Dose- and age-dependent effects of prenatal ethanol exposure on hippocampal metabotropic-glutamate receptor-stimulated phosphoinositide hydrolysis

N-Methyl-d-Aspartate Receptor Modulation by Nicotinamide Adenine Dinucleotide Phosphate Oxidase Type 2 Drives Synaptic Plasticity and Spatial Memory Impairments in Rats Exposed Pre- and Postnatally to Ethanol

Aims: Pre- and/or early postnatal ethanol exposure (prenatal alcohol exposure [PAE]) impairs synaptic plasticity as well as memory formation, but the mechanisms underlying these effects remain unclear. Both long-term potentiation (LTP) and spatial memory formation in the hippocampus involve the nicotinamide adenine dinucleotide phosphate oxidase type 2 (NOX2) enzyme. Previous studies have reported that N-methyl-d-aspartate receptor (NMDAR) activation increases NOX2-mediated superoxide generation, resulting in inhibition of NMDAR function, but whether NOX2 impacts NMDAR function in PAE animals leading to impaired LTP and memory formation remains unknown. We aim to evaluate whether the NOX2-NMDAR complex is involved in the long-lasting deleterious effects of PAE on hippocampal LTP and memory formation. Results: Here we provide novel evidence that PAE animals display impaired NMDAR-dependent LTP in the cornus ammonis field 1 (CA1) and NMDAR-mediated LTP in the dentate gyrus (DG). Moreover, PAE rats displayed increased NMDAR-mediated transmission in both hippocampal areas. Interestingly, NOX2 pharmacological inhibition restored NMDAR-mediated transmission and LTP in the CA1, but not in the DG. PAE also induced overexpression of NOX2 and CaMKII isoforms, but did not modify the content or the redox state of the N-methyl-d-aspartate receptor subunit-1 (NR1) subunit of NMDAR in both areas of the hippocampus. In addition, adolescent PAE rats orally fed the antioxidant and free radical scavenger apocynin exhibited significantly improved spatial memory acquisition. Innovation and Conclusion: By showing in PAE animals NOX2 overexpression and increased NMDAR-mediated transmission, which might lead to impaired synaptic plasticity and memory formation in a region-specific manner, we provide an important advance to our current understanding of the cellular mechanisms underlying PAE-dependent defective hippocampal function.

Long Term Depression in Rat Hippocampus and the Effect of Ethanol during Fetal Life

Alcohol (ethanol) disturbs cognitive functions including learning and memory in humans, non-human primates, and laboratory animals such as rodents. As studied in animals, cellular mechanisms for learning and memory include bidirectional synaptic plasticity, long-term potentiation (LTP), and long-term depression (LTD), primarily in the hippocampus. Most of the research in the field of alcohol has analyzed the effects of ethanol on LTP; however, with recent advances in the understanding of the physiological role of LTD in learning and memory, some authors have examined the effects of ethanol exposure on this particular signal. In the present review, I will focus on hippocampal LTD recorded in rodents and the effects of fetal alcohol exposure on this signal. A synthesis of the findings indicates that prenatal ethanol exposure disturbs LTD concurrently with LTP in offspring and that both glutamatergic and γ-aminobutyric acid (GABA) neurotransmissions are altered and contribute to LTD disturbances. Although the ultimate mode of action of ethanol on these two transmitter systems is not yet clear, novel suggestions have recently appeared in the literature.

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.

Acute and chronic effects of ethanol on learning-related synaptic plasticity

Alcoholism is associated with acute and long-term cognitive dysfunction including memory impairment, resulting in substantial disability and cost to society. Thus, understanding how ethanol impairs cognition is essential for developing treatment strategies to dampen its adverse impact. Memory processing is thought to involve persistent, use-dependent changes in synaptic transmission, and ethanol alters the activity of multiple signaling molecules involved in synaptic processing, including modulation of the glutamate and gamma-aminobutyric acid (GABA) transmitter systems that mediate most fast excitatory and inhibitory transmission in the brain. Effects on glutamate and GABA receptors contribute to ethanol-induced changes in long-term potentiation (LTP) and long-term depression (LTD), forms of synaptic plasticity thought to underlie memory acquisition. In this paper, we review the effects of ethanol on learning-related forms of synaptic plasticity with emphasis on changes observed in the hippocampus, a brain region that is critical for encoding contextual and episodic memories. We also include studies in other brain regions as they pertain to altered cognitive and mental function. Comparison of effects in the hippocampus to other brain regions is instructive for understanding the complexities of ethanol's acute and long-term pharmacological consequences.

