Role of glutamatergic and GABAergic systems in alcoholism

A rational approach to the pharmacotherapy of alcohol dependence

The use of alcohol is widespread in the world, and although there are many regular users, some individuals drink excessively. Understanding the time course of the development and maintenance of alcohol dependence is important in assessing the potential risk/benefit of an intervention and in accurately treating the problem. Most, although not all, literature suggests that alcoholism is a chronic, relapsing disorder and that there is a general progression from less to more severe problems. Understanding the neurobiology that underlies alcohol dependence as it relates to different clinical stages may help in the development of effective targeted pharmacological treatments. Important clinical stages that may be amenable to pharmacological intervention include the transition from alcohol use to heavy drinking particularly in vulnerable individuals, the cessation of heavy drinking in individuals who want to quit, and the prevention of relapse in individuals who have initiated abstinence but may struggle with craving or the desire to resume alcohol use. Neurotransmitter systems implicated in these stages include glutamate, gamma-aminobutyric acid, opioid, and serotonin systems that may act directly or via the indirect modulation of dopamine function. The treatment implications will also be discussed.

The alcohol-preferring P rat and animal models of excessive alcohol drinking

The alcohol-preferring, P, rat was developed by selective breeding to study ethanol drinking behavior and its consequences. Characterization of this line indicates the P rat meets all of the criteria put forth for a valid animal model of alcoholism, and displays, relative to their alcohol-non-preferring, NP, counterparts, a number of phenotypic traits associated with alcohol abuse and alcoholism. Behaviorally, compared with NP rats, P rats are less sensitive to the sedative and aversive effects of ethanol and more sensitive to the stimulatory effects of ethanol. Neurochemically, research with the P line indicates the endogenous dopaminergic, serotonergic, GABAergic, opiodergic, and peptidergic systems may be involved in a predisposition for alcohol abuse and alcoholism. Paralleling the clinical literature, genetically selected P rats display levels of ethanol intake during adolescence comparable to that seen during adulthood. Binge drinking has been associated with an increased risk for health and other problems associated with ethanol abuse. A model of binge-like drinking during the dark cycle indicates that P rats will consume 6 g/kg/day of ethanol in as little as three 1-hour access periods/day, which approximates the 24-hour intake of P rats with free-choice access to a single concentration of ethanol. The alcohol deprivation effect (ADE) is a transient increase in ethanol intake above baseline values upon re-exposure to ethanol access after an extended period of deprivation. The ADE has been proposed to be an animal model of relapse behavior, with the adult P rat displaying a robust ADE after prolonged abstinence. Overall, these findings indicate that the P rat can be effectively used in models assessing alcohol-preference, a genetic predisposition for alcohol abuse and/or alcoholism, and excessive drinking using protocols of binge-like or relapse-like drinking.

Sedative and GABAergic effects of ethanol on male and female rats

BACKGROUND

Women consume less alcohol than men, and yet they are more susceptible than men to the negative medical consequences of alcohol use, such as cirrhosis of the liver, cardiac disease, and cognitive impairments. This sex difference is also reflected in animal studies, in which male and female rats differ on both behavioral and electrophysiological measures. Given that one significant difference between males and females is the cycling fluctuations of the sex hormones, this study aimed to compare the relative sensitivity of adolescent and adult rats of both sexes and varying estrous stages to the behavioral and electrophysiological effects of ethanol.

METHODS

Adult female rats were lavaged daily for estrous cycle assessment. Following administration of 5 g/kg ethanol, adolescent and adult male and female animals were observed for loss of the righting reflex. Then, using whole-cell recording, we tested the response of spontaneous, gamma-aminobutyric acid (GABA(A)) receptor-mediated inhibitory postsynaptic currents (sIPSCs) in hippocampal slices from drug-naïve adult male and female rats.

RESULTS

Consistent with previous findings, adolescent animals were less sensitive than adults to the effect of ethanol on the righting reflex. In addition, adult proestrous and diestrous female rats were less sensitive than male rats to the sedative effects of ethanol. Finally, ethanol increased the frequency of sIPSCs in hippocampal pyramidal neurons and did so more potently in cells from male rats than in those from female rats.

CONCLUSIONS

Female animals are less sensitive to the behavioral sedative effects of ethanol than adult male rats, and the effect is pronounced in the proestrous and diestrous states. This sex difference may be related to differential sensitivity of GABA receptor-mediated central nervous system function to ethanol in females.

Basis of the gabamimetic profile of ethanol

This article summarizes the proceedings of a symposium held at the 2005 Research Society on Alcoholism meeting. The initial presentation by Dr. Wallner provided evidence that selected GABA(A) receptors containing the delta subunit display sensitivity to low intoxicating ethanol concentrations and this sensitivity is further increased by a mutation in the cerebellar alpha6 subunit, found in alcohol-hypersensitive rats. Dr. Mameli reported that ethanol affects gamma-aminobutyric acid (GABA) function by affecting neural circuits that influence GABA release. Dr. Parsons presented data from electrophysiological and microdialysis investigations that ethanol is capable of releasing GABA from presynaptic terminals. Dr. Morrow demonstrated that systemic ethanol increases neuroactive steroids in brain, the absence of which alters various functional responses to ethanol. Dr. Criswell presented evidence that the ability of ethanol to increase GABA was apparent in some, but not all, brain regions indicative of regional specificity. Further, Dr. Criswell demonstrated that neurosteroids alone and when synthesized locally by ethanol act postsynaptically to enhance the effect of GABA released by ethanol in a region specific manner. Collectively, this series of reports support the GABAmimetic profile of acutely administered ethanol being dependent on several specific mechanisms distinct from a direct effect on the major synaptic isoforms of GABA(A) receptors.

