Post-retrieval disruption of a cocaine conditioned place preference by systemic and intrabasolateral amygdala beta2- and alpha1-adrenergic antagonists

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.

Reactivation of cocaine contextual memory engages mechanistic target of rapamycin/S6 kinase 1 signaling

Mechanistic target of rapamycin (mTOR) C1 and its downstream effectors have been implicated in synaptic plasticity and memory. Our prior work demonstrated that reactivation of cocaine memory engages a signaling pathway consisting of Akt, glycogen synthase kinase-3β (GSK3β), and mTORC1. The present study sought to identify other components of mTORC1 signaling involved in the reconsolidation of cocaine contextual memory, including eukaryotic translation initiation factor 4E (eIF4E)-eIF4G interactions, p70 S6 kinase polypeptide 1 (p70S6K, S6K1) activity, and activity-regulated cytoskeleton (Arc) expression. Cocaine contextual memory was established in adult CD-1 mice using conditioned place preference. After cocaine place preference was established, mice were briefly re-exposed to the cocaine-paired context to reactivate the cocaine memory and brains examined. Western blot analysis showed that phosphorylation of the mTORC1 target, p70S6K, in nucleus accumbens and hippocampus was enhanced 60 min following reactivation of cocaine memories. Inhibition of mTORC1 with systemic administration of rapamycin or inhibition of p70S6K with systemic PF-4708671 after reactivation of cocaine contextual memory abolished the established cocaine place preference. Immunoprecipitation assays showed that reactivation of cocaine memory did not affect eIF4E-eIF4G interactions in nucleus accumbens or hippocampus. Levels of Arc mRNA were significantly elevated 60 and 120 min after cocaine memory reactivation and returned to baseline 24 h later. These findings demonstrate that mTORC1 and p70S6K are required for reconsolidation of cocaine contextual memory.

A three-compartment apparatus alters the brain concentration of cytokines and neurotrophic factors in cocaine-induced CPP in mice

Cocaine-induced neuroinflammation plays an important role in the pathophysiology of drug addiction. Evidence suggests that the immune response contributes for memory consolidation related to place preference behavior underlying cocaine administration in mice. Conditioned place preference (CPP) is a protocol extensively used to study the rewarding and/or aversive motivational effects of drug abuse in rodents, reproducing cocaine-seeking behavior in humans. Besides the variety of apparatus used in the CPP protocol, whether different types of apparatus are able to induce the same conditioned behavior response and neurobiological changes remains to be fully explored. We hypothesize that the immune response is involved in the cocaine-induced CPP and that the type of apparatus might influence this response. Herein, two- and three-compartment apparatuses were tested using the behavioral model of CPP. Cocaine-induced CPP was demonstrated in both apparatuses. However, mice injected with cocaine had decreased levels of IL-1β, IL-6, IL-10, and GDNF in the pre-frontal cortex, and decreased CX3CL1 in the striatum, in the CPP protocol using three compartments compared to controls. While similar levels were seen in the CPP protocol using two compartments. In conclusion, the current study demonstrated that the type of apparatus might influence the investigation of neurobiological mechanisms associated with cocaine-induced CPP. Our data also suggest that the three compartment-apparatus seems to be a more appropriate model to investigate the neuroinflammatory response related to cocaine addiction.

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.

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.

Alpha1-adrenergic receptor blockade in the ventral tegmental area attenuates acquisition of cocaine-induced pavlovian associative learning

Activity of the alpha₁-adrenergic receptor (α₁-AR) in the ventral tegmental area (VTA) modulates dopaminergic activity, implying its modulatory role in the behavioral functions of the dopamine (DA) system. Indeed, intra-VTA α₁-AR blockade attenuates conditioned stimulus dependent behaviors such as drug seeking responses signifying a role of the noradrenergic signaling in the VTA in conditioned behaviors. Importantly, the role of the VTA α₁-AR activity in Pavlovian associative learning with positive outcomes remains unknown. Here, we aimed to examine how intra-VTA α₁-AR blockade affects acquisition of cocaine-induced Pavlovian associative learning in the conditioned place preference (CPP) paradigm. The impact of α₁-AR blockade on cocaine-reinforced operant responding and cocaine-evoked ultrasonic vocalizations (USVs) was also studied. In addition, both α₁-AR immunoreactivity in the VTA and its role in phasic DA release in the nucleus accumbens (NAc) were assessed. We demonstrated cellular localization of α₁-AR expression in the VTA, providing a neuroanatomical substrate for the α₁-AR mechanism. We showed that prazosin (α₁-AR selective antagonist; 1 μg/0.5 μl) microinfusion attenuated electrically evoked DA transients in the NAc and dose-dependently (0.1-1 μg/0.5 μl) prevented the acquisition of cocaine CPP but did not affect cocaine-reinforced operant responding nor cocaine-induced positive affective state (measured as USVs). We propose that the VTA α₁-AR signaling is necessary for the acquisition of Pavlovian associative learning but does not encode hedonic value. Thus, α₁-AR signaling in the VTA might underlie salience encoding of environmental stimuli and reflect an ability of alerting/orienting functions, originating from bottom-up information processing to guide behaviors.

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

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

Targeting drug memory reconsolidation: a neural analysis

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

Clonidine, an α2 adrenergic receptor agonist, disrupts reconsolidation of a cocaine-paired environmental memory

Environmental cues can elicit robust cocaine reward memories, contributing to relapse to cocaine abuse. Memories can be manipulated pharmacologically by interfering with reconsolidation after reactivation. Clonidine, an α2 noradrenergic receptor agonist, was tested for its ability to block reconsolidation of cocaine environmental-paired memory. Male Sprague-Dawley rats completed an 8-day cocaine place conditioning procedure to establish a cocaine place preference. Cocaine memory was reactivated by exposure to the cocaine-paired environment in a drug-free state, followed immediately by administration of clonidine (10 or 50 µg/kg) or vehicle. Cocaine place preference was retested 24 h and 1 week later. Clonidine significantly attenuated the previously established cocaine place preference when tested 1 or 7 days later. To investigate the generalizability of this effect to other drug classes, morphine conditioned place preference was tested. Clonidine administration after morphine memory reactivation did not significantly alter the expression of morphine place preference. These results suggest that clonidine can interfere with reconsolidation of cocaine memory and may be a useful approach to reduce relapse.

