The psychological and neurochemical mechanisms of drug memory reconsolidation: implications for the treatment of addiction

Behaviorally conditioned effects of psychoactive drugs in experimental animals: What we have learned from nearly a century of research and what remains to be learned

Continuous treatment with drugs is a crucial requirement for managing various clinical conditions, including chronic pain and neuropsychiatric disorders such as depression or schizophrenia. Associative learning processes, i.e. Pavlovian conditioning, can play an important role for the effects of drugs and could open new avenues for optimizing patient treatment. In this narrative literature review, we summarize available data in experimental animals regarding the behaviorally conditioned effects of psychostimulants such as d-amphetamine and cocaine, the dopamine receptor agonist apomorphine, the dopamine receptor antagonist haloperidol, morphine and antidepressant drugs. In each section, the drug under discussion is briefly introduced, followed by a detailed examination of conditioning features, including doses and dosing regimens, characteristics of the conditioning process such as test environments or specific conditioned stimuli, testing and conditioned response characteristics, possible extinction or reconditioning or reversal training, neural mechanisms, and finally, the potential clinical relevance of the research area related to the drug. We focus on key outcomes, delve into methodical issues, identify gaps in current knowledge, and suggest future research directions.

Involvement of Pre-limbic Cortex-Nucleus accumbens projections in Context-Induced alcohol seeking

Alcohol use disorder (AUD) remains a critical public health issue worldwide, characterized by high relapse rates often triggered by contextual cues. This research investigates the neural mechanisms behind context-induced reinstatement of alcohol-seeking behavior, focusing on the nucleus accumbens and its interactions with the prelimbic cortex, employing Male Long-Evans rats in an ABA renewal model. In our experimental setup, rats were trained to self-administer 10 % ethanol in Context A, followed by extinction of lever pressing in the presence of discrete cues in Context B. The context-induced reinstatement of ethanol-seeking was then assessed by re-exposing rats to Context A or B under extinction conditions, aiming to simulate the environmental cues' influence on relapse behaviors. Three experiments were conducted: Experiment 1 utilized Fos-immunohistochemistry to examine neuronal activation in the nucleus accumbens; Experiment 2 applied the baclofen + muscimol inactivation technique to probe the functional importance of the nucleus accumbens core; Experiment 3 used Fos-immunofluorescence along with Retrobeads injection to investigate activation of neurons projecting from the prelimbic cortex to the nucleus accumbens core. Our findings revealed significant increases in Fos-immunoreactive nuclei within the nucleus accumbens core and shell during the reinstatement phase in Context A, underscoring the environment's potent effect on ethanol-seeking behavior. Additionally, inactivation of the nucleus accumbens core markedly reduced reinstatement, and there was a notable activation of neurons from the prelimbic cortex to the nucleus accumbens core in the ethanol-associated context. These results highlight the critical role of the nucleus accumbens core and its corticostriatal projections in the neural circuitry underlying context-driven ethanol seeking.

Inhibition of ERK1/2 or CRMP2 Disrupts Alcohol Memory Reconsolidation and Prevents Relapse in Rats

Relapse to alcohol abuse, often caused by cue-induced alcohol craving, is a major challenge in alcohol addiction treatment. Therefore, disrupting the cue-alcohol memories can suppress relapse. Upon retrieval, memories transiently destabilize before they reconsolidate in a process that requires protein synthesis. Evidence suggests that the mammalian target of rapamycin complex 1 (mTORC1), governing the translation of a subset of dendritic proteins, is crucial for memory reconsolidation. Here, we explored the involvement of two regulatory pathways of mTORC1, phosphoinositide 3-kinase (PI3K)-AKT and extracellular regulated kinase 1/2 (ERK1/2), in the reconsolidation process in a rat (Wistar) model of alcohol self-administration. We found that retrieval of alcohol memories using an odor-taste cue increased ERK1/2 activation in the amygdala, while the PI3K-AKT pathway remained unaffected. Importantly, ERK1/2 inhibition after alcohol memory retrieval impaired alcohol-memory reconsolidation and led to long-lasting relapse suppression. Attenuation of relapse was also induced by post-retrieval administration of lacosamide, an inhibitor of collapsin response mediator protein-2 (CRMP2)-a translational product of mTORC1. Together, our findings indicate the crucial role of ERK1/2 and CRMP2 in the reconsolidation of alcohol memories, with their inhibition as potential treatment targets for relapse prevention.

Craving modulates attentional bias towards alcohol in severe alcohol use disorder: An eye-tracking study

BACKGROUND AND AIMS

Competing models disagree on three theoretical questions regarding alcohol-related attentional bias (AB), a key process in severe alcohol use disorder (SAUD): (1) is AB more of a trait (fixed, associated with alcohol use severity) or state (fluid, associated with momentary craving states) characteristic of SAUD; (2) does AB purely reflect the over-activation of the reflexive/reward system or is it also influenced by the activity of the reflective/control system and (3) does AB rely upon early or later processing stages? We addressed these issues by investigating the time-course of AB and its modulation by subjective craving and cognitive load in SAUD.

DESIGN

A free-viewing eye-tracking task, presenting pictures of alcoholic and non-alcoholic beverages, combined with a concurrent cognitive task with three difficulty levels.

SETTING

A laboratory setting in the detoxification units of three Belgian hospitals.

PARTICIPANTS

We included 30 patients with SAUD self-reporting craving at testing time, 30 patients with SAUD reporting a total absence of craving and 30 controls matched on sex and age. All participants from SAUD groups met the DSM-5 criteria for SAUD.

MEASUREMENTS

We assessed AB through early and late eye-tracking indices. We evaluated the modulation of AB by craving (comparison between patients with/without craving) and cognitive load (variation of AB with the difficulty level of the concurrent task).

FINDINGS

Dwell time measure indicated that SAUD patients with craving allocated more attention towards alcohol-related stimuli than patients without craving (P < 0.001, d = 1.093), resulting in opposite approach/avoidance AB according to craving presence/absence. SAUD patients without craving showed a stronger avoidance AB than controls (P = 0.003, d = 0.806). AB did not vary according to cognitive load (P = 0.962, η2 p  = 0.004).

CONCLUSIONS

The direction of alcohol-related attentional bias (approach/avoidance) appears to be determined by patients' subjective craving at testing time and does not function as a stable trait of severe alcohol use disorder. Alcohol-related attentional bias appears to rely on later/controlled attentional stages but is not modulated by the saturation of the reflective/control system.

Drug memory reconsolidation: from molecular mechanisms to the clinical context

Since its rediscovery at the beginning of the 21st Century, memory reconsolidation has been proposed to be a therapeutic target for reducing the impact of emotional memories that can go awry in mental health disorders such as drug addiction (substance use disorder, SUD). Addiction can be conceptualised as a disorder of learning and memory, in which both pavlovian and instrumental learning systems become hijacked into supporting drug-seeking and drug-taking behaviours. The past two decades of research have characterised the details of the molecular pathways supporting the reconsolidation of pavlovian cue-drug memories, with more recent work indicating that the reconsolidation of instrumental drug-seeking memories also relies upon similar mechanisms. This narrative review considers what is known about the mechanisms underlying the reconsolidation of pavlovian and instrumental memories associated with drug use, how these approaches have translated to experimental medicine studies, and the challenges and opportunities for the clinical use of reconsolidation-based therapies.

