Hypoxia and brain development

Influence of allopurinol on evoked cortical afterdischarges during early ontogenesis

The aim of our study was to test the hypothesis, whether repeated allopurinol pre-treatment (in dose of 135 mg/kg s.c.) can influence changes of brain excitability caused by long-term hypoxia exposition in young immature rats. Rat pups were exposed together with their mother in to an intermittent hypobaric hypoxia (simulated altitude of 7 000 m) since the day of birth till the 11th day (youngest experimental group) or 17th day for 8 hours a day. Allopurinol was administered daily immediately before each hypoxia exposition. The duration of evoked afterdischarges (ADs) and the shape of evoked graphoelements were evaluated in 12, 18, 25 and 35-day-old freely moving male pups. Hypobaric hypoxia prolonged the duration of ADs in 12, 18 and 25-day-old rats. The ADs were prolonged in 35-day-old rats only after the first stimulation. Allopurinol shorted the duration of ADs only in 12-day-old pups. In older experimental group the effect of allopurinol treatment was less pronounced.

Sex and steroid hormones in early brain injury

Brain injury during development can have severe, long-term consequences. Using an array of animal models, we have an understanding of the etiology of perinatal brain injury. However, we have only recently begun to address the consequences of endogenous factors such as genetic sex and developmental steroid hormone milieu. Our limited understanding has sometimes led researchers to make over-generalizing and potentially dangerous statements regarding treatment for brain injury. Therefore this review acts as a cautionary tale, speaking to our need to understand the effects of sex and steroid hormone environment on the response to brain trauma in the neonate.

Effect of hypobaric hypoxia on the P2X receptors of pyramidal cells in the immature rat hippocampus CA1 sub-field

PRIMARY OBJECTIVE

This study was designed to evaluate the effect of hypobaric hypoxia (HH) on the function and expression of P2X receptors in rat hippocampus CA1 pyramidal cells.

RESEARCH DESIGN

The functional changes of P2X receptors were investigated through the cell HH model and the expressional alterations of P2X receptors were observed through the animal HH model.

METHODS AND PROCEDURE

P2X receptors mediated currents were recorded from the freshly dissociated CA1 pyramidal cells of 7-day-old SD rats by whole cell patch clamp recording. The expression and distribution of P2X receptors were observed through immunohistochemistry and western blot at HH 3-day and 7-day.

MAIN OUTCOMES AND RESULTS

In acute HH conditions, the amplitudes of ATP evoked peak currents were decreased compared to control. The immunohistochemistry and western blot results reflected there was no change in P2X receptors expression after 3 days HH injury, while P2X receptors expression was up-regulated in response to 7 days HH injury.

CONCLUSIONS

These findings supported the possibility that the function of P2X receptors was sensitive to HH damage and long-term function decrease should result in the expression increase of P2X receptors.

Social behavior impairment in offspring exposed to maternal seizures in utero

Human and animal models have demonstrated that maternal seizures in utero could be deleterious to the development of the offspring. This study focused on the social behavior of offspring exposed to seizures in utero. A pilocarpine model of temporal lobe epilepsy was induced in female Wistar rats that were mated after the first spontaneous seizure. Early after birth, pups from an epileptic mother were reared by a control mother. To evaluate the influence of the adoption process, two other groups were added: rat pups from control mothers cross-fostered with other control mothers, and rat pups reared by their birth mother. Animals exposed to seizures in utero showed impaired social behavior with no signs of anxiety-like behavior. This study demonstrated that epileptic seizures during pregnancy could be harmful to brain development and may increase the risk of developing neurodevelopmental disorders. The mechanisms underlying the abnormalities of social behavior are not well understood, and further studies in this field are warranted.

Hypoxic-ischemic injury decreases anxiety-like behavior in rats when associated with loss of tyrosine-hydroxylase immunoreactive neurons of the substantia nigra

Neonatal Sprague-Dawley rats were randomly divided into normal control, mild hypoxia-ischemia (HI), and severe HI groups (N = 10 in each group at each time) on postnatal day 7 (P7) to study the effect of mild and severe HI on anxiety-like behavior and the expression of tyrosine hydroxylase (TH) in the substantia nigra (SN). The mild and severe HI groups were exposed to hypoxia (8% O2/92% N2) for 90 and 150 min, respectively. The elevated plus-maze (EPM) test was performed to assess anxiety-like behavior by measuring time spent in the open arms (OAT) and OAT%, and immunohistochemistry was used to determine the expression of TH in the SN at P14, P21, and P28. OAT and OAT% in the EPM were significantly increased in both the mild (1.88-, 1.99-, and 2.04-fold, and 1.94-, 1.51-, and 1.46-fold) and severe HI groups (1.69-, 1.68-, and 1.87-fold, and 1.83-, 1.43-, and 1.39-fold, respectively; P < 0.05). The percent of TH-positive cells occupying the SN area was significantly and similarly decreased in both the mild (17.7, 40.2, and 47.2%) and severe HI groups (16.3, 32.2, and 43.8%, respectively; P < 0.05). The decrease in the number of TH-positive cells in the SN and the level of protein expression were closely associated (Pearson correlation analysis: r = 0.991, P = 0.000 in the mild HI group and r = 0.974, P = 0.000 in the severe HI group) with the impaired anxiety-like behaviors. We conclude that neonatal HI results in decreased anxiety-like behavior during the juvenile period of Sprague-Dawley rats, which is associated with the decreased activity of TH in the SN. The impairment of anxiety and the expression of TH are not likely to be dependent on the severity of HI.

