Fetal hypoxia insults and patterns of brain injury: insights from animal models

Rapid detection of fetal compromise using input length invariant deep learning on fetal heart rate signals

Standard clinical practice to assess fetal well-being during labour utilises monitoring of the fetal heart rate (FHR) using cardiotocography. However, visual evaluation of FHR signals can result in subjective interpretations leading to inter and intra-observer disagreement. Therefore, recent studies have proposed deep-learning-based methods to interpret FHR signals and detect fetal compromise. These methods have typically focused on evaluating fixed-length FHR segments at the conclusion of labour, leaving little time for clinicians to intervene. In this study, we propose a novel FHR evaluation method using an input length invariant deep learning model (FHR-LINet) to progressively evaluate FHR as labour progresses and achieve rapid detection of fetal compromise. Using our FHR-LINet model, we obtained approximately 25% reduction in the time taken to detect fetal compromise compared to the state-of-the-art multimodal convolutional neural network while achieving 27.5%, 45.0%, 56.5% and 65.0% mean true positive rate at 5%, 10%, 15% and 20% false positive rate respectively. A diagnostic system based on our approach could potentially enable earlier intervention for fetal compromise and improve clinical outcomes.

MRI predictors of long-term outcomes of neonatal hypoxic ischaemic encephalopathy: a primer for radiologists

This review aims to serve as a foundational resource for general radiologists, enhancing their understanding of the role of Magnetic Resonance Imaging (MRI) in early prognostication for newborns diagnosed with hypoxic ischaemic encephalopathy (HIE). The article explores the application of MRI as a predictive instrument for determining long-term outcomes in newborns affected by HIE. With HIE constituting a leading cause of neonatal mortality and severe long-term neurodevelopmental impairments, early identification of prognostic indicators is crucial for timely intervention and optimal clinical management. We examine current literature and recent advancements to provide an in-depth overview of MRI predictors, encompassing brain injury patterns, injury scoring systems, spectroscopy, and diffusion imaging. The potential of these MRI biomarkers in predicting long-term neurodevelopmental outcomes and the probability of epilepsy is also discussed.

Intrauterine inflammation and postnatal intravenous dopamine alter the neurovascular unit in preterm newborn lambs

BACKGROUND

Intrauterine inflammation is considered a major cause of brain injury in preterm infants, leading to long-term neurodevelopmental deficits. A potential contributor to this brain injury is dysregulation of neurovascular coupling. We have shown that intrauterine inflammation induced by intra-amniotic lipopolysaccharide (LPS) in preterm lambs, and postnatal dopamine administration, disrupts neurovascular coupling and the functional cerebral haemodynamic responses, potentially leading to impaired brain development. In this study, we aimed to characterise the structural changes of the neurovascular unit following intrauterine LPS exposure and postnatal dopamine administration in the brain of preterm lambs using cellular and molecular analyses.

METHODS

At 119-120 days of gestation (term = 147 days), LPS was administered into the amniotic sac in pregnant ewes. At 126-7 days of gestation, the LPS-exposed lambs were delivered, ventilated and given either a continuous intravenous infusion of dopamine at 10 µg/kg/min or isovolumetric vehicle solution for 90 min (LPS, n = 6; LPSDA, n = 6). Control preterm lambs not exposed to LPS were also administered vehicle or dopamine (CTL, n = 9; CTLDA, n = 7). Post-mortem brain tissue was collected 3-4 h after birth for immunohistochemistry and RT-qPCR analysis of components of the neurovascular unit.

RESULTS

LPS exposure increased vascular leakage in the presence of increased vascular density and remodelling with increased astrocyte "end feet" vessel coverage, together with downregulated mRNA levels of the tight junction proteins Claudin-1 and Occludin. Dopamine administration decreased vessel density and size, decreased endothelial glucose transporter, reduced neuronal dendritic coverage, increased cell proliferation within vessel walls, and increased pericyte vascular coverage particularly within the cortical and deep grey matter. Dopamine also downregulated VEGFA and Occludin tight junction mRNA, and upregulated dopamine receptor DRD1 and oxidative protein (NOX1, SOD3) mRNA levels. Dopamine administration following LPS exposure did not exacerbate any effects induced by LPS.

CONCLUSION

LPS exposure and dopamine administration independently alters the neurovascular unit in the preterm brain. Alterations to the neurovascular unit may predispose the developing brain to further injury.

Neuroquantification enhances the radiological evaluation of term neonatal hypoxic-ischaemic cerebral injuries

Background

Injury patterns in hypoxic-ischaemic brain injury (HIBI) are well recognised but there are few studies evaluating cerebral injury using neuroquantification models.

Objectives

Quantification of brain volumes in a group of patients with clinically determined cerebral palsy.

Method

In this retrospective study, 297 children with cerebral palsy were imaged for suspected HIBI with analysis of various cerebral substrates. Of these, 96 children over the age of 3 years with a clinical diagnosis of cerebral palsy and abnormal MRI findings underwent volumetric analyses using the NeuroQuant® software solution. The spectrum of volumetric changes and the differences between the various subtypes (and individual subgroups) of HIBI were compared.

Results

Compared with the available normative NeuroQuant® database, the average intracranial volume was reduced to the 1st percentile in all patient groups (p < 0.001). Statistically significant differences were observed among the types and subgroups of HIBI. Further substrate volume reductions were identified and described involving the thalami, brainstem, hippocampi, putamina and amygdala. The combined volumes of five regions of interest (frontal pole, putamen, hippocampus, brainstem and paracentral lobule) were consistently reduced in the Rolandic basal ganglia-thalamus (RBGT) subtype.

Conclusion

This study determined a quantifiable reduction of intracranial volume in all subtypes of HIBI and predictable selective cerebral substrate volume reduction in subtypes and subgroups. In the RBGT subtype, a key combination of five substrate injuries was consistently noted, and thalamic, occipital lobe and brainstem volume reduction was also significant when compared to the watershed subtype.

Contribution

This study demonstrates the value of integrating an artificial intelligence programme into the radiologists' armamentarium serving to quantify brain injuries more accurately in HIBI. Going forward this will be an inevitable evolution of daily radiology practice in many fields of medicine, and it would be beneficial for radiologists to embrace these technological innovations.

Edaravone Confers Neuroprotective, Anti-inflammatory, and Antioxidant Effects on the Fetal Brain of a Placental-ischemia Mouse Model

Reduced uterine perfusion pressure (RUPP) is a well-established model which mimics many clinical features of preeclampsia (PE). Edaravone is a free radical scavenger with neuroprotective, antioxidant and anti-inflammatory effects against different models of cerebral ischemia. Therefore, we aimed to elucidate the different potential mechanisms through which PE affects fetal brain development using our previously established RUPP-placental ischemia mouse model. In addition, we investigated the neuroprotective effect of edaravone against the RUPP-induced fetal brain development alterations. On gestation day (GD) 13, pregnant mice were divided into four groups; sham (SV), edaravone (SE), RUPP (RV), and RUPP+edaravone (RE). SV and SE groups underwent sham surgeries, however, RV and RE groups were subjected to RUPP surgery via bilateral uterine ligation. Edaravone (3mg/kg) was injected via tail i.v. injection from GD 14-18. The fetal brains from different groups were collected on GD 18 and subjected to further investigations. The results showed that RUPP altered the structure of fetal brain cortex, induced neurodegeneration, increased the expression of the investigated pro-inflammatory markers; TNF-α, IL-6, IL-1β, and MMP-9. RUPP resulted in microglial and astrocyte activation in the fetal brains, in addition to upregulation of Hif-1α and iNOS. Edaravone conferred a neuroprotective effect via alleviating the inflammatory response, restoring the neuronal structure and decreasing oxidative stress in the developing fetal brain. In conclusion, RUPP-placental ischemia mouse model could be a useful tool to further understand the underlying mechanisms of PE-induced child neuronal alterations. Edaravone could be a potential adjuvant therapy during PE to protect the developing fetal brain. The current study investigated the effects of a placenta-induced ischemia mouse model using reduced uterine perfusion pressure (RUPP) surgery on the fetal brain development and the potential neuroprotective effects of the drug edaravone. The study found that the RUPP model caused neurodegeneration and a pro-inflammatory response in the developing fetal brain, as well as hypoxia and oxidative stress. However, maternal injection of edaravone showed a strong ability to protect against these detrimental effects and target multiple pathways associated with neuronal damage. The current study suggests that the RUPP model could be useful for further study of the impact of preeclampsia on fetal brain development and that edaravone may have potential as a therapy for protecting against this damage.

Subcortical brain volumes in neonatal hypoxic-ischemic encephalopathy

BACKGROUND

Despite treatment with therapeutic hypothermia, hypoxic-ischemic encephalopathy (HIE) is associated with adverse developmental outcomes, suggesting the involvement of subcortical structures including the thalamus and basal ganglia, which may be vulnerable to perinatal asphyxia, particularly during the acute period. The aims were: (1) to examine subcortical macrostructure in neonates with HIE compared to age- and sex-matched healthy neonates within the first week of life; (2) to determine whether subcortical brain volumes are associated with HIE severity.

METHODS

Neonates (n = 56; HIE: n = 28; Healthy newborns from the Developing Human Connectome Project: n = 28) were scanned with MRI within the first week of life. Subcortical volumes were automatically extracted from T1-weighted images. General linear models assessed between-group differences in subcortical volumes, adjusting for sex, gestational age, postmenstrual age, and total cerebral volumes. Within-group analyses evaluated the association between subcortical volumes and HIE severity.