Twisted memories: Addiction-related engrams are strengthened by desire thinking

Associative learning plays a central role in addiction by reinforcing associations between environmental cues and addiction-related information. Unsupervised learning models posit that memories are adjusted based on how strongly these representations are coactivated during the retrieval process. From a different perspective, clinical models of addiction posit that the escalation and persistence of craving may depend on desire thinking, a thinking style orienting to prefigure information about positive addiction-related experiences. In the present work, we tested the main hypothesis that desire thinking is a key factor in the strengthening of addiction-related associations. A group of adult smoking volunteers (N = 26) engaged in a period of desire thinking before performing an associative learning task in which neutral words (cues) were shown along with images (smoking-related vs. neutral context) at different frequencies. Two retrieval tests were administered, one immediately after encoding and the other after 24 h, to test how the recall of associations changed as a function of retention interval. Two control groups, smokers (N = 21) and non-smokers (N = 22), performed a similar procedure, with a neutral imagination task replacing desire thinking. Participants who engaged in desire thinking increased their performance from the first to the second retrieval test only for the most frequent smoking-related associations. Crucially, this selective effect was not observed in the two control groups. These results provide behavioral evidence in support of the idea that desire thinking plays a role in strengthening addiction-related associations. Thus, this thinking process may be considered a target for reconsolidation-based conceptualizations of, and treatments for, addiction.

Future perspectives of emerging novel drug targets and immunotherapies to control drug addiction

Substance Use Disorder (SUD) is one of the major mental illnesses that is terrifically intensifying worldwide. It is becoming overwhelming due to limited options for treatment. The complexity of addiction disorders is the main impediment to understanding the pathophysiology of the illness. Hence, unveiling the complexity of the brain through basic research, identification of novel signaling pathways, the discovery of new drug targets, and advancement in cutting-edge technologies will help control this disorder. Additionally, there is a great hope of controlling the SUDs through immunotherapeutic measures like therapeutic antibodies and vaccines. Vaccines have played a cardinal role in eliminating many diseases like polio, measles, and smallpox. Further, vaccines have controlled many diseases like cholera, dengue, diphtheria, Haemophilus influenza type b (Hib), human papillomavirus, influenza, Japanese encephalitis, etc. Recently, COVID-19 was controlled in many countries by vaccination. Currently, continuous effort is done to develop vaccines against nicotine, cocaine, morphine, methamphetamine, and heroin. Antibody therapy against SUDs is another important area where serious attention is required. Antibodies have contributed substantially against many serious diseases like diphtheria, rabies, Crohn's disease, asthma, rheumatoid arthritis, and bladder cancer. Antibody therapy is gaining immense momentum due to its success rate in cancer treatment. Furthermore, enormous advancement has been made in antibody therapy due to the generation of high-efficiency humanized antibodies with a long half-life. The advantage of antibody therapy is its instant outcome. This article's main highlight is discussing the drug targets of SUDs and their associated mechanisms. Importantly, we have also discussed the scope of prophylactic measures to eliminate drug dependence.

Making Leaps and Hitting Boundaries in Reconsolidation: Overcoming Boundary Conditions to Increase Clinical Translatability of Reconsolidation-based Therapies

Reconsolidation results in the restabilisation, and thus persistence, of a memory made labile by retrieval, and interfering with this process is thought to enable modification or weakening of the original trace. As such, reconsolidation-blockade has been a focus of research aiming to target the maladaptive memories underlying mental health disorders, including post-traumatic stress disorder and drug addiction. Current first-line therapies are not effective for all patients, and a substantial proportion of those for whom therapies are effective later relapse. A reconsolidation-based intervention would be invaluable as an alternative treatment for these conditions. However, the translation of reconsolidation-based therapies to the clinic presents a number of challenges, with arguably the greatest being the overcoming of the boundary conditions governing the opening of the reconsolidation window. These include factors such as the age and strength of memory, and can broadly be divided into two categories: intrinsic features of the targeted memory itself, and parameters of the reactivation procedure used. With maladaptive memory characteristics inevitably varying amongst individuals, manipulation of the other limitations imposed by procedural variables have been explored to circumvent the boundary conditions on reconsolidation. Although several apparently discrepant results remain to be reconciled and these limitations yet to be truly defined, many studies have produced successful results which encouragingly demonstrate that boundary conditions may be overcome using various proposed strategies to enable translation of a reconsolidation-based intervention to clinical use.

The challenge of memory destabilisation: From prediction error to prior expectations and biomarkers

The re-ignition of memory reconsolidation research sparked by Karim Nader in the early 2000s led to great excitement that 'reconsolidation-based' interventions might be developed for mental health disorders such as post-traumatic stress disorder and substance use disorder. Two decades on, it is clear that reconsolidation-based interventions have been more challenging to translate to the clinic than initially thought. We argue that this challenge could be addressed with a better understanding of how prior expectations interact with information presented in a putative memory reactivation / cue reminder session, and through the identification of non-invasive biomarkers for memory destabilisation that would allow reminder sessions to be 'tuned' to enhance memory lability in an ad hoc manner.

Memory reactivation mediates emotional valence updating of contextual memory in mice with protracted morphine withdrawal

Mice subjected to morphine locomotor sensitization develop increased anxiety-behavior expression during protracted morphine withdrawal. This behavioral change is dependent on reexposure to the context of locomotor sensitization and reflects a state of conditioned anxiety. In this study, the effect of memory reconsolidation on the expression of conditioned anxiety in mice with protracted morphine withdrawal was examined. Five experimental protocols involving male C57BL/6 mice were used in which the animals were subjected to locomotor sensitization induced by morphine and reexposed to the context associated with the drug effect 28 days after locomotor sensitization and immediately after subjected to elevated plus maze. In experiment 1, mice were subjected or not to memory reactivation session and was observed that memory reactivation 27 days after sensitization reduced conditioned anxiety. In experiment 2, mice were subjected to memory reactivation, 24 h, 6 h or 1 h before contextual reexposure, and the effect of memory reactivation coincided with the temporal requirement for reconsolidation. In experiment 3, which involved exposure to a situation of acute stress immediately before memory reactivation, the mice demonstrated a return to increased conditioned anxiety. To confirm the influence of reconsolidation, in experiments 4 and 5, mice subjected to memory reactivation were treated with Nimodipine, diazepam or cyclohexamine, substances commonly used as pharmacological controls in reconsolidation experiments. Treatment with each substance separately inhibited the effect of reactivation in experiment 5 (presence of acute stressor) but not in experiment 4 (absence of acute stressor). These results suggest that, in our experimental model, reconsolidation is mediated through updating of the emotional valence of contextual memory associated with the administration of morphine.

Neuroplastic Changes in Addiction Memory-How Music Therapy and Music-Based Intervention May Reduce Craving: A Narrative Review

Recent findings indicate that Music Therapy (MT) and Music-Based Interventions (MBIs) may reduce craving symptoms in people with Substance Use Disorders (SUD). However, MT/MBIs can lead SUD clients to recall memories associated with their drug history and the corresponding strong emotions (addiction memories). Craving is a central component of SUD, possibly linked to relapse and triggered by several factors such as the recall of memories associated with the drug experience. Therefore, to address the topic of what elements can account for an improvement in craving symptoms after MT/MBIs, we conducted a narrative review that (1) describes the brain correlates of emotionally salient autobiographical memories evoked by music, (2) outlines neuroimaging and neurophysiological studies suggesting how the experience of craving may encompass the recall of emotionally filled moments, and (3) points out the role of perineuronal nets (PNNs) in addiction memory neuroplasticity. We highlight how autobiographical memory retrieval, music-evoked autobiographical memories, and craving share similar neural activations with PNNs which represent a causal element in the processing of addiction memory. We finally conclude by considering how the neuroplastic characteristics of addiction memory might represent the ground to update and/or recalibrate, within the therapy, the emotional content related to the recall.

