TrkB-mediated neuroprotection in female hippocampal neurons is autonomous, estrogen receptor alpha-dependent, and eliminated by testosterone: a proposed model for sex differences in neonatal hippocampal neuronal injury

BACKGROUND

Neonatal hypoxia ischemia (HI) related brain injury is one of the major causes of learning disabilities and memory deficits in children. In both human and animal studies, female neonate brains are less susceptible to HI than male brains. Phosphorylation of the nerve growth factor receptor TrkB has been shown to provide sex-specific neuroprotection following in vivo HI in female mice in an estrogen receptor alpha (ERα)-dependent manner. However, the molecular and cellular mechanisms conferring sex-specific neonatal neuroprotection remain incompletely understood. Here, we test whether female neonatal hippocampal neurons express autonomous neuroprotective properties and assess the ability of testosterone (T) to alter this phenotype.

METHODS

We cultured sexed hippocampal neurons from ERα+/+ and ERα-/- mice and subjected them to 4 h oxygen glucose deprivation and 24 h reoxygenation (4-OGD/24-REOX). Sexed hippocampal neurons were treated either with vehicle control (VC) or the TrkB agonist 7,8-dihydroxyflavone (7,8-DHF) following in vitro ischemia. End points at 24 h REOX were TrkB phosphorylation (p-TrkB) and neuronal survival assessed by immunohistochemistry. In addition, in vitro ischemia-mediated ERα gene expression in hippocampal neurons were investigated following testosterone (T) pre-treatment and TrkB antagonist therapy via q-RTPCR. Multifactorial analysis of variance was conducted to test for significant differences between experimental conditions.

RESULTS

Under normoxic conditions, administration of 3 µM 7,8-DHF resulted an ERα-dependent increase in p-TrkB immunoexpression that was higher in female, as compared to male neurons. Following 4-OGD/24-REOX, p-TrkB expression increased 20% in both male and female ERα+/+ neurons. However, with 3 µM 7,8-DHF treatment p-TrkB expression increased further in female neurons by 2.81 ± 0.79-fold and was ERα dependent. 4-OGD/24-REOX resulted in a 56% increase in cell death, but only female cells were rescued with 3 µM 7,8-DHF, again in an ERα dependent manner. Following 4-OGD/3-REOX, ERα mRNA increased ~ 3 fold in female neurons. This increase was blocked with either the TrkB antagonist ANA-12 or pre-treatment with T. Pre-treatment with T also blocked the 7,8-DHF- dependent sex-specific neuronal survival in female neurons following 4-OGD/24-REOX.

CONCLUSIONS

OGD/REOX results in sex-dependent TrkB phosphorylation in female neurons that increases further with 7,8-DHF treatment. TrkB phosphorylation by 7,8-DHF increased ERα mRNA expression and promoted cell survival preferentially in female hippocampal neurons. The sex-dependent neuroprotective actions of 7,8-DHF were blocked by either ANA-12 or by T pre-treatment. These results are consistent with a model for a female-specific neuroprotective pathway in hippocampal neurons in response to hypoxia. The pathway is activated by 7,8-DHF, mediated by TrkB phosphorylation, dependent on ERα and blocked by pre-exposure to T.

Retinal vascular recovery revealed by retinal imaging following neonatal hypoxia ischemia in mice: Is there a role for tyrosine kinase receptor modulation?

OBJECTIVE

Hypoxic ischemic encephalopathy (HIE) secondary to perinatal asphyxia leads to long-term visual disabilities. Dilated retinal exams in human newborns with HIE is an emerging diagnostic tool, but phenotypes of hypoxia ischemia (HI) related retinal vascular injury are unclear. 7,8-Dihydroxyflavone (7,8-DHF) is a TrkB agonist with protective effects on HI-related brain damage. We studied retinal vessels in a mouse model of neonatal HIE and the efficacy of 7,8-DHF in ameliorating HI-related retinal vascular injury.

