Generation of neurons in the rat dentate gyrus and hippocampus: effects of prenatal and postnatal treatment with ethanol

Stress-induced suppression of hippocampal neurogenesis in adult male rats is altered by prenatal ethanol exposure

In adulthood, both alcohol (ethanol) and stress are known to suppress hippocampal neurogenesis in male rats. Similarly, most studies report that prenatal alcohol exposure (PAE) reduces cell proliferation and/or cell survival in the hippocampus of adult males. Furthermore, PAE is known to have marked effects on behavioral and hypothalamic-pituitary-adrenal (HPA) responsiveness to stressors. However, no studies have examined the modulation of adult hippocampal neurogenesis by stress in PAE animals. We hypothesized that, in accordance with previous data, PAE would suppress basal levels of adult hippocampal neurogenesis, and further that stress acting on a sensitized HPA axis would have greater adverse effects on adult hippocampal neurogenesis in PAE than in control rats. Adult male offspring from PAE, pair-fed (PF) control, and ad libitum-fed control (C) groups were subjected to restraint stress (9 days, 1 h/day) or left undisturbed. Rats were then injected with bromodeoxyuridine (BrdU) on day 10, perfused 24 h (proliferation) or 3 weeks (survival) later, and brains processed for BrdU immunohistochemistry. We found that (1) under non-stressed conditions, PAE rats had a small but statistically significant suppressive effect on levels of hippocampal neurogenesis and (2) unexpectedly, repeated restraint stress significantly reduced neurogenesis in C and PF, but not PAE rats. We speculate that the failure of PAE males to mount an appropriate (i.e. suppressive) neurogenic response to stressors, implies reduced plasticity and adaptability or resilience, which could impact negatively on hippocampal structure and function.

Hippocampal cell loss and neurogenesis after fetal alcohol exposure: insights from different rodent models

Prenatal ethanol exposure is invariably detrimental to the developing central nervous system and the hippocampus is particularly sensitive to the teratogenic effects of ethanol. Prenatal ethanol exposure has been shown to result in hippocampal cell loss, altered neuronal morphology and impaired performance on hippocampal-dependent learning and memory tasks in rodents. The dentate gyrus (DG) of the hippocampus is one of the few brain regions where neurogenesis continues into adulthood. This process appears to have functional significance and these newly generated neurons are believed to play important functions in learning and memory. Recently, several groups have shown that adult hippocampal neurogenesis is compromised in animal models of fetal alcohol spectrum disorders (FASD). The direction and magnitude of any changes in neurogenesis, however, appear to depend on a variety of factors that include: the rodent model used; the blood alcohol concentration achieved; the developmental time point when alcohol was administered; and the frequency of ethanol exposure. In this review we will provide an overview of the different rodent models of FASD that are commonly used in this research, emphasizing each of their strengths and limitations. We will also present an up-to-date summary on the effects of prenatal/neonatal ethanol exposure on adult hippocampal neurogenesis and cell loss, highlighting some of the possible molecular mechanisms that might be involved.

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.

Prenatal exposure to ethanol affects postnatal neurogenesis in thalamus

The number of neurons in the ventrobasal thalamus (VB) in the adolescent rat is unaffected by prenatal exposure to ethanol. This is in sharp contrast to other parts of the trigeminal-somatosensory system, which exhibit 30-35% fewer neurons after prenatal ethanol exposure. The present study tested the hypothesis that prenatal ethanol exposure affects dynamic changes in the numbers of VB neurons; such changes reflect the sum of cell proliferation and death. Neuronal number in the VB was determined during the first postnatal month in the offspring of pregnant Long-Evans rats fed an ethanol-containing diet or pair-fed an isocaloric non-alcoholic liquid diet. Offspring were examined between postnatal day (P) 1 and P30. The size of the VB and neuronal number were determined stereologically. Prenatal exposure to ethanol did not significantly alter neuronal number on any individual day, nor was the prenatal generation of VB neurons affected. Interestingly, prenatal ethanol exposure did affect the pattern of the change in neuronal number over time; total neuronal number was stable in the ethanol-treated pups after P12, but it continued to rise in the controls until P21. In addition, the rate of cell proliferation during the postnatal period was greater in ethanol-treated animals. Thus, the rate of neuronal acquisition is altered by ethanol, and by deduction, there appears to be less ethanol-induced neuronal loss in the VB. A contributor to these changes is a latent effect of ethanol on postnatal neurogenesis in the VB and the apparent survival of new neurons.

Ethanol acutely inhibits ionotropic glutamate receptor-mediated responses and long-term potentiation in the developing CA1 hippocampus

BACKGROUND

Developmental ethanol (EtOH) exposure damages the hippocampus, causing long-lasting alterations in learning and memory. Alterations in glutamatergic synaptic transmission and plasticity may play a role in the mechanism of action of EtOH. This signaling is fundamental for synaptogenesis, which occurs during the third trimester of human pregnancy (first 12 days of life in rats).

METHODS

Acute coronal brain slices were prepared from 7- to 9-day-old rats. Extracellular and patch-clamp electrophysiological recording techniques were used to characterize the acute effects of EtOH on alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptor (AMPAR)- and N-methyl-D-aspartate receptor (NMDAR)-mediated responses and long-term potentiation (LTP) in the CA1 hippocampal region.

RESULTS

Ethanol (40 and 80 mM) inhibited AMPAR- and NMDAR-mediated field excitatory postsynaptic potentials (fEPSPs). EtOH (80 mM) also reduced AMPAR-mediated fEPSPs in the presence of an inhibitor of Ca2+ permeable AMPARs. The effect of 80 mM EtOH on NMDAR-mediated fEPSPs was significantly greater in the presence of Mg2+. EtOH (80 mM) neither affected the paired-pulse ratio of AMPAR-mediated fEPSPs nor the presynaptic volley. The paired-pulse ratio of AMPAR-mediated excitatory postsynaptic currents was not affected either, and the amplitude of these currents was inhibited to a lesser extent than that of fEPSPs. EtOH (80 mM) inhibited LTP of AMPAR-mediated fEPSPs.

CONCLUSIONS

Acute EtOH exposure during the third-trimester equivalent of human pregnancy inhibits hippocampal glutamatergic transmission and LTP induction, which could alter synapse refinement and ultimately contribute to the pathophysiology of fetal alcohol spectrum disorder.

Deficits in trace fear conditioning in a rat model of fetal alcohol exposure: dose-response and timing effects

In humans, prenatal alcohol exposure can result in significant impairments in several types of learning and memory, including declarative and spatial memory. Animal models have been useful for confirming that many of the observed effects are the result of alcohol exposure, and not secondary to poor maternal nutrition or adverse home environments. Wagner and Hunt (2006) reported that rats exposed to ethanol during the neonatal period (postnatal days [PDs] 4-9) exhibited impaired trace fear conditioning when trained as adolescents, but were unaffected in delay fear conditioning. The present series of three experiments represent a more detailed analysis of ethanol-induced deficits in trace conditioning. In Experiment 1, the dose of ethanol given to neonates was varied (3.0, 4.0, or 5.0g/kg/day). There was a dose-dependent reduction in trace conditioning, with the poorest performance observed in animals treated with the highest dose. In Experiment 2, it was found that the impairment in trace conditioning resulting from neonatal ethanol exposure was dependent on the duration of the trace interval used for training; less learning was evident in ethanol-exposed animals trained with longer trace interval durations. These results confirm other reports of delay-dependent memory deficits. Finally, Experiment 3 determined that ethanol exposure limited to the first half of the neonatal period (PDs 4-6) was more detrimental to later trace conditioning than exposure during the second half (PDs 7-9). These results support the hypothesis that trace-conditioning impairments resulting from early ethanol exposure are due to the drug's teratogenic effects on the developing hippocampus, as the findings parallel those observed in animals with discrete hippocampal lesions. Comparisons between delay and trace fear-conditioning performance in animals exposed to ethanol during the brain growth spurt provide a model system to study both selective learning impairments and possible treatment approaches for humans with fetal alcohol spectrum disorders.

Persistent deficits in heart rate response habituation following neonatal binge ethanol exposure

BACKGROUND

We have previously shown that the rate of habituation of the heart rate orienting response to a novel odor in rats is negatively affected by neonatal ethanol exposure. Thus far, however, only young rats (16 days of age) have been tested. Given the persistence of attention and memory problems evident in humans exposed to ethanol in utero, the purpose of this experiment was to examine the longer-term consequences of ethanol exposure on response habituation.

