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

Impact of Intrauterine Insults on Fetal and Postnatal Cerebellar Development in Humans and Rodents

Many children suffer from neurodevelopmental aberrations that have long-term effects. To understand the consequences of pathological processes during particular periods in neurodevelopment, one has to understand the differences in the developmental timelines of brain regions. The cerebellum is one of the first brain structures to differentiate during development but one of the last to achieve maturity. This relatively long period of development underscores its vulnerability to detrimental environmental exposures throughout gestation. Moreover, as postnatal functionality of the cerebellum is multifaceted, enveloping sensorimotor, cognitive, and emotional domains, prenatal disruptions in cerebellar development can result in a large variety of neurological and mental health disorders. Here, we review major intrauterine insults that affect cerebellar development in both humans and rodents, ranging from abuse of toxic chemical agents, such as alcohol, nicotine, cannabis, and opioids, to stress, malnutrition, and infections. Understanding these pathological mechanisms in the context of the different stages of cerebellar development in humans and rodents can help us to identify critical and vulnerable periods and thereby prevent the risk of associated prenatal and early postnatal damage that can lead to lifelong neurological and cognitive disabilities. The aim of the review is to raise awareness and to provide information for obstetricians and other healthcare professionals to eventually design strategies for preventing or rescuing related neurodevelopmental disorders.

Mechanisms of Ethanol-Induced Cerebellar Ataxia: Underpinnings of Neuronal Death in the Cerebellum

Ethanol consumption remains a major concern at a world scale in terms of transient or irreversible neurological consequences, with motor, cognitive, or social consequences. Cerebellum is particularly vulnerable to ethanol, both during development and at the adult stage. In adults, chronic alcoholism elicits, in particular, cerebellar vermis atrophy, the anterior lobe of the cerebellum being highly vulnerable. Alcohol-dependent patients develop gait ataxia and lower limb postural tremor. Prenatal exposure to ethanol causes fetal alcohol spectrum disorder (FASD), characterized by permanent congenital disabilities in both motor and cognitive domains, including deficits in general intelligence, attention, executive function, language, memory, visual perception, and communication/social skills. Children with FASD show volume deficits in the anterior lobules related to sensorimotor functions (Lobules I, II, IV, V, and VI), and lobules related to cognitive functions (Crus II and Lobule VIIB). Various mechanisms underlie ethanol-induced cell death, with oxidative stress and endoplasmic reticulum (ER) stress being the main pro-apoptotic mechanisms in alcohol abuse and FASD. Oxidative and ER stresses are induced by thiamine deficiency, especially in alcohol abuse, and are exacerbated by neuroinflammation, particularly in fetal ethanol exposure. Furthermore, exposure to ethanol during the prenatal period interferes with neurotransmission, neurotrophic factors and retinoic acid-mediated signaling, and reduces the number of microglia, which diminishes expected cerebellar development. We highlight the spectrum of cerebellar damage induced by ethanol, emphasizing physiological-based clinical profiles and biological mechanisms leading to cell death and disorganized development.

[Fetal alcohol exposure: when placenta would help to the early diagnosis of child brain impairments]

Alcohol consumption during pregnancy constitutes a major cause of neurodevelopmental and behavioral disabilities. Whereas it is possible for clinicians to establish a perinatal diagnosis of fetal alcohol syndrome, the more severe expression of fetal alcohol spectrum disorder (FASD), most FASD children are late or mis-diagnosed due to a lack of clear morphological and neurodevelopmental abnormalities. Several precious years of care are consequently lost. Recent data revealed a functional placenta-brain axis involved in the control of the fetal brain angiogenesis which is impaired by in utero alcohol exposure. Because in the developing fetal brain a correct angiogenesis is required for a correct neurodevelopment, these preclinical and clinical advances pave the way for a new generation of placental biomarkers for early diagnosis of FASD.

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.