Optogenetic Activation of the Basolateral Amygdala Promotes Both Appetitive Conditioning and the Instrumental Pursuit of Reward Cues

Reward-associated stimuli can both evoke conditioned responses and acquire reinforcing properties in their own right, becoming avidly pursued. Such conditioned stimuli (CS) can guide reward-seeking behavior in adaptive (e.g., locating food) and maladaptive (e.g., binge eating) ways. The basolateral amygdala (BLA) regulates conditioned responses evoked by appetitive CS, but less is known about how the BLA contributes to the instrumental pursuit of CS. Here we studied the influence of BLA neuron activity on both behavioral effects. Water-restricted male rats learned to associate a light-tone cue (CS) with water delivery into a port. During these Pavlovian conditioning sessions, we paired CS presentations with photo-stimulation of channelrhodopsin-2 (ChR2)-expressing BLA neurons. BLA photo-stimulation potentiated CS-evoked port entries during conditioning, indicating enhanced conditioned approach and appetitive conditioning. Next, new rats received Pavlovian conditioning without photo-stimulation. These rats then received instrumental conditioning sessions where they could press an inactive lever or an active lever that produced CS presentation, without water delivery. Rats pressed more on the active versus inactive lever, and pairing CS presentation with BLA-ChR2 photo-stimulation intensified responding for the CS. This suggests that BLA-ChR2 photo-stimulation enhanced CS incentive value. In a separate experiment, rats did not reliably self-administer BLA-ChR2 stimulations, suggesting that BLA neurons do not carry a primary reward signal. Last, intra-BLA infusions of d-amphetamine also intensified lever-pressing for the CS. The findings suggest that BLA-mediated activity facilitates CS control over behavior by enhancing both appetitive Pavlovian conditioning and instrumental pursuit of CS.SIGNIFICANCE STATEMENT Cues paired with rewards can guide animals to valuable resources such as food. Cues can also promote dysfunctional reward-seeking behavior, as in overeating. Reward-paired cues influence reward seeking through two major mechanisms. First, reward-paired cues evoke conditioned anticipatory behaviors to prepare for impending rewards. Second, reward-paired cues are powerful motivators and they can evoke pursuit in their own right. Here we show that increasing neural activity in the basolateral amygdala enhances both conditioned anticipatory behaviors and pursuit of reward-paired cues. The basolateral amygdala therefore facilitates cue-induced control over behavior by both increasing anticipation of impending rewards and making reward cues more attractive.

Context-Dependent and Context-Independent Effects of D1 Receptor Antagonism in the Basolateral and Central Amygdala during Cocaine Self-Administration

One way that drugs of abuse perturb the dopamine system is by triggering large amounts of extracellular dopamine to efflux into limbic regions. The basolateral (BLA) and central (CeA) nuclei of the amygdala have been shown to play distinct roles in value representation of primary and conditioned reward. However, the precise role of dopaminergic receptors in the BLA and the CeA during reward-related behaviors remains to be determined. Here we investigate the effects of dopamine D1 receptor blockade in the BLA and the CeA during asymptotic performance of cocaine self-administration and in a novel application of contextual renewal under continued access conditions. After more than three weeks of chained seek-take self-administration of cocaine, male Long Evans rats were given a bilateral intra-BLA or intra-CeA infusion of the D1 antagonist SCH-23390 (2 µg/0.3 µl) for multiple days. Intra-BLA D1 receptor blockade before, but not after the self-administration session, gradually suppressed drug seeking and taking responses and persisted with a change in context with continued D1 blockade. In contrast, intra-CeA D1 receptor blockade caused a rapid reduction in self-administration that showed renewal with a change in context with continued D1 blockade. Further, conditioned place aversion developed with intra-BLA but not intra-CeA infusions. Collectively, these results demonstrate that dopamine D1 receptors in the BLA and CeA both contribute to drug seeking and taking, but may do so through distinct mechanisms.

Drug-free and context-dependent locomotor hyperactivity in DBA/2 J mice previously treated with repeated cocaine: Relationship with behavioral sensitization and role of noradrenergic receptors

Drug-associated contexts and discrete cues can trigger motivational states responsible for drug-seeking behavior and relapse. In preclinical research, drug-free conditioned hyperactivity has been used to investigate the expression of memories associated with psychostimulant drug effects. Addictive drugs can produce long-lasting sensitization to their psychomotor actions, a phenomenon known as behavioral sensitization. The neuroplasticity underlying behavioral sensitization appears to be involved in pathological drug pursuit and abuse. In the present study we evaluated drug-free, context-dependent hyperactivity in DBA/2 J mice previously treated with cocaine and we explored whether this conditioned effect was related to behavioral sensitization. Given the role of noradrenergic (NA) neurotransmission in memory retrieval, consolidation and reconsolidation processes, we also investigated whether conditioned hyperactivity in a drug-free state was mediated by NA receptors. Animals underwent a sensitization protocol with six cocaine injections (0, 5, 10 or 20 mg/kg) paired to a particular floor cue. Three days after this sensitization phase, all animals were exposed to the same familiar floor environment without drug treatment. A second test with an unfamiliar floor was conducted 24 h later. Conditioned hyperactivity was also explored after one or three cocaine pairings and was evaluated for its duration (with repeated familiar vs. unfamiliar floor tests). In a series of pharmacological experiments, we evaluated the effects propranolol (a non-selective antagonist of β1- and β2-receptors) and prazosin (α1-receptor antagonist) on conditioned hyperactivity. Cocaine treatment produced both robust sensitization and drug-free conditioned hyperactivity, an effect that lasted up to 17 days (with cocaine 20 mg/kg). A significant correlation between the magnitude of cocaine sensitization and the level of conditioned hyperactivity was found. Propranolol, but not prazosin, blocked context-dependent hyperlocomotion in a drug-free state. Our data, together with a vast body of literature, indicate that the NA system plays a key role in the retrieval and behavioral expression of drug-associated memories.

Exploring Exercise- and Context-Induced Peptide Changes in Mice by Quantitative Mass Spectrometry

Recent research suggests that exercise may help facilitate abstinence from cocaine addiction, though the mechanisms are not well understood. In mice, wheel running accelerates the extinction of conditioned place preference (CPP) for cocaine, providing an animal model for evaluating potential neurological mechanisms. The objective of this study was to quantify dynamic changes in endogenous peptides in the amygdala and dentate gyrus of the hippocampus in mice exposed to a context paired with the effects of cocaine, and in response to exercise. Male C57BL/6J mice conditioned to cocaine were housed with or without running wheels for 30 days. Following a CPP test and final exposure to either a cocaine- or saline-associated context, peptides were measured in brain tissue extracts using label-free matrix-assisted laser desorption/ionization mass spectrometry (MS) and stable isotopic labeling with liquid chromatography and electrospray ionization MS. CPP in mice was significantly reduced with running, which correlated to decreased myelin basic protein derivatives in the dentate gyrus extracts, possibly reflecting increased unmyelinated granule neuron density. Exposure to a cocaine-paired context increased hemoglobin-derived peptides in runners and decreased an actin-derived peptide in sedentary animals. These results allowed us to characterize a novel set of biomarkers that are responsive to exercise in the hippocampus and in a cocaine-paired context in the amygdala.