Perinatal intermittent hypoxia alters γ-aminobutyric acid: a receptor levels in rat cerebellum

Perinatal hypoxia commonly causes brain injury in infants, but the time course and mechanisms underlying the preferential male injury are unclear. Intermittent hypoxia disturbs cerebellar γ-aminobutyric (GABA)-A receptor profiles during the perinatal period, possibly responding to transient excitatory processes associated with GABA(A) receptors. We examined whether hypoxic insults were particularly damaging to the male rodent cerebellum during a specific developmental time window. We evaluated cerebellar injury and GABA(A) receptor profiles following 5-h intermittent hypoxia (IH: 20.8% and 10.3% ambient oxygen, switched every 240s) or room-air control in groups of male and female rat pups on postnatal d 1-2, wk 1, or wk 3. The cerebella were harvested and compared between groups. The mRNA levels of GABA(A) receptors α6, normalized to a house-keeping gene GAPDH, and assessed using real-time reverse-transcriptase PCR assays were up-regulated by IH at wk 1, more extensively in male rats, with sex influencing the regulatory time-course. In contrast, GABA(A) α6 receptor protein expression levels, assessed using Western blot assays, reached a nadir at wk 1 in both male and female rats, possibly indicating involvement of a post-transcriptional mechanism. The extent of cerebellar damage and level of apoptosis, assessed by DNA fragmentation, were greatest in the wk 3 IH-exposed group. The findings suggest partial protection for female rats against early hypoxic insult in the cerebellum, and that down-regulation of GABA(A) receptors, rather than direct neural injury assessed by DNA fragmentation may modify cerebellar function, with potential later motor and other deficits.

Hyperthermic effects on behavior

This review focuses upon the past 8 years of research on hyperthermic effects on behavior. Heat stress and heat stoke become severe conditions when body temperatures exceed 40°C as this can lead to delirium, convulsions, coma, and death. The animal literature indicates that hyperthermia can increase glutamatergic and decrease GABAergic neurotransmission. Interestingly, µ-opiate receptor antagonists can attenuate the morphological and biochemical changes in brain, as well as, ameliorate some behavioral deficits induced by heart stress. In humans, heat stress can produce detrimental effects on motor and cognitive performance. Since most cognitive tasks require a motor response, some cognitive deficiencies may be attributed to decreased motor performance. Although hyperthermia may exert more deleterious effects on complex than simple cognitive tasks, systematic studies are needed to examine the effects of different levels and durations of hyperthermia (irrespective of dehydration) on cognition. Additionally, body temperatures should be carefully monitored where controls are run for baseline or brief exposures to a hyperthermic environment. Acute radiofrequency exposure can disrupt behavior when body temperatures increase >1°C with whole body SAR between 3.2-8.4 W/kg and time-averaged power densities at 8-140 mW/cm(2). Effects of lower levels of radiation are conflicting and some experiments fail to replicate even with the original investigators. This suggests either that brief exposure to the radiation is at a threshold where some individuals are affected while others are not, or that these levels are innocuous. Nevertheless, thermal changes appear to account for almost all of the behavioral effects reported.

Therapeutic neuroprotective effects of ginkgolide B on cortex and basal ganglia in a rat model of transient focal ischemia

Cerebral ischemia and reperfusion is one of the leading causes for death and severe disabilities in the world and often lead to irreversible brain damage over later lifespan. The aim of this study was to investigate the evolution of pathological damage in cerebral cortex and basal ganglia following ischemia and to evaluate the therapeutic neuroprotective effect of ginkgolide B in a rat model of stroke induced by middle cerebral artery occlusion (MCAO). TTC stain, brain water content and Evans-Blue extravasation were used to quantify brain damage. Our results demonstrated that basal ganglia undergo progressive pathological damage earlier following MCAO, and injury was stable and irreversible after 5 h following ischemia. However, onset of ischemia injury in cerebral cortex appeared later than basal ganglia and became evident about 3 h following MCAO, and injury was stable and irreversible after 6 h following ischemia. Blood brain barrier opened progressively, and it seemed to be significantly destroyed after 4 h following MCAO comparing with 0 h. Post-ischemic treatment with ginkgolide B improved neurological function and reduced infarct size in basal ganglia within 3 h and cerebral cortex within 5 h following MCAO. The therapeutic effect of ginkgolide B on extenuate brain edema and decrease blood brain barrier permeability were extended for 5h after ischemia, and more evident reversal effect were observed when administrated at earlier time.

