Damage to the choroid plexus, ependyma and subependyma as a consequence of perinatal hypoxia/ischemia

The Time Trajectory of Choroid Plexus Enlargement in Multiple Sclerosis

Choroid plexus (CP) can be seen as a watchtower of the central nervous system (CNS) that actively regulates CNS homeostasis. A growing body of literature suggests that CP alterations are involved in the pathogenesis of multiple sclerosis (MS) but the underlying mechanisms remain elusive. CPs are enlarged and inflamed in relapsing-remitting (RRMS) but also in clinically isolated syndrome (CIS) and radiologically isolated syndrome (RIS) stages, far beyond MS diagnosis. Increases in the choroid plexus/total intracranial volume (CP/TIV) ratio have been robustly associated with increased lesion load, higher translocator protein (TSPO) uptake in normal-appearing white matter (NAWM) and thalami, as well as with higher annual relapse rate and disability progression in highly active RRMS individuals, but not in progressive MS. The CP/TIV ratio has only slightly been correlated with magnetic resonance imaging (MRI) findings (cortical or whole brain atrophy) and clinical outcomes (EDSS score) in progressive MS. Therefore, we suggest that plexus volumetric assessments should be mainly applied to the early disease stages of MS, whereas it should be taken into consideration with caution in progressive MS. In this review, we attempt to clarify the pathological significance of the temporal CP volume (CPV) changes in MS and highlight the pitfalls and limitations of CP volumetric analysis.

Conflicting findings on the effectiveness of hydrogen therapy for ameliorating vascular leakage in a 5-day post hypoxic-ischemic survival piglet model

Neonatal hypoxic-ischemic encephalopathy (HIE) is a major cause of morbidity and mortality in newborns in both high- and low-income countries. The important determinants of its pathophysiology are neural cells and vascular components. In neonatal HIE, increased vascular permeability due to damage to the blood-brain barrier is associated with seizures and poor outcomes in both translational and clinical studies. In our previous studies, hydrogen gas (H₂) improved the neurological outcome of HIE and ameliorated the cell death. In this study, we used albumin immunohistochemistry to assess if H₂ inhalation effectively reduced the cerebral vascular leakage. Of 33 piglets subjected to a hypoxic-ischemic insult, 26 piglets were ultimately analyzed. After the insult, the piglets were grouped into normothermia (NT), H₂ ventilation (H₂), therapeutic hypothermia (TH), and H₂ combined with TH (H₂-TH) groups. The ratio of albumin stained to unstained areas was analyzed and found to be lower in the H₂ group than in the other groups, although the difference was not statistically significant. In this study, H₂ therapy did not significantly improve albumin leakage despite the histological images suggesting signs of improvement. Further investigations are warranted to study the efficacy of H₂ gas for vascular leakage in neonatal HIE.

Quantitative Evaluation of Brain Echogenicity in Hypoxic-Ischemic Encephalopathy in Term Neonates Compared with Controls

Purpose Neurosonography evaluation of neonatal hypoxic-ischemic encephalopathy (HIE) is mainly qualitative. We aimed to quantitatively compare the echogenicity of several brain regions in patients with HIE to healthy controls. Materials and Methods 20 term neonates with clinical/MRI evidence of HIE and 20 term healthy neonates were evaluated. Seven brain regions were assessed [frontal, parietal, occipital, and perirolandic white matter (WM), caudate nucleus head, lentiform nucleus, and thalamus]. The echogenicity of the calvarial bones (bone) and the choroid plexus (CP) was used for ratio calculation. Differences in the ratios were determined between neonates with HIE and controls. Results Ratios were significantly higher for HIE neonates in each region (p<0.05). The differences were greatest for the perirolandic WM, with CP and bone ratios being 0.23 and 0.22 greater, respectively, for the HIE compared to the healthy neonates (p<0.001). The perirolandic WM had a high AUC, at 0.980 for both the CP and bone ratios. The intra-observer reliability for all ratios was high, with the caudate to bone ratio being the lowest at 0.832 and the anterior WM to CP ratio being the highest at 0.992. Conclusion When coupled with internal controls, quantitative neurosonography represents a potential tool to identify early neonatal HIE changes. Larger cohort studies could reveal whether a quantitative approach can discern between degrees of severity of HIE. Future neurosonography protocols should be tailored to evaluate the perirolandic region, which requires posterior coronal scanning.

Apoptotic changes and aquaporin-1 expression in the choroid plexus of cerebral malaria patients

Background

Cerebral malaria (CM) is associated with sequestration of parasitized red blood cells (PRBCs) in the capillaries. Often, the association of CM with cerebral oedema is related with high mortality rate. Morphological changes of the choroid plexus (CP) and caspase-3 expression in CM have not been reported. In addition, limited knowledge is known regarding the role of aquaporin (AQP)-1 in CM. The present study evaluated changes in the CP, explored apoptotic changes and AQP-1 expression in CP epithelial cells (CPECs) in fatal CM patients.

Methods

CP from fatal Plasmodium falciparum malaria patients (5 non-CM [NCM], 16 CM) were retrieved and prepared for histopathological evaluation. Caspase-3 and AQP-1 expressions in CPECs were investigated by immunohistochemistry.

