Ethanol alters synaptic activity in cultured spinal cord neurons

The effects of acute alcohol consumption and eccentric muscle damage on neuromuscular function

Voluntary and electrically stimulated muscular performance was examined to identify the effects of acute alcohol consumption on neuromuscular function in the presence and absence of exercise-induced muscle damage (EIMD). After initial neuromuscular performance measures were made, 12 subjects completed a bout of eccentric exercise (EX) using the quadriceps muscles of 1 leg while the remaining 11 subjects did not exercise (NX). Subjects then consumed either an alcoholic beverage containing 1 g·kg–1body weight (ALC) or a nonalcoholic beverage (OJ). On another occasion the contralateral leg of both groups was tested and those in the EX group performed an equivalent bout of eccentric exercise after which the other beverage was consumed. Measurements of neuromuscular function were made pre-exercise and 36 and 60 h post-beverage consumption. Creatine kinase (CK) was measured pre-exercise and at 12, 36, and 60 h. Significantly greater (p < 0.01) decrements in maximal voluntary isometric contraction were observed with EX ALC at 36 and 60 h compared with EX OJ, and no change was seen in the NX group. Significant decreases in voluntary activation were observed at 36 h (p = 0.003) and 60 h (p = 0.01) with EX ALC only. Elevations in CK were observed at all posteccentric exercise time points (all p < 0.05) under both EX OJ and ALC. No change in electromyography or low-frequency fatigue was observed under either treatment in either group. These results suggest that decreased neural drive appears to contribute to alcohol’s effect on the magnitude of EIMD-related decrements in voluntary force generation.

Histiotypic electrophysiological responses of cultured neuronal networks to ethanol

Embryonic murine neuronal networks cultured on substrate-integrated microelectrode arrays were used to quantify acute electrophysiological effects of ethanol by using extracellular, multichannel recording of action potentials. Spontaneously active frontal cortex cultures showed repeatable, concentration-dependent sensitivities to ethanol, with initial inhibition at 20 mM and a spike rate 50% effective concentration (EC50) of 48.8+/-5.4 mM. Ethanol concentrations of greater than 100 mM led to cessation of activity. The ethanol inhibitions up to the maximum tested 160 mM were reversible. Although ethanol did not change the shape of action potentials, unit-specific spike pattern effects were found. At 40 mM, ethanol decreased neuronal firing in 71%, increased firing in 20%, and generated no effect in 9% of all units observed (14 cultures, 200 discriminated units). The effects of combined application of ethanol and fluoxetine were additive. Excellent agreement with findings obtained from experimental studies with animals validates the use of these in vitro systems for alcohol research.

Ethanol dual modulatory actions on spontaneous postsynaptic currents in spinal motoneurons

Recently we have shown that acute ethanol (EtOH) exposure suppresses dorsal root-evoked synaptic potentials in spinal motoneurons. To examine the synaptic mechanisms underlying the reduced excitatory activity, EtOH actions on properties of action potential-independent miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs) were studied in spinal motoneurons of newborn rats. Properties of mEPSCs generated by activation of N-methyl-D-aspartate receptors (NMDARs) and non-NMDA receptors and of mIPSCs mediated by glycine and gamma-aminobutyric acid-A receptors (GlyR and GABA(A)R) were examined during acute exposure to 70 and 200 mM EtOH. In the presence of 70 mM EtOH, the frequency of NMDAR- and non-NMDAR-mediated mEPSCs decreased to 53 +/- 5 and 45 +/- 7% (means +/- SE) of control values, respectively. In contrast, the frequency of GlyR- and GABA(A)R-mediated mIPSCs increased to 138 +/- 15 and 167 +/- 23% of control, respectively. Based on the quantal theory of transmitter release, changes in the frequency of miniature currents are correlated with changes in transmitter release, suggesting that EtOH decreased presynaptic glutamate release and increased the release of both glycine and GABA. EtOH did not change the amplitude or rise and decay times of either mEPSCs or mIPSCs, indicating that the presynaptic changes were not associated with changes in the properties of postsynaptic receptors/channels. Acute exposure to 200 mM EtOH increased mIPSC frequency two- to threefold, significantly higher than the increase induced by 70 mM EtOH. However, the decrease in mEPSC frequency was similar to that observed in 70 mM EtOH. Those findings implied that the regulatory effect of EtOH on glycine and GABA release was dose-dependent. Exposure to the higher EtOH concentration had opposite actions on mEPSC and mIPSC amplitudes: it attenuated the amplitude of NMDAR- and non-NMDAR-mediated mEPSCs to ~80% of control and increased GlyR- and GABA(A)R-mediated mIPSC amplitude by ~20%. EtOH-induced changes in the amplitude of postsynaptic currents were not associated with changes in their basic kinetic properties. Our data suggested that in spinal networks of newborn rats, EtOH was more effective in modulating the release of excitatory and inhibitory neurotransmitters than changing the properties of their receptors/channels.

