Vulnerability of premyelinating oligodendrocytes to white-matter damage in neonatal brain injury

Developmental Toxicity of Fine Particulate Matter: Multifaceted Exploration from Epidemiological and Laboratory Perspectives

Particulate matter of size ≤ 2.5 μm (PM2.5) is a critical environmental threat that considerably contributes to the global disease burden. However, accompanied by the rapid research progress in this field, the existing research on developmental toxicity is still constrained by limited data sources, varying quality, and insufficient in-depth mechanistic analysis. This review includes the currently available epidemiological and laboratory evidence and comprehensively characterizes the adverse effects of PM2.5 on developing individuals in different regions and various pollution sources. In addition, this review explores the effect of PM2.5 exposure to individuals of different ethnicities, genders, and socioeconomic levels on adverse birth outcomes and cardiopulmonary and neurological development. Furthermore, the molecular mechanisms involved in the adverse health effects of PM2.5 primarily encompass transcriptional and translational regulation, oxidative stress, inflammatory response, and epigenetic modulation. The primary findings and novel perspectives regarding the association between public health and PM2.5 were examined, highlighting the need for future studies to explore its sources, composition, and sex-specific effects. Additionally, further research is required to delve deeper into the more intricate underlying mechanisms to effectively prevent or mitigate the harmful effects of air pollution on human health.

Impaired glymphatic system revealed by DTI-ALPS in cerebral palsy due to periventricular leukomalacia: relation with brain lesion burden and hand dysfunction

PURPOSE

Preterm children with cerebral palsy (CP) often have varying hand dysfunction, while the specific brain injury with periventricular leukomalacia (PVL) cannot quite explain its mechanism. We aimed to investigate glymphatic activity using diffusion tensor image analysis along the perivascular space (DTI-ALPS) method and evaluate its association with brain lesion burden and hand dysfunction in children with CP secondary to PVL.

METHODS

We retrospectively enrolled 18 children with bilateral spastic CP due to PVL and 29 age- and sex-matched typically developing controls. The Manual Ability Classification System (MACS) was used to assess severity of hand dysfunction in CP. A mediation model was performed to explore the relationship among the DTI-ALPS index, brain lesion burden, and the MACS level in children with CP.

RESULTS

There were significant differences in the DTI-ALPS index between children with CP and their typically developing peers. The DTI-ALPS index of the children with CP was lower than that of the controls (1.448 vs. 1.625, P = 0.003). The mediation analysis showed that the DTI-ALPS index fully mediated the relationship between brain lesion burden and the MACS level (c' = 0.061, P = 0.665), explaining 80% of the effect.

CONCLUSION

This study provides new insights into the neural basis of hand dysfunction in children with CP, demonstrating an important role of glymphatic impairment in such patients. These results suggest that PVL might affect hand function in children with CP by disrupting glymphatic drainage.

Dynamic changes of oligodendrogenesis in neonatal rats with hypoxic-ischemic white matter injury

BACKGROUND

White matter injury (WMI) is an important type of preterm brain injury, which may result in severe neurological sequelae and lack of effective treatments. It is ascertained that selective vulnerability of oligodendrocytes is closely related to the WMI in preterm infants. But the alteration of the endogenous oligodendrogenesis over long time after hypoxic-ischemic WMI is still not clearly elucidated.

METHODS

We adopted an animal model of hypoxic-ischemic WMI in 3-day-old neonatal Sprague-Dawley rats. Immunofluorescence staining and western blotting were used to detect dynamic changes of oligodendrogenesis in the white matter region on postoperative day (POD) 1, 3, 7, 14, 28, 56 and 84.

RESULTS

In the sham group, the oligodendrocyte lineage in the white matter reached a developmental peak from POD 3 to 14. The proliferation and development of oligodendrocyte precursor cells (OPCs) occurred primarily within POD 14. The number of mature oligodendrocytes showed an upward trend and a dynamic change in proliferation over time. While in the WMI group, the oligodendrocyte lineage was upregulated on POD1 and 3 but downregulated on POD 7 and 14. The proliferation of OPCs increased on POD 1 and decreased on POD 3 and 7, with the total number of OPCs significantly reduced from POD 3 to 14. The number of mature oligodendrocytes decreased from POD 3 to 28, and return to the level of the sham group on POD 56 and 84, whereas the MBP expression was still significantly downregulated on POD 56 and 84.

CONCLUSIONS

Hypoxia-ischemia can have a long-term dynamic effect on the endogenous oligodendrogenesis of neonatal rat brain white matter. The proliferation of OPCs was promoted on POD 1 but inhibited from POD 3 to 14, which may be an early intervention target to improve oligodendrogenesis. The number of mature oligodendrocytes recover to the normal on POD 56 and 84 but the myelination is still blocked, which suggests it is essential to promote the maturation of oligodendrocyte and its function recovery at the same time within POD 28. Such efforts will provide the opportunity to test new interventions in pre-clinical studies for their promising clinical application.

Activin A rescues preterm brain injury through a novel Noggin/BMP4/Id2 signaling pathway

Activin A (Act A) has been reported to promote oligodendrocyte progenitor cell (OPC) differentiation in vitro and improve neurological outcomes in adult mice. However, the roles and mechanisms of action of Act A in preterm brain injury are unknown. In the present study, P5 rats were subjected to hypoxia‑ischemia to establish a neonatal white matter injury (WMI) model and Act A was injected via the lateral ventricle. Pathological characteristics, OPC differentiation, myelination, and neurological performance were analyzed. Further, the involvement of the Noggin/BMP4/Id2 signaling pathway in the roles of Act A in WMI was explored. Act A attenuated pathological damage, promoted OPC differentiation, enhanced myelin sheath and myelinated axon formation, and improved neurological performance of WMI rats. Moreover, Act A enhanced noggin expression, which, in turn, inhibited the expression of bone morphogenetic protein 4 (BMP4) and inhibitor of DNA binding 2 (Id2). Furthermore, upregulation of Id2 completely abolished the rescue effects of Act A in WMI rats. In conclusion, the present findings suggested that Act A rescues preterm brain injury via targeting a novel Noggin/BMP4/Id2 signaling pathway.

MicroRNA-21-5p agomir inhibits apoptosis of oligodendrocyte precursor cell and attenuates white matter injury in neonatal rats

BACKGROUND AND RESEARCH QUESTION/HYPOTHESIS

Excessive oligodendrocyte precursor cell (OPC) apoptosis occurs during intrauterine infection-induced white matter injury (WMI) in premature infants, preventing excessive apoptosis of OPCs is one of the mechanisms protecting WMI. Micro-RNA-21-5p (miR-21-5p) mediating anti-apoptotic activity was observed in other diseases. Therefore, the aim of this study was to determine whether miR-21-5p protects against WMI by modulating phosphatase and tensin homolog deleted on chromosome 10/phosphatidylinositol-3-kinase/protein kinase B (PTEN/PI3K/Akt) signaling pathway.

