Therapeutic Hypothermia Provides Variable Protection against Behavioral Deficits after Neonatal Hypoxia-Ischemia: A Potential Role for Brain-Derived Neurotrophic Factor

Ongoing loss of viable neurons for weeks after mild hypoxia-ischaemia

Mild hypoxic-ischaemic encephalopathy is common in neonates, and there are no evidence-based therapies. By school age, 30-40% of those patients experience adverse neurodevelopmental outcomes. The nature and progression of mild injury is poorly understood. We studied the evolution of mild perinatal brain injury using longitudinal two-photon imaging of transgenic fluorescent calcium-sensitive and insensitive proteins to provide a novel readout of neuronal viability and activity at cellular resolution in vitro and in vivo. In vitro, perinatal organotypic hippocampal cultures underwent 15-20 min of oxygen-glucose deprivation. In vivo, mild hypoxia-ischaemia was completed at post-natal day 10 with carotid ligation and 15 min of hypoxia (FiO2, 0.08). Consistent with a mild injury, minimal immediate neuronal death was seen in vitro or in vivo, and there was no volumetric evidence of injury by ex vivo MRI 2.5 weeks after injury (n = 3 pups/group). However, in both the hippocampus and neocortex, these mild injuries resulted in delayed and progressive neuronal loss by the second week after injury compared to controls; measured by fluorophore quenching (n = 6 slices/group in vitro, P < 0.001; n = 8 pups/group in vivo, P < 0.01). Mild hypoxia-ischaemia transiently suppressed cortical network calcium activity in vivo for over 2 h after injury (versus sham, n = 13 pups/group; P < 0.01). No post-injury seizures were seen. By 24 h, network activity fully recovered, and there was no disruption in the development of normal cortical activity for 11 days (n = 8 pups/group). The participation in network activity of individual neurons destined to die in vivo was indistinguishable from those that survived up to 4 days post-injury (n = 8 pups/group). Despite a lack of significant immediate neuronal death and only transient disruptions of network activity, mild perinatal brain injury resulted in a delayed and progressive increase of neuronal death in the hippocampus and neocortex. Neurons that died late were functioning normally for days after injury, suggesting a new pathophysiology of neuronal death after mild injury. Critically, the neurons destined to die late demonstrated multiple biomarkers of viability long after mild injury, suggesting their later death may be modified with neuroprotective interventions.

Blood glucose and β-hydroxybutyrate predict significant brain injury after hypoxia-ischemia in neonatal mice

BACKGROUND

The Vannucci procedure is widely used to model cerebral hypoxic-ischemic (HI) injury in neonatal rodents. Identifying minimally invasive biomarkers linked to brain injury would improve stratification of pups to experimental treatments. We hypothesized that extreme blood glucose (BG) and β-hydroxybutyrate (bHB) levels immediately after HI will correlate with severity of brain injury in this model.

METHODS

C57BL6 mice of both sexes underwent the Vannucci procedure with BG and bHB measured immediately after hypoxia. GFAP and α-fodrin were measured to assess injury severity at 4h, P11, P18 and P40. Open field (OF), Y-maze (YM), and Object-location task (OLT) were tested at P40.

RESULTS

Clinical seizures-like stereotypies during hypoxia were associated with lower post-hypoxia BG in HI-injured mice. Low BG after HI was related to higher GFAP expression, higher α-fodrin breakdown, lower residual regional volume, and worse working memory. BG was superior to bHB in ROC analysis with BG threshold of <111 mg/dL providing 100% specificity with 72% sensitivity for hippocampal HI-injury.

CONCLUSIONS

Post-hypoxic BG is a minimally invasive screening tool to identify pups with significant HI brain injury in the Vannucci model modified for mice improving our ability to stratify pups to experimental treatments to assess effectiveness.

IMPACT

End hypoxic-ischemic blood glucose levels are a reliable and inexpensive biomarker to detect hypoxic-ischemic brain injury in mice. Screening with blood glucose levels post-hypoxia allows appropriate stratification of those mouse pups most likely to be injured to experimental treatments improving validity and translatability of the results. These findings provide biological plausibility to the clinical observation that extreme blood glucose levels relate to worse outcomes after hypoxia-ischemia.

Neonatal hypoxia-ischemia alters the events governing the hippocampal critical period of postnatal synaptic plasticity leading to deficits in working memory in mice

Postnatal critical periods of synaptic plasticity (CPsp) are characterized by profound neural network refinement, which is shaped by synaptic activity and sculpted by maturation of the GABAergic network. Even after therapeutic hypothermia (TH), neonatal hypoxia-ischemia (HI) impairs two triggers for the initiation of the CPsp in the hippocampus: i) PSA-NCAM developmental decline and ii) parvalbumin (PV) + interneuron (IN) maturation. Thus, we investigated whether neonatal HI despite TH disturbs other events governing the onset, consolidation and closure of the postnatal CPsp in the hippocampus. We induced cerebral HI in P10 C57BL6 mice with right carotid ligation and 45 m of hypoxia (FiO2 = 0.08), followed by normothermia (36 °C, NT) or TH (31 °C) for 4 h with anesthesia-exposed shams as controls. ELISA, immunoblotting and immunohistochemistry were performed at 24 h (P11), 5 days (P15), 8 days (P18) and 30 days (P40) after HI injury. We specifically assessed: i) BDNF levels and TrkB activation, controlling the CPsp, ii) Otx2 and NPTX2 immunoreactivity (IR), engaging CPsp onset and iii) NogoR1, Lynx1 IR, PNN formation and myelination (MBP) mediating CPsp closure. Pups aged to P40 also received a battery of tests assessing working memory. Here, we documented deficits in hippocampal BDNF levels and TrkB activation at P18 in response to neonatal HI even with TH. Neonatal HI impaired in the CA1 the developmental increase in PV, Otx2, and NPTX2 between P11 and P18, the colocalization of Otx2 and PV at P18 and P40, the accumulation of NPTX2 in PV+ dendrites at P18 and P40, and the expression of NogoR at P40. Furthermore, neonatal HI decreased BDNF and impaired PNN development and myelination (MBP) at P40. Most of these abnormalities were insensitive to TH and correlated with memory deficits. Neonatal HI appears to disrupt many of the molecular and structural events initiating and consolidating the postnatal hippocampal CPsp, perhaps due to the early and delayed deficits in TrkB activation leading to memory deficits.

Intranasal therapies for neonatal hypoxic-ischemic encephalopathy: Systematic review, synthesis, and implications for global accessibility to care

Neonatal hypoxic-ischemic encephalopathy (HIE) is the leading cause of neurodevelopmental morbidity in term infants worldwide. Incidence of HIE is highest in low and middle-income communities with minimal access to neonatal intensive care and an underdeveloped infrastructure for advanced neurologic interventions. Moreover, therapeutic hypothermia, standard of care for HIE in high resourced settings, is shown to be ineffective in low and middle-income communities. With their low cost, ease of administration, and capacity to potently target the central nervous system, intranasal therapies pose a unique opportunity to be a more globally accessible treatment for neonatal HIE. Intranasal experimental therapeutics have been studied in both rodent and piglet models, but no intranasal therapeutics for neonatal HIE have undergone human clinical trials. Additional research must be done to expand the array of treatments available for use as intranasal therapies for neonatal HIE thus improving the neurologic outcomes of infants worldwide.

SMYD5 is a regulator of the mild hypothermia response

The mild hypothermia response (MHR) maintains organismal homeostasis during cold exposure and is thought to be critical for the neuroprotection documented with therapeutic hypothermia. To date, little is known about the transcriptional regulation of the MHR. We utilize a forward CRISPR-Cas9 mutagenesis screen to identify the histone lysine methyltransferase SMYD5 as a regulator of the MHR. SMYD5 represses the key MHR gene SP1 at euthermia. This repression correlates with temperature-dependent levels of histone H3 lysine 26 trimethylation (H3K36me3) at the SP1 locus and globally, indicating that the mammalian MHR is regulated at the level of histone modifications. We have identified 37 additional SMYD5-regulated temperature-dependent genes, suggesting a broader MHR-related role for SMYD5. Our study provides an example of how histone modifications integrate environmental cues into the genetic circuitry of mammalian cells and provides insights that may yield therapeutic avenues for neuroprotection after catastrophic events.

