Calpain-GRIP Signaling in Nucleus Accumbens Core Mediates the Reconsolidation of Drug Reward Memory

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.

The ventral hippocampus and nucleus accumbens as neural substrates for cocaine contextual memory reconsolidation

Drug craving triggered by cues that were once associated with drug intoxication is a major contributor to continued drug-seeking behaviors. Addictive drugs engage molecular pathways of associative learning and memory. Reactivated memories are vulnerable to disruption by interference with the process of reconsolidation, hence targeting reconsolidation could be a strategy to reduce cue-induced drug craving and relapse. Here we examined the circuitry of cocaine contextual memory reconsolidation and explored neuroplasticity following memory reactivation. Mice underwent chemogenetic inhibition of either nucleus accumbens (NA) neurons or the glutamatergic projection neurons from the ventral hippocampus (vHPC) to NA using inhibitory designer receptors exclusively activated by designer drugs (iDREADD). Mice underwent cocaine conditioned place preference followed by reactivation of the cocaine contextual memory. Clozapine-N-oxide (CNO) was administered after memory reactivation to inhibit either NA neurons or the accumbens-projecting vHPC neurons during the reconsolidation period. When retested 3 days later, a significant reduction in the previously established preference for the cocaine context was found in both conditions. FosTRAP2-Ai14 mice were used to identify neurons activated by cocaine memory recall and to evaluate plasticity in NA medium spiny neurons (MSNs) and vHPC pyramidal neurons upon recall of cocaine memories. Results indicate a significant increase in dendritic spine density in NA MSNs activated by cocaine memory recall, particularly of the thin spine type. Sholl analysis indicated longer dendritic length and more branching of NA MSNs after cocaine memory recall than without memory reactivation. vHPC neurons showed increased spine density, with the most robust change in stubby spines. These results implicate a circuit involving glutamatergic projections from the vHPC onto NA neurons which is necessary for the reconsolidation of cocaine memories. Interruption of cocaine memory reconsolidation reduced drug-seeking behavior.

Gut-derived bacterial LPS attenuates incubation of methamphetamine craving via modulating microglia

BACKGROUND

The microbiota-gut-brain axis plays a critical role in the pathophysiology of neuropsychiatric disorders, and the compositions of gut microbiota are altered by addictive drugs. However, the role of gut microbiota in the incubation of methamphetamine (METH) craving remains poorly understood.

METHODS

16S rRNA gene sequencing was performed to assess the richness and diversity of gut microbiota in METH self-administration model. Hematoxylin and eosin staining was performed to evaluate the integrity of intestinal barrier. Immunofluorescence and three-dimensional reconstruction were performed to assess the morphologic changes of microglia. Serum levels of lipopolysaccharide (LPS) were determined using the rat enzyme-linked immunosorbent assay kits. Quantitative real-time PCR was performed to assess transcript levels of dopamine receptor, glutamate ionotropic AMPA receptor 3 and brain-derived neurotrophic factor.

RESULTS

METH self-administration induced gut microbiota dysbiosis, intestinal barrier damage and microglia activation in the nucleus accumbens core (NAcc), which was partially recovered after prolonged withdrawal. Microbiota depletion via antibiotic treatment increased LPS levels and induced a marked change in the microglial morphology in the NAcc, as indicated by the decreases in the lengths and numbers of microglial branches. Depleting the gut microbiota also prevented the incubation of METH craving and increased the population of Klebsiella oxytoca. Furthermore, Klebsiella oxytoca treatment or exogenous administration of the gram-negative bacterial cell wall component LPS increased serum and central LPS levels, induced microglial morphological changes and reduced the dopamine receptor transcription in the NAcc. Both treatments and NAcc microinjections of gut-derived bacterial LPS significantly decreased METH craving after prolonged withdrawal.

CONCLUSIONS

These data suggest that LPS from gut gram-negative bacteria may enter circulating blood, activate microglia in the brain and consequently decrease METH craving after withdrawal, which may have important implications for novel strategies to prevent METH addiction and relapse.

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

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

Glutamate receptor-interacting protein 1 in D1- and D2-dopamine receptor-expressing medium spiny neurons differentially regulates cocaine acquisition, reinstatement, and associated spine plasticity

BACKGROUND

The nucleus accumbens (NAc) is involved in the expression of cocaine addictive phenotypes, including acquisition, extinction, and reinstatement. In the NAc, D1-medium spiny neurons (MSNs) encode cocaine reward, whereas D2-MSNs encode aversive responses in drug addiction. Glutamate receptor-interacting protein 1 (GRIP1) is known to be associated with cocaine addiction, but the role of GRIP1 in D1-MSNs and D2-MSNs of the NAc in cocaine acquisition and reinstatement remains unknown.

