Alcohol-seeking and relapse: A focus on incentive salience and contextual conditioning

ABA and AAB renewal of alcohol seeking in rats are reduced by exposure to beer before extinction

Three experiments with rats examined the impact of a retrieval-extinction procedure on ABA and AAB renewal of instrumental learning. In all experiments, rats were trained to run down an alley for alcoholic beer in Context A. Then, the instrumental response underwent extinction, which was conducted in Context B for Experiments 1 and 2, and in Context A for Experiment 3. In each experiment, one group of animals received a brief exposure to the beer prior to each extinction session, whereas this beer exposure was omitted for a second group. Moreover, Experiment 2 comprised a third group that was exposed to non-alcoholic beer before each extinction session. Finally, all rats were tested in their extinction context and in a second context, which was Context A for Experiments 1 and 2, and Context B for Experiment 3. We found ABA (Experiments 1 and 2) and AAB (Experiment 3) renewal of beer seeking in those animals for which beer exposure prior to extinction was omitted. However, response recovery was not evident when animals received exposure to beer before extinction, regardless of whether alcoholic or non-alcoholic beer was used. Our results suggest that the renewal of alcohol seeking can be prevented by means of the retrieval-extinction paradigm.

Integrating and fragmenting memories under stress and alcohol

Stress can powerfully influence the way we form memories, particularly the extent to which they are integrated or situated within an underlying spatiotemporal and broader knowledge architecture. These different representations in turn have significant consequences for the way we use these memories to guide later behavior. Puzzlingly, although stress has historically been argued to promote fragmentation, leading to disjoint memory representations, more recent work suggests that stress can also facilitate memory binding and integration. Understanding the circumstances under which stress fosters integration will be key to resolving this discrepancy and unpacking the mechanisms by which stress can shape later behavior. Here, we examine memory integration at multiple levels: linking together the content of an individual experience, threading associations between related but distinct events, and binding an experience into a pre-existing schema or sense of causal structure. We discuss neural and cognitive mechanisms underlying each form of integration as well as findings regarding how stress, aversive learning, and negative affect can modulate each. In this analysis, we uncover that stress can indeed promote each level of integration. We also show how memory integration may apply to understanding effects of alcohol, highlighting extant clinical and preclinical findings and opportunities for further investigation. Finally, we consider the implications of integration and fragmentation for later memory-guided behavior, and the importance of understanding which type of memory representation is potentiated in order to design appropriate interventions.

Augmenting glutamatergic, but not dopaminergic, activity in the nucleus accumbens shell disrupts responding to a discrete alcohol cue in an alcohol context

Discrete alcohol cues and contexts are relapse triggers for people with alcohol use disorder exerting particularly powerful control over behaviour when they co-occur. Here, we investigated the neural substrates subserving the capacity for alcohol-associated contexts to elevate responding to an alcohol-predictive conditioned stimulus (CS). Specifically, rats were trained in a distinct 'alcohol context' to respond by entering a fluid port during a discrete auditory CS that predicted the delivery of alcohol and were familiarized with a 'neutral context' wherein alcohol was never available. When conditioned CS responding was tested by presenting the CS without alcohol, we found that augmenting glutamatergic activity in the nucleus accumbens (NAc) shell by microinfusing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) reduced responding to an alcohol CS in an alcohol, but not neutral, context. Further, AMPA microinfusion robustly affected behaviour, attenuating the number, duration and latency of CS responses selectively in the alcohol context. Although dopaminergic inputs to the NAc shell were previously shown to be necessary for CS responding in an alcohol context, here, chemogenetic excitation of ventral tegmental area (VTA) dopamine neurons and their inputs to the NAc shell did not affect CS responding. Critically, chemogenetic excitation of VTA dopamine neurons affected feeding behaviour and elevated c-fos immunoreactivity in the VTA and NAc shell, validating the chemogenetic approach. These findings enrich our understanding of the substrates underlying Pavlovian responding for alcohol and reveal that the capacity for contexts to modulate responding to discrete alcohol cues is delicately underpinned by the NAc shell.

Pavlovian cue-evoked alcohol seeking is disrupted by ventral pallidal inhibition

Cues paired with alcohol can be potent drivers of craving, alcohol-seeking, consumption, and relapse. While the ventral pallidum is implicated in appetitive and consummatory responses across several reward classes and types of behaviors, its role in behavioral responses to Pavlovian alcohol cues has not previously been established. Here, we tested the impact of optogenetic inhibition of ventral pallidum on Pavlovian-conditioned alcohol-seeking in male Long Evans rats. Rats underwent Pavlovian conditioning with an auditory cue predicting alcohol delivery to a reward port and a control cue predicting no alcohol delivery, until they consistently entered the reward port more during the alcohol cue than the control cue. We then tested the within-session effects of optogenetic inhibition during 50% of cue presentations. We found that optogenetic inhibition of ventral pallidum during the alcohol cue reduced port entry likelihood and time spent in the port, and increased port entry latency. Overall, these results suggest that normal ventral pallidum activity is necessary for Pavlovian alcohol-seeking.

A translational rodent model of individual differences in sensitivity to the aversive properties of ethanol

BACKGROUND

A strong relationship exists between individual sensitivity to the aversive properties of ethanol and risk for alcohol use disorder (AUD). Despite this, our understanding of the neurobiological mechanisms underlying the subjective response to ethanol is limited. A major contributor to this lack of knowledge is the absence of preclinical models that enable exploration of this individual variability such as is possible in studies of humans.

METHODS

Adult male and female Long-Evans rats were trained to associate a novel tastant (saccharin) with acute exposure to either saline or ethanol (1.5 g/kg or 2.0 g/kg i.p.) over three conditioning days using a standard conditioned taste aversion (CTA) procedure. Variability in sensitivity to ethanol-induced CTA was phenotypically characterized using a median split across the populations studied.

RESULTS

When examining group averages, both male and female rats exposed to saccharin paired with either dose of ethanol exhibited lower saccharin intake relative to saline controls indicative of ethanol-induced CTA. Examination of individual data revealed a bimodal distribution of responses uncovering two distinct phenotypes present in both sexes. CTA-sensitive rats exhibited a rapid and progressive reduction in saccharin intake with each successive ethanol pairing. In contrast, saccharin intake was unchanged or maintained after an initial decrease from baseline levels in CTA-resistant rats. While CTA magnitude was similar between male and female CTA-sensitive rats, among CTA-resistant animals females were more resistant to the development of ethanol-induced CTA than males. Phenotypic differences were not driven by differences in baseline saccharin intake.

CONCLUSIONS

These data parallel work in humans by revealing individual differences in sensitivity to the aversive properties of ethanol that emerge immediately after initial exposure to ethanol in both sexes. This model can be used in future studies to investigate the neurobiological mechanisms that confer risk for AUD.

Affective imagery boosts the reward related delta power in hazardous drinkers

The Reward Positivity (RewP) is an event-related potential component with a delta band spectral representation that is elicited by reward receipt. Evidence suggests that RewP is modulated by both reward probability as well as affective valuation ("liking"). Here we determined whether RewP is a marker of enhanced hedonic salience of alcohol images in hazardous drinkers. We recruited 54 participants (Hazardous Drinkers = 28, Control = 26) who completed a reinforcement learning task with affective versus alcohol imagery during feedback. The learning task used images of puppies vs. alcohol paired with reinforcing feedback. Both groups rated categories of affective images (puppies, scenery, babies, neutral) similarly, but the hazardous drinking group rated alcohol significantly higher. There were no group differences in performance or in RewP amplitudes, even as a function of alcohol imagery. Contrary to prior findings, we did not observe a significant correlation between alcohol image rating and alcohol-specific RewP amplitude, although we did observe this relationship with the alcohol-specific delta band spectral representation of RewP. Within hazardous drinking group, there was significant correlation between hazardous drinking (AUDIT score) and alcohol-specific RewP indicating an inter-individual influence of drinking habits on affect specific RewP. These findings suggest a domain-specific enhancement of reward responsiveness in hazardous drinkers.