β-Adrenergic signaling is required for the induction of a labile state during memory reconsolidation

Memory reconsolidation is the process by which previously consolidated memories reenter a labile state through reactivation of the memory trace and are actively consolidated through de novo protein synthesis. Although extensive studies have shown that β-adrenergic signaling plays a critical role in the restabilization of reactivated memory, its role in the destabilization of long-term memory is not well-studied. In this study, we found that membrane excitability increased in hippocampal CA1 neurons immediately after the retrieval of contextual fear memory. Interestingly, this increase in membrane excitability diminished after treatment with propranolol (a β-adrenergic receptor antagonist), an NMDA receptor antagonist, and a PKA inhibitor. In addition, we found that administration of propranolol prior to, but not after, the retrieval of fear memory ameliorated the memory impairment caused by anisomycin, indicating that inhibition of β-adrenergic signaling blocks the destabilization of contextual fear memory. Taken together, these results indicate that β-adrenergic signaling via NMDA receptors and PKA signaling pathway induces a labile state of long-term memory through increased neuronal membrane excitability.

β1-Adrenoceptor in the Central Amygdala Is Required for Unconditioned Stimulus-Induced Drug Memory Reconsolidation

BACKGROUND

Drug memories become labile and reconsolidated after retrieval by presentation of environmental cues (conditioned stimulus) or drugs (unconditioned stimulus). Whether conditioned stimulus and unconditioned stimulus retrieval trigger different memory reconsolidation processes is not clear.

METHODS

Protein synthesis inhibitor or β-adrenergic receptor (β-AR) antagonist was systemically administrated or intra-central amygdala infused immediately after cocaine reexposure in cocaine-conditioned place preference or self-administration mice models. β-ARs were selectively knocked out in the central amygdala to further confirm the role of β-adrenergic receptor in cocaine reexposure-induced memory reconsolidation of cocaine-conditioned place preference.

RESULTS

Cocaine reexposure triggered de novo protein synthesis dependent memory reconsolidation of cocaine-conditioned place preference. Cocaine-priming-induced reinstatement was also impaired with post cocaine retrieval manipulation, in contrast to the relapse behavior with post context retrieval manipulation. Cocaine retrieval, but not context retrieval, induced central amygdala activation. Protein synthesis inhibitor or β1-adrenergic receptor antagonist infused in the central amygdala after cocaine retrieval, but not context retrieval, inhibited memory reconsolidation and reinstatement. β1-adrenergic receptor knockout in the central amygdala suppressed cocaine retrieval-triggered memory reconsolidation and reinstatement of cocaine conditioned place preference. β1-adrenergic receptor antagonism after cocaine retrieval also impaired reconsolidation and reinstatement of cocaine self-administration.

CONCLUSIONS

Cocaine reward memory triggered by unconditioned stimulus retrieval is distinct from conditioned stimulus retrieval. Unconditioned stimulus retrieval induced reconsolidation of cocaine reward memory depends on β1-adrenergic signaling in the central amygdala. Post unconditioned stimulus retrieval manipulation can prevent drug memory reconsolidation and relapse to cocaine, thus providing a potential strategy for the prevention of substance addiction.

SIGNIFICANCE STATEMENT

It is well known that drug memories become labile and reconsolidated upon retrieval by the presentation of conditioned stimulus (CS) or unconditioned stimulus (US). Whether CS and US retrieval trigger different memory reconsolidation processes is unknown. In this study, we found that US retrieval, but not CS retrieval, triggered memory reconsolidation of cocaine-conditioned place preference dependent on β1-AR and de novo protein synthesis in the central amygdala. Furthermore, cocaine priming-induced reinstatement was impaired with post US retrieval manipulation in contrast to the relapse behavior with post CS retrieval manipulation. In cocaine self-administration, β1-AR antagonism after US retrieval also impaired reconsolidation and reinstatement. Our study indicates that reconsolidation of cocaine reward memory triggered by US retrieval is distinct from CS retrieval. US retrieval induced reconsolidation of cocaine reward memory depends on β1-adrenergic signaling in the central amygdala.

Alpha(1)-adrenergic receptor blockade in the VTA modulates fear memories and stress responses

Activity of the ventral tegmental area (VTA) and its terminals has been implicated in the Pavlovian associative learning of both stressful and rewarding stimuli. However, the role of the VTA noradrenergic signaling in fear responses remains unclear. We aimed to examine how alpha₁-adrenergic receptor (α₁-AR) signaling in the VTA affects conditioned fear. The role of α₁-AR was assessed using the micro-infusions into the VTA of the selective antagonists (0.1-1µg/0.5µl prazosin and 1µg/0.5µl terazosin) in acquisition and expression of fear memory. In addition, we performed control experiments with α₁-AR blockade in the mammillary bodies (MB) - a brain region with α₁-AR expression adjacent to the VTA. Intra-VTA but not intra-MB α₁-AR blockade prevented formation and retrieval of fear memories. Importantly, local administration of α₁-AR antagonists did not influence footshock sensitivity, locomotion or anxiety-like behaviors. Similarly, α₁-AR blockade in the VTA had no effects on negative affect measured as number of 22kHz ultrasonic vocalizations during fear conditioning training. We propose that noradrenergic signaling in the VTA via α₁-AR regulates formation and retrieval of fear memories but not other behavioral responses to stressful environmental stimuli. It enhances the encoding of environmental stimuli by the VTA to form and retrieve conditioned fear memories and to predict future behavioral outcomes. Our results provide novel insight into the role of the VTA α₁-AR signaling in the regulation of stress responsiveness and fear memory.

Lack of β2-AR Increases Anxiety-Like Behaviors and Rewarding Properties of Cocaine

It is well known that β-adrenoceptors (β-ARs) play a critical role in emotional arousal and stressful events, but the specific contributions of the β2-AR subtype to the psychological disorders are largely unknown. To investigate whether β2-AR are involved in anxiety-like behavior and reward to addictive drugs, we conducted a series of behavioral tests on β2-AR knock-out (KO) mice. β2-AR KO mice exhibited increased preference for the dark compartment and closed arm in tests of Light/Dark box and elevated plus maze, indicating that β2-AR deletion elevates level of anxiety or innate fear. β2-AR KO mice also showed decreased immobility in tail suspension test (TST), suggesting that β2-AR deletion inhibits depression-like behavior. Interestingly, β2-AR ablation did not change basal locomotion but significantly increased locomotor activity induced by acute cocaine administration. β2-AR KO mice showed enhanced place preference for cocaine, which could be attenuated by β1-selective AR antagonist betaxolol. Consistently, β2-AR agonist suppressed cocaine-conditioned place preference (CPP). These data indicate that β2-AR deletion enhances acute response and reward to cocaine. Our results suggest that β2-AR regulates anxiety level, depression-like behavior and hedonic properties of cocaine, implicating that β2-AR are the potential targets for the treatment of emotional disorders and cocaine addiction.

