Time-specific effects of ethanol exposure on cranial nerve nuclei: gastrulation and neuronogenesis

Biomarkers of Affective Dysregulation Associated with In Utero Exposure to EtOH

INTRODUCTION

Children with fetal alcohol spectrum disorders (FASD) exhibit behavioral and affective dysregulation, including hyperactivity and depression. The mechanisms are not known, but they could conceivably be due to postnatal social or environmental factors. However, we postulate that, more likely, the affective dysregulation is associated with the effects of EtOH exposure on the development of fetal serotonergic (5-HT) and/or dopaminergic (DA) pathways, i.e., pathways that in postnatal life are believed to regulate mood. Many women who use alcohol (ethanol, EtOH) during pregnancy suffer from depression and take selective serotonin reuptake inhibitors (SSRIs), which might influence these monoaminergic pathways in the fetus. Alternatively, monoaminergic pathway abnormalities might reflect a direct effect of EtOH on the fetal brain. To distinguish between these possibilities, we measured their expressions in fetal brains and in fetal brain-derived exosomes (FB-Es) isolated from the mothers' blood. We hypothesized that maternal use of EtOH and/or SSRIs during pregnancy would be associated with impaired fetal neural development, detectable as abnormal levels of monoaminergic and apoptotic biomarkers in FB-Es.

METHODS

Fetal brain tissues and maternal blood were collected at 9-23 weeks of pregnancy. EtOH groups were compared with unexposed controls matched for gestational age (GA). The expression of 84 genes associated with the DA and 5-HT pathways was analyzed by quantitative reverse transcription polymerase chain reaction (qRT-PCR) on microarrays. FB-Es also were assayed for serotonin transporter protein (SERT) and brain-derived neurotrophic factor (BDNF) by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Six EtOH-exposed human fetal brain samples were compared to SSRI- or polydrug-exposed samples and to unexposed controls. EtOH exposure was associated with significant upregulation of DA receptor D3 and 5-HT receptor HTR2C, while HTR3A was downregulated. Monoamine oxidase A (MAOA), MAOB, the serine/threonine kinase AKT3, and caspase-3 were upregulated, while mitogen-activated protein kinase 1 (MAPK1) and AKT2 were downregulated. ETOH was associated with significant upregulation of the DA transporter gene, while SERT was downregulated. There were significant correlations between EtOH exposure and (a) caspase-3 activation, (b) reduced SERT protein levels, and (c) reduced BDNF levels. SSRI exposure independently increased caspase-3 activity and downregulated SERT and BDNF. Early exposure to EtOH and SSRI together was associated synergistically with a significant upregulation of caspase-3 and a significant downregulation of SERT and BDNF. Reduced SERT and BDNF levels were strongly correlated with a reduction in eye diameter, a somatic manifestation of FASD.

CONCLUSIONS

Maternal use of EtOH and SSRI during pregnancy each was associated with changes in fetal brain monoamine pathways, consistent with potential mechanisms for the affective dysregulation associated with FASD.

Effects of In Utero EtOH Exposure on 18S Ribosomal RNA Processing: Contribution to Fetal Alcohol Spectrum Disorder

Fetal alcohol spectrum disorders (FASD) are leading causes of neurodevelopmental disability. The mechanisms by which alcohol (EtOH) disrupts fetal brain development are incompletely understood, as are the genetic factors that modify individual vulnerability. Because the phenotype abnormalities of FASD are so varied and widespread, we investigated whether fetal exposure to EtOH disrupts ribosome biogenesis and the processing of pre-ribosomal RNAs and ribosome assembly, by determining the effect of exposure to EtOH on the developmental expression of 18S rRNA and its cleaved forms, members of a novel class of short non-coding RNAs (srRNAs). In vitro neuronal cultures and fetal brains (11-22 weeks) were collected according to an IRB-approved protocol. Twenty EtOH-exposed brains from the first and second trimester were compared with ten unexposed controls matched for gestational age and fetal gender. Twenty fetal-brain-derived exosomes (FB-Es) were isolated from matching maternal blood. RNA was isolated using Qiagen RNA isolation kits. Fetal brain srRNA expression was quantified by ddPCR. srRNAs were expressed in the human brain and FB-Es during fetal development. EtOH exposure slightly decreased srRNA expression (1.1-fold; p = 0.03). Addition of srRNAs to in vitro neuronal cultures inhibited EtOH-induced caspase-3 activation (1.6-fold, p = 0.002) and increased cell survival (4.7%, p = 0.034). The addition of exogenous srRNAs reversed the EtOH-mediated downregulation of srRNAs (2-fold, p = 0.002). EtOH exposure suppressed expression of srRNAs in the developing brain, increased activity of caspase-3, and inhibited neuronal survival. Exogenous srRNAs reversed this effect, possibly by stabilizing endogenous srRNAs, or by increasing the association of cellular proteins with srRNAs, modifying gene transcription. Finally, the reduction in 18S rRNA levels correlated closely with the reduction in fetal eye diameter, an anatomical hallmark of FASD. The findings suggest a potential mechanism for EtOH-mediated neurotoxicity via alterations in 18S rRNA processing and the use of FB-Es for early diagnosis of FASD. Ribosome biogenesis may be a novel target to ameliorate FASD in utero or after birth. These findings are consistent with observations that gene-environment interactions contribute to FASD vulnerability.

