Effects of acute ethanol exposure on glutamate release in the hippocampus of the fetal and adult guinea pig

High Ethanol and Acetaldehyde Inhibit Glutamatergic Transmission in the Hippocampus of Aldh2-Knockout and C57BL/6N Mice: an In Vivo and Ex Vivo Analysis

We aimed to investigate whether ethanol (EtOH) and acetaldehyde (AcH) can affect glutamate and its receptors GluN1 and GluA1 in the hippocampus of Aldh2-knockout (Aldh2-KO) and C57BL/6N (wild-type (WT)) mice. To do this, we first examined the effect of local administration of EtOH (100 mM, 200 mM, and 500 mM) and AcH (100 μM, 200 μM, and 500 μM) on extracellular glutamate levels in freely moving mice. Retrodialysis of 200 mM and 500 mM EtOH into the hippocampus of WT and Aldh2-KO mice produced significant decreases in extracellular glutamate levels (p < 0.05). A dose of 500 mM EtOH induced a greater decrease in Aldh2-KO mice (p < 0.05) than in WT mice, indicating the action of AcH. Similarly, perfusion of 200 μM and 500 μM AcH decreased glutamate in Aldh2-KO mice (p < 0.05), but this decrease was not seen in WT mice at any AcH dose. Second, we tested whether the EtOH- and AcH-induced decrease in glutamate was associated with decreases in GluN1 and GluA1 expression, as measured by real-time PCR and Western blot. We found a significant decrease in GluN1 (p < 0.05) and GluA1 (p < 0.05) subunits after a high dose of EtOH (4.0 g/kg) and AcH (200 mg/kg) in WT mice. However, a 2.0 g/kg dose of EtOH did not produce a consistent decrease in GluN1 or GluA1 between messenger RNA and protein. In Aldh2-KO mice, all three doses of EtOH (1.0 g/kg, 2.0 g/kg, and 4.0 g/kg) and AcH (50 mg/kg, 100 mg/kg, and 200 mg/kg) decreased GluN1 expression (p < 0.05), while moderate-to-high doses of EtOH (2.0 g/kg and 4.0 g/kg) and AcH (100 mg/kg and 200 mg/kg) decreased GluA1 expression (p < 0.05). Together, these in vivo and ex vivo data suggest that EtOH and AcH decrease extracellular glutamate in the hippocampus of mice with a concomitant decrease in GluN1 and GluA1 subunits, but these effects require relatively high concentrations and may, therefore, explain the consequences of EtOH intoxication.

Role of glutamatergic system and mesocorticolimbic circuits in alcohol dependence

Emerging evidence demonstrates that alcohol dependence is associated with dysregulation of several neurotransmitters. Alterations in dopamine, glutamate and gamma-aminobutyric acid release are linked to chronic alcohol exposure. The effects of alcohol on the glutamatergic system in the mesocorticolimbic areas have been investigated extensively. Several studies have demonstrated dysregulation in the glutamatergic systems in animal models exposed to alcohol. Alcohol exposure can lead to an increase in extracellular glutamate concentrations in mesocorticolimbic brain regions. In addition, alcohol exposure affects the expression and functions of several glutamate receptors and glutamate transporters in these brain regions. In this review, we discussed the effects of alcohol exposure on glutamate receptors, glutamate transporters and glutamate homeostasis in each area of the mesocorticolimbic system. In addition, we discussed the genetic aspect of alcohol associated with glutamate and reward circuitry. We also discussed the potential therapeutic role of glutamate receptors and glutamate transporters in each brain region for the treatment of alcohol dependence. Finally, we provided some limitations on targeting the glutamatergic system for potential therapeutic options for the treatment alcohol use disorders.

Regulation of NMDA receptor subunits after acute ethanol treatment in rat brain

AIMS

Tolerance to ethanol-induced inhibition of N-methyl-D-aspartate receptors (NMDARs) is thought to underlie the acute adaptive mechanisms against ethanol. To explore these compensatory upregulating mechanisms of NMDARs, we investigated the expression and phosphorylation of NMDAR subunits in vivo following an acute ethanol treatment.