METHODS

A lipopolysaccharide (LPS)-induced neonatal Sprague-Dawley (SD) rat model of preterm WMI was established. To explore the effect of miR-21-5p on WMI, we intraventricularly injected miR-21-5p agomir and miR-21-5p antagomir to activate or inhibit endogenous miR-21-5p. Immunofluorescent labelling of myelin basic protein, immunohistochemical labelling of 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNPase), and terminal deoxynucleotidyl transferase dUTP nick end labelling assays were conducted to observe pathological white matter changes. The antibody of anti-oligodendrocyte marker 4 (O4) was used to specifically recognise OPCs. The expressions of miR-21-5p and PTEN mRNA in the brain were detected with quantitative real-time polymerase chain reaction (qRT-PCR). PTEN, Akt, and phosphorylated Akt (p-Akt) protein levels were assayed with western blotting, and apoptotic proteins associated with PI3K/Akt signalling were quantified.

RESULTS

Intense white matter dysplasia and excessive OPC apoptosis were observed in the brains of rats with WMI. When the miR-21-5p agonist miR-21-5p agomir was used in the WMI group, apoptosis of OPCs was significantly reduced, and myelin maturation increased. MiR-21-5p agomir relieved WMI. MiR-21-5p agomir inhibited the mRNA and protein expression of PTEN, increased p-Akt phosphorylation, and decreased the expression and activation of related apoptotic proteins.On the other hand, the administration of miR-21-5p specific blocker, miR-21-5p antagomir, reduced the level of p-AKT, increased OPC apoptosis, and worsened WMI.

INTERPRETATION

Our findings revealed that miR-21-5p agomir had anti-OPC over-apoptotic effects and enhanced myelin development in WMI by modulating the PTEN/Akt signaling pathway.

DATA AVAILABILITY STATEMENT

The datasets used and or/analysed in the current study are available from the corresponding author on reasonable request.

Dynamic Changes in Brain Iron Metabolism in Neonatal Rats after Hypoxia-Ischemia

OBJECTIVES

The pathogenesis of hypoxic-ischemic white matter injury (WMI) in premature infants is still unclear, and the imbalance of cerebral iron metabolism may play an important role. Our study set out to investigate the changes in iron distribution, iron content and malondialdehyde (MDA) in disparate brain regions (parietal cortex, corpus callosum, hippocampus) within 84 days after hypoxia-ischemia (HI) in neonatal rats and to clarify the role of iron metabolism in WMI.

MATERIALS AND METHODS

We adopted a rat model of hypoxic-ischemic WMI. Alterations in iron metabolism were detected by iron staining and iron assay kits, and the degree of brain injury was determined by MDA assays.

RESULTS

Our results showed that different degrees of brain iron deposition occurred within 28 days after HI, and iron staining was the most obvious 3 days after HI. The iron content increased remarkably at 1-7 d after HI in the mixed tissues, especially at 3 d after HI. While the iron content in the parietal cortex and corpus callosum elevated obviously 14 days after HI. And the change trend of MDA was almost consistent with that of the iron content.

CONCLUSIONS

Our findings revealed that brain iron metabolism changed dynamically in 3-day-old neonatal rats suffering from HI, which may cause lipid peroxidation damage to brain tissues. This process may be one of the pathogeneses of hypoxic-ischemic WMI.

Oligodendrocyte Development and Implication in Perinatal White Matter Injury

Perinatal white matter injury (WMI) is the most common brain injury in premature infants and can lead to life-long neurological deficits such as cerebral palsy. Preterm birth is typically accompanied by inflammation and hypoxic-ischemic events. Such perinatal insults negatively impact maturation of oligodendrocytes (OLs) and cause myelination failure. At present, no treatment options are clinically available to prevent or cure WMI. Given that arrested OL maturation plays a central role in the etiology of perinatal WMI, an increased interest has emerged regarding the functional restoration of these cells as potential therapeutic strategy. Cell transplantation and promoting endogenous oligodendrocyte function are two potential options to address this major unmet need. In this review, we highlight the underlying pathophysiology of WMI with a specific focus on OL biology and their implication for the development of new therapeutic targets.

The Effect of Intraventricular Hemorrhage on Brain Development in Premature Infants: A Synthetic MRI Study

Objectives: Synthetic MRI can obtain multiple parameters in one scan, including T1 and T2 relaxation time, proton density (PD), brain volume, etc. This study aimed to investigate the parameter values T1 and T2 relaxation time, PD, and volume characteristics of intraventricular hemorrhage (IVH) newborn brain, and the ability of synthetic MRI parameters T1 and T2 relaxation time and PD to diagnose IVH.

Materials and methods: The study included 50 premature babies scanned with conventional and synthetic MRI. Premature infants were allocated to the case group (n = 15) and NON IVH (n = 35). The T1, T2, PD values, and brain volume were obtained by synthetic MRI. Then we assessed the impact of IVH on these parameters.

Results: In the posterior limbs of the internal capsule (PLIC), genu of the corpus callosum (GCC), central white matter (CWM), frontal white matter (FWM), and cerebellum (each p < 0.05), the T1 and T2 relaxation times of the IVH group were significantly prolonged. There were significant differences also in PD. The brain volume in many parts were also significantly reduced, which was best illustrated in gray matter (GM), cerebrospinal fluid and intracranial volume, and brain parenchymal fraction (BPF) (each p < 0.001, t = −5.232 to 4.596). The differential diagnosis ability of these quantitative values was found to be excellent in PLIC, CWM, and cerebellum (AUC 0.700–0.837, p < 0.05).

Conclusion: The quantitative parameters of synthetic MRI show well the brain tissue characteristic values and brain volume changes of IVH premature infants. T1 and T2 relaxation times and PD contribute to the diagnosis and evaluation of IVH.

Olig2 knockdown alleviates hypoxic-ischemic brain damage in newborn rats

OBJECTIVES

Neuronal damage is an important pathological mechanism in neonatal hypoxic-ischemic brain damage (HIBD). We found in our previous studies that oligodendrocyte transcription factor 2 (Olig2) downregulation was able to increase cell survival in the brain. However, the specific mechanism has yet to be clarified.

METHODS

Sprague-Dawley rats aged 3 d were randomly divided into three groups: the normal control group, the Olig2-RNAi group, and the RNAi-negative control group. The normal control group received no treatment, the Olig2-RNAi group received the Olig2 RNAi adenovirus, and the RNAi-negative control group was given the control adenovirus after the completion of the HIBD model. Infarct lesions and their volumes were observed by triphenyltetrazolium chloride (TTC) staining 3 d after the completion of the adenovirus local injection. The condition of the tissue was characterized by hematoxylin-eosin staining 7 d after the model was established, and cell viability was determined by azure methylene blue staining. Subcellular damage was analyzed by transmission electron microscopy. Rotarod analysis was performed to detect moving behavior ability and an MWM assay was conducted to evaluate the memory.