Genetically programmed retinoic acid deficiency during gastrulation phenocopies most known developmental defects due to acute prenatal alcohol exposure in FASD

Fetal Alcohol Spectrum Disorder (FASD) arises from maternal consumption of alcohol during pregnancy affecting 2%-5% of the Western population. In Xenopus laevis studies, we showed that alcohol exposure during early gastrulation reduces retinoic acid (RA) levels at this critical embryonic stage inducing craniofacial malformations associated with Fetal Alcohol Syndrome. A genetic mouse model that induces a transient RA deficiency in the node during gastrulation is described. These mice recapitulate the phenotypes characteristic of prenatal alcohol exposure (PAE) suggesting a molecular etiology for the craniofacial malformations seen in children with FASD. Gsc ^+/Cyp26A1 mouse embryos have a reduced RA domain and expression in the developing frontonasal prominence region and delayed HoxA1 and HoxB1 expression at E8.5. These embryos also show aberrant neurofilament expression during cranial nerve formation at E10.5 and have significant FASD sentinel-like craniofacial phenotypes at E18.5. Gsc ^+/Cyp26A1 mice develop severe maxillary malocclusions in adulthood. Phenocopying the PAE-induced developmental malformations with a genetic model inducing RA deficiency during early gastrulation strongly supports the alcohol/vitamin A competition model as a major molecular etiology for the neurodevelopmental defects and craniofacial malformations seen in children with FASD.

Molecular Markers in Maternal Blood Exosomes Allow Early Detection of Fetal Alcohol Spectrum Disorders

Prenatal alcohol exposure can cause developmental abnormalities (fetal alcohol spectrum disorders; FASD), including small eyes, face and brain, and neurobehavioral deficits. These cannot be detected early in pregnancy with available imaging techniques. Early diagnosis could facilitate development of therapeutic interventions. Banked human fetal brains and eyes at 9−22 weeks’ gestation were paired with maternal blood samples, analyzed for morphometry, protein, and RNA expression, and apoptotic signaling. Alcohol (EtOH)-exposed (maternal self-report) fetuses were compared with unexposed controls matched for fetal age, sex, and maternal race. Fetal brain-derived exosomes (FB-E) were isolated from maternal blood and analyzed for protein, RNA, and apoptotic markers. EtOH use by mothers, assessed by self-report, was associated with reduced fetal eye diameter, brain size, and markers of synaptogenesis. Brain caspase-3 activity was increased. The reduction in eye and brain sizes were highly correlated with amount of EtOH intake and caspase-3 activity. Levels of several biomarkers in FB-E, most strikingly myelin basic protein (MBP; r > 0.9), correlated highly with morphological abnormalities. Reduction in FB-E MBP levels was highly correlated with EtOH exposure (p < 1.0 × 10−10). Although the morphological features of FAS appear long before they can be detected by live imaging, FB-E in the mother’s blood may contain markers, particularly MBP, that predict FASD.

Abnormal growth and morphogenesis of placenta at term is linked to adverse fetal development after perigestational alcohol consumption up to early gestation in mouse

BACKGROUND

Gestation alcohol consumption produces fetal growth restriction and malformations by affecting the embryo-fetal development. Recently a relationship between abnormal placentation and fetal malformation and intrauterine growth retardation has been suggested. However, the effects of perigestational alcohol ingestion up to early pregnancy on the placenta at term and its association with fetal abnormalities are little known.

METHODS

In female mice, ethanol 10% in water was administered for 15 days previous and up to days 4 (D4), 8 (D8), or 10 (D10) of gestation (TF), and gestation continues without ethanol exposure. Control females (CF) received ethanol-free water. At day 18, feto-placental units and implantation sites were studied.

RESULTS

TF had increased resorptions and only fetuses from D8-TF and D10-TF had significantly increased weights versus CF. D4 and D10-TF-placentas had significantly reduced weights. All TF had increased junctional zone (JZ) and reduced labyrinth (Lab) areas (PAS-histology and morphometry) compared with CF. Fetuses with mainly with craniofacial abnormalities and skeletal defects (Alizarin red staining), significantly increase; while the fetal bone density (alizarin color intensity, ImageJ) was reduced in D4, D8 and D10-TF versus CF. Although all TF-placentas were histo-structural affected, TF-abnormal fetuses had the most severe placental anomalies, with junctional abundant glycogenic cells into the labyrinth, disorganized labyrinthine vascularization with signs of leukocyte infiltrates and feto-maternal blood mix.

CONCLUSIONS

Perigestational alcohol consumption up to early gestation induces at term fetal growth alterations, dysmorphology and defective skeleton, linked to deficient growth and abnormal morphogenesis of placenta, highlighting insight into the prenatal etiology of FASD.

Long-term protective effect of PACAP in a fetal alcohol syndrome (FAS) model

Prenatal ethanol exposure provokes teratogenic effects, due to oxidative stress and massive neuronal apoptosis in the developing brain that result in lifelong behavioral abnormalities. PACAP exerts anti-oxidative and neuroprotective activities on neuronal cells, and prevents ethanol neurotoxicity. The present study focused on the ability of PACAP to protect the brain of 30-day-old mice (P30) from prenatal alcohol exposure induced oxidative damage and toxicity. Pregnant mice were divided randomly into 4 groups, i.e. control group, ethanol group (1.5 g/kg ip daily injection), PACAP group (5 μg intrauterine daily injection) and an ethanol plus PACAP group. Offspring prenatally exposed to ethanol had decreased body weight and reduced cell survival. Moreover, production of ROS was sharply enhanced in the brain of prenatal ethanol-exposed animals, associated with an elevation in the activity of the antioxidant enzymes, and an increase of oxidative damages as shown by the accumulation of the lipid oxidation marker malondialdehyde and of protein carbonyl compounds. Intrauterine administration of PACAP during the gestational period restored the endogenous antioxidant system, prevented ROS overproduction and promoted the survival of dissociated cells from animals prenatally exposed to ethanol. Behavioral tests revealed that P30 animals exposed to ethanol during the prenatal period exhibited reduced motor activity, altered exploratory interest and increased anxiety. However, PACAP treatment significantly attenuated these behavioral impairments. This study demonstrates that PACAP exerts a potent neuroprotective effect against alcohol toxicity during brain development, and indicates that PACAP and/or PACAP analogs might be a useful tool for treatment of alcohol intoxication during pregnancy.