Dopamine D1 receptor agonist treatment attenuates extinction of morphine conditioned place preference while increasing dendritic complexity in the nucleus accumbens core

The dopamine D1 receptor (D1R) has a role in opioid reward and conditioned place preference (CPP), but its role in CPP extinction is undetermined. We examined the effect of D1R agonist SKF81297 on the extinction of opioid CPP and associated dendritic morphology in the nucleus accumbens (NAc), a region involved with reward integration and its extinction. During the acquisition of morphine CPP, mice received morphine and saline on alternate days; injections were given immediately before each of eight daily conditioning sessions. Mice subsequently underwent six days of extinction training designed to diminish the previously learned association. Mice were treated with either 0.5mg/kg SKF81297, 0.8mg/kg SKF81297, or saline immediately after each extinction session. There was a dose-dependent effect, with the highest dose of SKF81297 attenuating extinction, as mice treated with this dose had significantly higher CPP scores than controls. Analysis of medium spiny neuron morphology revealed that in the NAc core, but not in the shell, dendritic arbors were significantly more complex in the morphine conditioned, SKF81297-treated mice compared to controls. In separate experiments using mice conditioned with only saline, SKF81297 administration after extinction sessions had no effect on CPP and produced differing effects on dendritic morphology. At the doses used in our experiments, SKF81297 appears to maintain previously learned opioid conditioned behavior, even in the face of new information. The D1R agonist's differential, rather than unidirectional, effects on dendritic morphology in the NAc core suggests that it may be involved in encoding reward information depending on previously learned behavior.

Extinction of alcohol seeking is enhanced by compound extinction and the noradrenaline reuptake inhibitor atomoxetine

Alcohol-related stimuli can trigger relapse of alcohol-seeking behaviors even after extended periods of abstinence. Extinction of such stimuli provides a means for reducing their impact on relapse. However, the expression of extinction can be disrupted by exposure to the previous reinforcer as well as the simple passage of time. We investigated whether augmentation of prediction error or of noradrenaline neurotransmission by the reuptake inhibitor atomoxetine would enhance long-term extinction of alcohol-seeking behavior. Rats received Pavlovian conditioning of multiple stimuli signaling the delivery of an alcohol reward before individual extinction was given to each of these stimuli. Further extinction was then given to a target stimulus presented in compound with another alcohol-predictive stimulus intended to augment prediction error (Experiment 1) or after a systemic injection of atomoxetine (1.0 mg/kg; Experiment 2). Experiment 3 examined whether the compound stimulus effect relied on noradrenergic activity by testing the effects of the β-adrenergic antagonist propranolol, given prior to compound stimulus trials. Long-term retention of extinction learning was assessed a week later. Compound stimulus presentations enhanced long-term extinction as the stimulus extinguished in compound elicited less responding than a stimulus receiving equal extinction alone when tested a week later. This effect was mimicked by atomoxetine and blocked by propranolol given during extinction training. Thus, extinction of alcohol-seeking behavior can be improved by extinguishing multiple alcohol-predictive stimuli or enhancing noradrenaline neurotransmission during extinction training. Both behavioral and neurobiological processes could be exploited to enhance the outcome of extinction-based treatments for alcohol use disorders.

Translational Approaches Targeting Reconsolidation

Maladaptive learned responses and memories contribute to psychiatric disorders that constitute a significant socio-economic burden. Primary treatment methods teach patients to inhibit maladaptive responses, but do not get rid of the memory itself, which explains why many patients experience a return of symptoms even after initially successful treatment. This highlights the need to discover more persistent and robust techniques to diminish maladaptive learned behaviours. One potentially promising approach is to alter the original memory, as opposed to inhibiting it, by targeting memory reconsolidation. Recent research shows that reactivating an old memory results in a period of memory flexibility and requires restorage, or reconsolidation, for the memory to persist. This reconsolidation period allows a window for modification of a specific old memory. Renewal of memory flexibility following reactivation holds great clinical potential as it enables targeting reconsolidation and changing of specific learned responses and memories that contribute to maladaptive mental states and behaviours. Here, we will review translational research on non-human animals, healthy human subjects, and clinical populations aimed at altering memories by targeting reconsolidation using biological treatments (electrical stimulation, noradrenergic antagonists) or behavioural interference (reactivation-extinction paradigm). Both approaches have been used successfully to modify aversive and appetitive memories, yet effectiveness in treating clinical populations has been limited. We will discuss that memory flexibility depends on the type of memory tested and the brain regions that underlie specific types of memory. Further, when and how we can most effectively reactivate a memory and induce flexibility is largely unclear. Finally, the development of drugs that can target reconsolidation and are safe for use in humans would optimize cross-species translations. Increasing the understanding of the mechanism and limitations of memory flexibility upon reactivation should help optimize efficacy of treatments for psychiatric patients.

Chemogenetic and Optogenetic Activation of Gαs Signaling in the Basolateral Amygdala Induces Acute and Social Anxiety-Like States

Anxiety disorders are debilitating psychiatric illnesses with detrimental effects on human health. These heightened states of arousal are often in the absence of obvious threatening cues and are difficult to treat owing to a lack of understanding of the neural circuitry and cellular machinery mediating these conditions. Activation of noradrenergic circuitry in the basolateral amygdala is thought to have a role in stress, fear, and anxiety, and the specific cell and receptor types responsible is an active area of investigation. Here we take advantage of two novel cellular approaches to dissect the contributions of G-protein signaling in acute and social anxiety-like states. We used a chemogenetic approach utilizing the Gαs DREADD (rM3Ds) receptor and show that selective activation of generic Gαs signaling is sufficient to induce acute and social anxiety-like behavioral states in mice. Second, we use a recently characterized chimeric receptor composed of rhodopsin and the β2-adrenergic receptor (Opto-β2AR) with in vivo optogenetic techniques to selectively activate Gαs β-adrenergic signaling exclusively within excitatory neurons of the basolateral amygdala. We found that optogenetic induction of β-adrenergic signaling in the basolateral amygdala is sufficient to induce acute and social anxiety-like behavior. These findings support the conclusion that activation of Gαs signaling in the basolateral amygdala has a role in anxiety. These data also suggest that acute and social anxiety-like states may be mediated through signaling pathways identical to β-adrenergic receptors, thus providing support that inhibition of this system may be an effective anxiolytic therapy.

Effects of prazosin and doxazosin on yohimbine-induced reinstatement of alcohol seeking in rats

RATIONALE AND OBJECTIVES

Alpha-1 adrenoceptor antagonists, such as prazosin, show promise in treating alcoholism. In rats, prazosin reduces alcohol self-administration and relapse induced by footshock stress and the alpha-2 antagonist yohimbine, but the processes involved in these effects of prazosin are not known. Here, we present studies on the central mechanisms underlying the effects of prazosin on yohimbine-induced reinstatement of alcohol seeking.

