Severe alcohol-induced neuronal deficits in the hippocampus and neocortex of neonatal mice genetically deficient for neuronal nitric oxide synthase (nNOS)

Early Ethanol Exposure Inhibits the Differentiation of Hippocampal Dentate Gyrus Granule Cells in a Mouse Model of Fetal Alcohol Spectrum Disorders

BACKGROUND

Alcohol consumption during pregnancy may damage the developing central nervous system of the fetus and lead to brain structural and functional deficits in the children, known as fetal alcohol spectrum disorders. The underlying mechanisms have not been fully elucidated. Previously, using a third trimester-equivalent mouse model, ethanol (EtOH)-induced behavioral deficits (including spatial learning and memory dysfunction) in the mice were detected on postnatal day (PD) 35. The hippocampal formation is critically involved in spatial learning/memory and contains 2 major neuron populations: the pyramidal cells in the hippocampus proper and the dentate gyrus granule cells (DGGCs) in the dentate gyrus (DG). In rodents, while the pyramidal cells are almost exclusively generated prenatally, the DG granule neurons are majorly generated during the first 2 weeks postnatally, which coincides with the period of EtOH exposure in our mouse model. Therefore, in the current study the effects of EtOH exposure on the development of the DGGCs were examined.

METHODS

C57BL/6 mice were treated with 4 g/kg of EtOH by intubation on PD 4 to 10 to mimic alcohol exposure to the fetus during the third trimester in humans, and the development of DGGCs was examined by immunohistochemistry and quantified on PD 35.

RESULTS

EtOH exposure does not affect the number of total or newly generated DGGCs, but reduces the number of mature DGGCs on PD 35 in both male and female mice. The ratio of immature DGGCs over total DGGCs was increased, and the ratio of mature DGGCs over total DGGCs was decreased by EtOH exposure. In addition, no sex-dependent effects of EtOH treatment were detected.

CONCLUSION

Our data indicate that EtOH exposure in mice during PD 4 to 10 does not affect the generation/proliferation but inhibits the differentiation of the DGGCs on PD 35.

Regional Patterns of Alcohol-Induced Neuronal Loss Depend on Genetics: Implications for Fetal Alcohol Spectrum Disorder

BACKGROUND

Alcohol exposure during pregnancy can kill developing neurons and lead to fetal alcohol spectrum disorder (FASD). However, affected individuals differ in their regional patterns of alcohol-induced neuropathology. Because neuroprotective genes are expressed in spatially selective ways, their mutation could increase the vulnerability of some brain regions, but not others, to alcohol teratogenicity. The objective of this study was to determine whether a null mutation of neuronal nitric oxide synthase (nNOS) can increase the vulnerability of some brain regions, but not others, to alcohol-induced neuronal losses.

METHODS

Immunohistochemistry identified brain regions in which nNOS is present or absent throughout postnatal development. Mice genetically deficient for nNOS (nNOS-/- ) and wild-type controls received alcohol (0.0, 2.2, or 4.4 mg/g/d) over postnatal days (PD) 4 to 9. Mice were sacrificed in adulthood (~PD 115), and surviving neurons in the olfactory bulb granular layer and brain stem facial nucleus were quantified stereologically.

RESULTS

nNOS was expressed throughout postnatal development in olfactory bulb granule cells but was never expressed in the facial nucleus. In wild-type mice, alcohol reduced neuronal survival to similar degrees in both cell populations. However, null mutation of nNOS more than doubled alcohol-induced cell death in the olfactory bulb granule cells, while the mutation had no effect on the facial nucleus neurons. As a result, in nNOS-/- mice, alcohol caused substantially more cell loss in the olfactory bulb than in the facial nucleus.

CONCLUSIONS

Mutation of the nNOS gene substantially increases vulnerability to alcohol-induced cell loss in a brain region where the gene is expressed (olfactory bulb), but not in a separate brain region, where the gene is not expressed (facial nucleus). Thus, differences in genotype may explain why some individuals are vulnerable to FASD, while others are not, and may determine the specific patterns of neuropathology in children with FASD.