Extracellular signal-regulated kinase in the basolateral amygdala is required for reconsolidation of heroin-associated memory

Reconsolidation of heroin-associated memory is an independent memory process that occurs following retrieval, which is essential for the sustained capacity of an associative drug stimulus to precipitate heroin-seeking. Extracellular signal-regulated kinase (ERK) in the basolateral amygdala (BLA) mediates the reconsolidation of drug memory. In the present study, we utilized a rat model of drug craving and relapse to verify the hypothesis that the reconsolidation of heroin-associated memory requires ERK in an instrumental heroin-seeking behavior, focusing on the BLA brain region, which is crucial for synaptic plasticity and memory processes. We found that bilateral intra-BLA infusions of U0126 (1 μg/0.5 μl), an ERK inhibitor, immediately after retrieving heroin-associated memory significantly reduced cue-induced and drug-induced reinstatement and spontaneous recovery of heroin-seeking compared to the vehicle. Furthermore, this inhibitory effect was related to the characteristic of reconsolidation. Conversely, no effect was observed on the heroin-seeking behavior when the intra-BLA infusion of U0126 was administered 6 h after the heroin-associated memory retrieval or without memory retrieval. Together, these data suggest that disrupting the reconsolidation of heroin-associated memory via an ERK inhibitor may serve as a promising option for treating relapse in opiate addicts.

The effect of a methadone-initiated memory reconsolidation updating procedure in opioid use disorder: A translational study

BACKGROUND

Opioid use disorder (OUD) is a chronic relapsing psychiatric disorder. An unconditioned stimulus (US)-triggers a memory reconsolidation updating procedure (MRUP) that has been developed and demonstrated its effectiveness in decreasing relapse to cocaine and heroin in preclinical models. However, utilizations of abused drugs as the US to initiate MRUP can be problematic. We therefore designed a translational rat study and human study to evaluate the efficacy of a novel methadone-initiated MRUP.

METHODS

In the rodent study, male rats underwent heroin self-administration training for 10 consecutive days, and were randomly assigned to receive saline or methadone at 10 min, 1 h or 6 h before extinction training after 28-day withdrawal. The primary outcome was operant heroin seeking after reinstatement. In the human experimental study, male OUD patients were randomly assigned to get MRUP at 10 min or 6 h after methadone or methadone alone. The primary outcomes included experimental cue-induced heroin craving change, sustained abstinence and retention in the study at post intervention and the 5 monthly follow-up assessments. The secondary outcomes were changes in physiological responses including experimental cue-induced blood pressure and heart rate.

FINDINGS

Methadone exposure but not saline exposure at 10 min or 1 h before extinction decreased heroin-induced reinstatement of heroin seeking after 28-day of withdrawal in rats (F (8,80) = 8.26, p < 0.001). In the human study, when the MRUP was performed 10 min, but not 6 h after methadone dosing, the MRUP promoted sustained abstinence from heroin throughout 5 monthly follow-up assessments compared to giving methadone alone without MRUP (Hazard Ratio [95%CI] of 0.43 [0.22, 0.83], p = 0.01). The MRUP at 10 min, but not at 6 h after dosing also decreased experimental cue-induced heroin craving and blood pressure increases during the 6-month study duration (group × months × cue types, F (12, 63·3) = 2.41, p = 0.01).

INTERPRETATION

The approach of MRUP within about 1 to 6 h after a methadone dose potently improved several key outcomes of OUD patients during methadone maintenance treatment, and could be a potentially novel treatment to prevent opioid relapse.

FUNDING

National Natural Science Foundation of China (NO. U1802283, 81761128036, 82001400, 82001404 and 31671143) and Chinese National Programs for Brain Science and Brain-like Intelligence Technology (NO. 2021ZD0200800).

Procedures between training and reactivation influence the destabilization of instrumental sucrose memory

Memory destabilization and reconsolidation is hypothesized to be a fundamental mnemonic process that can underpin memory updating. Instrumental memories have been shown recently to be destabilized following a reactivation session that involves a change in instrumental reward contingency. However, the acquisition and performance of an instrumental response occurs in the presence of the learning of other reward-related memories. This may influence the ability of a given reactivation session to destabilize the previously learned instrumental memory. Here we present a series of experiments in male rats involving an instrumental memory trained on an FR1 schedule over 10 days, and then reactivated in a session that imposed a VR5 schedule of reinforcement. When MK-801 was injected prior to the VR5 reactivation session, it reliably impaired subsequent instrumental performance at test only when the reactivation session occurred 48 h, and not 24 h, after the end of training. The interposition between the end of training and the reactivation session of a context extinction session, an additional VR5 reactivation session, or indeed the simple experience of being handled and injected with vehicle, resulted in MK-801 no longer having an amnestic effect on test performance. While we do not have a clear account for the process and mechanism underpinning this apparent selectivity of the effect of the VR5 session to destabilize the instrumental memory, it does additionally highlight the need for greater understanding of the conditions that facilitate reactivation-induced memory destabilization.

A mechanistic overview of approaches for the treatment of psychostimulant dependence

Psychostimulant use disorder is a major health issue around the world with enormous individual, family-related and societal consequences, yet there are no effective pharmacological treatments available. In this review, a target-based overview of pharmacological treatments toward psychostimulant addiction will be presented. We will go through therapeutic approaches targeting different aspects of psychostimulant addiction with focus on three major areas; 1) drugs targeting signalling, and metabolism of the dopamine system, 2) drugs targeting either AMPA receptors or metabotropic glutamate receptors of the glutamate system and 3) drugs targeting the severe side-effects of quitting long-term psychostimulant use. For each of these major modes of intervention, findings from pre-clinical studies in rodents to clinical trials in humans will be listed, and future perspectives of the different treatment strategies as well as their potential side-effects will be discussed. Pharmaceuticals modulating the dopamine system, such as antipsychotics, DAT-inhibitors, and disulfiram, have shown some promising results. Cognitive enhancers have been found to increase aspects of behavioural control, and drugs targeting the glutamate system such as modulators of metabotropic glutamate receptors and AMPA receptors have provided interesting changes in relapse behaviour. Furthermore, CRF-antagonists directed toward alleviating the symptoms of the withdrawal stage have been examined with interesting resulting changes in behaviour. There are promising results investigating therapeutics for psychostimulant addiction, but further preclinical work and additional human studies with a more stratified patient selection are needed to prove sufficient evidence of efficacy and tolerability.

Disrupting reconsolidation by PKA inhibitor in BLA reduces heroin-seeking behavior

Drug abuse is considered a maladaptive pathology of emotional memory and is associated with craving and relapse induced by drug-associated stimuli or drugs. Reconsolidation is an independent memory process with a strict time window followed by the reactivation of drug-associated stimulus depending on the basolateral amygdala (BLA). Pharmacology or behavior treatment that disrupts the reconsolidation can effectively attenuate drug-seeking in addicts. Here, we hypothesized that heroin-memory reconsolidation requires cAMP-dependent protein kinase A (PKA) of BLA based on the fundamental effect of PKA in synaptic plasticity and memory process. After 10 days of acquisition, the rats underwent 11 days of extinction training and then received the intra-BLA infusions of the PKA inhibitor Rp-cAMPS at different time windows with/without a reactivation session. The results show that PKA inhibitor treatment in the reconsolidation time window disrupts the reconsolidation and consequently reduces cue-induced reinstatement, heroin-induced reinstatement, and spontaneous recovery of heroin-seeking behavior in the rats. In contrast, there was no effect on cue-induced reinstatement in the intra-BLA infusion of PKA inhibitor 6 h after reactivation or without reactivation. These data suggest that PKA inhibition disrupts the reconsolidation of heroin-associated memory, reduces subsequent drug seeking, and prevents relapse, which is retrieval-dependent, time-limited, and BLA-dependent.

Theta-Burst Stimulation Combined With Virtual-Reality Reconsolidation Intervention for Methamphetamine Use Disorder: Study Protocol for a Randomized-Controlled Trial

Background

Craving associated with drug-related memory is one of the key factors that induce the relapse of methamphetamine (MA). Disruption or modulation of the reconsolidation of drug-related memory may serve as an option for clinical treatment of MA addiction. This protocol proposes to use virtual reality (VR) to retrieve drug-associated memory and then use transcranial magnetic stimulation (TMS) at the neural circuit that encodes the reward value of drug cues to provide a non-invasive intervention during reconsolidation. We aim to evaluate the effectiveness of TMS treatment after VR retrieval on the reduction of cue reactivity and craving of MA.

