treatment. In addition, the activation of glial cells and NLRP3 inflammasome was reduced by ZJU-37 or/and hOPCs treatment in the neonatal rat WMI model. In vitro, it was also confirmed that ZJU-37 can suppress NLRP3 inflammasome activation in astrocytes induced by OGD. Not only that, the OGD-astrocyte-CM treated with ZJU-37 obviously attenuated OPC apoptosis and dysdifferentiation caused by the OGD-astrocyte-CM.

Conclusions

The novel RIP1/RIP3 dual inhibitor ZJU-37 may promote OPC survival, differentiation and myelination by inhibiting NLRP3 inflammasome activation in a neonatal rat model of WMI with hOPC graft.

GSK-3β inhibitor TWS119 alleviates hypoxic-ischemic brain damage via a crosstalk with Wnt and Notch signaling pathways in neonatal rats

Preterm infant brain injury is a leading cause of morbidity and disability in survivors of preterm infants. Unfortunately, the effective treatment remains absent. Recent evidence suggests that GSK-3β inhibitor TWS119 has a neuroprotectiverole in adult brain injury by activation of Wnt/β-catenin signaling pathway. However, the role on neonatal brain injury is not yet explored. The study aims to evaluate the effect of TWS119 at 7 d after hypoxic-ischemic brain damage and investigate the mechanism that it regulates Wnt and Notch signaling pathways at 24 h after hypoxic-ischemic brain damage in neonatal rats. Three-day-old rats were randomly divided into 3 groups: sham group, HI group and TWS119 group. The neonatal rats were subjected to left carotid artery ligation followed by 2 h of hypoxia (8.0% O₂). A single dose of TWS119 (30 mg/kg) was intraperitoneally injected 20 min prior to hypoxia-ischemia (HI). At 7 d after HI, TWS119 improved the tissue structure, reduced cell apoptosis, up-regulated bcl-2 expression, up-regulated the expression of PSD-95 and Synapsin-1. At 24 h after HI, it activated Wnt/β-catenin signaling pathway by up-regulation of β-catenin protein expression and wnt3a/wnt5a/wnt7a mRNA expression. Simultaneously, it suppressed Notch signaling pathway by down-regulation of Notch1 and HES-1 proteins expression. Our study suggested that TWS119 performed a neuroprotective function at 7 d after hypoxic-ischemic brain damage via a crosstalk with Wnt/β-catenin and Notch signaling pathways at 24 h after hypoxic-ischemic brain damage in neonatal rats.

Pre- and early postnatal enriched environmental experiences prevent neonatal hypoxia-ischemia late neurodegeneration via metabolic and neuroplastic mechanisms

Prenatal and early postnatal periods are important for brain development and neural function. Neonatal insults such as hypoxia-ischemia (HI) causes prolonged neural and metabolic dysregulation, affecting central nervous system maturation. There is evidence that brain hypometabolism could increase the risk of adult-onset neurodegenerative diseases. However, the impact of non-pharmacologic strategies to attenuate HI-induced brain glucose dysfunction is still underexplored. This study investigated the long-term effects of early environmental enrichment in metabolic, cell, and functional responses after neonatal HI. Thereby, male Wistar rats were divided according to surgical procedure, sham, and HI (performed at postnatal day 3), and the allocation to standard (SC) or enriched condition (EC) during gestation and lactation periods. In-vivo cerebral metabolism was assessed by means of [¹⁸ F]-FDG micro-positron emission tomography, and cognitive, biochemical, and histological analyses were performed in adulthood. Our findings reveal that HI causes a reduction in glucose metabolism and glucose transporter levels as well as hyposynchronicity in metabolic brain networks. However, EC during prenatal or early postnatal period attenuated these metabolic disturbances. A positive correlation was observed between [¹⁸ F]-FDG values and volume ratios in adulthood, indicating that preserved tissue by EC is metabolically active. EC promotes better cognitive scores, as well as down-regulation of amyloid precursor protein in the parietal cortex and hippocampus of HI animals. Furthermore, growth-associated protein 43 was up-regulated in the cortex of EC animals. Altogether, results presented support that EC during gestation and lactation period can reduce HI-induced impairments that may contribute to functional decline and progressive late neurodegeneration.

White matter injury after neonatal encephalopathy is associated with thalamic metabolite perturbations

BACKGROUND

Although thalamic magnetic resonance (MR) spectroscopy (MRS) accurately predicts adverse outcomes after neonatal encephalopathy, its utility in infants without MR visible deep brain nuclei injury is not known. We examined thalamic MRS metabolite perturbations in encephalopathic infants with white matter (WM) injury with or without cortical injury and its associations with adverse outcomes.

METHODS

We performed a subgroup analysis of all infants recruited to the MARBLE study with isolated WM or mixed WM/cortical injury, but no visible injury to the basal ganglia/thalamus (BGT) or posterior limb of the internal capsule (PLIC). We used binary logistic regression to examine the association of MRS biomarkers with three outcomes (i) WM injury score (1 vs. 2/3); (ii) cortical injury scores (0/1 vs. 2/3); and (iii) adverse outcomes (defined as death, moderate/severe disability) at two years (yes/no). We also assessed the accuracy of MRS for predicting adverse outcome.

FINDINGS

Of the 107 infants included in the analysis, five had adverse outcome. Reduced thalamic N-acetylaspartate concentration [NAA] (odds ratio 0.4 (95% CI 0.18-0.93)) and elevated thalamic Lactate/NAA peak area ratio (odds ratio 3.37 (95% CI 1.45-7.82)) were significantly associated with higher WM injury scores, but not with cortical injury. Thalamic [NAA] (≤5.6 mmol/kg/wet weight) had the best accuracy for predicting adverse outcomes (sensitivity 1.00 (95% CI 0.16-1.00); specificity 0.95 (95% CI 0.84-0.99)).

INTERPRETATION

Thalamic NAA is reduced in encephalopathic infants without MR visible deep brain nuclei injury and may be a useful predictor of adverse outcomes.

FUNDING

The National Institute for Health Research (NIHR).