METHODS

C57BL6/J mice at post-natal day (P) 9 received unilateral left carotid artery ligation followed by exposure to 10 % oxygen for 50 min. Phosphate buffered saline or 7,8-DHF (5 mg/kg) were administered daily for 7 days intraperitoneally. Control groups of naïve or carotid artery ligation only mice were studied. Fluorescein angiography was performed in acute (two weeks post-exposure) and chronic (four weeks post-exposure) time points. Retinal artery width, retinal vein width, and collateral vessel length were quantified.

RESULTS

Ligation of the common carotid artery alone caused retinal artery dilation in acute and chronic time points, but had no effect on retinal veins. At acute time point, HI caused increased retinal artery vasodilation, but was reversed by 7,8-DHF. HI caused short collateral vessel formation in ipsilateral eyes, rescued by 7,8-DHF treatment.

CONCLUSION

Retinal artery vasodilation and collateral vessel formation due to HI were rescued by 7,8-DHF treatment. Retinal and collateral vessel monitoring could be diagnostic biomarkers for HI severity. Studies to elucidate mechanisms of 7,8-DHF action on retinal vessels could aid development of therapies for neonatal HI.

AIF Overexpression Aggravates Oxidative Stress in Neonatal Male Mice After Hypoxia-Ischemia Injury

There are sex differences in the severity, mechanisms, and outcomes of neonatal hypoxia-ischemia (HI) brain injury, and apoptosis-inducing factor (AIF) may play a critical role in this discrepancy. Based on previous findings that AIF overexpression aggravates neonatal HI brain injury, we further investigated potential sex differences in the severity and molecular mechanisms underlying the injury using mice that overexpress AIF from homozygous transgenes. We found that the male sex significantly aggravated AIF-driven brain damage, as indicated by the injury volume in the gray matter (2.25 times greater in males) and by the lost volume of subcortical white matter (1.71 greater in males) after HI. As compared to females, male mice exhibited more severe brain injury, correlating with reduced antioxidant capacities, more pronounced protein carbonylation and nitration, and increased neuronal cell death. Under physiological conditions (without HI), the doublecortin-positive area in the dentate gyrus of females was 1.15 times larger than in males, indicating that AIF upregulation effectively promoted neurogenesis in females in the long term. We also found that AIF stimulated carbohydrate metabolism in young males. Altogether, these findings corroborate earlier studies and further demonstrate that AIF is involved in oxidative stress, which contributes to the sex-specific differences observed in neonatal HI brain injury.

The role of G-CSF neuroprotective effects in neonatal hypoxic-ischemic encephalopathy (HIE): current status

Hypoxic-ischemic encephalopathy (HIE) is an important cause of permanent damage to central nervous system (CNS) that may result in neonatal death or manifest later as mental retardation, epilepsy, cerebral palsy, or developmental delay. The primary cause of this condition is systemic hypoxemia and/or reduced cerebral blood flow with long-lasting neurological disabilities and neurodevelopmental impairment in neonates. About 20 to 25% of infants with HIE die in the neonatal period, and 25-30% of survivors are left with permanent neurodevelopmental abnormalities. The mechanisms of hypoxia-ischemia (HI) include activation and/or stimulation of myriad of cascades such as increased excitotoxicity, oxidative stress, N-methyl-D-aspartic acid (NMDA) receptor hyperexcitability, mitochondrial collapse, inflammation, cell swelling, impaired maturation, and loss of trophic support. Different therapeutic modalities have been implicated in managing neonatal HIE, though translation of most of these regimens into clinical practices is still limited. Therapeutic hypothermia, for instance, is the most widely used standard treatment in neonates with HIE as studies have shown that it can inhibit many steps in the excito-oxidative cascade including secondary energy failure, increases in brain lactic acid, glutamate, and nitric oxide concentration. Granulocyte-colony stimulating factor (G-CSF) is a glycoprotein that has been implicated in stimulation of cell survival, proliferation, and function of neutrophil precursors and mature neutrophils. Extensive studies both in vivo and ex vivo have shown the neuroprotective effect of G-CSF in neurodegenerative diseases and neonatal brain damage via inhibition of apoptosis and inflammation. Yet, there are still few experimentation models of neonatal HIE and G-CSF's effectiveness, and extrapolation of adult stroke models is challenging because of the evolving brain. Here, we review current studies and/or researches of G-CSF's crucial role in regulating these cytokines and apoptotic mediators triggered following neonatal brain injury, as well as driving neurogenesis and angiogenesis post-HI insults.

