How contexts promote and prevent relapse to drug seeking

Unlocking the role of dorsal hippocampal α4β2 nicotinic acetylcholine receptors in Ethanol-Induced conditioned place preference in mice

Alcohol Use Disorder (AUD) presents a significant and challenging public health concern, marked by a dearth of effective pharmacological treatments. Understanding the neurobiological underpinnings of AUD is of paramount importance for the development of efficacious interventions. The process of addiction entails the acquisition of associative behaviors, prominently engaging the dorsal region of the hippocampus for encoding these associative memories. Nicotinic receptor systems have been implicated in mediating the rewarding effects of ethanol, as well as memory and learning processes. In our current investigation, we delved into the role of α4β2 nicotinic acetylcholine receptors (nAChRs) within the dorsal hippocampus in the context of ethanol-induced conditioned place preference (CPP), a robust model for scrutinizing the rewarding properties and drug-associated behaviors. To establish CPP, ethanol (2 g/kg) was administered intraperitoneally during a 8-day conditioning phase. Fos immunohistochemistry was employed to assess the involvement of discrete subregions within the dorsal hippocampus in ethanol-induced CPP. Additionally, we probed the influence of α4β2 nAChRs on CPP via microinjections of a selective nAChR antagonist, dihydro-β-erythroidine (DHBE, at dosages of 6, 12, and 18 µg/0.5 µL per hemisphere) within the hippocampus. Our results unveiled that ethanol-induced CPP was associated with an increase Fos -positive cells in various subregions of the dorsal hippocampus, including CA1, CA2, CA3, and the dentate gyrus. Intrahippocampal administration of DHBE (at doses of 6 and 18 µg/0.50 µL per hemisphere) effectively blocked ethanol-induced CPP, while leaving locomotor activity unaffected. These findings underscore the critical involvement of the dorsal hippocampus and α4β2 nAChRs in the acquisition of ethanol-associated learning and reward.

Cocaine reward and reinstatement in adolescent versus adult rodents

Adolescence is a critical juncture when initiation of drug use intersects with profound developmental changes in the brain. Adolescent drug use increases the risk to develop substance use disorders (SUDs) later in life, but the mechanisms that confer this vulnerability are not understood. SUDs are defined by cycles of use, abstinence, and relapse. Intense craving during drug-free periods is often triggered by cues and environmental contexts associated with previous use. In contrast to our understanding of stimuli that elicit craving and relapse in adults, the behavioral processes that occur during periods of abstinence and relapse in adolescents are poorly understood. The current mini-review will summarize findings from preclinical rodent studies that used cocaine conditioned place preference and operant cocaine self-administration to examine subsequent effects on reward, relapse and incubation of craving.

Influence of reconsolidation in maintenance of cocaine-associated contextual memories formed during adolescence or adulthood

Adolescents are at increased risk to develop substance use disorders and suffer from relapse throughout life. Targeted weakening of drug-associated memories has been shown to reduce relapse-like behavior in adult rats, however this process has been understudied in adolescents. We aimed to examine whether adolescent-formed, cocaine-associated memories could be manipulated via reconsolidation mechanisms. To accomplish this objective, we used an abbreviated operant cocaine self-administration paradigm (ABRV Coc-SA). Adult and adolescent rats received jugular catheterization surgery followed by ABRV Coc-SA in a distinct context for 2 h, 2×/day over 5 days. Extinction training (EXT) occurred in a second context for 2 h, 2×/day over 4 days. To retrieve cocaine-context memories, rats were exposed to the cocaine-paired context for 15 min, followed by subcutaneous injection of vehicle or the protein synthesis inhibitor cycloheximide (2.5 mg/kg). Two additional EXT sessions were conducted before a 2 h reinstatement test in the cocaine-paired context to assess cocaine-seeking behavior. We find that both adult and adolescent cocaine-exposed rats show similar levels of cocaine-seeking behavior regardless of post-reactivation treatment. Our results suggest that systemic treatment with the protein synthesis inhibitor cycloheximide does not impair reconsolidation of cocaine-context memories and subsequent relapse during adulthood or adolescence.

Role of Piriform Cortex and Its Afferent Projections in Relapse to Fentanyl Seeking after Food Choice-Induced Voluntary Abstinence

We previously demonstrated a role of piriform cortex (Pir) in relapse to fentanyl seeking after food choice-induced voluntary abstinence. Here, we used this model to further study the role of Pir and its afferent projections in fentanyl relapse. We trained male and female rats to self-administer palatable food pellets for 6 d (6 h/day) and fentanyl (2.5 µg/kg/infusion, i.v.) for 12 d (6 h/day). We assessed relapse to fentanyl seeking after 12 voluntary abstinence sessions, achieved through a discrete choice procedure between fentanyl and palatable food (20 trials/session). We determined projection-specific activation of Pir afferents during fentanyl relapse with Fos plus the retrograde tracer cholera toxin B (injected into Pir). Fentanyl relapse was associated with increased Fos expression in anterior insular cortex (AI) and prelimbic cortex (PL) neurons projecting to Pir. We next used an anatomical disconnection procedure to determine the causal role of these two projections (AI→Pir and PL→Pir) in fentanyl relapse. Contralateral but not ipsilateral disconnection of AI→Pir projections decreased fentanyl relapse but not reacquisition of fentanyl self-administration. In contrast, contralateral but not ipsilateral disconnection of PL→Pir projections modestly decreased reacquisition but not relapse. Fluorescence-activated cell sorting and quantitative PCR data showed molecular changes within Pir Fos-expressing neurons associated with fentanyl relapse. Finally, we found minimal or no sex differences in fentanyl self-administration, fentanyl versus food choice, and fentanyl relapse. Our results indicate that AI→Pir and PL→Pir projections play dissociable roles in nonreinforced relapse to fentanyl seeking versus reacquisition of fentanyl self-administration after food choice-induced voluntary abstinence.SIGNIFICANCE STATEMENT We previously showed a role of Pir in fentanyl relapse after food choice-induced voluntary abstinence in rats, a procedure mimicking human abstinence or a significant reduction in drug self-administration because of the availability of alternative nondrug rewards. Here, we aimed to further characterize the role of Pir in fentanyl relapse by investigating the role of Pir afferent projections and analyzing molecular changes in relapse-activated Pir neurons. We identified dissociable roles of two Pir afferent projections (AI→Pir and PL→Pir) in relapse to fentanyl seeking versus reacquisition of fentanyl self-administration after voluntary abstinence. We also characterized molecular changes within Pir Fos-expressing neurons associated with fentanyl relapse.

