Neurosteroids, GABAA receptors, and ethanol dependence

Post-Finasteride Syndrome And Post-Ssri Sexual Dysfunction: Two Clinical Conditions Apparently Distant, But Very Close

Post-finasteride syndrome and post-SSRI sexual dysfunction, are two poorly explored clinical conditions in which men treated for androgenetic alopecia with finasteride or for depression with SSRI antidepressants show persistent side effects despite drug suspension (e.g., sexual dysfunction, psychological complaints, sleep disorders). Because of some similarities in the symptoms, common pathological mechanisms are proposed here. Indeed, as discussed, clinical studies and preclinical data obtained so far suggest an important role for brain modulators (i.e., neuroactive steroids), neurotransmitters (i.e., serotonin, and cathecolamines), and gut microbiota in the context of the gut-brain axis. In particular, the observed interconnections of these signals in these two clinical conditions may suggest similar etiopathogenetic mechanisms, such as the involvement of the enzyme converting norepinephrine into epinephrine (i.e., phenylethanolamine N-methyltransferase). However, despite the current efforts, more work is still needed to advance the understanding of these clinical conditions in terms of diagnostic markers and therapeutic strategies.

Effect of chronic unpredictable stress in female Wistar-Kyoto rats subjected to progesterone withdrawal: Relevance for Premenstrual Dysphoric Disorder neurobiology

Premenstrual Dysphoric Disorder (PMDD) is related to an abrupt drop in progesterone and impairments in the HPA axis that cause anxiety. Suffering persons report higher daily-life stress and anxiety proneness that may contribute to developing PMDD, considered a chronic stress-related disorder. Here, we explored the effect of chronic unpredictable stress (CUS) in rats subjected to progesterone withdrawal (PW) and evaluated gene expression of HPA axis activation in the stress-vulnerable Wistar-Kyoto (WKY) rat strain that is prone to anxiety. Ovariectomized WKY rats were randomly assigned to CUS or Standard-housed conditions (SHC) for 30 days. To induce PW, animals received 2 mg/kg of progesterone on day 25th for 5 days; 24 h later, they were tested using the anxiety-like burying behavior test (BBT). After behavioral completion, rats were euthanized, and brains were extracted to measure Crh (PVN) and Nr3c1 (hippocampus) mRNA. Blood corticosterone and vasopressin levels were determined. Results showed that PW exacerbated anxiety-like behaviors through passive coping in CUS-WKY. PW decreased Crh-PVN mRNA and the Nr3c1-hippocampal mRNA expression in SHC. CUS decreased Crh-PVN mRNA compared to SHC, and no further changes were observed by PW or BBT exposure. CUS reduced Nr3c1-hippocampal gene expression compared to SHC animals, and lower Nr3c1 mRNA was detected due to BBT. The PW increased corticosterone in SHC and CUS rats; however, CUS blunted corticosterone when combined with PW+BBT and similarly occurred in vasopressin concentrations. Chronic stress blunts the response of components of the HPA axis regulation when PW and BBT (systemic and psychogenic stressors, respectively) are presented. This response may facilitate less adaptive behaviors through passive coping in stress-vulnerable subjects in a preclinical model of premenstrual anxiety.

Epigenetic Regulation of GABAergic Neurotransmission and Neurosteroid Biosynthesis in Alcohol Use Disorder

BACKGROUND

Alcohol use disorder (AUD) is a chronic relapsing brain disorder. GABAA receptor (GABAAR) subunits are a target for the pharmacological effects of alcohol. Neurosteroids play an important role in the fine-tuning of GABAAR function in the brain. Recently, we have shown that AUD is associated with changes in DNA methylation mechanisms. However, the role of DNA methylation in the regulation of neurosteroid biosynthesis and GABAergic neurotransmission in AUD patients remains under-investigated.

METHODS

In a cohort of postmortem brains from 20 male controls and AUD patients, we investigated the expression of GABAAR subunits and neurosteroid biosynthetic enzymes and their regulation by DNA methylation mechanisms. Neurosteroid levels were quantified by gas chromatography-mass spectrometry.

RESULTS

The α 2 subunit expression was reduced due to increased DNA methylation at the gene promoter region in the cerebellum of AUD patients, a brain area particularly sensitive to the effects of alcohol. Alcohol-induced alteration in GABAAR subunits was also observed in the prefrontal cortex. Neurosteroid biosynthesis was also affected with reduced cerebellar expression of the 18kDa translocator protein and 3α-hydroxysteroid dehydrogenase mRNAs. Notably, increased DNA methylation levels were observed at the promoter region of 3α-hydroxysteroid dehydrogenase. These changes were associated with markedly reduced levels of allopregnanolone and pregnanolone in the cerebellum.

CONCLUSION

Given the key role of neurosteroids in modulating the strength of GABAAR-mediated inhibition, our data suggest that alcohol-induced impairments in GABAergic neurotransmission might be profoundly impacted by reduced neurosteroid biosynthesis most likely via DNA hypermethylation.

Phenobarbital Monotherapy for the Management of Alcohol Withdrawal Syndrome in Surgical-Trauma Patients

BACKGROUND

Benzodiazepine is first-line therapy for alcohol withdrawal syndrome (AWS), and phenobarbital is an alternative therapy. However, its use has not been well validated in the surgical-trauma patient population.

OBJECTIVE

To describe the use of fixed-dose phenobarbital monotherapy for the management of patients at risk for AWS in the surgical-trauma intensive care unit.

METHODS

Surgical-trauma critically ill patients who received phenobarbital monotherapy, loading dose followed by a taper regimen, for the management of AWS were included in this evaluation. The effectiveness of phenobarbital monotherapy to treat AWS and prevent development of AWS-related complications were evaluated. Safety end points assessed included significant hypotension, bradycardia, respiratory depression, and need for invasive mechanical ventilation.

RESULTS

A total of 31 patients received phenobarbital monotherapy; the majority of patients were at moderate risk for developing AWS (n = 20; 65%) versus high risk (n = 11; 35%). None of the patients developed AWS-related complications; all patients were successfully managed for their AWS. Nine patients (29%) received nonbenzodiazepine adjunct therapy for agitation post-phenobarbital initiation. Three patients (10%) experienced hypotension, and 3 (10%) were intubated. None of the patients had clinically significant bradycardia or respiratory depression.

CONCLUSION AND RELEVANCE

Fixed-dose phenobarbital monotherapy appears to be well tolerated and effective in the management of AWS. Further evaluation is needed to determine the extent of benefit with the use of phenobarbital monotherapy for management of AWS.

Differential effects of ethanol on behavior and GABAA receptor expression in adult zebrafish (Danio rerio) with alternative stress coping styles

Variation in stress responses between individuals are linked to factors ranging from stress coping styles to sensitivity of neurotransmitter systems. Many anxiolytic compounds (e.g. ethanol) can increase stressor engagement through modulation of neurotransmitter systems and are used to investigate stress response mechanisms. There are two alternative suites of correlated behavioral and physiological responses to stressors (stress coping styles) that differ in exploration tendencies: proactive and reactive stress coping styles. By chronically treating individuals differing in stress coping style with ethanol, a GABA-acting drug, we assessed the role of the GABAergic system on the behavioral stress response. Specifically, we investigated resulting changes in stress-related behavior (i.e. exploratory behavior) and whole-brain GABAA receptor subunits (gabra1, gabra2, gabrd, & gabrg2) in response to a novelty stressor. We found that ethanol-treated proactive individuals showed lower stress-related behaviors than their reactive counterparts. Proactive individuals showed significantly higher expression of gabra1, gabra2, and gabrg2 compared to reactive individuals and ethanol treatment resulted in upregulation of gabra1 and gabrg2 in both stress coping styles. These results suggest that impacts of ethanol on stress-related behaviors vary by stress coping style and that expression of select GABAA receptor subunits may be one of the underlying mechanisms.

Alcohol use disorder and sleep disturbances: a feed-forward allostatic framework

The development of alcohol use disorder (AUD) involves binge or heavy drinking to high levels of intoxication that leads to compulsive intake, the loss of control in limiting intake, and a negative emotional state when alcohol is removed. This cascade of events occurs over an extended period within a three-stage cycle: binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation. These three heuristic stages map onto the dysregulation of functional domains of incentive salience/habits, negative emotional states, and executive function, mediated by the basal ganglia, extended amygdala, and frontal cortex, respectively. Sleep disturbances, alterations of sleep architecture, and the development of insomnia are ubiquitous in AUD and also map onto the three stages of the addiction cycle. During the binge/intoxication stage, alcohol intoxication leads to a faster sleep onset, but sleep quality is poor relative to nights when no alcohol is consumed. The reduction of sleep onset latency and increase in wakefulness later in the night may be related to the acute effects of alcohol on GABAergic systems that are associated with sleep regulation and the effects on brain incentive salience systems, such as dopamine. During the withdrawal/negative affect stage, there is a decrease in slow-wave sleep and some limited recovery in REM sleep when individuals with AUD stop drinking. Limited recovery of sleep disturbances is seen in AUD within the first 30 days of abstinence. The effects of withdrawal on sleep may be related to the loss of alcohol as a positive allosteric modulator of GABAA receptors, a decrease in dopamine function, and the overactivation of stress neuromodulators, including hypocretin/orexin, norepinephrine, corticotropin-releasing factor, and cytokines. During the preoccupation/anticipation stage, individuals with AUD who are abstinent long-term present persistent sleep disturbances, including a longer latency to fall asleep, more time awake during the night, a decrease in slow-wave sleep, decreases in delta electroencephalogram power and evoked delta activity, and an increase in REM sleep. Glutamatergic system dysregulation that is observed in AUD is a likely substrate for some of these persistent sleep disturbances. Sleep pathology contributes to AUD pathology, and vice versa, possibly as a feed-forward drive to an unrecognized allostatic load that drives the addiction process.

