Prenatal Systemic Hypoxia-Ischemia and Oligodendroglia Loss in Cerebellum

Investigation of altered spontaneous brain activity in patients with bronchial asthma using the percent amplitude of fluctuation method: a resting-state functional MRI study

Purpose

To explore the regions of aberrant spontaneous brain activity in asthma patients and their potential impacts using the Percent amplitude of fluctuation (PerAF) analysis method.

Patients and methods

In this study, a total of 31 bronchial asthma (BA) patients were ultimately included, comprising 17 males and 14 females. Subsequently, 31 healthy control subjects (HCS) were recruited, consisting of 17 males and 14 females, and they were matched with the BA group based on age, sex, and educational status. The PerAF analysis technique was employed to study the differences in spontaneous brain activity between the two groups. The SPM12 toolkit was used to carry out a two sample t-test on the collected fMRI data, in order to examine the differences in PerAF values between the asthma patients and the healthy controls. We employed the Montreal Cognitive Assessment (MoCA) scale and the Hamilton Depression Scale (HAMD) to evaluate the cognitive and emotional states of the two groups. Pearson correlation analysis was utilized to ascertain the relationship between changes in the PerAF values within specific brain regions and cognitive as well as emotional conditions.

Results

Compared with the healthy control group, areas of the brain with reduced PerAF in asthma patients included the inferior cerebellum, fusiform gyrus, right inferior orbital frontal gyrus, left middle orbital frontal gyrus, left/right middle frontal gyrus (MFG), dorsal lateral superior frontal gyrus (SFGdl), left superior temporal gyrus (STG), precuneus, right inferior parietal lobule (IPL), and left/right angular gyrus. BA patients exhibit mild cognitive impairments and a propensity for emotional disturbances. Furthermore, the perAF values of the SFGdl region are significantly positively correlated with the results of the MoCA cognitive assessment, while negatively correlated with the HAMD evaluation.

Conclusion

Through the application of PerAF analysis methods, we discovered that several brain regions in asthma patients that control the amplitude of respiration, vision, memory, language, attention, and emotional control display abnormal changes in intrinsic brain activity. This helps characterize the neural mechanisms behind cognitive, sensory, and motor function impairments in asthma patients, providing valuable insights for potential therapeutic targets and disease management strategies.

Evaluation of Pain Prevalence in Children Who Experienced Perinatal Hypoxia-Ischemia Events: Characteristics and Associations With Sociodemographic Factors

INTRODUCTION

Pain in children who suffer from hypoxia-ischemia (HI) events is still not widely studied. Hypoxia-ischemia is characterized by the momentary or permanent cessation of blood flow and, consequently, of oxygen supply, becoming the main cause of encephalopathy in children. Hyperalgesia was identified in animals undergoing prenatal hypoxia-ischemia by researchers from the Universidade do Estado do Rio de Janeiro (UERJ). Premature and asphyxiated newborns have been admitted to the neonatal intensive care unit (NICU) of Pedro Ernesto University Hospital (HUPE) in Brazil and are monitored by the Outpatient Follow-up of High-Risk Newborns Project (SARAR), but no pain assessment was performed.

OBJECTIVE

To assess pain in children born in high-risk situations, such as prematurity and perinatal asphyxia, with higher chances of perinatal HI, discharged from the NICU/HUPE, and followed by SARAR.

METHODOLOGY

The study was approved by the HUPE Research Ethics Committee. The epidemiological, descriptive, cross-sectional study started in 2021 and finished in 2023, with the application of the pain assessment tool or instrument adapted from the Lübeck Pain-Screening Questionnaire to the caregivers and with the collection of growth and development data. The population consisted of asphyxiated infants born with a gestational age greater than 35 weeks and submitted to the Therapeutic Hypothermia protocol and premature infants discharged from the NICU between two (gestational age 1 (GA1)) and 12 years old. For most of them, pain prevalence was assessed according to its frequency and intensity, as were sociodemographic variables of the child and mother, neural alterations, and the Children's Developmental Scale (DENVER II). The percentage differences between the evaluated factors and the presence of pain were performed using Fisher's exact test and medians using the non-parametric Wilcoxon rank-sum test, both appropriate for the small sample of children. Significance levels of 10% were considered for trends and 5% for statistically significant differences.

