The activation of NMDA receptor-ERK pathway in the central amygdala is required for the expression of morphine-conditioned place preference in the rat

Degradation of perineuronal nets in the medial prefrontal cortex promotes extinction and reduces reinstatement of methamphetamine-induced conditioned place preference in female mice

The high rate of relapse to compulsive methamphetamine (MA)-taking and seeking behaviors after abstinence constitutes a major obstacle to the treatment of MA addiction. Perineuronal nets (PNNs), essential components of the extracellular matrix, play a critical role in synaptic function, learning, and memory. Abnormalities in PNNs have been closely linked to a series of neurological diseases, such as addiction. However, the exact role of PNNs in MA-induced related behaviors remains elusive. Here, we established a MA-induced conditioned place preference (CPP) paradigm in female mice and found that the number and average optical density of PNNs increased significantly in the medial prefrontal cortex (mPFC) of mice during the acquisition, extinction, and reinstatement stages of CPP. Notably, the removal of PNNs in the mPFC via chondroitinase ABC (ChABC) before extinction training not only facilitated the extinction of MA-induced CPP and attenuated the relapse of extinguished MA preference but also significantly reduced the activation of c-Fos in the mPFC. Similarly, the ablation of PNNs in the mPFC before reinstatement markedly lessened the reinstatement of MA-induced CPP, which was accompanied by the decreased expression of c-Fos in the mPFC. Collectively, our results provide more evidence for the implication of degradation of PNNs in facilitating extinction and preventing relapse of MA-induced CPP, which indicate that targeting PNNs may be an effective therapeutic option for MA-induced CPP memories.

NMDA receptor within nucleus accumbens shell regulates propofol self-administration through D1R/ERK/CREB signalling pathway

Addictive properties of propofol have been demonstrated in both humans and animals. The nucleus accumbens (NAc) shell (NAsh) in the brain, along with the interactions between N-methyl-D-aspartate receptor (NMDAR) and the dopamine D1 receptor (D1R), as well as their downstream ERK/CREB signalling pathway in the NAc, are integral in regulating reward-seeking behaviour. Nevertheless, it remains unclear whether NMDARs and the NMDAR-D1R/ERK/CREB signalling pathway in the NAsh are involved in mediating propofol addiction. To investigate it, we conducted experiments with adult male Sprague-Dawley rats to establish a model of propofol self-administration behaviour. Subsequently, we microinjected D-AP5 (a competitive antagonist of NMDARs, 1.0-4.0 μg/0.3 μL/site) or vehicle into bilateral NAsh in rats that had previously self-administered propofol to examine the impact of NMDARs within the NAsh on propofol self-administration behaviour. Additionally, we examined the protein expressions of NR2A and NR2B subunits, and the D1R/ERK/CREB signalling pathways within the NAc. The results revealed that propofol administration behaviour was enhanced by D-AP5 pretreatment in NAsh, accompanied by elevated expressions of phosphorylation of NR2A (Tyr1246) and NR2B (Tyr1472) subunits. There were statistically significant increases in the expressions of D1Rs, as well as in the phosphorylated ERK1/2 (p-ERK1/2) and CREB (p-CREB). This evidence substantiates a pivotal role of NMDARs in the NAsh, with a particular emphasis on the NR2A and NR2B subunits, in mediating propofol self-administration behaviour. Furthermore, it suggests that this central reward processing mechanism may operate through the NMDAR-D1R/ERK/CREB signal transduction pathway.

β_lactam antibiotics against drug addiction: A novel therapeutic option

Drug addiction as a problem for the health of the individual and the society is the result of a complex process in which there is an interaction between brain nuclei and neurotransmitters (such as glutamate). β-lactam antibiotics, due to their enhancing properties on the glutamate transporter glutamate transporter-1, can affect and counteract the addictive mechanisms of drugs through the regulation of extracellular glutamate. Since glutamate is a key neurotransmitter in the development of drug addiction, it seems that β-lactams can be considered as a promising treatment for addiction. However, more research in this field is necessary to identify other mechanisms involved in their effectiveness. This article is a review of the studies conducted on the effect of β-lactam administration in preventing the development of drug addiction, as well as their possible cellular and molecular mechanisms. This review suggests the clinical use of β-lactam antibiotics that have weak antimicrobial properties (such as clavulanic acid) in the treatment of drug dependence.

