Role of ERK in cocaine addiction

Activation of RMTg projections to the VTA reverse cocaine-induced molecular adaptation in the reward system

The rostromedial tegmental nucleus (RMTg) plays a crucial role in regulating reward-related behavior by exerting inhibitory control over the ventral tegmental area (VTA). This modulation of dopamine neuron activity within the VTA is essential for maintaining homeostasis in the reward system. Recently we have shown that activation of RMTg projections to the VTA during the acquisition of cocaine-conditioned place preference (CPP) reduces the rewarding properties of cocaine and decreases VTA dopamine neuron activity. By inhibiting dopamine neurons in the VTA, we hypothesized that RMTg projections hold the potential to restore reward system homeostasis disrupted by repeated cocaine use, and attenuate molecular adaptations in the reward system, including alterations in signaling pathways. Our study demonstrates that enhancing the GABAergic inputs from the RMTg to the VTA can mitigate cocaine-induced molecular changes in key regions, namely the VTA, nucleus accumbens (NAc), and prefrontal cortex (PFC). Specifically, we found that cocaine-induced alteration in the phosphorylation state of ERK (pERK) and GluA1 on serine 845 (S845) and serine 831 (S831), that play a major role in plasticity by controlling the activity and trafficking of AMPA receptors, were significantly reversed following optic stimulation of RMTg afferents to the VTA. These findings highlight the therapeutic potential of targeting the RMTg-VTA circuitry for mitigating cocaine reward. Ultimately, this research may pave the way for novel therapeutic interventions that restore balance in the reward system and alleviate the detrimental effects of cocaine.

Basolateral amygdala corticotropin releasing factor receptor 2 interacts with nonmuscle myosin II to destabilize memory in males

Preclinical studies show that inhibiting the actin motor ATPase nonmuscle myosin II (NMII) with blebbistatin (Blebb) in the basolateral amgydala (BLA) depolymerizes actin, resulting in an immediate, retrieval-independent disruption of methamphetamine (METH)-associated memory in male and female adult and adolescent rodents. The effect is highly selective, as NMII inhibition has no effect in other relevant brain regions (e.g., dorsal hippocampus [dPHC], nucleus accumbens [NAc]), nor does it interfere with associations for other aversive or appetitive stimuli, including cocaine (COC). To understand the mechanisms responsible for drug specific selectivity we began by investigating, in male mice, the pharmacokinetic differences in METH and COC brain exposure . Replicating METH's longer half-life with COC did not render the COC association susceptible to disruption by NMII inhibition. Therefore, we next assessed transcriptional differences. Comparative RNA-seq profiling in the BLA, dHPC and NAc following METH or COC conditioning identified crhr2, which encodes the corticotropin releasing factor receptor 2 (CRF2), as uniquely upregulated by METH in the BLA. CRF2 antagonism with Astressin-2B (AS2B) had no effect on METH-associated memory after consolidation, allowing for determination of CRF2 influences on NMII-based susceptibility. Pretreatment with AS2B prevented the ability of Blebb to disrupt an established METH-associated memory. Alternatively, combining CRF2 overexpression and agonist treatment, urocortin 3 (UCN3), in the BLA during conditioning rendered COC-associated memory susceptible to disruption by NMII inhibition, mimicking the Blebb-induced, retrieval-independent memory disruption seen with METH. These results suggest that BLA CRF2 receptor activation during memory formation in male mice can prevent stabilization of the actin-myosin cytoskeleton supporting the memory, rendering it vulnerable to disruption by NMII inhibition. CRF2 represents an interesting target for BLA-dependent memory destabilization via downstream effects on NMII.

Cellular and molecular basis of drug addiction: The role of neuronal ensembles in addiction

Addiction has been conceptualized as a disease of learning and memory. Learned associations between environmental cues and unconditioned rewards induced by drug administration, which play a critical role in addiction, have been shown to be encoded in sparsely distributed populations of neurons called neuronal ensembles. This review aims to highlight how synaptic remodeling and alterations in signaling pathways that occur specifically in neuronal ensembles contribute to the pathogenesis of addiction. Furthermore, a causal link between transcriptional and epigenetic modifications in neuronal ensembles and the development of the addictive state is proposed. Translational studies of molecular and cellular changes in neuronal ensembles that contribute to drug-seeking behavior, will allow the identification of molecular and circuit targets and interventions for substance use disorders.

Interactions between estradiol and ERK, but not mTOR, signaling is necessary for enhanced cocaine-induced conditioned place preference in female rats