The effects of ethanol on pre-synaptic components of synaptic transmission in a model glutamatergic synapse: the crayfish neuromuscular junction

We have elucidated some of the mechanisms by which ethanol (EtOH) reduces synaptic efficacy at model glutamatergic synapses. The crayfish phasic and tonic neuromuscular junctions are superb models for directly assessing the effects of EtOH on pre-synaptic components of synaptic transmission. The ability to perform quantal analysis of synaptic transmission has allowed us to assess pre-synaptic alterations of release. Using this system, we report that the application of EtOH, within a range observed in intoxicated humans (44 and 88 mM), resulted in a diminution of excitatory post-synaptic potentials (EPSP) amplitudes. Additionally, using focal macro-patch recordings, quantal synaptic currents were recorded to assess the pre-synaptic component as potential target sites for EtOH's action. At the tonic neuromuscular junctions, EtOH (88 mM) reduced the probability of release (p), and in some cases, reduced the number of the release sites (n), but did not alter facilitation index nor did it affect the latency of vesicular release. At the phasic neuromuscular junction, a reduction in synaptic charge occurred during the presence of EtOH. Thus, the observed decrease in synaptic strength is at least partially attributable to a pre-synaptic alteration, specifically the release of fewer vesicles.

Ethanol reduces excitability in a subgroup of primary sensory neurons by activation of BK(Ca) channels

Ethanol effects on the central nervous system have been well investigated and described in recent years; modulations, by ethanol, of several ligand-gated and voltage-gated ion channels have been found. In this paper, we describe a shortening of action potential duration (APD) by ethanol in approximately equal to 40% of small diameter neurons in rat dorsal root ganglia (DRG). In these neurons, designated as group A neurons, we observed an ethanol-induced increase in whole-cell outward-current. As iberiotoxin, a specific blocker of large-conductance calcium-activated K+ channels (BK(Ca) channels), blocks the effects of ethanol, we investigated the interaction between these channels and ethanol in outside-out patches. Open probability of BK(Ca) channels was increased 2-6 x depending on the concentration (40-80 mM approximately equal to 2-4 per thousand v/v) of ethanol. Functional consequences were a prolongation of the refractory period, which was reversible after addition of iberiotoxin, and reduced firing frequency during ethanol application. In contrast, another type of neuron (group B) showed a prolonged APD during application of ethanol which was irreversible in most cases. In 90% of cases, neurons of group A showed a positive staining for isolectin B4 (I-B4), a marker for nociceptive neurons. We suggest that the activation of BK(Ca) channels induced by clinically relevant concentrations of ethanol, the resulting modulations of APD and refractory period of DRG neurons, might contribute to clinically well-known ethanol-induced analgesia and paresthesia.

Ethanol reduces neuronal excitability and excitatory synaptic transmission in the developing rat spinal cord

Effects of acute ethanol (EtOH) exposure on motoneuron excitability and properties of synaptic transmission were examined in spinal cords of postnatal rats. Whole-cell patch clamp recordings and intracellular recordings with high-resistance electrodes were carried out in motoneurons of 1- to 4-day-old postnatal rats. To determine the effects of extracellular EtOH on action potential waveform, properties of current-evoked soma action potentials and motoneuron ability to generate repetitive action potential firing were examined. During a brief EtOH (70 mM) exposure, larger depolarizing current was required for action potential generation, the duration of the after hyperpolarizing potential increased, and fewer action potentials were produced during a prolonged intracellular current injection. These effects were reversed within 20 min of EtOH removal from the extracellular solution. To determine whether the reduced probability of action potential generation was associated with changes in synaptic transmission, properties of evoked synaptic potentials and spontaneous synaptic currents were investigated. In the presence of EtOH, the amplitude of dorsal root-evoked synaptic potentials was reduced, the frequency of spontaneous excitatory postsynaptic currents decreased, while the frequency of inhibitory postsynaptic currents increased. Our data suggested that acute EtOH exposure suppressed motoneuron electrical activity by decreasing motoneuron excitability and shifting the balance between excitatory and inhibitory synaptic transmission toward inhibition.