RESULTS

Of the 86 children included in our search, 26 (30%) were born with a gestational age greater than 35 weeks and diagnosed with perinatal asphyxia (hereinafter referred to as the asphyxiation group), and 60 (70%) were premature. Pain was reported by 22 (25%) children, of whom 54.4% reported moderate or severe pain. The head and abdomen were the most reported sites (36%). Differences were observed in the percentage distribution of pain between asphyxiates and premature infants (11% vs. 32%; p-value 0.061 on the Fisher test) and between females and males (34% vs. 17%; p-value 0.085 on the Fisher test). Black and Brown children had higher median pain scale values than White children (p-value < 0.027, Wilcoxon rank sum test).

CONCLUSION

There is a higher prevalence of pain in girls, in the head, in premature infants, and greater intensity among Black and Brown children. Therefore, knowing the pain profile can help improve their quality of life by offering treatments.

Consequences of oxygen deprivation on myelination and sex-dependent alterations

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

Depressive-like behavior and impaired synaptic plasticity in the prefrontal cortex as later consequences of prenatal hypoxic-ischemic insult in rats

Perinatal hypoxia-ischemia (HI) is a leading cause of morbidity and mortality among newborns. Infants with HI encephalopathy may experience lasting consequences, such as depression, in adulthood. In this study, we examined depressive-like behavior, neuronal population, and markers of monoaminergic and synaptic plasticity in the prefrontal cortex (PFC) of adolescent rats subjected to a prenatal HI model. Pregnant rats underwent a surgery in which uterine and ovarian blood flow was blocked for 45 min at E18 (HI procedure). Sham-operated subjects were also generated (SH procedure). Behavioral tests were conducted on male and female pups from P41 to P43, and animals were histologically processed or dissected for western blotting at P45. We found that the HI groups consumed less sucrose in the sucrose preference test and remained immobile for longer periods in the forced swim test. Additionally, we observed a significant reduction in neuronal density and PSD95 levels in the HI group, as well as a smaller number of synaptophysin-positive cells. Our results underscore the importance of this model in investigating the effects of HI-induced injuries, as it reproduces an increase in depressive-like behavior and suggests that the HI insult affects circuits involved in mood modulation.

Disrupted gut microbiota aggravates spatial memory dysfunction induced by high altitude exposure: A link between plateau environment and microbiome-gut-brain axis

Approximately 400 million people work and live in high-altitude areas and suffer from memory dysfunction worldwide. Until now, the role of the intestinal flora in plateau-induced brain damage has rarely been reported. To address this, we investigated the effect of intestinal flora on spatial memory impairment induced by high altitudes based on the microbiome-gut-brain axis theory. C57BL/6 mice were divided into three groups: control, high-altitude (HA), and high-altitude antibiotic treatment (HAA) group. The HA and HAA groups were exposed to a low-pressure oxygen chamber that simulated an altitude of 4000 m above sea level (m. a. s.l.) for 14 days, with the air pressure in the chamber set at 60-65 kPa. The results showed that spatial memory dysfunction induced by the high-altitude environment was aggravated by antibiotic treatment, manifesting as lowered escape latency and hippocampal memory-related proteins (BDNF and PSD-95). 16 S rRNA sequencing showed a remarkable separation of the ileal microbiota among the three groups. Antibiotic treatment exacerbated the reduced richness and diversity of the ileal microbiota in mice in the HA group. Lactobacillaceae were the main target bacteria and were significantly reduced in the HA group, which was exacerbated by antibiotic treatment. Meanwhile, reduced intestinal permeability and ileal immune function in mice exposed high-altitude environment was also aggravated by antibiotic treatment, as indicated by the lowered tight junction proteins and IL-1β and IFN-γ levels. Furthermore, indicator species analysis and Netshift co-analysis revealed that Lactobacillaceae (ASV11) and Corynebacteriaceae (ASV78, ASV25, and ASV47) play important roles in high-altitude exposure-induced memory dysfunction. Interestingly, ASV78 was negatively correlated with IL-1β and IFN-γ levels, indicating that ASV78 may be induced by reduced ileal immune function, which mediates high-altitude environment exposure-induced memory dysfunction. This study provides evidence that the intestinal flora is effective in preventing brain dysfunction caused by exposure to high-altitude environments, suggesting a relationship between the microbiome-gut-brain axis and altitude exposure.