Effect of Selective Lesions of Nucleus Accumbens µ-Opioid Receptor-Expressing Cells on Heroin Self-Administration in Male and Female Rats: A Study with Novel Oprm1-Cre Knock-in Rats

The brain µ-opioid receptor (MOR) is critical for the analgesic, rewarding, and addictive effects of opioid drugs. However, in rat models of opioid-related behaviors, the circuit mechanisms of MOR-expressing cells are less known because of a lack of genetic tools to selectively manipulate them. We introduce a CRISPR-based Oprm1-Cre knock-in transgenic rat that provides cell type-specific genetic access to MOR-expressing cells. After performing anatomic and behavioral validation experiments, we used the Oprm1-Cre knock-in rats to study the involvement of NAc MOR-expressing cells in heroin self-administration in male and female rats. Using RNAscope, autoradiography, and FISH chain reaction (HCR-FISH), we found no differences in Oprm1 expression in NAc, dorsal striatum, and dorsal hippocampus, or MOR receptor density (except dorsal striatum) or function between Oprm1-Cre knock-in rats and wildtype littermates. HCR-FISH assay showed that iCre is highly coexpressed with Oprm1 (95%-98%). There were no genotype differences in pain responses, morphine analgesia and tolerance, heroin self-administration, and relapse-related behaviors. We used the Cre-dependent vector AAV1-EF1a-Flex-taCasp3-TEVP to lesion NAc MOR-expressing cells. We found that the lesions decreased acquisition of heroin self-administration in male Oprm1-Cre rats and had a stronger inhibitory effect on the effort to self-administer heroin in female Oprm1-Cre rats. The validation of an Oprm1-Cre knock-in rat enables new strategies for understanding the role of MOR-expressing cells in rat models of opioid addiction, pain-related behaviors, and other opioid-mediated functions. Our initial mechanistic study indicates that lesioning NAc MOR-expressing cells had different effects on heroin self-administration in male and female rats.SIGNIFICANCE STATEMENT The brain µ-opioid receptor (MOR) is critical for the analgesic, rewarding, and addictive effects of opioid drugs. However, in rat models of opioid-related behaviors, the circuit mechanisms of MOR-expressing cells are less known because of a lack of genetic tools to selectively manipulate them. We introduce a CRISPR-based Oprm1-Cre knock-in transgenic rat that provides cell type-specific genetic access to brain MOR-expressing cells. After performing anatomical and behavioral validation experiments, we used the Oprm1-Cre knock-in rats to show that lesioning NAc MOR-expressing cells had different effects on heroin self-administration in males and females. The new Oprm1-Cre rats can be used to study the role of brain MOR-expressing cells in animal models of opioid addiction, pain-related behaviors, and other opioid-mediated functions.

Context-drug-associations and reinstatement of drug-seeking behavior in male rats: Adolescent and adult time-dependent effects

RATIONALE

Drug use during adolescence results in a life-long risk to develop substance-use disorders. Adolescent rats are sensitive to different drug-associated cues, compared to adults; however, the contribution of adolescent-formed context-drug-associations to elicit relapse-like behavior is underexplored.

OBJECTIVES

The present study compared the effect of adolescent vs adult-formed context-drug associations to elicit time-dependent increases in cocaine-seeking behavior. This objective was accomplished using an abbreviated (ABRV) operant cocaine self-administration (Coc-SA), Extinction (EXT) paradigm, with cocaine-seeking tests occurring 1 day after training (T1, early relapse) or following 15 days of abstinence (T15, late relapse).

METHODS

Adolescent and adult rats received ABRV Coc-SA in a distinct context (2 hr, 2x/day over 5 days) then EXT in a second context (2 hr, 2x/day over 4 days). Adolescent or adult cocaine-exposed rats were then tested (2 hr, non-rewarded) in either the previous EXT or Coc-paired contexts during early or late relapse.

RESULTS & CONCLUSIONS

As previously reported, both adolescent and adult cocaine-exposed rats displayed similar magnitudes of cocaine intake and lever presses during Coc-SA, EXT, and early relapse. Independent analysis of adolescent and adult groups revealed differences in lever responding, specifically rats with cocaine exposure during adolescence showed time-dependent increases in lever responding during late relapse. These data suggest that cocaine-context associations formed during adolescence can elicit craving during adulthood and that these age-specific differences in contextual sensitivity may not be immediately observed at early relapse periods.

The intersection of empathy and addiction

Empathy, the ability to perceive the affective state of another, is a complex process that is integral to many of the prosocial behaviors expressed in humans and across the animal kingdom. Research into the behavioral and neurobiological underpinnings of empathic behaviors has increased in recent years. Growing evidence suggests changes in empathy may contribute to a myriad of psychiatric illnesses, including substance use disorder (SUD). Indeed, both clinical and preclinical research in SUD demonstrates a strong relationship between drug taking or relapse events and changes to empathic behavior. Further, there is significant overlap in the underlying neural substrates of these complex behaviors, including the insula, paraventricular nucleus of thalamus (PVT), and the paraventricular nucleus of the hypothalamus (PVN). In this review, we will discuss our current understanding of the interplay between empathic behaviors and SUD. We will also examine the underlying neurobiology that may regulate this interaction, focusing specifically on the insula, PVT, and PVN. Finally, we discuss the biologic and therapeutic importance of taking empathic processes into consideration when discussing SUD.

Can we enhance the clinical efficacy of cognitive and psychological approaches to treat substance use disorders through understanding their neurobiological mechanisms?

Despite decades of research in the field of addiction, relapse rates for substance use disorders remain high. Consequently, there has been growing focus on providing evidence-based treatments for substance use disorders, resulting in the increased development and use of cognitive and psychological interventions. Such treatment approaches, including contingency management, community-reinforcement approach, and cognitive bias modification, have shown promising clinical efficacy in reducing substance use and promoting abstinence during treatment. However, these interventions are still somewhat limited in achieving sustained periods of abstinence post-treatment. The neurobiological mechanisms underpinning these treatment approaches remain largely unknown and under-studied, in part, due to a lack of translational animal models. The adoption of a reverse translational approach may assist in development of more representative models that can facilitate elucidation of the mechanisms behind these clinically relevant interventions. This review examines our current understanding of addiction neurobiology from clinical, preclinical research and existing animal models, and considers how the efficacy of such behavioral-oriented interventions alone, or in combination with pharmacotherapy, may be enhanced to improve treatment outcomes.