Genotype Differences in Sensitivity to the Anticonvulsant Effect of the Synthetic Neurosteroid Ganaxolone during Chronic Ethanol Withdrawal

Sensitivity to anticonvulsant effects of the γ-aminobutyric acid_A receptor-active neurosteroid allopregnanolone (ALLO) during ethanol withdrawal varies across genotypes, with high sensitivity in genotypes with mild withdrawal and low sensitivity in genotypes with high withdrawal. The present studies determined whether the resistance to ALLO during withdrawal in mouse genotypes with high handling-induced convulsions (HICs) during withdrawal could be overcome with use of ganaxolone (GAN), the metabolically stable derivative of ALLO. In separate studies, male and female Withdrawal Seizure-Prone (WSP-1) and DBA/2J (D2) mice were exposed to air (controls) or 72-h ethanol vapor and then were scored for HICs during withdrawal (hourly for the first 12 h, then at hours 24 and 25). After the HIC scoring at hours 5 and 9, mice were injected with 10 mg/kg GAN or vehicle. Area under the HIC curve (AUC) for hours 5-12 was analyzed. In control WSP-1 mice, GAN significantly reduced AUC by 52% (males) and 63% (females), with effects that were absent or substantially reduced during withdrawal. In contrast, GAN significantly reduced AUC in both control and ethanol-withdrawing male and female D2 mice. AUC was decreased by 81% (males) and 70% (females) in controls and by 35% (males) and 21% (females) during withdrawal. The significant anticonvulsant effect of GAN during withdrawal in D2 but not WSP-1 mice suggests that different mechanisms may contribute to ALLO insensitivity during withdrawal in these two genotypes. Importantly, the results in D2 mice suggest that GAN may be a useful treatment for ethanol withdrawal-induced seizures.

Missense Gamma-Aminobutyric Acid Receptor Polymorphisms Are Associated with Reaction Time, Motor Time, and Ethanol Effects in Vivo

Background: The Gamma-aminobutyric acid type A receptor (GABA-A receptor) is affected by ethanol concentrations equivalent to those reached during social drinking. At these concentrations, ethanol usually causes impairment in reaction and motor times in most, but not all, individuals.

Objectives: To study the effect of GABA-A receptor variability in motor and reaction times, and the effect of low ethanol doses.

Methods: Two hundred and fifty healthy subjects received one single dose of 0.5 g/Kg ethanol per os. Reaction and motor times were determined before ethanol challenge (basal), and when participants reached peak ethanol concentrations. We analyzed all common missense polymorphisms described in the 19 genes coding for the GABA-A receptor subunits by using TaqMan probes.

Results: The GABRA6 rs4454083 T/C polymorphisms were related to motor times, with individuals carrying the C/C genotype having faster motor times, both, at basal and at peak ethanol concentrations. The GABRA4 rs2229940 T/T genotype was associated to faster reaction times and with lower ethanol effects, determined as the difference between basal reaction time and reaction time at peak concentrations. All these associations remained significant after correction for multiple comparisons. No significant associations were observed for the common missense SNPs GABRB3 rs12910925, GABRG2 rs211035, GABRE rs1139916, GABRP rs1063310, GABRQ rs3810651, GABRR1 rs12200969 or rs1186902, GABRR2 rs282129, and GABRR3 rs832032.

Conclusions: This study provides novel information supporting a role of missense GABA-A receptor polymorphisms in reaction time, motor time and effects of low ethanol doses in vivo.

Gonadal hormones affect alcohol drinking, but not cue+yohimbine-induced alcohol seeking, in male and female rats

Alcohol use disorder (AUD) is a chronic, relapsing disease characterized by maladaptive patterns of alcohol drinking and seeking. Though sex differences exist in the etiology of AUD, much remains to be elucidated concerning the mechanisms underlying sex-related vulnerability to developing excessive alcohol-motivated behavior. While a large body of evidence points to an important role of circulating gonadal hormones in mediating cocaine reinforcement, findings are less consistent with respect to ethanol. Critically, the effects of gonadal hormones on the reinstatement of ethanol seeking, a model of "craving"-like behavior that reveals pronounced sex differences, has not yet been examined. Thus, the goal of the present experiment was to directly compare manipulations of gonadal hormones in male and female rats on ethanol-motivated behavior. Rats received sham or gonadectomy surgery with or without hormone replacement prior to and throughout three weeks of operant ethanol self-administration to determine the effects of chronically high or low gonadal hormone levels on ethanol drinking. Hormone treatment ceased during extinction training, and the effects of an acute injection of either testosterone (in males) or estradiol (in females) on cue+yohimbine-induced reinstatement of ethanol seeking was determined. Separate groups of gonadally-intact female rats went through similar training, but the effects of either the antiestrogen, fulvestrant, the selective estrogen receptor modulator, clomiphene, or the estrogen receptor β antagonist, PHTPP, on the reinstatement of ethanol seeking were determined. Chronic estradiol replacement produced significant increases in ethanol drinking in female rats, while chronic testosterone significantly decreased ethanol drinking in male rats. Gonadectomy alone only produced modest shifts in drinking towards the opposite-sex pattern, and did not eliminate the robust sex differences that persisted regardless of hormone manipulations. Neither prior chronic nor acute hormone manipulations altered cue+yohimbine-induced reinstatement of ethanol seeking, though blockade of estrogen receptors tended to reduce reinstatement in gonadally-intact females. Overall, our findings indicate that gonadal hormones at least partially mediate, but do not totally account for the sex differences evident in ethanol self-administration, and circulating gonadal hormones have little effect on the reinstatement of ethanol seeking. These results provide a foundation for future studies examining the neuronal mechanisms underlying sex differences in ethanol drinking and seeking.

Effect of Peripheral μ-, δ-, and κ-Opioid Ligands on the Development of Tolerance to Ethanol-Induced Analgesia

We studied the rate of development of tolerance to the ethanol-induced analgesia under the effect of μ-, δ-, and κ-opioid agonists and antagonists not crossing the blood-brain barrier and rapidly inactivated by gastric and duodenal proteolytic enzymes. Activation of gastric κ-opioid receptors eliminated the analgesic effect of ethanol and accelerated the development of tolerance to ethanol-induced analgesia. In contrast, activation of gastric μ-opioid receptors decelerated the development of this tolerance. Activation of gastric δ-opioid receptors produced no effect on examined tolerance. μ-Opioid receptor antagonist decelerated and δ-opioid receptor antagonist accelerated the development of tolerance to ethanol-induced analgesia. Thus, the state of gastric opioid receptors affects the manifestation of ethanol-induced analgesia and the development of tolerance to this effect.

Voluntary ethanol consumption reduces GABAergic neuroactive steroid (3α,5α)3-hydroxypregnan-20-one (3α,5α-THP) in the amygdala of the cynomolgus monkey

Neuroactive steroids such as (3α,5α)3-hydroxypregnan-20-one (3α,5α-THP, allopregnanolone) enhance the gamma-aminobutyric acid (GABA)-ergic effects of ethanol and modulate excessive drinking in rodents. Moreover, chronic ethanol consumption reduces 3α,5α-THP levels in human plasma, rat hippocampus and mouse limbic regions. We explored the relationship between 3α,5α-THP levels in limbic brain areas and voluntary ethanol consumption in the cynomolgus monkey following daily self-administration of ethanol for 12 months and further examined the relationship to hypothalamic-pituitary-adrenal (HPA) axis function prior to ethanol exposure. Monkeys were subjected to scheduled induction of ethanol consumption followed by free access to ethanol or water for 22 h/day over 12 months. Immunohistochemistry was performed using an anti-3α,5α-THP antibody. Prolonged voluntary drinking resulted in individual differences in ethanol consumption that ranged from 1.2 to 4.2 g/kg/day over 12 months. Prolonged ethanol consumption reduced cellular 3α,5α-THP immunoreactivity by 13 ± 2 percent (P < 0.05) in the lateral amygdala and 17 ± 2 percent (P < 0.05) in the basolateral amygdala. The effect of ethanol was most pronounced in heavy drinkers that consumed ≥3 g/kg ≥ 20 percent of days. Consequently, 3α,5α-THP immunoreactivity in both the lateral and basolateral amygdala was inversely correlated with average daily ethanol intake (Spearman r = -0.87 and -0.72, respectively, P < 0.05). However, no effect of ethanol and no correlation between drinking and 3α,5α-THP immunoreactivity were observed in the basomedial amygdala. 3α,5α-THP immunoreactivity following ethanol exposure was also correlated with HPA axis function prior to ethanol exposure. These data indicate that voluntary ethanol drinking reduces amygdala levels of 3α,5α-THP in non-human primates and that amygdala 3α,5α-THP levels may be linked to HPA axis function.