Experimental modeling of hypoxia in pregnancy and early postnatal life

The important role of equilibrium of environmental factors during the embryo-fetal period is undisputable. Women of reproductive age are increasingly exposed to various environmental risk factors such as hypoxia, prenatal viral infections, use of drugs, smoking, complications of birth or stressful life events. These early hazards represent an important risk for structural and/or functional maldevelopment of the fetus and neonates. Impairment of oxygen/energy supply during the pre- and perinatal period may affect neuronal functions and induce cell death. Thus when death of the newborn is not occurring following intrauterine hypoxia, various neurological deficits, including hyperactivity, learning disabilities, mental retardation, epilepsy, cerebral palsy, dystonia etc., may develop both in humans and in experimental animals. In our animal studies we used several approaches for modeling hypoxia in rats during pregnancy and shortly after delivery, i.e. chronic intrauterine hypoxia induced by the antiepileptic drug phenytoin, neonatal anoxia by decreased oxygen saturation in 2-day-old pups. Using these models we were able to test potential protective properties of natural (vitamin E, melatonin) and synthetic (stobadine) compounds. Based on our results, stobadine was also able to reduce hypoxia-induced hyperactivity and the antioxidant capacity of stobadine exceeded that of vitamin E and melatonin, and contrary to vitamin E, stobadine had no adverse effects on developing fetus and offspring.

Adenosine A₂a receptors and O₂ sensing in development

Reduced mitochondrial oxidative phosphorylation, via activation of adenylate kinase and the resulting exponential rise in the cellular AMP/ATP ratio, appears to be a critical factor underlying O₂ sensing in many chemoreceptive tissues in mammals. The elevated AMP/ATP ratio, in turn, activates key enzymes that are involved in physiologic adjustments that tend to balance ATP supply and demand. An example is the conversion of AMP to adenosine via 5'-nucleotidase and the resulting activation of adenosine A(₂A) receptors, which are involved in acute oxygen sensing by both carotid bodies and the brain. In fetal sheep, A(₂A) receptors associated with carotid bodies trigger hypoxic cardiovascular chemoreflexes, while central A(₂A) receptors mediate hypoxic inhibition of breathing and rapid eye movements. A(₂A) receptors are also involved in hypoxic regulation of fetal endocrine systems, metabolism, and vascular tone. In developing lambs, A(₂A) receptors play virtually no role in O₂ sensing by the carotid bodies, but brain A(₂A) receptors remain critically involved in the roll-off ventilatory response to hypoxia. In adult mammals, A(₂A) receptors have been implicated in O₂ sensing by carotid glomus cells, while central A(₂A) receptors likely blunt hypoxic hyperventilation. In conclusion, A(₂A) receptors are crucially involved in the transduction mechanisms of O₂ sensing in fetal carotid bodies and brains. Postnatally, central A(₂A) receptors remain key mediators of hypoxic respiratory depression, but they are less critical for O₂ sensing in carotid chemoreceptors, particularly in developing lambs.

Protective effects of hydrogen on fetal brain injury during maternal hypoxia

This study aimed to investigate the effects of hydrogen on fetal brain injury during maternal hypoxia. Pregnant rats (n=12, at gestational day 17) were randomly assigned into three groups; air, hypoxia, and hypoxia plus hydrogen groups were put into a chamber and flushed with room air (21% O2 and 79% N2), hypoxia (8% O2 and 92% N2), and hypoxia with hydrogen mixture (2% H2, 8% O2 and 90% N2), respectively, for 4 consecutive hours. After birth, body and brain weights, body-righting reflex, and negative geotropism of neonates were measured, and then pups were killed at days 1 and 7. Oligodendrocytes were studied at post-natal day 1 by immunohistochemistry. We found significant decreases in body weight in the hypoxia group (P<0.05 vs. room air group), but not in the hypoxia plus hydrogen group (P>0.05 vs. room air group). Even though brain weight was not different among groups, the brain weight to body weight ratio in the room air group was significantly (P<0.05) lower than that in the hypoxia alone or hypoxia plus hydrogen groups. Body-righting reflex at day 1 and negative geotropism at days 3-4 showed deficiency in hypoxia animals when compared with the room air group (P<0.05). Hydrogen treatment improved the body-righting reflex and negative geotropism (P<0.05 vs. room air group). The above-mentioned functional changes caused by hypoxia were not associated with morphology and cell death of oligodendrocytes. Therefore, the maternal hypoxia-induced body weight loss, and functional abnormalities and hydrogen treatment during hypoxia offered a protective effect and improved functions in neonates.

Notch signaling: key role in intrauterine infection/inflammation, embryonic development, and white matter damage?

The mechanisms or pathophysiologies that lead to cerebral white matter damage during development are complex and not fully understood. It is postulated that exposure of the preterm brain to inflammatory cytokines during intrauterine infection/inflammation contributes to brain white matter damage, and this damage may affect the function and differentiation of progenitor oligodendrocyte cells under physiological conditions. The Notch pathway, an important signaling pathway controlling various cells' differentiation, functions in the timing of oligodendrocyte differentiation, and Notch signaling may contribute to white matter damage and may mediate neurogenesis in a pathophysiological phase. Recent studies have led to recognition of the role of the Notch pathway in neurogenesis in cerebral ischemic damage and in myelination and axonal damage of neurodegenerative diseases. Moreover, Notch plays a critical role in steering an immune response toward inflammation by regulating expression of various cytokines and proinflammatory cytokines resulting in the activation of Notch signaling. Thus, the Notch signaling pathway likely plays a key role in intrauterine infection/inflammation, brain development, and white matter damage, and future research directed toward understanding its role will be important. Insofar as Notch signaling could have an important effect on neurogenesis, mobilization of progenitor cells is one strategy for compensating for the neuronal losses seen in white matter damage after intrauterine infection/inflammation.