SMYD5 is a regulator of the mild hypothermia response

The mild hypothermia response (MHR) maintains organismal homeostasis during cold exposure and is thought to be critical for the neuroprotection documented with therapeutic hypothermia. To date, little is known about the transcriptional regulation of the MHR. We utilize a forward CRISPR-Cas9 mutagenesis screen to identify the histone lysine methyltransferase SMYD5 as a regulator of the MHR. SMYD5 represses the key MHR gene SP1 at euthermia. This repression correlates with temperature-dependent levels of H3K36me3 at the SP1-locus and globally, indicating that the mammalian MHR is regulated at the level of histone modifications. We have identified 37 additional SMYD5 regulated temperature-dependent genes, suggesting a broader MHR-related role for SMYD5. Our study provides an example of how histone modifications integrate environmental cues into the genetic circuitry of mammalian cells and provides insights that may yield therapeutic avenues for neuroprotection after catastrophic events.

A biochemical feedback signal for hypothermia treatment for neonatal hypoxic-ischemic encephalopathy: focusing on central nervous system proteins in biofluids

Hypothermia has been widely used to treat moderate to severe neonatal hypoxic-ischemic encephalopathy (HIE), yet evaluating the effects of hypothermia relies on clinical neurology, neuroimaging, amplitude-integrated electroencephalography, and follow-up data on patient outcomes. Biomarkers of brain injury have been considered for estimating the effects of hypothermia. Proteins specific to the central nervous system (CNS) are components of nervous tissue, and once the CNS is damaged, these proteins are released into biofluids (cerebrospinal fluid, blood, urine, tears, saliva), and they can be used as markers of brain damage. Clinical reports have shown that CNS-specific marker proteins (CNSPs) were early expressed in biofluids after brain damage and formed unique biochemical profiles. As a result, these markers may serve as an indicator for screening brain injury in infants, monitoring disease progression, identifying damage region of brain, and assessing the efficacy of neuroprotective measures. In clinical work, we have found that there are few reports on using CNSPs as biological signals in hypothermia for neonatal HIE. The aim of this article is to review the classification, origin, biochemical composition, and physiological function of CNSPs with changes in their expression levels after hypothermia for neonatal HIE. Hopefully, this review will improve the awareness of CNSPs among pediatricians, and encourage future studies exploring the mechanisms behind the effects of hypothermia on these CNSPs, in order to reduce the adverse outcome of neonatal HIE.

Neonatal Hypoxia-Ischemia alters Brain-Derived Contactin-2-Positive Extracellular Vesicles in the Mouse Plasma

Neonatal encephalopathy (NE) impairs white matter development and results in long-term neurodevelopmental deficits. Leveraging prior findings of altered neuronal proteins carried by brain-derived extracellular vesicles (EVs) that are marked by a neural-specific cell surface glycoprotein Contactin-2 (CNTN2) in NE infants, the present study aimed to determine the correlation between brain and circulating CNTN2+-EVs and whether NE alters circulating CNTN2+-EV levels in mice. Brain tissue and plasma were collected from postnatal day (P)7, 10, 11, 15 mice to determine the baseline CNTN2 correlation between these two compartments (n = 4-7/time point/sex). NE was induced in P10 pups. Brain and plasma samples were collected at 1, 3, 6, 24, and 120 h (n = 4-8/time point/sex). CNTN2 from brain tissue and plasma EVs were quantified using ELISA. ANOVA and linear regression analyses were used to evaluate changes and correlations between brain and plasma CNTN2+-EVs. In baseline experiments, CNTN2 in brain tissue and plasma EVs peaked at P10 with no sex-difference. Brain and plasma CNTN2+-EV showed a positive correlation across early postnatal ages. NE pups showed an elevated CNTN2 in brain tissue and EVs at 1 h and only in brain tissue at 24 h. NE also abolished the positive plasma-brain correlation. The findings establish a link for central CNTN2 and its release into circulation during early postnatal life. The immediate elevation and release of CNTN2 following NE highlight a potential molecular response shortly after a brain injurious event. Our findings further support the utility of circulating brain-derived EVs as a possible bioindicator of NE.

Mode of delivery alters sensitivity to thermal and chemical stimuli in adult rats: An experimental study

Background

The mode of delivery might prompt a long-lasting alteration in physiological and behavioral responsiveness in offspring.

Objective

This study was intended to evaluate if the mode of delivery could alter sensitivity to thermal and chemical stimuli in female rats.

Materials and Methods

56 adult female Wistar rats (200-220 gr) that were born by vaginal or cesarean section (C-section) were used (n = 28/each). Inflammatory pain was induced by subcutaneous injection of formalin into the hind paw. The thermal nociceptive threshold was determined by tail-flick and hot plate tests. Besides, the Western blot test was used to evaluate the spinal cord levels of c-Fos and c-Jun proteins.

Results

Formalin-induced inflammation was significantly decreased in C-section group as compared to vaginally born rats (p < 0.001). The baseline nociceptive threshed and morphine-induced analgesia were significantly increased in C-section groups in comparison to vaginally born rats. In addition, the levels of c-Fos and c-Jun proteins were significantly decreased in the spinal cord of C-section rats as compared to vaginally born animals (p < 0.01). Morphine treatment could decrease the expression of c-Fos and c-Jun in the C-section group (p < 0.05).

Conclusion

Overall, C-section rats showed lower spinal nociceptive processing and neuronal activity later in life, compared to the vaginal born rats.

TrkB-mediated sustained neuroprotection is sex-specific and Erα-dependent in adult mice following neonatal hypoxia ischemia

BACKGROUND

Neonatal hypoxia ischemia (HI) related brain injury is one of the major causes of life-long neurological morbidities that result in learning and memory impairments. Evidence suggests that male neonates are more susceptible to the detrimental effects of HI, yet the mechanisms mediating these sex-specific responses to neural injury in neonates remain poorly understood. We previously tested the effects of treatment with a small molecule agonist of the tyrosine kinase B receptor (TrkB), 7,8-dihydroxyflavone (DHF) following neonatal HI and determined that females, but not males exhibit increased phosphorylation of TrkB and reduced apoptosis in their hippocampi. Moreover, these female-specific effects of the TrkB agonist were found to be dependent upon the expression of Erα. These findings demonstrated that TrkB activation in the presence of Erα comprises one pathway by which neuroprotection may be conferred in a female-specific manner. The goal of this study was to determine the role of Erα-dependent TrkB-mediated neuroprotection in memory and anxiety in young adult mice exposed to HI during the neonatal period.

METHODS

In this study, we used a unilateral hypoxic ischemic (HI) mouse model. Erα+/+ or Erα-/- mice were subjected to HI on postnatal day (P) 9 and mice were treated with either vehicle control or the TrkB agonist, DHF, for 7 days following HI. When mice reached young adulthood, we used the novel object recognition, novel object location and open field tests to assess long-term memory and anxiety-like behavior. The brains were then assessed for tissue damage using immunohistochemistry.

RESULTS

Neonatal DHF treatment prevented HI-induced decrements in recognition and location memory in adulthood in females, but not in males. This protective effect was absent in female mice lacking Erα. The female-specific improved recognition and location memory outcomes in adulthood conferred by DHF therapy after neonatal HI tended to be or were Erα-dependent, respectively. Interestingly, DHF triggered anxiety-like behavior in both sexes only in the mice that lacked Erα. When we assessed the severity of injury, we found that DHF therapy did not decrease the percent tissue loss in proportion to functional recovery. We additionally observed that the presence of Erα significantly reduced overall HI-associated mortality in both sexes.

CONCLUSIONS

These observations provide evidence for a therapeutic role for DHF in which TrkB-mediated sustained recovery of recognition and location memories in females are Erα-associated and dependent, respectively. However, the beneficial effects of DHF therapy did not include reduction of gross tissue loss but may be derived from the enhanced functioning of residual tissues in a cell-specific manner.

Dexmedetomidine alleviates cognitive impairment by promoting hippocampal neurogenesis via BDNF/TrkB/CREB signaling pathway in hypoxic-ischemic neonatal rats

AIMS

Dexmedetomidine (DEX) has been reported to alleviate hypoxic-ischemic brain damage (HIBD) in neonates. This study aimed to investigate whether DEX improves cognitive impairment by promoting hippocampal neurogenesis via the BDNF/TrkB/CREB signaling pathway in neonatal rats with HIBD.

METHODS

HIBD was induced in postnatal day 7 rats using the Rice-Vannucci method, and DEX (25 μg/kg) was administered intraperitoneally immediately after the HIBD induction. The BDNF/TrkB/CREB pathway was regulated by administering the TrkB receptor antagonist ANA-12 through intraperitoneal injection or by delivering adeno-associated virus (AAV)-shRNA-BDNF via intrahippocampal injection. Western blot was performed to measure the levels of BDNF, TrkB, and CREB. Immunofluorescence staining was utilized to identify the polarization of astrocytes and evaluate the levels of neurogenesis in the dentate gyrus of the hippocampus. Nissl and TTC staining were performed to evaluate the extent of neuronal damage. The MWM test was conducted to evaluate spatial learning and memory ability.