Cellular GABAergic Neuroactive Steroid (3α,5α)-3-Hydroxy-Pregnan-20-One (3α,5α-THP) Immunostaining Levels Are Increased in the Ventral Tegmental Area of Human Alcohol Use Disorder Patients: A Postmortem Study

BACKGROUND

The GABAergic neuroactive steroid (3α,5α)-3-hydroxy-pregnan-20-one (3α,5α-THP; allopregnanolone) enhances GABAergic activity and produces subjective effects similar to ethanol (EtOH). The effect of chronic alcohol exposure on 3α,5α-THP concentrations has been studied in mouse, rat, and monkey limbic brain areas. Chronic EtOH exposure produced divergent brain region and cell-specific changes in 3α,5α-THP concentrations in animal studies. However, 3α,5α-THP levels in similar human brain regions have never been examined in individuals diagnosed with alcohol use disorder (AUD). Therefore, we used immunohistochemistry (IHC) to examine 3α,5α-THP levels in the ventral tegmental area (VTA), substantia nigra pars medialis (SNM), and amygdala of human postmortem brains of patients diagnosed with AUD compared with social drinkers. The effects of sex and liver disease on 3α,5α-THP concentrations were examined in the aforementioned brain regions.

METHODS

Human postmortem brains of AUD patients and age-matched controls were obtained from the New South Wales Brain Tissue Resource Center. IHC was performed using anti-3α,5α-THP antibody on formalin-fixed paraffin-embedded brain sections to detect cellular 3α,5α-THP levels. Immunoreactivity was analyzed by pixel density/mm² for the comparison between AUD patients and controls.

RESULTS

3α,5α-THP immunoreactivity was increased by 23.2 ± 9% in the VTA of AUD patients compared with age-matched controls (p = 0.014). Moreover, a 29.6 ± 10% increase in 3α,5α-THP immunoreactivity was observed in the SNM of male AUD patients compared with male controls (p < 0.01), but not in female subjects. 3α,5α-THP immunoreactivity in the VTA and SNM regions did not differ between noncirrhotic and cirrhotic AUD patients. A sex difference in 3α,5α-THP immunoreactivity (female 51 ± 18% greater than male) was observed among control subjects in the SNM, but no other brain region. 3α,5α-THP immunoreactivity in the basolateral amygdala and lateral amygdala was negatively correlated with the length of the tissue fixation time as well as the age of the subjects, precluding assessment of the effect of AUD.

CONCLUSIONS

Cellular 3α,5α-THP levels in VTA are increased in human AUD patients, an effect that is likely independent of sex and liver disease. The differences between animal models and human studies should be factored into the interpretation of the physiological significance of elevated 3α,5α-THP levels in humans.

Nicotine and Nicotine Abstinence Do Not Interfere with GABAA Receptor Neuroadaptations During Alcohol Abstinence

BACKGROUND

Alcohol dependence and tobacco smoking are highly comorbid, and treating both conditions simultaneously is controversial. Previously, we showed that tobacco smoking interferes with GABAA receptor neuroadaptations during alcohol withdrawal in humans, while this effect did not occur with continued nicotine use during alcohol abstinence in nonhuman primates. Here, we extend our previous work by measuring GABAA receptor availability with positron emission tomography (PET) during drug abstinence in nonhuman primates exposed to alcohol alone, nicotine and alcohol together, and alcohol abstinence with continued nicotine exposure.

METHODS

Twenty-four adolescent male rhesus macaques orally self-administered alcohol and nicotine, available separately in water and saccharin, over 20 weeks. The groups included alcohol alone (n = 8); nicotine and alcohol with simultaneous abstinence (n = 8); nicotine and alcohol with alcohol abstinence while nicotine was still available (n = 8); and a pilot group of animals consuming nicotine alone (n = 6). Animals were imaged with [(11)C]flumazenil PET to measure binding potential (BPND), an index of GABAA receptor availability. Imaging occurred at baseline (drug-naíve), and following alcohol and/or nicotine cessation at 1 day, 8 days, and 12 weeks of abstinence. Generalized linear mixed models were used to examine the time course of [(11)C]flumazenil BPND during alcohol abstinence across groups.

RESULTS

Animals consumed 3.95 ± 1.22 g/kg/d alcohol and 55.4 ± 35.1 mg/kg/d nicotine. No significant group effects were observed in [(11)C]flumazenil BPND during alcohol abstinence; however, a main effect of time was detected. Post hoc analyses indicated that all groups abstaining from alcohol exhibited significantly increased GABAA receptor availability at 1 day and 8 days (but not 12 weeks) of abstinence relative to baseline, while no changes in [(11)C]flumazenil BPND during nicotine abstinence alone were observed.

CONCLUSIONS

These data indicate that neither nicotine nor nicotine abstinence interferes with GABAA receptor neuroadaptations during alcohol withdrawal. This conclusion is consistent with our previous study and does not contradict the use of nicotine replacement therapies or non-nicotinic-acting pharmaceuticals to quit smoking during alcohol withdrawal from a GABAergic perspective.

Functional Connectivity and Quantitative EEG in Women with Alcohol Use Disorders: A Resting-State Study

This study was aimed at exploring the electroencephalographic features associated with alcohol use disorders (AUD) during a resting-state condition, by using quantitative EEG and Functional Connectivity analyses. In addition, we explored whether EEG functional connectivity is associated with trait impulsivity. Absolute and relative powers and Synchronization Likelihood (SL) as a measure of functional connectivity were analyzed in 15 AUD women and fifteen controls matched in age, gender and education. Correlation analysis between self-report impulsivity as measured by the Barratt impulsiveness Scale (BIS-11) and SL values of AUD patients were performed. Our results showed increased absolute and relative beta power in AUD patients compared to matched controls, and reduced functional connectivity in AUD patients predominantly in the beta and alpha bands. Impaired connectivity was distributed at fronto-central and occipito-parietal regions in the alpha band, and over the entire scalp in the beta band. We also found that impaired functional connectivity particularly in alpha band at fronto-central areas was negative correlated with non-planning dimension of impulsivity. These findings suggest that functional brain abnormalities are present in AUD patients and a disruption of resting-state EEG functional connectivity is associated with psychopathological traits of addictive behavior.

How Imaging Glutamate, γ-Aminobutyric Acid, and Dopamine Can Inform the Clinical Treatment of Alcohol Dependence and Withdrawal

Neuroimaging studies have dramatically advanced our understanding of the neurochemical basis of alcohol dependence, a major public health issue. In this paper, we review the research generated from neurochemical specific imaging modalities including magnetic resonance spectroscopy, positron emission tomography, and single-photon emission computed tomography in studies of alcohol dependence and withdrawal. We focus on studies interrogating γ-aminobutyric acid (GABA), glutamate, and dopamine, as these are prominent neurotransmitter systems implicated in alcohol dependence. Highlighted findings include diminished dopaminergic functioning and modulation of the GABA system by tobacco smoking during alcohol withdrawal. Then, we consider how these findings impact the clinical treatment of alcohol dependence and discuss directions for future experiments to address existing gaps in the literature, for example, sex differences and smoking comorbidity. These and other considerations provide opportunities to build upon the current neurochemistry imaging literature of alcohol dependence and withdrawal, which may usher in improved therapeutic and relapse prevention strategies.

Alcohol and violence: neuropeptidergic modulation of monoamine systems

Neurobiological processes underlying the epidemiologically established link between alcohol and several types of social, aggressive, and violent behavior remain poorly understood. Acute low doses of alcohol, as well as withdrawal from long-term alcohol use, may lead to escalated aggressive behavior in a subset of individuals. An urgent task will be to disentangle the host of interacting genetic and environmental risk factors in individuals who are predisposed to engage in escalated aggressive behavior. The modulation of 5-hydroxytryptamine impulse flow by gamma-aminobutyric acid (GABA) and glutamate, acting via distinct ionotropic and metabotropic receptor subtypes in the dorsal raphe nucleus during alcohol consumption, is of critical significance in the suppression and escalation of aggressive behavior. In anticipation and reaction to aggressive behavior, neuropeptides such as corticotropin-releasing factor, neuropeptide Y, opioid peptides, and vasopressin interact with monoamines, GABA, and glutamate to attenuate and amplify aggressive behavior in alcohol-consuming individuals. These neuromodulators represent novel molecular targets for intervention that await clinical validation. Intermittent episodes of brief social defeat during aggressive confrontations are sufficient to cause long-lasting neuroadaptations that can lead to the escalation of alcohol consumption.

Corticosterone enhances the potency of ethanol against hippocampal long-term potentiation via local neurosteroid synthesis

Corticosterone is known to accumulate in brain after various stressors including alcohol intoxication. Just as severe alcohol intoxication is typically required to impair memory formation only high concentrations of ethanol (60 mM) acutely inhibit long-term potentiation (LTP), a cellular memory mechanism, in naïve hippocampal slices. This LTP inhibition involves synthesis of neurosteroids, including allopregnanolone, and appears to involve a form of cellular stress. In the CA1 region of rat hippocampal slices, we examined whether a lower concentration of ethanol (20 mM) inhibits LTP in the presence of corticosterone, a stress-related modulator, and whether corticosterone stimulates local neurosteroid synthesis. Although low micromolar corticosterone alone did not inhibit LTP induction, we found that 20 mM ethanol inhibited LTP in the presence of corticosterone. At 20 mM, ethanol alone did not stimulate neurosteroid synthesis or inhibit LTP. LTP inhibition by corticosterone plus ethanol was blocked by finasteride, an inhibitor of 5α-reductase, suggesting a role for neurosteroid synthesis. We also found that corticosterone alone enhanced neurosteroid immunostaining in CA1 pyramidal neurons and that this immunostaining was further augmented by 20 mM ethanol. The enhanced neurosteroid staining was blocked by finasteride and the N-methyl-D-aspartate antagonist, 2-amino-5-phosphonovalerate (APV). These results indicate that corticosterone promotes neurosteroid synthesis in hippocampal pyramidal neurons and can participate in ethanol-mediated synaptic dysfunction even at moderate ethanol levels. These effects may contribute to the influence of stress on alcohol-induced cognitive impairment.

