Hypoxia-ischemia disrupts directed interactions within neonatal prefrontal-hippocampal networks

Socioemotional and Psychological Outcomes of Hypoxic-Ischemic Encephalopathy: A Systematic Review

BACKGROUND AND OBJECTIVES

Therapeutic hypothermia has reduced the risk of death or major disability following perinatal hypoxic-ischemic encephalopathy (HIE); however, many children who experience perinatal HIE still go on to develop personal and behavioral challenges, which can be difficult for caregivers and a public health burden for society. Our objective with this review is to systematically identify and synthesize studies that evaluate associations between perinatal HIE and socioemotional or psychological outcomes.

METHODS

We screened all search-returned journal articles from Cochrane Library, Embase, Medline, PsycINFO, Scopus, and Web of Science from data inception through February 1, 2023. Keywords related to HIE (eg, neonatal encephalopathy, neonatal brain injury) and outcomes (eg, social*, emotion*, behav* problem, psycholog*, psychiatr*) were searched with a predefined search string. We included all observational human studies reporting socioemotional or psychological sequelae of term HIE. Study data were recorded on standardized sheets, and the Newcastle-Ottawa Scale was adapted to assess study quality.

RESULTS

We included 43 studies documenting 3244 HIE participants and 2132 comparison participants. We found statistically significant associations between HIE and social and emotional, behavioral, and psychological and psychiatric deficits throughout infancy, childhood, and adolescence (19 studies). The authors of the included studies also report nonsignificant findings (11 studies) and outcomes without statistical comparison (25 studies).

CONCLUSIONS

Perinatal HIE may be a risk factor for a range of socioemotional and psychological challenges in the short- and long-term. Routine screening, early intervention, and follow-up support may be particularly beneficial to this population.

Pharmacological modulation of HIF-1 in the treatment of neuropsychiatric disorders

Hypoxia-inducible factor 1 has been identified as an important therapeutic target in psychiatric illnesses. Hypoxia is a condition in which tissues do not receive enough oxygen, resulting in less oxidative energy production. HIF-1, the master regulator of molecular response to hypoxia, is destabilized when oxygen levels fall. HIF-1, when activated, increases the gene transcription factors that promote adaptive response and longevity in hypoxia. HIF-regulated genes encode proteins involved in cell survival, energy metabolism, angiogenesis, erythropoiesis, and vasomotor control. Multiple genetic and environmental variables contribute to the pathophysiology of psychiatric disease. This review focuses on the most recent findings indicating the role of oxygen deprivation in CNS damage, with strong attention on HIF-mediated pathways. Several pieces of evidence suggested that, in the case of hypoxia, induction and maintenance of HIF-1 target genes may help reduce nerve damage. Major new insights into the molecular mechanisms that control HIF's sensitivity to oxygen are used to make drugs that can change the way HIF works as a therapeutic target for some CNS diseases.

Sex and age differences in social and cognitive function in offspring exposed to late gestational hypoxia

BACKGROUND

Gestational sleep apnea is a hypoxic sleep disorder that affects 8-26% of pregnancies and increases the risk for central nervous system dysfunction in offspring. Specifically, there are sex differences in the sensitivity of the fetal hippocampus to hypoxic insults, and hippocampal impairments are associated with social dysfunction, repetitive behaviors, anxiety, and cognitive impairment. Yet, it is unclear whether gestational sleep apnea impacts these hippocampal-associated functions and if sex and age modify these effects. To examine the relationship between gestational sleep apnea and hippocampal-associated behaviors, we used chronic intermittent hypoxia (CIH) to model late gestational sleep apnea in pregnant rats. We hypothesized that late gestational CIH would produce sex- and age-specific social, anxiety-like, repetitive, and cognitive impairments in offspring.

METHODS

Timed pregnant Long-Evans rats were exposed to CIH or room air normoxia from GD 15-19. Behavioral testing of offspring occurred during either puberty or young adulthood. To examine gestational hypoxia-induced behavioral phenotypes, we quantified hippocampal-associated behaviors (social function, repetitive behaviors, anxiety-like behaviors, and spatial memory and learning), hippocampal neuronal activity (glutamatergic NMDA receptors, dopamine transporter, monoamine oxidase-A, early growth response protein 1, and doublecortin), and circulating hormones in offspring.

