Chronic alcohol neuroadaptation and stress contribute to susceptibility for alcohol craving and relapse

Rodent models for compulsive alcohol intake

Continued seeking and drinking of alcohol despite adverse legal, health, economic, and societal consequences is a central hallmark of human alcohol use disorders. This compulsive drive for alcohol, defined by resistance to adverse and deleterious consequences, represents a major challenge when attempting to treat alcoholism clinically. Thus, there has long been interest in developing pre-clinical rodent models for the compulsive drug use that characterizes drug addiction. Here, we review recent studies that have attempted to model compulsive aspects of alcohol and cocaine intake in rodents, and consider technical and conceptual issues that need to be addressed when trying to recapitulate compulsive aspects of human addiction. Aversion-resistant alcohol intake has been examined by pairing intake or seeking with the bitter tastant quinine or with footshock, and exciting recent work has used these models to identify neuroadaptations in the amygdala, cortex, and striatal regions that promote compulsive intake. Thus, rodent models do seem to reflect important aspects of compulsive drives that sustain human addiction, and will likely provide critical insights into the molecular and circuit underpinnings of aversion-resistant intake as well as novel therapeutic interventions for compulsive aspects of addiction.

Alcohol stress response dampening during imminent versus distal, uncertain threat

Research indicates that fear and anxiety are distinct processes with separable neurobiological substrates. Predictable versus unpredictable shock administration has been used to elicit fear versus anxiety, respectively. Recent research has demonstrated that alcohol may reduce anxiety but not fear. However, previous manipulations of predictability have varied both probability and temporal uncertainty of shock threat, leaving unresolved questions regarding which stimulus characteristics elicit anxiety and are sensitive to alcohol stress-response dampening (SRD). We developed a novel paradigm to closely parallel basic research in animals that systematically varied temporal uncertainty of threat while holding threat probability constant. Intoxicated (0.08% target blood alcohol concentration), placebo, and no-alcohol control participants viewed a series of visual threat cues. Certain cue duration (5 s) blocks were equivalent to predictable shock blocks eliciting fear in earlier research. Uncertain cue duration (5, 20, 50, or 80 s, intermixed) blocks introduced temporal uncertainty regarding impending shock to elicit anxiety. Startle potentiation relative to matched cue periods in no-shock blocks provided the primary measure of affective response. All threat cues produced robust startle potentiation. Alcohol reduced startle potentiation during the first 5 s of threat cue presentation in uncertain but not certain duration blocks. Alcohol also reduced startle potentiation at later times among longer uncertain duration cues, suggesting that alcohol SRD persisted. Trait negative emotionality and binge drinking status moderated alcohol SRD magnitude during uncertain threat. These translational findings corroborate previous reports regarding distinct substrates of fear versus anxiety and have implications for both alcoholism etiology and comorbidity with anxiety disorders.

Corticotropin releasing factor: a key role in the neurobiology of addiction

Drug addiction is a chronically relapsing disorder characterized by loss of control over intake and dysregulation of stress-related brain emotional systems. Since the discovery by Wylie Vale and his colleagues of corticotropin-releasing factor (CRF) and the structurally-related urocortins, CRF systems have emerged as mediators of the body's response to stress. Relatedly, CRF systems have a prominent role in driving addiction via actions in the central extended amygdala, producing anxiety-like behavior, reward deficits, excessive, compulsive-like drug self-administration and stress-induced reinstatement of drug seeking. CRF neuron activation in the medial prefrontal cortex may also contribute to the loss of control. Polymorphisms in CRF system molecules are associated with drug use phenotypes in humans, often in interaction with stress history. Drug discovery efforts have yielded brain-penetrant CRF1 antagonists with activity in preclinical models of addiction. The results support the hypothesis that brain CRF-CRF1 systems contribute to the etiology and maintenance of addiction.

Cue reactivity is associated with duration and severity of alcohol dependence: an FMRI study

INTRODUCTION

With the progression of substance dependence, drug cue-related brain activation is thought to shift from motivational towards habit pathways. However, a direct association between cue-induced brain activation and dependence duration has not yet been shown. We therefore examined the relationship between alcohol cue-reactivity in the brain, cue-induced subjective craving and alcohol dependence duration and severity. Since alcohol dependence is highly comorbid with depression/anxiety, which may modulate brain responses to alcohol cues, we also examined the relation between comorbid depression/anxiety and cue-reactivity.

METHODS

We compared 30 alcohol dependent patients with 15 healthy controls and 15 depression/anxiety patients during a visual alcohol cue-reactivity task using functional magnetic resonance imaging blood oxygenated level-dependent responses and subjective craving as outcomes. Within the alcohol dependent group we correlated cue-reactivity with alcohol dependence severity and duration, with cue-induced craving and with depression/anxiety levels.

RESULTS

Alcohol dependent patients showed greater cue-reactivity in motivational brain pathways and stronger subjective craving than depression/anxiety patients and healthy controls. Depression/anxiety was not associated with cue-reactivity, but depression severity in alcohol dependent patients was positively associated with craving. Within alcohol dependence, longer duration of alcohol dependence was associated with stronger cue-related activation of the posterior putamen, a structure involved in habits, whereas higher alcohol dependence severity was associated with lower cue-reactivity in the anterior putamen, an area implicated in goal-directed behavior preceding habit formation.

CONCLUSION

Cue-reactivity in alcohol dependence is not modulated by comorbid depression or anxiety. More importantly, the current data confirm the hypothesis of a ventral to dorsal striatal shift of learning processes with longer dependence duration, which could underlie increasingly habitual substance use with progressing substance dependence.

The impact of social isolation on HPA axis function, anxiety-like behaviors, and ethanol drinking

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis is often observed in alcoholics and humans subjected to early life stress, and animal models of ethanol (EtOH) dependence. We examined HPA axis function in a rodent model of early life stress that engenders increases in behavioral and neurobiological risk factors of alcoholism. Long-Evans male rats were group housed (GH) or socially isolated (SI) for 6 weeks during adolescence. We examined the corticosterone (CORT) response to stress with and without dexamethasone (DEX) and anxiety-like behaviors. Following the DEX suppression test and behavioral assays, half of the cohort engaged in 6 weeks of EtOH drinking in a homecage, two-bottle choice intermittent access model. A subset of the cohort was not exposed to EtOH, but was used for electrophysiological measurement of glutamatergic synaptic plasticity in the basolateral amygdala (BLA). Correlational analyses examined relationships between measures of CORT, anxiety-like behaviors, and EtOH intake/preference. With DEX pre-treatment, SI rats failed to suppress CORT in response to an acute stress; GH rats showed a significant suppression. In SI rats, there was a significant negative correlation between baseline CORT and elevated plus maze open arm time, as well as significant positive correlations between baseline CORT and both EtOH intake and preference. No significant relationships between baseline CORT and behavioral measures were observed in GH rats. Glutamatergic plasticity in the BLA was similar in magnitude between GH and SI rats, and was not altered by exogenous application of CORT. These data suggest that HPA axis function is affected by SI, and this is related to antecedent anxiety-like behavior and may predispose for future EtOH self-administration. Relationships between HPA axis function, anxiety, and EtOH measures in SI rats further strengthens the utility of this paradigm in modeling vulnerability for affective disorders and alcoholism.

The neurobiology of alcohol craving and relapse

A major block to recovery from alcoholism is substantial alcohol craving and the chronic relapsing nature of the illness. This chapter reviews relevant structural and functional neuroimaging studies and discusses neural mechanisms underlying alcohol craving and relapse in the context of influential risk factors (i.e., alcohol, alcohol cue, and stress). Review of neuroimaging studies suggests that neuroadaptations in the cortico-striatal-limbic circuit encompassing the medial prefrontal cortex, orbitofrontal cortex, anterior cingulate cortex, striatum, and amygdala significantly contribute to overwhelming alcohol craving and early relapse after a period of abstinence. The cortico-striatal-limbic circuit plays an important role in the modulation of emotion, reward, and decision making. As functional and structural chronic alcohol-related neuroadaptations are consistently reported in this circuit, it is likely that sensitization of this circuit from continued alcohol abuse may contribute to high alcohol craving and early relapse via impairments in the prefrontal executive function related to emotion regulation and decision making. This vulnerable neurobiologic state may be manifested as compulsive craving and intense urge to resume alcohol drinking in the face of environmental risk factors, including alcohol, alcohol cue, or stressful live events.

