Acute ethanol alters the firing pattern and glutamate response of cerebellar Purkinje neurons in culture

GAD65 deficient mice are susceptible to ethanol-induced impairment of motor coordination and facilitation of cerebellar neuronal firing

γ-aminobutyric acid (GABA) is a major inhibitory neurotransmitter and its concentrations in the brain could be associated with EtOH-induced impairment of motor coordination. GABA is synthesized by two isoforms of glutamate decarboxylase (GAD): GAD65 and GAD67. Mice deficient in GAD65 (GAD65-KO) can grow up to adulthood, and show that GABA concentration in their adult brains was 50-75% that of wild-type C57BL/6 mice (WT). Although a previous study showed that there was no difference in recovery from the motor-incoordination effect of acute intraperitoneally administered injections of 2.0 g/kg EtOH between WT and GAD65-KO, the sensitivity of GAD65-KO to acute EtOH-induced ataxia has not been fully understood. Here, we sought to determine whether motor coordination and spontaneous firing of cerebellar Purkinje cells (PCs) in GAD65-KO are more sensitive to the effect of EtOH than in WT. Motor performance in WT and GAD65-KO was examined by rotarod and open-field tests following acute administration of EtOH at lower-doses, 0.8, 1.2 and 1.6 g/kg. In a rotarod test, there was no significant difference between WT and GAD65-KO in terms of baseline motor coordination. However, only the KO mice showed a significant decrease in rotarod performance of 1.2 g/kg EtOH. In the open-field test, GAD65-KO showed a significant increase in locomotor activity after 1.2 and 1.6 g/kg EtOH injections, but not WT. In in vitro studies of cerebellar slices, the firing rate of PCs was increased by 50 mM EtOH in GAD65-KO compared with WT, whereas no difference was observed in the effect of EtOH at more than 100 mM between the genotypes. Taken together, GAD65-KO are more susceptible to the effect of acute EtOH exposure on motor coordination and PC firing than WT. This different sensitivity could be attributed to the basal low GABA concentration in the brain of GAD65-KO.

Dose-dependent sensorimotor impairment in human ocular tracking after acute low-dose alcohol administration

Key points

Oculomotor behaviours are commonly used to evaluate sensorimotor disruption due to ethanol (EtOH).

The current study demonstrates the dose‐dependent impairment in oculomotor and ocular behaviours across a range of ultra‐low BACs (<0.035%).

Processing of target speed and direction, as well as pursuit eye movements, are significantly impaired at 0.015% BAC, suggesting impaired neural activity within brain regions associated with the visual processing of motion.

Catch‐up saccades during steady visual tracking of the moving target compensate for the reduced vigour of smooth eye movements that occurs with the ingestion of low‐dose alcohol.

Saccade dynamics start to become ‘sluggish’ at as low as 0.035% BAC.

Pupillary light responses appear unaffected at BAC levels up to 0.065%.

Abstract

Changes in oculomotor behaviours are often used as metrics of sensorimotor disruption due to ethanol (EtOH); however, previous studies have focused on deficits at blood‐alcohol concentrations (BACs) above about 0.04%. We investigated the dose dependence of the impairment in oculomotor and ocular behaviours caused by EtOH administration across a range of ultra‐low BACs (≤0.035%). We took repeated measures of oculomotor and ocular performance from sixteen participants, both pre‐ and post‐EtOH administration. To assess the neurological impacts across a wide range of brain areas and pathways, our protocol measured 21 largely independent performance metrics extracted from a range of behavioural responses ranging from ocular tracking of radial step‐ramp stimuli, to eccentric gaze holding, to pupillary responses evoked by light flashes. Our results show significant impairment of pursuit and visual motion processing at 0.015% BAC, reflecting degraded neural processing within extrastriate cortical pathways. However, catch‐up saccades largely compensate for the tracking displacement shortfall caused by low pursuit gain, although there still is significant residual retinal slip and thus degraded dynamic acuity. Furthermore, although saccades are more frequent, their dynamics are more sluggish (i.e. show lower peak velocities) starting at BAC levels as low as 0.035%. Small effects in eccentric gaze holding and no effect in pupillary response dynamics were observed at levels below 0.07%, showing the higher sensitivity of the pursuit response to very low levels of blood alcohol, under the conditions of our study.

