Glucocorticoid and polyamine interactions in the plasticity of glutamatergic synapses that contribute to ethanol-associated dependence and neuronal injury

Cross-species epigenetic regulation of nucleus accumbens KCNN3 transcripts by excessive ethanol drinking

The underlying genetic and epigenetic mechanisms driving functional adaptations in neuronal excitability and excessive alcohol intake are poorly understood. Small-conductance Ca2+-activated K+ (KCa2 or SK) channels encoded by the KCNN family of genes have emerged from preclinical studies as a key contributor to alcohol-induced functional neuroadaptations in alcohol-drinking monkeys and alcohol-dependent mice. Here, this cross-species analysis focused on KCNN3 DNA methylation, gene expression, and single nucleotide polymorphisms, including alternative promoters in KCNN3, that could influence surface trafficking and function of KCa2 channels. Bisulfite sequencing analysis of the nucleus accumbens tissue from alcohol-drinking monkeys and alcohol-dependent mice revealed a differentially methylated region in exon 1A of KCNN3 that overlaps with a predicted promoter sequence. The hypermethylation of KCNN3 in the accumbens paralleled an increase in the expression of alternative transcripts that encode apamin-insensitive and dominant-negative KCa2 channel isoforms. A polymorphic repeat in macaque KCNN3 encoded by exon 1 did not correlate with alcohol drinking. At the protein level, KCa2.3 channel expression in the accumbens was significantly reduced in very heavy-drinking monkeys. Together, our cross-species findings on epigenetic dysregulation of KCNN3 represent a complex mechanism that utilizes alternative promoters to potentially impact the firing of accumbens neurons. Thus, these results provide support for hypermethylation of KCNN3 as a possible key molecular mechanism underlying harmful alcohol intake and alcohol use disorder.

Cross-species epigenetic regulation of nucleus accumbens KCNN3 transcripts by excessive ethanol drinking

The underlying genetic and epigenetic mechanisms driving functional adaptations in neuronal excitability and excessive alcohol intake are poorly understood. Small-conductance Ca2+-activated K+ (KCa2 or SK) channels encoded by the KCNN family of genes have emerged from preclinical studies as a key contributor to alcohol-induced functional neuroadaptations in alcohol-drinking monkeys and alcohol dependent mice. Here, this cross-species analysis focused on KCNN3 DNA methylation, gene expression, and single nucleotide polymorphisms including alternative promoters in KCNN3 that could influence surface trafficking and function of KCa2 channels. Bisulfite sequencing analysis of the nucleus accumbens tissue from alcohol-drinking monkeys and alcohol dependent mice revealed a differentially methylated region in exon 1A of KCNN3 that overlaps with a predicted promoter sequence. The hypermethylation of KCNN3 in the accumbens paralleled an increase in expression of alternative transcripts that encode apamin-insensitive and dominant-negative KCa2 channel isoforms. A polymorphic repeat in macaque KCNN3 encoded by exon 1 did not correlate with alcohol drinking. At the protein level, KCa2.3 channel expression in the accumbens was significantly reduced in very heavy drinking monkeys. Together, our cross-species findings on epigenetic dysregulation of KCNN3 represent a complex mechanism that utilizes alternative promoters to impact firing of accumbens neurons. Thus, these results provide support for hypermethylation of KCNN3 as a possible key molecular mechanism underlying harmful alcohol intake and alcohol use disorder.

PT150 blocks the rewarding properties of ethanol and attenuates ethanol-induced reduction of egg laying in Coturnix quail

RATIONALE

Alcohol use disorder (AUD) has been shown to be associated with a dysregulated stress system. Reducing the stress hormone corticosterone (CORT), that binds to glucocorticoid receptors, may attenuate the rewarding properties of drugs of abuse. However, the effect of blocking corticosterone receptors on ethanol reward has yet to be investigated.

OBJECTIVES

The current study investigated whether the stress hormone receptor antagonist, PT150, would block the rewarding properties of ethanol via the glucocorticoid receptor system and attenuate other ethanol-induced effects.

METHODS

A conditioned place preference (CPP) procedure was used to examine the rewarding properties of ethanol in an avian preclinical model. Ethanol was paired with the least preferred chamber. On alternate days, water was paired with the preferred chamber. After eight pairings, a place preference test was given that allowed subjects to have access to both chambers. Half of the subjects received PT150 prior to ethanol administration. The other half received vehicle. Time spent in each chamber during the preference tests, locomotor activity during the pairings, and egg production in female birds was recorded.