Chronic intermittent ethanol exposure and withdrawal alters (3α,5α)-3-hydroxy-pregnan-20-one immunostaining in cortical and limbic brain regions of C57BL/6J mice

BACKGROUND

The GABAergic neuroactive steroid (3α,5α)-3-hydroxy-pregnan-20-one (3α,5α-THP; allopregnanolone) has been studied during withdrawal from ethanol (EtOH) in humans, rats, and mice. Serum 3α,5α-THP levels decreased, and brain levels were not altered following acute EtOH administration (2 g/kg) in male C57BL/6J mice; however, the effects of chronic intermittent ethanol (CIE) exposure on 3α,5α-THP levels have not been examined. Given that CIE exposure changes subsequent voluntary EtOH drinking in a time-dependent fashion following repeated cycles of EtOH exposure, we conducted a time-course analysis of CIE effects on 3α,5α-THP levels in specific brain regions known to influence drinking behavior.

METHODS

Adult male C57BL/6J mice were exposed to 4 cycles of CIE to induce EtOH dependence. All mice were sacrificed and perfused at 1 of 2 time points, 8 or 72 hours following the final exposure cycle. Free-floating brain sections (40 μm; 3 to 5 sections/region/animal) were immunostained and analyzed to determine relative levels of cellular 3α,5α-THP.

RESULTS

Withdrawal from CIE exposure produced time-dependent and region-specific effects on immunohistochemical detection of 3α,5α-THP levels across cortical and limbic brain regions. A transient reduction in 3α,5α-THP immunoreactivity was observed in the central nucleus of the amygdala 8 hours after withdrawal from CIE (-31.4 ± 9.3%). Decreases in 3α,5α-THP immunoreactivity were observed 72 hours following withdrawal in the medial prefrontal cortex (-25.0 ± 9.3%), nucleus accumbens core (-29.9 ± 6.6%), and dorsolateral striatum (-18.5 ± 6.0%), while an increase was observed in the CA3 pyramidal cell layer of the hippocampus (+42.8 ± 19.5%). Sustained reductions in 3α,5α-THP immunoreactivity were observed at both time points in the lateral amygdala (8 hours -28.3 ± 12.8%; 72 hours -27.5 ± 12.4%) and in the ventral tegmental area (8 hours -26.5 ± 9.9%; 72 hours -31.6 ± 13.8%).

CONCLUSIONS

These data suggest that specific neuroadaptations in 3α,5α-THP levels may be present in regions of brain that mediate anxiety, stress, and reinforcement relevant to EtOH dependence. The changes that occur at different time points likely modulate neurocircuitry involved in EtOH withdrawal as well as the elevated drinking observed after CIE exposure.

Glycine and GABA(A) ultra-sensitive ethanol receptors as novel tools for alcohol and brain research

A critical obstacle to developing effective medications to prevent and/or treat alcohol use disorders is the lack of specific knowledge regarding the plethora of molecular targets and mechanisms underlying alcohol (ethanol) action in the brain. To identify the role of individual receptor subunits in ethanol-induced behaviors, we developed a novel class of ultra-sensitive ethanol receptors (USERs) that allow activation of a single receptor subunit population sensitized to extremely low ethanol concentrations. USERs were created by mutating as few as four residues in the extracellular loop 2 region of glycine receptors (GlyRs) or γ-aminobutyric acid type A receptors (GABA(A)Rs), which are implicated in causing many behavioral effects linked to ethanol abuse. USERs, expressed in Xenopus oocytes and tested using two-electrode voltage clamp, demonstrated an increase in ethanol sensitivity of 100-fold over wild-type receptors by significantly decreasing the threshold and increasing the magnitude of ethanol response, without altering general receptor properties including sensitivity to the neurosteroid, allopregnanolone. These profound changes in ethanol sensitivity were observed across multiple subunits of GlyRs and GABA(A)Rs. Collectively, our studies set the stage for using USER technology in genetically engineered animals as a unique tool to increase understanding of the neurobiological basis of the behavioral effects of ethanol.

Quantification of ten neuroactive steroids in plasma in Withdrawal Seizure-Prone and -Resistant mice during chronic ethanol withdrawal

RATIONALE

The rapid membrane actions of neuroactive steroids, particularly via an enhancement of γ-aminobutyric acidA receptors (GABAARs), participate in the regulation of central nervous system excitability. Prior evidence suggests an inverse relationship between endogenous GABAergic neuroactive steroid levels and behavioral changes in excitability during ethanol withdrawal.

OBJECTIVES

Previously, we found that ethanol withdrawal significantly decreased plasma allopregnanolone (ALLO) levels, a potent GABAergic neuroactive steroid, and decreased GABAAR sensitivity to ALLO in Withdrawal Seizure-Prone (WSP) but not in Withdrawal Seizure-Resistant (WSR) mice. However, the effect of ethanol withdrawal on levels of other endogenous GABAAR-active steroids is not known.

METHODS

After validation of a gas chromatography-mass spectrometry method for the simultaneous quantification of ten neuroactive steroids, we analyzed plasma from control male WSP-1 and WSR-1 mice and during ethanol withdrawal.

RESULTS

We quantified levels of nine neuroactive steroids in WSP-1 and WSR-1 plasma; levels of pregnanolone were not detectable. Basal levels of five neuroactive steroids were higher in WSR-1 versus WSP-1 mice. Ethanol withdrawal significantly suppressed five neuroactive steroids in WSP-1 and WSR-1 mice, including ALLO.

CONCLUSIONS

Due to lower basal levels of some GABAAR-active steroids in WSP-1 mice, a withdrawal-induced decrease in WSP-1 mice may have a greater physiological consequence than a similar decrease in WSR-1 mice. Because WSP-1 mice also exhibit a reduction in GABAAR sensitivity to neuroactive steroids during withdrawal, it is possible that the combined decrease in neuroactive steroids and GABAAR sensitivity during ethanol withdrawal in WSP-1 mice represents a neurochemical substrate for severe ethanol withdrawal.

5α-reductase type I expression is downregulated in the prefrontal cortex/Brodmann's area 9 (BA9) of depressed patients

RATIONALE

The implications of the neurosteroid 3α-hydroxy-5α-pregnan-20-one [allopregnanolone (Allo)] in neuropsychiatric disorders have been highlighted in several recent clinical investigations. For instance, Allo levels are decreased in the cerebrospinal fluid (CSF) of patients with posttraumatic stress disorder (PTSD) and major unipolar depression. Neurosteroidogenic antidepressants [i.e., selective brain steroidogenic stimulants (SBSSs)], including fluoxetine and analogs, correct this decrease in a manner that correlates with improved depressive symptoms. Allo positively and allosterically modulates GABA action at postsynaptic and extrasynaptic GABAA receptors. It is synthesized in both the human and rodent brain cortices by principal glutamatergic pyramidal neurons from progesterone by the sequential action of 5α-reductase type I (5α-RI), which is the rate-limiting step enzyme in Allo biosynthesis, and 3α-hydroxysteroid dehydrogenase (3α-HSD), which converts 5α-dehydroprogesterone into Allo.

HYPOTHESIS

We thus hypothesized that decreased CSF levels of Allo in depressed patients could reflect a brain dysfunction of 5α-RI.

METHODS

In a pilot study of samples from six patients per group [six depressed patients and six nonpsychiatric subjects (NPS)], we studied the expression of 5α-RI messenger RNA (mRNA) in prefrontal cortex Brodmann's area 9 (BA9) and cerebellum from depressed patients obtained from the Maryland Brain Collection at the Maryland Psychiatric Research Center (Baltimore, MD) that were age-matched with NPS.

RESULTS

The levels of 5α-RI mRNA were decreased from 25 ± 5.8 in NPS to 9.1 ± 3.1 fmol/pmol neuronal specific enolase (NSE) (t1,10 = 2.7, P = 0.02) in depressed patients. These differences are absent in the cerebellum of the same patients. The levels of neurosteroids were determined in the prefrontal cortex BA9 of depressed patients obtained from the Stanley Foundation Brain Bank Neuropathology Consortium, Bethesda (MD). The BA9 levels of Allo in male depressed patients failed to reach statistical difference from the levels of NPS (1.63 ± 1.01 pg/mg, n = 8, in NPS and 0.82 ± 0.33 pg/mg, n = 5, in nontreated depressed patients). However, depressed patients who had received antidepressant treatment (three patients SSRI and one TCA) exhibited increased BA9 Allo levels (6.16 ± 2.5 pg/mg, n = 4, t1,9 = 2.4, P = 0.047) when compared with nontreated depressed patients.

CONCLUSIONS

Although in a small number of patients, this finding is in-line with previous reports in the field that have observed an increase of Allo levels in CSF and plasma of depressed patients following antidepressant treatment. Hence, the molecular mechanisms underlying major depression may include a GABAergic neurotransmission deficit caused by a brain Allo biosynthesis downregulation, which can be normalized by SBSSs.

Divergent neuroactive steroid responses to stress and ethanol in rat and mouse strains: relevance for human studies

RATIONALE

Neuroactive steroids are endogenous or synthetic steroids that rapidly alter neuronal excitability via membrane receptors, primarily γ-aminobutyric acid type A (GABAA) receptors. Neuroactive steroids regulate many physiological processes including hypothalamic-pituitary-adrenal (HPA) axis function, ovarian cycle, pregnancy, aging, and reward. Moreover, alterations in neuroactive steroid synthesis are implicated in several neuropsychiatric disorders.