Addictive drugs modify neurogenesis, synaptogenesis and synaptic plasticity to impair memory formation through neurotransmitter imbalances and signaling dysfunction

Drug abuse changes neurophysiological functions at multiple cellular and molecular levels in the addicted brain. Well-supported scientific evidence suggests that drugs negatively affect memory formation, decision-making and inhibition, and emotional and cognitive behaviors. The mesocorticolimbic brain regions are involved in reward-related learning and habitual drug-seeking/taking behaviors to develop physiological and psychological dependence on the drugs. This review highlights the importance of specific drug-induced chemical imbalances resulting in memory impairment through various neurotransmitter receptor-mediated signaling pathways. The mesocorticolimbic modifications in the expression levels of brain-derived neurotrophic factor (BDNF) and the cAMP-response element binding protein (CREB) impair reward-related memory formation following drug abuse. The contributions of protein kinases and microRNAs (miRNAs), along with the transcriptional and epigenetic regulation have also been considered in memory impairment underlying drug addiction. Overall, we integrate the research on various types of drug-induced memory impairment in distinguished brain regions and provide a comprehensive review with clinical implications addressing the upcoming studies.

CNTN1 in the Nucleus Accumbens is Involved in Methamphetamine-Induced Conditioned Place Preference in Mice

Methamphetamine (Meth), a commonly used central nervous system stimulant, is highly addictive. Currently, there is no effective treatment for Meth dependence and abuse, although cell adhesion molecules (CAMs) have been shown to play an important role in the formation and remodeling of synapses in the nervous system while also being involved in addictive behavior. Contactin 1 (CNTN1) is a CAM that is widely expressed in the brain; nevertheless, its role in Meth addiction remains unclear. Therefore, in the present study, we established mouse models of single and repeated Meth exposure and subsequently determined that CNTN1 expression in the nucleus accumbens (NAc) was upregulated in mice following single or repeated Meth exposure, whereas CNTN1 expression in the hippocampus was not significantly altered. Intraperitoneal injection of the dopamine receptor 2 antagonist haloperidol reversed Meth-induced hyperlocomotion and upregulation of CNTN1 expression in the NAc. Additionally, repeated Meth exposure also induced conditioned place preference (CPP) in mice and upregulated the expression levels of CNTN1, NR2A, NR2B, and PSD95 in the NAc. Using an AAV-shRNA-based approach to specifically silence CNTN1 expression in the NAc via brain stereotaxis reversed Meth-induced CPP and decreased the expression levels of NR2A, NR2B, and PSD95 in the NAc. These findings suggest that CNTN1 expression in the NAc plays an important role in Meth-induced addiction, and the underlying mechanism may be related to the expression of synapse-associated proteins in the NAc. The results of this study improved our understanding of the role of cell adhesion molecules in Meth addiction.

Contributions of extracellular-signal regulated kinase 1/2 activity to the memory trace

The ability to learn from experience and consequently adapt our behavior is one of the most fundamental capacities enabled by complex and plastic nervous systems. Next to cellular and systems-level changes, learning and memory formation crucially depends on molecular signaling mechanisms. In particular, the extracellular-signal regulated kinase 1/2 (ERK), historically studied in the context of tumor growth and proliferation, has been shown to affect synaptic transmission, regulation of neuronal gene expression and protein synthesis leading to structural synaptic changes. However, to what extent the effects of ERK are specifically related to memory formation and stabilization, or merely the result of general neuronal activation, remains unknown. Here, we review the signals leading to ERK activation in the nervous system, the subcellular ERK targets associated with learning-related plasticity, and how neurons with activated ERK signaling may contribute to the formation of the memory trace.

Glutamatergic Systems and Memory Mechanisms Underlying Opioid Addiction

Glutamate is the main excitatory neurotransmitter in the brain and is of critical importance for the synaptic and circuit mechanisms that underlie opioid addiction. Opioid memories formed over the course of repeated drug use and withdrawal can become powerful stimuli that trigger craving and relapse, and glutamatergic neurotransmission is essential for the formation and maintenance of these memories. In this review, we discuss the mechanisms by which glutamate, dopamine, and opioid signaling interact to mediate the primary rewarding effects of opioids, and cover the glutamatergic systems and circuits that mediate the expression, extinction, and reinstatement of opioid seeking over the course of opioid addiction.