RESULTS

Ethanol treatment resulted in a CPP and pretreatment of PT150 blocked the acquisition of the ethanol-induced place preference. Neither ethanol nor PT150 altered locomotor activity. Pretreatment of PT150 also increased egg production in female quail treated with ethanol.

CONCLUSIONS

These findings suggest repeated ethanol pairings with visual cues can produce a CPP. Furthermore, pretreatment of PT150 may be a potential pharmacotherapy for blocking the rewarding properties of ethanol and may enhance egg production in female quail treated with ethanol.

Low but not moderate amounts of caffeine increase co-consumption of ethanol in C57BL/6J mice

The increasingly popular combination of "energy drinks" containing high amounts of caffeine and alcohol has been shown to induce a stimulated, rather than sedated, state which may result in increased binge drinking and increased risk for alcohol-attributable accidents. We sought to examine consumption patterns of and withdrawal from alcohol and caffeine using a voluntary co-consumption animal model. Male and female adult C57BL/6J mice were given access to increasing doses of caffeine (0.01-0.05%) and/or alcohol (3-20%) in a two-bottle choice, intermittent access voluntary paradigm with fluid consumption recorded daily. Anxiety-like behavior during withdrawal was assessed via elevated plus maze or open field test in experiment 2. Increasing both alcohol and caffeine simultaneously in Experiment 1 resulted in no significant changes in co-consumption compared to mice given access to only alcohol or caffeine. Experiment 2 held caffeine concentration steady while slowly increasing alcohol content and resulted in mice consuming more alcohol when it was consumed in tandem with low dose caffeine. Both male and female mice consumed more caffeine when it was paired with alcohol; however, no significant differences were observed during withdrawal behavior. These results suggest that caffeine may dose-dependently positively influence alcohol consumption in mice and echo clinical literature suggesting that caffeine and alcohol together may result in a heightened state of stimulation and lead to further binge drinking. The intermittent access paradigm affords increased translational validity regarding investigations of alcohol and caffeine co-consumption and may be useful in identifying the neurobiological mechanisms concerning co-consumption of such substances.

Alcohol Use Disorder, Neurodegeneration, Alzheimer's and Parkinson's Disease: Interplay Between Oxidative Stress, Neuroimmune Response and Excitotoxicity

Alcohol use disorder (AUD) has been associated with neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease. Prolonged excessive alcohol intake contributes to increased production of reactive oxygen species that triggers neuroimmune response and cellular apoptosis and necrosis via lipid peroxidation, mitochondrial, protein or DNA damage. Long term binge alcohol consumption also upregulates glutamate receptors, glucocorticoids and reduces reuptake of glutamate in the central nervous system, resulting in glutamate excitotoxicity, and eventually mitochondrial injury and cell death. In this review, we delineate the following principles in alcohol-induced neurodegeneration: (1) alcohol-induced oxidative stress, (2) neuroimmune response toward increased oxidants and lipopolysaccharide, (3) glutamate excitotoxicity and cell injury, and (4) interplay between oxidative stress, neuroimmune response and excitotoxicity leading to neurodegeneration and (5) potential chronic alcohol intake-induced development of neurodegenerative diseases, including Alzheimer’s and Parkinson’s disease.

A Novel Sulfonamide, 4-FS, Reduces Ethanol Drinking and Physical Withdrawal Associated With Ethanol Dependence

Carbonic anhydrase (CA) is abundant in glial cells in the brain and CA type II isoform (CA II) activity in the hippocampus plays an important role in buffering extracellular pH transients produced by neural activity. Chronic ethanol exposure results in respiratory and metabolic acidosis, producing shifts in extracellular pH in the brain and body. These neurophysiological changes by ethanol are hypothesized to contribute to the continued drinking behavior and physical withdrawal behavior in subjects consuming ethanol chronically. We explored whether chronic ethanol self-administration (ethanol drinking, 10% v/v; ED) without or under the influence of chronic intermittent ethanol vapor (CIE-ED) experience alters the expression of CA II in the hippocampus. Postmortem hippocampal tissue analyses demonstrated that CA II levels were enhanced in the hilus region of the hippocampus in ED and CIE-ED rats. We used a novel molecule-4-fluoro-N-(4-sulfamoylphenyl) benzenesulfonamide (4-FS)-a selective CA II inhibitor, to determine whether CA II plays a role in ethanol self-administration in ED and CIE-ED rats and physical withdrawal behavior in CIE-ED rats. 4-FS (20 mg/kg, i.p.) reduced ethanol self-administration in ED rats and physical withdrawal behavior in CIE-ED rats. Postmortem hippocampal tissue analyses demonstrated that 4-FS reduced CA II expression in ED and CIE-ED rats to control levels. In parallel, 4-FS enhanced GABAA receptor expression, reduced ratio of glutamatergic GluN2A/2B receptors and enhanced the expression of Fos, a marker of neuronal activation in the ventral hippocampus in ED rats. These findings suggest that 4-FS enhanced GABAergic transmission and increased activity of neurons of inhibitory phenotypes. Taken together, these findings support the role of CA II in assisting with negative affective behaviors associated with moderate to severe alcohol use disorders (AUD) and that CA II inhibitors are a potential therapeutic target to reduce continued drinking and somatic withdrawal symptoms associated with moderate to severe AUD.