METHODS

In experiment 1, we trained rats to self-administer alcohol (12 % w/v, 1 h/day), extinguished their responding, and tested the effects of prazosin, administered ICV (2 and 6 nmol) or systemically (1 mg/kg) on yohimbine (1.25 mg/kg)-induced reinstatement. In experiment 2, we determined potential central sites of action by analyzing effects of prazosin (1 mg/kg) on yohimbine (1.25 mg/kg)-induced Fos expression. In experiment 3, we determined the effects of doxazosin (1.25, 2.5, and 5 mg/kg), an alpha-1 antagonist with a longer half-life on yohimbine-induced reinstatement.

RESULTS

Yohimbine-induced reinstatement of alcohol seeking was reduced significantly by ICV and systemic prazosin (50 and 69 % decreases, respectively). Systemic prazosin reduced yohimbine-induced Fos expression in the prefrontal cortex, accumbens shell, ventral bed nucleus of the stria terminalis, and basolateral amygdala (46-67 % decreases). Doxazosin reduced yohimbine-induced reinstatement of alcohol seeking (78 % decrease).

CONCLUSIONS

Prazosin acts centrally to reduce yohimbine-induced alcohol seeking. The Fos mapping study suggests candidate sites where it may act. Doxazosin is also effective in reducing yohimbine-induced reinstatement. These data provide information on the mechanisms of alpha-1 antagonists on yohimbine-induced alcohol seeking and indicate their further investigation for the treatment of alcoholism.

Inhibition of Lactate Transport Erases Drug Memory and Prevents Drug Relapse

BACKGROUND

Drug memories that associate drug-paired stimuli with the effects of abused drugs contribute to relapse. Exposure to drug-associated contexts causes consolidated drug memories to be in a labile state, during which manipulations can be given to impair drug memories. Although substantial evidence demonstrates the crucial role of neuronal signaling in addiction, little is known about the contribution of astrocyte-neuron communication.

METHODS

Rats were trained for cocaine-induced conditioned place preference (CPP) or self-administration and microinjected with the glycogen phosphorylation inhibitor 1,4-dideoxy-1,4-imino-D-arabinitol into the basolateral amygdala (BLA) immediately after retrieval. The concentration of lactate was measured immediately after retrieval via microdialysis, and the CPP score and number of nosepokes were recorded 24 hours later. Furthermore, we used antisense oligodeoxynucleotides to disrupt the expression of astrocytic lactate transporters (monocarboxylate transporters 1 and 2) in the BLA after retrieval, tested the expression of CPP 1 day later, and injected L-lactate into the BLA 15 minutes before retrieval to rescue the effects of the oligodeoxynucleotides.

RESULTS

Injection of 1,4-dideoxy-1,4-imino-D-arabinitol into the BLA immediately after retrieval prevented the subsequent expression of cocaine-induced CPP, decreased the concentration of lactate in the BLA, and reduced the number of nosepokes for cocaine self-administration. Disrupting the expression of monocarboxylate transporters 1 and 2 in the BLA also caused subsequent deficits in the expression of cocaine-induced CPP, which was rescued by pretreatment with L-lactate.

CONCLUSIONS

Our results suggest that astrocyte-neuron lactate transport in the BLA is critical for the reconsolidation of cocaine memory.

Influence of Betaxolol on the Methamphetamine Dependence in Mice

OBJECTIVE

The noradrenaline system is involved in the reward effects of various kinds of abused drugs. Betaxolol (BTX) is a highly selective β1-antagonist. In the present study, we evaluated the effect of BTX on methamphetamine (MAP)-induced conditioned place preference (CPP) and hyperactivity in mice.

METHODS

The mice (n=72) were treated with MAP or saline every other day for a total of 6 days (from day 3 to day 8; 3-times MAP and 3-times saline). Each mouse was given saline (1 mL/kg) or MAP (1 mg/kg, s.c.) or BTX (5 mg/kg, i.p.) or MAP with BTX (5 mg/kg, i.p.) 30 min prior to the administration of MAP (1 mg/kg, s.c.) every other day and paired with for 1 h (three-drug and three-saline sessions). We then compared the CPP score between the two groups. After the extinction of CPP, the mice were given BTX (5 mg/kg, i.p.) or saline (1 mL/kg) 24 h prior to a priming injection of MAP, and were then immediately tested to see whether the place preference was reinstated.

RESULTS

The repeated administration of BTX 30 min prior to the exposure to MAP significantly reduced the development of MAP-induced CPP. When BTX was administered 24 h prior to the CPP-testing session on day 9, it also significantly attenuated the CPP, but did not result in any change of locomotor activity. In the drug-priming reinstatement study, the extinguished CPP was reinstated by a MAP (0.125 mg/kg, s.c.) injection and this was significantly attenuated by BTX.

CONCLUSION

These findings suggest that BTX has a therapeutic and preventive effect on the development, expression, and drug-priming reinstatement of MAP-induced CPP.

Epigenetics and memory: causes, consequences and treatments for post-traumatic stress disorder and addiction

Understanding the interaction between fear and reward at the circuit and molecular levels has implications for basic scientific approaches to memory and for understanding the etiology of psychiatric disorders. Both stress and exposure to drugs of abuse induce epigenetic changes that result in persistent behavioral changes, some of which may contribute to the formation of a drug addiction or a stress-related psychiatric disorder. Converging evidence suggests that similar behavioral, neurobiological and molecular mechanisms control the extinction of learned fear and drug-seeking responses. This may, in part, account for the fact that individuals with post-traumatic stress disorder have a significantly elevated risk of developing a substance use disorder and have high rates of relapse to drugs of abuse, even after long periods of abstinence. At the behavioral level, a major challenge in treatments is that extinguished behavior is often not persistent, returning with changes in context, the passage of time or exposure to mild stressors. A common goal of treatments is therefore to weaken the ability of stressors to induce relapse. With the discovery of epigenetic mechanisms that create persistent molecular signals, recent work on extinction has focused on how modulating these epigenetic targets can create lasting extinction of fear or drug-seeking behavior. Here, we review recent evidence pointing to common behavioral, systems and epigenetic mechanisms in the regulation of fear and drug seeking. We suggest that targeting these mechanisms in combination with behavioral therapy may promote treatment and weaken stress-induced relapse.