METHODS

Ethanol (5.25 g/kg/d) was administered intragastrically to male and female Sprague-Dawley rats on postnatal days (PD) 4 to 9, and controls were given sham intubations. Animals were tested for heart rate orienting and response habituation to a novel olfactory stimulus (amyl acetate) on PD 16, 23, or 30.

RESULTS

Animals tested on PD 16 or 23 showed normal heart rate deceleration to the novel odor, a measure of the orienting response. However, ethanol-treated subjects showed impaired response habituation compared with sham controls. While controls exhibited complete habituation within 4 to 5 trials, ethanol-treated animals continued to respond throughout the testing session, with little decrement in heart rate response magnitude across 10 stimulus presentations. A different pattern of responding was observed in animals tested during adolescence (PD 30). Control animals failed to show the typical heart rate decrease indicative of orienting, and instead showed a tendency toward tachycardia. In contrast, ethanol-treated animals tested on PD 30 showed orienting bradycardia that persisted for several trials.

CONCLUSIONS

These data suggest that there are relatively long-term consequences of neonatal ethanol exposure on nonassociative memory. This impairment in habituation may be relevant to the distractibility and poor focused attention that is pervasive among humans diagnosed with fetal alcohol spectrum disorders.

The effects of exercise on adolescent hippocampal neurogenesis in a rat model of binge alcohol exposure during the brain growth spurt

Exposure to alcohol during the brain growth spurt results in impaired cognition and learning in adulthood. This impairment is accompanied by permanent structural changes in the hippocampal formation. Exercise improves performance on hippocampal-dependent learning and memory tasks and increases adult neurogenesis in the rat hippocampal dentate gyrus. The present study examined the effects of wheel running during adolescence on dentate gyrus cell proliferation and neurogenesis after postnatal binge-like alcohol exposure. On postnatal days (PD) 4-9, pups were either intubated with alcohol in a binge-like manner, sham intubated, or reared normally. On PD30-42, all animals were randomly assigned to two adolescent conditions: wheel running or inactive control. Animals were injected with BrdU every day between PD32 and PD42 and perfused on PD42 or PD72. In inactive control animals at both PD42 and PD72, cell proliferation and neurogenesis did not differ between postnatal treatment groups. Wheel running significantly increased the number of BrdU-labeled cells on PD42 in all three postnatal treatments. On PD72, only the normal controls showed significant increases in survival of newly generated cells resulting from the wheel running. These results indicate that adolescent wheel running can induce comparable increases in cell proliferation and neurogenesis in alcohol-exposed and control rats, but the long-term survival of those newly generated cells is impaired relative normal controls. Exercise may provide a means to stimulate neurogenesis, with implications for amelioration of hippocampal-dependent learning impairments associated with alcohol exposure. However, benefits requiring long-lasting survival of the newly generated cells will depend on identifying ways to promote survival.

Binge-like postnatal alcohol exposure triggers cortical gliogenesis in adolescent rats

The long-term effects of binge-like postnatal alcohol exposure on cell proliferation and differentiation in the adolescent rat neocortex were examined. Unlike the hippocampal dentate gyrus, where proliferation of progenitors results primarily in addition of granule cells in adulthood, the vast majority of newly generated cells in the intact mature rodent neocortex appear to be glial cells. The current study examined cytogenesis in the motor cortex of adolescent and adult rats that were exposed to 5.25 g/kg/day of alcohol on postnatal days (PD) 4-9 in a binge manner. Cytogenesis was examined at PD50 (through bromodeoxyuridine [BrdU] labeling) and survival of these newly generated cells was evaluated at PD80. At PD50, significantly more BrdU-positive cells were present in the motor cortex of alcohol-exposed rats than controls. Confocal analysis revealed that the majority (>60%) of these labeled cells also expressed NG2 chondroitin sulfate proteoglycan (NG2 glia). Additionally, survival of these newly generated cortical cells was affected by neonatal alcohol exposure, based on the greater reduction in the number of BrdU-labeled cells from PD50 to PD80 in the alcohol-exposed animals compared to controls. These findings demonstrate that neonatal alcohol exposure triggers an increase in gliogenesis in the adult motor cortex.

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.

Binge drinking during pregnancy and risk of seizures in childhood: a study based on the Danish National Birth Cohort

Seizures are often found in children with fetal alcohol syndrome, but it is not known whether binge drinking during pregnancy by nonalcoholic women is associated with an increased risk of seizure disorders in children. The authors conducted a population-based cohort study of 80,526 liveborn singletons in the Danish National Birth Cohort (1996-2002). Information on maternal binge drinking (intake of > or = 5 drinks on a single occasion) was collected in 2 computer-assisted telephone interviews during pregnancy. Children were followed for up to 8 years. Information on neonatal seizures, epilepsy, and febrile seizures was retrieved from the Danish National Hospital Register. Results showed that exposure to binge drinking episodes during pregnancy was not associated with an increased risk of seizure disorders in children, except for those exposed at 11-16 gestational weeks. These children had a 3.15-fold increased risk of neonatal seizures (95% confidence interval: 1.37, 7.25) and a 1.81-fold increased risk of epilepsy (95% confidence interval: 1.13, 2.90). These findings suggest that maternal binge drinking during a specific time period of pregnancy may be associated with an increased risk of specific seizure disorders in the offspring. The results are exploratory, however, and need to be replicated.

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.

Interference of ethanol and methylmercury in the developing central nervous system

Studies involving alcohol and its interactions with other neurotoxicants represent the focus of several works of research due to the fact that the use of alcohol can sometimes leads to serious health problems. Fetal exposure to alcohol and mercury has a high incidence in some regions of Brazil, where there are pregnant women who are alcoholics and live in mining areas. This work was conducted to examine the effects of combined exposure to ethanol (EtOH) and methylmercury (MeHg) in rats during the development of the central nervous system (CNS). Experimental behavioral animal models/tests were used in order to examine locomotion, anxiety, depression and memory. Pregnant rats received tap water or EtOH 22.5% w/v (6.5 g/kg per day), by gavage) during pregnancy and breast-feeding. On the 15th day of pregnancy, some groups received 8 mg/kg of MeHg (by gavage). The groups were as follows: control, EtOH, MeHg and EtOH+MeHg. The experimental results showed that the EtOH, MeHg and EtOH+MeHg groups reduced the percentage of frequency and time spent in the open arms entries of the elevated plus-maze (EPM) test, when compared to the control group. This result suggests an anxiogenic behavioral response. The MeHg group increased locomotor activity in the arena and the immobility time in the forced swimming test, suggestive of depression-like behavior. The EtOH+MeHg group showed greater reductions in the percentages of frequency and time spent in the open arms entries in the EPM test, suggesting a sedative-behavior since the frequency of enclosed arm entries was affected. In the inhibitory avoidance task, the EtOH+MeHg group reduced the latency of the step-down response onto the grid floor, suggesting a cognitive and behavior dysfunctions. Taken together, the results suggest that EtOH and/or MeHg intoxication during the developing CNS may be a risk for deficits related to locomotor impairment, anxiety, depression and neurocognitive functions. There is a possibility that EtOH may prevent some of the MeHg responses, but the precise mechanism of action involved in this process needs to be considered for future research.

Ethanol neurotoxicity and dentate gyrus development

Maternal alcohol ingestion during pregnancy adversely affects the developing fetus, often leading to fetal alcohol syndrome (FAS). One of the most severe consequences of FAS is brain damage that is manifested as cognitive, learning, and behavioral deficits. The hippocampus plays a crucial role in such abilities; it is also known as one of the brain regions most vulnerable to ethanol-induced neurotoxicity. Our recent studies using morphometric techniques have further shown that ethanol neurotoxicity appears to affect the development of the dentate gyrus in a region-specific manner; it was found that early postnatal ethanol exposure causes a transitory deficit in the hilus volume of the dentate gyrus. It is strongly speculated that such structural modifications, even transitory ones, appear to result in developmental abnormalities in the brain circuitry and lead to the learning disabilities observed in FAS children. Based on reports on possible factors deciding ethanol neurotoxicity to the brain, we review developmental neurotoxicity to the dentate gyrus of the hippocampal formation.

