A novel UCS memory retrieval-extinction procedure to inhibit relapse to drug seeking

Paraventricular thalamus to nucleus accumbens circuit activation decreases long-term relapse of alcohol-seeking behaviour in male mice

BACKGROUND

Some studies have highlighted the crucial role of aversion in addiction treatment. The pathway from the anterior paraventricular thalamus (PVT) to the shell of the nucleus accumbens (NAc) has been reported as an essential regulatory pathway for processing aversion and is also closely associated with substance addiction. However, its impact on alcohol addiction has been relatively underexplored. Therefore, this study focused on the role of the PVT-NAc pathway in the formation and relapse of alcohol addiction-like behaviour, offering a new perspective on the mechanisms of alcohol addiction.

RESULTS

The chemogenetic inhibition of the PVT-NAc pathway in male mice resulted in a notable decrease in the establishment of ethanol-induced conditioned place aversion (CPA), and NAc-projecting PVT neurons were recruited due to aversive effects. Conversely, activation of the PVT-NAc pathway considerably impeded the formation of ethanol-induced conditioned place preference (CPP). Furthermore, during the memory reconsolidation phase, activation of this pathway effectively disrupted the animals' preference for alcohol-associated contexts. Whether it was administered urgently 24 h later or after a long-term withdrawal of 10 days, a low dose of alcohol could still not induce the reinstatement of ethanol-induced CPP.

CONCLUSIONS

Our results demonstrated PVT-NAc circuit processing aversion, which may be one of the neurobiological mechanisms underlying aversive counterconditioning, and highlighted potential targets for inhibiting the development of alcohol addiction-like behaviour and relapse after long-term withdrawal.

Regulation of histone acetylation by garcinol blocks the reconsolidation of heroin-associated memory

Drug-associated long-term memories underlie substance use disorders, including heroin use disorder (HUD), which are difficult to eliminate through existing therapies. Addictive memories may become unstable when reexposed to drug-related cues and need to be stabilized again through protein resynthesis. Studies have shown the involvement of histone acetylation in the formation and reconsolidation of long-term drug-associated memory. However, it remains unknown whether and how histone acetyltransferases (HAT), the essential regulators of histone acetylation, contribute to the reconsolidation of heroin-associated memories. Herein, we investigated the function of HAT in the reconsolidation concerning heroin-conditioned memory by using a rat self-administration model. Systemic administration of the HAT inhibitor garcinol inhibited cue and heroin-priming induced reinstatement of heroin seeking, indicating the treatment potential of garcinol for relapse prevention.

Interfering with reconsolidation by rimonabant results in blockade of heroin-associated memory

Drug-associated pathological memory remains a critical factor contributing to the persistence of substance use disorder. Pharmacological amnestic manipulation to interfere with drug memory reconsolidation has shown promise for the prevention of relapse. In a rat heroin self-administration model, we examined the impact of rimonabant, a selective cannabinoid receptor indirect agonist, on the reconsolidation process of heroin-associated memory. The study showed that immediately administering rimonabant after conditioned stimuli (CS) exposure reduced the cue- and herion + cue-induced heroin-seeking behavior. The inhibitory effects lasted for a minimum of 28 days. The effect of Rimonabant on reduced drug-seeking was not shown when treated without CS exposure or 6 hours after CS exposure. These results demonstrate a disruptive role of rimonabant on the reconsolidation of heroin-associated memory and the therapeutic potential in relapse control concerning substance use disorder.

rTMS effects on urges and severity of tobacco use disorder operate independently of a retrieval-extinction component and involve frontal-striatal pathways

BACKGROUND

Although smoking remains a leading cause of preventable disease, the treatment options for smoking are limited. The present study evaluated the neural features underlying effects of repetitive transcranial magnetic stimulation (rTMS) for reducing smoking cravings. In addition, the efficacy of a simulated retrieval-extinction procedure to augment rTMS efficacy was examined.

METHODS

Sixty-one individuals with tobacco use disorder (TUD) were randomized into three groups: classic rTMS, retrieval rTMS (viewed smoking videos before rTMS), and sham rTMS. rTMS was performed on the left dorsolateral prefrontal cortex (DLPFC) over 5 days using a standard figure-8 coil. Smoking cravings and brain responses to smoking cues were measured before and after rTMS treatment. Changes in functional connectivity (FC) among different brain regions were calculated.

RESULTS

rTMS reduced smoking urges in TUD. Both active-rTMS groups demonstrated greater activations of the DLPFC, caudate, and bilateral insula relative to the sham group. Increased FC was observed between executive and reward network brain regions, and decreased FC was observed within reward network regions. Compared with standard rTMS, retrieval-extinction rTMS demonstrated similar outcomes and was associated with less activation of the medial frontal gyrus.

CONCLUSIONS

rTMS increased activations in brain regions implicated in executive control and reward processing. Strengthened prefrontal-striatal pathway suggests that rTMS enhanced top-down control over smoking cravings. The retrieval-extinction process, although associated with some different and multiple similar neural correlates as the standard rTMS, did not enhance cessation outcomes.

Memory consolidation drives the enhancement of remote cocaine memory via prefrontal circuit

Remote memory usually decreases over time, whereas remote drug-cue associated memory exhibits enhancement, increasing the risk of relapse during abstinence. Memory system consolidation is a prerequisite for remote memory formation, but neurobiological underpinnings of the role of consolidation in the enhancement of remote drug memory are unclear. Here, we found that remote cocaine-cue associated memory was enhanced in rats that underwent self-administration training, together with a progressive increase in the response of prelimbic cortex (PrL) CaMKII neurons to cues. System consolidation was required for the enhancement of remote cocaine memory through PrL CaMKII neurons during the early period post-training. Furthermore, dendritic spine maturation in the PrL relied on the basolateral amygdala (BLA) input during the early period of consolidation, contributing to remote memory enhancement. These findings indicate that memory consolidation drives the enhancement of remote cocaine memory through a time-dependent increase in activity and maturation of PrL CaMKII neurons receiving a sustained BLA input.