METHODS

Male Sprague-Dawley rats were given 4 g/kg ethanol, and the phospho-S896-NR1, NR2A and NR2B subunits of NMDAR were immunoblotted from the cerebral cortex and hippocampus. We also examined the mRNAs and ubiquitinated forms of the NR2A and NR2B subunits.

RESULTS

Acute ethanol treatment increased phospho-S896-NR1 at 30 min in the cerebral cortex and hippocampus, and the increase was maintained until 2 h in the hippocampus. Ethanol increased total NR2A and NR2B expression at 30 min in the cortex and hippocampus, and the NR2A increase was maintained until 2 h in the hippocampus. The increased expression of the NR2A and NR2B subunits was not associated with statistically significant alterations in mRNA expression or protein ubiquitination.

CONCLUSION

Acute ethanol treatment increased NR1 subunit phosphorylation and NR2A and NR2B subunit expression in the cerebral cortex and hippocampus of rats. These effects of ethanol on the NMDAR subunits may underlie the mechanisms that compensate for ethanol-induced inhibition of NMDARs. However, the regulation of NR2A and NR2B in this paradigm is not dependent on transcriptional changes.

Acute ethanol suppresses glutamatergic neurotransmission through endocannabinoids in hippocampal neurons

Ethanol exposure during fetal development is a leading cause of long-term cognitive impairments. Studies suggest that ethanol exposure have deleterious effects on the hippocampus, a brain region that is important for learning and memory. Ethanol exerts its effects, in part, via alterations in glutamatergic neurotransmission, which is critical for the maturation of neuronal circuits during development. The current literature strongly supports the growing evidence that ethanol inhibits glutamate release in the neonatal CA1 hippocampal region. However, the exact molecular mechanism responsible for this effect is not well understood. In this study, we show that ethanol enhances endocannabinoid (EC) levels in cultured hippocampal neurons, possibly through calcium pathways. Acute ethanol depresses miniature post-synaptic current (mEPSC) frequencies without affecting their amplitude. This suggests that ethanol inhibits glutamate release. The CB1 receptors (CB1Rs) present on pre-synaptic neurons are not altered by acute ethanol. The CB1R antagonist SR 141716A reverses ethanol-induced depression of mEPSC frequency. Drugs that are known to enhance the in vivo function of ECs occlude ethanol effects on mEPSC frequency. Chelation of post-synaptic calcium by EGTA antagonizes ethanol-induced depression of mEPSC frequency. The activation of CB1R with the selective agonist WIN55,212-2 also suppresses the mEPSC frequency. This WIN55,212-2 effect is similar to the ethanol effects and is reversed by SR141716A. In addition, tetani-induced excitatory post-synaptic currents (EPSCs) are depressed by acute ethanol. SR141716A significantly reverses ethanol effects on evoked EPSC amplitude in a dual recording preparation. These observations, taken together, suggest the participation of ECs as retrograde messengers in the ethanol-induced depression of synaptic activities.

Acute and chronic ethanol alter glutamatergic transmission in rat central amygdala: an in vitro and in vivo analysis

The modulation of glutamatergic transmission by ethanol may contribute to ethanol intoxication, reinforcement, tolerance, and dependence. Therefore, we used in vitro electrophysiological and in vivo microdialysis techniques to investigate the effects of acute and chronic ethanol on glutamatergic transmission in the central nucleus of amygdala (CeA). Superfusion of 5-66 mM ethanol decreased compound glutamatergic EPSPs and EPSCs in CeA neurons, with half-maximal inhibition elicited by 14 mM ethanol. Ethanol (44 mM) decreased both non-NMDAR- and NMDAR-mediated EPSPs and EPSCs by 21%. Both the ethanol- and ifenprodil-induced depression of NMDAR-mediated EPSPs and EPSCs was enhanced in rats that received chronic ethanol treatment (CET). Ifenprodil also occluded the ethanol effect, suggesting that NR2B subunit-containing receptors may be involved. With local applications of NMDA, acute ethanol elicited a greater inhibition of NMDA currents in slices taken from CET (47%) compared with naive (30%) animals, suggesting that CET sensitizes NMDA receptors to ethanol. Acute ethanol also reduced paired pulse facilitation of EPSPs and EPSCs only in CET animals, suggesting acute ethanol-induced increase of glutamate release. This finding was supported by in vivo experiments showing that infusion of ethanol (0.1-1 M) via reverse microdialysis significantly increased glutamate release into the CeA dialysate but only after CET. Moreover, baseline CeA glutamate content was significantly higher in CET compared with naive animals. These combined findings suggest that CET and withdrawal lead to neuroadaptations of glutamatergic transmission at both presynaptic and postsynaptic sites in CeA, and glutamatergic synapses in CeA may play an important role in ethanol dependence.