RESULTS

TTC staining showed a smaller brain injury area in the Olig2-RNAi group than in the RNAi-negative control group. Hematoxylin-eosin staining indicated the presence of severe cell injury in the hippocampal region after HIBD, which improved after Olig2 knockdown. Azure methylene blue staining and electron microscopy results suggested that the cells improved after Olig2 knockdown. The rats stayed longer on the rotating rod, and their latency in the water maze test was gradually shortened relative to that of the rats in the Olig2-RNAi negative control group.

CONCLUSION

Olig2 knockdown can promote the repair of hypoxic-ischemic brain damage in newborn rats.

GluA2 overexpression in oligodendrocyte progenitors promotes postinjury oligodendrocyte regeneration

Oligodendrocyte precursor cells (OPCs) are essential for developmental myelination and oligodendrocyte regeneration after CNS injury. These progenitors express calcium-permeable AMPA receptors (AMPARs) and form direct synapses with neurons throughout the CNS, but the roles of this signaling are unclear. To enable selective alteration of the properties of AMPARs in oligodendroglia, we generate mice that allow cell-specific overexpression of EGFP-GluA2 in vivo. In healthy conditions, OPC-specific GluA2 overexpression significantly increase their proliferation in an age-dependent manner but did not alter their rate of differentiation into oligodendrocytes. In contrast, after demyelinating brain injury in neonates or adults, higher GluA2 levels promote both OPC proliferation and oligodendrocyte regeneration, but do not prevent injury-induced initial cell loss. These findings indicate that AMPAR GluA2 content regulates the proliferative and regenerative behavior of adult OPCs, serving as a putative target for better myelin repair.

Microstructure of the Dorsal Anterior Cingulum Bundle in Very Preterm Neonates Predicts the Preterm Behavioral Phenotype at 5 Years of Age

BACKGROUND

The cingulum bundle (CB), specifically the dorsal anterior portion of the CB, plays an important role in psychiatric illnesses; however, its role during early development is unclear. This study investigated whether neonatal white matter microstructure in the CB and its subregions is associated with subsequent preterm behavioral phenotype symptoms (internalizing, inattention, and social deficits) in very preterm (VPT) children.

METHODS

Diffusion magnetic resonance imaging data were obtained on a 3T scanner in 138 sleeping nonsedated neonates: 55 full-term neonates (gestational age ≥ 36 weeks) and 83 VPT neonates (gestational age < 30 weeks). The CB was tracked using probabilistic tractography and split into anterior and posterior portions. When children were 5 years of age, parents (n = 80) and teachers (n = 63) of VPT children completed questionnaires of preterm behavioral phenotype symptoms. Linear regression models were used to relate measures of neonatal CB microstructure and childhood preterm behavioral phenotype symptoms (n = 56 parent report, n = 45 teacher report).

RESULTS

Mean diffusivity in the anterior and posterior CB was increased in VPT neonates compared with full-term neonates. Increased fractional anisotropy and decreased mean diffusivity in the right anterior CB, but not in the posterior CB, were related to increased preterm behavioral phenotype symptoms in VPT children as reported by parents and teachers.

CONCLUSIONS

Aberrations in the anterior portion of the right CB may underlie the early development of the preterm behavioral phenotype. This finding provides the foundation for future mechanistic and therapeutic investigations into the role of the anterior cingulum in the development of psychopathology in VPT infants.

Air Pollution Is Associated with Poor Cognitive Function in Taiwanese Adults

The issue of air pollution is gaining increasing attention worldwide, and mounting evidence has shown an association between air pollution and cognitive decline. The aim of this study was to investigate the relationships between air pollutants and cognitive impairment using the Mini-Mental State Exam (MMSE) and its sub-domains. In this study, we used data from the Taiwan Biobank combined with detailed daily data on air pollution. Cognitive function was assessed using the MMSE and its five subgroups of cognitive functioning. After multivariable linear regression analysis, a high level of particulate matter with an aerodynamic diameter of ≤2.5 μm (PM_2.5), low ozone (O₃), high carbon monoxide (CO), high sulfur dioxide (SO₂), high nitric oxide (NO), high nitrogen dioxide (NO₂), and high nitrogen oxide (NO_x) were significantly associated with low total MMSE scores. Further, high SO₂ and low O₃ were significantly associated with low MMSE G1 scores. Low O₃, high CO, high SO₂, high NO₂, and high NO_x were significantly associated with low MMSE G4 scores, and high PM_2.5, high particulate matter with an aerodynamic diameter of ≤10 μm (PM₁₀), high SO₂, high NO₂, and high NO_x were significantly associated with low MMSE G5 scores. Our results showed that exposure to different air pollutants may lead to general cognitive decline and impairment of specific domains of cognitive functioning, and O₃ may be a protective factor. These findings may be helpful in the development of policies regarding the regulation of air pollution.

HIFα Regulates Developmental Myelination Independent of Autocrine Wnt Signaling

The developing CNS is exposed to physiological hypoxia, under which hypoxia-inducible factor α (HIFα) is stabilized and plays a crucial role in regulating neural development. The cellular and molecular mechanisms of HIFα in developmental myelination remain incompletely understood. A previous concept proposes that HIFα regulates CNS developmental myelination by activating the autocrine Wnt/β-catenin signaling in oligodendrocyte progenitor cells (OPCs). Here, by analyzing a battery of genetic mice of both sexes, we presented in vivo evidence supporting an alternative understanding of oligodendroglial HIFα-regulated developmental myelination. At the cellular level, we found that HIFα was required for developmental myelination by transiently controlling upstream OPC differentiation but not downstream oligodendrocyte maturation and that HIFα dysregulation in OPCs but not oligodendrocytes disturbed normal developmental myelination. We demonstrated that HIFα played a minor, if any, role in regulating canonical Wnt signaling in the oligodendroglial lineage or in the CNS. At the molecular level, blocking autocrine Wnt signaling did not affect HIFα-regulated OPC differentiation and myelination. We further identified HIFα-Sox9 regulatory axis as an underlying molecular mechanism in HIFα-regulated OPC differentiation. Our findings support a concept shift in our mechanistic understanding of HIFα-regulated CNS myelination from the previous Wnt-dependent view to a Wnt-independent one and unveil a previously unappreciated HIFα-Sox9 pathway in regulating OPC differentiation.SIGNIFICANCE STATEMENT Promoting disturbed developmental myelination is a promising option in treating diffuse white matter injury, previously called periventricular leukomalacia, a major form of brain injury affecting premature infants. In the developing CNS, hypoxia-inducible factor α (HIFα) is a key regulator that adapts neural cells to physiological and pathologic hypoxic cues. The role and mechanism of HIFα in oligodendroglial myelination, which is severely disturbed in preterm infants affected with diffuse white matter injury, is incompletely understood. Our findings presented here represent a concept shift in our mechanistic understanding of HIFα-regulated developmental myelination and suggest the potential of intervening with an oligodendroglial HIFα-mediated signaling pathway to mitigate disturbed myelination in premature white matter injury.