RESULTS

Neonates with HIE had smaller bilateral thalamic, basal ganglia and right hippocampal and cerebellar volumes compared to controls (all, p < 0.02). Within the HIE group, mild HIE severity was associated with smaller volumes of the left and right basal ganglia (both, p < 0.007) and the left hippocampus and thalamus (both, p < 0.04).

CONCLUSIONS

Findings suggest that, despite advances in neonatal care, HIE is associated with significant alterations in subcortical brain macrostructure.

IMPACT

Compared to their healthy counterparts, infants with HIE demonstrate significant alterations in subcortical brain macrostructure on MRI acquired as early as 4 days after birth. Smaller subcortical volumes impacting sensory and motor regions, including the thalamus, basal ganglia, and cerebellum, were seen in infants with HIE. Mild and moderate HIE were associated with smaller subcortical volumes.

Neuroserpin As an Adjuvant Therapy for Hypothermia on Brain Injury in Neonatal Hypoxic-Ischemic Rats

OBJECTIVE

 We aimed to assess the effects of neuroserpin and its combination with hypothermia on hypoxic-ischemic (HI) brain injury in neonatal rats. Neuroserpin is an axon-secreted serine protease inhibitor and is important for brain development, neuronal survival, and synaptic plasticity.

STUDY DESIGN

 Male Wistar-Albino rats on postnatal day 7 (P7) were randomly divided into five groups: sham group (n = 10), (HI; n = 10), hypoxic-ischemic hypothermia (HIH; n = 10), hypoxic-ischemic neuroserpin (HIN; n = 10), and hypoxic-ischemic neuroserpin-hypothermia (HINH; n = 10). The P7 rat brain's maturation is similar to a late preterm human brain at 34 to 36 weeks of gestation. HI was induced in rats on P7 as previously described. A single dose of 0.2 µM neuroserpin (HINH and HIN) or an equivalent volume of phosphate-buffered saline (sham, HIH, and HI) was administered intraventricularly by a Hamilton syringe immediately after hypoxia. In the follow-up, pups were subjected to systemic hypothermia or normothermia for 2 hours. Euthanasia was performed for histopathological evaluation on P10. Apoptosis was detected by caspase-3 activity and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining and was counted in the hippocampus.

RESULTS

 In comparison to the HI group, the TUNEL-positive and caspase-3-positive neurons in the sham, HIN, HIH, and HINH groups were considerably lower (13.4 ± 1.0 vs. 1.9 ± 0.9, 6.0 ± 0.9, 5.3 ± 1.6, and 4.0 ± 1.1; p < 0.001) and (13.5 ± 1.7 vs. 1.2 ± 0.7, 9.1 ± 2.7, 4.8 ± 1.0, and 3.9 ± 1.6; p < 0.001). HIN, HIH, and HINH, compared to the sham group, showed more TUNEL-positive and caspase-3-positive neurons (6.0 ± 0.9, 5.3 ± 1.6, 4.0 ± 1.1 vs. 1.9 ± 0.9 and 9.1 ± 2.7, 4.8 ± 1.0, 3.9 ± 1.6 vs. 1.2 ± 0.7; p < 0.001). The HINH group (synergistic effect) had significantly fewer TUNEL-positive neurons and caspase-3-positive neurons than the HIN group (4.0 ± 1.1vs. 6.0 ± 0.9 and 3.9 ± 1.6 vs. 9.1 ± 2.7; p < 0.001).

CONCLUSION

 Our study showed that both neuroserpin alone and as an adjuvant treatment for hypothermia may have a neuroprotective effect on brain injury.

KEY POINTS

· Neuroserpin decreased brain injury.. · Neuroserpin showed a synergistic effect when used as an adjuvant treatment for hypothermia.. · The neuroprotective effect of neuroserpine was related to its antiapoptotic properties..

Association of cerebral metabolic rate following therapeutic hypothermia with 18-month neurodevelopmental outcomes after neonatal hypoxic ischemic encephalopathy

BACKGROUND

Therapeutic hypothermia (TH) is standard of care for moderate to severe neonatal hypoxic ischemic encephalopathy (HIE) but many survivors still suffer lifelong disabilities and benefits of TH for mild HIE are under active debate. Development of objective diagnostics, with sensitivity to mild HIE, are needed to select, guide, and assess response to treatment. The objective of this study was to determine if cerebral oxygen metabolism (CMRO2) in the days after TH is associated with 18-month neurodevelopmental outcomes as the first step in evaluating CMRO2's potential as a diagnostic for HIE. Secondary objectives were to compare associations with clinical exams and characterise the relationship between CMRO2 and temperature during TH.

METHODS

This was a prospective, multicentre, observational, cohort study of neonates clinically diagnosed with HIE and treated with TH recruited from the tertiary neonatal intensive care units (NICUs) of Boston Children's Hospital, Brigham and Women's Hospital, and Beth Israel Deaconess Medical Center between December 2015 and October 2019 with follow-up to 18 months. In total, 329 neonates ≥34 weeks gestational age admitted with perinatal asphyxia and suspected HIE were identified. 179 were approached, 103 enrolled, 73 received TH, and 64 were included. CMRO2 was measured at the NICU bedside by frequency-domain near-infrared and diffuse correlation spectroscopies (FDNIRS-DCS) during the late phases of hypothermia (C), rewarming (RW) and after return to normothermia (NT). Additional variables were body temperature and clinical neonatal encephalopathy (NE) scores, as well as findings from magnetic resonance imaging (MRI) and spectroscopy (MRS). Primary outcome was the Bayley Scales of Infant and Toddler Development, Third Edition (BSID-III) at 18 months, normed (SD) to 100 (15).

FINDINGS

Data quality for 58 neonates was sufficient for analysis. CMRO2 changed by 14.4% per °C (95% CI, 14.2-14.6) relative to its baseline at NT while cerebral tissue oxygen extraction fraction (cFTOE) changed by only 2.2% per °C (95% CI, 2.1-2.4) for net changes from C to NT of 91% and 8%, respectively. Follow-up data for 2 were incomplete, 33 declined and 1 died, leaving 22 participants (mean [SD] postnatal age, 19.1 [1.2] month; 11 female) with mild to moderate HIE (median [IQR] NE score, 4 [3-6]) and 21 (95%) with BSID-III scores >85 at 18 months. CMRO2 at NT was positively associated with cognitive and motor composite scores (β (SE) = 4.49 (1.55) and 2.77 (1.00) BSID-III points per 10-10 moL/dl × mm2/s, P = 0.009 and P = 0.01 respectively; linear regression); none of the other measures were associated with the neurodevelopmental outcomes.

INTERPRETATION

Point of care measures of CMRO2 in the NICU during C and RW showed dramatic changes and potential to assess individual response to TH. CMRO2 following TH outperformed conventional clinical evaluations (NE score, cFTOE, and MRI/MRS) at predicting cognitive and motor outcomes at 18 months for mild to moderate HIE, providing a promising objective, physiologically-based diagnostic for HIE.

FUNDING

This clinical study was funded by an NIH grant from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, United States (R01HD076258).

Velocity Time Integral: A Novel Method for Assessing Fetal Anemia

The velocity time integral (VTI) is a clinical Doppler ultrasound measurement of blood flow, measured by the area under the wave curve and equivalent to the distance traveled by the blood. This retrospective study assessed the middle cerebral artery (MCA) VTI of fetuses in pregnancies complicated by maternal alloimmunization. Doppler indices of the MCA were retrieved from electronic medical records. Systolic deceleration-diastolic time, systolic acceleration time, VTI, and peak systolic velocity (PSV) were measured at 16-40 weeks gestation. Cases with PSV indicating fetal anemia (cutoff 1.5 MoM) and normal PSV were compared. The study included 255 Doppler ultrasound examinations. Of these, 41 were at 16-24 weeks (group A), 100 were at 25-32 weeks (group B), and 114 were at 33-40 weeks (group C). VTI increased throughout gestation (5.5 cm, 8.6 cm, and 12.1 cm in groups A, B, and C, respectively, p = 0.003). VTI was higher in waveforms calculated to have MCA-PSV ≥ 1.5 MoM compared to those with MCA-PSV < 1.5 MoM (9.1 cm vs. 14.1 cm, respectively, p < 0.001), as was VTI/s (22.04 cm/s vs. 33.75 cm/s, respectively; p < 0.001). The results indicate that the MCA VTI increases significantly among fetuses with suspected anemia, indicating higher perfusion of hemodiluted blood to the brain. This feasible measurement might provide a novel additional marker for the development of fetal anemia.