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.

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.

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.

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

This study was designed to test the hypothesis that chronic prenatal ethanol exposure decreases basal and stimulated L-glutamate release in the hippocampus of young, postnatal guinea pigs. Timed, pregnant guinea pigs were randomly assigned to one of the following three chronic treatment groups: 4 g ethanol/kg maternal body weight/day, isocaloric-sucrose and pair-feeding to the ethanol group, and water. Each oral treatment was given daily throughout gestation. Spontaneous locomotor activity was increased on postnatal day (PD) 10, and brain and hippocampal weights were decreased on PD 12 in the offspring of the ethanol group compared with the isocaloric-sucrose/pair-fed and water groups. On PD 12, the 45 mM K(+)- and 10 microM veratridine-stimulated release of glutamate in transverse hippocampal slices was decreased in the ethanol group compared with the two control groups. This alteration in glutamate release produced by chronic prenatal ethanol exposure may decrease the efficiency of excitatory synaptic transmission in the hippocampus during postnatal life.

Effect of chronic prenatal ethanol exposure on nitric oxide synthase I and III proteins in the hippocampus of the near-term fetal guinea pig

Chronic prenatal ethanol exposure suppresses nitric oxide synthase (NOS) enzymatic activity, in the hippocampus of the near-term fetal guinea pig at gestational day (GD) 62. The objective of this study was to determine if this decrease in NOS activity is the result of decreased NOS I and NOS III protein expression. Pregnant guinea pigs received oral administration of 4 g ethanol/kg maternal body weight/day (n = 8), isocaloric-sucrose/pair feeding (n = 8), or water (n = 8) from GD 2 to GD 61. The NOS I and NOS III protein expression and localization in the hippocampus were determined using Western blot analysis and immunohistochemistry, respectively. The chronic ethanol regimen produced fetal body, brain, and hippocampal growth restriction compared with the isocaloric-sucrose/pair fed and water groups but did not affect the expression or localization of NOS I and NOS III proteins in the hippocampus. The decrease in NOS enzymatic activity induced by chronic prenatal ethanol exposure may be the result of posttranslational modification of NOS I and/or NOS III protein in the hippocampus of the near-term fetal guinea pig.

Effect of systemic ethanol on basal and stimulated glutamate releases in the nucleus accumbens of freely moving Sprague-Dawley rats: a microdialysis study

This study was conducted to assess the impact of systemic ethanol (EOH) on the glutamatergic transmission in the nucleus accumbens (NACC). Extracellular concentrations of glutamate (GLU) in the NACC of freely moving Sprague-Dawley rats were monitored by intracerebral microdialysis. Intraperitoneal injection of EOH at a dose of 2 g/kg significantly decreased basal extracellular GLU by 21%. In addition, administration of the same dose of EOH significantly attenuated 150 mM K+-stimulated GLU release from the NACC by more than 50%. Since K+-stimulated GLU release has been demonstrated to derive largely from nerve terminal depolarization, reductions of K+-evoked GLU release may reflect in part the effect of EOH on the neurotransmitter pool. The present results suggest that EOH may suppress glutamatergic transmission in the NACC by lowering presynaptic GLU release.

