Environmental influences on the pace of brain development.

Childhood socio-economic status (SES), a measure of the availability of material and social resources, is one of the strongest predictors of lifelong well-being. Here we review evidence that experiences associated with childhood SES affect not only the outcome but also the pace of brain development. We argue that higher childhood SES is associated with protracted structural brain development and a prolonged trajectory of functional network segregation, ultimately leading to more efficient cortical networks in adulthood. We hypothesize that greater exposure to chronic stress accelerates brain maturation, whereas greater access to novel positive experiences decelerates maturation. We discuss the impact of variation in the pace of brain development on plasticity and learning. We provide a generative theoretical framework to catalyse future basic science and translational research on environmental influences on brain development.

Assessment of the Association Between Congenital Heart Defects and Brain Injury in Fetuses through Magnetic Resonance Imaging.

BACKGROUND: Congenital heart defects (CHD) may be associated with neurodevelopmental abnormalities mainly due to brain hypoperfusion. This defect is attributed to the major cardiac operations these children underwent, but also to hemodynamic instability during fetal life. Advances in imaging techniques have identified changes in brain magnetic resonance imaging (MRI)in children with CHD. OBJECTIVES: To examine the correlation between CHD and brain injury using fetal brain MRI. METHODS: We evaluated 46 fetuses diagnosed with CHD who underwent brain MRI. CHD was classified according to in situs anomalies, 4 chamber view (4CV), outflow tracts, arches, and veins as well as cyanotic or complex CHD. We compared MRI results of different classes of CHD and CHD fetuses to a control group of 113 healthy brain MRI examinations. RESULTS: No significant differences were found in brain pathologies among different classifications of CHD. The anteroposterior percentile of the vermis was significantly smaller in fetuses with abnormal 4CV. A significantly higher biparietal diameter was found in fetuses with abnormal arches. A significantly smaller transcerebellar diameter was found in fetuses with abnormal veins. Compared to the control group, significant differences were found in overall brain pathology in cortex abnormalities and in extra axial findings in the study group. Significantly higher rates of overall brain pathologies, ventricle pathologies, cortex pathologies, and biometrical parameters were found in the cyanotic group compared to the complex group and to the control group. CONCLUSIONS: Fetuses with CHD demonstrate findings in brain MRI that suggest an in utero pathogenesis of the neurological and cognitive anomalies found during child development.

Accuracy of in-utero MRI to detect fetal brain abnormalities and prognosticate developmental outcome: postnatal follow-up of the MERIDIAN cohort.

BACKGROUND: In utero MRI (iuMRI) detects fetal brain abnormalities more accurately than ultrasonography and provides additional clinical information in around half of pregnancies. We aimed to study whether postnatal neuroimaging after age 6 months changes the diagnostic accuracy of iuMRI and its ability to predict developmental outcome. METHODS: Families enrolled in the MERIDIAN study whose child survived to age 3 years were invited to have a case note review and assessment of developmental outcome with the Bayley Scales of Infant and Toddler Development, the Ages and Stages Questionnaire, or both. A paediatric neuroradiologist, masked to the iuMRI results, reviewed the postnatal neuroimaging if the clinical report differed from iuMRI findings. Diagnostic accuracy was recalculated. A paediatric neurologist and neonatologist categorised participants' development as normal, at risk, or abnormal, and the ability of iuMRI and ultrasonography to predict developmental outcome were assessed. FINDINGS: 210 participants had case note review, of whom 81 (39%) had additional investigations after age 6 months. The diagnostic accuracy of iuMRI remained higher than ultrasonography (proportion of correct cases was 529 [92%] of 574 vs 387 [67%] of 574; absolute difference 25%, 95% CI 21 to 29; p<0·0001). Developmental outcome data were analysed in 156 participants, and 111 (71%) were categorised as normal or at risk. Of these 111 participants, prognosis was normal or favourable for 56 (51%) using ultrasonography and for 76 (69%) using iuMRI (difference in specificity 18%, 95% CI 7 to 29; p=0·0008). No statistically significant difference was seen in infants with abnormal outcome (difference in sensitivity 4%, 95% CI -10 to 19; p=0·73). INTERPRETATION: iuMRI remains the optimal tool to identify fetal brain abnormalities. It is less accurate when used to predict developmental outcome, although better than ultrasonography for identifying children with normal outcome. Further work is needed to determine how the prognostic abilities of iuMRI can be improved. FUNDING: National Institute for Health Research Health Technology Assessment programme.