Chronic psychosocial stress causes delayed extinction and exacerbates reinstatement of ethanol-induced conditioned place preference in mice

RATIONALE

We have shown previously, using an animal model of voluntary ethanol intake and ethanol-conditioned place preference (EtOH-CPP), that exposure to chronic psychosocial stress induces increased ethanol intake and EtOH-CPP acquisition in mice.

OBJECTIVE

Here, we examined the impact of chronic subordinate colony (CSC) exposure on EtOH-CPP extinction, as well as ethanol-induced reinstatement of CPP.

METHODS

Mice were conditioned with saline or 1.5 g/kg ethanol and were tested in the EtOH-CPP model. In the first experiment, the mice were subjected to 19 days of chronic stress, and EtOH-CPP extinction was assessed during seven daily trials without ethanol injection. In the second experiment and after the EtOH-CPP test, the mice were subjected to 7 days of extinction trials before the 19 days of chronic stress. Drug-induced EtOH-CPP reinstatement was induced by a priming injection of 0.5 g/kg ethanol.

RESULTS

Compared to the single-housed colony mice, CSC mice exhibited increased anxiety-like behavior in the elevated plus maze (EPM) and the open field tests. Interestingly, the CSC mice showed delayed EtOH-CPP extinction. More importantly, CSC mice showed increased alcohol-induced reinstatement of the EtOH-CPP behavior.

CONCLUSION

Taken together, this study indicates that chronic psychosocial stress can have long-term effects on EtOH-CPP extinction as well as drug-induced reinstatement behavior and may provide a suitable model to study the latent effects of chronic psychosocial stress on extinction and relapse to drug abuse.

Substance abuse, memory, and post-traumatic stress disorder

A large body of literature demonstrates the effects of abused substances on memory. These effects differ depending on the drug, the pattern of delivery (acute or chronic), and the drug state at the time of learning or assessment. Substance use disorders involving these drugs are often comorbid with anxiety disorders, such as post-traumatic stress disorder (PTSD). When the cognitive effects of these drugs are considered in the context of the treatment of these disorders, it becomes clear that these drugs may play a deleterious role in the development, maintenance, and treatment of PTSD. In this review, we examine the literature evaluating the cognitive effects of three commonly abused drugs: nicotine, cocaine, and alcohol. These three drugs operate through both common and distinct neurobiological mechanisms and alter learning and memory in multiple ways. We consider how the cognitive and affective effects of these drugs interact with the acquisition, consolidation, and extinction of learned fear, and we discuss the potential impediments that substance abuse creates for the treatment of PTSD.

The cytokine mRNA increase induced by withdrawal from chronic ethanol in the sterile environment of brain is mediated by CRF and HMGB1 release

BACKGROUND

Many neurobiological factors may initiate and sustain alcoholism. Recently, dysregulation of the neuroimmune system by chronic ethanol (CE) has implicated Toll-like receptor 4 (TLR4) activation. Even though TLR4s are linked to CE initiation of brain cytokine mRNAs, the means by which CE influences neuroimmune signaling in brain in the absence of infection remains uncertain. Therefore, the hypothesis is tested that release of an endogenous TLR4 agonist, high-mobility group box 1 (HMGB1) and/or corticotropin-releasing factor (CRF) during CE withdrawal are responsible for CE protocols increasing cytokine mRNAs.

METHODS

Acute ethanol (EtOH; 2.75 g/kg) and acute lipopolysaccharide (LPS; 250 μg/kg) dosing on cytokine mRNAs are first compared. Then, the effects of chronic LPS exposure (250 μg/kg for 10 days) on cytokine mRNAs are compared with changes induced by CE protocols (15 days of continuous 7% EtOH diet [CE protocol] or 3 intermittent 5-day cycles of 7% EtOH diet [CIE protocol]). Additionally, TLR4, HMGB1, and downstream effector mRNAs are assessed after CE, CIE, and chronic LPS. To test whether HMGB1 and/or CRF support the CE withdrawal increase in cytokine mRNAs, the HMGB1 antagonists, glycyrrhizin and ethyl pyruvate, and a CRF1 receptor antagonist (CRF1RA) are administered during 24 hours of CE withdrawal.

RESULTS

While cytokine mRNAs were not increased following acute EtOH, acute LPS increased all cytokine mRNAs 4 hours after injection. CE produced no change in cytokine mRNAs prior to CE removal; however, the CE and CIE protocols increased cytokine mRNAs by 24 hours after withdrawal. In contrast, chronic LPS produced no cytokine mRNA changes 24 hours after LPS dosing. TLR4 mRNA was elevated 24 hours following both CE protocols and chronic LPS exposure. While chronic LPS had no effect on HMGB1 mRNA, withdrawal from CE protocols significantly elevated HMGB1 mRNA. Systemic administration of HMGB1 antagonists or a CRF1RA significantly reduced the cytokine mRNA increase following CE withdrawal. The CRF1RA and the HMGB1 antagonist, ethyl pyruvate, also reduced the HMGB1 mRNA increase that followed CE withdrawal.

CONCLUSIONS

By blocking HMGB1 or CRF action during CE withdrawal, evidence is provided that HMGB1 and CRF release are critical for the CE withdrawal induction of selected brain cytokine mRNAs. Consequently, these results clarify a means by which withdrawal from CE exposure activates neuroimmune function in the sterile milieu of brain.

Evidence for TNFα action on excitatory and inhibitory neurotransmission in the central amygdala: a brain site influenced by stress

Anxiety-like responses to stress are accompanied by elevation of brain cytokine-mRNAs. Because cytokines microinjected into central-amygdala (CeA) substitute for stress in a behavioral paradigm, the possibility was raised that cytokines increased by stress influence behavior by affecting CeA-neural activity. Previously, cytokines increased firing-rate of CeA-neurons comparable to that induced by corticotropin-releasing factor (CRF). In this investigation, tumor-necrosis-factor-α (TNFα) increased amplitude, but not frequency of mEPSCs from CeA-neurons. Additionally, TNFα decreased the threshold for triggering action potentials from CeA-neurons without altering membrane-properties during current-clamp recording. Glutamate-receptor-antagonist blockade of mEPSCs and the TNFα-induced reduction in firing threshold implicated glutamate in these changes. A phosphatidyl-inositol-3-kinase-antagonist prevented the TNFα-induced increased in amplitude of mEPSCs, documenting a TNFα intracellular influence. Additionally, TNFα increased frequency, but not amplitude of mIPSCs. CRF-receptor-antagonists were found to prevent the TNFα-induced increase in mIPSC-frequency, without altering the TNFα-induced amplitude increase in mEPSCs or the reduced threshold for action-potentials by TNFα. To clarify how TNFα was increasing CRF-release in the presence of tetrodotoxin, the possibility tested was whether preventing glial-activation would prevent this elevated mIPSC-frequency blocked by CRF-receptor antagonists. Minocycline, which blocks glial activation, prevented the TNFα-induced increase in mIPSC-frequency - a finding consistent with glia contributing to the CRF-involvement in this TNFα action. To fully understand the means by which a CRF1-receptor-antagonist and minocycline prevent TNFα from increasing mIPSC-frequency will require further clarification. Nonetheless, these data provide convincing evidence that release of TNFα by stress could alter neural activity of CeA-neurons by influencing GABA-and glutamate function.