Mental development is associated with cortical connectivity of the ventral and nonspecific thalamus of preterm newborns

INTRODUCTION

The thalamus is a key hub for regulating cortical connectivity. Dysmaturation of thalamocortical networks that accompany white matter injury has been hypothesized as neuroanatomical correlate of late life neurocognitive impairment following preterm birth. Our objective was to find a link between thalamocortical connectivity measures at term equivalent age and two-year neurodevelopmental outcome in preterm infants.

METHODS

Diffusion tensor MRI data of 58 preterm infants (postmenstrual age at birth, mean (SD), 29.71 (1.47) weeks) were used in the study. We utilized probabilistic diffusion tractography to trace connections between the cortex and thalami. Possible associations between connectivity strength, the length of the probabilistic fiber pathways, and developmental scores (Bayley Scales of Infant Development, Second Edition) were analyzed using multivariate linear regression models.

RESULTS

We found strong correlation between mental developmental index and two complementary measures of thalamocortical networks: Connectivity strength projected to a cortical skeleton and pathway length emerging from thalamic voxels (partial correlation, R = .552 and R = .535, respectively, threshold-free cluster enhancement, corrected p-value < .05), while psychomotor development was not associated with thalamocortical connectivity. Post hoc stepwise linear regression analysis revealed that parental socioeconomic scale, postmenstrual age, and the duration of mechanical ventilation at the intensive care unit contribute to the variability of outcome.

CONCLUSIONS

Our findings independently validated previous observations in preterm infants, providing additional evidence injury or dysmaturation of tracts emerging from ventral-specific and various nonspecific thalamus projecting to late-maturing cortical regions are predictive of mental, but not psychomotor developmental outcomes.

Erythropoietin Gene Polymorphism rs551238 is Associated with a Reduced Susceptibility to Brain Injury in Preterm Infants

BACKGROUND

Single Nucleotide Polymorphisms (SNPs) in the Erythropoietin (EPO) promoter region have been shown to influence EPO protein expression, and high blood levels of EPO are associated with an increased risk of brain injury in very preterm infants. Here, we investigated the genotype distributions and association of three EPO gene polymorphisms (rs1617640, rs551238, and rs507392) with the risk of brain injury in preterm infants.

METHODS

304 preterm infants with a gestational age of 28 to 34 weeks were enrolled in this study. Brain injury was evaluated by brain ultrasound and MRI examination. EPO gene Single- Nucleotide Polymorphisms (SNPs) were genotyped by the Agena MassARRAY system, and their association with brain injury susceptibility in preterm infants was analyzed.

RESULTS

EPO polymorphism rs551238 showed a significant difference in the genotypic distributions between the brain injury group and the control group, and was significantly correlated with reduced susceptibility to brain injury in preterm infants according to the results obtained from both the additive model (OR = 0.520, 95% CI: 0.339-0.799, P = 0.003) and the dominant model (OR = 0.523, 95% CI: 0.332-0.853, P = 0.009). EPO polymorphisms rs1617640 and rs507392 did not meet the Hardy-Weinberg equilibrium in the study population (P < 0.05) and were, thus, not subjected to further analysis for their impacts on brain injuries.

CONCLUSION

The "C" allele of rs551238 was correlated with a reduced risk of brain injury in preterm infants which may serve as a potential marker for brain injury prediction in preterm infants.

Experimentally Induced Sepsis Causes Extensive Hypomyelination in the Prefrontal Cortex and Hippocampus in Neonatal Rats

Neonatal sepsis is associated with cognitive deficit in the later life. Axonal myelination plays a pivotal role in neurotransmission and formation of learning and memory. This study aimed to explore if systemic lipopolysaccharide (LPS) injection would induce hypomyelination in the prefrontal cortex and hippocampus in developing septic neonatal rats. Sprague-Dawley rats (1-day old) were injected with LPS (1 mg/kg) intraperitoneally. By electron microscopy, axonal hypomyelination was evident in the subcortical white matter and hippocampus. The expression of myelin proteins including CNPase, MBP, PLP and MAG was downregulated in both areas of the brain at 7, 14 and 28 days after LPS injection. The frequency of MBP and PLP-positive oligodendrocyte was significantly reduced using in situ hybridization in the cerebral cortex and hippocampus at the corresponding time points after LPS injection, whereas the expression of NG2 and PDGFRα was noticeably increased. In tandem with this was reduction of Olig1 and Olig2 expressions which are involved in differentiation/maturation of OPCs. Expression of NFL, NFM, and NFH was significantly downregulated, indicating that axon development was disrupted after LPS injection. Morris Water Maze behavioral test, Open field test, Rotarod test, and Pole test were used to evaluate neurological behaviors of 28 days rats. The rats in the LPS group showed the impairment of motor coordination, balance, memory, and learning ability and represented bradykinesia and anxiety-like behavior. The present results suggest that following systemic LPS injection, differentiation/maturation of OPCs was affected which may be attributed to the inhibition of transcription factors Olig1 and Olig2 expression resulting in impairment to axonal development. It is suggested that this would ultimately lead to axonal hypomyelination in the prefrontal cortex and hippocampus, which may be associated with neurological deficits in later life.

Traffic-related particulate matter affects behavior, inflammation, and neural integrity in a developmental rodent model

Recent studies indicate that exposure to airborne particulate matter (PM) is associated with cognitive delay, depression, anxiety, autism, and neurodegenerative diseases; however, the role of PM in the etiology of these outcomes is not well-understood. Therefore, there is a need for controlled animal studies to better elucidate the causes and mechanisms by which PM impacts these health outcomes. We assessed the effects of gestational and early life exposure to traffic-related PM on social- and anxiety-related behaviors, cognition, inflammatory markers, and neural integrity in juvenile male rats. Gestating and lactating rats were exposed to PM from a Boston (MA, USA) traffic tunnel for 5 h/day, 5 days/week for 6 weeks (3 weeks gestation, 3 weeks lactation). The target exposure concentration for the fine fraction of nebulized PM, measured as PM2.5, was 200 μg/m3. To assess anxiety and cognitive function, F1 male juveniles underwent elevated platform, cricket predation, nest building, social behavior and marble burying tests at 32-60 days of age. Upon completion of behavioral testing, multiple cytokines and growth factors were measured in these animals and their brains were analyzed with diffusion tensor MRI to assess neural integrity. PM exposure had no effect on litter size or weight, or offspring growth; however, F1 litters developmentally exposed to PM exhibited significantly increased anxiety (p = 0.04), decreased cognition reflected in poorer nest-organization (p = 0.04), and decreased social play and allogrooming (p = 0.003). MRI analysis of ex vivo brains revealed decreased structural integrity of neural tissues in the anterior cingulate and hippocampus in F1 juveniles exposed to PM (p < 0.01, p = 0.03, respectively). F1 juvenile males exposed to PM also exhibited significantly decreased plasma levels of both IL-18 (p = 0.03) and VEGF (p = 0.04), and these changes were inversely correlated with anxiety-related behavior. Chronic exposure of rat dams and their offspring to traffic-related PM during gestation and lactation decreases social behavior, increases anxiety, impairs cognition, decreases levels of inflammatory and growth factors (which are correlated with behavioral changes), and disrupts neural integrity in the juvenile male offspring. Our findings add evidence that exposure to traffic-related air pollution during gestation and lactation is involved in the etiology of autism spectrum disorder and other disorders which include social and cognitive deficits and/or increased anxiety.