Ethanol and neurotransmitter interactions--from molecular to integrative effects

There is extensive evidence that ethanol interacts with a variety of neurotransmitters. Considerable research indicates that the major actions of ethanol involve enhancement of the effects of gamma-aminobutyric acid (GABA) at GABAA receptors and blockade of the NMDA subtype of excitatory amino acid (EAA) receptor. Ethanol increases GABAA receptor-mediated inhibition, but this does not occur in all brain regions, all cell types in the same region, nor at all GABAA receptor sites on the same neuron, nor across species in the same brain region. The molecular basis for the selectivity of the action of ethanol on GaBAA receptors has been proposed to involve a combination of benzodiazepine subtype, beta 2 subunit, and a splice variant of the gamma 2 subunit, but substantial controversy on this issue currently remains. Chronic ethanol administration results in tolerance, dependence, and an ethanol withdrawal (ETX) syndrome, which are mediated, in part, by desensitization and/or down-regulation of GABAA receptors. This decrease in ethanol action may involve changes in subunit expression in selected brain areas, but these data are complex and somewhat contradictory at present. The sensitivity of NMDA receptors to ethanol block is proposed to involve the NMDAR2B subunit in certain brain regions, but this subunit does not appear to be the sole determinant of this interaction. Tolerance to ethanol results in enhanced EAA neurotransmission and NMDA receptor upregulation, which appears to involve selective increases in NMDAR2B subunit levels and other molecular changes in specific brain loci. During ETX a variety of symptoms are seen, including susceptibility to seizures. In rodents these seizures are readily triggered by sound (audiogenic seizures). The neuronal network required for these seizures is contained primarily in certain brain stem structures. Specific nuclei appear to play a hierarchical role in generating each stereotypical behavioral phases of the convulsion. Thus, the inferior colliculus acts to initiate these seizures, and a decrease in effectiveness of GABA-mediated inhibition in these neurons is a major initiation mechanism. The deep layers of superior colliculus are implicated in generation of the wild running behavior. The pontine reticular formation, substantia nigra and periaqueductal gray are implicated in generation of the tonic-clonic seizure behavior. The mechanisms involved in the recruitment of neurons within each network nucleus into the seizure circuit have been proposed to require activation of a critical mass of neurons. Achievement of critical mass may involve excess EAA-mediated synaptic neurotransmission due, in part, to upregulation as well as other phenomena, including volume (non-synaptic diffusion) neurotransmission. Effects of ETX on receptors observed in vitro may undergo amplification in vivo to allow the excess EAA action to be magnified sufficiently to produce synchronization of neuronal firing, allowing participation of the nucleus in seizure generation. GABA-mediated inhibition, which normally acts to limit excitation, is diminished in effectiveness during ETX, and further intensifies this excitation.

Neuroanatomical and neurophysiological mechanisms involved in central nervous system dysfunctions induced by prenatal alcohol exposure

One of the most severe consequences of maternal ethanol consumption is the damage to the developing central nervous system, which is manifested by long-term cognitive and behavioral deficits in the offspring. Prenatal exposure to ethanol affects many crucial neurochemical and cellular components of the developing brain. Ethanol interferes with all of the stages of brain development, and the severity of the damage depends on the amount of ethanol intake and level of exposure. Experimental observations also indicate that the toxic effects of ethanol are not uniform: some brain regions are more affected than others and, even within a given region, some cell populations are more vulnerable than others. The neocortex, the hippocampus, and the cerebellum are the regions in which the neurotoxic effects of ethanol have been associated with the behavioral deficits. At the cellular level, ethanol disrupts basic developmental processes, including interference with division and proliferation, cell growth, and differentiation and the migration of maturing cells. Alterations in astroglia development and in neuronal-glial interactions may also influence the development of the nervous system. An impairment of several neurotransmitter systems and/or their receptors, as well as changes in the endocrine environment during brain development, are also important factors involved in the behavioral dysfunctions observed after prenatal ethanol exposure. Finally, some molecular mechanisms of ethanol-induced behavioral dysfunctions will be discussed.

Hippocampal nitric oxide synthase in the fetal guinea pig: effects of chronic prenatal ethanol exposure

The effects of chronic maternal administration of ethanol on nitric oxide synthase (NOS) activity and the numbers of NOS containing neurons, and CA1 and CA3 pyramidal neurons in the hippocampus of the near term fetal guinea pig at gestational day (GD) 62 were investigated. Pregnant guinea pigs received oral administration of 4 g ethanol/kg maternal body weight (n = 5), isocaloric sucrose/pair feeding (n = 5) or water (n = 5), or no treatment (NT; n = 5) from GD 2 to GD 61. NOS activity in the 25,000 x g supernatant of hippocampal homogenate was determined using a radiometric assay. The numbers of NOS containing neurons, and CA1 and CA3 pyramidal neurons were determined using NADPH diaphorase histochemistry and cresyl violet staining, respectively. The chronic ethanol regimen produced a maternal blood ethanol concentration of 193 +/- 13 mg/dl at 1 h after the second divided dose on GD 57. Chronic ethanol exposure produced fetal body, brain, and hippocampal growth restriction and decreased fetal hippocampal NOS activity compared with the isocaloric sucrose/pair feeding, water, and NT experimental groups, but did not affect the number of NOS containing and CA1 or CA3 pyramidal neurons. These data demonstrate that, in the near term fetus, chronic maternal administration of ethanol suppresses hippocampal NOS activity and consequent formation of NO, without loss of NOS containing neurons and prior to loss of CA1 pyramidal neurons that occurs in the adult.