Chronic Smoking and Alcoholism Change Expression of Selective Genes in the Human Prefrontal Cortex

BACKGROUND

Alcoholism is commonly associated with chronic smoking. A number of gene expression profiles of regions within the human mesocorticolimbic system have identified potential alcohol-sensitive genes; however, the influence of smoking on these changes was not taken into account. This study addressed the impact of alcohol and smoking on the expression of 4 genes, previously identified as alcoholism-sensitive, in the human prefrontal cortex (PFC).

METHODS

mRNA expression of apolipoprotein D, tissue inhibitor of the metalloproteinase 3, high-affinity glial glutamate transporter and midkine, was measured in the PFC of alcoholic subjects and controls with and without smoking comorbidity using real-time polymerase chain reaction.

RESULTS

The results show that alcohol affects transcription of some of these genes. Additionally, smoking has a marked influence on gene expression.

CONCLUSION

This study emphasizes the need for careful case selection in future gene expression studies to delineate the adaptive molecular process associated with smoking and alcohol.

Methyl parathion: an organophosphate insecticide not quite forgotten

Methyl parathion (MP), a toxic organophosphate insecticide approved for outdoor use only, is classified by the World Health Organization (WHO) as a Category Ia (extremely toxic) and by the United States Environmental Protection Agency (U.S. EPA) as a Toxicity Category I (most toxic) insecticide. In several U.S. states in the late 1980s and early 1990s, toxic exposures were created by the illegal use of MP indoors by uncertified pest control operators. As the health effects of MP exposure became evident with increasing public awareness, intervention by the U.S. government, in collaboration with several agencies and public initiatives, led to investigations of MP exposure. After evidence of MP metabolites from urine samples confirmed the exposure, in 1998 the indoor use of MP was banned in the U.S. to protect human health, especially that of children, and the environment. Toxic exposures to MP also occurred in developing countries. In El Salvador, occupational exposure to MP in farmers introduced environmental exposures among agricultural families, who presented with the cholinergic features of MP toxicity. Suicidal MP poisoning was reported in Nepal. A fatal accidental poisoning in children in Peru reflected the serious health risk of pesticides in developing countries. The negligence of pesticide exporters raised human rights issues over the tragedy. Nevertheless, MP exposure remains a potential health risk in both the U.S. and the developing world. Preventive measures in reducing the use of toxic chemicals should be taken seriously to protect human health and the environment.

Ionotropic glutamate receptor gene GRIK3 SER310ALA functional polymorphism is related to delirium tremens in alcoholics

Upregulation of glutamatergic neurotransmission resulting from chronic ethanol intoxication may cause a hyperexcitable state during alcohol withdrawal, which may lead to seizures and delirium tremens. The aim of our study was to evaluate the association between a history of alcohol withdrawal-induced seizures and delirium tremens, and a functional polymorphism (Ser310Ala) of the GRIK3 gene coding for the glutamatergic kainate receptor subunit GlurR7 in a sample of well-characterized alcoholics compared to controls. In total, 233 patients meeting DSM-IV alcohol dependence criteria and 309 controls, all of German descent, were investigated. GRIK3 functional polymorphism was determined using PCR (polymerase chain reaction) of lymphocyte DNA. History of alcohol withdrawal-induced delirium tremens and seizures were obtained using the SSAGA (Semi-Structured Assessment for the Genetics of Alcoholism). Data were cross-checked with in-patients' clinical files. While a significant relationship between history of delirium tremens and the Ser310 allele was detected, no significant results were obtained for alcohol withdrawal-related seizures. Although this result is suggestive for a significant role of this polymorphism in the pathogenesis of delirium tremens in alcohol-dependent individuals, further investigation and confirmation are warranted.

Effect of prenatal exposure to ethanol on glutamate and GABA immunoreactivity in macaque somatosensory and motor cortices: Critical timing of exposure

The present study explored the effects of gestational ethanol exposure on enduring changes in the distribution of projection neurons and local circuit neurons in somatosensory/motor cortex. Critical events in corticogenesis occur during macaque gestation: the first six weeks of gestation include the period of primary stem cell production and the next 18 weeks are marked by the birth, migration, early differentiation, and death of cortical neurons. Monkeys were exposed to ethanol (or saline) one day per week during the first six or during the entire 24 weeks of gestation. Offspring were killed as adolescents. Projection neurons and local circuit neurons were identified immunohistochemically with antibodies directed against glutamate and anti-GABA, respectively. In all animals, both projection neurons and local circuit neurons were distributed in all laminae of both somatosensory and motor cortices. Ethanol did not affect the size of Cresyl Violet-stained, glutamate-positive, or GABA-immunolabeled somata, however, it did decrease neuronal density. The total density of Cresyl Violet-stained neurons was reduced in monkeys treated with ethanol (or saline) one day per week during the first six weeks of gestation and during the entire 24 weeks of gestation. Similar reductions were detected for glutamate- and GABA-positive neurons. The densities of Cresyl Violet-stained and of glutamate- and GABA-expressing neurons were reduced in all cortical layers. The only exception was layer V which was unaffected in monkeys treated with ethanol (or saline) one day per week during the first six weeks of gestation and during the entire 24 weeks of gestation. Thus, the parallel effects on both neuronal subpopulations suggest that ethanol targets a population of undetermined neuronal precursors.

Alphaxalone and epiallopregnanolone in rats trained to discriminate ethanol

BACKGROUND

Neurosteroids with a 3 alpha-hydroxy orientation share pharmacological effects with ethanol, increase in brain after ethanol administration, and may mediate ethanol effects. 3beta-hydroxy neurosteroids antagonize in vitro and some, but not all in vivo effects of ethanol and 3 alpha-hydroxy neurosteroids.