RESULTS

Late gestational CIH induced sex- and age-specific differences in social, repetitive, and memory functions in offspring. In female pubertal offspring, CIH impaired social function, increased repetitive behaviors, and elevated circulating corticosterone levels but did not impact memory. In contrast, CIH transiently induced spatial memory dysfunction in pubertal male offspring but did not impact social or repetitive functions. Long-term effects of gestational CIH on social behaviors were only observed in female offspring, wherein CIH induced social disengagement and suppression of circulating corticosterone levels in young adulthood. No effects of gestational CIH were observed in anxiety-like behaviors, hippocampal neuronal activity, or circulating testosterone and estradiol levels, regardless of sex or age of offspring.

CONCLUSIONS

Our results indicate that hypoxia-associated pregnancy complications during late gestation can increase the risk for behavioral and physiological outcomes in offspring, such as social dysfunction, repetitive behaviors, and cognitive impairment, that are dependent on sex and age.

Honey on brain health: A promising brain booster

Since ancient times, honey has been employed in many aspects of everyday life, the most popular of which is as a natural sweetener. Honey is used not only as a nutritional product but also in health as a supplement and in various applications, especially related to brain booster health. Brain health is the capacity to carry out all mental functions necessary for cognition, such as learning and judging, utilizing language, and recalling. This review presents the current trend of research on honey, particularly the interest in underlying mechanisms related to brain booster health. A total of 34 original articles addressing brain health from the consumption of honey were analyzed. We identified four main brain health benefits, which are memory booster, neuroprotective effect, anti-stress, and anti-nociceptive potentials with the proposed underlying mechanism. A lot of attention has been paid to the role that honey plays in brain health research, with the goal of examining the link between honey and brain health as well as the mechanism underlying it, the findings from this review may be potentially beneficial to develop new therapeutic roles for honey to help determine the best and most promising to benefit and boost overall brain health.

Long-Term Outcomes after Neonatal Hypoxic-Ischemic Encephalopathy in the Era of Therapeutic Hypothermia: A Longitudinal, Prospective, Multicenter Case-Control Study in Children without Overt Brain Damage

Background. Data on long-term outcomes in the era before therapeutic hypothermia (TH) showed a higher incidence of cognitive problems. Since the introduction of TH, data on its results are limited. Methods. Our sample population consisted of 40 children with a history of hypoxic-ischemic encephalopathy (HIE) treated with TH, with an average age of 6.25 years (range 5.5, 7.33), 24 (60%) males; and 33 peers with an average age of 8.8 years (6.08, 9.41), 17 (51%) males. Long-term follow-up data belong to two centers in Padova and Torino. We measured general intelligence (WPPSI-III or WISC-IV) and neuropsychological functioning (language, attention, memory, executive functions, social skills, visual motor abilities). We also administered questionnaires to their parents on the children’s psychopathological profiles and parental stress. Results. We found differences between groups in several cognitive and neuropsychological domains: intelligence, visuomotor skills, executive functions, and attention. Interestingly, IQ test results effectively differentiated between the groups (HIE vs. controls). Furthermore, the incidence of psychopathology appears to be significantly higher in children with HIE (35%) than in control peers (12%). Conclusions. Our study supports previous findings on a higher incidence of neuropsychological, cognitive, and psychopathological sequelae after HIE treated with TH. As hypothesized, TH does not appear to ameliorate the outcome after neonatal HIE in those children who survive without major sequelae.

Rodent models used in preclinical studies of deep brain stimulation to rescue memory deficits

Deep brain stimulation paradigms might be used to treat memory disorders in patients with stroke or traumatic brain injury. However, proof of concept studies in animal models are needed before clinical translation. We propose here a comprehensive review of rodent models for Traumatic Brain Injury and Stroke. We systematically review the histological, behavioral and electrophysiological features of each model and identify those that are the most relevant for translational research.