Discriminative stimulus effects of glutamate release inhibitors in rats trained to discriminate ethanol

In a drug discrimination paradigm with rats trained to discriminate ethanol (1 g/kg IP) from saline we studied two substances, lamotrigine and riluzole, which are regarded as glutamate release inhibitors concerning their ability to substitute for ethanol. Both substances have been shown to act primarily on voltage-gated sodium channels; however, Lamotrigine dose dependently generalized to the ethanol cue, whereas riluzole did not. These results reflect the different high-dose effects of both sustances at voltage-gated calcium channels, where lamotrigine has inhibitory effects, but not riluzole, and provide further evidence for a role of voltage-gated calcium channels in the mediation of the effects of ethanol.

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.

Carbon monoxide formation in the guinea pig hippocampus: ontogeny and effect of in vitro ethanol exposure

Carbon monoxide (CO) is considered to be a novel neuronal messenger in the brain, similar to nitric oxide. The ontogeny of CO formation in transverse hippocampal slices of the guinea pig was elucidated at selected prenatal and postnatal ages, and the effect of in vitro ethanol exposure on hippocampal CO formation was determined. There was a higher rate of hippocampal CO formation in the fetus at gestational day (GD) 50 and GD 62 (term, about GD 68) compared with the adult. In vitro ethanol exposure (50 and 100 mM) decreased hippocampal CO formation in the GD 62 fetus, which was prevented by incubation with 500 microM L-glutamate.

Heme oxygenase activity and acute and chronic ethanol exposure in the hippocampus, frontal cerebral cortex, and cerebellum of the near-term fetal guinea pig

Heme oxygenase (HO) catalyzes the oxidation of heme to produce carbon monoxide, which is considered to be a novel neuronal messenger in the brain and may play a role in neuronal development. The objective of this study was to determine the effects of in vitro, acute in vivo, and chronic in vivo ethanol exposure on HO activity in the hippocampus, frontal cerebral cortex, and cerebellum of the near-term fetal guinea pig. HO activity was determined using a gas chromatographic method to quantitate CO formation in the microsomal fraction of the homogenate of each selected brain region, incubated with saturating concentrations of heme, NADPH, and O2. Fetal body, brain, hippocampal, and cerebellar weights were recorded. In vitro ethanol exposure (25-100 mM) did not affect hippocampal, cerebral cortical, or cerebellar HO activity of the fetal guinea pig at gestational day (GD) 62 (term, about GD 68). Acute maternal oral administration of 4 g ethanol/kg maternal body weight at GD 62 did not affect HO activity in these three fetal brain areas compared with control fetuses (maternal administration of isocaloric sucrose or water). For chronic daily maternal oral administration of 4 g ethanol/kg maternal body weight throughout gestation, fetal body, brain, hippocampal, and cerebellar weights were decreased at GD 62 compared with isocaloric-sucrose/pair-fed and water treatment control groups. Furthermore, isocaloric-sucrose/pair-feeding treatment decreased fetal body and brain weights compared with water treatment. Chronic in vivo ethanol exposure did not alter HO activity in the near-term fetal hippocampus, frontal cerebral cortex, or cerebellum. This is the first study of the effect of ethanol exposure on HO activity in the developing brain of any species. The data demonstrate, for ethanol CNS teratogenesis in the guinea pig manifesting as fetal brain growth restriction, there is no associated change in HO activity in the hippocampus, frontal cerebral cortex, or cerebellum.