METHODS

We assessed the discriminative stimulus and rate altering effects of alphaxalone, a 3 alpha-hydroxy neurosteroid, and epiallopregnanolone, a 3beta-hydroxy neurosteroid, in rats trained to discriminate either 0.8 g/kg or 1.2 g/kg ethanol. The ability of epiallopregnanolone to antagonize the discriminative stimulus or rate-altering effects of ethanol or alphaxalone was also assessed.

RESULTS

Ethanol had similar discriminative ED50s (0.5 g/kg) in both groups; however rats trained with the lower ethanol dose were more sensitive to rate-decreasing effects of ethanol. Alphaxalone occasioned ethanol-appropriate responding in both training groups, although less effectively in rats trained on the lower ethanol dose (maximum 65% versus 80% ethanol-appropriate responding). No difference in sensitivity to the rate-decreasing effects of alphaxalone was present between groups. Epiallopregnanolone did not reliably occasion ethanol-appropriate responding in either training group, and rats trained on the lower ethanol dose were slightly more sensitive to epiallopregnanolone rate decreasing effects. Epiallopregnanolone did not alter any effects of ethanol or alphaxalone.

CONCLUSIONS

Our results agree with previous reports that 3 alpha-hydroxy neurosteroids occasion ethanol-appropriate responding, while 3beta-hydroxy neurosteroids do not; as well as reports showing no antagonism of the discriminative stimulus or rate-suppressant effects of ethanol or 3 alpha-hydroxy neurosteroids by 3beta-hydroxy neurosteroids. Results of the present study demonstrate that ethanol and 3 alpha-hydroxy neurosteroids share discriminative stimulus effects. However, these results are inconsistent with the hypothesis that such neurosteroids mediate the discriminative stimulus of ethanol.

Identifikation von Risikogenen für Alkoholabhängigkeit

Alcohol dependence is one of the most common addictive diseases and known to be in part genetically transmitted, based on an oligogenic background in which each gene involved contributes only little to the resulting phenotype. Besides influencing other signal transduction mechanisms, alcohol specifically inhibits the NMDA signaling cascade, which mediates the excitatory effects of glutamate in the brain. Target molecules, sensitive to ethanol, include the NMDA receptors as well as downstream molecules of the glutamatergic system, glutamate transporters, and associated regulatory proteins. Adaptive processes of the glutamatergic system during chronic alcohol consumption may play a major role for later development of reward symptoms. Candidate gene studies, including association studies and animal models, are powerful and sensitive for detecting oligogenic effects and thus important to alcoholism research.

Effects of Chronic Alcohol Consumption in a Visual Attention Task and an Auditory Oddball Task: An Event-Related Potential Study

BACKGROUND

In alcohol-dependent individuals changes in brain functioning, as measured with Event Related Potentials (ERP) have been reported.

METHODS

In the present study a visual attention and an auditory oddball task were used to investigate possible differences between light, moderate, and heavy social drinkers and excessive drinkers. It was hypothesized that with increasing alcohol intake an increasing number of ERP components elicited in the visual attention task and the auditory oddball task would show diminished amplitudes.

RESULTS

No differences were found between light, moderate, and heavy social drinkers. A trend for a smaller P3 amplitude in the visual attention task was found when comparing the alcohol-dependent participants with the light social drinkers. It is argued that this difference might be an effect of alcohol dependence and/or a reflection of possible unknown or undetected family history of alcohol-related disturbances.

CONCLUSIONS

In the current study, even at rather large amounts of regular alcohol intake, no evidence was found for any toxic effect of social alcohol use neither in a visual attention task nor in an auditory oddball task.

Effect of natural and synthetic polyamines on ethanol intake in UChB drinker rats

Because of the important glutamatergic mediation of the behavioral effects of ethanol, glutamatergic agents have attracted attention for the treatment of ethanol abuse and dependence in preclinical and clinical studies. In the present study, we investigated the effect of pharmacological doses of the natural polyamines putrescine, spermine, and spermidine and the synthetic polyamine N,N'-bis-(3-aminopropyl)cyclohexane-1,4-diamine (DCD) on alcohol consumption in a free-choice paradigm carried out in genetically high-ethanol-consumer UChB rats. Short 3-day treatment with either polyamine, administered p.o., significantly reduced ethanol intake without modifying water and food intakes. Neither polyamine was able to increase markedly blood acetaldehyde in rats submitted to a standard challenge dose of ethanol, to rule out a disulfiram-like effect. Besides, blood ethanol disappearance after a test dose of ethanol was not affected by the synthetic polyamine DCD. Long-term treatment with DCD dose-dependently reduced ethanol intake in UChB rats without producing any observable effect on overt behavior, food consumption, and total fluid intake. The present results indicate that pharmacological doses of polyamines can reduce ethanol consumption in genetically drinking rats without producing significant side effects, suggesting that modulation of brain N-methyl-d-aspartate receptors by polyamines could represent a suitable strategy to reduce appetite for ethanol. However, caution must be exercised in interpreting the results because polyamines can also affect neuronal excitability by acting at other receptor targets, such as AMPA and kainate receptors, as well as at some voltage-dependent ion channels.