Oculomotor behaviours are commonly used to evaluate sensorimotor disruption due to ethanol (EtOH).

The current study demonstrates the dose‐dependent impairment in oculomotor and ocular behaviours across a range of ultra‐low BACs (<0.035%).

Processing of target speed and direction, as well as pursuit eye movements, are significantly impaired at 0.015% BAC, suggesting impaired neural activity within brain regions associated with the visual processing of motion.

Catch‐up saccades during steady visual tracking of the moving target compensate for the reduced vigour of smooth eye movements that occurs with the ingestion of low‐dose alcohol.

Saccade dynamics start to become ‘sluggish’ at as low as 0.035% BAC.

Pupillary light responses appear unaffected at BAC levels up to 0.065%.

Acute alcohol and cognition: Remembering what it causes us to forget

Addiction has been conceptualized as a specific form of memory that appropriates typically adaptive neural mechanisms of learning to produce the progressive spiral of drug-seeking and drug-taking behavior, perpetuating the path to addiction through aberrant processes of drug-related learning and memory. From that perspective, to understand the development of alcohol use disorders, it is critical to identify how a single exposure to alcohol enters into or alters the processes of learning and memory, so that involvement of and changes in neuroplasticity processes responsible for learning and memory can be identified early. This review characterizes the effects produced by acute alcohol intoxication as a function of brain region and memory neurocircuitry. In general, exposure to ethanol doses that produce intoxicating effects causes consistent impairments in learning and memory processes mediated by specific brain circuitry, whereas lower doses either have no effect or produce a facilitation of memory under certain task conditions. Therefore, acute ethanol does not produce a global impairment of learning and memory, and can actually facilitate particular types of memory, perhaps particular types of memory that facilitate the development of excessive alcohol use. In addition, the effects on cognition are dependent on brain region, task demands, dose received, pharmacokinetics, and tolerance. Additionally, we explore the underlying alterations in neurophysiology produced by acute alcohol exposure that help to explain these changes in cognition and highlight future directions for research. Through understanding the impact that acute alcohol intoxication has on cognition, the preliminary changes potentially causing a problematic addiction memory can better be identified.

Acute maternal oxidant exposure causes susceptibility of the fetal brain to inflammation and oxidative stress

Background

Maternal exposure to environmental stressors poses a risk to fetal development. Oxidative stress (OS), microglia activation, and inflammation are three tightly linked mechanisms that emerge as a causal factor of neurodevelopmental anomalies associated with prenatal ethanol exposure. Antioxidants such as glutathione (GSH) and CuZnSOD are perturbed, and their manipulation provides evidence for neuroprotection. However, the cellular and molecular effects of GSH alteration in utero on fetal microglia activation and inflammation remain elusive.

Methods

Ethanol (EtOH) (2.5 g/kg) was administered to pregnant mice at gestational days 16–17. One hour prior to ethanol treatment, N-acetylcysteine (NAC) and L-buthionine sulfoximine (BSO) were administered to modulate glutathione (GSH) content in fetal and maternal brain. Twenty-four hours following ethanol exposure, GSH content and OS in brain tissues were analyzed. Cytokines and chemokines were selected based on their association with distinctive microglia phenotype M1-like (IL-1β, IFN γ, IL-6, CCL3, CCL4, CCL-7, CCL9,) or M2-like (TGF-β, IL-4, IL-10, CCL2, CCL22, CXCL10, Arg1, Chi1, CCR2 and CXCR2) and measured in the brain by qRT-PCR and ELISA. In addition, Western blot and confocal microscopy techniques in conjunction with EOC13.31 cells exposed to similar ethanol-induced oxidative stress and redox conditions were used to determine the underlying mechanism of microglia activation associated with the observed phenotypic changes.