An ultra high-throughput method for single-cell joint analysis of open chromatin and transcriptome.

Simultaneous profiling of transcriptome and chromatin accessibility within single cells is a powerful approach to dissect gene regulatory programs in complex tissues. However, current tools are limited by modest throughput. We now describe an ultra high-throughput method, Paired-seq, for parallel analysis of transcriptome and accessible chromatin in millions of single cells. We demonstrate the utility of Paired-seq for analyzing the dynamic and cell-type-specific gene regulatory programs in complex tissues by applying it to mouse adult cerebral cortex and fetal forebrain. The joint profiles of a large number of single cells allowed us to deconvolute the transcriptome and open chromatin landscapes in the major cell types within these brain tissues, infer putative target genes of candidate enhancers, and reconstruct the trajectory of cellular lineages within the developing forebrain.

The ratio of cavum septi pellucidi width to anteroposterior cerebellar diameter: A novel index as a diagnostic adjunct for prenatal diagnosis of trisomy 18.

AIM: To explore the effectiveness of cavum septi pellucidi (CSP) width to anteroposterior cerebellar diameter (APCD) ratio as a diagnostic adjunct for prenatal diagnosis of trisomy 18. METHODS: Images of normal fetal brain within 15 and 35 weeks were stored in our center from 2016 to 2017. Images of aneuploid fetuses were retrospectively collected from 2004 to 2017. The transverse cerebellar diameter, APCD and CSP width were measured. CSP/APCD and APCD/transverse cerebellar diameter ratios were calculated and compared between euploid and aneuploid fetuses. RESULTS: One thousand and forty one fetuses were analyzed, including 817 euploid fetuses and 224 aneuploid fetuses (trisomy 21 117 cases, trisomy 18 82 cases, trisomy 13 9 cases, sex-linked 16 cases). No correlation had been found between both ratios and gestational weeks (P > 0.05). In aneuploid groups, means of ratios were both significantly different just between trisomy 18 group and euploid group (P < 0.05). The best area under the curve was shown by the CSP/APCD ratio. The cutoff value of CSP/APCD was 0.46 (sensitivity 87.0%, specificity 85.0%). CONCLUSION: A wide CSP or cerebellar hypoplasia warrants a more detailed ultrasound screening and genetic counseling. A larger CSP/APCD ratio alerts us to trisomy 18 syndrome, especially in cases with subtle anomalies.

Assessment of epigenetic changes and oxidative DNA damage in rat pups exposed to polychlorinated biphenyls and the protective effect of curcumin in the prenatal period.

Background Polychlorinated biphenyls (PCBs) are persistent organic chemicals that exert neurotoxic and endocrine disrupting effects. The aims of this study were to examine the effects of prenatal Aroclor 1254 (PCBs mixture) exposure on central nervous system tissues DNA and to evaluate the effects of curcumin. Methods Rat pups were assigned to three groups: [Group 1], Aroclor 1254 administrated group; [Group 2], Aroclor 1254 and curcumin administrated group; and [Group 3], control group. Plasma, cerebrum, cerebellum, pons and medulla oblongata tissue homogenates 8-hydroxy-2'-deoxyguanosine [8-(OH)DG] levels and plasma freeT4 levels were determined. Global DNA methylation and hydroxymethylation status were determined in cerebrum, cerebellum, pons and medulla oblongata. To this aim, DNA 5-hydroxymethylcytosine and 5-methylcytosine levels were measured, respectively. Results Mean cerebellum and cerebral cortex 5-hydroxymethylcytosine and 5-methylcytosine levels were higher in the control group than in the experimental groups. Mean plasma, cerebellum and cerebral cortex 8-(OH)DG concentrations were higher in Group 1 than the control group. No statistically significant difference was observed between Group 2 and the control group in terms of cerebellum and cerebral cortex 8-(OH)DG concentrations. Histopathological changes were also observed in the cerebral cortex and cerebellum of rat pups exposed to Aroclor 1254. PCBs exposure changes both DNA methylation and hypomethylation status and induces cerebellar and cerebral cortex DNA damage in the prenatal period. Exogenous curcumin may have protective effect on PCBs-induced DNA damage in cerebellum and cerebral cortex.