Development of two novel treatments to promote smoking cessation: Savor and retrieval-extinction training pilot clinical trial findings

Despite decades of progress, cigarette smoking remains a significant contributor to disease burden. This effect is especially pronounced for specific priority populations, such as individuals who live in rural communities, in that the burden of tobacco smoking is greater among these groups than in urban areas and the general population. The present study aims to evaluate the feasibility and acceptability of two novel tobacco treatment interventions delivered through remote telehealth procedures to individuals who smoke in the state of South Carolina. Results also include exploratory analyses of smoking cessation outcomes. Study I evaluated savoring, a strategy based on mindfulness practices, alongside nicotine replacement therapy (NRT). Study II evaluated retrieval-extinction training (RET), a memory-modification paradigm alongside NRT. In Study I (savoring), recruitment and retention data showed high interest and engagement in the intervention components, and participants who received this intervention decreased cigarette smoking throughout the course of the treatment (ps < .05). In Study II (RET), results showed high interest and moderate engagement in treatment, although exploratory outcome analyses did not demonstrate significant treatment effects on smoking behaviors. Overall, both studies showed promise in generating interest among individuals who smoke in participating in remotely delivered, telehealth smoking cessation interventions with novel therapeutic targets. A brief savoring intervention appeared to have effects on cigarette smoking throughout treatment, whereas RET did not. Gaining insight from the present pilot study, future studies may improve the efficacy of these procedures and incorporate the treatment components into more robust available treatments. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

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.

Manipulating critical memory periods to treat psychiatry disorders

The persistence of pathological memory is the basis of several psychiatric disorders. Memory retrieval induces "reconsolidation", a time interval during which the original memory becomes labile and destabilized. Time- and retrieval-dependent processes and memory reconsolidation are critical periods for memory interference. Modulating memory reconsolidation has received considerable research attention as a treatment protocol for several psychiatric conditions such as posttraumatic stress disorder, addiction, anxiety, and trauma-related disorders. This specific time window provides an opportunity for intervention regarding mental diseases. This article reviews the effect of modulating memory reconsolidation using behavioral-, brain stimulation-, and pharmacological-based interventions, which may help bridge the gap between intervention in laboratories and application in clinical practice. The potential advantages, limitations, challenges, and opportunities for memory reconsolidation manipulations were discussed.

Disrupting astrocyte-neuron lactate transport prevents cocaine seeking after prolonged withdrawal

Energy supply, especially the transfer of lactate from astrocytes to neurons, is critical for neuronal plasticity. However, its role in the incubation of cocaine craving remains largely unknown. Using an extended-access self-administration model and in vivo 1H-magnetic resonance spectroscopy, we found that lactate synthesis in the central amygdala (CeA) is required for the intensified cocaine craving after prolonged withdrawal. Furthermore, incubated cocaine seeking was associated with a selective increase in monocarboxylate transporter 2 (MCT2) and MCT4 expression levels. Down-regulation of astrocytic MCT4 or neuronal MCT2 using targeted antisense oligonucleotides or cell type-specific shRNA attenuated cocaine craving and reduced the expression of plasticity-related proteins and excitatory synaptic transmission. Meanwhile, lactate administration rescued MCT4 but not MCT2 disruption-induced behavioral changes due to the inability of lactate to be transported into neurons. Together, our study highlights the critical role of astrocyte-neuron lactate transport in the CeA in the incubation of cocaine craving and suggests a potential therapeutic target for drug addiction.

Activation of Epac in the BLA disrupts reconsolidation and attenuates heroin-seeking behaviour

The susceptibility to drug cravings evoked by stimuli poses a formidable hurdle in the treatment of addiction and the prevention of relapse. Pharmacological interventions targeting drug-associated memories hold promise for curbing relapse by impeding the process of memory reconsolidation, predominantly governed by cAMP signalling. Exchange Protein Activated by cAMP (Epac) serves as a distinctive mediator of cAMP signalling, which has been implicated in reinforcing the effects of cocaine and facilitating the acquisition. Nonetheless, the role of Epac in heroin-related memory and the subsequent seeking behaviour remains enigmatic. In this study, we explored the impact of Epac activation on the reconsolidation process of drug-related memories associated with heroin self-administration. Over the course of 10 consecutive days, rats underwent training, wherein they acquired the behaviour of nose poking to obtain heroin accompanied by a tone + light cue. This nose-poking behaviour was subsequently extinguished when heroin infusion and cue presentation were discontinued. Subsequently, we administered 8-pCPT-cAMP (8-CPT), an Epac-specific activator, into the basolateral amygdala at various time points, either in the presence or absence of a conditioned stimulus. Our findings demonstrate that administering 8-CPT immediately after memory retrieval effectively reduces cue- and heroin-induced reinstatement, with the observed effects persisting significantly for a minimum of 28 days. However, infusion of 8-CPT for a duration of 6 h following the memory retrieval trial, or without it altogether, had no discernible impact. Thus, these findings strongly suggest that Epac activation can disrupt the reconsolidation of heroin-associated memory, thereby diminishing the reinstatement of heroin-seeking behaviour.

The Cdk5 inhibitor β-butyrolactone impairs reconsolidation of heroin-associated memory in the rat basolateral amygdala

The persistence of maladaptive heroin-associated memory, which is triggered by drug-related stimuli that remind the individual of the drug's pleasurable and rewarding effects, can impede abstinence efforts. Cyclin-dependent kinase 5 (Cdk5), a neuronal serine/threonine protein kinase that plays a role in multiple neuronal functions, has been demonstrated to be involved in drug addiction and learning and memory. Here, we aimed to investigate the role of cdk5 activity in the basolateral amygdala (BLA) in relapse to heroin seeking, using a self-administration rat model. Male rats underwent 10 days of heroin self-administration training, during which an active nose poke resulted in an intravenous infusion of heroin that was accompanied by a cue. The rats then underwent nose poke extinction for 10 days, followed by subsequent tests of heroin-seeking behaviour. We found that intra-BLA infusion of β-butyrolactone (100 ng/side), a Cdk5 inhibitor, administered 5 min after reactivation, led to a subsequent decrease in heroin-seeking behaviour. Further experiments demonstrated that the effects of β-butyrolactone are dependent on reactivated memories, temporal-specific and long-lasting on relapse of heroin-associated memory. Results provide suggestive evidence that the activity of Cdk5 in BLA is critical for heroin-associated memory and that the specific inhibitor, β-butyrolactone, may hold potential as a substance for the treatment of heroin abuse.