Modulation of hippocampal long-term potentiation by slow increases in ethanol concentration

To determine how acute ethanol intoxication may alter memory processing, we examined the effects of stepwise increases in ethanol on long-term potentiation (LTP) in rat hippocampal slices. LTP was inhibited by acute administration of 60 mM ethanol, but was readily induced if ethanol was increased gradually to 60 mM over 75 min. Administration of 2-amino-5 phosphonovalerate (APV), an N-methyl-D-aspartate receptor (NMDAR) antagonist, during the stepwise increase in ethanol inhibited LTP, suggesting involvement of NMDARs in the development of tolerance. However, APV and nifedipine, an inhibitor of L-type calcium channels, failed to inhibit LTP when administered following the slow increase in ethanol. Ethanol-tolerant LTP was inhibited by thapsigargin, suggesting a major role for intracellular calcium release in this form of plasticity. The unique properties of ethanol-tolerant LTP suggest that memories formed during binge drinking are not acquired by standard synaptic mechanisms and that acute tolerance may involve the induction of novel mechanisms to maintain function.

Prenatal ethanol exposure reduces mGluR5 receptor number and function in the dentate gyrus of adult offspring

BACKGROUND

Previous studies in our laboratory indicated that metabotropic glutamate receptor (mGluR)-stimulated phosphoinositide hydrolysis is markedly reduced in the hippocampal formation of adult rat offspring whose mothers drank moderate amounts of ethanol during pregnancy. In the present study, we extended these observations by measuring the impact of prenatal ethanol exposure on proteins associated with the mGluR5 receptor-effector system along with two mGluR5 agonist-mediated responses in dentate gyrus of adult offspring.

METHODS

Sprague-Dawley rat dams consumed one of three diets throughout gestation: (1) a BioServ liquid diet that contained 5% ethanol (v/v), (2) pair-fed an isocalorically equivalent amount of 0% ethanol liquid diet, or (3) lab chow ad libitum. Microdissected slices of dentate gyrus were prepared from adult female offspring from each diet group and used for (1) Western blot analyses of mGluR5, the G-proteins Galphaq and Galpha11, and phospholipase C-beta1; (2) 2-chloro-5-hydroxyphenylglycine (CHPG)-stimulated growth associated protein 43 (GAP-43) phosphorylation; or (3) CHPG potentiation of electrically evoked [H]-D-aspartate (D-ASP) release from dentate gyrus slices.

RESULTS

In tissue prepared from untreated control rats, CHPG produced a dose-dependent increase in phosphate incorporation into GAP-43, with maximal agonist stimulation occurring at 20 microM of CHPG. CHPG produced a quantitatively similar dose-dependent increase in the potentiation of electrically evoked D-ASP release from dentate gyrus slices from untreated controls. Fetal ethanol exposure reduced the amount of dentate gyrus mGluR5 receptor protein by 36% compared with the diet control groups. There were no significant differences between diet groups in the two G-proteins or phospholipase C-beta1 protein. Fetal ethanol exposure reduced CHPG-stimulated GAP-43 phosphorylation to approximately one half the amount of CHPG stimulation observed in the control diet groups. Prenatal ethanol exposure also reduced CHPG potentiation of D-ASP release to a similar degree compared with control.

CONCLUSIONS

These results indicate that prenatal exposure to moderate quantities of ethanol reduces mGluR5 expression in the dentate gyrus of adult offspring. Although the subcellular site(s) for reduced mGluR5 expression cannot be discerned from Western blot data, the quantitatively similar effects of prenatal ethanol exposure on mGluR5 agonist stimulation of presynaptically localized GAP-43 phosphorylation and CHPG potentiation of evoked D-ASP release suggest that the presynaptic nerve terminal is one site where prenatal ethanol exposure has reduced mGluR5 receptor number and function. Furthermore, these data implicate these neurochemical alterations as one factor contributing to the hippocampal synaptic plasticity and behavioral deficits that we have observed previously in prenatal ethanol-exposed offspring.

Multiple memory systems: the power of interactions

Two relatively simple theories of brain function will be used to demonstrate the explanatory power of multiple memory systems in your brain interacting cooperatively or competitively to directly or indirectly influence cognition and behaviour. The view put forth in this mini-review is that interactions between memory systems produce normal and abnormal manifestations of behaviour, and by logical extension, an understanding of these complex interactions holds the key to understanding debilitating brain and psychiatric disorders.