Dissociation of β1- and β2-adrenergic receptor subtypes in the retrieval of cocaine-associated memory

Drug seeking is maintained by encounters with drug-associated cues, and disrupting retrieval of these drug-cue associations would reduce the risk of relapse. Retrieval of cocaine-associated memories is dependent on β-adrenergic receptor (β-AR) activation, and blockade of these receptors induces a persistent retrieval deficit. Whether retrieval of cocaine-associated memory is mediated by a specific β-AR subtype, however, remains unclear. Using a cocaine conditioned place preference (CPP) procedure, we examined whether retrieval of a cocaine CPP memory is mediated collectively by β1- and β2-ARs, or by one of these β-AR subtypes alone. We show that co-blockade of β1- and β2-ARs abolished CPP expression on that and subsequent drug-free CPP tests, resulting in a long-lasting retrieval deficit that prevented subsequent cocaine-induced reinstatement. To dissociate the necessity of either β1- or β2-ARs alone, we administered subtype-specific antagonists prior to retrieval. Administration of a β1-AR antagonist before the initial CPP trial dose-dependently reduced expression of a CPP on that and subsequent drug-free trials as compared to vehicle administration. In contrast, administration of a β2-AR antagonist had no effect on initial CPP expression, although the highest dose reduced subsequent CPP expression. Importantly, either β1- or β2-AR blockade prior to an initial retrieval trial prevented subsequent cocaine-induced reinstatement. Our findings indicate that the β1-AR subtype mediates retrieval of a cocaine CPP, and that acutely blocking either β1- or β2-ARs can prevent subsequent cocaine-induced reinstatement. Thus, β-AR antagonists, particularly β1-ARs antagonists, could serve as adjuncts for addiction therapies to prevent retrieval of drug-associated memories and provide protection against relapse.

Histone-mediated epigenetics in addiction

Many of the brain regions, neurotransmitter systems, and behavioral changes that occur after occasional drug use in healthy subjects and after chronic drug abuse in addicted patients are well characterized. An emerging literature suggests that epigenetic processes, those processes that regulate the accessibility of DNA to regulatory proteins within the nucleus, are keys to how addiction develops and how it may be treated. Investigations of the regulation of chromatin, the organizational system of DNA, by histone modification are leading to a new understanding of the cellular and behavioral alterations that occur after drug use. We will describe how, when, and where histone tails are modified and how some of the most recognized histone regulation patterns are involved in the cycle of addiction, including initial and chronic drug intake, withdrawal, abstinence, and relapse. Finally, we consider how an approach that targets histone modifications may promote successful treatment.

Noradrenergic regulation of fear and drug-associated memory reconsolidation

Emotional and traumatic experiences lead to the development of particularly strong memories that can drive neuropsychiatric disorders, such as posttraumatic stress disorder (PTSD) and drug addiction. Disruption of these memories would therefore serve as a powerful treatment option, and targeting the pathologic emotional, but not declarative, component of a memory would be ideal for clinical intervention. Research reveals that after retrieval of a consolidated memory, the memory can be destabilized, and must then be reconsolidated through synaptic plasticity to allow subsequent retrieval. Disruption of reconsolidation-related plasticity would therefore impair specific, reactivated memories. Noradrenergic signaling strengthens synaptic plasticity and is essential for encoding the emotional components of memory. Consistent with this, investigations have now revealed that noradrenergic signaling is a critical mechanism for reconsolidation of emotional memories in rodent and human models. Here, we discuss these investigations and promising clinical trials indicating that disruption of noradrenergic signaling during reconsolidation may abolish the pathologic emotional, but not declarative, component of memories allowing alleviation of neuropsychiatric disorders including PTSD and drug addiction.

Cue configuration effects in acquisition and extinction of a cocaine-induced place preference

A pervasive finding in animal models of substance abuse is that associations form quickly between contexts and drugs of abuse, such as cocaine. Studies of conditioned place preference (CPP) demonstrate that animals approach cues previously paired with cocaine. This is a commonly used preparation, but the configuration of the CPP apparatus differs across laboratories. Two common apparatus configurations for CPP are one compartment (in which the animal has access to the entire apparatus and spatial cues are irrelevant) or two compartments (in which access is restricted to one half of the apparatus and spatial cues are relevant). We compared the effects of acquisition and extinction of cocaine-induced CPP as a function of configuration. During CPP acquisition, C57BL/6J mice received cocaine paired with one tactile floor (conditioned stimulus; CS+) and saline paired with the other (CS-). CS+ and CS- trials occurred on alternate days in one of three configurations: one-compartment (exposure to the entire apparatus during CS+ or CS-), two-compartment consistent position (exposure to CS+ or CS- in adjacent, spatially distinct compartments), or two-compartment alternating position (exposure to CS+ or CS- in adjacent compartments that alternated spatial locations across days). A stronger preference for the CS+ floor occurred in two- versus one-compartment groups, with the strongest preference observed when cocaine was paired with alternating chamber positions. In contrast, greater loss of preference occurred after extinction in a one-compartment procedure, regardless of one- or two-compartment acquisition history. These findings suggest that a two-compartment configuration facilitated acquisition but attenuated extinction of a cocaine-induced CPP. The use of different CPP configurations may distinguish the underlying substrates and relevant cues for acquisition and extinction processes in cocaine abuse.

Differential effects of dorsal hippocampal inactivation on expression of recent and remote drug and fear memory

Drugs of abuse generate strong drug-context associations, which can evoke powerful drug cravings that are linked to reinstatement in animal models and to relapse in humans. Work in learning and memory has demonstrated that contextual memories become more distributed over time, shifting from dependence on the hippocampus for retrieval to dependence on cortical structures. Implications for such changes in the structure of memory retrieval to addiction are unknown. Thus, to determine if the passage of time alters the substrates of conditioned place preference (CPP) memory retrieval, we investigated the effects of inactivation of the dorsal hippocampus (DH) with the GABA-A receptor agonist muscimol on expression of recent or remote CPP. We compared these effects with the same manipulation on expression of contextual fear conditioning. DH inactivation produced similar deficits in expression of both recent and remote CPP, but blocked expression of recent but not remote contextual fear memory. We describe the implications of these findings for mechanisms underlying long-term storage of contextual information.

Larval zebrafish model for FDA-approved drug repositioning for tobacco dependence treatment

Cigarette smoking remains the most preventable cause of death and excess health care costs in the United States, and is a leading cause of death among alcoholics. Long-term tobacco abstinence rates are low, and pharmacotherapeutic options are limited. Repositioning medications approved by the U.S. Food and Drug Administration (FDA) may efficiently provide clinicians with new treatment options. We developed a drug-repositioning paradigm using larval zebrafish locomotion and established predictive clinical validity using FDA-approved smoking cessation therapeutics. We evaluated 39 physician-vetted medications for nicotine-induced locomotor activation blockade. We further evaluated candidate medications for altered ethanol response, as well as in combination with varenicline for nicotine-response attenuation. Six medications specifically inhibited the nicotine response. Among this set, apomorphine and topiramate blocked both nicotine and ethanol responses. Both positively interact with varenicline in the Bliss Independence test, indicating potential synergistic interactions suggesting these are candidates for translation into Phase II clinical trials for smoking cessation.