Optimizing the management of acute, prolonged decelerations and fetal bradycardia based on the understanding of fetal pathophysiology

Any acute and profound reduction in fetal oxygenation increases the risk of anaerobic metabolism in the fetal myocardium and, hence, the risk of lactic acidosis. On the contrary, in a gradually evolving hypoxic stress, there is sufficient time to mount a catecholamine-mediated increase in the fetal heart rate to increase the cardiac output and redistribute oxygenated blood to maintain an aerobic metabolism in the fetal central organs. When the hypoxic stress is sudden, profound, and sustained, it is not possible to continue to maintain central organ perfusion by peripheral vasoconstriction and centralization. In case of acute deprivation of oxygen, the immediate chemoreflex response via the vagus nerve helps reduce fetal myocardial workload by a sudden drop of the baseline fetal heart rate. If this drop in the fetal heart rate continues for >2 minutes (American College of Obstetricians and Gynecologists' guideline) or 3 minutes (National Institute for Health and Care Excellence or physiological guideline), it is termed a prolonged deceleration, which occurs because of myocardial hypoxia, after the initial chemoreflex. The revised International Federation of Gynecology and Obstetrics guideline (2015) considers the prolonged deceleration to be a "pathologic" feature after 5 minutes. Acute intrapartum accidents (placental abruption, umbilical cord prolapse, and uterine rupture) should be excluded immediately, and if they are present, an urgent birth should be accomplished. If a reversible cause is found (maternal hypotension, uterine hypertonus or hyperstimulation, and sustained umbilical cord compression), immediate conservative measures (also called intrauterine fetal resuscitation) should be undertaken to reverse the underlying cause. In reversible causes of acute hypoxia, if the fetal heart rate variability is normal before the onset of deceleration, and normal within the first 3 minutes of the prolonged deceleration, then there is an increased likelihood of recovery of the fetal heart rate to its antecedent baseline within 9 minutes with the reversal of the underlying cause of acute and profound reduction in fetal oxygenation. The continuation of the prolonged deceleration for >10 minutes is termed "terminal bradycardia," and this increases the risk of hypoxic-ischemic injury to the deep gray matter of the brain (the thalami and the basal ganglia), predisposing to dyskinetic cerebral palsy. Therefore, any acute fetal hypoxia, which manifests as a prolonged deceleration on the fetal heart rate tracing, should be considered an intrapartum emergency requiring an immediate intervention to optimize perinatal outcome. In uterine hypertonus or hyperstimulation, if the prolonged deceleration persists despite stopping the uterotonic agent, then acute tocolysis is recommended to rapidly restore fetal oxygenation. Regular clinical audit of the management of acute hypoxia, including the "the onset of bradycardia to delivery interval," may help identify organizational and system issues, which may contribute to poor perinatal outcomes.

Fetal defenses against intrapartum head compression-implications for intrapartum decelerations and hypoxic-ischemic injury

Uterine contractions during labor and engagement of the fetus in the birth canal can compress the fetal head. Its impact on the fetus is unclear and still controversial. In this integrative physiological review, we highlight evidence that decelerations are uncommonly associated with fetal head compression. Next, the fetus has an impressive ability to adapt to increased intracranial pressure through activation of the intracranial baroreflex, such that fetal cerebral perfusion is well-maintained during labor, except in the setting of prolonged systemic hypoxemia leading to secondary cardiovascular compromise. Thus, when it occurs, fetal head compression is not necessarily benign but does not seem to be a common contributor to intrapartum decelerations. Finally, the intracranial baroreflex and the peripheral chemoreflex (the response to acute hypoxemia) have overlapping efferent effects. We propose the hypothesis that these reflexes may work synergistically to promote fetal adaptation to labor.

Cerebral Blood Flow of the Neonatal Brain after Hypoxic-Ischemic Injury

OBJECTIVE

Hypoxic-ischemic encephalopathy (HIE) in infants can have long-term adverse neurodevelopmental effects and markedly reduce quality of life. Both the initial hypoperfusion and the subsequent rapid reperfusion can cause deleterious effects in brain tissue. Cerebral blood flow (CBF) assessment in newborns with HIE can help detect abnormalities in brain perfusion to guide therapy and prognosticate patient outcomes.

STUDY DESIGN

The review will provide an overview of the pathophysiological implications of CBF derangements in neonatal HIE, current and emerging techniques for CBF quantification, and the potential to utilize CBF as a physiologic target in managing neonates with acute HIE.

CONCLUSION

The alterations of CBF in infants during hypoxia-ischemia have been studied by using different neuroimaging techniques, including nitrous oxide and xenon clearance, transcranial Doppler ultrasonography, contrast-enhanced ultrasound, arterial spin labeling MRI, 18F-FDG positron emission tomography, near-infrared spectroscopy (NIRS), functional NIRS, and diffuse correlation spectroscopy. Consensus is lacking regarding the clinical significance of CBF estimations detected by these different modalities. Heterogeneity in the imaging modality used, regional versus global estimations of CBF, time for the scan, and variables impacting brain perfusion and cohort clinical characteristics should be considered when translating the findings described in the literature to routine practice and implementation of therapeutic interventions.

KEY POINTS

· Hypoxic-ischemic injury in infants can result in adverse long-term neurologic sequelae.. · Cerebral blood flow is a useful biomarker in neonatal hypoxic-ischemic injury.. · Imaging modality, variables affecting cerebral blood flow, and patient characteristics affect cerebral blood flow assessment..

Hypoxic-Ischemic Encephalopathy: Changing Outcomes Across the Spectrum

Neonatal hypoxic-ischemic encephalopathy (HIE) is a leading cause of death and neurodevelopmental impairment in neonates. Therapeutic hypothermia (TH) is the only established effective therapy and randomized trials affirm that TH reduces death and disability in moderate-to-severe HIE. Traditionally, infants with mild HIE were excluded from these trials due to the perceived low risk for impairment. Recently, multiple studies suggest that infants with untreated mild HIE may be at significant risk of abnormal neurodevelopmental outcomes. This review will focus on the changing landscape of TH, the spectrum of HIE presentations and their neurodevelopmental outcomes.

Epilepsy syndromes in cerebral palsy: varied, evolving and mostly self-limited

Seizures occur in approximately one-third of children with cerebral palsy. This study aimed to determine epilepsy syndromes in children with seizures and cerebral palsy due to vascular injury, anticipating that this would inform treatment and prognosis. We studied a population-based cohort of children with cerebral palsy due to prenatal or perinatal vascular injuries, born 1999-2006. Each child's MRI was reviewed to characterize patterns of grey and white matter injury. Children with syndromic or likely genetic causes of cerebral palsy were excluded, given their inherent association with epilepsy and our aim to study a homogeneous cohort of classical cerebral palsy. Chart review, parent interview and EEGs were used to determine epilepsy syndromes and seizure outcomes. Of 256 children, 93 (36%) had one or more febrile or afebrile seizures beyond the neonatal period and 87 (34%) had epilepsy. Children with seizures were more likely to have had neonatal seizures, have spastic quadriplegic cerebral palsy and function within Gross Motor Function Classification System level IV or V. Fifty-six (60%) children with seizures had electroclinical features of a self-limited focal epilepsy of childhood; we diagnosed these children with a self-limited focal epilepsy-variant given the current International League Against Epilepsy classification precludes a diagnosis of self-limited focal epilepsy in children with a brain lesion. Other epilepsy syndromes were focal epilepsy-not otherwise specified in 28, infantile spasms syndrome in 11, Lennox-Gastaut syndrome in three, genetic generalized epilepsies in two and febrile seizures in nine. No epilepsy syndrome could be assigned in seven children with no EEG. Twenty-one changed syndrome classification during childhood. Self-limited focal epilepsy-variant usually manifested with a mix of autonomic and brachio-facial motor features, and occipital and/or centro-temporal spikes on EEG. Of those with self-limited focal epilepsy-variant, 42/56 (75%) had not had a seizure for >2 years. Favourable seizure outcomes were also seen in some children with infantile spasms syndrome and focal epilepsy-not otherwise specified. Of the 93 children with seizures, at last follow-up (mean age 15 years), 61/91 (67%) had not had a seizure in >2 years. Children with cerebral palsy and seizures can be assigned specific epilepsy syndrome diagnoses typically reserved for normally developing children, those syndromes commonly being age-dependent and self-limited. Compared to typically developing children with epilepsy, self-limited focal epilepsy-variant occurs much more commonly in children with cerebral palsy and epilepsy. These findings have important implications for treatment and prognosis of epilepsy in cerebral palsy, and research into pathogenesis of self-limited focal epilepsy.

Creatine in the fetal brain: A regional investigation of acute global hypoxia and creatine supplementation in a translational fetal sheep model

Background

Creatine supplementation during pregnancy is a promising prophylactic treatment for perinatal hypoxic brain injury. Previously, in near-term sheep we have shown that fetal creatine supplementation reduces cerebral metabolic and oxidative stress induced by acute global hypoxia. This study investigated the effects of acute hypoxia with or without fetal creatine supplementation on neuropathology in multiple brain regions.

Methods

Near-term fetal sheep were administered continuous intravenous infusion of either creatine (6 mg kg^-1 h^-1) or isovolumetric saline from 122 to 134 days gestational age (dGA; term is approx. 145 dGA). At 131 dGA, global hypoxia was induced by a 10 min umbilical cord occlusion (UCO). Fetuses were then recovered for 72 h at which time (134 dGA) cerebral tissue was collected for either RT-qPCR or immunohistochemistry analyses.

Results

UCO resulted in mild injury to the cortical gray matter, thalamus and hippocampus, with increased cell death and astrogliosis and downregulation of genes involved in regulating injury responses, vasculature development and mitochondrial integrity. Creatine supplementation reduced astrogliosis within the corpus callosum but did not ameliorate any other gene expression or histopathological changes induced by hypoxia. Of importance, effects of creatine supplementation on gene expression irrespective of hypoxia, including increased expression of anti-apoptotic (BCL-2) and pro-inflammatory (e.g., MPO, TNFa, IL-6, IL-1β) genes, particularly in the gray matter, hippocampus, and striatum were identified. Creatine treatment also effected oligodendrocyte maturation and myelination in white matter regions.

Conclusion

While supplementation did not rescue mild neuropathology caused by UCO, creatine did result in gene expression changes that may influence in utero cerebral development.