Startle response to unpredictable threat in comorbid panic disorder and alcohol dependence

BACKGROUND

Although the adverse consequences of comorbid panic disorder (PD) and alcohol dependence (AD) are well-established, relatively little is known about the mechanisms underlying their co-occurrence. Several researchers have postulated that alcohol's ability to dampen response to unpredictable threat may be an important motivational factor in comorbid PD and AD. To date, no research has examined these processes using a clinical sample and it is unclear whether individuals with PD and AD evidence different reactivity to unpredictable threat relative to individuals with PD-only.

METHODS

The aim of the current study was to examine differences in aversive responding during predictable and unpredictable threat-of-shock in three groups of individuals with: (1) current PD and remitted AD (PD and AD), (2) current PD but no lifetime diagnosis of AD (PD-only), and (3) no lifetime diagnoses of PD or AD (controls). Aversive responding was assessed using a well-established electromyography (EMG) startle paradigm.

RESULTS

Results indicated that PD and AD individuals evidenced greater startle potentiation during unpredictable (but not predictable) threat relative to controls and PD-only individuals (who did not differ).

CONCLUSIONS

These findings suggest that heightened reactivity to unpredictable threat may be an important process in PD and AD comorbidity and a possible key motivational factor underlying engagement in alcohol use.

Chronic alcohol produces neuroadaptations to prime dorsal striatal learning

Drug addictions including alcoholism are characterized by degradation of executive control over behavior and increased compulsive drug seeking. These profound behavioral changes are hypothesized to involve a shift in the regulation of behavior from prefrontal cortex to dorsal striatum (DLS). Studies in rodents have shown that ethanol disrupts cognitive processes mediated by the prefrontal cortex, but the potential effects of chronic ethanol on DLS-mediated cognition and learning are much less well understood. Here, we first examined the effects of chronic EtOH on DLS neuronal morphology, synaptic plasticity, and endocannabinoid-CB1R signaling. We next tested for ethanol-induced changes in striatal-related learning and DLS in vivo single-unit activity during learning. Mice exposed to chronic intermittent ethanol (CIE) vapor exhibited expansion of dendritic material in DLS neurons. Following CIE, DLS endocannabinoid CB1 receptor signaling was down-regulated, and CB1 receptor-dependent long-term depression at DLS synapses was absent. CIE mice showed facilitation of DLS-dependent pairwise visual discrimination and reversal learning, relative to air-exposed controls. CIE mice were also quicker to extinguish a stimulus-reward instrumental response and faster to reduce Pavlovian approach behavior under an omission schedule. In vivo single-unit recording during learning revealed that CIE mice had augmented DLS neuronal activity during correct responses. Collectively, these findings support a model in which chronic ethanol causes neuroadaptations in the DLS that prime for greater DLS control over learning. The shift to striatal dominance over behavior may be a critical step in the progression of alcoholism.

Disrupted ventromedial prefrontal function, alcohol craving, and subsequent relapse risk

IMPORTANCE

Alcohol dependence is a chronic relapsing illness; stress, alcohol-related cues, and neutral-relaxing states significantly influence craving and relapse risk. However, neural mechanisms underlying the association between these states and alcohol craving and relapse risk remain unclear.

OBJECTIVES

To identify neural correlates associated with alcohol craving and relapse outcomes in 45 treatment-engaged, 4- to 8-week abstinent alcohol-dependent (AD) patients, and to compare brain responses of 30 demographically matched AD patients and 30 healthy control subjects during stress, alcohol, and neutral-relaxing cues.

DESIGN

Functional magnetic resonance imaging study while participants were engaging in brief individualized script-driven imagery trials of stress, alcohol cues, and neutral-relaxing scenarios, and a prospective clinical outcome design to assess alcohol relapse 90 days postdischarge from inpatient treatment in the AD group.

SETTINGS

Inpatient treatment setting in a community mental health center and hospital-based research unit.

PATIENTS

Forty-five recovering AD patients in inpatient treatment for examining relapse, and 30 healthy control subjects demographically matched to 30 AD patients (subgroup of the relapse sample) for group comparisons.

INTERVENTION

Twelve-step recovery-based addiction treatment for the patient group.

MAIN OUTCOMES AND MEASURES

Brain response, alcohol craving, and relapse outcome measures (time to relapse and relapse severity).

RESULTS

Increased ventromedial prefrontal cortex (vmPFC) and anterior cingulate cortex (ACC) activation during neutral-relaxing trials was correlated with high alcohol cue-induced and stress-induced craving in early recovering AD patients (x = 6, y = 43, z = -6; P < .01, whole-brain corrected). This vmPFC/ACC hyperactivity significantly predicted subsequent alcohol relapse, with a hazards ratio greater than 8 for increased relapse risk. Additionally, vmPFC/ACC hyperactivation during neutral trials and reduced activity during stress trials were each predictive of greater days of alcohol used after relapse (P < .01, whole-brain corrected). In contrast, matched control subjects showed the reverse pattern of vmPFC/ACC responses to stress, alcohol cues, and relaxed trials (F = 6.42; P < .01, whole-brain corrected).

CONCLUSIONS AND RELEVANCE

Findings indicate that disrupted vmPFC/ACC function plays a role in jeopardizing recovery from alcoholism and may serve as a neural marker to identify those at risk for alcohol relapse.

Cortical activation of accumbens hyperpolarization-active NMDARs mediates aversion-resistant alcohol intake

Compulsive drinking despite serious adverse medical, social and economic consequences is a characteristic of alcohol use disorders in humans. Although frontal cortical areas have been implicated in alcohol use disorders, little is known about the molecular mechanisms and pathways that sustain aversion-resistant intake. Here, we show that nucleus accumbens core (NAcore) NMDA-type glutamate receptors and medial prefrontal (mPFC) and insula glutamatergic inputs to the NAcore are necessary for aversion-resistant alcohol consumption in rats. Aversion-resistant intake was associated with a new type of NMDA receptor adaptation, in which hyperpolarization-active NMDA receptors were present at mPFC and insula but not amygdalar inputs in the NAcore. Accordingly, inhibition of Grin2c NMDA receptor subunits in the NAcore reduced aversion-resistant alcohol intake. None of these manipulations altered intake when alcohol was not paired with an aversive consequence. Our results identify a mechanism by which hyperpolarization-active NMDA receptors under mPFC- and insula-to-NAcore inputs sustain aversion-resistant alcohol intake.

Cytisine modulates chronic voluntary ethanol consumption and ethanol-induced striatal up-regulation of ΔFosB in mice

Chronic administration of ethanol induces persistent accumulation of ΔFosB, an important transcription factor, in the midbrain dopamine system. This process underlies the progression to addiction. Previously, we have shown that cytisine, a neuronal nicotinic acetylcholine receptor (nAChR) partial agonist, reduces various ethanol-drinking behaviors and ethanol-induced striatal dopamine function. However, the effects of cytisine on chronic ethanol drinking and ethanol-induced up-regulation of striatal ΔFosB are not known. Therefore, we examined the effects of cytisine on chronic voluntary ethanol consumption and associated striatal ΔFosB up-regulation in C57BL/6J mice using behavioral and biochemical methods. Following the chronic voluntary consumption of 15% (v/v) ethanol under a 24-h two-bottle choice intermittent access (IA; 3 sessions/week) or continuous access (CA; 24 h/d and 7 d/week) paradigm, mice received repeated intraperitoneal injections of saline or cytisine (0.5 or 3.0 mg/kg). Ethanol and water intake were monitored for 24 h post-treatment. Pretreatment with cytisine (0.5 or 1.5 mg/kg) significantly reduced ethanol consumption and preference in both paradigms at 2 h and 24 h post-treatment. The ΔFosB levels in the ventral and dorsal striatum were determined by Western blotting 18-24 h after the last point of ethanol access. In addition, cytisine (0.5 mg/kg) significantly attenuated up-regulation of ΔFosB in the ventral and dorsal striatum following chronic ethanol consumption in IA and CA paradigms. The results indicate that cytisine modulates chronic voluntary ethanol consumption and reduces ethanol-induced up-regulation of striatal ΔFosB. Further, the data suggest a critical role of nAChRs in chronic ethanol-induced neurochemical adaptations associated with ethanol addiction.