METHODS

A conditioned place preference apparatus was used to establish cocaine acquisition, extinction, and reinstatement in mouse models. GRIP1 expression was evaluated using Western blotting. Furthermore, GRIP1-siRNA and GRIP1 overexpression lentivirus were used to interfere with GRIP1 in the NAc. After the behavioral test, green fluorescent protein immunostaining of brain slices was used to detect spine density.

RESULTS

GRIP1 expression decreased during cocaine acquisition and reinstatement. GRIP1-siRNA enhanced cocaine-induced CPP behavior in acquisition and reinstatement and regulated associated spine plasticity. Importantly, the decreased GRIP1 expression that mediated cocaine acquisition and reinstatement was mainly driven by the interference of the GRIP1-GluA2 interaction in D1-MSNs and could be blocked by the interference of the GRIP1-GluA2 interaction in D2-MSNs. Interference with the GRIP1-GluA2 interaction in D1- and D2-MSNs decreased spine density in D1- and D2-MSNs, respectively.

CONCLUSION

GRIP1 in D1- and D2-MSNs of the NAc differentially modulates cocaine acquisition and reinstatement. GRIP1 downregulation in D1-MSNs has a positive effect on cocaine acquisition and reinstatement, while GRIP1 downregulation in D2-MSNs has a negative effect. Additionally, GRIP1 downregulation in D1-MSNs plays a leading role in cocaine acquisition and reinstatement.

Individual differences in cocaine-induced conditioned place preference in male rats: Behavioral and transcriptomic evidence

BACKGROUND

Substance use disorder emerges in a small proportion of drug users and has the characteristics of a chronic relapsing pathology.

AIMS

Our study aimed to demonstrate and characterize the variability in the expression of the rewarding effects of cocaine in the conditioned place preference (CPP) paradigm.

METHODS

A cocaine-CPP paradigm in male Sprague-Dawley rats with an extinction period of 12 days and reinstatement was conducted. A statistical model was developed to distinguish rats expressing or not a cocaine-induced place preference.

RESULTS

Two groups of rats were identified: rats that did express rewarding effects (CPP expression (CPPE), score >102 s) and rats that did not (no CPP expression (nCPPE), score between -85 and 59 s). These two groups did not show significant differences in a battery of behavioral tests. To identify differentially expressed genes in the CPPE and nCPPE groups, a whole-transcriptome ribonucleic acid-sequencing analysis was performed in the nucleus accumbens (NAc) 24 h after the CPP test. Four immediate early genes (Fos, Egr2, Nr4a1, and Zbtb37) were differentially expressed in the NAc of CPPE rats after expression of CPP. Variability in cocaine-induced place preference persisted in the CPPE and nCPPE groups after the extinction and reinstatement phases. Transcriptomic differences observed after reinstatement were distinct from those observed immediately after expression of CPP.

CONCLUSION

These new findings provide insights into the identification of mechanisms underlying interindividual variability in the response to cocaine's rewarding effects.

Effects of 3-methylmethcathinone on conditioned place preference and anxiety-like behavior: Comparison with methamphetamine

3-Methylmethcathinone (3-MMC), a drug belonging to synthetic cathinones family, raised public attention due to its harmful health effects and abuse potential. Although it has similar properties to other cathinone derivatives, the behavioral effects of 3-MMC remain largely unknown. In the present research, we evaluated the rewarding effect of 3-MMC using conditioned place preference (CPP) paradigm and its effect on anxiety-like behavior using elevated plus maze (EPM) and compared with methamphetamine (METH). Then, we performed a whole-brain c-Fos mapping to identify the specific brain regions in response to 3-MMC exposure and explored the changes of synaptic transmission in nucleus accumbens (NAc) using patch-clamp recording after chronic 3-MMC and METH exposure. 3-MMC induced CPP at higher doses of 3 or 10 mg/kg in rats and acute exposure of 3 mg/kg 3-MMC to rats produced anxiolytic-like effect, while anxiety-like behavior was increased after 7 days of injection with 3-MMC. Whole-brain immunostaining revealed increased c-Fos expression in anterior cingulate cortex (ACC), NAc and ventral tegmental area (VTA) after chronic 3-MMC injection compared with saline, which was similar to METH. Especially, 3-MMC induced more neural activation of VTA compared with METH. Finally, we found that amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) in NAc was decreased after chronic 3-MMC injection, while frequency of sIPSCs and spontaneous excitatory postsynaptic currents (sEPSCs) were not affected. Taken together, our results revealed the addictive potential of 3-MMC and its effect on anxiety-like behavior, which warn the risks of 3-MMC abuse and justify the control of synthetic cathinones. And 3-MMC selectively inhibit inhibitory but not excitatory transmission onto neurons in NAc, which may contribute to its effects.

