Development of spontaneous and glutamate-evoked activity is altered by chronic ethanol in cultured cerebellar Purkinje neurons

Acute β-tetrabromoethylcyclohexane (β-TBECH) treatment inhibits the electrical activity of rat Purkinje neurons

Brominated flame-retardants are environmentally pervasive and persistent synthetic chemicals, some of which have been demonstrated to disrupt neuroendocrine signaling and electrical activity of neurons. 1,2-dibromo-4-(1,2-dibromoethyl)-cyclohexane (TBECH) lacks the toxicity of other classes of BFRs, however its safety is still questioned, as little is known of its neurological effects. Therefore, we sought to determine if TBECH could acutely alter the electrical activity of Purkinje neurons maintained in vitro. Briefly, cerebella from gestational day 20 rats were dissociated and maintained for up to three weeks in culture. Action potentials of Purkinje neurons were detected by cell-attached patch clamp before, during, and after application of β-TBECH. β-TBECH decreased action potential activity in a dose-dependent manner with an apparent EC₅₀ of 396 nM. β-TBECH did not significantly alter the coefficient of variation, a measure of the regularity of firing, suggesting that the mechanism of β-TBECH's effects on firing frequency may be independent of Purkinje neuron intracellular calcium handling. Because levels of β-TBECH in exposed individuals may not approach the EC₅₀, these data suggest that any abnormal neurodevelopment or behavior linked with β-TBECH exposure may result from endocrinological effects as opposed to direct disruption of electrical activity.

Chronic exposure to alcohol alters network activity and morphology of cultured hippocampal neurons

The effects of chronic exposure to moderate concentrations of ethanol were studied in cultured hippocampal neurons. Network activity, assessed by imaging of [Ca(2+)]i variations, was markedly suppressed following 5 days of exposure to 0.25-1% ethanol. The reduced activity was sustained following extensive washout of ethanol, but the activity recovered by blockade of inhibition with bicuculline. This reduction of network activity was associated with a reduction in rates of mEPSCs, but not in a change in inhibitory synaptic activity. Chronic exposure to ethanol caused a significant reduction in the density of mature dendritic spines, without an effect on dendritic length or arborization. These results indicate that chronic exposure to ethanol causes a reduction in excitatory network drive in hippocampal neurons adding another dimension to the chronic effects of alcohol abuse.

Resveratrol can only partially attenuate ethanol-induced oxidative stress in embryonic chick brains

Ethanol (EtOH) exposure promotes increased levels of reactive oxygen species that degrade unsaturated long-chain membrane fatty acids within embryonic chick brains and is associated with apoptosis and reduced embryo viability. In vitro studies have demonstrated that resveratrol, a known antioxidant, attenuated EtOH-induced damage. In order to test whether or not resveratrol can attenuate EtOH-induced embryonic damage, fertile chicken eggs were injected daily with EtOH (6.05 mmol/kg egg) and various concentrations of trans-resveratrol (0-29.5 mmol/kg egg) during the first three days of embryonic development. At 11 days of embryonic development, viable embryos were collected, brains isolated, and brain membrane fatty acid composition analyzed. Embryonic EtOH exposure promoted fewer viable embryos at 11 days of development as compared to controls. Embryonic EtOH exposure also promoted reduced levels of unsaturated long-chain membrane fatty acids, increased levels of saturated short-chain membrane fatty acids, and elevated brain lipid hydroperoxides (LPO) levels. Embryonic exposure to moderate (2.95 nmol/kg egg) and high (29.5 nmol/kg egg) levels of trans-resveratrol attenuated EtOH-induced changes in brain membrane fatty acid composition but failed to attenuate EtOH-induced increases in brain LPO levels and increased brain Casp-3 activities.

