Effects of chronic prenatal ethanol exposure on hippocampal glutamate release in the postnatal guinea pig

Effects of pre-natal alcohol exposure on hippocampal synaptic plasticity: Sex, age and methodological considerations

The consumption of alcohol during gestation is detrimental to the developing central nervous system (CNS). The severity of structural and functional brain alterations associated with alcohol intake depends on many factors including the timing and duration of alcohol consumption. The hippocampal formation, a brain region implicated in learning and memory, is highly susceptible to the effects of developmental alcohol exposure. Some of the observed effects of alcohol on learning and memory may be due to changes at the synaptic level, as this teratogen has been repeatedly shown to interfere with hippocampal synaptic plasticity. At the molecular level alcohol interferes with receptor proteins and can disrupt hormones that are important for neuronal signaling and synaptic plasticity. In this review we examine the consequences of prenatal and early postnatal alcohol exposure on hippocampal synaptic plasticity and highlight the numerous factors that can modulate the effects of alcohol. We also discuss some potential mechanisms responsible for these changes as well as emerging therapeutic avenues that are beginning to be explored.

Fetal Alcohol Spectrum Disorder: Potential Role of Endocannabinoids Signaling

One of the unique features of prenatal alcohol exposure in humans is impaired cognitive and behavioral function resulting from damage to the central nervous system (CNS), which leads to a spectrum of impairments referred to as fetal alcohol spectrum disorder (FASD). Human FASD phenotypes can be reproduced in the rodent CNS following prenatal ethanol exposure. Several mechanisms are expected to contribute to the detrimental effects of prenatal alcohol exposure on the developing fetus, particularly in the developing CNS. These mechanisms may act simultaneously or consecutively and differ among a variety of cell types at specific developmental stages in particular brain regions. Studies have identified numerous potential mechanisms through which alcohol can act on the fetus. Among these mechanisms are increased oxidative stress, mitochondrial damage, interference with the activity of growth factors, glia cells, cell adhesion molecules, gene expression during CNS development and impaired function of signaling molecules involved in neuronal communication and circuit formation. These alcohol-induced deficits result in long-lasting abnormalities in neuronal plasticity and learning and memory and can explain many of the neurobehavioral abnormalities found in FASD. In this review, the author discusses the mechanisms that are associated with FASD and provides a current status on the endocannabinoid system in the development of FASD.

Pre-administration of G9a/GLP inhibitor during synaptogenesis prevents postnatal ethanol-induced LTP deficits and neurobehavioral abnormalities in adult mice

It has been widely accepted that deficits in neuronal plasticity underlie the cognitive abnormalities observed in fetal alcohol spectrum disorder (FASD). Exposure of rodents to acute ethanol on postnatal day 7 (P7), which is equivalent to the third trimester of fetal development in human, induces long-term potentiation (LTP) and memory deficits in adult animals. However, the molecular mechanisms underlying these deficits are not well understood. Recently, we found that histone H3 dimethylation (H3K9me2), which is mediated by G9a (lysine dimethyltransferase), is responsible for the neurodegeneration caused by ethanol exposure in P7 mice. In addition, pharmacological inhibition of G9a prior to ethanol treatment at P7 normalized H3K9me2 proteins to basal levels and prevented neurodegeneration in neonatal mice. Here, we tested the hypothesis that pre-administration of G9a/GLP inhibitor (Bix-01294, Bix) in conditions in which ethanol induces neurodegeneration would be neuroprotective against P7 ethanol-induced deficits in LTP, memory and social recognition behavior in adult mice. Ethanol treatment at P7 induces deficits in LTP, memory and social recognition in adult mice and these deficits were prevented by Bix pretreatment at P7. Together, these findings provide physiological and behavioral evidence that the long-term harmful consequences on brain function after ethanol exposure with a third trimester equivalent have an epigenetic origin.