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.

How has molecular pharmacology contributed to our understanding of the mechanism(s) of general anesthesia?

This review discusses the mechanism(s) of general anesthesia from a pharmacological viewpoint; in particular, the ability of drugs to produce many different effects is emphasised. The problems of experimental measurement of general anesthesia are discussed, and the possibilities for antagonism and potentiation of anesthesia considered. Physicochemical studies on anesthesia are described, as are the advancement of ideas beyond consideration of lipids and proteins as separate sites of action. The importance of studies on different areas of the brain is highlighted, and the review finishes with a survey of the effects of general anesthetics on synaptic transmission which emphasises the problems of extrapolation from in vitro to in vivo.

Perturbation of target-directed neurite outgrowth in embryonic CNS co-cultures grown in the presence of ethanol

Studies were conducted to determine the influence of ethanol on target-directed fiber outgrowth in culture, using embryonic chick spinal cord-muscle, and fetal rat septal-hippocampal co-cultured explants. Process extension from the spinal cord and septal explants in control cultures was selectively oriented toward the appropriate target tissue. Ethanol in the culture medium (500 mg/dl) eliminated this target-oriented outgrowth in both systems, although the overall extent of neurite outgrowth was not affected. In an effort to further characterize the source of this disruption, target explants were grown alone, with and without ethanol, and the target-conditioned culture media was subsequently harvested and placed on newly plated spinal cord or septal explants, to determine whether ethanol decreased the target production of soluble substances. To determine whether deposition of substrate-bound materials by the target tissue was affected by ethanol, spinal cord or septal explants were plated in wells which had previously been occupied by the appropriate target tissue. These studies revealed that ethanol significantly inhibited production of soluble and substrate-bound materials by muscle explants, but not by hippocampal explants. It was concluded that the ethanol-induced loss of target-directed neurite outgrowth in the spinal cord explants could be accounted for primarily by the attenuated production of neurotropic/neurotropic substances by the muscle tissue. The loss of target-directionality in the septal explants appeared to be due to other factors, possibly related to ethanol-induced compromise of the capacity of the septal neurons to respond appropriately to target-derived neurotrophic/neurotropic substances. The implications of these results for the fetal alcohol syndrome are considered.

Inhibition of plasma membrane and mitochondrial transmembrane potentials by ethanol

The actions of ethanol and its primary oxidative metabolite, acetaldehyde, on plasma membrane and mitochondrial transmembrane potentials were examined in rat brain using fluorescence techniques. Subchronic treatment of adult rats with ethanol resulted in a significant depolarization of both the plasma and mitochondrial membranes when the mean blood ethanol level of the rats was 59 +/- 11 mM (mean +/- SEM, n = 6). Acute dosing of animals (4.5 g/kg, i.p.) failed to show any significant alterations. Various concentrations of ethanol, added in vitro to a crude synaptosomal preparation isolated from the rat cerebrocortex (P2) from untreated animals, depolarized both the plasma and mitochondrial transmembrane potentials in a dose-related manner. Addition of acetaldehyde in vitro did not reveal any significant effects on plasma or mitochondrial transmembrane potential.

Ethanol influences on the chick embryo spinal cord motor system: analyses of motoneuron cell death, motility, and target trophic factor activity and in vitro analyses of neurotoxicity and trophic factor neuroprotection

A series of in vivo and in vitro experiments were conducted to determine the influence of prenatally administered ethanol on several aspects of the developing chick embryo spinal cord motor system. Specifically, we examined: (1) the effect of chronic ethanol administration during the natural cell death period on spinal cord motoneuron numbers; (2) the influence of ethanol on ongoing embryonic motility; (3) the effect of ethanol exposure on neurotrophic activity in motoneuron target tissue (limb bud); and (4) the responsiveness of cultured spinal cord neurons to ethanol, and the potential of target-derived neurotrophic factors to ameliorate ethanol neurotoxicity. These studies revealed the following: Chronic prenatal ethanol exposure reduces the number of motoneurons present in the lateral motor column after the cell death period [embryonic day 12 (E12)]. Ethanol tends to inhibit embryonic motility, particularly during the later stages viewed (E9-E11). Chronic ethanol exposure reduces the neurotrophic activity contained in target muscle tissue. Such diminished support could contribute to the observed motoneuron loss. Direct exposure of spinal cord neurons to ethanol decreases neuronal survival and process outgrowth in a dose-dependent manner, but the addition of target muscle extract to ethanol-containing cultures can ameliorate this ethanol neurotoxicity. These studies demonstrate ethanol toxicity in a population not previously viewed in this regard and suggest a mechanism that may be related to this cell loss (i.e., decreased neurotrophic support).