PLGF, a placental marker of fetal brain defects after in utero alcohol exposure

Most children with in utero alcohol exposure do not exhibit all features of fetal alcohol syndrome (FAS), and a challenge for clinicians is to make an early diagnosis of fetal alcohol spectrum disorders (FASD) to avoid lost opportunities for care. In brain, correct neurodevelopment requires proper angiogenesis. Since alcohol alters brain angiogenesis and the placenta is a major source of angiogenic factors, we hypothesized that it is involved in alcohol-induced brain vascular defects. In mouse, using in vivo repression and overexpression of PLGF, we investigated the contribution of placenta on fetal brain angiogenesis. In human, we performed a comparative molecular and morphological analysis of brain/placenta angiogenesis in alcohol-exposed fetuses. Results showed that prenatal alcohol exposure impairs placental angiogenesis, reduces PLGF levels and consequently alters fetal brain vasculature. Placental repression of PLGF altered brain VEGF-R1 expression and mimicked alcohol-induced vascular defects in the cortex. Over-expression of placental PGF rescued alcohol effects on fetal brain vessels. In human, alcohol exposure disrupted both placental and brain angiogenesis. PLGF expression was strongly decreased and angiogenesis defects observed in the fetal brain markedly correlated with placental vascular impairments. Placental PGF disruption impairs brain angiogenesis and likely predicts brain disabilities after in utero alcohol exposure. PLGF assay at birth could contribute to the early diagnosis of FASD.

Acute oligodendrocyte loss with persistent white matter injury in a third trimester equivalent mouse model of fetal alcohol spectrum disorder

Alcohol exposure during central nervous system (CNS) development can lead to fetal alcohol spectrum disorder (FASD). Human imaging studies have revealed significant white matter (WM) abnormalities linked to cognitive impairment in children with FASD; however, the underlying mechanisms remain unknown. Here, we evaluated both the acute and long-term impacts of alcohol exposure on oligodendrocyte number and WM integrity in a third trimester-equivalent mouse model of FASD, in which mouse pups were exposed to alcohol during the first 2 weeks of postnatal development. Our results demonstrate a 58% decrease in the number of mature oligodendrocytes (OLs) and a 75% decrease in the number of proliferating oligodendrocyte progenitor cells (OPCs) within the corpus callosum of alcohol-exposed mice at postnatal day 16 (P16). Interestingly, neither mature OLs nor OPCs derived from the postnatal subventricular zone (SVZ) were numerically affected by alcohol exposure, indicating heterogeneity in susceptibility based on OL ontogenetic origin. Although mature OL and proliferating OPC numbers recovered by postnatal day 50 (P50), abnormalities in myelin protein expression and microstructure within the corpus callosum of alcohol-exposed subjects persisted, as assessed by western immunoblotting of myelin basic protein (MBP; decreased expression) and MRI diffusion tensor imaging (DTI; decreased fractional anisotropy). These results indicate that third trimester-equivalent alcohol exposure leads to an acute, albeit recoverable, decrease in OL lineage cell numbers, accompanied by enduring WM injury. Additionally, our finding of heterogeneity in alcohol susceptibility based on the developmental origin of OLs may have therapeutic implications in FASD and other disorders of WM development.

Ethanol exposure during development reduces GABAergic/glycinergic neuron numbers and lobule volumes in the mouse cerebellar vermis

Cerebellar alterations are a hallmark of Fetal Alcohol Spectrum Disorders and are thought to be responsible for deficits in fine motor control, motor learning, balance, and higher cognitive functions. These deficits are, in part, a consequence of dysfunction of cerebellar circuits. Although the effect of developmental ethanol exposure on Purkinje and granule cells has been previously characterized, its actions on other cerebellar neuronal populations are not fully understood. Here, we assessed the impact of repeated ethanol exposure on the number of inhibitory neurons in the cerebellar vermis. We exposed pregnant mice to ethanol in vapor inhalation chambers during gestational days 12-19 and offspring during postnatal days 2-9. We used transgenic mice expressing the fluorescent protein, Venus, in GABAergic/glycinergic neurons. Using unbiased stereology techniques, we detected a reduction in Venus positive neurons in the molecular and granule cell layers of lobule II in the ethanol exposed group at postnatal day 16. In contrast, ethanol produced a more widespread reduction in Purkinje cell numbers that involved lobules II, IV-V and IX. We also found a reduction in the volume of lobules II, IV-V, VI-VII, IX and X in ethanol-exposed pups. These findings indicate that second and third trimester-equivalent ethanol exposure has a greater impact on Purkinje cells than interneurons in the developing cerebellar vermis. The decrease in the volume of most lobules could be a consequence of a reduction in cell numbers, dendritic arborizations, or axonal projections.