A Novel Role for the Endocannabinoid System in Ameliorating Motivation for Alcohol Drinking and Negative Behavioral Affect after Traumatic Brain Injury in Rats

Traumatic brain injury (TBI) is associated with psychiatric dysfunction-including pain, cognitive impairment, anxiety, and increased alcohol use. We previously demonstrated that inhibiting endocannabinoid degradation post-TBI with JZL184 attenuates neuroinflammation and neuronal hyperexcitability at the site of injury and improves neurobehavioral recovery. This study aimed to determine the effect of JZL184 on post-TBI behavioral changes related to psychiatric dysfunction and post-TBI neuroadaptations in brain regions associated with these behaviors. We hypothesized that JZL184 would attenuate post-TBI behavioral and neural changes in alcohol-drinking rats. Adult male Wistar rats were trained to operantly self-administer alcohol before receiving lateral fluid percussion injury. Thirty minutes post-TBI, rats received JZL184 (16 mg/kg, i.p.) or vehicle. Spatial memory (Y-maze), anxiety-like behavior (open field), alcohol motivation (progressive ratio responding), and mechanosensitivity (Von Frey) were measured 3-10 days post-injury, and ventral striatum (VS) and central amygdala (CeA) tissue were collected for western blot analysis of phosphorylated glutamate receptor subunit 1 (GluR1) and glucocorticoid receptor (GR). TBI impaired spatial memory, increased anxiety-like behavior, and increased motivated alcohol drinking. JZL184 prevented these changes. TBI also increased phosphorylated GluR1 and GR in the CeA (but not the VS) compared with sham controls. JZL184 attenuated post-TBI GR phosphorylation in the CeA. These findings suggest that TBI produces comorbid cognitive dysfunction, increased alcohol motivation, and anxiety-like behavior, possibly related to amygdala dysfunction, and these changes are prevented by systemic post-TBI endocannabinoid degradation inhibition. Thus, boosting endocannabinoid tone post-TBI may represent a viable therapeutic strategy for TBI-related psychiatric comorbidities such as alcohol use disorder and anxiety.

Activation of neural stem cells from quiescence drives reactive hippocampal neurogenesis after alcohol dependence

Neural stem cell-driven adult neurogenesis contributes to the integrity of the hippocampus. Excessive alcohol consumption in alcoholism results in hippocampal degeneration that may recover with abstinence. Reactive, increased adult neurogenesis during abstinence following alcohol dependence may contribute to recovery, but the mechanism driving reactive neurogenesis is not known. Therefore, adult, male rats were exposed to alcohol for four days and various markers were used to examine cell cycle dynamics, the percentage and number of neural progenitor cell subtypes, and the percentage of quiescent versus activated progenitors. Using a screen for cell cycle perturbation, we showed that the cell cycle is not likely altered at 7 days in abstinence. As the vast majority of Bromodeoxyuridine-positive (+) cells were co-labeled with progenitor cell marker, Sox2, we then developed a quadruple fluorescent labeling scheme to examine Type-1, -2a, -2b and -3 progenitor cells simultaneously. Prior alcohol dependence indiscriminately increased all subtypes at 7 days, the peak of the reactive proliferation. An evaluation of the time course of reactive cell proliferation revealed that cells begin proliferating at 5 days post alcohol, where only actively dividing Type 2 progenitors were increased by alcohol. Furthermore, prior alcohol increased the percentage of actively dividing Sox2+ progenitors, which supported that reactive neurogenesis is likely due to the activation of progenitors out of quiescence. These observations were associated with granule cell number returning to normal at 28 days. Therefore, activating stem and progenitor cells out of quiescence may be the mechanism underlying hippocampal recovery in abstinence following alcohol dependence.