Chronic Ethanol-Induced Subtype- and Subregion-Specific Decrease in the mRNA Expression of Metabotropic Glutamate Receptors in Rat Hippocampus

BACKGROUND

Chronic ethanol consumption is known to induce adaptive changes in the hippocampal glutamatergic transmission and alter NMDA receptor binding and subunit expression. Metabotropic glutamate (mGlu) receptors have been shown to function as modulators of neuronal excitability and can fine tune glutamatergic transmission. This study was aimed to determine whether chronic ethanol treatment could change the messenger RNA (mRNA) expression of mGlu receptors in the hippocampus.

METHODS

Male Sprague Dawley rats were fed a Lieber-DeCarli liquid diet with 5% (w/v) ethanol or isocaloric amount of maltose for 2 months. Quantitative in situ hybridization was carried out using coronal brain sections through the hippocampus.

RESULTS

The results revealed decreases in mRNA expression of several mGlu receptors in different subregions of the hippocampus. In the dentate gyrus, mGlu3 and mGlu5 receptor mRNA levels were significantly lower in the ethanol-treated rats than in the control rats. In the CA3 region, the mRNA expression of mGlu1, mGlu5, and mGlu7 receptors showed substantial decreases after ethanol exposure. The mGlu7 receptor mRNA levels were also declined in the CA1 region and the polymorph layer of the dentate gyrus. No changes were found in mRNA expression of mGlu2, mGlu4, and mGlu8 receptors.

CONCLUSIONS

Considering the involvement of hippocampal mGlu receptors in learning and memory processes as well as in neurotoxicity and seizure production, the reduced expression of these receptors might contribute to ethanol withdrawal-induced seizures and also may play a role in cognitive deficits and brain damage caused by long-term ethanol consumption.

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.

Fear conditioning-induced alterations of phospholipase C-beta1a protein level and enzyme activity in rat hippocampal formation and medial frontal cortex

We investigated the effects of one-trial fear conditioning on phospholipase C-beta1a catalytic activity and protein level in hippocampal formation and medial frontal cortex of untreated control rats and rats prenatally exposed to ethanol. One hour following fear conditioning of untreated control rats, phospholipase C-beta1a protein level was increased in the hippocampal cytosolic fraction and decreased in the hippocampal membrane and cortical cytosolic and cortical membrane fractions. Twenty-four hours after fear conditioning, phospholipase C-beta1a protein level was reduced in the hippocampal cytosolic fraction and elevated in the cortical nuclear fraction; in addition, 24 h after conditioning, phospholipase C-beta1a activity in the cortical cytosolic fraction was increased. Rats that were exposed prenatally to ethanol displayed attenuated contextual fear conditioning, whereas conditioning to the acoustic-conditioned stimulus was not different from controls. In behavioral control (unconditioned) rats, fetal ethanol exposure was associated with reduced phospholipase C-beta1a enzyme activity in the hippocampal nuclear, cortical cytosolic, and cortical membrane fractions and increased phospholipase C-beta1a protein level in the hippocampal membrane and cortical cytosolic fractions. In certain cases, prenatal ethanol exposure modified the relationship between fear conditioning and changes in phospholipase C-beta1a protein level and/or activity. The majority of these effects occurred 1 h, rather than 24 h, after fear conditioning. Multivariate analysis of variance revealed interactions between fear conditioning, subcellular fraction, and prenatal ethanol exposure for measures of phospholipase C-beta1a protein level in hippocampal formation and phospholipase C-beta1a enzyme activity in medial frontal cortex. In the majority of cases, fear conditioning-induced changes in hippocampal phospholipase C-beta1a protein level were augmented in rats prenatally exposed to ethanol. In contrast, fear conditioning-induced changes in cortical phospholipase C-beta1a activity were, often, in opposite directions in prenatal ethanol-exposed compared to diet control rats. We speculate that alterations in subcellular phospholipase C-beta1a catalytic activity and protein level contribute to contextual fear conditioning and that learning deficits observed in rats exposed prenatally to ethanol result, in part, from dysfunctions in phospholipase C-beta1a signal transduction.

Ethanol exposure during the third trimester equivalent results in long-lasting decreased synaptic efficacy but not plasticity in the CA1 region of the rat hippocampus