Results

We show that a single episode of mild to moderate OS in the last trimester of gestation causes GSH depletion, increased protein and lipid peroxidation and inflammatory responses inclined towards a M1-like microglial phenotype (IL-1β, IFN-γ) in fetal brain tissue observed at 6–24 h post exposure. Maternal brain is resistant to many of these marked changes. Using EOC 13.31 cells, we show that GSH homeostasis in microglia is crucial to restore its anti-inflammatory state and modulate inflammation. Microglia under oxidative stress maintain a predominantly M1 activation state. Additionally, GSH depletion prevents the appearance of the M2-like phenotype, while enhancing morphological changes associated with a M1-like phenotype. This observation is also validated by an increased expression of inflammatory signatures (IL-1β, IFN-γ, IL-6, CCL9, CXCR2). In contrast, conserving intracellular GSH concentrations eliminates OS which precludes the nuclear translocation and more importantly the phosphorylation of the NFkB p105 subunit. These cells show significantly more pronounced elongations, ramifications, and the enhanced expression of M2-like microglial phenotype markers (IL-10, IL-4, TGF-β, CXCL10, CCL22, Chi, Arg, and CCR2).

Conclusions

Taken together, our data show that maintaining GSH homeostasis is not only important for quenching OS in the developing fetal brain, but equally critical to enhance M2 like microglia phenotype, thus suppressing inflammatory responses elicited by environmental stressors.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-0965-8) contains supplementary material, which is available to authorized users.

Gaze-evoked nystagmus induced by alcohol intoxication

KEY POINTS

The cerebellum is the core structure controlling gaze stability. Chronic cerebellar diseases and acute alcohol intoxication affect cerebellar function, inducing, among others, gaze instability as gaze-evoked nystagmus. Gaze-evoked nystagmus is characterized by increased centripetal eye-drift. It is used as an important diagnostic sign for patients with cerebellar degeneration and to assess the 'driving while intoxicated' condition. We quantified the effect of alcohol on gaze-holding using an approach allowing, for the first time, the comparison of deficits induced by alcohol intoxication and cerebellar degeneration. Our results showed that alcohol intoxication induces a two-fold increase of centripetal eye-drift. We establish analysis techniques for using controlled alcohol intake as a model to support the study of cerebellar deficits. The observed similarity between the effect of alcohol and the clinical signs observed in cerebellar patients suggests a possible pathomechanism for gaze-holding deficits.

ABSTRACT

Gaze-evoked nystagmus (GEN) is an ocular-motor finding commonly observed in cerebellar disease, characterized by increased centripetal eye-drift with centrifugal correcting saccades at eccentric gaze. With cerebellar degeneration being a rare and clinically heterogeneous disease, data from patients are limited. We hypothesized that a transient inhibition of cerebellar function by defined amounts of alcohol may provide a suitable model to study gaze-holding deficits in cerebellar disease. We recorded gaze-holding at varying horizontal eye positions in 15 healthy participants before and 30 min after alcohol intake required to reach 0.6‰ blood alcohol content (BAC). Changes in ocular-motor behaviour were quantified measuring eye-drift velocity as a continuous function of gaze eccentricity over a large range (±40 deg) of horizontal gaze angles and characterized using a two-parameter tangent model. The effect of alcohol on gaze stability was assessed analysing: (1) overall effects on the gaze-holding system, (2) specific effects on each eye and (3) differences between gaze angles in the temporal and nasal hemifields. For all subjects, alcohol consumption induced gaze instability, causing a two-fold increase [2.21 (0.55), median (median absolute deviation); P = 0.002] of eye-drift velocity at all eccentricities. Results were confirmed analysing each eye and hemifield independently. The alcohol-induced transient global deficit in gaze-holding matched the pattern previously described in patients with late-onset cerebellar degeneration. Controlled intake of alcohol seems a suitable disease model to study cerebellar GEN. With alcohol resulting in global cerebellar hypofunction, we hypothesize that patients matching the gaze-holding behaviour observed here suffered from diffuse deficits in the gaze-holding system as well.