Women rapidly progress from recreational cocaine use to dependence, consume greater quantities of cocaine, experience more positive subjective effects of cocaine and have higher incidences of relapse during abstinence. These effects have been replicated in animal models of cocaine addiction and indicate an enhanced sensitivity and therefore, vulnerability of females to cocaine addiction. Furthermore, it has been demonstrated that estradiol (E2) is a key mediator of the aforementioned effects of cocaine in women and female animals. However, studies identifying the influence of E2 on cocaine-associated reward and its underlying neurobiological mechanisms are lacking. Here, we further explored the influence of E2 on cocaine conditioned place preference in female rats. We show that E2 mediates cocaine-conditioned reward by potentiating cocaine-context associations. In addition, the E2-mediated increases in cocaine-induced CPP are associated with increased activation of ERK1/2 and mTOR proteins in the nucleus accumbens, dorsal striatum, and ventral tegmental area. To assess the involvement of ERK1/2 and mTOR in E2-mediated enhanced cocaine-CPP, we inhibited ERK1/2 and/or mTOR activity during cocaine-conditioning and before CPP-test. Inhibition of ERK1/2 during conditioning blocked cocaine-CPP in females, inhibition mTOR was without effect, and inhibiting ERK1/2 and mTOR before CPP-test blocked cocaine-CPP. In conclusion, we have established that E2 enhances cocaine-conditioned reward by potentiating cocaine-context associations formed during conditioning. Additionally, activation of ERK1/2 during cocaine-conditioning is necessary for the potentiation of cocaine-conditioned reward by E2. SIGNIFICANCE STATEMENT: Studies characterizing the molecular substrates underlying the effects of E2 during the formation of cocaine-context associations are virtually unknown. In this study, we established the influence of E2 during the formation of cocaine-CPP and characterized the role of ERK1/2 and mTOR activity on this effect within significant nodes of the reward pathway. The elucidation of the role of E2 in cocaine-induced intracellular signaling fills a significant gap in our knowledge regarding the mechanisms by which E2 affects intracellular signaling pathways to indicate the motivational salience of a stimulus. These data are crucial to our understanding of how fluctuating hormone levels can render females increasing sensitive to the rewarding effects of cocaine.

Psychiatric adverse reactions to non-selective RET multi-kinase inhibitors: a large-scale pharmacovigilance analysis

Objective: The development of non-selective multi-kinase inhibitors (MKIs) has improved the. survival outcomes of patients with cancers. Psychiatric disorders represent an MKIs related AE of particular concern, as they are often ignored and may harm the patient's personal and social functioning. Therefore, we use the public database to describe and evaluate psychiatric adverse events related to various non-selective RET MKIs. Provide evidence for optimizing drug administration in the clinic. Methods: We analyzed spontaneous reports submitted to the Food and Drug Administration Adverse Events Reporting System FDA Adverse Event Reporting System in an observational and retrospective manner. Selecting psychiatric AEs to non-selective RET multikinase inhibitors (sorafenib, lenvatinib, vandetanib, cabozantinib, and sunitinib). We used Reporting Odds Ratio (ROR), Proportional Reporting Ratio (PRR), Bayesian Confidence Propagation Neural Network (BCPNN), and multi-item gamma Poisson shrinker (MGPS) algorithms to analyze suspected adverse reactions of psychiatric related induced by non-selective RET MKIs between January 2004 and September 2022. Results: As of September 2022, 1,108 non-selective RET MKIs ICSRs were related to psychiatric AEs. 706 were ADR ICSRs, and 402 were non-ADR ICSRs. There were more ADR cases in males (69.5%), and 71.8% of the cases were submitted from North America. The age group most frequently affected by psychiatric ADRs was individuals aged 50-64 years for sorafenib, whereas 65-74 years for sunitinib, cabozantinib, and lenvatinib. In all psychiatric ADRs ICSRs, excluding missing data (n = 329), the most common adverse outcome was hospitalization (260/377, 69.0%), and the most serious was death (100/377, 26.5%). What calls for special attention is that the percentage of death rate for sunitinib was highest (24/54, 44.4%) in sunitinib-related psychiatric ADRs ICSRs, (excluding missing data, n = 44), followed by lenvatinib (4/14, 28.6%). Based on ROR, PRR, BCPNN, and MGPS methods, sorafenib, sunitinib, cabozantinib, and lenvatinib are significantly associated with all ADRs, the strongest association was the association between cabozantinib and feeding disorder. Conclusion: Despite the limitations, our study found that, except for vandetanib, other four drugs have been reported to have significant psychiatric side effects. Clinicians need to recognize and monitor these potentially fatal adverse events. If it is suitable for treatment with vandetanib, doctors should choose vandetanib for treatment.

The transcriptional response to acute cocaine is inverted in male mice with a history of cocaine self-administration and withdrawal throughout the mesocorticolimbic system

A large body of work has demonstrated that cocaine-induced changes in transcriptional regulation play a central role in the onset and maintenance of cocaine use disorder. An underappreciated aspect of this area of research, however, is that the pharmacodynamic properties of cocaine can change depending on an organism's previous drug-exposure history. In this study, we utilized RNA sequencing to characterize how the transcriptome-wide effects of acute cocaine exposure were altered by a history of cocaine self-administration and long-term withdrawal (30 days) in the ventral tegmental area (VTA), nucleus accumbens (NAc), and prefrontal cortex (PFC) in male mice. First, we found that the gene expression patterns induced by a single cocaine injection (10 mg/kg) were discordant between cocaine-naïve mice and mice in withdrawal from cocaine self-administration. Specifically, the same genes that were upregulated by acute cocaine in cocaine-naïve mice were downregulated by the same dose of cocaine in mice undergoing long-term withdrawal; the same pattern of opposite regulation was observed for the genes downregulated by initial acute cocaine exposure. When we analyzed this dataset further, we found that the gene expression patterns that were induced by long-term withdrawal from cocaine self-administration showed a high degree of overlap with the gene expression patterns of acute cocaine exposure - even though animals had not consumed cocaine in 30 days. Interestingly, cocaine re-exposure at this withdrawal time point reversed this expression pattern. Finally, we found that this pattern was similar across the VTA, PFC, NAc, and within each brain region the same genes were induced by acute cocaine, re-induced during long-term withdrawal, and reversed by cocaine re-exposure. Together, we identified a longitudinal pattern of gene regulation that is conserved across the VTA, PFC, and NAc, and characterized the genes constituting this pattern in each brain region.