Mineralocorticoid and glucocorticoid receptors in hippocampus: their impact on neurons survival and behavioral impairment after neonatal brain injury

Glucocorticoids (GC) exert multiple effects within the central nervous system via mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) activation. MR expression is associated with a neuroprotective phenotype, whereas GR activation is implicated in the induction of an endangered neural phenotype and the opposite actions are most evident in hippocampus, where these receptors are predominantly present. Hippocampus has an overall inhibitory influence on the activity of the hypothalamic-pituitary-adrenal (HPA) axis and it has been suggested that efficient learning and adequate stress response depend on the appropriate functioning of the axis brought by coordinated activation of MR and GR in this region. There is a growing body of evidence that perinatal asphyxia causes irreversible damage to the brain leading to neurons loss in regions vulnerable to oxygen shortage especially in hippocampus. In the present review, some aspects of recently acquired insight in the role of GC receptors in promoting neuronal death and survival after hippocampal injury are discussed. Since the unbalance of MR and GR in hippocampus creates a condition of disturbed neuroendocrine regulation their potential impact on behavioral impairment will also be reviewed.

Ontogenetic characteristics of behavior in rats subjected to hypoxia on day 14 or day 18 of embryogenesis

Physiological development, motor activity, and cognitive functions were studied in rats subjected to acute normobaric hypoxic hypoxia (3 h at an O2 concentration of 7%) at different stages of embryogenesis (days E14 or E18). Prenatal hypoxia was found to lead to delays in physiological development and the establishment of motor behavior during the first month of postnatal ontogenesis. These changes were more marked in rats subjected to hypoxia on day 14 of intrauterine development and disappeared with age. In adult rats, regardless of the timing of exposure to hypoxia (E14 or E18), learning ability was degraded and long-term and short-term memory were impaired. These results suggest that exposure to the pathogenic factor during the main period of neuroblast generation and migration (E14) was significant both for physiological development and the establishment of motor behavior in the animals and for the execution of the cognitive functions of the brain, while exposure during the period at which maturation and differentiation processes dominate in the brain (E18) was more significant in relation to the execution of cognitive functions.

Modeling premature brain injury and recovery

Premature birth is a growing and significant public health problem because of the large number of infants that survive with neurodevelopmental sequelae from brain injury. Recent advances in neuroimaging have shown that although some neuroanatomical structures are altered, others improve over time. This review outlines recent insights into brain structure and function in these preterm infants at school age and relevant animal models. These animal models have provided scientists with an opportunity to explore in depth the molecular and cellular mechanisms of injury as well as the potential of the brain for recovery. The endogenous potential that the brain has for neurogenesis and gliogenesis, and how environment contributes to recovery, are also outlined. These preclinical models will provide important insights into the genetic and epigenetic mechanisms responsible for variable degrees of injury and recovery, permitting the exploration of targeted therapies to facilitate recovery in the developing preterm brain.

Human fetal brain chemistry as detected by proton magnetic resonance spectroscopy

Magnetic resonance spectroscopy represents an invaluable tool for the in vivo study of brain development at the chemistry level. Whereas magnetic resonance spectroscopy has received wide attention in pediatric and adult settings, only a few studies were performed on the human fetal brain. They revealed changes occurring throughout gestation in the levels of the main metabolites detected by proton magnetic resonance spectroscopy (N-acetylaspartate, choline, myo-inositol, creatine, and glutamate), providing a reference for the normal metabolic brain development. Throughout the third trimester of gestation, N-acetylaspartate gradually increases, whereas choline undergoes a slow reduction during the process of myelination. Less clear are the modifications in creatine, myo-inositol, and glutamate levels. Under conditions of fetal distress, the meaning of lactate detection is unclear, and further studies are needed. Another field for investigation involves the possibility of early detection of glutamate levels in fetuses at risk for hypoxic-ischemic encephalopathy, because the role of glutamate excitotoxicity in this context is well-established. Because metabolic modifications may precede functional or morphologic changes in the central nervous system, magnetic resonance spectroscopy may likely serve as a powerful, noninvasive tool for the early diagnosis and prognosis of different pathologic conditions.

Effect of hyperthermia and anoxia on glucocorticoid and mineralocorticoid receptor expression in neonatal rat hippocampus

Brief periods of neonatal asphyxia are frequently observed. Within the CNS, the hippocampus is known to be particularly vulnerable to the damaging effects of hypoxia/ischaemia. The hippocampus contains the highest concentration of both mineralocorticoid (MR) and glucocorticoid (GR) receptors and the balance between MR/GR activation influences cell birth and death. MR occupation appears to promote prosurvival actions, while GR overactivation favours neurodegeneration. It has been widely recognized that core body temperature is a critical determinant of the severity of hypoxic-ischemic brain injury; indeed, hyperthermia exacerbates the degree of damage. Therefore, the aim of the present investigation was to study the effect of elevated body temperature in newborn rats under control conditions or during neonatal exposure to a critical anoxia, on changes of MR and GR mRNA expression in the rat hippocampus. 2-day-old rats were exposed to anoxia in 100% nitrogen atmosphere. Rectal temperature was kept at 33 degrees C (typical for the rat neonates), or elevated to a level typical for febrile (39 degrees C) adults. Control rats were exposed to atmospheric air under the respective thermal conditions. The changes in MR and GR mRNA expression in hippocampus were examined 24h after exposure. Our data show that hyperthermia with or without added anoxia, causes induction of MR mRNA expression in neonatal rat hippocampus without any effect on GR mRNA expression. We suggest this elevation of MR plays an important role in modulating the survival of neurons in the injured hippocampus.