Ethanol affects NMDA receptor signaling at climbing fiber-Purkinje cell synapses in mice and impairs cerebellar LTD

Ethanol profoundly influences cerebellar circuit function and motor control. It has recently been demonstrated that functional N-methyl-(D)-aspartate (NMDA) receptors are postsynaptically expressed at climbing fiber (CF) to Purkinje cell synapses in the adult cerebellum. Using whole cell patch-clamp recordings from mouse cerebellar slices, we examined whether ethanol can affect NMDA receptor signaling in mature Purkinje cells. NMDA receptor-mediated currents were isolated by bath application of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzol[f]quinoxaline (NBQX). The remaining (D)-2-amino-5-phosphonovaleric acid ((D)-APV)-sensitive current was reduced by ethanol at concentrations as low as 10 mM. At a concentration of 50 mM ethanol, the blockade of (D)-APV-sensitive CF-excitatory postsynaptic currents was significantly stronger. Ethanol also altered the waveform of CF-evoked complex spikes by reducing the afterdepolarization. This effect was not seen when NMDA receptors were blocked by (D)-APV before ethanol wash-in. In contrast to CF synaptic transmission, parallel fiber (PF) synaptic inputs were not affected by ethanol. Finally, ethanol (10 mM) impaired long-term depression (LTD) at PF to Purkinje cell synapses as induced under control conditions by paired PF and CF activity. However, LTD induced by pairing PF stimulation with depolarizing voltage steps (substituting for CF activation) was not blocked by ethanol. These observations suggest that the sensitivity of cerebellar circuit function and plasticity to low concentrations of ethanol may be caused by an ethanol-mediated impairment of NMDA receptor signaling at CF synapses onto cerebellar Purkinje cells.

Regulation of brain anandamide by acute administration of ethanol

The endogenous cannabinoid acylethanolamide AEA (arachidonoylethanolamide; also known as anandamide) participates in the neuroadaptations associated with chronic ethanol exposure. However, no studies have described the acute actions of ethanol on AEA production and degradation. In the present study, we investigated the time course of the effects of the intraperitoneal administration of ethanol (4 g/kg of body mass) on the endogenous levels of AEA in central and peripheral tissues. Acute ethanol administration decreased AEA in the cerebellum, the hippocampus and the nucleus accumbens of the ventral striatum, as well as in plasma and adipose tissue. Parallel decreases of a second acylethanolamide, PEA (palmitoylethanolamide), were observed in the brain. Effects were observed 45-90 min after ethanol administration. In vivo studies revealed that AEA decreases were associated with a remarkable inhibition of the release of both anandamide and glutamate in the nucleus accumbens. There were no changes in the expression and enzymatic activity of the main enzyme that degrades AEA, the fatty acid amidohydrolase. Acute ethanol administration did not change either the activity of N-acyltransferase, the enzyme that catalyses the synthesis of the AEA precursor, or the expression of NAPE-PLD (N-acylphosphatidylethanolamine-hydrolysing phospholipase D), the enzyme that releases AEA from membrane phospholipid precursors. These results suggest that receptor-mediated release of acylethanolamide is inhibited by the acute administration of ethanol, and that this effect is not derived from increased fatty acid ethanolamide degradation.

Competing presynaptic and postsynaptic effects of ethanol on cerebellar purkinje neurons

BACKGROUND

Ethanol has actions on cerebellar Purkinje neurons that can result either in a net excitation or in inhibition of neuronal activity. The present study examines the interplay of presynaptic and postsynaptic mechanisms to determine the net effect of ethanol on the neuronal firing rate of cerebellar Purkinje neurons.