Effects of maternal administration of vitamins C and E on ethanol neurobehavioral teratogenicity in the guinea pig

Consumption of ethanol during human pregnancy can produce a wide spectrum of teratogenic effects, including neurobehavioral dysfunction. This study, in the guinea pig, tested the hypothesis that chronic maternal administration of antioxidant vitamins C plus E, together with ethanol, mitigates ethanol neurobehavioral teratogenicity. Pregnant guinea pigs received one of the following four chronic oral regimens: ethanol and vitamins C plus E; ethanol and vitamin vehicle; isocaloric-sucrose/pair-feeding and vitamins C plus E; or isocaloric-sucrose/pair-feeding and vehicle. Vitamins C (250 mg) plus E (100mg) or vehicle were given daily, and ethanol (4 g/kg maternal body weight/day) (E) or isocaloric-sucrose/pair-feeding was given for 5 consecutive days followed by 2 days of no treatment each week throughout gestation. One neonate from selected litters was studied on postnatal day (PD) 0. Neurobehavioral function was determined by measuring task acquisition and task retention using an 8-day moving-platform version of the Morris water-maze task, starting on PD 45. Thereafter, in vivo electrophysiologic assessment of changes in hippocampal synaptic plasticity was conducted. There was an ethanol-induced decrease in neonatal brain weight compared with sucrose. The vitamins C plus E regimen protected hippocampal weight relative to brain weight in ethanol offspring, and mitigated the ethanol-induced deficit in the task-retention component of the water-maze task. However, in the sucrose group, this Vit regimen produced deficits in both task acquisition and task retention. The vitamins C plus E regimen did not mitigate the ethanol-induced impairment of hippocampal long-term potentiation. These results indicate that maternal administration of this high-dose vitamins C plus E regimen throughout gestation has limited efficacy and potential adverse effects as a therapeutic intervention for E neurobehavioral teratogenicity.

Effects of chronic prenatal ethanol exposure on NMDA receptor number and affinity for [3H]MK-801 in the cerebral cortex of the young postnatal and adult guinea-pig

The objective of this study was to test the hypothesis that chronic prenatal ethanol exposure (CPEE) produces changes in the number and/or affinity of N-methyl-D-aspartate (NMDA) receptors in the cerebral cortex that are developmental-age-dependent. Timed, pregnant Dunkin-Hartley-strain guinea-pigs received oral intubation of one of the following regimens, given daily as two equally divided doses 2 h apart, from gestational day (GD) 2 to GD 67 (term, ~GD 68): (i) 4 g ethanol kg(-1) maternal bodyweight; (ii) isocaloric sucrose with pair feeding; or (iii) water. Maternal blood ethanol concentration was measured on GD 57 or 58 at 1 h after the daily dose, and was 51.1 +/- 8.5 mM (235 +/- 39 mg dL(-1); n = 8). At postnatal day (PD) 11 (pre-weaning) and PD 61 (adulthood), body, brain and cerebral cortical weights of the offspring were measured. The number of NMDA receptors and their affinity for [(3)H]MK-801 were measured in a crude cerebral cortical membrane preparation using saturation isotherm analysis to determine the B(max) and K(D). Chronic prenatal ethanol exposure decreased offspring brain and cerebral cortical weights at PD 11 and PD 61. At PD 11, there was no CPEE-induced change of [(3)H]MK-801 binding characteristics in the cerebral cortex. At PD 61, both B(max) and K(D) for [(3)H]MK-801 binding to cerebral cortical NMDA receptors were decreased by CPEE compared with the isocaloric sucrose/pair-fed and water treatment groups. Loss of cerebral cortical NMDA receptors and increased affinity of the remaining receptors for [(3)H]MK-801 in the adult guinea-pig, compared with no change in the number or affinity of these receptors in the young postnatal offspring, demonstrated that the effects of CPEE on these ionotropic glutamate receptors are developmental-age-dependent.

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.