Critical needs in drug discovery for cessation of alcohol and nicotine polysubstance abuse

Polysubstance abuse of alcohol and nicotine has been overlooked in our understanding of the neurobiology of addiction and especially in the development of novel therapeutics for its treatment. Estimates show that as many as 92% of people with alcohol use disorders also smoke tobacco. The health risks associated with both excessive alcohol consumption and tobacco smoking create an urgent biomedical need for the discovery of effective cessation treatments, as opposed to current approaches that attempt to independently treat each abused agent. The lack of treatment approaches for alcohol and nicotine abuse/dependence mirrors a similar lack of research in the neurobiology of polysubstance abuse. This review discusses three critical needs in medications development for alcohol and nicotine co-abuse: (1) the need for a better understanding of the clinical condition (i.e. alcohol and nicotine polysubstance abuse), (2) the need to better understand how these drugs interact in order to identify new targets for therapeutic development and (3) the need for animal models that better mimic this human condition. Current and emerging treatments available for the cessation of each drug and their mechanisms of action are discussed within this context followed by what is known about the pharmacological interactions of alcohol and nicotine. Much has been and will continue to be gained from studying comorbid alcohol and nicotine exposure.

Corticosterone enhances N-methyl-D-aspartate receptor signaling to promote isolated ventral tegmental area activity in a reconstituted mesolimbic dopamine pathway

Elevations in circulating corticosteroids during periods of stress may influence activity of the mesolimbic dopamine reward pathway by increasing glutamatergic N-methyl-D-aspartate (NMDA) receptor expression and/or function in a glucocorticoid receptor-dependent manner. The current study employed organotypic co-cultures of the ventral tegmental area (VTA) and nucleus accumbens (NAcc) to examine the effects of corticosterone exposure on NMDA receptor-mediated neuronal viability. Co-cultures were pre-exposed to vehicle or corticosterone (CORT; 1 μM) for 5 days prior to a 24 h co-exposure to NMDA (200 μM). Co-cultures pre-exposed to a non-toxic concentration of corticosterone and subsequently NMDA showed significant neurotoxicity in the VTA only. This was evidenced by increases in propidium iodide uptake as well as decreases in immunoreactivity of the neuronal nuclear protein (NeuN). Co-exposure to the NMDA receptor antagonist 2-amino-7-phosphonovaleric acid (APV; 50 μM) or the glucocorticoid receptor (GR) antagonist mifepristone (10 μM) attenuated neurotoxicity. In contrast, the combination of corticosterone and NMDA did not produce any significant effects on either measure within the NAcc. Cultures of the VTA and NAcc maintained without synaptic contact showed no response to CORT or NMDA. These results demonstrate the ability to functionally reconstitute key regions of the mesolimbic reward pathway ex vivo and to reveal a GR-dependent enhancement of NMDA receptor-dependent signaling in the VTA.

Acute oral administration of the novel, competitive and selective glucocorticoid receptor antagonist ORG 34517 reduces the severity of ethanol withdrawal and related hypothalamic-pituitary-adrenal axis activation

BACKGROUND

The development of ethanol dependence is associated with alterations in hypothalamic-pituitary-adrenal (HPA) axis and activation of type II glucocorticoid receptors (GR). These effects may contribute to withdrawal-associated anxiety, craving and relapse to drinking. The present studies examined acute and oral administration of the novel, selective and competitive GR antagonist ORG 34517 on the severity of ethanol withdrawal.

METHODS

Adult, male Sprague-Dawley rats were administered ethanol (4g/kg/i.g.) twice daily for 5 days followed by 2 days of withdrawal for 1, 2 or 3 consecutive cycles. Blood ethanol levels (BELs) were determined at 0930 on Day 4 of each week, while blood corticosterone levels (BCLs) were obtained at 11:00hours on the first day of each ethanol withdrawal. During early withdrawal, subjects received oral administration of ORG 345617 (60mg/kg/i.g.) or a placebo and withdrawal was monitored.

RESULTS

Peak BELs of 225.52mg/dl were observed during the third week. Withdrawal from three cycles of the regimen produced marked behavioral abnormalities (e.g., aggression, rigidity, and hypoactivity) and significant increases in BCLs of ethanol-dependent subjects. Acute, oral administration of ORG 34517 during early withdrawal significantly reduced both the severity of ethanol withdrawal, as reflected in reduced rigidity, aggression, and hypoactivity, and elevations in BCL without producing any sedative-like effects.

CONCLUSIONS

The present findings demonstrate that repeated ethanol exposure and withdrawal is associated with significant behavioral abnormalities and dysregulation of HPA axis activation. Further these data suggest that selective GR antagonists should be further considered as putative pharmacotherapies for treatment of ethanol dependence.