Micro-computed tomography: a new diagnostic tool in postmortem assessment of brain anatomy in small fetuses.

PURPOSE: The aim of our study was to evaluate the postmortem micro-CT anatomy of early fetal human fetal brains, either in situ or isolated. METHODS: We studied 12 ex vivo specimens, 9 whole human fetuses (9-18 GW), and 3 isolated samples (16-26 GW). Specimens were fixed in formalin, then immersed in Lugol solution. Images were evaluated by two neuroradiologists. The depiction of CNS structures was defined based on the comparison between micro-CT images and a reference histologic anatomical Atlas of human brain development. RESULTS: Micro-CT provided informative high-resolution brain images in all cases, with the exception of one case (9 weeks) due to advanced maceration. All major CNS structures (i.e., brain hemispheres, layering, ventricles, germinal neuroepithelium, basal ganglia, corpus callosum, major cranial nerves, and structures of the head and neck) were recognizable. CONCLUSIONS: Micro-CT imaging of the early fetal brain is feasible and provides high-quality images that correlate with the histological Atlas of the human brain, offering multiplanar and volumetric images that can be stored and shared for clinical, teaching, and research purposes.

Socio-economic status and the developing brain in adolescence: A systematic review.

Socioeconomic status is associated with differences in social, cognitive, and behavioral outcomes for adolescents. Correspondingly, the period reflects continued dynamic, complex, and adaptive brain development. Research demonstrates associations between the developing adolescent brain and SES; however, such research has not been systematically integrated. We undertook a systematic search of studies and review 21 papers that examined both SES and brain development or functioning as measured during adolescence or young adulthood in nonclinical populations (13-25 years old). Few studies focused on architecture and such findings were varied. The majority of studies focused on functioning with two themes emerging. First, studies demonstrate different activation in regions of interest to cognitive and behavioral tasks relative to SES. Second, when similar neurological activation is evident, they can be related to different behavioral observations relative to SES. There is also evidence of different neurological functioning associated with SES with regard to different conceptualizations and coding of SES. Further, some of the reviewed studies identified potential mediators to the relationship, such as parenting practices, stress, and IQ. Overall, the findings suggest it is important to consider SES and neighborhood context within neuroscience research and practice.

Assessment of prenatal cerebral and cardiac metabolic changes in a rabbit model of fetal growth restriction based on 13C-labelled substrate infusions and ex vivo multinuclear HRMAS.