METHODS

Whole-cell voltage-clamp recording of miniature inhibitory postsynaptic currents (mIPSCs) from Purkinje neurons in cerebellar slices was used to examine the effect of ethanol on presynapticsynaptic release of gamma-aminobutyric acid (GABA) and glutamate. Extracellular recording was used to examine the net action of both presynaptic and postsynaptic effects of ethanol on the firing rate of Purkinje neurons.

RESULTS

Under whole-cell voltage clamp, the frequency of bicuculline-sensitive miniature postsynaptic currents (mIPSCs) was increased dose-dependently by 25, 50, and 100 mM ethanol without any change in amplitude or decay time. Despite this evidence of increased release of GABA by ethanol, application of 50 mM ethanol caused an increase in firing in some neurons and a decrease in firing in others with a nonrandom distribution. When both glutamatergic and GABAergic influences were removed by simultaneous application of 6-cyano-7-nitroquinoxaline-2,3-dione and picrotoxin, respectively, ethanol caused only an increase in firing rate.

CONCLUSIONS

These data are consistent with a dual action of ethanol on cerebellar Purkinje neuron activity. Specifically, ethanol acts presynaptically to increase inhibition by release of GABA, while simultaneously acting postsynaptically to increase intrinsic excitatory drive.

Effect of chronic ethanol ingestion on Purkinje and Golgi cell firing in vivo and on motor coordination in mice

As motor coordination impairment is a common symptom of acute and chronic alcohol intoxication, different studies have been conducted on cerebellar Purkinje cell sensitivity to ethanol since Purkinje cell firing constitutes the final integrative output of the cerebellar cortex. However, the effects of chronic ethanol ingestion on Purkinje firing and other cerebellar neurons such as Golgi cells remain unknown. Here, we studied the extracellular discharge of Purkinje and Golgi cells in four groups of non-anesthetized mice drinking ad libitum either 0%, 6%, 12% or 18% ethanol isocallorically compensated with sucrose 25% during a 3-month period. No difference in Golgi cell firing was found with respect to ethanol consumption. The only group that presented significant differences in Purkinje cell firing compared to the other groups was the 18% ethanol-drinking group. These mice presented decreased simple spike and complex spike firing and increased complex spike duration and pause. The 18% ethanol-drinking group was also the only one to present a slight but significant motor coordination impairment (evaluated by rotarod and runway) in naïve task. No motor coordination impairment was noticed in task learned before ethanol consumption. These results suggest that chronic high doses of ethanol are necessary to produce Purkinje cell firing alterations and measurable motor coordination impairment in naïve task. These alterations in Purkinje cell firing did not affect the ability to learn or to recall a motor coordination task.

Role of NMDA receptors in pentobarbital tolerance/dependence

Effects of continuous pentobarbital administration on binding characteristics of [3H]MK-801 in the rat brain were examined by autoradiography. Animals were rendered tolerant to pentobarbital using i.c.v. infusion of pentobarbital (300 micrograms/10 microliters/hr for 7 days) by osmotic minipumps and dependent by abrupt withdrawal from pentobarbital. The levels of [3H]MK-801 binding were elevated in rats 24-hr after withdrawal from pentobarbital while there were no changes except in septum and anterior ventral nuclei in tolerant rats. For assessing the role of NMDA receptor in barbiturate action, an NMDA receptor antagonist (MK-801, 2.7 femto g/10 microliters/hr) was co-infused with pentobarbital. The pentobarbital-infused group had a shorter duration of pentobarbital-induced loss of righting reflex (sleeping time) than that of the control group, and MK-801 alone did not affect the righting reflex. However, co-infusion of MK-801 blocked hyperthermia, and prolonged the onset of convulsions induced by t-butylbicyclophosphorothionate (TBPS) in pentobarbital withdrawal rats. In addition, elevated [35S]TBPS binding was significantly attenuated by co-infusion with MK-801. These results suggest the involvement of NMDA receptor up-regulation in pentobarbital withdrawal and that the development of dependence can be attenuated by the treatment of subtoxic dose of MK-801.