Methods

This is a randomized, double-blind, sham-controlled, parallel group trial, targeting participants with MA use disorder aged from 18 to 45 years old. Forty-five eligible volunteers in Shanxi Drug Rehabilitation Center will be recruited and be randomly allocated into three parallel groups, receiving either 1) MA-related cues retrieval in VR combined with active TMS (MA VR scene + TBS) or 2) sham TMS (MA VR scene + sham TBS), or 3) neutral cues retrieval in VR combined with active TMS (neutral VR scene + TBS). Two sessions of post-VR-retrieval TBS will be scheduled on two separate days within 1 week. The primary outcome will detect the memory-related activity by the electroencephalography (EEG) reactivity to drug cues in VR scenes. Secondary outcomes are the self-reported MA craving in VR scene, the physiological parameter (cue-induced heart rate) and the scores of psychological questionnaires including anxiety, depression, and mood. All primary and secondary outcomes will be assessed at baseline, 1-week, and 1-month post-intervention. Assessments will be compared between the groups of 1) MA VR scene + TBS, 2) MA VR scene + sham TBS and 3) neutral VR scene + TBS.

Discussion

This will be the first study to examine whether the TMS modulation after VR retrieval can reduce self-reported craving and drug-related cue reactivity. It will promote the understanding of the neural circuit mechanism of the reconsolidation-based intervention and provide an effective treatment for MA use disorder patients.

Clinical Trial Registration

[Chinese Clinical Trial Registry], identifier [ChiCTR1900026902]. Registered on 26 October 2019.

Attentional bias in alcohol drinkers: A systematic review of its link with consumption variables

In severe alcohol use disorder (SAUD), attentional bias refers to the preferential allocation of attentional resources toward alcohol-related cues. Dominant models consider that this bias plays a key role in the emergence and maintenance of SAUD. We evaluate the available experimental support for this assumption through a systematic literature review, providing a critical synthesis of studies exploring the links between alcohol consumption and attentional bias. Using PRISMA guidelines, we explored three databases (PsycINFO, PubMed, Scopus) and extracted 95 papers. We assessed their methodological quality and categorized them based on the population targeted, namely patients with SAUD or subclinical populations with various drinking patterns. We also classified papers according to the measures used (i.e., behavioral or eye-tracking measures). Overall, subclinical populations present an alcohol-related bias, but many studies in SAUD did not find such bias, nor approach/avoidance patterns. Moreover, attentional bias fluctuates alongside motivational states rather than according to alcohol use severity, which questions its stability. We provide recommendations to develop further theoretical knowledge and overcome methodological shortcomings.

The incentive amplifying effects of nicotine: Roles in alcohol seeking and consumption

Nicotine has a unique profile among drugs of abuse. To the noninitiated user, nicotine has powerful aversive effects and its relatively weak euphorigenic effects undergo rapid tolerance. Despite this, nicotine is commonly abused despite negative heath consequences, and nicotine users have enormous difficulty quitting. Further, nicotine is one of the most commonly co-abused substances, in that it is often taken in combination with other drugs. One explanation of this polydrug use is that nicotine has multiple appetitive and consummatory conditioning effects. For example, nicotine is a reinforcement enhancer in that it can potently increase the incentive value of other stimuli, including those surrounding drugs of abuse such as alcohol. In addition, nicotine also has a unique profile of neurobiological effects that alter regulation of alcohol intake and interoception. This review discusses the psychological and biological mechanisms surrounding nicotine's appetitive conditioning and consummatory effects, particularly its interactions with alcohol.

Deconstructing and reconstructing behaviour relevant to mental health disorders: The benefits of a psychological approach, with a focus on addiction

RUTHERFORD, L.G. and Milton, A.L. Deconstructing and reconstructing behaviour relevant to mental health disorders: what can psychology offer? NEUROSCI BIOBEHAV REV XX(X)XXX-XXX, 2021. - Current treatments for mental health disorders are successful only for some patients, and there is an unmet clinical need for new treatment development. One challenge for treatment development has been how best to model complex human conditions in animals, where mechanism can be more readily studied with a range of neuroscientific techniques. We suggest that an approach to modelling based on associative animal learning theory provides a good framework for deconstructing complex mental health disorders such that they can be studied in animals. These individual simple models can subsequently be used in combination to 'reconstruct' a more complex model of the mental health disorder of interest. Using examples primarily from the field of drug addiction, we explore the 'psychological approach' and suggest that in addition to facilitating translation and backtranslation of tasks between animal models and patients, it is also highly concordant with the concept of triangulation.

Sign- and goal-tracking score does not correlate with addiction-like behavior following prolonged cocaine self-administration

RATIONALE

In classical conditioning, sign-tracking reflects behavior directed toward a conditioned stimulus (CS) in expectation of a reward (unconditioned stimulus, US); in contrast, goal-tracking describes behavior directed toward the location of delivery of a US. As cues previously paired with drugs of abuse promote drug-seeking and drug-taking behavior in both animals and humans and thus contribute to the severity of substance abuse, sign-tracking may represent a maladaptive cue-focused behavior that may increase addiction vulnerability as compared to goal-tracking. Recent studies do, in fact, support this possibility. Previous work in this area has focused primarily on paradigms using relatively limited exposure to drug rather than extended drug intake.

OBJECTIVES

Here, we used the DSM-IV-based 3-criteria (3-CRIT) model and examined whether a relationship exists between sign- or goal-tracking phenotypes and the prevalence of criteria associated with addiction-like behavior following extended cocaine self-administration as measured in this model.

METHODS

Forty-six male Sprague Dawley rats underwent a Pavlovian conditioned approach (PCA) procedure and were characterized along a continuum as goal-trackers (GTs), intermediates (INTs), or sign-trackers (STs). The animals were subsequently trained to intravenous self-administer cocaine during 45 self-administration (SA) sessions and characterized for the 3 criteria outlined in the model: persistence of drug-seeking, motivation for cocaine-taking, and resistance to punishment.

RESULTS

We performed correlational analyses on the traits measured, finding no relationships between PCA score and addiction-like characteristics measured using the 3-CRIT model of addiction. However, STs showed significantly greater resistance to punishment than GTs.

CONCLUSIONS

Phenotyping along a continuum of PCA scores may not be a valid predictor for identifying vulnerability to the addiction-like behaviors examined using the 3-CRIT model. However, PCA phenotype may predict a single feature of the 3-CRIT model, resistance to punishment, among those rats classified as either STs or GTs.

Cocaine memory reactivation induces functional adaptations within parvalbumin interneurons in the rat medial prefrontal cortex

Substance use disorder is a complex disease created in part by maladaptive learning and memory mechanisms following repeated drug use. Exposure to drug-associated stimuli engages prefrontal cortex circuits, and dysfunction of the medial prefrontal cortex (mPFC) is thought to underlie drug-seeking behaviors. Growing evidence supports a role for parvalbumin containing fast-spiking interneurons (FSI) in modulating prefrontal cortical microcircuit activity by influencing the balance of excitation and inhibition, which can influence learning and memory processes. Most parvalbumin FSIs within layer V of the prelimbic mPFC are surrounded by specialized extracellular matrix structures called perineuronal nets (PNN). Previous work by our group found that cocaine exposure altered PNN-surrounded FSI function, and pharmacological removal of PNNs reduced cocaine-seeking behavior. However, the role of FSIs and associated constituents (parvalbumin and PNNs) in cocaine-related memories was not previously explored and is still unknown. Here, we found that reactivation of a cocaine conditioned place preference memory produced changes in cortical PNN-surrounded parvalbumin FSIs, including decreased parvalbumin intensity, increased parvalbumin cell axis diameter, decreased intrinsic excitability, and increased excitatory synaptic input. Further investigation of intrinsic properties revealed changes in the interspike interval, membrane capacitance, and afterhyperpolarization recovery time. Changes in these specific properties suggest an increase in potassium-mediated currents, which was validated with additional electrophysiological analysis. Collectively, our results indicate that cocaine memory reactivation induces functional adaptations in PNN-surrounded parvalbumin neurons, which likely alters cortical output to promote cocaine-seeking behavior.