Glutamate Receptor Interacting Protein 1 in the Dorsal CA1 Drives Alpha-amino-3-hydroxy-5-methyl-4-Isoxazolepropionic Acid Receptor Endocytosis and Exocytosis Bidirectionally and Mediates Forgetting, Exploratory, and Anxiety-like Behavior

Endocytosis of GluA2-containing alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) in CA1 of the hippocampus regulates forgetting; deficits in forgetting nociceptive memory can induce serious stress disorders. As a transporter of GluA2-containing AMPAR, the functions of glutamate receptor interacting protein 1 (GRIP1) in forgetting and possible stress responses remain unclear. Lentivirus-mediated interference of GRIP1 expression or function in the dorsal CA1 of the hippocampus in mice indicated that GRIP1 overexpression enhanced spatial memory, impaired forgetting in a Barnes maze, and induced anxiety-like behavior in the open field and elevated plus-maze test. In contrast, GRIP1 knockdown impaired learning capacity. Furthermore, inhibition of the PDZ2 and PDZ4/5 domains of GRIP1 and GluA2-dn enhanced learning capacity, whereas GluA2-dn impaired spatial memory; inhibition of the PDZ2 and PDZ4/5 domains of GRIP1 also decreased forgetting capacity to some extent. Importantly, inhibition of both the PDZ2 and PDZ4/5 domains of GRIP1 induced anxiety-like behavior but not GluA2-dn. Furthermore, optogenetic control of both GluA1 and GluA2 insertion into the postsynaptic membrane impaired memory and induced anxiety-like behavior. In vitro experiments showed that GRIP1-ov and -dn, inhibition of PDZ2 and PDZ4/5 domains of GRIP1, and GluA2-dn decreased glycine-induced GluA1 and GluA2 exocytosis; meanwhile, GRIP1-ov and -dn, and interference of PDZ2 and PDZ4/5 domains of GRIP1 blocked AMPA- and NMDA-induced GluA1 and GluA2 endocytosis. Overall, these results suggest that GRIP1 drives AMPA receptor endocytosis and exocytosis bidirectionally; furthermore, GRIP1-induced stabilization of anchoring postsynaptic GluA1 and GluA2 impairs forgetting and induces anxiety-like behavior. GRIP1 may provide a potential therapeutic target in posttraumatic syndromes and anxiety disorders.

Anshen Dingzhi prescription in the treatment of PTSD in mice: Investigation of the underlying mechanism from the perspective of hippocampal synaptic function

BACKGROUND

Anshen Dingzhi prescription (ADP) is an important prescription for the treatment of mental diseases in traditional Chinese medicine and is widely used to treat neuropsychiatric disorders.

PURPOSE

To explore the ameliorative effect of ADP on post-traumatic stress disorder (PTSD)-like behaviors in mice and determine the underlying mechanism.

METHODS

The constituents of ADP were analyzed by UPLC-Q-TOF/MS. The PTSD-like behaviors of mice subjected to single prolonged stress (SPS) were evaluated using behavioral tests. Potential pathological changes in the hippocampus were assessed by hematoxylin and eosin (H&E) staining. Western blotting and immunohistochemistry (IHC) were employed to detect the expression of proteins involved in relevant signaling pathways.

RESULTS

Five quality control markers (ginsenoside Rg1, ginsenoside Rb1, tenuifolin, poricoic acid B, and α-asarone) were detected in the ADP solution. The ginsenoside Rg1 content in ADP was found to be 0.114 mg/g. Mice subjected to SPS showed obvious fear generalization and anxiety-like behaviors. ADP treatment prevented the behavioral changes caused by exposure to SPS. Compared with control animals, the number of normal pyramidal cells in the hippocampal CA1 region of mice exposed to SPS was decreased and the number of degenerating pyramidal cells was increased; however, ADP administration could counteract these effects. Furthermore, the protein expression of BDNF, p-TrkB, μ-calpain, PSD95, GluN2A, GluA1, p-AKT, p-mTOR, and ARC was decreased, while that of PTEN and GluN2B was increased in the hippocampus of mice subjected to SPS compared with that in control animals; however, these changes in protein expression were reversed following ADP treatment. Importantly, the ameliorative effect of ADP on PTSD-like behaviors and synaptic protein expression were inhibited by rapamycin administration.