Testing pharmacotherapies for alcohol use disorder with cue exposure paradigms: A systematic review and quantitative synthesis of human laboratory trial methodology

Alcohol cue exposure is a widely used experimental paradigm for screening pharmacotherapies for alcohol use disorder (AUD). Medication-related reductions in cue-reactivity signal early efficacy and inform medications development. Yet, across trials, the design of cue exposure, parameter testing, and outcome reporting is heterogeneous. This systematic review is a quantitative synthesis of trial methodologies and effect size estimation for AUD medication-related craving and psychophysiological outcomes under the cue exposure paradigm. A PubMed search was conducted on January 3, 2022 based on identified pharmacotherapies for peer-reviewed articles reported in English. Study-level characteristics, including sample descriptors, paradigm design, analytic approach, and Cochrane Risk of Bias, along with descriptive statistics for cue-exposure outcomes, were coded by two independent raters. Study-level effect sizes were estimated for craving and psychophysiological outcomes separately and sample-level effect sizes were calculated for each medication. Thirty-six trials, comprising 1640 participants and testing 19 different medications satisfied eligibility criteria. All studies reported on biological sex (71% male participants on average). The exposure paradigms implemented used in vivo (n = 26), visual (n = 8), and audio script (n = 2) cues. Some trials included means for craving by medication condition in text (k = 7) or figures (k = 18). The quantitative synthesis included 63 effect sizes (craving kes  = 47; psychophysiological kes  = 16) from 28 unique randomized trials testing 15 medications for effects on cue reactivity. For cue-induced craving, eight medications (kes range: 1-12) demonstrated small-to-medium effects (Cohen's d range: |0.24-0.64|) compared to placebo, with individuals randomized to receive medication reporting lower craving following cue exposure. Recommendations are provided to promote further consilience, so that the utility of cue exposure paradigms can be maximized in the development of effective AUD pharmacotherapies. Future work should explore the predictive utility of medication-related reductions in cue-reactivity on clinical outcomes.

Unconditioned and conditioned anxiolytic effects of Sodium Valproate on flavor neophobia and fear conditioning

In three experiments with rats, we analyzed the potential anxiolytic effects of sodium valproate, an anticonvulsant drug that has shown additional pharmacodynamic effects in animal models, including anxiolytic action. Since previous results have revealed that injecting valproate before allowing animals to consume a novel flavor solution resulted in an attenuation of neophobia, we predicted a similar effect when the novel flavor is presented on a drug-free trial in the presence of a context previously associated with the drug. In line with this hypothesis, in our first experiment we observed a reduction in neophobia to a novel flavor for those animals tested in the presence of the context associated with Sodium Valproate. However, a control group that received the drug before being allowed access to the novel flavor showed a significant reduction in consumption. Experiment 2 revealed that the unconditioned effects of the drug include a deleterious effect on the animals' locomotor activity that probably interferes with drinking behavior. Finally, in a third experiment, we directly tested the potential anxiolytic properties of sodium valproate by injecting the drug before implementing a fear conditioning procedure. These findings are explained in terms of the unconditioned anxiolytic action of the drug and the formation of an association between the context and the effects of the drug that evokes a conditioned response reminiscent of such anxiolytic effect.

A translational rodent model of individual differences in sensitivity to the aversive properties of ethanol

Background

A strong relationship exists between individual sensitivity to the aversive properties of ethanol and risk for alcohol use disorder (AUD). Despite this, our understanding of the neurobiological mechanisms underlying subjective response to ethanol is relatively poor. A major contributor to this is the absence of preclinical models that enable exploration of this individual variability similar to studies performed in humans.

Methods

Adult male and female Long-Evans rats were trained to associate a novel tastant (saccharin) with acute exposure to either saline or ethanol (1.5 g/kg or 2.0 g/kg i.p.) over three conditioning days using a standard conditioned taste aversion (CTA) procedure. Variability in sensitivity to ethanol-induced CTA was phenotypically characterized using a median split across the populations studied.

Results

When examining group averages, both male and female rats that had saccharin paired with either dose of ethanol exhibited reduced saccharin intake relative to saline controls of ethanol-induced CTA. Examination of individual data revealed a bimodal distribution of responses uncovering two distinct phenotypes present in both sexes. CTA-sensitive rats exhibited a rapid and progressive reduction in saccharin intake with each successive ethanol pairing. In contrast, saccharin intake was unchanged or maintained after an initial decrease from baseline levels in CTA-resistant rats. While CTA magnitude was similar between male and female CTA-sensitive rats, CTA-resistant females were more resistant to the development of ethanol-induced CTA than their male counterparts. Phenotypic differences were not driven by differences in baseline saccharin intake. CTA sensitivity correlated with behavioral signs of intoxication in only a subset of rats.

Conclusions

These data parallel work in humans by revealing individual differences in sensitivity to the aversive properties of ethanol that emerge immediately after initial exposure to ethanol in both sexes. This model can be leveraged in future studies to investigate the neurobiological mechanisms that confer risk for AUD.

Cues associated with repeated ethanol exposure facilitate the corticosterone response to ethanol and immunological challenges in adult male Sprague Dawley rats: implications for neuroimmune regulation

Background: We previously found a conditioned increase in central neuroinflammatory markers (Interleukin 6; IL-6) following exposure to alcohol-associated cues. Recent studies suggest (unconditioned) induction of IL-6 is entirely dependent on ethanol-induced corticosterone.Objectives: The goals of these present studies were to test whether alcohol-paired cues facilitated the hypothalamic-pituitary-adrenal (HPA) axis response to either a subthreshold priming alcohol dose or an immune or psychological stress challengeMethods: In Experiment 1 (N = 64), adult male Sprague Dawley rats were trained (paired or unpaired, four pairings total) with  either vehicle or 2 g/kg alcohol [intragastric (i.g.) or intraperitoneal (i.p.)] injections. In Experiments 2 (N = 28) and 3 (N = 30), male rats were similarly trained but with 4 g/kg alcohol i.g. intubations. On test day, all rats were either administered a 0.5 g/kg alcohol dose (i.p. or i.g. Experiment 1), a 100 µg/kg i.p. lipopolysaccharide (LPS) challenge (Experiment 2), or a restraint challenge (Experiment 3), and exposed to alcohol-associated cues. Blood plasma was collected for analysis.Results: Alcohol-associated cues facilitated the plasma corticosterone response to a subthreshold dose of alcohol (F1,28 = 4.85, p < .05) and an immune challenge (F8,80 = 6.23, p < .001), but not a restraint challenge (F2,27 = 0.18, p > .05).Conclusion: These findings reveal that the impact of the cues associated with alcohol intoxication on the HPA axis may be context-specific. This work illustrates how HPA axis learning processes form in the early stages of alcohol use and has important implications for how the HPA and neuroimmune conditioning may develop in alcohol use disorder in humans and facilitate the response to a later immune challenge.

Learning processes in relapse to alcohol use: lessons from animal models

RATIONALE

Alcohol use is reliably preceded by discrete and contextual stimuli which, through diverse learning processes, acquire the capacity to promote alcohol use and relapse to alcohol use.

OBJECTIVE

We review contemporary extinction, renewal, reinstatement, occasion setting, and sex differences research within a conditioning framework of relapse to alcohol use to inform the development of behavioural and pharmacological therapies.

KEY FINDINGS

Diverse learning processes and corresponding neurobiological substrates contribute to relapse to alcohol use. Results from animal models indicate that cortical, thalamic, accumbal, hypothalamic, mesolimbic, glutamatergic, opioidergic, and dopaminergic circuitries contribute to alcohol relapse through separable learning processes. Behavioural therapies could be improved by increasing the endurance and generalizability of extinction learning and should incorporate whether discrete cues and contexts influence behaviour through direct excitatory conditioning or occasion setting mechanisms. The types of learning processes that most effectively influence responding for alcohol differ in female and male rats.

CONCLUSION

Sophisticated conditioning experiments suggest that diverse learning processes are mediated by distinct neural circuits and contribute to relapse to alcohol use. These experiments also suggest that gender-specific behavioural and pharmacological interventions are a way towards efficacious therapies to prevent relapse to alcohol use.