Chronic prenatal ethanol exposure and increased concentration of fatty acid ethyl esters in meconium of term fetal Guinea pig

In humans, the occurrence of prenatal exposure to ethanol is difficult to validate objectively. Increased concentration of fatty acid ethyl esters (FAEE) in the meconium of the newborn may be a biomarker of prenatal ethanol exposure. The validity of this proposed biomarker was tested in pregnant guinea pigs that received chronic oral administration of 4 g ethanol/kg maternal body weight/day (n=8), isocaloric-sucrose/pair-feeding (n=8) or water (n=2) throughout gestation. At gestational day 65 (term, gestational day 66 to 69), each dam and her offspring were euthanized, and meconium was collected from the term fetal large intestine. Eight individual FAEE (lauric, myristic, palmitic, palmitoleic, stearic, oleic, linolenic and arachidonic AEE) were measured by gas chromatography--flame ionization detection and confirmed by gas chromatography--mass spectrometry. The chronic maternal ethanol regimen decreased fetal body weight and brain weight. There was virtually no measurable FAEE in the meconium for the water group (n=3 fetuses). For meconium of the ethanol offspring (n=25 fetuses) compared with the sucrose offspring (n=23 fetuses), the total FAEE concentration was 8-fold higher; and lauric, palmitic, stearic and oleic AEE concentrations were at least 5-fold higher for the ethanol group. The data indicate that fetal meconium FAEE constitute a biomarker of prenatal ethanol exposure for a maternal ethanol regimen that restricts fetal development, with an inverse relationship between meconium total FAEE concentration and both body weight and brain weight.

Chronic prenatal ethanol exposure increases apoptosis in the hippocampus of the term fetal guinea pig

It is hypothesized that chronic prenatal ethanol exposure (CPEE), via maternal ethanol administration, increases mitochondrial-directed apoptosis in the hippocampus of the term fetus that precedes loss of hippocampal CA1 pyramidal cells. To test this hypothesis, timed pregnant guinea pigs received chronic oral administration of: 4 g ethanol/kg maternal body weight/day, isocaloric-sucrose/pair-feeding or water throughout gestation. At gestational day 65 (term fetus) and postnatal day 0 (neonate), individual offspring were euthanized, and the brain was excised and dissected. CPEE, compared with the isocaloric-sucrose/pair-fed and water control groups, decreased the brain weight of the term fetus and neonate. CPEE did not alter the density of CA1 pyramidal cells in the hippocampus of the term fetus and neonate. In the term fetus, CPEE increased cytochrome c content in the cytosolic fraction of the hippocampus, altered the mitochondrial localization of cytochrome c in cells of the dorsal hippocampus, and increased the percentage of cells in the dorsal hippocampus containing activated caspase-3 and cleaved poly(ADP-ribose) polymerase. The data indicate that CPEE increases neuroapoptosis in the hippocampus of term fetus, which appears to occur via an intrinsic, mitochondrial-directed mechanism initiated by leakage of pro-apoptotic cytochrome c from mitochondria into the cytoplasm.

Chronic prenatal ethanol exposure alters glucocorticoid signalling in the hippocampus of the postnatal Guinea pig

The present study tested the hypothesis that chronic prenatal ethanol exposure causes long-lasting changes in glucocorticoid signalling in postnatal offspring. Pregnant guinea pigs were treated with ethanol (4 g/kg maternal body weight/day), isocaloric-sucrose/pair-feeding or water throughout gestation, and maternal saliva cortisol concentration was determined 2 h after treatment at different stages of gestation. Electrically-stimulated release of glutamate and GABA, in the presence or absence of dexamethasone, as well as glucocorticoid and mineralocorticoid receptor mRNA expression, was determined in the hippocampus and prefrontal cortex of adult offspring of treated pregnant guinea pigs. Maternal saliva cortisol concentration increased throughout pregnancy, which was associated with increased foetal plasma and amniotic fluid cortisol concentration. Ethanol administration to pregnant guinea pigs increased maternal saliva cortisol concentration during early and mid-gestation. In late gestation, ethanol administration did not increase saliva cortisol concentration above that induced by pregnancy. Chronic prenatal ethanol exposure had no effect on stimulated glutamate or GABA release, but selectively prevented dexamethasone-mediated suppression of stimulated glutamate release, and decreased expression of mineralocorticoid, but not glucocorticoid, receptor mRNA in the hippocampus of adult offspring. These data indicate that maternal ethanol administration leads to excessively increased maternal cortisol concentration that can impact negatively the developing foetal brain, leading to persistent postnatal deficits in glucocorticoid regulation of glutamate signalling in the adult hippocampus.