Ethanol-mediated alterations in oligodendrocyte differentiation in the developing brain

INTRODUCTION

Alterations of white matter integrity and subsequent white matter structural deficits are consistent findings in Fetal Alcohol Syndrome (FAS), but knowledge regarding the molecular mechanisms underlying these abnormalities is incomplete. Experimental rodent models of FAS have shown dysregulation of cytokine expression leading to apoptosis of oligodendrocyte precursor cells (OPCs) and altered oligodendrocyte (OL) differentiation, but whether this is representative of human FAS pathogenesis has not been determined.

METHODS

Fetal brain tissue (12.2-21.4 weeks gestation) from subjects undergoing elective termination of pregnancy was collected according to an IRB-approved protocol. Ethanol (EtOH) exposure status was classified based on a detailed face-to-face questionnaire adapted from the National Institute on Alcohol Abuse and Alcoholism Prenatal Alcohol and Sudden Infant Death Syndrome and Stillbirth (PASS) study. Twenty EtOH-exposed fetuses were compared with 20 gestational age matched controls. Cytokine and OPC marker mRNA expression was quantified by Real-Time Polymerase chain reaction (qRT-PCR). Patterns of protein expression of OPC markers and active Capase-3 were studied by Fluorescence Activated Cell Sorting (FACS).

RESULTS

EtOH exposure was associated with reduced markers of cell viability, OPC differentiation, and OL maturation, while early OL differentiation markers were unchanged or increased. Expression of mRNAs for proteins specific to more mature forms of OL lineage (platelet-derived growth factor α (PDGFRα) and myelin basic protein (MBP) was lower in the EtOH group than in controls. Expression of the multifunctional growth and differentiation-promoting growth factor IGF-1, which is essential for normal development, also was reduced. Reductions were not observed for markers of early stages of OL differentiation, including Nuclear transcription factor NK-2 homeobox locus 2 (Nkx2.2). Expression of mRNAs for the proinflammatory cytokine, tumor necrosis factor-α (TNFα), and several proinflammatory chemokines was higher in the EtOH group compared to controls, including: Growth regulated protein alpha/chemokine (C-X-C motif) ligand 1 (GRO-α/CXCL1), Interleukin 8/chemokine (C-X-C motif) ligand 8 (IL8/CXCL8), Chemokine (C-X-C motif) ligand 6/Granulocyte chemotactic protein 2 (CXCL16/GCP2), epithelial-derived neutrophil-activating protein 78/chemokine (C-X-C motif) ligand 5 (ENA-78/CXCL5), monocyte chemoattractant protein-1 (MCP-1). EtOH exposure also was associated with an increase in the proportion of cells expressing markers of early stage OPCs, such as A2B5 and NG2. Finally, apoptosis (measured by caspase-3 activation) was increased substantially in the EtOH group compared to controls.

CONCLUSION

Prenatal EtOH exposure is associated with excessive OL apoptosis and/or delayed OL maturation in human fetal brain. This is accompanied by markedly dysregulated expression of several chemokines and cytokines, in a pattern predictive of increased OL cytotoxicity and reduced OL differentiation. These findings are consistent with findings in animal models of FAS.

Unveiling Sex-Based Differences in the Effects of Alcohol Abuse: A Comprehensive Functional Meta-Analysis of Transcriptomic Studies

The abuse of alcohol, one of the most popular psychoactive substances, can cause several pathological and psychological consequences, including alcohol use disorder (AUD). An impaired ability to stop or control alcohol intake despite adverse health or social consequences characterize AUD. While AUDs predominantly occur in men, growing evidence suggests the existence of distinct cognitive and biological consequences of alcohol dependence in women. The molecular and physiological mechanisms participating in these differential effects remain unknown. Transcriptomic technology permits the detection of the biological mechanisms responsible for such sex-based differences, which supports the subsequent development of novel personalized therapeutics to treat AUD. We conducted a systematic review and meta-analysis of transcriptomics studies regarding alcohol dependence in humans with representation from both sexes. For each study, we processed and analyzed transcriptomic data to obtain a functional profile of pathways and biological functions and then integrated the resulting data by meta-analysis to characterize any sex-based transcriptomic differences associated with AUD. Global results of the transcriptomic analysis revealed the association of decreased tissue regeneration, embryo malformations, altered intracellular transport, and increased rate of RNA and protein replacement with female AUD patients. Meanwhile, our analysis indicated that increased inflammatory response and blood pressure and a reduction in DNA repair capabilities are associated with male AUD patients. In summary, our functional meta-analysis of transcriptomic studies provides evidence for differential biological mechanisms of AUD patients of differing sex.

Episodic Prenatal Exposure To Ethanol Affects Postnatal Neurogenesis In The Macaque Dentate Gyrus And Visual Recognition Memory

Fetal alcohol syndrome (FAS) is a prime cause of cognitive dysfunction. The present study tested the hypotheses (a) that gestational ethanol exposure results in deficits in hippocampal-related behaviors and associated neurogenesis and (b) that the period of gastrulation is a time of vulnerability. Pregnant macaques were intubated with ethanol or saline once per week for 3, 6, or 24 weeks. Exposures included or omitted the period of gastrulation. Offspring were given behavioral tests including a Visual-Paired Comparison (VPC), a hippocampal-associated memory task, and euthanized as adolescents. Their dentate gyri were processed for immunohistochemical identification of cells passing through the cell cycle (Ki-67 and proliferating cell nuclear antigen), exiting the cell cycle (p21), or passing through early stages of neuronal morphogenesis (Tuj1). Performance in neurobehavioral tasks was unaffected by ethanol exposure, the notable exception being performance in the VPC that was poorer for macaques exposed to ethanol including gastrulation. Anatomical studies show that the expression of Ki-67 was greater and ratio of p21-positive cells to the ratio of Ki-67-expressing cells was lower in animals in which the ethanol exposure included gastrulation. On the other hand, no ethanol-induced differences in TuJ1 expression were detected. Thus, the dentate gyrus is a bellwether of long-term consequences of gestational ethanol exposure. Targeted effects of ethanol on early neural generation (cell cycle and cycle exit) correlate with the timing-dependent degradation in VPC performance and exposure during gastrulation results in notable deficits. These changes evidence a pattern of fetal programming underlying FAS.