Hypoxic Ischemic Encephalopathy in Units Reporting to the Ibero-American Society of Neonatology Network: Prevalence and Mortality

INTRODUCTION

Hypoxic ischemic encephalopathy is a neurological condition occurring immediately after birth following a perinatal asphytic episode. Therapeutic hypothermia is a safe and effective intervention to reduce mortality and major disability in survivors. In Latin America, perinatal asphyxia is a major problem, but no data are available characterizing its current situation in the region or the impact of hypoxic ischemic encephalopathy on its management.

OBJECTIVE

Understand the prevalence, mortality and use of therapeutic hypothermia in newborns at ≥36 weeks gestational age with hypoxic ischemic encephalopathy admitted to neonatal units reporting to the Ibero-American Society of Neonatology Network.

METHODS

The Ibero-American Society of Neonatology Network groups various neonatology centers in Latin America that share information and collaborate on research and medical care. We evaluated data on newborns with ≥36 weeks gestational age reported during 2019. Each unit received a guide with definitions and questions based on the Society's 7th Clinical Consensus. Evaluated were encephalopathy frequency and severity, Apgar score, need for resuscitation at birth, use of therapeutic hypothermia and clinical evolution at discharge. Our analysis includes descriptive statistics and comparisons made using the chi-square test.

RESULTS

We examined reports of 2876 newborns from 33 units and 6 countries. In 2849 newborns with available data, hypoxic encephalopathy prevalence was 5.1% (146 newborns): 27 (19%) mild, 36 (25%) moderate, 43 (29%) severe, and 40 (27%) of unknown intensity. In those with moderate and severe encephalopathy, frequencies of Apgar scores ≤3 at the first minute (p = 0.001), Apgar scores ≤3 at the fifth minute (p ⟨0.001) and advanced resuscitation (p = 0.007) were higher. Therapeutic hypothermia was performed in only 13% of newborns (19). Neonatal mortality from encephalopathy was 42% (61).

CONCLUSIONS

Hypoxic ischemic encephalopathy is a neonatal condition that results in high mortality and severe neurological sequelae. In this study, the overall prevalence was 5.1% with a mortality rate of 42%. Although encephalopathy was moderate or severe in 54% of reported cases, treatment with hypothermia was not performed in 87% of newborns. These data reflect a regional situation that requires urgent action.

Prophylactic inhibition of NF-κB expression in microglia leads to attenuation of hypoxic ischemic injury of the immature brain

Background

Periventricular leukomalacia (PVL), a devastating brain injury affecting premature infants, is the most common cause of cerebral palsy. PVL is caused by hypoxia ischemia (HI) and is characterized by white matter necrotic lesions, microglial activation, upregulation of NF-κB, and neuronal death. The microglia is the main cell involved in PVL pathogenesis. The goal of this study was to investigate the role of microglial NF-κB activity and its prophylactic inhibition in a neonate mouse model of HI.

Methods

Transgenic mice with specific knockout NF-κB in microglia and colony stimulating factor 1 receptor Cre with floxed IKKβ (CSF-1R Cre + IKKβ^flox/wt ) were used. Postnatal day 5 (P5) mice underwent sham or bilateral temporary carotid artery ligation followed by hypoxia. After HI insult, inflammatory cytokines, volumetric MRI, histopathology, and immunohistochemistry for oligodendroglia and microglial activation markers were analyzed. Long-term neurobehavioral assessment, including grip strength, rotarod, and open field testing, was performed at P60.

Results

We demonstrate that selective inhibition of NF-κB in microglia decreases HI-induced brain injury by decreasing microglial activation, proinflammatory cytokines, and nitrative stress. Rescue of oligodendroglia is evidenced by immunohistochemistry, decreased ventriculomegaly on MRI, and histopathology. This selective inhibition leads to attenuation of paresis, incoordination, and improved grip strength, gait, and locomotion.