Tobacco Nitrosamine Exposures Contribute to Fetal Alcohol Spectrum Disorder Associated Cerebellar Dysgenesis

Variability in the phenotypic features and severity of fetal alcohol spectrum disorder (FASD) is not fully linked to alcohol dose. We hypothesize that FASD-type neurodevelopmental abnormalities may be caused by exposures to the tobacco-specific nitrosamine, NNK, since a high percentage of pregnant women who drink also smoke. In vitro experiments using PNET2 human cerebellar neuronal cultures examined ethanol and NNK effects on viability and mitochondrial function. Early postnatal rat cerebellar slice cultures were used to examine effects of ethanol and NNK on cerebellar histology and neuroglial and stress protein expression. Ethanol (50 mM) decreased viability and ATP content and increased mitochondrial mass, while NNK (100 μM or higher) selectively inhibited mitochondrial function. The slice culture studies demonstrated striking adverse effects of ethanol, NNK and ethanol+NNK exposures manifested by architectural disorganization of the cortex with relative reductions of internal granule cells, increases in external granule cells, and loss of Purkinje cells. Ethanol, NNK, and ethanol+NNK inhibited expression of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE), and increased levels of 4-hydroxynonenal (HNE). In addition, ethanol increased activated Caspase 3, NNK decreased tau and phospho-tau, and ethanol+NNK inhibited expression of Aspartyl-β-hydroxylase (ASPH), which mediates neuronal migration. In conclusion, ethanol and NNK were shown to exert independent but overlapping adverse effects on cerebellar cortical development, neuronal viability, function, and neuroglial protein expression. These findings support our hypothesis that NNK exposures via tobacco smoking in pregnancy can contribute to FASD-associated neurodevelopmental abnormalities.

Potential Co-Factor Role of Tobacco Specific Nitrosamine Exposures in the Pathogenesis of Fetal Alcohol Spectrum Disorder

BACKGROUND

Cerebellar developmental abnormalities in Fetal Alcohol Spectrum Disorder (FASD) are linked to impairments in insulin signaling. However, co-morbid alcohol and tobacco abuses during pregnancy are common. Since smoking leads to tobacco specific Nitrosamine (NNK) exposures which have been shown to cause brain insulin resistance, we hypothesized that neurodevelopmental abnormalities in FASD could be mediated by ethanol and/or NNK.

METHODS

Long Evans rat pups were intraperitoneal (IP) administered ethanol (2 g/kg) on postnatal days (P) 2, 4, 6 and/or NNK (2 mg/kg) on P3, P5, and P7 to simulate third trimester human exposures. The Cerebellar function, histology, insulin and Insulin-like Growth Factor (IGF) signaling, and neuroglial protein expression were assessed.

RESULTS

Ethanol, NNK and ethanol+NNK groups had significant impairments in motor function (rotarod tests), abnormalities in cerebellar structure (Purkinje cell loss, simplification and irregularity of folia, and altered white matter), signaling through the insulin and IGF-1 receptors, IRS-1, Akt and GSK-3β, and reduced expression of several important neuroglial proteins. Despite similar functional effects, the mechanisms and severity of NNK and ethanol+NNK induced alterations in cerebellar protein expression differed from those of ethanol.

CONCLUSIONS

Ethanol and NNK exert independent but overlapping adverse effects on cerebellar development, function, insulin signaling through cell survival, plasticity, metabolic pathways, and neuroglial protein expression. The results support the hypothesis that tobacco smoke exposure can serve as a co-factor mediating long-term effects on brain structure and function in FASD.