Brief Environmental Enrichment exposure enhances contextual-induced sucrose-seeking with and without memory reactivation in rats

Chronic Environmental Enrichment (EE) has been shown to prevent the relapse to addictive behaviours, such as drug-taking and -seeking. Recently, acute EE was shown to reduce cue-induced sucrose-seeking, but its effects on contextual (Cx)-induced sucrose-seeking is still unknown. Here we report the effects of brief EE exposure on Cx-induced sucrose-seeking with and without prior Cx-memory reactivation. Adult male Sprague-Dawley rats were trained to sucrose self-administration associated to a specific conditioning Cx (CxA), followed by a 7-day extinction in a different Cx (CxB). Afterwards, rats were exposed for 22 h to EE, and 1 h later to either i) Cx-induced sucrose-seeking (1 h, renewal without Cx-memory reactivation), ii) or two different Cx-memory reactivations: short (2-min) and long (15-min) CxA-retrieval session (Cx-Ret). In Cx-Ret experiments, CxA-induced sucrose-seeking test (1 h) was done after a subsequent 3-day extinction phase. The assessment of molecular markers of memory reactivation/reconsolidation, Zif-268 and rpS6P, was performed 2 h after Cx-Ret. Brief EE exposure enhanced Cx-induced sucrose-seeking without and with short but not long Cx-retrieval. Moreover, EE impaired discriminative responding at test prior to long, whereas improved it with or without short Cx-retrieval. Different changes in Zif-268 and rpS6P expression induced by short vs. long Cx-Ret were correlated to behavioural data, suggesting the occurrence of different memory processes affected by EE. Our data show that brief EE exposure may differently affect subsequent appetitive relapse depending on the modality of re-exposure to conditioned context. This finding suggests caution and further studies to understand the proper conditions for the use of EE against appetitive and addiction disorders.

The interaction between Environmental Enrichment and fluoxetine in inhibiting sucrose-seeking renewal in mice depend on social living condition

RATIONALE

Several single or combined therapeutic approaches have been developed to treat addiction, however with partial efficacy in preventing relapse. Recently, the living environment has been suggested as a critical intervening factor determining the treatment outcomes. Despite accumulating evidence confirming a role of living conditions in the vulnerability to addictive behaviours, their impact on single or integrative therapeutic strategies preventing relapse is yet to be identified.

OBJECTIVES

Here, we explore the possible interaction between brief Environmental Enrichment (EE) exposure and acute fluoxetine administration in inhibiting sucrose-seeking behaviours, and whether this effect could be affected by living environment.

METHODS

Social and isolated adult male C57BL/6 mice were trained to sucrose self-administration associated to a specific conditioning context (CxA), followed by a 7-day extinction in a different context (CxB). Afterwards, mice were exposed for 22 h to EE and then injected with fluoxetine (10 mg/kg, i.p.) 1 h before a CxA-induced sucrose-seeking test.

RESULTS

Brief EE exposure and acute fluoxetine administration alone inhibited context-induced sucrose-seeking in both housing conditions; however, they exhibited additive properties only in social condition.

CONCLUSIONS

Our data show that social environment may influence the EE/fluoxetine interaction in inhibiting relapse to sucrose. These findings suggest that setting up proper living conditions to boost the efficacy of therapeutic approaches may represent a fundamental strategy to treat addiction disorders.

Inactivation of the infralimbic cortex decreases discriminative stimulus-controlled relapse to cocaine seeking in rats

Persistent susceptibility to cue-induced relapse is a cardinal feature of addiction. Discriminative stimuli (DSs) are one type of drug-associated cue that signal drug availability (DS+) or unavailability (DS-) and control drug seeking prior to relapse. We previously established a trial-based procedure in rats to isolate DSs from context, conditioned stimuli, and other drug-associated cues during cocaine self-administration and demonstrated DS-controlled cocaine seeking up to 300 abstinence days. The behavioral and neural mechanisms underlying trial-based DS-control of drug seeking have rarely been investigated. Here we show that following discrimination training in our trial-based procedure, the DS+ and DS- independently control the expression and suppression of cocaine seeking during abstinence. Using microinjections of GABA_A + GABA_B receptor agonists (muscimol + baclofen) in medial prefrontal cortex, we report that infralimbic, but not prelimbic, subregion of medial prefrontal cortex is critical to persistent DS-controlled relapse to cocaine seeking after prolonged abstinence, but not DS-guided discriminated cocaine seeking or DS-controlled cocaine self-admininstration. Finally, using ex vivo whole-cell recordings from pyramidal neurons in the medial prefrontal cortex, we demonstrate that the disruption of DS-controlled cocaine seeking following infralimbic cortex microinjections of muscimol+baclofen is likely a result of suppression of synaptic transmission in the region via a presynaptic mechanism of action.

Ventral pallidum cellular and pathway specificity in drug seeking

The ventral pallidum (VP) is central to the reinforcing effects across a variety of drugs and relapse to drug seeking. Emerging studies from animal models of reinstatement reveal a complex neurobiology of the VP that contributes to different aspects of relapse to drug seeking. This review builds on classical understanding of the VP as part of the final common pathway of relapse but also discusses the properties of the VP as an independent structure. These include VP neural anatomical subregions, cellular heterogeneity, circuitry, neurotransmitters and peptides. Collectively, this review provides a current understanding of the VP from molecular to circuit level architecture that contributes to both the appetitive and aversive symptoms of drug addiction. We show the complex neurobiology of the VP in drug seeking, emphasizing its critical role in addiction, and review strategic approaches that target the VP to reduce relapse rates.

Sex differences in the effect of chronic delivery of the buprenorphine analogue BU08028 on heroin relapse and choice in a rat model of opioid maintenance

BACKGROUND AND PURPOSE

Maintenance treatment with opioid agonists (buprenorphine, methadone) decreases opioid use and relapse. We recently modelled maintenance treatment in rats and found that chronic delivery of buprenorphine or the μ opioid receptor partial agonist TRV130 decreased relapse to oxycodone seeking and taking. Here, we tested the buprenorphine analogue BU08028 on different heroin relapse-related measures and heroin versus food choice.

EXPERIMENTAL APPROACH

For relapse assessment, we trained male and female rats to self-administer heroin (6 h·day^-1 , 14 days) in Context A and then implanted osmotic minipumps containing BU08028 (0, 0.03 or 0.1 mg·kg^-1 ·d^-1 ). Effects of chronic BU08028 delivery were tested on (1) incubation of heroin-seeking in a non-drug Context B, (2) extinction responding reinforced by heroin-associated discrete cues in Context B, (3) reinstatement of heroin-seeking induced by re-exposure to Context A and (4) re-acquisition of heroin self-administration in Context A. For choice assessment, we tested the effect of chronic BU08028 delivery on heroin versus food choice.