New Approaches for Alcohol Use Disorder Treatment via Memory Retrieval and Reconsolidation Manipulations

Relapse to alcohol seeking and drinking is a major clinical challenge in alcohol use disorder and is frequently brought about by cue-induced craving, caused by exposure to cues that evoke alcohol-related memories. It has been postulated that memories become labile for manipulation shortly after their retrieval and then restabilize in a "memory reconsolidation" process. Disruption or interference with the reconsolidation of drug-associated memories has been suggested as a possible strategy to reduce or even prevent cue-induced craving and relapse. Here, we review literature demonstrating the capacity of behavioral or pharmacological manipulations to reduce relapse in animal models and humans when applied after a short retrieval of memories associated with alcohol, suggestively disrupting the reconsolidation of such memories. We suggest that while there is a clear potential of using post-retrieval manipulations to target specific relapse-evoking memories, future research should be more systematic, standardized, and translational. Specifically, we discuss several critical limitations and boundary conditions, which should be addressed to improve consistency and replicability in the field and lead to the development of an efficient reconsolidation-based relapse prevention therapy.

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)

DNA methyltransferase activity in the basolateral amygdala is critical for reconsolidation of a heroin reward memory

The persistence of drug memory contributes to relapse to drug seeking. The association between repeated drug exposure and drug-related cues leads to cravings triggered by drug-paired cues. The erasure of drug memories has been considered a promising way to inhibit cravings and prevent relapse. The re-exposure to drug-related cues destabilizes well-consolidated drug memories, during which a de novo protein synthesis-dependent process termed “reconsolidation” occurs to restabilize the reactivated drug memory. Disrupting reconsolidation of drug memories leads to the attenuation of drug-seeking behavior in both animal models and people with addictions. Additionally, epigenetic mechanisms regulated by DNA methyltransferase (DNMT) are involved in the reconsolidation of fear and cocaine reward memory. In the present study, we investigated the role of DNMT in the reconsolidation of heroin reward memory. In the heroin self-administration model in rats, we tested the effects of DNMT inhibition during the reconsolidation process on cue-induced reinstatement, heroin-priming-induced reinstatement, and spontaneous recovery of heroin-seeking behavior. We found that the bilateral infusion of 5-azacytidine (5-AZA) inhibiting DNMT into the basolateral amygdala (BLA) immediately after heroin reward memory retrieval, but not delayed 6 h after retrieval or without retrieval, decreased subsequent cue-induced and heroin-priming-induced reinstatement of heroin-seeking behavior. These findings demonstrate that inhibiting the activity of DNMT in BLA during the reconsolidation of heroin reward memory attenuates heroin-seeking behavior, which may provide a potential strategy for the therapeutic of heroin addiction.

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.

Inhibition of Glycogen Synthase Kinase 3β Activity in the Basolateral Amygdala Disrupts Reconsolidation and Attenuates Heroin Relapse

Exposure to a heroin-associated conditioned stimulus can reactivate drug reward memory, trigger drug cravings, and induce relapse in heroin addicts. The amygdala, a brain region related to emotions and motivation, is involved in processing rewarding stimulus. Recent evidence demonstrated that disrupting the reconsolidation of the heroin drug memories attenuated heroin seeking which was associated with the basolateral amygdala (BLA). Meanwhile, neural functions associated with learning and memory, like synaptic plasticity, are regulated by glycogen synthase kinase 3 beta (GSK-3β). In addition, GSK-3β regulated memory processes, like retrieval and reconsolidation of cocaine-induced memory. Here, we used a heroin intravenous self-administration (SA) paradigm to illustrate the potential role of GSK-3β in the reconsolidation of drug memory. Therefore, we used SB216763 as a selective inhibitor of GSK-3β. We found that injecting the selective inhibitor SB216763 into the BLA, but not the central amygdala (CeA), immediately after heroin-induced memory retrieval disrupted reconsolidation of heroin drug memory and significantly attenuated heroin-seeking behavior in subsequent drug-primed reinstatement, suggesting that GSK-3β is critical for reconsolidation of heroin drug memories and inhibiting the activity of GSK-3β in BLA disrupted heroin drug memory and reduced relapse. However, no retrieval or 6 h after retrieval, administration of SB216763 into the BLA did not alter heroin-seeking behavior in subsequent heroin-primed reinstatement, suggesting that GSK-3β activity is retrieval-dependent and time-specific. More importantly, a long-term effect of SB216763 treatment was observed in a detectable decrease in heroin-seeking behavior, which lasted at least 28 days. All in all, this present study demonstrates that the activity of GSK-3β in BLA is required for reconsolidation of heroin drug memory, and inhibiting GSK-3β activity of BLA disrupts reconsolidation and attenuates heroin relapse.

Ca2+-permeable AMPA receptors set the threshold for retrieval of drug memories

Frequent relapse prevents the successful treatment of substance use disorders and is triggered in part by retrieval of drug-associated memories. Drug-conditioned behaviours in rodents are reinstated upon drug memory retrieval following re-exposure to cues previously associated with the drug, or the drug itself. Therapies based on mechanistic insights from rodent studies have focused on amnesic procedures of cue-drug associations but with so far limited success. Conversely, more recent studies propose that inhibiting drug memory retrieval offers improved anti-relapse efficacy. However, mechanisms of memory retrieval are poorly understood. Here, we used a conditioned place preference (CPP) procedure in mice to investigate the cellular and molecular underpinnings of drug-induced memory retrieval. After extinction training of CPP, Ca²⁺-permeable AMPA receptors (CP-AMPARs) accumulated at drug-generated silent synapses of nucleus accumbens (NAc) medium spiny neurons. The NAc CP-AMPARs regulated the retrieval mechanism of drug memories after extinction. Specifically, we used different priming doses of cocaine, fentanyl, or a cue associated with drug exposure to reinstate CPP, providing different memory retrieval conditions. Although both high and low doses of these two drugs induced CPP reinstatement, compromising CP-AMPAR accumulation impaired CPP reinstatement, induced by low doses of each drug or the cue. This threshold effect was mediated by NAc CP-AMPARs as region specific knock-down of PSD-95 prevented low-dose cocaine-induced retrieval selectively. These results demonstrate the NAc as a brain region and CP-AMPARs as key synaptic substrates that govern the threshold for drug-induced retrieval and behavioural expression of drug memories.

The evidence for and against reactivation-induced memory updating in humans and nonhuman animals

Systematic investigation of reactivation-induced memory updating began in the 1960s, and a wave of research in this area followed the seminal articulation of "reconsolidation" theory in the early 2000s. Myriad studies indicate that memory reactivation can cause previously consolidated memories to become labile and sensitive to weakening, strengthening, or other forms of modification. However, from its nascent period to the present, the field has been beset by inconsistencies in researchers' abilities to replicate seemingly established effects. Here we review these many studies, synthesizing the human and nonhuman animal literature, and suggest that these failures-to-replicate reflect a highly complex and delicately balanced memory modification system, the substrates of which must be finely tuned to enable adaptive memory updating while limiting maladaptive, inaccurate modifications. A systematic approach to the entire body of evidence, integrating positive and null findings, will yield a comprehensive understanding of the complex and dynamic nature of long-term memory storage and the potential for harnessing modification processes to treat mental disorders driven by pervasive maladaptive memories.