Retraining the addicted brain: a review of hypothesized neurobiological mechanisms of mindfulness-based relapse prevention

Addiction has generally been characterized as a chronic relapsing condition (Leshner, 1999). Several laboratory, preclinical, and clinical studies have provided evidence that craving and negative affect are strong predictors of the relapse process. These states, as well as the desire to avoid them, have been described as primary motives for substance use. A recently developed behavioral treatment, mindfulness-based relapse prevention (MBRP), was designed to target experiences of craving and negative affect and their roles in the relapse process. MBRP offers skills in cognitive-behavioral relapse prevention integrated with mindfulness meditation. The mindfulness practices in MBRP are intended to increase discriminative awareness, with a specific focus on acceptance of uncomfortable states or challenging situations without reacting "automatically." A recent efficacy trial found that those randomized to MBRP, as compared with those in a control group, demonstrated significantly lower rates of substance use and greater decreases in craving following treatment. Furthermore, individuals in MBRP did not report increased craving or substance use in response to negative affect. It is important to note, areas of the brain that have been associated with craving, negative affect, and relapse have also been shown to be affected by mindfulness training. Drawing from the neuroimaging literature, we review several plausible mechanisms by which MBRP might be changing neural responses to the experiences of craving and negative affect, which subsequently may reduce risk for relapse. We hypothesize that MBRP may affect numerous brain systems and may reverse, repair, or compensate for the neuroadaptive changes associated with addiction and addictive-behavior relapse.

Neurobiology of an endophenotype: modeling the progression of alcohol addiction in rodents

Most adults in Western society consume alcohol on a regular basis with few or no negative consequences. However, for certain individuals, alcohol use escalates, leading to uncontrolled drinking bouts, craving, and repeated episodes of relapse. The transition from regulated to uncontrolled and compulsive drinking is a defining feature (i.e. an endophenotype) of alcohol addiction. This behavioral progression can be modeled in rodent paradigms that parallel the diagnostic criteria for addiction in humans. Using these criteria as a framework, this review outlines the neurobiological factors associated with increased vulnerability to excessive, compulsive, and dysregulated alcohol intake in rodents. We conclude by noting gaps in the literature and outline important directions for future research.

Behavioral, biological, and chemical perspectives on targeting CRF(1) receptor antagonists to treat alcoholism

BACKGROUND

Alcohol use disorders are chronic disabling conditions for which existing pharmacotherapies have only modest efficacy. In the present review, derived from the 2012 Behavior, Biology and Chemistry "Translational Research in Addiction" symposium, we summarize the anti-relapse potential of corticotropin-releasing factor type 1 (CRF(1)) receptor antagonists to reduce negative emotional symptoms of acute and protracted alcohol withdrawal and stress-induced relapse to alcohol seeking.

METHODS

We review the biology of CRF(1) systems, the activity of CRF(1) receptor antagonists in animal models of anxiolytic and antidepressant activity, and experimental findings in alcohol addiction models. We also update the clinical trial status of CRF(1) receptor antagonists, including pexacerfont (BMS-562086), emicerfont (GW876008), verucerfont (GSK561679), CP316311, SSR125543A, R121919/NBI30775, R317573/19567470/CRA5626, and ONO-2333Ms. Finally, we discuss the potential heterogeneity and pharmacogenomics of CRF(1) receptor pharmacotherapy for alcohol dependence.

RESULTS

The evidence suggests that brain penetrant-CRF(1) receptor antagonists have therapeutic potential for alcohol dependence. Lead compounds with clinically desirable pharmacokinetic properties now exist, and longer receptor residence rates (i.e., slow dissociation) may predict greater CRF(1) receptor antagonist efficacy. Functional variants in genes that encode CRF system molecules, including polymorphisms in Crhr1 (rs110402, rs1876831, rs242938) and Crhbp genes (rs10055255, rs3811939) may promote alcohol seeking and consumption by altering basal or stress-induced CRF system activation.

CONCLUSIONS

Ongoing clinical trials with pexacerfont and verucerfont in moderately to highly severe dependent anxious alcoholics may yield insight as to the role of CRF(1) receptor antagonists in a personalized medicine approach to treat drug or alcohol dependence.

Mindfulness-based relapse prevention for substance craving

Craving, defined as the subjective experience of an urge or desire to use substances, has been identified in clinical, laboratory, and preclinical studies as a significant predictor of substance use, substance use disorder, and relapse following treatment for a substance use disorder. Various models of craving have been proposed from biological, cognitive, and/or affective perspectives, and, collectively, these models of craving have informed the research and treatment of addictive behaviors. In this article we discuss craving from a mindfulness perspective, and specifically how mindfulness-based relapse prevention (MBRP) may be effective in reducing substance craving. We present secondary analyses of data from a randomized controlled trial that examined MBRP as an aftercare treatment for substance use disorders. In the primary analyses of the data from this trial, Bowen and colleagues (2009) found that individuals who received MBRP reported significantly lower levels of craving following treatment, in comparison to a treatment-as-usual control group, which mediated subsequent substance use outcomes. In the current study, we extend these findings to examine potential mechanisms by which MBRP might be associated with lower levels of craving. Results indicated that a latent factor representing scores on measures of acceptance, awareness, and nonjudgment significantly mediated the relation between receiving MBRP and self-reported levels of craving immediately following treatment. The mediation findings are consistent with the goals of MBRP and highlight the importance of interventions that increase acceptance and awareness, and help clients foster a nonjudgmental attitude toward their experience. Attending to these processes may target both the experience of and response to craving.

Stress system changes associated with marijuana dependence may increase craving for alcohol and cocaine

OBJECTIVE

To date, little research exists defining bio-behavioral adaptations associated with both marijuana abuse and risk of craving and relapse to other drugs of abuse during early abstinence.

METHOD

Fifty-nine treatment-seeking individuals dependent on alcohol and cocaine were recruited. Thirty of these individuals were also marijuana (MJ) dependent; 29 were not. Twenty-six socially drinking healthy controls were also recruited. All participants were exposed to three 5-min guided imagery conditions (stress, alcohol/cocaine cue and relaxing), presented randomly, one per day across three consecutive days. Measures of craving, anxiety, heart rate, blood pressure, plasma adrenocorticotrophic hormone and cortisol were collected at baseline and subsequent recovery time points.

RESULTS

The MJ-dependent group showed increased basal anxiety ratings and cardiovascular output alongside enhanced alcohol craving and cocaine craving, and dampened cardiovascular response to stress and cue. They also demonstrated elevated cue-induced anxiety and stress-induced cortisol and adrenocorticotrophic hormone levels, which were not observed in the non-MJ-dependent group or controls. Cue-related alcohol craving and anxiety were both predictive of a shorter number of days to marijuana relapse following discharge from inpatient treatment.

CONCLUSIONS

Findings provide some support for drug cross-sensitization in terms of motivational processes associated with stress-related and cue-related craving and relapse.

The Effects of Maternal Separation on Adult Methamphetamine Self-Administration, Extinction, Reinstatement, and MeCP2 Immunoreactivity in the Nucleus Accumbens

The maternal separation (MS) paradigm is an animal model of early life stress. Animals subjected to MS during the first 2 weeks of life display altered behavioral and neuroendocrinological stress responses as adults. MS also produces altered responsiveness to and self-administration (SA) of various drugs of abuse including cocaine, ethanol, and amphetamine. However, no studies have yet examined the effects of MS on methamphetamine (METH) SA. This study was performed to examine the effects of MS on the acquisition of METH SA, extinction, and reinstatement of METH-seeking behavior in adulthood. Given the known influence of early life stress and drug exposure on epigenetic processes, we also investigated group differences in levels of the epigenetic marker methyl CpG binding protein 2 (MeCP2) in the nucleus accumbens (NAc) core. Long-Evans pups and dams were separated on postnatal days (PND) 2-14 for either 180 (MS180) or 15 min (MS15). Male offspring were allowed to acquire METH SA (0.05 mg/kg/infusion) in 15 2-h daily sessions starting at PND67, followed by extinction training and cue-induced reinstatement of METH-seeking behavior. Rats were then assessed for MeCP2 levels in the NAc core by immunohistochemistry. The MS180 group self-administered significantly more METH and acquired SA earlier than the MS15 group. No group differences in extinction or cue-induced reinstatement were observed. MS15 rats had significantly elevated MeCP2-immunoreactive cells in the NAc core as compared to MS180 rats. Together, these data suggest that MS has lasting influences on METH SA as well as epigenetic processes in the brain reward circuitry.