Mini-Review: Effects of Ethanol on GABAA Receptor-Mediated Neurotransmission in the Cerebellar Cortex--Recent Advances

Studies from several laboratories have shown that ethanol impairs cerebellar function, in part, by altering GABAergic transmission. Here, we discuss recent advances in our understanding of the acute effects of ethanol on GABA(A) receptor-mediated neurotransmission at cerebellar cortical circuits, mainly focusing on electrophysiological studies with slices from laboratory animals. These studies have shown that acute ethanol exposure increases GABA release at molecular layer interneuron-to-Purkinje cell synapses and also at reciprocal synapses between molecular layer interneurons. In granule cells, studies with rat cerebellar slices have consistently shown that acute ethanol exposure both potentiates tonic currents mediated by extrasynaptic GABA(A) receptors and also increases the frequency of spontaneous inhibitory postsynaptic currents mediated by synaptic GABA(A) receptors. These effects have been also documented in some granule cells from mice and nonhuman primates. Currently, there are two distinct models on how ethanol produces these effects. In one model, ethanol primarily acts by directly potentiating extrasynaptic GABA(A) receptors, including a population that excites granule cell axons and stimulates glutamate release onto Golgi cells. In the other model, ethanol acts indirectly by increasing spontaneous Golgi cell firing via inhibition of the Na(+)/K(+) ATPase, a quinidine-sensitive K(+) channel, and neuronal nitric oxide synthase. It was also demonstrated that a direct inhibitory effect of ethanol on tonic currents can be unmasked under conditions of low protein kinase C activity. In the last section, we briefly discuss studies on the chronic effect of ethanol on cerebellar GABA(A) receptor-mediated transmission and highlight potential areas where future research is needed.

Deficient PKR in RAX/PKR Association Ameliorates Ethanol-Induced Neurotoxicity in the Developing Cerebellum

Ethanol-induced neuronal loss is closely related to the pathogenesis of fetal alcohol spectrum disorders. The cerebellum is one of the brain areas that are most sensitive to ethanol. The mechanism underlying ethanol neurotoxicity remains unclear. Our previous in vitro studies have shown that the double-stranded RNA (dsRNA)-activated protein kinase (PKR) regulates neuronal apoptosis upon ethanol exposure and ethanol activates PKR through association with its intracellular activator RAX. However, the role of PKR and its interaction with RAX in vivo have not been investigated. In the current study, by utilizing N-PKR-/- mice, C57BL/6J mice with a deficient RAX-binding domain in PKR, we determined the critical role of RAX/PKR association in PKR-regulated ethanol neurotoxicity in the developing cerebellum. Our data indicate that while N-PKR-/- mice have a similar BAC profile as wild-type mice, ethanol induces less brain/body mass reduction as well as cerebellar neuronal loss. In addition, ethanol promotes interleukin-1β (IL-1β) secretion, and IL-1β is a master cytokine regulating inflammatory response. Importantly, ethanol-promoted IL-1β secretion is inhibited in the developing cerebellum of N-PKR-/- mice. Thus, RAX/PKR interaction and PKR activation regulate ethanol neurotoxicity in the developing cerebellum, which may involve ethanol-induced neuroinflammation. Further, PKR could be a possible target for pharmacological intervention to prevent or treat fetal alcohol spectrum disorder (FASD).

Differential Effects of 3rd Trimester-Equivalent Binge Ethanol and Tobacco-Specific Nitrosamine Ketone Exposures on Brain Insulin Signaling in Adolescence

BACKGROUND

Fetal alcohol spectrum disorder (FASD) is associated with impairments in insulin and insulin-like growth factor (IGF) signaling through Akt pathways and altered expression of neuro-glial proteins needed for structural and functional integrity of the brain. However, alcohol abuse correlates with smoking, and tobacco smoke contains 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), which like other nitrosamines, impairs insulin and IGF signaling.