What research with animals is telling us about alcohol-related neurodevelopmental disorder

The substantial advances in understanding fetal alcohol syndrome over the past 20 years were made in large part because of research with animals. This review illustrates recent progress in animal research by focusing primarily on the central nervous system effects of prenatal alcohol exposure. Current findings suggest further progress in understanding consequences, risk factors, mechanisms, prevention and treatment will depend on continued research with animals.

The effects of methylmercury on endogenous dopamine efflux from mouse striatal slices

The present study investigated the effects of in vitro methylmercury (MeHg) exposure on endogenous dopamine (DA) efflux from mouse striatal slices. MeHg produced a concentration-dependent increase in the spontaneous efflux of DA which was independent of the availability of Ca2+ in the superfusion medium. The Ca(2+)-dependent K(+)-evoked release of DA was significantly enhanced by 50 and 100 microM MeHg. This increase could not be solely accounted for by the MeHg-induced increased in spontaneous DA efflux. The K(+)-stimulated efflux of DA was enhanced by MeHg in both the presence and absence of Ca2+ in the superfusion medium, suggesting that under depolarizing conditions, DA efflux induced by MeHg has a Ca(2+)-independent component. The alterations in DA efflux occurred at concentrations of MeHg previously found in the CNS of animals exhibiting symptoms of MeHg intoxication suggesting that alterations in DA neurotransmission in the striatum may contribute to the symptoms of MeHg toxicity.

Brain nitric oxide synthase activity is decreased by intravenous anesthetics

Nitric oxide is produced from L-arginine in a variety of cells, and in neuronal tissue, by the action of nitric oxide synthase. Inhibitors to nitric oxide synthase reduce the threshold for anesthesia and anesthetics reduce nitric oxide synthase activity in neutrophils. We investigated the effect of four intravenous anesthetics and an anticonvulsant on rat brain nitric oxide synthase activity using the stoichiometric conversion of oxyhemoglobin to methemoglobin by nitric oxide. Enzyme activity was assayed in the presence of 0, 0.01, 0.1, and 1.00 microM thiopental, ketamine, etomidate, midazolam, and phenytoin. Thiopental (P = 0.001), ketamine (P = 0.0002), midazolam (P = 0.0024), and etomidate (P = 0.0006) caused a decrease in nitric oxide synthase activity. Phenytoin had no effect on enzyme activity. We conclude that the intravenous anesthetics, but not the nonsedative anticonvulsant tested, have a significant effect on neuronal nitric oxide synthase activity.

Effect of chronic maternal ethanol administration on nitric oxide synthase activity in the hippocampus of the mature fetal guinea pig

Nitric oxide is a novel messenger that is involved in neuronal cell-cell communication and seems to play a neurotrophic role in normal brain development. Chronic prenatal ethanol exposure can produce central nervous system (CNS) teratogenesis, in which one of the target sites is the hippocampus. The main objective of our study was to test the following hypothesis: chronic maternal administration of an ethanol dosage regimen that produces CNS teratogenesis decreases nitric oxide synthase (NOS) activity in the fetal hippocampus. The ontogeny of NOS activity in the hippocampus of the developing guinea pig was further elucidated at two prenatal and two postnatal ages. The effects of chronic maternal oral administration of 4 g of ethanol/kg maternal body weight/day, isocaloric sucrose and pair feeding, or water [given as two equally divided doses 2 hr apart from gestational day (GD) 2 to GD 61] on body, brain, and hippocampal weights and hippocampal NOS activity were determined in the mature fetal guinea pig at GD 62 (term, about GD 68). NOS activity in the 25,000 x g supernatant fraction of hippocampal homogenate was measured using an optimized radiometric assay, based on the oxidation of L-[14C]arginine to L-[14C]citrulline. For the chronic ethanol regimen, the maternal blood ethanol concentration at 1 hr after the second divided dose on GD 57 was 157 +/- 45 mg/dl. Chronic maternal administration of ethanol decreased fetal body, brain, and hippocampal weights, compared with the isocaloric-sucrose/pair-fed and water treatment groups. The rate of L-[14C]citrulline formation and NOS activity in the fetal hippocampus were decreased in the ethanol treatment group, compared with the isocaloric-sucrose/ pair-fed and water treatment groups. There was no difference in the rate of L-[14C]citrulline formation, NOS activity, and fetal hippocampal and body weights between the isocaloric-sucrose/pair-fed and water treatment groups; however, fetal brain weight was decreased in the isocaloric-sucrose group, compared with the water group. Data of this study support the research hypothesis by demonstrating that chronic maternal administration of ethanol decreases fetal hippocampal NOS activity that is correlated with restricted growth of this brain region.