Differentially sensitive neuronal subpopulations in the central nervous system and the formation of hindbrain heterotopias in ethanol-exposed zebrafish

BACKGROUND

A cardinal feature of prenatal ethanol exposure is CNS damage, resulting in a continuum of neurological and behavioral impairments that are described by the term fetal alcohol spectrum disorders (FASD). FASDs are variable and depend on several factors, including the amount, timing, and duration of prenatal ethanol exposure. To enhance interventions for CNS dysfunction, it is necessary to identify ethanol-sensitive neuronal populations and expand the understanding of factors that modify ethanol teratogenesis.

METHODS

To investigate the susceptibility of different neuronal subtypes, we exposed transgenic zebrafish (Danio rerio) to several ethanol concentrations (0.25, 0.5, 1.0, 1.5, or 2.0%), at different hours post fertilization (hpf; 0, 6, or 24 hpf), for various durations (0-24, 0-48, 4-24, 6-24, 6-48,or 24-48 hpf). Following exposure, embryo survival rates were determined, and CNS neurogenesis, differentiation, and patterning were assessed.

RESULTS

Embryo survival rates decrease as ethanol concentrations increase and drastically decline when exposed from 0-24 hpf compared to 4-24 hpf. Abnormal tangential migration of facial motor neurons is observed in isl1:gfp embryos exposed to ethanol concentrations as low as 0.25%, and the formation of IVth ventricle heterotopias are revealed by embryos exposed to ≥1.0% ethanol. Whereas, expression of olig2:dsred and ptf1a:gfp in the cerebellum and spinal cord are largely unaffected. While levels of etv4 mRNA are overtly resistant to ethanol, we observe significant reductions in ptch2 mRNA levels.

CONCLUSIONS

These data show differentially sensitive CNS neuron subpopulations with susceptibility to low levels of ethanol. In addition, these data reveal the formation of ethanol-induced hindbrain heterotopias.

Variations in brain defects result from cellular mosaicism in the activation of heat shock signalling

Repetitive prenatal exposure to identical or similar doses of harmful agents results in highly variable and unpredictable negative effects on fetal brain development ranging in severity from high to little or none. However, the molecular and cellular basis of this variability is not well understood. This study reports that exposure of mouse and human embryonic brain tissues to equal doses of harmful chemicals, such as ethanol, activates the primary stress response transcription factor heat shock factor 1 (Hsf1) in a highly variable and stochastic manner. While Hsf1 is essential for protecting the embryonic brain from environmental stress, excessive activation impairs critical developmental events such as neuronal migration. Our results suggest that mosaic activation of Hsf1 within the embryonic brain in response to prenatal environmental stress exposure may contribute to the resulting generation of phenotypic variations observed in complex congenital brain disorders.

Prenatal exposure to environmental stressors is known to impair cortical development. Here the authors show that upon exposure to stressors, the activation of Hsf1-Hsp signalling is highly variable among cells in the embryonic cortex of mice, and either too much or too little activation can result in defects in cortical development.

Direct effects of ethanol on neuronal differentiation: An in vitro analysis of viability and morphology

The deleterious effects of ethanol (EtOH) on the brain have been widely described, but its effects on the neuronal cytoskeleton during differentiation have not yet been firmly established. In this context, our aim was to investigate the direct effect of EtOH on cortical neurons during the period of differentiation. Primary cultures of cortical neurons obtained from 1-day-old rats were exposed to EtOH after 7days of culture, and viability and morphology were analyzed at structural and ultrastructural levels after 24-h EtOH exposure. EtOH caused a significant reduction of 73±7% in the viability of cultured cortical neurons, by preferentially inducing apoptotic cellular death. This effect was accompanied by an increase in caspase 3 and 9 expression. Furthermore, EtOH induced a reduction in total dendrite length and in the number of dendrites per cell. Ultrastructural studies showed that EtOH increased the number of lipidic vacuoles, lysosomes and multilamellar vesicles and induced a dilated endoplasmatic reticulum lumen and a disorganized Golgi apparatus with a ring-shape appearance. Microtubules showed a disorganized distribution. Apposition between pre- and postsynaptic membranes without a defined synaptic cleft and a delay in presynaptic vesicle organization were also observed. Synaptophysin and PSD95 expression, proteins pre- and postsynaptically located, were reduced in EtOH-exposed cultures. Overall, our study shows that EtOH induces neuronal apoptosis and changes in the cytoskeleton and membrane proteins related with the establishment of mature synapses. These direct effects of EtOH on neurons may partially explain its effects on brain development.

Prenatal ethanol exposure impairs spatial cognition and synaptic plasticity in female rats

Chronic prenatal ethanol exposure (CPEE) can impair long-term potentiation (LTP) in the male hippocampus. Sexually specific alterations were frequently reported in female animals that had been prenatally exposed to ethanol. This study aimed to examine the effects of CPEE on spatial learning and memory, as well as on hippocampal synaptic plasticity in female adolescent rats. Female offspring were selected from dams that had been exposed to 4 g/kg/day of ethanol throughout the gestational period. Subsequently, performance in the Morris water maze (MWM) was determined, while LTP and depotentiation were measured in the hippocampal CA3-CA1 pathway. In the behavioral test, the escape latencies in both initial and reversal training stages were significantly prolonged. Interestingly, LTP was considerably enhanced while depotentiation was significantly depressed. Our results suggest a critical role of synaptic plasticity balance, which may prominently contribute to the cognitive deficits present in CPEE offspring.