CONCLUSIONS

ADP administration improves PTSD-like behaviors in mice and this effect may be mediated through an mTOR-dependent improvement in synaptic function in the hippocampus.

CircTmeff-1 in the nucleus accumbens regulates the reconsolidation of cocaine-associated memory

Reconsolidation of drug memories is the process of restoring unstable memories after unconditioned (UCS; e.g., drugs) or conditioned stimulus (CS; e.g., drug-paired contexts), and provides promise for prevention of drug relapse. Circular RNAs (circRNAs) have important effects on the transcription and post-transcriptional regulation of gene expression. However, the role of circRNAs in the reconsolidation of drug memories is unclear. Here, we observed that cocaine-induced memory retrieval significantly increased circTmeff-1 level in the nucleus accumbens (NAc) core but not shell. Importantly, the disrupted expression of circTmeff-1 using virus in the NAc core damaged the reconsolidation of cocaine-associated memories. The knockdown of circTmeff-1 in the NAc shell or without UCS retrieval or 9 h after UCS retrieval had no such effects. Mechanistically, using bioinformatic analysis and loss- or gain- of function assays, we revealed that antagomiR-206 reversed the inhibitory effect of circTmeff-1 knockdown on the expression of brain-derived neurotrophic factor (BDNF) during the reconsolidation of cocaine-associated memories. Taken together, these results demonstrate the role of circTmeff-1 in the reconsolidation of cocaine-associated memory and that circTmeff-1 may function as a decoy for miR-206 to regulate the expression of BDNF.

Transcriptomic Analysis of Long Non-coding RNA-MicroRNA-mRNA Interactions in the Nucleus Accumbens Related to Morphine Addiction in Mice

Recent research suggest that some non-coding RNAs (ncRNAs) are important regulators of chromatin dynamics and gene expression in nervous system development and neurological diseases. Nevertheless, the molecular mechanisms of long non-coding RNAs (lncRNAs), acting as competing endogenous RNAs (ceRNAs), underlying morphine addiction are still unknown. In this research, RNA sequencing (RNA-seq) was used to examine the expression profiles of lncRNAs, miRNAs and mRNAs on the nucleus accumbens (NAc) tissues of mice trained with morphine or saline conditioned place preference (CPP), with differential expression of 31 lncRNAs, 393 miRNAs, and 371 mRNAs found. A ceRNA network was established for reciprocal interactions for 9 differentially expressed lncRNAs (DElncRNAs), 10 differentially expressed miRNAs (DEmiRNAs) and 12 differentially expressed mRNAs (DEmRNAs) based on predicted miRNAs shared by lncRNAs and mRNAs. KEGG pathway enrichment analyses were conducted to explore the potential functions of DEmRNAs interacting with lncRNAs in the ceRNA network. These DEmRNAs were enriched in synaptic plasticity-related pathways, including pyrimidine metabolism, ECM-receptor interaction, and focal adhesion. The correlation between the relative expression of lncRNAs, miRNAs and mRNAs was analyzed to further validate predicted ceRNA networks, and the Lnc15qD3-miR-139-3p-Lrp2 ceRNA regulatory interaction was determined. These results suggest that the comprehensive network represents a new insight into the lncRNA-mediated ceRNA regulatory mechanisms underlying morphine addiction and provide new potential diagnostic and prognostic biomarkers for morphine addiction.

The Mechanisms and Boundary Conditions of Drug Memory Reconsolidation

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

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

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

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.

Decreased Neuronal Excitability in Medial Prefrontal Cortex during Morphine Withdrawal is associated with enhanced SK channel activity and upregulation of small GTPase Rac1

Rationale: Neuroadaptations in the medial prefrontal cortex (mPFC) and Nucleus Accumbens (NAc) play a role in the disruption of control-reward circuits in opioid addiction. Small Conductance Calcium-Activated Potassium (SK) channels in the mPFC have been implicated in neuronal excitability changes during morphine withdrawal. However, the mechanism that modulates SK channels during withdrawal is still unknown.