RESULTS

The levels of BDNF and neurogenesis exhibited a notable decrease in the hippocampus of neonatal rats after HIBD, as determined by RNA-sequencing technology. Our results demonstrated that treatment with DEX effectively increased the protein expression of BDNF and the phosphorylation of TrkB and CREB, promoting neurogenesis in the dentate gyrus of the hippocampus in neonatal rats with HIBD. Specifically, DEX treatment significantly augmented the expression of BDNF in hippocampal astrocytes, while decreasing the proportion of detrimental A1 astrocytes and increasing the proportion of beneficial A2 astrocytes in neonatal rats with HIBD. Furthermore, inhibiting the BDNF/TrkB/CREB pathway using either ANA-12 or AAV-shRNA-BDNF significantly counteracted the advantageous outcomes of DEX on hippocampal neurogenesis, neuronal survival, and cognitive improvement.

CONCLUSIONS

DEX promoted neurogenesis in the hippocampus by activating the BDNF/TrkB/CREB pathway through the induction of polarization of A1 astrocytes toward A2 astrocytes, subsequently mitigating neuronal damage and cognitive impairment in neonates with HIBD.

Potential Key Proteins, Molecular Networks, and Pathways in Perinatal Hypoxia

Perinatal hypoxia is a common risk factor for CNS development. Using bioinformatics databases, a list of 129 genes involved in perinatal hypoxia was selected from the literature and analyzed with respect to proteins important for biological processes influencing the brain development. Functional enrichment analysis using the DAVID database was performed to identify relevant Gene Ontology (GO) biological processes like response to hypoxia, inflammatory response, positive and negative regulation of apoptosis, and positive and negative regulation of cell proliferation. The selected GO processes contain 17-30 proteins and show an enrichment of 6.3-14.3-fold. The STRING protein-protein interaction network and the Cytoscape data analyzer were used to identify interacting proteins playing a significant role in these processes. The two top protein pairs referring to the proteins with highest degrees and the corresponding proteins connected by high score edges exert opposite or regulatory functions and are essential for the balance between damaging, repairing, protective, or epigenetic processes. The GO response to hypoxia is characterized by the high score protein-protein interaction pairs CASP3/FAS promoting apoptosis and by the protective acting BDNF/MECP2 protein pair. Core components of the GO processes positive and negative regulation of apoptosis are the proteins CASP3/FAS/AKT/eNOS/RPS6KB1 involved in several signal pathways. The GO processes cell proliferation are characterized by the high-score protein-protein interaction pairs MYC/ MAPK1, JUN/MAPK1, IL6/IL1B, and JUN/HDAC1. The study provides new insights into the pathophysiology of perinatal hypoxia and is of importance for future investigations, diagnostics, and therapy of perinatal hypoxia.

Early Neuroprotective Effects of Bovine Lactoferrin Associated with Hypothermia after Neonatal Brain Hypoxia-Ischemia in Rats

Neonatal hypoxic-ischemic (HI) encephalopathy (HIE) in term newborns is a leading cause of mortality and chronic disability. Hypothermia (HT) is the only clinically available therapeutic intervention; however, its neuroprotective effects are limited. Lactoferrin (LF) is the major whey protein in milk presenting iron-binding, anti-inflammatory and anti-apoptotic properties and has been shown to protect very immature brains against HI damage. We hypothesized that combining early oral administration of LF with whole body hypothermia could enhance neuroprotection in a HIE rat model. Pregnant Wistar rats were fed an LF-supplemented diet (1 mg/kg) or a control diet from (P6). At P7, the male and female pups had the right common carotid artery occluded followed by hypoxia (8% O2 for 60') (HI). Immediately after hypoxia, hypothermia (target temperature of 32.5-33.5 °C) was performed (5 h duration) using Criticool®. The animals were divided according to diet, injury and thermal condition. At P8 (24 h after HI), the brain neurochemical profile was assessed using magnetic resonance spectroscopy (1H-MRS) and a hyperintense T2W signal was used to measure the brain lesions. The mRNA levels of the genes related to glutamatergic excitotoxicity, energy metabolism and inflammation were assessed in the right hippocampus. The cell markers and apoptosis expression were assessed using immunofluorescence in the right hippocampus. HI decreased the energy metabolites and increased lactate. The neuronal-astrocytic coupling impairments observed in the HI groups were reversed mainly by HT. LF had an important effect on astrocyte function, decreasing the levels of the genes related to glutamatergic excitotoxicity and restoring the mRNA levels of the genes related to metabolic support. When combined, LF and HT presented a synergistic effect and prevented lactate accumulation, decreased inflammation and reduced brain damage, pointing out the benefits of combining these therapies. Overall, we showed that through distinct mechanisms lactoferrin can enhance neuroprotection induced by HT following neonatal brain hypoxia-ischemia.

TrkB-mediated sustained neuroprotection is sex-specific and ERα dependent in adult mice following neonatal hypoxia ischemia

Background

Neonatal hypoxia ischemia (HI) related brain injury is one of the major causes of life-long neurological morbidities that result in learning and memory impairments. Evidence suggests that male neonates are more susceptible to the detrimental effects of HI, yet the mechanisms mediating these sex-specific responses to neural injury in neonates remain poorly understood. We previously tested the effects of treatment with a small molecule agonist of the tyrosine kinase B receptor (TrkB), 7,8-dihydroxyflavone (DHF) following neonatal HI and determined that females, but not males exhibit increased phosphorylation of TrkB and reduced apoptosis in their hippocampi. Moreover, these female-specific effects of the TrkB agonist were found to be dependent upon the expression of ERα. These findings demonstrated that TrkB activation in the presence of ERα comprises one pathway by which neuroprotection may be conferred in a female-specific manner. The goal of this study was to determine the role of ERα-dependent TrkB-mediated neuroprotection in memory and anxiety in young adult mice exposed to HI during the neonatal period.

Methods

In this study we used a unilateral hypoxic ischemic (HI) mouse model. ERα+/+ or ERα-/- mice were subjected to HI on postnatal day (P) 9 and mice were treated with either vehicle control or the TrkB agonist, DHF, for seven days following HI. When mice reached young adulthood, we used the novel object recognition, novel object location and open field tests to assess long-term memory and anxiety like behavior. The brains were then assessed for tissue damage using immunohistochemistry.

Results

Neonatal DHF treatment prevented HI-induced decrements in recognition and location memory in adulthood in females, but not in males. This protective effect was absent in female mice lacking ERα. Thus, the female-specific and ERα-dependent neuroprotection conferred by DHF therapy after neonatal HI was associated with improved learning and memory outcomes in adulthood. Interestingly, DHF triggered anxiety like behavior in both sexes only in the mice that lacked ERα. When we assessed the severity of injury, we found that DHF therapy did not decrease the percent tissue loss in proportion to functional recovery. We additionally observed that the presence of ERα significantly reduced overall HI-associated mortality in both sexes.

Conclusions

These observations provide evidence for a therapeutic role for DHF in which sustained recovery of memory in females is TrkB-mediated and ERα-dependent. However, the beneficial effects of DHF therapy did not include reduction of gross tissue loss but may be derived from the enhanced functioning of residual tissues in a cell-specific manner.

Restraint stress during neonatal hypoxia-ischemia alters brain injury following normothermia and hypothermia

Rodent models of neonatal hypoxic-ischemic (HI) injury require a subset of animals to be immobilized for continuous temperature monitoring during the insult and subsequent treatment. Restrained animals are discarded from the analysis due to the effect of restraint on the brain injury as first demonstrated by Thoresen et al 1996. However, the effects of restraint on responses to hypothermic (HT) post-insult therapy are not well described. We examine the effects of restraint associated with different probe placements on HI brain injury. We have conducted a meta-analysis of 23 experiments comparing probe rats (skin n = 42, rectal n = 35) and free-moving matched non-probe controls (n = 80) that underwent HI injury (left common carotid artery ligation and 90 min 8% O₂ ) at postnatal day 7 (P7), followed by 5 h of NT (37°C) or HT (32°C). On P14, brain regions were analyzed for injury (by neuropathology and area loss), microglial reactivity and brain-derived neurotrophic factor (BDNF). HI injury was mitigated in NT skin and rectal probe rats, with greater neuroprotection among the rectal probe rats. Following HT, the skin probe rats maintained the restraint-associated neuroprotection, while brain injury was significantly exacerbated among the rectal probe rats. Microglial reactivity strongly correlated with the acquired injury, with no detectable difference between the groups. Likewise, we observed no differences in BDNF signal intensity. Our findings suggest a biphasic neuroprotection from restraint stress, which becomes detrimental in combination with HT and the presumed discomfort from the rectal probe. This finding is useful in highlighting unforeseen effects of common experimental designs or routine clinical management.