Developmental Alcohol Exposure Impairs Activity-Dependent S-Nitrosylation of NDEL1 for Neuronal Maturation

Neuronal nitric oxide synthase is involved in diverse signaling cascades that regulate neuronal development and functions via S-Nitrosylation-mediated mechanism or the soluble guanylate cyclase (sGC)/cyclic guanosine monophosphate (cGMP) pathway activated by nitric oxide. Although it has been studied extensively in vitro and in invertebrate animals, effects on mammalian brain development and underlying mechanisms remain poorly understood. Here we report that genetic deletion of "Nos1" disrupts dendritic development, whereas pharmacological inhibition of the sGC/cGMP pathway does not alter dendritic growth during cerebral cortex development. Instead, nuclear distribution element-like (NDEL1), a protein that regulates dendritic development, is specifically S-nitrosylated at cysteine 203, thereby accelerating dendritic arborization. This post-translational modification is enhanced by N-methyl-D-aspartate receptor-mediated neuronal activity, the main regulator of dendritic formation. Notably, we found that disruption of S-Nitrosylation of NDEL1 mediates impaired dendritic maturation caused by developmental alcohol exposure, a model of developmental brain abnormalities resulting from maternal alcohol use. These results highlight S-Nitrosylation as a key activity-dependent mechanism underlying neonatal brain maturation and suggest that reduction of S-Nitrosylation of NDEL1 acts as a pathological factor mediating neurodevelopmental abnormalities caused by maternal alcohol exposure.

Activation of cyclic GMP-dependent protein kinase blocks alcohol-mediated cell death and calcium disruption in cerebellar granule neurons

Alcohol during brain development leads to the widespread neuronal death observed in fetal alcohol spectrum disorders (FASD). In comparison, the mature brain is less vulnerable to alcohol. Studies into maturation-acquired alcohol resistance uncovered a protective mechanism that reduces alcohol-induced neuronal death through nitric oxide-cGMP-cyclic GMP-dependent protein kinase (NO-cGMP-cGK) signaling. However, the downstream processes underlying this neuroprotection remain unclear. Alcohol can disrupt levels of intracellular calcium ([Ca²⁺]_i) in vulnerable neuronal populations to trigger cell death in both in vivo and in vitro models of FASD. Since cGK has been demonstrated to regulate and inhibit intracellular Ca²⁺ release, we examined the hypothesis that cGK confers alcohol resistance by preventing [Ca²⁺]_i disruptions. Alcohol resistance, determined by neuronal survival after 24 h of alcohol exposure, was examined in primary cerebellar granule neuron (CGN) cultures derived from 5 to 7 day-old neonatal mice with an activator, 8-Br-cGMP, and/or an inhibitor, Rp-8-pCPT-cGMPS, of cGK signaling. Intracellular Ca²⁺ responses to alcohol were measured by ratiometric Ca²⁺ imaging in Fura-2-loaded CGN cultures after 8-Br-cGMP treatment. Our results indicate that activating cGK with 8-Br-cGMP before alcohol administration provided neuroprotection, which the cGK inhibitor, Rp-8-pCPT-cGMPS, blocked. Alcohol exposure elevated [Ca²⁺]_i, whereas 8-Br-cGMP pretreatment reduced both the level of the alcohol-induced rise in [Ca²⁺]_i as well as the number of cells that responded to alcohol by increasing [Ca²⁺]_i. These findings associate alcohol resistance, mediated by cGK signaling, to reduction of the persistent and toxic increase in [Ca²⁺]_i from alcohol exposure.

Role of neuronal nitric oxide synthase (nNOS) at medulla in tachycardia induced by repeated administration of ethanol in conscious rats

Background

Intake of ethanol (alcohol) has been shown to influence cardiovascular function; the underlying brain mechanism remains unclear. Noting that nitric oxide (NO) system in the CNS is involved in the regulation of cardiovascular function, the present study examined the role of NO in medulla in ethanol-induced cardiovascular changes.