The effect of acute and chronic exposure to ethanol on the developing encephalon: a review

OBJECTIVES: to compare the acute and chronic effects of ethanol on the neural development, by analysis of the ontogenetic neural structure of mammals. METHODS: searches were performed in the following electronic databases: MEDLINE, SciElo, PubMed, LILACS, CAPES periodical, and the Open Journal System. The descriptors used were: "chronic ethanol toxicity", "chronic alcohol toxicity", "acute ethanol toxicity", "acute alcohol", "neural ontogenic development", "neuronal migration disturbances", "neural structure". The following inclusion criteria were used: articles published between 2003 and 2007, some classic articles in the field and an important neuropsychology textbook. RESULTS: the analysis of papers revealed that, although several studies of the chronic effects of ethanol exposure on the mammalian nervous system have been conducted, only a few have investigated the acute effects of ethanol on specific days of gestation, and these studies have revealed important disorders relating to the cerebral tissue. CONCLUSIONS: it should be recommended that women refrain from the consumption of ethanol during gestational phase to protect the fetus' health. Furthermore, the acute consumption of ethanol by women nearing the eighth or ninth week of gestation has been shown to be potentially harmful to the nervous tissue of the fetus.

Effects of moderate chronic ethanol consumption on hippocampal nicotinic receptors and associative learning

A number of studies have reported that ethanol exposure induces changes in different brain systems. The hippocampus is a brain region that is very vulnerable to ethanol exposition, which functionally results in impairment of learning and memory processes reported in heavy drinkers. Hippocampal nicotinic receptors are involved in learning and memory. In this study, we determined the effects of ethanol on the main hippocampal subtypes of neural nicotinic receptors (alpha7 and alpha4beta2) in rats non-selected for alcohol consumption, in order to check for possible changes on these receptors that could be linked with alterations in learning acquisition. Binding assays were carried out with [3H]methyllycaconitine ([3H]MLA) to study the alpha7 and [3H]nicotine to study alpha4beta2 receptors. Auto-shaping, continuous ratio and extinction procedures were used as behavioral tests. The results show that moderate chronic ethanol consumption for 10 weeks produces: (a) a decrease of both hippocampal nicotinic receptor subtypes without alterations in affinity; (b) no differences in behavioral performance between control rats and ethanol-drinking rats in auto-shaping and continuous ratio; (c) an improvement of performance of extinction paradigm. These results indicate that chronic ethanol consumption, at moderate levels, induces changes in hippocampal nicotinic receptors but does not impair acquisition and performance of new associative learning and even improves some kind of paradigms. These results may have implications in the biochemical basis of interactions between alcohol and nicotine and the effects of these drugs on behavior.

Prenatal ethanol exposure alters core body temperature and corticosterone rhythms in adult male rats

Ethanol's effects on the developing brain include alterations in morphology and biochemistry of the hypothalamus. To examine the potential functional consequences of ethanol's interference with hypothalamic differentiation, we studied the long-term effects of prenatal ethanol exposure on basal circadian rhythms of core body temperature (CBT) and heart rate (HR). We also examined the late afternoon surge in corticosterone (CORT). Core body temperature and HR rhythms were studied in separate groups of animals at 4, 8, and 20 months of age. The normal late afternoon rise in plasma CORT was examined in freely moving male rats at 6 months of age via an indwelling right atrial cannula. Results showed that the CBT circadian rhythm exhibited an earlier rise after the nadir of the rhythm in fetal alcohol-exposed (FAE) males at all ages compared to controls. At 8 months of age, the amplitude of the CBT circadian rhythm in FAE males was significantly reduced to the level observed in controls at 20 months. No significant effects of prenatal ethanol exposure were observed on basal HR rhythm at any age. The diurnal rise in CORT secretion was blunted and prolonged in 6-month-old FAE males compared to controls. Both control groups exhibited a robust surge in CORT secretion around the onset of the dark phase of the light cycle, which peaked at 7:30 p.m. Whereas FAE males exhibited a linear rise beginning in mid afternoon, which peaked at 9:30 p.m. These results indicate that exposure to ethanol during the period of hypothalamic development can alter the long-term regulation of circadian rhythms in specific physiological systems.

Single alcohol exposure in early life damages hippocampal stem/progenitor cells and reduces adult neurogenesis

Alcohol exposure during pregnancy may cause fetal alcohol syndrome (FAS), characterized by impaired cognitive functions. Neurogenesis occurs in the adult hippocampus and is functionally associated with learning, memory, and mood disorders. However, whether early postnatal exposure to alcohol impairs neurogenesis and through which mechanisms it occurs is poorly understood. Here, we report that a single episode of alcohol exposure in postnatal day 7 (P7) decreases neurogenesis in the adult hippocampus. Furthermore, we demonstrate a co-localization of glial fibrillar acidic protein, nestin, and vimentin with activated caspase-3 12 h after ethanol treatment. Finally, we show that the number of primary neurospheres derived from the hippocampi of alcohol-exposed mice is reduced compared to controls. These findings suggest that alcohol exposure in postnatal mice reduces the pool of neural stem/progenitor cells in the DG, and subsequently results in a decrease of adult neurogenesis. This may explain certain aspects of impaired hippocampal functions in FAS.

S100B-mediated protection against the pro-apoptotic effects of ethanol on fetal rhombencephalic neurons

Previously, this laboratory demonstrated that ethanol treatment significantly reduces the number of developing serotonin (5-HT) and other fetal rhombencephalic neurons in rats by augmenting apoptosis. Using a 5-HT(1A) agonist we were able to attenuate the ethanol-associated reduction and apoptosis of 5-HT and rhombencephalic neurons. The downstream pro-survival effects of 5-HT(1A) stimulation were associated with the activation of phosphatidylinositol 3'kinase (PI-3K) and its subsequent up-regulation of specific NF-kappaB-dependent pro-survival genes. Using an in vitro model, we investigated the hypothesis that S100B, a protein which is released from astrocytes following 5-HT(1A) agonist stimulation, can reduce apoptosis in ethanol-treated rat fetal rhombencephalic neurons. We also evaluated whether the anti-apoptotic effects of S100B on fetal rhombencephalic neurons were linked to the activation of the PI-3K-->pAkt pro-survival pathway and the expression of two NF-kappaB-dependent pro-survival genes: XIAP and Bcl-2. Moreover, we determined whether S100B's pro-survival effects were associated with mitogen activated protein kinase kinase (MAPKK)-->p42/p44 MAPK. The results of these investigations demonstrated that S100B treatment prevented ethanol-associated apoptosis of fetal rhombencephalic neurons. In addition, it appears that these neuroprotective effects are linked to activation of the PI-3K pathways, because the PI-3K inhibitor LY294002 blocks the neuroprotective effects of S100B. Moreover, S100B increases the formation of pAkt and the up-regulation of two downstream NF-kappaB-dependent pro-survival genes: XIAP and Bcl-2. Although the MAPKK inhibitor PD98059 reduced the number of surviving neurons in S100B-treated cultures, S100B did not activate MAPKK.

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

During the development of the central nervous system, neurons pass through critical periods or periods of vulnerability. We explored periods of vulnerability for cranial nerve nuclei by determining the effects of acute exposure to ethanol during development on the number of neurons in mature brainstem. Long-Evans rats were injected with 2.9 g ethanol/kg body weight on one day between gestational day (G) 7 and G13, inclusive. Two hours later, animals received a second injection of 1.45 g/kg. Controls were injected with equivalent volumes of saline. Brainstems of 31-day-old offspring were cryosectioned and stained with cresyl violet. Stereological methods were used to determine the volume and numerical density of neurons in three trigeminal sensory nuclei (the principal sensory nucleus of the trigeminal nerve, and the oral and interpolar subnuclei of the spinal trigeminal nuclear complex) and three motor nuclei (the trigeminal, facial, and hypoglossal nuclei). The numbers of neurons in most nuclei were lower following early (on G7 and/or G8) or later (on G12 and/or G13) exposure. Only the trigeminal interpolar nucleus was affected by neither early nor late ethanol exposure. Thus, prenatal exposure to ethanol affects the number of neurons in brainstem nuclei in a time-dependent manner. Windows of vulnerability coincide with gastrulation (G7/G8) and the period of neuronal generation (G12/G13).