Results

Histologically, apoptotic changes in CPECs were significantly observed in the CM group compared with the NCM and normal control (NC) groups (p < 0.05). These changes included cytoplasmic and nuclear condensation/shrinkage of CPECs and detachment of CPECs from the basement membrane. The apoptotic changes were positively correlated with caspase-3 expression in the nuclei of CPECs. In addition, AQP-1 expression in CPECs was significantly decreased in the CM group compared with the NCM and NC groups (all p < 0.001). A negative correlation (r_s =  − 0.450, p = 0.024) was documented between caspase-3 expression in the nuclei of CPECs and AQP-1.

Conclusions

Apoptotic changes and altered AQP-1 expression may contribute to CPEC dysfunction and subsequently reduce cerebrospinal fluid production, affecting the water homeostasis in the brains of patients with CM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04044-6.

Neurogenesis Is Reduced at 48 h in the Subventricular Zone Independent of Cell Death in a Piglet Model of Perinatal Hypoxia-Ischemia

Cellular and tissue damage triggered after hypoxia-ischemia (HI) can be generalized and affect the neurogenic niches present in the central nervous system. As neuroregeneration may be critical for optimizing functional recovery in neonatal encephalopathy, the goal of the present work was to investigate the neurogenic response to HI in the neurogenic niche of the subventricular zone (SVZ) in the neonatal piglet. A total of 13 large white male piglets aged <24 h were randomized into two groups: i) HI group (n = 7), animals submitted to transient cerebral HI and resuscitation; and ii) Control group (n = 6), non-HI animals. At 48 h, piglets were euthanized, and the SVZ and its surrounding regions, such as caudate and periventricular white matter, were analyzed for histology using hematoxylin-eosin staining and immunohistochemistry by evaluating the presence of cleaved caspase 3 and TUNEL positive cells, together with the cell proliferation/neurogenesis markers Ki67 (cell proliferation), GFAP (neural stem cells processes), Sox2 (neural stem/progenitor cells), and doublecortin (DCX, a marker of immature migrating neuroblasts). Hypoxic-ischemic piglets showed a decrease in cellularity in the SVZ independent of cell death, together with decreased length of neural stem cells processes, neuroblast chains area, DCX immunoreactivity, and lower number of Ki67 + and Ki67 + Sox2 + cells. These data suggest a reduction in both cell proliferation and neurogenesis in the SVZ of the neonatal piglet, which could in turn compromise the replacement of the lost neurons and the achievement of global repair.

The impact of hypoxia on blood-brain, blood-CSF, and CSF-brain barriers

The blood-brain barrier (BBB), blood-cerebrospinal fluid (CSF) barrier (BCSFB), and CSF-brain barriers (CSFBB) are highly regulated barriers in the central nervous system comprising complex multicellular structures that separate nerves and glia from blood and CSF, respectively. Barrier damage has been implicated in the pathophysiology of diverse hypoxia-related neurological conditions, including stroke, multiple sclerosis, hydrocephalus, and high-altitude cerebral edema. Much is known about the damage to the BBB in response to hypoxia, but much less is known about the BCSFB and CSFBB. Yet, it is known that these other barriers are implicated in damage after hypoxia or inflammation. In the 1950s, it was shown that the rate of radionucleated human serum albumin passage from plasma to CSF was five times higher during hypoxic than normoxic conditions in dogs, due to BCSFB disruption. Severe hypoxia due to administration of the bacterial toxin lipopolysaccharide is associated with disruption of the CSFBB. This review discusses the anatomy of the BBB, BCSFB, and CSFBB and the impact of hypoxia and associated inflammation on the regulation of those barriers.

Altered secretory and neuroprotective function of the choroid plexus in progressive multiple sclerosis

The choroid plexus (CP) is a key regulator of the central nervous system (CNS) homeostasis through its secretory, immunological and barrier properties. Accumulating evidence suggests that the CP plays a pivotal role in the pathogenesis of multiple sclerosis (MS), but the underlying mechanisms remain largely elusive. To get a comprehensive view on the role of the CP in MS, we studied transcriptomic alterations of the human CP in progressive MS and non-neurological disease controls using RNA sequencing. We identified 17 genes with significantly higher expression in progressive MS patients relative to that in controls. Among them is the newly described long non-coding RNA HIF1A-AS3. Next to that, we uncovered disease-affected pathways related to hypoxia, secretion and neuroprotection, while only subtle immunological and no barrier alterations were observed. In an ex vivo CP explant model, a subset of the upregulated genes responded in a similar way to hypoxic conditions. Our results suggest a deregulation of the Hypoxia-Inducible Factor (HIF)-1 pathway in progressive MS CP. Importantly, cerebrospinal fluid levels of the hypoxia-responsive secreted peptide PAI-1 were higher in MS patients with high disability relative to those with low disability. These findings provide for the first time a complete overview of the CP transcriptome in health and disease, and suggest that the CP environment becomes hypoxic in progressive MS patients, highlighting the altered secretory and neuroprotective properties of the CP under neuropathological conditions. Together, these findings provide novel insights to target the CP and promote the secretion of neuroprotective factors into the CNS of progressive MS patients.

Age- and sex-dependent effects of metformin on neural precursor cells and cognitive recovery in a model of neonatal stroke

Resident neural stem and progenitor cells, collectively termed neural precursor cells (NPCs), reside in a well-defined neurogenic niche in the subventricular zone (SVZ) and contribute to ongoing postnatal neurogenesis. It is well established that the NPC niche can alter the behavior of NPCs. NPC activation is a promising therapeutic strategy for brain repair. The drug metformin has been shown to activate neural stem cells, promote differentiation, and lead to functional motor recovery in a neonatal stroke model. We demonstrate that metformin-induced NPC expansion and functional recovery is sex hormone dependent. Metformin increases the size of the NPC pool in adult females, but not males, and promotes cognitive recovery in a model of brain injury in females, but not males. Our data demonstrate that metformin has age- and sex-dependent effects on NPCs that correlate with functional recovery, which has important implications for neural repair.