Interaction of ethanol and allosteric modulators with GABAA-activated currents in adult medial septum/diagonal band neurons

Behavioral and electrophysiological studies suggest that neurons in the medial septum may express ethanol sensitive GABAA receptors. In the present study, patch-clamp recordings of whole-cell currents were used to directly characterize the ethanol sensitivity of GABAA receptors on acutely dissociated neurons, isolated from the medial septum/nucleus of the diagonal band (MS/nDB) of the adult rat brains. MS/nDB neurons displayed inward currents in response to GABA applied rapidly with a large-bore dual pipette system. The currents were mediated by the activation of GABAA receptors, since they reversed near the calculated reversal potential for chloride and were completely blocked by bicuculline. GABA responses were concentration dependent with an EC50 of 8.7 microM GABA and a slope of 1.35 suggesting cooperativity. Pharmacologically relevant concentrations of ethanol (3-300 mM) neither significantly increased nor decreased mean responses to GABA in neurons from Sprague Dawley or High Alcohol Sensitivity (HAS) rats. Mean GABA currents were significantly increased by 300 mM ethanol in neurons from 'ethanol sensitive' Fischer 344, ACI and Wistar Kyoto inbred rats. In subsets of neurons, 12.5 to 57.1% of those tested from these 5 rats strains, ethanol (30-300 mM) significantly increased GABA currents by > or = 20%. An additional, 10 percent of cells from Sprague Dawley rats showed ethanol-induced inhibition of GABA-activated current by < or = 20%. Allosteric modulators pentobarbital (10 microM), midazolam (1 microM) and lanthanum (300 microM), enhanced, while zinc (30 microM) decreased GABA-activated currents in all neurons, consistent with the well-known actions of these agents. These results suggest that GABAA receptors on MS/dDB neurons are pharmacologically similar to those on other neurons with respect to regulation by allosteric modulators. On the other hand, ethanol sensitivity of GABAA receptors varies considerably from cell to cell ranging from significant enhancement to inhibition of GABA-activated current.

Ethanol inhibits ligand-activated Ca2+ channels in human B lymphocytes

Ethanol reportedly is immunosuppressive, interfering with lymphocyte proliferation. To investigate the basis for this immunosuppression, the effects of acute treatment with ethanol were studied on Ca2+ mobilization in tonsillar B lymphocytes and the human lymphoblastoid B-cell line, Ramos. The level of intracellular Ca2+ was monitored in cells loaded with the fluorescent dye indo-1 following stimulation with either anti-IgM antibody or platelet activating factor. The effect of ethanol was also examined on the induction of the early proto-oncogene c-fos in these cells. Ethanol inhibited ligand-activated Ca2+ mobilization due to transmembrane influx but not intracellular store release, in a dose- and time-dependent manner. This inhibition was not due to the inability of anti-IgM to bind to its surface receptor nor to membrane depolarization induced by ethanol. Ethanol also inhibited the Ca2(+)-dependent induction by anti-IgM of c-fos in these cells. The inhibitory effects of ethanol on ligand-activated Ca2+ channels and subsequent induction of c-fos may provide the basis for its immunosuppressive action.

Comparison of the effects of ethanol and chlordiazepoxide on electrophysiological activity in the fascia dentata and hippocampus regio superior

Acute intoxicating doses of ethanol-producing blood alcohol levels of 120-200 mg% increase paired-pulse (PP) inhibition in the dentate gyrus of anesthetized rats suggesting that ethanol increases recurrent inhibitory processes (Wiesner, J.B., and S.J. Henriksen (1987) Ethanol enhances recurrent inhibition in the dentate gyrus of the hippocampus. Neurosci. Lett. 79:169-173). To further understanding of the neuronal mechanisms underlying this phenomenon, the authors studied the effects of the benzodiazepine (BZ), chlordiazepoxide, and acute intoxicating levels of ethanol on extracellular field potential recordings and single-unit activity in the dentate gyrus and area CA1 of the hippocampus. In the dentate, ethanol had no effect on population excitatory postsynaptic potential (pEPSP) amplitudes or slopes; decreased population spike (PS) amplitudes (25%); increased PP inhibition; decreased dentate granule cell (DGC) spontaneous activity (58%); had no effect on putative interneuron spontaneous activity; and markedly increased post field potential-evoked interneuron discharges (IDs, 218%). Chlordiazepoxide had no effect on pEPSP amplitudes or slopes or PS amplitudes; increased PP inhibition; decreased DGC (62%) and interneuron (72%) spontaneous activity; and markedly decreased IDs (89%). In CA1, ethanol had no effect on pEPSP amplitudes or slopes; decreased PS amplitudes (26%); had no effect on PP responses; decreased pyramidal cell (PC) spontaneous activity (39%); had no effect on interneuron spontaneous activity; and markedly increased IDs (97%). Chlordiazepoxide had no effect on pEPSP amplitudes or slopes or PS amplitudes; had no effect on PP responses; decreased PC spontaneous activity (41%); and had no effect on interneuron spontaneous activity or IDs. The results suggest that the BZs decrease principal cell excitability by postsynaptic facilitation of inhibitory processes, whereas ethanol decreases principal cell excitability indirectly by increasing the excitability of inhibitory interneurons.