Increased GABA release in the central amygdala of ethanol-dependent rats

The central nucleus of amygdala (CeA) is important in regulating alcohol consumption and plays a major role in the anxiogenic response to ethanol withdrawal. We showed previously that acute ethanol augments GABA(A) receptor-mediated IPSPs and IPSCs, possibly by a presynaptic mechanism. Here, we have examined the interaction of acute ethanol with the GABAergic system in chronic ethanol-treated (CET) rats using an in vitro CeA slice preparation and in vivo brain microdialysis. We found that in CeA slices from CET rats, the baseline evoked IPSP and IPSC amplitudes were increased, and paired-pulse facilitation ratios were lower than in naive rats, suggesting an increased GABAergic transmission after chronic ethanol treatment. Interestingly, acute ethanol (5-66 mm) significantly enhanced IPSPs and IPSCs equally in CET and naive rats, indicating a lack of tolerance for this effect of acute ethanol. Analysis of miniature IPSC frequency suggests that the increased GABAergic transmission by both acute and chronic ethanol arises from a presynaptic mechanism involving enhanced vesicular release of GABA. These data are supported by microdialysis studies showing that CET rats presented a fourfold increase in baseline GABA dialysate content compared with naive rats. In vivo administration of ethanol (0.1, 0.3, and 1.0 m) produced a dose-dependent increase in GABA release in the CeA dialysate in both CET and naive rats. These combined findings suggest that acute and chronic ethanol increases GABA release in CeA and support previous reports that the behavioral actions of ethanol are mediated, in part, by increased GABAergic transmission in the CeA.

Ethanol withdrawal reduces cerebellar parvalbumin expression in a manner reversed by estrogens

Parvalbumin (PA) is a calcium-binding protein that has been implicated in neuroprotection. We examined whether the stimulus effect of ethanol withdrawal (EW) alters the expression of PA in a manner that is prevented by 17beta-estradiol (E2). Ovariectomized rats implanted with E2 (EW/E2) or oil (EW/Oil) pellets received chronic ethanol (7.5%, w/v, 5 weeks) or control dextrin diets (Dex/Oil). At 24h of EW, rats were tested for overt EW signs, and the cerebellum was prepared for immunoblotting and immunohistological assessment for PA. The EW/Oil group showed a higher EW sign score, a lower PA expression, and fewer PA-positive Purkinje neurons than the dextrin control group. In the EW/E2 group, EW sign scores, PA expression, and PA-positive Purkinje neurons were not significantly different from those in the control dextrin group. These data suggest that E2 treatment protects against the PA-suppression associated with EW toxicity.

Environmental and intraperitoneal ethanol influences morphine antinociceptive effect in mice

The ability of acute environmental or intraperitoneal (i.p.) ethanol to influence morphine antinociceptive effect was studied in mice. In order to induce tolerance to morphine analgesia, mice received daily injections of 10 mg/Kg morphine over a period of 10 days. Mice were divided into three groups: i.p. ethanol (E), environmental ethanol (E*), and control saline (M). During the induction of tolerance these groups were treated identically except on days 1 and 11. On these days, 10 minutes prior to morphine injection, mice received either i.p. ethanol (1g/Kg), environmental ethanol (a bottle of 10% ethanol placed next to the animals cage during the experiments), or an equivalent volume of saline. Analgesia was assessed using a standard hot plate protocol and dose-response cumulative curves for morphine analgesia were obtained on days 1 and 11. On day 1, both the i.p. and environmental administration of ethanol showed similar morphine-potentiation effects [Mean Effective Dose: ED50 (M1)=4.5 mg/kg; ED50 (E1)=2.4 mg/kg; ED50 (E*1)=2.1 mg/kg]. On day 11, control group mice showed a reduction of morphine analgesia at test [ED50 (M11)=14.1 mg/kg]. Mice receiving i.p. and environmental ethanol again showed a leftward shift in dose-response cumulative curves for morphine antinociception with respect to controls [ED50 (E11)=9.1 mg/kg; ED50 (E*11)=4.7 mg/kg]. I.p. ethanol administration at non-antinociceptive doses enhances the morphine antinociception effect similarly in tolerant and non-tolerant (naive) mice. The presence of environmental ethanol can also induce a similar pattern of increase in morphine antinociception effect.

Pharmacotherapy of alcohol use disorders

Therapeutic interventions to treat alcoholism have increased in number, including several pharmacotherapies. Aspects of epidemiology, gender, and psychiatric comorbidity as well as a brief overview of neurobiology are presented as an introduction. The medications used clinically for the treatment of alcoholism, disulfiram and naltrexone, approved by the Food and Drug Administration in the United States for the treatment of alcoholism and acamprosate, a medication used extensively in Europe that is currently being evaluated in the United States, are reviewed in detail. An overview of the serotonergic agents is also provided. Finally, future directions, including new medications and some clinical strategies that show promise but are not yet used extensively clinically, are mentioned.

Influence of ethanol on the threshold for electroshock-induced seizures and electrically-evoked hippocampal afterdischarges

The anticonvulsant activity of ethanol was investigated in two representative models of experimental epilepsy. In the maximal electroshock seizure threshold test in mice, ethanol (0.5-2 g/kg i.p.) dose-dependently raised the electroconvulsive threshold for tonic seizures. In co-medication with valproate and carbamazepine, ethanol significantly increased the anticonvulsant effectiveness of both antiepileptic drugs. Subchronic premedication of ethanol did not reveal marked decrease of its additive anticonvulsant action and only tended to reduce the effectiveness of valproate and carbamazepine. No changes of the plasma levels of both antiepileptics could be detected. Furthermore, in the hippocampal afterdischarge model in rats, ethanol dose-dependently raised the focal stimulation threshold and significantly increased the anticonvulsant efficacy of co-administered carbamazepine after acute application. Subchronic premedication of ethanol tended to reduce the effectiveness of the latter. In conclusion, the present results indicated pronounced anticonvulsant effects of ethanol against generalized tonic-clonic as well as complex partial seizures which did not reveal strong tolerance after subchronic administration.