Maternal Hyperhomocysteinemia Produces Memory Deficits Associated with Impairment of Long-Term Synaptic Plasticity in Young Rats

Maternal hyperhomocysteinemia (HCY) is a common pregnancy complication caused by high levels of the homocysteine in maternal and fetal blood, which leads to the alterations of the cognitive functions, including learning and memory. In the present study, we investigated the mechanisms of these alterations in a rat model of maternal HCY. The behavioral tests confirmed the memory impairments in young and adult rats following the prenatal HCY exposure. Field potential recordings in hippocampal slices demonstrated that the long-term potentiation (LTP) was significantly reduced in HCY rats. The whole-cell patch-clamp recordings in hippocampal slices demonstrated that the magnitude of NMDA receptor-mediated currents did not change while their desensitization decreased in HCY rats. No significant alterations of glutamate receptor subunit expression except GluN1 were detected in the hippocampus of HCY rats using the quantitative real-time PCR and Western blot methods. The immunofluorescence microscopy revealed that the number of synaptopodin-positive spines is reduced, while the analysis of the ultrastructure of hippocampus using the electron microscopy revealed the indications of delayed hippocampal maturation in young HCY rats. Thus, the obtained results suggest that maternal HCY disturbs the maturation of hippocampus during the first month of life, which disrupts LTP formation and causes memory impairments.

MAPK: A Key Player in the Development and Progression of Stroke

Conclusion:

Stroke is a complex disease caused by genetic and environmental factors, and its etiological mechanism has not been fully clarified yet, which brings great challenges to its effective prevention and treatment. MAPK signaling pathway regulates gene expression of eukaryotic cells and basic cellular processes such as cell proliferation, differentiation, migration, metabolism and apoptosis, which are considered as therapeutic targets for many diseases. Up to now, mounting evidence has shown that MAPK signaling pathway is involved in the pathogenesis and development of ischemic stroke. However, the upstream kinase and downstream kinase of MAPK signaling pathway are complex and the influencing factors are numerous, the exact role of MAPK signaling pathway in the pathogenesis of ischemic stroke has not been fully elucidated. MAPK signaling molecules in different cell types in the brain respond variously after stroke injury, therefore, the present review article is committed to summarizing the pathological process of different cell types participating in stroke, discussed the mechanism of MAPK participating in stroke. We further elucidated that MAPK signaling pathway molecules can be used as therapeutic targets for stroke, thus promoting the prevention and treatment of stroke.

Chronic Exposure to High Altitude: Synaptic, Astroglial and Memory Changes

Long-term operations carried out at high altitude (HA) by military personnel, pilots, and astronauts may trigger health complications. In particular, chronic exposure to high altitude (CEHA) has been associated with deficits in cognitive function. In this study, we found that mice exposed to chronic HA (5000 m for 12 weeks) exhibited deficits in learning and memory associated with hippocampal function and were linked with changes in the expression of synaptic proteins across various regions of the brain. Specifically, we found decreased levels of synaptophysin (SYP) (p < 0.05) and spinophilin (SPH) (p < 0.05) in the olfactory cortex, post synaptic density−95 (PSD-95) (p < 0.05), growth associated protein 43 (GAP43) (p < 0.05), glial fibrillary acidic protein (GFAP) (p < 0.05) in the cerebellum, and SYP (p < 0.05) and PSD-95 (p < 0.05) in the brainstem. Ultrastructural analyses of synaptic density and morphology in the hippocampus did not reveal any differences in CEHA mice compared to SL mice. Our data are novel and suggest that CEHA exposure leads to cognitive impairment in conjunction with neuroanatomically-based molecular changes in synaptic protein levels and astroglial cell marker in a region specific manner. We hypothesize that these new findings are part of highly complex molecular and neuroplasticity mechanisms underlying neuroadaptation response that occurs in brains when chronically exposed to HA.