Rescuing prefrontal cAMP-CREB pathway reverses working memory deficits during withdrawal from prolonged alcohol exposure

Both human and animal studies indicate that alcohol withdrawal following chronic alcohol consumption (CAC) impairs many of the cognitive functions which rely on the prefrontal cortex (PFC). A candidate signaling cascade contributing to memory deficits during alcohol withdrawal is the protein kinase A (PKA)/cAMP-responsive element binding (CREB) cascade, although the role of PKA/CREB cascade in behavioral and molecular changes during sustained withdrawal period remains largely unknown. We demonstrated that 1 week (1W) or 6 weeks (6W) withdrawal after 6-month CAC impairs working memory (WM) in a T-maze spontaneous alternation task and reduces phosphorylated CREB (pCREB) in the PFC but not the dorsal CA1 region (dCA1) of the hippocampus compared with CAC and water conditions. In contrast, both CAC-unimpaired and withdrawn-impaired mice exhibited decreased pCREB in dCA1 as well as reduced histone H4 acetylation in PFC and dCA1, compared with water controls. Next, we showed that enhancing CREB activity through rolipram administration prior to testing improved WM performance in withdrawn mice but impaired WM function in water mice. In addition, WM improvement correlates positively with increased pCREB level selectively in the PFC of withdrawn mice. Results further indicate that direct infusion of the PKA activator (Sp-cAMPS) into the PFC significantly improves or impairs, respectively, WM performance in withdrawn and water animals. In contrast, Sp-cAMPS had no effect on WM when infused into the dCA1. Collectively, these results provide strong support that dysregulation of PKA/CREB-dependent processes in prefrontal neurons is a critical molecular signature underlying cognitive decline during alcohol withdrawal.

Alcohol and adult hippocampal neurogenesis: promiscuous drug, wanton effects

Adult neurogenesis is now widely accepted as an important contributor to hippocampal integrity and function but also dysfunction when adult neurogenesis is affected in neuropsychiatric diseases such as alcohol use disorders. Excessive alcohol consumption, the defining characteristic of alcohol use disorders, results in a variety of cognitive and behavioral impairments related wholly or in part to hippocampal structure and function. Recent preclinical work has shown that adult neurogenesis may be one route by which alcohol produces hippocampal neuropathology. Alcohol is a pharmacologically promiscuous drug capable of interfering with adult neurogenesis through multiple mechanisms. This review will discuss the primary mechanisms underlying alcohol-induced changes in adult hippocampal neurogenesis including alcohol's effects on neurotransmitters, CREB and its downstream effectors, and the neurogenic niche.

Putative association between the -1415 T/C polymorphism of spermidine/spermine N1-acetyltransferase (SSAT1) gene and alcohol use disorders in women and men

BACKGROUND

The activity of N-methyl-D-aspartate (NMDA) glutamate receptor, which responds to the levels of polyamines, modifies the neurotoxicity caused by ethanol. We aimed to investigate if the functionality of the spermidine/spermine N1-acetyltransferase (SSAT1) gene could be associated with a differential risk for alcoholism.

METHODS

We studied a sample of 586 subjects: 104 alcohol-dependent patients, 273 patients with psychiatric disorders but without substance dependence, and 209 healthy controls. After gender stratification, the allele frequency distribution of the SSAT1 gene was compared between these three groups.

RESULTS

In females, the TC genotype was significantly more frequent in alcohol-dependent patients than in non-alcohol-dependent psychiatric controls (χ(2 )= 7.509 df = 2, p = 0.023). A trend was found when alcohol-dependent females were compared with the healthy control group (χ(2 )= 4.897 df = 2, p = 0.086). No statistical differences were found among the males.

DISCUSSION AND CONCLUSION

Gender differences in the regulation of SSAT1 gene expression may possibly be due to gender-specific effects of stress, ethanol toxicity, and/or polyamines levels. Further studies are needed to confirm our findings.