Reinstatement of Pavlovian responses to alcohol cues by stress

RATIONALE

Stress may contribute to relapse to alcohol use in part by enhancing reactivity to cues previously paired with alcohol. Yet, standard models of stress-induced reinstatement generally use contingent presentations of alcohol-paired cues to reinforce instrumental behaviors, making it difficult to isolate the ability of cues to invigorate alcohol-seeking.

OBJECTIVE

Here we sought to test the impact of stress on behavioral responses to alcohol-paired cues, using a model of stress-induced reinstatement of Pavlovian conditioned approach, inspired by Nadia Chaudhri's work on context-induced reinstatement.

METHODS

Long Evans rats were trained to associate one auditory cue with delivery of alcohol or sucrose and an alternative auditory cue with no reward. Following extinction training, rats were exposed to a stressor prior to being re-exposed to the cues under extinction conditions. We assessed the effects of yohimbine, intermittent footshock and olfactory cues paired with social defeat on responses to alcohol-paired cues and the effects of yohimbine on responses to sucrose-paired cues.

RESULTS

The pharmacological stressor, yohimbine, enhanced alcohol seeking in a Pavlovian setting, but not in a cue-selective manner. Intermittent footshock and social defeat cues did not enhance alcohol seeking in this paradigm.

CONCLUSIONS

While yohimbine elicited reinstatement of reward-seeking in a Pavlovian setting, these effects may be unrelated to activation of stress systems or to interactions with specific cues.

Basolateral amygdala and orbitofrontal cortex, but not dorsal hippocampus, are necessary for the control of reward-seeking by occasion setters

Reward-seeking in the world is driven by cues that can have ambiguous predictive and motivational value. To produce adaptive, flexible reward-seeking, it is necessary to exploit occasion setters, other distinct features in the environment, to resolve the ambiguity of Pavlovian reward-paired cues. Despite this, very little research has investigated the neurobiological underpinnings of occasion setting, and as a result little is known about which brain regions are critical for occasion setting. To address this, we exploited a recently developed task that was amenable to neurobiological inquiry where a conditioned stimulus is only predictive of reward delivery if preceded in time by the non-overlapping presentation of a separate cue-an occasion setter. This task required male rats to maintain and link cue-triggered expectations across time to produce adaptive reward-seeking. We interrogated the contributions of the basolateral amygdala and orbitofrontal cortex to occasion setting as these regions are thought to be critical for the computation and exploitation of state value, respectively. Reversible inactivation of either structure prior to the occasion-setting task resulted in a profound inability of rats to use the occasion setter to guide reward-seeking. In contrast, inactivation of the dorsal hippocampus, a region fundamental for context-specific responding was without effect nor did inactivation of the basolateral amygdala or orbitofrontal cortex in a standard Pavlovian conditioning preparation affect conditioned responding. We conclude that neural activity within the orbitofrontal cortex and basolateral amygdala circuit is necessary to update and resolve ambiguity in the environment to promote cue-driven reward-seeking.

Conditioned place preferences for virtual alcohol cues

This study examined whether a conditioned place preference (CPP) could be established for a virtual reality (VR) room that previously contained virtual alcohol stimuli. 298 undergraduates with varying levels of alcohol use completed six, three-minute conditioning sessions in which they were confined to one of two visually-distinct VR rooms: one of the VR rooms contained virtual alcohol cues (CS+) while the other VR room was neutral (CS-). Following conditioning, participants completed a three-minute test session during which they had unrestricted access to both VR rooms and neither room contained any alcohol-related cues. Although no virtual alcohol cues were present, participants with alcohol use (n = 248) spent significantly longer in CS+ relative to CS- compared to participants with alcohol non-use (n = 50) during the test session. This is the first study to show that a CPP can be established using virtual alcohol cues, in the absence of any actual alcohol administration. However, participants with alcohol use did not subjectively report enjoying CS+ more than CS- and explicitly chose CS- as their preferred room. Interestingly, these findings suggest that implicit and explicit measures of CPP may tap into distinct, separable processes and should be investigated further.

Using Imagination to Integrate Contextual Effects in a Cue-Reactivity Paradigm in Patients with Alcohol Use Disorder: A Functional Magnetic Resonance Imaging Pilot Study

INTRODUCTION

In individuals with alcohol use disorder (AUD), the brain areas underlying cue-induced reactions (e.g., cingulum, striatum, thalamus) and altered activation of these regions have been identified by functional neuroimaging. Neuronal responses to a complex alcohol-related context are yet to investigate. To better understand contextual effects as well as the interplay of cue-induced neural reactions and context exposure, the present study implemented an imagination procedure during functional magnetic resonance imaging (fMRI).

METHODS

Thirteen patients with AUD and 13 healthy controls completed two rounds of a cue-reactivity paradigm inside an MRI scanner. Two individualized imagination tasks were conducted before each of the two cue reactivity tasks. A 2 (group) × 2 (imagination) × 2 (picture-type) analysis of variance (ANOVA) was performed.

RESULTS

The ANOVA revealed a main effect for imagination with higher activation in bilateral thalamus and right caudate nucleus and an interaction effect between imagination and group in right thalamus and left caudate nucleus, due to the patient group reacting stronger during alcohol-related imagination. These structures are involved in relaying sensory information and habit learning. No main or interaction effects of picture type were observed.

CONCLUSIONS

These results support the view that context effects alter the neural responses in thalamus and nucleus caudatus in patients with AUD, and that imagination tasks are suited to incorporate contextual influences in neurophysiological research designs. Future research needs to investigate whether the failure to observe a picture-type effect was due to limited statistical power and omission to individualize picture set, or whether an imagination procedure interferes with the evocation of picture-type effects.

A critical review of front-loading: A maladaptive drinking pattern driven by alcohol's rewarding effects

Front-loading is a drinking pattern in which alcohol intake is skewed toward the onset of reward access. This phenomenon has been reported across several different alcohol self-administration protocols in a wide variety of species, including humans. The hypothesis of the current review is that front-loading emerges in response to the rewarding effects of alcohol and can be used to measure the motivation to consume alcohol. Alternative or additional hypotheses that we consider and contrast with the main hypothesis are that: (1) front-loading is directed at overcoming behavioral and/or metabolic tolerance and (2) front-loading is driven by negative reinforcement. Evidence for each of these explanations is reviewed. We also consider how front-loading has been evaluated statistically in previous research and make recommendations for defining this intake pattern in future studies. Because front-loading may predict long-term maladaptive alcohol drinking patterns leading to the development of alcohol use disorder (AUD), several future directions are proposed to elucidate the relationship between front-loading and AUD.

Role of 5-HT2A receptors in the effects of ayahuasca on ethanol self-administration using a two-bottle choice paradigm in male mice

RATIONALE

Ayahuasca has been proposed as a potential treatment of alcohol (ethanol) use disorder (AUD). The serotonin 5-HT2A receptor agonist N,N-dimethyltryptamine (DMT) is the main psychoactive component of ayahuasca, suggesting that its therapeutic effects may be mediated by 5-HT2A receptors.

OBJECTIVES

The aim of the present study was to investigate the effects of ayahuasca on the expression of ethanol self-administration using a two-bottle choice procedure and the role of 5-HT2A receptors in those effects.

METHODS

Male mice had intermittent access to ethanol (10% v/v) in a two-bottle choice procedure for 30 days. Animals were then submitted to 3 treatment phases, each followed by ethanol re-exposure tests. During the treatment phase, every 3 days, animals received i.p. injections of either vehicle or the 5-HT2A receptor antagonist M100907 (M100, 1 mg/kg) followed by an i.g. (gavage) administration of vehicle or ayahuasca (100 mg/kg) and were exposed to the self-administration apparatus with no ethanol availability. During re-exposure tests, animals were submitted to the same conditions as during acquisition, with no treatments prior to those sessions.

RESULTS

Treatment with ayahuasca blocked the expression of ethanol self-administration, decreasing ethanol intake and preference during re-exposure tests. Pretreatment with M100 blocked the effects of ayahuasca on ethanol drinking without significantly attenuating ethanol self-administration.