OBJECTIVES

This review will summarize the pharmacological properties and physiological regulation of neuroactive steroids, with a particular focus on divergent neuroactive steroid responses to stress and ethanol in rats, mice, and humans.

RESULTS

GABAergic neuroactive steroids exert a homeostatic regulation of the HPA axis in rats and humans, whereby the increase in neuroactive steroid levels following acute stress counteracts HPA axis hyperactivity and restores homeostasis. In contrast, in C57BL/6J mice, acute stress decreases neurosteroidogenesis and neuroactive steroids exert paradoxical excitatory effects upon the HPA axis. Rats, mice, and humans also differ in the neuroactive steroid responses to ethanol. Genetic variation in neurosteroidogenesis may explain the different neuroactive steroid responses to stress or ethanol.

CONCLUSIONS

Rats and mouse strains show divergent effects of stress and ethanol on neuroactive steroids in both plasma and brain. The study of genetic variation in the various processes that determine neuroactive steroids levels as well as their effects on cell signaling may underlie these differences and may play a relevant role for the potential therapeutic benefits of neuroactive steroids.

Effect of low doses of progesterone in the expression of the GABA(A) receptor α4 subunit and procaspase-3 in the hypothalamus of female rats

Progesterone is a steroid which regulates neural function, thereby modulating neurotransmission, cell survival, and behavior. Previous studies by our group have shown that chronic administration of low doses of progesterone in diestrus II female rats has an antidepressant-like effect in the forced swimming test (FST). Depression is associated with the several neurotransmitters systems, including GABA and serotonin, and with neurodegeneration and cell death in some brain circuits. The aim of this study was to verify the effect of progesterone on the protein expression of the GABA(A) receptor α4 subunit, serotonin transporter (SERT), Akt, extracellular signal-regulated kinase (Erk), and caspase-3 in the hypothalamus of diestrus II female rats exposed to the FST. Female rats were treated with a daily injection of progesterone (0.4 mg/kg) or vehicle, during two complete oestrous cycles. On the day of the experiment, the animals were euthanized 30 min after the FST, the hypothalamus was dissected and protein expression of GABA(A) receptor α4 subunit, SERT, Akt, Erk, and caspase-3 was evaluated. Progesterone increased the expression of GABA(A) receptor α4 subunit but did not change the expression of SERT. Progesterone decreased the expression of procaspase-3 in the hypothalamus without changing the activation of Akt and Erk in this structure. In summary, our results suggest that progesterone acts to increase the expression of the GABA(A) receptor α4 subunit and decrease the expression of procaspase-3 in the hypothalamus of female rats. Such effects may be involved in the antidepressant-like effect of progesterone in female rats exposed to the FST.

Ethanol alters local cellular levels of (3α,5α)-3-hydroxypregnan-20-one (3α,5α-THP) independent of the adrenals in subcortical brain regions

The neuroactive steroid (3α,5α)-3-hydroxypregnan-20-one (3α,5α-THP or allopregnanolone) is a positive modulator of GABAA receptors synthesized in the brain, adrenal glands, and gonads. In rats, ethanol activates the hypothalamic-pituitary-adrenal axis and elevates 3α,5α-THP in plasma, cerebral cortex, and hippocampus. In vivo, these effects are dependent on both the pituitary and adrenal glands. In vitro, however, ethanol locally increases 3α,5α-THP in hippocampal slices, in the absence of adrenal influence. Therefore, it is not known whether ethanol can change local brain levels of 3α,5α-THP in vivo, independent of the adrenals. To directly address this controversy, we administered ethanol (2 g/kg) or saline to rats that underwent adrenalectomy (ADX) or received sham surgery and performed immunohistochemistry for 3α,5α-THP. In the medial prefrontal cortex (mPFC), ethanol increased 3α,5α-THP after sham surgery, compared with saline controls, with no ethanol-induced change in 3α,5α-THP following ADX. In subcortical regions, 3α,5α-THP was increased independent of adrenals in the CA1 pyramidal cell layer, dentate gyrus polymorphic layer, bed nucleus of the stria terminalis, and paraventricular nucleus of the hypothalamus. Furthermore, ethanol decreased 3α,5α-THP labeling in the nucleus accumbens shore and central nucleus of the amygdala, independent of the adrenal glands. These data indicate that ethanol dynamically regulates local 3α,5α-THP levels in several subcortical regions; however, the adrenal glands contribute to 3α,5α-THP elevations in the mPFC. Using double immunofluorescent labeling we determined that adrenal dependence of 3α,5α-THP induction by ethanol is not due to a lack of colocalization of 3α,5α-THP with the cholesterol transporters steroidogenic acute regulatory protein (StAR) or translocator protein (TSPO).

Effect of meta-chlorobenzhydryl urea (m-ClBHU) on benzodiazepine receptor system in rat brain during experimental alcoholism

Chronic alcohol intake induces neuroadaptive changes in benzodiazepine receptors modulating GABAA receptors that promote alcohol addiction. Analysis of benzodiazepine receptors in the brain of Wistar rats differing by alcohol preference has demonstrated that affinity of [(3)H]flunitrazepam and [(3)H]Ro5-4864 binding with membrane fraction was reduced, while the density of specific binding sites in the brain cortex of heavy drinking and low drinking rats was increased in comparison with rats nonpreferring alcohol. Administration of anticonvulsant meta-chlorobenzhydryl urea increased affinity of benzodiazepine receptors in the brain cortex of heavy drinking rats, which improved GABA neurotransmission in the brain of these animals and reduced alcohol consumption.

Failure of acute ethanol administration to alter cerebrocortical and hippocampal allopregnanolone levels in C57BL/6J and DBA/2J mice

BACKGROUND

Ethanol (EtOH) administration increases brain allopregnanolone levels in rats, and this increase contributes to sensitivity to EtOH's behavioral effects. However, EtOH's effects on allopregnanolone may differ across species. We investigated the effects of acute EtOH administration on allopregnanolone, progesterone, and corticosterone levels in cerebral cortex and hippocampus of C57BL/6J and DBA/2J mice, 2 inbred strains with different alcohol sensitivity.

METHODS

Naïve male C57BL/6J and DBA/2J mice received EtOH (1, 2, 3, or 4 g/kg, intraperitoneally [i.p.]) or saline and were euthanized 1 hour later. For the time-course study, mice received EtOH (2 g/kg, i.p.) and were euthanized 15, 30, 60, and 120 minutes later. Steroids were measured by radioimmunoassay.

RESULTS

Acute EtOH administration did not alter cerebrocortical and hippocampal levels of allopregnanolone and progesterone in these strains at any of the doses and time points examined. Acute EtOH dose-dependently increased cerebrocortical corticosterone levels by 319, 347, and 459% in C57BL/6J mice at the doses of 2, 3, and 4 g/kg, and by 371, 507, 533, and 692% in DBA/2J mice at the doses of 1, 2, 3, and 4 g/kg, respectively. Similar changes were observed in the hippocampus. EtOH's effects on cerebrocortical corticosterone levels were also time dependent in both strains. Moreover, acute EtOH administration time-dependently increased plasma levels of progesterone and corticosterone. Finally, morphine administration increased cerebrocortical allopregnanolone levels in C57BL/6J (+77, +93, and +88% at 5, 10, and 30 mg/kg, respectively) and DBA/2J mice (+81% at 5 mg/kg), suggesting that the impairment in brain neurosteroidogenesis may be specific to EtOH.

CONCLUSIONS

These results underline important species differences on EtOH-induced brain neurosteroidogenesis. Acute EtOH increases brain and plasma corticosterone levels but does not alter cerebrocortical and hippocampal concentrations of allopregnanolone and progesterone in naïve C57BL/6J and DBA/2J mice.

Alcohol and the sleeping brain

Alcohol acts as a sedative that interacts with several neurotransmitter systems important in the regulation of sleep. Acute administration of large amounts of alcohol prior to sleep leads to decreased sleep-onset latency and changes in sleep architecture early in the night, when blood alcohol levels are high, with subsequent disrupted, poor-quality sleep later in the night. Alcohol abuse and dependence are associated with chronic sleep disturbance, lower slow-wave sleep, and more rapid-eye-movement sleep than normal, that last long into periods of abstinence and may play a role in relapse. This chapter outlines the evidence for acute and chronic alcohol effects on sleep architecture and sleep electroencephalogram, evidence for tolerance with repeated administration, and possible underlying neurochemical mechanisms for alcohol's effects on sleep. Also discussed are sex differences as well as effects of alcohol on sleep homeostasis and circadian regulation. Evidence for the role of sleep disruption as a risk factor for developing alcohol dependence is discussed in the context of research conducted in adolescents. The utility of sleep-evoked potentials in the assessment of the effects of alcoholism on sleep and the brain and in abstinence-mediated recovery is also outlined. The chapter concludes with a series of questions that need to be answered to determine the role of sleep and sleep disturbance in the development and maintenance of problem drinking and the potential beneficial effects of the treatment of sleep disorders for maintenance of abstinence in alcoholism.