Structural reorganization of pyramidal neurons in the medial prefrontal cortex of alcohol dependent rats is associated with altered glial plasticity

In rodents, chronic intermittent ethanol vapor exposure (CIE) produces alcohol dependence, alters the activity of pyramidal neurons and decreases the number of glial progenitors in the medial prefrontal cortex (mPFC). Adult male Wistar rats were exposed to CIE and were injected with mitotic markers to label and phenotype proliferating cells to test the hypothesis that CIE produces concurrent alterations in the structure of pyramidal neurons and the cell cycle kinetics and developmental stages of glial progenitors in the mPFC. Medial prefrontal cortical tissue was processed for Golgi-Cox staining, immunohistochemistry and Western blotting analysis. CIE increased dendritic arborization and spine densities within basal and apical dendrites of pyramidal neurons via aberrant reorganization of actin cytoskeleton-associated molecules. CIE concomitantly increased the expression of total NR2B subunits without affecting phosphorylation of NR2B at Tyr-1472 or levels of PSD-95. CIE reduced the length of S-phase of the cell cycle of glial progenitors and reduced proliferation and differentiation of progenitors into bHLH transcription factor Olig2-expressing premyelinating oligodendrocyte progenitor cells (OPCs). CIE also produced a corresponding hyperphosphorylation of Olig2, and reduced expression of myelin basic protein. Our findings demonstrate that CIE-induced alterations in OPCs and myelin-related proteins are associated with profound alterations in the structure of pyramidal neurons. In sum, our results not only provide evidence that alcohol dependence leads to pathological changes in the mPFC, which may in part define a cellular basis for cognitive impairments associated with alcoholism, but also show dependence-associated morphological changes in the PFC at the single neuron level.

Cluster and meta-analyses on factors influencing stress-induced alcohol drinking and relapse in rodents

Numerous preclinical studies have focused on the identification of biological and environmental factors that modulate stress and alcohol interactions. Although there is a good qualitative description of the determinants of alcohol consumption in rodents, the magnitude of the variables influencing stress-induced ethanol intake and its dynamics are still poorly understood. We therefore carried out a clustered meta-analysis on stress-induced alcohol consumption in 1520 rats. Two-step clustering of the literature-derived dataset suggests a strong dependency of the experimental outcome on the method used to measure alcohol intake. Free-choice home cage drinking versus operant self-administration is the most critical determinant of stress-induced increases in alcohol consumption in rats. Stress does not typically result in enhanced alcohol consumption in operant self-administration paradigms, whereas it leads to increased home cage drinking. Stress-induced alcohol consumption is age dependent, with adults being more sensitive than adolescents. In addition, foot shock and forced swim stress enhance alcohol intake, while restraint stress does not. In contrast, a meta-analysis of 327 rats on stress-induced reinstatement of alcohol-seeking behavior shows less influence of those modulating factors, and usually foot shock or yohimbine leads to a reinstatement of approximately 300 percent of extinction level responding. Via accurate characterization of the significant factors in the interplay of alcohol consumption, relapse and stress, our quantitative description not only improves the understanding of underlying mechanisms, but also provides an appropriate framework for the optimal experimental design of preclinical studies that more accurately translates to the human condition.

Neurochemical mechanisms of alcohol withdrawal

Alcohol dependence encompasses a serious medical and societal problem that constitutes a major public health concern. A serious consequence of dependence is the emergence of symptoms associated with the alcohol withdrawal syndrome when drinking is abruptly terminated or substantially reduced. Clinical features of alcohol withdrawal include signs of central nervous system hyperexcitability, heightened autonomic nervous system activation, and a constellation of symptoms contributing to psychologic discomfort and negative affect. The development of alcohol dependence is a complex and dynamic process that ultimately reflects a maladaptive neurophysiologic state. Perturbations in a wide range of neurochemical systems, including glutamate, γ-aminobutyric acid, monoamines, a host of neuropeptide systems, and various ion channels produced by the chronic presence of alcohol ultimately compromise the functional integrity of the brain. These neuroadaptations not only underlie the emergence and expression of many alcohol withdrawal symptoms, but also contribute to enhanced relapse vulnerability as well as perpetuation of uncontrolled excessive drinking. This chapter highlights the hallmark features of the alcohol withdrawal syndrome, and describes neuroadaptations in a wide array of neurotransmitter and neuromodulator systems (amino acid and monoamine neurotransmitter, neuropeptide systems, and various ion channels) as they relate to the expression of various signs and symptoms of alcohol withdrawal, as well as their relationship to the significant clinical problem of relapse and uncontrolled dangerous drinking.

Long-term ethanol and corticosterone co-exposure sensitize the hippocampal ca1 region pyramidal cells to insult during ethanol withdrawal in an NMDA GluN2B subunit-dependent manner

BACKGROUND

Chronic ethanol (EtOH) exposure produces neuroadaptations in NMDA receptor function and/or abundance and alterations in hypothalamic-pituitary-adrenal (HPA) axis functioning that contribute to neuronal excitation and neurotoxicity during ethanol withdrawal (EWD). Both EtOH and corticosterone (CORT) promote synthesis of polyamines, which allosterically potentiate NMDA receptor function at the GluN2B subunit. The current studies investigated the effect of 10-day EtOH and CORT co-exposure on toxicity during EWD in rat hippocampal explants and hypothesized that alterations in function and/or density of GluN2B subunits contribute to the toxicity.