Inhibition of miR-200b-3p alleviates hypoxia-ischemic brain damage via targeting Slit2 in neonatal rats

BACKGROUND

Brain damage in premature infants often occurs in very low birth weight infants (VLBW) as a result of hypoxia-ischemia and can lead to cognitive impairment and movement disorders. Many miRNAs have been demonstrated to participate in hypoxia-ischemic brain damage (HIBD). This study was designed to investigate the roles of miR-200b-3p in brain damage of neonatal rats induced by hypoxia-ischemia.

METHODS AND RESULTS

Three-day-old SD rats were used to establish the model of hypoxia-ischemic brain injury mimicking premature infants. RT-qPCR showed that miR-200b-3p was up-regulated in rat brains at the early stage following hypoxia-ischemic treatment. Bioinformatics analysis identified that Slit2 is a target gene of miR-200b-3p and luciferase reporter gene assay confirmed that miR-200b-3p can interact with and target Slit2 mRNA. Inhibition of miR-200b-3p by antagomir increased Slit2 expression at both the mRNA and protein levels in rat brains. TUNEL assay and transmission electron microscopy (TEM) analysis showed decreased numbers of apoptotic neurons in the hypoxia-ischemia-treated animals as a result of administration of miR-200b-3p antagomir. Administration of miR-200b-3p antagomir attenuated spatial and learning memory loss in the animals induced by hypoxia-ischemia as compared to controls.

CONCLUSION

Our study has demonstrated that Slit2 is a target gene of miR-200b-3p and that the hypoxia-ischemic brain damage in neonatal rats was alleviated by inhibiting miR-200b-3p via Slit2. miR-200b-3p may be a potential therapeutic target of HIBD for further investigation.

Hypoxia-ischemia in the immature rodent brain impairs serotonergic neuronal function in certain dorsal raphé nuclei

Neonatal hypoxia-ischemia (HI) results in losses of serotonergic neurons in specific dorsal raphé nuclei. However, not all serotonergic raphé neurons are lost and it is therefore important to assess the function of remaining neurons in order to understand their potential to contribute to neurological disorders in the HI-affected neonate. The main objective of this study was to determine how serotonergic neurons, remaining in the dorsal raphé nuclei after neonatal HI, respond to an external stimulus (restraint stress). On postnatal day 3 (P3), male rat pups were randomly allocated to one of the following groups: (i) control + no restraint (n = 5), (ii) control + restraint (n = 6), (iii) P3 HI + no restraint (n = 5) or (iv) P3 HI + restraint (n = 7). In the two HI groups, rat pups underwent surgery to ligate the common carotid artery and were then exposed to 6% O₂ for 30 minutes. Six weeks after P3 HI, on P45, rats were subjected to restraint stress for 30 minutes. Using dual immunolabeling for Fos protein, a marker for neuronal activity, and serotonin (5-hydroxytrypamine; 5-HT), numbers of Fos-positive 5-HT neurons were determined in five dorsal raphé nuclei. We found that restraint stress alone increased numbers of Fos-positive 5-HT neurons in all five dorsal raphé nuclei compared to control animals. However, following P3 HI, the number of stress-induced Fos-positive 5-HT neurons was decreased significantly in the dorsal raphé ventrolateral, interfascicular and ventral nuclei compared with control animals exposed to restraint stress. In contrast, numbers of stress-induced Fos-positive 5-HT neurons in the dorsal raphé dorsal and caudal nuclei were not affected by P3 HI. These data indicate that not only are dorsal raphé serotonergic neurons lost after neonatal HI, but also remaining dorsal raphé serotonergic neurons have reduced differential functional viability in response to an external stimulus. Procedures were approved by the University of Queensland Animal Ethics Committee (UQCCR958/08/NHMRC) on February 27, 2009.

Tissue Injury and Astrocytic Reaction, But Not Cognitive Deficits, Are Dependent on Hypoxia Duration in Very Immature Rats Undergoing Neonatal Hypoxia-Ischemia

Preterm birth and hypoxia-ischemia (HI) are major causes of neonatal death and neurological disabilities in newborns. The widely used preclinical HI model combines carotid occlusion with hypoxia exposure; however, the relationship between different hypoxia exposure periods with brain tissue loss, astrocyte reactivity and behavioral impairments following HI is lacking. Present study evaluated HI-induced behavioral and morphological consequences in rats exposed to different periods of hypoxia at postnatal day 3. Wistar rats of both sexes were assigned into four groups: control group, HI-120 min, HI-180 min and HI-210 min. Neurodevelopmental reflexes, exploratory abilities and cognitive function were assessed. At adulthood, tissue damage and reactive astrogliosis were measured. Animals exposed to HI-180 and HI-210 min had delayed neurodevelopmental reflexes compared to control group. Histological assessment showed tissue loss that was restricted to the ipsilateral hemisphere in lower periods of hypoxia exposure (120 and 180 min) but affected both hemispheres when 210 min was used. Reactive astrogliosis was increased only after 210 min of hypoxia. Interestingly, cognitive deficits were induced regardless the duration of hypoxia and there were correlations between behavioral parameters and cortex, hippocampus and corpus callosum volumes. These results show the duration of hypoxia has a close relationship with astrocytic response and tissue damage progression. Furthermore, the long-lasting cognitive memory deficit and its association with brain structures beyond the hippocampus suggests that complex anatomical changes should be involved in functional alterations taking place as hypoxia duration is increased, even when the cognitive impairment limit is achieved.

Animal models of developmental motor disorders: parallels to human motor dysfunction in cerebral palsy

Cerebral palsy (CP) is the most common motor disability in children. Much of the previous research on CP has focused on reducing the severity of brain injuries, whereas very few researchers have investigated the cause and amelioration of motor symptoms. This research focus has had an impact on the choice of animal models. Many of the commonly used animal models do not display a prominent CP-like motor phenotype. In general, rodent models show anatomically severe injuries in the central nervous system (CNS) in response to insults associated with CP, including hypoxia, ischemia, and neuroinflammation. Unfortunately, most rodent models do not display a prominent motor phenotype that includes the hallmarks of spasticity (muscle stiffness and hyperreflexia) and weakness. To study motor dysfunction related to developmental injuries, a larger animal model is needed, such as rabbit, pig, or nonhuman primate. In this work, we describe and compare various animal models of CP and their potential for translation to the human condition.