Role of a genetic polymorphism in the corticotropin-releasing factor receptor 1 gene in alcohol drinking and seeking behaviors of marchigian sardinian alcohol-preferring rats

Marchigian Sardinian alcohol-preferring (msP) rats exhibit innate preference for alcohol, are highly sensitive to stress and stress-induced alcohol seeking. Genetic analysis showed that over-expression of the corticotropin-releasing factor (CRF) system of msP rats is correlated with the presence of two single nucleotide polymorphisms (SNPs) occurring in the promoter region (position -1836 and -2097) of the CRF1 receptor (CRF1-R) gene. Here we examined whether these point mutations were associated to the innate alcohol preference, stress-induced drinking, and seeking. We have recently re-derived the msP rats to obtain two distinct lines carrying the wild type (GG) and the point mutations (AA), respectively. The phenotypic characteristics of these two lines were compared with those of unselected Wistar rats. Both AA and GG rats showed similar patterns of voluntary alcohol intake and preference. Similarly, the pharmacological stressor yohimbine (0.0, 0.625, 1.25, and 2.5 mg/kg) elicited increased operant alcohol self-administration under fixed and progressive ratio reinforcement schedules in all three lines. Following extinction, yohimbine (0.0, 0.625, 1.25, and 2.5 mg/kg) significantly reinstated alcohol seeking in the three groups. However, at the highest dose this effect was no longer evident in AA rats. Treatment with the CRF1-R antagonist antalarmin (0, 5, 10, and 20 mg/kg) significantly reduced alcohol-reinforced lever pressing in the AA line (10 and 20 mg/kg) while a weaker or no effect was observed in the Wistar and the GG group, respectively. Finally, antalarmin significantly reduced yohimbine-induced increase in alcohol drinking in all three groups. In conclusion, these specific SNPs in the CRF1-R gene do not seem to play a primary role in the expression of the msP excessive drinking phenotype or stress-induced drinking but may be associated with a decreased threshold for stress-induced alcohol seeking and an increased sensitivity to the effects of pharmacological blockade of CRF1-R on alcohol drinking.

β1-adrenoceptor activation is required for ethanol enhancement of lateral paracapsular GABAergic synapses in the rat basolateral amygdala

Ethanol (EtOH) potentiation of GABAergic neurotransmission in the basolateral amygdala (BLA) may contribute to the acute anxiolytic effects of this drug. Previous studies have shown that BLA pyramidal neurons receive GABAergic input from two distinct sources: local interneurons and a cluster of GABAergic cells termed lateral paracapsular (LPCS) interneurons. It is noteworthy that whereas EtOH enhances local GABAergic synapses via a presynaptic increase in GABA release, EtOH potentiation of LPCS inhibition is mediated via a distinct mechanism that requires adrenoceptor (AR) activation. Here, we sought to further characterize the interaction between the AR system and EtOH enhancement of LPCS GABAergic synapses by using in vitro electrophysiology techniques in male Sprague-Dawley rats. Exogenous norepinephrine (NE) enhanced LPCS-evoked inhibitory postsynaptic currents (eIPSCs) via the activation of β-ARs, because this effect was blocked by propranolol. EtOH potentiation of LPCS eIPSCs was also blocked by propranolol and significantly reduced by NE pretreatment, suggesting that NE and EtOH may enhance LPCS inhibition via a common mechanism. EtOH enhancement of LPCS eIPSCs was significantly reduced by a selective β1-, but not β2- or β3-, AR antagonist, and both EtOH and NE potentiation of LPCS IPSCs was blocked by postsynaptic disruption of cAMP signaling. These data suggest that EtOH enhances LPCS synapses via a postsynaptic β1-AR, cAMP-dependent cascade. Because enhancement of LPCS inhibition can reduce anxiety-like behaviors, these findings shed light on a novel mechanism that may play a role in some of the anxiolytic effects of EtOH that are thought to contribute to the development and progression of alcoholism.

Temptation to drink as a predictor of drinking outcomes following psychosocial treatment for alcohol dependence

BACKGROUND

Alcohol craving, defined as the subjective experience of an urge or desire to use alcohol, has been identified in numerous settings as a significant predictor of alcohol use and alcohol relapse following treatment for alcohol use disorders. Yet, numerous limitations to the conceptualization and measurement of drinking temptation have led many researchers to question whether self-reported drinking temptation is a useful construct for evaluating treatments for alcohol use disorders.

METHODS

Secondary analyses of data from Project MATCH, a multisite randomized clinical trial, were conducted to examine the association between a single-item measure of self-reported "temptation to drink" and drinking outcomes. The first goal was to determine whether temptation to drink changed during the course of treatment for alcohol dependence. The second goal was to assess the predictive validity of temptation to drink, assessed during the fourth session of treatment, as a predictor of past 30-day drinking rates and past 90-day drinking-related consequences at 1 and 3 years following treatment.

RESULTS

The temptation to drink decreased significantly during treatment, and self-reported temptation to drink during the fourth session of treatment was significantly associated with numerous drinking outcomes (including quantity, frequency, and consequences) at 1 year posttreatment (R = 0.04 to 0.11) and number of drinks per drinking day at 3 years following treatment (R = 0.02). A dichotomous measure of temptation to drink (not at all tempted vs. all other levels of temptation) had greater sensitivity as a predictor of drinking outcomes at 1 and 3 years posttreatment than alternative drinking measures (e.g., any drinking, any heavy drinking days) assessed during treatment.

CONCLUSIONS

A single-item measure of temptation to drink was a reasonable predictor of short- and long-term drinking outcomes following treatment and comparable to commonly used measures of drinking outcomes for alcohol clinical trials.

Alcohol dependence as a chronic pain disorder

Dysregulation of pain neurocircuitry and neurochemistry has been increasingly recognized as playing a critical role in a diverse spectrum of diseases including migraine, fibromyalgia, depression, and PTSD. Evidence presented here supports the hypothesis that alcohol dependence is among the pathologies arising from aberrant neurobiological substrates of pain. In this review, we explore the possible influence of alcohol analgesia and hyperalgesia in promoting alcohol misuse and dependence. We examine evidence that neuroanatomical sites involved in the negative emotional states of alcohol dependence also play an important role in pain transmission and may be functionally altered under chronic pain conditions. We also consider possible genetic links between pain transmission and alcohol dependence. We propose an allostatic load model in which episodes of alcohol intoxication and withdrawal, traumatic stressors, and injury are each capable of dysregulating an overlapping set of neural substrates to engender sensory and affective pain states that are integral to alcohol dependence and comorbid conditions such as anxiety, depression, and chronic pain.

Adolescent rearing conditions influence the relationship between initial anxiety-like behavior and ethanol drinking in male Long Evans rats

BACKGROUND

Rodent studies have demonstrated that adolescent social isolation results in many behavioral perturbations, including increases in anxiety-like behaviors. Socially isolated (SI) rats have also been shown to self-administer greater amounts ethanol (EtOH) in some, but not all, studies. Here, we tested whether juvenile social isolation increases EtOH drinking using an intermittent procedure that engenders relatively high intake in normally reared animals. We also compared the behavioral phenotype of rats reared under social isolation or group-housed conditions with adult rats housed under conditions commonly used in EtOH-drinking studies.