Methods

Ethanol was administered by oral gavage at dose of 3.2 g/kg once every day for 8 consecutive days. Changes in blood pressure (BP) and heart rate (HR) in response to ethanol were measured by radiotelemetry method in freely moving female Sprague-Dawley rats. NO modulators were applied by intracerebroventricular (ICV) injection. The protein levels of nitric oxide synthase (NOS) and NO content in rostroventral medulla were measured by Western blot and nitrate/nitrite colorimetric assay kit, respectively.

Results

Ethanol intake had little effects on basal BP and HR following 8 consecutive day treatments. A significant increase in HR but not BP following ethanol intake was observed at 6th and 8th, but not at 1st and 4th day treatments as compared with saline group. A decrease in the protein expression of neuronal NOS (nNOS) but not inducible NOS or endothelial NOS and a decline in the level of NO in the medulla 30 min after ethanol administration was observed at 8th day treatment. ICV treatment with NO donors attenuated ethanol-induced tachycardia effects at 8th day treatment. Ethanol produced significantly tachycardia responses when ICV nNOS inhibitors were given at 1st day treatment.

Conclusion

Our results suggest that medulla nNOS/NO pathways play an important role in ethanol regulation of HR.

Ethanol-Induced Neurodegeneration and Glial Activation in the Developing Brain

Ethanol induces neurodegeneration in the developing brain, which may partially explain the long-lasting adverse effects of prenatal ethanol exposure in fetal alcohol spectrum disorders (FASD). While animal models of FASD show that ethanol-induced neurodegeneration is associated with glial activation, the relationship between glial activation and neurodegeneration has not been clarified. This review focuses on the roles of activated microglia and astrocytes in neurodegeneration triggered by ethanol in rodents during the early postnatal period (equivalent to the third trimester of human pregnancy). Previous literature indicates that acute binge-like ethanol exposure in postnatal day 7 (P7) mice induces apoptotic neurodegeneration, transient activation of microglia resulting in phagocytosis of degenerating neurons, and a prolonged increase in glial fibrillary acidic protein-positive astrocytes. In our present study, systemic administration of a moderate dose of lipopolysaccharides, which causes glial activation, attenuates ethanol-induced neurodegeneration. These studies suggest that activation of microglia and astrocytes by acute ethanol in the neonatal brain may provide neuroprotection. However, repeated or chronic ethanol can induce significant proinflammatory glial reaction and neurotoxicity. Further studies are necessary to elucidate whether acute or sustained glial activation caused by ethanol exposure in the developing brain can affect long-lasting cellular and behavioral abnormalities observed in the adult brain.

The neuronal nitric oxide synthase (nNOS) gene and neuroprotection against alcohol toxicity

When a mother abuses alcohol during pregnancy, the offspring can suffer a myriad of abnormalities, collectively known as fetal alcohol spectrum disorder (FASD). Foremost among these abnormalities is central nervous system dysfunction, which commonly manifests itself as mental retardation, clumsiness, hyperactivity, and poor attention span. These behavior problems are due, in large part, to alcohol-induced neuronal losses in the developing fetal brain. However, not all fetuses are equally affected by maternal alcohol consumption during pregnancy. While some fetuses are severely affected and develop hallmarks of FASD later in life, others exhibit no evident neuropathology or behavioral abnormalities. This variation is likely due, at least in part, to differences in fetal genetics. This review focuses on one particular gene, neuronal nitric oxide synthase, whose mutation worsens alcohol-induced neuronal death, both in vitro and in vivo. In addition, ectopic expression of the neuronal nitric oxide synthase gene protects neurons against alcohol toxicity. The gene encodes an enzyme that produces nitric oxide (NO), which facilitates the protective effects of neuronal growth factors and which underlies the ability of neurons to resist alcohol toxicity as they mature. Nitric oxide exerts its protective effects against alcohol via a specific signaling pathway, the NO-cGMP-PKG pathway. Pharmacologic manipulation of this pathway could be of therapeutic use in preventing or ameliorating FASD.