Neuron activity in the anterolateral motor cortex in operant food-acquiring and alcohol-acquiring behavior

The interactions of the neuronal mechanisms of food-acquiring behavior and newly formed operant alcohol-acquiring behavior were studied by recording the activity of individual neurons in the anterolateral area of the motor cortex in chronically alcoholized rabbits. Adult animals learned food-acquiring behavior in a cage with two feeders and two pedals, in the comers (the food in the feeders was presented after pressing the corresponding pedal). After nine months of chronic alcoholization, the same rabbits learned an alcohol-acquiring behavior in the same experimental cage (gelatin capsules filled with 15% ethanol solution were placed in the feeders instead of food). Analysis of neuron activity showed that the set of neurons involved in supporting food-acquiring and alcohol-acquiring behaviors overlapped, though not completely. These experiments not only help us understand the neuronal mechanisms of the newly formed and the previously formed behaviors, but also facilitate the development of concepts of the similarity of the neuronal mechanisms of long-term memory and long-term modifications of the nervous system, occurring in conditions of repeated intake of addictive substances.

Chronic prenatal ethanol exposure alters hippocampal GABAA receptors and impairs spatial learning in the guinea pig

Chronic prenatal ethanol exposure (CPEE) can injure the developing brain, and may lead to the fetal alcohol syndrome (FAS). Previous studies have demonstrated that CPEE upregulates gamma-aminobutyric acid type A (GABA(A)) receptor expression in the cerebral cortex, and decreases functional synaptic plasticity in the hippocampus, in the adult guinea pig. This study tested the hypothesis that CPEE increases GABA(A) receptor expression in the hippocampus of guinea pig offspring that exhibit cognitive deficits in a hippocampal-dependent spatial learning task. Timed, pregnant guinea pigs were treated with ethanol (4 g/kg maternal body weight per day), isocaloric-sucrose/pair-feeding, or water throughout gestation. GABA(A) receptor subunit protein expression in the hippocampus was measured at two development ages: near-term fetus and young adult. In young adult guinea pig offspring, CPEE increased spontaneous locomotor activity in the open-field and impaired task acquisition in the Morris water maze. CPEE did not change GABA(A) receptor subunit protein expression in the near-term fetal hippocampus, but increased expression of the beta2/3-subunit of the GABA(A) receptor in the hippocampus of young adult offspring. CPEE did not change either [(3)H]flunitrazepam binding or GABA potentiation of [(3)H]flunitrazepam binding, but decreased the efficacy of allopregnanolone potentiation of [(3)H]flunitrazepam binding, to hippocampal GABA(A) receptors in adult offspring. Correlational analysis revealed a relationship between increased spontaneous locomotor activity and growth restriction in the hippocampus induced by CPEE. Similarly, an inverse relationship was found between performance in the water maze and the efficacy of allopregnanolone potentiation of [(3)H]flunitrazepam binding in the hippocampus. These data suggest that alterations in hippocampal GABA(A) receptor expression and pharmacological properties contribute to hippocampal-related behavioral and cognitive deficits associated with CPEE.

Does drug abuse beget drug abuse? Behavioral analysis of addiction liability in animal models of prenatal drug exposure

Prenatal exposure to drugs of abuse is the single largest preventable cause of developmental compromise of American children today. In the clinical population, it is difficult to determine the independent effects of gestational exposure to a single drug on brain development, in part due to the confounding effects of additional risk factors that are encountered in the substance-abusing population. The enormous clinical and societal problem of gestational toxicity of drugs of abuse, both legal and illegal, has driven the need to develop and investigate animal models of gestational drug exposure in which these variables can be controlled. More specifically, as clinical data are gathered suggesting an increased liability to substance abuse among children of drug-abusing mothers, a mechanistic understanding of the lasting effects of early drug exposure on the developing brain and the behavioral repertoire of the developing animal is crucial. In this review we summarize experimental animal research that investigates the role of drug exposure in utero on the functional development of specific brain circuits that are involved in the reinforcing effects of drugs of abuse, and on the behaviors that are mediated by these brain reward systems.