Neuronal firing patterns of organotypic rat spinal cord cultures in normal and in ACTH/alpha-MSH(4-10) analog (BIM 22015)-supplemented medium

The spontaneous and evoked electrical patterns of spinal cord explants from 13- to 14-day old rat fetuses grown from 2 to 8 weeks in vitro were compared when fed either with a standard or with an adrenocorticotropic hormone/alpha-melanocyte stimulating hormone (4-10) analog (BIM 22015)-supplemented medium. Standard and BIM 22015-treated cultures developed similar patterns of extracellularly recorded activity which consisted of mostly phasic but also tonic discharges. The standard cultures when treated by BIM 22015 in acute experiments (100 micrograms/ml) showed a decrease in their frequency of discharges which fired in a regular tonic pattern. These effects were neither age- nor dose-dependent but were increased in Ca2+ free medium. The ventral cord neurons chronically fed with BIM 22015 showed a strongly bursting pattern resembling strychnine-induced synchronized bursts. Both these effects, inhibitory (acute) and excitatory (chronic), of the BIM upon spinal cord cultured ventral horn neurons are discussed as possible calcium-dependent phenomena.

Acute alcohol alters the excitability of cerebellar Purkinje neurons and hippocampal neurons in culture

Acute exposure to ethanol at 22 and 44 mM concentrations altered several features of the current-evoked voltage responses of cerebellar Purkinje neurons and hippocampal neurons studied in culture model systems. Whole cell current clamp techniques were used. At 22 mM, ethanol depressed current-evoked spiking in the hippocampal neurons but enhanced the current-evoked spiking in the Purkinje neurons. In both neuronal types, 44 mM ethanol depressed spiking, the amplitude of the afterhyperpolarization generated at the termination of a current pulse and the amplitude of the off-response generated at the termination of a hyperpolarizing pulse. Ethanol had little or no effect on resting membrane potential or the passive membrane properties measured near resting level in either neuronal type. Some changes in the current-voltage curves were observed at more depolarized or hyperpolarized potentials in both neuronal types. In the Purkinje neurons, where spontaneous activity was a prominent feature of some recordings, exposure to ethanol reduced the frequency of the spontaneous events. These results indicate that acute exposure to ethanol at intoxicating doses alters the membrane excitability of these two CNS neuronal types. The ethanol induced changes in neuronal excitability presumably contribute to the changes in firing properties observed in extracellular recordings from these neuronal types in vivo and the behavioral effects observed during alcohol intoxication in animal models.

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.

The potentiating effects of ethanol on the blue light depolarization of the retinal pigment epithelium

The retinal pigment epithelium (RPE) is the site of two major effects of ethanol. In humans, ethanol produces a slow damped oscillation in the steady electrical potential of the eye, which is generated primarily by the RPE. It has also been shown that ethanol potentiates the reversible, depolarizing effect of blue light on the transepithelial potential (TEP) of the isolated RPE. The present study demonstrates that in addition to the depolarizing effect of blue light on the TEP, a secondary, compensatory potential arises, which functions to maintain the TEP. The magnitude of the secondary response varies somewhat among preparations. It appears that ethanol eliminates or reduces the secondary, compensatory potential change which results in a large depolarization of the TEP when the RPE is irradiated with blue light. Microelectrode studies reveal that ethanol hyperpolarizes both the apical and basal membranes of the RPE with a greater effect noted in the apical membrane. This would account for the corneal positive potential elicited by ethanol in the human eye. Brief exposures (2-3 min) of blue light, after administration of 0.5% ethanol, results in a large (25-30 mV) depolarization of both membrane potentials as compared with 3 to 5 mV in untreated tissue. On the basis of our observations, it is hypothesized that some of the potentiating effects of ethanol in combination with other agents may result from an interference with a cellular adaptive response to impaired respiration rather than an additive effect on a common mechanism.