CONCLUSIONS

Treatment with ayahuasca during alcohol abstinence blocked the expression of alcohol self-administration in mice, and 5-HT2A receptor activation is critical for those effects to emerge. Our findings support a potential for ayahuasca and other 5-HT2A receptor agonists as adjunctive pharmacotherapies for the treatment of AUD.

Compulsive Alcohol Seeking and Relapse: Central Role of Conditioning Factors Associated with Alleviation of Withdrawal States by Alcohol

Background and Purpose

Learned associations between environmental stimuli and drugs of abuse represent a major factor in the chronically relapsing nature of drug addiction. In drug dependent subjects these associations must be presumed to include associations linked to reversal of adverse withdrawal states by drug use—“withdrawal‐associated learning” (WDL). However, their significance in drug seeking has received little experimental scrutiny.

Experimental Approach

Using alcohol as a drug of abuse, the behavioural consequences of WDL were investigated in animal models of relapse and compulsive drug seeking by comparing the effects of WD L‐associated stimuli versus stimuli associated with alcohol without WDL experience in nondependent and post‐dependent rats. Brain sites activated by exposure to the respective stimuli were identified by c‐fos immunohistochemistry.

Key Results

(1) WDL‐associated stimuli elicited significant alcohol seeking. In rats with WDL experience, stimuli associated with alcohol in the nondependent state no longer elicited robust alcohol seeking. (2) Responding elicited by WDL‐associated stimuli, but not stimuli conditioned to alcohol in the nondependent state, was resistant to footshock punishment and increased response effort requirements for presentation of WDL‐related stimuli. (3) Stimuli conditioned to alcohol in rats with a dependence but not WDL history did not sustain punished responding or tolerance of increased effort. (4) The central nucleus of the amygdala was identified as a site selectively responsive to WDL stimulus exposure.

Conclusion and Implications

Environmental stimuli associated with reversal of adverse withdrawal states by alcohol elicit compulsive‐like alcohol seeking and establish WDL as a major, not well‐recognized factor, in relapse vulnerability.

Alcohol approach bias is associated with both behavioral and neural Pavlovian-to-instrumental transfer effects in alcohol-dependent patients

Background

Even after qualified detoxification, alcohol-dependent (AD) patients may relapse to drinking alcohol despite their decision to abstain. Two mechanisms may play important roles. First, the impact of environmental cues on instrumental behavior (i.e., Pavlovian-to-instrumental transfer [PIT] effect), which was found to be stronger in prospectively relapsing AD patients than in abstaining patients. Second, an automatic approach bias toward alcohol stimuli was observed in AD patients, and interventions targeting this bias reduced the relapse risk in some studies. Previous findings suggest a potential behavioral and neurobiological overlap between these two mechanisms.

Methods

In this study, we examined the association between alcohol approach bias and both behavioral and neural non-drug-related PIT effects in AD patients after detoxification. A total of 100 AD patients (17 females) performed a PIT task and an alcohol approach/avoidance task. Patients were followed for 6 months.

Results

A stronger alcohol approach bias was associated with both a more pronounced behavioral PIT effect and stronger PIT-related neural activity in the right nucleus accumbens. Moreover, the association between alcohol approach bias and behavioral PIT increased with the severity of alcohol dependence and trait impulsivity and was stronger in patients who relapsed during follow-up in the exploratory analysis.

Conclusions

These findings indicate partial behavioral and neurobiological overlap between alcohol approach bias and the PIT effect assessed with our tasks. The association was stronger in patients with more severe alcohol dependence.

The role of context on responding to an alcohol-predictive cue in female and male rats

In male rats, physical contexts that are associated with alcohol can amplify the response to a discrete, alcohol-predictive conditioned stimulus (CS), and amplify prime-induced reinstatement. Here, we examined these effects as a function of biological sex. Male and female Long-Evans rats were acclimated to drinking ethanol (15% v/v) in their home cages. Next, they were trained to associate an auditory conditioned stimulus (CS) (10 s; white noise or clicker; 15 trials per session) with ethanol delivery (0.2 mL per CS; 3.0 mL per session) into a fluid port for oral intake. Training occurred in a distinctive context containing specific visual, olfactory, and tactile stimuli. During alternating sessions, rats were exposed to a second context wherein they did not receive ethanol. At test, CS trials occurred in both contexts without ethanol delivery. Rats then underwent extinction using repeated unreinforced presentations of the CS in both contexts. An alcohol-primed reinstatement test was then conducted, in which 0.2 mL of ethanol was presented at the start of the session and during the first CS trial, after which no ethanol was delivered for the remainder of the session. At both test and reinstatement, male rats made significantly more CS port-entries in the context associated with alcohol delivery than in the context in which alcohol was never experienced. Unlike males, female rats made a similar number of CS port-entries at the test in both the alcohol context and the neutral context. The reinstatement observed in female rats was also not affected by context. These findings suggest that the capacity of an alcohol-associated context to modulate responding to a discrete, alcohol-predictive cue is less pronounced in female than male rats.

Ibogaine Blocks Cue- and Drug-Induced Reinstatement of Conditioned Place Preference to Ethanol in Male Mice

Ibogaine is a psychedelic extracted from the plant Tabernanthe iboga Baill. (Apocynaceae), natural from Africa, and has been proposed as a potential treatment for substance use disorders. In animal models, ibogaine reduces ethanol self-administration. However, no study to date has investigated the effects of ibogaine on ethanol-induced conditioned place preference (CPP). The present study aimed to investigate the effects of repeated treatment with ibogaine on the reinstatement of CPP to ethanol in male mice. The rewarding effects of ethanol (1.8 g/kg, i. p.) or ibogaine (10 or 30 mg/kg, p. o.) were investigated using the CPP model. Furthermore, we evaluated the effects of repeated treatment with ibogaine (10 or 30 mg/kg, p. o.) on the reinstatement of ethanol-induced CPP. Reinstatement was evaluated under two conditions: 1) during a priming injection re-exposure test in which animals received a priming injection of ethanol and had free access to the CPP apparatus; 2) during a drug-free test conducted 24 h after a context-paired re-exposure, in which subjects received an injection of ethanol and were confined to the compartment previously conditioned to ethanol. Our results show that ethanol, but not ibogaine, induced CPP in mice. Treatment with ibogaine after conditioning with ethanol blocked the reinstatement of ethanol-induced CPP, both during a drug priming reinstatement test and during a drug-free test conducted after re-exposure to ethanol in the ethanol-paired compartment. Our findings add to the literature suggesting that psychedelics, in particular ibogaine, may have therapeutic properties for the treatment of alcohol use disorder at doses that do not have rewarding effects per se.

Identification of a G-Protein-Independent Activator of GIRK Channels

G-protein-gated inwardly rectifying K⁺ (GIRK) channels are essential effectors of inhibitory neurotransmission in the brain. GIRK channels have been implicated in diseases with abnormal neuronal excitability, including epilepsy and addiction. GIRK channels are tetramers composed of either the same subunit (e.g., homotetramers) or different subunits (e.g., heterotetramers). Compounds that specifically target subsets of GIRK channels in vivo are lacking. Previous studies have shown that alcohol directly activates GIRK channels through a hydrophobic pocket located in the cytoplasmic domain of the channel. Here, we report the identification and functional characterization of a GIRK1-selective activator, termed GiGA1, that targets the alcohol pocket. GiGA1 activates GIRK1/GIRK2 both in vitro and in vivo and, in turn, mitigates the effects of a convulsant in an acute epilepsy mouse model. These results shed light on the structure-based development of subunit-specific GIRK modulators that could provide potential treatments for brain disorders.