Chronic prenatal ethanol exposure impairs conditioned responding and enhances GABA release in the hippocampus of the adult guinea pig

In this study, we assessed the effects of chronic prenatal ethanol exposure (CPEE) on spatial navigation in the water maze, conditioned responding using food-reinforced lever pressing, and amino acid neurotransmitter release from the hippocampus of the adult guinea pig. Pregnant guinea pigs were treated with ethanol (3 g/kg of maternal body weight/day), isocaloric-sucrose/pair-feeding, or water throughout gestation. Adult offspring were trained in two-lever operant chambers to respond for sucrose pellets, with one lever designated as the reward lever. There were no group differences in response acquisition or lever discrimination on a fixed-ratio 1 (FR-1) schedule. During extinction sessions, CPEE offspring maintained higher levels of responding on the previously reinforced lever, suggesting that CPEE increases perseveration and/or impairs response inhibition but does not affect operant responding for an appetitive reinforcer or the ability to discriminate rewarding from nonrewarding stimuli. In contrast, there was no effect of CPEE on performance in the water maze in the maternal ethanol regimen used in this study. CPEE did not alter electrically evoked glutamate or GABA release from hippocampal brain slices. However, when slices were tested after delivery of a tetanizing stimulation (five 5-s trains at 100 Hz), post-tetanic potentiation of electrically stimulated GABA release was greater in hippocampal slices obtained from CPEE offspring, whereas post-tetanic potentiation of electrically stimulated glutamate release was unaffected. These data suggest that conditioned learning is a sensitive behavioral measure of CPEE-induced brain injury. Increased activity-dependent potentiation of GABA release in the hippocampus may contribute to alterations in synaptic plasticity observed in CPEE offspring.

Brain growth spurt-prenatal ethanol exposure and the guinea pig hippocampal glutamate signaling system

This study tested the hypothesis that prenatal ethanol exposure (PEE) during the brain growth spurt (BGS) in the guinea pig suppresses the glutamate-NMDA receptor-nitric oxide synthase (NOS) signaling system in the developing hippocampus. Pregnant guinea pigs [term, about gestational day (GD) 68] received daily oral administration of 2 g ethanol/kg maternal body weight/day on GD 43 and/or GD 44 and then 4 g ethanol/kg maternal body weight/day from GD 45 to GD 62, isocaloric-sucrose/pair-feeding or water. Offspring were studied at GD 63 (near-term fetus) and postnatal day (PD) 10 (young postnatal life). Maternal blood ethanol concentration during ethanol treatment, pregnancy outcome variables, no change in spontaneous locomotor activity, and decreased brain and cerebral cortical weight data were reported previously [Neurotoxicol. Teratol. 23 (2001) 355]. This BGS-PEE regimen did not affect hippocampal stimulated glutamate release in young postnatal offspring, NMDA receptors as assessed by [3H]MK-801 binding, or NOS activity in near-term fetal offspring. Furthermore, BGS-PEE did not affect the number of hippocampal CA1 and CA3 pyramidal cells and dentate gyrus granule cells in defined locations of these three regions in the hippocampal formation. These findings are in contrast to the effects of chronic prenatal exposure to this ethanol regimen throughout gestation, including suppression of the hippocampal glutamate-NMDA receptor-NOS signaling system, decreased number of hippocampal CA1 pyramidal cells, increased spontaneous locomotor activity, and impaired performance in the Morris water maze.