Suppression of PDGF induces neuronal apoptosis after neonatal cerebral hypoxia and ischemia by inhibiting P-PI3K and P-AKT signaling pathways

Neonatal hypoxic-ischemic encephalopathy (HIE) always results in severe neurologic dysfunction, nevertheless effective treatments are limited and the underlying mechanism also remains unclear. In this study, we firstly established the neonatal HIE model in the postnatal day 7 SD rats, Zea-Longa score and TTC staining were employed to assess the neurological behavior and infarct volume of the brain after cerebral hypoxia-ischemia (HI). Afterwards, protein chip was adopted to detect the differential proteins in the right cortex, hippocampus and lung, ultimately, PDGF was noticed. Then, immunohistochemistry, immunofluorescence double staining of NeuN/PDGF, and western blot were used to validate the expression level of PDGF in the cortex and hippocampus at 6 hours (h), 12 h and 24 h after HI. To determine the role of PDGF, the primary cortical neurons were prepared and performed PDGF shRNA administration. The results showed that HIE induced a severe behavioral dysfunction and brain infarction in neonatal rats, and the expression of PDGF in right cortex and hippocampus was remarkably increased after HI. Whereas, suppressing PDGF resulted in a significant loss of neurons and inhibition of neurite growth. Moreover, the protein level of P-PI3K and P-AKT signaling pathways were largely decreased following PDGF-shRNA application in the cortical neurons. In conclusion, PDGF suppression aggravated neuronal dysfunction, and the underlying mechanism is associated with inhibiting the phosphorylation of P-PI3K and P-AKT. Together, PDGF regulating PI3K and AKT may be an important panel in HIE events and therefore may provide possible strategy for the treatment of HIE in future clinic trail.

Extracellular Vesicles Derived from Wharton's Jelly Mesenchymal Stem Cells Prevent and Resolve Programmed Cell Death Mediated by Perinatal Hypoxia-Ischemia in Neuronal Cells

Hypoxic-ischemic (HI) insult in the perinatal phase harbors a high risk of encephalopathy in the neonate. Brain cells undergo apoptosis, initiating neurodegeneration. So far, therapeutic approaches such as cooling remain limited. Transplantation of mesenchymal stem cells (MSCs) exhibits therapeutic success despite the short-time survival in the host brain, providing strong evidence that their beneficial effects are largely based on secreted factors, including extracellular vesicles (EVs). The aim of this study was to investigate the effects of human Wharton’s jelly MSC (hWJ-MSC)-derived EVs on neuroprotection and neuroregeneration, using an in vitro model of oxygen–glucose deprivation/reoxygenation (OGD/R) mimicking HI injury in the mouse neuroblastoma cell line neuro2a (N2a). hWJ-MSC-derived EVs were isolated from cell culture supernatants by multistep centrifugation and identified by endosomal marker expression and electron microscopy. OGD/R significantly increased DNA fragmentation and caspase 3 (Casp3) transcription in N2a cells relative to undamaged cells. OGD/R-mediated DNA fragmentation and Casp3 expression could be prevented as well as resolved by the addition of hWJ-MSC-derived EV before and after OGD, respectively. hWJ-MSC-derived EV also tended to increase the phosphorylation of the B cell lymphoma 2 (Bcl2) family member Bcl-2-antagonist of cell death (BAD) in N2a cells, when added prior or post OGD, thereby inactivating the proapoptotic function of BAD. Fluorescence confocal microscopy revealed the close localization of hWJ-MSC-derived EVs to the nuclei of N2a cells. Furthermore, EVs released their RNA content into the cells. The expression levels of the microRNAs (miRs) let-7a and let-7e, known regulators of Casp3, were inversely correlated to Casp3. Our data suggest that hWJ-MSC-derived EVs have the potential to prevent and resolve HI-induced apoptosis in neuronal cells in the immature neonatal brain. Their antiapoptotic effect seems to be mediated by the transfer of EV-derived let-7-5p miR.

Brain Metabolism Alterations Induced by Pregnancy Swimming Decreases Neurological Impairments Following Neonatal Hypoxia-Ischemia in Very Immature Rats

Introduction: Prematurity, through brain injury and altered development is a major cause of neurological impairments and can result in motor, cognitive and behavioral deficits later in life. Presently, there are no well-established effective therapies for preterm brain injury and the search for new strategies is needed. Intra-uterine environment plays a decisive role in brain maturation and interventions using the gestational window have been shown to influence long-term health in the offspring. In this study, we investigated whether pregnancy swimming can prevent the neurochemical metabolic alterations and damage that result from postnatal hypoxic-ischemic brain injury (HI) in very immature rats.

Methods: Female pregnant Wistar rats were divided into swimming (SW) or sedentary (SE) groups. Following a period of adaptation before mating, swimming was performed during the entire gestation. At postnatal day (PND3), rat pups from SW and SE dams had right common carotid artery occluded, followed by systemic hypoxia. At PND4 (24 h after HI), the early neurochemical profile was measured by ¹H-magnetic resonance spectroscopy. Astrogliosis, apoptosis and neurotrophins protein expression were assessed in the cortex and hippocampus. From PND45, behavioral testing was performed. Diffusion tensor imaging and neurite orientation dispersion and density imaging were used to evaluate brain microstructure and the levels of proteins were quantified.

Results: Pregnancy swimming was able to prevent early metabolic changes induced by HI preserving the energetic balance, decreasing apoptotic cell death and astrogliosis as well as maintaining the levels of neurotrophins. At adult age, swimming preserved brain microstructure and improved the performance in the behavioral tests.

Conclusion: Our study points out that swimming during gestation in rats could prevent prematurity related brain damage in progeny with high translational potential and possibly interesting cost-benefits.