Alcohol conditioned contexts enhance positive subjective alcohol effects and consumption

Associations between alcohol and the places it is consumed are important at all stages of alcohol abuse and addiction. However, it is not clear how the associations are formed in humans or how they influence drinking, and there are few effective strategies to prevent their pathological effects on alcohol use. We used a human laboratory model to study the effects of alcohol environments on alcohol consumption. Healthy regular binge drinkers completed conditioned place preference (CPP) with 0 vs. 80 mg/100 mL alcohol (Paired Group). Control participants (Unpaired Group) completed sessions without explicit alcohol-room pairings. After conditioning, participants completed alcohol self-administration in either the alcohol- or no alcohol-paired room. Paired group participants reported greater subjective stimulation and euphoria, and consumed more alcohol in the alcohol-paired room in comparison to the no alcohol-paired room, and controls tested in either room. Moreover, the strength of conditioning significantly predicted drinking; participants who exhibited the strongest CPP consumed the most alcohol in the alcohol-paired room. This is the first empirical evidence that laboratory-conditioned alcohol environments directly influence drinking. The results also confirm the viability of the model to examine the mechanisms by which alcohol environments stimulate drinking and to test strategies to counteract their influence on behavior.

The synthetically produced predator odor 2,5-dihydro-2,4,5-trimethylthiazoline increases alcohol self-administration and alters basolateral amygdala response to alcohol in rats

Post-traumatic stress disorder (PTSD) is a psychiatric illness that can increase the risk for developing an alcohol use disorder (AUD). While clinical data has been useful in identifying similarities in the neurobiological bases of these disorders, preclinical models are essential for understanding the mechanism(s) by which stressors increase the risk for escalated alcohol consumption. The purpose of these studies was to examine if exposure of male Long-Evans rats to the synthetically derived predator odor 2,5-dihydro-2,4,5-trimethylthiazoline (TMT; a component of fox feces) would increase sweetened alcohol self-administration, potentially by facilitating transfer of salience towards cues, and alter neuronal response to alcohol as measured by the immediate early gene c-Fos. In experiment 1, rats exposed to repeated (4×) TMT showed reductions in port entries in Pavlovian conditioned approach and increases in sweetened alcohol self-administration. In experiment 2, rats exposed to repeated TMT showed blunted basolateral amygdala c-Fos response to alcohol. In experiment 3, rats exposed to single, but not repeated TMT, showed increases in sweetened alcohol self-administration, and no change in anxiety-like behavior or hyperarousal. In experiment 4, rats continued to show a significant corticosterone response to TMT after repeated exposures. In summary, exposure of male rats to TMT can cause escalations in sweetened alcohol self-administration and reduction in BLA response to alcohol. These studies outline and utilize a novel preclinical model that can be used to further neurobiological understanding of the emergence of escalated alcohol consumption following stress exposure.

Basolateral Amygdala to Nucleus Accumbens Communication Differentially Mediates Devaluation Sensitivity of Sign- and Goal-Tracking Rats

Rats rely on communication between the basolateral amygdala (BLA) and nucleus accumbens (NAc) to express lever directed approach in a Pavlovian lever autoshaping (PLA) task that distinguishes sign- and goal-tracking rats. During PLA, sign-tracking rats preferentially approach an insertable lever cue, while goal-tracking rats approach a foodcup where rewards are delivered. While sign-tracking rats inflexibly respond to cues even after the associated reward is devalued, goal-tracking rats flexibly reduce responding to cues during outcome devaluation. Here, we sought to determine whether BLA-NAc communication, which is necessary for sign, but not goal-tracking, drives a rigid appetitive approach of sign-tracking rats that are insensitive to manipulations of outcome value. Using a contralateral chemogenetic inactivation design, we injected contralateral BLA and NAc core with inhibitory DREADD (hm4Di-mCherry) or control (mCherry) constructs. To determine sign- and goal-tracking groups, we trained rats in five PLA sessions in which brief lever insertion predicts food pellet delivery. We sated rats on training pellets (devalued condition) or chow (valued condition) before systemic clozapine injections (0.1 mg/kg) to inactivate BLA and contralateral NAc during two outcome devaluation probe tests, in which we measured lever and foodcup approach. Contralateral BLA-NAc chemogenetic inactivation promoted a flexible lever approach in sign-tracking rats but disrupted the flexible foodcup approach in goal-tracking rats. Consistent with a prior BLA-NAc disconnection lesion study, we find contralateral chemogenetic inactivation of BLA and NAc core reduces lever, but not the foodcup approach in PLA. Together these findings suggest rigid appetitive associative encoding in BLA-NAc of sign-tracking rats hinders the expression of flexible behavior when outcome value changes.

Dissociable mesolimbic dopamine circuits control responding triggered by alcohol-predictive discrete cues and contexts

Context can influence reactions to environmental cues and this elemental process has implications for substance use disorder. Using an animal model, we show that an alcohol-associated context elevates entry into a fluid port triggered by a conditioned stimulus (CS) that predicted alcohol (CS-triggered alcohol-seeking). This effect persists across multiple sessions and, after it diminishes in extinction, the alcohol context retains the capacity to augment reinstatement. Systemically administered eticlopride and chemogenetic inhibition of ventral tegmental area (VTA) dopamine neurons reduce CS-triggered alcohol-seeking. Chemogenetically silencing VTA dopamine terminals in the nucleus accumbens (NAc) core reduces CS-triggered alcohol-seeking, irrespective of context, whereas silencing VTA dopamine terminals in the NAc shell selectively reduces the elevation of CS-triggered alcohol-seeking in an alcohol context. This dissociation reveals new roles for divergent mesolimbic dopamine circuits in the control of responding to a discrete cue for alcohol and in the amplification of this behaviour in an alcohol context.

Memory biases in alcohol use disorder: enhanced memory for contexts associated with alcohol prospectively predicts alcohol use outcomes

Memory for prior drinking experiences may powerfully drive later alcohol use in familiar drinking contexts, yet we know little about what patients with alcohol use disorder (AUD) remember of alcohol-related episodes. Although animal and theoretical models of addiction emphasize the importance of different memory systems for understanding maladaptive use, clinical research parsing what AUD patients remember from alcohol-related episodes is lacking. The current study applied a novel memory task in which moderate drinkers (N = 30) and treatment-seeking individuals with alcohol use disorder (AUD: N = 29) encoded associations between photographs of objects (alcoholic beverages and neutral items) and photographs of neutral scenes. At least 24 h later, two types of memory were assessed: item memory (object recognition) and associative memory (cued recognition of scenes associated with objects). To assess which memories predicted drinking, real-world behavior was assessed in patients with AUD at baseline and for 4 weeks following memory tests. Despite demographic differences, the results showed broadly impaired item memory in AUD compared with moderate drinkers (p < 0.001), but enhanced associative memory for scenes paired with alcohol (p = 0.015). These associative memory biases were especially pronounced for stimuli rated as more affectively salient. Furthermore, stronger but less detailed memory for alcohol-related associations (i.e., choosing the correct scene but the incorrect photograph) significantly predicted heavier baseline (p = 0.002) and higher subsequent (p = 0.01) drinking in patients with AUD. These findings reveal a novel alcohol-related memory bias in AUD, and uncover the importance of associative memory for understanding real-world heavy alcohol use.

Alcohol Causes Lasting Differential Transcription in Drosophila Mushroom Body Neurons

Repeated alcohol experiences can produce long-lasting memories for sensory cues associated with intoxication. These memories can problematically trigger relapse in individuals recovering from alcohol use disorder (AUD). The molecular mechanisms by which ethanol changes memories to become long-lasting and inflexible remain unclear. New methods to analyze gene expression within precise neuronal cell types can provide further insight toward AUD prevention and treatment. Here, we used genetic tools in Drosophila melanogaster to investigate the lasting consequences of ethanol on transcription in memory-encoding neurons. Drosophila rely on mushroom body (MB) neurons to make associative memories, including memories of ethanol-associated sensory cues. Differential expression analyses revealed that distinct transcripts, but not genes, in the MB were associated with experiencing ethanol alone compared to forming a memory of an odor cue associated with ethanol. Adult MB-specific knockdown of spliceosome-associated proteins demonstrated the necessity of RNA-processing in ethanol memory formation. These findings highlight the dynamic, context-specific regulation of transcription in cue-encoding neurons, and the lasting effect of ethanol on transcript usage during memory formation.