Genetic absence of nNOS worsens fetal alcohol effects in mice. II: microencephaly and neuronal losses

BACKGROUND

Prenatal alcohol exposure can kill developing neurons, leading to microencephaly and mental retardation. However, not all fetuses are equally vulnerable to alcohol's neurotoxic effects. While some fetuses are severely affected and are ultimately diagnosed with fetal alcohol syndrome (FAS), others have no evidence of neuropathology and are behaviorally normal. These widely different outcomes among alcohol-exposed fetuses are likely due, in part, to genetic differences. Some fetuses possess genotypes that make them much more vulnerable than others to alcohol's teratogenic effects. However, to date, only 1 gene has been identified whose mutation can worsen alcohol-induced behavioral deficits in an animal model of FAS. That gene is neuronal nitric oxide synthase (nNOS). The purpose of this study was to determine whether mutation of nNOS can likewise worsen alcohol-induced microencephaly and lead to permanent neuronal deficits.

METHODS

Wild-type and nNOS(-/-) mice received alcohol (0.0, 2.2, or 4.4 mg/g) daily over postnatal days (PDs) 4 to 9. Beginning on PD 85, the mice underwent a series of behavioral tests; the results of which are reported in the companion paper. The brains were then weighed, and stereological cell counts were performed on the cerebral cortex and hippocampal formation, which are the brain regions that mediate the aforementioned behavioral tasks.

RESULTS

Alcohol caused dose-dependent microencephaly, but only in the nNOS(-/-) mice and not in wild-type mice. Alcohol-induced neuronal losses were more severe in the nNOS(-/-) mice than in the wild-type mice in all of the brain regions examined, including the cerebral cortex, hippocampal CA3 subregion, hippocampal CA1 subregion, and dentate gyrus.

CONCLUSIONS

Targeted mutation of the nNOS gene increases the vulnerability of the developing brain to alcohol-induced growth restriction and neuronal losses. This increased neuropathology is associated with worsened behavioral dysfunction. The results demonstrate the critical importance of genotype in determining the outcome of developmental alcohol exposure.

Genetic absence of nNOS worsens fetal alcohol effects in mice. I: behavioral deficits

BACKGROUND

Alcohol abuse during pregnancy often induces neuropsychological problems in the offspring, including learning disorders, attention deficits, and behavior problems, all of which are prominent components of fetal alcohol spectrum disorders (FASD). However, not all children who were exposed to alcohol in utero are equally affected by it. While some children have major deficits, others are spared. This unequal vulnerability is likely due largely to differences in fetal genetics. Some fetuses appear to have certain genotypes that make them much more prone to FASD. However, to date, no gene has been identified that worsens alcohol-induced brain dysfunction. Nitric oxide (NO) is a gaseous molecule that can protect developing neurons against alcohol-induced death. In the brain, NO is produced by neuronal nitric oxide synthase (nNOS). In this study, we examined whether homozygous mutation of the nNOS gene in mice worsens the behavioral deficits of developmental alcohol exposure.

METHODS

Wild-type and nNOS(-/-) mice received alcohol (0.0, 2.2, or 4.4 mg/g) daily over postnatal days (PDs) 4 to 9. Beginning on PD 85, the mice underwent a series of behavioral tests, including open field activity, the Morris water maze, and paired pulse inhibition.

RESULTS

For the wild-type mice, alcohol impaired performance only in the water maze. In contrast, for the nNOS(-/-) mice, alcohol impaired performance on all 3 tasks. Furthermore, the nNOS(-/-) mice were substantially more impaired than wild-type mice in their performance on all 3 of the behavioral tests and at both the low (2.2) and high (4.4) doses of alcohol.

CONCLUSIONS

Targeted disruption of the nNOS gene worsens the behavioral impact of developmental alcohol exposure and allows alcohol-induced learning problems to emerge that are not seen in wild type. This is the first demonstration that a specific genotype can interact with alcohol to worsen functional brain deficits in an animal model of FASD.