Fetal alcohol syndrome is a major cause of mental retardation. We investigated possible long-lasting effects of alcohol on the hippocampus using a model for human third trimester brain development. Treatment of neonatal rats with an ethanol vapor atmosphere of 39.4+/-2.6 mg ethanol/liter of air for 3 h a day from postnatal day 4 through 9 produced daily blood ethanol levels of 351+/-14 mg/dL. Separation control animals were removed from their mothers in parallel with the ethanol vapor treatment, while suckle controls were left to develop normally. We prepared hippocampal slices from these animals between postnatal days 45 and 60 and recorded extracellular responses to Schaffer collateral stimulation. The maximum population spike in the CA1 pyramidal region and population excitatory postsynaptic potentials in the stratum radiatum did not differ significantly between groups. However, slices prepared from ethanol-treated rats as opposed to separation and suckle controls required larger stimulus currents to produce normal postsynaptic responses. In addition, the ratio of the population excitatory postsynaptic potential (pEPSP) slope to the presynaptic volley was significantly reduced in ethanol-treated rats. Ethanol vapor-treated rats and separation control rats did not exhibit any significant changes in long-term potentiation or paired-pulse potentiation compared with normal suckle controls. These results suggest that early postnatal ethanol treatment produces a long-lasting reduction in synaptic efficacy but not plasticity.

N-Methyl-D-aspartate inhibits apoptosis through activation of phosphatidylinositol 3-kinase in cerebellar granule neurons. A role for insulin receptor substrate-1 in the neurotrophic action of n-methyl-D-aspartate and its inhibition by ethanol

Primary cultured rat cerebellar granule neurons underwent apoptosis when switched from medium containing 25 mM K+ to one containing 5 mM K+. N-methyl-D-aspartate (NMDA) protected granule neurons from apoptosis in medium containing 5 mM K+. Inhibition of apoptosis by NMDA was blocked by the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor LY294002, but it was unaffected by the mitogen-activated protein kinase kinase inhibitor PD 98059. The antiapoptotic action of NMDA was associated with an increase in the tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1), an increase in the binding of the regulatory subunit of PI 3-kinase to IRS-1, and a stimulation of PI 3-kinase activity. In the absence of extracellular Ca2+, NMDA was unable to prevent apoptosis or to phosphorylate IRS-1 and activate PI 3-kinase. Significant inhibition of NMDA-mediated neuronal survival by ethanol (10-15%) was observed at 1 mM, and inhibition was half-maximal at 45-50 mM. Inhibition of neuronal survival by ethanol corresponded with a marked reduction in the capacity of NMDA to increase the concentration of intracellular Ca2+, phosphorylate IRS-1, and activate PI 3-kinase. These data demonstrate that the neurotrophic action of NMDA and its inhibition by ethanol are mediated by alterations in the activity of a PI 3-kinase-dependent antiapoptotic signaling pathway.

Neonatal alcohol exposure reduces NMDA induced Ca2+ signaling in developing cerebellar granule neurons

Glutamatergic neurotransmission through NMDA receptors is critical for both neurogenesis and mature function of the central nervous system (CNS), and is thought to be one target for developmentally-induced damage by alcohol to brain function. In the current study we examined Ca2+ signaling linked to NMDA receptor activation as a potential site for alcohol's detrimental effects on the developing nervous system. We compared Ca2+ signals to NMDA in granule neurons cultured from cerebella of rat neonates exposed to alcohol (ethanol) during development with responses to NMDA recorded in separated control groups. Alcohol exposure was by the vapor chamber method on postnatal days 4-7. An intermittent exposure paradigm was used where the pups were exposed to alcohol vapor for 2. 5 h/day to produce peak BALs of approximately 320 mg%. Control pups were placed in an alcohol-free chamber for a similar time period or remained with their mother. After culture under alcohol-free conditions for up to 9 days, Ca2+ signaling in response to NMDA was measured using fura-2 Ca2+ imaging. Results show that the peak amplitude of the Ca2+ signal to NMDA was significantly smaller in cultured granule neurons obtained from alcohol-treated pups compared to granule neurons from control pups. In contrast, the Ca2+ signal to K+ depolarization was not depressed by the alcohol treatment. Resting Ca2+ levels were also altered by the alcohol treatment. These results show that intermittent alcohol exposure during development in vivo can induce long-term changes in CNS neurons that affect the Ca2+ signaling pathway linked to NMDA receptors and resting Ca2+ levels. Such changes could play an important role in the CNS dysfunction associated with alcohol exposure during CNS development.

Prenatal ethanol exposure enhances glutamate release stimulated by quisqualate in rat cerebellar granule cell cultures