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

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

Ethanol- and nicotine-induced membrane changes in embryonic and neonatal chick brains

In order to study the effects of EtOH and/or nicotine on brain membrane fatty acid composition, various concentrations of EtOH and/or nicotine were injected into the air sac of chicken eggs at 0 days of incubation. Controls were injected with saline. Experimental groups were injected with either 200 micromol EtOH/kg egg, 100 micromol nicotine/kg egg, 200 micromol nicotine/kg egg, 200 micromol EtOH/kg and 100 micromol nicotine/kg egg, or 200 micromol EtOH/kg and 200 micromol nicotine/kg egg. In all experimental groups, EtOH- and nicotine-induced decreases in brain long-chain polyunsaturated membrane fatty acids were observed in stage 44 embryos, stage 45 embryos, and neonatal chicks. These EtOH- and nicotine-induced decreases in brain membrane polyunsaturated fatty acids correlated with elevated levels of brain lipid hydroperoxides and reduced brain acetylcholinesterase (AChE; EC. 3.1.1.7) activities.

Antisense knockdown of calcium-dependent K+ channels in developing cerebellar Purkinje neurons

Normal developmental upregulation of K(Ca) channel activity in cultured rat cerebellar Purkinje neurons was selectively inhibited by antisense oligonucleotide sequence (3 microM) targeted against the rslo transcript. The knockdown was specific; delayed rectifier and apamin-sensitive K+ channel abundances in Purkinje neurons were not affected by rslo antisense. Sense oligonucleotides (3 microM), used as a control, had no effect on channel abundance. Quantitative morphometric analyses of anti-calbindin-labeled Purkinje neurons showed no differences between neurons in control, sense and antisense treatment groups, and confirmed that the presence of the added oligonucleotide in the sense and antisense treatment conditions had no discernable toxic effects on neuronal health, for which neurite outgrowth is a sensitive indicator. These results confirm the identification of the developmentally regulated K(Ca) channel as the product of the gene rslo in cerebellar Purkinje neurons.

Expression of Niemann-Pick type C transcript in rodent cerebellum in vivo and in vitro

This study assesses the developmental expression of the Niemann-Pick type C mRNA in vivo and in vitro in rat cerebellum. NPC is an autosomal recessive neurovisceral lipid storage disease associated with an alteration in cholesterol trafficking. In the mouse model of NPC and in the early onset form of human NPC, Purkinje neurons are among the first neurological targets, suffering stunted growth during postnatal development and dying, leading to ataxia. Recently, the genes responsible for human (NPC1) and mouse (Npc1) NPC disease have been cloned. Based on a highly homologous domain, we designed primers to look for levels of Npc1 mRNA with a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) approach using cyclophilin as an internal standard. Total RNA was isolated from various postnatal developmental stages of the rat cerebellum as template for the analyses. Npc1 transcripts were observed at postnatal day 0 and at later stages of development, both in vivo and in vitro from primary cerebellar cultures. To identify the location of Npc1 inside the cerebellum, we performed immunostaining with an anti-Npc1 antibody in primary rat cerebellar cultures identifying reactive Purkinje neurons by double-labeling with the Purkinje specific marker calbindin and sub-populations of glial cells. In summary, Npc1 is expressed in rat cerebellum in vivo and in vitro and is expressed during early postnatal development as well as in the adult cerebellum. Since Npc1 is expressed at similar levels throughout development, the vulnerability of Purkinje neurons to this disease is likely to involve disruption of an interaction with other developmentally-regulated proteins.

Differential expression of three classes of voltage-gated Ca(2+) channels during maturation of the rat cerebellum in vitro