BACKGROUND: We have used a previously reported rabbit model of fetal growth restriction (FGR), reproducing perinatal neurodevelopmental and cardiovascular impairments, to investigate the main relative changes in cerebral and cardiac metabolism of term FGR fetuses during nutrient infusion. METHODS: FGR was induced in 9 pregnant New Zealand rabbits at 25 days of gestation: one horn used as FGR, by partial ligation of uteroplacental vessels, and the contralateral as control (appropriate for gestation age, AGA). At 30 days of gestation, fasted mothers under anesthesia were infused i.v. with 1-13C-glucose (4 mothers), 2-13C-acetate (3 mothers), or not infused (2 mothers). Fetal brain and heart samples were quickly harvested and frozen down. Brain cortex and heart apex regions from 30 fetuses were studied ex vivo by HRMAS at 4°C, acquiring multinuclear 1D and 2D spectra. The data were processed, quantified by peak deconvolution or integration, and normalized to sample weight. RESULTS: Most of the total 13C-labeling reaching the fetal brains/hearts (80-90%) was incorporated to alanine and lactate (cytosol), and to the glutamine-glutamate pool (mitochondria). Acetate-derived lactate (Lac C2C3) had a slower turnover in FGR brains (~ -20%). In FGR hearts, mitochondrial turnover of acetate-derived glutamine (Gln C4) was slower (-23%) and there was a stronger accumulation of phospholipid breakdown products (glycerophosphoethanolamine and glycerophosphocholine, +50%), resembling the profile of non-infused control hearts. CONCLUSIONS: Our results indicate specific functional changes in cerebral and cardiac metabolism of FGR fetuses under nutrient infusion, suggesting glial impairment and restricted mitochondrial metabolism concomitant with slower cell membrane turnover in cardiomyocytes, respectively. These prenatal metabolic changes underlie neurodevelopmental and cardiovascular problems observed in this FGR model and in clinical patients, paving the way for future studies aimed at evaluating metabolic function postnatally and in response to stress and/or treatment.

Imaging Evidence of the Effect of Socio-Economic Status on Brain Structure and Development.

Numerous studies have shown an association between children's socio-economic status (SES) and disparities in neurocognitive development, achievements, and function later in life. Research focus has recently shifted to imaging of the brain's response to the child's environment. This review summarizes the emerging studies on the influences of early-life SES on brain structure and development, and addresses the relation between brain development and enriched environments. The studies provide evidence of significant associations between SES and brain structure, growth and maturation, not only in healthy infants and children but also in infants with medical conditions. This suggests that the relation between SES and later-life function and achievements operates through alterations in brain maturation. Although the brain changes seem to persist without intervention, animal models of environmental enrichment show the potential of SES-related brain changes to be reversible and dynamic. This review underscores the critical need for reducing the impact of socio-economic disparities and early targeted and prolonged interventions, and highlights the potential of these interventions leading to optimal opportunities for our youngest.

Sensitive neurotoxicity assessment of bisphenol A using double immunocytochemistry of DCX and MAP2.

Bisphenol A (BPA) is an environmental toxin widely used in manufacturing industries. Studies conducted on the neurotoxicity of BPA demonstrated that at excessive, high concentrations (≥ 200 µM) adverse responses occurred which were not detectable using traditional toxicity tests at lower chemical quantities than 200 µM. Thus, a method capable of effectively detecting neurotoxicity at low concentrations (≤ 100 µM) was devised. Bisphenol A-mediated neurotoxicity was examined in primary cultured neurons using various methods, including Western blot, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity and reactive oxygen species assays. These methods confirmed BPA-induced toxicity at 200 µM, but no marked effect was observed at concentrations below 200 µM. However, when immunocytochemistry (ICC) was performed using a co-immunofluorescence assay of doublecortin (DCX) and microtubule-associated protein 2 (MAP2), BPA adversely affected neuronal maturation in neural progenitor cells at concentrations as low as 100 µM, at which the three traditional methods failed to detect any neurotoxic effect. Our DCX/MAP2 ICC findings indicate that low concentrations of BPA are toxic to developing neurons, and suggest that the devised double ICC technique might provide an effective means of assessing neurotoxic effects of environmental toxins at low concentrations.

Quantitative Assessment of Normal Fetal Brain Myelination Using Fast Macromolecular Proton Fraction Mapping.