Motor Impairing Effects of Ethanol and Diazepam in Rats Selectively Bred for High and Low Ethanol Consumption in a Limited-Access Paradigm

BACKGROUND

Some clinical studies suggest that an initial low-level response in ethanol sensitivity is a good predictor of risk for developing subsequent high levels of ethanol consumption in humans; however, there are some inconsistencies in the data. In experimental research, this association between low ethanol sensitivity and high ethanol intake has not been consistently reported in studies that have used rat lines that have been genetically selected for differences in ethanol intake under continuous access conditions (e.g., UChA versus UchB, P versus NP, AA versus ANA). The present study investigated ethanol sensitivity in high (HARF) and low (LARF) ethanol-preferring rats selectively bred under limited-access conditions. For comparative purposes, motor impairment induced by diazepam was also examined.

METHODS

Motor impairment was assessed using the tilt plane. Ethanol (1.25, 2.0, and 2.5 g/kg, intraperitoneally) was administered to ethanol-naive male and female HARF and LARF rats, and their performance was assessed at t = 0, 30, and 60 min. Blood ethanol levels were measured in a separate group of ethanol-naive rats. Finally, in a separate group of male and female HARF and LARF rats, diazepam-induced (1, 3, and 10 mg/kg, intraperitoneally) motor impairments were evaluated in a similar manner.

RESULTS

In the ethanol study, HARF rats showed greater dose-dependent impairments than their LARF counterparts. Male rats exhibited greater sensitivity to ethanol-induced impairment than their female counterparts. These observations were unrelated to sex or line differences in the blood ethanol levels achieved. Similar impairments were observed with diazepam, with HARF rats exhibiting greater motor impairment than LARF rats.

CONCLUSIONS

The results suggest that selective breeding for high and low ethanol drinking in a limited-access paradigm has led to inherent differences in sensitivity to ethanol- and diazepam-induced motor impairments. The pattern of diazepam-induced impairments suggests possible variations in GABA(A) receptor activity, although more research is necessary to determine such involvement.

Alcohol and gene expression in the central nervous system

AIMS

To describe recent research focusing on the analysis of gene and protein expression relevant to understanding ethanol consumption, dependence and effects, in order to identify common themes.

METHODS

A selective literature search was used to collate the relevant data.

RESULTS

Over 160 genes have been individually assessed before or after ethanol administration, as well as in genetically selected lines. Techniques for studying gene expression include northern blots, differential display, real time reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization. More recently, high throughput functional genomic technology, such as DNA microarrays, has been used to examine gene expression. Recent gene expression analyses have dramatically increased the number of candidate genes (nine array papers have illuminated 600 novel gene transcripts that may contribute to alcohol abuse and alcoholism).

CONCLUSIONS

Although functional genomic experiments (transcriptome analysis) have failed to identify a single alcoholism gene, they have illuminated important pathways and gene products that may contribute to the risk of alcohol abuse and alcoholism.

UPREGULATION OF GLUTAMATE RECEPTOR SUBTYPES DURING ALCOHOL WITHDRAWAL IN RATS

AIMS

To investigate glutamate receptor subtypes during alcohol withdrawal.

METHODS

Rats were exposed to severe alcohol intoxication for 84 h and then decapitated at 0, 12 and 36 h after the last alcohol dose (n = 7 per group). Alcohol was administered five times a day by intragastric intubation. The densities of N-methyl-D-aspartate (NMDA) and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors were studied in membranes from the forebrain by using the specific ligands [3H]MK-801 and [3H]AMPA, respectively.

RESULTS

Although no change in the maximal density (B(max)) of [3H]MK-801 binding sites was observed at the time of withdrawal, [3H]MK-801 binding was increased by 49% 12 h into the withdrawal reaction compared with the control group. At 36 h post alcohol the B(max) of the [3H]MK-801 binding was still increased by 24% compared with the control group; however, this difference was not statistically significant. When investigated at the time of withdrawal from chronic alcohol intoxication, no significant alterations in the B(max) of the [3H]AMPA binding was detected, but 12 h into the withdrawal reaction the [3H]AMPA binding was markedly increased by 94%. At 36 h post alcohol the [3H]AMPA binding had returned to control levels. No significant alterations in the dissociation constant (K(D)) of either [3H]MK-801 or [3H]AMPA binding was observed at any time point.

CONCLUSIONS

NMDA and AMPA receptors are involved in the cerebral hyperactivity of alcohol withdrawal.

Pharmacotherapy for alcohol-related disorders: what clinicians should know

Alcohol-related disorders are a major public health problem in the United States. Alcohol interacts with several neurotransmitter systems causing both acute and chronic effects in the brain. While the mainstay of treatment of alcohol-related disorders, with the exception of alcohol withdrawal, has historically been psychosocial, pharmacotherapy is increasingly being investigated and incorporated into standard clinical practice. Patients with alcohol use disorders and comorbid psychiatric conditions, most commonly depressive and anxiety disorders, can benefit from symptom-targeted pharmacotherapy, even if the patient fails to achieve abstinence from alcohol. Although benzodiazepines remain the treatment of choice to treat alcohol withdrawal, a variety of other agents is being investigated, particularly in the outpatient setting. Further randomized clinical trials of alcohol-related disorder pharmacotherapy, particularly of comorbid subpopulations, are needed to better inform clinical decision making. The routine exclusion of alcohol-dependent patients from pharmacotherapy trials of psychiatric disorders presents a barrier to gathering more data. Recommendations for future research are discussed.

Differential effects of chronic ethanol administration and withdrawal on gamma-aminobutyric acid type A and NMDA receptor subunit proteins in male and female rat brain

BACKGROUND

Investigations have shown that chronic ethanol exposure results in selective alterations in levels of gamma-aminobutyric acid (GABA)A and NMDA receptor subunits. We previously reported significant sex differences in these chronic ethanol-induced adaptations. Because we have more recently found important sex differences in timing for the development of and recovery from ethanol dependence, we wanted to ascertain whether there were associations between overt expression of withdrawal and neuroadaptations at the level of GABAA and NMDA receptors.