The role of allopregnanolone in depression and anxiety

Neuroactive steroids such as allopregnanolone do not only act as transcriptional factors in the regulation of gene expression after intracellular back-oxidation into the 5-α pregnane steroids but may also alter neuronal excitability through interactions with specific neurotransmitter receptors. In particular, certain 3α-reduced metabolites of progesterone such as 3α,5α-tetrahydroprogesterone (allopregnanolone) and 3α,5β-tetrahydroprogesterone (pregnanolone) are potent positive allosteric modulators of the GABA(A) receptor complex. During the last years, the downregulation of neurosteroid biosynthesis has been intensively discussed to be a possible contributor to the development of anxiety and depressive disorder. Reduced levels of allopregnanolone in the peripheral blood or cerebrospinal fluid were found to be associated with major depression, anxiety disorders, premenstrual dysphoric disorder, negative symptoms in schizophrenia, or impulsive aggression. The importance of allopregnanolone for the regulation of emotion and its therapeutical use in depression and anxiety may not only involve GABAergic mechanisms, but probably also includes enhancement of neurogenesis, myelination, neuroprotection, and regulatory effects on HPA axis function. Certain pharmacokinetic obstacles limit the therapeutic use of natural neurosteroids (low bioavailability, oxidation to the ketone). Until now synthetic neuroactive steroids could not be established in the treatment of anxiety disorders or depression. However, the translocator protein (18 kDa) (TSPO) which is important for neurosteroidogenesis has been identified as a potential novel target. TSPO ligands such as XBD 173 increase neurosteroidogenesis and have anxiolytic effects with a favorable side effect profile.

The influence of the menstrual cycle on the result of brain examination with hydrogen magnetic resonance spectroscopy - a pilot study

BACKGROUND AND PURPOSE

Hydrogen magnetic resonance spectroscopy (1HMRS) is nowadays one of the basic tools for noninvasive brain metabolism assessment. The study focuses on the important problem of the influence of hormone fluctuation during the menstrual cycle on brain metabolism, assessed by 1HMRS for clinical diagnostics.

MATERIAL AND METHODS

In 11 healthy regularly menstruating women, 1HMRS was performed at the start (phase I), in the middle (phase II) and at the end (phase III) of the menstrual cycle. The relative concentration ratios of 12 brain metabolites in every woman in all cycle phases were examined, in 6 different volumes of interest (VOIs). Finally, statistically significant differences in relative metabolite ratios between the phases examined in given locations were sought.

RESULTS

Statistically significant relations between menstrual cycle phases and relative ratios of 4 metabolites - Lac/Cr, NAA/Cr, Glx1/Cr and Glx2/Cr - in different brain locations were found. In all locations, mean NAA/Cr ratios were greater in phase I compared to the other phases. A similar relationship was found for Glx1/Cr ratio in one location (left occipital lobe). For Lac/Cr and Glx2/Cr ratios, a higher mean ratio value was obtained in phase II compared to phases I and III in the right occipital lobe and left basal ganglia, respectively.

CONCLUSIONS

Menstrual cycle phase should be considered in planning a date and interpretation of 1HMRS examination, performed for the verification of a disease manifesting as brain metabolite disturbances in the 1HMRS spectrum.

GABAA receptor-mediated tonic depolarization in developing neural circuits

The activation of GABAA receptors (the type A receptors for γ-aminobutyric acid) produces two distinct forms of responses, phasic (i.e., transient) and tonic (i.e., persistent), that are mediated by synaptic and extrasynaptic GABAA receptors, respectively. During development, the intracellular chloride levels are high so activation of these receptors causes a net outward flow of anions that leads to neuronal depolarization rather than hyperpolarization. Therefore, in developing neural circuits, tonic activation of GABAA receptors may provide persistent depolarization. Recently, it became evident that GABAA receptor-mediated tonic depolarization alters the structure of patterned spontaneous activity, a feature that is common in developing neural circuits and is important for neural circuit refinement. Thus, this persistent depolarization may lead to a long-lasting increase in intracellular calcium level that modulates network properties via calcium-dependent signaling cascades. This article highlights the features of GABAA receptor-mediated tonic depolarization, summarizes the principles for discovery, reviews the current findings in diverse developing circuits, examines the underlying molecular mechanisms and modulation systems, and discusses their functional specializations for each developing neural circuit.

The paradox of the paroxysm: can seizure precipitants help explain human ictogenesis?

An epileptic brain is permanently in a diseased state, but seizures occur rarely and without warning. Here we examine this paradox, common to paroxysmal diseases. We review the problem in the context of the prototypic acquired epilepsies of the medial temporal lobe. We ask how an epileptic temporal lobe differs from a healthy one and examine biological mechanisms that may explain the transition to seizure. Attempts to predict seizure timing from analyses of brain electrical activity suggest that the neurological processes involved may be initiated significantly before a seizure. Furthermore, whereas seizures are said to occur without warning, some patients say they know when a seizure is imminent. Several factors, including sleep deprivation, oscillations in hormonal levels, or withdrawal from drugs, increase the probability of a seizure. We ask whether these seizure precipitants might act through common neuronal mechanisms. Several precipitating factors seem to involve relief from a neurosteroid modulation of gamma-amino butyric acid receptor type A (GABAA) receptors. We propose tests of this hypothesis.

Local changes in neurosteroid levels in the substantia nigra reticulata and the ventral tegmental area alter chronic ethanol withdrawal severity in male withdrawal seizure-prone mice

BACKGROUND

Allopregnanolone (ALLO) is a potent positive modulator of γ-aminobutyric acidA receptors (GABAA Rs) that affects ethanol (EtOH) withdrawal. Finasteride (FIN), a 5α-reductase inhibitor that blocks the formation of ALLO and other GABAergic neurosteroids, alters EtOH sensitivity. Recently, we found that Withdrawal Seizure-Prone mice from the first genetic replicate (WSP-1) exhibited behavioral tolerance to the anticonvulsant effect of intrahippocampal ALLO during EtOH withdrawal and that intrahippocampal FIN significantly increased EtOH withdrawal severity. The purpose of this study was to determine whether neurosteroid manipulations in the substantia nigra reticulata (SNR) and ventral tegmental area (VTA) produced effects during EtOH withdrawal comparable to those seen with intrahippocampal ALLO and FIN.

METHODS

Male WSP-1 mice were surgically implanted with bilateral guide cannulae aimed at the SNR or VTA at 2 weeks prior to EtOH vapor or air exposure for 72 hours. Initial studies examined the anticonvulsant effect of a single ALLO infusion (0, 100, or 400 ng/side) at a time corresponding to peak withdrawal in the air- and EtOH-exposed mice. Separate studies examined the effect of 4 FIN infusions (0 or 10 μg/side/d) during the development of physical dependence on the expression of EtOH withdrawal.

RESULTS

ALLO infusion exerted a potent anticonvulsant effect in EtOH-naïve mice, but a diminished anticonvulsant effect during EtOH withdrawal. Administration of FIN into the SNR exerted a delayed proconvulsant effect in EtOH-naïve mice, whereas infusion into the VTA increased EtOH withdrawal duration.

CONCLUSIONS

Activation of local GABAA Rs in the SNR and VTA via ALLO infusion is sufficient to exert an anticonvulsant effect in naïve mice and to produce behavioral tolerance to the anticonvulsant effect of ALLO infusion during EtOH withdrawal. Thus, EtOH withdrawal reduced sensitivity of GABAA Rs to GABAergic neurosteroids in 2 neuroanatomical substrates within the basal ganglia in WSP-1 male mice.

Effect of acute ethanol and acute allopregnanolone on spatial memory in adolescent and adult rats

The effects of ethanol differ in adolescent and adult rats on a number of measures. The evidence of the effects of ethanol on spatial memory in adolescents and adults is equivocal. Whether adolescents are more or less sensitive to ethanol-induced impairment of spatial memory acquisition remains unclear; with regard to the effects of acute ethanol on spatial memory retrieval there is almost no research looking into any age difference. Thus, we examined the effects of acute ethanol on spatial memory in the Morris Watermaze in adolescents and adults. Allopregnanolone (ALLO) is a modulator of the GABA(A) receptor and has similar behavioral effects as ethanol. We sought to also determine the effects of allopreganolone on spatial memory in adolescent and adults. Male adolescent (post natal [PN]28-30) and adult (PN70-72) rats were trained in the Morris Watermaze for 6 days and acute doses of ethanol (saline, 1.5 and 2.0 g/kg) or ALLO (vehicle, 9 and 18 mg/kg) were administered on Day 7. A probe trial followed on Day 8. As expected, there were dose effects; higher doses of both ethanol and ALLO impaired spatial memory. However, in both the ethanol and ALLO conditions adolescents and adults had similar spatial memory impairments. The current results suggest that ethanol and ALLO both impair hippocampal-dependent spatial memory regardless of age in that once learning has occurred, ethanol or ALLO does not differentially impair the retrieval of spatial memory in adolescents and adults. Given the mixed results on the effect of ethanol on cognition in adolescent rats, additional research is needed to ascertain the factors critical for the reported differential results.

Tolerance to allopregnanolone with focus on the GABA-A receptor

Many studies have suggested a relationship between stress, sex steroids, and negative mental and mood changes in humans. The progesterone metabolite allopregnanolone is a potent endogenous ligand of the γ-amino butyric acid -A (GABA-A) receptor, and the most discussed neuroactive steroid. Variations in the levels of neuroactive steroids that influence the activity of the GABA-A receptor cause a vulnerability to mental and emotional pathology. There are physiological conditions in which allopregnanolone production increases acutely (e.g. stress) or chronically (e.g. menstrual cycle, pregnancy), thus exposing the GABA-A receptor to high and continuous allopregnanolone concentrations. In such conditions, tolerance to allopregnanolone may develop. We have shown that both acute and chronic tolerances can develop to the effects of allopregnanolone. Following the development of acute allopregnanolone tolerance, there is a decrease in the abundance of the GABA-A receptor α4 subunit and the expression of the α4 subunit mRNA in the ventral-posteriomedial nucleus of the thalamus. Little is known about the mechanism behind allopregnanolone tolerance and its effects on assembly of the GABA-A receptor composition. The exact mechanism of the allopregnanolone tolerance phenomena remains unclear. The purpose of this review is to summarize certain aspects of current knowledge concerning allopregnanolone tolerance and changes in the GABA-A receptors.