Voltage-gated Ca(2+) channels provide a mode of Ca(2+) influx that is essential for intracellular signaling in many cells. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to assess the relative amounts of mRNAs encoding three classes of Ca(2+) channels (alpha1A, alpha1B and alpha1E) during development, in cultures established from prenatal rat cerebellar cortex. Ca(2+) channel transcript levels were standardized to a constitutive marker (cyclophilin). For all three classes of Ca(2+) channels, transcript levels were highest at early stages (4-10 days in vitro) and declined with age. This developmental pattern was differentially regulated by a depolarizing agent, tetraethylammonium chloride (TEA, 1 mM). Chronic depolarization yielded a significant elevation in transcript levels for alpha1B (N-type) and alpha1E (R-type) Ca(2+) channels during neuronal maturation (10-21 days in vitro), but dramatically suppressed transcript levels for the alpha1A (P-type) Ca(2+) channel at all stages of development. The effects of TEA on alpha1A, alpha1B and alpha1E transcript levels were mimicked by increasing external K(+) (from 5 to 10 mM). The regulatory effects of depolarization on transcript levels were dependent on extracellular Ca(2+) for alpha1E but not for alpha1A. For alpha1B, transcript levels depended on extracellular Ca(2+) only for increased K(+) as the depolarizing stimulus, but not for TEA. These results suggest that levels of Ca(2+) channel transcripts in rat cerebellum are developmentally regulated in vitro and can be influenced differentially by transmembrane signaling via chronic depolarization and Ca(2+) entry. Dynamic regulation of Ca(2+) channel expression may be relevant to the different functional roles of Ca(2+) channels and their regional localization within neurons.

Chronic ethanol treatment alters AMPA-induced calcium signals in developing Purkinje neurons

Cerebellar Purkinje neurons developing in culture were treated chronically with 30 mM (140 mg%; 3-11 days in vitro) ethanol to study the actions of prolonged ethanol exposure on responses to exogenous application of AMPA, a selective agonist at the AMPA subtype of ionotropic glutamate receptors. There was no consistent difference between control and chronic ethanol-treated neurons in resting membrane potential, input resistance, or the amplitude or duration of the membrane responses to AMPA (1 or 5 microM applied by brief microperfusion) as measured using the nystatin patch method of whole cell recording. In additional studies, the Ca2+ signal to AMPA was examined using the Ca2+ sensitive dye fura-2. The mean peak Ca2+ signal elicited by 5 microM AMPA was enhanced in the dendritic region (but not the somatic region) of chronic ethanol-treated Purkinje neurons compared to control neurons. In contrast, there was no difference between control and chronic ethanol-treated neurons in the peak amplitude of the Ca2+ signal to 1 microM AMPA, whereas the recovery of the Ca2+ signals was more rapid in both somatic and dendritic regions of ethanol-treated neurons. Resting Ca2+ levels in the somatic and dendritic regions were similar between control and ethanol-treated neurons. These data show that the membrane and Ca2+ responses to AMPA in Purkinje neurons are differentially affected by prolonged ethanol exposure during development. Moreover, chronic ethanol exposure produces a selective enhancement of AMPA-evoked dendritic Ca2+ signals under conditions reflecting intense activation (i.e., 5 microM AMPA), whereas both somatic and dendritic Ca2+ signals are attenuated with smaller levels of activation (i.e., 1 microM AMPA). Because Ca2+ is an important regulator of numerous intracellular functions, chronic ethanol exposure during development could produce widespread changes in the development and function of the cerebellum.

Increased calcium-dependent K+ channel activity contributes to the maturation of cellular firing patterns in developing cerebellar Purkinje neurons

Developmental changes in neuronal excitability reflect the regulated expression of ion channels and receptors. Purkinje neurons of the rat cerebellum progress from slow irregular firing to a fast pacemaker-like pattern during postnatal development in vivo. In this study, a comparable period of development in culture was investigated at the protein level using cell-attached single channel recordings to quantify the abundance of active calcium-dependent (KCa) and delayed rectifier (KD) potassium channels. In control cultures, KCa channel activity increased whereas KD channel activity was not significantly different with developmental age. The increase in active KCa channels was antagonized by chronic treatment with the blocker, tetraethylammonium (TEA, 1 mM), which also retarded the normal development of cellular firing patterns. The consequences of chronic TEA treatment were assessed in cultures after thorough washout of the TEA-containing culture medium. Current clamp analyses (nystatin-perforated patches) showed that control Purkinje neurons progressed from a single spike mode to a repetitive firing mode, with a concomitant decrease in action potential duration and an increase in maximal firing rate. Chronic TEA treatment prevented these changes; Purkinje neurons retained the slow firing rate and long duration action potentials that are typical of the immature state. These data suggest that the developmental increase in KCa channel activity may be required for the maturation of cellular firing patterns in cerebellar Purkinje neurons.