Home sweet home: the neural stem cell niche throughout development and after injury

Neural stem cells and their progeny reside in two distinct neurogenic niches within the mammalian brain: the subventricular zone and the dentate gyrus. The interplay between the neural stem cells and the niche in which they reside can have significant effects on cell kinetics and neurogenesis. A comprehensive understanding of the changes to the niche that occur through postnatal development and aging, as well as following injury, is relevant for developing therapeutics and interventions to promote neural repair. We discuss changes that occur within the neural stem and progenitor cell populations, the vasculature, extracellular matrix, microglia, and secreted proteins through aging which impact cell behavior within the neurogenic niches. We examine neural precursor cell and niche responses to injury in neonatal hypoxia-ischemia, juvenile cranial irradiation, and adult stroke. This review examines the interplay between the niche and stem cell behavior through aging and following injury as a means to understand intrinsic and extrinsic factors that regulate neurogenesis in vivo.

The choroid plexus as a site of damage in hemorrhagic and ischemic stroke and its role in responding to injury

While the impact of hemorrhagic and ischemic strokes on the blood–brain barrier has been extensively studied, the impact of these types of stroke on the choroid plexus, site of the blood-CSF barrier, has received much less attention. The purpose of this review is to examine evidence of choroid plexus injury in clinical and preclinical studies of intraventricular hemorrhage, subarachnoid hemorrhage, intracerebral hemorrhage and ischemic stroke. It then discusses evidence that the choroid plexuses are important in the response to brain injury, with potential roles in limiting damage. The overall aim of the review is to highlight deficiencies in our knowledge on the impact of hemorrhagic and ischemic strokes on the choroid plexus, particularly with reference to intraventricular hemorrhage, and to suggest that a greater understanding of the response of the choroid plexus to stroke may open new avenues for brain protection.

Mechanisms of mouse neural precursor expansion after neonatal hypoxia-ischemia

Neonatal hypoxia-ischemia (H-I) is the leading cause of brain damage resulting from birth complications. Studies in neonatal rats have shown that H-I acutely expands the numbers of neural precursors (NPs) within the subventricular zone (SVZ). The aim of these studies was to establish which NPs expand after H-I and to determine how leukemia inhibitory factor (LIF) insufficiency affects their response. During recovery from H-I, the number of Ki67(+) cells in the medial SVZ of the injured hemisphere increased. Similarly, the number and size of primary neurospheres produced from the injured SVZ increased approximately twofold versus controls, and, upon differentiation, more than twice as many neurospheres from the damaged brain were tripotential, suggesting an increase in neural stem cells (NSCs). However, multimarker flow cytometry for CD133/LeX/NG2/CD140a combined with EdU incorporation revealed that NSC frequency diminished after H-I, whereas that of two multipotential progenitors and three unique glial-restricted precursors expanded, attributable to changes in their proliferation. By quantitative PCR, interleukin-6, LIF, and CNTF mRNA increased but with significantly different time courses, with LIF expression correlating best with NP expansion. Therefore, we evaluated the NP response to H-I in LIF-haplodeficient mice. Flow cytometry revealed that one subset of multipotential and bipotential intermediate progenitors did not increase after H-I, whereas another subset was amplified. Altogether, our studies demonstrate that neonatal H-I alters the composition of the SVZ and that LIF is a key regulator for a subset of intermediate progenitors that expand during acute recovery from neonatal H-I.

Brain barrier properties and cerebral blood flow in neonatal mice exposed to cerebral hypoxia-ischemia

Insults to the developing brain often result in irreparable damage resulting in long-term deficits in motor and cognitive functions. The only treatment today for hypoxic-ischemic encephalopathy (HIE) in newborns is hypothermia, which has limited clinical benefit. We have studied changes to the blood-brain barriers (BBB) as well as regional cerebral blood flow (rCBF) in a neonatal model of HIE to further understand the underlying pathologic mechanisms. Nine-day old mice pups, brain roughly equivalent to the near-term human fetus, were subjected to hypoxia-ischemia. Hypoxia-ischemia increased BBB permeability to small and large molecules within hours after the insult, which normalized in the following days. The opening of the BBB was associated with changes to BBB protein expression whereas gene transcript levels were increased showing direct molecular damage to the BBB but also suggesting compensatory mechanisms. Brain pathology was closely related to reductions in rCBF during the hypoxia as well as the areas with compromised BBB showing that these are intimately linked. The transient opening of the BBB after the insult is likely to contribute to the pathology but at the same time provides an opportunity for therapeutics to better reach the infarcted areas in the brain.