Novel androstenetriol interacts with the mitochondrial translocator protein and controls steroidogenesis

Steroid hormones are metabolically derived from multiple enzymatic transformations of cholesterol. The controlling step in steroid hormone biogenesis is the delivery of cholesterol from intracellular stores to the cytochrome P450 enzyme CYP11A1 in the mitochondrial matrix. The 18-kDa translocator protein (TSPO) plays an integral part in this mitochondrial cholesterol transport. Consistent with its role in intracellular cholesterol movement, TSPO possesses a cholesterol recognition/interaction amino acid consensus (CRAC) motif that has been demonstrated to bind cholesterol. To further investigate the TSPO CRAC motif, we performed molecular modeling studies and identified a novel ligand, 3,17,19-androsten-5-triol (19-Atriol) that inhibits cholesterol binding at the CRAC motif. 19-Atriol could bind a synthetic CRAC peptide and rapidly inhibited hormonally induced steroidogenesis in MA-10 mouse Leydig tumor cells and constitutive steroidogenesis in R2C rat Leydig tumor cells at low micromolar concentrations. Inhibition at these concentrations was not due to toxicity or inhibition of the CYP11A1 enzyme and was reversed upon removal of the compound. In addition, 19-Atriol was an even more potent inhibitor of PK 11195-stimulated steroidogenesis, with activity in the high nanomolar range. This was accomplished without affecting PK 11195 binding or basal steroidogenesis. Finally, 19-Atriol inhibited mitochondrial import and processing of the steroidogenic acute regulatory protein without any effect on TSPO protein levels. In conclusion, we have identified a novel androstenetriol that can interact with the CRAC domain of TSPO, can control hormonal and constitutive steroidogenesis, and may prove to be a useful tool in the therapeutic control of diseases of excessive steroid formation.

Pentylenetetrazol produces a state-dependent conditioned place aversion to alcohol withdrawal in mice

The purpose of this study was to determine if aversive effects of alcohol withdrawal could be detected in mice using the place conditioning procedure and whether the GABA(A) receptor antagonist, pentylenetetrazol (PTZ), would increase the aversive effects of alcohol withdrawal and increase the probability of detecting conditioned place aversion. Subjects were alcohol-naïve mice from a specific line selectively bred for low alcohol preference (LAP1; n=91) and were assigned to three groups: alcohol withdrawal, PTZ alone, and PTZ+alcohol withdrawal. On four trials, mice received either a 4.0 g/kg intraperitoneal (i.p.) injection of alcohol (alcohol withdrawal, PTZ+alcohol withdrawal groups) or saline (PTZ group) 8 h prior to being placed on a distinctive floor texture for a 30-min conditioning session. Five minutes before these sessions, mice in the PTZ and PTZ+alcohol withdrawal groups received PTZ (5.0 mg/kg; i.p.) and the alcohol withdrawal group received saline. On intervening days mice received two saline injections at the same time points prior to being placed on a different floor texture. Post-conditioning floor preference was assessed in two 60-min tests; the first test was drug-free and the second test was state-dependent. Neither alcohol withdrawal nor PTZ produced significant place conditioning. The PTZ+alcohol withdrawal group showed a significant place aversion during the state-dependent test. These data suggest that the combined stimulus properties of PTZ and alcohol withdrawal facilitated the expression of conditioned place aversion to alcohol withdrawal.

Alcohol Pathophysiology

There is no specialized alcohol addiction area in the brain; rather, alcohol acts on a wide range of excitatory and inhibitory nervous networks to modulate neurotransmitters actions by binding with and altering the function of specific proteins. With no hemato-encephalic barrier for alcohol, its actions are strongly related to the amount of intake. Heavy alcohol intake is associated with both structural and functional changes in the central nervous system with long-term neuronal adaptive changes contributing to the phenomena of tolerance and withdrawal. The effects of alcohol on the function of neuronal networks are heterogeneous. Because ethanol affects neural activity in some brain sites but is without effect in others, its actions are analyzed in terms of integrated connectivities in the functional circuitry of neuronal networks, which are of particular interest because of the cognitive interactions discussed in the manuscripts contributing to this review. Recent molecular data are reviewed as a support for the other contributions dealing with cognitive disturbances related to alcohol acute and addicted consumption.

Differential effects of ethanol on serum GABAergic 3alpha,5alpha/3alpha,5beta neuroactive steroids in mice, rats, cynomolgus monkeys, and humans

BACKGROUND

Acute ethanol administration increases plasma and brain levels of progesterone and deoxycorticosterone-derived neuroactive steroids (3alpha,5alpha)-3-hydroxypregnan-20-one (3alpha,5alpha-THP) and (3alpha,5alpha)-3,21-dihydroxypregnan-20-one (3alpha,5alpha-THDOC) in rats. However, little is known about ethanol effects on GABAergic neuroactive steroids in mice, nonhuman primates, or humans. We investigated the effects of ethanol on plasma levels of 3alpha,5alpha- and 3alpha,5beta-reduced GABAergic neuroactive steroids derived from progesterone, deoxycorticosterone, dehydroepiandrosterone, and testosterone using gas chromatography-mass spectrometry.

METHODS

Serum levels of GABAergic neuroactive steroids and pregnenolone were measured in male rats, C57BL/6J and DBA/2J mice, cynomolgus monkeys, and humans following ethanol administration. Rats and mice were injected with ethanol (0.8 to 2.0 g/kg), cynomolgus monkeys received ethanol (1.5 g/kg) intragastrically, and healthy men consumed a beverage containing 0.8 g/kg ethanol. Steroids were measured after 60 minutes in all species and also after 120 minutes in monkeys and humans.

RESULTS

Ethanol administration to rats increased levels of 3alpha,5alpha-THP, 3alpha,5alpha-THDOC, and pregnenolone at the doses of 1.5 g/kg (+228, +134, and +860%, respectively, p < 0.001) and 2.0 g/kg (+399, +174, and +1125%, respectively, p < 0.001), but not at the dose of 0.8 g/kg. Ethanol did not alter levels of the other neuroactive steroids. In contrast, C57BL/6J mice exhibited a 27% decrease in serum 3alpha,5alpha-THP levels (p < 0.01), while DBA/2J mice showed no significant effect of ethanol, although both mouse strains exhibited substantial increases in precursor steroids. Ethanol did not alter any of the neuroactive steroids in cynomolgus monkeys at doses comparable to those studied in rats. Finally, no effect of ethanol (0.8 g/kg) was observed in men.

CONCLUSIONS

These studies show clear species differences among rats, mice, and cynomolgus monkeys in the effects of ethanol administration on circulating neuroactive steroids. Rats are unique in their pronounced elevation of GABAergic neuroactive steroids, while this effect was not observed in mice or cynomolgus monkeys at comparable ethanol doses.

The role of GABA(A) receptors in the acute and chronic effects of ethanol: a decade of progress

The past decade has brought many advances in our understanding of GABA(A) receptor-mediated ethanol action in the central nervous system. We now know that specific GABA(A) receptor subtypes are sensitive to ethanol at doses attained during social drinking while other subtypes respond to ethanol at doses attained by severe intoxication. Furthermore, ethanol increases GABAergic neurotransmission through indirect effects, including the elevation of endogenous GABAergic neuroactive steroids, presynaptic release of GABA, and dephosphorylation of GABA(A) receptors promoting increases in GABA sensitivity. Ethanol's effects on intracellular signaling also influence GABAergic transmission in multiple ways that vary across brain regions and cell types. The effects of chronic ethanol administration are influenced by adaptations in GABA(A) receptor function, expression, trafficking, and subcellular localization that contribute to ethanol tolerance, dependence, and withdrawal hyperexcitability. Adolescents exhibit altered sensitivity to ethanol actions, the tendency for higher drinking and longer lasting GABAergic adaptations to chronic ethanol administration. The elucidation of the mechanisms that underlie adaptations to ethanol exposure are leading to a better understanding of the regulation of inhibitory transmission and new targets for therapies to support recovery from ethanol withdrawal and alcoholism.

Sex differences in acute ethanol withdrawal severity after adrenalectomy and gonadectomy in Withdrawal Seizure-Prone and Withdrawal Seizure-Resistant mice

Recent findings suggest that the ability of ethanol (EtOH) to increase the levels of neurosteroids with potent gamma-aminobutyric acid (GABA)ergic properties can influence measures of EtOH sensitivity. Earlier studies determined that removal of the adrenals and gonads diminished the steroidogenic effect of EtOH and significantly increased acute EtOH withdrawal severity in two inbred mouse strains that differed in withdrawal severity, suggesting the contribution of anticonvulsant GABAergic steroids to acute withdrawal in intact animals. Thus, the goal of the present study was to investigate the consequence of steroid removal on acute EtOH withdrawal through excision of the adrenals and gonads, in another genetic animal model of EtOH withdrawal differences, the Withdrawal Seizure-Prone (WSP) and Withdrawal Seizure-Resistant (WSR) selected lines. Male and female WSP and WSR mice underwent surgical removal of the adrenals and gonads or no organ removal (SHAM). One to 2 weeks later, baseline handling-induced convulsions (HICs) were assessed, mice were given a 4 g/kg dose of EtOH, and HICs were measured hourly for 12 h and then at 24 h. The combination surgery significantly increased EtOH withdrawal in WSP and WSR female mice, as measured by area under the curve (AUC) and peak HIC scores. The AUC was significantly positively correlated with plasma corticosterone levels and significantly negatively correlated with progesterone levels. In contrast, surgical status did not alter withdrawal severity in male WSP and WSR mice. Overall, the increase in acute EtOH withdrawal severity in female WSP and WSR mice after adrenalectomy and gonadectomy corroborate our recent evidence that withdrawal from a high dose of EtOH can be modulated by anticonvulsant steroids produced in the periphery.