HIGHLIGHTS

- Prematurity is a major cause of neurodevelopmental impairments;

- Swimming during pregnancy reduces brain damage after HI injury;

- Pregnancy is an important but underestimated preventive window.

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.

Intranasal Delivery of Umbilical Cord-Derived Mesenchymal Stem Cells Preserves Myelination in Perinatal Brain Damage

Preterm white matter injury (WMI) is an important cause for long-term disability. Stem cell transplantation has been proposed as a novel therapeutic approach. However, intracerebral transplantation is not feasible for clinical purpose in newborns. Intranasal delivery of cells to the brain might be a promising, noninvasive therapeutic approach to restore the damaged brain. Therefore, our goal is to study the remyelinating potential of human Wharton's jelly mesenchymal stem cells (hWJ-MSCs) after intranasal delivery. Wistar rat pups, previously brain-damaged by a combined hypoxic-ischemic and inflammatory insult, received hWJ-MSC (150,000 cells in 3 μL) that were intranasally delivered twice to each nostril (600,000 cells total). WMI was assessed by immunohistochemistry and western blot for myelination, astrogliosis, and microgliosis. The expression of preoligodendrocyte markers, and neurotrophic factors, was analyzed by real-time polymerase chain reaction. Animals treated with intranasally delivered hWJ-MSC showed increased myelination and decreased gliosis compared to untreated animals. hWJ-MSC may, therefore, modulate the activation of microglia and astrocytes, resulting in a change of the brain microenvironment, which facilitates the maturation of oligodendrocyte lineage cells. This is the first study to show that intranasal delivery of hWJ-MSC in rats prevented hypomyelination and microgliosis in a model of WMI in the premature rat brain. Further studies should address the dose and frequency of administration.

[Long-term effect of oligodendrocyte precursor cell transplantation on a rat model of white matter injury in the preterm infant]

OBJECTIVE

To investigate the long-term effect of oligodendrocyte precursor cell (OPC) transplantation on a rat model of white matter injury (WMI) in the preterm infant.

METHODS

A total of 80 Sprague-Dawley rats aged 3 days were randomly divided into sham-operation group, model control group, 5-day ventricular/white matter transplantation group, 9-day ventricular/white matter transplantation group, 14-day ventricular/white matter transplantation group (n=10 each). All groups except the sham-operation group were treated with right common carotid artery ligation and hypoxia for 80 minutes to establish a rat model of WMI in the preterm infant. OPCs were prepared from the human fetal brain tissue (10-12 gestational weeks). At 5, 9, and 14 days after modeling, 3×10⁵ OPCs were injected into the right lateral ventricle or white matter in each transplantation group, and myelin sheath and neurological function were evaluated under an electron microscope at ages of 60 and 90 days.

RESULTS

Electron microscopy showed that at an age of 60 days, each transplantation group had a slight improvement in myelin sheath injury compared with the model control group; at an age of 90 days, each transplantation group had significantly thickened myelin sheath and reduced structural damage compared with the model control group, and the 14-day transplantation groups had the most significant changes. There were no significant differences in the degree of myelin sheath injury between the ventricular and white matter transplantation groups at different time points. At an age of 60 or 90 days, the transplantation groups had a significantly higher modified neurological severity score (mNSS) than the sham-operation group and a significantly lower mNSS than the model control group (P<0.05).

CONCLUSIONS

OPC transplantation may have a long-term effect in the treatment of WMI in the preterm infant, and delayed transplantation may enhance its therapeutic effect.

Longer hypoxia-ischemia periods to neonatal rats causes motor impairments and muscular changes

Prematurity and hypoxia-ischemia (HI) can lead to movement disorders in infants. Considering that mild-moderate HI induced at postnatal day (PND) 3 has failed to produce motor disabilities similar to those seen in pre-term newborns, the main goal of the present study was to verify whether longer hypoxia periods would mimic motor function impairment, brain and muscle morphological alterations. Forty-nine Wistar rat pups of both sexes were randomly assigned to surgical control (CG) and HI groups. HI animals were submitted to the Levine-Rice model at PND 3, and exposed to 120 (HI-120'), 180 (HI-180') or 210 (HI-210') minutes of hypoxia (FiO₂: 0.08). Sensorimotor function was assessed as from PND 35-45, by means of grasping strength, adhesive removal, cylinder and ladder walking tests. Histological staining was used to quantify the striatal volume and the cross-sectional area (CSA) of skeletal muscles. Cylinder and adhesive removal test evidenced that HI-180' and HI-210' groups had asymmetrical use of the forepaws when compared to controls. HI animals showed a decrease in the step placement quality and an increase in step errors when compared to CG (P⩽0.05). Reduction in striatal volume correlates with behavioral assessment, HI-180' and HI-210' groups presented lower biceps brachii and tibialis anterior CSA. These results show that rats exposed to longer hypoxic periods at PND3 have encephalic and sensorimotor impairments that mimic those observed in preterm infants. Morphological changes in muscle tissue evidence a new pathophysiological characteristic of the HI model that might be of relevance for the study of sensorimotor deficits.

Rodent Hypoxia-Ischemia Models for Cerebral Palsy Research: A Systematic Review

Cerebral palsy (CP) is a complex multifactorial disorder, affecting approximately 2.5-3/1000 live term births, and up to 22/1000 prematurely born babies. CP results from injury to the developing brain incurred before, during, or after birth. The most common form of this condition, spastic CP, is primarily associated with injury to the cerebral cortex and subcortical white matter as well as the deep gray matter. The major etiological factors of spastic CP are hypoxia/ischemia (HI), occurring during the last third of pregnancy and around birth age. In addition, inflammation has been found to be an important factor contributing to brain injury, especially in term infants. Other factors, including genetics, are gaining importance. The classic Rice-Vannucci HI model (in which 7-day-old rat pups undergo unilateral ligation of the common carotid artery followed by exposure to 8% oxygen hypoxic air) is a model of neonatal stroke that has greatly contributed to CP research. In this model, brain damage resembles that observed in severe CP cases. This model, and its numerous adaptations, allows one to finely tune the injury parameters to mimic, and therefore study, many of the pathophysiological processes and conditions observed in human patients. Investigators can recreate the HI and inflammation, which cause brain damage and subsequent motor and cognitive deficits. This model further enables the examination of potential approaches to achieve neural repair and regeneration. In the present review, we compare and discuss the advantages, limitations, and the translational value for CP research of HI models of perinatal brain injury.