Oxytocin Attenuates Expression, but Not Acquisition, of Sucrose Conditioned Place Preference in Rats

Maladaptation of reward processing for natural rewards, such as sucrose or sugar, may play a role in the development of diseases such as obesity and diabetes. Furthermore, uncovering mechanisms to disrupt or reverse maladaptation of reward-seeking behaviors for natural reinforcers can provide insight into treatment of such diseases, as well as disorders such as addiction. As such, studying the effects of potential pharmacotherapeutics on maladaptive sugar-seeking behavior offers valuable clinical significance. Sucrose conditioned place preference (CPP) paradigms can offer insight into aspects of reward processes as it provides a way to assess acquisition and expression of context-reward associations. The present study examined the effect of peripheral oxytocin injections on sucrose CPP in rats. Oxytocin, when administered prior to CPP test, attenuated expression of sucrose CPP. However, oxytocin, when administered during sucrose conditioning, did not affect subsequent place preference. These findings suggest oxytocin sufficiently attenuates expression of sucrose-associated place preference.

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

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

Peripubertal stress of male, but not female rats increases morphine-induced conditioned place preference and locomotion in adulthood

Animal studies demonstrate that peripubertal social stress markedly increases the risk for subsequent substance use in adulthood. However, whether non-social stress has a similar long-term impact is not clear, and whether male and female animals show different sensitivity to peripubertal non-social stress has not been examined. In the present study, we addressed these issues by introducing two non-social stressors (elevated platform and predator odor 2,5-Dihydro-2,4,5-trimethylthiazoline) to male and female Wistar rats during adolescence (postnatal days 28-30, 34, 36, 40, and 42), then tested reward-related behaviors during adulthood, including morphine-induced conditioned place preference (CPP, 1 mg/kg morphine or 5 mg/kg morphine) and hyperlocomotor activity (5 mg/kg morphine). We found that adult male rats, but not females who were exposed to peripubertal non-social stressors showed enhanced morphine-induced CPP. Moreover, morphine-induced increase in locomotor activity was also significantly increased in adult male rats, but not in females. These results indicate that peripubertal exposure to repeated non-social stress may enhance sensitivity to the rewarding effects of opioids in adulthood in a sex-dependent manner, with males being even more sensitive than females in this regard.

Morphine Dependence is Attenuated by Treatment of 3,4,5-Trimethoxy Cinnamic Acid in Mice and Rats

The effect of 3, 4, 5-trimethoxy cinnamic acid (TMCA) against morphine-induced dependence in mice and rats was investigated. Mice were pretreated with TMCA and then morphine was injected intraperitoneally; whereas rats were treated with TMCA (i.p.) and infused with morphine into the lateral ventricle of brain. Naloxone-induced morphine withdrawal syndrome and conditioned place preference test were performed. Moreover, western blotting and immunohistochemistry were used to measure protein expressions. Number of naloxone-precipitated jumps and conditioned place preference score in mice were attenuated by TMCA. Likewise, TMCA attenuated morphine dependent behavioral patterns such as diarrhea, grooming, penis licking, rearing, teeth chattering, and vocalization in rats. Moreover, the expression levels of pNR1and pERK in the frontal cortex of mice and cultured cortical neurons were diminished by TMCA. In the striatum, pERK expression was attenuated despite unaltered expression of pNR1 and NR1. Interestingly, morphine-induced elevations of FosB/ΔFosB⁺ cells were suppressed by TMCA (50, 100 mg/kg) in the nucleus accumbens sub-shell region of mice. In conclusion, TMCA could be considered as potential therapeutic agent against morphine-induced dependence.