Adrenaline rush: the role of adrenergic receptors in stimulant-induced behaviors

Psychostimulants, such as cocaine and amphetamines, act primarily through the monoamine neurotransmitters dopamine (DA), norepinephrine, and serotonin. Although stimulant addiction research has largely focused on DA, medication development efforts targeting the dopaminergic system have thus far been unsuccessful, leading to alternative strategies aimed at abating stimulant abuse. Noradrenergic compounds have shown promise in altering the behavioral effects of stimulants in rodents, nonhuman primates, and humans. In this review, we discuss the contribution of each adrenergic receptor (AR) subtype (α1, α2, and β) to five stimulant-induced behaviors relevant to addiction: locomotor activity, conditioned place preference, anxiety, discrimination, and self-administration. AR manipulation has diverse effects on these behaviors; each subtype profoundly influences outcomes in some paradigms but is inconsequential in others. The functional neuroanatomy and intracellular signaling mechanisms underlying the impact of AR activation/blockade on these behaviors remain largely unknown, presenting a new frontier for research on psychostimulant-AR interactions.

Interaction between Antagonist of Cannabinoid Receptor and Antagonist of Adrenergic Receptor on Anxiety in Male Rat

INTRODUCTION

Anxiety is among the most common and treatable mental disorders. Adrenergic and cannabinoid systems have an important role in the neurobiology of anxiety. The elevated plus-maze (EPM) has broadly been used to investigate anxiolytic and anxiogenic compounds. The present study investigated the effects of intraperitoneal (IP) injection of cannabinoid CB1 receptor antagonist (AM251) in the presence of alpha-1 adrenergic antagonist (Prazosin) on rat behavior in the EPM.

METHODS

In this study, the data were obtained from male Wistar rat, which weighing 200- 250 g. Animal behavior in EPM were videotaped and saved in computer for 10 min after IP injection of saline, AM251 (0.3 mg/kg), Prazosin (0.3 mg/kg) and AM251 + Prazosin, subsequently scored for conventional indices of anxiety. During the test period, the number of open and closed arms entries, the percentage of entries into the open arms of the EPM, and the spent time in open and closed arms were recorded. Diazepam was considered as a positive control drug with anxiolytic effect (0.3, 0.6, 1.2 mg/kg).

RESULTS

Diazepam increased the number of open arm entries and the percentage of spent time on the open arms. IP injection of AM251 before EPM trial decreased open arms exploration and open arm entry. Whereas, Prazosin increased open arms exploration and open arm entry. This study showed that both substances in simultaneous injection have conflicting effects on the responses of each of these two compounds in a single injection.

DISCUSSION

Injection of CB1 receptor antagonist may have an anxiogenic profile in rat, whereas adrenergic antagonist has an anxiolytic effect. Further investigations are essential for better understanding of anxiolytic and anxiogenic properties and neurobiological mechanisms of action and probable interactions of the two systems.

Inhibition of hippocampal β-adrenergic receptors impairs retrieval but not reconsolidation of cocaine-associated memory and prevents subsequent reinstatement

Retrieval of drug-associated memories is critical for maintaining addictive behaviors, as presentation of drug-associated cues can elicit drug seeking and relapse. Recently, we and others have demonstrated that β-adrenergic receptor (β-AR) activation is necessary for retrieval using both rat and human memory models. Importantly, blocking retrieval with β-AR antagonists persistently impairs retrieval and provides protection against subsequent reinstatement. However, the neural locus at which β-ARs are required for maintaining retrieval and subsequent reinstatement is unclear. Here, we investigated the necessity of dorsal hippocampus (dHipp) β-ARs for drug-associated memory retrieval. Using a cocaine conditioned place preference (CPP) model, we demonstrate that local dHipp β-AR blockade before a CPP test prevents CPP expression shortly and long after treatment, indicating that dHipp β-AR blockade induces a memory retrieval disruption. Furthermore, this retrieval disruption provides long-lasting protection against cocaine-induced reinstatement. The effects of β-AR blockade were dependent on memory reactivation and were not attributable to reconsolidation disruption as blockade of β-ARs immediately after a CPP test had little effect on subsequent CPP expression. Thus, cocaine-associated memory retrieval is mediated by β-AR activity within the dHipp, and disruption of this activity could prevent cue-induced drug seeking and relapse long after treatment.

Differential effect of beta-adrenergic receptor antagonism in basolateral amygdala on reconsolidation of aversive and appetitive memories associated with morphine in rats

Positive and negative emotional experiences induced by addictive drugs play an important role in the development of dysfunctional drug-related memory, which becomes resistant to extinction and contributes to high rate of relapse. Those memories may undergo a process called reconsolidation that in some cases can be disrupted by pharmacological treatment. The basolateral amygdala (BLA) has been shown to mediate the reconsolidation of drug-related appetitive memory, but its role in withdrawal-related aversive memory remains elusive. The present study used conditioned place preference (CPP) and conditioned place aversion (CPA) paradigms to investigate the role of BLA and its noradrenergic receptors in reconsolidation of morphine-associated emotional memory in rats. We found that inhibition of protein synthesis in BLA disrupted the reconsolidation of morphine CPP (m-CPP) and CPA related to morphine withdrawal (m-CPA). A high dose of the β-noradrenergic receptor antagonist propranolol (3 µg) in BLA-impaired reconsolidation of m-CPA but not m-CPP, whereas a low dose (0.3 µg) was ineffective. In contrast, neither low nor high doses of the α-noradrenergic receptor antagonist phentolamine (1 or 10 µg) blocked the reconsolidation of m-CPP and m-CPA. In addition, infusion of propranolol (3 µg) into nucleus accumbens after retrieval of either m-CPP or m-CPA did not affect its reconsolidation. The findings indicate that appetitive and aversive addictive memories share common neural substrates in BLA, but the specific neurotransmitter mechanism on reconsolidation of morphine-associated negative and positive memories can be dissociable.

Memory reconsolidation in aversive and appetitive settings

Memory reconsolidation has been observed across species and in a number of behavioral paradigms. The majority of memory reconsolidation studies have been carried out in Pavlovian fear conditioning and other aversive memory settings, with potential implications for the treatment of post-traumatic stress disorder. However, there is a growing literature on memory reconsolidation in appetitive reward-related memory paradigms, including translational models of drug addiction. While there appears to be substantial similarity in the basic phenomenon and underlying mechanisms of memory reconsolidation across unconditioned stimulus valence, there are also notable discrepancies. These arise both when comparing aversive to appetitive paradigms and also across different paradigms within the same valence of memory. We review the demonstration of memory reconsolidation across different aversive and appetitive memory paradigms, the commonalities and differences in underlying mechanisms and the conditions under which each memory undergoes reconsolidation. We focus particularly on whether principles derived from the aversive literature are applicable to appetitive settings, and also whether the expanding literature in appetitive paradigms is informative for fear memory reconsolidation.