Glia Not Neurons: Uncovering Brain Dysmaturation in a Rat Model of Alzheimer's Disease

Sporadic Alzheimer's disease (AD) is a severe disorder of unknown etiology with no definite time frame of onset. Recent studies suggest that middle age is a critical period for the relevant pathological processes of AD. Nonetheless, sufficient data have accumulated supporting the hypothesis of "neurodevelopmental origin of neurodegenerative disorders": prerequisites for neurodegeneration may occur during early brain development. Therefore, we investigated the development of the most AD-affected brain structures (hippocampus and prefrontal cortex) using an immunohistochemical approach in senescence-accelerated OXYS rats, which are considered a suitable model of the most common-sporadic-type of AD. We noticed an additional peak of neurogenesis, which coincides in time with the peak of apoptosis in the hippocampus of OXYS rats on postnatal day three. Besides, we showed signs of delayed migration of neurons to the prefrontal cortex as well as disturbances in astrocytic and microglial support of the hippocampus and prefrontal cortex during the first postnatal week. Altogether, our results point to dysmaturation during early development of the brain-especially insufficient glial support-as a possible "first hit" leading to neurodegenerative processes and AD pathology manifestation later in life.

Acrobatic exercise recovers object recognition memory impairment in hypoxic-ischemic rats

Neonatal hypoxia-ischemia (HI) can lead to cognitive impairments and motor dysfunction. Acrobatic exercises (AE) were proposing as therapeutic option to manage HI motor deficits, however, the cognitive effects after this treatment are still poorly understood. Therefore, we evaluated the effects of AE protocol on memory impairments and brain plasticity markers after Rice-Vannucci HI rodent model. Wistar rats on the 7th postnatal day (PND) were submitted to HI model and after weaning (PND22) were trained for 5 weeks with AE protocol, then subsequently submitted to cognitive tests. Our results showed recovery in novel object recognition (NOR) memory, but not, spatial Morris Water Maze (WM) memory after AE treatment in HI rats. BDNF and synaptophysin neuroplasticity markers indicate plastic alterations in the hippocampus and striatum, with maintenance of synaptophysin despite the reduction of total volume tissue, besides, hippocampal HI-induced ipsilateral BDNF increased, and striatum contralateral BDNF decreased were noted. Nevertheless, the exercise promoted functional recovery and seems to be a promising strategy for HI treatment, however, future studies identifying neuroplastic pathway for this improvement are needed.

Animal models for neonatal brain injury induced by hypoxic ischemic conditions in rodents

Neonatal hypoxia-ischemia and resulting encephalopathies are of significant concern. Intrapartum asphyxia is a leading cause of neonatal death globally. Among surviving infants, there remains a high incidence of hypoxic-ischemic encephalopathy due to neonatal hypoxic-ischemic brain injury, manifesting as mild conditions including attention deficit hyperactivity disorder, and debilitating disorders such as cerebral palsy. Various animal models of neonatal hypoxic brain injury have been implemented to explore cellular and molecular mechanisms, assess the potential of novel therapeutic strategies, and characterize the functional and behavioural correlates of injury. Each of the animal models has individual advantages and limitations. The present review looks at several widely-used and alternative rodent models of neonatal hypoxia and hypoxia-ischemia; it highlights their strengths and limitations, and their potential for continued and improved use.

Expression of synaptophysin and BDNF in the medial prefrontal cortex following early life stress and neonatal hypoxia-ischemia

This study aims at investigating whether early stress interacts with brain injury due to neonatal hypoxia-ischemia (HI). To this end, we examined possible changes in synaptophysin (SYN) and brain-derived neurotrophic factor (BDNF) expression in the medial prefrontal cortex (mPFC) of maternally separated rats that were subsequently exposed to a HI episode. Rat pups (n = 11) were maternally separated during postnatal days 1 to 6 (3hr/day), while another group was left undisturbed (n = 11). On postnatal day 7, a subgroup (n = 12) from each postnatal manipulation was exposed to HI. Synaptophysin and BDNF expression was estimated in mPFC prelimbic and anterior cingulate subregions of the ipsilateral and contralateral to the occluded common carotid artery hemispheres. Maternally separated rats expressed significantly less BDNF and SYN in both hemispheres. Neonatal HI significantly reduced BDNF and SYN expression in the ipsilateral mPFC only and this reduction was not further altered by early stress. Our findings indicate the enduring negative effect of a short period of maternal separation on the expression of mPFC SYN and BDNF. They, also, reveal that the HI-associated decreases in these markers are limited to the ipsilateral mPFC and are not exacerbated by early stress. These decreases may have important functional implications given the role of prefrontal area in high-order cognition.