KEY RESULTS

Chronic BU08028 delivery decreased incubation of heroin seeking. Unexpectedly, BU08028 increased re-acquisition of heroin self-administration selectively in females. Chronic BU08028 had minimal effects on context-induced reinstatement and heroin versus food choice in both sexes. Finally, exploratory post hoc analyses suggest that BU08028 decreased extinction responding selectively in males.

CONCLUSIONS AND IMPLICATIONS

Chronic BU08028 delivery had both beneficial and detrimental, sex-dependent, effects on different triggers of heroin relapse and minimal effects on heroin choice in both sexes. Results suggest that BU08028 would not be an effective opioid maintenance treatment in humans.

Choose your path: Divergent basolateral amygdala efferents differentially mediate incentive motivation, flexibility and decision-making

To survive in a complex environment, individuals form associations between environmental stimuli and rewards to organize and optimize reward seeking behaviors. The basolateral amygdala (BLA) uses these learned associations to inform decision-making processes. In this review, we describe functional projections between BLA and its cortical and striatal targets that promote learning and motivational processes central to decision-making. Specifically, we compare and contrast divergent projections from the BLA to the orbitofrontal (OFC) and to the nucleus accumbens (NAc) and examine the roles of these pathways in associative learning, value-guided decision-making, choice behaviors, as well as cue and context-driven drug seeking. Finally, we consider how these projections are involved in disorders of motivation, with a focus on Substance Use Disorder.

Cognition in the Chronic Pain Experience: Preclinical Insights

Acutely, pain is protective. It promotes escape from, and future avoidance of, noxious stimuli through strong and often lifetime associative memories. However, with persistent acute pain or when pain becomes chronic, these memories can promote negative emotions and poor decisions often associated with deleterious behaviors. In this review, we discuss how preclinical studies can provide insights into the relationship between cognition and chronic pain. We also discuss the concept of pain as a cognitive disorder and new strategies for treating chronic pain that emphasize inhibiting the formation of pain memories or promoting 'forgetting' of established pain memories.

BEHAVIORAL AND NEUROBIOLOGICAL MECHANISMS OF PAVLOVIAN AND INSTRUMENTAL EXTINCTION LEARNING

This article reviews the behavioral neuroscience of extinction, the phenomenon in which a behavior that has been acquired through Pavlovian or instrumental (operant) learning decreases in strength when the outcome that reinforced it is removed. Behavioral research indicates that neither Pavlovian nor operant extinction depends substantially on erasure of the original learning but instead depends on new inhibitory learning that is primarily expressed in the context in which it is learned, as exemplified by the renewal effect. Although the nature of the inhibition may differ in Pavlovian and operant extinction, in either case the decline in responding may depend on both generalization decrement and the correction of prediction error. At the neural level, Pavlovian extinction requires a tripartite neural circuit involving the amygdala, prefrontal cortex, and hippocampus. Synaptic plasticity in the amygdala is essential for extinction learning, and prefrontal cortical inhibition of amygdala neurons encoding fear memories is involved in extinction retrieval. Hippocampal-prefrontal circuits mediate fear relapse phenomena, including renewal. Instrumental extinction involves distinct ensembles in corticostriatal, striatopallidal, and striatohypothalamic circuits as well as their thalamic returns for inhibitory (extinction) and excitatory (renewal and other relapse phenomena) control over operant responding. The field has made significant progress in recent decades, although a fully integrated biobehavioral understanding still awaits.

Dorsal hippocampus plays a causal role in context-induced reinstatement of alcohol-seeking in rats

Drug addiction is a chronic mental disorder characterized by frequent relapses. Contextual cues associated with drug use to play a critical causal role in drug-seeking behavior. The hippocampus has been implicated in encoding drug associative memories. Here we examine whether the dorsal hippocampus mediates context-induced reinstatement of alcohol-seeking. Male Long-Evans rats were trained to self-administer alcohol in Context A. Alcohol self-administration was extinguished in a distinct context (Context B). On the test day, animals were re-exposed to the alcohol Context A or the extinction Context B. Next, to assess a causal role for the dorsal hippocampus in context-induced alcohol-seeking, on the test day, we injected cobalt chloride (CoCl2; a nonselective synapse inhibitor) or vehicle into the dorsal hippocampus, and 15 min later, rats were tested by re-exposing them to the drug-associated context. The re-exposure to the alcohol-associated Context A reinstated alcohol seeking and increased Fos-positive cells in the dorsal hippocampus neurons (CA1, CA3, and Dentate Gyrus). Pharmacological inactivation with cobalt chloride of the dorsal hippocampus attenuated the reinstatement of alcohol-seeking. Our data suggest that the dorsal hippocampus may be involved in context-induced alcohol-seeking behavior.

Role of adolescent-formed, context-drug-associations on reinstatement of drug-seeking behavior in rats

RATIONALE

Drug use during adolescence results in a lifelong risk to develop substance-use disorders. Adolescent rats are less reactive to cocaine-associated cues compared with adults; however, the contribution of adolescent-formed, context-drug-associations to elicit relapse-like behavior is underexplored. Although it is known that social isolation can impact drug-seeking behavior, the effects of housing conditions on context-induced, cocaine-seeking during adolescence vs adulthood are unknown.

OBJECTIVES

The present study compared the effect of adolescent vs adult-formed context-drug associations under different housing conditions (pair vs single) on cocaine-seeking behavior during adolescence or adulthood. This objective was accomplished using operant cocaine self-administration (Coc-SA) under a standard, non-abbreviated (Non-ABRV) or modified abbreviated (ABRV) paradigm.

METHODS

In experiment 1, adolescent and adult rats received Non-ABRV Coc-SA in a distinct context (2 h, 1×/day, 10 days), and extinction training (EXT) in a second context (1 h, 1×/day, 8 days) with reinstatement test (TEST) during adulthood in the cocaine-paired context. In experiments 2 and 3, rats received all behavioral phases during adolescence or adulthood: ABRV Coc-SA (2 h, 2×/day, 5 days), EXT (1 h, 4×/day, 2 days) with TEST in a cocaine-paired or novel, unpaired context. All experiments included pair and single-housing conditions.

RESULTS AND CONCLUSIONS

Age at cocaine exposure did not influence behavior in Non-ABRV or ABRV paradigms. Under Non-ABRV conditions, adolescent and adult single-housed rats had higher seeking behavior than pair housed. These data suggest that social isolation influences context-induced, cocaine-seeking regardless of age at drug exposure and provides a condensed, ABRV paradigm to investigate context-induced, cocaine-seeking behavior during adolescence.