Importance of genetics in fetal alcohol effects: null mutation of the nNOS gene worsens alcohol-induced cerebellar neuronal losses and behavioral deficits

The cerebellum is a major target of alcohol-induced damage in the developing brain. However, the cerebella of some children are much more seriously affected than others by prenatal alcohol exposure. As a consequence of in utero alcohol exposure, some children have substantial reductions in cerebellar volume and corresponding neurodevelopmental problems, including microencephaly, ataxia, and balance deficits, while other children who were exposed to similar alcohol quantities are spared. One factor that likely plays a key role in determining the impact of alcohol on the fetal cerebellum is genetics. However, no specific gene variant has yet been identified that worsens cerebellar function as a consequence of developmental alcohol exposure. Previous studies have revealed that mice carrying a homozygous mutation of the gene for neuronal nitric oxide synthase (nNOS-/- mice) have more severe acute alcohol-induced neuronal losses from the cerebellum than wild type mice. Therefore, the goals of this study were to determine whether alcohol induces more severe cerebellum-based behavioral deficits in nNOS-/- mice than in wild type mice and to determine whether these worsened behavior deficits are associated with worsened cerebellar neuronal losses. nNOS-/- mice and their wild type controls received alcohol (0.0, 2.2, or 4.4mg/g) daily over postnatal days 4-9. In adulthood, the mice underwent behavioral testing, followed by neuronal quantification. Alcohol caused dose-related deficits in rotarod and balance beam performance in both nNOS-/- and wild type mice. However, the alcohol-induced behavioral deficits were substantially worse in the nNOS-/- mice than in wild type. Likewise, alcohol exposure led to losses of Purkinje cells and cerebellar granule cells in mice of both genotypes, but the cell losses were more severe in the nNOS-/- mice than in wild type. Behavioral performances were correlated with neuronal number in the nNOS-/- mice, but not in wild type. Thus, homozygous mutation of the nNOS gene increases vulnerability to alcohol-induced cerebellar dysfunction and neuronal loss. nNOS is the first gene identified whose mutation worsens alcohol-induced cerebellar behavioral deficits.

The role of NOX enzymes in ethanol-induced oxidative stress and apoptosis in mouse embryos

Reactive oxygen species (ROS) play an important role in ethanol-induced apoptosis and teratogenesis. However, the major sources of ROS in ethanol-exposed embryos have remained undefined. This study was conducted to determine the role of NADPH oxidase (NOX) in ethanol-induced oxidative stress and apoptosis in mouse embryos. Analyses of mRNA expression indicated that ethanol treatment resulted in a significant increase in mRNA expression of NOX catalytic subunit Duox-1 in gestational day 9 (GD 9:0) mouse embryos. Ethanol exposure also resulted in significant increases in mRNA expression of NOX regulatory subunits, p22phox, p67phox, NOXA1 and NOXO1. In addition, a significant increase in NOX enzyme activity was found in the ethanol-exposed embryos as compared to controls. Co-treatment with the NOX inhibitor, diphenyleneiodonium (DPI), significantly prevented ethanol-induced increases in NOX enzyme activity, ROS generation and oxidative DNA damage in ethanol-exposed embryos. DPI treatment also resulted in a reduction in caspase-3 activation, decreased caspase-3 activity and diminished prevalence of apoptosis in ethanol-exposed embryos. These results support the hypothesis that NOX is a critical source of ROS in ethanol-exposed embryos and that it plays an important role in ethanol-induced oxidative stress and pathogenesis.

A single exposure to alcohol during brain development induces microencephaly and neuronal losses in genetically susceptible mice, but not in wild type mice