Prenatal-through-postnatal exposure to moderate levels of ethanol leads to damage on the hippocampal CA1 field of juvenile rats

Experimental paradigms conducted to assess the neurotoxic effects of ethanol exposure on hippocampus development have yielded controversial findings. Hippocampal CA1 population and some cytoarchitectural parameters of pyramidal cells were studied after exposure to ethanol during early development, in rats. Examination of 30-day-old offspring of rats exposed to moderate levels of ethanol during gestation through lactation showed an increased volume of the hippocampal CA1 field compared to untreated or pair-fed control pups, as well as a reduced number of pyramidal neurons. In addition, the number of spines from surviving CA1 pyramidal neurons was reduced. Furthermore, stubby and wide spines were proportionally increased, while the proportion of mushroom and ramified spines was reduced; no variation in the proportion of thin spines was observed. Because alcoholic women usually drink alcohol before, during, and after pregnancy, a broad-range experimental model of alcohol exposure was used in this study. The present findings show that experimental exposure to moderate levels of ethanol, resembling the human situation in alcoholic mothers, leads to loss of hippocampal CA1 pyramidal neurons, along with several pathological and plastic events in the dendritic arborization of these neurons. Some ethanol-induced excitotoxicity-related mechanisms, which may be underlying these effects, are discussed.

Chronic prenatal ethanol exposure increases glucocorticoid-induced glutamate release in the hippocampus of the near-term foetal guinea pig

Exposure to high cortisol concentration can injure the developing brain, possibly via an excitotoxic mechanism involving glutamate (Glu). The present study tested the hypothesis that chronic prenatal ethanol exposure (CPEE) activates the foetal hypothalamic-pituitary-adrenal axis to produce high cortisol exposure in the foetal compartment and alters sensitivity to glucocorticoid-induced Glu release in the foetal hippocampus. Pregnant guinea pigs received daily oral administration of ethanol (4 g/kg maternal body weight/day) or isocaloric-sucrose/pair-feeding from gestational day (GD) 2 until GD 63 (term, approximately GD 68) at which time they were euthanised, 1 h after their final treatment. Adrenocorticotrophic hormone (ACTH) and cortisol concentrations were determined in foetal plasma. Basal and electrically stimulated Glu and gamma-aminobutyric acid (GABA) efflux in the presence or absence of dexamethasone (DEX), a selective glucocorticoid-receptor agonist, were determined ex vivo in foetal hippocampal slices. Glucocorticoid receptor (GR), mineralocorticoid receptor (MR) and N-methyl-D-aspartate (NMDA) receptor NR1 subunit mRNA expression were determined in situ in the hippocampus and dentate gyrus. In the near-term foetus, CPEE increased foetal plasma ACTH and cortisol concentrations. Electrically stimulated glutamate, but not GABA, release was increased in CPEE foetal hippocampal slices. Low DEX concentration (0.3 microM) decreased stimulated glutamate, but not GABA, release in both CPEE and control foetal hippocampal slices. High DEX concentration (3.0 microM) increased basal release of Glu, but not GABA, in CPEE foetal hippocampal slices. GR, but not MR, mRNA expression was elevated in the hippocampus and dentate gyrus, whereas NR1 mRNA expression was increased in the CA1 and CA3 fields of the foetal hippocampus. These data demonstrate that CPEE increases high glucocorticoid concentration-induced Glu release in the foetal hippocampus, presumably as a consequence of increased GR expression. These effects of CPEE, coupled with increased glutamate release and increased NMDA receptor expression, may predispose the near-term foetal hippocampus to GR and Glu-NMDA receptor-mediated neurodevelopmental toxicity.

The alcoholism generator

Alcohol exposure largely affects 3 populations: fetuses, adolescents, and adults. These 3 developmental stages are inextricably intertwined such that elevated alcohol exposure at any time increases the probability of exposure at the others. This circular interdependency is called the alcoholism generator. Furthermore, exposure to large amounts of alcohol at these 3 times can cause cognitive dysfunction, largely through mechanisms of alcohol-induced perturbations in neurogenesis and synaptogenesis. Breaking this cycle is key to reducing problem alcohol drinking and the associated sequelae.

Impaired trace fear conditioning following neonatal ethanol: reversal by choline

Neonatal ethanol exposure in animals results in performance deficits on tests of hippocampus-dependent spatial memory, and recent studies have shown that extra dietary choline can ameliorate some of these impairments. In this experiment, rats were administered 5.25 g/kg ig ethanol per day or sham intubations on Postnatal Days (PD) 4-9 and choline (0.1 ml of an 18.8 mg/ml solution) or saline subcutaneously on PD 4-20. On PD 30, rats were given delay or trace fear conditioning trials and were tested for conditioned stimulus-elicited freezing 24 hr later. Neonatal ethanol produced a profound impairment in trace conditioning that was reversed by choline. Groups did not differ in delay conditioned responding, indicating that neonatal ethanol produces a relatively selective cognitive deficit that can be alleviated with supplemental choline.

The effects of ethanol and the serotonin(1A) agonist ipsapirone on the expression of the serotonin(1A) receptor and several antiapoptotic proteins in fetal rhombencephalic neurons

Previously, this laboratory demonstrated that ethanol reduces the number of developing serotonin (5-HT)-containing neurons by increasing apoptosis. We also found that 5-HT(1A) agonists attenuate the proapoptotic effects of ethanol and the ethanol-mediated reduction of fetal 5-HT neurons. These neuroprotective effects are mediated in part by the ability of 5-HT(1A) agonists to activate the phosphatidyl 3'-kinase (PI-3K) prosurvival pathway. NF-kappaB is one of the downstream effectors activated by this pathway. In the present study, we used quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) to determine the effects of 50mM ethanol and 100nM of ipsapirone, a 5-HT(1A) agonist, on the expression of several NF-kappaB-dependent antiapoptotic genes: X-linked inhibitor of apoptosis protein (XIAP), cIAP1, cIAP2, Bcl-2, and Bcl-xl. We also investigated the effects of ethanol and ipsapirone on the expression of the gene encoding the 5-HT(1A) receptor. The results demonstrate that ethanol reduces the expression of several prosurvival genes: XIAP, cIAP1, cIAP2, Bcl-2, and Bcl-xl. Importantly, the ethanol-mediated reduction in the expression of XIAP and Bcl-xl was prevented by co-treatment with ipsapirone. Thus, the damaging effects of ethanol are likely to involve a reduction in several prosurvival proteins. Moreover, the protective effects of ipsapirone on ethanol-treated neurons might involve their ability to prevent the reduction of XIAP and Bcl-xl. Although ipsapirone treatment decreased the expression of cIAP1, Bcl-2, and Bcl-xl in control neurons, our prior studies suggest that their survival is not reduced by ipsapirone. We also observed an increased expression of the 5-HT(1A) receptor in ipsapirone-treated control neurons.

Astrocyte control of fetal cortical neuron glutathione homeostasis: up-regulation by ethanol

Ethanol increases apoptotic neuron death in the developing brain and at least part of this may be mediated by oxidative stress. In cultured fetal rat cortical neurons, Ethanol increases levels of reactive oxygen species (ROS) within minutes of exposure and reduces total cellular glutathione (GSH) shortly thereafter. This is followed by onset of apoptotic cell death. These responses to Ethanol can be blocked by elevating neuron GSH with N-acetylcysteine or by co-culturing neurons with neonatal cortical astrocytes. We describe here mechanisms by which the astrocyte-neuron gamma-glutamyl cycle is up-regulated by Ethanol, enhancing control of neuron GSH in response to the pro-oxidant, Ethanol. Up to 6 days of Ethanol exposure had no consistent effects on activities of gamma-glutamyl cysteine ligase or glutathione synthetase, and GSH content remained unchanged (p < 0.05). However, glutathione reductase was increased with 1 and 2 day Ethanol exposures, 25% and 39% for 2.5 and 4.0 mg/mL Ethanol by 1 day, and 11% and 16% for 2.5 and 4.0 mg/mL at 2 days, respectively (p < 0.05). A 24 h exposure to 4.0 mg/mL Ethanol increased GSH efflux from astrocyte up to 517% (p < 0.05). Ethanol increased both gamma-glutamyl transpeptidase expression and activity on astrocyte within 24 h of exposure (40%, p = 0.05 with 4.0 mg/mL) and this continued for at least 4 days of Ethanol treatment. Aminopeptidase N activity on neurons increased by 62% and 55% within 1 h of Ethanol for 2.5 and 4.0 mg/mL concentration, respectively (p < 0.05), remaining elevated for 24 h of treatment. Thus, there are at least three key points of the gamma-glutamyl cycle that are up-regulated by Ethanol, the net effect being to enhance neuron GSH homeostasis, thereby protecting neurons from Ethanol-mediated oxidative stress and apoptotic death.