Differential involvement of nucleus tractus solitarius projections and locus coeruleus projections to the basolateral amygdala in morphine-associated memory destabilization

Drug-related memory can be transiently destabilized by memory retrieval, after which memories are reconsolidated. Neurons in the basolateral amygdala (BLA) that are activated by emotional information may be one of the key mechanisms underlying this destabilization. However, the specific neural circuits underlying this destabilization process remain unknown. Because BLA receives noradrenergic inputs from the nucleus tractus solitarius (NTS) and locus coeruleus (LC), we studied the role of afferent projections into the BLA in the destabilization of morphine self-administration memory in rats. We first showed that morphine (unconditioned stimulus, US) + morphine-associated conditioned stimuli (CS) exposure, rather than CS exposure alone, destabilized morphine self-administration memory. Then, we measured projection-specific activation after the US + CS or CS retrieval test using c-fos (activity marker)-labeling in projection areas. Compared with CS exposure, we found that US + CS exposure induced more neuronal activation in the BLA and NTS but not in the LC. Next, we determined the effects of chemogenetic inactivation or activation of NTS or LC projections to BLA (NTS → BLA or LC → BLA) on this destabilization. We found that NTS → BLA, but not LC → BLA inactivation during memory retrieval, prevented memory destabilization induced by US + CS exposure. Furthermore, NTS → BLA, but not LC → BLA activation during CS retrieval induced destabilization. Thus, our results identify a specific neural circuit underlying the transformation of a stable opiate-associated memory into an unstable memory and subsequently guide reconsolidation.

Effects of retrieval-extinction training on internet gaming disorder

BACKGROUND AND AIMS

Internet gaming disorder (IGD) leads to serious impairments in cognitive functions, and lacks of effective treatments. Cue-induced craving is a hallmark feature of this disease and is associated with addictive memory elements. Memory retrieval-extinction manipulations could interfere with addictive memories and attenuate addictive syndromes, which might be a promising intervention for IGD. The aims of this study were to explore the effect of a memory retrieval-extinction manipulation on gaming cue-induced craving and reward processing in individuals with IGD.

METHODS

A total of 49 individuals (mean age: 20.52 ± 1.58) with IGD underwent a memory retrieval-extinction training (RET) with a 10-min interval (R-10min-E, n = 24) or a RET with a 6-h interval (R-6h-E, n = 25) for two consecutive days. We assessed cue-induced craving pre- and post-RET, and at the 1- and 3-month follow-ups. The neural activities during reward processing were also assessed pre- and post-RET.

RESULTS

Compared with the R-6h-E group, gaming cravings in individuals with IGD were significantly reduced after R-10min-E training at the 3-month follow-up (P < 0.05). Moreover, neural activities in the individuals with IGD were also altered after R-10min-E training, which was corroborated by enhanced reward processing, such as faster responses (P < 0.05) and stronger frontoparietal functional connectivity to monetary reward cues, while the R-6h-E training had no effects.

DISCUSSION AND CONCLUSIONS

The two-day R-10min-E training reduced addicts' craving for Internet games, restored monetary reward processing in IGD individuals, and maintained long-term efficacy.

The role of hippocampus in memory reactivation: an implication for a therapeutic target against opioid use disorder

Purpose of the review

The abuse of opioids induces many terrible problems in human health and social stability. For opioid-dependent individuals, withdrawal memory can be reactivated by context, which is then associated with extremely unpleasant physical and emotional feelings during opioid withdrawal. The reactivation of withdrawal memory is considered one of the most important reasons for opioid relapse, and it also allows for memory modulation based on the reconsolidation phenomenon. However, studies exploring withdrawal memory modulation during the reconsolidation window are lacking. By summarizing the previous findings about the reactivation of negative emotional memories, we are going to suggest potential neural regions and systems for modulating opioid withdrawal memory.

Recent findings

Here, we first present the role of memory reactivation in its modification, discuss how the hippocampus participates in memory reactivation, and discuss the importance of noradrenergic signaling in the hippocampus for memory reactivation. Then, we review the engagement of other limbic regions receiving noradrenergic signaling in memory reactivation. We suggest that noradrenergic signaling targeting hippocampus neurons might play a potential role in strengthening the disruptive effect of withdrawal memory extinction by facilitating the degree of memory reactivation.

Summary

This review will contribute to a better understanding of the mechanisms underlying reactivation-dependent memory malleability and will provide new therapeutic avenues for treating opioid use disorders.

Continuous theta-burst stimulation over the right dorsolateral prefrontal cortex disrupts fear memory reconsolidation in humans

Continuous theta-burst stimulation (cTBS), a non-invasive brain stimulation technique, can induce long-lasting changes in synaptic plasticity, vital for memory reconsolidation. For this study, a total of 170 participants completed four experiments by a randomized controlled design. Succeeding fear conditioning, the subjects received cTBS over the right dorsolateral prefrontal cortex (dlPFC) or vertex (control) with or without exposure to the conditioned stimulus to reactivate the original fear memory, and then underwent fear response tests. Compared with cTBS over the vertex and without memory reactivation, only cTBS over the right dlPFC after reactivation decreased the fear response for both recent and remote fear memories. This procedure was effective only during the reconsolidation window. The disruptive effect of cTBS over the right dlPFC on fear memory reconsolidation was delay-dependent. These findings demonstrate that cTBS time-dependently and delay-dependently prevents the return of fear and may have clinical potential for treating fear-related disorders.

Potential roles of the gut microbiota in the manifestations of drug use disorders

Drug use disorders (DUDs) not only cause serious harm to users but also cause huge economic, security, and public health burdens to families and society. Recently, several studies have shown that gut microbiota (GM) can affect the central nervous system and brain functions. In this review, we focus on the potential role of the GM in the different stages of DUDs. First, the GM may induce individuals to seek novel substances. Second, the gut microbiota is involved in the decomposition and absorption of drugs. Symptoms of individuals who suffer from DUDs are also related to intestinal microorganisms. Third, the effects of the GM and its metabolites on drug relapse are mainly reflected in the reward effect and drug memory. In conclusion, recent studies have preliminarily explored the relationship between GM and DUDs. This review deepens our understanding of the mechanisms of DUDs and provides important information for the future development of clinical treatment for DUDs.