The anxiolytic etifoxine protects against convulsant and anxiogenic aspects of the alcohol withdrawal syndrome in mice

Change in the function of gamma-aminobutyric acid(A) (GABA(A)) receptors attributable to alterations in receptor subunit composition is one of main molecular mechanisms with those affecting the glutamatergic system which accompany prolonged alcohol (ethanol) intake. These changes explain in part the central nervous system hyperexcitability consequently to ethanol administration cessation. Hyperexcitability associated with ethanol withdrawal is expressed by physical signs, such as tremors, convulsions, and heightened anxiety in animal models as well as in humans. The present work investigated the effects of anxiolytic compound etifoxine on ethanol-withdrawal paradigms in a mouse model. The benzodiazepine diazepam was chosen as reference compound. Ethanol was given to NMRI mice by a liquid diet at 3% for 8 days, then at 4% for 7 days. Under these conditions, ethanol blood level ranged between 0.5 and 2 g/L for a daily ethanol intake varying from 24 to 30 g/kg. These parameters permitted the emergence of ethanol-withdrawal symptoms once ethanol administration was terminated. Etifoxine (12.5-25 mg/kg) and diazepam (1-4 mg/kg) injected intraperitoneally 3h 30 min after ethanol removal, decreased the severity in handling-induced tremors and convulsions in the period of 4-6h after withdrawal from chronic ethanol treatment. In addition when administered at 30 and 15 min, respectively, before the light and dark box test, etifoxine (50mg/kg) and diazepam (1mg/kg) inhibited enhanced aversive response 8h after ethanol withdrawal. Etifoxine at 25 and 50 mg/kg doses was without effects on spontaneous locomotor activity and did not exhibit ataxic effects on the rota rod in animals not treated with ethanol. These findings demonstrate that the GABAergic compound etifoxine selectively reduces the physical signs and anxiety-like behavior associated with ethanol withdrawal in a mouse model and may hold promise in the treatment of ethanol-withdrawal syndrome in humans.

Associations of glutamate decarboxylase genes with initial sensitivity and age-at-onset of alcohol dependence in the Irish Affected Sib Pair Study of Alcohol Dependence

BACKGROUND

The relation of gamma-aminobutyric acid (GABA) to alcohol dependence (AD) has been widely studied. Several previous studies suggest that GABA may be involved in alcohol withdrawal, tolerance, and the symptoms that form an AD diagnosis. The genes coding for glutamate decarboxylase (GAD), the rate-limiting enzyme in GABA synthesis, are of potential interest for their association to ethanol consumption and AD. There are two isoforms of GAD, GAD1 and GAD2, which were reported to be associated with AD in males of Han Taiwanese (GAD1) and Russian (GAD2) ancestry. The present study examined the association of the two GAD isoforms with AD and relevant alcohol-related traits in the Irish Affected Sib Pair Study of Alcohol Dependence [Prescott, C.A., Sullivan, P.F., Myers, J.M., Patterson, D.G., Devitt, M., Halberstadt, L.J., Walsh, D., Kendler, K.S., 2005. The Irish Affected Sib Pair Study of Alcohol Dependence: study methodology and validation of diagnosis by interview and family history. Alcohol.-Clin. Exp. Res. 29 (3) 417-429].

METHODS

Participants were recruited in Ireland, including 575 independent cases who met DSM-IV AD criteria and 530 controls, screened for heavy drinking. We first conducted case-control analyses of the GAD genes with AD and, within the cases, examined associations with age at onset of AD, withdrawal symptoms, and two quantitative measures: initial sensitivity and tolerance (based on scales from the Self-Rating of the Effects of Ethanol) [Schuckit, M.A., Smith, T.L., Tipp, J.E., 1997. The self-rating of the effects of alcohol (SRE) form as a retrospective measure of the risk for alcoholism. Addiction 92, 979-988]. A total of 29 SNPs were genotyped for GAD1 and GAD2 using the Illumina GoldenGate protocols. Statistical procedures were implemented to control for false discovery rates (FDR).

RESULTS

Nine of 29 markers with minor allele frequencies less than 0.01 were removed from standard analysis; the remaining 20 markers were all in Hardy-Weinberg equilibrium. Three markers in the intronic regions of GAD1 were associated with initial sensitivity to alcohol (P=0.002); the associations remained significant after a FDR based correction for multiple testing. In addition, one marker located 3kb upstream of GAD1 exhibited association with age at onset of AD (P=0.0001). Gender specific effects were observed in results of both single marker and haplotype analyses.

CONCLUSION

We found no evidence for the association of GAD genes with AD but significant association of GAD1 with initial sensitivity and age at onset of AD. Our findings suggest that the underlying pathophysiology regulated by genes like GAD1 may be more directly related to the component processes that form AD than to the clinical disorder.

Role of acetaldehyde in ethanol-induced elevation of the neuroactive steroid 3alpha-hydroxy-5alpha-pregnan-20-one in rats

BACKGROUND

Systemic ethanol administration increases neuroactive steroid levels that increase ethanol sensitivity. Acetaldehyde is a biologically active compound that may contribute to behavioral and rewarding effects of ethanol. We investigated the role of acetaldehyde in ethanol-induced elevations of 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP) levels in cerebral cortex.

METHODS

Male Sprague-Dawley rats were administered ethanol, and plasma acetaldehyde concentrations were measured by gas chromatography to determine relevant concentrations. Rats were then administered acetaldehyde directly, acetaldehyde plus cyanamide to block its degradation, or ethanol in the presence of inhibitors of ethanol metabolism, to determine effects on 3alpha,5alpha-THP levels in cerebral cortex.

RESULTS

Ethanol administration (2 g/kg) to rats results in a peak acetaldehyde concentration of 6-7 microM at 10 minutes that remains stable for the duration of the time points tested. Direct administration of acetaldehyde eliciting this plasma concentration does not increase cerebral cortical 3alpha,5alpha-THP levels, and inhibition of ethanol-metabolizing enzymes to modify acetaldehyde formation does not alter ethanol-induced 3alpha,5alpha-THP levels. However, higher doses of acetaldehyde (75 and 100 mg/kg), in the presence of cyanamide to prevent its metabolism, are capable of increasing cortical 3alpha,5alpha-THP levels.

CONCLUSIONS

Physiological concentrations of acetaldehyde are not responsible for ethanol-induced increases in 3alpha,5alpha-THP, but a synergistic role for acetaldehyde with ethanol may contribute to increases in 3alpha,5alpha-THP levels and ethanol sensitivity.

Assessment of GABAA benzodiazepine receptor (GBzR) sensitivity in patients with alcohol dependence

AIM

The aim of this study was to measure GABAA benzodiazepine receptor (GBzR) sensitivity in alcohol-dependent patients and compare with matched non-dependent drinkers.

METHODS

Nine abstinent alcohol-dependent male patients, age matched with nine male non-dependent social drinkers, received an intravenous infusion of midazolam. Objective (saccadic eye movement slowing) and subjective (visual analogue scales) measurements were recorded at 15-min intervals for 2 h.

RESULTS

There were no differences in objective or subjective measures.

CONCLUSIONS

Our hypothesis that patients with alcohol dependence would have less slowing of their eye movements in response to this challenge, reflecting reduced GBzR sensitivity, was not confirmed. The reasons for this could mean that GBzR function returns to normal with abstinence, or that this paradigm is unable to measure the subtle subtype-specific changes in GBzR sensitivity that occur following dependent alcohol use.

Translational aspects of pharmacological research into anxiety disorders: the stress-induced hyperthermia (SIH) paradigm

In anxiety research, the search for models with sufficient clinical predictive validity to support the translation of animal studies on anxiolytic drugs to clinical research is often challenging. This review describes the stress-induced hyperthermia (SIH) paradigm, a model that studies the activation of the autonomic nervous system in response to stress by measuring body temperature. The reproducible and robust SIH response, combined with ease of testing, make the SIH paradigm very suitable for drug screening. We will review the current knowledge on the neurobiology of the SIH response, discuss the role of GABA(A) and serotonin (5-HT) pharmacology, as well as how the SIH response relates to infectious fever. Furthermore, we will present novel data on the SIH response variance across different mice and their sensitivity to anxiolytic drugs. The SIH response is an autonomic stress response that can be successfully studied at the level of its physiology, pharmacology, neurobiology and genetics and possesses excellent animal-to-human translational properties.

GABA(A) receptors and alcohol

There is substantial evidence that GABAergic neurotransmission is important for many behavioral actions of ethanol and there are reports spanning more than 30 years of literature showing that low to moderate (3-30 mM) concentrations of ethanol enhance GABAergic neurotransmission. A key question is which GABA receptor subunits are sensitive to low concentrations of ethanol in vivo and in vitro. Recent evidence points to a role for extrasynaptic receptors. Another question is which behavioral actions of alcohol result from enhancement of GABAergic neurotransmission. Some clues are beginning to emerge from studies of knock-out and knock-in mice and from genetic analysis of human alcoholics. These approaches are converging on a role for GABAergic actions in regulating alcohol consumption and, perhaps, the development of alcoholism.