Dose-dependent effects of acute in vivo ethanol exposure on extracellular glutamate concentration in the cerebral cortex of the near-term fetal sheep

The cerebral cortex is a target site of ethanol teratogenesis. L-Glutamate is a major excitatory neurotransmitter that plays an important neurotrophic role in brain development. It has been proposed that optimal function of the glutamate neuronal system is required for normal brain development; overactivation could lead to excitotoxic-induced neuronal injury, whereas underactivation could delay/restrict brain development. The objective of this study was to test the hypothesis that acute in vivo ethanol exposure alters basal glutamate release in the fetal cerebral cortex. The experimental approach involved measuring fetal cortical extracellular glutamate concentration using the technique of in vivo microdialysis. Near-term fetal sheep were chronically instrumented with a microdialysis probe placed in the parasagittal cortex. At 124 +/- 3 days of gestation, the effects of maternal intravenous infusion of 2 g or 4 g ethanol/kg maternal body weight or an equivalent volume of saline, given as four equally divided doses over 5 hr, on fetal cerebral cortical extracellular glutamate concentration were determined. None of the three treatment regimens produced fetal or maternal demise during the time course of the study. There was an ethanol dose-dependent increase, p = 0.005, in extracellular glutamate concentration in the fetal cerebral cortex. This increase was paroxysmal in nature and was not directly related to the fetal blood ethanol concentration. In view of the proposed role for glutamate in neuronal development, this apparent ethanol-induced increase in glutamate release may be important in the pathogenesis of ethanol teratogenesis involving the cerebral cortex.

Effects of ethanol on respiratory activity in the neonatal rat brainstem-spinal cord preparation

Ethanol (1-12 mM) added to the superfusion medium of the isolated brainstem-spinal cords of newborn rats did not affect phrenic activity but significantly reduced hypoglossal activity by 54%, 67% and 55% at 3, 6 and 12 mM, respectively. Although the reasons for the suppression of hypoglossal activity remain unknown, this preparation may be a useful model for determining why cranial motoneurons are more vulnerable than phrenic motoneurons to various agents and, more generally, how ethanol impairs neural function.

Effect of chronic maternal ethanol administration on glutamate and N-methyl-D-aspartate binding sites in the hippocampus of the near-term fetal guinea pig

The objective of this study was to determine the effect of chronic maternal administration of ethanol on hippocampal L-glutamate (glutamate) and N-methyl-D-aspartate (NMDA) binding sites in the near-term fetal guinea pig. Starting on gestational day (GD) 2, pregnant guinea pigs received one of the following oral treatments up to and including GD 62 (term, about GD 68): 4 g ethanol.kg maternal body weight-1.day-1; isocaloric sucrose and pair-feeding; or water. Maternal blood ethanol concentration was determined at 1 h after the daily ethanol dose on GD 59. Fetuses were studied at GD 63 (mature, near-term fetus). Fetal body weight and brain weight were determined. The density (Bmax) and affinity (Kd) of the glutamate and NMDA binding sites in the fetal hippocampus were measured using a radioligand membrane binding assay; saturation analysis was conducted on hippocampal synaptic membrane preparation (HSMP). Maternal blood ethanol concentration on GD 59 was 269 +/- 111 (SD) mg/dl (59 +/- 24 mM). There was no maternal or embryonic fetal lethality in any of the three treatment groups, and ethanol treatment did not affect maternal body weight gain compared with sucrose or water treatment. Fetal brain weight, but not body weight, was decreased in the ethanol treatment group compared with the sucrose and water treatment groups. The Bmax values of the glutamate and NMDA binding sites were decreased in the ethanol treatment group compared with the sucrose and water treatment groups; there was no difference in the Kd values of the glutamate and NMDA binding sites among the three treatment groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide synthase activity in the hippocampus, frontal cerebral cortex, and cerebellum of the guinea pig: ontogeny and in vitro ethanol exposure