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.

Morphological consequences of altered calcium-dependent transmembrane signaling on the development of cultured cerebellar Purkinje neurons

Morphometric analyses of cultured rat Purkinje neurons, visualized with anti-calbindin, demonstrated that elevated KCl (10 mM) significantly increased dendritic outgrowth and branching. The response was blocked by NiCl2 (50 microM; R-type Ca2+ channel antagonist). Cells grown in low external Ca2+ (100 nM) showed no loss of responsiveness to elevated potassium. However, thapsigargin (1 microM; Ca(2+)-ATPase blocker) inhibited dendrite outgrowth, suggesting that intracellular calcium stores may be important in governing development.

Regulation of Ca2+-dependent K+ channel expression in rat cerebellum during postnatal development

Potassium channels govern duration and frequency of excitable membrane events and may regulate signals that are important in neuronal development. This study assesses the developmental expression of the large conductance Ca2+-dependent K+ channel in vivo and in vitro in rat cerebellum. In vivo, transcript levels for the Ca2+-dependent K+ channel (KCa) were shown by Northern analysis to increase during development, whereas transcript levels for the voltage-gated K+ channel Kv3.1, a delayed rectifier (KD), remained relatively constant. A comparable pattern was demonstrated by expression in Xenopus oocytes of poly(A)-enriched RNA isolated from postnatal rat cerebella. In cerebellar cultures, increased external K+ provided a simple manipulation of cell excitability that influenced KCa transcript levels during development. With low external K+ (5.3 mM), the levels of KCa channel transcript (assessed by semiquantitative PCR) remained constant throughout development. However, in culture medium that supported significant dendritic outgrowth (10 mM extracellular K+), an upregulation of KCa transcript level was observed similar to that seen in vivo. Tetraethylammonium (TEA; 1 mM) similarly enhanced KCa expression, suggesting that depolarizing stimuli increased KCa expression. The stimulatory effects of increased K+ or TEA on KCa expression required extracellular Ca2+ and were abolished in low external calcium (0.1 mM, buffered with EGTA), although morphological development and survival were not impaired. The regulation of KCa channel expression by depolarization and Ca2+ entry provides evidence of a logical feedback mechanism governing Ca2+ signals that may be significant in cerebellar development.

Chronic alcohol reduces calcium signaling elicited by glutamate receptor stimulation in developing cerebellar neurons

The effect of chronic alcohol (33 mM ethanol) on Ca2+ signals elicited by glutamate receptor agonists (quisqualate and NMDA) was examined in developing cerebellar Purkinje and granule neurons in culture. The neurons were exposed to alcohol during the second week in culture, the main period of morphological and physiological development. The Ca2+ signals were measured with fura-2 based microscopic video imaging. Chronic exposure to alcohol during development significantly reduced the peak amplitude of the Ca2+ signals to quisqualate (1 microM; Quis) in both the somatic and dendritic regions of the Purkinje neurons. The dendritic region was affected to a greater extent than the somatic region. Granule neurons also showed a reduced somatic Ca2+ signal to Quis (dendrites not measured) in the alcohol-treated cultures, indicating that the effect was not limited to Purkinje neurons. In addition to the effects on in the response to Quis, the peak amplitude of the Ca2+ signals to NMDA (100 microM) was reduced by chronic alcohol exposure during development in both the cultured Purkinje and granule neurons. Resting Ca2+ levels were not consistently affected by alcohol treatment in either neuronal type. These results indicate that Ca2+ signaling linked to glutamate receptor activation is an important target of alcohol in the developing nervous system and could be a contributing factor in the altered CNS function and development observed in animal models of fetal alcohol syndrome.