Sexual dimorphism and brain lateralization impact behavioral and histological outcomes following hypoxia-ischemia in P3 and P7 rats

Neonatal cerebral hypoxia-ischemia (HI) is a major cause of neurological disorders and the most common cause of death and permanent disability worldwide, affecting 1-2/1000 live term births and up to 60% of preterm births. The Levine-Rice is the main experimental HI model; however, critical variables such as the age of animals, sex and hemisphere damaged still receive little attention in experimental design. We here investigated the influence of sex and hemisphere injured on the functional outcomes and tissue damage following early (hypoxia-ischemia performed at postnatal day 3 (HIP3)) and late (hypoxia-ischemia performed at postnatalday 7 (HIP7)) HI injury in rats. Male and female 3- (P3) or 7-day-old (P7) Wistar rats had their right or left common carotid artery occluded and exposed to 8% O2 for 1.5h. Sham animals had their carotids exposed but not occluded nor submitted to the hypoxic atmosphere. Behavioral impairments were assessed in the open field arena, in the Morris water maze and in the inhibitory avoidance task; volumetric extent of tissue damage was assessed using cresyl violet staining at adult age, after completing behavioral assessment. The overall results demonstrate that: (1) HI performed at the two distinct ages cause different behavioral impairments and histological damage in adult rats (2) behavioral deficits following neonatal HIP3 and HIP7 are task-specific and dependent on sex and hemisphere injured (3) HIP7 animals presented the expected motor and cognitive deficits (4) HIP3 animals displayed discrete but significant cognitive impairments in the left hemisphere-injured females (5) HI brain injury and its consequences are determined by animal's sex and the damaged hemisphere, markedly in HIP3-injured animals.

Lactoferrin during lactation protects the immature hypoxic-ischemic rat brain

Objective

Lactoferrin (Lf) is an iron-binding glycoprotein secreted in maternal milk presenting anti-inflammatory and antioxidant properties. It shows efficient absorption into the brain from nutritional source. Brain injury frequently resulting from cerebral hypoxia-ischemia (HI) has a high incidence in premature infants with ensuing neurodevelopmental disabilities. We investigated the neuroprotective effect of maternal nutritional supplementation with Lf during lactation in a rat model of preterm HI brain injury using magnetic resonance imaging (MRI), brain gene, and protein expression.

Methods

Moderate brain HI was induced using unilateral common carotid artery occlusion combined with hypoxia (6%, 30 min) in the postnatal day 3 (P3) rat brain (24–28 weeks human equivalent). High-field multimodal MRI techniques were used to investigate the effect of maternal Lf supplementation through lactation. Expression of cytokine coding genes (TNF-α and IL-6), the prosurvival/antiapoptotic AKT protein and caspase-3 activation were also analyzed in the acute phase after HI.

Results

MRI analysis demonstrated reduced cortical injury in Lf rats few hours post-HI and in long-term outcome (P25). Lf reduced HI-induced modifications of the cortical metabolism and altered white matter microstructure was recovered in Lf-supplemented rats at P25. Lf supplementation significantly decreased brain TNF-α and IL-6 gene transcription, increased phosphorylated AKT levels and reduced activation of caspase-3 at 24 h post-injury.

Interpretation

Lf given through lactation to rat pups with cerebral HI injury shows neuroprotective effects on brain metabolism, and cerebral gray and white matter recovery. This nutritional intervention may be of high interest for the clinical field of preterm brain neuroprotection.

Subplate in a rat model of preterm hypoxia-ischemia

Objective

Hypoxia–ischemia (HI) in preterm infants primarily leads to injuries in the cerebral white matter. However, there is growing evidence that perinatal injury in preterms can also involve other zones including the cortical gray matter. In a neonatal rat model of HI, selective vulnerability of subplate has been suggested using BrdU birth-dating methods. In this study, we aimed to investigate the neuropathological changes of the subplate and deep layers of the cortex following cerebral HI in neonatal rats with specific cell markers.

Methods

P2 rats underwent permanent occlusion of the right common carotid artery followed by a period of hypoxia. P8 rats were analyzed using immunohistochemistry; subplate and deep layers cells were quantified and compared with sham-operated case.

Results

A large variability in the extent of the cerebral injury was apparent. For the three analyzed subplate populations (Nurr1+, Cplx3+, and Ctgf+ cells), no significant cell reduction was observed in mild and moderate cases. Only in severe cases, subplate cells were strongly affected, but these injuries were always accompanied by the cell reductions in layers VI and V.

Interpretation

We could therefore not confirm a specific vulnerability of subplate cells compared to other deep layers or the white matter in our model.

The effect of hypothermia therapy on cortical laminar disruption following ischemic injury in neonatal mice

Hypothermia has been proposed as a treatment for reducing neuronal damage in the brain induced by hypoxic ischemia. In the developing brain, hypoxic ischemia-induced injury may give rise to cerebral palsy (CP). However, it is unknown whether hypothermia might affect the development of CP. The purpose of this study was to investigate whether hypothermia would have a protective effect on the brains of immature, 3-day old (P3) mice after a challenge of cerebral ischemia. Cerebral ischemia was induced in P3 mice with a right common carotid artery ligation followed by hypoxia (6% O2, 37°C) for 30 min. Immediately after hypoxic ischemia, mice were exposed to hypothermia (32°C) or normothermia (37°C) for 24 h. At 4 weeks of age, mouse motor development was tested in a behavioral test. Mice were sacrificed at P4, P7, and 5 weeks to examine brain morphology. The laminar structure of the cortex was examined with immunohistochemistry (Cux1/Ctip2); the number of neurons was counted; and the expression of myelin basic protein (MBP) was determined. The hypothermia treatment was associated with improved neurological outcomes in the behavioral test. In the normothermia group, histological analyses indicated reduced numbers of neurons, reduced cortical laminar thickness in the deep, ischemic cortical layers, and significant reduction in MBP expression in the ischemic cortex compared to the contralateral cortex. In the hypothermia group, no reductions were noted in deep cortical layer thickness and in MBP expression in the ischemic cortex compared to the contralateral cortex. At 24 h after the hypothermia treatment prevented the neuronal cell death that had predominantly occurred in the ischemic cortical deep layers with normothermia treatment. Our findings may provide a preclinical basis for testing hypothermal therapies in patients with CP induced by hypoxic ischemia in the preterm period.