METHODS

Organotypic hippocampal slice cultures were exposed to CORT (0.01-1.0 μM) during 10-day EtOH exposure (50 mM) and 1 day of EWD. EtOH-naïve cultures were exposed to CORT for 11 days. Additional cultures were exposed to a membrane impermeable form of CORT (BSA-CORT) with and without 10-day EtOH exposure and EWD. Cytotoxicity (uptake of propidium iodide) was assessed in the pyramidal cell layer of the CA1 region. Western blot analysis was employed to assess the density of GluN2B subunits following EtOH and CORT exposure.

RESULTS

EWD did not produce overt neurotoxicity. However, co-exposure to EtOH/EWD and CORT produced significant neurotoxicity in the CA1 region pyramidal cell layer. Ifenprodil, a GluN2B polyamine site antagonist, significantly reduced toxicity from EtOH and CORT (0.1 μM) co-exposure during EWD. However, Western blots did not reveal differences in GluN2B subunit density among groups. Exposure to BSA-CORT did not produce toxicity, suggesting that membrane-bound CORT receptors did not significantly contribute to the observed toxicity.

CONCLUSIONS

These data suggest that CORT and EtOH co-exposure result in increased function of polyamine-sensitive GluN2B subunits, but this toxicity does not appear dependent on the abundance of hippocampal NMDA GluN2B subunits or membrane-bound CORT receptor function.

Sex differences in neuroadaptation to alcohol and withdrawal neurotoxicity

Recent work suggests that sex differences exist with regard to both the nature of neuroadaptation to alcohol during the development of dependence, and possibly, the neurodegenerative consequences of alcohol dependence. Volumetric studies in human samples show that females may demonstrate increased volumetric brain loss with equal or lesser dependence histories than males. Furthermore, animal studies demonstrate sex differences in glutamatergic, GABAergic, and adenosinergic receptor signaling and endocrine responses following prolonged alcohol exposure. These differences may influence the development of dependence, neuronal function, and viability, particularly during alcohol withdrawal. The present review discusses the current state of knowledge in this regard. It is concluded that there exists a clear need for a more extensive examination of potential sex differences in neurodegenerative consequences of alcohol dependence in men and women, particularly with regard to the role that alterations in amino acid signaling and hypothalamic-pituitary-adrenal axis function may play. Furthermore, we note the need for expanded examination of the unique role that alcohol withdrawal-associated neuronal activity may have in the development of dependence-associated neurotoxicity.

Mifepristone pretreatment reduces ethanol withdrawal severity in vivo

BACKGROUND

Prolonged ethanol (EtOH) intake may perturb function of the hypothalamic-pituitary-adrenal axis in a manner that promotes dependence and influences EtOH withdrawal severity. Prior in vivo and in vitro studies suggest that corticosteroids, in particular, may be elevated during EtOH intoxication and withdrawal, suggesting that intracellular glucocorticoid receptors (GRs) may promote the development of EtOH dependence.

METHODS

Adult male Sprague-Dawley rats were subjected to a 4-day binge-like EtOH administration regimen (3 to 5 g/kg/i.g. every 8 hours designed to produce peak blood EtOH levels (BELs) of <300 mg/dl). Subgroups of animals received s.c. injection of the GR antagonist mifepristone (20 or 40 mg/kg in peanut oil at 0800 hours on each of the 4 days prior to withdrawal). BELs were assessed at 0900 and 1500 hours on Days 2 (D2) and 4 (D4) of the regimen. BEL, blood corticosterone levels (BCLs), and EtOH withdrawal-associated behavioral abnormalities were assessed 10 to 12 hours after the final EtOH administration.

RESULTS

Daily mean EtOH doses for D1 to D4 of the regimen were 14.4, 9.9, 7.1, and 8.6 g/kg, respectively. The EtOH gavage regimen produced mean BELs of 255 mg/dl at 0900 on D2 and 156.2 mg/dl at 0900 on D4 of the regimen. Withdrawal from the EtOH exposure regimen, beginning 10 hours after the last EtOH administration, produced significant elevations in BCL and behavioral abnormalities including tremors, stereotypy, and "wet dog shakes." Mifepristone administration did not alter food intake or weight during the 4-day regimen, nor were there drug-dependent differences in BEL or BCL on withdrawal day. Although mifepristone produced no significant changes in behavior of EtOH-naïve animals, pretreatment with mifepristone (40 mg/kg) significantly reduced the severity of EtOH withdrawal.