PARP-1 is required for retrieval of cocaine-associated memory by binding to the promoter of a novel gene encoding a putative transposase inhibitor

Reward-related memory is an important factor in cocaine seeking. One necessary signaling mechanism for long-term memory formation is the activation of poly(ADP-ribose) polymerase-1 (PARP-1), via poly(ADP-ribosyl)ation. We demonstrate herein that auto-poly(ADP-ribosyl)ation of activated PARP-1 was significantly pronounced during retrieval of cocaine-associated contextual memory, in the central amygdala (CeA) of rats expressing cocaine-conditioned place preference (CPP). Intra-CeA pharmacological and short hairpin RNA depletion of PARP-1 activity during cocaine-associated memory retrieval abolished CPP. In contrast, PARP-1 inhibition after memory retrieval did not affect CPP reconsolidation process and subsequent retrievals. Chromatin immunoprecipitation sequencing revealed that PARP-1 binding in the CeA is highly enriched in genes involved in neuronal signaling. We identified among PARP targets in CeA a single gene, yet uncharacterized and encoding a putative transposase inhibitor, at which PARP-1 enrichment markedly increases during cocaine-associated memory retrieval and positively correlates with CPP. Our findings have important implications for understanding drug-related behaviors, and suggest possible future therapeutic targets for drug abuse.

Differential effects of the MEK inhibitor SL327 on the acquisition and expression of ethanol-elicited conditioned place preference and aversion in mice

The involvement of mitogen-activating extracellular kinase (MEK) in place conditioning may vary depending on the motivational sign (positive or negative) and nature (pharmacological or nociceptive) of the unconditioned stimulus (US) and on the phase (acquisition or expression) of the learning process. This study investigated the role of MEK on the acquisition and expression of ethanol-elicited (given 2 g/kg) backward (preference, CPP) and forward (aversion, CPA) place conditioning. The MEK inhibitor SL327 (50 mg/kg for CPP, and 50 and 100 mg/kg for CPA) was administered to CD-1 mice 60 minutes before an ethanol dose (acquisition) or 60 minutes before the post-conditioning tests (expression). Ethanol significantly elicited CPP and CPA; SL327 (50 mg/kg) significantly blocked the acquisition of ethanol-elicited CPP, but not that of CPA. Moreover, SL327 (50 and 100 mg/kg) significantly reduced the expression of ethanol-elicited CPP, but not that of CPA. Finally, SL327 also prevented ethanol-elicited (given 2 g/kg) increases of phosphorylated extracellular signal regulated kinase (pERK)-positive neurons in the nucleus accumbens and other nuclei of the extended amygdala. Overall, these results confirmed the differential involvement of MEK in the acquisition and expression of drug-elicited place conditioning and suggested its differential involvement in distinct behavioral outcomes, depending on the motivational sign of the (same) US and on the significance of the experimental phase of the learning process.

Morphine dependence is attenuated by red ginseng extract and ginsenosides Rh2, Rg3, and compound K

BACKGROUND

Red ginseng and ginsenosides have shown plethoric effects against various ailments. However, little is known regarding the effect of red ginseng on morphine-induced dependence and tolerance. We therefore investigated the effect of red ginseng extract (RGE) and biotransformed ginsenosides Rh2, Rg3, and compound K on morphine-induced dependence in mice and rats.

METHODS

While mice were pretreated with RGE and then morphine was injected intraperitoneally, rats were infused with ginsenosides and morphine intracranially for 7 days. Naloxone-induced morphine withdrawal syndrome was estimated and conditioned place preference test was performed for physical and psychological dependence, respectively. Western blotting was used to measure protein expressions.

RESULTS

Whereas RGE inhibited the number of naloxone-precipitated jumps and reduced conditioned place preference score, it restored the level of glutathione in mice. Likewise, ginsenosides Rh2, Rg3, and compound K attenuated morphine-dependent behavioral patterns such as teeth chattering, grooming, wet-dog shake, and escape behavior in rats. Moreover, activated N-methyl-D-aspartate acid receptor subunit 1 and extracellular signal-regulated kinase in the frontal cortex of rats, and cultured cortical neurons from mice were downregulated by ginsenosides Rh2, Rg3, and compound K despite their differential effects.

CONCLUSION

RGE and biotransformed ginsenosides could be considered as potential therapeutic agents against morphine-induced dependence.