Effects of prenatal ethanol exposure on extracellular glutamate accumulation stimulated by glutamate receptor agonists were studied in rat cerebellar granule cell cultures. The prenatal exposure to ethanol was achieved via maternal consumption of a Sustacal liquid diet containing either 5% ethanol or isocaloric sucrose (pair-fed) substituted for ethanol from gestation d 11 until the day of parturition. Neither the basal level of extracellular glutamate nor the increased accumulation of glutamate stimulated by KCl (40 mM) or by ionotropic glutamate receptor agonists, N-methyl-D-aspartate (NMDA) or kainate (KA) (100 microM each), in cells prepared from the ethanol-fed group was significantly different from that in cells prepared from the pair-fed group. Glutamate accumulation stimulated by quisqualate (QA, 100 microM) or by trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid (t-ACPD, 250 microM) in the ethanol-fed group was higher than that in the pair-fed group by 116 and 36%, respectively. In the presence of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 100 microM), an ionotropic QA receptor antagonist, the QA-induced accumulation of glutamate in the ethanol-fed group was still higher than that in the pair-fed group. In the presence of MK-801 (5 microM), an antagonist of the NMDA receptor, the enhanced accumulation of glutamate stimulated by either QA or t-ACPD was still observable in the ethanol-fed group as compared to the pair-fed group. Addition of (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG, 500 microM), a selective antagonist of the metabotropic glutamate receptor, abolished the enhanced accumulation of glutamate stimulated by either QA or t-ACPD in the ethanol-fed group. Although immunoblotting of mGluR1 and mGluR2/3 did not show apparent differences between the pair-fed and the ethanol-fed groups, the overall results suggest that the effect of prenatal ethanol exposure was selectively through a pathway mediated by the metabotropic glutamate receptor.

Molecular pathogenesis of alcohol withdrawal seizures: the modified lipid-protein interaction mechanism

The phrase alcohol withdrawal seizures (AWS) refers to seizures that result from the withdrawal of alcohol after a period of chronic alcohol administration. A mechanism of AWS is postulated, namely the modified lipid-protein interaction (MLPI) mechanism. This hypothesis is based upon an evaluation of the mechanisms of membrane fluidity, calcium channels, gamma-aminobutyric acid (GABA) and glutamate in the molecular pathogenesis of AWS. The mechanism hypothesizes that acute ethanol treatment alters the neuronal membrane lipids which then perturbs protein events, such as affecting the GABAA receptors, NMDA receptors and voltage-dependent Ca2+ channels synergistically or in combination. Subsequent adaptations in these systems occur after prolonged administration of ethanol. A sudden withdrawal of ethanol then leads to hyperexcitability which results in AWS.

Prenatal exposure to moderate levels of ethanol can have long-lasting effects on hippocampal synaptic plasticity in adult offspring

Prenatal ethanol exposure has been associated with long-lasting intellectual impairments in children. Previous studies using animal models of fetal ethanol exposure suggest that these deficits are, at least in part, linked to neurochemical abnormalities in the hippocampal formation. We explored whether prenatal exposure to moderate quantities of ethanol produced functional deficits at the entorhinal cortical perforant path-dentate granule cell connection by examining some electrophysiological properties, including the induction of long-term potentiation (LTP). Rat dams consumed one of three diets throughout gestation: 1) a BioServ liquid diet containing 5% (v/v) ethanol (26% ethanol-derived calories), which produces a maternal peak blood ethanol concentration of 83 mg/dl; 2) pair-fed an isocalorically equivalent amount of 0% ethanol liquid diet; or 3) Purina rat chow ad libitum. Adult offspring (120-150 days of age) from each experimental diet group were anesthetized with urethane and field excitatory postsynaptic potentials (EPSPs) and population spikes were measured in the dentate gyrus in response to ipsilateral perforant path stimulation. We examined input-output functions using a wide range of single pulse stimulation intensities and induction of LTP using high-frequency stimulation. In the 50-500 microA range of single pulse intensities, there were no significant differences among the diet groups in dentate gyrus evoked potentials. In response to high-frequency stimulation, prenatal ethanol-exposed rats showed a smaller increase in field EPSPs and population spikes compared with rats from either of the two control groups. Thus, prenatal exposure to moderate ethanol levels can produce a long-lasting deficit in synaptic enhancement in a neural pathway believed to be critical in certain forms of learning and memory. This deficit in hippocampal synaptic plasticity may, in part, account for cognitive impairments seen in children whose mothers consumed ethanol during pregnancy.