Maternal high-sugar diet changes offspring vulnerability to reinstatement of cocaine-seeking behavior: Role of melanocortin-4 receptors

Maternal diet significantly influences the proper development of offspring in utero. Modifications of diet composition may lead to metabolic and mental disorders that may predispose offspring to a substance use disorder. We assessed the impact of a maternal high-sugar diet (HSD, rich in sucrose) consumed during pregnancy and lactation on the offspring phenotype in the context of the rewarding and motivational effects of cocaine and changes within the central melanocortin (MC) system. Using an intravenous cocaine self-administration model, we showed that maternal HSD leads to increased relapse of cocaine-seeking behavior in male offspring. In addition, we demonstrated that cocaine induces changes in the level of MC-4 receptors in the offspring brain, and these changes depend on maternal diet. These studies also reveal that an MC-4 receptor antagonist reduces the reinstatement of cocaine-seeking behavior, and offspring exposed to maternal HSD are more sensitive to its effects than offspring exposed to the maternal control diet. Taken together, the results suggest that a maternal HSD and MC-4 receptors play an important role in cocaine relapse.

Complementary Roles for Ventral Pallidum Cell Types and Their Projections in Relapse

The ventral pallidum (VP) is a key node in the neural circuits controlling relapse to drug seeking. How this role relates to different VP cell types and their projections is poorly understood. Using male rats, we show how different forms of relapse to alcohol-seeking are assembled from VP cell types and their projections to lateral hypothalamus (LH) and ventral tegmental area (VTA). Using RNAScope in situ hybridization to characterize activity of different VP cell types during relapse to alcohol-seeking provoked by renewal (context-induced reinstatement), we found that VP Gad1 and parvalbumin (PV), but not vGlut2, neurons show relapse-associated changes in c-Fos expression. Next, we used retrograde tracing, chemogenetic, and electrophysiological approaches to study the roles of VPGad1 and VPPV neurons in relapse. We show that VPGad1 neurons contribute to contextual control over relapse (renewal), but not to relapse during reacquisition, via projections to LH, where they converge with ventral striatal inputs onto LHGad1 neurons. This convergence of striatopallidal inputs at the level of individual LHGad1 neurons may be critical to balancing propensity for relapse versus abstinence. In contrast, VPPV neurons contribute to relapse during both renewal and reacquisition via projections to VTA. These findings identify a double dissociation in the roles for different VP cell types and their projections in relapse. VPGad1 neurons control relapse during renewal via projections to LH. VPPV neurons control relapse during both renewal and reacquisition via projections to VTA. Targeting these different pathways may provide tailored interventions for different forms of relapse.SIGNIFICANCE STATEMENT Relapse to drug or reward seeking after a period of extinction or abstinence remains a key impediment to successful treatment. The ventral pallidum, located in the ventral basal ganglia, has long been recognized as an obligatory node in a 'final common pathway' for relapse. Yet how this role relates to the considerable VP cellular and circuit heterogeneity is not well understood. We studied the cellular and circuit architecture for VP in relapse control. We show that different forms of relapse have complementary VP cellular and circuit architectures, raising the possibility that targeting these different neural architectures may provide tailored interventions for different forms of relapse.

Vagus nerve stimulation during extinction learning reduces conditioned place preference and context-induced reinstatement of cocaine seeking

BACKGROUND

Drug use causes the formation of strong cue/reward associations which persist long after cessation of drug-taking and contribute to the long-term risk of relapse. Extinguishing these associations may reduce cue-induced craving and relapse. Previously, we found that pairing vagus nerve stimulation (VNS) with extinction of cocaine self-administration reduces cue-induced reinstatement; however, it remains unclear whether this was primarily caused by extinguishing the context, the instrumental response, or both.

OBJECTIVE

Hypothesis: We hypothesized that VNS can facilitate the extinction of both contextual cues and instrumental responding.

METHODS

Extinction of context was first tested using Pavlovian conditioned place preference (CPP). Next, the impact of VNS on the extinction of instrumental responding was assessed under ABA and AAA context conditions. In each extinction context separate groups of rats were either provided the opportunity to perform the instrumental response, or the levers were retracted for the duration of extinction training. Reinstatement was induced by reintroduction of the conditioned stimuli and/or the drug-paired context. Data were analyzed using one-way or two-way repeated measures ANOVAs.

RESULTS

VNS during extinction reduced reinstatement of CPP. VNS also reduced cue- and context-induced reinstatement of the instrumental response under both AAA and ABA conditions. The subjects' ability to engage with the lever during extinction was crucial for this effect. P values < 0.05 were considered significant.

CONCLUSIONS

Craving occurs in response to a range of conditioned stimuli and contexts; VNS may improve outcomes of behavioral therapy by facilitating extinction of both an instrumental response and/or contextual cues.

Occasion setting

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

Separate vmPFC Ensembles Control Cocaine Self-Administration Versus Extinction in Rats

Recent studies suggest that the ventral medial prefrontal cortex (vmPFC) encodes both operant drug self-administration and extinction memories. Here, we examined whether these opposing memories are encoded by distinct neuronal ensembles within the vmPFC with different outputs to the nucleus accumbens (NAc) in male and female rats. Using cocaine self-administration (3 h/d for 14 d) and extinction procedures, we demonstrated that vmPFC was similarly activated (indexed by Fos) during cocaine-seeking tests after 0 (no-extinction) or 7 extinction sessions. Selective Daun02 lesioning of the self-administration ensemble (no-extinction) decreased cocaine seeking, whereas Daun02 lesioning of the extinction ensemble increased cocaine seeking. Retrograde tracing with fluorescent cholera toxin subunit B injected into NAc combined with Fos colabeling in vmPFC indicated that vmPFC self-administration ensembles project to NAc core while extinction ensembles project to NAc shell. Functional disconnection experiments (Daun02 lesioning of vmPFC and acute dopamine D1-receptor blockade with SCH39166 in NAc core or shell) confirm that vmPFC ensembles interact with NAc core versus shell to play dissociable roles in cocaine self-administration versus extinction, respectively. Our results demonstrate that neuronal ensembles mediating cocaine self-administration and extinction comingle in vmPFC but have distinct outputs to the NAc core and shell that promote or inhibit cocaine seeking.SIGNIFICANCE STATEMENT Neuronal ensembles within the vmPFC have recently been shown to play a role in self-administration and extinction of food seeking. Here, we used the Daun02 chemogenetic inactivation procedure, which allows selective inhibition of neuronal ensembles identified by the activity marker Fos, to demonstrate that different ensembles for cocaine self-administration and extinction memories coexist in the ventral mPFC and interact with distinct subregions of the nucleus accumbens.