Maternal alcohol abuse during pregnancy can damage the fetal brain and lead to fetal alcohol syndrome (FAS). Despite public warnings discouraging alcohol use during pregnancy, many pregnant women continue to drink intermittently because they do not believe that occasional exposures to alcohol can be harmful to a fetus. However, because of genetic differences, some fetuses are much more susceptible than others to alcohol-induced brain injury. Thus, a relatively low quantity of alcohol that may be innocuous to most fetuses could damage a genetically susceptible fetus. Neuronal nitric oxide synthase (nNOS) can protect developing mouse neurons against alcohol toxicity by synthesizing neuroprotective nitric oxide. This study examined whether a single exposure to alcohol, which causes no evident injury in wild type mice, can damage the brains of mice genetically deficient for nNOS (nNOS-/- mice). Wild type and nNOS-/- mice received intraperitoneal injections of alcohol (0.0, 2.2, or 4.4mg/g body weight) either as a single dose on postnatal day (PD) 4 or as repeated daily doses over PD4-9. Brain volumes and neuronal numbers within the hippocampus and cerebral cortex were determined on PD10. Alcohol exposure on PD4-9 restricted brain growth and caused neuronal death in both strains of mice, but the severity of microencephaly and neuronal loss were more severe in the nNOS-/- mice than in wild type. The 4.4 mg/g alcohol dose administered on PD4 alone caused significant neuronal loss and microencephaly in the nNOS-/- mice, while this same dose caused no evident injury in the wild type mice. Thus, during development, a single exposure to alcohol can injure a genetically vulnerable brain, while it leaves a wild type brain unaffected. Since the genes that confer alcohol resistance and vulnerability in developing humans are unknown, any particular human fetus is potentially vulnerable. Thus, women should be counseled to consume no alcohol during pregnancy.

Nrf2-mediated transcriptional induction of antioxidant response in mouse embryos exposed to ethanol in vivo: implications for the prevention of fetal alcohol spectrum disorders

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that is important in protection against oxidative stress. This study was designed to determine the role of Nrf2 signaling in transcriptional activation of detoxifying and antioxidant genes in an in vivo mouse fetal alcohol syndrome model. Maternal ethanol treatment was found to increase both Nrf2 protein levels and Nrf2-ARE binding in mouse embryos. It also resulted in a moderate increase in the mRNA expression of Nrf2 downstream target detoxifying and antioxidant genes as well as an increase in the expression of antioxidant proteins. Pretreatment with the Nrf2 inducer, 3H-1,2 dithiole-3-thione (D3T), significantly increased Nrf2 protein levels and Nrf2-ARE binding, and strongly induced the mRNA expression of Nrf2 downstream target genes. It also increased the expression of antioxidant proteins and the activities of the antioxidant enzymes. Additionally, D3T pretreatment resulted in a significant decrease in ethanol-induced reactive oxygen species generation and apoptosis in mouse embryos. These results demonstrate that Nrf2 signaling is involved in the induction of antioxidant response in ethanol-exposed embryos. In addition, the potency of D3T in inducing antioxidants as well as in diminishing ethanol-induced apoptosis suggests that further exploration of the antiteratogenic effect of this compound will be fruitful.

The protective effect of neuronal nitric oxide synthase (nNOS) against alcohol toxicity depends upon the NO-cGMP-PKG pathway and NF-kappaB

Fetal alcohol syndrome (FAS) stems from maternal alcohol abuse during pregnancy and is an important cause of mental retardation and hyperactivity in children. In the developing brain, alcohol can kill neurons, leading to microencephaly. However, due to their genetic makeup, some individuals are less vulnerable than others to alcohol's neurotoxic effects. Animal studies have demonstrated that one particular gene, neuronal nitric oxide synthase (nNOS), protects developing neurons in vivo against alcohol-induced death. We utilized pharmacologic techniques to demonstrate that nNOS protects neurons against alcohol toxicity by activating the NO-cGMP-PKG signaling pathway. Cerebellar granule cell cultures derived from mice carrying a null mutation for nNOS (nNOS-/- mice) were substantially more vulnerable than cultures from wild-type mice to alcohol-induced cell death. However, activation of the pathway at sites downstream of nNOS protected the cultures against alcohol toxicity. Conversely, blockade of the pathway rendered wild-type cultures vulnerable to alcohol-induced death. We further identified NF-kappaB as the downstream effector through which nNOS and the NO-cGMP-PKG pathway signal their neuroprotective effects. Tumor necrosis factor-alpha (TNF-alpha), which activates NF-kappaB, ameliorated alcohol-induced cell death in nNOS-/- and wild-type cultures, while an NF-kappaB inhibitor (NFi) blocked the protective effects of TNF-alpha and worsened alcohol-induced cell death. Furthermore, NFi blocked the protective effects of NO-cGMP-PKG pathway activators, demonstrating that NF-kappaB is downstream of the NO-cGMP-PKG pathway. As wild-type neurons matured in culture, they became resistant to alcohol toxicity. However, this maturation-dependent alcohol resistance did not occur in nNOS-/- mice and could be reversed in wild-type mice with NFi, demonstrating that nitric oxide and NF-kappaB are crucial for the development of alcohol resistance with age. Thus, nNOS protects developing neurons against alcohol toxicity by activating the NO-cGMP-PKG-NF-kappaB pathway and is crucial for the acquisition of maturation-dependent alcohol resistance.