Effects of chronic prenatal ethanol exposure on cGMP content and glutamate release in the hippocampus of the neonatal guinea pig

The glutamate-N-methyl-D-aspartate (NMDA) receptor-nitric oxide synthase (NOS)-cGMP signal transduction system plays key neurotrophic and intercellular communication roles in the hippocampus. In the guinea pig, chronic prenatal ethanol exposure (CPEE), via maternal ethanol administration, suppresses the hippocampal glutamate-NMDA receptor-NOS pathway in the near-term fetus and decreases stimulated glutamate release in the hippocampus of young postnatal offspring, with no effect on NMDA receptor number or NOS activity. At present, the effect of CPEE on cGMP, a key second messenger of the glutamate signal transduction system, in the hippocampus is not known. The objective of this study was to test the hypothesis that CPEE suppresses the hippocampal glutamate signal transduction system in the neonatal guinea pig at the levels of cGMP content and glutamate release. Timed pregnant guinea pigs received chronic oral administration of 4 g ethanol/kg maternal body weight/day, isocaloric-sucrose/pair-feeding, or water treatment throughout gestation. CPEE decreased brain and hippocampal weights at postnatal day (PD) 1 and PD 5 (P<.05). CPEE did not affect basal, NMDA (1, 10, or 100 microM)-stimulated, or K(+) (15 or 30 mM)-stimulated cGMP content in transverse hippocampal slices at PD 1 or 5. At 60 mM K(+), however, CPEE decreased stimulated hippocampal cGMP content at PD 1 (P<.05) and increased stimulated cGMP content at PD 5 (P<.05). In transverse hippocampal slices, CPEE did not affect basal or K(+) (40 or 45 mM)-stimulated glutamate release at PD 1 or 5, or NMDA (50 microM)-stimulated glutamate release at PD 1, but did decrease NMDA (50 microM)-stimulated glutamate release at PD 5 (P<.05). The data demonstrate that the effects of CPEE on stimulated cGMP content and glutamate release in the hippocampus of the neonatal guinea pig are stimulating agent- and age-dependent.

Impaired acquisition in the water maze and hippocampal long-term potentiation after chronic prenatal ethanol exposure in the guinea-pig

In the hippocampus, the CA1 region is selectively vulnerable to the effects of chronic prenatal ethanol exposure. In the guinea-pig, the number of CA1 pyramidal cells is decreased after chronic prenatal ethanol exposure. We tested the hypotheses that chronic prenatal ethanol exposure (through maternal ethanol ingestion) results in impairments in spatial learning and short- and long-term plasticity in the CA1 region of the postnatal guinea-pig hippocampus. Timed, pregnant guinea-pigs were treated with ethanol (4 g/kg maternal body weight/day), isocaloric sucrose/pair-feeding, or water throughout gestation. Offspring were studied between postnatal days 40 and 80. In the Morris water maze, animals exposed to ethanol prenatally showed slower acquisition of an escape response to a hidden platform over 5 days of training. The amplitude of the field excitatory postsynaptic potential in the CA1 region in response to contralateral CA3 stimulation was decreased in offspring exposed to ethanol prenatally. Two forms of short-term plasticity (paired-pulse and frequency facilitation) were unaffected by chronic prenatal ethanol exposure. Long-term potentiation (LTP) in response to high-frequency CA3 stimulation was induced reliably and maintained over 60 min in isocaloric-sucrose and water control animals. However, LTP failed to be induced in the CA1 area of the hippocampus in prenatal ethanol-exposed offspring. These data show that chronic prenatal ethanol exposure, through maternal ethanol administration, impairs spatial performance and LTP in CA1 neurons. Hippocampal dysfunction could contribute importantly to the cognitive and behavioural deficits resulting from chronic prenatal ethanol exposure.

In vitro ethanol exposure decreases potassium-stimulated, but not veratridine-stimulated, glutamate release in the guinea pig hippocampus

In this study we determined the effect of in vitro ethanol exposure on stimulated glutamate release in transverse hippocampal slices (400-microm thickness) of the young postnatal guinea pig (PD 12) by using two chemical stimuli with different mechanisms of action. Ethanol (50 mM) decreased K+ (45 mM)-, but not veratridine (10 microM)-, stimulated glutamate release. The study findings demonstrate that in vitro ethanol exposure produces differential inhibition of stimulated glutamate release in the hippocampus, dependent on the stimulating agent.