Pierre M, Rastogi N, Nugent M, Duck SA, Kirkwood A, Chavez-Valdez R. Dysregulation of ErbB4 Signaling Pathway in the Dorsal Hippocampus after Neonatal Hypoxia-Ischemia and Late Deficits in PV+ Interneurons, Synaptic Plasticity and Working Memory

Neonatal hypoxic-ischemic (HI) injury leads to deficits in hippocampal parvalbumin (PV)⁺ interneurons (INs) and working memory. Therapeutic hypothermia (TH) does not prevent these deficits. ErbB4 supports maturation and maintenance of PV⁺ IN. Thus, we hypothesized that neonatal HI leads to persistent deficits in PV⁺ INs, working memory and synaptic plasticity associated with ErbB4 dysregulation despite TH. P10 HI-injured mice were randomized to normothermia (NT, 36 °C) or TH (31 °C) for 4 h and compared to sham. Hippocampi were studied for α-fodrin, glial fibrillary acidic protein (GFAP), and neuroregulin (Nrg) 1 levels; erb-b2 receptor tyrosine kinase 4 (ErbB4)/ Ak strain transforming (Akt) activation; and PV, synaptotagmin (Syt) 2, vesicular-glutamate transporter (VGlut) 2, Nrg1, and ErbB4 expression in coronal sections. Extracellular field potentials and behavioral testing were performed. At P40, deficits in PV⁺ INs correlated with impaired memory and coincided with blunted long-term depression (LTD), heightened long-term potentiation (LTP) and increased Vglut2/Syt2 ratio, supporting excitatory-inhibitory (E/I) imbalance. Hippocampal Nrg1 levels were increased in the hippocampus 24 h after neonatal HI, delaying the decline documented in shams. Paradoxically ErbB4 activation decreased 24 h and again 30 days after HI. Neonatal HI leads to persistent deficits in hippocampal PV⁺ INs, memory, and synaptic plasticity. While acute decreased ErbB4 activation supports impaired maturation and survival after HI, late deficit reemergence may impair PV⁺ INs maintenance after HI.

Development of a composite diffusion tensor imaging score correlating with short-term neurological status in neonatal hypoxic-ischemic encephalopathy

Hypoxic-ischemic encephalopathy (HIE) is the most common cause of neonatal acquired brain injury. Although conventional MRI may predict neurodevelopmental outcomes, accurate prognostication remains difficult. As diffusion tensor imaging (DTI) may provide an additional diagnostic and prognostic value over conventional MRI, we aimed to develop a composite DTI (cDTI) score to relate to short-term neurological function. Sixty prospective neonates treated with therapeutic hypothermia (TH) for HIE were evaluated with DTI, with a voxel size of 1 × 1 × 2 mm. Fractional anisotropy (FA) and mean diffusivity (MD) from 100 neuroanatomical regions (FA/MD *100 = 200 DTI parameters in total) were quantified using an atlas-based image parcellation technique. A least absolute shrinkage and selection operator (LASSO) regression was applied to the DTI parameters to generate the cDTI score. Time to full oral nutrition [short-term oral feeding (STO) score] was used as a measure of short-term neurological function and was correlated with extracted DTI features. Seventeen DTI parameters were selected with LASSO and built into the final unbiased regression model. The selected factors included FA or MD values of the limbic structures, the corticospinal tract, and the frontotemporal cortices. While the cDTI score strongly correlated with the STO score (rho = 0.83, p = 2.8 × 10-16), it only weakly correlated with the Sarnat score (rho = 0.27, p = 0.035) and moderately with the NICHD-NRN neuroimaging score (rho = 0.43, p = 6.6 × 10-04). In contrast to the cDTI score, the NICHD-NRN score only moderately correlated with the STO score (rho = 0.37, p = 0.0037). Using a mixed-model analysis, interleukin-10 at admission to the NICU (p = 1.5 × 10-13) and tau protein at the end of TH/rewarming (p = 0.036) and after rewarming (p = 0.0015) were significantly associated with higher cDTI scores, suggesting that high cDTI scores were related to the intensity of the early inflammatory response and the severity of neuronal impairment after TH. In conclusion, a data-driven unbiased approach was applied to identify anatomical structures associated with some aspects of neurological function of HIE neonates after cooling and to build a cDTI score, which was correlated with the severity of short-term neurological functions.

Impact of Hypoxia-Ischemia on Neurogenesis and Structural and Functional Outcomes in a Mild-Moderate Neonatal Hypoxia-Ischemia Brain Injury Model

Hypoxic-ischemic encephalopathy (HIE) is a common type of brain injury caused by a lack of oxygen and blood flow to the brain during the perinatal period. The incidence of HIE is approximately 2−3 cases per 1000 live births in high-income settings; while in low- and middle-income countries, the incidence is 3−10-fold higher. Therapeutic hypothermia (TH) is the current standard treatment for neonates affected by moderate−severe HIE. However, more than 50% of all infants with suspected HIE have mild encephalopathy, and these infants are not treated with TH because of their lower risk of adverse outcomes. Despite this, several analyses of pooled data provide increasing evidence that infants who initially have mild encephalopathy may present signs of more significant brain injury later in life. The purpose of this study was to expand our knowledge about the effect of mild−moderate hypoxia-ischemia (HI) at the cellular, structural, and functional levels. An established rat model of mild−moderate HI was used, where postnatal day (P) 7 rats were exposed to unilateral permanent occlusion of the left carotid artery and 90 min of 8% hypoxia, followed by TH or normothermia (NT) treatment. The extent of injury was assessed using histology (P14 and P42) and MRI (P11 and P32), as well as with short-term and long-term behavioral tests. Neurogenesis was assessed by BrdU staining. We showed that mild−moderate HI leads to a progressive loss of brain tissue, pathological changes in MRI scans, as well as an impairment of long-term motor function. At P14, the median area loss assessed by histology for HI animals was 20% (p < 0.05), corresponding to mild−moderate brain injury, increasing to 55% (p < 0.05) at P42. The data assessed by MRI corroborated our results. HI led to a decrease in neurogenesis, especially in the hippocampus and the lateral ventricle at early time points, with a delayed partial recovery. TH was not neuroprotective at early time points following mild−moderate HI, but prevented the increase in brain damage over time. Additionally, rats treated with TH showed better long-term motor function. Altogether, our results bring more light to the understanding of pathophysiology following mild-moderate HI. We showed that, in the context of mild-moderate HI, TH failed to be significantly neuroprotective. However, animals treated with TH showed a significant improvement in motor, but not cognitive long-term function. These results are in line with what is observed in some cases where neonates with mild HIE are at risk of neurodevelopmental deficits in infancy or childhood. Whether TH should be used as a preventive treatment to reduce adverse outcomes in mild-HIE remains of active interest, and more research has to be carried out in order to address this question.

Retained Primitive Reflexes and Potential for Intervention in Autistic Spectrum Disorders

We provide evidence to support the contention that many aspects of Autistic Spectrum Disorder (ASD) are related to interregional brain functional disconnectivity associated with maturational delays in the development of brain networks. We think a delay in brain maturation in some networks may result in an increase in cortical maturation and development in other networks, leading to a developmental asynchrony and an unevenness of functional skills and symptoms. The paper supports the close relationship between retained primitive reflexes and cognitive and motor function in general and in ASD in particular provided to indicate that the inhibition of RPRs can effect positive change in ASD.

Enhanced drug delivery to the reproductive tract using nanomedicine reveals therapeutic options for prevention of preterm birth

Inflammation contributes to nearly 4 million global premature births annually. Here, we used a mouse model of intrauterine inflammation to test clinically used formulations, as well as engineered nanoformulations, for the prevention of preterm birth (PTB). We observed that neither systemic 17a-hydroxyprogesterone caproate (Makena) nor vaginal progesterone gel (Crinone) was sufficient to prevent inflammation-induced PTB, consistent with recent clinical trial failures. However, we found that vaginal delivery of mucoinert nanosuspensions of histone deacetylase (HDAC) inhibitors, in some cases with the addition of progesterone, prevented PTB and resulted in delivery of live pups exhibiting neurotypical development. In human myometrial cells in vitro, the P4/HDAC inhibitor combination both inhibited cell contractility and promoted the anti-inflammatory action of P4 by increasing progesterone receptor B stability. Here, we demonstrate the use of vaginally delivered drugs to prevent intrauterine inflammation-induced PTB resulting in the birth of live offspring in a preclinical animal model.