Maturation-dependent alcohol resistance in the developing mouse: cerebellar neuronal loss and gene expression during alcohol-vulnerable and -resistant periods

BACKGROUND

Alcohol abuse during pregnancy injures the fetal brain. One of alcohol's most important neuroteratogenic effects is neuronal loss. Rat models have shown that the cerebellum becomes less vulnerable to alcohol-induced neuronal death as it matures. We determined if maturation-dependent alcohol resistance occurs in mice and compared patterns of gene expression during the alcohol resistant and sensitive periods.

METHODS

Neonatal mice received alcohol daily over postnatal day (PD) 2 to 4 or PD8 to 10. Purkinje cells and granule cells were quantified on PD25. The temporal expression patterns of 4 neuro-developmental genes and 3 neuro-protective genes in the cerebellum were determined daily over PD0 to 15 to determine how gene expression changes as the cerebellum transitions from alcohol-vulnerable to alcohol-resistant. The effect of alcohol on expression of these genes was determined when the cerebellum is alcohol sensitive (PD4) and resistant (PD10).

RESULTS

Purkinje and granule cells were vulnerable to alcohol-induced death at PD2 to 4, but not at PD8 to 10. Acquisition of maturation-dependent alcohol resistance coincided with changes in the expression of neurodevelopmental genes. The vulnerability of cerebellar neurons to alcohol toxicity declined in parallel with decreasing levels of Math1 and Cyclin D2, markers of immature granule cells. Likewise, the rising resistance to alcohol toxicity paralleled increasing levels of GABA alpha-6 and Wnt-7a, markers of mature granule neurons. Expression of growth factors and genes with survival promoting function (IGF-1, BDNF, and cyclic AMP response element binding protein) did not rise as the cerebellum transitioned from alcohol-vulnerable to alcohol-resistant. All 3 were expressed at substantial levels during the vulnerable period and were not expressed at higher levels later. Acute alcohol exposure altered the expression of neurodevelopmental genes and growth factor genes when administered either during the alcohol vulnerable period or resistant period. However, the patterns in which gene expression changed varied among the genes and depended on timing of alcohol administration.

CONCLUSIONS

Mice have a temporal window of vulnerability in the first week of life, during which cerebellar neurons are more sensitive to alcohol toxicity than during the second week. Expression of genes governing neuronal maturation changes in synchrony with the acquisition of alcohol resistance. Growth factors do not rise as the cerebellum transitions from alcohol-vulnerable to alcohol-resistant. Thus, a process intrinsic to neuronal maturation, rather than rising levels of growth factors, likely underlies maturation-dependent alcohol resistance.

Genetic influence on dysmorphogenesis in embryos from different rat strains exposed to ethanol in vivo and in vitro

BACKGROUND

The aim was to investigate the susceptibility of embryos from 2 rat strains (U and H) to a 48 hours ethanol exposure in early pregnancy, both in vivo and in vitro.

METHODS

The embryos were studied on gestational days 9 to 11. We used 1 ethanol dose in vivo (6 g/kg x 2), 3 different ethanol concentrations in vitro (88 mM, 132 mM, 176 mM) and also attempted to diminish the teratogenic effect in vitro by supplying the antioxidant N-acetylcysteine (NAC, 0.5 mM) to the culture medium.