Conclusion

We conclude that NF-κb activation in microglia plays a major role in the pathogenesis of hypoxic ischemic injury of the immature brain, and its prophylactic inhibition offers significant neuroprotection. Using a specific inhibitor of microglial NF-κB may offer a new prophylactic or therapeutic alternative in preterm infants affected by HI and possibly other neurological diseases in which microglial activation plays a role.

Subacute metformin treatment reduces inflammation and improves functional outcome following neonatal hypoxia ischemia

Hypoxia-ischemia (HI) injury is a leading cause of neonatal death and long-term disability, and existing treatment options for HI offer only modest benefit. Early intervention with the drug metformin has been shown to promote functional improvement in numerous rodent models of injury and has pleiotropic cellular effects in the brain. We have previously shown that 1 week of metformin treatment initiated 24 ​h after HI in neonatal mice resulted in improved motor and cognitive performance, activation of endogenous neural precursor cells (NPCs), and increased oligodendrogenesis. While promising, a limitation to this work is that immediate pharmacological intervention is not always possible in the clinic. Herein, we investigated whether delaying metformin treatment to begin in the subacute phase post-HI would still effectively promote recovery. Male and female C57/BL6 mice received HI injury postnatally, and metformin treatment began 7 days post-HI for up to 4 weeks. Motor and cognitive performance was assessed across time using behavioural tests (cylinder, foot fault, puzzle box). We found that metformin improved motor and cognitive behaviour, decreased inflammation, and increased oligodendrocytes in the motor cortex. Our present findings demonstrate that a clinically relevant subacute metformin treatment paradigm affords the potential to treat neonatal HI, and that improved outcomes occur through modulation of the inflammatory response and oligodendrogenesis.

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Subacute metformin treatment improves functional recovery after neonatal hypoxia ischemia.

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Metformin reduces the number of microglia present in the brain early after injury.

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Metformin increases the number of oligodendrocytes present in the chronic post-injury phase.

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Metformin treatment has therapeutic potential in the treatment of hypoxic ischemic brain damage.

Multiple doses of umbilical cord blood cells improve long-term brain injury in the neonatal rat

BACKGROUND

Hypoxic ischemic (HI) insults during pregnancy and birth can result in neurodevelopmental disorders, such as cerebral palsy. We have previously shown that a single dose of umbilical cord blood (UCB) cells is effective at reducing short-term neuroinflammation and improves short and long-term behavioural outcomes in rat pups. A single dose of UCB was not able to modulate long-term neuroinflammation or brain tissue loss. In this study we examined whether multiple doses of UCB can modulate neuroinflammation, decrease cerebral tissue damage and improve behavioural outcomes when followed up long-term.

METHODS

HI injury was induced in postnatal day 10 (PND10) rat pups using the Rice-Vannucci method of carotid artery ligation. Pups received either 1 dose (PND11), or 3 doses (PND11, 13, 20) of UCB cells. Rats were followed with behavioural testing, to assess both motor and cognitive outcomes. On PND50, brains were collected for analysis.

RESULTS

HI brain injury in rat pups caused significant behavioural deficits. These deficits were significantly improved by multiple doses of UCB. HI injury resulted in a significant decrease in brain weight and left hemisphere tissue, which was improved by multiple doses of UCB. HI resulted in increased cerebral apoptosis, loss of neurons and upregulation of activated microglia. Multiple doses of UCB modulated these neuropathologies. A single dose of UCB at PND11 did not improve behavioural or neuropathological outcomes.

CONCLUSIONS

Treatment with repeated doses of UCB is more effective than a single dose for reducing tissue damage, improving brain pathology and restoring behavioural deficits following perinatal brain injury.

Ischemic stroke in neonatal and adult astrocytes

The objective of this paper is to review current information regarding astrocytes function after a stroke in neonatal and adult brain. Based on the current literature, there are some molecular differences related to blood brain barrier (BBB) homeostasis disruption, inflammation and reactive oxygen species (ROS) mediated injury between the immature and mature brain after an ischemic event. In particular, astrocytes, the main glial cells in brain, play a different role in neonatal and adult brain after stroke, as time course of glial activation is strongly age dependent. Moreover, the present review provides further insight into the therapeutic approaches of using neonatal and adult astrocytes after stroke. More research will be needed in order to translate them into an effective treatment against stroke, the second main cause of death and disability worldwide.