METHODS

Western blot analysis was used to assay protein levels for several GABAA and NMDA receptor subunits in rat cerebral cortex and hippocampus by using subunit-selective antibodies. Rats were fed 6% ethanol in a liquid diet with pair-fed controls. Feeding, harvesting of tissue, and Western blot experiments were all conducted while maintaining the paired design. Tissue was harvested after 3 days of ethanol exposure, 9 days of ethanol exposure, or 3 days of ethanol withdrawal after 14 days of liquid diet administration.

RESULTS

We again found sex-, subunit-, and brain region-selective effects of ethanol administration and withdrawal for GABAA and NMDA receptors. There was a strong association between increased GABAA receptor alpha4 subunit levels and previously determined withdrawal-induced changes in seizure susceptibility, highlighted by the sex differences in ethanol exposure length required to cause withdrawal signs. In addition, results obtained after 9 days of ethanol administration were in general agreement with previous findings after 14 days of ethanol administration.

CONCLUSIONS

These data further support the suggestion that alterations in subunit assembly of GABAA and NMDA receptors may have some mechanistic role in neuroadaptations underlying ethanol dependence and withdrawal. Furthermore, significant sex differences in these adaptations suggest that multiple types of adaptations may be elicited, depending on innate differences in the actions/effects of ethanol.

Integrative Neurobiology of the Alcohol Withdrawal Syndrome???From Anxiety to Seizures

This article represents the proceedings of a symposium presented at the 2003 Research Society on Alcoholism meeting in Ft. Lauderdale, Florida, organized and chaired by Carl L. Faingold. The presentations were (1) Overview, by Carl L. Faingold; (2) Stress, Multiple Alcohol Withdrawals, and Anxiety, by Darin Knapp; (3) Relationship Between Genetic Differences in Alcohol Drinking and Alcohol Withdrawal, by Julia Chester; (4) Neuronal Mechanisms in the Network for Alcohol Withdrawal Seizures: Modulation by Excitatory Amino Acid Receptors, by Carl L. Faingold; and (5) Treatment of Acute Alcohol Withdrawal and Long-Lasting Alterations in Hippocampal Neuronal Networks, by Larry P. Gonzalez. The presentations emphasized the importance of using intact behaving animals to advance the understanding of the human alcohol withdrawal syndrome. This involves applying and amplifying the neurophysiological and neurotransmitter findings observed in vitro to the network-based neurobiological mechanisms that are involved in several important aspects of the specific behaviors observed clinically. The symposium provided evidence that the organizational aspects of neuronal networks in the intact nervous system add another nexus for the action of alcohol and drugs to treat alcohol withdrawal that may not be readily studied in isolated neural elements used in in vitro approaches.

Baclofen: Alcohol Withdrawal

Off-Label Drug Uses

This Hospital Pharmacy feature is extracted from Off-Label DrugFacts, a quarterly publication available from Facts and Comparisons. Off-Label DrugFacts is a practitioner-oriented resource for information about specific FDA-unapproved drug uses. This new guide to the literature will enable the health care professional/clinician to quickly identify published studies on off-label uses and to determine if a specific use is rational in a patient care scenario. The most relevant data are provided in tabular form so that the reader can easily identify the scope of information available. A summary of the data—including, background, study design, patient population, dosage information, therapy duration, results, safety, and therapeutic considerations—precedes each table of published studies. References direct the reader to the full literature for more comprehensive information prior to patient care decisions. Direct questions or comments on “Off-Label Drug Uses” to hospitalpharmacy@drugfacts.com .

Ethanol withdrawal hyper-responsiveness mediated by NMDA receptors in spinal cord motor neurons

1. Following ethanol (EtOH) exposure, population excitatory postsynaptic potentials (pEPSPs) in isolated spinal cord increase to a level above control (withdrawal hyper-responsiveness). The present studies were designed to characterize this phenomenon and in particular to test the hypothesis that protein kinases mediate withdrawal. 2. Patch-clamp studies were carried out in motor neurons in rat spinal cord slices. Currents were evoked by brief pulses of glutamate, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) or N-methyl-D-aspartic acid (NMDA). 3. Of 15 EtOH-sensitive neurons in which currents were evoked by glutamate, four (27%) displayed withdrawal hyper-responsiveness in the washout period. Mean current area after washout was 129.6+/-5% of control. 4. When currents were evoked by AMPA, two of 10 neurons (20%) displayed withdrawal hyper-responsiveness, with a mean current area 122+/-8% of control on washout. 5. Of a group of 11 neurons in which currents were evoked by NMDA, nine (82%) displayed withdrawal hyper-responsiveness. Mean increase in current area at the end of the washout period was to 133+/-6% of control (n=9, P<0.001). When NMDA applications were stopped during the period of EtOH exposure, mean area of NMDA-evoked responses on washout was only 98.0+/-5% of control (n=6, P>0.05). 6. The tyrosine kinase inhibitor genistein (10-20 microM) blocked withdrawal hyper-responsiveness. Of six EtOH-sensitive neurons, the mean NMDA-evoked current area after washout was 89+/-6% of control, P>0.05. 7 The protein kinase A (PKA) inhibitor Rp-cAMP (20-500 microM) did not block withdrawal hyper-responsiveness. On washout, the mean NMDA-evoked current area was 124+/-6% of control (n=5, P<0.05). 8 Two broad-spectrum specific protein kinase C (PKC) inhibitors, GF-109203X (0.3 microM) and chelerythrine chloride (0.5-2 nM), blocked withdrawal hyper-responsiveness. Responses on washout were 108+/-7%, n=5 and 88+/-4%, n=4 of control, respectively, P>0.05. 9 NMDA activation during EtOH exposure is necessary for withdrawal hyper-responsiveness. Both tyrosine kinase and PKC, but not PKA, appear to be essential for EtOH withdrawal hyper-responsiveness mediated by postsynaptic NMDA receptors in spinal cord motor neurons.