BACKGROUND AND PURPOSE: Fast macromolecular proton fraction mapping is a recently emerged MRI method for quantitative myelin imaging. Our aim was to develop a clinically targeted technique for macromolecular proton fraction mapping of the fetal brain and test its capability to characterize normal prenatal myelination. MATERIALS AND METHODS: This prospective study included 41 pregnant women (gestational age range, 18-38 weeks) without abnormal findings on fetal brain MR imaging performed for clinical indications. A fast fetal brain macromolecular proton fraction mapping protocol was implemented on a clinical 1.5T MR imaging scanner without software modifications and was performed after a clinical examination with an additional scan time of <5 minutes. 3D macromolecular proton fraction maps were reconstructed from magnetization transfer-weighted, T1-weighted, and proton density-weighted images by the single-point method. Mean macromolecular proton fraction in the brain stem, cerebellum, and thalamus and frontal, temporal, and occipital WM was compared between structures and pregnancy trimesters using analysis of variance. Gestational age dependence of the macromolecular proton fraction was assessed using the Pearson correlation coefficient (r). RESULTS: The mean macromolecular proton fraction in the fetal brain structures varied between 2.3% and 4.3%, being 5-fold lower than macromolecular proton fraction in adult WM. The macromolecular proton fraction in the third trimester was higher compared with the second trimester in the brain stem, cerebellum, and thalamus. The highest macromolecular proton fraction was observed in the brain stem, followed by the thalamus, cerebellum, and cerebral WM. The macromolecular proton fraction in the brain stem, cerebellum, and thalamus strongly correlated with gestational age (r = 0.88, 0.80, and 0.73; P < .001). No significant correlations were found for cerebral WM regions. CONCLUSIONS: Myelin is the main factor determining macromolecular proton fraction in brain tissues. Macromolecular proton fraction mapping is sensitive to the earliest stages of the fetal brain myelination and can be implemented in a clinical setting.

Neurodevelopment: The Impact of Nutrition and Inflammation During Preconception and Pregnancy in Low-Resource Settings.

The rapid pace of fetal development by far exceeds any other stage of the life span, and thus, environmental influences can profoundly alter the developmental course. Stress during the prenatal period, including malnutrition and inflammation, impact maternal and fetal neurodevelopment with long-term consequences for physical and mental health of both the mother and her child. One primary consequence of maternal malnutrition, inflammation, and other sources of prenatal stress is a poor birth outcome, such as prematurity or growth restriction. These phenotypes are often used as indications of prenatal adversity. In fact, the original evidence supporting the fetal programming hypothesis came from studies documenting an association between birth phenotype and the development of subsequent physical and mental health problems. Fetal growth restriction in both term and preterm infants is associated with neonatal morbidities and a wide variety of behavioral and psychological diagnoses in childhood and adolescence, including attention-deficit/hyperactivity disorder, anxiety, depression, internalizing and thought problems, poor social skills, and autism spectrum disorder. Improving maternal-child health requires interventions that begin before pregnancy and continue throughout gestation and into the postpartum period. Such interventions might include supporting pregnancy intention, maternal nutrition, health/medical care, mental health, and providing social support. This article discusses the impact of maternal nutrition and inflammation during preconception and pregnancy among women living in low-resource settings, with an emphasis on key knowledge gaps that need to be addressed to guide program and policy decisions at local, regional and global levels.

The assessment of fetal brain growth in diabetic pregnancy using in utero magnetic resonance imaging.

AIM: To assess fetal brain growth over the third trimester in pregnant women with diabetes using in utero magnetic resonance imaging (iuMRI) to determine if greater brain growth occurs in type 1 (T1DM) when compared to gestational (GDM) diabetes mellitus. MATERIALS AND METHODS: Each consented participant was scanned at three fixed times during the third trimester using iuMRI. One hundred and fifty-seven patients were approached, 48 participants were recruited, and 36 complete data sets were analysed. Three-dimensional (3D) iuMRI volume data sets were manually segmented using software to construct models of the fetal brain from which brain volumes could be calculated. Inter-rater analysis was performed, and volume differences and growth rates were compared between T1DM and GDM. RESULTS: Recruitment proved difficult with low uptake and high attrition rates (77.1%). Inter-rater analysis revealed excellent correlation (intraclass correlation coefficient=0.93, p<0.001) and agreement with no significant difference between operators (p=0.194). There was no evidence of increased brain volume in the T1DM group. Growth rates between visit 1 and 3 for T1DM and GDM were not significantly different (p=0.095). CONCLUSION: T1DM brain volumes were not significantly larger than GDM volumes and there was no significant divergence of brain growth over the third trimester. Constructing volume models from 3D iuMRI acquisitions is a novel technique that can be used to assess fetal brain growth. No specialist software or knowledge is required. Larger studies attempting to recruit pregnant women in the later stages of pregnancy should employ multicentre recruitment to overcome recruitment difficulties and high attrition rates.