Cerebral hemodynamic response during the resuscitation period after hypoxic-ischemic insult predicts brain injury on day 5 after insult in newborn piglets

Perinatal hypoxic-ischemic brain injury of neonates remains a significant problem worldwide. During the resuscitation period, changes in cerebral hemoglobin oxygen saturation (ScO₂) have been identified by near-infrared spectroscopy (NIRS). However, in asphyxiated neonates, the relationship between these changes and brain injury is not known. Three-wavelength near-infrared time-resolved spectroscopy, an advanced technology for NIRS, allows for the estimation of ScO₂ and cerebral blood volume (CBV). Here, we studied changes in ScO₂ and CBV during the resuscitation period after hypoxic-ischemic insult and the relationship between these changes after insult and histopathological brain injuries on day 5 after insult using an asphyxiated piglet model. Of 36 newborn piglets subjected to hypoxic-ischemic insult, 29 were analyzed. ScO₂ and CBV were measured 0, 5, 10, 15, and 30 min after the insult. Brain tissue was histologically evaluated on day 5. ScO₂ and CBV increased immediately after the insult, reached a peak, and then maintained a consistent value. The increase in CBV 5 to 30 min after the insult was significantly correlated with histopathological injury scores. However, there was no correlation with ScO₂. In conclusion, an increase in CBV within 30 min after hypoxic-ischemic insult reflects the histopathological brain injury on day 5 after insult in a piglet model.

An Inexpensive Open-Source Chamber for Controlled Hypoxia/Hyperoxia Exposure

Understanding hypoxia/hyperoxia exposure requires either a high-altitude research facility or a chamber in which gas concentrations are precisely and reproducibly controlled. Hypoxia-induced conditions such as hypoxic-ischemic encephalopathy (HIE), obstructive or central apneas, and ischemic stroke present unique challenges for the development of models with acute or chronic hypoxia exposure. Many murine models exist to study these conditions; however, there are a variety of different hypoxia exposure protocols used across laboratories. Experimental equipment for hypoxia exposure typically includes flow regulators, nitrogen concentrators, and premix oxygen/nitrogen tanks. Commercial hypoxia/hyperoxia chambers with environmental monitoring are incredibly expensive and require proprietary software with subscription fees or highly expensive software licenses. Limitations exist in these systems as most are single animal systems and not designed for extended or intermittent hypoxia exposure. We have developed a simple hypoxia chamber with off-the-shelf components, and controlled by open-source software for continuous data acquisition of oxygen levels and other environmental factors (temperature, humidity, pressure, light, sound, etc.). Our chamber can accommodate up to two mouse cages and one rat cage at any oxygen level needed, when using a nitrogen concentrator or premixed oxygen/nitrogen tank with a flow regulator, but is also scalable. Our system uses a Python-based script to save data in a text file using modules from the sensor vendor. We utilized Python or R scripts for data analysis, and we have provided examples of data analysis scripts and acquired data for extended exposure periods (≤7 days). By using FLOS (Free-Libre and open-source) software and hardware, we have developed a low-cost and customizable system that can be used for a variety of exposure protocols. This hypoxia/hyperoxia exposure chamber allows for reproducible and transparent data acquisition and increased consistency with a high degree of customization for each experimenter’s needs.

Creatine supplementation reduces the cerebral oxidative and metabolic stress responses to acute in utero hypoxia in the late-gestation fetal sheep

Abstract

Prophylactic creatine treatment may reduce hypoxic brain injury due to its ability to sustain intracellular ATP levels thereby reducing oxidative and metabolic stress responses during oxygen deprivation. Using microdialysis, we investigated the real‐time in vivo effects of fetal creatine supplementation on cerebral metabolism following acute in utero hypoxia caused by umbilical cord occlusion (UCO). Fetal sheep (118 days’ gestational age (dGA)) were implanted with an inflatable Silastic cuff around the umbilical cord and a microdialysis probe inserted into the right cerebral hemisphere for interstitial fluid sampling. Creatine (6 mg kg⁻¹ h⁻¹) or saline was continuously infused intravenously from 122 dGA. At 131 dGA, a 10 min UCO was induced. Hourly microdialysis samples were obtained from −24 to 72 h post‐UCO and analysed for percentage change of hydroxyl radicals (^•OH) and interstitial metabolites (lactate, pyruvate, glutamate, glycerol, glycine). Histochemical markers of protein and lipid oxidation were assessed at post‐mortem 72 h post‐UCO. Prior to UCO, creatine treatment reduced pyruvate and glycerol concentrations in the microdialysate outflow. Creatine treatment reduced interstitial cerebral ^•OH outflow 0 to 24 h post‐UCO. Fetuses with higher arterial creatine concentrations before UCO presented with reduced levels of hypoxaemia (PO2 and SO2) during UCO which associated with reduced interstitial cerebral pyruvate, lactate and ^•OH accumulation. No effects of creatine treatment on immunohistochemical markers of oxidative stress were found. In conclusion, fetal creatine treatment decreased cerebral outflow of ^•OH and was associated with an improvement in cerebral bioenergetics following acute hypoxia.

Key points

Fetal hypoxia can cause persistent metabolic and oxidative stress responses that disturb energy homeostasis in the brain. Creatine in its phosphorylated form is an endogenous phosphagen; therefore, supplementation is a proposed prophylactic treatment for fetal hypoxia.

Fetal sheep instrumented with a cerebral microdialysis probe were continuously infused with or without creatine‐monohydrate for 10 days before induction of 10 min umbilical cord occlusion (UCO; 131 days’ gestation). Cerebral interstitial fluid was collected up to 72 h following UCO.

Prior to UCO, fetal creatine supplementation reduced interstitial cerebral pyruvate and glycerol concentrations.

Fetal creatine supplementation reduced cerebral hydroxyl radical efflux up to 24 h post‐UCO. Fetuses with higher arterial creatine concentrations before UCO and reduced levels of systemic hypoxaemia during UCO were associated with reduced cerebral interstitial pyruvate, lactate and ^•OH following UCO.

Creatine supplementation leads to some improvements in cerebral bioenergetics following in utero acute hypoxia.

Magnetic Resonance Imaging in (Near-)Term Infants with Hypoxic-Ischemic Encephalopathy

Hypoxic-ischemic encephalopathy (HIE) is a major cause of neurological sequelae in (near-)term newborns. Despite the use of therapeutic hypothermia, a significant number of newborns still experience impaired neurodevelopment. Neuroimaging is the standard of care in infants with HIE to determine the timing and nature of the injury, guide further treatment decisions, and predict neurodevelopmental outcomes. Cranial ultrasonography is a helpful noninvasive tool to assess the brain before initiation of hypothermia to look for abnormalities suggestive of HIE mimics or antenatal onset of injury. Magnetic resonance imaging (MRI) which includes diffusion-weighted imaging has, however, become the gold standard to assess brain injury in infants with HIE, and has an excellent prognostic utility. Magnetic resonance spectroscopy provides complementary metabolic information and has also been shown to be a reliable prognostic biomarker. Advanced imaging modalities, including diffusion tensor imaging and arterial spin labeling, are increasingly being used to gain further information about the etiology and prognosis of brain injury. Over the past decades, tremendous progress has been made in the field of neonatal neuroimaging. In this review, the main brain injury patterns of infants with HIE, the application of conventional and advanced MRI techniques in these newborns, and HIE mimics, will be described.

Short-term morbidity and types of intrapartum hypoxia in the newborn with metabolic acidaemia: a retrospective cohort study

Objectives

To assess labour characteristics in relation to the occurrence of Composite Adverse neonatal Outcome (CAO) within a cohort of fetuses with metabolic acidaemia.

Design

Retrospective cohort study.

Setting

Three Italian tertiary maternity units.

Population

431 neonates born with acidaemia ≥36 weeks.

Methods

Intrapartum CTG traces were assigned to one of these four types of labour hypoxia: acute, subacute, gradually evolving and chronic hypoxia. The presence of CAO was defined by the occurrence of at least one of the following: Sarnat Score grade ≥2, seizures, hypothermia and death <7 days from birth.

Main outcome measures

To compare the type of hypoxia on the intrapartum CTG traces among the acidaemic neonates with and without CAO.

Results

The occurrence of a CAO was recorded in 15.1% of neonates. At logistic regression analysis, the duration of the hypoxia was the only parameter associated with CAO in the case of an acute or subacute pattern (odds ratio [OR] 1.3; 95% CI 1.02–1.6 and OR 1.04; 95% CI 1.0–1.1, respectively), whereas both the duration of the hypoxic insult and the time from PROM to delivery were associated with CAO in those with a gradually evolving pattern (OR 1.13; 95% CI 1.01–1.3 and OR 1.04; 95% CI 1.0–1.7, respectively). The incidence of CAO was higher in fetuses with chronic antepartum hypoxia than in those showing CTG features of intrapartum hypoxia (64.7 vs. 13.0%; P < 0.001).

Conclusions

The frequency of CAO seems related to the duration and the type of the hypoxic injury, being higher in fetuses showing CTG features of antepartum chronic hypoxia.

Tweetable abstract

This study demonstrates that in a large population of neonates with metabolic acidaemia at birth, the overall incidence of short‐term adverse outcome is around 15%. Such risk seems closely correlated to the duration and the type of hypoxic injury, being higher in fetuses admitted in labour with antepartum chronic hypoxia than those experiencing intrapartum hypoxia.

This study demonstrates that in a large population of neonates with metabolic acidaemia at birth, the overall incidence of short‐term adverse outcome is around 15%. Such risk seems closely correlated to the duration and the type of hypoxic injury, being higher in fetuses admitted in labour with antepartum chronic hypoxia than those experiencing intrapartum hypoxia.