Social Interaction With Relapsed Partner Facilitates Cocaine Relapse in Rats

Social factors strongly contribute to drug use and relapse, and epidemiological studies have found that members of peer groups influence each other to use drugs. However, previous animal models mostly failed to incorporate social factors and demonstrate the effects of social partners on drug addiction and relapse. In the present study, we investigated the transfer of relapse to cocaine seeking between drug-addicted partners in rats. Male Sprague-Dawley rats were pair-housed and subjected to training and extinction of cocaine self-administration and conditioned place preference (CPP). 24 h after extinction test, the targeted rats interacted with a cocaine-primed (relapsed) partner or stranger, or saline-injected (unrelapsed) partner for 30 min, after which the targeted rats were tested for drug seeking behavior. We found that social interaction with a relapsed partner increased drug seeking behavior in cocaine self-administration and CPP models in rats, while social interaction with an unrelapsed partner or relapsed stranger had no effect on cocaine seeking. Moreover, the effect of social interaction on cocaine seeking could last for at least 1 day. Our findings demonstrate a facilitation effect of relapsed social partners on drug relapse in rats and provide a novel animal model for social transfer of drug relapse.

The Mechanisms and Boundary Conditions of Drug Memory Reconsolidation

Drug addiction can be seen as a disorder of maladaptive learning characterized by relapse. Therefore, disrupting drug-related memories could be an approach to improving therapies for addiction. Pioneering studies over the last two decades have revealed that consolidated memories are not static, but can be reconsolidated after retrieval, thereby providing candidate pathways for the treatment of addiction. The limbic-corticostriatal system is known to play a vital role in encoding the drug memory engram. Specific structures within this system contribute differently to the process of memory reconsolidation, making it a potential target for preventing relapse. In addition, as molecular processes are also active during memory reconsolidation, amnestic agents can be used to attenuate drug memory. In this review, we focus primarily on the brain structures involved in storing the drug memory engram, as well as the molecular processes involved in drug memory reconsolidation. Notably, we describe reports regarding boundary conditions constraining the therapeutic potential of memory reconsolidation. Furthermore, we discuss the principles that could be employed to modify stored memories. Finally, we emphasize the challenge of reconsolidation-based strategies, but end with an optimistic view on the development of reconsolidation theory for drug relapse prevention.

Animal Models of the Behavioral Symptoms of Substance Use Disorders

To more effectively manage substance use disorders, it is imperative to understand the neural, genetic, and psychological underpinnings of addictive behavior. To contribute to this understanding, considerable efforts have been made to develop translational animal models that capture key behavioral characteristics of addiction on the basis of DSM5 criteria of substance use disorders. In this review, we summarize empirical evidence for the occurrence of addiction-like behavior in animals. These symptoms include escalation of drug use, neurocognitive deficits, resistance to extinction, exaggerated motivation for drugs, increased reinstatement of drug seeking after extinction, preference for drugs over nondrug rewards, and resistance to punishment. The occurrence of addiction-like behavior in laboratory animals has opened the opportunity to investigate the neural, genetic, and psychological background of key aspects of addiction, which may ultimately contribute to the prevention and treatment of substance use disorders.

High-Frequency Deep Brain Stimulation of the Substantia Nigra Pars Reticulata Facilitates Extinction and Prevents Reinstatement of Methamphetamine-Induced Conditioned Place Preference

Persistent and stable drug memories lead to a high rate of relapse among addicts. A number of studies have found that intervention in addiction-related memories can effectively prevent relapse. Deep brain stimulation (DBS) exhibits distinct therapeutic effects and advantages in the treatment of neurological and psychiatric disorders. In addition, recent studies have also found that the substantia nigra pars reticulata (SNr) could serve as a promising target in the treatment of addiction. Therefore, the present study aimed to investigate the effect of DBS of the SNr on the reinstatement of drug-seeking behaviors. Electrodes were bilaterally implanted into the SNr of rats before training of methamphetamine-induced conditioned place preference (CPP). High-frequency (HF) or low-frequency (LF) DBS was then applied to the SNr during the drug-free extinction sessions. We found that HF DBS, during the extinction sessions, facilitated extinction of methamphetamine-induced CPP and prevented drug-primed reinstatement, while LF DBS impaired the extinction. Both HF and LF DBS did not affect locomotor activity or induce anxiety-like behaviors of rats. Finally, HF DBS had no effect on the formation of methamphetamine-induced CPP. In conclusion, our results suggest that HF DBS of the SNr could promote extinction and prevent reinstatement of methamphetamine-induced CPP, and the SNr may serve as a potential therapeutic target in the treatment of drug addiction.

Apparent reconsolidation interference without generalized amnesia

Memories remain dynamic after consolidation, and when reactivated, they can be rendered vulnerable to various pharmacological agents that disrupt the later expression of memory (i.e., amnesia). Such drug-induced post-reactivation amnesia has traditionally been studied in AAA experimental designs, where a memory is initially created for a stimulus A (be it a singular cue or a context) and later reactivated and tested through exposure to the exact same stimulus. Using a contextual fear conditioning procedure in rats and midazolam as amnestic agent, we recently demonstrated that drug-induced amnesia can also be obtained when memories are reactivated through exposure to a generalization stimulus (GS, context B) and later tested for that same generalization stimulus (ABB design). However, this amnestic intervention leaves fear expression intact when at test animals are instead presented with the original training stimulus (ABA design) or a novel generalization stimulus (ABC design). The underlying mechanisms of post-reactivation memory malleability and of MDZ-induced amnesia for a generalization context remain largely unknown. Here, we evaluated whether, like typical CS-mediated (or AAA) post-reactivation amnesia, GS-mediated (ABB) post-reactivation amnesia displays key features of a destabilization-based phenomenon. We first show that ABB post-reactivation amnesia is critically dependent on prediction error at the time of memory reactivation and provide evidence for its temporally graded nature. In line with the known role of GluN2B-NMDA receptor activation in memory destabilization, we further demonstrate that pre-reactivation administration of ifenprodil, a selective antagonist of GluN2B-NMDA receptors, prevents MDZ-induced ABB amnesia. In sum, our data reveal that ABB MDZ-induced post-reactivation amnesia exhibits the hallmark features of a destabilization-dependent phenomenon. Implication of our findings for a reconsolidation-based account of post-reactivation amnesia are discussed.