Effect of ethanol on extracellular 5-HT and glutamate in the nucleus accumbens and prefrontal cortex: comparison between the Lewis and Fischer 344 rat strains

The present study investigated the impact of systemic (i.p.) ethanol administration on extracellular levels of serotonin and glutamate in the prefrontal cortex and the nucleus accumbens in Lewis and Fischer 344 rat strains using in vivo microdialysis. At 1.0 g/kg, ethanol elicited a significant increase in nucleus accumbens-dialysate levels of both 5-HT (44% +/- 16, P = 0.002) and glutmate (90% +/- 43, P = 0.009) in Lewis rats. In Fischer rats, there was no increase in 5-HT (6% +/- 7: P = 0.5), and a trend toward an increase in glutamate (88% +/- 46: P = 0.1). The 0.5 and 2.0 g/kg doses did not result in any significant change in extracellular 5-HT or glutamate in the nucleus accumbens or prefrontal cortex of either strain. The basal levels of glutamate, in both brain regions, were significantly lower in Lewis than in Fischer 344 rats. The basal levels of 5-HT were also lower in the nucleus accumbens of Lewis rats. These findings suggest that enhanced sensitivity of the mesoaccumbens 5-HT or glutamate systems to ethanol and/or inherent low basal levels of 5-HT or glutamate activity may be associated with the predisposition to alcohol-drinking behavior seen in Lewis rats.

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

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

Seizures during ethanol withdrawal are blocked by focal microinjection of excitant amino acid antagonists into the inferior colliculus and pontine reticular formation

Physical dependence on ethanol can result in seizure susceptibility during ethanol withdrawal. In rats, generalized tonic-clonic seizures are precipitated by auditory stimulation during the ethanol withdrawal syndrome. Excitant amino acids (EAAs) are implicated as neurotransmitters in the inferior colliculus and the brain stem reticular formation, which play important roles in the neuronal network for genetic models of audiogenic seizures (AGSs). Ethanol blocks the actions of EAAs in various brain regions, including the inferior colliculus. In this study, dependence was produced by intragastric administration of ethanol for 4 days. During ethanol withdrawal, AGSs were blocked by systemic administration of competitive or noncompetitive NMDA antagonists 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) or dizocilpine (MK-801). Focal microinjections of NMDA or non-NMDA antagonists into the inferior colliculus or the pontine reticular formation also inhibited AGSs. MK-801 was the most potent anticonvulsant systemically. When injected into the inferior colliculus, CPP had a more potent anticonvulsant effect than either MK-801 or the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione. The inferior colliculus was more sensitive than the pontine reticular formation to the anticonvulsant effects of both competitive NMDA and non-NMDA antagonists. The results of the present support the idea that continued ethanol administration may lead to development of supersensitivity to the action of EAAs in inferior colliculus and pontine reticular formation neurons. This may be a critical mechanism subserving AGS susceptibility during ethanol withdrawal.

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.

High ethanol sensitivity of recombinant AMPA-type glutamate receptors expressed in mammalian cells

The effect of ethanol (EtOH) on ion current mediated by recombinant alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate (KA) receptors was examined in transfected human embryonic kidney 293 cells using whole-cell recording. Inhibition of KA-activated current was observed in the presence of intoxicating EtOH concentrations. The potency with which EtOH inhibited current was similar for receptors formed by different subunits or subunit combinations. EtOH also inhibited KA-activated current in cultured neurons from fetal rat cortex. However, the potency of EtOH inhibition in cortical neurons was lower than that observed in 293 cells expressing recombinant receptors. The properties of receptors in cultured neurons, other than EtOH sensitivity, were similar to those displayed by recombinant AMPA/KA receptors. These observations indicate that some forms of non-NMDA ionotropic glutamate receptors have relatively high EtOH sensitivity. These receptors appear to differ in some respect from AMPA/kainate receptors expressed endogenously in cortical neurons.