Cerebral haemodynamic response to somatosensory stimulation in preterm lambs and 7-10-day old lambs born at term: Direct synchrotron microangiography assessment

Neurovascular coupling has been well-defined in the adult brain, but variable and inconsistent responses have been observed in the neonatal brain. The mechanisms that underlie functional haemodynamic responses in the developing brain are unknown. Synchrotron radiation (SR) microangiography enables in vivo high-resolution imaging of the cerebral vasculature. We exploited SR microangiography to investigate the microvascular changes underlying the cerebral haemodynamic response in preterm (n = 7) and 7-10-day old term lambs (n = 4), following median nerve stimulation of 1.8, 4.8 and 7.8 sec durations.Increasing durations of somatosensory stimulation significantly increased the number of cortical microvessels of ≤200 µm diameter in 7-10-day old term lambs (p < 0.05) but not preterm lambs where, in contrast, stimulation increased the diameter of cerebral microvessels with a baseline diameter of ≤200 µm. Preterm lambs demonstrated positive functional responses with increased oxyhaemoglobin measured by near infrared spectroscopy, while 7-10-day old term lambs demonstrated both positive and negative responses. Our findings suggest the vascular mechanisms underlying the functional haemodynamic response differ between the preterm and 7-10-day old term brain. The preterm brain depends on vasodilatation of microvessels without recruitment of additional vessels, suggesting a limited capacity to mount higher cerebral haemodynamic responses when faced with prolonged or stronger neural stimulation.

Pathophysiology of Perinatal Asphyxia in Humans and Animal Models

Perinatal asphyxia is caused by lack of oxygen delivery (hypoxia) to end organs due to an hypoxemic or ischemic insult occurring in temporal proximity to labor (peripartum) or delivery (intrapartum). Hypoxic–ischemic encephalopathy is the clinical manifestation of hypoxic injury to the brain and is usually graded as mild, moderate, or severe. The search for useful biomarkers to precisely predict the severity of lesions in perinatal asphyxia and hypoxic–ischemic encephalopathy (HIE) is a field of increasing interest. As pathophysiology is not fully comprehended, the gold standard for treatment remains an active area of research. Hypothermia has proven to be an effective neuroprotective strategy and has been implemented in clinical routine. Current studies are exploring various add-on therapies, including erythropoietin, xenon, topiramate, melatonin, and stem cells. This review aims to perform an updated integration of the pathophysiological processes after perinatal asphyxia in humans and animal models to allow us to answer some questions and provide an interim update on progress in this field.

A proposed magnetic resonance imaging grading system for the spectrum of central neonatal parasagittal hypoxic–ischaemic brain injury

Aim

To describe the spectrum of parasagittal injury on MRI studies performed on children following severe perinatal term hypoxia–ischaemia, using a novel MRI grading system, and propose a new central pattern correlated with neuropathologic features.

Methods

MR scans of 297 patients with perinatal term hypoxia–ischaemia were evaluated for typical patterns of brain injury. A total of 83 patients that demonstrated the central/basal ganglia–thalamus and perirolandic pattern of injury were categorised according to the degree of severity. The perirolandic injury was graded by the degree of interhemispheric widening, paracentral lobule involvement and perirolandic cortex destruction leading to a tiered categorisation. Of these 83 patients, 19 had the most severe subtype of injury. A detailed analysis of the clinical data of a subset of 11 of these 19 patients was conducted.

Results

We demonstrated the mild subtype in 21/83(25%), the moderate subtype in 22/83(27%) and the severe subtype in 21/83(25%). A fourth pattern was identified in 19/83(23%) patients with a diamond-shaped expansion of the interhemispheric fissure, concomitant thalamic, putaminal, hippocampal and other smaller substrate involvement indicative of the most destructive subtype.

Conclusions

We propose a new MR grading system of injury at the parasagittal perirolandic region related to severe, sustained central perinatal term hypoxia–ischaemia. We also introduce a previously undescribed pattern of injury, the most severe form of this spectrum, seen especially after prolongation of the second stage of labour. This constellation of high metabolic substrate, targeted tissue destruction is consistently demonstrated by MRI, termed the massive paramedian injury pattern.

Fetoscopic insufflation of heated-humidified carbon dioxide during simulated spina bifida repair is safe under controlled anesthesia in the fetal lamb

OBJECTIVE

To assess the safety of Partial-Amniotic-Insufflation-of-heated-humidified-CO₂ (hPACI) during fetoscopic spina bifida repair (fSB-repair).

METHOD

A simulated fSB-repair through an exteriorized uterus under hPACI was performed in 100-day fetal lambs (term = 145 days) under a laboratory anesthesia protocol (n = 5; group 1) which is known to induce maternal-fetal acidosis and hypercapnia. Since these may not occur clinically, we applied a clinical anesthesia protocol (n = 5; group 2), keeping maternal parameters within physiological conditions, that is, controlled maternal arterial carbon dioxide (CO2) pressure (pCO₂  = 30 mmHg), blood pressure (≥67 mmHg), and temperature (37.1-39.8°C). Our superiority study used fetal pH as the primary outcome.

RESULTS

Compared to group 1, controlled anesthesia normalized fetal pH (7.23 ± 0.02 vs. 7.36 ± 0.02, p < 0.001), pCO₂ (70.0 ± 9.1 vs. 43.0 ± 1.0 mmHg, p = 0.011) and bicarbonate (27.8 ± 1.1 vs. 24.0 ± 0.9 mmol/L, p = 0.071) at baseline. It kept them within clinically acceptable limits (pH ≥ 7.23, pCO₂  ≤ 70 mmHg, bicarbonate ≤ 30 mm/L) for ≥120 min of hPACI as opposed to ≤30 min in group one. Fetal pO₂ and lactate were comparable between groups and generally within normal range. Fetal brain histology demonstrated fewer apoptotic cells and higher neuronal density in the prefrontal cortex in group two. There was no difference in fetal membrane inflammation, which was mild.

CONCLUSION

Fetoscopic insufflation of heated-humidified CO₂ during simulated fSB-repair through an exteriorized uterus can be done safely under controlled anesthesia.

Unanswered questions regarding therapeutic hypothermia for neonates with neonatal encephalopathy

Therapeutic hypothermia (TH) is now well established to improve intact survival after neonatal encephalopathy (NE). However, many questions could not be addressed by the randomized controlled trials. Should late preterm newborns with NE be cooled? Is cooling beneficial for mild NE? Is the current therapeutic time window optimal, or could it be shortened or prolonged? Will either milder or deeper hypothermia be effective? Does infection/inflammation exposure in the perinatal period in combination with NE offer potentially beneficial preconditioning or might it obviate hypothermic neuroprotection? In the present review, we dissect the evidence, for whom, when and how can TH best be delivered, and highlight areas that need further research.

Cerebral blood volume increment after resuscitation measured by near-infrared time-resolved spectroscopy can estimate degree of hypoxic-ischemic insult in newborn piglets

Neonatal hypoxic–ischemic encephalopathy is a notable cause of neonatal death and developmental disabilities. To achieve better outcomes, it is important in treatment strategy selection to categorize the degree of hypoxia ischemia and evaluate dose response. In an asphyxia piglet model with histopathological brain injuries that we previously developed, animals survived 5 days after insult and showed changes in cerebral blood volume (CBV) that reflected the severity of injuries. However, little is known about the relationship between changes in CBV during and after insult. In this study, an HI event was induced by varying the amount and timing of inspired oxygen in 20 anesthetized piglets. CBV was measured using near-infrared time-resolved spectroscopy before, during, and 6 h after insult. Change in CBV was calculated as the difference between the peak CBV value during insult and the value at the end of insult. The decrease in CBV during insult was found to correlate with the increase in CBV within 6 h after insult. Heart rate exhibited a similar tendency to CBV, but blood pressure did not. Because the decrement in CBV was larger in severe HI, the CBV increment immediately after insult is considered useful for assessing degree of HI insult.

Brief hypoxia in late gestation sheep causes prolonged disruption of fetal electrographic, breathing behaviours and can result in early labour

KEY POINTS

Brief episodes of severe fetal hypoxia can arise in late gestation as a result of interruption of normal umbilical blood flow Systemic parameters and blood chemistry indicate complete recovery within 1-2 hours, although the long-term effects on fetal brain functions are unknown Fetal sheep were subjected to umbilical cord occlusion (UCO) for 10 min at 131 days of gestation, and then monitored intensively until onset of labour or delivery (<145 days of gestation) Normal patterns of fetal behaviour, including breathing movements, episodes of high and low voltage electorcortical activity, eye movements and postural (neck) muscle activity, were disrupted for 3-10 days after the UCO Preterm labour and delivery occurred in a significant number of the pregnancies after UCO compared to the control (sham-UCO) cohort.