Blockade of β-Adrenergic Receptors by Propranolol Disrupts Reconsolidation of Drug Memory and Attenuates Heroin Seeking

Persistent traces of drug reward memories contribute to intense craving and often trigger relapse. A number of pharmacological interventions on drug-associated memories have shown significant benefits in relapse prevention at a preclinical level but their translational potential is limited due to deleterious side effects. Propranolol, a non-specific β-adrenergic receptors antagonist, is known for its ability to erase maladaptive memories associated with nicotine or cocaine in rodents and humans. However, little is known about its effect on reconsolidation of heroin memory and heroin seeking. In the present study, rats with a history of intravenous heroin self-administration received the propranolol treatment (10 mg/kg; i.p.) at different time windows with or without CS (conditioned stimulus) exposure. Our results showed that propranolol, when administered immediately after CS exposure but not 6 h later, can significantly attenuate cue-induced and drug-primed reinstatement of heroin seeking, suggesting that propranolol has the ability to disrupt heroin memory and reduce relapse. The propranolol treatment without retrieval of drug memory had no effect on subsequent reinstatement of heroin seeking, suggesting that its interfering effects are retrieval-dependent. Importantly, the effects of propranolol were long lasting as rats showed diminished drug seeking even 28 days after the treatment. Altogether, our study suggests that propranolol can interfere with reconsolidation of heroin memory and reduce subsequent drug seeking, making it an attractive therapeutic candidate for the treatment of opioid addiction and relapse prevention.

Active suppression prevents the return of threat memory in humans

Unbidden distressing memories inflict serious damage on mental health. Extant research highlights the importance of associative learning in modulating aversive memory. We report that conscious active suppression eliminates learned fear responses independent of memory triggers and is related to individual difference in thought control ability; in contrast, thought diversion only reduces cue-specific fear response. These results suggest potential avenues for treatment of persistent maladaptive memories by engaging declarative mnemonic control mechanisms.

Ye Wang et al. show that conscious thought active suppression eliminates learned fear responses whereas thought diversion only reduces cue-specific fear response. This study suggests that declarative control mechanisms may be utilized to treat persistent maladaptive memories.

Targeting the Reconsolidation of Licit Drug Memories to Prevent Relapse: Focus on Alcohol and Nicotine

Alcohol and nicotine are widely abused legal substances worldwide. Relapse to alcohol or tobacco seeking and consumption after abstinence is a major clinical challenge, and is often evoked by cue-induced craving. Therefore, disruption of the memory for the cue–drug association is expected to suppress relapse. Memories have been postulated to become labile shortly after their retrieval, during a “memory reconsolidation” process. Interference with the reconsolidation of drug-associated memories has been suggested as a possible strategy to reduce or even prevent cue-induced craving and relapse. Here, we surveyed the growing body of studies in animal models and in humans assessing the effectiveness of pharmacological or behavioral manipulations in reducing relapse by interfering with the reconsolidation of alcohol and nicotine/tobacco memories. Our review points to the potential of targeting the reconsolidation of these memories as a strategy to suppress relapse to alcohol drinking and tobacco smoking. However, we discuss several critical limitations and boundary conditions, which should be considered to improve the consistency and replicability in the field, and for development of an efficient reconsolidation-based relapse-prevention therapy.

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.

Generalization and recovery of post-retrieval amnesia

Selective amnesia for previously established memories can be induced by administering drugs that impair protein synthesis shortly after memory reactivation. Competing theoretical accounts attribute this selective post-retrieval amnesia to drug-induced engram degradation (reconsolidation blockade) or to incorporation of sensory features of the reactivation experience into the memory representation, hampering later retrieval in a drug-free state (memory integration). Here we present evidence that critically challenges both accounts. In contextual fear conditioning in rats, we find that amnesia induced by administration of midazolam (MDZ) after reexposure to the training context A generalizes readily to a similar context B. Amnesia is also observed when animals are exposed to the similar context B prior to MDZ administration and later tested for fear to context B but recovers when instead testing for fear to the original training context A or an equally similar but novel context C. Next to their theoretical implications for the nature of forgetting, our findings raise important questions about the viability of reconsolidation-based interventions for the treatment of emotional disorders. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Propranolol-induced inhibition of unconditioned stimulus-reactivated fear memory prevents the return of fear in humans

Fear memories can be reactivated by a fear-associated conditioned stimulus (CS) or unconditioned stimulus (US) and then undergo reconsolidation. Propranolol administration during CS retrieval-induced reconsolidation can impair fear memory that is specific to the reactivated CS. However, from a practical perspective, the US is often associated with multiple CSs, and each CS can induce a fear response. The present study sought to develop and test a US-based memory retrieval interference procedure with propranolol to disrupt the original fear memory and eliminate all CS-associated fear responses in humans. We recruited 127 young healthy volunteers and conducted three experiments. All of the subjects acquired fear conditioning, after which they received the β-adrenergic receptor antagonist propranolol (40 mg) or placebo (vitamin C) and were exposed to the US or CS to reactivate the original fear memory. Fear responses were measured. Oral propranolol administration 1 h before US retrieval significantly decreased subsequent fear responses and disrupted associations between all CSs and the US. However, propranolol administration before CS retrieval only inhibited the fear memory that was related to the reactivated CS. Moreover, the propranolol-induced inhibition of fear memory reconsolidation that was retrieved by the US had a relatively long-lasting effect (at least 2 weeks) and was also effective for remote fear memory. These findings indicate that the US-based memory retrieval interference procedure with propranolol can permanently decrease the fear response and prevent the return of fear for all CSs in humans. This procedure may open new avenues for treating fear-related disorders.

Sex differences in the effects of a combined behavioral and pharmacological treatment strategy for cocaine relapse prevention in an animal model of cue exposure therapy

Brief interventions of environmental enrichment (EE) or the glycine transporter-1 inhibitor Org24598 administered with cocaine-cue extinction training were shown previously to inhibit reacquisition of cocaine self-administration in male rats trained to self-administer a moderate 0.3 mg/kg dose of cocaine. Determining how EE and Org24598 synergize in combination in an animal model of cue exposure therapy is novel. Important changes made in this investigation were increasing the cocaine training dose to 1.0 mg/kg and determining sex differences. Adult male and female rats self-administering 1.0 mg/kg cocaine for 35-40 daily sessions exhibited an addiction-like phenotype under a second-order schedule of cocaine delivery and cue presentation. Rats next underwent 6 weekly extinction training sessions for which treatments consisted of EE or NoEE and Vehicle or Org24598 (3.0 mg/kg in males; 3.0 or 7.5 mg/kg in females). Rats then were tested for reacquisition of cocaine self-administration for 15 daily sessions. In males, the combined EE +3.0 mg/kg Org24598 treatment facilitated extinction learning and inhibited reacquisition of cocaine self-administration to a greater extent than no treatment and to individual EE or 3.0 mg/kg Org24598 treatments. In females, EE +7.5 mg/kg Org24598 facilitated extinction learning, but did not inhibit reacquisition of cocaine self-administration. Thus, there were sex differences in the ability of EE + Org24598 administered in conjunction with extinction training to inhibit cocaine relapse in rats exhibiting an addiction-like phenotype. These findings suggest that this multimodal treatment approach might be a feasible option during cue exposure therapy in cocaine-dependent men, but not women.