Neurotoxic effects of alcohol and acetaldehyde during embryonic development

Alcohol drinking during pregnancy results in abnormal fetal development, including fetal alcohol syndrome (FAS) in humans and experimental animals. FAS is characterized by two major effects, including central nervous system (CNS) dysfunction and multiple anomalies recognizable mainly as a typical face. However, the mechanisms of alcohol-induced embryotoxicity have not been clearly demonstrated. The aim of the present study was to investigate the possible mechanisms underlying ethanol-induced FAS in the developing embryo. First, ethanol-induced developmental abnormalities were investigated in vitro. Postimplantation embryos at gestation day (GD) 9.5 were cultured for 48 h and observed for morphological changes. Ethanol-mediated changes in proteins regulated apoptosis (p53 and bcl-2), antioxidant (vitamin E and catalase) activities, generation of reactive oxygen species (ROS), and oxidative DNA damage shown as 8-hydroxy-2'-deoxyguanosine (8-OHdG) were measured in embryonic midbrain cells. Alcohol or acetaldehyde significantly induced cytotoxicity in cultured rat embryonic midbrain cells. The levels of p53, bcl-2, and 8-OHdG were concomitantly changed by alcohol and acetaldehyde treatment in midbrain cells. Injured cells induced by ROS were increased by alcohol or acetaldehyde treatment in midbrain cells. Cotreatment with alcohol or acetaldehyde and catalase decreased cytotoxicity in midbrain cells. In postimplantation embryo culture, alcohol or acetaldehyde-treated embryos showed retardation of embryonic growth and development in a concentration-dependent manner. These results indicate that alcohol and its metabolite acetaldehyde induce fetal developmental abnormalities by disrupting cellular differentiation and growth. Data demonstrate that some antioxidants can partially protect against the alcohol-induced embryonic developmental toxicity.

Signaling pathways involved with serotonin1A agonist-mediated neuroprotection against ethanol-induced apoptosis of fetal rhombencephalic neurons

Previously, this laboratory demonstrated that developing serotonin (5-HT) neurons and other fetal rhombencephalic neurons are reduced by in vivo and in vitro exposure to ethanol, effects that are related to ethanol's augmentation of apoptosis. We also found that 5-HT1A agonists diminished the ethanol-associated reduction of 5-HT neurons and other fetal rhombencephalic neurons by attenuating the pro-apoptotic effects of ethanol. Presently, we investigated the hypothesis that the protective/anti-apoptotic effects of a 5-HT1A agonist on fetal rhombencephalic neurons are mediated by activation of the phosphatidylinositol 3' kinase (PI-3K) and/or the mitogen-activated protein kinase kinase (MAPKK) pathway. Apoptotic and non-apoptotic fetal rhombencephalic neurons were quantitated in primary cultures that were treated with 50 mM ethanol and with 100 nM of a 5-HT1A agonist such as 8-OH-DPAT [8-hydroxy 2-(di-n-propylamino)tetralin], ipsapirone, or buspirone. Analysis of neurons stained with Hoechst 33342 demonstrated the anti-apoptotic effects of 5-HT1A agonists and implicated the involvement of the PI-3K pathway and possibly the MAPKK pathway with the protective effects of these drugs. The protective effects were blocked by a 5-HT1A antagonist (WAY 100635), an inhibitor of PI-3K (LY294002), and an inhibitor of MAPKK (PD98059). Western blot analyses showed that ethanol treatment reduces basal pAkt levels. These analyses also provide support for the involvement of the PI-3K pathway; ipsapirone stimulated the phosphorylation of Akt in control and ethanol-treated neurons, and these effects were antagonized by LY294002.

Postnatal ethanol exposure disrupts signal detection in adult rats

Human prenatal ethanol exposure that occurs during a period of increased synaptogenesis known as the "brain growth spurt" has been associated with significant impairments in attention, learning, and memory. The present experiment assessed whether administration of ethanol during the brain growth spurt in the rat, which occurs shortly after birth, disrupts attentional performance. Rats were administered 5.25 g/kg/day ethanol via intragastric intubation from postnatal days (PD) 4-9, sham-intubation, or no intubation (naïve). Beginning at PD 90, animals were trained to asymptotic performance in a two-lever attention task that required discrimination of brief visual signals from trials with no signal presentation. Finally, manipulations of background noise and inter-trial interval duration were conducted. Early postnatal ethanol administration did not differentially affect acquisition of the attention task. However, after rats were trained to asymptotic performance levels, those previously exposed to ethanol demonstrated a deficit in detection of signals but not of non-signals compared to sham-intubated and naïve rats. The signal detection deficit persisted whenever these animals were re-trained in the standard task, but further task manipulations failed to interact with ethanol pretreatment. The present data support the hypothesis that early postnatal ethanol administration disrupts aspects of attentional processing in the rat.

Early postnatal exposure to alcohol reduces the number of neurons in the occipital but not the parietal cortex of the rat

BACKGROUND

The rat brain undergoes a period of rapid growth in the early postnatal period. During this time, the neocortex seems to be vulnerable to ethanol injury. Subdivisions of the neocortex develop in a temporospatial gradient that is likely to determine their vulnerability to ethanol-induced damage and whether damage is permanent. Therefore, the authors investigated the effect of postnatal ethanol exposure on the neocortex and specific subregions at the cessation of exposure and in the mature brain.

METHODS

Four-day-old rat pups with intragastric cannulae were artificially reared from postnatal day (PN) 4 through PN9. Of 12 daily feeds, two consecutive feeds contained either ethanol (4.5 g/kg) or an isocaloric maltose/dextrin solution. On PN10 or PN115, animals were perfused intracardially, and the brains were removed. Stereological methods were used to determine the total number of neurons and glial cells in, and the volume of, the neocortex, the parietal cortex, and the occipital cortex.

RESULTS

Exposure to ethanol did not affect body or brain weight at PN10. In contrast, at PN115 forebrain weight was significantly lower in ethanol-exposed animals compared with control-treated animals. There was no effect of treatment on body weight at PN115. On PN10, neocortical volume was 15% smaller in the ethanol-exposed animals compared with controls, with no change in the total number of neurons or glial cells. Occipital cortical volume was reduced by 22% in the ethanol-exposed animals, with a significant deficit in the total number of neurons (ethanol-exposed, 2.62 x 10; gastrostomy control, 3.20 x 10). There was no effect of ethanol exposure on the total number of glial cells in the occipital cortex or on any parameter in the parietal cortex. There was also no significant effect of ethanol exposure on the occipital cortex on PN115.

CONCLUSIONS

These findings provide support for the hypothesis that a specific area or cell population might be differentially vulnerable to ethanol exposure during the brain growth spurt and that cell deficits evident on PN10 may not be permanent.

Diet-brain connections: role of neurotoxicants

In certain cases, the consumption of food or beverages can lead to intoxication and disease. Such food-induced intoxications may be due to microbial toxins, to toxic substances naturally occurring in some foods, or to contaminants or residues of various kinds. Some of these agents have neurotoxic properties and may contribute to the etiology of certain psychiatric disorders or neurodegenerative diseases. This paper reviews a selected number of dietary neurotoxicants that naturally, or as a result of human interventions, find their way into food or beverages, and have been associated with neurotoxic outcomes in humans. Chosen examples include domoic acid, a phycotoxin associated with amnesic shellfish poisoning; β-N-oxalylamine-l-alanine (l-BOAA), present in chickling peas and believed to be responsible for neurolathyrism; and two alcohols, methanol and ethanol, which can cause severe neurotoxic effects in adults and the developing fetus.