A Nonrewarding NMDA Receptor Antagonist Impairs the Acquisition, Consolidation, and Expression of Morphine Conditioned Place Preference in Mice

N-methyl-D-aspartate (NMDA) receptor antagonists block morphine-induced conditioned place preference (CPP). Although polyamines are endogenous modulators of the NMDA receptor, it is not known whether polyaminergic agents induce CPP or modulate morphine-induced CPP. Here, we examined whether polyamine ligands modify morphine CPP acquisition, consolidation, and expression. Adult male albino Swiss mice received saline (0.9 % NaCl, intraperitoneally (i.p.)) or morphine (5 mg/kg, i.p.) and were respectively confined to a black or a white compartment for 30 min for four consecutive days for CPP induction. The effect of arcaine (3 mg/kg, i.p.) or spermidine (30 mg/kg, i.p.), respectively, an antagonist and an agonist of the polyamine-binding site at the NMDA receptor, on the acquisition, consolidation, and expression of morphine CPP was studied. In those experiments designed to investigate whether spermidine prevented or reversed the effect of arcaine, spermidine (30 mg/kg, i.p.) was administered 15 min before or 15 min after arcaine, respectively. Arcaine and spermidine did not induce CPP or aversion per se. Arcaine (3 mg/kg, i.p.) impaired the acquisition, consolidation, and expression of morphine CPP. Spermidine prevented the impairing effect of arcaine on the acquisition of morphine CPP but not the impairing effect of arcaine on consolidation or expression of morphine CPP. These results suggest that arcaine may impair morphine CPP acquisition by modulating the polyamine-binding site at the NMDA receptor. However, the arcaine-induced impairment of consolidation and expression of morphine CPP seems to involve other mechanisms.

Molecular and neuronal plasticity mechanisms in the amygdala-prefrontal cortical circuit: implications for opiate addiction memory formation

The persistence of associative memories linked to the rewarding properties of drugs of abuse is a core underlying feature of the addiction process. Opiate class drugs in particular, possess potent euphorigenic effects which, when linked to environmental cues, can produce drug-related "trigger" memories that may persist for lengthy periods of time, even during abstinence, in both humans, and other animals. Furthermore, the transitional switch from the drug-naïve, non-dependent state to states of dependence and withdrawal, represents a critical boundary between distinct neuronal and molecular substrates associated with opiate-reward memory formation. Identifying the functional molecular and neuronal mechanisms related to the acquisition, consolidation, recall, and extinction phases of opiate-related reward memories is critical for understanding, and potentially reversing, addiction-related memory plasticity characteristic of compulsive drug-seeking behaviors. The mammalian prefrontal cortex (PFC) and basolateral nucleus of the amygdala (BLA) share important functional and anatomical connections that are involved importantly in the processing of associative memories linked to drug reward. In addition, both regions share interconnections with the mesolimbic pathway's ventral tegmental area (VTA) and nucleus accumbens (NAc) and can modulate dopamine (DA) transmission and neuronal activity associated with drug-related DAergic signaling dynamics. In this review, we will summarize research from both human and animal modeling studies highlighting the importance of neuronal and molecular plasticity mechanisms within this circuitry during critical phases of opiate addiction-related learning and memory processing. Specifically, we will focus on two molecular signaling pathways known to be involved in both drug-related neuroadaptations and in memory-related plasticity mechanisms; the extracellular-signal-regulated kinase system (ERK) and the Ca(2+)/calmodulin-dependent protein kinases (CaMK). Evidence will be reviewed that points to the importance of critical molecular memory switches within the mammalian brain that might mediate the neuropathological adaptations resulting from chronic opiate exposure, dependence, and withdrawal.

Neuronal extracellular signal-regulated kinase (ERK) activity as marker and mediator of alcohol and opioid dependence

Early pioneering work in the field of biochemistry identified phosphorylation as a crucial post-translational modification of proteins with the ability to both indicate and arbitrate complex physiological processes. More recent investigations have functionally linked phosphorylation of extracellular signal-regulated kinase (ERK) to a variety of neurophysiological mechanisms ranging from acute neurotransmitter action to long-term gene expression. ERK phosphorylation serves as an intracellular bridging mechanism that facilitates neuronal communication and plasticity. Drugs of abuse, including alcohol and opioids, act as artificial yet powerful rewards that impinge upon natural reinforcement processes critical for survival. The graded progression from initial exposure to addiction (or substance dependence) is believed to result from drug- and drug context-induced adaptations in neuronal signaling processes across brain reward and stress circuits following excessive drug use. In this regard, commonly abused drugs as well as drug-associated experiences are capable of modifying the phosphorylation of ERK within central reinforcement systems. In addition, chronic drug and alcohol exposure may drive ERK-regulated epigenetic and structural alterations that underlie a long-term propensity for escalating drug use. Under the influence of such a neurobiological vulnerability, encountering drug-associated cues and contexts can produce subsequent alterations in ERK signaling that drive relapse to drug and alcohol seeking. Current studies are determining precisely which molecular and regional ERK phosphorylation-associated events contribute to the addiction process, as well as which neuroadaptations need to be targeted in order to return dependent individuals to a healthy state.