Effect of ethanol on the maturation of the spontaneous transmitter release by regenerated nerve endings

The cellular mechanisms involved in the theratogentic action of ethanol are not well known, but neuron outgrowth and synaptogenesis are regarded as the periods in which ethanol causes its major damage in the nervous system. The effects of chronic treatment with ethanol on the maturation of the spontaneous transmitter release by regenerated nerve endings in the rat were studied. The sciatic nerve was crushed and miniature end plate potentials (mepps) were recorded intracellularly in the re-innervated extensor digitorum longus muscle at different points in time after denervation; end plate potentials (epps) were also recorded. Two main effects were observed in the re-innervated muscles of ethanol-treated rats: (1) the appearance of spontaneous and evoked transmitter release was delayed and (2) the subsequent increase in frequency of mepps is faster. The possible mechanisms involved in these effects are discussed.

Effects of ethanol on CA1 and CA3 pyramidal cells in the hippocampal slice preparation: an intracellular study

Superfusion of ethanol (10-350 mM) sometimes caused weak hyperpolarization, but more often elicited weak depolarization or biphasic depolarizing, hyperpolarizing responses in CA1 and CA3 pyramidal neurons of the hippocampal slice. The occasional polarizations were sometimes accompanied by, but not always correlated with, small increases or decreases in input resistance. However, many cells in both areas showed no detectable change in membrane potential (36% of cells) or input resistance (57% of cells), even at very high ethanol concentrations (86-200 mM). Spontaneous spiking, when present, was occasionally accelerated or decelerated, although in CA3 a biphasic speeding-slowing sequence was often seen. The afterhyperpolarizations following bursts of action potentials evoked by current (CA1) or occurring spontaneously (CA3) were most often either slightly reduced in amplitude (CA3) or not affected (CA1) by ethanol superfusion. In contrast, synaptic potentials evoked by stimulation of the hilar mossy fiber pathway (for CA3) or the stratum radiatum (for CA1) were more sensitive to ethanol: excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) were most often reduced in amplitude in both CA1 and CA2, even at low ethanol concentrations (10-50 mM). The action on IPSPs may be exerted presynaptically, because responses to locally applied GABA were little affected. These results suggest that hippocampal evoked synaptic activity may be more sensitive than postsynaptic membrane properties to physiologically relevant ethanol concentrations.

Electrophysiology of ethanol on central neurons

With respect to the theme of this volume, the results of our recent studies on three neuronal model systems point to several relevant conclusions: ethanol may interact electrophysiologically with certain anesthetics such as urethane; ethanol can selectively enhance responses to certain neurotransmitters; resting membrane properties of individual neurons show a wide range of sensitivities to ethanol and are generally fairly insensitive; the synapse--independent of specific transmitters--seems most sensitive to ethanol. As regards the first point, it has long been known that ethanol and anesthetics have features in common, including the ability to alter the lipid components of biological membranes (see R. A. Harris et al., L. L. M. van Deenen et al., M. J. Hudspith et al., E. Rubin et al., and C. C. Cunningham & P. I. Spach in this volume), so interactions between the two are not unexpected. However, our electrophysiological findings suggest great caution and appropriate controls be used in in-vivo studies of anesthetized animals, as the interactions derived may actually reverse the usual effect of ethanol. The enhancement of responses to ACh and SS (second point) might be assumed to arise postsynaptically in the target cells recorded and are seen with low, intoxicating doses of ethanol. Whether this potentiation involves enhancement of specific agonist binding to the receptor or facilitation of the function of the ionic channel linked to the receptor remains to be determined. It is not hard to imagine that ethanol could perturb membrane properties near receptors, to alter their conformation and ligand binding, or perhaps even uncover hidden receptors. The relative insensitivity of the resting membrane properties (third point) may suggest that membrane channels responsible for these functions (e.g., 'leak' channels for Na+ and K+ ions) do not usually interact with the lipid components affected by ethanol, at least at low, 'intoxicating' ethanol concentrations. Finally, the reduction of synaptic potentials by ethanol may indicate a presynaptic locus of action, as the response to the transmitter for at least one of these synaptic potentials (GABA) was not altered. These data would seem to indicate that synaptic release of the transmitter is reduced by ethanol, at least in the hippocampal slice. The high sensitivity of this presynaptic element for ethanol could indicate that the machinery for synaptic release, such as conductances for calcium entry (see REF. 39) or the action of second messenger systems (e.g., those leading to synapsin phosphorylation) are particularly sensitive to ethanol.(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation of GABAA receptor activity by alphaxalone