Effects of prenatal ethanol exposure on voltage-dependent calcium entry into neonatal whole brain-dissociated neurons

The effect of prenatal ethanol exposure on voltage-dependent calcium entry into neonatal-dissociated neurons was studied. Dissociated whole brain cells were isolated from neonates of prenatally ethanol-treated (ET), pair-fed (PF) control, and ad libitum (AL) control groups and loaded with fura-2. Prenatal ethanol exposure resulted in a significant reduction of calcium entry into K(+)-depolarized cells, compared with AL and PF control treatments. Initially, in dissociated cells from AL control animals, it was found that nifedipine (1 microM), omega-agatoxin (100 nM), and omega-conotoxin (500 nM), to a much lesser extent, significantly inhibited the 45 mM KCl-stimulated calcium entry. To determine the inhibitory action of prenatal ethanol exposure on N-, P-, and L-type voltage-dependent calcium channels, treatment of neonatal-dissociated neurons with different combinations of omega-conotoxin, omega-agatoxin, and nifedipine, respectively, was compared in the prenatal ethanol and control treatment groups. The inhibition of K(+)-stimulated increase in calcium entry by prenatal ethanol exposure was significantly less in the presence or absence of single antagonist conditions (ET < AL and PF). There was no apparent interaction of ethanol exposure and antagonist condition. However, the reduced calcium entry after prenatal ethanol exposure was superseded by the stronger inhibition in dual and triple antagonist conditions. The magnitude of the calcium response inhibition by the antagonist combinations was similar among the ET, PF, and AL groups. Thus, these results suggest that prenatal ethanol exposure decreases voltage-dependent calcium entry into neonatal-dissociated neurons in a manner that does not seem to involve the selective inhibition of any individual N-, P-, or L-type calcium channel.

Effects of alcohol exposure and artificial rearing during development on septal and hippocampal neurotransmitters in adult rats

The effect of alcohol exposure during the early postnatal period in the rat on the hippocampus and septal region was investigated. The alcohol group was given 5 g/kg/day of ethanol from postnatal days 4 to 10 via an artificial rearing procedure. Control groups consisted of a gastrostomy control group that was treated in the same manner as the alcohol group, but not exposed to alcohol and a suckle control group that was reared normally by dams. Between 90 and 100 days of age, the hippocampus and septal region were assayed under nonstressed or stressed conditions using HPLC with electrochemical detection. Alcohol-exposed female rats exhibited increased hippocampal noradrenaline concentrations under stressed conditions, increased septal serotonin, and 5-hydroxyindoleacetic acid (5-HIAA) concentrations under nonstressed conditions, and decreased septal dopamine concentrations under stressed conditions. Artificially reared male rats (regardless of alcohol exposure) exhibited an increase in hippocampal noradrenaline concentrations under stressed conditions; a decrease in hippocampal 5-HIAA concentrations under nonstressed conditions; and a decrease in septal noradrenaline, serotonin, 5-HIAA, and dopamine concentrations under nonstressed conditions. The results suggest that female rats may be more susceptible to alcohol exposure during the postnatal period than male rats and that male rats may be more susceptible to the effects of artificial rearing than female rats.

Influence of chronic prenatal ethanol on cholinergic neurons of the septohippocampal system

This study characterized the influence of full-term gestational ethanol exposure on choline acetyltransferase (ChAT)-immunoreactive neurons that project to the hippocampus, within the medial septal (MS) nucleus and the vertical limb of the diagonal band of Broca (DBv). On gestation days 1-22, pregnant dams were fed either a vitamin fortified ethanol-containing liquid diet, pair fed a calorically equivalent sucrose-containing diet, or given rat chow ad libitum. In a previous study, we found that chronic prenatal exposure to ethanol, in this manner, resulted in a significant decline in the ontogenetic upregulation of ChAT activity in the septal area during the second postnatal week, but was followed by recovery to control levels by adulthood. On postnatal days 14 and 60 (P14 and P60) the brains were prepared for ChAT immunocytochemistry. Ethanol exposure had little influence on the number of ChAT-positive neurons in the MS nucleus of animals at either age. Ethanol exposure had no effect on neuronal size or ChAT staining intensity of MS or DBv neurons when compared to chow-fed offspring. Although age-related increases in cholinergic neuronal numbers and decreases in neuronal size were observed between juvenile and adult animals, prenatal ethanol exposure did not appear to influence these postnatal changes in the population as a whole. Overall, these findings suggest that the anatomical maturation of septal cholinergic neurons may be relatively insensitive to prenatal ethanol exposure under conditions of a vitamin-rich dietary supplementation, while biochemical development within this region may be more susceptible to early ethanol influences.