Altered Neural Networks in the Papez Circuit: Implications for Cognitive Dysfunction after Cerebral Ischemia

Cerebral ischemia remains a leading cause of mortality worldwide. Although the incidence of death has decreased over the years, surviving patients may suffer from long-term cognitive impairments and have an increased risk for dementia. Unfortunately, research aimed toward developing therapies that can improve cognitive outcomes following cerebral ischemia has proved difficult given the fact that little is known about the underlying processes involved. Nevertheless, mechanisms that disrupt neural network activity may provide valuable insight, since disturbances in both local and global networks in the brain have been associated with deficits in cognition. In this review, we suggest that abnormal neural dynamics within different brain networks may arise from disruptions in synaptic plasticity processes and circuitry after ischemia. This discussion primarily concerns disruptions in local network activity within the hippocampus and other extra-hippocampal components of the Papez circuit, given their role in memory processing. However, impaired synaptic plasticity processes and disruptions in structural and functional connections within the Papez circuit have important implications for alterations within the global network, as well. Although much work is required to establish this relationship, evidence thus far suggests there is a link. If pursued further, findings may lead toward a better understanding of how deficits in cognition arise, not only in cerebral ischemia, but in other neurological diseases as well.

Usefulness of vortioxetine noted in depression secondary to hypoxic brain injury and residual cognitive deficits

We report on our experience of treating depression secondary to hypoxic brain injury with the antidepressant vortioxetine to share in the growing body of evidence. Our patient was referred to a community mental health team with depression, amotivation and memory difficulties following a myocardial infarction and cardiac arrest 2 years prior. Regardless of motor recovery, major cognitive deficits remained; however, neurorehabilitation was impossible due to severe depression. We tried vortioxetine in the light of two failed antidepressants and saw a remarkable improvement in mood, motivation and engagement.

Ventral hippocampal projections to the medial prefrontal cortex regulate social memory

Inputs from the ventral hippocampus (vHIP) to the medial prefrontal cortex (mPFC) are implicated in several neuropsychiatric disorders. Here, we show that the vHIP-mPFC projection is hyperactive in the Mecp2 knockout mouse model of the autism spectrum disorder Rett syndrome, which has deficits in social memory. Long-term excitation of mPFC-projecting vHIP neurons in wild-type mice impaired social memory, whereas their long-term inhibition in Rett mice rescued social memory deficits. The extent of social memory improvement was negatively correlated with vHIP-evoked responses in mPFC slices, on a mouse-per-mouse basis. Acute manipulations of the vHIP-mPFC projection affected social memory in a region and behavior selective manner, suggesting that proper vHIP-mPFC signaling is necessary to recall social memories. In addition, we identified an altered pattern of vHIP innervation of mPFC neurons, and increased synaptic strength of vHIP inputs onto layer five pyramidal neurons as contributing factors of aberrant vHIP-mPFC signaling in Rett mice.

The Role of Diffusion Tensor Imaging in Detecting Hippocampal Injury Following Neonatal Hypoxic-Ischemic Encephalopathy

BACKGROUND AND PURPOSE

Neonatal hypoxic-ischemic injury of the brain and resultant encephalopathy (HIE) leads to major developmental impairments by school age. Conventional/anatomical MRI often fails to detect hippocampal injury in mild cases. We hypothesize that diffusion tensor imaging (DTI) has greater sensitivity for identifying subtle hippocampal injury.

METHODS

We retrospectively analyzed DTI data collected from a cohort of neonates with HIE and controls. Conventional MRI sequences were classified qualitatively according to severity using a modified Barkovich scale. Using multivariate linear regression, we compared hippocampal DTI scalars of HIE patients and controls. Spearman correlation was used to test the association of DTI scalars in the hippocampal and thalamic regions. A multiple regression analysis tested the association of the DTI scalars with short-term outcomes.