HYPOTHESIS

NNK exposure can serve as a co-factor in mediating long-term neuro-developmental abnormalities associated with FASD.

DESIGN

Long Evans rat pups were IP administered ethanol (2 g/kg) on postnatal days (P) 2, 4, 6 and/or NNK (2 mg/kg) on P3, P5, and P7, simulating third trimester human exposures. Temporal lobes from P30 rats (young adolescent) were used to measure signaling through the insulin/IGF-1/Akt pathways by multiplex ELISAs, and expression of neuroglial proteins by duplex ELISAs.

RESULTS

Ethanol, NNK, and ethanol + NNK exposures significantly inhibited insulin receptor tyrosine phosphorylation, and IRS-1 and myelin-associated glycoprotein expression. However, the major long-term adverse effects on Akt pathway downstream signaling and its targeted proteins including choline acetyltransferase, Tau, pTau, ubiquitin, and aspartate-β-hydroxylase were due to NNK rather than ethanol.

CONCLUSION

Alcohol and tobacco exposures can both contribute to long-term brain abnormalities currently regarded fetal ethanol effects. However, the findings suggest that many of the adverse effects on brain function are attributable to smoking, including impairments in signaling through survival and metabolic pathways, and altered expression of genes that regulate myelin synthesis, maturation and integrity and synaptic plasticity. Therefore, public health measures should address both substances of abuse to prevent "FASD".

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.

MicroRNA-29b regulates ethanol-induced neuronal apoptosis in the developing cerebellum through SP1/RAX/PKR cascade

Neuronal loss is a prominent etiological factor for fetal alcohol spectrum disorders. The cerebellum is one of the areas in the developing central nervous system that is most sensitive to ethanol, especially during the temporal window of ethanol vulnerability. MicroRNAs are small, non-coding RNAs capable of regulating diverse cellular functions including apoptosis. Ethanol exposure has been shown to interfere with the expression of microRNAs. However, the role of microRNAs in ethanol neurotoxicity is still not clear. In the present study, we identified a particular microRNA, miR-29b, as a novel target of ethanol in the developing cerebellar granule neurons. We discovered that ethanol exposure suppressed miR-29b and induced neuronal apoptosis. Overexpression of miR-29b rendered neurons protection against ethanol-induced apoptosis. Furthermore, our data indicated that miR-29b mediated ethanol neurotoxicity through the SP1/RAX/PKR cascade. More importantly, the expression of miR-29b is developmentally regulated, which may account for, at least partially, the temporal window of ethanol sensitivity in the developing cerebellum.

Effects of ethanol exposure on nervous system development in zebrafish

Alcohol (ethanol) is a teratogen that adversely affects nervous system development in a wide range of animal species. In humans numerous congenital abnormalities arise as a result of fetal alcohol exposure, leading to a spectrum of disorders referred to as fetal alcohol spectrum disorder (FASD). These abnormalities include craniofacial defects as well as neurological defects that affect a variety of behaviors. These human FASD phenotypes are reproduced in the rodent central nervous system (CNS) following prenatal ethanol exposure. While the study of ethanol effects on zebrafish development has been more limited, several studies have shown that different strains of zebrafish exhibit differential susceptibility to ethanol-induced cyclopia, as well as behavioral deficits. Molecular mechanisms underlying the effects of ethanol on CNS development also appear to be shared between rodent and zebrafish. Thus, zebrafish appear to recapitulate the observed effects of ethanol on human and mouse CNS development, indicating that zebrafish can serve as a complimentary developmental model system to study the molecular basis of FASD. Recent studies examining the effect of ethanol exposure on zebrafish nervous system development are reviewed, with an emphasis on attempts to elucidate possible molecular pathways that may be impacted by developmental ethanol exposure. Recent work from our laboratories supports a role for perturbed extracellular matrix function in the pathology of ethanol exposure during zebrafish CNS development. The use of the zebrafish model to assess the effects of ethanol exposure on adult nervous system function as manifested by changes in zebrafish behavior is also discussed.