L-glutamate abolishes differential responses to alcohol deprivation in mice

Hybrid mice produced by crossing CBA and C57BL lines were deprived of alcohol for three days after prolonged prior access. Subsequently, when access was first given to a flavored 30% alcohol solution, about half of the mice showed a greatly elevated rate of drinking during the first 1.5 h, characteristic of the alcohol-deprivation effect (ADE), but other mice showed no increase. Repeating the test three weeks later showed that having or lacking an ADE is a stable group characteristic. Behavioral differences were found on cross-maze and slip funnel tests between mice that had an ADE and those that lacked it. Topical application of L-glutamate to the frontal cortex prevented the subsequent elevation of alcohol drinking during the first 1.5 h after deprivation but did not alter drinking during the remaining 22.5 h. L-glutamate treatment also affected those cross-maze behaviors found to be related to the ADE. The results suggest that frontal cortex neurons sensitive to L-glutamate are necessary for the ADE and that comparisons between hybrid mice having and lacking an ADE might be used for determining the neuronal mechanisms responsible for the effect.

Chronic ethanol intoxication induces differential effects on GABAA and NMDA receptor function in the rat brain

The effect of long-term treatment with ethanol was investigated on the function of gamma-aminobutyric acid A (GABAA) and N-methyl-d-aspartic acid (NMDA) receptors. Rats were rendered ethanol-dependent by repeated forced administration of a 20% ethanol solution (12 to 18 g/kg/day po) for 6 days and tested while still intoxicated or at different time intervals after withdrawal. t-[35S]Butylbicyclophosphorothionate (35S-TBPS) binding was increased by 30% in cortical homogenates of rats killed 1 to 3 hr after last ethanol administration, when compared with saline-treated animals. However, GABA-stimulated 36Cl- uptake and its enhancement by flunitrazepam was decreased in the ethanol-treated animals. 35S-TBPS binding and 36Cl- influx measured 9 to 24 hr following the last ethanol injection, when withdrawal signs were present, were unmodified with respect to saline-treated rats. Moreover, the effects of both isoniazid and FG 7142 on 35S-TBPS binding were unchanged in ethanol-dependent rats tested at 1 to 3 and 9 to 24 hr, compared with controls. In contrast, ethanol-withdrawn rats tested at 9 to 24 hr showed a dramatic enhancement in their sensitivity to the convulsant action of isoniazid (50 to 250 mg/kg, sc). The same animals were also more susceptible to the convulsant action of NMDA (0.5 to 5 micrograms/5 microliters/rat intracerebroventricularly) and kainic acid (12 mg/kg, ip), and this effect was paralleled by an enhancement (+25%) in the density of 3H-MK 801 recognition sites in the hippocampus.(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)

Ethanol decreases the velocity of spike propagation along a fast motor axon

Intracellular recordings were made from the fast bender excitor motor axon in autotomized crab limbs bathed in normal saline, and in salines made with up to 240 mM of ethanol. The presence of ethanol reduced the amplitude, the rise time and the decay time of the evoked action potential, and decreased the velocity at which the spike was conducted down the axon. There was a linear relationship between each of these four parameters and the concentration of ethanol in the saline. The close relationship between spike rise time and conduction velocity suggests that ethanol slows the rate of membrane depolarization by the spike and thus decreases the velocity at which action potentials are propagated along the axon.

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.