METHODS

Male Long Evans rats were procured immediately postweaning and were group housed for 1 week. Subjects were then randomly divided into 2 groups: SI rats, housed individually for 6 weeks and group-housed (GH) rats (4/cage). A third group was procured as young adults and was housed individually upon arrival for 1 week (standard housing condition). Rats were then tested in a plus-maze and novelty assay, and then, all subjects were singly housed and EtOH drinking was assessed.

RESULTS

SI rats displayed increased anxiety-like behaviors on the plus-maze, a greater locomotor response to a novel environment, and increased EtOH intake, relative to GH rats. Age-matched standard housed (STD) rats exhibited an anxiety-like behavioral profile on the plus-maze that was similar to SI, and not GH rats, and also drank EtOH at levels comparable with SI subjects. In addition, anxiety-like behavior on the plus-maze correlated with intermittent EtOH intake in SI and GH rats.

CONCLUSIONS

These data further support the validity of the rodent juvenile social isolation model for studies directed at elucidating behavioral and neurobiological mechanisms linking anxiety and EtOH drinking. These findings further suggest that housing conditions commonly employed in rodent drinking studies may recapitulate the anxiety-like and EtOH-drinking phenotype engendered by a juvenile social isolation procedure.

Neurochemical and neurostructural plasticity in alcoholism

The behavioral manifestations of alcoholism are primarily attributable to the numerous and lasting adaptations that occur in the brain as a result of chronic heavy alcohol consumption. As will be reviewed here, these adaptations include alcohol-induced plasticity in chemical neurotransmission, density and morphology of dendritic spines, as well as neurodegeneration and cerebral atrophy. Within the context of these neuroadaptations that have been observed in both human and animal studies, we will discuss how these changes potentially contribute to the cognitive and behavioral dysfunctions that are hallmark features of alcoholism, as well as how they reveal novel potential pharmacological targets for the treatment of this disorder.

Therapeutic mechanisms of classic hallucinogens in the treatment of addictions: from indirect evidence to testable hypotheses

Alcohol and drug addiction are major public health problems, and existing treatments are only moderately effective. Although there has been interest for over half a century in the therapeutic use of classic hallucinogens to treat addictions, clinical research with these drugs was halted at an early stage in the early 1970s, leaving many fundamental questions unanswered. In the past two decades, clinical research on classic hallucinogens has resumed, although addiction treatment trials are only now beginning. The purpose of this paper is to provide a targeted review of the research most relevant to the therapeutic potential of hallucinogens, and to integrate this information with current thinking about addiction and recovery. On the basis of this information, we present a heuristic model which organizes a number of hypotheses that may be tested in future research. We conclude that existing evidence provides a convincing rationale for further research on the effects of classic hallucinogens in the treatment of addiction.

Guanfacine effects on stress, drug craving and prefrontal activation in cocaine dependent individuals: preliminary findings

Cocaine dependence is associated with increased stress and drug cue-induced craving and physiological arousal but decreased prefrontal activity to emotional and cognitive challenge. As these changes are associated with relapse risk, we investigated the effects of α2 receptor agonist guanfacine on these processes. Twenty-nine early abstinent treatment-seeking cocaine dependent individuals were randomly assigned to either daily placebo or guanfacine (up to 3 mg) for four weeks. In a laboratory experiment, all patients were exposed to three 10-min guided imagery conditions (stress/stress, drug cue/drug cue, stress/drug cue), one per day, consecutively in a random, counterbalanced order. Subjective craving, anxiety and arousal as well as cardiovascular output were assessed repeatedly. Brain response to stress, drug cue and relaxing imagery was also assessed during a functional magnetic resonance (fMRI) imaging session. In the current study, guanfacine was found to be safe and well-tolerated. Lower basal heart rate and blood pressure was observed in the guanfacine versus placebo group. Guanfacine lowered stress and cue-induced nicotine craving and cue-induced cocaine craving, anxiety and arousal. The guanfacine group also showed increased medial and lateral prefrontal activity following stress and drug cue exposure compared with placebo. Data suggest further exploration of guanfacine is warranted in terms of its potential for reducing stress-induced and cue-induced drug craving and arousal.

Brain fMRI study of crave induced by cue pictures in online game addicts (male adolescents)

OBJECTIVE

To study crave-related cerebral regions induced by game figure cues in online game addicts. fMRI brain imaging was done when the subjects were shown picture cues of the WoW (World of Warcraft, Version: 4.1.014250) game.

METHODS

10 male addicts of WoW were selected as addicts' group, and 10 other healthy male non-addicts who were matched by age, were used as non-game addicts' group. All volunteers participated in fMRI paradigms. WoW associated cue pictures and neutral pictures were shown. We examined functional cerebral regions activated by the pictures with 3.0 T Philips MRI. The imaging signals' database was analyzed by SPM5. The correlation between game craving scores and different image results were assessed.

RESULTS

When the game addicts watch the pictures, some brain areas show increased signal activity namely: dorsolateral prefrontal cortex, bilateral temporal cortex, cerebellum, right inferior parietal lobule, right cuneus, right hippocampus, parahippocampal gyrus, left caudate nucleus. But in these same brain regions we did not observe remarkable activities in the control group. Differential image signal densities of the addict group were subtracted from the health control group, results of which were expressed in the bilateral dorsolateral prefrontal cortex, anterior cingulate cortex, inferior parietal lobe and inferior temporal gyrus, cerebellum, right insular and the right angular gyrus. The increased imaging signal densities were significant and positively correlated with the craving scale scores in the bilateral prefrontal cortex, anterior cingulate cortex and right inferior parietal lobe.

CONCLUSIONS

Craving of online game addicts was successfully induced by game cue pictures. Crave related brain areas are: dorsolateral prefrontal cortex, anterior cingulate cortex, and right inferior parietal lobe. The brain regions are overlapped with cognitive and emotion related processing brain areas.

Allostasis and addiction: role of the dopamine and corticotropin-releasing factor systems

Allostasis, originally conceptualized to explain persistent morbidity of arousal and autonomic function, is defined as the process of achieving stability through physiological or behavioral change. Two types of biological processes have been proposed to describe the mechanisms underlying allostasis in drug addiction, a within-system adaptation and a between-system adaptation. In the within-system process, the drug elicits an opposing, neutralizing reaction within the same system in which the drug elicits its primary and unconditioned reinforcing actions, while in the between-system process, different neurobiological systems that the one initially activated by the drug are recruited. In this review, we will focus our interest on alterations in the dopaminergic and corticotropin releasing factor systems as within-system and between-system neuroadaptations respectively, that underlie the opponent process to drugs of abuse. We hypothesize that repeated compromised activity in the dopaminergic system and sustained activation of the CRF-CRF1R system with withdrawal episodes may lead to an allostatic load contributing significantly to the transition to drug addiction.

Immune system inflammation in cocaine dependent individuals: implications for medications development

OBJECTIVES

Cocaine dependence is a chronic stress state. Furthermore, both stress and substance abuse have robust and reciprocal effects on immune system cytokines, which are known to be powerful modulators of mood. We therefore examine basal and provoked changes in peripheral cytokines in cocaine dependent individuals to better understand their role in the negative reinforcing effects of cocaine.

METHODS

Twenty-eight (16 F/12 M) treatment-seeking cocaine dependent individuals and 27 (14 F/13 M) social drinkers were exposed to three 5-min guided imagery conditions (stress, drug cue, relaxing) presented randomly across consecutive days. Measures of salivary cortisol, tumor necrosis factor alpha (TNFα), interleukin-10 (IL-10), and interleukin-1 receptor antagonist (IL-1ra) were collected at baseline and various post-imagery time-points.

RESULTS

Cocaine abusers demonstrated decreased basal IL-10 compared with social drinkers. They also showed significant elevations in pro-inflammatory TNFα when exposed to stress compared with when they were exposed to relaxing imagery. This was not observed in the social drinkers. Conversely, social drinkers demonstrated increases in the anti-inflammatory markers, IL-10 and IL-1ra, following exposure to cue, which were not seen in the dependent individuals.