Chronic prenatal ethanol exposure alters the normal ontogeny of choline acetyltransferase activity in the rat septohippocampal system

In animal models of fetal alcohol syndrome (FAS), the hippocampus has been shown to be especially sensitive to the effects of prenatal ethanol exposure, exhibiting neuronal loss and alterations in neuritic process elaboration. We have characterized the influence of chronic prenatal ethanol treatment (CPET) on the postnatal expression of choline acetyltransferase (ChAT) in the hippocampus and the septal area that contains neurons that provide the primary cholinergic innervation to the hippocampus. On gestation days 1-22, pregnant rats were either fed an ethanol-containing liquid diet, pair-fed a calorically equivalent sucrose-containing diet, or given rat chow ad libitum. In Chow control animals, the ontogenetic progression of ChAT activity in the septal area and hippocampus was characterized by a significant period of upregulation during the 2nd and 3rd postnatal weeks, exhibiting and an approximate 5-fold increase (septal area) and 7-fold increase (hippocampus) by postnatal day 21 (P21). At P14, ethanol exposure reduced septal and hippocampal ChAT activity levels, compared with those of pair-fed offspring. ChAT activity reached control levels by P21 in ethanol-exposed pups, suggesting that the earlier decline in activity may reflect a delay in the ontogenetic upregulation. In addition, there was a trend toward increased septal and hippocampal ChAT activities at P1 and P7 in both liquid diet groups. This liquid diet-stimulated increase may mask the effects of ethanol on early postnatal ChAT expression in the septohippocampal system. The results suggest that prenatal ethanol exposure may influence factors that regulate the developmental expression of ChAT in the septohippocampal system.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulatory effects of acute ethanol on metabotropic glutamate responses in cultured Purkinje neurons

Ethanol has been shown to affect several transmitter- and voltage-gated channels in the brain, although little attention has focused on potential interactions between ethanol and metabotropic glutamate receptors (mGluRs). This is of interest as mGluRs are now recognized to be important components of synaptically mediated responses, including short- and long-term changes in the efficacy of neurotransmission. Cerebellar Purkinje neurons are sensitive to the effects of ethanol and express high levels of mGluRs. We made extracellular recordings from cerebellar Purkinje neurons at 21-37 days in culture to examine the effect of ethanol on mGluR-mediated responses. mGluRs were activated by pressure ejection of 300 microM (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD), a selective agonist of mGluRs, or 5 microM quisqualate (Quis). As Quis activates both ionotropic and metabotropic glutamate receptors, 50 microM 6,7-dinitroquinoxaline-2,3-dione (DNQX) was used to block the ionotropic component of Quis-mediated responses. Both ACPD and Quis produced biphasic changes in firing rates consisting of an initial brief excitatory phase (5-20 s) followed by a prolonged inhibitory phase (10 s to 2.5 min), and induced the generation of bursts. Addition of 33 mM (150 mg%) ethanol to the recording medium had little effect on ACPD-mediated responses. In the presence of 66 mM (300 mg%) ethanol, however, ACPD-mediated responses exhibited an increase in the total response duration, with no change in the percent excitation or the induction of bursts as compared to controls. On the other hand, 66 mM ethanol decreased Quis-induced burst activity, while having no effect on the percent excitation or the total response duration.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol exposure during brain development reduces 3H-MK-801 binding and enhances metabotropic-glutamate receptor-stimulated phosphoinositide hydrolysis in rat hippocampus

Glutamate receptors play important roles during brain development. We have investigated the effect of chronic maternal alcohol intake on the ontogenic profile of hippocampal glutamate receptor subtypes in their offspring. Binding of 3H-MK-801 to N-methyl-D-aspartate (NMDA) receptor was measured in isolated membranes from the hippocampus of the offspring of pair-fed control and alcohol-fed rats at different times during the postnatal life. Phosphatidylinositol triphosphate (PIP2) hydrolysis was also assayed to provide a measure of the possible effect of ethanol on the metabotropic glutamate receptor (mGluR). In pair-fed control rats, at postnatal day (PND) 3, the 3H-MK-801 binding represents 60% of adult values. Binding then rises to 170% at PND 11, and gradually decreases to adult levels. A transient overshoot in the mGluR-coupled PIP2 hydrolysis was also observed during postnatal development in rat hippocampus. Alcohol-exposed rats showed a similar pattern, but a significant decrease in the specific binding for NMDA receptor was observed on all the postnatal days analyzed. In addition, alcohol exposure significantly decreases the number of specific 3H-MK-801 binding sites, with no change in the affinity of the sites for 3H-MK-801. Moreover, this treatment enhanced the mGluR-activated PIP2 hydrolysis in hippocampus of alcohol-exposed rats. These results may contribute to an understanding of the toxic effects of ethanol on the developing central nervous system (CNS) and help explain the cognitive deficits associated with prenatal alcohol exposure.