Chronic prenatal ethanol exposure increases GABA(A) receptor subunit protein expression in the adult guinea pig cerebral cortex

Excessive consumption of ethanol during pregnancy can produce teratogenic effects in offspring and is the leading cause of mental deficiency in the Western world. The objective of this study was to examine the effects of chronic prenatal ethanol exposure on the number of GABA(A) receptors and relative protein levels for GABA(A) receptor alpha1 and beta2/3 subunits in the adult guinea pig cerebral cortex. Timed pregnant Dunkin-Hartley strain guinea pigs were given one of the following oral treatments daily throughout gestation: 4 gm of ethanol per kilogram of maternal body weight, isocaloric-sucrose with pair feeding, or isovolumetric water with ad libitum access to food. The ethanol treatment resulted in a peak maternal blood ethanol concentration of 328 +/- 55 mg/dl (71.3 +/- 12.0 mm) on gestational day 57 (term, approximately 68 d). Chronic prenatal exposure to ethanol resulted in increased spontaneous locomotor activity throughout development and decreased cerebral cortical weight in adult offspring. The number of cerebral cortical [(3)H]muscimol binding sites was increased in adult offspring from the ethanol treatment group, and there was a corresponding increase in the amount of GABA(A) receptor alpha1 and beta2/3 subunit proteins in these same animals. For individual offspring, there were correlations between locomotor activity and cerebral cortical weight, as well as between cerebral cortical weight and GABA(A) receptor neurochemistry. There was no effect of chronic prenatal ethanol exposure on [(3)H]MK-801 binding in this tissue. These data demonstrate that chronic prenatal ethanol exposure has long-term consequences on the regulation of GABA(A) receptor expression in the cerebral cortex.

Effect of prenatal ethanol exposure during the brain growth spurt of the guinea pig

This study tested the hypothesis that prenatal ethanol exposure during the last third of gestation, including the brain growth spurt (BGS), in the guinea pig produces neurobehavioural teratogenicity, manifesting as brain growth restriction and hyperactivity. Pregnant guinea pigs (term, about gestational day (GD) 68) received oral administration of ethanol (2 g/kg maternal body weight per day on GD 43 and/or GD 44 and then 4 g/kg maternal body weight per day from GD 45 to GD 62), isocaloric-sucrose/pair-feeding, or water. Maternal blood ethanol concentration (BEC) on GD 57 or 58, at 1 h after the daily dose, was 340+/-76 mg/dl (n=8). Ethanol treatment decreased brain, cerebral cortical, hippocampal, and cerebellar weights at GD 63 (P<0.05), and decreased brain and cerebral cortical weights at postnatal day 10 (P<0.05), with no effect on body weight and no apparent effect on spontaneous locomotor activity. The data demonstrate that, in the guinea pig, prenatal ethanol exposure during the last third of gestation, including the BGS, decreases brain weight that persists into postnatal life, which is associated with growth restriction of the cerebral cortex. However, this prenatal ethanol exposure regimen, including the BGS, does not increase spontaneous locomotor activity in contrast to the persistent hyperactivity that occurs after chronic ethanol exposure throughout gestation.

Ethanol neurobehavioral teratogenesis and the role of the hippocampal glutamate-N-methyl-D-aspartate receptor-nitric oxide synthase system

The purpose of this review is to evaluate a proposed mechanism for ethanol neurobehavioral teratogenesis in the hippocampus, involving suppression of the glutamate-N-methyl-D-aspartate (NMDA) receptor-nitric oxide synthase (NOS) system. It is postulated that suppression of this signal transduction system in the fetus by chronic maternal consumption of ethanol plays a key role in hippocampal dysmorphology and dysfunction in postnatal life. This mechanism is evaluated critically based on the current literature and our research findings. In view of the apparent time course for loss of CA1 pyramidal cells in the hippocampus produced by chronic prenatal ethanol exposure that manifests in early postnatal life, it is proposed that therapeutic intervention, which targets the glutamate-NMDA receptor-NOS system, may prevent or lessen the magnitude of postnatal hippocampal dysfunction.