Assessment of sex specific endocrine disrupting effects in the prenatal and pre-pubertal rodent brain.

BACKGROUND: Brain sex differences are found in nearly every region of the brain and fundamental to sexually dimorphic behaviors as well as disorders of the brain and behavior. These differences are organized during gestation and early adolescence and detectable prior to puberty. Endocrine disrupting compounds (EDCs) interfere with hormone action and are thus prenatal exposure is hypothesized to disrupt the formation of sex differences, and contribute to the increased prevalence of pediatric neuropsychiatric disorders that present with a sex bias. OBJECTIVE: Available evidence for the ability of EDCs to impact the emergence of brain sex differences in the rodent brain was reviewed here, with a focus on effects detected at or before puberty. METHODS: The peer-reviewed literature was searched using PubMed, and all relevant papers published by January 31, 2015 were incorporated. Endpoints of interest included molecular cellular and neuroanatomical effects. Studies on behavioral endpoints were not included because numerous reviews of that literature are available. RESULTS: The hypothalamus was found to be particularly affected by estrogenic EDCs in a sex, time, and exposure dependent manner. The hippocampus also appears vulnerable to endocrine disruption by BPA and PCBs although there is little evidence from the pre-pubertal literature to make any conclusions about sex-specific effects. Gestational EDC exposure can alter fetal neurogenesis and gene expression throughout the brain including the cortex and cerebellum. The available literature primarily focuses on a few, well characterized EDCs, but little data is available for emerging contaminants. CONCLUSION: The developmental EDC exposure literature demonstrates evidence of altered neurodevelopment as early as fetal life, with sex specific effects observed throughout the brain even before puberty.

Unsupervised lineage-based characterization of primate precursors reveals high proliferative and morphological diversity in the OSVZ.

Generation of the primate cortex is characterized by the diversity of cortical precursors and the complexity of their lineage relationships. Recent studies have reported miscellaneous precursor types based on observer classification of cell biology features including morphology, stemness, and proliferative behavior. Here we use an unsupervised machine learning method for Hidden Markov Trees (HMTs), which can be applied to large datasets to classify precursors on the basis of morphology, cell-cycle length, and behavior during mitosis. The unbiased lineage analysis automatically identifies cell types by applying a lineage-based clustering and model-learning algorithm to a macaque corticogenesis dataset. The algorithmic results validate previously reported observer classification of precursor types and show numerous advantages: It predicts a higher diversity of progenitors and numerous potential transitions between precursor types. The HMT model can be initialized to learn a user-defined number of distinct classes of precursors. This makes it possible to 1) reveal as yet undetected precursor types in view of exploring the significant features of precursors with respect to specific cellular processes; and 2) explore specific lineage features. For example, most precursors in the experimental dataset exhibit bidirectional transitions. Constraining the directionality in the HMT model leads to a reduction in precursor diversity following multiple divisions, thereby suggesting that one impact of bidirectionality in corticogenesis is to maintain precursor diversity. In this way we show that unsupervised lineage analysis provides a valuable methodology for investigating fundamental features of corticogenesis.

Assessment of Intracranial Structure Volumes in Fetuses With Growth Restriction by 3-Dimensional Sonography Using the Extended Imaging Virtual Organ Computer-Aided Analysis Method.