Inhibition of progenitor cell proliferation in the dentate gyrus of rats following post-weaning lead exposure

Although lead is a potent developmental neurotoxin, the effects of postnatal lead exposure on progenitor cell proliferation in the hippocampus has not been examined. Postnatal day 25 rats were fed a lead containing diet (1500 ppm lead acetate) for 30-35 days and administered bromodeoxyuridine (BrdU, 50 mg/kg, i.p.) during the last 5 days of lead exposure. Animals were killed 24 h after the last BrdU injection. Proliferation of new cells in the subgranular zone and dentate gyrus was significantly decreased in lead-exposed rats compared to control animals that ate a similar diet devoid of lead. These results suggest that postnatal lead exposure can have significant deleterious effects on progenitor cell proliferation and thus the structure and function of the hippocampus.

The serotonin-1A agonist ipsapirone prevents ethanol-associated death of total rhombencephalic neurons and prevents the reduction of fetal serotonin neurons

Previously, this laboratory showed that in utero and in vitro ethanol exposure significantly reduces developing serotonin (5-HT) neurons and that treatment with a 5-HT1A agonist such as buspirone or ipsapirone prevents the ethanol-associated loss. The present study investigated whether ethanol decreases fetal rhombencephalic neurons, including 5-HT neurons, by causing apoptosis. We also investigated whether ipsapirone prevents the ethanol-associated deficit of fetal rhombencephalic neurons by reducing apoptosis. The results of these studies strongly suggest that the ethanol-associated reduction in fetal rhombencephalic neurons that accompanies both in utero and in vitro exposure to physiological concentrations of ethanol is associated with increased apoptosis in these neurons. A physiological concentration of ethanol (i.e., 50 mM) increases apoptosis in fetal rhombencephalic neurons and decreases the number 5-HT neurons. It also appears that the 5-HT1A agonist ipsapirone provides neuroprotection to these neurons by reducing apoptosis. Another mechanism by which ethanol-associated apoptosis can be blocked is by including serum proteins in the media at a concentration of 1% or higher; this concentration of serum proteins is high in comparison to the protein concentration in cerebrospinal fluid.

Alcohol-Induced Neurodegeneration: When, Where and Why?

This manuscript reviews the proceedings of a symposium organized by Drs. Antonio Noronha and Fulton Crews presented at the 2003 Research Society on Alcoholism meeting. The purpose of the symposium was to examine recent findings on when alcohol induced brain damage occurs, e.g., during intoxication and/or during alcohol withdrawal. Further studies investigate specific brain regions (where) and the mechanisms (why) of alcoholic neurodegeneration. The presentations were (1) Characterization of Synaptic Loss in Cerebella of Mature and Senescent Rats after Lengthy Chronic Ethanol Consumption, (2) Ethanol Withdrawal Both Causes Neurotoxicity and Inhibits Neuronal Recovery Processes in Rat Organotypic Hippocampal Cultures, (3) Binge Drinking-Induced Brain Damage: Genetic and Age Related Effects, (4) Binge Ethanol-Induced Brain Damage: Involvement of Edema, Arachidonic Acid and Tissue Necrosis Factor alpha (TNFalpha), and (5) Cyclic AMP Cascade, Stem Cells and Ethanol. Taken together these studies suggest that alcoholic neurodegeneration occurs through multiple mechanisms and in multiple brain regions both during intoxication and withdrawal.

Developmental neuropathology of environmental agents

The developing central nervous system (CNS) is more vulnerable to injury than the adult one. Although a great deal of research has been devoted to subtle effects of developmental exposure, such as neurobehavioral changes, this review instead focuses on a number of chemicals that have been shown, in several experimental models as well as humans, to cause morphological changes in the developing nervous system. Chemicals that are discussed include methylmercury (MeHg), lead (Pb), antiepileptic drugs, and ethanol. Additionally, the issue of silent neurotoxicity, i.e., persistent morphological and/or biochemical injury that remains clinically unapparent until later in life, is discussed.

Effects of age and alcohol exposure during early life on pyramidal cell numbers in the CA1-CA3 region of the rat hippocampus

We have previously shown that exposing rats to a relatively high dose of ethanol during early postnatal life can result in an alteration in spatial learning ability. The hippocampal formation is known to be involved in the control of this ability. The purpose of the present study was to determine whether exposure of rats to ethanol during early postnatal life had either immediate or delayed effects on the numbers of pyramidal cells in the CA1-CA3 subregion of the hippocampus. Wistar rats were exposed to a relatively high daily dose of ethanol at postnatal day 10-15 by placing them for 3 h/day in a chamber containing ethanol vapor. Groups of ethanol-treated (ET), separation control (SC), and mother-reared control (MRC) rats were anesthetized and killed at 16 and 30 days of age by perfusion with phosphate-buffered 2.5% glutaraldehyde. The Cavalieri principle was used to determine the volumes of the CA1 and CA2+CA3 regions. The physical disector method was used to estimate the numerical density of neurons in each of the subdivisions. The total number of pyramidal cells was calculated by multiplying the appropriate estimates of the numerical density by the volume. There were significant age-related reductions in the total numbers of pyramidal cells at 16-30 days of age irrespective of the groups examined. Ethanol treated rats were found to have slightly but significantly fewer pyramidal cell neurons than either the MRC or SC groups. These observations indicate that pyramidal cells in the hippocampus may be vulnerable to a relatively high dose of ethanol exposure during this short period of early postnatal life.

Ethanol-induced neuronal death in organotypic cultures of rat cerebral cortex

Ethanol can affect normal development of the cerebral cortex, e.g., it can disrupt cell migration and exacerbate cell death. In vitro studies using primary cultures or cell lines provide further evidence that cell migration and death are altered by ethanol exposure. Organotypic cultures are more complex than primary cell cultures, and maintain some normal connectivity, thus providing a "more in vivo-like" model of brain development. We predict that exposing organotypic cultures of fetal rat cerebral cortex to ethanol results in changes similar to those described in vivo. Organotypic cultures of brains from 16-day-old fetuses were exposed to ethanol (0, 200, 400 or 800 mg/dl) for 72 h. Stereological methods were used to assess the frequency of viable and dying cells. Dying cells were identified as having DNA with polyadenylated tails or as having condensed chromatin. A small amount of cell death was evident in the marginal zone (MZ) and cortical plate (CP) of control cultures. The MZ, normally a cell body-poor layer, was enriched with somata following exposure to 400 mg/dl ethanol. Ethanol-induced cell death in the MZ; the amount of cell death was doubled following exposure to 800 mg/dl ethanol. The CP was more sensitive than the MZ; cell death increased following treatment with 400 mg/dl ethanol. Thus, organotypic cultures show that ethanol disrupts neuronal migration and increases cell death in the developing cerebral cortex. The effects of ethanol were site-specific and concentration-dependent. These changes are similar to those described in vivo.

Ethanol-induced oxidative stress precedes mitochondrially mediated apoptotic death of cultured fetal cortical neurons

In utero ethanol exposure elicits apoptotic cell death in the fetal brain, and this may be mediated by oxidative stress. Our studies utilize cultured fetal rat cortical neurons and illustrate that ethanol elicits a rapid onset of oxidative stress, which culminates in mitochondrially mediated apoptotic cell death. Cells exposed to ethanol (2.5 mg/ml) remained attached to their polylysine matrix during a 24-hr exposure, but they exhibited distinct signs of oxidative stress, decreased viability, and apoptosis. Confocal microscopy of live cortical neurons pretreated with dichlorodihydrofluorescein diacetate demonstrated an increase in reactive oxygen species (ROS) within 5 min of ethanol exposure. The levels of ROS further increased by 58% within 1 hr (P <.05) and by 82% within 2 hr (P <.05), accompanied by increases of mitochondrial 4-hydroxynonenal (HNE). These early events were followed by decreased trypan blue exclusion of 10% to 32% (P <.05) at the 6- to 24-hr time points, respectively. This culminates in apoptotic death, with increases of Annexin V binding of 43%, 89%, 123%, and 238%, at 2, 6, 12, and 24 hr of ethanol treatment, respectively, as well as DNA fragmentation increases of 50% and 65% by 12 and 24 hr, respectively. Release of cytochrome c by mitochondria increased by 53% at 6 hr of exposure (P <.05), concomitant with activation of caspase 3 (52% at 12 hr, P <.05). Pretreatment with N-acetylcysteine increased cellular glutathione and prevented apoptosis. These studies provide a time line illustrating that oxidative stress and formation of a proapoptotic lipid peroxidation product, HNE, precede a cascade of mitochondrially mediated events in cultured fetal cortical neurons, culminating in apoptotic death. The prevention of apoptosis by augmentation of glutathione stores also strongly supports a role for oxidative stress in ethanol-mediated apoptotic death of fetal cortical neurons.