Continuous exposure of cultured rat cerebellar macroneurons to ethanol-depressed NMDA and KCl-stimulated elevations of intracellular calcium

This series of experiments measured ethanol-induced changes in levels of free intracellular calcium. Cerebellar macroneurons, harvested from rat embryos on embryonic day 17, were cultured in the presence of 75 mM ethanol for 24, 48, or 96 hr. Intracellular calcium concentrations in control and ethanol-exposed neurons did not differ after 24 hr, but they were significantly elevated in the neurons exposed to ethanol for 48 or 96 hr. Similarly, increases in intracellular calcium elicited by stimulation with 50 microM NMDA were not significantly different in control and ethanol-exposed neurons after 24 hr. After 48 and 96 hr, however, NMDA-stimulated increases in intracellular calcium levels in control neurons were significantly greater than in the ethanol-exposed neurons. These results showed that, when calcium levels were elevated by prolonged exposure to ethanol, the neurons were significantly less responsive to NMDA stimulation. Increases in intracellular calcium elicited by stimulation with 30 mM KCI were not significantly different in the control and treated neurons after 24 and 48 hr of ethanol exposure. After 96 hr of exposure to ethanol, however, there was a significant increase in intracellular calcium levels in control neurons following KCI stimulation, but not in the ethanol-exposed neurons. The fact that neuronal responses to KCI stimulation were depressed only following 96 hr of exposure to ethanol makes it unlikely that voltage-regulated channels were the primary mediators of the ethanol-induced elevations in intracellular calcium in chronically exposed neurons.

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.

Possible role of glutamatergic neurotransmission in regulating ethanol-evoked brain ascorbate release

It was found that systemic application of ethanol induced brain ascorbate (AA) release. In order to study the mechanism of ethanol-evoked AA release, the role of brain glutamatergic neurotransmission was investigated using in vivo voltammetry in the striatum of freely moving rats. Pretreatment with L-trans-pyrrolidine-2,4-dicarboxylate (PDC, 10 nmol, i.c.v.), a glutamate (Glu) uptake blocker, potentiated ethanol (1 g/kg, intraperitoneal injection, i.p.)-evoked release of brain AA. N-methyl-D-aspartate (NMDA, 1 nmol, i.c.v.) produced a fast transient increase in extracellular AA, whereas alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA, 1 nmol, i.c.v.) produced a decrease in extracellular AA (75.8 +/- 3% of control). Kainate (KA, 1 nmol, i.c.v.) produced an initial decrease (48.7 +/- 11.7% of control) then an increase (250 +/- 68.5% of control) in extracellular AA. These results suggest that systemic administration of ethanol may affect the release or uptake of brain glutamatergic neurotransmitters which appear to regulate brain AA release. The NMDA, but not the non-NMDA, type of Glu receptor may be responsible for this regulation.

Chronic exposure to alcohol during development alters the calcium currents of cultured cerebellar Purkinje neurons

The effect of chronic exposure to alcohol during development on the calcium currents of rat cerebellar Purkinje neurons was studied in a culture model system using voltage clamp techniques. The neurons were exposed to 30 mM alcohol (ethanol) during the main period of morphological and physiological development. The calcium currents were measured at the end of the treatment period, which lasted for 8-10 days. The currents were evoked by a series of depolarizing test commands from holding potentials of -62 mV and -90 mV. The evoked currents were qualitatively similar in control and alcohol-treated neurons and were comprised of a high threshold slowly inactivating calcium current and a low threshold rapidly inactivating calcium current. The low threshold current could be observed in isolation at test potentials ranging from -50 to -30 mV. The mean peak amplitude of this current was significantly smaller in the alcohol-treated neurons compared to controls. At more depolarized test potentials, the high threshold current dominated the current response, which was characterized by an initial peak that slowly declined to a smaller relatively sustained level. The mean amplitude of the high threshold current at both peak and sustained levels was significantly larger in the alcohol-treated neurons compared to controls. Measurement of cell size indicated that alcohol-treated neurons were approximately 25% smaller than control neurons, a difference that could contribute to the smaller low threshold current observed in these neurons. These data show that chronic exposure to alcohol during the development can significantly influence the amplitude of calcium currents of the cultured Purkinje neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic exposure to alcohol during development alters the responses to excitatory amino acids in cultured Purkinje neurons