Forebrain and hindbrain development in zebrafish is sensitive to ethanol exposure involving agrin, Fgf, and sonic hedgehog function

BACKGROUND

Ethanol is a teratogen that affects numerous developmental processes in the nervous system, which includes development and survival of GABAergic and glutamatergic neurons. Possible molecular mechanisms accounting for ethanol's effects on nervous system development include perturbed fibroblast growth factor (Fgf) and Sonic hedgehog (Shh) signaling. In zebrafish, forebrain GABAergic neuron development is dependent on Fgf19 and Shh signaling. The present study was conducted to test the hypothesis that ethanol affects GABAergic and glutamatergic neuron development by disrupting Fgf, Shh, and agrin function.

METHODS

Zebrafish embryos were exposed to varying concentrations of ethanol during a range of developmental stages, in the absence or presence of morpholino oligonucleotides (MOs) that disrupt agrin or Shh function. In situ hybridization was used to analyze glutamic acid decarboxylase (GAD1) gene expression, as well as markers of glutamatergic neurons.

RESULTS

Acute ethanol exposure results in marked reduction in GAD1 gene expression in forebrain and hindbrain, and reduction of glutamatergic neuronal markers in hindbrain. Subthreshold ethanol exposure, combined with agrin or Shh MO treatment, produces a similar diminution in expression of markers for GABAergic and glutamatergic neurons. Consistent with the ethanol effects on Fgf and Shh pathways, Fgf19, Fgf8, or Shh mRNA overexpression rescues ethanol-induced decreases in GAD1 and Atonal1a gene expression.

CONCLUSIONS

These studies demonstrate that GABAergic and glutamatergic neuron development in zebrafish forebrain or cerebellum is sensitive to ethanol exposure, and provides additional evidence that a signaling pathway involving agrin, Fgfs and Shh may be a critical target of ethanol exposure during zebrafish embryogenesis.

Mechanisms of ethanol-induced death of cerebellar granule cells

Maternal ethanol exposure during pregnancy may cause fetal alcohol spectrum disorders (FASD). FASD is the leading cause of mental retardation. The most deleterious effect of fetal alcohol exposure is inducing neuroapoptosis in the developing brain. Ethanol-induced loss of neurons in the central nervous system underlies many of the behavioral deficits observed in FASD. The cerebellum is one of the brain areas that are most susceptible to ethanol during development. Ethanol exposure causes a loss of both cerebellar Purkinje cells and granule cells. This review focuses on the toxic effect of ethanol on cerebellar granule cells (CGC) and the underlying mechanisms. Both in vitro and in vivo studies indicate that ethanol induces apoptotic death of CGC. The vulnerability of CGC to ethanol-induced death diminishes over time as neurons mature. Several mechanisms for ethanol-induced apoptosis of CGC have been suggested. These include inhibition of N-methyl-D-aspartate receptors, interference with signaling by neurotrophic factors, induction of oxidative stress, modulation of retinoid acid signaling, disturbance of potassium channel currents, thiamine deficiency, and disruption of translational regulation. Cultures of CGC provide an excellent system to investigate cellular/molecular mechanisms of ethanol-induced neurodegeneration and to evaluate interventional strategies. This review will also discuss the approaches leading to neuroprotection against ethanol-induced neuroapoptosis.

Acute and chronic ethanol intake: effects on spatial and non-spatial memory in rats

Abusive alcohol consumption produces neuronal damage and biochemical alterations in the mammal brain followed by cognitive disturbances. In this work rats receiving chronic and acute alcohol intake were evaluated in a spontaneous delayed non-matching to sample/position test. Chronic alcohol-treated rats had free access to an aqueous ethanol solution as the only available liquid source from the postnatal day 21 to the end of experiment (postnatal day 90). Acute alcoholic animals received an injection of 2 g/kg ethanol solution once per week. Subjects were evaluated in two tests (object recognition and spatial recognition) based on the spontaneous delayed non-matching to sample or to position paradigm using delays of 1 min, 15 min and 60 min. Results showed that chronic and acute alcohol intake impairs the rats' performance in both tests. Moreover, chronic alcohol-treated rats were more altered than acute treated animals in both tasks. Our results support the idea that chronic and acute alcohol administration during postnatal development caused widespread brain damage resulting in behavioral disturbances and learning disabilities.