Ischemia-Triggered Glutamate Excitotoxicity From the Perspective of Glial Cells

A plethora of neurological disorders shares a final common deadly pathway known as excitotoxicity. Among these disorders, ischemic injury is a prominent cause of death and disability worldwide. Brain ischemia stems from cardiac arrest or stroke, both responsible for insufficient blood supply to the brain parenchyma. Glucose and oxygen deficiency disrupts oxidative phosphorylation, which results in energy depletion and ionic imbalance, followed by cell membrane depolarization, calcium (Ca²⁺) overload, and extracellular accumulation of excitatory amino acid glutamate. If tight physiological regulation fails to clear the surplus of this neurotransmitter, subsequent prolonged activation of glutamate receptors forms a vicious circle between elevated concentrations of intracellular Ca²⁺ ions and aberrant glutamate release, aggravating the effect of this ischemic pathway. The activation of downstream Ca²⁺-dependent enzymes has a catastrophic impact on nervous tissue leading to cell death, accompanied by the formation of free radicals, edema, and inflammation. After decades of “neuron-centric” approaches, recent research has also finally shed some light on the role of glial cells in neurological diseases. It is becoming more and more evident that neurons and glia depend on each other. Neuronal cells, astrocytes, microglia, NG2 glia, and oligodendrocytes all have their roles in what is known as glutamate excitotoxicity. However, who is the main contributor to the ischemic pathway, and who is the unsuspecting victim? In this review article, we summarize the so-far-revealed roles of cells in the central nervous system, with particular attention to glial cells in ischemia-induced glutamate excitotoxicity, its origins, and consequences.

Environmental enrichment ameliorates perinatal brain injury and promotes functional white matter recovery

Hypoxic damage to the developing brain due to preterm birth causes many anatomical changes, including damage to the periventricular white matter. This results in the loss of glial cells, significant disruptions in myelination, and thereby cognitive and behavioral disabilities seen throughout life. Encouragingly, these neurological morbidities can be improved by environmental factors; however, the underlying cellular mechanisms remain unknown. We found that early and continuous environmental enrichment selectively enhances endogenous repair of the developing white matter by promoting oligodendroglial maturation, myelination, and functional recovery after perinatal brain injury. These effects require increased exposure to socialization, physical activity, and cognitive enhancement of surroundings-a complete enriched environment. Using RNA-sequencing, we identified oligodendroglial-specific responses to hypoxic brain injury, and uncovered molecular mechanisms involved in enrichment-induced recovery. Together, these results indicate that myelin plasticity induced by modulation of the neonatal environment can be targeted as a therapeutic strategy for preterm birth.

The Role of Circular RNAs in Brain Injury

Circular RNAs are an increasingly important topic in non-coding RNA biology, drawing considerable attention in recent years. Accumulating evidence suggests a critical role for circular RNAs in both early and latent stages of disease pathogenesis. Circular RNAs are abundantly expressed in brain tissue, with significant implications for neural development and disease progression. Disruption of these processes, including those seen in response to brain injury, can have serious consequences such as hemiplegia, aphasia, coma, and death. In this review, we describe the role of circular RNAs in the context of brain injury and explore the potential connection between circular RNAs, brain hypoxic ischemic injury, ischemia-reperfusion injury, and traumatic injury.

Reducing myeloperoxidase activity decreases inflammation and increases cellular protection in ischemic stroke

Myeloperoxidase (MPO) is a pro-inflammatory enzyme abundantly secreted by activated myeloid cells after stroke. We show that when MPO activity is either blocked by the specific inhibitor 4-aminobenzoic acid hydrazide (ABAH) in wildtype (WT) mice or congenitally absent (MPO-/-), there was decreased cell loss, including degenerating neurons and oligodendrocytes, in the ischemic brains compared to vehicle-treated WT mice after stroke. MPO inhibition also reduced the number of activated myeloid cells after ischemia. MPO inhibition increased cytoprotective heat shock protein 70 (Hsp70) by 70% and p-Akt by 60%, while decreased the apoptotic marker p53 level by 62%, compared to vehicle-treated mice after ischemia. Similarly, MPO inhibition increased the number of Hsp70+/NeuN+ cells after stroke by 60%. Notably, MPO inhibition significantly improved neurological outcome compared with the vehicle-treated group after stroke. We further found longer treatment periods resulted in larger reduction of infarct size and greater neurobehavioral improvement from MPO inhibition, even when given days after stroke. Therefore, MPO inhibition with ABAH or MPO deficiency creates a protective environment that decreased inflammatory cell recruitment and increased expression of survival factors to improve functional outcome. MPO inhibition may represent a promising therapeutic target for stroke therapy, possibly even days after stroke has occurred.

Hypoxia of Rats Subjected to Carotid Artery Ligation Results in Impaired Neurogenesis and Reduced Number of Cortical Neurons

BACKGROUND/AIM

Cerebral ischemia is a major cause of abnormal brain development. In a cerebral ischemia model, periventricular leukomalacia (PVL), white matter lesion and a decrease in the number of subcortical neurons were observed. The aim of this study was to investigate the effect of hypoxia on neurogenesis and cell survival.

MATERIALS AND METHODS

In seven-day postnatal rats, the right carotid artery was ligated. The rats were incubated either in a regular normoxic chamber (control group) or in a hypoxic chamber (PVL group, 8% 02 and 92% N2 at 37°C) for 2 h. Nestin- and NeuN-positive neurons were detected by immunohistochemistry.

RESULTS

The densities of nestin-immunoreactivity (IR) cells in the cerebral parietal cortex and subventricular zone were increased with hypoxia. NeuN-IR cells in the cerebral cortex were significantly decreased in the PVL group.

CONCLUSION

Perinatal white matter injury induced neurogenesis, while the survival of neurons was decreased in the cerebral cortex.

Research Progress on the Role and Mechanism of Action of Activin A in Brain Injury

Activin A belongs to the transforming growth factor superfamily and has a variety of biological functions. Studies have revealed that activin A can regulate the body's immune and inflammatory responses and participate in the regulation of cell death. In addition, activin A also has neurotrophic function and plays an important role in the repair of brain damage. This article summarizes recent advances in understanding the role and mechanism of action of activin A in brain injury and provides new hints into the application of activin A in the treatment of brain injury.

Inhibition of microglial activation by minocycline reduced preoligodendrocyte injury in a neonatal rat brain slice model

BACKGROUND

Periventricular leukomalacia is a common white-matter injury after neonatal cardiac surgery; however, its potential cellular mechanism remains uncertain. There is limited study regarding periventricular leukomalacia treatment.