The effects of chronic alcohol exposure during development on the responses evoked by glutamate and the selective excitatory amino acid receptor agonists quisqualate (Quis) and kainate were studied in cultured cerebellar Purkinje neurons. The cultures were treated with 22 mM or 44 mM ethanol continuously for one or two weeks during the main period of morphological and physiological development. Extracellular recordings used for most studies characterized the responses to all 3 agonists as initial increase in simple spike firing, usually including a period of burst activity, followed by reduced activity or total inhibition, then return to control firing pattern. Analysis of these responses and background spontaneous activity showed several significant differences between control and ethanol treated Purkinje neurons. Background spontaneous firing, agonist evoked firing, the initial period of activity of the response to Quis, and the inhibitory period of the response to glutamate were all significantly reduced in the chronically treated neurons; the inhibitory period of the response to kainate was significantly increased. In contrast to the effects of chronic ethanol exposure, acutely administered ethanol significantly increased background spontaneous firing and the inhibitory period of the response to Quis. Thus, administering both acute and chronic ethanol altered the responses evoked by excitatory amino acids in the developing Purkinje neurons. The effect of chronic ethanol exposure on some response components was similar for all agonists tested and may be linked to changes in intrinsic membrane properties. However, alterations in the inhibitory component of the agonist responses were agonist specific, indicating that receptor-linked actions of ethanol were involved.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic exposure to alcohol during development alters the membrane properties of cerebellar Purkinje neurons in culture

The active and passive membrane properties of developing Purkinje neurons in control cultures and cultures chronically treated with 20 or 40 mM ethanol for 1 or 2 weeks were examined using whole-cell current-clamp techniques. The membrane properties were characterized by the features of the voltage responses evoked by intracellular current injection of a series of depolarizing and hyperpolarizing current pulses. Analysis of these responses and background spontaneous activity showed several differences between the control and ethanol-treated Purkinje neurons: (1) membrane input resistance was significantly larger in the ethanol-treated neurons; (2) the percentage of neurons exhibiting immature firing patterns was significantly higher in the ethanol-treated neurons; (3) the afterhyperpolarization following a current-evoked train of action potentials was significantly larger in the ethanol-treated neurons; (4) spontaneous activity (synaptic potentials and synaptically evoked spike events) was significantly reduced in neurons treated with 40 mM ethanol for 1 week; spontaneous activity in neurons treated with 20 mM ethanol for 1 or 2 weeks was similar to that observed in the control group. These differences indicate that ethanol exposure during development directly alters the physiological properties of this CNS neuronal type. These neuronal actions of ethanol may contribute to the behavioral deficits observed in animals models of fetal alcohol syndrome. Similar target sites of ethanol action are likely to be present in the human CNS neurons and may be involved in human fetal alcohol syndrome.

Effects of chronic ethanol on currents carried through calcium channels in Aplysia

Voltage clamp techniques were used to monitor the effects of chronic exposure to ethanol (EtOH) on current carried through calcium channels in an identified neuron of cultured abdominal ganglia from Aplysia californica. Exposure to 200 mM EtOH for periods up to 3 weeks did not change the baseline characteristics of current carried through calcium channels, nor did it alter its acute sensitivity to either 100 mM or 300 mM EtOH challenge. The currents that we examined were equivalent when carried by calcium or barium, and EtOH had similar effects on currents carried by these two ions. The population of voltage-dependent calcium channels studied here does not show development of tolerance after chronic exposure to EtOH.