Neutralizing anti-interleukin-1β antibodies modulate fetal blood-brain barrier function after ischemia

We have previously shown that increases in blood-brain barrier permeability represent an important component of ischemia-reperfusion related brain injury in the fetus. Pro-inflammatory cytokines could contribute to these abnormalities in blood-brain barrier function. We have generated pharmacological quantities of mouse anti-ovine interleukin-1β monoclonal antibody and shown that this antibody has very high sensitivity and specificity for interleukin-1β protein. This antibody also neutralizes the effects of interleukin-1β protein in vitro. In the current study, we hypothesized that the neutralizing anti-interleukin-1β monoclonal antibody attenuates ischemia-reperfusion related fetal blood-brain barrier dysfunction. Instrumented ovine fetuses at 127 days of gestation were studied after 30 min of carotid occlusion and 24h of reperfusion. Groups were sham operated placebo-control- (n=5), ischemia-placebo- (n=6), ischemia-anti-IL-1β antibody- (n=7), and sham-control antibody- (n=2) treated animals. Systemic infusions of placebo (0.154M NaCl) or anti-interleukin-1β monoclonal antibody (5.1±0.6 mg/kg) were given intravenously to the same sham or ischemic group of fetuses at 15 min and 4h after ischemia. Concentrations of interleukin-1β protein and anti-interleukin-1β monoclonal antibody were measured by ELISA in fetal plasma, cerebrospinal fluid, and parietal cerebral cortex. Blood-brain barrier permeability was quantified using the blood-to-brain transfer constant (Ki) with α-aminoisobutyric acid in multiple brain regions. Interleukin-1β protein was also measured in parietal cerebral cortices and tight junction proteins in multiple brain regions by Western immunoblot. Cerebral cortical interleukin-1β protein increased (P<0.001) after ischemia-reperfusion. After anti-interleukin-1β monoclonal antibody infusions, plasma anti-interleukin-1β monoclonal antibody was elevated (P<0.001), brain anti-interleukin-1β monoclonal antibody levels were higher (P<0.03), and interleukin-1β protein concentrations (P<0.03) and protein expressions (P<0.001) were lower in the monoclonal antibody-treated group than in placebo-treated-ischemia-reperfusion group. Monoclonal antibody infusions attenuated ischemia-reperfusion-related increases in Ki across the brain regions (P<0.04), and Ki showed an inverse linear correlation (r= -0.65, P<0.02) with anti-interleukin-1β monoclonal antibody concentrations in the parietal cortex, but had little effect on tight junction protein expression. We conclude that systemic anti-interleukin-1β monoclonal antibody infusions after ischemia result in brain anti-interleukin-1β antibody uptake, and attenuate ischemia-reperfusion-related interleukin-1β protein up-regulation and increases in blood-brain barrier permeability across brain regions in the fetus. The pro-inflammatory cytokine, interleukin-1β, contributes to impaired blood-brain barrier function after ischemia in the fetus.

Molecular features of neural stem cells enable their enrichment using pharmacological inhibitors of survival-promoting kinases

Isolating a pure population of neural stem cells (NSCs) has been difficult since no exclusive surface markers have been identified for panning or FACS purification. Moreover, additional refinements for maintaining NSCs in culture are required, since NSCs generate a variety of neural precursors (NPs) as they proliferate. Here, we demonstrate that post-natal rat NPs express low levels of pro-apoptotic molecules and resist phosphatidylinositol 3'OH kinase and extracellular regulated kinase 1/2 inhibition as compared to late oligodendrocyte progenitors. Furthermore, maintaining subventricular zone precursors in LY294002 and PD98059, inhibitors of PI3K and ERK1/2 signaling, eliminated lineage-restricted precursors as revealed by enrichment for Nestin(+)/SOX-2(+) cells. The cells that survived formed neurospheres and 89% of these neurospheres were tripotential, generating neurons, astrocytes, and oligodendrocytes. Without this enrichment step, less than 50% of the NPs were Nestin(+)/SOX-2(+) and 42% of the neurospheres were tripotential. In addition, neurospheres enriched using this procedure produced 3-times more secondary neurospheres, supporting the conclusion that this procedure enriches for NSCs. A number of genes that enhance survival were more highly expressed in neurospheres compared to late oligodendrocyte progenitors. Altogether, these studies demonstrate that primitive neural precursors can be enriched using a relatively simple and inexpensive means that will facilitate cell replacement strategies using stem cells as well as other studies whose goal is to reveal the fundamental properties of primitive neural precursors.

Vulnerability of fourth ventricle choroid plexus in sudden unexplained fetal and infant death syndromes related to smoking mothers

The human choroid plexuses in the ventricular system represent the main source of cerebrospinal fluid secretion and constitute a major barrier interface that controls the brain's environment. The present study focused on the choroid plexus of the fourth ventricle, the main cavity of the brainstem containing important nuclei and/or structures mediating autonomic vital functions. In serial sections of 84 brainstems of subjects aged from 17 gestational weeks to 8 postnatal months of life, the deaths due to both known and unknown causes, we examined the cytoarchitecture and the developmental steps of the fourth ventricle choroid plexus to determine whether this structure shows morphological and/or functional alterations in unexplained perinatal deaths (Sudden Infant Death Syndrome and Sudden Intrauterine Unexplained Death Syndrome). High incidence of histological and immunohistochemical alterations (prevalence of epithelial dark cells, the presence of cystic cells in the stroma, decreased number of blood capillaries, hyperexpression of Substance P and apoptosis) were prevalently observed in unexplained death victims (p<0.05 vs. controls). A significant correlation was found between maternal smoking in pregnancy and choroidal neuropathological parameters (p<0.01). This work underscores the negative effects of prenatal exposure to nicotine on the development of the autonomic nervous system, and in particular of the fourth ventricle choroid plexus that is a very vulnerable structure in the developing CSF-brain system.