METHODS

A neonatal rat brain slice perfusion model was used for reproducing the condition of cardiopulmonary bypass, and oxygen glucose deprivation simulated circulatory arrest. Seven-day-old Sprague-Dawley rats were randomly divided into 7 groups: (1) control group with 36°C; (2) 60 minutes of oxygen glucose deprivation group on 15°C, 25°C, 36°C, respectively; and (3) 60 minutes of oxygen glucose deprivation group on 15°C, 25°C, 36°C, plus minocycline (10 μmol/L), respectively. Immunohistochemistry, Western blot, and inflammatory mediators were compared after the perfusion procedures in the different groups.

RESULTS

This neonatal rat brain slice perfusion with oxygen glucose deprivation model could replicate the pathophysiologic process and injury after cardiopulmonary bypass and hypothermic circulatory arrest. With the increase of oxygen glucose deprivation perfusion temperature, we found that both microglia activation and preoligodendrocyte loss increased. The application of minocycline can significantly inhibit microglial activation and preoligodendrocyte cells loss in the normothermic (36°C) and moderate hypothermia (25°C) oxygen glucose deprivation groups (P < .05), with accompanying significant decreasing microglial inflammatory productions; however, no significant improvement was found in the deep hypothermia (15°C) group.

CONCLUSIONS

The microglial activation may play a key role in preoligodendrocyte injury in the ex vivo neonatal rat brain slice perfusion and circulatory arrest model. Inhibition of microglial activation with minocycline may be an attractive target for white-matter protection during cardiopulmonary bypass and hypothermic circulatory arrest.

Prediction of cognitive and motor development in preterm children using exhaustive feature selection and cross-validation of near-term white matter microstructure

BACKGROUND

Advanced neuroimaging and computational methods offer opportunities for more accurate prognosis. We hypothesized that near-term regional white matter (WM) microstructure, assessed on diffusion tensor imaging (DTI), using exhaustive feature selection with cross-validation would predict neurodevelopment in preterm children.

METHODS

Near-term MRI and DTI obtained at 36.6 ± 1.8 weeks postmenstrual age in 66 very-low-birth-weight preterm neonates were assessed. 60/66 had follow-up neurodevelopmental evaluation with Bayley Scales of Infant-Toddler Development, 3rd-edition (BSID-III) at 18-22 months. Linear models with exhaustive feature selection and leave-one-out cross-validation computed based on DTI identified sets of three brain regions most predictive of cognitive and motor function; logistic regression models were computed to classify high-risk infants scoring one standard deviation below mean.

RESULTS

Cognitive impairment was predicted (100% sensitivity, 100% specificity; AUC = 1) by near-term right middle-temporal gyrus MD, right cingulate-cingulum MD, left caudate MD. Motor impairment was predicted (90% sensitivity, 86% specificity; AUC = 0.912) by left precuneus FA, right superior occipital gyrus MD, right hippocampus FA. Cognitive score variance was explained (29.6%, cross-validated Rˆ2 = 0.296) by left posterior-limb-of-internal-capsule MD, Genu RD, right fusiform gyrus AD. Motor score variance was explained (31.7%, cross-validated Rˆ2 = 0.317) by left posterior-limb-of-internal-capsule MD, right parahippocampal gyrus AD, right middle-temporal gyrus AD.

CONCLUSION

Search in large DTI feature space more accurately identified neonatal neuroimaging correlates of neurodevelopment.

The effects of mild germinal matrix-intraventricular haemorrhage on the developmental white matter microstructure of preterm neonates: a DTI study

OBJECTIVES

To evaluate white matter (WM) microstructural changes in preterm neonates (PN) with mild germinal matrix-intraventricular haemorrhage (mGMH-IVH) (grades I and II) and no other associated MRI abnormalities, and correlate them with gestational age (GA) and neurodevelopmental outcome.

METHODS

Tract-based spatial-statistics (TBSS) was performed on DTI of 103 patients studied at term-equivalent age, to compare diffusional parameters (fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), axial diffusivity (AD)) between mGMH-IVH neonates (24/103) and controls matched by GA at birth and sex. The relationship between DTI abnormalities, GA and neurodevelopmental outcome assessed with Griffiths' Developmental Scale-Revised:0-2 was explored using TBSS and Spearman-correlation analysis (p < .05).

RESULTS

Affected neonates had lower FA, higher RD and MD of the corpus callosum, limbic pathways and cerebellar tracts. Extremely preterm neonates (GA < 29 weeks) presented more severe microstructural impairment (higher RD and MD) in periventricular regions. Neonates of GA ≥ 29 weeks had milder WM alterations (lower FA), also in subcortical WM. DTI abnormalities were associated with poorer locomotor, eye-hand coordination and performance outcomes at 24 months.

CONCLUSIONS

WM microstructural changes occur in PN with mGMH-IVH with a GA-dependent selective vulnerability of WM regions, and correlate with adverse neurodevelopmental outcome at 24 months.

KEY POINTS

• DTI-TBSS analysis identifies WM microstructural changes in preterm neonates with mGMH-IVH. • Extremely preterm neonates with mGMH-IVH presented more severe impairment of WM microstructure. • Extremely preterm neonates with mGMH-IVH presented microstructural impairment of periventricular WM. • mGMH-IVH affects subcortical WM in preterm neonates with gestational age ≥ 29 weeks. • WM microstructural alterations are related to neurodevelopmental impairments at 24 months.

All Wrapped Up: Environmental Effects on Myelination

To date, studies have demonstrated the dynamic influence of exogenous environmental stimuli on multiple regions of the brain. This environmental influence positively and negatively impacts programs governing myelination, and acts on myelinating oligodendrocyte (OL) cells across the human lifespan. Developmentally, environmental manipulation of OL progenitor cells (OPCs) has profound effects on the establishment of functional cognitive, sensory, and motor programs. Furthermore, central nervous system (CNS) myelin remains an adaptive entity in adulthood, sensitive to environmentally induced structural changes. Here, we discuss the role of environmental stimuli on mechanisms governing programs of CNS myelination under normal and pathological conditions. Importantly, we highlight how these extrinsic cues can influence the intrinsic power of myelin plasticity to promote functional recovery.

Early identification of cerebral visual impairments in infants born extremely preterm

AIM

Children born extremely preterm are at risk of visual processing problems related to brain damage. Damage in visual pathways can remain undetected by conventional magnetic resonance imaging (MRI) and functional consequences cannot always be predicted. The aim of this study was to assess the efficacy of processing visual information in infants born extremely preterm at a corrected age of 1 year using a communication-free visual function test based on eye tracking.

METHOD

Infants born extremely preterm (<29wks' gestation) without apparent white and grey matter damage on conventional MRI at 30 weeks' postmenstrual age were included (19 males, 1.01y [0.96-1.24] (median [25th-75th centiles]); 11 females, 0.99y [0.98-1.01]). At the corrected age of 1 year, reaction times to fixation (RTF) of specific visual properties displayed on an eye-tracker monitor were quantified and compared with results from a comparison group (eight males, 1.28y [1.01-1.33]; nine females, 1.10y [0.90-1.20]).