Disrupting Reconsolidation by Systemic Inhibition of mTOR Kinase via Rapamycin Reduces Cocaine-Seeking Behavior

Drug addiction is considered maladaptive learning, and drug-related memories aroused by the presence of drug related stimuli (drug context or drug-associated cues) promote recurring craving and reinstatement of drug seeking. The mammalian target of rapamycin signaling pathway is involved in reconsolidation of drug memories in conditioned place preference and alcohol self-administration (SA) paradigms. Here, we explored the effect of mTOR inhibition on reconsolidation of addiction memory using cocaine self-administration paradigm. Rats received intravenous cocaine self-administration training for 10 consecutive days, during which a light/tone conditioned stimulus was paired with each cocaine infusion. After acquisition of the stable cocaine self-administration behaviors, rats were subjected to nosepoke extinction (11 days) to extinguish their behaviors, and then received a 15 min retrieval trial with or without the cocaine-paired tone/light cue delivery or without. Immediately or 6 h after the retrieval trial, rapamycin (10 mg/kg) was administered intraperitoneally. Finally, cue-induced reinstatement, cocaine-priming-induced reinstatement and spontaneous recovery of cocaine-seeking behaviors were assessed in rapamycin previously treated animals, respectively. We found that rapamycin treatment immediately after a retrieval trial decreased subsequent reinstatement of cocaine seeking induced by cues or cocaine itself, and these effects lasted at least for 28 days. In contrast, delayed intraperitoneal injection of rapamycin 6 h after retrieval or rapamycin injection without retrieval had no effects on cocaine-seeking behaviors. These findings indicated that mTOR inhibition within the reconsolidation time-window impairs the reconsolidation of cocaine associated memory, reduces cocaine-seeking behavior and prevents relapse, and these effects are retrieval-dependent and temporal-specific.

Epigenetic Mechanisms in Drug Relapse

A growing body of evidence from the past 15 years implicates epigenetic mechanisms in the behavioral effects of addictive drugs. The main focus of these studies has been epigenetic mechanisms of psychomotor sensitization and drug reinforcement, as assessed by the conditioned place preference and drug self-administration procedures. Some of these studies have documented long-lasting changes in the expression of epigenetic enzymes and molecules that persist for weeks after the last drug exposure. These observations have inspired more recent investigations on the epigenetic mechanisms of relapse to drug seeking after prolonged abstinence. Here, we review studies that have examined epigenetic mechanisms (e.g., histone modifications, chromatin remodeler-associated modifications, and DNA methylation) that contribute to relapse to cocaine, amphetamine, methamphetamine, morphine, heroin, nicotine, or alcohol seeking, as assessed in rodent models. We first provide a brief overview of studies that have examined persistent epigenetic changes in the brain after prolonged abstinence from noncontingent drug exposure or drug self-administration. Next, we review studies on the effect of either systemic or brain site-specific epigenetic manipulations on the reinstatement of drug-conditioned place preference after extinction of the learned preference, the reinstatement of drug seeking after operant drug self-administration and extinction of the drug-reinforced responding, and the incubation of drug craving (the time-dependent increase in drug seeking after cessation of drug self-administration). We conclude by discussing the implications of these studies for understanding mechanisms contributing to persistent relapse vulnerability after prolonged abstinence. We also discuss the implications of these results for translational research on the potential use of systemically administered epigenetic enzyme inhibitors for relapse prevention in human drug users.

Drug overdose deaths, addiction neuroscience and the challenges of translation

In this article, we argue that the rapid rise in drug overdose deaths in America is a tragedy that draws attention to fundamental conceptual and experimental problems in addiction science that have significant human consequences. Despite enormous economic investment, political support and claims to have revolutionised addiction medicine, neurobiological models are yet to produce a treatment for substance addiction. This is partly, we claim, because neurobiology is unable to explain essential features of addiction and relapse that neurobehavioral models of addiction are better placed to investigate. We show how addiction neuroscience turned to long-term memory to explain the chronicity of addiction and persistent relapses long after neurochemical traces have left the body. The turn to memory may in time help to close the translational gap facing addiction medicine, but it is our view in this article that the primary value of memory theory lays in its potential to create new critical friendships between biological and social sciences that are attuned to the lived experience and suffering of stigmatised people. The value of the memory turn may rest upon the capacity of these critical friendships to wean addiction science off its long-term dependence on disease concepts of human distress.

Working memory training improves emotion regulation in drug abstainers: Evidence from frontal alpha asymmetry

Drug addiction has been associated with unsuccessful emotion regulation, which can be improved by working memory training (WMT) in healthy populations. This study aimed to assess the effect of WMT on emotion regulation in drug abstainers. We divided 40 male drug abstainers into two groups: (i) the training group (n=20) participated in a running memory task for 20 days, and (ii) the control group (n=20) did not participate in any training task. We assessed the emotion regulation questionnaire (ERQ) and frontal electroencephalographic (EEG) activity while viewing pictures (including neutral, positive, negative and drug-related contents) for all participants before and after the training. After WMT for 20 days, the training group adopted more spontaneous emotion regulation strategies compared with control group. The asymmetry scores of training group improved while viewing negative and drug-related pictures compared to pretest, which suggests that they converted from right-brain asymmetry to left-brain asymmetry. However, the control group declined both in the ERQ scores and the asymmetry scores. These results suggest that WMT improves the emotion regulation of drug abstainers.

Investigating the efficacy of the reminder-extinction procedure to disrupt contextual threat memories in humans using immersive Virtual Reality

Upon reactivation, consolidated memories can enter a temporary labile state and require restabilisation, known as reconsolidation. Interventions during this reconsolidation period can disrupt the reactivated memory. However, it is unclear whether different kinds of memory that depend on distinct brain regions all undergo reconsolidation. Evidence for reconsolidation originates from studies assessing amygdala-dependent memories using cue-conditioning paradigms in rodents, which were subsequently replicated in humans. Whilst studies providing evidence for reconsolidation of hippocampus-dependent memories in rodents have predominantly used context conditioning paradigms, studies in humans have used completely different paradigms such as tests for wordlists or stories. Here our objective was to bridge this paradigm gap between rodent and human studies probing reconsolidation of hippocampus-dependent memories. We modified a recently developed immersive Virtual Reality paradigm to test in humans whether contextual threat-conditioned memories can be disrupted by a reminder-extinction procedure that putatively targets reconsolidation. In contrast to our hypothesis, we found comparable recovery of contextual conditioned threat responses, and comparable retention of subjective measures of threat memory, episodic memory and exploration behaviour between the reminder-extinction and standard extinction groups. Our result provide no evidence that a reminder before extinction can prevent the return of context conditioned threat memories in humans.

Drug-Induced Conditioned Place Preference and Its Practical Use in Substance Use Disorder Research

The conditioned place preference (CPP) paradigm is a well-established model utilized to study the role of context associations in reward-related behaviors, including both natural rewards and drugs of abuse. In this review article, we discuss the basic history, various uses, and considerations that are tied to this technique. There are many potential takeaway implications of this model, including negative affective states, conditioned drug effects, memory, and motivation, which are all considered here. We also discuss the neurobiology of CPP including relevant brain regions, molecular signaling cascades, and neuromodulatory systems. We further examine some of our prior findings and how they integrate CPP with self-administration paradigms. Overall, by describing the fundamentals of CPP, findings from the past few decades, and implications of using CPP as a research paradigm, we have endeavored to support the case that the CPP method is specifically advantageous for studying the role of a form of Pavlovian learning that associates drug use with the surrounding environment.