Comparing ABA, AAB, and ABC Renewal of Appetitive Pavlovian Conditioned Responding in Alcohol- and Sucrose-Trained Male Rats

Conditioned responding can be renewed by re-exposure to the conditioning context following extinction in a different context (ABA renewal) or by removal from the extinction context (AAB or ABC renewal). ABA renewal is robust in Pavlovian and operant conditioning paradigms. However, fewer studies have investigated AAB and ABC renewal of appetitive conditioning, and those that did predominantly used operant conditioning tasks. Renewal has theoretical relevance for extinction and for exposure-based treatments for substance use disorders that aim to extinguish reactivity to drug-predictive cues. We therefore investigated ABA, AAB, and ABC renewal of Pavlovian conditioned responding to cues that predicted either alcohol or sucrose. Male, Long-Evans rats (Charles River) were exposed to either 15% ethanol (Study 1: “alcohol”) or 10% sucrose (Study 2: “sucrose”) in their home cages. Next, they were trained to discriminate between two auditory stimuli (white noise and clicker; 10 s) in conditioning chambers equipped with distinct olfactory, visual, and tactile contextual stimuli (context A). One conditioned stimulus (CS+) was paired with fluid delivery (0.2 ml/CS+; 3.2 ml/session; alcohol or sucrose in separate experiments), and the second CS (CS−) was not. In all sessions (conditioning, extinction, and test), each CS was presented 16 times/session on a variable-time 67-s schedule, and entries into the fluid port were recorded. CS+ port entries were then extinguished by withholding fluid delivery either in context A or in a second, different context (context B). Next, we assessed ABA, AAB, and ABC renewal in the absence of fluid delivery. During extinction, CS+ port entries were initially elevated in context A relative to context B. ABA renewal of CS+ port entries occurred in both alcohol- and sucrose-trained rats. ABC renewal approached statistical significance when data from both experiments were combined. No AAB renewal was observed, and, in fact, alcohol-trained rats showed AAB suppression. These results corroborate the reliability of ABA renewal and suggest that ABC renewal is a modest effect that may require greater statistical power to detect. From a treatment perspective, the lack of AAB renewal suggests that exposure-based treatments for substance use disorders might benefit from implementation in real-world, drug-use contexts.

Allosteric modulation of metabotropic glutamate receptors in alcohol use disorder: Insights from preclinical investigations

Metabotropic glutamate (mGlu) receptors are family C G protein-coupled receptors (GPCRs) that modulate neuronal excitability and synaptic transmission throughout the nervous system. Owing to recent advances in development of subtype-selective allosteric modulators of mGlu receptors, individual members of the mGlu receptor family have been proposed as targets for treating a variety of neurological and psychiatric disorders, including substance use disorders. In this chapter, we highlight preclinical evidence that allosteric modulators of mGlu receptors could be useful for reducing alcohol consumption and preventing relapse in alcohol use disorder (AUD). We begin with an overview of the preclinical models that are used to study mGlu receptor involvement in alcohol-related behaviors. Alcohol exposure causes adaptations in both expression and function of various mGlu receptor subtypes, and pharmacotherapies aimed at reversing these adaptations have the potential to reduce alcohol consumption and seeking. Positive allosteric modulators (PAMs) of mGlu₂ and negative allosteric modulators of mGlu₅ show particular promise for reducing alcohol intake and/or preventing relapse. Finally, this chapter discusses important considerations for translating preclinical findings toward the development of clinically useful drugs, including the potential for PAMs to avoid tolerance issues that are frequently observed with repeated administration of GPCR agonists.

Role of the treatment environment in the effects of aripiprazole on ethanol-induced behavioral sensitization and conditioned place preference in female mice

BACKGROUND

Evidence suggests that aripiprazole, a partial dopamine D2 and serotonin 5-HT1A receptor agonist and 5-HT2A receptor antagonist, show significant efficacy in reducing alcohol use. We have previously demonstrated that treatment with aripiprazole blocked the reinstatement of cocaine-induced behavioral sensitization in a context-dependent manner, suggesting that the treatment environment may modulate the therapeutic effects of aripiprazole. The present study aimed to evaluate the effects of treatment with aripiprazole on ethanol-induced behavioral sensitization and conditioned place preference in female mice, and the role of the treatment environment in those effects.

METHODS

Adult female mice were either sensitized with ethanol injections in the open-field apparatus, or conditioned with ethanol in the conditioned place preference (CPP) apparatus. Animals were then treated with vehicle or 0.1 mg/kg aripiprazole paired to the test environment (open-field or CPP apparatus) or not (home-cage treatments) for 4 alternate days, and the subsequent expression of behavioral sensitization or CPP to ethanol was evaluated during or following an ethanol re-exposure, respectively.

RESULTS

Repeated treatment with aripiprazole attenuated the expression of ethanol-induced behavioral sensitization regardless of the treatment environment. Treatment with aripiprazole was only effective at preventing the reinstatement of ethanol-induced CPP when paired with the ethanol-associated environment, but not when administered in the home-cage.

CONCLUSIONS

The present findings corroborate previous studies suggesting the effectiveness of aripiprazole for the treatment of alcohol use disorder. Our results also point to an important role of the treatment environment in the therapeutic effects of aripiprazole in rodent models of ethanol abuse.

Context controls the timing of responses to an alcohol-predictive conditioned stimulus

Context can influence the number of responses elicited by a discrete, appetitive conditioned stimulus (CS) but can context control when a CS elicits a response? To test this fundamental question, we gave male, Long-Evans rats Pavlovian conditioning sessions in which the same auditory conditioned stimulus (CS, 30 s, 15 trials/session) was presented in 2 different physical contexts on alternating days, according to a within-subjects design. In one context, called the early context, alcohol (15 % ethanol, 0.2 ml/trial) was delivered from the onset of the 5^th second until the termination of the 10^th second of the 30 s CS. In the second late context, alcohol was delivered from the onset of the 25^th second until the termination of the 30^th second of the same CS. In a comparison of the last session of training, the probability of making a conditioned response during the first four seconds of the CS was significantly higher in the early context than in the late context. This result shows that context can signal when an unconditioned stimulus occurs in relation to a CS and highlights a role for context in controlling precisely timed alcohol-seeking responses.

Effects of Limited and Extended Pavlovian Training on Devaluation Sensitivity of Sign- and Goal-Tracking Rats

Individual differences in Pavlovian approach predict differences in devaluation sensitivity. Recent studies indicate goal-tracking (GT) rats are sensitive to outcome devaluation while sign-tracking (ST) rats are not. With extended training in Pavlovian lever autoshaping (PLA), GT rats display more lever-directed behavior, typical of ST rats, suggesting they may become insensitive to devaluation with more Pavlovian training experience. Here, we use a within-subject satiety-induced outcome devaluation procedure to test devaluation sensitivity after limited and extended PLA training in GT and ST rats. We trained rats in PLA to determine GT and ST groups. Then, we sated rats on either the training pellets (devalued condition) or homecage chow (valued condition) prior to brief non-reinforced test sessions after limited (sessions 5/6) and extended (sessions 17/18) PLA training. GT rats decreased conditioned responding under devalued relative to valued conditions after both limited and extended training, demonstrating they are sensitive to satiety devaluation regardless of the amount of PLA training. While ST rats were insensitive to satiety devaluation after limited training, their lever directed behavior became devaluation sensitive after extended training. To determine whether sign-tracking rats also displayed sensitivity to illness-induced outcome devaluation after extended training, we trained a separate cohort of rats in extended PLA and devalued the outcome with lithium chloride injections after pellet consumption in the homecage. ST rats failed to decrease conditioned responding after illness-induced outcome devaluation, while Non-ST rats (GT and intermediates) were sensitive to illness-induced outcome devaluation after extended training. Together, our results confirm devaluation sensitivity is stable in GT rats across training and devaluation approaches. Extended training unmasks devaluation sensitivity in ST rats after satiety, but not illness-induced devaluation, suggesting ST rats respond appropriately by decreasing responding to cues during state-dependent but not inference-based devaluation. The differences in behavioral flexibility across tracking groups and devaluation paradigms have translational relevance for the understanding state- vs. inference-based reward devaluation as it pertains to drug addiction vulnerability.