RESULTS

The infants in the preterm group had longer response times in detecting colour patterns (red-green) and motion compared with infants in the comparison group. No impairments were detected in oculomotor functions (saccades, pursuit, and fixations).

INTERPRETATION

The data suggest that delays in processing visual information can be identified in children born extremely preterm. The delays might be ascribed to deficits in neuronal connectivity in visual pathways at a microstructural level.

Developmental neurotoxicity of inhaled ambient ultrafine particle air pollution: Parallels with neuropathological and behavioral features of autism and other neurodevelopmental disorders

Accumulating evidence from both human and animal studies show that brain is a target of air pollution. Multiple epidemiological studies have now linked components of air pollution to diagnosis of autism spectrum disorder (ASD), a linkage with plausibility based on the shared mechanisms of inflammation. Additional plausibility appears to be provided by findings from our studies in mice of exposures from postnatal day (PND) 4-7 and 10-13 (human 3rd trimester equivalent), to concentrated ambient ultrafine (UFP) particles, considered the most reactive component of air pollution, at levels consistent with high traffic areas of major U.S. cities and thus highly relevant to human exposures. These exposures, occurring during a period of marked neuro- and gliogenesis, unexpectedly produced a pattern of developmental neurotoxicity notably similar to multiple hypothesized mechanistic underpinnings of ASD, including its greater impact in males. UFP exposures induced inflammation/microglial activation, reductions in size of the corpus callosum (CC) and associated hypomyelination, aberrant white matter development and/or structural integrity with ventriculomegaly (VM), elevated glutamate and excitatory/inhibitory imbalance, increased amygdala astrocytic activation, and repetitive and impulsive behaviors. Collectively, these findings suggest the human 3rd trimester equivalent as a period of potential vulnerability to neurodevelopmental toxicity to UFP, particularly in males, and point to the possibility that UFP air pollution exposure during periods of rapid neuro- and gliogenesis may be a risk factor not only for ASD, but also for other neurodevelopmental disorders that share features with ASD, such as schizophrenia, attention deficit disorder, and periventricular leukomalacia.

Neonatal brain microstructure correlates of neurodevelopment and gait in preterm children 18-22 mo of age: an MRI and DTI study

BACKGROUND

Near-term brain structure was examined in preterm infants in relation to neurodevelopment. We hypothesized that near-term macrostructural brain abnormalities identified using conventional magnetic resonance imaging (MRI), and white matter (WM) microstructure detected using diffusion tensor imaging (DTI), would correlate with lower cognitive and motor development and slower, less-stable gait at 18-22 mo of age.

METHODS

One hundred and two very-low-birth-weight preterm infants (≤1,500 g birth weight; ≤32 wk gestational age) were recruited prior to routine near-term brain MRI at 36.6 ± 1.8 wk postmenstrual age. Cerebellar and WM macrostructure was assessed on conventional structural MRI. DTI was obtained in 66 out of 102 and WM microstructure was assessed using fractional anisotropy and mean diffusivity (MD) in six subcortical brain regions defined by DiffeoMap neonatal atlas. Neurodevelopment was assessed with Bayley-Scales-of-Infant-Toddler-Development, 3rd-Edition (BSID-III); gait was assessed using an instrumented mat.

RESULTS

Neonates with cerebellar abnormalities identified using MRI demonstrated lower mean BSID-III cognitive composite scores (89.0 ± 10.1 vs. 97.8 ± 12.4; P = 0.002) at 18-22 mo. Neonates with higher DTI-derived left posterior limb of internal capsule (PLIC) MD demonstrated lower cognitive and motor composite scores (r = -0.368; P = 0.004; r = -0.354; P = 0.006) at 18-22 mo; neonates with higher genu MD demonstrated slower gait velocity (r = -0.374; P = 0.007). Multivariate linear regression significantly predicted cognitive (adjusted r(2) = 0.247; P = 0.002) and motor score (adjusted r(2) = 0.131; P = 0.017).

CONCLUSION

Near-term cerebellar macrostructure and PLIC and genu microstructure were predictive of early neurodevelopment and gait.

Low-grade intraventricular hemorrhage disrupts cerebellar white matter in preterm infants: evidence from diffusion tensor imaging

INTRODUCTION

Recent diffusion tensor imaging (DTI) studies have demonstrated that leakage of hemosiderin into cerebrospinal fluid (CSF), which is caused by high-grade intraventricular hemorrhage (IVH), can affect cerebellar development in preterm born infants. However, a direct effect of low-grade IVH on cerebellar development is unknown. Thus, we evaluated the cerebellar and cerebral white matter (WM) of preterm infants with low-grade IVH.

METHODS

Using DTI tractography performed at term-equivalent age, we analyzed 42 infants who were born less than 30 weeks gestational age (GA) at birth (22 with low-grade IVH, 20 without). These infants were divided into two birth groups depending on GA, and we then compared the presence and absence of IVH which was diagnosed by cerebral ultrasound (CUS) within 10 days after birth or conventional magnetic resonance imaging (MRI) at term-equivalent age in each group. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) at the superior cerebellar peduncle (SCP), middle cerebellar peduncle (MCP), motor tract, and sensory tract were measured.

RESULTS

In the SCP, preterm born infants with IVH had lower FA values compared with infants without IVH. In particular, younger preterm birth with IVH had lower FA values in the SCP and motor tract and higher ADC values in the MCP.

CONCLUSION

Low-grade IVH impaired cerebellar and cerebral WM, especially in the SCP. Moreover, younger preterm infants exhibited greater disruptions to cerebellar WM and the motor tract than infants of older preterm birth.

What are the Best Animal Models for Testing Early Intervention in Cerebral Palsy?

Interventions to treat cerebral palsy should be initiated as soon as possible in order to restore the nervous system to the correct developmental trajectory. One drawback to this approach is that interventions have to undergo exceptionally rigorous assessment for both safety and efficacy prior to use in infants. Part of this process should involve research using animals but how good are our animal models? Part of the problem is that cerebral palsy is an umbrella term that covers a number of conditions. There are also many causal pathways to cerebral palsy, such as periventricular white matter injury in premature babies, perinatal infarcts of the middle cerebral artery, or generalized anoxia at the time of birth, indeed multiple causes, including intra-uterine infection or a genetic predisposition to infarction, may need to interact to produce a clinically significant injury. In this review, we consider which animal models best reproduce certain aspects of the condition, and the extent to which the multifactorial nature of cerebral palsy has been modeled. The degree to which the corticospinal system of various animal models human corticospinal system function and development is also explored. Where attempts have already been made to test early intervention in animal models, the outcomes are evaluated in light of the suitability of the model.