Role of prefrontal cortex in the extinction of drug memories

It has been recognized that drug addiction engages aberrant process of learning and memory, and substantial studies have focused on developing effective treatment to erase the enduring drug memories to reduce the propensity to relapse. Extinction, a behavioral intervention exposing the individuals to the drug-associated cues repeatedly, can weaken the craving and relapse induced by drug-associated cues, but its clinic efficacy is limited. A clear understanding of the neuronal circuitry and molecular mechanism underlying extinction of drug memory will facilitate the successful use of extinction therapy in clinic. As a key component of mesolimbic system, medial prefrontal cortex (mPFC) has received particular attention largely in that PFC stands at the core of neural circuits for memory extinction and manipulating mPFC influences extinction of drug memories and subsequent relapse. Here, we review the recent advances in both animal models of drug abuse and human addicted patients toward the understanding of the mechanistic link between mPFC and drug memory, with particular emphasis on how mPFC contributes to the extinction of drug memory at levels ranging from neuronal architecture, synaptic plasticity to molecular signaling and epigenetic regulation, and discuss the clinic relevance of manipulating the extinction process of drug memory to prevent craving and relapse through enhancing mPFC function.

Common neurocircuitry mediating drug and fear relapse in preclinical models

BACKGROUND

Comorbidity of anxiety disorders, stressor- and trauma-related disorders, and substance use disorders is extremely common. Moreover, therapies that reduce pathological fear and anxiety on the one hand, and drug-seeking on the other, often prove short-lived and are susceptible to relapse. Considerable advances have been made in the study of the neurobiology of both aversive and appetitive extinction, and this work reveals shared neural circuits that contribute to both the suppression and relapse of conditioned responses associated with trauma or drug use.

OBJECTIVES

The goal of this review is to identify common neural circuits and mechanisms underlying relapse across domains of addiction biology and aversive learning in preclinical animal models. We focus primarily on neural circuits engaged during the expression of relapse.

KEY FINDINGS

After extinction, brain circuits involving the medial prefrontal cortex and hippocampus come to regulate the expression of conditioned responses by the amygdala, bed nucleus of the stria terminalis, and nucleus accumbens. During relapse, hippocampal projections to the prefrontal cortex inhibit the retrieval of extinction memories resulting in a loss of inhibitory control over fear- and drug-associated conditional responding.

CONCLUSIONS

The overlapping brain systems for both fear and drug memories may explain the co-occurrence of fear and drug-seeking behaviors.

Preclinical studies of stress, extinction, and prefrontal cortex: intriguing leads and pressing questions

BACKGROUND

Stress is associated with cognitive and emotional dysfunction, and increases risk for a variety of psychological disorders, including depression and posttraumatic stress disorder. Prefrontal cortex is critical for executive function and emotion regulation, is a target for stress hormones, and is implicated in many stress-influenced psychological disorders. Extinction of conditioned fear provides an excellent model system for examining how stress-induced changes in corticolimbic structure and function are related to stress-induced changes in neural function and behavior, as the neural circuitry underlying this behavior is well characterized.

OBJECTIVES

This review examines how acute and chronic stress influences extinction and describes how stress alters the structure and function of the medial prefrontal cortex, a potential neural substrate for these effects. In addition, we identify important unanswered questions about how stress-induced change in prefrontal cortex may mediate extinction deficits and avenues for future research.

KEY FINDINGS

A substantial body of work demonstrates deficits in extinction after either acute or chronic stress. A separate and substantial literature demonstrates stress-induced neuronal remodeling in medial prefrontal cortex, along with several key neurohormonal contributors to this remodeling, and there is substantial overlap in prefrontal mechanisms underlying extinction and the mechanisms implicated in stress-induced dysfunction of-and neuronal remodeling in-medial prefrontal cortex. However, data directly examining the contribution of changes in prefrontal structure and function to stress-induced extinction deficits is currently lacking.

CONCLUSIONS

Understanding how stress influences extinction and its neural substrates as well as individual differences in this effect will elucidate potential avenues for novel interventions for stress-sensitive disorders characterized by deficits in extinction.

Modeling cocaine relapse in rodents: Behavioral considerations and circuit mechanisms

Addiction is a chronic relapsing disorder, in that most addicted individuals who choose to quit taking drugs fail to maintain abstinence in the long-term. Relapse is especially likely when recovering addicts encounter risk factors like small "priming" doses of drug, stress, or drug-associated cues and locations. In rodents, these same factors reinstate cocaine seeking after a period of abstinence, and extensive preclinical work has used priming, stress, or cue reinstatement models to uncover brain circuits underlying cocaine reinstatement. Here, we review common rat models of cocaine relapse, and discuss how specific features of each model influence the neural circuits recruited during reinstated drug seeking. To illustrate this point, we highlight the surprisingly specific roles played by ventral pallidum subcircuits in cocaine seeking reinstated by either cocaine-associated cues, or cocaine itself. One goal of such studies is to identify, and eventually to reverse the specific circuit activity that underlies the inability of some humans to control their drug use. Based on preclinical findings, we posit that circuit activity in humans also differs based on the triggers that precipitate craving and relapse, and that associated neural responses could help predict the triggers most likely to elicit relapse in a given person. If so, examining circuit activity could facilitate diagnosis of subgroups of addicted people, allowing individualized treatment based on the most problematic risk factors.

A Human Polymorphism in CHRNA5 Is Linked to Relapse to Nicotine Seeking in Transgenic Rats

Tobacco addiction is a chronic and relapsing disorder with an important genetic component that represents a major public health issue. Meta-analysis of large-scale human genome-wide association studies (GWASs) identified a frequent non-synonymous SNP in the gene coding for the α5 subunit of nicotinic acetylcholine receptors (α5SNP), which significantly increases the risk for tobacco dependence and delays smoking cessation. To dissect the neuronal mechanisms underlying the vulnerability to nicotine addiction in carriers of the α5SNP, we created rats expressing this polymorphism using zinc finger nuclease technology and evaluated their behavior under the intravenous nicotine-self-administration paradigm. The electrophysiological responses of their neurons to nicotine were also evaluated. α5SNP rats self-administered more nicotine at high doses and exhibited higher nicotine-induced reinstatement of nicotine seeking than wild-type rats. Higher reinstatement was associated with altered neuronal activity in several discrete areas that are interconnected, including in the interpeduncular nucleus (IPN), a GABAergic structure that strongly expresses α5-containing nicotinic receptors. The altered reactivity of IPN neurons of α5SNP rats to nicotine was confirmed electrophysiologically. In conclusion, the α5SNP polymorphism is a major risk factor for nicotine intake at high doses and for relapse to nicotine seeking in rats, a dual effect that reflects the human condition. Our results also suggest an important role for the IPN in the higher relapse to nicotine seeking observed in α5SNP rats.