Expression of the Nrf2-system at the blood-CSF barrier is modulated by neonatal inflammation and hypoxia-ischemia

Transcription factor NF-E2-related factor-2 (Nrf2) is a key regulator of endogenous anti-oxidant systems shown to play a neuroprotective role in the adult by preserving blood-brain barrier function. The choroid plexus, site for the blood-CSF barrier, has been suggested to be particularly important in maintaining brain barrier function in development. We investigated the expression of Nrf2- and detoxification-system genes in choroid plexus following systemic LPS injections, unilateral cerebral hypoxia-ischemia (HI) as well as the combination of LPS and HI (LPS/HI). Plexuses were collected at different time points after LPS, HI and LPS/HI in 9-day old mice. mRNA levels of Nrf2 and many of its target genes were analyzed by quantitative PCR. Cell death was analyzed by caspase-3 immunostaining and TUNEL. LPS caused down-regulation of the Nrf2-system genes while HI increased expression at earlier time points. LPS exposure prior to HI prevented many of the HI-induced gene increases. None of the insults resulted in any apparent cell death to choroidal epithelium. These data imply that the function of the inducible anti-oxidant system in the choroid plexus is down-regulated by inflammation, even if choroid cells are not structurally damaged. Further, LPS prevented the endogenous antioxidant response following HI, suggesting the possibility that the choroid plexus may be at risk if LPS is united with an insult that increases oxidative stress such as hypoxia-ischemia.

Effect of cerebral hypothermia and asphyxia on the subventricular zone and white matter tracts in preterm fetal sheep

Prolonged, moderate cerebral hypothermia is consistently neuroprotective after experimental hypoxia-ischemia. We have previously shown that hypothermia is also protective after profound asphyxia in the preterm brain. However, there is a concern whether hypothermia could suppress the proliferative response to injury in the white matter or subventricular zone (SVZ). Preterm (0.7 gestation) fetal sheep received complete umbilical cord occlusion for 25 min followed by cerebral hypothermia (extradural temperature reduced from 39.4±0.3 to 29.5±2.6°C) from 90 min to 70h after the end of occlusion or sham cooling. Occlusion-normothermia was associated with no effect on CNPase+ cells, but loss of O4+ oligodendrocytes, induction of cleaved caspase-3, and IB4+ microglia in the gyral and periventricular white matter compared to sham-occlusion (p < 0.05), with a significant increase in KI67+ cells in the periventricular white matter (p < 0.05). Hypothermia was associated with significant protection of O4+ cells, with suppression of IB4+ microglia and KI67+ cells in the periventricular white matter. There was no significant change in astrocytes, microglia, KI67+, or caspase-3+ cells in the SVZ after asphyxia. In conclusion, this study provides strong support for the selective vulnerability of immature oligodendrocytes to a highly relevant insult in the fetal sheep. Although white matter protection with cerebral hypothermia was associated with reduced proliferation in the white matter tracts, it did not impair proliferation in the SVZ.

Ependymal alterations in sudden intrauterine unexplained death and sudden infant death syndrome: possible primary consequence of prenatal exposure to cigarette smoking

Background

The ependyma, the lining providing a protective barrier and filtration system separating brain parenchyma from cerebrospinal fluid, is still inadequately understood in humans. In this study we aimed to define, by morphological and immunohistochemical methods, the sequence of developmental steps of the human ependyma in the brainstem (ventricular ependyma) and thoracic spinal cord (central canal ependyma) of a large sample of fetal and infant death victims, aged from 17 gestational weeks to 8 postnatal months. Additionally, we investigated a possible link between alterations of this structure, sudden unexplained fetal and infant death and maternal smoking.

Results

Our results demonstrate that in early fetal life the human ependyma shows a pseudostratified cytoarchitecture including many tanycytes and ciliated cells together with numerous apoptotic and reactive astrocytes in the subependymal layer. The ependyma is fully differentiated, with a monolayer of uniform cells, after 32 to 34 gestational weeks. We observed a wide spectrum of ependymal pathological changes in sudden death victims, such as desquamation, clusters of ependymal cells in the subventricular zone, radial glial cells, and the unusual presence of neurons within and over the ependymal lining. These alterations were significantly related to maternal smoking in pregnancy.

Conclusions

We conclude that in smoking mothers, nicotine and its derivatives easily reach the cerebrospinal fluid in the fetus, immediately causing ependymal damage. Consequently, we suggest that the ependyma should be examined in-depth first in victims of sudden fetal or infant death with mothers who smoke.

Ischemia induced neural stem cell proliferation and differentiation in neonatal rat involved vascular endothelial growth factor and transforming growth factor-beta pathways

Brain ischemia is a leading cause of mortality and morbidity in premature infants. Knowing the fate of neural stem cells in the subventricular zone (SVZ) after ischemia and the mechanisms that determine this fate would be useful in manipulating neural stem cell proliferation and differentiation and possibly in reversing ischemic damage. We sought to identify the genes involved in the proliferation and differentiation of neural stem cells after exposure to ischemia in a 3-day-old rat model that approximates ischemia in premature infants. Proliferating cells were labeled by bromodeoxyuridine (BrdU) through intraperitoneal injection. Using immunfluorescence assays, we observed the proliferation and differentiation of neural stem cells. Genes were identified with GeneChip and real-time quantitative polymerase chain reaction analysis. Ischemic rats had more BrdU-positive cells in the SVZ at all four time points and more neural stem cells differentiation into neurons, astrocytes, and oligodendrocytes. GeneChip analysis showed a 3- to 10-fold increase in the mRNA expression of vascular endothelial growth factor, transforming growth factor-beta, and their receptors in the SVZ. PCR assays and Western blot analyses confirmed these results, indicating that vascular endothelial growth factor and transforming growth factor-beta might be two of the factors that involve post-ischemic neural stem cell proliferation and differentiation.