Decreased neurotrophic response to birth hypoxia in the etiology of schizophrenia

BACKGROUND

Obstetric complications, particularly fetal hypoxia, are associated with increased risk for schizophrenia later in life. Such factors are also related to increased severity of certain neuropathological features of schizophrenia, including hippocampal and cortical gray matter reduction, among individuals with a genetic susceptibility to the disorder. However, the molecular mechanisms underlying these associations are unknown. Here, we sought to determine whether neurotrophic factors, which are stimulated as part of a neuroprotective response to fetal distress, are differentially expressed in cord blood samples at the time of birth following fetal hypoxia, maternal hypertension/small for gestational age status, and/or prematurity among individuals who developed schizophrenia as adults, as compared with control subjects.

METHODS

One hundred eleven cases with psychotic disorders (70 with schizophrenia) and 333 control subjects matched for gender, race, and date of birth were drawn from the Philadelphia cohort of the National Collaborative Perinatal Project in a nested case-control study. Brain-derived neurotrophic factor (BDNF) was assayed from cord and maternal blood samples taken at delivery and stored at -20 degrees C for 45 to 50 years.

RESULTS

Among control subjects, birth hypoxia was associated with a significant (10%) increase in BDNF in cord samples, while among cases, hypoxia was associated with a significant (20%) decrease in BDNF. This differential response to fetal hypoxia was specific to schizophrenia and was not explained by other obstetric complications or by the BDNF valine (val) to methionine (met) polymorphism at codon 66 (val66met).

CONCLUSIONS

These findings provide serologically based prospective evidence of disrupted neurotrophic signaling in response to birth hypoxia in the molecular pathogenesis of schizophrenia.

Developmental motor deficits induced by combined fetal exposure to lipopolysaccharide and early neonatal hypoxia/ischemia: a novel animal model for cerebral palsy in very premature infants

A critical issue in animal models of perinatal brain injury is to adapt the pertinent pathophysiological scenarios to their corresponding developmental window in order to induce neuropathological and behavioral characteristics reminiscent to perinatal cerebral palsy (CP). A major problem in most of these animal models designed up to now is that they do not present motor deficits characteristic of CP. Using a unique rat paradigm of prenatal inflammation combined to an early postnatal hypoxia-ischemia pertinent to the context of very early premature human newborns, we were interested in finding out if such experimental conditions might reproduce both histological damages and behavioral deficits previously described in the human context. We showed that exposure to lipopolysaccharide (LPS) or hypoxia-ischemia (H/I) induced behavioral alterations in animals subjected to forced motor activity. When both LPS and H/I aggressions were combined, the motor deficits reached their highest intensity and affected both spontaneous and forced motor activities. LPS+H/I-exposed animals also showed extensive bilateral cortical and subcortical lesions of the motor networks affecting the frontal cortices and underlying white matters fascicles, lenticular nuclei and the substantia nigra. These neuropathological lesions and their associated motor behavioral deficits are reminiscent of those observed in very preterm human neonates affected by subsequent CP and validate the value of the present animal model to test new therapeutic strategies which might open horizons for perinatal neuroprotection.

Abnormal neurological responses in young adult offspring caused by excess omega-3 fatty acid (fish oil) consumption by the mother during pregnancy and lactation

Consuming omega-3 fatty acids (omega-3 FA) during pregnancy and lactation benefits fetal and infant brain development and might reduce the severity of preterm births by prolonging pregnancy. However, diets that are relatively rich in omega-3 FA can adversely affect fetal and infant development and the auditory brainstem response (ABR), a measure of brain development and sensory function. We previously examined the offspring of female rats fed excessive, adequate or deficient amounts of omega-3 FA during pregnancy and lactation. The 24-day-old offspring in the Excess group, compared to the Control group, had postnatal growth retardation and poor hearing acuity and prolonged neural transmission times as evidenced by the ABR. The Deficient group was intermediate. The current study followed these offspring to see if these poor outcomes persisted into young adulthood. Based on prior findings, we hypothesized that the Excess and Deficient offspring would "catch-up" to the Control offspring by young adulthood. Female Wistar rats received one of the three diet conditions from day 1 of pregnancy through lactation. The three diets were the Control omega-3 FA condition (omega-3/omega-6 ratio approximately 0.14), the Excess omega-3 FA condition (omega-3/omega-6 ratio approximately 14.0) and Deficient omega-3 FA condition (omega-3/omega-6 ratio approximately 0% ratio). The Control diet contained 7% soybean oil; whereas the Deficient and Excess omega-3 FA diets contained 7% safflower oil and 7% fish oil, respectively. One male and female offspring per litter were ABR-tested as young adults using tone pip stimuli of 2, 4, 8 and 16 kHz. The postnatal growth retardation and prolonged neural transmission times in the Excess and Deficient pups had dissipated by young adulthood. In contrast, the Excess group had elevated ABR thresholds (hearing loss) at all tone pip frequencies in comparison to the Control and Deficient groups. The Deficient group had worse ABR thresholds than the Control group in response to the 8 kHz tone pips only. The Excess group also had ABR amplitude-intensity profiles suggestive of hyperacusis. These results are consistent with the Barker hypothesis concerning the fetal and neonatal origins of adult diseases. Thus, consuming diets that are excessively rich or deficient in omega-3 FA during pregnancy and lactation seems inadvisable because of risks for long-lasting adverse effects on brain development and sensory function.