Alcohol-induced neuronal death in central extended amygdala and pyriform cortex during the postnatal period of the rat

Mothers who consume alcohol during pregnancy may cause a neurotoxic syndrome defined as fetal alcohol spectrum disorder (FASD) in their offspring. This disorder is characterized by reduction in brain size, cognitive deficits and emotional/social disturbances. These alterations are thought to be caused by an alcohol-induced increase in apoptosis during neurodevelopment. Little is known about neuroapoptosis in the central extended amygdala and the pyriform cortex, which are key structures in emotional/social behaviors. The goal of this study was to determine the vulnerability of neuroapoptotic alcohol effects in those areas. Rats were administered alcohol (2.5g/kg s.c. at 0 and 2h) or saline on postnatal day (PND) 7, 15 and 20. The Amino-cupric-silver technique was used to evaluate neurodegeneration and immunohistochemistry to detect activated caspases 3-8 and 9 at 2h, 4, 6, 8, 12 and 24h after drug administration. We measured blood alcohol levels each hour, from 2 to 8h post second administration of alcohol in each of the ages studied. Results showed alcohol induced apoptotic neurodegeneration in the central extended amygdala on PND 7 and 15, and pyriform cortex on PND 7, 15 and 20. These structures showed activation of caspase 3 and 9 but not of caspase 8 suggesting that alcohol-induced apoptosis could occur by the intrinsic pathway. The pharmacokinetic differences between ages did not associate with the neurodegeneration age dependence. In conclusion, these limbic areas are damaged by alcohol, and each one has their own window of vulnerability during the postnatal period. The possible implications in emotional/social features in FASD are discussed.

Protection of neurons and microglia against ethanol in a mouse model of fetal alcohol spectrum disorders by peroxisome proliferator-activated receptor-γ agonists

Fetal alcohol spectrum disorders (FASD) result from ethanol exposure to the developing fetus and are the most common cause of mental retardation in the United States. These disorders are characterized by a variety of neurodevelopmental and neurodegenerative anomalies which result in significant lifetime disabilities. Thus, novel therapies are required to limit the devastating consequences of FASD. Neuropathology associated with FASD can occur throughout the central nervous system (CNS), but is particularly well characterized in the developing cerebellum. Rodent models of FASD have previously demonstrated that both Purkinje cells and granule cells, which are the two major types of neurons in the cerebellum, are highly susceptible to the toxic effects of ethanol. The current studies demonstrate that ethanol decreases the viability of cultured cerebellar granule cells and microglial cells. Interestingly, microglia have dual functionality in the CNS. They provide trophic and protective support to neurons. However, they may also become pathologically activated and produce inflammatory molecules toxic to parenchymal cells including neurons. The findings in this study demonstrate that the peroxisome proliferator-activated receptor-γ agonists 15-deoxy-Δ12,15 prostaglandin J2 and pioglitazone protect cultured granule cells and microglia from the toxic effects of ethanol. Furthermore, investigations using a newly developed mouse model of FASD and stereological cell counting methods in the cerebellum elucidate that ethanol administration to neonates is toxic to both Purkinje cell neurons as well as microglia, and that in vivo administration of PPAR-γ agonists protects these cells. In composite, these studies suggest that PPAR-γ agonists may be effective in limiting ethanol-induced toxicity to the developing CNS.