The modulation of the gamma-aminobutyric acidA (GABAA) receptor by alphaxalone has been investigated by use of voltage-clamp recordings from enzymatically isolated bovine chromaffin cells maintained in cell culture. Alphaxalone (greater than 30 nM) reversibly and dose-dependently potentiated the amplitude of membrane currents elicited by locally applied GABA (100 microM). The potentiation was not associated with a change in the reversal potential of GABA-evoked currents and was not influenced by the benzodiazepine receptor antagonist, Ro15-1788 (300 nM). At relatively high concentrations (greater than 1 microM), alphaxalone directly elicited a membrane current. It is concluded that such currents result from GABAA receptor activation since they were reversibly suppressed by bicuculline (3 microM), dose-dependently enhanced by phenobarbitone (100-500 microM), and had a similar reversal potential (approximately 0 mV) to currents elicited by GABA. Additionally, on outside-out membrane patches, alphaxalone activated single channel currents with amplitudes and a reversal potential similar to those evoked by GABA. Alphaxalone (30 nM-1 microM) had no effect upon the amplitude of membrane currents elicited by locally applied acetylcholine (ACh) (100 microM). However, higher concentrations of alphaxalone (10-100 microM) reversibly suppressed ACh-evoked currents, the IC50 for blockade being 20 microM. The beta-hydroxy isomer of alphaxalone, betaxalone (100 nM-1 microM), did not potentiate GABA-induced currents, nor did higher concentrations of the steroid (10-100 microM) directly evoke a membrane current. However, over the latter concentration range, betaxalone suppressed the amplitude of currents elicited either by GABA or ACh. The relevance of the present results to the anaesthetic action of alphaxalone is discussed together with the broader implications of steroidal modulation of the GABAA receptor.

The effects of ethanol on the electrophysiology of calcium channels

Acute ethanol intoxication affects many systems in the body, especially the central nervous system. Because early experiments using axonal preparations required very high concentrations of ethanol to produce ionic current alterations, researchers turned their attention away from specific effects on electrogenesis and looked for effects at the synapse. The role of Ca2+ in the release of neurotransmitters was well known and was considered a possible site of action for ethanol. Indeed, several studies demonstrated that ethanol alters Ca2+ binding or transport in synaptosomes and neural tissue. The purpose of this chapter is to present electrophysiological evidence for the acute effects of ethanol on calcium channels. It is necessary first to define the relevant ethanol concentrations and to describe the characteristics of tissue preparations that may best help to determine the effects of ethanol. A discussion of these two points along with a brief synopsis of the role of Ca2+ in excitable tissues is presented. This is followed by a discussion of the effects of ethanol on Ca2+ and Ca2+-activated conductances in both nonmammalian and mammalian cells, and a model is presented in an attempt to unify the experimental evidence of the acute effects of ethanol.

Effect of ethanol on the spontaneous transmitter release by nerve endings in the process of maturation

Ethanol stimulates the spontaneous transmitter release from motor nerve endings, as shown by the increase of miniature end plate potential (m.e.p.p.) frequency at the neuro-muscular junction. The stimulation of acetylcholine spontaneous quantal release by ethanol is greater in regenerating than in mature nerve endings. The different effects of ethanol on regenerating nerve endings may be related to changes of chemical-physical membrane properties.

Effect of perinatally administered ethanol on the development of the cerebellar granule cell

The effect of perinatally administered ethanol on the postnatal development of cerebellar granule cells was studied in mice which received 25% of their caloric intake as ethanol. Timed-pregnant females were given ethanol in a chocolate-flavored liquid from gestation day 12 until postnatal day 7, then the mice were returned to a chow and water regime. The pups were killed on postnatal day 14 and the tissue processed for Golgi analysis of the dendritic arbor. Camera lucida drawings were made of the granule cells and these drawings were subsequently analyzed using a Zeiss Videoplan. Examination of the granule cells revealed that there was a significant decrease in dendritic length and in the extent of the dendritic field. In addition, there was a delayed maturation of the terminal dendritic processes. These results are in accord with other reports in the literature which suggest that the altered dendritic patterns seen in ethanol toxicity may be one of the causative factors in the minimal brain dysfunction that is characteristic of the fetal alcohol syndrome.