Melatonin attenuates hypoxia-induced ultrastructural changes and increased vascular permeability in the developing hippocampus

Hypoxic injury in the perinatal period may be involved in damaging the developing hippocampus. The damage may be mediated by excess production of vascular endothelial growth factor (VEGF) and nitric oxide (NO). We examined the hippocampus of neonatal Wistar rats subjected to hypoxia for VEGF and NO production. The mRNA and protein expression of hypoxia inducible factor-1alpha, endothelial, neuronal, inducible nitric oxide synthase and VEGF was found to be up-regulated significantly after the hypoxic exposure. Tissue VEGF concentration and NO production were also increased. By electron microscopy, swollen dendrites, vacuolated axons and hypertrophic astrocyte end feet associated with blood vessels were observed in hypoxic animals. In hypoxic rats, the passage of rhodamine isothiocyanate (RhIC) and horseradish peroxidase, administered intraperitoneally or intravenously, was observed through vascular walls. Furthermore, immunoglobulin G was localized in the neuropil and neurons. We suggest that increased VEGF and NO production in hypoxia had resulted in increased vascular permeability, leading to structural alteration of the dendrites and axons. Melatonin administration reduced VEGF and NO levels as well as leakage of RhIC, suggesting that it has a therapeutic potential in reducing hypoxia-associated damage in the developing hippocampus.

Developmental plasticity of the carotid chemoafferent pathway in rats that are hypoxic during the prenatal period

The chemoreflex pathway undergoes postnatal maturation, and the perinatal environment plays a critical role in shaping respiratory control system. We investigated the role of prenatal hypoxia on the maturation of the chemoreflex neural circuits regulating ventilation in rat. Effects of hypoxia (10% O2) from the 5th to the 20th day of gestation were studied on male offspring at birth and on postnatal days 3, 7, 21 and 68. Maturation of the respiratory control system was assessed by in vivo tyrosine hydroxylase (TH) activity measurement in peripheral chemoreceptors (carotid bodies, petrosal ganglia), and in brainstem catecholaminergic cell groups (A2C2c and A1C1 areas in the medulla, A5 and A6 areas in the pons). Resting ventilation and ventilatory response to hypoxia were evaluated as functional sequelae. In peripheral structures, prenatal hypoxia reduced TH activity within the first postnatal week and enhanced it later. In contrast, in central areas, prenatal hypoxia upregulated TH activity within the first postnatal week and downregulated it later. The in vivo TH activity impairment is therefore tissue specific, with an opposite effect on the peripheral and central neural circuits. A shift of the effect of prenatal hypoxia occurred between 1 and 3 weeks, indicating a postnatal temporal effect of prenatal hypoxia. An important period in the development of the chemoafferent pathway occurred between the first and the third postnatal week. Functionally, prenatal hypoxia impaired resting ventilation and ventilatory response to hypoxia. The alterations of the catecholaminergic components of the chemoafferent pathway resulting from prenatal hypoxia might contribute to impair postnatal respiratory behaviour.

Gap junctional intercellular communication in hypoxia-ischemia-induced neuronal injury

Brain hypoxia-ischemia is a relatively common and serious problem in neonates and in adults. Its consequences include long-term histological and behavioral changes and reduction in seizure threshold. Gap junction intercellular communication is pivotal in the spread of hypoxia-ischemia related injury and in mediating its long-term effects. This review provides a comprehensive and critical review of hypoxia-ischemia and hypoxia in the brain and the potential role of gap junctions in the spread of the neuronal injury induced by these insults. It also presents the effects of hypoxia-ischemia and of hypoxia on the state of gap junctions in vitro and in vivo. Understanding the mechanisms involved in gap junction-mediated neuronal injury due to hypoxia will lead to the development of novel therapeutic strategies.