RESULTS

Fifty-five neonates with HIE (42% males) and 13 controls (54% males) were included. Hippocampal DTI scalars were similar between HIE and control groups, even when restricting the HIE group to those with moderate-to-severe injury (8 subjects). DTI scalars of the thalamus were significantly lower in the moderate-to-severely affected patients compared to controls (right fractional anisotropy [FA] .148 vs. .182, P = .01; left FA .147 vs. .181, P = .03). Hippocampal and thalamic DTI scalars were correlated (P < .001). Hippocampal DTI scalars were not associated with short-term outcomes.

CONCLUSIONS

Quantitative DTI analysis of the hippocampus in neonates following HIE is a feasible technique to examine neuronal injury. Although DTI scalars were useful in identifying thalamic injury in our cohort, hippocampal DTI analysis did not provide additional information regarding hippocampal injury following HIE.

Modulation of Neocortical Development by Early Neuronal Activity: Physiology and Pathophysiology

Animal and human studies revealed that patterned neuronal activity is an inherent feature of developing nervous systems. This review summarizes our current knowledge about the mechanisms generating early electrical activity patterns and their impact on structural and functional development of the cerebral cortex. All neocortical areas display distinct spontaneous and sensory-driven neuronal activity patterns already at early phases of development. At embryonic stages, intermittent spontaneous activity is synchronized within small neuronal networks, becoming more complex with further development. This transition is accompanied by a gradual shift from electrical to chemical synaptic transmission, with a particular role of non-synaptic tonic currents before the onset of phasic synaptic activity. In this review article we first describe functional impacts of classical neurotransmitters (GABA, glutamate) and modulatory systems (e.g., acetylcholine, ACh) on early neuronal activities in the neocortex with special emphasis on electrical synapses, nonsynaptic and synaptic currents. Early neuronal activity influences probably all developmental processes and is crucial for the proper formation of neuronal circuits. In the second part of our review, we illustrate how specific activity patterns might interfere with distinct neurodevelopmental processes like proliferation, migration, axonal and dendritic sprouting, synapse formation and neurotransmitter specification. Finally, we present evidence that transient alterations in neuronal activity during restricted perinatal periods can lead to persistent changes in functional connectivity and therefore might underlie the manifestation of neurological and neuropsychiatric diseases.

Effect of Hypoxic Injury in Mood Disorder

Hypoxemia is a common complication of the diseases associated with the central nervous system, and neurons are highly sensitive to the availability of oxygen. Neuroplasticity is an important property of the neural system controlling breathing, memory, and cognitive ability. However, the underlying mechanism has not yet been clearly elucidated. In recent years, several pieces of evidence have highlighted the effect of hypoxic injury on neuronal plasticity in the pathogenesis and treatment of mood disorder. Therefore, the present study reviewed the relevant articles regarding hypoxic injury and neuronal plasticity and discussed the pathological changes and physiological functions of neurons in hypoxemia in order to provide a translational perspective to the relevance of hypoxic injury and mood disorder.

Unbiased Quantification of Subplate Neuron Loss following Neonatal Hypoxia-Ischemia in a Rat Model

BACKGROUND

Cellular targets of neonatal hypoxia-ischemia (HI) include both oligodendrocyte and neuronal lineages with differences in the patterns of vulnerable cells depending upon the developmental stage at which the injury occurs. Injury to the developing white matter is a characteristic feature of human preterm brain injury. Data are accumulating, however, for neuronal injury in the developing cerebral cortex. In the most widely used rodent model of preterm HI brain injury, conflicting data have been reported regarding the sensitivity of subplate neurons to early neonatal HI, with some reports of selective vulnerability and others that find no increased loss of subplate neurons in comparison with other cortical layers. Methods used to identify subplate neurons and quantify their numbers vary across studies.

OBJECTIVE

To use recently developed cortical layer-specific markers quantified with definitive stereologic methods to determine the magnitude and specificity of subplate neuron cell loss following neonatal HI in a rodent model.

METHODS

Postnatal day 2 (P2) rats underwent right common carotid artery coagulation followed by 2-3 h of hypoxia (5.6% oxygen). Categorically moderately injured brains were stained with subplate and cortical layer III-V markers (Complexin3 and Foxp1, respectively) at P8 and P21 (Foxp1 only). An Optical Fractionator was used to quantify subplate and middle/lower cortical neuronal numbers and these were compared across groups (naive control, hypoxia hemisphere, and HI hemisphere).