ABSTRACT

Complications arising from antepartum events such as impaired umbilical blood flow can cause significant fetal hypoxia. These complications can be unpredictable, as well as difficult to detect, and thus we lack a detailed understanding of the (patho)physiological changes that occur between the antenatal in utero event and birth. In the present study, we assessed the consequences of brief (∼10 min) umbilical cord occlusion (UCO) in fetal sheep at ∼0.88 gestation on fetal plasma cortisol concentrations and fetal behaviour [electrocortical (EcoG), electo-oculargram (EOG), nuchal muscle electromyography (EMG) and breathing activities] in the days following UCO. UCO caused a rapid onset of fetal hypoxaemia, hypercapnia, and acidosis; however, by 6 h, all blood parameters and cardiovascular status were normalized and not different from the control (Sham-UCO) cohort. Subsequently, the incidence of fetal breathing movements decreased compared to the control group, and abnormal behavioural patterns developed over the days following UCO and leading up to the onset of labour, which included increased high voltage and sub-low voltage ECoG and EOG activities, as well as decreased nuchal EMG activity. Fetuses subjected to UCO went into labour 7.9 ± 3.6 days post-UCO (139.5 ± 3.2 days of gestation) compared to the control group fetuses at 13.6 ± 3.3 days post-sham UCO (144 ± 2.2 days of gestation; P < 0.05), despite comparable increases in fetal plasma cortisol and a similar body weight at birth. Thus, a single transient episode of complete UCO late in gestation in fetal sheep can result in prolonged effects on fetal brain activity and premature labour, suggesting persisting effects on fetal cerebral metabolism.

Early environmental enrichment rescues memory impairments provoked by mild neonatal hypoxia-ischemia in adolescent mice

Hypoxia-ischemia (HI) is a consequence of a lack of oxygen and glucose support to the developing brain, which causes several neurodevelopmental impairments. Environmental enrichment (EE) is considered an option to recover the alterations observed in rodents exposed to HI. The aim of this study was to investigate the impact of early EE on memory, hippocampal volume and brain-derived neurotrophic factor (Bbnf) and glucocorticoid receptor (Nr3c1) gene expression of mice exposed to HI. At P10, pups underwent right carotid artery permanent occlusion followed by 35 min of 8% O₂ hypoxic environment. Starting at P11, animals were reared in EE or in standard cage (HI-SC or SHAM-SC) conditions until behavioral testing (P45). SHAM pups did not undergo carotid ligation and hypoxic exposure. Memory performance was assessed in the Y-maze, Novel object recognition, and Barnes maze. Animals were then sacrificed for analysis of hippocampal volume and Bdnf and Nr3c1 gene expression. We observed that animals exposed to HI performed worse in all three tests compared to SHAM animals. Furthermore, HI animals exposed to EE did not differ from SHAM animals in all tasks. Moreover, HI decreased hippocampal volume, while animals reared in early EE were not different compared to SHAM animals. Animals exposed to HI also showed upregulated hippocampal Bdnf expression compared to SHAM animals. We conclude that early EE from P11 to P45 proved to be effective in recovering memory impairments and hippocampal volume loss elicited by HI. Nevertheless, Bdnf expression was not associated with the improvements in memory performance observed in animals exposed to EE after a hypoxic-ischemic event.

A systematic review of neurogenesis in animal models of early brain damage: Implications for cerebral palsy

Brain damage during early life is the main factor in the development of cerebral palsy (CP), which is one of the leading neurodevelopmental disorders in childhood. Few studies, however, have focused on the mechanisms of cell proliferation, migration, and differentiation in the brain of individuals with CP. We thus conducted a systematic review of preclinical evidence of structural neurogenesis in early brain damage and the underlying mechanisms involved in the pathogenesis of CP. Studies were obtained from Embase, Pubmed, Scopus, and Web of Science. After screening 2329 studies, 29 studies, covering a total of 751 animals, were included. Prenatal models based on oxygen deprivation, inflammatory response and infection, postnatal models based on oxygen deprivation or hypoxic-ischemia, and intraventricular hemorrhage models showed varying neurogenesis responses according to the nature of the brain damage, the time period during which the brain injury occurred, proliferative capacity, pattern of migration, and differentiation profile in neurogenic niches. Results mainly from rodent studies suggest that prenatal brain damage impacts neurogenesis and curbs generation of neural stem cells, while postnatal models show increased proliferation of neural precursor cells, improper migration, and reduced survival of new neurons.

Deceleration area and capacity during labour-like umbilical cord occlusions identify evolving hypotension: a controlled study in fetal sheep

OBJECTIVE

Cardiotocography is widely used to assess fetal well-being during labour. The positive predictive value of current clinical algorithms to identify hypoxia-ischaemia is poor. In experimental studies, fetal hypotension is the strongest predictor of hypoxic-ischaemic injury. Cohort studies suggest that deceleration area and deceleration capacity of the fetal heart rate trace correlate with fetal acidaemia, but it is not known whether they are indices of fetal arterial hypotension.

DESIGN

Prospective, controlled study.

SETTING

Laboratory.

SAMPLE

Near-term fetal sheep.

METHODS

One minute of complete umbilical cord occlusions (UCOs) every 5 minutes (1:5 min, n = 6) or every 2.5 minutes (1:2.5 min, n = 12) for 4 hours or until fetal mean arterial blood pressure fell <20 mmHg.

MAIN OUTCOME MEASURES

Deceleration area and capacity during the UCO series were related to evolving hypotension.

RESULTS

The 1:5 min group developed only mild metabolic acidaemia, without hypotension. By contrast, 10/12 fetuses in the 1:2.5-min group progressively developed severe metabolic acidaemia and hypotension, reaching 16.8 ± 0.9 mmHg after 71.2 ± 6.7 UCOs. Deceleration area and capacity remained unchanged throughout the UCO series in the 1:5-min group, but progressively increased in the 1:2.5-min group. The severity of hypotension was closely correlated with both deceleration area (P < 0.001, R²  = 0.66, n = 18) and capacity (P < 0.001, R²  = 0.67, n = 18). Deceleration area and capacity predicted development of hypotension at a median of 103 and 123 minutes before the final occlusion, respectively.

CONCLUSIONS

Both deceleration area and capacity were strongly associated with developing fetal hypotension, supporting their potential to improve identification of fetuses at risk of hypotension leading to hypoxic-ischaemic injury during labour.

TWEETABLE ABSTRACT

Deceleration area and capacity of fetal heart rate identify developing hypotension during labour-like hypoxia.

Heart rate variability in Dorper sheep in the fetal and neonatal periods until 120 days of age: Use of the technique in the field

The evaluation of the autonomic cardiac functions may be performed through the analysis of the heart rate variability. Heart rate variability is defined as the fluctuations in the heart rhythm or rate, and represents a useful tool in the evaluation of the autonomic nervous system through the sympathetic and parasympathetic components, as well as its balance and its reflexes on the cardiorespiratory control system. Fetal electrocardiography provides important information regarding the well-being of the fetus since, in human fetuses, there are changes in the behavior of the fetal heart rate during the second and third trimesters of pregnancy due to an increase in parasympathetic activity. Therefore, considering the importance of evaluating fetal viability, this study aims at evaluating the behavior of fetal heart rate and heart rate variability in Dorper sheep, as well as the activity of the autonomic nervous system during fetal life and in newborn lambs. The species is often used in experimental studies and autonomic nervous system activity is a prognostic index, therefore, the diagnosis of modifications in the sympathovagal balance may represent an early index for fetal viability and well-being in lambs. The analyses were performed in 10 Dorper sheep during pregnancy and in 10 lambs after birth until 120 days of age. There was a decrease in the fetal heart rate and heart rate variability indexes during the fifth month of pregnancy, but without statistical significance for the period evaluated. The heart rate of the lambs decreased gradually until they were 21 days old. The indexes SDNN (standard deviation of RR intervals) and RMSSD (square root of the mean of successive differences between adjacent RR intervals) diverged according to age, being high at day 60. Fetal viability is relevant in sheep fetuses to avoid losses during pregnancy and risks to the health of the mother. In the species, there seems to be a predominance of parasympathetic activity starting from the 21st day of age. Heart rate variability may be employed as a tool in the evaluation of the fetus and development of lambs, since changes in its behavior may represent an adverse effect to fetal and neonatal health.

Perspectives from the Society for Pediatric Research. Neonatal encephalopathy clinical trials: developing the future

The next phase of clinical trials in neonatal encephalopathy (NE) focuses on hypothermia adjuvant therapies targeting alternative recovery mechanisms during the process of hypoxic brain injury. Identifying infants eligible for neuroprotective therapies begins with the clinical detection of brain injury and classification of severity. Combining a variety of biomarkers (serum, clinical exam, EEG, movement patterns) with innovative clinical trial design and analyses will help target infants with the most appropriate and timely treatments. The timing of magnetic resonance imaging (MRI) and MR spectroscopy after NE both assists in identifying the acute perinatal nature of the injury (days 3-7) and evaluates the full extent and evolution of the injury (days 10-21). Early, intermediate outcome of neuroprotective interventions may be best defined by the 21-day neuroimaging, with recognition that the full neurodevelopmental trajectory is not yet defined. An initial evaluation of each new therapy at this time point may allow higher-throughput selection of promising therapies for more extensive investigation. Functional recovery can be assessed using a trajectory of neurodevelopmental evaluations targeted to a prespecified and mechanistically derived hypothesis of drug action. As precision medicine revolutionizes healthcare, it should also include the redesign of NE clinical trials to allow safe, efficient, and targeted therapeutics. IMPACT: As precision medicine revolutionizes healthcare, it should also include the redesign of NE clinical trials to allow faster development of safe, effective, and targeted therapeutics. This article provides a multidisciplinary perspective on the future of clinical trials in NE; novel trial design; study management and oversight; biostatistical methods; and a combination of serum, imaging, and neurodevelopmental biomarkers can advance the field and improve outcomes for infants affected by NE. Innovative clinical trial designs, new intermediate trial end points, and a trajectory of neurodevelopmental evaluations targeted to a prespecified and mechanistically derived hypothesis of drug action can help address common challenges in NE clinical trials and allow for faster selection and validation of promising therapies for more extensive investigation.