17beta-estradiol protects the neonatal brain from hypoxia-ischemia

Hypoxia-ischemia is relatively common in human infants. Hypoxia-ischemia can occur as a result of complications associated with prematurity or birth, frequently leading to altered brain development and cognitive and behavioral deficits that persist throughout life. Despite the relative frequency of neonatal hypoxic-ischemic encephalopathy, the immature brain sustains relatively less damage than an adult who experiences a similar crisis of oxygen and nutrient deprivation. Therefore, factors may be present that protect the developing brain. During late gestation, the infant brain encounters high levels of the steroid hormone 17beta-estradiol. This observation, combined with evidence supporting 17beta-estradiol as a neuroprotective agent, led us to hypothesize that increasing the basal level of 17beta-estradiol would reduce the amount of hypoxia-ischemia induced injury to the neonatal brain. To test that hypothesis we administered 17beta-estradiol using either a repeated dosing paradigm or a single dose paradigm to immature male and female rats. Here we show that the repeated dosing paradigm (three doses of 17beta-estradiol) provided approximately 70% protection of the hippocampus, basal ganglia, and amygdala. By contrast, a single administration of 17beta-estradiol 24 h prior to hypoxia-ischemia conferred little protection. The only exception was the pyramidal layer of the female hippocampus, which was modestly protected (16% reduction in damage). The protection afforded by the multiple administrations of 17beta-estradiol was similar for females and males, with the only exception being the male amygdala, which displayed less damage than the female amgydala. We conclude that 17beta-estradiol acts as a potent neuroprotective agent against hypoxia-ischemia induced damage to the developing brain, and that pretreating infants at risk for hypoxic-ischemic injury may be advisable.

Cognitive function in outbred house mice after 22 weeks of drinking oxygenated water

Oxygen-enriched drinking water, which is increasingly sold worldwide, is claimed to "keep both the body and the mind healthy." However, currently there is no scientific evidence for such a statement. Therefore, we assessed the effect of 22 weeks of drinking oxygenated water on cognitive performance in healthy mice, using a spatial learning task and behavioral observations. Thirty-six female mice (age 3 to 6 months) received either hyperoxic or normal tap water (approximately 6.6 vs. 1.8 microg O(2) g(-1) day(-1), respectively) throughout the study period. Mice were weighed one to two times per month, and a blood sample was taken from the tail to determine the hematocrit. In addition, red blood cells were counted microscopically one and two months after the start of the experiment. Four weeks after the last blood sample (21 weeks after the start of the experiment), exploration behavior and locomotor activity were observed on a holeboard, and learning ability tests were performed using an elevated open maze. No significant differences were seen between groups for any of the parameters investigated. Thus, the study does not support the hypothesis that drinking oxygenated water improves cognitive function or hematological parameters in mice.

Role of acetylcholine in neurotransmission of the carotid body

Acetylcholine (ACh) has been considered an important excitatory neurotransmitter in the carotid body (CB). Its physiological and pharmacological effects, metabolism, release, and receptors have been well documented in several species. Various nicotinic and muscarinic ACh receptors are present in both afferent nerve endings and glomus cells. Therefore, ACh can depolarize or hyperpolarize the cell membrane depending on the available receptor type in the vicinity. Binding of ACh to its receptor can create a wide variety of cellular responses including opening cation channels (nicotinic ACh receptor activation), releasing Ca(2+) from intracellular storage sites (via muscarinic ACh receptors), and modulating activities of K(+) and Ca(2+) channels. Interactions between ACh and other neurotransmitters (dopamine, adenosine, nitric oxide) have been known, and they may induce complicated responses. Cholinergic biology in the CB differs among species and even within the same species due to different genetic composition. Development and environment influence cholinergic biology. We discuss these issues in light of current knowledge of neuroscience.

Impaired spatial working memory and altered choline acetyltransferase (CHAT) immunoreactivity and nicotinic receptor binding in rats exposed to intermittent hypoxia during sleep

Exposure to intermittent hypoxia (IH), such as occurs in sleep-disordered breathing (SDB), is associated with cognitive impairment, neurodegeneration, oxidative stress, and inflammatory responses within rodent brain regions such as the basal forebrain. In this region, damage to cholinergic neurons correlates with working memory deficits in a number of neurodegenerative disorders, suggesting that degeneration of cholinergic systems may also contribute to the working memory impairments observed after IH exposures. We therefore examined basal forebrain choline acetyltransferase (CHAT) immunohistochemistry, nicotinic receptor binding in the prefrontal cortex (PFC), and working memory, in male rats tested on a delayed matching to place (DMP) task in the water maze following exposure to either room air (RA) or intermittent hypoxia (IH; alternating 90s epochs of 21% and 10% O(2) during sleep). IH-treated animals displayed impaired working memory with respect to controls, along with significant reductions in CHAT-stained neurons in the medial septal nucleus, in both the vertical and horizontal limbs of the diagonal band, and the substantia inominata after 14 days of IH exposure. In addition, increases in nicotinic binding and receptor affinity in the PFC were observed after 14 days of IH exposure. Thus, a loss of cholinergic neuronal phenotype in the basal forebrain may contribute to the cognitive impairments associated with CIH exposure. However, compensatory mechanisms may also be activated in other brain regions, and may provide potential therapeutic targets for the cognitive impairments associated with SDB.