The nucleus accumbens shell in reinstatement and extinction of drug seeking

The contexts where drugs are self-administered have important control over relapse and extinction of drug-seeking behavior. The nucleus accumbens shell (AcbSh) is essential to this contextual control over drug-seeking behavior. It has been consistently implicated in both the expression of context-induced reinstatement and the expression of extinction, across a variety of drug classes and other rewards. Here, we review the evidence linking AcbSh to the extinction and reinstatement of drug seeking. We consider whether this dual role can be linked to known heterogeneities in AcbSh cell types, their major afferents, and their major efferents. We show that although these heterogeneities are each important and can determine extinction vs. reinstatement, they do not seem adequate to explain the body of findings from the behavioral literature. Rather, we suggest that this functional specialization of AcbSh may be more profitably viewed in terms of the segregation and compartmentalization of AcbSh channels.

Role of Glutamatergic Projections from the Ventral CA1 to Infralimbic Cortex in Context-Induced Reinstatement of Heroin Seeking

The prelimbic cortex (PL) and infralimbic cortex (IL) play a role in context-induced reinstatement of heroin seeking in an animal model of drug relapse. Both the PL and IL receive direct glutamatergic projections from the ventral CA1 (vCA1), which is also involved in context-induced reinstatement of cocaine and heroin seeking. Here we studied the role of vCA1-PL and vCA1-IL projections in context-induced reinstatement of heroin seeking by using electrophysiological, neuropharmacological, chemogenetic, and molecular methods. We showed that context-induced reinstatement of heroin seeking caused selective activation of the vCA1-IL but not vCA1-PL glutamatergic projections, decreased synaptosomal GluA2 expression in the IL, impaired basal synaptic transmission, and facilitation of long-term depression (LTD) in the vCA1-IL pathway. Additionally, chemogenetic inactivation of the vCA1-IL but not vCA1-PL pathway decreased context-induced reinstatement of heroin seeking. Inactivation of the vCA1-IL pathway also reversed synaptosomal GluA2 downregulation and basal transmission reduction, and blocked LTD induction. Taken together, our results demonstrate a critical role of the vCA1-IL glutamatergic projection in context-induced reinstatement of heroin seeking in a rat model of drug relapse.

Transient inactivation of the paraventricular nucleus of the thalamus enhances cue-induced reinstatement in goal-trackers, but not sign-trackers

RATIONALE

The paraventricular nucleus of the thalamus (PVT) has been shown to mediate cue-motivated behaviors, such as sign- and goal-tracking, as well as reinstatement of drug-seeking behavior. However, the role of the PVT in mediating individual variation in cue-induced drug-seeking behavior remains unknown.

OBJECTIVES

This study aimed to determine if inactivation of the PVT differentially mediates cue-induced drug-seeking behavior in sign-trackers and goal-trackers.

METHODS

Rats were characterized as sign-trackers (STs) or goal-trackers (GTs) based on their Pavlovian conditioned approach behavior. Rats were then exposed to 15 days of cocaine self-administration, followed by a 2-week forced abstinence period and then extinction training. Rats then underwent tests for cue-induced reinstatement and general locomotor activity, prior to which they received an infusion of either saline (control) or baclofen/muscimol (B/M) to inactivate the PVT.

RESULTS

Relative to control animals of the same phenotype, GTs show a robust increase in cue-induced drug-seeking behavior following PVT inactivation, whereas the behavior of STs was not affected. PVT inactivation did not affect locomotor activity in either phenotype.

CONCLUSION

In GTs, the PVT appears to inhibit the expression of drug-seeking, presumably by attenuating the incentive value of the drug cue. Thus, inactivation of the PVT releases this inhibition in GTs, resulting in an increase in cue-induced drug-seeking behavior. PVT inactivation did not affect cue-induced drug-seeking behavior in STs, suggesting that the role of the PVT in encoding the incentive motivational value of drug cues differs between STs and GTs.

Context-induced relapse to cocaine seeking after punishment-imposed abstinence is associated with activation of cortical and subcortical brain regions

We recently developed a rat model of context-induced relapse to alcohol seeking after punishment-imposed abstinence to mimic relapse after self-imposed abstinence due to adverse consequences of drug use. Here, we determined the model's generality to cocaine and have begun to explore brain mechanisms of context-induced relapse to cocaine seeking after punishment-imposed abstinence, using the activity marker Fos. In exp. 1, we trained rats to self-administer cocaine (0.75 mg/kg/infusion, 6 hours/day, 12 days) in context A. Next, we transferred them to context B where for the paired group, but not unpaired group, 50 percent of cocaine-reinforced lever presses caused aversive footshock. We then tested the rats for cocaine seeking under extinction conditions in contexts A and B. We also retested them for relapse after retraining in context A and repunishment in context B. In exp. 2, we used Fos immunoreactivity to determine relapse-associated neuronal activation in brain regions of rats exposed to context A, context B or neither context. Results showed the selective shock-induced suppression of cocaine self-administration and context-induced relapse after punishment-imposed abstinence in rats exposed to paired, but not unpaired, footshock. Additionally, context-induced relapse was associated with selective activation of dorsal and ventral medial prefrontal cortex, anterior insula, dorsal striatum, basolateral amygdala, paraventricular nucleus of the thalamus, lateral habenula, substantia nigra, ventral subiculum, and dorsal raphe, but not nucleus accumbens, central amygdala, lateral hypothalamus, ventral tegmental area and other brain regions. Together, context-induced relapse after punishment-imposed abstinence generalizes to rats with a history of cocaine self-administration and is associated with selective activation of cortical and subcortical regions.