Increased peak end-expiratory pressure in ventilated preterm lambs changes cerebral microvascular perfusion: direct synchrotron microangiography assessment

Positive end-expiratory pressure (PEEP) improves oxygenation in mechanically ventilated preterm neonates by preventing lung collapse. However, high PEEP may alter cerebral blood flow secondarily to the increased intrathoracic pressure, predisposing to brain injury. The precise effects of high PEEP on cerebral hemodynamics in the preterm brain are unknown. We aimed to assess the effect of PEEP on microvessels in the preterm brain by using synchrotron radiation (SR) microangiography, which enables in vivo real-time high-resolution imaging of the cerebral vasculature. Preterm lambs (0.8 gestation, n = 4) were delivered via caesarean section, anesthetized, and ventilated. SR microangiography of the right cerebral hemisphere was performed with iodine contrast administered into the right carotid artery during PEEP ventilation of 5 and 10 cmH₂O. Carotid blood flow was measured using an ultrasonic flow probe placed around the left carotid artery. An increase of PEEP from 5 to 10 cmH₂O increased the diameter of small cerebral vessels (<150 µm) but decreased the diameter of larger cerebral vessels (>500 µm) in all four lambs. Additionally, the higher PEEP increased the cerebral contrast transit time in three of the four lambs. Carotid blood flow increased in two lambs, which also had increased carbon dioxide levels during PEEP 10. Our results suggest that PEEP of 10 cmH₂O alters the preterm cerebral hemodynamics, with prolonged cerebral blood flow transit and engorgement of small cerebral microvessels likely due to the increased intrathoracic pressure. These microvascular changes are generally not reflected in global assessment of cerebral blood flow or oxygenation.NEW & NOTEWORTHY An increase of positive end-expiratory pressure (PEEP) from 5 to 10 cmH₂O increased the diameter of small cerebral vessels (<150 µm) but decreased the diameter of larger cerebral vessels (>500 µm). This suggests increased intrathoracic pressure due to high PEEP can drive microvessel engorgement in the preterm brain, which may play a role in cerebrovascular injury.

Cooling and immunomodulation for treating hypoxic-ischemic brain injury

Therapeutic hypothermia is now well established to partially reduce disability in term and near-term infants with moderate-severe hypoxic-ischemic encephalopathy. Preclinical and clinical studies have confirmed that current protocols for therapeutic hypothermia are near optimal. The challenge is now to identify complementary therapies that can further improve outcomes, in combination with therapeutic hypothermia. Overall, anti-excitatory and anti-apoptotic agents have shown variable or even no benefit in combination with hypothermia, suggesting overlapping mechanisms of neuroprotection. Inflammation appears to play a critical role in the pathogenesis of injury in the neonatal brain, and thus, there is potential for drugs with immunomodulatory properties that target inflammation to be used as a therapy in neonates. In this review, we examine the evidence for neuroprotection with immunomodulation after hypoxia-ischemia. For example, stem cell therapy can reduce inflammation, increase cell survival, and promote cell maturation and repair. There are also encouraging preclinical data from small animals suggesting that stem cell therapy can augment hypothermic neuroprotection. However, there is conflicting evidence, and rigorous testing in translational animal models is now needed.

Usefulness of pathological examinations of the central nervous system for monitoring and controlling perinatal lamb mortality

Correct diagnosis of cause of death is necessary to suggest the most effective management interventions to reduce perinatal lamb mortality. Haemorrhage on the surface of the brain has been used as a field diagnostic tool to allocate lambs to a cause of death category, but the usefulness of this method was unclear. This study aimed to evaluate whether gross pathology was related to neuronal death and whether haemorrhage of the central nervous system (CNS) was distinct between differing causes of death, enabling indicators to be used in field diagnoses. Lambs dying from natural causes (n = 64) and from euthanasia (n = 7) underwent postmortem examination, then the brain and spinal cord were extracted and examined histologically. Histological changes consistent with neuronal death were not detected in any lamb. Haemorrhage of the meninges and/or parenchyma of the CNS occurred in all lambs. The age of the haemorrhage indicated that it occurred near the time of death in most lambs. Dilation of blood vessels varied in severity but appeared to be unrelated to causal diagnosis, severity of subcutaneous oedema, breathing or milk status. Moderate or severe dilation of blood vessels and haemorrhage of the CNS did not occur in all lambs with alternative clear indicators of dystocia and occurred in all death classifications, so it could not be used as diagnostic indicators for classification of cause of death. Dilation and haemorrhage were unrelated to neuronal damage and may have been artefactual. In conclusion, haemorrhage of the CNS was not indicative of neuronal damage and could not be used to distinguish between lambs with clear indicators of differing causes of death, so it is not recommended as a field diagnostic tool.

A Systematic Review of Magnesium Sulfate for Perinatal Neuroprotection: What Have We Learnt From the Past Decade?

There is an important unmet need to improve long term outcomes of encephalopathy for preterm and term infants. Meta-analyses of large controlled trials suggest that maternal treatment with magnesium sulfate (MgSO₄) is associated with a reduced risk of cerebral palsy and gross motor dysfunction after premature birth. However, to date, follow up to school age has found an apparent lack of long-term clinical benefit. Because of this inconsistency, it remains controversial whether MgSO₄ offers sustained neuroprotection. We systematically reviewed preclinical and clinical studies reported from January 1 2010, to January 31 2020 to evaluate the most recent advances and knowledge gaps relating to the efficacy of MgSO₄ for the treatment of perinatal brain injury. The outcomes of MgSO₄ in preterm and term-equivalent animal models of perinatal encephalopathy were highly inconsistent between studies. None of the perinatal rodent studies that suggested benefit directly controlled body or brain temperature. The majority of the studies did not control for sex, study long term histological and functional outcomes or use pragmatic treatment regimens and many did not report controlling for potential study bias. Finally, most of the recent preterm or term human studies that tested the potential of MgSO₄ for perinatal neuroprotection were relatively underpowered, but nevertheless, suggest that any improvements in neurodevelopment were at best modest or absent. On balance, these data suggest that further rigorous testing in translational preclinical models of perinatal encephalopathy is essential to ensure safety and best regimens for optimal preterm neuroprotection, and before further clinical trials of MgSO₄ for perinatal encephalopathy at term are undertaken.

Prenatal Hypoxia and Placental Oxidative Stress: Insights from Animal Models to Clinical Evidences

Hypoxia is a common form of intrauterine stress characterized by exposure to low oxygen concentrations. Gestational hypoxia is associated with the generation of reactive oxygen species. Increase in oxidative stress is responsible for damage to proteins, lipids and DNA with consequent impairment of normal cellular functions. The purpose of this review is to propose a summary of preclinical and clinical evidences designed to outline the correlation between fetal hypoxia and oxidative stress. The results of the studies described show that increases of oxidative stress in the placenta is responsible for changes in fetal development. Specifically, oxidative stress plays a key role in vascular, cardiac and neurological disease and reproductive function dysfunctions. Moreover, the different finding suggests that the prenatal hypoxia-induced oxidative stress is associated with pregnancy complications, responsible for changes in fetal programming. In this way, fetal hypoxia predisposes the offspring to congenital anomalies and chronic diseases in future life. Several antioxidant agents, such as melatonin, erythropoietin, vitamin C, resveratrol and hydrogen, shown potential protective effects in prenatal hypoxia. However, future investigations will be needed to allow the implementation of these antioxidants in clinical practice for the promotion of health in early intrauterine life, in fetuses and children.

Cortical ischaemic patterns in term partial-prolonged hypoxic-ischaemic injury-the inter-arterial watershed demonstrated through atrophy, ulegyria and signal change on delayed MRI scans in children with cerebral palsy

The inter-arterial watershed zone in neonates is a geographic area without discernible anatomic boundaries and difficult to demarcate and usually not featured in atlases. Schematics currently used to depict the areas are not based on any prior anatomic mapping, compared to adults.Magnetic resonance imaging (MRI) of neonates in the acute to subacute phase with suspected hypoxic-ischaemic injury (HII) can demonstrate signal abnormality and restricted diffusion in the cortical and subcortical parenchyma of the watershed regions.In the chronic stage of partial-prolonged hypoxic-ischaemic injury, atrophy and ulegyria can make the watershed zone more conspicuous as a region. Our aim is to use images extracted from a sizable medicolegal database (approximately 2000 cases), of delayed MRI scans in children with cerebral palsy, to demonstrate the watershed region.To achieve this, we have selected cases diagnosed on imaging as having sustained a term pattern of partial-prolonged HII affecting the hemispheric cortex, based on the presence of bilateral, symmetric atrophy with ulegyria. From these, we have identified those patients demonstrating injury along the whole watershed continuum as well as those demonstrating selective anterior or posterior watershed predominant injury for demonstration.Recognition of this zone is essential for diagnosing partial-prolonged hypoxic-ischaemic injury sustained in term neonates. The images presented in this pictorial review provide a template for identifying the cortical watershed distribution when there is milder regional (anterior, parasagittal, peri-Sylvian and posterior) watershed injury and for more severe injury where multiple regions are injured in combination or as a continuum.

Prognostic Value of Clinical Tests in Neonates With Hypoxic-Ischemic Encephalopathy Treated With Therapeutic Hypothermia: A Systematic Review and Meta-Analysis

Background and Objective: There remains an unmet clinical need for markers that predict outcomes in the hypothermia-treated (HT) infants with HIE. The aim of this meta-analysis was to investigate the prognostic accuracy of currently available clinical tests performed in the immediate post-natal period for predicting neurological outcomes between 18 months and 3 years of age in HT near-term and term infants with perinatal asphyxia and HIE.