OBJECTIVES: To assess intracranial structure volumes by 3-dimensional (3D) sonography in fetuses with growth restriction. METHODS: We conducted a prospective cross-sectional case-control study involving 59 fetuses with growth restriction (38 fetuses with estimated weight <3rd percentile and 21 fetuses with estimated weight between 3rd and 10th percentiles, according to Hadlock et al [Radiology 1984; 150:535-540]) and 54 controls between 24 and 34 weeks' gestation. The following fetal intracranial structure volumes were assessed: cerebellum, brain, and frontal region. The volume was assessed by 3D sonography using the extended imaging virtual organ computer-aided analysis method with 10 sequential planes. Analysis of variance was used to compare fetal groups. The intraclass correlation coefficient was used to assess intraobserver and interobserver reproducibility. RESULTS: Statistical significance between the brain, frontal region, and cerebellar volumes and a relationship between the frontal region and the brain in fetuses with estimated weights below the 3rd percentile and controls were observed (P < .001; P < .001; and P = .002; and P = .008, respectively). Good intraobserver and interobserver reproducibility was observed for the fetal brain, frontal region, and cerebellar volumes, with intraclass correlation coefficients of 0.998, 0.997, 0.997, 0.999, 0.997, and 0.998, respectively. CONCLUSIONS: The intracranial structure volumes assessed by 3D sonography using the extended imaging virtual organ computer-aided analysis method were reduced in fetuses with growth restriction (estimated weight <3rd percentile).

[Development of Higher Brain Function Tests in Rodents and Its Application to Neurotoxicity Assessment of Environmental Chemicals].

The brain during developmental period is thought to be highly sensitive to environmental insults including exposure to chemicals. However, it has been extremely difficult to detect and assess the features and degree of adversity particularly at low exposure levels. I describe here the effects of maternal exposure to dioxin on higher brain functions later in life, which we detected using our originally developed behavioral tests for quantifying higher brain functions in rodents. We first found changes in the mRNA expression levels of glutamate NMDA receptor subunits that have critical roles in learning and memory function in the neocortex and hippocampus. To assess the neocortical and hippocampal functions in rats, we established novel behavioral tests for assessing paired-associate learning, which is the hippocampal and medial prefrontal NMDA-dependent function. Maternal exposure to dioxin, at a low level of which does not affect simple memory formation, resulted in the disturbance of the paired-associate learning. On the basis of the above learning paradigm, we next developed a behavioral flexibility task and a social competitive task for mice using the automated behavioral assessment system 'IntelliCage': this system can accommodate 16 mice at the same time to monitor and record their behavior. Using this system, we found that male mice born to dams exposed to very low doses of dioxin showed inflexibility in a serial reversal learning task and socially low-dominance behavior under a competitive situation. Immunohistochemical analysis of putative neuronal activity markers revealed hypoactivity in the medial prefrontal cortex (mPFC) of dioxin-exposed mice. We speculate that mPFC hypoactivity reflects the dioxin-induced higher brain dysfunction and may be associated with some psychiatric illnesses and related problems. These behavioral tests were found to be useful for studying the higher brain functions of rats and mice.

Assessment of oxidative stress in hippocampus, cerebellum and frontal cortex in rat pups exposed to lead (Pb) during specific periods of initial brain development.

Epidemiological studies in children have proved that lead (Pb) exposure causes deficits in neural and cognitive functions. The present study assessed the oxidative stress on postnatal day 30, in the hippocampus, cerebellum and frontal cortex of rat pups exposed to Pb during specific periods of early brain development. Five groups of rat pups were investigated, and 0.2% Pb acetate in drinking was the dosage used. (i) Gestation and lactation (GL) group (n = 9) of rat pups was exposed to Pb during gestation and lactation through their mother, (ii) gestation (G) group (n = 9) of rat pups was exposed to Pb during gestation only, (iii) lactation (L) group (n = 9) of rat pups was exposed to Pb during lactation only, (iv) pre-gestation (PG) group (n = 9) of rat pups was born to mothers who were exposed to Pb for 1 month before conception, and (v) normal control (NC) (n = 9) group of rats pups had no exposure to Pb during gestation and lactation period. From the present study, it is evident that Pb exposure during different periods of early brain development (GL, G, L and PG groups) causes oxidative stress and lactation period (postnatal period) of Pb exposure produces maximum oxidative stress.