Adult aggression during an initial social encounter: effects of neonatal anoxia and relation to juvenile open-field activity

In male Long-Evans hooded rats, we examined: (1) combined effects of neonatal anoxia and novelty exposure on aggression during adulthood; (2) open-field activity before juvenility as a predictor for adult aggression. Litters of neonates were exposed to either 100% N2 gas (Anoxia) or room air (Control) for 25 min on postnatal Day 1 (P1). Within each of the Anoxia and Control conditions, one half of the neonates were individually exposed to a non-home cage for 3 min daily during P2-21 (Novel: N(Anoxia)=15; N(Control)=13) while the other half remained in the home cage (Home: N(Anoxia)=15; N(Control)=13). Prior to the onset of juvenility (P25), open-field activity was measured during four 20-s trials. At the onset of adulthood (P100-101), we measured the occurrence of biting during four 5-min sessions of social interaction between pairs of rats. Neonatal anoxia and novelty exposure had contrasting effects on adult aggression with the former increasing aggression and the latter having no statistically significant effect. The open-field measures before the onset of juvenility were significantly correlated with the occurrence of biting behavior during adulthood, suggesting that activity in a novel environment observed very briefly in early life may serve as a predictor for adult aggression.

Intermittent hypoxia impairs performance of adult mice in the two-way shuttle box but not in the Morris water maze

We have previously found that neonatal intermittent hypobaric hypoxia exposure enhanced mouse spatial, but impaired associative, cognition. This study sought to investigate the effects of hypobaric hypoxia on adult mice cognition. Mice were exposed to 2, 5, 10, 15, or 25 days of intermittent hypoxia (IH; 4 hr/day) at 2 km (16.0% O2) or 5 km (10.8% O2) altitudes in a hypobaric chamber for the Morris water maze (MWM) test and exposed to IH for 2, 10, or 25 days for the shuttle-box test. Amino acid dynamics in vivo in the hippocampus and amygdala of mice exposed to 2 km hypoxia were analyzed by high-pressure liquid chromatography. The results in MWM task showed that IH-2d to -25d at 2 km or 5 km did not change the escape latencies of mice in the training test or the retention of platform in the probe test. In the shuttle-box task, however, IH-10d at 5 km significantly reduced mouse avoidances in the acquisition test on day 4, and IH-10d at 2 km reduced avoidances in the retention test; IH-25d at 5 km significantly reduced avoidances of mice throughout the acquisition days. Glutamate in the amygdala persisted in declining to 69% of baseline at 8 hr posthypoxia (P = 0.040 vs. GLU released during 30 min before hypoxia) during the posthypoxia stage. These results suggest that adult hypobaric IH impairs the hippocampal-independent, but not the hippocampal-dependent, task in mice. The different GLU releases in the hippocampus and amygdala in response to hypoxia are involved in the different behaviors.

Memory functions of children born with asymmetric intrauterine growth restriction

OBJECTIVE

Learning difficulties are frequently diagnosed in children born with intrauterine growth restriction (IUGR). Models of various animal species with IUGR were studied and demonstrated specific susceptibility and alterations of the hippocampal formation and its related neural structures. The main purpose was to study memory functions of children born with asymmetric IUGR in a large-scale cohort using a long-term prospective paradigm.

METHODS

One hundred and ten infants diagnosed with IUGR were followed-up from birth to 9 years of age. Their performance was compared with a group of 63 children with comparable gestational age and multiple socioeconomic factors. Memory functions (short-term, super- and long-term spans) for different stimuli types (verbal and visual) were evaluated using Visual Auditory Digit Span tasks (VADS), Rey Auditory Verbal Learning Test (Rey-AVLT), and Rey Osterrieth Complex Figure Test (ROCF).

RESULTS

Children with IUGR had short-term memory difficulties that hindered both serial verbal processing system and simultaneous processing of high-load visuo-spatial stimuli. The difficulties were not related to prematurity, neonatal complications or growth catch-up, but were augmented by lower maternal education. Recognition skills and benefits from reiteration, typically affected by hippocampal dysfunction, were preserved in both groups.

CONCLUSIONS

Memory profile of children born with IUGR is characterized primarily by a short-term memory deficit that does not necessarily comply with a typical hippocampal deficit, but rather may reflect an executive short-term memory deficit characteristic of anterior hippocampal-prefrontal network. Implications for cognitive intervention are discussed.

Formation of the structural and ultrastructural organization of the striatum in early postnatal ontogenesis of rats in altered conditions of embryonic development

Light (Nissl and Golgi methods) and electron microscopy methods were used to study the formation of the structure of the striatum during the first two weeks after birth in rats subjected to acute hypoxia at different times of embryogenesis. The dynamics of the physiological development of the same population of rats were studied in parallel. Hypoxia at day 13.5 of embryogenesis was found to lead to delayed neurogenesis (delayed establishment of elements of the neuropil and differentiation of cells) and abnormalities in the structure of the striatum (degeneration, particularly chromatolysis, of neurons and the appearance of glial nodes). Morphometric analysis demonstrated a decrease in the total number of cells in the striatum; small changes in large neurons were seen. Hypoxia at day 18.5 of embryogenesis produced no significant changes. Structural abnormalities were accompanied by changes in the process of the animals' physiological development. The data obtained here show that changes in the conditions of embryogenesis (hypoxia) during the period of the most intense proliferation of neuroblasts in the forebrain lead to impairment of the process of formation of striatal nervous tissue and the body as a whole in the period of early postnatal ontogenesis.