Corpus callosum and visual cortex of mice with deletion of the NMDA-NR1 receptor. II. Attenuation of prenatal alcohol exposure effects

Offspring of transgenic mice with deletion of the NMDA-NR1 (NR1) receptor received prenatal alcohol exposure during most of gestation. Before and after birth, offspring were sacrificed in order to examine the morphological consequences of the prenatal exposure. Previously, we reported that the dendritic arborization of corpus callosum projection neurons (CCpn) in visual cortex was abnormal in rats given prenatal alcohol exposure; the effects were dose-dependent [Neurotoxicol. Teratol. 24 (2002) 719-732]. The same parameters were examined in the transgenic mice. Crystals of DiI were placed into the CC of mice at different ages that had been prenatally exposed to alcohol. Controls included untreated transgenic mice, and transgenic mice with the same nutritional and handling stressors. Compared to Controls, prenatal alcohol exposure caused the NR1+/+ mice to expand the dendritic arbor of CCpn in visual cortex. The dendritic arbors had increased branch numbers and length; these increases were dose-dependent. In contrast, the prenatally exposed NR1-/- mice showed normal dendritic arbors with all prenatal alcohol doses. In addition, prenatal alcohol exposure was found to have morbidity and teratogenic effects on offspring. In seven separate indicators of the effects of prenatal alcohol exposure, only one indicator was present but reduced in NR1-/- offspring, indicating that total deletion of the NMDA-NR1 receptor throughout development largely blocks but sometimes attenuates the effects of prenatal alcohol exposure. Similarly, in seven separate indicators of the effects of prenatal alcohol exposure, five indicators were attenuated in NR1+/- compared to NR1+/+ offspring, although affected more than in NR1-/-; this suggests a gene-dose effect. The results indicate that functional NMDA-NR1 receptors are necessary for the neurotoxic and teratogenic effects of prenatal alcohol exposure. This study will aid in understanding how the NMDA receptors play an important role in prenatal alcohol effects on brain development.

Critical periods for ethanol-induced cell loss in the hippocampal formation

Rodent models of fetal alcohol syndrome (FAS) have revealed discrepant findings in ethanol's (EtOH) ability to alter the survival of principal neurons within hippocampal areas CA1, CA3 and the dentate gyrus (DG). One issue is the lack of systematic examination of the timing of EtOH exposure over key periods of hippocampal cell development. The present study examined whether systematic developmental EtOH exposure produces long-term hippocampal cell loss that is related to a specific time course in which either generation, migration or synaptogenic events in this neural region occurs. EtOH treatment occurred during the periods equivalent to the first, second, third and all three trimesters in humans using similar administration procedures for both mothers and pups. Unbiased stereological estimates of the total number of pyramidal and granule cells within hippocampal regions CA1, CA3 and DG were performed when rats reached adulthood. The findings confirm previous reports that area CA1 is highly susceptible to EtOH exposure that occurs during either the early neonatal period or all three trimesters equivalent, while areas CA3 and DG are more resistant to EtOH-induced insult during all periods of hippocampal development examined.

Embryonic exposure to exogenous alpha- and gamma-tocopherol partially attenuates ethanol-induced changes in brain morphology and brain membrane fatty acid composition

Previous studies demonstrated that embryonic exposure to ethanol (EtOH) promoted a reduction in brain mass, a reduction in brain neuron densities, and a reduction in membrane long-chain polyunsaturated fatty acids (PUFAs) in embryonic chick brains. These EtOH-induced reductions in brain membrane PUFAs may be the result of lipid peroxidation because embryonic exposure to exogenous alpha- or gamma-tocopherol partially attenuated EtOH-induced reductions in membrane PUFAs. In this paper, we report that embryonic exposure to exogenous alpha- or gamma-tocopherol attenuated EtOH-induced decreases in endogenous levels of alpha-tocopherol in both embryonic chick brains and liver. Embryonic exposure to exogenous alpha- or gamma-tocopherol also partially attenuated EtOH-induced reductions in brain neuron densities within the cerebral hemispheres of embryonic chick brains. Finally, embryonic exposure to exogenous alpha- or gamma-tocopherol also partially attenuated EtOH-induced reductions in long-chain PUFAs in 2-day old neonatal chick brains.

Human neural stem cells are more sensitive than astrocytes to ethanol exposure

BACKGROUND

Exposure to ethanol (EtOH) can be deleterious to the developing central nervous system. The mechanisms by which EtOH exposure induces neural pathology in utero remain unclear. However, EtOH-induced increases in protein kinase C (PKC) have been associated with apoptosis in human primary cell cultures. Although the toxic effects of EtOH on differentiated neural cells have been studied in laboratory animal models, the susceptibility of the human neural stem cells (NSCs) that predominate in the central nervous system during embryonic development has not been addressed.

METHODS

For this study, fetal human brain cells, which satisfied the criteria for NSCs by being CD133-positive, nestin-positive, and differentiated glial fibrillary acidic protein-positive human astrocytes, were studied. The cytotoxic potential of EtOH in NSC and astrocyte cultures was studied by using morphological and biochemical methods. In addition, membrane and cytosolic fraction PKC activity for each cell type was assessed.

RESULTS

NSC showed a dose-dependent increase in EtOH-induced toxicity as estimated by terminal transferase-mediated dUTP nick end labeling (TUNEL) stain and viability assays. TUNEL staining indicating DNA degradation consistent with programmed (apoptotic) cell death was detectable in 90% of NSC 16 hr after 2 hr exposure to 10 mM EtOH. NSC also showed a concentration-dependent increase in membrane, but not cytosol, PKC activity over the same EtOH dose range. By contrast, astrocytes showed no cytotoxic effects at any concentrations of EtOH used (0-10 mM). PKC activity of both the membrane and cytosolic fragments from astrocytes also was unaffected by this range of doses.

CONCLUSIONS

This study demonstrates the susceptibility of human NSCs, compared with astrocytes, to EtOH and indicates that alterations in PKC signal transduction in NSC may play a role in EtOH-induced neuropathological processes.

Neurodegeneration and production of the new cells in the dentate gyrus of juvenile rat hippocampus after a single administration of ethanol

Administration of ethanol during brain development induces widespread neuronal loss in various structures of the brain. Here, we show that a single administration of ethanol given during the early postnatal period can induce not only neuronal death, but also an increase in proliferation of the progenitor cells in the dentate gyrus of hippocampal formation in rats. Ethanol (1.5 or 3 g/kg, i.p.) administered to 10-day-old rats induced massive neuronal degeneration as evidenced by TUNEL assay in the dentate gyrus. The neuronal death induced by a high dose of ethanol (3 g/kg) was accompanied by an enhanced proliferation of the progenitor cells labeled by bromodeoxyuridine (BrdU, 50 mg/kg, i.p.) in dentate gyrus. One and 3 weeks following ethanol or saline administration, ethanol-treated rats still had significantly more BrdU-labeled cells than control animals. In ethanol-treated rats, a higher proportion of newly born cells acquired the phenotype of immature postmitotic neurons whereas the final differentiation into calbindin-expressing granule cells remained unchanged. The proportion of astroglial cells was also increased in ethanol-treated rats. Thus, ethanol given in high doses not only induces neurodegeneration but also initiates the process of neuro- and gliogenesis, which might be responsible for the neuronal and glial reorganization of the dentate gyrus.