Intermittent blood flow restriction does not reduce atrophy following anterior cruciate ligament reconstruction

BACKGROUND

A previous study has reported a 50% reduction in disuse atrophy of the quadriceps during the first 14 days after anterior cruciate ligament (ACL) reconstruction. A follow-up trial is needed to confirm these promising results. The present study aims to investigate the effect of an occlusion stimulus on quadriceps atrophy after ACL reconstruction.

METHODS

A total of 24 subjects participated in the study. They were randomized into two groups. Starting the 2nd day after surgery, the occlusion group received an occlusion stimulus for 5 min, followed by removal of the occlusive pressure for 3 min. This was repeated five times in one training session, twice daily. During the period of occlusive stimulus, the subjects performed 20 low load exercises for the quadriceps. The control group followed the same exercise protocol, but without the occlusion stimulus. Changes in quadriceps anatomical cross section area (ACSA) were measured using axial magnetic resonance (MR) images at 40% and 50% of the length of the femur.

RESULTS

Both groups had a significant reduction of quadriceps ACSA from 2 days before surgery to 16 days after surgery. During the intervention period, the occlusion group lost 13.8% ± 1.1% (mean ± SEM) and the control group lost 13.1% ± 1.0% of their quadriceps ACSA, respectively. There was no significant difference between the occlusion and control groups with regards to atrophy of the quadriceps muscles.

CONCLUSION

In conflict with other studies using a similar protocol, application of blood flow restriction the first 14 days after ACL reconstruction did not reduce quadriceps ACSA muscle atrophy measured by MR in a population of athletes.

Changes in Brain Swelling and Infarction Volume over Four Days After Hypoxia Ischemia in Neonatal Rats

The leading cause of morbidity and mortality in infants is hypoxia-ischemia (HI). The current therapies for HI have limited success, in part due to a lack of understanding of HI pathophysiology and underlying mechanisms. Herein, a neonatal rat model of HI was used to examine the changes in brain swelling and infarct volume over 4 days after HI. Forty-four P10 rat pups were sacrificed at 2, 3, or 4 days post-HI. After sacrifice, the brains were removed, sliced, and stained with TTC (2,3,5-triphenyl-2H-tetrazolium chloride). Images of TTC-stained brains were used for measurement of the ipsilateral hemisphere brain volumes and infarct volumes, calculated using standard equations. The hemispheric brain volumes of HI animals in all groups was lower than that of sham animals and decreased as the post-HI sacrifice time increased. The infarct volume of HI animals was larger than that of sham animals. Infarct volumes tended to decrease over the days post-HI. The change in infarct volume is likely the result of a combination of brain growth and repair mechanisms. However, changes in the hemispheric brain volume may include tissue growth and repair mechanism, so also may be a limitation of the current algorithm used for calculating ipsilateral hemisphere brain volume.

Astrocytic β1-integrin affects cellular composition of murine blood brain barrier in the cerebral cortex

The blood brain barrier (BBB) is composed of endothelial cells, astrocytes, and pericytes and maintains functional homeostasis by regulating transport of ions, fluid and cells between blood and neural tissue. The cellular and molecular pathways that contribute to the formation of the BBB in the developing brain have not been fully deciphered. β1-integrin (β1-itg) within endothelial cells is known to play a critical role in vasculogenesis. However, the role of astrocytic β1-itg in BBB development is not known. Our study used a mouse glial fibrillary acidic protein (GFAP)-cre transgenic line to selectively ablate β1-itg within astrocytes. We found that deletion of astrocytic β1-itg had a striking effect on the different cell types that form the BBB. Mutant mice had a decreased density of aquaporin-4 immunoreactivity within the perivascular astrocytic end-feet. We also found decreases in immunoreactivity for vimentin and CD-31 within endothelial cells. These changes were not accompanied by functional changes in BBB under physiological conditions as assessed by extravasation of large and small molecular weight molecules. However, mutant mice had an increased incidence of severe cystic injury in response to neonatal hypoxia. Our findings show that astrocytic β1-itg has an important role in defining cellular properties of the blood brain barrier in the cerebral cortex.