Human immunodeficiency virus type 1 gp120 and ethanol coexposure in rat organotypic brain slice cultures: Curtailment of gp120-induced neurotoxicity and neurotoxic mediators by moderate but not high ethanol concentrations

Human immunodeficiency virus type 1 (HIV-1) envelope protein gp120, implicated with other retroviral proteins in acquired immunodeficiency syndrome (AIDS)-related dementia, causes neuronal degeneration by inciting cascades of neurotoxic mediators from glia. It also may facilitate neuronal glutamate (N-methyl-D-aspartate, NMDA) receptor-mediated excitotoxicity by interacting at the glycine coagonist site. The authors reported that preconditioning rat organotypic hippocampal-cortical slice cultures subchronically with ethanol at concentrations occurring during moderate drinking (20 to 30 mM) prevented gp120's induction of neurotoxic mediators and intracellular calcium, as well as neuronal death. The authors now find that the acute copresence of ethanol in moderate as opposed to high concentrations similarly blocks the retroviral protein's neurotoxic effects in brain slice cultures, assessed with lactate dehydrogenase (LDH) release and propidium iodide (PI) labeling. As with ethanol preconditioning, neuroprotection against gp120 by moderate ethanol coexposure appears secondary to abrogation of the retroviral protein's early induction of arachidonic acid (AA), glutamate, and superoxide (but not nitric oxide) elevations/release. Additionally, experiments indicate that 30 mM ethanol is sufficient to inhibit the NMDA receptor, particularly in the presence of added glycine, thus hindering potential direct neuronal stimulation by gp120. However, in contrast to moderate ethanol, 100 mM ethanol, a concentration tolerated only in chronic alcoholics, potentiates gp120-dependent neurotoxicity (PI labeling) in the hippocampal CA1 region, augments LDH release, and fails to curtail gp120's actions on AA, glutamate, and superoxide-but does suppress nitric oxide induction. The results indicate dominant roles for AA, superoxide, and glutamate-mediated oxidative stress in gp120's neurotoxic mechanism, but perhaps a less important role for NMDA receptor stimulation, which would be constrained at both ethanol concentrations employed. We suggest that ethanol's concentration-dependent, two-edged sword behavior could alter the development of dementia in HIV-1-infected individuals during social consumption or abuse. Further studies are needed to elucidate the differing apparently glial effects of the two concentrations of ethanol.

Role of GABA abnormalities in the inferior colliculus pathophysiology - audiogenic seizures

gamma-Aminobutyric acid (GABA), acting at GABA(A) receptors, mediates inhibition in inferior colliculus (IC) central nucleus (ICc) neurons and plays a prominent role in mediating acoustically evoked non-monotonicity, offset inhibition, and binaural inhibition, and is also important in tonic inhibition. The IC plays an important role in a number of pathophysiological conditions that involve hearing, including tinnitus, age-related hearing loss, and audiogenic seizures (AGS). AGS are a major form of rodent neurological disorder that can be genetically mediated and can also be readily induced in both young and mature animals. A deficit in GABA-mediated inhibition in IC neurons has been shown to be a critical mechanism in genetic and induced forms of AGS. Thus, both endogenously evoked GABA-mediated inhibition and exogenously applied GABA are reduced in efficacy in IC neurons of rats that are susceptible to AGS. GABA-mediated inhibition in IC neurons is significantly more easily blocked by a GABA(A) antagonist in genetic and induced forms of AGS in vivo and in vitro. AGS can be induced in normal animals by treatments that reduce the effectiveness of GABA in the IC. Glutamate-mediated excitation is a critical element of neurotransmission in IC neurons, and excessive activation of glutamate receptors in the IC is also strongly implicated as the other major mechanism in the pathophysiology of AGS. These neurotransmitter abnormalities result in excessive firing of ICc neurons that acts as the critical initiation mechanism for triggering seizures in response to intense acoustic stimuli.

Neurodevelopmental liabilities in alcohol dependence: central serotonin and dopamine dysfunction

Alcoholism is a complex disorder with symptoms ranging from abuse to dependence, often comorbid with depression, antisocial personality, or anxiety. Neurodevelopmental causes of the disorder are unknown but inferences are possible from current knowledge. Neurobiological studies implicate multiple brain changes, which may be characterized as premorbid or morbid. These studies have also examined specific aspects of the alcohol dependence syndrome, including alcohol reinforcement and craving. Here, we review the evidence for vulnerability factors in alcohol dependence, with an emphasis on central serotonin (5-HT) and dopamine (DA). Serotonin dysfunction likely contributes to the development of alcoholism since studies of alcohol-preferring rodents show decreased 5-HT function on many measures. We have shown that serotonin-enhancing drugs reduce consumption and craving in mild to moderate alcoholics, yet similar studies in severely dependent individuals remain inconclusive. Studies indicate that serotonin dysfunction may contribute to the development of dependence via impaired impulse control and/or mood regulation. The mesocorticolimbic dopamine pathway represents another important pathophysiological target in alcoholism. Differences in D(2) receptor density, dopamine sensitivity, and gene expression have been linked to consumption, reinforcement, craving, and relapse. However, while DA agonists reduce self-administration in animals, we found no effect in humans with long-acting bromocriptine, a D(2) agonist. Dopamine may contribute differentially to the development of dependence via its effects on alcohol wanting, reinforcement, and reward memory. Although animal experiments show consistent roles for serotonin and dopamine in alcohol dependence, human studies are not always concordant. Such discrepancies highlight the complexity of dependence-related behaviors in humans and of identifying vulnerabilities to alcoholism.