Fetal alcohol exposure and temporal vulnerability: effects of binge-like alcohol exposure on the developing rat hippocampus

Children with fetal alcohol syndrome (FAS) display altered performance in tasks of learning and memory, behaviours thought to be associated with the hippocampus. Altered hippocampal structure has been reported in some FAS children; therefore, a rat model system was used to determine whether the size and numbers of pyramidal cells in regions CA1 and CA3 of the hippocampal formation and granule cells in the dentate gyrus were altered by alcohol exposure during different periods of development. Rat pups were exposed to alcohol in utero during the second trimester-equivalent (E10-20), the first two trimesters-equivalent (E1-20), during the time of hippocampal pyramidal cell neurogenesis (E16-20), part of the third trimester-equivalent (P4-9), and all three trimesters-equivalent (E1-20+P4-9). Control animals (nutritional and untreated) were reared for all treatment conditions. All pups were perfused on P10. CA1 volume, pyramidal cell density, and number were reduced in pups treated with alcohol during the third trimester-equivalent, whether unique or as exposure during all three trimesters-equivalent. CA3 volume was reduced in alcohol-treated animals across all gestational ages; however, pyramidal cell density and number in this region were only reduced in animals treated with alcohol during the third trimester-equivalent. Volume of the dentate gyrus did not appear to be affected by alcohol treatment. Granule cell density and number in this region were reduced in animals treated with alcohol during the third trimester-equivalent. The third trimester-equivalent in the rat appears to be a developmental period during which the hippocampus is particularly susceptible to the effects of alcohol consumption. The resulting damage to the hippocampus may contribute to the behavioural deficits related to learning and memory noted in children with FAS.

Nerve growth factor and chronic ethanol treatment alter calcium homeostasis in developing rat septal neurons

Chronic ethanol treatment (CET) during development produces cellular adaptations resulting in tolerance to the acute effects of ethanol (EtOH). The objectives of this study were to determine whether CET during the prenatal period (PCET) followed by a period of in vitro CET (PCET-CET) altered intracellular calcium [Ca(2+)](i) and produced tolerance to acute EtOH treatment (AET), and whether nerve growth factor (NGF) modulated the effects of PCET-CET in cultured developing rat septal neurons. Fetuses were obtained from EtOH-fed and sucrose-fed (diet-control) female rats. Neurons from PCET fetuses were cultured in the presence of NGF (+NGF) and 200 mg/dl (mg %) EtOH and diet-control cultures received NGF and no EtOH. PCET and diet-control cultures were then divided into two groups, +NGF and -NGF (withdrawn from NGF), and exposed acutely to one of five doses of EtOH during stimulation with potassium (K(+)) chloride. [Ca(2+)](i) was measured using fura-2. PCET-CET did not affect resting [Ca(2+)](i). PCET-CET decreased and acute EtOH withdrawal increased overall K(+)-stimulated changes in [Ca(2+)](i), but only in +NGF PCET neurons. Reducing the level of EtOH from 200 to 100 mg % decreased overall K(+)-stimulated [Ca(2+)](i) in -NGF PCET neurons. The effects of PCET-CET or PCET-CET combined with NGF on overall K(+)-stimulated changes in [Ca(2+)](i) occurred mostly in the early and middle phases of the K(+)-response. NGF reduced overall K(+)-stimulated changes in [Ca(2+)](i) in PCET neurons during EtOH withdrawal and during AET with 200 mg % EtOH and increased overall K(+)-stimulated changes in [Ca(2+)](i) during AET with 400 and 800 mg % EtOH. There was no effect of NGF on overall K(+)-stimulated changes in [Ca(2+)](i) in diet-control neurons with the exception that NGF-treatment decreased overall K(+)-stimulated changes in [Ca(2+)](i) during AET with 400 mg % EtOH. The effects of AET on overall K(+)-stimulated changes in [Ca(2+)](i) mostly occurred in +NGF PCET neurons. In conclusion, CET during development of the brain could adversely affect Ca(2+)-dependent functions such as neuronal migration, neurite outgrowth, and synaptogenesis in neurons even in the presence of neurotrophin support.

Effects of alcohol exposure during early life on neuron numbers in the rat hippocampus. I. Hilus neurons and granule cells

We previously showed that 16-day-old rats exposed to a relatively high dose of ethanol at 10-15 postnatal days of age have fewer neurons in the hilus region of the hippocampus compared with controls. Dentate gyrus granule cell numbers, however, showed no statistically significant changes attributable to the ethanol treatment. It is possible that some of the changes in brain morphology, brought about as a result of the exposure to ethanol during early life, may not be manifested until later in life. This question has been further addressed in an extension to our previous study. Wistar rats were exposed to a relatively high daily dose of ethanol on postnatal days 10-15 by placement in a chamber containing ethanol vapour, for 3 h/day. The blood ethanol concentration was found to be approximately 430 mg/dl at the end of the period of exposure. Groups of ethanol-treated (ET), separation control (SC), and mother-reared control (MRC) rats were anaesthetised and killed either at 16 or 30 days of age by perfusion with phosphate-buffered 2.5% glutaraldehyde. The Cavalieri principle and the physical disector methods were used to estimate, respectively, the regional volumes and neuron cell numerical densities in the hilus and granule cell regions of the dentate gyrus. The total numbers of neurons in the hilus region and granule cell layer were computed from these estimates. It was found that 16-day-old animals had 398,000-441,000 granule cells, irrespective of group. The numbers of granule cells increased such that by 30 days of age, rats had 487,000-525,500 granule cells. However, there were no significant differences between ethanol-treated rats and their age-matched controls in granule cell numbers. In contrast, ethanol-treated rats had slightly but significantly fewer neurons in the hilus region than did control animals at 16 days of age, but not at 30 days of age. Therefore, it appears that a short period of ethanol exposure during early life can have effects on neuron numbers of some hippocampal neurons, but not others. The effects on hilar neuron numbers, observed as a result of such short periods of ethanol treatment, appeared to be transitory.

Neural stem cells and alcohol

This article summarizes the proceedings of a symposium held at the 2002 Research Society on Alcoholism Meeting in San Francisco, California. The aim of this symposium was to review research on the effects of ethanol on neural stems cells and neurogenesis. Ethanol is known to alter neurogenesis during development; however, recent studies indicate that the brain forms new neurons from stem cells throughout life. Furthermore, stem cells can be transplanted into the brain, creating exciting new possibilities to study brain function. The symposium covered these research areas. Dr. Michael W. Miller reviewed knowledge on the effects of ethanol on stem cell proliferation and differentiation during development. Dr. Wu Ma described studies in culture indicating that (1) neural stem cells express functional muscarinic acetylcholine receptors (mAchR), (2) mAchR-mediated proliferation involves Ca signaling and mitogen-activated protein kinase phosphorylation, and (3) phosphoinositol-3 kinase is a downstream effector for mAchR-mediated cell proliferation via activation of Akt. Drs. Kim Nixon and Fulton T. Crews followed with in vivo studies on ethanol's effects on adult neural stem cell proliferation and differentiation. Dr. W. Michael Zawada described studies directed at dopamine neuron cell transplants into mammalian central nervous system. These studies clearly establish that ethanol has significant effects on stem cells.

Experience effects on brain development: possible contributions to psychopathology

Researchers and clinicians are increasingly recognizing that psychological and psychiatric disorders are often developmentally progressive, and that diagnosis often represents a point along that progression that is defined largely by our abilities to detect symptoms. As a result, strategies that guide our searches for the root causes and etiologies of these disorders are beginning to change. This review describes interactions between genetics and experience that influence the development of psychopathologies. Following a discussion of normal brain development that highlights how specific cellular processes may be targeted by genetic or environmental factors, we focus on four disorders whose origins range from genetic (fragile X syndrome) to environmental (fetal alcohol syndrome) or a mixture of both factors (depression and schizophrenia). C.H. Waddington's canalization model (slightly modified) is used as a tool to conceptualize the interactive influences of genetics and experience in the development of these psychopathologies. Although this model was originally proposed to describe the 'canalizing' role of genetics in promoting normative development, it serves here to help visualize, for example, the effects of adverse (stressful) experience in the kindling model of depression, and the multiple etiologies that may underlie the development of schizophrenia. Waddington's model is also useful in understanding the canalizing influence of experience-based therapeutic approaches, which also likely bring about 'organic' changes in the brain. Finally, in light of increased evidence for the role of experience in the development and treatment of psychopathologies, we suggest that future strategies for identifying the underlying causes of these disorders be based less on the mechanisms of action of effective pharmacological treatments, and more on increased knowledge of the brain's cellular mechanisms of plastic change.

NMDA receptor subunit expression following early postnatal exposure to ethanol

Changes in NMDA receptor function following early postnatal exposure to ethanol may be related to the expression of NMDA receptor subunits. Following early postnatal exposure to ethanol, the expression of NMDA receptor subunits was examined. In cortex from ethanol-exposed rat pups at postnatal day 21, NR2A was significantly increased. There was no change in NR2B, thus suggesting that ethanol exposure during the third-trimester equivalent produces distinct effects on the NMDA receptor.