NMDA agonists and antagonists alter the hypnotic response to ethanol in LS and SS mice

Involvement of glutamate neurotransmission in the differential response of long-sleep (LS) and short-sleep (SS) mice to acute ethanol was examined by measuring the effect of centrally administered glutamate receptor agonists and antagonists on blood ethanol concentration (BEC) at loss of righting response following intragastric administration of ethanol. NMDA coinjected with glycine, and quinolinic acid (QA), decreased sensitivity to ethanol in both lines of mice. SS mice were more sensitive to QA than were LS. The NMDA antagonists 2-amino-5-phosphonovaleric acid (APV), MK-801 and an inhibitor of glutamate synthesis, methionine sulfoximine, increased sensitivity to ethanol in both lines of mice. MK-801 effects were line dependent with SS being more sensitive. In addition, coinjection of APV, Mg++ or Zn++ with QA blocked the decrease in sensitivity seen with QA alone. These results demonstrate that NMDA agonists and antagonists alter the acute hypnotic response to ethanol in both LS and SS mice, and support the hypothesis that ethanol exerts its effects in part by altering glutamatergic neurotransmission.

The noncompetitive N-methyl-D-aspartate antagonists, MK-801, phencyclidine and ketamine, increase the potency of general anesthetics

The potency of general anesthetics from different chemical classes was tested after pretreatment with subanesthetic doses of noncompetitive N-methyl-D-aspartate (NMDA) antagonists in mice. Changes in general anesthetic potency were assessed by determination of alteration of duration of loss of righting reflex for ethanol and pentobarbital and changes in the minimum alveolar concentration (MAC) for the volatile anesthetics, halothane and diethyl ether. The ability of the noncompetitive NMDA antagonists, MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclo-hepten-5,10-imine ], phencyclidine (PCP) and ketamine, to increase the potency of general anesthetics paralleled their potency as NMDA antagonists and their affinity for the PCP receptor site of the NMDA receptor-ionophore complex (MK-801 greater than PCP greater than ketamine). These results indicate that block of central NMDA receptors may contribute to the production of anesthesia by a variety of agents.

The effect of chronic ethanol on glutamate binding in human and rat brain

Quantitative autoradiographic techniques demonstrate that chronic alcohol administration causes a decrease in [3H]-glutamate binding to hippocampal N-methyl-D-aspartate (NMDA) receptors. A 14% decrease in [3H]-glutamate binding in the hippocampal CA1 region is seen both in the rat after five days of ethanol administration and in postmortem hippocampal tissues from alcoholics. In the rat, 24 hr ethanol withdrawal values are intermediate between control and alcohol binding levels. There was no significant effect of ethanol on [3H]-glutamate binding in the cortex or caudate.

Ethanol potentiates and blocks NMDA-activated single-channel currents in rat hippocampal pyramidal cells

Single-channel currents activated by N-methyl-D-aspartate (NMDA) were characterized using the outside-out patch clamp technique in cultured hippocampal cells from the rat. Several conductance states were observed, and the main one of 47 pS was further analyzed for channel lifetime and frequency. Open times decreased with hyperpolarization of the membrane. In view of recent evidence linking NMDA receptors to central nervous system processes such as learning and memory and ethanol (EtOH) tolerance, the effects of EtOH (0.01-1%, v/v, or congruent to 1.74-174 mM) were studied in this preparation. Two effects of EtOH could be discerned: (i) at low concentrations (1.74-8.65 mM) an increase in the probability of opening (p open) of the NMDA-activated channel currents, without change in the mean channel open time, and (ii) at higher concentrations (86.5-174 mM) a decrease in p open with a concomitant decrease in the mean open time. It is suggested that EtOH, even at rather low concentrations, may affect important brain functions.