Retrieval-Dependent Mechanisms Affecting Emotional Memory Persistence: Reconsolidation, Extinction, and the Space in Between

Maladaptive emotional memories contribute to the persistence of many mental health disorders, and therefore the prospect of disrupting these memories to produce long-term reductions in relapse is of great clinical appeal. Reducing the impact of maladaptive emotional memories on behaviour could be achieved by two retrieval-dependent manipulations that engage separate mnemonic processes: "reconsolidation disruption" and "extinction enhancement." Extinction occurs during a prolonged re-exposure session in the absence of the expected emotional outcome and is widely accepted as reflecting the formation of a new, inhibitory memory that prevents behavioural expression of the original trace. Reconsolidation, by contrast, involves the destabilisation of the original memory, allowing for subsequent updating and restabilisation in specific brain regions, unless the re-stabilization process is prevented through specific pharmacological or behavioural interventions. Both destabilisation of the original memory and memory extinction require that re-exposure induces prediction error-a mismatch between what is expected and what actually occurs-but the parameters that allow reconsolidation and extinction to occur, and control the transition between them, have not been well-characterised. Here, we review what is known about the induction of memory destabilisation and extinction, and the transition period that separates these mnemonic processes, drawing on preclinical and clinical examples. A deeper understanding of the processes that determine the alternative routes to memory persistence or inhibition is critical for designing new and more reliable clinical treatments targeting maladaptive emotional memories.

Electroconvulsive Shock Does Not Impair the Reconsolidation of Cued and Contextual Pavlovian Threat Memory

Existing memories, when retrieved under certain circumstances, can undergo modification through the protein synthesis-dependent process of reconsolidation. Disruption of this process can lead to the weakening of a memory trace, an approach which is being examined as a potential treatment for disorders characterized by pathological memories, such as Post-Traumatic Stress Disorder. The success of this approach relies upon the ability to robustly attenuate reconsolidation; however, the available literature brings into question the reliability of the various drugs used to achieve such a blockade. The identification of a drug or intervention that can reliably disrupt reconsolidation without requiring intracranial access for administration would be extremely useful. Electroconvulsive shock (ECS) delivered after memory retrieval has been demonstrated in some studies to disrupt memory reconsolidation; however, there exists a paucity of literature characterizing its effects on Pavlovian fear memory. Considering this, we chose to examine ECS as an inexpensive and facile means to impair reconsolidation in rats. Here we show that electroconvulsive seizure induction, when administered after memory retrieval, (immediately, after 30 min, or after 1 h), does not impair the reconsolidation of cued or contextual Pavlovian fear memories. On the contrary, ECS administration immediately after extinction training may modestly impair the consolidation of fear extinction memory.

Targeting drug memory reconsolidation: a neural analysis

Addiction can be conceptualised as a disorder of maladaptive learning and memory. Therefore, maladaptive drug memories supporting drug-seeking and relapse behaviours may present novel treatment targets for therapeutic approaches based upon reconsolidation-blockade. It is known that different structures within the limbic corticostriatal system contribute differentially to different types of maladaptive drug memories, including pavlovian associations between environmental cues and contexts with the drug high, and instrumental memories underlying drug-seeking. Here, we review the mechanisms underlying drug memory reconsolidation in the amygdala, striatum, and hippocampus, noting similarities and differences, and opportunities for future research.

Crisis, what crisis? Addiction neuroscience and the challenges of translation

In this article we interrogate the claim that there is an opioid crisis: a dramatic rise in drug overdose fatalities in the United States over the past two decades that is also spreading to other countries.  The usual argument is that this crisis is largely explained by errant prescription practices leading to an oversupply of opioids, leading to addiction, premature mortality and drug overdose deaths, both among those prescribed opioids for pain relief, and those obtaining them on the illegal market.  We argue, that this view is highly problematic and that it is likely to entrench deeper problems with how substance addiction has been perceived and known. In this article, we develop an alternative picture of the addiction crisis based on four years of research and collaboration with addiction neuroscientists. Drug overdose deaths, we claim, are symptoms of what we term the ‘structural distribution of social despair.’ We argue that this is compounded by a translation crisis at the heart of addiction neuroscience. For all its dominance, the ‘dopamine hypothesis’ of addiction that shaped understandings for some three decades, has still not produced a single effective treatment. However, this translation crisis also represents an opportunity for ‘the memory turn’ in addiction neuroscience as it seeks to translate its emerging conception of addiction as a problem of memory into effective forms of treatment. We conclude by arguing that, for the ‘memory turn’ to underpin effective interventions into ‘the opioid crisis’, a new relation between neuroscientists and social scientists of addiction is needed, one that proceeds from the lived experience of human beings.

Memory reconsolidation impairments in sign-tracking to an audiovisual compound stimulus

Studies of memory reconsolidation of pavlovian memories have typically employed unimodal conditioned stimuli, despite the use of multimodal compound stimuli in other settings. Here we studied sign-tracking behaviour to a compound audiovisual stimulus. First, we observed not unexpectedly that sign-tracking was poorer to the audiovisual compound than to unimodal visual stimuli. Then, we showed that, depending on the parameters of compound stimulus re-exposure at memory reactivation, systemic MK-801 treatment either impaired extinction to improve sign-tracking at test, or disrupted reconsolidation to impair test behaviour. When memory reactivation consisted of re-exposure to only the auditory component of the compound stimulus, we observed sign-tracking impairments following MK-801 treatment, but only under certain test conditions. This was in contrast to the consistent impairment following reactivation with the full audiovisual compound. Moreover, the parameters of auditory stimulus presentation to enable MK-801-induced impairment at test varied depending on whether the stimulus was presented within or outside the training context. These findings suggest that behaviour under the control of appetitive pavlovian compound stimuli can be modulated by targeting both extinction and reconsolidation, and that it is not necessary to re-expose to the full compound stimulus in order to achieve a degree of modulation of behaviour.

The Efficacy of Lidocaine in Disrupting Cocaine Cue-Induced Memory Reconsolidation

RATIONAL

Cue-induced craving memories, linked to drug-seeking behaviors, require key molecular processes for memory reconsolidation. Lidocaine, a sodium channel blocker, inhibits NMDA receptor activation and suppresses nitric oxide and ERK production. These processes are required for memory re-consolidation; inhibiting them may reduce cue-related craving memories in cocaine dependent subjects.

OBJECTIVES

To assess the efficacy of lidocaine in decreasing cue-induced cocaine craving and cocaine use.

METHODS

Treatment-seeking cocaine-dependent participants (n = 33, 25 men) were recruited. Personalized craving and relaxation scripts were developed. Participants were then randomly assigned in a double-blind design to either receive intravenous lidocaine immediately following a cocaine craving script (lidocaine/craving), saline following a craving script (saline/craving), or lidocaine following a relaxation script (lidocaine/relax). One week following the infusion, cue-induced craving was assessed in the same paradigm without an infusion. Cocaine use and craving were assessed for 4 weeks following infusion.

RESULTS

The administration of lidocaine during craving induction (lidocaine/craving) did not decrease cue-induced craving during craving reactivation one week later or craving and cocaine use over the 4-week follow-up period compared to the saline/craving group. There were no significant differences in craving and cocaine use between the lidocaine/relax and saline/craving groups.

CONCLUSION

Lidocaine administered following craving induction did not decrease subsequent cue-induced craving or cocaine use. Blocking the reconsolidation of craving-related memories with pharmacological agents remains an important area of investigation.

Retrieval-Driven Hippocampal NPTX2 Plasticity Facilitates the Extinction of Cocaine-Associated Context Memory

BACKGROUND

Postretrieval extinction attenuates the pathological memory associated with psychiatric states such as drug addiction in both humans and rodents. The extinction of a learned response requires gene transcription and protein synthesis after memory retrieval in a time-dependent manner, yet the precise physiological basis after retrieval to allow extinction to neutralize a learned behavior is not fully understood.