Neonatal hypoxia-ischaemia disrupts descending neural inputs to dorsal raphé nuclei

Neuronal losses have been shown to occur in the brainstem following a neonatal hypoxic-ischaemic (HI) insult. In particular serotonergic neurons, situated in the dorsal raphé nuclei, appear to be vulnerable to HI injury. Nonetheless the mechanisms contributing to losses of serotonergic neurons in the brainstem remain to be elucidated. One possible mechanism is that disruption of neural projections from damaged forebrain areas to dorsal raphé nuclei may play a role in the demise of serotonergic neurons. To test this, postnatal day 3 (P3) rat pups underwent unilateral common carotid artery ligation followed by hypoxia (6% O₂ for 30 min). On P38 a retrograde tracer, fluorescent-coupled choleratoxin b, was deposited in the dorsal raphé dorsal (DR dorsal) nucleus or the dorsal raphé ventral (DR ventral) nucleus. Compared to control animals, P3 HI animals had significant losses of retrogradely labelled neurons in the medial prefrontal cortex, preoptic area and lateral habenula after tracer deposit in the DR dorsal nucleus. On the other hand, after tracer deposit in the DR ventral nucleus, we found significant reductions in numbers of retrogradely labelled neurons in the hypothalamus, preoptic area and medial amygdala in P3 HI animals compared to controls. Since losses of descending inputs are associated with decreases in serotonergic neurons in the brainstem raphé nuclei, we propose that disruption of certain descending neural inputs from the forebrain to the DR dorsal and the DR ventral nuclei may contribute to losses of serotonergic neurons after P3 HI. It is important to delineate the phenotypes of different neuronal networks affected by neonatal HI, and the mechanisms underpinning this damage, so that interventions can be devised to target and protect axons from the harmful effects of neonatal HI.

Neonatal tryptophan depletion and corticosterone supplementation modify emotional responses in adult male mice

The serotonergic system and the hypothalamic-pituitary-adrenal (HPA) axis are crucially involved in the regulation of emotions. Specifically, spontaneous and/or environmentally mediated modulations of the functionality of these systems early in development may favour the onset of depressive- and anxiety-related phenotypes. While the independent contribution of each of these systems to the emergence of abnormal phenotypes has been detailed in clinical and experimental studies, only rarely has their interaction been systematically investigated. Here, we addressed the effects of reduced serotonin and environmental stress during the early stages of postnatal life on emotional regulations in mice. To this aim, we administered, to outbred CD1 mouse dams, during their first week of lactation, a tryptophan deficient diet (T) and corticosterone via drinking water (C; 80μg/ml). Four groups of dams (animal facility rearing, AFR; T treated, T; C treated, C; T and C treated, TC) and their male offspring were used in the study. Maternal care was scored throughout treatment and adult offspring were tested for: anhedonia (progressive ratio schedule); anxiety-related behaviour (approach-avoidance conflict paradigm); BDNF, dopamine and serotonin concentrations in selected brain areas. T, C and TC treatments reduced active maternal care compared to AFR. Adult TC offspring showed significantly increased anxiety- and anhedonia-related behaviours, reduced striatal and increased hypothalamic BDNF and reduced dopamine and serotonin in the prefrontal cortex and their turnover in the hippocampus. Thus, present findings support the view that neonatal variations in the functionality of the serotonergic system and of HPA axis may jointly contribute to induce emotional disturbances in adulthood.

Hypoxia-ischemia induces hypo-phosphorylation of collapsin response mediator protein 2 in a neonatal rat model of periventricular leukomalacia

Collapsin response mediator protein2 (CRMP2) is a brain-specific protein involved in neuronal polarity and axonal guidance, and phosphorylation of CRMP2 regulates the function and the activity. CRMP2 has shown to be implicated in several neurodegenerative diseases (Alzheimer's disease, epilepsy and ischemia) and this study was designed to assess the role of CRMP2 in periventricular leukomalacia (PVL). We developed a PVL model using 3-day-old rats to investigate the expression and phosphorylation of CRMP2 in the newborn brain. Hypoxia-ischemia was applied by unilateral carotid ligation followed by exposure to 5% oxygen for 30min. Pathological changes were evaluated from 0h to 21d post-HI, and white matter damage including severe necrosis, white matter rarefaction and lateral ventricle dilatation were found. In the PVL model astrogliosis and axonal damage were detected in the injured white matter by immunohistochemistry at 48-168h post-HI, and delayed myelination was verified by Western blotting after 21-day post-HI. We confirmed that this model showed neuropathological features of PVL. Next, significant changes of CRMP2 were observed in the brain of the PVL model. Western blotting and immunohistochemistry showed that cleavage and hypo-phosphorylation of CRMP2 occurred after 48h post-HI in the PVL brain. Our results suggest that cleaved CRMP2 could represent hypo-phosphorylated-CRMP2 and HI could induce activation of CRMP2 in the PVL brain. The activated CRMP2 may play an important role in neuronal plasticity in PVL. Our findings suggest that future treatment strategies of PVL should target the phosphorylation mechanism of CRMP2.

Age- and region-specific effects of anticonvulsants and bumetanide on 4-aminopyridine-induced seizure-like events in immature rat hippocampal-entorhinal cortex slices

PURPOSE

Seizure-like events (SLEs) induced by 4-aminopyridine in rat organotypic slices cultures, which are prepared early after birth, are resistant to standard antiepileptic drugs. In this study we tested the hypothesis that pharmacoresistance may be an intrinsic property of the immature brain.