CONCLUSIONS

Cocaine dependent individuals demonstrate an elevated inflammatory state both at baseline and following exposure to the stress imagery condition. Cytokines may reflect potentially novel biomarkers in addicted populations for treatment development.

Alcohol stress response dampening: selective reduction of anxiety in the face of uncertain threat

Problematic alcohol use and stress response dampening (SRD) are intimately interconnected. Recent evidence suggests that alcohol produces selective SRD during uncertain but not certain threat. We systematically varied shock probability in a novel task assessing alcohol SRD during low probable/uncertain threat, while holding temporal precision of threat constant. Intoxicated (0.08% target blood alcohol concentration) and placebo participants completed a cued shock threat task in which probability of shock administration at the offset of brief visual cues varied parametrically. High probability (100%) shock cues represented certain threat as used in earlier research, while lower probability (20% and 60%) shock cues provided novel uncertain threat conditions. Startle potentiation during cues and inter-trial intervals (ITIs) served as the measure of affective response. General linear model analysis indicated that alcohol SRD magnitude increased monotonically as threat uncertainty increased. Alcohol SRD was significantly greater during 20% and 60% shock threat relative to 100% shock threat. Alcohol also significantly reduced startle potentiation during distal threat in shock-free ITIs. Alcohol SRD magnitude during distal/uncertain threat was meaningfully moderated by individual differences in negative affectivity and weekly alcohol consumption. This work advances understanding of which properties of uncertainty are relevant to anxiety and anxiolytic effects of alcohol.

mGluR5 receptors in the basolateral amygdala and nucleus accumbens regulate cue-induced reinstatement of ethanol-seeking behavior

Pharmacological blockade of the type 5 metabotropic glutamate receptor (mGluR5) attenuates cue-induced reinstatement of ethanol-seeking behavior, yet the brain regions involved in these effects are not yet known. The purpose of the present study was to determine if local blockade of mGluR5 receptors in the basolateral amygdala (BLA) and/or the nucleus accumbens (NAc), two brain regions known to be involved in stimulus-reward associations, attenuate the reinstatement of ethanol-seeking behavior induced by ethanol-paired cues. As a control for possible non-specific effects, the effects of mGluR5 blockade in these regions on cue-induced reinstatement of sucrose-seeking were also assessed. Male Wistar rats were implanted with bilateral microinjection cannulae aimed at the BLA or NAc. Following recovery, animals were trained to self-administer ethanol (10% w/v) or 45 mg sucrose pellets on an FR1 schedule of reinforcement in 30 min daily sessions using a sucrose fading procedure. Following stabilization of responding, animals underwent extinction training. Next, animals received infusions of vehicle or the selective mGluR5 antagonist MTEP (3 μg/μl) into the BLA or NAc prior to cue-induced reinstatement testing sessions. mGluR5 blockade eliminated cue-induced reinstatement of alcohol - but not sucrose-seeking behavior. Results from this study indicate that mGluR5 receptors in the BLA and NAc mediate cue-induced reinstatement of ethanol-seeking behavior, and provide two potential neuroanatomical sites of action where systemically administered mGluR5 antagonists attenuate cue-induced reinstatement. These data are consistent with previous findings that cue-induced reinstatement of ethanol-seeking increases neuronal activity and glutamatergic transmission in these two regions.

Bridging Animal and Human Models: Translating From (and to) Animal Genetics

Genetics play an important role in the development and course of alcohol abuse, and understanding genetic contributions to this disorder may lead to improved preventative and therapeutic strategies in the future. Studies both in humans and in animal models are necessary to fully understand the neurobiology of alcoholism from the molecular to the cognitive level. By dissecting the complex facets of alcoholism into discrete, well-defined phenotypes that are measurable in both human populations and animal models of the disease, researchers will be better able to translate findings across species and integrate the knowledge obtained from various disciplines. Some of the key areas of alcoholism research where consilience between human and animal studies is possible are alcohol withdrawal severity, sensitivity to rewards, impulsivity, and dysregulated alcohol consumption.

Exercise as an adjunct treatment for opiate agonist treatment: review of the current research and implementation strategies

Opiate dependence is a significant public health concern linked to poor quality of life, comorbid psychiatric disorders, and high costs to society. Current opiate agonist treatments are an effective but limited intervention. Adjunctive interventions could improve and augment opiate agonist treatment outcomes, including drug abstinence, quality of life, and physical health. This article reviews exercise as an adjunctive intervention for opiate agonist treatment, especially in regards to improving mood and overall quality of life, while reducing other substance use. Poor adherence and dropout frequently prevent many individuals from garnering the many physical and mental health benefits of exercise. Strategies for implementing an exercise intervention, including safety considerations, are discussed.

Stress and the HPA axis: role of glucocorticoids in alcohol dependence

Stress has long been suggested to be an important correlate of uncontrolled drinking and relapse. An important hormonal response system to stress-the hypothalamic-pituitary-adrenal (HPA) axis-may be involved in this process, particularly stress hormones known as glucocorticoids and primarily cortisol. The actions of this hormone system normally are tightly regulated to ensure that the body can respond quickly to stressful events and return to a normal state just as rapidly. The main determinants of HPA axis activity are genetic background, early-life environment, and current life stress. Alterations in HPA axis regulation are associated with problematic alcohol use and dependence; however, the nature of this dysregulation appears to vary with respect to stage of alcohol dependence. Much of this research has focused specifically on the role of cortisol in the risk for, development of, and relapse to chronic alcohol use. These studies found that cortisol can interact with the brain's reward system, which may contribute to alcohol's reinforcing effects. Cortisol also can influence a person's cognitive processes, promoting habit-based learning, which may contribute to habit formation and risk of relapse. Finally, cortisol levels during abstinence may be useful clinical indicators of relapse vulnerability in alcohol-dependent people.

Stress, epigenetics, and alcoholism

Acute and chronic stressors have been associated with alterations in mood and increased anxiety that may eventually result in the development of stress-related psychiatric disorders. Stress and associated disorders, including anxiety, are key factors in the development of alcoholism because alcohol consumption can temporarily reduce the drinker's dysphoria. One molecule that may help mediate the relationship between stress and alcohol consumption is brain-derived neurotrophic factor (BDNF), a protein that regulates the structure and function of the sites where two nerve cells interact and exchange nerve signals (i.e., synapses) and which is involved in numerous physiological processes. Aberrant regulation of BDNF signaling and alterations in synapse activity (i.e., synaptic plasticity) have been associated with the pathophysiology of stress-related disorders and alcoholism. Mechanisms that contribute to the regulation of genetic information without modification of the DNA sequence (i.e., epigenetic mechanisms) may play a role in the complex control of BDNF signaling and synaptic plasticity-for example, by modifying the structure of the DNA-protein complexes (i.e., chromatin) that make up the chromosomes and thereby modulating the expression of certain genes. Studies regarding the epigenetic control of BDNF signaling and synaptic plasticity provide a promising direction to understand the mechanisms mediating the interaction between stress and alcoholism.

Is alcohol dependence best viewed as a chronic relapsing disorder?

This 'For Debate' paper starts by recognizing the growing trend towards considering alcohol dependence as a chronic relapsing disorder. We argue that the adoption of this model results from focusing on those in treatment for alcohol dependence rather than considering the larger number of people in the general population who meet criteria for alcohol dependence at some point in their lives. The majority of the general population who ever experience alcohol dependence do not behave as though they have a chronic relapsing disorder: they do not seek treatment, resolve their dependence themselves and do not relapse repeatedly. We suggest that caution is therefore needed in using the chronic relapsing disorder label. Our primary concerns are that this formulation privileges biological aspects of dependence to the detriment of psychological and social contributions, it inhibits much-needed developments in understanding alcohol dependence and leads to inefficient distributions of public health and clinical care resources for alcohol dependence. We invite debate on this issue.

How does stress lead to risk of alcohol relapse?