Involvement of the dorsal hippocampus in expression and extinction of cocaine-induced conditioned place preference

A key aspect of substance abuse is that drug taking often occurs in a specific context. As a consequence, exposure to drug-associated contexts can trigger cravings and relapse, even after long periods of abstinence. Although many studies have demonstrated that the hippocampus is critical for developing and retrieving contextual and spatial memories, comparatively little is known about the role of the hippocampus in acquiring and inhibiting memories involving contexts and drugs of abuse. We examined the effects of hippocampal inactivation on expression of cocaine-induced conditioned place preference (CPP) after initial acquisition or extinction of CPP in C57BL/6 mice. During acquisition of CPP, distinct tactile cues were paired with cocaine (20 mg kg^-1 , intraperitoneal, CS+) and different tactile cues were paired with saline (CS-) on alternate days. Groups differed in whether the CS+ and CS- cues were presented in the same large space (one-compartment procedure) or distinct small spaces (two-compartment procedure), as previous findings demonstrate that a two-compartment configuration facilitates acquisition and attenuates extinction of a cocaine-induced CPP. Microinjection of the GABA_A agonist, muscimol, into the dorsal hippocampus impaired (1) retrieval of a place preference after acquisition, (2) extinction of a place preference, and (3) retrieval of extinction. These effects differed depending on the spatial configuration during acquisition or extinction, suggesting that the dorsal hippocampus may differentially modulate drug seeking during retrieval and extinction of CPP.

Role of Anterior Intralaminar Nuclei of Thalamus Projections to Dorsomedial Striatum in Incubation of Methamphetamine Craving

Relapse to methamphetamine (Meth) seeking progressively increases after withdrawal from drug self-administration (incubation of Meth craving). We previously demonstrated a role of dorsomedial striatum (DMS) dopamine D1 receptors (D1Rs) in this incubation. Here, we studied the role of afferent glutamatergic projections into the DMS and local D1R-glutamate interaction in this incubation in male rats. We first measured projection-specific activation on day 30 relapse test by using cholera toxin b (retrograde tracer) + Fos (activity marker) double-labeling in projection areas. Next, we determined the effect of pharmacological reversible inactivation of lateral or medial anterior intralaminar nuclei of thalamus (AIT-L or AIT-M) on incubated Meth seeking on withdrawal day 30. We then used an anatomical asymmetrical disconnection procedure to determine whether an interaction between AIT-L→DMS glutamatergic projections and postsynaptic DMS D1Rs contributes to incubated Meth seeking. We also determined the effect of unilateral inactivation of AIT-L and D1R blockade of DMS on incubated Meth seeking, and the effect of contralateral disconnection of AIT-L→DMS projections on nonincubated Meth seeking on withdrawal day 1. Incubated Meth seeking was associated with selective activation of AIT→DMS projections; other glutamatergic projections to DMS were not activated. AIT-L (but not AIT-M) inactivation or anatomical disconnection of AIT-L→DMS projections decreased incubated Meth seeking. Unilateral inactivation of AIT-L or D1R blockade of the DMS had no effect on incubated Meth craving, and contralateral disconnection of AIT-L→DMS projections had no effect on nonincubated Meth seeking. Our results identify a novel role of AIT-L and AIT-L→DMS glutamatergic projections in incubation of drug craving and drug seeking.SIGNIFICANCE STATEMENT Methamphetamine seeking progressively increases after withdrawal from drug self-administration, a phenomenon termed incubation of methamphetamine craving. We previously found that D1R-mediated dopamine transmission in the dorsomedial striatum plays a critical role in this incubation phenomenon. Here, we used neuroanatomical and neuropharmacological methods in rats to demonstrate that an interaction between the glutamatergic projection from the lateral anterior intralaminar nuclei of the thalamus to the dorsomedial striatum and local dopamine D1 receptors plays a critical role in relapse to methamphetamine seeking after prolonged withdrawal. Our study identified a novel motivation-related thalamostriatal projection critical to relapse to drug seeking.

Opposite Effects of Basolateral Amygdala Inactivation on Context-Induced Relapse to Cocaine Seeking after Extinction versus Punishment

Studies using the renewal procedure showed that basolateral amygdala (BLA) inactivation inhibits context-induced relapse to cocaine-seeking after extinction. Here, we determined whether BLA inactivation would also inhibit context-induced relapse after drug-reinforced responding is suppressed by punishment, an animal model of human relapse after self-imposed abstinence due to adverse consequences of drug use. We also determined the effect of central amygdala (CeA) inactivation on context-induced relapse.We trained rats to self-administer cocaine for 12 d (6 h/d) in Context A and then exposed them to either extinction or punishment training for 8 d in Context B. During punishment, 50% of cocaine-reinforced lever-presses produced an aversive footshock of increasing intensity (0.1-0.5 or 0.7 mA). We then tested the rats for relapse to cocaine seeking in the absence of cocaine or shock in Contexts A and B after BLA or CeA injections of vehicle or GABA agonists (muscimol-baclofen). We then retrained the rats for cocaine self-administration in Context A, repunished or re-extinguished lever pressing in Context B, and retested for relapse after BLA or CeA inactivation.BLA or CeA inactivation decreased context-induced relapse in Context A after extinction in Context B. BLA, but not CeA, inactivation increased context-induced relapse in Context A after punishment in Context B. BLA or CeA inactivation provoked relapse in Context B after punishment but not extinction. Results demonstrate that amygdala's role in relapse depends on the method used to achieve abstinence and highlights the importance of studying relapse under abstinence conditions that more closely mimic the human condition.SIGNIFICANCE STATEMENT Relapse to drug use during abstinence is often provoked by re-exposure to the drug self-administration environment or context. Studies using the established extinction-reinstatement rodent model of drug relapse have shown that inactivation of the basolateral amygdala inhibits context-induced drug relapse after extinction of the drug-reinforced responding. Here, we determined whether basolateral amygdala inactivation would also inhibit relapse after drug-reinforced responding is suppressed by punishment, a model of human relapse after self-imposed abstinence. Unexpectedly, we found that basolateral amygdala inactivation had opposite effects on relapse provoked by re-exposure to the drug self-administration environment after extinction versus punishment. Our results demonstrate that depending on the historical conditions that lead to abstinence, amygdala activity can either promote or inhibit relapse.

The Anterior Insular Cortex→Central Amygdala Glutamatergic Pathway Is Critical to Relapse after Contingency Management

Despite decades of research on neurobiological mechanisms of psychostimulant addiction, the only effective treatment for many addicts is contingency management, a behavioral treatment that uses alternative non-drug reward to maintain abstinence. However, when contingency management is discontinued, most addicts relapse to drug use. The brain mechanisms underlying relapse after cessation of contingency management are largely unknown, and, until recently, an animal model of this human condition did not exist. Here we used a novel rat model, in which the availability of a mutually exclusive palatable food maintains prolonged voluntary abstinence from intravenous methamphetamine self-administration, to demonstrate that the activation of monosynaptic glutamatergic projections from anterior insular cortex to central amygdala is critical to relapse after the cessation of contingency management. We identified the anterior insular cortex-to-central amygdala projection as a new addiction- and motivation-related projection and a potential target for relapse prevention.