Effects of acamprosate and some polyamine site ligands of NMDA receptor on short-term memory in rats

The aim of this study was to evaluate the effect of multiple acamprosate (500.0 mg/kg, p.o.) administration on short-term memory, using the social recognition test in rats. Ifenprodil (1.0 mg/kg, i.p.), arcaine (5.0 mg/kg, i.p.) and spermidine (20.0 mg/kg, i.p.) were chosen as polyamine ligands and their action or interaction with acamprosate was also studied. The doses used did not show any sedative activity, which was assessed by measuring locomotor activity and the hypnotic effect of ethanol. The findings suggest that acute acamprosate treatment did not impair short-term memory. Multiple acamprosate and a single spermidine or arcaine administration led to better performance in the memory test, whereas no significant difference was observed in ifenprodil-treated rats. Co-administration of a single arcaine or spermidine dose with multiple acamprosate produced worse results. This means that the effect of repeated acamprosate administration can be changed by the co-administration of other polyamine ligands, so that care should be taken in interpreting.

The "French Paradox" and beyond: neuroprotective effects of polyphenols

Chronic ethanol ingestion is known to cause oxidative damage to a number of organs including the brain. This is partly due to the ability of ethanol to enhance oxygen free radical production and lipid peroxidation. Increase in oxidative stress has been regarded as an important underlying factor for a number of human health problems including cardiovascular diseases, aging, as well as many age-related neurodegenerative diseases. The strikingly low incidences of coronary heart diseases (CHD) in France, despite intake of a high-fat diet, have been attributed to the consumption of red wine containing high levels of polyphenolic compounds. In recent years, understanding the "French Paradox" has stimulated new research interest to investigate whether polyphenolic antioxidants may offer protective effects beyond the cardiovascular system, and whether polyphenols from other botanical sources may similarly offer beneficial effects to human health. Our studies with animal models have provided information clearly indicating the ability of grape polyphenols to ameliorate neuronal damages due to chronic ethanol consumption. Studies with resveratrol, an important component of grape polyphenols, also show protective effects on neuron cell death induced by ethanol and other oxidative agents. These studies demonstrate an urgent need to extend research beyond the "French Paradox" towards better understanding molecular mechanisms of action of polyphenolic compounds and their application to human health.

Inhibition of N-methyl-D-aspartic acid-nitric oxide synthase in rat hippocampal slices by ethanol. Evidence for the involvement of tetrahydrobiopterin but not lipid peroxidation

The ionotropic glutamatergic receptor system, especially the subtype mediated by N-methyl-D-aspartic acid (NMDA), is known to exhibit special sensitivity to the effect of ethanol. This is due partly to the ability of ethanol to modulate the production of nitric oxide through the NMDA-nitric oxide synthase (NOS) pathway. In this study, we examined the effects of ethanol on basal and NMDA-stimulated NOS activity in rat hippocampal slices by measuring the conversion of [(14)C]-arginine into [(14)C]-citrulline in an incubation system containing the necessary cofactors. Stimulation of hippocampal slices with NMDA (100 microM) enhanced NOS activity by 43% (n = 12). Although ethanol did not alter NOS activity when added to the incubation system during NMDA stimulation, it dose-dependently inhibited NMDA-NOS activity when added to the slices during the 90-min preincubation period. Further assay of NOS activity with brain cytosolic fraction indicated an inhibitory effect of ethanol (200 mM) when the assay was carried out in the absence of exogenous tetrahydrobiopterin (BH4), a redox-active cofactor for NOS. Incubation of brain homogenates resulted in a time-dependent increase in the levels of lipid peroxidation products, but ethanol did not further enhance these products. Taken together, these results provide evidence for the role of BH4 but not oxidative stress in the inhibitory effect of ethanol on NMDA-NOS activity in rat hippocampal slices.

Neurons in the deep layers of superior colliculus are a requisite component of the neuronal network for seizures during ethanol withdrawal

Ethanol withdrawal (ETX) in ethanol-dependent animals and humans often results in seizure susceptibility. The deep layers of superior colliculus (DLSC) are proposed to be involved in the neuronal networks of several types of seizures. In rodents, ETX results in susceptibility to audiogenic seizures (AGS), and the DLSC are implicated as a critical component of the seizure network in a genetic form of AGS. Ethanol inhibits NMDA receptors, and the binding at these receptors is increased during ETX in certain brain regions. Therefore, the effect of focal microinjection into DLSC of a competitive NMDA receptor antagonist, DL-2-amino-7-phosphonoheptanoic acid (AP7) on ETX seizures was examined. AP7 (2 and 5 nmol/side) microinjected bilaterally into DLSC suppressed AGS, supporting a critical role of the DLSC in the AGS network during ETX. DLSC neuronal firing changes in behaving rats were subsequently examined, using chronically implanted microwire electrodes. Acoustically-evoked DLSC firing was significantly suppressed during ethanol intoxication and during ETX. However, DLSC neurons began firing tonically 1-2 s before the onset of the wild running behavior of AGS. Acoustically-evoked DLSC firing was suppressed during post-ictal depression with recovery beginning as the righting reflex returned. These data support a requisite role of the DLSC in AGS during ETX. These neuronal firing changes suggest an important role of DLSC neurons in generation of the wild running phase of AGS during ETX, which may be a general pathophysiological mechanism and a critical event in the initiation of wild running, since a similar pattern was seen previously in a genetic form of AGS.