Minocycline reduces neuronal death and attenuates microglial response after pediatric asphyxial cardiac arrest

The mechanisms leading to delayed neuronal death after asphyxial cardiac arrest (ACA) in the developing brain are unknown. This study aimed at investigating the possible role of microglial activation in neuronal death in developing brain after ACA. Postnatal day-17 rats were subjected to 9 mins of ACA followed by resuscitation. Rats were randomized to treatment with minocycline, (90 mg/kg, intraperitoneally (i.p.)) or vehicle (saline, i.p.) at 1 h after return of spontaneous circulation. Thereafter, minocycline (22.5 mg/kg, i.p.) was administrated every 12 h until sacrifice. Microglial activation (evaluated by immunohistochemistry using ionized calcium-binding adapter molecule-1 (Iba1) antibody) coincided with DNA fragmentation and neurodegeneration in CA1 hippocampus and cortex (assessed by deoxynucleotidyltransferase-mediated dUTP nick-end labeling (TUNEL), Fluoro-Jade-B and Nissl stain). Minocycline significantly decreased both the microglial response and neuronal degeneration compared with the vehicle. Asphyxial CA significantly enhanced proinflammatory cytokine and chemokine levels in hippocampus versus control (assessed by multiplex bead array assay), specifically tumor necrosis factor-alpha (TNF-alpha), macrophage inflammatory protein-1alpha (MIP-1alpha), regulated upon activation, normal T-cell expressed and secreted (RANTES), and growth-related oncogene (GRO-KC) (P<0.05). Minocycline attenuated ACA-induced increases in MIP-1alpha and RANTES (P<0.05). These data show that microglial activation and cytokine production are increased in immature brain after ACA. The beneficial effect of minocycline suggests an important role for microglia in selective neuronal death after pediatric ACA, and a possible therapeutic target.

Basic fibroblast growth factor stimulates the proliferation and differentiation of neural stem cells in neonatal rats after ischemic brain injury

A little is known about the proliferation and fate of neural stem cells in the subventricular zone (SVZ) after cerebral ischemia. However, how endogenous neural stem cells are activated in the premature brain is not clear, although basic fibroblast growth factor (bFGF) is important in neurogenesis. To investigate the effect of bFGF on the proliferation and differentiation of neural stem cells after brain ischemia, we observed cellular changes in the subventricular zone (SVZ) of 3-day-old rats (approximately equivalent to premature infants) using immunofluorescence assays, Western blot analysis, and real-time quantitative PCR methods. The bilateral common carotid artery (BCCA) was occluded in 108 animals, then half received bFGF 10ng/g. Besides, 54 rats without ischemia as normal control. Proliferating cells were labeled by bromodeoxyuridine (BrdU) through intraperitoneal injection in a pulsed or a cumulative protocol. Rats were killed at 4, 7, and 14 days after ischemic injury. The number of proliferating cells in the SVZ in bFGF-treated rats was higher than that in untreated rats; bFGF also promoted neural stem cell differentiation into neurons, astrocytes, and oligodendrocytes. Western blot analysis and real-time quantitative PCR assays confirmed these results. We suggest that bFGF promotes the repair of ischemia brain injury through increasing the proliferation of neural stem cells and their differentiation into neurons, astrocytes, and oligodendrocytes.

Vascular endothelial growth factor and nitric oxide production in response to hypoxia in the choroid plexus in neonatal brain

Damage to the choroid plexus in 1-day-old Wistar rats subjected to hypoxia was investigated. The mRNA and protein expression of hypoxia-inducible factor-1alpha (HIF-1alpha), endothelial, neuronal, inducible nitric oxide synthase (eNOS, nNOS, iNOS), and vascular endothelial growth factor (VEGF) along with nitric oxide (NO) production and VEGF concentration was up-regulated significantly in hypoxic rats. Ultrastructurally, the choroid plexus epithelial cells showed massive accumulation of glycogen. A striking feature was the extrusion of cytoplasmic fragments from the apical cell surfaces into the ventricular lumen following the hypoxic insult. Intraventricular macrophages showed increased expression of complement type 3 receptors, major histocompatibility complex class I and II antigens, and ED1 antigens. Following an intravenous injection of horseradish peroxidase (HRP), a large number of intraventricular macrophages were labeled suggesting enhanced leakage of the tracer from the blood vessels in the choroid plexus connective tissue stroma into the ventricular lumen. We suggest that increased production of NO in hypoxia is linked to the structural alteration of the choroid plexus, and along with VEGF, may lead to increased vascular permeability. Melatonin treatment reduced VEGF and NO levels as well as leakage of HRP suggesting its potential value in ameliorating damage in choroid plexus pathologies.