Accumulation of PSA-NCAM marks nascent neurodegeneration in the dorsal hippocampus after neonatal hypoxic-ischemic brain injury in mice

Neonatal hypoxia-ischemia (nHI) disrupts hippocampal GABAergic development leading to memory deficits in mice. Polysialic-acid neural-cell adhesion molecule (PSA-NCAM) developmentally declines to trigger GABAergic maturation. We hypothesized that nHI changes PSA-NCAM abundance and cellular distribution, impairing GABAergic development, and marking nascent neurodegeneration. Cell degeneration, atrophy, and PSA-NCAM immunoreactivity (IR) were measured in CA1 of nHI-injured C57BL6 mice related to: (i) cellular subtype markers; (ii) GAD65/67 and synatophysin (SYP), pre-synaptic markers; (iii) phospho-Ser³⁹⁶Tau, cytoskeletal marker; and (iv) GAP43, axonalregeneration marker. PSA-NCAM IR was minimal in CA1 of shams at P11. After nHI, PSA-NCAM IR was increased in injured pyramidal cells (PCs), minimal in parvalbumin (PV)⁺INs, and absent in glia. PSA-NCAM IR correlated with injury severity and became prominent in perikaryal cytoplasm at P18. GAD65/67 and SYP IRs only weakly related to PSA-NCAM after nHI. Injured phospho-Ser³⁹⁶Tau⁺ PCs and PV⁺INs variably co-expressed PSA-NCAM at P40. While PCs with cytoplasmic marginalized PSA-NCAM had increased perisomatic GAP43, those with perikaryal cytoplasmic PSA-NCAM had minimal GAP43. PSA-NCAM increased in serum of nHI-injured mice. Increased PSA-NCAM is likely a generic acute response to nHI brain injury. PSA-NCAM aberrant cellular localization may aggravate neuronal degeneration. The significance of PSA-NCAM as a biomarker of recovery from nHI and nascent neurodegeneration needs further study.

Effects of prenatal photobiomodulation treatment on neonatal hypoxic ischemia in rat offspring

Neonatal hypoxic-ischemic (HI) injury is a severe complication often leading to neonatal death and long-term neurobehavioral deficits in children. Currently, the only treatment option available for neonatal HI injury is therapeutic hypothermia. However, the necessary specialized equipment, possible adverse side effects, and limited effectiveness of this therapy creates an urgent need for the development of new HI treatment methods. Photobiomodulation (PBM) has been shown to be neuroprotective against multiple brain disorders in animal models, as well as limited human studies. However, the effects of PBM treatment on neonatal HI injury remain unclear. Methods: Two-minutes PBM (808 nm continuous wave laser, 8 mW/cm2 on neonatal brain) was applied three times weekly on the abdomen of pregnant rats from gestation day 1 (GD1) to GD21. After neonatal right common carotid artery ligation, cortex- and hippocampus-related behavioral deficits due to HI insult were measured using a battery of behavioral tests. The effects of HI insult and PBM pretreatment on infarct size; synaptic, dendritic, and white matter damage; neuronal degeneration; apoptosis; mitochondrial function; mitochondrial fragmentation; oxidative stress; and gliosis were then assessed. Results: Prenatal PBM treatment significantly improved the survival rate of neonatal rats and decreased infarct size after HI insult. Behavioral tests revealed that prenatal PBM treatment significantly alleviated cortex-related motor deficits and hippocampus-related memory and learning dysfunction. In addition, mitochondrial function and integrity were protected in HI animals treated with PBM. Additional studies revealed that prenatal PBM treatment significantly alleviated HI-induced neuroinflammation, oxidative stress, and myeloid cell/astrocyte activation. Conclusion: Prenatal PBM treatment exerts neuroprotective effects on neonatal HI rats. Underlying mechanisms for this neuroprotection may include preservation of mitochondrial function, reduction of inflammation, and decreased oxidative stress. Our findings support the possible use of PBM treatment in high-risk pregnancies to alleviate or prevent HI-induced brain injury in the perinatal period.

Sex specific correlation between GABAergic disruption in the dorsal hippocampus and flurothyl seizure susceptibility after neonatal hypoxic-ischemic brain injury

Since neonatal hypoxia-ischemia (HI) disrupts the hippocampal (Hp) GABAergic network in the mouse and Hp injury in this model correlates with flurothyl seizure susceptibility only in male mice, we hypothesized that GABAergic disruption correlates with flurothyl seizure susceptibility in a sex-specific manner. C57BL6 mice were exposed to HI (Vannucci model) versus sham procedures at P10, randomized to normothermia (NT) or therapeutic hypothermia (TH), and subsequently underwent flurothyl seizure testing at P18. Only in male mice, Hp atrophy correlated with seizure susceptibility. The number of Hp parvalbumin positive interneurons (PV⁺INs) decreased after HI in both sexes, but TH attenuated this deficit only in females. In males only, seizure susceptibility directly correlated with the number of PV⁺INs, but not somatostatin or calretinin expressing INs. Hp GABA_B receptor subunit levels were decreased after HI, but unrelated to later seizure susceptibility. In contrast, Hp GABA_A receptor α1 subunit (GABA_ARα1) levels were increased after HI. Adjusting the number of PV⁺ INs for their GABA_ARα1 expression strengthened the correlation with seizure susceptibility in male mice. Thus, we identified a novel Hp sex-specific GABA-mediated mechanism of compensation after HI that correlates with flurothyl seizure susceptibility warranting further study to better understand potential clinical translation.

Monocytic Infiltrates Contribute to Autistic-like Behaviors in a Two-Hit Model of Neurodevelopmental Defects

Growing evidence suggests that early-life interactions among genetic, immune, and environment factors may modulate neurodevelopment and cause psycho-cognitive deficits. Maternal immune activation (MIA) induces autism-like behaviors in offspring, but how it interplays with perinatal brain injury (especially birth asphyxia or hypoxia ischemia [HI]) is unclear. Herein we compared the effects of MIA (injection of poly[I:C] to dam at gestational day 12.5), HI at postnatal day 10, and the combined MIA/HI insult in murine offspring of both sexes. We found that MIA induced autistic-like behaviors without microglial activation but amplified post-HI NFκB signaling, pro-inflammatory responses, and brain injury in offspring. Conversely, HI neither provoked autistic-like behaviors nor concealed them in the MIA offspring. Instead, the dual MIA/HI insult added autistic-like behaviors with diminished synaptic density and reduction of autism-related PSD-95 and Homer-1 in the hippocampus, which were missing in the singular MIA or HI insult. Further, the dual MIA/HI insult enhanced the brain influx of Otx2-positive monocytes that are associated with an increase of perineuronal net-enwrapped parvalbumin neurons. Using CCR2-CreER mice to distinguish monocytes from the resident microglia, we found that the monocytic infiltrates gradually adopted a ramified morphology and expressed the microglial signature genes (Tmem119, P2RY12, and Sall1) in post-MIA/HI brains, with some continuing to express the proinflammatory cytokine TNFα. Finally, genetic or pharmacological obstruction of monocytic influx significantly reduced perineuronal net-enwrapped parvalbumin neurons and autistic-like behaviors in MIA/HI offspring. Together, these results suggest a pathologic role of monocytes in the two-hit (immune plus neonatal HI) model of neurodevelopmental defects.SIGNIFICANCE STATEMENT In autism spectrum disorders (ASDs), prenatal infection or maternal immune activation (MIA) may act as a primer for multiple genetic and environmental factors to impair neurodevelopment. This study examined whether MIA cooperates with neonatal cerebral hypoxia ischemia to promote ASD-like aberrations in mice using a novel two-hit model. It was shown that the combination of MIA and neonatal hypoxia ischemia produces autistic-like behaviors in the offspring, and has synergistic effects in inducing neuroinflammation, monocytic infiltrates, synaptic defects, and perineuronal nets. Furthermore, genetic or pharmacological intervention of the MCP1-CCR2 chemoattractant pathway markedly reduced monocytic infiltrates, perineuronal nets, and autistic-like behaviors. These results suggest reciprocal escalation of immune and neonatal brain injury in a subset of ASD that may benefit from monocyte-targeted treatments.