Considering Drug-Associated Contexts in Substance Use Disorders and Treatment Development

Environmental contexts that are reliably associated with the use of pharmacologically active substances are hypothesized to contribute to substance use disorders. In this review, we provide an updated summary of parallel preclinical and human studies that support this hypothesis. Research conducted in rats shows that environmental contexts that are reliably paired with drug use can renew extinguished drug-seeking behavior and amplify responding elicited by discrete, drug-predictive cues. Akin to drug-associated contexts, interoceptive drug stimuli produced by the psychopharmacological effects of drugs can also influence learning and memory processes that play a role in substance use disorders. Findings from human laboratory studies show that drug-associated contexts, including social stimuli, can have profound effects on cue reactivity, drug use, and drug-related cognitive expectancies. This translationally relevant research supports the idea that treatments for substance use disorders could be improved by considering drug-associated contexts as a factor in treatment interventions. We conclude this review with ideas for how to integrate drug-associated contexts into treatment-oriented research based on 4 approaches: pharmacology, brain stimulation, mindfulness-based relapse prevention, and cognitive behavioral group therapy. Throughout, we focus on alcohol- and tobacco-related research, which are two of the most prevalent and commonly misused drugs worldwide for which there are known treatments.

Brain activation to cannabis- and alcohol-related words in alcohol use disorder

Cannabis abuse commonly co-occurs with alcohol use disorder (AUD). With increased acceptance and accessibility to cannabis in the US, it is imperative to understand the psychological and neural mechanisms of concurrent alcohol and cannabis use. We hypothesized that neural alcohol-cue conditioning may extent to other drug-related stimuli, such as cannabis, and underwrite the loss of control over reward-driven behavior. Task-activated fMRI examined the neural correlates of alcohol- and cannabis-related word cues in 21 abstinent AUD and 18 control subjects. Relative to controls, AUD showed behavioral attentional biases and frontal hypoactivation to both alcohol- and cannabis-related words. This cue-elicited prefrontal hypoactivation was related to higher lifetime alcohol consumption (pcorrected < 0.02) and modulated by past cannabis use histories (p ≦ 0.001). In particular, frontal hypoactivation to both alcohol and cannabis cues was pronounced in AUD without prior cannabis exposure. Overall, frontal control mechanisms in abstinent AUD were not sufficiently engaged to override automatic alcohol and cannabis-related intrusions, enhancing the risk for relapse and potentially for alcohol and cannabis co-use with the increased social acceptance and accessibility in the US.

Evidence for incentive salience sensitization as a pathway to alcohol use disorder

The incentive salience sensitization (ISS) theory of addiction holds that addictive behavior stems from the ability of drugs to progressively sensitize the brain circuitry that mediates attribution of incentive salience (IS) to reward-predictive cues and its behavioral manifestations. In this article, we establish the plausibility of ISS as an etiological pathway to alcohol use disorder (AUD). We provide a comprehensive and critical review of evidence for: (1) the ability of alcohol to sensitize the brain circuitry of IS attribution and expression; and (2) attribution of IS to alcohol-predictive cues and its sensitization in humans and non-human animals. We point out gaps in the literature and how these might be addressed. We also highlight how individuals with different alcohol subjective response phenotypes may differ in susceptibility to ISS as a pathway to AUD. Finally, we discuss important implications of this neuropsychological mechanism in AUD for psychological and pharmacological interventions attempting to attenuate alcohol craving and cue reactivity.

Cue-Elicited Anxiety and Alcohol Craving as Indicators of the Validity of ALCO-VR Software: A Virtual Reality Study

BACKGROUND

This study is part of a larger project aiming to develop a virtual reality (VR) software to be implemented as a clinical tool for patients diagnosed with alcohol use disorder (AUD). The study is based on previous research in which we identified factors that elicit craving for alcohol in a sample of AUD patients, and which led to the development of a virtual reality software to be used in cue exposure treatments of alcohol use disorder (ALCO-VR). The main objective of this study was to test the effectiveness of ALCO-VR to elicit cue-induced craving and anxiety responses among social drinkers (SD) and AUD patients. Our secondary objective was to explore which responses (cue-induced craving or anxiety) can best differentiate between AUD patients and the SD group.

METHOD

Twenty-seven individuals (13 AUD patients and 14 SD) participated in this study after giving written informed consent. Their anxiety and alcohol craving levels were measured by different instruments at different stages of the procedure. The VR equipment consisted of Oculus Rift technology, and the software consisted of the ALCO-VR platform.

RESULTS

Our data indicate that the ALCO-VR software can elicit responses of anxiety and alcohol craving, especially in the group of AUD patients. The cue-induced anxiety response differentiated AUD patients and the SD group better than the cue-induced craving response.

CONCLUSIONS

The general interest in applying new technologies to the assessment and treatment of mental health disorders has led to the development of immersive real-life simulations based on the advantages of VR technology. Our study concluded that the ALCO-VR software can elicit anxiety and craving responses and that cue-induced anxiety responses can distinguish between AUD and SD groups better than cue-induced craving. The data on craving and anxiety were assessed consistently by different instruments. In addition, we consider that ALCO-VR is able to ecologically assess cue-induced anxiety and alcohol craving levels during exposure to VR alcohol-related environments.

Metabotropic Glutamate Receptor Subtype 5 in Alcohol-Induced Negative Affect

Allosteric modulators of metabotropic glutamate 5 receptors (mGlu5 receptors) have been identified as a promising treatment to independently alleviate both negative affective states and ethanol-seeking and intake. However, these conditions are often comorbid and might precipitate one another. Acute and protracted ethanol withdrawal can lead to negative affective states. In turn, these states are primary drivers of alcohol relapse, particularly among women. The current review synthesizes preclinical studies that have observed the role of mGlu5 receptor modulation in negative affective states following ethanol exposure. The primary behavioral assays discussed are ethanol-seeking and intake, development and extinction of ethanol-associated cues and contexts, behavioral despair, and anxiety-like activity. The work done to-date supports mGlu5 receptor modulation as a promising target for mediating negative affective states to reduce ethanol intake or prevent relapse. Limitations in interpreting these data include the lack of models that use alcohol-dependent animals, limited use of adolescent and female subjects, and a lack of comprehensive evaluations of negative affective-like behavior.

Occasion setting

Occasion setting refers to the ability of 1 stimulus, an occasion setter, to modulate the efficacy of the association between another, conditioned stimulus (CS) and an unconditioned stimulus (US) or reinforcer. Occasion setters and simple CSs are readily distinguished. For example, occasion setters are relatively immune to extinction and counterconditioning, and their combination and transfer functions differ substantially from those of simple CSs. Similarly, the acquisition of occasion setting is favored when stimuli are separated by longer intervals, by empty trace intervals, and are of different modalities, whereas the opposite conditions typically favor the acquisition of simple associations. Furthermore, the simple conditioning and occasion setting properties of a single stimulus can be independent, for example, that stimulus may simultaneously predict the occurrence of a reinforcer and indicate that another stimulus will not be reinforced. Many behavioral phenomena that are intractable to simple associative analysis are better understood within an occasion setting framework. Besides capturing the distinction between direct and modulatory control common to many arenas in neuroscience, occasion setting provides a model for the hierarchical organization of memory for events and event relations, and for contextual control more broadly. Although early lesion studies further differentiated between occasion setting and simple conditioning functions, little is known about the neurobiology of occasion setting. Modern techniques for precise manipulation and monitoring of neuronal activity in multiple brain regions are ideally suited for disentangling contributions of simple conditioning and occasion setting in associative learning. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Occasion setters attain incentive motivational value: implications for contextual influences on reward-seeking

The context in which reward-paired cues are encountered can resolve ambiguity and set the occasion for appropriate reward-seeking. The psychological processes by which contexts regulate reward-seeking remain unclear as contexts are diffuse and difficult to isolate from other stimuli. To overcome this, we modeled a context as a phasic and discrete event—an occasion setter (OS)—which allowed for control over its presentation and influence on cue-driven reward-seeking. This allowed us to directly assess how OSs regulate the predictive and motivational significance of Pavlovian cues. Male rats (n = 50) were trained in a Pavlovian procedure where the presentation of an ambiguous conditioned stimulus (CS) was reinforced only if preceded by an occasion setting cue. We assessed the motivational value of the OS and CS alone or in combination using tests of conditioned reinforcement. Rats enhanced conditioned approach to the reward port during the CS when it was preceded by the OS. When allowed the opportunity, rats responded more to obtain presentations of the CS in combination with the OS than the CS alone. Critically, rats also worked to obtain presentations of the OS alone more than the CS alone, and this was resistant to manipulations of the value of the OS. We conclude that occasion setting can act via incentive motivational mechanisms and that, apart from resolving predictive information about ambiguous reward-paired cues, OSs themselves generate states of appetitive motivation that can facilitate reward-seeking.