Prenatal hypoxia produces memory deficits associated with impairment of long-term synaptic plasticity in young rats

Prenatal hypoxia often results in dramatic alterations in developmental profiles and behavioral characteristics, including learning and memory, in later life. Despite the accumulation of considerable amounts of experimental data, the mechanisms underlying developmental deficits caused by prenatal hypoxia remain unclear. In the present study, we investigated whether prenatal hypoxia on embryonic day 14 (E14) affected synaptic properties in the hippocampus and hippocampal-related cognitive functions in young rats. We found that 20- to 30-d-old rats subjected to prenatal hypoxia had significantly disturbed basal synaptic transmission in CA3-CA1 synapses and a two-fold decrease in hippocampal long-term synaptic potentiation. These alterations were accompanied by a significant decline in the protein level of GluN2B but not GluN2A NMDA receptor subunits. In addition, the number of synaptopodin-positive dendritic spines in the CA1 area of the hippocampus was reduced in the rats exposed to prenatal hypoxia. These changes resulted in significant learning and memory deficits in a novel object recognition test.

Mild Neonatal Brain Hypoxia-Ischemia in Very Immature Rats Causes Long-Term Behavioral and Cerebellar Abnormalities at Adulthood

Systemic hypoxia-ischemia (HI) often occurs during preterm birth in human. HI induces injuries to hinder brain cells mainly in the ipsilateral forebrain structures. Such HI injuries may cause lifelong disturbances in the distant regions, such as the contralateral side of the cerebellum. We aimed to evaluate behavior associated with the cerebellum, to acquire cerebellar abundant metabolic alterations using in vivo 1H magnetic resonance spectroscopy (1H MRS), and to determine GFAP, NeuN, and MBP protein expression in the left cerebellum, in adult rats after mild early postnatal HI on the right forebrain at day 3 (PND3). From PND45, HI animals exhibited increased locomotion in the open field while there is neither asymmetrical forelimb use nor coordination deficits in the motor tasks. Despite the fact that metabolic differences between two cerebellar hemispheres were noticeable, a global increase in glutamine of HI rats was observed and became significant in the left cerebellum compared to the sham-operated group. Furthermore, increases in glutamate, glycine, the sum of glutamate and glutamine and total choline, only occurred in the left cerebellum of HI rats. Remarkably, there were decreased expression of MBP and NeuN but no detectable reactive astrogliosis in the contralateral side of the cerebellum of HI rats. Taken together, the detected alterations observed in the left cerebellum of HI rats may reflect disequilibrium in the glutamate-glutamine cycle and a delay in the return of glutamine from astrocytes to neurons from hypoxic-ischemic origin. Our data provides in vivo evidence of long-term changes in the corresponding cerebellum following mild neonatal HI in very immature rats, supporting the notion that systemic HI could cause cell death in the cerebellum, a distant region from the expected injury site.

HIGHLIGHTS

-Neonatal hypoxia-ischemia (HI) in very immature rats induces hyperactivity toward adulthood.-1H magnetic resonance spectroscopy detects long-term cerebellar metabolic changes in adult rats after neonatal HI at postnatal day 3.-Substantial decreases of expression of neuronal and myelin markers in adult rats cerebellum after neonatal cortical mild HI.

Corpus callosum and cerebellar vermis size in very preterm infants: Relationship to long-term neurodevelopmental outcome

BACKGROUND

The neonatal changes of corpus callosum or cerebellar volume in preterm infants have been shown to link with abnormal mentality and motor disability in early childhood. This study aims to predict the long-term neurological outcomes by measuring these changes on neonatal brain ultrasound in preterm infants.

METHODS

Our cohort consisted of infants aged below 32 weeks' gestation with very low birth body weights who completed neuro-assessments at 5 years of age. Corpus callosum or cerebellar vermis were measured at 28-30 weeks and at 37-40 weeks gestational age in premature infants with cerebral palsy (CP), mental retardation (MR) and normal control premature infants.