Perinatal hypoxic/ischemic brain injury induces persistent production of striatal neurons from subventricular zone progenitors

Ischemia-induced production of new striatal neurons in young and adult rodents has been studied. However, it is unclear whether neonatal hypoxic/ischemic (H/I) brain injury-induced neuronogenesis in the striatum is transient or sustained, nor has it been established whether these new neurons arise from progenitors within the striatum or from precursors residing in the adjacent subventricular zone. Here, we report that from 2 weeks to 5 months after H/I there are more doublecortin-positive (Dcx+) cells and Dcx+/NeuN+ cells in the damaged striatum compared to the contralateral striatum. After the S-phase marker 5-bromo-2'-deoxyuridine (BrdU) was injected at both short and long intervals (2 days and 2 months) after H/I to label newly born cells, more BrdU+/Dcx+ and BrdU+/NeuN+ cells were observed in the ipsilateral striatum compared to the contralateral striatum. Retroviral fate-mapping studies demonstrated that these newly born striatal neurons are generated from precursors within the subventricular zone. Altogether, these observations indicate the neonatal brain initiates a prolonged regenerative response from the precursors of the subventricular zone (SVZ) that results in persistent production of new striatal neurons.

Differential activation of microglia in neurogenic versus non-neurogenic regions of the forebrain

Proliferation decreases in the neurogenic subventricular zone (SVZ) of mice after aspiration lesions of the cerebral cortex. We hypothesized that microglial activation may contribute to this given microglial activation attenuates neurogenesis in the hippocampus. Using CD45, CD11b, IB4, and IL-6 immunohistochemistry (IHC), BrdU IHC, and fluorescent bead tracking of peripheral monocytes into the brain, we compared microglial activation in the SVZ to non-neurogenic forebrain regions. SVZ microglia exhibited greater constitutive activation and proliferation than did microglia in non-neurogenic regions. In contrast to the SVZ, the dentate gyrus (DG) contained relatively few CD45(+) cells. After aspiration cerebral cortex lesions, microglia became activated in the cerebral cortex, corpus callosum, and striatum. SVZ microglial activation did not increase, and similarly, microglia in the DG were less activated after injury than in adjacent non-neurogenic regions. We next showed that SVZ microglia are not categorically refractory to activation, since deep cortical contusion injuries increased SVZ microglial activation. Macrophages migrate into the brain during development, but it is unclear if this is recapitulated after injury. Infiltration of microbead-labeled macrophages into the brain did not change after injury, but resident SVZ microglia were induced to migrate toward the injury. Our data show that both constitutive and postlesion levels of microglial activation differ between neurogenic and non-neurogenic regions.

Cell death, caspase activation, and HMGB1 release of porcine choroid plexus epithelial cells during Streptococcus suis infection in vitro

The choroid plexus epithelium constitutes the structural basis of the blood-cerebrospinal fluid barrier. We previously demonstrated that Streptococcus suis (S. suis), a relevant cause of bacterial meningitis in pigs and humans, affects porcine choroid plexus epithelial cell (PCPEC) barrier function and integrity. We now characterized PCPEC cell death and investigated whether apoptosis or necrosis is responsible for the cytotoxicity after infection with different S. suis isolates. We found S. suis strain-dependent histone associated DNA-fragments quantified by ELISA. This response could partially be inhibited by cylcoheximide, cytochalasin D, dexamethasone, herbimycin A, but most effectively by the pan-caspase inhibitor zVAD-fmk. We further detected caspase-3 and -9 activation after infection with all tested S. suis isolates that could also be blocked by zVAD-fmk. However, we found a significantly stronger caspase activity with the protein kinase inhibitor staurosporine. All tested S. suis isolates induced loss of cell viability in PCPEC as shown with the Live/Dead assay, but strain dependent lactate dehydrogenase-release. Both parameters could not be influenced by zVAD-fmk. Immunostaining showed release of high-mobility group box 1 (HMGB1) protein from the nucleus, indicative of necrosis. Transmission electron microscopy showed cell swelling, cytoplasmic vacuolization, loss of membrane integrity, nuclear fermentation but no nuclear condensation, indices for a primarily necrotic cell morphology. Taken together, our findings indicate that S. suis causes cell death in PCPEC by different mechanisms. Although apoptosis may be involved in the process of PCPEC cell death, necrosis seems to be the predominant mechanism. Through inflammation in the choroid plexus during bacterial meningitis, the blood-cerebrospinal fluid barrier function will be compromised.

Gray matter oligodendrocyte progenitors and neurons die caspase-3 mediated deaths subsequent to mild perinatal hypoxic/ischemic insults

With significant improvements in neonatal care, fewer infants sustain severe injury as a consequence of hypoxia/ischemia (H/I). However, the majority of experimental studies have inflicted moderate to severe injuries, or they have assessed damage to the caudal forebrain; therefore, to better understand how a mild H/I episode affects the structures and cells of the rostral forebrain, we assessed the relative vulnerabilities of cells in the neocortex, striatum, corpus callosum, choroid plexus and subventricular zone (SVZ). To inflict mild H/I injury, the right common carotid artery was ligated followed by 1 h of hypoxia (8% O(2)) at 37 degrees C. Regional vulnerabilities were assessed using TUNEL, active caspase-3 and hematoxylin and eosin staining at 24 and 48 h of recovery. Scattered columns of cell death were observed in the neocortex with deep-layer neurons more vulnerable than more superficial neurons. The majority of these dying neurons appeared to be dying apoptotic rather than necrotic deaths. In addition, approximately 1/3 of the apoptotic cells in the neocortex were O4+ oligodendrocyte progenitors. We also observed a decrease in NG2 staining within the affected regions of the forebrain. By contrast, active caspase-3+/S-100beta+ astrocytes were not observed. Neurons and O4+ oligodendrocyte progenitors also died apoptotic deaths within the striatum. The lining cells of the choroid plexus also sustained damage. Elevated numbers of apoptotic cells were observed in the most lateral region of the SVZ and some of these dying cells were O4+. The most novel finding of this study, that oligodendrocyte progenitors in the gray matter are damaged and eliminated as a consequence of perinatal H/I, provides new insights into the histopathology and neurological deficits observed in infants who sustain mild H/I brain injuries.