Gender differences involved in the pathophysiology of the perinatal hypoxic-ischemic damage

Hypoxic-ischemic encephalopathy (HIE) is a neonatal condition that occurs as a consequence of perinatal asphyxia, which is caused by a number of factors, commonly via compression of the umbilical cord, placental abruption, severe meconium aspiration, congenital cardiac or pulmonary anomalies and birth trauma. Experimental studies have confirmed that male rat pups show a higher resistance to HIE treatment. Moreover, the long-term consequences of hypoxia in male are more severe in comparison to female rat pups. These sex differences can be attributed to the pathophysiology of hypoxia-ischemia, whereby studies are beginning to establish such gender-specific distinctions. The current and sole treatment for HIE is hypothermia, in which a reduction in temperature prevents long-term effects, such as cerebral palsy or seizures. However, in most cases hypothermia is not a sufficient treatment as indicated by a high mortality rate. In the present review, we discuss the gender differences within the pathophysiology of hypoxia-ischemia and delve into the role of gender in the incidence, progression and severity of the disease. Furthermore, this may result in the development of potential novel treatment approaches for targeting and preventing the long-term consequences of HIE.

Neonatal Hypoxic-Ischemic Encephalopathy Yields Permanent Deficits in Learning Acquisition: A Preclinical Touchscreen Assessment

Neonatal hypoxic-ischemic encephalopathy (HIE) remains a common problem world-wide for infants born at term. The impact of HIE on long-term outcomes, especially into adulthood, is not well-described. To facilitate identification of biobehavioral biomarkers utilizing a translational platform, we sought to investigate the impact of HIE on executive function and cognitive outcomes into adulthood utilizing a murine model of HIE. HIE mice (unilateral common carotid artery occlusion to induce ischemia, followed by hypoxia with a FiO2 of 0.08 for 45 min) and control mice were tested on discrimination and reversal touchscreen tasks (using their noses) shown to be sensitive to loss of basal ganglia or cortical function, respectively. We hypothesized that the HIE injury would result in deficits in reversal learning, revealing complex cognitive and executive functioning impairments. Following HIE, mice had a mild discrimination impairment as measured by incorrect responses but were able to learn the paradigm to similar levels as controls. During reversal, HIE mice required significantly more total trials, errors and correction trials across the paradigm. Analysis of specific stages showed that reversal impairments in HIE were driven by significant increases in all measured parameters during the late learning, striatal-mediated portion of the task. Together, these results support the concept that HIE occurring during the neonatal period results in abnormal neurodevelopment that persists into adulthood, which can impact efficient associated learning. Further, these data show that utilization of an established model of HIE coupled with touchscreen learning provides valuable information for screening therapeutic interventions that could mitigate these deficits to improve the long-term outcomes of this vulnerable population.

Disease-directed engineering for physiology-driven treatment interventions in neurological disorders

Neurological disease is killing us. While there have long been attempts to develop therapies for both acute and chronic neurological diseases, no current treatments are curative. Additionally, therapeutic development for neurological disease takes 15 years and often costs several billion dollars. More than 96% of these therapies will fail in late stage clinical trials. Engineering novel treatment interventions for neurological disease can improve outcomes and quality of life for millions; however, therapeutics should be designed with the underlying physiology and pathology in mind. In this perspective, we aim to unpack the importance of, and need to understand, the physiology of neurological disease. We first dive into the normal physiological considerations that should guide experimental design, and then assess the pathophysiological factors of acute and chronic neurological disease that should direct treatment design. We provide an analysis of a nanobased therapeutic intervention that proved successful in translation due to incorporation of physiology at all stages of the research process. We also provide an opinion on the importance of keeping a high-level view to designing and administering treatment interventions. Finally, we close with an implementation strategy for applying a disease-directed engineering approach. Our assessment encourages embracing the complexity of neurological disease, as well as increasing efforts to provide system-level thinking in our development of therapeutics for neurological disease.

Decreased body temperature during anoxia affects the endogenous BDNF level in tertiary phase of injury

Asphyxia before, during, or after birth is an important cause of perinatal mortality and morbidity. The mechanism underlying neurological damage resulting from anoxia episode is complex and is not limited to the anoxia episode. Although the benefits of therapeutic hypothermia in secondary failure of oxidative metabolism have long been known, the principle of this therapy in tertiary phase of repair and reorganization have not yet to be fully elucidated. Currently brain-derived neurotrophic factor (BDNF) is also considered to be beneficial to neuronal survival. Therefore, our experiments aimed at determining the effects of low body temperature during simulated perinatal anoxia on the level of the neurotrophic brain-derived factor (BDNF) and on the correlation between the level of BDNF (proBDNF and mBDNF) and the level of active caspase-3 (marker of apoptosis) in developing brain in tertiary phase after exposure. The results demonstrated that the ability of BDNF to inhibit caspase-3 activation and subsequent apoptosis likely accounts in large part for its protection against neuronal damage only in rats maintaining the low body temperature.

Roles Played by the Na+/Ca2+ Exchanger and Hypothermia in the Prevention of Ischemia-Induced Carrier-Mediated Efflux of Catecholamines into the Extracellular Space: Implications for Stroke Therapy

The release of [³H]dopamine ([³H]DA) and [³H]noradrenaline ([³H]NA) in acutely perfused rat striatal and cortical slice preparations was measured at 37 °C and 17 °C under ischemic conditions. The ischemia was simulated by the removal of oxygen and glucose from the Krebs solution. At 37 °C, resting release rates in response to ischemia were increased; in contrast, at 17 °C, resting release rates were significantly reduced, or resting release was completely prevented. The removal of extracellular Ca²⁺ further increased the release rates of [³H]DA and [³H]NA induced by ischemic conditions. This finding indicated that the Na⁺/Ca²⁺ exchanger (NCX), working in reverse in the absence of extracellular Ca²⁺, fails to trigger the influx of Ca²⁺ in exchange for Na⁺ and fails to counteract ischemia by further increasing the intracellular Na⁺ concentration ([Na⁺]_i). KB-R7943, an inhibitor of NCX, significantly reduced the cytoplasmic resting release rate of catecholamines under ischemic conditions and under conditions where Ca²⁺ was removed. Hypothermia inhibited the excessive release of [³H]DA in response to ischemia, even in the absence of Ca²⁺. These findings further indicate that the NCX plays an important role in maintaining a high [Na⁺]_i, a condition that may lead to the reversal of monoamine transporter functions; this effect consequently leads to the excessive cytoplasmic tonic release of monoamines and the reversal of the NCX. Using HPLC combined with scintillation spectrometry, hypothermia, which enhances the stimulation-evoked release of DA, was found to inhibit the efflux of toxic DA metabolites, such as 3,4-dihydroxyphenylacetaldehyde (DOPAL). In slices prepared from human cortical brain tissue removed during elective neurosurgery, the uptake and release values for [³H]NA did not differ from those measured at 37 °C in slices that were previously maintained under hypoxic conditions at 8 °C for 20 h. This result indicates that hypothermia preserves the functions of the transport and release mechanisms, even under hypoxic conditions. Oxidative stress (H₂O₂), a mediator of ischemic brain injury enhanced the striatal resting release of [³H]DA and its toxic metabolites (DOPAL, quinone). The study supports our earlier findings that during ischemia transmitters are released from the cytoplasm. In addition, the major findings of this study that hypothermia of brain slice preparations prevents the extracellular calcium concentration ([Ca²⁺]_o)-independent non-vesicular transmitter release induced by ischemic insults, inhibiting Na⁺/Cl⁻-dependent membrane transport of monoamines and their toxic metabolites into the extracellular space, where they can exert toxic effects.