METHODS

Frequently recurring SLEs presumably representing status epilepticus were induced by 4-aminopyridine in acute rat hippocampal-entorhinal cortex slices obtained from postnatal day 3-19 (P3-P19), and the effects of carbamazepine, phenytoin, valproic acid, and phenobarbital were examined. In addition, bumetanide was tested, which blocks the Na(+) -K(+) -2Cl(-) (NKCC1) cotransporter, and also acetazolamide, which blocks the carbonic anhydrase and thereby the accumulation of bicarbonate inside neurons.

RESULTS

The efficacy of all antiepileptic drugs in blocking SLEs was dependent on postnatal age, with low efficacy in P3-P5 slices. Antiepileptic drugs suppressed SLEs more readily in the medial entorhinal cortex (ECm) than in the CA3. In P3-P5 slices, valproic acid and phenobarbital increased both tonic and clonic seizure-like activities in the CA3, whereas phenytoin and carbamazepine blocked tonic-like but prolonged clonic-like activity. In P3-P5 slices, bumetanide often blocked SLEs in the CA3, but was not as effective in the ECm. Like with other antiepileptic drugs, the seizure-suppressing effects of acetazolamide increased with postnatal age.

CONCLUSION

We conclude that pharmacoresistance may be inherent to very immature tissue and suggest that expression of the NKCC1 cotransporter might contribute to pharmacoresistance.

CD133+ cells from human umbilical cord blood reduce cortical damage and promote axonal growth in neonatal rat organ co-cultures exposed to hypoxia

To evaluate the effect of CD133(+) cells (endothelial progenitor cells) on the hypoxia-induced suppression of axonal growth of cortical neurons and the destruction of blood vessels (endothelial cells), we used anterograde axonal tracing and immunofluorescence in organ co-cultures of the cortex and the spinal cord from 3-day-old neonatal rats. CD133(+) cells prepared from human umbilical cord blood were added to the organ co-cultures after hypoxic insult, and axonal growth, vascular damage and apoptosis were evaluated. Anterograde axonal tracing with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate was used to analyze axonal projections from the cortex to the spinal cord. Immunolabeling co-cultured tissues of the cortex and the spinal cord were used to investigate the effect of CD133(+) cells on the survival of blood vessels and apoptosis in the brain cortex. Hypoxia remarkably suppressed axonal growth in organ co-cultures of the cortex and the spinal cord, and this suppression was significantly restored by the addition of CD133(+) cells. CD133(+) cells also reduced the hypoxia-induced destruction of the cortical blood vessels and apoptosis. CD133(+) cells had protective effects on hypoxia-induced injury of neurons and blood vessels of the brain cortex in vitro. These results suggest that CD133(+) cell transplantation may be a possible therapeutic intervention for perinatal hypoxia-induced brain injury.

Effects of acute perinatal asphyxia in the rat hippocampus

In the present work, we have used a rat animal model to study the early effects of intrauterine asphyxia occurring no later than 60 min following the cesarean-delivery procedure. Transitory hypertonia accompanied by altered posture was observed in asphyxiated pups, which also showed appreciably increased lactate values in plasma and hippocampal tissues. Despite this, there was no difference in terms of either cell viability or metabolic activities such as oxidation of lactate, glucose, and glycine in the hippocampus of those fetuses submitted to perinatal asphyxia with respect to normoxic animals. Moreover, a significant decrease in glutamate, but not GABA uptake was observed in the hippocampus of asphyctic pups. Since intense ATP signaling especially through P2X(7) purinergic receptors can lead to excitotoxicity, a feature which initiates neurotransmission failure in experimental paradigms relevant to ischemia, here we assessed the expression level of the P2X(7) receptor in the paradigm of perinatal asphyxia. A three-fold increase in P2X(7) protein was transiently observed in hippocampus immediately following asphyxia. Nevertheless, further studies are needed to delineate whether the P2X(7) receptor subtype is involved in the pathogenesis, contributing to ongoing brain injury after intrapartum asphyxia. In that case, new pharmacologic intervention strategies providing neuroprotection during the reperfusion phase of injury might be identified.

Delayed P2X4R expression after hypoxia-ischemia is associated with microglia in the immature rat brain

In a preterm hypoxia-ischemia model in the post-natal day 3 rat, we characterized how the expression of purine ionotropic P2X(4) receptors change in the brain post-insult. After hypoxia-ischemia, P2X(4) receptor expression increased significantly and was associated with a late increase in ionised calcium binding adapter molecule-1 protein expression indicative of microglia cell activation. Minocycline, a potent inhibitor of microglia, attenuated the hypoxia-ischemia-induced increase in P2X(4) receptor expression. We postulate that P2X(4) receptor-positive microglia may represent a population of secondary injury-induced activated microglia. Future studies will determine whether this population contributes to the progression of injury in the immature brain.

Selective losses of brainstem catecholamine neurons after hypoxia-ischemia in the immature rat pup

Hypoxic-ischemic (HI) injury in the preterm neonate incurs numerous functional deficits, however little is known about the neurochemically-defined brain nuclei that may underpin them. Key candidates are the brainstem catecholamine neurons. Using an immature animal model, the postnatal day (P)-3 (P3) rat pup, we investigated the effects of HI on brainstem catecholamine neurons in the locus coeruleus, nucleus tractus solitarius (NTS), and ventrolateral medulla (VLM). On P21, we found that prior P3 HI significantly reduced numbers of catecholaminergic neurons in the locus coeruleus, NTS, and VLM. Only locus coeruleus A6, NTS A2, and VLM A1 noradrenergic neurons, but not NTS C2 and VLM C1 adrenergic neurons, were lost. There was also an associated reduction in dopamine-beta-hydroxylase-positive immunolabeling in the forebrain. These findings suggest neonatal HI can affect specific neurochemically-defined neuronal populations in the brainstem and that noradrenergic neurons are particularly vulnerable to HI injury.