Calcium signals elicited by quisqualate in cultured Purkinje neurons show developmental changes in sensitivity to acute alcohol

The effect of acute alcohol (33 mM ethanol) on calcium signaling evoked by glutamate receptor activation was studied in cultured cerebellar Purkinje and granule neurons at different stages of development. Calcium signals were measured by microscopic imaging using the calcium sensitive dye fura-2. At an early stage in development (10 days in vitro), acute alcohol enhanced the calcium signals evoked in Purkinje neurons by exogenous application of quisqualate, an agonist at ionotropic and metabotropic glutamate receptors. In contrast, in mature cultured Purkinje neurons (21-24 days in vitro) the calcium signals produced by quisqualate were reduced by alcohol. At an intermediate stage of development (14 days in vitro) reflecting the main period of morphological and physiological maturation, alcohol had no significant effect on the response to quisqualate. Alcohol's actions were significantly altered by manipulation of the intracellular stores with caffeine, implicating intracellular stores in alcohol's actions. Calcium signals produced by quisqualate in the cultured granule neurons were also altered by acute alcohol, in a manner similar to that observed in the Purkinje neurons. These data demonstrate that calcium signaling pathways are a site of alcohol action in developing CNS neurons and that the cellular consequences of alcohol exposure can change with development. Such actions of alcohol could have significant effects on the immature nervous system, where the precise timing of appropriate signaling levels are important aspects of the maturation process.

Prenatal ethanol exposure reduces phosphoinositide hydrolysis stimulated by quisqualate in rat cerebellar granule cell cultures

Prenatal ethanol exposure-induced alteration in poly-phosphoinositide (PPI) hydrolysis stimulated by excitatory amino acids (EAA) was studied in rat cerebellar granule cells previously labeled with [3H]myoinositol. The prenatal exposure to ethanol was achieved via maternal consumption of a Sustacal (chocolate flavored) liquid diet containing either 5% ethanol (w/v, 35% of calories) or isocaloric sucrose (pair-fed) substituted for ethanol from gestation d 11 until the day of parturition. The ionotropic glutamate receptor agonists, N-methyl-D-aspartate, kainate or (+/-)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) (100 microM each) induced a two- to four-fold increase in PPI hydrolysis over the basal level, regardless of the liquid dietary treatment. Stimulation with quisqualate (QA), an agonist activating both metabotropic and ionotropic glutamate receptors, resulted in a much stronger and dose-dependent response in PPI hydrolysis and exposure in utero to ethanol significantly reduced this response. Tetrodotoxin, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), or (+/-)-3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid (CPP) had no effect on QA-stimulated PPI hydrolysis nor on the suppression of this hydrolysis by ethanol. Exposure in utero to ethanol did not affect PPI hydrolysis stimulated by a selective metabotropic glutamate receptor agonist, trans-(+/-)-l-amino-1,3-cyclopentanedicarboxylic acid (t-ACPD). Although the PPI hydrolysis stimulated by t-ACPD could be blocked by (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG), an antagonist of the metabotropic glutamate receptor, MCPG was incapable of affecting QA-induced PPI hydrolysis and the suppressive effects of prenatal ethanol exposure on this hydrolysis. Taken together, the data suggest that the long-lasting suppressive effects of prenatal ethanol exposure on QA-stimulated PPI hydrolysis in cerebellar granule cell cultures is through a metabotropic QA receptor pathway that may be different from the one activated by t-ACPD.

Selective effects of ethanol exposure on metabotropic glutamate receptor and guanine nucleotide stimulated phospholipase C activity in primary cultures of astrocytes

The effects of acute and chronic ethanol exposures on the stimulation of inositol specific phospholipase C by metabotropic glutamate receptor activation were determined in primary cultures of rat cortical astrocytes. Phospholipase C activity was monitored by the formation of [3H]inositol phosphates in the presence of lithium in cells prelabelled with [3H]inositol. Acute exposure to 200 mM ethanol had no significant effect on either basal or L-glutamate stimulated [3H]inositol phosphate formation. In cells chronically exposed to ethanol for 4 days, the [3H]inositol phosphate responses to L-glutamate, quisqualate, and the selective metabotropic receptor agonist, 1S,3R-1-amino-cyclopentane-1,3 dicarboxylic acid (trans-ACPD), were significantly inhibited when compared to control (untreated) cells. In contrast, chronic ethanol exposure had no significant effect on the [3H]inositol phosphate response to endothelin-1, a peptide structurally and functionally unrelated to L-glutamate. Similarly, the stimulation of [3H]inositol phosphate formation by the stable GTP analog, guanine 5'-(gamma-thiotrisphosphate), was also unaffected by chronic ethanol exposure. The results suggest that chronic ethanol exposure does not affect the coupling of GTP binding proteins to phospholipase C, but rather acts in a selective manner to either alter the metabotropic receptor number or to disrupt the normal coupling of this receptor to its GTP binding protein, which may in turn affect receptor affinity.