Hippocampal long-term potentiation is disrupted during expression and extinction but is restored after reinstatement of morphine place preference

Learned associations between environmental cues and morphine use play an important role in the maintenance and/or relapse of opioid addiction. Although previous studies suggest that context-dependent morphine treatment alters glutamatergic transmission and synaptic plasticity in the hippocampus, their role in morphine conditioned place preference (CPP) and reinstatement remains unknown. We investigated changes in synaptic plasticity and NMDAR expression in the hippocampus after the expression, extinction, and reinstatement of morphine CPP. Here we report that morphine CPP is associated with increased basal synaptic transmission, impaired hippocampal long-term potentiation (LTP), and increased synaptic expression of the NR1 and NR2b NMDAR subunits. Changes in synaptic plasticity, synaptic NR1 and NR2b expression, and morphine CPP were absent when morphine was not paired with a specific context. Furthermore, hippocampal LTP was impaired and synaptic NR2b expression was increased after extinction of morphine CPP, indicating that these alterations in plasticity may be involved in the mechanisms underlying the learning of drug-environment associations. After extinction of morphine CPP, a priming dose of morphine was sufficient to reinstate morphine CPP and was associated with LTP that was indistinguishable from saline control groups. In contrast, morphine CPP extinguished mice that received a saline priming dose did not show CPP and had disrupted hippocampal LTP. Finally, we found that reinstatement of morphine CPP was prevented by the selective blockade of the NR2b subunit in the hippocampus. Together, these data suggest that alterations in synaptic plasticity and glutamatergic transmission play an important role in the reinstatement of morphine CPP.

Opiate exposure and withdrawal induces a molecular memory switch in the basolateral amygdala between ERK1/2 and CaMKIIα-dependent signaling substrates

Opiate reward memories are powerful triggers for compulsive opiate-seeking behaviors. The basolateral amygdala (BLA) is an important structure for the processing of opiate-related associative memories and is functionally linked to the mesolimbic dopamine (DA) pathway. Transmission through intra-BLA DA D1-like and D2-like receptors independently modulates the formation of opiate reward memories as a function of opiate-exposure state. Thus, in the opiate-naive state, intra-BLA D1 transmission is required for opiate-related memory formation. Once opiate dependence and withdrawal has developed, a functional switch to a DA D2-mediated memory mechanism takes place. However, the downstream molecular signaling events that control this functional switch between intra-BLA DA D1 versus D2 receptor transmission are not currently understood. Using an unbiased place conditioning procedure in rats combined with molecular analyses, we report that opiate reward memory acquisition requires intra-BLA ERK1/2 signaling only in the previously opiate-naive state. However, following chronic opiate exposure and withdrawal, intra-BLA reward memory processing switches to a CaMKIIα-dependent memory substrate. Furthermore, the ability of intra-BLA DA D1 or D2 receptor transmission to modulate the motivational salience of opiates similarly operates through a D1-mediated ERK-dependent mechanism in the opiate-naive state, but switches to a D2-mediated CaMKIIα-dependent mechanism in the dependent/withdrawn state. Protein analysis of BLA tissue revealed a downregulation of ERK1/2 phosphorylation and a dramatic reduction in both total and phosphorylated CaMKIIα signaling, specifically in the opiate-dependent/withdrawn state, demonstrating functional control of ERK1/2-dependent versus CaMKIIα-dependent memory mechanisms within the BLA, controlled by opiate-exposure state.