Post-insult minocycline treatment attenuates hypoxia-ischemia-induced neuroinflammation and white matter injury in the neonatal rat: a comparison of two different dose regimens

An increase in the number of activated microglia in the brain is a key feature of neuroinflammation after a hypoxic-ischemic insult to the preterm neonate and can contribute to white matter injury in the brain. Minocycline is a potent inhibitor of microglia and may have a role as a neuroprotective agent that ameliorates brain injury after hypoxia-ischemia in neonatal animal models. However to date large doses, pre-insult administration and short periods of treatment after hypoxia-ischemia have mostly been investigated in animal models making it difficult to translate minocycline's potential applicability to protect the human preterm neonatal brain exposed to hypoxia-ischemia. We investigated whether repeated doses of minocycline can minimize white matter injury and neuroinflammation one week after hypoxia-ischemia (right carotid artery ligation and 30 min 6% O(2)) in the post-natal day 3 rat pup. Two dosage regimens of minocycline were administered for one week; a high dose of 45 mg/kg 2h after hypoxia-ischemia then 22.5 mg/kg daily or a low dose 22.5 mg/kg 2h after hypoxia-ischemia then 10 mg/kg. Post-natal day 3 hypoxia-ischemia significantly reduced myelin content, numbers of O1- and O4-positive oligodendrocyte progenitor cells and increased activated microglia one week later on post-natal day 10. The low dose minocycline regimen was as effective as the high dose in ameliorating neuroinflammation after post-natal day 3 hypoxia-ischemia. However only the high dose regimen significantly attenuated reductions in O1- and O4-positive oligodendrocyte progenitor cells and myelin content. The low dose only significantly attenuated the reduction in O1-positive oligodendrocyte cell counts. Repeated, daily, post-insult treatment with minocycline abolished neuroinflammation and may provide neuroprotection to white matter for up to one week after hypoxia-ischemia in a rodent preterm model. The present findings suggest the potential clinical relevance of a repeated, daily minocycline treatment strategy, administered after a hypoxia-ischemia insult, as a therapeutic intervention for hypoxia-ischemia-affected preterm neonates.

Glial responses to neonatal hypoxic-ischemic injury in the rat cerebral cortex

Neurogenesis is nearly completed after birth, whereas gliogenic activities remain intense during the postnatal period in the developing rat cortex. These include involution of radial glia, proliferation of astrocytes and oligodendrocytes and myelin formation. Little is known about the effects of hypoxic-ischemic (HI) injury on these critical postnatal processes. Here we explored the glial reactions to mild HI injury of the neonatal rat cerebral cortex at P3. We show that the HI lesion results in disruption of the normal radial glia architecture, which was paralleled by an increase in GFAP immunopositive reactive astrocytes. The morphology of these latter cells and the fact that they were immunolabelled for both nestin and GFAP suggest an accelerated transformation of radial glia into astrocytes. In addition, BrdU/GFAP immunostaining revealed a significant increase of double-labelled cells indicating an acute proliferation of astrocytes after HI. This enhanced proliferative activity of astrocytes persisted for several weeks. We found an elevated number and increased mitotic activity of both NG2-positive oligodendrocyte progenitors and RIP-positive oligodendrocytes after injury. These findings imply that glial responses are central to cortical tissue remodelling following neonatal ischemia and represent a potential target for therapeutic approaches.

ADHD-like hyperactivity, with no attention deficit, in adult rats after repeated hypoxia during the equivalent of extreme prematurity

The most common behavioural disorder seen in children and adolescents born extremely prematurely is attention deficit hyperactivity disorder (ADHD). The hyperactive/impulsive sub-type of ADHD or the inattentive sub-type or the hyperactive/impulsive/inattentive sub-type can be evident. These sub-types of ADHD can persist into adulthood. The aim of this study was to investigate the relevance of a new immature rat model of repeated hypoxic exposure to these behavioural characteristics of extreme prematurity. More specifically, this study aimed to measure ADHD-like hyperactivity in response to delayed reward, and inattention, in repeated hypoxic versus repeated normoxic rats. Sprague-Dawley rats were exposed to either repeated hypoxia or repeated normoxia during postnatal days (PN) 1-3. The rat brain during PN1-3 is generally considered to be developmentally equivalent to the human brain during extreme prematurity. The rats were then behaviourally tested at 16 months-of-age on a multiple component fixed interval-extinction test. This test detects ADHD-like hyperactivity in response to delayed reward, as well as inattention. It was found that the repeated hypoxic rats exhibited ADHD-like hyperactivity in response to delayed reward, but no attention deficit, when compared to repeated normoxic rats. These findings provide a new animal model to investigate the biological mechanisms and treatment of ADHD-like hyperactivity due to repeated hypoxia during the equivalent of extreme prematurity.

Response to novelty, social and self-control behaviors, in rats exposed to neonatal anoxia: modulatory effects of an enriched environment

Perinatal asphyxia is a concern for public health and may promote subtle and long-lasting neuropsychiatric disorders. In the present study, newborn Wistar rat pups underwent a repeated 20-min exposure to a 100% N2 atmosphere (or air) on postnatal days (pnd) 1, 3, 5, and 7. Half of the animals were housed during adolescence (pnd 21-35) in an enriched environment. The consequences on behavior were assessed throughout adolescence to adulthood. When scored for social performance, adolescent rats exposed to neonatal asphyxia exhibited exaggerated levels of anogenital sniffing behavior, which was normalized by enriched living. In air-exposed controls, enriched living increased the expression of affiliative and novelty-seeking behaviors, as compared to standard housing. However, this enrichment-induced behavioral plasticity was not found in rats neonatally exposed to asphyxia. At adulthood, levels of impulsivity and 5-HT2A receptors in the striatum were markedly increased in neonatal-asphyxia rats kept in standard-housing conditions. Interestingly, impulsivity and receptor density were normalized by enriched rearing during adolescence. These findings indicate profound long-lasting behavioral alterations as a consequence of repeated neonatal asphyxia in rats. Beneficial effects of stimulation by an enriched environment during the still-plastic window of adolescence are suggested in these animals.