Decreased nitric oxide (NO) formation, resulting from inhibition of NO synthase (NOS), may be important in the pathogenesis of ethanol central nervous system teratogenesis. The objectives of this study were to determine the ontogeny of NOS activity in the hippocampus, frontal cerebral cortex, and cerebellum of the developing guinea pig, and to test the hypothesis that direct exposure to ethanol inhibits NOS activity in these brain regions at selected developmental ages. NOS activity was quantitated by an optimized radiometric assay. The ontogeny study demonstrated that NOS activity in the hippocampus and frontal cortex was not fully developed prenatally, and apparently increased during postnatal life to attain adult level of activity at postnatal day > 60. In the cerebellum, NOS activity increased during prenatal life to an apparent maximum in the mature near-term fetus at gestational day 63 (term, about 68 days), and then apparently declined during postnatal life to attain adult level of activity. In vitro ethanol exposure (25-100 mM) did not affect NOS activity in the hippocampus, frontal cortex, or cerebellum at any developmental age studied. These data indicate that, although the ontogeny of NOS activity varies between brain regions, ethanol does not directly affect NOS activity in the developing guinea pig. The effects of acute and chronic in utero ethanol exposure on NOS activity in these brain regions are currently being investigated.

Glutamate and N-methyl-D-aspartate binding sites in the guinea pig hippocampus: ontogeny and effect of acute in vitro ethanol exposure

The objectives of this study were to characterize the ontogeny of the L-glutamate (glutamate) and N-methyl-D-aspartate (NMDA) binding sites in the developing guinea pig hippocampus, and to determine the effect of acute in vitro ethanol exposure on these binding sites. Specific [3H]glutamate binding and NMDA-sensitive [3H]glutamate binding were determined using a guinea pig hippocampal synaptic membrane preparation (HSMP). To characterize the ontogeny of the density (Bmax) and affinity (Kd) of the glutamate and NMDA binding sites, saturation analysis was conducted on HSMP of guinea pigs at gestational day (GD) 50 (immature fetus; term, GD 68), GD 62 (mature, near-term fetus), postnatal day (PD) 13 (neonate), and PD > 60 (adult). To examine the effect of ethanol on the glutamate and NMDA binding sites, HSMP of guinea pigs at GD 50, GD 62, PD 13, and PD > 60 was incubated with ethanol (0-100 mM), followed by determination of specific [3H]glutamate binding and NMDA-sensitive [3H]glutamate binding. To determine the effect of 50 mM ethanol on the Bmax and Kd of the glutamate and NMDA binding sites, HSMP of guinea pigs at GD 62 and PD > 60 was incubated with 0 or 50 mM ethanol followed by saturation analysis. The Bmax values of the hippocampal glutamate and NMDA binding sites were greater at GD 62 and PD 13 compared with GD 50 and PD > 60, but there was no change in the Kd of the binding sites throughout development.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of adenosine A1 receptor activation in ethanol-induced inhibition of stimulated glutamate release in the hippocampus of the fetal and adult guinea pig

The role of adenosine A1 receptor activation in ethanol-induced inhibition of stimulated L-glutamate (Glu) release was determined in transverse hippocampal slices of the near-term fetal guinea pig and the adult guinea pig. Exposure of the slices to 48 mM ethanol inhibited K(+)-stimulated Glu efflux. Pretreatment with 8-cyclopentyltheophylline (CPT), a selective adenosine A1 receptor antagonist, blocked the ethanol-induced inhibition of K(+)-stimulated Glu efflux in the near-term fetal and adult hippocampus. In the near-term fetus, 2-chloro-N6-cyclopentyladenosine (CCPA), a selective adenosine A1 agonist, and exogenous adenosine each blocked K(+)-stimulated Glu efflux similar to that produced by 48 mM ethanol. In the adult, although K+ increased Glu efflux in the presence of CCPA or adenosine, the magnitude of increase was less than that of the K(+)-stimulated Glu efflux for the control conditions. Exposure to ethanol alone or ethanol plus CPT produced a transient increase in endogenous adenosine efflux in the near-term fetal and adult hippocampus, which was not temporally related to the ethanol-induced inhibition of K(+)-stimulated Glu efflux. Overall, the data indicate that adenosine A1 receptor activation mediates ethanol-induced inhibition of stimulated Glu release in the hippocampus of the near-term fetal and adult guinea pig.