METHODS

In a cocaine conditioned place preference paradigm, we used a ribosomal tagging strategy to measure the translational state of hippocampal pyramidal neurons after the retrieval of cocaine-associated context memory. Using approaches of electrophysiology, neuronal tracing, and a doxycycline-dependent robust activity marking system, we investigated the cellular and molecular basis of retrieval-induced plasticity that facilitated the extinction.

RESULTS

Bioinformatics analysis discovered the specific translational regulation of signaling pathways by retrieval and revealed Nptx2 as the hub gene. Manipulating Nptx2 in dorsal hippocampus bidirectionally regulated the extinction of cocaine-associated context memory as well as the retrieval-driven synaptic remodeling. The pentraxin (PTX) domain of NPTX2 recruited GluA1-AMPA receptors and enhanced the extinction and excitatory synaptic transmission that was prevented by overexpressing carboxyl cytoplasmic tail of GluA1. Furthermore, Nptx2 in retrieval-activated neurons was required for the extinction.

CONCLUSIONS

The retrieval-driven upregulation of Nptx2 contributes to the synaptic remodeling in dorsal hippocampus and facilitates the extinction of cocaine-associated context memory, indicating a potential target for the treatment of cue-induced cocaine seeking.

Protocols for instrumental memory reconsolidation in rodents: A methodological review

BACKGROUND

Memory reconsolidation enables the update of a previously consolidated memory trace after its reactivation. Although Pavlovian memory reconsolidation has been widely demonstrated, instrumental memory reconsolidation is still debated. Early studies suggested that instrumental memories did not undergo reconsolidation and therefore could not be disrupted, whereas other authors suggested that these memories are just more resistant to destabilization and reconsolidation in comparison to Pavlovian memories.

AIM AND RESULTS

The present paper reviews the behavioral protocols used to investigate appetitive instrumental memory reconsolidation in rodents and describes in detail the specific methods used for memory retrieval, with a critical analysis of the different experimental parameters.

CONCLUSIONS

The modalities under which the reconsolidation of appetitive (sucrose or drugs of abuse) instrumental memories occurs have been explored and partially elucidated. Further investigations are recommended on the boundary conditions that constrain instrumental memory reactivation.

Checking responses of goal- and sign-trackers are differentially affected by threat in a rodent analog of obsessive-compulsive disorder

In obsessive–compulsive disorder (OCD), functional behaviors such as checking that a door is locked become dysfunctional, maladaptive, and debilitating. However, it is currently unknown how aversive and appetitive motivations interact to produce functional and dysfunctional behavior in OCD. Here we show a double dissociation in the effects of anxiogenic cues and sensitivity to rewarding stimuli on the propensity to develop functional and dysfunctional checking behavior in a rodent analog of OCD, the observing response task (ORT). While anxiogenic manipulations of perceived threat (presentation of threat-associated contextual cues) and actual threat (punishment of incorrect responding on the ORT) enhanced functional checking, dysfunctional checking was unaffected. In contrast, rats that had previously been identified as “sign-trackers” on an autoshaping task—and therefore were highly sensitive to the incentive salience of appetitive environmental cues—selectively showed elevated levels of dysfunctional checking under a range of conditions, but particularly so under conditions of uncertainty. These data indicate that functional and dysfunctional checking are dissociable and supported by aversive and appetitive motivational processes, respectively. While functional checking is modulated by perceived and actual threat, dysfunctional checking recruits appetitive motivational processes, possibly akin to the “incentive habits” that contribute to drug-seeking in addiction.

Glutamatergic basolateral amygdala to anterior insular cortex circuitry maintains rewarding contextual memory

Findings have shown that anterior insular cortex (aIC) lesions disrupt the maintenance of drug addiction, while imaging studies suggest that connections between amygdala and aIC participate in drug-seeking. However, the role of the BLA → aIC pathway in rewarding contextual memory has not been assessed. Using a cre-recombinase under the tyrosine hydroxylase (TH+) promoter mouse model to induce a real-time conditioned place preference (rtCPP), we show that photoactivation of TH+ neurons induced electrophysiological responses in VTA neurons, dopamine release and neuronal modulation in the aIC. Conversely, memory retrieval induced a strong release of glutamate, dopamine, and norepinephrine in the aIC. Only intra-aIC blockade of the glutamatergic N-methyl-D-aspartate receptor accelerated rtCPP extinction. Finally, photoinhibition of glutamatergic BLA → aIC pathway produced disinhibition of local circuits in the aIC, accelerating rtCPP extinction and impairing reinstatement. Thus, activity of the glutamatergic projection from the BLA to the aIC is critical for maintenance of rewarding contextual memory.

Retrieval-Extinction and Relapse Prevention: Rewriting Maladaptive Drug Memories?

Addicted individuals are highly susceptible to relapse when exposed to drug-associated conditioned stimuli (CSs; "drug cues") even after extensive periods of abstinence. Until recently, these maladaptive emotional drug memories were believed to be permanent and resistant to change. The rediscovery of the phenomenon of memory reconsolidation-by which retrieval of the memory can, under certain conditions, destabilize the previously stable memory before it restabilizes in its new, updated form-has led to the hypothesis that it may be possible to disrupt the strong maladaptive drug-memories that trigger a relapse. Furthermore, recent work has suggested that extinction training "within the reconsolidation window" may lead to a long-term reduction in relapse without the requirement for pharmacological amnestic agents. However, this so-called "retrieval-extinction" effect has been inconsistently observed in the literature, leading some to speculate that rather than reflecting memory updating, it may be the product of facilitation of extinction. In this mini review article, we will focus on factors that might be responsible for the retrieval-extinction effects on preventing drug-seeking relapse and how inter-individual differences may influence this therapeutically promising effect. A better understanding of the psychological and neurobiological mechanisms underpinning the "retrieval-extinction" paradigm, and individual differences in boundary conditions, should provide insights with the potential to optimize the translation of "retrieval-extinction" to clinical populations.

Neurochemical Evidence of Preclinical and Clinical Reports on Target-Based Therapy in Alcohol Used Disorder

Alcohol use disorder (AUD) is a chronic relapsing disorder, which enforces a person to compulsively seek alcohol, restricting control over alcohol intake leads to emergence of an undesired emotional state during abstinence. There are recent advances for better understanding of neurocircuitry involved in the pathophysiology of AUD. Alcohol interaction with neuronal membrane proteins results in changes in neuronal circuits. It is also linked with the potential medication and their clinical validation concerning their pharmacological targets for alcoholic abstinence. This review covers research work from the past few decades on the therapeutic advances on treatment of alcohol dependence; further detailing the fundamental neurochemical mechanisms after alcohol administration. It also covers interaction of alcohol with GABAergic, glutaminergic, dopaminergic, serotonergic and opioid systems. This review further elaborated the neurobiology of noradrenergic, cholinergic and cannabinoid systems and their interaction with AUD. Elaborative information of potential drug targets under current exploration for AUD treatment with their mechanisms are reported here along with clinical outcomes and the associated side effects.

Reconsolidation impairment of reward memory by stimulating stress response

Research in memory reconsolidation has raised hope for new treatment options of persistent psychiatric disorders like substance dependence and post-traumatic stress disorder (PTSD). While animal research showed successful memory modification by interfering with reconsolidation, human research requires less invasive techniques. In our pilot study, we aimed to reduce appetitive memory reconsolidation of a newly acquired reward memory by exerting a stressor. Thirty healthy participants were randomly assigned to two groups performing a monetary reward paradigm at a personal computer. Day 1 was considered to allow for memory acquisition; on day 2, the experimental group was exposed to a frightening stimulus in the reconsolidation window; and day 3 again served to determine reward memory effects. Measures of reward memory were reaction times to reward announcing stimuli (ie, showing instrumental behavior), actual reward gained, and electrodermal response as a measure for reward anticipation. We found significantly smaller reaction time improvements to reward stimuli over time in the experimental group, as well as reduced achievements in monetary reward. Electrodermal response to reward announcing stimuli was lower in the experimental group after intervention, whereas it was higher in the untreated group. Thus, we argue in favor of the reconsolidation hypothesis, assuming our intervention had successfully interfered with the reconsolidation process. This points towards future treatment options that interfere with an addiction memory.