Prazosin differentially affects extinction of cocaine conditioned place preference on the basis of dose and initial preference

Recent work has shown that α1-adrenergic receptor blockade impairs extinction in fear conditioning paradigms in rodents. However, studies of the role of α1-adrenergic receptors in extinction using other conditioning paradigms, such as those examining the conditioned effects of drug of abuse, have yielded inconsistent results. In this article, we reanalyze and extend previously reported findings of the effect of prazosin, an α1-adrenergic receptor antagonist, on the extinction of a cocaine-induced conditioned place preference in rats, using a median split of performance during the initial test for preference. This new reanalysis, which includes further extinction testing, indicated a paradoxical dose effect. A single post-test administration of a lower dose of prazosin, 0.3 mg/kg intraperitoneally, impaired extinction in rats that showed a below-median preference during initial testing, but had no effect on extinction in rats that showed an above-median preference during initial testing. In contrast, a single post-test administration of a higher dose of prazosin, 1.0 mg/kg intraperitoneally, enhanced extinction in rats that showed an above-median preference during initial testing, but had no effect on extinction in rats that showed a below-median preference during initial testing. Consistent with other studies of fear and drug conditioning, these results suggest the involvement of the α1-adrenergic receptor in the formation of extinction memories, but also indicate a potentially important differential effect on extinction on the basis of the dose of prazosin and the strength of the initial learning.

Region-specific role of Rac in nucleus accumbens core and basolateral amygdala in consolidation and reconsolidation of cocaine-associated cue memory in rats

RATIONALE AND OBJECTIVES

Drug reinforcement and the reinstatement of drug seeking are associated with the pathological processing of drug-associated cue memories that can be disrupted by manipulating memory consolidation and reconsolidation. Ras-related C3 botulinum toxin substrate (Rac) is involved in memory processing by regulating actin dynamics and neural structure plasticity. The nucleus accumbens (NAc) and amygdala have been implicated in the consolidation and reconsolidation of emotional memories. Therefore, we hypothesized that Rac in the NAc and amygdala plays a role in the consolidation and reconsolidation of cocaine-associated cue memory.

METHODS

Conditioned place preference (CPP) and microinjection of Rac inhibitor NSC23766 were used to determine the role of Rac in the NAc and amygdala in the consolidation and reconsolidation of cocaine-associated cue memory in rats.

RESULTS

Microinjections of NSC23766 into the NAc core but not shell, basolateral (BLA), or central amygdala (CeA) after each cocaine-conditioning session inhibited the consolidation of cocaine-induced CPP. A microinjection of NSC23766 into the BLA but not CeA, NAc core, or NAc shell immediately after memory reactivation induced by exposure to a previously cocaine-paired context disrupted the reconsolidation of cocaine-induced CPP. The effect of memory disruption on cocaine reconsolidation was specific to reactivated memory, persisted at least 2 weeks, and was not reinstated by a cocaine-priming injection.

CONCLUSIONS

Our findings indicate that Rac in the NAc core and BLA are required for the consolidation and reconsolidation of cocaine-associated cue memory, respectively.

Drink, drugs and disruption: memory manipulation for the treatment of addiction

Addiction is a complex disorder, and one characterised by the acquisition of maladaptive instrumental (drug-seeking and drug-taking) and pavlovian (cue-drug associations) memories. These memories markedly contribute to the long-term risk of relapse, so reduction of the impact of these memories on behaviour could potentially be an important addition to current therapies for addiction. Memory reconsolidation may provide such a target for disrupting well-consolidated pavlovian cue-drug memories following an extensive drug history. Reconsolidation can be disrupted either by administering amnestic drugs in conjunction with a memory reactivation session, or by updating the memory adaptively through the induction of 'superextinction'. More work is needed before these therapies are ready for translation to the clinic, but if found clinically effective memory manipulation promises a radical new way of treating addiction.

Role of amygdala in drug memory

Drug addiction is a chronic brain disorder with the hallmark of a high rate of relapse to compulsive drug seeking and drug taking even after long-term abstinence. Addiction has been considered as an aberrant memory that has been termed "addiction memory." Drug-related memory plays a critical role in the maintenance of learned addictive behaviors and emergence of relapse. Disrupting these long-lasting memories by administering amnestic agents or other manipulations during specific phases of drug memory is a promising strategy for relapse prevention. Recent studies on the processes of drug addiction and relapse have demonstrated that the amygdala is involved in associative drug addiction learning processes. In this review, we focus on preclinical studies that used conditioned place preference and self-administration models to investigate the differential roles of the amygdala in each phase of drug-related memory, including acquisition, consolidation, retrieval, reconsolidation, and extinction. These studies indicate that the amygdala plays a critical role in both cue-associative learning and the expression of cue-induced relapse to drug-seeking behavior.

Neurobiological dissociation of retrieval and reconsolidation of cocaine-associated memory

Drug use is provoked by the presentation of drug-associated cues, even following long periods of abstinence. Disruption of these learned associations would therefore limit relapse susceptibility. Drug-associated memories are susceptible to long-term disruption during retrieval and shortly after, during memory reconsolidation. Recent evidence reveals that retrieval and reconsolidation are dependent on β-adrenergic receptor (β-AR) activation. Despite this, whether retrieval and reconsolidation are dependent on identical or distinct neural mechanisms is unknown. The prelimbic medial prefrontal cortex (PL-mPFC) and basolateral amygdala (BLA) have been implicated in the expression and reconsolidation of associative memories. Therefore, we investigated the necessity of β-AR activation within the PL-mPFC and BLA for cocaine-associated memory retrieval and reconsolidation in rats. Before or immediately after a cocaine-induced conditioned place preference (CPP) retrieval trial, β-AR antagonists were infused into the PL-mPFC or BLA, followed by daily testing. PL-mPFC infusions before, but not after, a CPP trial disrupted CPP memory retrieval and induced a persistent deficit in retrieval during subsequent trials. In contrast, BLA β-AR blockade had no effect on initial CPP memory retrieval, but prevented CPP expression during subsequent trials indicative of reconsolidation disruption. Our results reveal a distinct dissociation between the neural mechanisms required for cocaine-associated memory retrieval and reconsolidation. Using patch-clamp electrophysiology, we also show that application of a β-AR antagonist prevents norepinephrine-induced potentiation of PL-mPFC pyramidal cell and γ-aminobutyric-acid (GABA) interneuron excitability. Thus, targeted β-AR blockade could induce long-term deficits in drug-associated memory retrieval by reducing neuronal excitability, providing a novel method of preventing cue-elicited drug seeking and relapse.