CONCLUSIONS

Findings suggest that activation of GRs promotes neuroadaptation to binge-like EtOH exposure, contributing to the development of EtOH dependence. Further, GRs may represent therapeutic targets to be exploited in reducing the severity of EtOH withdrawal.

The role of the glucocorticoids in developing resilience to stress and addiction

There is emerging evidence that individuals have the capacity to learn to be resilient by developing protective mechanisms that prevent them from the maladaptive effects of stress that can contribute to addiction. The emerging field of the neuroscience of resilience is beginning to uncover the circuits and molecules that protect against stress-related neuropsychiatric diseases, such as addiction. Glucocorticoids (GCs) are important regulators of basal and stress-related homeostasis in all higher organisms and influence a wide array of genes in almost every organ and tissue. GCs, therefore, are ideally situated to either promote or prevent adaptation to stress. In this review, we will focus on the role of GCs in the hypothalamic-pituitary adrenocortical axis and extra-hypothalamic regions in regulating basal and chronic stress responses. GCs interact with a large number of neurotransmitter and neuropeptide systems that are associated with the development of addiction. Additionally, the review will focus on the orexinergic and cholinergic pathways and highlight their role in stress and addiction. GCs play a key role in promoting the development of resilience or susceptibility and represent important pharmacotherapeutic targets that can reduce the impact of a maladapted stress system for the treatment of stress-induced addiction.

The Interplay between the Hippocampus and Amygdala in Regulating Aberrant Hippocampal Neurogenesis during Protracted Abstinence from Alcohol Dependence

The development of alcohol dependence involves elevated anxiety, low mood, and increased sensitivity to stress, collectively labeled negative affect. Particularly interesting is the recent accumulating evidence that sensitized extrahypothalamic stress systems [e.g., hyperglutamatergic activity, blunted hypothalamic-pituitary-adrenal (HPA) hormonal levels, altered corticotropin-releasing factor signaling, and altered glucocorticoid receptor signaling in the extended amygdala] are evident in withdrawn dependent rats, supporting the hypothesis that pathological neuroadaptations in the extended amygdala contribute to the negative affective state. Notably, hippocampal neurotoxicity observed as aberrant dentate gyrus (DG) neurogenesis (neurogenesis is a process where neural stem cells in the adult hippocampal subgranular zone generate DG granule cell neurons) and DG neurodegeneration are observed in withdrawn dependent rats. These correlations between withdrawal and aberrant neurogenesis in dependent rats suggest that alterations in the DG could be hypothesized to be due to compromised HPA axis activity and associated hyperglutamatergic activity originating from the basolateral amygdala in withdrawn dependent rats. This review discusses a possible link between the neuroadaptations in the extended amygdala stress systems and the resulting pathological plasticity that could facilitate recruitment of new emotional memory circuits in the hippocampus as a function of aberrant DG neurogenesis.

Independent contributions of alcohol and stress axis hormones to painful peripheral neuropathy

Painful small-fiber peripheral neuropathy is a debilitating complication of chronic alcohol abuse. Evidence from previous studies suggests that neuroendocrine mechanisms, in combination with other, as yet unidentified actions of alcohol, are required to produce this neuropathic pain syndrome. In addition to neurotoxic effects of alcohol, in the setting of alcohol abuse neuroendocrine stress axes release glucocorticoids and catecholamines. Since receptors for these stress hormones are located on nociceptors, at which they can act to cause neuronal dysfunction, we tested the hypothesis that alcohol and stress hormones act on the nociceptor, independently, to produce neuropathic pain. We used a rat model, which allows the distinction of the effects of alcohol from those produced by neuroendocrine stress axis mediators. We now demonstrate that topical application of alcohol and exposure to unpredictable sound stress, each alone, has no effect on the nociceptive threshold. However, when animals that had previous exposure to alcohol were subsequently exposed to stress, they rapidly developed mechanical hyperalgesia. Conversely, sound stress followed by topical alcohol exposure also produced mechanical hyperalgesia. The contribution of stress hormones was prevented by spinal intrathecal administration of oligodeoxynucleotides antisense to β(2)-adrenergic or glucocorticoid receptor mRNA, which attenuates receptor level in nociceptors, as well as by adrenal medullectomy. These experiments establish an independent role of alcohol and stress hormones on the primary afferent nociceptor in the induction of painful peripheral neuropathy.