Long term creatine monohydrate supplementation, following neonatal hypoxic ischemic insult, improves neuromuscular coordination and spatial learning in male albino mouse

Creatine is known to rescue animals following brain damage. Present study was designed to demonstrate the effect of long term (15 week) supplementation of 2% creatine monohydrate (Cr), following neonatal hypoxic ischemic insult, on learning and memory formation in male albino mouse. Albino mice pups were subjected to right common carotid artery ligation followed by 8% hypoxia for 25 minutes. Following weaning, animals were separated and grouped on the basis of dietry supplementation for 15 weeks followed by a battery of neurological tests including Morris water maze, open field and rota rod. It was observed that HI mice fed on 2% Cr for 15 weeks performed better than their littermates mice on normal rodent diet during water maze (learning and memory) and rotating rod (neuro-muscular coordination and balance) test while the results of open field test remained unaffected. It was also observed that Cr treated animals had a reduced brain infarct volume than untreated but this difference did not reached statistical significance. We have also observed an overall increase in body weight in Cr treated mice during the study. Over all our results are indicating that long term Cr supplementation is beneficial for male albino following hypoxic ischemic insult.

Cell size anomalies in the auditory thalamus of rats with hypoxic-ischemic injury on postnatal day 3 or 7

Children born prematurely (<37 weeks gestational age) or at very low birth weight (VLBW; <1500g) are at increased risk for hypoxic ischemic (HI) brain injuries. Term infants can also suffer HI from birth complications. In both groups, blood/oxygen delivery to the brain is compromised, often resulting in brain damage and later cognitive delays (e.g., language deficits). Literature suggests that language delays in a variety of developmentally impaired populations (including specific language impairment (SLI), dyslexia, and early HI-injury) may be associated with underlying deficits in rapid auditory processing (RAP; the ability to process and discriminate brief acoustic cues). Data supporting a relationship between RAP deficits and poor language outcomes is consistent with the "magnocellular theory," which purports that damage to or loss of large (magnocellular) cells in thalamic nuclei could underlie disruptions in temporal processing of sensory input, possibly including auditory (medial geniculate nucleus; MGN) information This theory could be applied to neonatal HI populations that show subsequent RAP deficits. In animal models of neonatal HI, persistent RAP deficits are seen in postnatal (P)7 HI injured rats (who exhibit neuropathology comparable to term birth injury), but not in P1-3 HI injured rodents (who exhibit neuropathology comparable to human pre-term injury). The current study sought to investigate the mean cell size, cell number, and cumulative probability of cell size in the MGN of P3 HI and P7 HI injured male rats that had previously demonstrated behavioral RAP deficits. Pilot data from our lab (Alexander, 2011) previously revealed cell size abnormalities (a shift toward smaller cells) in P7 but not P1 HI injured animals when compared to shams. Our current finding support this result, with evidence of a significant shift to smaller cells in the experimental MGN of P7 HI but not P3 HI subjects. P7 HI animals also showed significantly fewer cells in the affected (right) MGN as compared P3 HI and shams animals. Moreover, cell number in the right hemisphere was found to correlate with gap detection (fewer cells=worse performance) in P7 HI injured subjects. These findings could be applied to clinical populations, providing an anatomic marker that may index potential long-term language disabilities in HI injured infants and possibly other at-risk populations.