Methods: Rats were exposed for one week to daily morphine injections (10 mg·kg^-1 s.c.) followed by conditional place preference (CPP) assessment. One week after withdrawal, electrophysiological, morphological and molecular biological methods were applied to investigate the effects of morphine on SK channels in mPFC, including infralimbic (IL), prelimbic (PrL) cortices and NAc (core and shell). We verified the hypothesis that Rac1, a member of Rho family of small GTPases, implicated in SK channel regulation, modulate SK channel neuroadaptations during opiate withdrawal.

Results: One week after morphine withdrawal, the neuronal excitability of layer 5 pyramidal neurons in IL was decreased, but not in PrL. Whereas, the excitability was increased in NAc-shell, but not in NAc-core. In mPFC, the expression of the SK3 subunit was enhanced after one-week of withdrawal compared to controls. In the IL, Rac1 signaling was increased during withdrawal, and the Rac1 inhibitor NSC23766 disrupted SK current, which increased neuronal firing. Suppression of Rac1 inhibited morphine-induced CPP and expression of SK channels in IL.

Conclusions: These findings highlight the potential value of SK channels and the upstream molecule Rac1, which may throw light on the therapeutic mechanism of neuromodulation treatment for opioid dependence.

Endogenous opiates and behavior: 2017

This paper is the fortieth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2017 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Can cocaine-induced neuroinflammation explain maladaptive cocaine-associated memories?

Persistent and intrusive memories define a number of psychiatric disorders, including posttraumatic stress disorder and substance use disorder. In the latter, memory for drug-paired cues plays a critical role in sustaining compulsive drug use as these are potent triggers of relapse. As with many drugs, cocaine-cue associated memory is strengthened across presentations as cues become reliable predictors of drug availability. Recently, the targeting of cocaine-associated memory through disruption of the reconsolidation process has emerged as a potential therapeutic strategy; reconsolidation reflects the active process by which memory is re-stabilized after retrieval. In addition, a separate line of work reveals that neuroinflammatory markers, regulated by cocaine intake, play a role in memory processes. Our review brings these two literatures together by summarizing recent findings on cocaine-associated reconsolidation and cocaine-induced neuroinflammation. We discuss the interactions between reconsolidation processes and neuroinflammation following cocaine use, concluding with a new perspective on treatment to decrease risk of relapse to cocaine use.

Glutamate receptor interacting protein acts within the prefrontal cortex to blunt cocaine seeking

Glutamate receptor interacting protein (GRIP) is a neuronal scaffolding protein that anchors GluA2-containing AMPA receptors to the cell membrane. GRIP plays a critical role in activity-dependent synaptic plasticity, including that which occurs after drug exposure. Given that cocaine administration alters glutamate receptor trafficking within the prefrontal cortex (PFC), a better understanding of the role of receptor trafficking proteins could lead to a more complete understanding of addictive phenotypes. AMPA receptor trafficking in general, and GRIP specifically, is known to play a role in cocaine seeking and conditioned reward in the nucleus accumbens, but its role in the PFC has not been characterized. The current study demonstrates that conditional deletion of GRIP1 in the medial prefrontal cortex increases the motivation for cocaine and potentiates cue-induced reinstatement of cocaine seeking in male and female mice. As no effects of PFC GRIP1 deletion were seen in reinstatement of food seeking, strategy set-shifting, or reversal learning the effects on cocaine seeking are not related to generalized alterations in cognitive function. While disrupting GRIP1 might be expected to lead to decreased AMPA transmission, our electrophysiological data indicate an increase in sEPSC amplitude in the prefrontal cortex and a corresponding decrease in paired pulse facilitation in the nucleus accumbens. Taken together this suggests a strengthening of the PFC to NAc input following prefrontal GRIP1 deletion that may mediate the enhanced drug seeking behavior.

The role of nucleus accumbens shell on acquisition and retrieval stages of morphine state dependent learning

AIM

In the present study, the effect of transient inactivation of the shell subregion of the nucleus accumbens (NAC shell) by lidocaine on the acquisition and retrieval stages of passive avoidance learning (PAL) and memory and morphine state-dependent learning (SDL) in male wistar rats was investigated.

METHODOLOGY

Adult male wistar rats weighing (220-250 g) were used. Lidocaine hydrochloride was bilaterally injected into the shell area of the nucleus accumbens 5 min before of subcutaneous morphine administration.