Empirical findings from human laboratory and brain-imaging studies are consistent with clinical observations and indicate that chronic alcohol-related dysfunction in emotional and stress responses plays a role in motivation to consume alcohol in people with alcohol use disorders. Recent findings on differences in stress responsivity in alcohol-dependent versus nondependent social drinkers demonstrate alterations in stress pathways that partially may explain the significant contribution of stress-related mechanisms on craving and relapse susceptibility. These findings have significant implications for clinical practice, including (1) the development of novel brain and stress biology-related measures of relapse risk that could serve as biomarkers to identify those most at risk of alcohol relapse during early recovery from alcoholism; and (2) the development of novel interventions that target stress-related effects on the motivation to drink alcohol and on relapse outcomes.

Alcohol dose effects on stress response to cued threat vary by threat intensity

RATIONALE

Clarification of alcohol's effect on stress response during threat is critical to understand motivation for alcohol use and related alcohol-use disorders. Evaluation of stress response dampening (SRD) effects of alcohol has been limited by nonsystematic use of varied experimental methods and measures.

OBJECTIVES

This experiment parametrically varied alcohol dose and shock threat intensity among social drinkers to examine their effects on startle potentiation, a physiological measure of the affective component of the stress response.

METHODS

Ninety-six participants were assigned to one of four beverage groups: placebo and target blood alcohol concentration (BAC) groups of 0.04%, 0.075%, and 0.11%. Participants viewed colored cues presented in shock and no-shock blocks. Distinct colored cues predicted imminent low, moderate, or high intensity electric shock administration. Startle potentiation during shock threat relative to no-shock cues indexed affective response.

RESULTS

High threat increased startle potentiation relative to moderate/low intensity threat. Startle potentiation decreased as BAC increased. Threat intensity moderated this BAC effect with the strongest BAC effect observed during high threat. Analysis of individual difference moderators revealed reduced effect of BAC among heavier, more problematic drinkers.

CONCLUSIONS

Clear alcohol SRD effects were observed. These SRD effects were greatest at higher BACs and during more potent threat. Failure to account for these factors may partially explain inconsistent findings in past laboratory SRD research. Furthermore, they suggest greater reinforcement from alcohol at higher doses and among individuals with greater stress. Moderation of SRD effects by alcohol consumption and problems point to possible important risk factors.

Effect of prazosin and guanfacine on stress-induced reinstatement of alcohol and food seeking in rats

RATIONALE AND OBJECTIVES

Relapse to alcohol use during abstinence or maladaptive eating habits during dieting is often provoked by stress. The anxiogenic drug yohimbine, which causes stress-like responses in humans and non-humans, reliably reinstates alcohol and food seeking in a rat relapse model. Yohimibine is a prototypical alpha-2 adrenoceptor antagonist, but results from studies on noradrenaline's role in yohimbine-induced reinstatement of drug and food seeking are inconclusive. Here, we further addressed this issue by studying the effect of the alpha-1 adrenoceptor antagonist prazosin and the alpha-2 adrenoceptor agonist guanfacine on yohimbine-induced reinstatement.

METHODS

In exp. 1, we trained rats to self-administer alcohol (12% w/v, 1 h/day), and after extinction of alcohol-reinforced lever pressing, we tested prazosin's (0.5, 1.0, and 2.0 mg/kg, i.p.) or guanfacine's (0.125, 0.25, and 0.5 mg/kg, i.p.) effect on yohimbine (1.25 mg/kg, i.p.)-induced reinstatement; we also examined prazosin's effect on intermittent-footshock-stress-induced reinstatement. In exp. 2, we trained food-restricted rats to self-administer 45 mg food pellets and first examined prazosin's or guanfacine's effects on food-reinforced responding, and then, after extinction of lever presses, on yohimbine-induced reinstatement.

RESULTS

Prazosin (0.5-2.0 mg/kg) blocked yohimbine-induced reinstatement of food and alcohol seeking, as well as footshock-induced reinstatement of alcohol seeking. Guanfacine attenuated yohimbine-induced reinstatement of alcohol seeking at the highest dose (0.5 mg/kg), but its effect on yohimbine-induced reinstatement of food seeking was not significant. Neither prazosin nor guanfacine affected high-rate food-reinforced responding.

CONCLUSIONS

Results demonstrate an important role of postsynaptic alpha-1 adrenoceptors in stress-induced reinstatement of alcohol and food seeking.

Effects of a stressor and corticotrophin releasing factor on ethanol deprivation-induced ethanol intake and anxiety-like behavior in alcohol-preferring P rats

RATIONALE

Stress may elevate ethanol drinking and anxiety associated with ethanol drinking. Studies to identify relevant neurobiological substrates are needed.

OBJECTIVE

To assess roles of brain regions in corticotrophin releasing factor (CRF) effects on stressor-enhanced, ethanol deprivation-induced drinking and anxiety-like behavior.

METHODS

Ethanol-preferring rats (P rats) were exposed to three cycles of a two-bottle choice paradigm with two 2-day deprivation periods that included 1 h exposure to a restraint stressor. To assess the role of CRF and to identify relevant brain regions, a CRF-1 receptor antagonist (SSR125543; 10 ug) was injected into the nucleus accumbens (NAC), amygdala (Amyg), or dorsal raphe nucleus (DRN) prior to exposure to the restraint stressor. In a second study, CRF (0.5 ug) was injected into one of these regions, or the ventral tegmental area (VTA), or paraventricular nucleus of the hypothalamus (PVN).

RESULTS

Applying the restraint stressor during deprivation increased voluntary intake and sensitized anxiety-like behavior. Antagonist injection into the NAC prevented increased drinking without affecting anxiety-like behavior, whereas injection into the Amyg or DRN prevented the anxiety-like behavior without affecting drinking. To confirm CRF actions in the stressor effect, CRF was injected into selected brain regions. NAC injections (but not the VTA, Amyg, DRN, or PVN) facilitated drinking but did not change anxiety-like behavior. Injections into the DRN or Amyg (but not PVN or VTA) enhanced anxiety-like behavior.

CONCLUSIONS

Results emphasize that a restraint stressor elevates ethanol intake and sensitizes ethanol deprivation-induced anxiety-like behavior through CRF1 receptors in the NAC and Amyg/DRN, respectively.

Pharmacological blockade of corticotropin-releasing hormone receptor 1 (CRH1R) reduces voluntary consumption of high alcohol concentrations in non-dependent Wistar rats

BACKGROUND

A dysregulation of the corticotropin-releasing hormone (CRH) system has been implicated in the development of excessive alcohol consumption and dependence. The aim of the present study was to evaluate whether the CRH system is also recruited when non-dependent Wistar rats escalate to high alcohol intake in the intermittent (alternate days) model of drinking.

METHODS

We compared intermittent and continuous access to 20% (v/v) alcohol in a two-bottle free choice drinking paradigm. Following a total of twenty 24-hour exposures for every experimental group, we assessed signs of alcohol withdrawal, including anxiety-like behavior and sensitivity to stress. The selective CRH1 receptor (CRH1R) antagonist antalarmin (0, 10, 20 mg/kg, i.p.) was tested on alcohol consumption.

RESULTS

Intermittent access to 20% alcohol led non-selected Wistar rats to escalate their voluntary intake to a high and stable level, whereas continuously exposed animals maintained a lower consumption. These groups did not differ in physical withdrawal signs. In addition, no differences were found when anxiogenic-like behavior was studied, neither under basal conditions or following restraint stress. Nevertheless, sensitivity to the treatment with the CRH1R antalarmin was observed since a reduction of 20% alcohol intake was found in both groups of animals regardless of the regimen of alcohol exposure. In addition, antalarmin was effective when injected to animals exposed to intermittent 10% (v/v) alcohol whereas it failed to suppress 10% continuous alcohol intake.

CONCLUSIONS

Pharmacological blockade of CRH1R reduced alcohol drinking when sustained high levels of intake were achieved suggesting that the CRH system plays a key role when high doses of ethanol are consumed by non-dependent subjects. This supports the notion that CRH system not only maintains the dependent state but also engages the transition to dependence.