RESULTS

Following HI at P2 in rats, the total Complexin3-expressing subplate neuron number decreases significantly in the HI hemisphere compared with naive controls or hypoxia alone (HI vs. control 26,747 ± 7,952 vs. 35,468 ± 8,029, p = 0.04; HI vs. hypoxia, 26,747 ± 7,952 vs. 40,439 ± 7,363, p = 0.003). In contrast, the total Foxp1-expressing layer III-V cell number did not differ across the 3 conditions at P8 (HI vs. control 1,195,085 ± 436,609 vs. 1,234,640 ± 178,540, p = 0.19; HI vs. hypoxia, 1,195,085 ± 436,609 vs. 1,289,195 ± 468,941, p = 0.35) and at P21 (HI vs. control 1,265,190 ± 48,089 vs. 1,195,632 ± 26,912, p = 0.19; HI vs. hypoxia, 1,265,190 ± 48,089 vs. 1,309,563 ± 41,669, p = 0.49).

CONCLUSIONS

There is significant biological variability inherent in both the subplate neuron cell number and the pattern and severity of cortical injury following HI at P2 in rats. Despite this variability, the subplate neuron cell number is lower following P2 HI in animals with mild or moderate cortical injury, whereas the middle-to-lower-layer cortical neuronal number is unchanged. In more severe cases, neurons are lost from the lower cortical layers, suggesting a relative vulnerability of subplate neurons.

Docosahexaenoic Acid Reduces Cerebral Damage and Ameliorates Long-Term Cognitive Impairments Caused by Neonatal Hypoxia-Ischemia in Rats

As the interest in the neuroprotective possibilities of docosahexaenoic acid (DHA) for brain injury has grown in the recent years, we aimed to investigate the long-term effects of this fatty acid in an experimental model of perinatal hypoxia-ischemia in rats. To this end, motor activity, aspects of learning, and memory function and anxiety, as well as corticofugal connections visualized by using tracer injections, were evaluated at adulthood. We found that in the hours immediately following the insult, DHA maintained mitochondrial inner membrane integrity and transmembrane potential, as well as the integrity of synaptic processes. Seven days later, morphological damage at the level of the middle hippocampus was reduced, since neurons and myelin were preserved and the astroglial reactive response and microglial activation were seen to be diminished. At adulthood, the behavioral tests revealed that treated animals presented better long-term working memory and less anxiety than non-treated hypoxic-ischemic animals, while no difference was found in the spontaneous locomotor activity. Interestingly, hypoxic-ischemic injury caused alterations in the anterograde corticofugal neuronal connections which were not so evident in rats treated with DHA. Thus, our results indicate that DHA treatment can lead to long-lasting neuroprotective effects in this experimental model of neonatal hypoxia-ischemic brain injury, not only by mitigating axonal changes but also by enhancing cognitive performance at adulthood.

Thalamic and Entorhinal Network Activity Differently Modulates the Functional Development of Prefrontal-Hippocampal Interactions

Precise information flow during mnemonic and executive tasks requires the coactivation of adult prefrontal and hippocampal networks in oscillatory rhythms. This interplay emerges early in life, most likely as an anticipatory template of later cognitive performance. At neonatal age, hippocampal theta bursts drive the generation of prefrontal theta-gamma oscillations. In the absence of direct reciprocal interactions, the question arises of which feedback mechanisms control the early entrainment of prefrontal-hippocampal networks. Here, we demonstrate that prefrontal-hippocampal activity couples with discontinuous theta oscillations and neuronal firing in both lateral entorhinal cortex and ventral midline thalamic nuclei of neonatal rats. However, these two brain areas have different contributions to the neonatal long-range communication. The entorhinal cortex mainly modulates the hippocampal activity via direct axonal projections. In contrast, thalamic theta bursts are controlled by the prefrontal cortex via mutual projections and contribute to hippocampal activity. Thus, the neonatal prefrontal cortex modulates the level of hippocampal activation by directed interactions with the ventral midline thalamus. Similar to the adult task-related communication, theta-band activity ensures the feedback control of long-range coupling in the developing brain.