Activation of ERK1/2 is required for normal response of isosexual social interactions in male rats

Previous studies have indicated involvement of the mitogen-activated protein kinase (MAPK) pathway in heterosexual interactions among rats. Very few studies, however, have focused its role in isosexual social interactions. We studied the male rat's isosexual social interactional behavior using (i) the three-chambered social interaction box and (ii) phosphorylated extracellular signal-regulated kinase 1 and 2 (pERK1/2) to localize the brain regions that are activated during isosexual behavior. When faced with the social target side of the box versus the inanimate side, all rats preferred the social target side. Within 10min, isosexual social interactions induced a rapid increase in pERK1/2 expression in the brain, especially the main olfactory epithelial (MOE)-related brain regions. After ZnSO4-induced olfactory deprivation, rats showed no preference for either the social target or inanimate side, with a concomitant decrease in pERK1/2 expression in MOE-related brain regions. Additionally, to determine the role of pERK1/2 in isosexual social interactional behavior, rats were injected intraperitoneally with SL327 (30mg/kg, a MAPK kinase inhibitor). Although SL327 dramatically down-regulated expression of brain pERK1/2, experimental animals also spent significantly more time in the social target side. These results indicate that (i) A brief interacting with a male partner induced rapidly phosphorylated ERK1/2 in the rat's brain. (ii) Destroy the function of MOE abolished the rats' isosexual social interactional behavior. (iii) Suppressed the phosphorylated ERK1/2 in the rats' brain disrupt their normal social behaviour.

Central amygdala GluA1 facilitates associative learning of opioid reward

GluA1 subunits of AMPA glutamate receptors are implicated in the synaptic plasticity induced by drugs of abuse for behaviors of drug addiction, but GluA1 roles in emotional learning and memories of drug reward in the development of drug addiction remain unclear. In this study of the central nucleus of the amygdala (CeA), which is critical in emotional learning of drug reward, we investigated how adaptive changes in the expression of GluA1 subunits affected the learning process of opioid-induced context-reward association (associative learning) for the acquisition of reward-related behavior. In CeA neurons, we found that CeA GluA1 expression was significantly increased 2 h after conditioning treatment with morphine, but not 24 h after the conditioning when the behavior of conditioned place reference (CPP) was fully established in rats. Adenoviral overexpression of GluA1 subunits in CeA accelerated associative learning, as shown by reduced minimum time of morphine conditioning required for CPP acquisition and by facilitated CPP extinction through extinction training with no morphine involved. Adenoviral shRNA-mediated downregulation of CeA GluA1 produced opposite effects, inhibiting the processes of both CPP acquisition and CPP extinction. Adenoviral knockdown of CeA GluA2 subunits facilitated CPP acquisition, but did not alter CPP extinction. Whole-cell recording revealed enhanced electrophysiological properties of postsynaptic GluA2-lacking AMPA receptors in adenoviral GluA1-infected CeA neurons. These results suggest that increased GluA1 expression of CeA AMPA receptors facilitates the associative learning of context-drug reward, an important process in both development and relapse of drug-seeking behaviors in drug addiction.

Endogenous opiates and behavior: 2011

This paper is the thirty-fourth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2011 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).

Combined action of MK-801 and ceftriaxone impairs the acquisition and reinstatement of morphine-induced conditioned place preference, and delays morphine extinction in rats

OBJECTIVE

It is well established that glutamate and its receptors, particularly the N-methyl-D-aspartate receptor (NMDAR), play a significant role in addiction and that the inhibition of glutamatergic hyperfunction reduces addictive behaviors in experimental animals. Specifically, NMDAR antagonists such as MK-801, and an inducer of the expression of glutamate transporter subtype-1 (GLT-1) (ceftriaxone) are known to inhibit addictive behavior. The purpose of this study was to determine whether the combined action of a low dose of MK-801 and a low dose of ceftriaxone provides better inhibition of the acquisition, extinction, and reinstatement of morphine-induced conditioned place preference (CPP) than either compound alone.

METHODS

A morphine-paired CPP experiment was used to study the effects of low doses of MK-801, ceftriaxone and a combination of both on reward-related memory (acquisition, extinction, and reinstatement of morphine preference) in rats.