Delayed injury of hippocampal interneurons after neonatal hypoxia-ischemia and therapeutic hypothermia in a murine model

Delayed hippocampal injury and memory impairments follow neonatal hypoxia-ischemia (HI) despite the use of therapeutic hypothermia (TH). Death of hippocampal pyramidal cells occurs acutely after HI, but characterization of delayed cell death and injury of interneurons (INs) is unknown. We hypothesize that injury of INs after HI is: (i) asynchronous to that of pyramidal cells, (ii) independent of injury severity, and (iii) unresponsive to TH. HI was induced in C57BL6 mice at p10 with unilateral right carotid ligation and 45 min of hypoxia (FiO₂  = 0.08). Mice were randomized to normothermia (36 °C, NT) or TH (31 °C) for 4 hr after HI and anesthesia-exposed shams were use as controls. Brains were studied at 24 hr (p11) or 8 days (p18) after HI. Vglut1, GAD65/67, PSD95, parvalbumin (PV) and calbindin-1 (Calb1) were measured. Cell death was assessed using cresyl violet staining and TUNEL assay. Hippocampal atrophy and astroglyosis at p18 were used to assess injury severity and to correlate with number of PV + INs. VGlut1 level decreased by 30% at 24 hr after HI, while GAD65/67 level decreased by ∼50% in forebrain 8 days after HI, a decrease localized in CA1 and CA3. PSD95 levels decreased in forebrain by 65% at 24 hr after HI and remained low 8 days after HI. PV + INs increased in numbers (per mm² ) and branching between p11 and p18 in sham mice but not in NT and TH mice, resulting in 21-52% fewer PV + INs in injured mice at p18. Calb1 protein and mRNA were also reduced in HI injured mice at p18. At p18, somatodendritic attrition of INs was evident in all injured mice without evidence of cell death. Neither hippocampal atrophy nor astroglyosis correlated with the number of PV + INs at p18. Thus, HI exposure has long lasting effects in the hippocampus impairing the development of the GABAergic system with only partial protection by TH independent of the degree of hippocampal injury. © 2018 Wiley Periodicals, Inc.

Thermal conditions during neonatal anoxia affect the endogenous level of brain-derived neurotrophic factor

Anoxia during delivery is a complication that can disturb infant brain development leading to various types of neurological disorders. Our studies have shown that increased body temperature of newborn rats of both sexes intensifies the postanoxic oxidative stress and prevents triggering the endogenous adaptive response such as HIF-1α activation. Currently, brain-derived neurotrophic factor-BDNF is considered to be a modulator of neuronal plasticity. In the developing brain, mature BDNF and its precursor exhibit prosurvival action through the TrkB receptor and proapoptotic functions binding to p75^NTR , respectively. The aim of our experiments was to check the effects of body temperature on the postanoxic level of BDNF and on the expression of its receptors as well as on the marker of apoptosis-caspase-3 in the rat brain. Two-day-old Wistar Han rats (male/female ratio, 1:1) were exposed to anoxia in 100% nitrogen atmosphere for 10 min in different thermal conditions, which allowed them to regulate their rectal temperature at the following levels: normothermic-33°C; hyperthermic-37°C; and extremely hyperthermic-39°C. Thermal conditions during neonatal anoxia affected the level of proBDNF, BDNF as well as their receptors and caspase-3 in the forebrain. The increased BDNF protein level followed by decreased caspase-3 protein level was probably dependent on body temperature under anoxic conditions and was observed only in rats maintaining decreased body temperature. The positive effect of BDNF was not observed under hyperthermic conditions. Moreover, BDNF level changes correlated with body temperature probably affected the learning and spatial memory in juvenile rats.

Calbindin-1 Expression in the Hippocampus following Neonatal Hypoxia-Ischemia and Therapeutic Hypothermia and Deficits in Spatial Memory

Hippocampal injury following neonatal hypoxia-ischemia (HI) leads to memory impairments despite therapeutic hypothermia (TH). In the hippocampus, the expression of calbindin-1 (Calb1), a Ca2+-buffering protein, increases during postnatal development and decreases with aging and neurodegenerative disorders. Since persistent Ca2+ dysregulation after HI may lead to ongoing injury, persistent changes in hippocampal expression of Calb1 may contribute to memory impairments after neonatal HI. We hypothesized that, despite TH, neonatal HI persistently decreases Calb1 expression in the hippocampus, a change associated with memory deficits in the mouse. We induced cerebral HI in C57BL6 mice at postnatal day 10 (P10) with right carotid ligation and 45 min of hypoxia (FiO2 = 0.08), followed by normothermia (36°C, NT) or TH (31°C) for 4 h with anesthesia-shams as controls. Nissl staining and glial fibrillary acidic protein (GFAP) immunohistochemistry (IHC) were used to grade brain injury and astrogliosis at P11, P18, and P40 prior to the assessment of Calb1 expression by IHC. The subset of mice followed to P40 also performed a memory behavior task (Y-maze) at P22-P26. Nonparametric statistics stratified by sex were applied. In both anterior and posterior coronal brain sections, hippocampal Calb1 expression doubled between P11 and P40 due to an increase in the cornus ammonis (CA) field (Kruskal-Wallis [KW] p < 0.001) and not the dentate gyrus (DG). Neonatal HI produced delayed (P18) and late (P40) deficits in the expression of Calb1 exclusively in the CA field (KW p = 0.02) in posterior brain sections. TH did not attenuate Calb1 deficits after HI. Thirty days after HI injury (at P40), GFAP scores in the hippocampus (p < 0.001, r = -0.47) and CA field (p < 0.001, r = -0.39) of posterior brain sections inversely correlated with their respective Calb1 expression. Both sexes demonstrated deficits in Y-maze testing, including approximately 40% lower spontaneous alterations performance and twice as much total impairment compared to sham mice (KW p < 0.001), but it was only in females that these deficits correlated with the Calb1 expression in the hippocampal CA field (p < 0.05) of the posterior sections. Hippocampal atrophy after neonatal HI also correlated with worse deficits in Y-maze testing, but it did not predict Calb1 deficits. Neonatal HI produces a long-lasting Calb1 deficit in the hippocampal CA field during development, which is not mitigated by TH. Late Calb1 deficit after HI may be the result of persistent astrogliosis and can lead to memory impairment, particularly in female mice.

Seizure Susceptibility Correlates with Brain Injury in Male Mice Treated with Hypothermia after Neonatal Hypoxia-Ischemia

Hypoxic-ischemic encephalopathy is a common neonatal brain injury associated with significant morbidity and mortality despite the administration of therapeutic hypothermia (TH). Neonatal seizures and subsequent chronic epilepsy are frequent in this patient population and current treatments are partially effective. We used a neonatal murine hypoxia-ischemia (HI) model to test whether the severity of hippocampal and cortical injury predicts seizure susceptibility 8 days after HI and whether TH mitigates this susceptibility. HI at postnatal day 10 (P10) caused hippocampal injury not mitigated by TH in male or female pups. TH did not confer protection against flurothyl seizure susceptibility at P18 in this model. Hippocampal (R2 = 0.33, p = 0.001) and cortical (R2 = 0.33, p = 0.003) injury directly correlated with seizure susceptibility in male but not female pups. Thus, there are sex-specific consequences of neonatal HI on flurothyl seizure susceptibility in a murine neonatal HI model. Further studies are necessary to elucidate the underlying mechanisms of sex dimorphism in seizure susceptibility after neonatal HI.

Strain-Related Differences in Mouse Neonatal Hypoxia-Ischemia

Neonatal hypoxic-ischemic brain injury is commonly studied by means of the Vannucci procedure in mice or rats (unilateral common carotid artery occlusion followed by hypoxia). Previously, we modified the postnatal day 7 (P7) rat procedure for use in mice, and later demonstrated that genetic strain strongly influences the degree of brain injury in the P7 mouse model of hypoxia-ischemia (HI). Recently, the P9 or P10 mouse brain was recognized as the developmental equivalent of a term neonatal human brain, rather than P7. Consequently, the Vannucci procedure has again been modified, and a commonly used protocol employs 10% oxygen for 50 min in C57Bl/6 mice. Strain differences have yet to be described for the P9/P10 mouse model. In order to determine if the strain differences we previously reported in the P7 mouse model are present in the P9 model, we compared 2 commonly used strains, CD1 and C57Bl/6J, in both the P7 (carotid ligation [in this case, right] followed by exposure to 8% oxygen for 30 min) and P9 (carotid ligation [in this case left] followed by exposure to 10% oxygen) models of HI. Experiments using the P7 model were performed in 2001-2012 and those using the P9 model were performed in 2012-2016. Five to seven days after the HI procedure, mice were perfused with 4% paraformaldehyde, their brains were sectioned on a Vibratome (50 µm) and alternate sections were stained with Perl's iron stain or cresyl violet. Brain sections were examined microscopically and scored for the degree of injury. Since brains in the P7 group had been scored previously with a slightly different system, they were reanalyzed using our current scoring system which scores injury in 11 regions: the anterior, middle, and posterior cortex; the anterior, middle, and posterior striatum; CA1, CA2, CA3, and the dentate gyrus of the hippocampus and thalamus, on a scale from 0 (none) to 3 (cystic infarct) for a total score of 0-33. Brains in the P9 group were scored with the same system. Given the same insult, the P7 CD1 mice had greater injury than the C57Bl/6J mice, which agrees with our previous findings. The P9 CD1 mice also had greater injury than the C57Bl/6J mice. This study confirms that CD1 mice are more susceptible to injury than C57Bl/6J mice and that strain selection is important when using mouse models of HI.