Low and moderate prenatal ethanol exposures of mice during gastrulation or neurulation delays neurobehavioral development

Human and animal studies show significant delays in neurobehavioral development in offspring after prolonged prenatal exposure to moderate and high ethanol doses resulting in high blood alcohol concentration (BECs). However, none have investigated the effects of lower ethanol doses given acutely during specific developmental time periods. Here, we sought to create a mouse model for modest and circumscribed human drinking during the 3rd and 4th weeks of pregnancy. We acutely treated mice during embryo gastrulation on gestational day (GD) 7 or neurulation on GD8 with a low or moderate ethanol dose given via gavage that resulted in BECs of 107 and 177 mg/dl, respectively. We assessed neonatal physical development (pinnae unfolding, and eye opening); weight gain from postnatal day (PD) 3-65; and neurobehavioral maturation (pivoting, walking, cliff aversion, surface righting, vertical screen grasp, and rope balance) from PD3 to 17. We used a multiple linear regression model to determine the effects of dose, sex, day of treatment and birth in animals dosed during gastrulation or neurulation, relative to their vehicle controls. We found that ethanol exposure during both time points (GD7 and GD8) resulted in some delays of physical development and significant sensorimotor delays of pivoting, walking, and thick rope balance, as well as additional significant delays in cliff aversion and surface righting after GD8 treatment. We also found that treatment with the low ethanol dose more frequently affected neurobehavioral development of the surviving pups than treatment with the moderate ethanol dose, possibly due to a loss of severely affected offspring. Finally, mice born prematurely were delayed in their physical and sensorimotor development. Importantly, we showed that brief exposure to low dose ethanol, if administered during vulnerable periods of neuroanatomical development, results in significant neurobehavioral delays in neonatal mice. We thus expand concerns about alcohol consumption during the 3rd and 4th weeks of human pregnancy to include occasional light to moderate drinking.

Acute exposure to ethanol on gestational day 15 affects social motivation of female offspring

Alterations in social behavior are a hallmark of many neurodevelopmental disorders in humans. In rodents, social behavior is affected by prenatal insults. The outcomes are dependent on the timing of the insult as well as the sex and age of the animal tested. The limbic system is particularly important for social behavior, and a peak of neurogenesis within this system occurs on gestational day (G)15. Neurons appear particularly vulnerable to ethanol insult around the time they become post-mitotic. We tested the hypothesis that acute exposure to ethanol on G15 would result in significant social behavior deficits. Accordingly, Long Evans pregnant females were injected with ethanol (2.9 g/kg) or an equivalent volume of saline on G15. Offspring were assessed in a modified social interaction test on postnatal day (P) 28, P42, or P75, i.e., during early adolescence, late adolescence, or young adulthood. Prenatal ethanol exposure decreased social investigation in P28 females and transformed social preference into social avoidance in 75-day-old females. Contact behavior, play fighting, and locomotor activity differed as a function of age, but were not significantly affected by ethanol exposure. Males demonstrated significantly more contact behavior and play fighting at P42 than at P28 or P70, whereas there were no age-related changes in females. Adult females showed more locomotor activity than adult males. Overall, prenatal ethanol exposure on G15 enhanced social anxiety in females, with these effects seen in adulthood only.

Acute prenatal exposure to a moderate dose of valproic acid increases social behavior and alters gene expression in rats

Prenatal exposure to moderate doses of valproic acid (VPA) produces brainstem abnormalities, while higher doses of this teratogen elicit social deficits in the rat. In this pilot study, we examined effects of prenatal exposure to a moderate dose of VPA on behavior and on transcriptomic expression in three brain regions that mediate social behavior. Pregnant Long Evans rats were injected with 350 mg/kg VPA or saline on gestational day 13. A modified social interaction test was used to assess social behavior and social preference/avoidance during early and late adolescence and in adulthood. VPA-exposed animals demonstrated more social investigation and play fighting than control animals. Social investigation, play fighting, and contact behavior also differed as a function of age; the frequency of these behaviors increased in late adolescence. Social preference and locomotor activity under social circumstances were unaffected by treatment or age. Thus, a moderate prenatal dose of VPA produces behavioral alterations that are substantially different from the outcomes that occur following exposure to a higher dose. At adulthood, VPA-exposed subjects exhibited transcriptomic abnormalities in three brain regions: anterior amygdala, cerebellar vermis, and orbitofrontal cortex. A common feature among the proteins encoded by the dysregulated genes was their ability to be modulated by acetylation. Analysis of the expression of individual exons also revealed that genes involved in post-translational modification and epigenetic regulation had particular isoforms that were ubiquitously dysregulated across brain regions. The vulnerability of these genes to the epigenetic effects of VPA may highlight potential mechanisms by which prenatal VPA exposure alters the development of social behavior.

Loss of motoneurons in the ventral compartment of the rat hypoglossal nucleus following early postnatal exposure to alcohol

Perinatal alcohol exposure (AE) has multiple detrimental effects on cognitive and various behavioral outcomes, but little is known about its impact on the autonomic functions. In a rat model of fetal alcohol spectrum disorders (FASD), we investigated neurochemical and neuroanatomical alterations in two brainstem nuclei, the hypoglossal nucleus (XIIn) and the dorsal nucleus of the vagus nerve (Xdn). One group of male Sprague-Dawley rats (n=6) received 2.625 g/kg ethanol intragastrically twice daily on postnatal days (PD) 4-9, a period equivalent to the third trimester of human pregnancy, and another group (n=6) was sham-intubated. On PD 18-19, the rats were perfused and medullary sections were immunohistochemically processed for choline acetyltransferase (ChAT) or two aminergic receptors that mediate excitatory drive to motoneurons, α₁-adrenergic (α₁-R) and serotonin 2A (5-HT(2A)-R), and c-Fos. Based on ChAT labeling, AE rats had reduced numbers of motoneurons in the ventral XIIn (XIIn-v; 35.4±1.3 motoneurons per side and section vs. 40.0±1.2, p=0.022), but not in the dorsal XIIn or Xdn. Consistent with ChAT data, both the numbers of α₁-R-labeled motoneurons in the XIIn-v and the area of the XIIn-v measured using 5-HT(2A)-R staining were significantly smaller in AE rats (19.7±1.5 vs. 25.0±1.4, p=0.031 and 0.063 mm² ±0.002 vs. 0.074±0.002, p=0.002, respectively). Concurrently, both 5-HT(2A)-R and c-Fos staining tended to be higher in AE rats, suggesting an increased activation. Thus, postnatal AE causes motoneuronal loss in the XIIn-v. This may compromise upper airway control and contribute to increased risk of upper airway obstructions and sudden infant death in FASD victims.