RESULTS

The U embryos were more damaged by ethanol than the H embryos, both in vivo and in vitro. NAC addition diminished, but failed to completely normalize, the embryonic maldevelopment. Ethanol increased the Bax/Bcl-2 ratio in the U embryos both in vivo and in vitro, but not in the H embryos. Furthermore, ethanol caused increased Caspase-3 immunostaining in U embryos, but not in H embryos. Ethanol exposure in vivo did not alter CuZnSOD and MnSOD mRNA levels in U and H embryos. In vitro, however, the ethanol-exposed U embryos increased their CuZnSOD and MnSOD mRNA levels, whereas the CuZnSOD mRNA was unchanged and MnSOD mRNA decreased in the H embryos, in neither strain did NAC exert any effect. The U embryos increased catalase gene expression in response to ethanol in vivo, but decreased catalase mRNA levels in vitro, changes normalized by NAC. The H embryos did not alter catalase mRNA levels in vivo, but increased gene expression in vitro, with no NAC effect. Ethanol affected the gene expression of the other ROS scavenging enzymes and the developmental genes studied - Bmp-4, Ret, Shh, Pax-6 - similarly in the 2 strains.

CONCLUSIONS

The findings support a role for genetic predisposition, oxidative stress, and apoptosis in ethanol teratogenicity, and suggest that the teratogenic predisposition of the more susceptible U rats may reside, at least in part, in the regulation of the ROS scavenging enzymes in the U embryos.

Stimulation of the cAMP pathway protects cultured cerebellar granule neurons against alcohol-induced cell death by activating the neuronal nitric oxide synthase (nNOS) gene

Neuronal loss is a key component of fetal alcohol syndrome pathophysiology. Therefore, identification of molecules and signaling pathways that ameliorate alcohol-induced neuronal death is important. We have previously reported that neuronal nitric oxide synthase (nNOS) can protect developing cerebellar granule neurons (CGN) against alcohol-induced death both in vitro and in vivo. However, the upstream signal controlling nNOS expression in CGN is unknown. Activated cAMP response element binding protein (CREB) has been strongly linked to the survival of multiple cell types, including CGN. Furthermore, the promoter of the nNOS gene contains two cAMP response elements (CRE). Using cultures of CGN, we tested the hypothesis that cAMP mediates nNOS activation and the protective effect of nNOS against alcohol-induced cell death. Forskolin, an activator of the cAMP pathway, stimulated expression of a reporter gene under the control of the nNOS promoter, and this stimulation was substantially reduced when the two CREs were mutated. Forskolin increased nNOS mRNA levels several fold, increased production of nitric oxide, and abolished alcohol's toxic effect in wild type CGN. Furthermore, forskolin's protective effect was substantially reduced in CGN cultures genetically deficient for nNOS (from nNOS-/- mice). Delivery of nNOS cDNA using a replication-deficient adenoviral vector into nNOS-/- CGN abolished alcohol-induced neuronal death. In addition, overexpression of nNOS in wild type CGN ameliorated alcohol-induced cell death. These results indicate that the neuroprotective effect of the cAMP pathway is mediated, in part, by the pathway's downstream target, the nNOS gene.

L1 cell adhesion molecule is neuroprotective of alcohol induced cell death

L1 cell adhesion molecule (L1), a protein critical for appropriate development of the central nervous system, is a target for ethanol teratogenicity. Ethanol inhibits both L1 mediated cell adhesion as well as L1 mediated neurite outgrowth. L1 has been shown to increase cell survival in cerebellar granule cells while ethanol has been shown to increase cell death. We sought to determine if L1 protected cells from ethanol induced cell death. Cerebellar granule cells from postnatal day 6 rat pups were cultured on either poly l-lysine with or without an L1 substratum. Alcohol was added at 2h post-plating and cell survival was measured at various times. L1 substratum significantly increased cell survival at 72 and 120 h. Ethanol significantly reduced cell survival at 48 h, with no effect at 72 or 120 h, both in the presence and absence of L1. At 48 h, L1 significantly increased cell survival in the presence of ethanol. We conclude that ethanol interferes with processes other than L1-L1 interactions in causing cell death, and that ethanol effects would be more severe in the absence of L1.