Overexcitement and disinhibition. Dynamic neurotransmitter interactions in alcohol withdrawal

In alcohol withdrawal, abnormalities occur in a number of neurotransmitter systems: there is reduced inhibitory function, and increased activity of excitatory systems. The former, indicated by reduced GABA and alpha-2-adrenoceptor activity, acts in conjunction with, and is exacerbated by, the latter, which itself may be due to the potentiation of NMDA activity by depletion of magnesium, and overactivity of catecholaminergic and CRF neurones. These dysfunctions produce immediate effects and may also contribute to the long-term changes in brain excitability by a kindling-like process. It is possible that early and active treatment may oppose this process. Present strategies for treatment of alcohol withdrawal enhance GABA and alpha-2 inhibitory, or reduce excitatory, mechanisms. Future possibilities include the use of CRF and/or NMDA antagonists.

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.

Neuropharmacological and clinical aspects of alcohol withdrawal

Abnormalities in the function or activity of several neurotransmitter systems have been demonstrated after acute and chronic, exposure to alcohol, and in alcohol withdrawal. The changes can be divided into alterations in function of inhibitory and excitatory systems. Inhibitory dysfunction is indicated by reduced gamma-aminobutyric acid and alpha-2-adrenoceptor activity. In conjunction with, and exacerbating this, is increased activity of excitatory systems, perhaps the most significant of which is the probable potentiation of N-methyl-D-aspartate activity by depletion of magnesium. There is additional, and possibly secondary, overactivity of catecholamine and corticotropin releasing factor neuronal systems. Other, less specific changes include increased numbers of calcium channels, which would increase neuronal excitability. The evidence for these changes is presented, and the implications for new treatment regimes for alcohol withdrawal are discussed.

The response of primary cultured adult mouse sensory neurons to ethanol, propanol, acetaldehyde and acrolein treatments

Primary cultures of adult mouse sensory neurons maintained for 8 days in vitro (8 div), in both the presence of non-neuronal cell (NNC) outgrowth and in NNC-reduced cultures, were exposed to doses of ethanol, propanol, acetaldehyde and acrolein. The effects on cell viability were monitored: LD50's of 600 microM acrolein and 100 mM propanol were obtained after 24 h exposures and after 48 h with 1 mM acetaldehyde and 500 mM ethanol. Morphological effects were evident by scanning electron microscopy with sub-acute doses for each agent, using both lower concentrations and shorter exposures. Membrane pitting of the perikaryon and a reduction in the proportion of neurons bearing neurites were common signs of toxic insult. The neurites of treated cells were thicker and more irregular than those of untreated cells; this proved a good indicator of specific neurotoxicity rather than merely a cytotoxic response. Fetal calf serum in the medium lessened the response of neurons to ethanol treatments. Comparison with other in vitro studies suggests these primary cultures are a more sensitive system than established cell lines of neuronal origin for use in neurotoxicity testing.

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.

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

The effects of continuous exposure to ethanol on the cytological and physiological development of a central nervous system (CNS) neuron were studied using the cultured Purkinje neuron of the rat cerebellar cortex. Purkinje neurons in fetal rat brain cultures which are established at one day before birth show development comparable to that described in vivo in other studies. In culture, Purkinje neurons progress from immature rounded cells with fine neurites to mature neurons with a branched dendritic structure. These structural changes are accompanied by an increase in the duration and complexity of the excitatory response to glutamate, by transitions in the patterns of spontaneous activity, and by an increase in mean firing rate. Our results demonstrate that chronic exposure to a low concentration of ethanol (90 mg%; 19.5 mM) during development selectively alters the electrophysiological but not the morphological properties of Purkinje neurons. Specifically, ethanol treatment reduces the responsiveness of these neurons to glutamate, delays the expected developmental transitions in patterns of spontaneous activity, and induces increased spontaneous bursting activity, particularly at the stage of dendritic formation. Impairment of responsiveness to glutamate is significant in that it may reflect the compromise by ethanol of a major excitatory pathway in the cerebellar cortex, resulting from the decreased efficacy of glutamatergic input from parallel fibers. In contrast to the results of other studies using adult neurons as a model for the effects of ethanol, our work suggests that the developing CNS neuron does not become tolerant; that is, in the continuing presence of ethanol, it does not express physiological function equivalent to that of the control.