Molecular and circuit mechanisms regulating cocaine memory

Risk of relapse is a major challenge in the treatment of substance use disorders. Several types of learning and memory mechanisms are involved in substance use and have implications for relapse. Associative memories form between the effects of drugs and the surrounding environmental stimuli, and exposure to these stimuli during abstinence causes stress and triggers drug craving, which can lead to relapse. Understanding the neural underpinnings of how these associations are formed and maintained will inform future advances in treatment practices. A large body of research has expanded our knowledge of how associative memories are acquired and consolidated, how they are updated through reactivation and reconsolidation, and how competing extinction memories are formed. This review will focus on the vast literature examining the mechanisms of cocaine Pavlovian associative memories with an emphasis on the molecular memory mechanisms and circuits involved in the consolidation, reconsolidation, and extinction of these memories. Additional research elucidating the specific signaling pathways, mechanisms of synaptic plasticity, and epigenetic regulation of gene expression in the circuits involved in associative learning will reveal more distinctions between consolidation, reconsolidation, and extinction learning that can be applied to the treatment of substance use disorders.

Basolateral amygdala is required for reconsolidation updating of heroin-associated memory after prolonged withdrawal

Postretrieval extinction procedures are effective nonpharmacological interventions for disrupting drug-associated memories. Nonetheless, the conditioned stimulus (CS) memory retrieval-extinction procedure is ineffective in inhibiting drug craving and relapse after prolonged withdrawal, which significantly undermines its therapeutic potential. In the present study, we showed that, unlike the CS memory retrieval-extinction procedure, noncontingent heroin injections (unconditioned stimulus [UCS]) 1 hour before the extinction sessions decreased the heroin-priming-induced reinstatement, renewal, and spontaneous recovery of heroin seeking after 28 days of withdrawal (ie, remote heroin-associated memories) in rats. The UCS retrieval manipulation induced reactivation of the basolateral amygdala (BLA) after prolonged withdrawal, and this reactivation was absent with the CS retrieval manipulation. Chemogenetic inactivation of the BLA abolished the inhibitory effect of the UCS memory retrieval-extinction procedure on heroin-priming-induced reinstatement after prolonged withdrawal. Furthermore, the combination of chemogenetic reactivation of BLA and CS retrieval-extinction procedure resembled the inhibitory effect of UCS retrieval-extinction procedure on heroin seeking after prolonged withdrawal. We also observed that the inhibitory effect of the UCS retrieval-extinction procedure is mediated by regulation of AMPA receptor endocytosis in the BLA. Our results demonstrate critical engagement of the BLA in reconsolidation updating of heroin-associated memory after prolonged withdrawal, extending our knowledge of the boundary conditions of the reconsolidation of drug-associated memories.

Berberine Facilitates Extinction of Drug-Associated Behavior and Inhibits Reinstatement of Drug Seeking

A high rate of relapse is a major clinical problem among drug-addicted individuals. Persistent traces of drug-associated reward memories contribute to intense craving and often trigger relapse. A number of interventions on drug-associated memories have shown significant benefits in relapse prevention. Among them are pre- or post-extinction pharmacological manipulations that facilitate the extinction of drug-associated behavior. Berberine, a bioactive isoquinoline alkaloid, has been recently reported to provide therapeutic benefits for a number of central nervous system (CNS) disorders, including morphine addiction. The present study aimed to investigate whether berberine could serve as a post-extinction pharmacological intervention agent to reduce risks of reinstatement of drug seeking. We found that an intragastric administration of berberine at doses of 25 and 50 mg/kg during the critical time window significantly facilitated the extinction of morphine-reward related behavior in free access and confined conditioned place preference (CPP) extinction paradigms, and subsequently, it prevented reinstatement and spontaneous recovery of morphine-induced CPP in mice. Intriguingly, the berberine treatment with or without extinction training altered expression of plasticity-related proteins such as brain-derived neurotrophic factor (BDNF), AMPA receptors (GluA1 and GluA2) in the nucleus accumbens (NAc). Moreover, the post-extinction berberine treatment significantly reduced reinstatement of cocaine-induced CPP and operant intravenous self-administration (IVSA) memories in rats. Altogether, our findings suggest that extinction training combined with the post-extinction berberine treatment can facilitate extinction of drug-associated behavior making it an attractive therapeutic candidate in relapse prevention.

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.

Pi4KIIα Regulates Unconditioned Stimulus-Retrieval-Induced Fear Memory Reconsolidation through Endosomal Trafficking of AMPA Receptors

Targeting memory reconsolidation is an effective intervention for treating posttraumatic stress disorder (PTSD). Disrupting unconditioned stimulus (US)-retrieval-induced fear memory reconsolidation has become an effective therapeutic approach to attenuate fear memory, but the underlying molecular mechanisms remain unknown. Here, we report that US-retrieval-dependent increase in phosphatidylinositol 4-kinase IIα (Pi4KIIα) promotes early endosomal trafficking of AMPA receptors, leading to the enhancement of synaptic efficacy in basolateral amygdala (BLA) neurons. The inhibition of Pi4KIIα by an inhibitor or short hairpin RNA impaired contextual fear memory reconsolidation. This disruptive effect persisted for at least 2 weeks, which was restored by Pi4KIIα overexpression with TAT-Pi4KIIα. Furthermore, the blockade of early endosomal trafficking following US retrieval reduced synaptosomal membrane GluA1 levels and decreased subsequent fear expression. These data demonstrate that Pi4KIIα in the BLA is crucial for US-retrieval-induced fear memory reconsolidation, the inhibition of which might be an effective therapeutic strategy for treating PTSD.