Methods: A comprehensive review of the Embase, Cochrane library, and PubMed databases was performed to identify studies that evaluated the prognostic value of clinical tests for neurological outcomes in HT near-term and term infants with perinatal asphyxia and hypoxic-ischemic encephalopathy. Pooled sensitivity and specificity with corresponding 95% confidence intervals and area under the receiver operating characteristic (ROC) curve (AUC) were calculated.

Results: Of the 1,144 relevant studies, 26 studies describing four clinical tests conducted in 1458 HT near-term or term infants were included. For predicting an unfavorable neurological outcome, of the imaging techniques, MRI within 2 weeks of birth performed best on sensitivity 0.85 (95% CI 0.79–0.89), specificity 0.72 (95% CI 0.66–0.77), and AUC 0.88; among the neurophysiological tests, multichannel EEG (Electroencephalogram) demonstrated the sensitivity 0.63 (95% CI 0.49–0.76), specificity 0.82 (95% CI 0.70–0.91), and AUC 0.88, and for aEEG (amplitude-integrated electroencephalography) background pattern pooled sensitivity, specificity and AUC were 0.90 (95% CI 0.86–0.94), 0.46 (95% CI 0.42–0.51), and 0.78 whereas for SEPs (Somatosensory evoked potentials), pooled sensitivity and specificity were 0.52 (95% CI 0.34–0.69), 0.76 (95% CI 0.63–0.87), and AUC 0.84, respectively.

Conclusions: In the wake of the era of TH, MRI and neurophysiological tests (aEEG or EEG) were promising predictors of adverse outcomes, while SEPs need high-quality studies to confirm the findings. Continued follow-up of the children and well-designed large prospective studies are essential to determine whether these benefits are maintained in later childhood.

The physiology of intrapartum fetal compromise at term

Uterine contractions in labor result in a 60% reduction in uteroplacental perfusion, causing transient fetal and placental hypoxia. A healthy term fetus with a normally developed placenta is able to accommodate this transient hypoxia by activation of the peripheral chemoreflex, resulting in a reduction in oxygen consumption and a centralization of oxygenated blood to critical organs, namely the heart, brain, and adrenals. Providing there is adequate time for placental and fetal reperfusion between contractions, these fetuses will be able to withstand prolonged periods of intermittent hypoxia and avoid severe hypoxic injury. However, there exists a cohort of fetuses in whom abnormal placental development in the first half of pregnancy results in failure of endovascular invasion of the spiral arteries by the cytotrophoblastic cells and inadequate placental angiogenesis. This produces a high-resistance, low-flow circulation predisposing to hypoperfusion, hypoxia, reperfusion injury, and oxidative stress within the placenta. Furthermore, this renders the placenta susceptible to fluctuations and reduction in uteroplacental perfusion in response to external compression and stimuli (as occurs in labor), further reducing fetal capillary perfusion, placing the fetus at risk of inadequate gas/nutrient exchange. This placental dysfunction predisposes the fetus to intrapartum fetal compromise. In the absence of a rare catastrophic event, intrapartum fetal compromise occurs as a gradual process when there is an inability of the fetal heart to respond to the peripheral chemoreflex to maintain cardiac output. This may arise as a consequence of placental dysfunction reducing pre-labor myocardial glycogen stores necessary for anaerobic metabolism or due to an inadequate placental perfusion between contractions to restore fetal oxygen and nutrient exchange. If the hypoxic insult is severe enough and long enough, profound multiorgan injury and even death may occur. This review provides a detailed synopsis of the events that can result in placental dysfunction, how this may predispose to intrapartum fetal hypoxia, and what protective mechanisms are in place to avoid hypoxic injury.

Advanced nanotherapies to promote neuroregeneration in the injured newborn brain

Neonatal brain injury affects thousands of babies each year and may lead to long-term and permanent physical and neurological problems. Currently, therapeutic hypothermia is standard clinical care for term newborns with moderate to severe neonatal encephalopathy. Nevertheless, it is not completely protective, and additional strategies to restore and promote regeneration are urgently needed. One way to ensure recovery following injury to the immature brain is to augment endogenous regenerative pathways. However, novel strategies such as stem cell therapy, gene therapies and nanotechnology have not been adequately explored in this unique age group. In this perspective review, we describe current efforts that promote neuroprotection and potential targets that are unique to the developing brain, which can be leveraged to facilitate neuroregeneration.

Distinct Vulnerability and Resilience of Human Neuroprogenitor Subtypes in Cerebral Organoid Model of Prenatal Hypoxic Injury

Prenatal hypoxic injury (HI) is a leading cause of neurological disability. The immediate and long-term effects of hypoxia on progenitor homeostasis and developmental progression during early human brain development remain unclear. This gap is due to difficulty to access human fetal brain tissues and inadequate animal models to study human corticogenesis. Recent optimizations of cerebral organoid models derived from human embryonic stem (ES) cells present new opportunities to investigate pathophysiology of prenatal HI. Here, we implemented a transient HI model using human cerebral organoids with dorsal forebrain specification. We demonstrated that transient hypoxia resulted in immediate and prolonged apoptosis in cerebral organoids, with outer radial glia (oRG), a progenitor population more prominent in primates, and differentiating neuroblasts/immature neurons suffering larger losses. In contrast, neural stem cells in ventricular zone displayed relative resilience to HI and exhibited a shift of cleavage plane angle favoring symmetric division, thereby providing a mechanism to replenish the stem cell pool. Furthermore, we defined the vulnerable window and neurodifferentiation stages that are particularly sensitive to HI. Understanding cell type-specific and stage-dependent effects of prenatal HI on survival and mitotic behavior of human neuroprogenitor subtypes during early human corticogenesis helps elucidate the etiology of neurodevelopmental disorders, and provides a therapeutic starting point to protect the vulnerable populations at critical timeframes.

Fetal brain sparing in a mouse model of chronic maternal hypoxia

Hypoxic stress is a common occurrence during human pregnancy, yet little is known about its effects on the fetal brain. This study examined the fetal hemodynamic responses to chronic hypoxia in an experimental mouse model of chronic maternal hypoxia (11% O₂ from E14.5 to E17.5). Using high-frequency Doppler ultrasound, we found fetal cerebral and ductus venosus blood flow were both elevated by 69% and pulmonary blood flow was decreased by 62% in the fetuses exposed to chronic hypoxia compared to controls. This demonstrates that brain sparing persists during chronic fetal hypoxia and is mediated by "streaming," where highly oxygenated blood preferentially flows through the ductus venosus towards the cerebral circulation, bypassing the liver and the lungs. Consistent with these changes in blood flow, the fetal brain volume measured by MRI is preserved, while the liver and lung volumes decreased compared to controls. However, hypoxia exposed fetuses were rendered vulnerable to an acute hypoxic challenge (8% O₂ for 3 min), demonstrating global blood flow decreases consistent with imminent fetal demise rather than elevated cerebral blood flow. Despite this vulnerability, there were no differences in adult brain morphology in the mice exposed to chronic maternal hypoxia compared to controls.

The optimal choices of animal models of white matter injury

White matter injury, the most common neurological injury in preterm infants, is a major cause of chronic neurological morbidity, including cerebral palsy. Although there has been great progress in the study of the mechanism of white matter injury in newborn infants, its pathogenesis is not entirely clear, and further treatment approaches are required. Animal models are the basis of study in pathogenesis, treatment, and prognosis of white matter injury in preterm infants. Various species have been used to establish white matter injury models, including rodents, rabbits, sheep, and non-human primates. Small animal models allow cost-effective investigation of molecular and cellular mechanisms, while large animal models are particularly attractive for pathophysiological and clinical-translational studies. This review focuses on the features of commonly used white matter injury animal models, including their modelling methods, advantages, and limitations, and addresses some clinically relevant animal models that allow reproduction of the insults associated with clinical conditions that contribute to white matter injury in human infants.

Latent Phase Detection of Hypoxic-Ischemic Spike Transients in the EEG of Preterm Fetal Sheep Using Reverse Biorthogonal Wavelets & Fuzzy Classifier

Hypoxic-ischemic (HI) studies in preterms lack reliable prognostic biomarkers for diagnostic tests of HI encephalopathy (HIE). Our group's observations from in utero fetal sheep models suggest that potential biomarkers of HIE in the form of developing HI micro-scale epileptiform transients emerge along suppressed EEG/ECoG background during a latent phase of 6-7h post-insult. However, having to observe for the whole of the latent phase disqualifies any chance of clinical intervention. A precise automatic identification of these transients can help for a well-timed diagnosis of the HIE and to stop the spread of the injury before it becomes irreversible. This paper reports fusion of Reverse-Biorthogonal Wavelets with Type-1 Fuzzy classifiers, for the accurate real-time automatic identification and quantification of high-frequency HI spike transients in the latent phase, tested over seven in utero preterm sheep. Considerable high performance of 99.78 ± 0.10% was obtained from the Rbio-Wavelet Type-1 Fuzzy classifier for automatic identification of HI spikes tested over 42h of high-resolution recordings (sampling-freq:1024Hz). Data from post-insult automatic time-localization of high-frequency HI spikes reveals a promising trend in the average rate of the HI spikes, even in the animals with shorter occlusion periods, which highlights considerable higher number of transients within the first 2h post-insult.