Effects of early postnatal exposure to ethanol on retinal ganglion cell morphology and numbers of neurons in the dorsolateral geniculate in mice

BACKGROUND

The adverse effects of fetal and early postnatal ethanol intoxication on peripheral organs and the central nervous system are well documented. Ocular defects have also been reported in about 90% of children with fetal alcohol syndrome, including microphthalmia, loss of neurons in the retinal ganglion cell (RGC) layer, optic nerve hypoplasia, and dysmyelination. However, little is known about perinatal ethanol effects on retinal cell morphology. Examination of the potential toxic effects of alcohol on the neuron architecture is important because the changes in dendritic geometry and synapse distribution directly affect the organization and functions of neural circuits. Thus, in the present study, estimations of the numbers of neurons in the ganglion cell layer and dorsolateral geniculate nucleus (dLGN), and a detailed analysis of RGC morphology were carried out in transgenic mice exposed to ethanol during the early postnatal period.

METHODS

The study was carried out in male and female transgenic mice expressing yellow fluorescent protein (YFP) controlled by a Thy-1 (thymus cell antigen 1) regulator on a C57 background. Ethanol (3 g/kg/d) was administered to mouse pups by intragastric intubation throughout postnatal days (PDs) 3 to 20. Intubation control (IC) and untreated control (C) groups were included. Blood alcohol concentration was measured in separate groups of pups on PDs 3, 10, and 20 at 4 different time points, 1, 1.5, 2, and 3 hours after the second intubation. Numbers of neurons in the ganglion cell layer and in the dLGN were quantified on PD20 using unbiased stereological procedures. RGC morphology was imaged by confocal microscopy and analyzed using Neurolucida software.

RESULTS

Binge-like ethanol exposure in mice during the early postnatal period from PDs 3 to 20 altered RGC morphology and resulted in a significant decrease in the numbers of neurons in the ganglion cell layer and in the dLGN. In the alcohol exposure group, out of 13 morphological parameters examined in RGCs, soma area was significantly reduced and dendritic tortuosity significantly increased. After neonatal exposure to ethanol, a decrease in total dendritic field area and an increase in the mean branch angle were also observed. Interestingly, RGC dendrite elongation and a decrease in the spine density were observed in the IC group, as compared to both ethanol-exposed and pure control subjects. There were no significant effects of alcohol exposure on total retinal area.

CONCLUSIONS

Early postnatal ethanol exposure affects development of the visual system, reducing the numbers of neurons in the ganglion cell layer and in the dLGN, and altering RGCs' morphology.

Molecular and behavioral aspects of the actions of alcohol on the adult and developing brain

The brain is one of the major target organs of alcohol actions. Alcohol abuse can lead to alterations in brain structure and functions and, in some cases, to neurodegeneration. Cognitive deficits and alcohol dependence are highly damaging consequences of alcohol abuse. Clinical and experimental studies have demonstrated that the developing brain is particularly vulnerable to alcohol, and that drinking during gestation can lead to a range of physical, learning and behavioral defects (fetal alcohol spectrum disorders), with the most dramatic presentation corresponding to fetal alcohol syndrome. Recent findings also indicate that adolescence is a stage of brain maturation and that heavy drinking at this stage can have a negative impact on brain structure and functions causing important short- and long-term cognitive and behavioral consequences. The effects of alcohol on the brain are not uniform; some brain areas or cell populations are more vulnerable than others. The prefrontal cortex, the hippocampus, the cerebellum, the white matter and glial cells are particularly susceptible to the effects of ethanol. The molecular actions of alcohol on the brain are complex and involve numerous mechanisms and signaling pathways. Some of the mechanisms involved are common for the adult brain and for the developing brain, while others depend on the developmental stage. During brain ontogeny, alcohol causes irreversible alterations to the brain structure. It also impairs several molecular, neurochemical and cellular events taking place during normal brain development, including alterations in both gene expression regulation and the molecules involved in cell-cell interactions, interference with the mitogenic and growth factor response, enhancement of free radical formation and derangements of glial cell functions. However, in both adult and adolescent brains, alcohol damages specific brain areas through mechanisms involving excitotoxicity, free radical formation and neuroinflammatory damage resulting from activation of the innate immune system mediated by TLR4 receptors. Alcohol also acts on specific membrane proteins, such as neurotransmitter receptors (e.g. NMDA, GABA-A), ion channels (e.g. L-type Ca²⁺ channels, GIRKs), and signaling pathways (e.g. PKA and PKC signaling). These effects might underlie the wide variety of behavioral effects induced by ethanol drinking. The neuroadaptive changes affecting neurotransmission systems which are more sensitive to the acute effects of alcohol occur after long-term alcohol consumption. Alcohol-induced maladaptations in the dopaminergic mesolimbic system, abnormal plastic changes in the reward-related brain areas and genetic and epigenetic factors may all contribute to alcohol reinforcement and alcohol addiction. This manuscript reviews the mechanisms by which ethanol impacts the adult and the developing brain, and causes both neural impairments and cognitive and behavioral dysfunctions. The identification and the understanding of the cellular and molecular mechanisms involved in ethanol toxicity might contribute to the development of treatments and/or therapeutic agents that could reduce or eliminate the deleterious effects of alcohol on the brain.