Sex differences in behavioral outcome following neonatal hypoxia ischemia: insights from a clinical meta-analysis and a rodent model of induced hypoxic ischemic brain injury

Hypoxia ischemia (HI; reduced oxygen and/or blood flow to the brain) is one of the most common injuries among preterm infants and term infants with birth complications. Both populations show cognitive/behavioral deficits, including impairments in sensory, learning/memory, and attention domains. Clinical data suggests a sex difference in HI outcomes, with males exhibiting more severe cognitive/behavioral deficits relative to matched females. Our laboratory has also reported more severe behavioral deficits among male rats with induced HI relative to females with comparable injury (Hill et al., 2011a,b). The current study initially examined published clinical studies from the past 20years where long-term IQ outcome scores for matched groups of male and female premature infants were reported separately (IQ being the most common outcome measure). A meta-analysis revealed a female "advantage," as indicated by significantly better scores on performance and full scale IQ (but not verbal IQ) for premature females. We then utilized a rodent model of neonatal HI injury to assess sham and postnatal day 7 (P7) HI male and female rats on a battery of behavioral tasks. Results showed expected deficits in HI male rats, but also showed task-dependent sex differences, with HI males having significantly larger deficits than HI females on some tasks but equivalent deficits on other tasks. In contrast to behavioral results, post mortem neuropathology associated with HI was comparable across sex. These findings suggest: 1) neonatal female "protection" in some behavioral domains, as indexed by superior outcome following early injury relative to males; and 2) female protection may entail sex-specific plasticity or compensation, rather than a reduction in gross neuropathology. Further exploration of the mechanisms underlying this sex effect could aid in neuroprotection efforts for at-risk neonates in general, and males in particular. Moreover, our current report of comparable anatomical damage coupled with differences in cognitive outcomes (by sex) provides a framework for future studies to examine neural mechanisms underlying sex differences in cognition and behavior in general.

Behavioral and histological outcomes following neonatal HI injury in a preterm (P3) and term (P7) rodent model

Hypoxia-ischemia (HI) occurs when blood and/or oxygen delivery to the brain is compromised. HI injuries can occur in infants born prematurely (<37 weeks gestational age) or at very low birth weight (<1500 g), as well as in term infants with birth complications. In both preterm and term HI populations, brain injury is associated with subsequent behavioral deficits. Neonatal HI injury can be modeled in rodents (e.g., the Rice-Vannucci method, via cautery of right carotid followed by hypoxia). When this injury is induced early in life (between postnatal day (P)1-5), neuropathologies typical of human preterm HI are modeled. When injury is induced later (P7-12), neuropathologies typical of those seen in HI term infants are modeled. The current study sought to characterize the similarities/differences between outcomes following early (P3) and late (P7) HI injury in rats. Male rats with HI injury on P3 or P7, as well as sham controls, were tested on a variety of behavioral tasks in both juvenile and adult periods. Results showed that P7 HI rats displayed deficits on motor learning, rapid auditory processing (RAP), and other learning/memory tasks, as well as a reduction in volume in various neuroanatomical structures. P3 HI animals showed only transient deficits on RAP tasks in the juvenile period (but not in adulthood), yet robust deficits on a visual attention task in adulthood. P3 HI animals did not show any significant reductions in brain volume that we could detect. These data suggest that: (1) behavioral deficits following neonatal HI are task-specific depending on timing of injury; (2) P3 HI rats showed transient deficits on RAP tasks; (3) the more pervasive behavioral deficits seen following P7 HI injury were associated with substantial global tissue loss; and (4) persistent deficits in attention in P3 HI subjects might be linked to neural connectivity disturbances rather than a global loss of brain volume, given that no such pathology was found. These combined findings can be applied to our understanding of differing long-term outcomes following neonatal HI injury in premature versus term infants.

Transgenerational effects of neonatal hypoxia-ischemia in progeny

Neonatal hypoxia-ischemia (HI) affects 60% of low birth weight infants and up to 40% of preterm births. Cell death and brain injury after HI have been shown to cause long-lasting behavioral deficits. By using a battery of behavioral tests on second generation 3-week-old rodents, we found that neonatal HI is associated with behavioral outcomes in the progeny of HI-affected parents. Our results suggest an epigenetic transfer mechanism of some of the neurological symptoms associated with neonatal HI. Elucidating the transfer of brain injury to the next generation after HI calls attention to the risks associated with HI injury and the need for proper treatment to reverse these effects. Assessing the devastating extent of HI's reach serves as a cautionary tale to the risks associated with neonatal HI, and provides an incentive to create improved therapeutic measures to treat HI.