P2Y receptors in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia, affecting more than 10% of people over the age of 65. Age is the greatest risk factor for AD, although a combination of genetic, lifestyle and environmental factors also contribute to disease development. Common features of AD are the formation of plaques composed of beta-amyloid peptides (Aβ) and neuronal death in brain regions involved in learning and memory. Although Aβ is neurotoxic, the primary mechanisms by which Aβ affects AD development remain uncertain and controversial. Mouse models overexpressing amyloid precursor protein and Aβ have revealed that Aβ has potent effects on neuroinflammation and cerebral blood flow that contribute to AD progression. Therefore, it is important to consider how endogenous signalling in the brain responds to Aβ and contributes to AD pathology. In recent years, Aβ has been shown to affect ATP release from brain and blood cells and alter the expression of G protein-coupled P2Y receptors that respond to ATP and other nucleotides. Accumulating evidence reveals a prominent role for P2Y receptors in AD pathology, including Aβ production and elimination, neuroinflammation, neuronal function and cerebral blood flow.

Neonatal physiological correlates of near-term brain development on MRI and DTI in very-low-birth-weight preterm infants

Structural brain abnormalities identified at near-term age have been recognized as potential predictors of neurodevelopment in children born preterm. The aim of this study was to examine the relationship between neonatal physiological risk factors and early brain structure in very-low-birth-weight (VLBW) preterm infants using structural MRI and diffusion tensor imaging (DTI) at near-term age.

Structural brain MRI, diffusion-weighted scans, and neonatal physiological risk factors were analyzed in a cross-sectional sample of 102 VLBW preterm infants (BW ≤ 1500 g, gestational age (GA) ≤ 32 weeks), who were admitted to the Lucile Packard Children's Hospital, Stanford NICU and recruited to participate prior to routine near-term brain MRI conducted at 36.6 ± 1.8 weeks postmenstrual age (PMA) from 2010 to 2011; 66/102 also underwent a diffusion-weighted scan. Brain abnormalities were assessed qualitatively on structural MRI, and white matter (WM) microstructure was analyzed quantitatively on DTI in six subcortical regions defined by DiffeoMap neonatal brain atlas. Specific regions of interest included the genu and splenium of the corpus callosum, anterior and posterior limbs of the internal capsule, the thalamus, and the globus pallidus. Regional fractional anisotropy (FA) and mean diffusivity (MD) were calculated using DTI data and examined in relation to neonatal physiological risk factors including gestational age (GA), bronchopulmonary dysplasia (BPD), necrotizing enterocolitis (NEC), retinopathy of prematurity (ROP), and sepsis, as well as serum levels of C-reactive protein (CRP), glucose, albumin, and total bilirubin.

Brain abnormalities were observed on structural MRI in 38/102 infants including 35% of females and 40% of males. Infants with brain abnormalities observed on MRI had higher incidence of BPD (42% vs. 25%) and sepsis (21% vs. 6%) and higher mean and peak serum CRP levels, respectively, (0.64 vs. 0.34 mg/dL, p = .008; 1.57 vs. 0.67 mg/dL, p= .006) compared to those without. The number of signal abnormalities observed on structural MRI correlated to mean and peak CRP (rho = .316, p = .002; rho = .318, p= .002). The number of signal abnormalities observed on MRI correlated with thalamus MD (left: r= .382, p= .002; right: r= .400, p= .001), controlling for PMA-at-scan. Thalamus WM microstructure demonstrated the strongest associations with neonatal risk factors. Higher thalamus MD on the left and right, respectively, was associated with lower GA (r = −.322, p = .009; r= −.381, p= .002), lower mean albumin (r = −.276, p= .029; r= −.385, p= .002), and lower mean bilirubin (r = −.293, p= .020; r= −.337 p= .007).

Results suggest that at near-term age, thalamus WM microstructure may be particularly vulnerable to certain neonatal risk factors. Interactions between albumin, bilirubin, phototherapy, and brain development warrant further investigation. Identification of physiological risk factors associated with selective vulnerability of certain brain regions at near-term age may clarify the etiology of neurodevelopmental impairment and inform neuroprotective treatment for VLBW preterm infants.

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Biomarkers of inflammation in preterm infants correlated with brain abnormalities detected on near-term structural MRI.

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Biomarkers of inflammation in preterm infants correlated with near-term WM microstructure assessed on DTI.

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Signal abnormalities observed on near-term structural MRI correlated with increased thalamus MD.

Brain microstructural development at near-term age in very-low-birth-weight preterm infants: an atlas-based diffusion imaging study

At near-term age the brain undergoes rapid growth and development. Abnormalities identified during this period have been recognized as potential predictors of neurodevelopment in children born preterm. This study used diffusion tensor imaging (DTI) to examine white matter (WM) microstructure in very-low-birth-weight (VLBW) preterm infants to better understand regional WM developmental trajectories at near-term age. DTI scans were analyzed in a cross-sectional sample of 45 VLBW preterm infants (BW≤1500g, GA≤32weeks) within a cohort of 102 neonates admitted to the NICU and recruited to participate prior to standard-of-care MRI, from 2010 to 2011, 66/102 also had DTI. For inclusion in this analysis, 45 infants had DTI, no evidence of brain abnormality on MRI, and were scanned at PMA ≤40weeks (34.7-38.6). White matter microstructure was analyzed in 19 subcortical regions defined by DiffeoMap neonatal brain atlas, using threshold values of trace <0.006mm(2)s(-1) and FA >0.15. Regional fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were calculated and temporal-spatial trajectories of development were examined in relation to PMA and brain region location. Posterior regions within the corona radiata (CR), corpus callosum (CC), and internal capsule (IC) demonstrated significantly higher mean FA values compared to anterior regions. Posterior regions of the CR and IC demonstrated significantly lower RD values compared to anterior regions. Centrally located projection fibers demonstrated higher mean FA and lower RD values than peripheral regions including the posterior limb of the internal capsule (PLIC), cerebral peduncle, retrolenticular part of the IC, posterior thalamic radiation, and sagittal stratum. Centrally located association fibers of the external capsule had higher FA and lower RD than the more peripherally-located superior longitudinal fasciculus (SLF). A significant relationship between PMA-at-scan and FA, MD, and RD was demonstrated by a majority of regions, the strongest correlations were observed in the anterior limb of the internal capsule, a region undergoing early stages of myelination at near-term age, in which FA increased (r=.433, p=.003) and MD (r=-.545, p=.000) and RD (r=-.540, p=.000) decreased with PMA-at-scan. No correlation with PMA-at-scan was observed in the CC or SLF, regions that myelinate later in infancy. Regional patterns of higher FA and lower RD were observed at this near-term age, suggestive of more advanced microstructural development in posterior compared to anterior regions within the CR, CC, and IC and in central compared to peripheral WM structures. Evidence of region-specific rates of microstructural development was observed. Temporal-spatial patterns of WM microstructure development at near-term age have important implications for interpretation of near-term DTI and for identification of aberrations in typical developmental trajectories that may signal future impairment.