RESULTS

There are 12 patients in MR group, 12 in CP group and 27 patients as controls for final analysis. There was no significant difference in other factors between study groups except lower gestational age (P = 0.043) in CP group. Respiratory distress syndrome was more common in MR group (P = 0.037) and cystic periventricular leukomalacia was more common in CP group (P < 0.001) than controls. After adjusting for sex and birth body weight, the MR group had smaller cerebellar vermis area at 37-40 gestational weeks (P = 0.002) than controls. They also reduced the growth of corpus callosum area (difference = -0.12 ± 0.16, P = 0.029) and cerebellar vermis area (difference = 1.10 ± 0.44, P = 0.020) from 28 to 30 gestational weeks to 37-40 gestational weeks compared with controls (difference = 0.03 ± 0.15, 1.92 ± 0.70, respectively). In contrast, the CP group had reduced the growth of corpus callosum body (difference = -0.02 ± 0.18, P = 0.034) compared with controls (difference = 0.03 ± 0.04). They subsequently had smaller body thickness of corpus callosum (0.10 ± 0.02, P = 0.015) at 37-40 gestational weeks than controls (0.14 ± 0.04).

CONCLUSIONS

Serial monitoring corpus callosum and cerebellar vermis size in early life of very preterm babies may predict the motor or mentality neurological outcome at 5 years of age.

Role of Prenatal Hypoxia in Brain Development, Cognitive Functions, and Neurodegeneration

This review focuses on the role of prenatal hypoxia in the development of brain functions in the postnatal period and subsequent increased risk of neurodegenerative disorders in later life. Accumulating evidence suggests that prenatal hypoxia in critical periods of brain formation results in significant changes in development of cognitive functions at various stages of postnatal life which correlate with morphological changes in brain structures involved in learning and memory. Prenatal hypoxia also leads to a decrease in brain adaptive potential and plasticity due to the disturbance in the process of formation of new contacts between cells and propagation of neuronal stimuli, especially in the cortex and hippocampus. On the other hand, prenatal hypoxia has a significant impact on expression and processing of a variety of genes involved in normal brain function and their epigenetic regulation. This results in changes in the patterns of mRNA and protein expression and their post-translational modifications, including protein misfolding and clearance. Among proteins affected by prenatal hypoxia are a key enzyme of the cholinergic system-acetylcholinesterase, and the amyloid precursor protein (APP), both of which have important roles in brain function. Disruption of their expression and metabolism caused by prenatal hypoxia can also result, apart from early cognitive dysfunctions, in development of neurodegeneration in later life. Another group of enzymes affected by prenatal hypoxia are peptidases involved in catabolism of neuropeptides, including amyloid-β peptide (Aβ). The decrease in the activity of neprilysin and other amyloid-degrading enzymes observed after prenatal hypoxia could result over the years in an Aβ clearance deficit and accumulation of its toxic species which cause neuronal cell death and development of neurodegeneration. Applying various approaches to restore expression of neuronal genes disrupted by prenatal hypoxia during postnatal development opens an avenue for therapeutic compensation of cognitive dysfunctions and prevention of Aβ accumulation in the aging brain and the model of prenatal hypoxia in rodents can be used as a reliable tool for assessment of their efficacy.

Hypoxia and myelination deficits in the developing brain

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

GABA function may be related to the impairment of learning and memory caused by systemic prenatal hypoxia-ischemia

Intrauterine adverse conditions may be responsible for long-lasting damages which impact health even during adult phase. Hypoxic-ischemic (HI) events are a relevant cause of newborn mortality and the principal factor leading to permanent brain lesions. Using a model in which the ovarian and uterine flux of a pregnant rat is obstructed for 45 min we have described oligodendrocyte death, astrogliosis and neuronal loss. In this work we investigated hippocampal neuronal population and performed a functional evaluation of memory and learning of young rats that had been affected by prenatal HI. Anesthetized Wistar rats on the 18th gestation day had the uterine horns exposed and the ovarian and uterine arteries clamped for 45 min (HI group). Sham-operated rats (SH group) had the horns exposed but no arteries were clamped. We measured the levels of different proteins related to excitatory/inhibitory transmission in the hippocampi of young pups (P45). Histological evaluation was also performed in order to characterize hippocampal neuronal population. Rats from both groups were tested through Novel Object Recognition Test (NORT) using two inter-trial intervals: 5 min and 8 h. Here we show a loss in the total number of hippocampal neurons although the immunostaining of parvalbumin and levels of GAD enzyme were increased in HI group. Functional assessment indicated a marked difference concerning HI learning and memory abilities. Our results reflect permanent damages concerning GABA function which may disturb neurotransmitter homeostasis leading to the observed deficits in learning and memory.