Acute alcohol and cognition: Remembering what it causes us to forget

Addiction has been conceptualized as a specific form of memory that appropriates typically adaptive neural mechanisms of learning to produce the progressive spiral of drug-seeking and drug-taking behavior, perpetuating the path to addiction through aberrant processes of drug-related learning and memory. From that perspective, to understand the development of alcohol use disorders, it is critical to identify how a single exposure to alcohol enters into or alters the processes of learning and memory, so that involvement of and changes in neuroplasticity processes responsible for learning and memory can be identified early. This review characterizes the effects produced by acute alcohol intoxication as a function of brain region and memory neurocircuitry. In general, exposure to ethanol doses that produce intoxicating effects causes consistent impairments in learning and memory processes mediated by specific brain circuitry, whereas lower doses either have no effect or produce a facilitation of memory under certain task conditions. Therefore, acute ethanol does not produce a global impairment of learning and memory, and can actually facilitate particular types of memory, perhaps particular types of memory that facilitate the development of excessive alcohol use. In addition, the effects on cognition are dependent on brain region, task demands, dose received, pharmacokinetics, and tolerance. Additionally, we explore the underlying alterations in neurophysiology produced by acute alcohol exposure that help to explain these changes in cognition and highlight future directions for research. Through understanding the impact that acute alcohol intoxication has on cognition, the preliminary changes potentially causing a problematic addiction memory can better be identified.

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.

Opposing roles for amygdala and vmPFC in the return of appetitive conditioned responses in humans

Learning accounts of addiction and obesity emphasize the persistent power of Pavlovian reward cues to trigger craving and increase relapse risk. While extinction can reduce conditioned responding, Pavlovian relapse phenomena-the return of conditioned responding following successful extinction-challenge the long-term success of extinction-based treatments. Translational laboratory models of Pavlovian relapse could therefore represent a valuable tool to investigate the mechanisms mediating relapse, although so far human research has mostly focused on return of fear phenomena. To this end we developed an appetitive conditioning paradigm with liquid food rewards in combination with a 3-day design to investigate the return of appetitive Pavlovian responses and the involved neural structures in healthy subjects. Pavlovian conditioning (day 1) was assessed in 62 participants, and a subsample (n = 33) further completed extinction (day 2) and a reinstatement test (day 3). Conditioned responding was assessed on explicit (pleasantness ratings) and implicit measures (reaction time, skin conductance, heart rate, startle response) and reinstatement effects were further evaluated using fMRI. We observed a return of conditioned responding during the reinstatement test, evident by enhanced skin conductance responses, accompanied by enhanced BOLD responses in the amygdala. On an individual level, psychophysiological reinstatement intensity was significantly anticorrelated with ventromedial prefrontal cortex (vmPFC) activation, and marginally anticorrelated with enhanced amygdala-vmPFC connectivity during late reinstatement. Our results extend evidence from return of fear phenomena to the appetitive domain, and highlight the role of the vmPFC and its functional connection with the amygdala in regulating appetitive Pavlovian relapse.

Nicotine Produces a High-Approach, Low-Avoidance Phenotype in Response to Alcohol-Associated Cues in Male Rats

BACKGROUND

Nicotine and alcohol use are highly comorbid. Modulation of drug-paired extrinsic and intrinsic cues likely plays a role in this interaction, as cues can acquire motivational properties and augment drug seeking. The motivational properties of cues can be measured through Pavlovian conditioning paradigms, in which cues either elicit approach following pairing with the reinforcing properties of alcohol or elicit avoidance following pairing with the aversive consequences of alcohol. The present experiments tested whether nicotine would enhance the incentive properties of an appetitive ethanol (EtOH) cue and diminish the avoidance of an aversive EtOH cue in Pavlovian paradigms.

METHODS

In experiment 1, male Long-Evans rats with or without prior chronic intermittent access to EtOH were administered nicotine or saline injections prior to Pavlovian conditioned approach (PavCA) sessions, during which conditioned approach to the cue ("sign-tracking") or the EtOH delivery location ("goal-tracking") was measured. In experiment 2, male Long-Evans rats were administered nicotine or saline injections prior to pairing a flavor cue with increasing doses of EtOH (i.p.) in an adaptation of the conditioned taste avoidance (CTA) paradigm.

RESULTS

Results from PavCA indicate that, regardless of EtOH exposure, nicotine enhanced responding elicited by EtOH-paired cues with no effect on a similar cue not explicitly paired with EtOH. Furthermore, nicotine reduced sensitivity to EtOH-induced CTA, as indicated by a rightward shift in the dose-response curve of passively administered EtOH. The ED₅₀ , or the dose of EtOH that produced a 50% reduction in intake relative to baseline, was significantly higher in nicotine-treated rats compared to saline-treated rats.

CONCLUSIONS

We conclude that nicotine increases the approach and diminishes the avoidance elicited by Pavlovian cues paired, respectively, with the reinforcing and aversive properties of EtOH consumption in male rats. As such, nicotine may enhance alcoholism liability by engendering an attentional bias toward cues that predict the reinforcing outcomes of drinking.

Reconsolidation of sucrose instrumental memory in rats: The role of retrieval context

Memory reconsolidation enables the update of a previously consolidated memory trace after its reactivation. Although Pavlovian memory reconsolidation has been widely demonstrated, instrumental memory reconsolidation is still debated. The most critical issue on instrumental memory reconsolidation findings have mainly been linked to the presence of specific boundary conditions for reactivation, for instance contextual parameters. In this study, we investigated the role of the spatial context on molecular markers of sucrose instrumental memory reactivation. Following withdrawal, rats previously conditioned to sucrose self-administration underwent either instrumental memory retrieval or no-retrieval in the conditioned context (Context A, AA condition) or in a modified version of the conditioned context (Context B, AB condition). Two hours later, the level of GluA1 and GluN2B receptors, Zif268 and phosphorylated-rpS6 (rpS6P) was measured in key brain areas for memory reactivation. Retrieval in Context A significantly increased GluA1Rs and GluN2BRs in amygdala compared to no-retrieval, indicating that memory successfully reactivated and destabilized. Moreover, Zif268 level was significantly increased after retrieval in Context A in the nucleus accumbens shell, central and basolateral amygdala but not in the hippocampus, while retrieval in Context B significantly increased Zif268 level in all brain areas. On the other hand, rpS6P level was increased in the nucleus accumbens shell and central amygdala, but decreased in the hippocampus, after retrieval in Context A, while retrieval in Context B did not change rpS6P level in brain areas, except for a small but significant decrease in hippocampus. While the increase of Zif268 level indicated that memory reactivation has been triggered in both the conditions, the lack of change in rpS6P levels after retrieval in Context B - in particular in the central amygdala - suggests that the reconsolidation process could not occur after memory reactivation in a context different from the conditioned one.

Advances in behavioral animal models of alcohol use disorder

Alcohol use disorder (AUD) is a multifaceted neuropsychiatric disease that combines behavioral, psychosocial, and neurobiological aspects. Over the previous decade, animal models have advanced in modeling the major psychological constructs that characterize AUD. These advances pave the road for more sophisticated behavioral models that capture addiction-related aspects, such as alcohol craving, compulsive seeking and intake, dependence, and relapse. In this review, we survey the recent progress in behavioral animal modeling of five aspects of AUD: alcohol consumption, dependence, and seeking; compulsivity in alcohol intake despite adverse outcomes; vulnerability and resilience factors in alcohol addiction; relapse despite treatment; and relapse prevention by manipulating alcohol-associated memory reconsolidation. These advances represent a general attempt to grasp the complexity and multidimensional nature of AUD, and to focus on behavioral characteristics that better reflect and model this disorder.