The effect of memantine in harmaline-induced tremor and neurodegeneration

Essential tremor (ET) is one of the most common and most disabling movement disorders among adults. The drug treatment of ET remains unsatisfactory. Additional therapies are required for patients with inadequate response or intolerable side effects. The current study aims to investigate the anti-tremogenic and neuroprotective effects of memantine (NMDA receptor antagonist) on the harmaline model of transient action tremor. The effects of memantine were further compared with ethanol. Three separate groups of male Wistar rats were injected either with saline, ethanol (1.5 gr/kg), or memantine (5 mg/kg) 15 min prior to a single intraperitoneal injection of harmaline (20 mg/kg). Tremor and locomotion were evaluated by a custom-built tremor and locomotion analysis system. After 24 h of harmaline injection, cellular viability, and apoptosis were assessed using crystal violet staining, and caspase-3 immunostaining, respectively. Harmaline caused neuronal cell loss and caspase-3 mediated apoptosis in cerebellar granular and purkinje cells as well as the inferior olivary neurons. Despite a reduction in tremor intensity and duration with ethanol, this compound resulted in cell loss in cerebellum and olivary nucleus. Memantine exhibited neuroprotective efficacy on cerebellar and inferior olivary neurons albeit weaker anti-tremor effect compared to ethanol. In conclusion, anti-tremogenic and neuroprotective effects do not necessarily overlap. Memantine is a potential treatment for ET particularly given its neuroprotective efficacy.

Ethanol-induced small heat shock protein genes in the differentiation of mouse embryonic neural stem cells

Neural stem cells (NSCs) of the neuroepithelium differentiate into one of three central nervous system (CNS) cell lineages: neurons, astrocytes, or oligodendrocytes. In this study, the differentiation potential of NSCs from the forebrain of embryonic day 15 (E15) mouse embryos was analyzed using immunocytochemistry. NSCs were differentiated early in the presence or absence of ethanol (50 mM), and gene expression patterns among NSCs, differentiated cells and ethanol-treated differentiated cells were assessed by microarray and real-time PCR analysis. Genes that were up-regulated in differentiated cells both in the presence and in the absence of ethanol when compared to NSCs were related to the Wnt signaling pathway, including Ctnna1, Wnt5a, Wnt5b, Wnt7a, Fzd3, and Fzd2; genes related to cell adhesion, including Cadm1, Ncam1, and Ncam2; and genes encoding small heat shock proteins, including HspB2, HspB7, and HspB8. In particular, the expression levels of HspB2 and HspB7 were elevated in ethanol-treated differentiated cells compared to non-treated differentiated cells. The gene expression patterns of various heat shock transcription factors (HSFs), proteins that regulate the transcription of heat shock genes, were also analyzed. The expression levels of HSF2 and HSF5 increased in differentiated cells in the presence and absence of ethanol when compared to NSCs. Of these two genes, HSF5 demonstrated an enhanced up-regulation, particularly in ethanol-treated differentiated cells compared to cells that were differentiated in the absence of ethanol. These results imply that HspB2 and HspB7, which are small heat shock proteins with tissue-restricted expression profiles, might be up-regulated by ethanol during the short-term differentiation of NSCs.

Fetal alcohol syndrome, Tourette syndrome, and hyperactivity in nine adopted children

Much attention has been paid in recent years to the role of prenatal exposure to alcohol. Fetal alcohol syndrome is one of the most severe afflictions resulting from such exposure. The present report documents the cases of adopted children diagnosed with fetal alcohol syndrome who developed both Tourette syndrome and attention deficit-hyperactivity disorder. Out of a population of 138 adopted children with behavior issues whose clinical histories were reviewed retrospectively, 9 children (6.5%) presented this constellation. Epidemiologic data, clinical data, neurologic examination findings, complementary testing, and developmental data were recorded. All nine patients studied had initial psychomotor retardation, despite the frequent case of subsequent intelligence quotient normalization. From a behavioral perspective, half of the cases presented obsessive-compulsive disorder and problems with social relations. Aggressive behavior was common. These cases also presented a high degree of severity of both tics and hyperactivity. The most common drug treatment was methylphenidate. This constellation of fetal alcohol syndrome, Tourette syndrome, and attention deficit-hyperactivity disorder is scantly reported in the literature and is likely underdiagnosed. This particular constellation poses its own prognosis and requires its own treatment.

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.

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.