•

Unconditioned stimulus (US) retrieval induces a transient increase in Pi4KIIα expression

•

Pi4KIIα regulates early endosomal trafficking of AMPARs during memory reconsolidation

•

Pi4KIIα contributes to US-retrieval-induced synaptic enhancement in rat BLA

•

Pi4KIIα inhibition after US retrieval impairs fear expression and shows long-term effects

Reactivation of the Unconditioned Stimulus Inhibits the Return of Fear Independent of Cortisol

Reconsolidation is the post-retrieval stabilization of memories, a time-limited process during which reactivated (i.e., retrieved) memories can be updated with new information, become stronger or weaker, depending on the specific treatment. We have previously shown that the stress hormone cortisol has an enhancing effect on the reconsolidation of fear memories in men. This effect was specific, i.e., limited to the conditioned stimulus (CS) that was reactivated, and did not generalize to other previously reinforced, but not reactivated CS. Based on these results, we suggested that cortisol plays a critical role in the continuous strengthening of reactivated emotional memories, contributing to their persistence and robustness. In the current study, we aimed to achieve a more generalized reconsolidation enhancement using an alternative reactivation method, i.e., by a low-intensity unconditioned stimulus (UCS) presentation instead of the more common unreinforced CS presentation. In previous studies, UCS reactivation was shown to lead to a more generalized reconsolidation effect. Therefore, we hypothesized that the combination of cortisol treatment and UCS reactivation would lead to an enhanced fear memory reconsolidation, which would generalize from previously reinforced CS to stimuli that resemble it. We tested 75 men in a 3-day fear conditioning paradigm: fear acquisition training on day 1; UCS reactivation/no reactivation and pharmacological treatment (20 mg hydrocortisone/placebo) on day 2; extinction training, reinstatement and test (of original and modified stimuli) on day 3. In contrast to our hypothesis, UCS reactivation prevented the return of fear [observed in skin conductance responses (SCR)] regardless of the pharmacological manipulation: while reinstatement to the original CS was found in the no-reactivation group, both reactivation groups (cortisol and placebo) showed no reinstatement. As the only methodological difference between our previous study and the current one was the reactivation method, we focus on UCS reactivation as the main explanation for these unexpected findings. We suggest that the robust prediction error generated by the UCS reactivation method (as opposed to CS reactivation), combined with the lower UCS intensity, has by itself weakened the emotional value of the UCS, thus preventing the return of fear to the CS that was associated with it. We call for future research to support these findings and to examine the potential of this reactivation method, or variations thereof, as a tool for therapeutic use.

On the Resistance to Relapse to Cocaine-Seeking Following Impairment of Instrumental Cocaine Memory Reconsolidation

Reconsolidation normally functions to update and maintain memories in the long-term. However, this process can be disrupted pharmacologically to weaken memories. Exploiting such experimental amnesia to disrupt the maladaptive reward memories underpinning addiction may provide a novel therapeutic avenue to prevent relapse. Here, we tested whether targeted disruption of the reconsolidation of instrumental (operant) lever pressing for cocaine resulted in protection against different forms of relapse in a rat self-administration model. We first confirmed that systemic injection of the non-competitive N-methyl–D-aspartate receptor (NMDAR) antagonist MK-801 did impair reconsolidation to reduce spontaneous instrumental drug-seeking memory at test. This deficit was not rescued by pharmacological induction of stress with the anxiogenic α₂-noradrenergic receptor antagonist yohimbine. In contrast, cocaine-seeking was restored to control levels following priming with cocaine itself, or presentation of a cocaine-associated cue. These results suggest that while stress-induced relapse can be reduced by disruption of instrumental memory reconsolidation, the apparent sparing of the pavlovian cue-drug memory permitted other routes to relapse. Therefore, future reconsolidation-based therapeutic strategies for addictive drug-seeking may need to target both instrumental and pavlovian memories.

Post-retrieval Extinction Prevents Reconsolidation of Methamphetamine Memory Traces and Subsequent Reinstatement of Methamphetamine Seeking

Methamphetamine abuse has become a serious public health problem. However, effective treatment for methamphetamine addiction remains elusive, especially considering its high rate of relapse after treatment. A conditioned stimulus (CS) memory retrieval–extinction procedure has been demonstrated to decrease reinstatement of cocaine, heroin, and alcohol seeking in rats, and to reduce cue-induced cravings in heroin and nicotine addicts. The goal of the present study is to explore the effect of the CS memory retrieval–extinction procedure on methamphetamine seeking in rats and the underlying mechanisms. We found that daily retrieval of methamphetamine-associated memories 1 h before extinction sessions decreased subsequent drug priming-induced reinstatement, spontaneous recovery, and renewal of methamphetamine seeking. We also found that retrieval of methamphetamine-associated memories induced neuronal activation in the basolateral amygdala (BLA), while presenting extinction within the time window of reconsolidation abolished the neuronal activation in BLA. These results indicate that the CS memory retrieval–extinction procedure could prevent reconsolidation of methamphetamine memory traces in BLA and subsequent methamphetamine craving and relapse.

Ants learn fast and do not forget: associative olfactory learning, memory and extinction in Formica fusca

Learning is a widespread phenomenon that allows behavioural flexibility when individuals face new situations. However, learned information may lose its value over time. If such a memory endures, it can be deleterious to individuals. The process of extinction allows memory updating when the initial information is not relevant anymore. Extinction is widespread among animals, including humans. We investigated associative appetitive learning in an ant species that is widely distributed in the Northern Hemisphere, Formica fusca. We studied acquisition and memory between 1 h and one week after conditioning, as well as the extinction process. Ants learn very rapidly, their memory lasts up to 3 days, decreases slowly over time and is highly resistant to extinction, even after a single conditioning trial. Using a pharmacological approach, we show that this single-trial memory critically depends on protein synthesis (long-term memory). These results indicate that individual ant workers of F. fusca show remarkable learning and memory performances. Intriguingly, they also show a strong resistance to updating learned associations. Resistance to extinction may be advantageous when the environment is stochastic and individuals need to switch often from one learned task to another.

Neurochemical and molecular mechanisms underlying the retrieval-extinction effect

Extinction within the reconsolidation window, or 'retrieval-extinction', has received much research interest as a possible technique for targeting the reconsolidation of maladaptive memories with a behavioural intervention. However, it remains to be determined whether the retrieval-extinction effect-a long-term reduction in fear behaviour, which appears resistant to spontaneous recovery, renewal and reinstatement-depends specifically on destabilisation of the original memory (the 'reconsolidation-update' account) or represents facilitation of an extinction memory (the 'extinction-facilitation' account). We propose that comparing the neurotransmitter systems, receptors and intracellular signalling pathways recruited by reconsolidation, extinction and retrieval-extinction will provide a way of distinguishing between these accounts.