Perinatal hypoxia/ischemia damages and depletes progenitors from the mouse subventricular zone

Hypoxia-ischemia (H/I) as a result of asphyxia at term remains a major cause of neurologic disability. Our previous studies in the P7 rat model of perinatal H/I have shown that progenitors within the subventricular zone (SVZ) are vulnerable to this insult. Since many investigators are using transgenic and knockout mice to determine the importance of specific molecules in the evolution of damage after a stroke, there is a need to perform comparative studies on the relative vulnerability of the mouse SVZ. Here we assess damage to the SVZ of 5-, 7- and 10-day-old C57BL/6 mice after unilateral common carotid artery cauterization followed by 70 min of H/I (10% O2). Whereas 5- and 7-day-old mice sustained little SVZ damage as assessed by hematoxylin and eosin staining, there was a 16% reduction of cellularity in 10-day-old animals by 18 h of recovery. Additionally, swollen cells were observed in the medial region of the SVZ of 10-day-old mice. However, few caspase-3+ and TUNEL+ cells were observed in this region, which contains the putative neural stem cells. Rather, the majority of the dying cells were situated in the mediolateral and lateral tail of the SVZ. At 18 h of recovery, there was a 2-fold increase in the frequency of TUNEL+ cells in the ipsilateral SVZ as well as a 3-fold increase in the frequency of active-caspase-3+ cells. We conclude that progenitors within the neonatal mouse SVZ are vulnerable to hypoxic/ischemic insult. The demise of these early progenitors likely leads to depletion of neuronal and late oligodendrocyte progenitors, contributing to cerebral dysgenesis.

Glutamate enhances survival and proliferation of neural progenitors derived from the subventricular zone

Extracellular glutamate levels increase as a consequence of perinatal hypoxia/ischemia, causing the death of neurons and oligodendrocytes. Precursors in the subventricular zone (SVZ) also die following perinatal hypoxia/ischemia; therefore we hypothesized that glutamate would stimulate the death of neural precursors. Here we demonstrate using calcium imaging that SVZ derived neural stem/progenitor cells respond to both ionotropic and metabotropic excitatory amino acids. Therefore, we tested the effects of high levels of glutamate receptor agonists on the proliferation, survival, and differentiation of SVZ derived neural stem/progenitor cells in vitro. We show that high levels of glutamate, up to 1 mM, are not toxic to neural precursor cultures. In fact, stimulation of either the kainate receptor or group 2 metabotropic glutamate receptors (group 2 mGluR) reduces basal levels of apoptosis and increases neural precursor proliferation. Furthermore, group 2 mGluR activation expands the number of multipotent progenitor cells present in these cultures while maintaining equivalent mature cell production. We conclude that the glutamate released following perinatal hypoxia/ischemia may act to acutely promote the proliferation of multipotent precursors in the subventricular zone.

Neural stem cells in the subventricular zone are resilient to hypoxia/ischemia whereas progenitors are vulnerable

Perinatal hypoxic-ischemic (H/I) brain injury remains a major cause of neurologic disability. Because we have previously demonstrated that this insult depletes cells from the subventricular zone (SVZ), the goal of the present investigation was to compare the relative vulnerability to H/I of neural stem cells versus progenitors. The dorsolateral SVZs of P6 rats were examined at 2 to 48 hours of recovery from H/I using hematoxylin and eosin, in situ end labeling (ISEL), terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick end labeling (TUNEL), electron microscopy, and immunofluorescence. Pyknotic nuclei and ISEL cells were observed by 4 hours of recovery, peaked at 12 hours, and persisted for at least 48 hours. Many active-caspase-3 cells were observed at 12 hours and they comprised one third of the total TUNEL population. Electron microscopy revealed that hybrid cell deaths predominated at 12 hours of recovery. Importantly, few dying cells were observed in the medial SVZ, where putative stem cells reside, and no nestin medial SVZ cells showed caspase-3 activation. By contrast, active-caspase-3/PSA-NCAM progenitors were prominent in the lateral SVZ. These data demonstrate that early progenitors are vulnerable to H/I, whereas neural stem cells are resilient. The demise of these early progenitors may lead to the depletion of neuronal and late oligodendrocyte progenitors, contributing to cerebral dysgenesis after perinatal insults.

Roles of the mammalian subventricular zone in brain development

There has been enormous progress in uncovering the contributions of the subventricular zone (SVZ) to the developing brain. Here, we review the roles of four anatomically defined embryologic divisions of the SVZ of the mammalian brain: the lateral ganglionic eminence (LGE), the medial ganglionic eminence (MGE), the caudal ganglionic eminence (CGE), and the fetal neocortical SVZ (SVZn), as well as the roles of the two major anatomically defined regions of the postnatal SVZ, the anterior SVZ (SVZa) and the dorsolateral SVZ (SVZdl). We describe the types of cells within each subdivision of the SVZ, the types of brain cells that they generate during embryonic, fetal, and perinatal development, and when known the mechanisms that regulate their differentiation. This review provides a critical analysis of the literature, from which current and future studies on the SVZ can be formulated and evaluated.