The medial prefrontal cortex is required for responding to alcohol-predictive cues but only in the absence of alcohol delivery

BACKGROUND

The prelimbic medial prefrontal cortex is implicated in promoting drug-seeking in relapse tests. However, drug-seeking behaviour is typically extinguished before a test and tests normally occur without drug delivery.

AIMS

We investigated the involvement of the prelimbic and the infralimbic cortex in responding elicited by a non-extinguished cue for alcohol that was presented without alcohol in an alcohol-associated context or a neutral context, and in responding to the same cue when it was paired with alcohol.

METHODS

Male, Long-Evans rats (220-240 g on arrival) were acclimated to 15% ethanol (v/v; 'alcohol') and then trained to associate a conditioned stimulus (10 s white noise; 15 trials/session) with alcohol delivery into a fluid port (0.2 mL/conditioned stimulus, 3 mL per session) for oral intake. Conditioning sessions occurred in a specific 'alcohol context' and were alternated daily with exposure to a second 'neutral' context that contained neither the conditioned stimulus nor alcohol.

RESULTS

At test, functional prelimbic cortex inactivation using baclofen/muscimol reduced fluid port entries elicited by a non-extinguished conditioned stimulus that was presented without alcohol, but had no subsequent impact on port entries when the conditioned stimulus was paired with alcohol. Similar results were obtained following infralimbic cortex inactivation; however, infralimbic cortex inactivation also non-specifically reduced port entries in the absence of alcohol.

CONCLUSIONS

These data indicate that the prelimbic and infralimbic cortex are involved in responding to cues for alcohol when alcohol delivery is omitted, but suggest that other brain regions are engaged in responding to such cues in the presence of alcohol.

Shared gray matter reductions across alcohol use disorder and posttraumatic stress disorder in the anterior cingulate cortex: A dual meta-analysis

The considerable comorbidity of posttraumatic stress disorder (PTSD) and alcohol use disorders (AUD) poses a greater public health burden than either condition alone. Although there is a substantial body of evidence linking the direct neurotoxic effect of heavy drinking to gray matter (GM) deficits, as well as a growing body of literature supporting a strong association between PTSD and GM alterations, there is scant research interrogating the direct interaction of the two disorders. In order to generate data-driven, specific hypotheses regarding the overlapping neural substrates of PTSD and AUD, we conducted a meta-analysis of GM volumes in each disorder relative to healthy control subjects. We found shared GM deficits in the anterior cingulate cortex (ACC) across both disorders relative to healthy control participants. These findings suggest that reduced volumes of the ACC across PTSD and AUD may have implications for the development, expression, or treatment of symptoms linked to these frequently co-existing disorders. Recommendations are made for future work aimed at delineating the specific and shared effects of traumatic stress and alcoholism on neural integrity.

Modeling Relapse to Pavlovian Alcohol-Seeking in Rats Using Reinstatement and Spontaneous Recovery Paradigms

BACKGROUND

Animal models are critical for studying causal explanations of relapse. Using a Pavlovian conditioning procedure with alcohol, we examined relapse after extinction triggered by either re-exposure to alcohol (reinstatement) or a delay between extinction and test (spontaneous recovery).

METHODS

Male, Long-Evans rats were acclimated to 15% alcohol in the home-cage using an intermittent-access 2-bottle choice procedure. Next, they received Pavlovian conditioning sessions in which an auditory-conditioned stimulus (CS; 20 second white noise; 8 trials/session; variable time 240 seconds) was paired with 15% alcohol (0.3 ml/CS; 2.4 ml/session) that was delivered into a fluid port for oral ingestion. In subsequent extinction and test sessions, CS presentations occurred as before, but without alcohol.

RESULTS

In experiment 1, exposure to either alcohol or water in the fluid port following extinction reinstated CS-elicited port entries at test 24 hours later. In a follow-up study using the same procedure (experiment 2), reinstatement was more robustly stimulated by alcohol, compared to a familiar lemon-flavored liquid. In experiment 3, systemic alcohol injections (0, 0.5, or 1.0 g/kg, intraperitoneal) administered either 24 hours or 15 minutes before test did not reinstate CS-elicited alcohol-seeking. Importantly, enzymatic assays in experiment 4 revealed detectable levels of alcohol in the blood following oral alcohol intake or intraperitoneal injection, suggesting that a pharmacological effect was likely with either route of administration. Last, in experiment 5, a 23-day delay between extinction and test resulted in a robust spontaneous recovery of CS-elicited alcohol-seeking.

CONCLUSIONS

The reinstatement and spontaneous recovery effects revealed herein provide evidence of viable new behavioral paradigms for testing interventions against relapse.

Ayahuasca and Its DMT- and β-carbolines - Containing Ingredients Block the Expression of Ethanol-Induced Conditioned Place Preference in Mice: Role of the Treatment Environment

Ayahuasca is a hallucinogenic beverage produced from the decoction of Banisteriopsis caapi (Bc) and Psychotria viridis (Pv), β-carboline- and N,N-dimethyltryptamine(DMT)-containing plants, respectively. Accumulating evidence suggests that ayahuasca may have therapeutic effects on ethanol abuse. It is not known, however, whether its effects are dependent on the presence of DMT or if non-DMT-containing components would have therapeutic effects. The aim of the present study was to investigate the rewarding properties of ayahuasca (30, 100, and 300 mg/kg, orally), Bc (132, 440, and 1320 mg/kg, orally) and Pv (3.75, 12.5 and 37.5 mg/kg, i.p.) extracts and their effects on ethanol (1.8 g/kg, i.p.) reward using the conditioned place preference (CPP) paradigm in male mice. Animals were conditioned with ayahuasca, Bc or Pv extracts during 8 sessions. An intermediate, but not a high, dose of ayahuasca induced CPP in mice. Bc and Pv did not induce CPP. Subsequently, the effects of those extracts were tested on the development of ethanol-induced CPP. Ayahuasca, Bc or Pv were administered before ethanol injections during conditioning sessions. While Bc and Pv exerted no effects on ethanol-induced CPP, pretreatment with ayahuasca blocked the development of CPP to ethanol. Finally, the effects of a post-ethanol-conditioning treatment with ayahuasca, Bc or Pv on the expression of ethanol-induced CPP were tested. Animals were conditioned with ethanol, and subsequently treated with either ayahuasca, Bc or Pv in the CPP environment previously associated with saline or ethanol for 6 days. Animals were then reexposed to ethanol and ethanol-induced CPP was quantified on the following day. Treatment with all compounds in the ethanol-paired environment blocked the expression of ethanol-induced CPP. Administration of an intermediate, but not a high, dose of ayahuasca and Bc, as well as Pv administration, in the saline-paired compartment blocked the expression of ethanol-induced CPP. The present study sheds light into the components underlying the therapeutic effects of ayahuasca on ethanol abuse, indicating that ayahuasca and its plant components can decrease ethanol reward at doses that do not exert abuse liability. Importantly, the treatment environment seems to influence the therapeutic effects of ayahuasca and Bc, providing important insights into clinical practice.