SIGNIFICANCE STATEMENT

Memories are encoded by finely tuned interactions within large-scale neuronal networks. This cognitive performance is not inherited, but progressively matures in relationship with the establishment of long-range coupling in the immature brain. The hippocampus initiates and unidirectionally drives the oscillatory entrainment of neonatal prefrontal cortex, yet feedback interactions that precisely control this early communication are still unresolved. Here, we identified distinct roles of entorhinal cortex and ventral midline thalamus for the functional development of prefrontal-hippocampal interactions. While entorhinal oscillations modulate the hippocampal activity by timing the neuronal firing via monosynaptic afferents, thalamic nuclei act as a relay station routing prefrontal activation back to hippocampus. Understanding the mechanisms of network maturation represents the prerequisite for assessing circuit dysfunction in neurodevelopmental disorders.

Behavioral benefits of maternal swimming are counteracted by neonatal hypoxia-ischemia in the offspring

Hypoxia-ischemia (HI) represents one of the most common causes of neonatal encephalopathy. The central nervous system injury comprises several mechanisms, including inflammatory, excitotoxicity, and redox homeostasis unbalance leading to cell death and cognitive impairment. Exercise during pregnancy is a potential therapeutic tool due to benefits offered to mother and fetus. Swimming during pregnancy elicits a strong metabolic programming in the offspring's brain, evidenced by increased antioxidant enzymes, mitochondrial biogenesis, and neurogenesis. This article aims to evaluate whether the benefits of maternal exercise are able to prevent behavioral brain injury caused by neonatal HI. Female adult Wistar rats swam before and during pregnancy (30min/day, 5 days/week, 4 weeks). At 7(th) day after birth, the offspring was submitted to HI protocol and, in adulthood (60(th) day), it performed the behavioral tests. It was observed an increase in motor activity in the open field test in HI-rats, which was not prevented by maternal exercise. The rats subjected to maternal swimming presented an improved long-term memory in the object recognition task, which was totally reversed by neonatal HI encephalopathy. BDNF brain levels were not altered; suggesting that HI or maternal exercise effects were BDNF-independent. In summary, our data suggest a beneficial long-term effect of maternal swimming, despite not being robust enough to protect from HI injury.

Reduced Cortical Activity Impairs Development and Plasticity after Neonatal Hypoxia Ischemia

Survivors of preterm birth are at high risk of pervasive cognitive and learning impairments, suggesting disrupted early brain development. The limits of viability for preterm birth encompass the third trimester of pregnancy, a "precritical period" of activity-dependent development characterized by the onset of spontaneous and evoked patterned electrical activity that drives neuronal maturation and formation of cortical circuits. Reduced background activity on electroencephalogram (EEG) is a sensitive marker of brain injury in human preterm infants that predicts poor neurodevelopmental outcome. We studied a rodent model of very early hypoxic-ischemic brain injury to investigate effects of injury on both general background and specific patterns of cortical activity measured with EEG. EEG background activity is depressed transiently after moderate hypoxia-ischemia with associated loss of spindle bursts. Depressed activity, in turn, is associated with delayed expression of glutamate receptor subunits and transporters. Cortical pyramidal neurons show reduced dendrite development and spine formation. Complementing previous observations in this model of impaired visual cortical plasticity, we find reduced somatosensory whisker barrel plasticity. Finally, EEG recordings from human premature newborns with brain injury demonstrate similar depressed background activity and loss of bursts in the spindle frequency band. Together, these findings suggest that abnormal development after early brain injury may result in part from disruption of specific forms of brain activity necessary for activity-dependent circuit development.

SIGNIFICANCE STATEMENT

Preterm birth and term birth asphyxia result in brain injury from inadequate oxygen delivery and constitute a major and growing worldwide health problem. Poor outcomes are noted in a majority of very premature (<25 weeks gestation) newborns, resulting in death or life-long morbidity with motor, sensory, learning, behavioral, and language disabilities that limit academic achievement and well-being. Limited progress has been made to develop therapies that improve neurologic outcomes. The overall objective of this study is to understand the effect of early brain injury on activity-dependent brain development and cortical plasticity to develop new treatments that will optimize repair and recovery after brain injury.