RESULTS

pre-training and pre-test infusion of lidocaine into the NAC shell significantly impaired PAL and memory. Furthermore, Pre-training administration of morphine (5 mg/kg, s.c.) in a step-through passive avoidance task induced state-dependent learning with impaired memory retrieval on the test day. The impairment of memory was restored after pre-test administration of the same dose of morphine. This phenomenon has been named as morphine state dependent learning (SDL). Moreover, Pre-training and pre-test inactivation of the NAC shell impaired morphine SDL.

CONCLUSIONS

The results suggest the role of NAC shell as a common structure in the PAL and morphine SDL. It is suggested that NAC shell as a common area plays a critical role in the acquisition and retrieval stages of PAL and also morphine SDL.

Reconsolidation blockade for the treatment of addiction: challenges, new targets, and opportunities

Addiction is a chronic, relapsing disorder. The progression to pathological drug-seeking is thought to be driven by maladaptive learning processes which store and maintain associative memory, linking drug highs with cues and actions in the environment. These memories can encode Pavlovian associations which link predictive stimuli (e.g., people, places, and paraphernalia) with a hedonic drug high, as well as instrumental learning about the actions required to obtain drug-associated incentives. Learned memories are not permanent however, and much recent interest has been generated in exploiting the process of reconsolidation to erase or significantly weaken maladaptive memories to treat several mental health disorders, including addictions. Normally reconsolidation serves to update and maintain the adaptive relevance of memories, however administration of amnestic agents within the critical "reconsolidation window" can weaken or even erase maladaptive memories. Here we discuss recent advances in the field, including ongoing efforts to translate preclinical reconsolidation research in animal models into clinical practice.

Calpain modulates fear memory consolidation, retrieval and reconsolidation in the hippocampus

It has been proposed that long-lasting changes in dendritic spines provide a physical correlate for memory formation and maintenance. Spine size and shape are highly plastic, controlled by actin polymerization/depolymerization cycles. This actin dynamics are regulated by proteins such as calpain, a calcium-dependent cysteine protease that cleaves the structural cytoskeleton proteins and other targets involved in synaptic plasticity. Here, we tested whether the pharmacological inhibition of calpain in the dorsal hippocampus affects memory consolidation, retrieval and reconsolidation in rats trained in contextual fear conditioning. We first found that post-training infusion of the calpain inhibitor PD150606 impaired long-term memory consolidation, but not short-term memory. Next, we showed that pre-test infusion of the calpain inhibitor hindered memory retrieval. Finally, blocking calpain activity after memory reactivation disrupted reconsolidation. Taken together, our results show that calpain play an essential role in the hippocampus by enabling memory formation, expression and reconsolidation.

Potential Alzheimer's Disease Therapeutics Among Weak Cysteine Protease Inhibitors Exhibit Mechanistic Differences Regarding Extent of Cathepsin B Up-Regulation and Ability to Block Calpain

Cysteine protease inhibitors have long been part of drug discovery programs for Alzheimer's disease (AD), traumatic brain injury (TBI), and other disorders. Select inhibitors reduce accumulating proteins and AD pathology in mouse models. One such compound, Z-Phe-Aladiazomethylketone (PADK), exhibits a very weak IC₅₀ (9-11 μM) towards cathepsin B (CatB), but curiously PADK causes marked up-regulation of the Aβ-degrading CatB and improves spatial memory. Potential therapeutic and weak inhibitor E64d (14 μM IC₅₀) also up-regulates CatB. PADK and E64d were compared regarding the blockage of calcium-induced cytoskeletal deterioration in brain samples, monitoring the 150-kDa spectrin breakdown product (SBDP) known to be produced by calpain. PADK had little to no effect on SBDP production at 10-100 μM. In contrast, E64d caused a dose-dependent decline in SBDP levels with an IC₅₀ of 3-6 μM, closely matching its reported potency for inhibiting μ-calpain. Calpain also cleaves the cytoskeletal organizing protein gephyrin, producing 49-kDa (GnBDP49) and 18-kDa (GnBDP18) breakdown products. PADK had no apparent effect on calcium-induced gephyrin fragments whereas E64d blocked their production. E64d also protected the parent gephyrin in correspondence with reduced BDP levels. The findings of this study indicate that PADK's positive and selective effects on CatB are consistent with human studies showing exercise elevates CatB and such elevation correlates with improved memory. On the other hand, E64d exhibits both marginal CatB enhancement and potent calpain inhibition. This dual effect may be beneficial for treating AD. Alternatively, the potent action on calpain-related pathology may explain E64d's protection in AD and TBI models.