Embryo developmental disruption during organogenesis produced by CF-1 murine periconceptional alcohol consumption

The aim was to study the control females (CF)-1 mouse embryo differentiation, growth, morphology on embryonic E- and N-cadherin expression at midgestation after periconceptional moderate alcohol ingestion. Adult female mice were exposed to 10% ethanol in drinking water for 17 days previous to and up to day 10 of gestation (ethanol-exposed females, EF) and were compared with nonexposed CF. EF presented reduced quantities of E10 to E10.5 embryos, greater percentage of embryos at stages less than E7.5, reduced implantation site numbers/female, and increased resorptions compared with CF. EF-embryo growth was significantly affected as evidenced by reduced cephalic and body sizes of E10 and E10.5 embryos (scanning electron microscopy) and decreased protein content of E10.5 embryos vs. CF embryos. A significantly higher percentage of EF-E10-10.5 embryos presented abnormal neural tube (NT) closure vs. the percentage of CF. E10 embryos from EF presented elevated tissue disorganization, pyknosis and nuclear condensation in somites, mesenchymal and neuroepithelial tissue. Immunohistochemical E- and N-cadherin distribution patterns were similar in organic structures of E10 embryos between groups. However, western blot revealed that E- and N-cadherin expression levels were significantly increased in EF-derived embryos vs. controls. Perigestational ethanol consumption by CF-1 mice induced significant damage in the organogenic embryogenesis by producing delayed differentiation, growth deficiencies, and increasing the frequency of NT defects. Ethanol exposure may disrupt cell-cell adhesion leading to upregulation of E- and N-cadherin expression suggesting that deregulation of cell adhesion molecules could be involved in the disruption of embryo development at organogenesis in CF-1 mouse.

Role of neurotrophins on postnatal neurogenesis in the thalamus: prenatal exposure to ethanol

A second wave of neuronal generation occurs in the ventrobasal nucleus of the rat thalamus (VB) during the first three postnatal weeks. The present study tested the hypotheses (1) that postnatal neurogenesis in the VB is neurotrophin-regulated and (2) that ethanol-induced changes in this proliferation are mediated by neurotrophins. The first studies examined the effects of neurotrophins on the numbers of cycling cells in ex vivo preparations of the VB from 3-day-old rats. The proportion of cycling (Ki-67-positive) VB cells was higher in cultured thalamic slices treated with neurotrophins than in controls. Interestingly, this increase occurred with nerve growth factor (NGF) alone or with a combination of NGF and brain-derived neurotrophic factor (BDNF), but not with BDNF alone. Based on these data, the VBs from young offspring of pregnant rats fed an ethanol-containing or an isocaloric non-alcoholic liquid diet were examined between postnatal day (P) 1 and P31. Studies used enzyme-linked immunosorbent assays and immunoblots to explore the effects of ethanol on the expression of neurotrophins, their receptors, and representative signaling proteins. Ethanol altered the expression of neurotrophins and receptors throughout the first postnatal month. Expression of NGF increased, but there was no change in the expression of BDNF. The high affinity receptors (TrkA and TrkB) were unchanged but ethanol decreased expression of the low affinity receptor, p75. One downstream signaling protein, extracellular signal-regulated kinase (ERK), decreased but Akt expression was unchanged. Thus, postnatal cell proliferation in the VB of young rat pups is neurotrophin-responsive and is affected by ethanol.

Acute prenatal exposure to ethanol and social behavior: effects of age, sex, and timing of exposure

During development of the central nervous system, neurons pass through critical periods of vulnerability to environmental factors. Exposure to ethanol during gastrulation or during neuronal generation results in a permanent reduction in the number of neurons in trigeminal-associated cranial nerve nuclei. Normal functioning of the trigeminal system is required for social behavior, the present study examined the effects of acute prenatal exposure to ethanol on social interactions across ontogeny. Pregnant Long-Evans rats were injected with 2.9 g/kg ethanol (i.p., 20%, v/v solution; peak blood ethanol concentrations of ∼300 mg/dl) or an equivalent volume of saline on gestational day (G) 7 (gastrulation) or G12 (neuronal generation). Subsequently, social investigation, play fighting, contact behavior, social motivation, and overall locomotor activity in the social context were assessed in male and female off-spring during early adolescence, late adolescence, or adulthood, on postnatal day (P) 28, P42, or P75, respectively, using a modified social interaction test. Ethanol exposure on G7 resulted in mild changes of social behavior evident in young adolescents only. In contrast, animals exposed to ethanol on G12 demonstrated pronounced behavioral deficits throughout ontogeny, with deficits being most robust in male off-spring. Males exposed to ethanol on G12 showed decreases in social investigation, contact behavior, and play fighting, whereas a decrease in social motivation, i.e., transformation of social preference into social avoidance, was evident at P42 and P75 regardless of sex. These findings show that acute exposure to ethanol alters social behavior, and that the timing of the exposure defines the behavioral outcome.

Impact of ethanol on the developing GABAergic system

Alcohol intake during pregnancy has a tremendous impact on the developing brain. Embryonic and early postnatal alcohol exposures have been investigated experimentally to elucidate the fetal alcohol spectrum disorders' (FASD) milieu, and new data have emerged to support a devastating effect on the GABAergic system in the adult and developing nervous system. GABA is a predominantly inhibitory neurotransmitter that during development excites neurons and orchestrates several developmental processes such as proliferation, migration, differentiation, and synaptogenesis. This review summarizes and brings new data on neurodevelopmental aspects of the GABAergic system with FASD in experimental telencephalic models.