RESULTS

A low dose of neither MK-801 (0.05 mg/kg, i.p.) nor ceftriaxone (25 mg/kg, i.p.) alone effectively impaired CPP behaviors. However, when applied in combination, they reduced the acquisition of morphine-induced CPP and completely prevented morphine reinstatement. Their combination also notably impaired the extinction of morphine-induced CPP.

CONCLUSION

The combined action of a low dose of an NMDAR antagonist (MK-801) and GLT-1 activation by ceftriaxone effectively changed different phases of CPP behavior.

Glutamate mechanisms underlying opiate memories

As the major excitatory neurotransmitter in the brain, glutamate plays an undisputable integral role in opiate addiction. This relates, in part, to the fact that addiction is a disorder of learning and memory, and glutamate is required for most types of memory formation. As opiate addiction develops, the addict becomes conditioned to engage in addictive behaviors, and these behaviors can be triggered by opiate-associated cues during abstinence, resulting in relapse. Some medications for opiate addiction exert their therapeutic effects at glutamate receptors, especially the NMDA receptor. Understanding the neural circuits controlling opiate addiction, and the locus of glutamate's actions within these circuits, will help guide the development of targeted pharmacotherapeutics for relapse.

Activation of Anterior Cingulate Cortex Extracellular Signal-Regulated Kinase-1 and -2 (ERK1/2) Regulates Acetic Acid-Induced, Pain-Related Anxiety in Adult Female Mice

In visceral pain, anxiety and pain occur simultaneously, but the etiogenesis of this effect is not yet well-described. The anterior cingulate cortex (ACC) is known to be associated with the affective response to noxious stimuli. The aim of the current study is to define the role of ACC extracellular signal-regulated (ERK)-1 and-2 (ERK1/2) activity in the development of pain-related anxiety/depression and the nocifensive response in acetic acid (AA)-elicited visceral pain. The model of visceral pain was created by intraperitoneal (ip) injection of AA to female Kunming mice. We found that AA injection resulted in a dynamic, bilateral ERK1/2 activation pattern in the ACC. Inhibition of ERK1/2 activation 2 hr after AA injection by subcutaneous (sc) injection of the mitogen-activating extracellular kinase (MEK) inhibitor, SL327, had no effect on the nocifensive responses, but did attenuate anxiety-like behavior, as determined by elevated plus-maze and open-field testing results. These data suggest that AA-induced visceral pain activates expression of ACC ERK1/2, which regulates visceral pain-related anxiety, but not the nocifensive response.

Intra-amygdala inhibition of ERK(1/2) potentiates the discriminative stimulus effects of alcohol

Extracellular signal-regulated kinase (ERK(1/2)) has been implicated in modulating drug seeking behavior and is a target of alcohol and other drugs of abuse. Given that the discriminative stimulus (subjective/interoceptive) effects of drugs are determinants of abuse liability and can influence drug seeking behavior, we examined the role of ERK(1/2) in modulating the discriminative stimulus effects of alcohol. Using drug discrimination procedures, rats were trained to discriminate a moderate intragastric (IG) alcohol dose (1g/kg) versus water (IG). Following an alcohol (1g/kg) discrimination session phosphorylated ERK(1/2) (pERK(1/2)) immunoreactivity (IR) was significantly elevated in the amygdala, but not the nucleus accumbens. Therefore, we hypothesized that intra-amygdala inhibition of ERK(1/2) would disrupt expression of the discriminative stimulus effects of alcohol. However, intra-amygdala or accumbens administration of the MEK/ERK(1/2) inhibitor U0126 (1 and 3μg) had no effect on the discriminative stimulus effects of the training dose of alcohol (1g/kg). Contrary to our hypothesis, intra-amygdala infusion of U0126 (3μg) potentiated the discriminative stimulus effects of a low alcohol dose (0.5g/kg) and had no effect following nucleus accumbens infusion. Importantly, site-specific inhibition of pERK(1/2) in each brain region was confirmed. Therefore, the increase in pERK(1/2) IR in the amygdala following systemic alcohol administration may be reflective of the widespread effects of alcohol on the brain (activation/inhibition of brain circuits), whereas the site specific microinjection studies confirmed functional involvement of intra-amygdala ERK(1/2). These findings show that activity of the ERK signaling pathway in the amygdala can influence the discriminative stimulus effects of alcohol.