The duration of hypothermia affects short-term neuroprotection in a mouse model of neonatal hypoxic ischaemic injury

Neonatal hypoxic-ischaemic encephalopathy (HIE) is major cause of neonatal mortality and morbidity. Therapeutic hypothermia is standard clinical care for moderate hypoxic-ischaemic (HI) brain injury, however it reduces the risk of death and disability only by 11% and 40% of the treated infants still develop disabilities. Thus it is necessary to develop supplementary therapies to complement therapeutic hypothermia in the treatment of neonatal HIE. The modified Rice-Vannucci model of HI in the neonatal mouse is well developed and widely applied with different periods of hypothermia used as neuroprotective strategy in combination with other agents. However, different studies use different periods, time of initiation and duration of hypothermia following HI, with subsequent varying degrees of neuroprotection. So far most rodent data is obtained using exposure to 5-6h of therapeutic hypothermia. Our aim was to compare the effect of exposure to three different short periods of hypothermia (1h, 1.5h and 2h) following HI insult in the postnatal day 7 C57/Bl6 mouse, and to determine the shortest period providing neuroprotection. Our data suggests that 1h and 1.5h of hypothermia delayed by 20min following a 60min exposure to 8%O2 do not prove neuroprotective. However, 2h of hypothermia significantly reduced tissue loss, TUNEL+ cell death and microglia and astroglia activation. We also observed improved functional outcome 7 days after HI. We suggest that the minimal period of cooling necessary to provide moderate short term neuroprotection and appropriate for the development and testing of combined treatment is 2h.

Gender-dependent changes in physical development, BDNF content and GSH redox system in a model of acute neonatal hypoxia in rats

Perinatal hypoxia-ischaemia is one of the leading factors that negatively influence the development of the central nervous system. Our aim was to investigate the effects of sex on the outcomes of acute neonatal hypoxia (ANH) in rat pups. Male and female Wistar rats were exposed to a hypoxic condition (8% oxygen for 120 min) at postnatal day 2 (P2). Immediately after ANH an increase in HIF1-α gene expression was observed in the rat brains, independently of sex. Brain-derived neurotrophic factor (BDNF) and glutathione peroxidase-4 gene expression was increased in female animals only. Hypoxic pups of both sexes showed a decreased reduced/oxidised glutathione (GSH/GSSG) ratio in the blood and only males had an increased GSH content in the whole brain immediately after hypoxia. Furthermore, an increased BDNF content in the brain was found in both male and female rat pups at 0 h and in serum 4 h after hypoxia, but at 4 h after hypoxia only males had an increased BDNF level in the brain. Only hypoxic males displayed retarded performance in the righting reflex, but in a negative geotaxis test hypoxic pups of both sexes had an increased turnaround time. Moreover, hypoxic female but not male pups demonstrated less weight gain than control littermates for the entire observation period (until P18). These results demonstrate that ANH at P2 leads to both molecular and physiological impairments in a sex-specific manner and the described model could be used to represent mild hypoxic brain damage in very preterm infants.

Alterations in inter-alpha inhibitor protein expression after hypoxic-ischemic brain injury in neonatal rats

Hypoxic-ischemic (HI) brain injury is frequently associated with premature and/or full-term birth-related complications that reflect widespread damage to cerebral cortical structures. Inflammation has been implicated in the long-term evolution and severity of HI brain injury. Inter-Alpha Inhibitor Proteins (IAIPs) are immune modulator proteins that are reduced in systemic neonatal inflammatory states. We have shown that endogenous IAIPs are present in neurons, astrocytes and microglia and that exogenous treatment with human plasma purified IAIPs decreases neuronal injury and improves behavioral outcomes in neonatal rats with HI brain injury. In addition, we have shown that endogenous IAIPs are reduced in the brain of the ovine fetus shortly after ischemic injury. However, the effect of HI on changes in circulating and endogenous brain IAIPs has not been examined in neonatal rats. In the current study, we examined changes in endogenous IAIPs in the systemic circulation and brain of neonatal rats after exposure to HI brain injury. Postnatal day 7 rats were exposed to right carotid artery ligation and 8% oxygen for 2h. Sera were obtained immediately, 3, 12, 24, and 48h and brains 3 and 24h after HI. IAIPs levels were determined by a competitive enzyme-linked immunosorbent assay (ELISA) in sera and by Western immunoblots in cerebral cortices. Serum IAIPs were decreased 3h after HI and remained lower than in non-ischemic rats up to 7days after HI. IAIP expression increased in the ipsilateral cerebral cortices 24h after HI brain injury and in the hypoxic contralateral cortices. However, 3h after hypoxia alone the 250kDa IAIP moiety was reduced in the contralateral cortices. We speculate that changes in endogenous IAIPs levels in blood and brain represent constituents of endogenous anti-inflammatory neuroprotective mechanism(s) after HI in neonatal rats.

2-Iminobiotin Superimposed on Hypothermia Protects Human Neuronal Cells from Hypoxia-Induced Cell Damage: An in Vitro Study

Perinatal asphyxia represents one of the major causes of neonatal morbidity and mortality. Hypothermia is currently the only established treatment for hypoxic-ischemic encephalopathy (HIE), but additional pharmacological strategies are being explored to further reduce the damage after perinatal asphyxia. The aim of this study was to evaluate whether 2-iminobiotin (2-IB) superimposed on hypothermia has the potential to attenuate hypoxia-induced injury of neuronal cells. In vitro hypoxia was induced for 7 h in neuronal IMR-32 cell cultures. Afterwards, all cultures were subjected to 25 h of hypothermia (33.5°C), and incubated with vehicle or 2-IB (10, 30, 50, 100, and 300 ng/ml). Cell morphology was evaluated by brightfield microscopy. Cell damage was analyzed by LDH assays. Production of reactive oxygen species (ROS) was measured using fluorometric assays. Western blotting for PARP, Caspase-3, and the phosphorylated forms of akt and erk1/2 was conducted. To evaluate early apoptotic events and signaling, cell protein was isolated 4 h post-hypoxia and human apoptosis proteome profiler arrays were performed. Twenty-five hour after the hypoxic insult, clear morphological signs of cell damage were visible and significant LDH release as well as ROS production were observed even under hypothermic conditions. Post-hypoxic application of 2-IB (10 and 30 ng/ml) reduced the hypoxia-induced LDH release but not ROS production. Phosphorylation of erk1/2 was significantly increased after hypoxia, while phosphorylation of akt, protein expression of Caspase-3 and cleavage of PARP were only slightly increased. Addition of 2-IB did not affect any of the investigated proteins. Apoptosis proteome profiler arrays performed with cellular protein obtained 4 h after hypoxia revealed that post-hypoxic application of 2-IB resulted in a ≥ 25% down regulation of 10/35 apoptosis-related proteins: Bad, Bax, Bcl-2, cleaved Caspase-3, TRAILR1, TRAILR2, PON2, p21, p27, and phospho Rad17. In summary, addition of 2-IB during hypothermia is able to attenuate hypoxia-induced neuronal cell damage in vitro. Combination treatment of hypothermia with 2-IB could be a promising strategy to reduce hypoxia-induced neuronal cell damage and should be considered in further animal and clinical studies.

Promoting neuroregeneration after perinatal arterial ischemic stroke: neurotrophic factors and mesenchymal stem cells

Newborns suffering from perinatal arterial ischemic stroke (PAIS) are at risk of neurodevelopmental problems. Current treatment options for PAIS are limited and mainly focus on supportive care, as presentation of PAIS is beyond the time window of current treatment strategies. Therefore, recent focus has shifted to interventions that stimulate regeneration of damaged brain tissue. From animal models, it is known that the brain increases its neurogenic capability after ischemic injury, by promoting neural cell proliferation and differentiation. However, neurogenesis is not maintained at the long term, which consequently impedes full repair leading to adverse consequences later in life. Boosting neuroregeneration of the newborn brain using treatment with neurotrophic factors and/or mesenchymal stem cells (MSCs) may be promising novel therapeutic strategies to improve neurological prospects and quality of life of infants with PAIS. This review focuses on effectiveness of neurotrophic growth factors, including erythropoietin, brain-derived neurotrophic factor, vascular endothelial growth factor, glial-derived neurotrophic factor, and MSC therapy, in both experimental neonatal stroke studies and first clinical trials for neonatal ischemic brain injury.