Vulnerability of macaque cranial nerve neurons to ethanol is time- and site-dependent

The present study tested the hypotheses that vulnerability to ethanol depends upon (1) population-based characteristics of the neuronal progenitors and (2) the maturation of that population by examining the effects of prenatal exposure to ethanol on brainstem nuclei derived from different rhombomeres and from the alar and basal plates. Macaca nemestrina received an ethanol-containing solution 1 day per week during the first 6 (Et6) or 24 (Et24) weeks of gestation. Control animals received an equivalent volume of saline. The treatment regime for some animals included early gastrulation (gestational day [G] 19 or G20), whereas others were treated later (on G21 or G24). Brainstems were cryosectioned and stained with cresyl violet. Stereological methods were used to determine the numbers of neurons in six different nuclei: the abducens, vagal, and hypoglossal motor nuclei and sensory components of the trigeminal brainstem nuclear complex (the principal, oral, and interpolar subnuclei). There were no differences in the numbers of neurons in any of the nuclei between controls and Et6-, or controls and Et24-treated monkeys. In contrast, the number of trigeminal sensory neurons was significantly (P<.05) lower in animals treated on G19/G20 than in control. No differences between controls and monkeys treated on G21/G24 were detected. No motor nuclei exhibited an ethanol-induced change. These data together with data on the trigeminal motor nucleus show that vulnerability to ethanol (1) is greater in sensory nuclei than in motor nuclei and (2) is temporally restricted to the time of gastrulation.

Lability of neuronal lineage decisions is revealed by acute exposures to ethanol

Developing neurons pass through periods of sensitivity to environmental factors, e.g., alterations induced by ethanol are defined when the exposure occurs. We tested the hypothesis that timely episodic prenatal exposure to ethanol can change the lineage of cortical neurons. This study exploited mice in which many layer V neurons expressed a Thy1-YFPh transgene and endogenously fluoresced yellow. Fetuses were exposed to ethanol or saline on gestational day (G) 14 (when layer V neurons were generated) or on G 15 or 17 (when these layer V neurons were migrating). Fetuses dosed on G 14 exhibited an increased frequency of YFP+ neurons across cortex. This contrasted with a decreased frequency following ethanol exposure on G 17. Ethanol did not affect overall density of layer V neurons or their generation. Thus, the magnitude and valence of ethanol-induced changes in YFP+ neurons are time-dependent. Cell lineage is defined at the time of origin and the window of lability for this definition continues into the early post-mitotic (migratory) period.

Fetal ethanol exposure increases ethanol intake by making it smell and taste better

Human epidemiologic studies reveal that fetal ethanol exposure is highly predictive of adolescent ethanol avidity and abuse. Little is known about how fetal exposure produces these effects. It is hypothesized that fetal ethanol exposure results in stimulus-induced chemosensory plasticity. Here, we asked whether gestational ethanol exposure increases postnatal ethanol avidity in rats by altering its taste and odor. Experimental rats were exposed to ethanol in utero via the dam's diet, whereas control rats were either pair-fed an iso-caloric diet or given food ad libitum. We found that fetal ethanol exposure increased the taste-mediated acceptability of both ethanol and quinine hydrochloride (bitter), but not sucrose (sweet). Importantly, a significant proportion of the increased ethanol acceptability could be attributed directly to the attenuated aversion to ethanol's quinine-like taste quality. Fetal ethanol exposure also enhanced ethanol intake and the behavioral response to ethanol odor. Notably, the elevated intake of ethanol was also causally linked to the enhanced odor response. Our results demonstrate that fetal exposure specifically increases ethanol avidity by, in part, making it taste and smell better. More generally, they establish an epigenetic chemosensory mechanism by which maternal patterns of drug use can be transferred to offspring. Given that many licit (e.g., tobacco products) and illicit (e.g., marijuana) drugs have noteworthy chemosensory components, our findings have broad implications for the relationship between maternal patterns of drug use, child development, and postnatal vulnerability.

Effect of gestational ethanol exposure on parvalbumin and calretinin expressing hippocampal neurons in a chick model of fetal alcohol syndrome

Fetal alcohol syndrome (FAS), a condition occurring in some children of mothers who have consumed alcohol during pregnancy, is characterized by physical deformities and learning and memory deficits. The chick hippocampus, whose functions are controlled by interneurons expressing calcium-binding proteins parvalbumin (PV) and calretinin (CR), is involved in learning and memory mechanisms. Effects on growth and development and hippocampal morphology were studied in chick embryos exposed to 5% and 10% ethanol volume/volume (vol/vol) for 2 or 8 days of gestation. There was a significant dose-dependent reduction (P<.05) in body weight and mean number per section of PV and CR expressing hippocampal neurons in ethanol-exposed chicks, without alterations in neuronal nuclear size or hippocampal volume, compared appropriate controls. Moreover, when chicks exposed to 5% ethanol for 2 and 8 days of gestation were compared, no significant differences were found in body parameters or neuronal counts. Similarly, exposure to 10% ethanol did not induce any significant changes in chicks exposed for 2 or 8 gestational days. Thus, these results suggest that gestational ethanol exposure induces a reduction in the mean number per section of PV and CR expressing hippocampal neurons, and could be a possible mechanism responsible for learning and memory disorders in FAS.

Foetal Alcohol Spectrum Disorders and alterations in brain and behaviour

The term 'Foetal Alcohol Spectrum Disorders (FASD)' refers to the range of disabilities that may result from prenatal alcohol exposure. This article reviews the effects of ethanol on the developing brain and its long-term structural and neurobehavioural consequences. Brain imaging, neurobehavioural and experimental studies demonstrate the devastating consequences of prenatal alcohol exposure on the developing central nervous system (CNS), identifying specific brain regions affected, the range of severity of effects and mechanisms involved. In particular, neuroimaging studies have demonstrated overall and regional volumetric and surface area reductions, abnormalities in the shape of particular brain regions, and reduced and increased densities for white and grey matter, respectively. Neurobehaviourally, FASD consists of a continuum of long-lasting deficits affecting multiple aspects of cognition and behaviour. Experimental studies have also provided evidence of the vulnerability of the CNS to the teratogenic effects of ethanol and have provided new insight on the influence of risk factors in the type and severity of observed brain abnormalities. Finally, the potential molecular mechanisms that underlie the neuroteratological effects of alcohol are discussed, with particular emphasis on the role of glial cells in long-term neurodevelopmental liabilities.