Systemic ethanol: selective enhancement of responses to acetylcholine and somatostatin in hippocampus

In rat hippocampal pyramidal cells tested in situ by iontophoresis of several neurotransmitters, ethanol significantly enhanced excitatory responses to acetylcholine and inhibitory responses to somatostatin-14 but had no statistically significant effect on excitatory responses to glutamate or inhibitory responses to gamma-aminobutyric acid or, in preliminary tests, to norepinephrine or serotonin. The effects of ethanol on responses to acetylcholine and somatostatin-14 may provide insight into synaptic mechanisms underlying the behavioral consequences of ethanol intoxication.

Aging: effect on the interaction of ethanol and pentobarbital with the benzodiazepine-GABA receptor-ionophore complex

Benzodiazepine receptor binding and modulation by pentobarbital and ethanol was studied using the detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate to solubilize the gamma-aminobutyric acid (GABA)-benzodiazepine receptor-ionophore complex from the brains of Fischer 344 rats of 3-4, 12-15 and more than 28 months of age. The affinity of the benzodiazepine binding site was significantly lower in the young rats compared to either the mature or senescent animals. However, no age-related changes in the maximum number of benzodiazepine binding sites or GABA concentrations occurred in the detergent extract. Pentobarbital produced practically identical dose-dependent enhancement of [3H]flunitrazepam specific binding in all 3 age groups. In contrast, ethanol between 0.1 and 200 microM failed to produce a dose-dependent effect on [3H]flunitrazepam specific binding in any age group. The effect of pentobarbital and ethanol on [35S]t-butyl-bicyclophosphorothionate [( 35S]TBPS) specific binding to the picrotoxinin binding site was examined in the above solubilized receptor/ionophore complex under the same binding conditions. Both sedative-hypnotics produced a dose-dependent decrease in [35S]TBPS specific binding. However, pentobarbital was over 10,000 times more potent. It appears that ethanol may not enhance [3H]flunitrazepam specific binding in this solubilized preparation because of its weak action at the picrotoxinin binding site.

Prolongation of inhibitory postsynaptic currents by pentobarbitone, halothane and ketamine in CA1 pyramidal cells in rat hippocampus

Spontaneous inhibitory postsynaptic currents (i.p.s.cs) were recorded in voltage-clamped CA1 neurones in rat hippocampal slices. The exponential decay of i.p.s.cs was prolonged by concentrations of sodium pentobarbitone as low as 50 microM. With concentrations up to 100 microM, there was no change in the amplitude or rise time of the currents but current amplitude was depressed at 200 microM. The prolongation of currents increased with drug concentration within the range tested (50 to 200 microM). Halothane, at concentrations from 1 to 5%, also increased the time constant of decay of i.p.s.cs. The effect increased with concentration and was fully reversible. Ketamine, at a concentration of 0.5 mM, increased the time constant of decay of i.p.s.cs by 50 to 80% and the effect was reversible. Ethanol (10-200 mM), nitrous oxide (75-80%), and caffeine (10 microM-5 mM) had no detectable effect on the i.p.s.cs. It is suggested that pentobarbitone, halothane and ketamine increase the time constant of decay of the i.p.s.cs by stabilizing the open state of channels activated by gamma-aminobutyric acid.

Postsynaptic actions of ethanol and methanol in crayfish neuromuscular junctions

Actions of ethanol and methanol on excitatory postsynaptic channels activated by quisqualate were investigated in opener muscles from the first walking leg and the claw of crayfish. Both ethanol and methanol reduced the elementary currents [i] that flow through channels operated by quisqualate in a concentration-dependent manner but did not affect the apparent mean open time, tau noise, of the channels estimated from power spectra. 0.26 mol/l ethanol, or 1 mol/l methanol, respectively, reduced [i] e-fold. Ethanol also markedly decreased the size and the decay time constant tau (sEPSCs) of spontaneous excitatory postsynaptic currents (sEPSCs). At ten fibres, on the average, 0.26 mol/l ethanol decreased tau (sEPSCs) by a factor 1.56 +/- 0.24 (SD). tau (sIPSCs) and tau noise of inhibitory postsynaptic currents apparently were not affected by ethanol. Moreover the size of elementary inhibitory postsynaptic currents did not decrease in the presence of this alcohol. Thus, in crayfish opener muscles ethanol seems to selectively depress excitatory postsynaptic currents.