Basolateral Amygdala Corticotrophin Releasing Factor Receptor 2 Interacts with Nonmuscle Myosin II to Destabilize Memory

Inhibiting the actin motor ATPase nonmuscle myosin II (NMII) with blebbistatin (Blebb) in the basolateral amgydala (BLA) depolymerizes actin, resulting in an immediate, retrieval-independent disruption of methamphetamine (METH)-associated memory. The effect is highly selective, as NMII inhibition has no effect in other relevant brain regions (e.g. dorsal hippocampus [dPHC], nucleus accumbens [NAc]), nor does it interfere with associations for other aversive or appetitive stimuli, including cocaine (COC). To investigate a potential source of this specificity, pharmacokinetic differences in METH and COC brain exposure were examined. Replicating METH's longer half-life with COC did not render the COC association susceptible to disruption by NMII inhibition. Therefore, transcriptional differences were next assessed. Comparative RNA-seq profiling in the BLA, dHPC and NAc following METH or COC conditioning identified crhr2, which encodes the corticotrophin releasing factor receptor 2 (CRF2), as uniquely upregulated by METH in the BLA. CRF2 antagonism with Astressin-2B (AS2B) had no effect on METH-associated memory after consolidation, allowing for determination of CRF2 influences on NMII-based susceptibility after METH conditioning. Pretreatment with AS2B occluded the ability of Blebb to disrupt an established METH-associated memory. Alternatively, the Blebb-induced, retrieval-independent memory disruption seen with METH was mimicked for COC when combined with CRF2 overexpression in the BLA and its ligand, UCN3 during conditioning. These results indicate that BLA CRF2 receptor activation during learning can prevent stabilization of the actin-myosin cytoskeleton supporting the memory, rendering it vulnerable to disruption via NMII inhibition. CRF2 represents an interesting target for BLA-dependent memory destabilization via downstream effects on NMII.

Morphine and dopamine: Low dose apomorphine can prevent both the induction and expression of morphine locomotor sensitization and conditioning

The disinhibition of dopamine neurons in the VTA by morphine is considered an important contributor to the reward potency of morphine. In this report, three experiments were conducted in which a low dose of apomorphine (0.05mg/kg) was used as a pretreatment to reduce dopamine activity. Locomotor hyperactivity was used as the behavioral response to morphine (10.0mg/kg). In the first experiment, five treatments with morphine induced the development of locomotor and conditioned hyperactivity that were prevented by apomorphine given 10min prior to morphine. Apomorphine before either vehicle or morphine induced equivalent reductions in locomotion. In the second experiment, the apomorphine pretreatment was initiated after induction of a conditioned hyperactivity and the apomorphine prevented the expression of the conditioning. To assess the effects of the apomorphine on VTA and the nucleus accumbens, ERK measurements were carried out after the induction of locomotor and conditioned hyperactivity. Increased ERK activation was found and these effects were prevented by the apomorphine in both experiments. A third experiment was conducted to assess the effects of acute morphine on ERK before locomotor stimulation was induced by morphine. Acute morphine did not increase locomotion, but a robust ERK response was produced indicating that the morphine induced ERK activation was not secondary to locomotor stimulation. The ERK activation was again prevented by the apomorphine pretreatment. We suggest that contiguity between the ongoing behavioral activity and the morphine activation of the dopamine reward system incentivizes and potentiates the ongoing behavior generating equivalent behavioral sensitization and conditioned effects.

Amelioration of Nicotine-Induced Conditioned Place Preference Behaviors in Mice by an FABP3 Inhibitor

We previously demonstrated that fatty acid-binding protein 3 null (FABP3−/−) mice exhibit resistance to nicotine-induced conditioned place preference (CPP). Here, we confirm that the FABP3 inhibitor, MF1 ((4-(2-(1-(2-chlorophenyl)-5-phenyl-1H-pyrazol-3-yl)phenoxy) butanoic acid), successfully reduces nicotine-induced CPP scores in mice. MF1 (0.3 or 1.0 mg/kg) was orally administered 30 min before nicotine, and CPP scores were assessed in the conditioning, withdrawal, and relapse phases. MF1 treatment decreased CPP scores in a dose-dependent manner. Failure of CPP induction by MF1 (1.0 mg/kg, p.o.) was associated with the inhibition of both CaMKII and ERK activation in the nucleus accumbens (NAc) and hippocampal CA1 regions. MF1 treatment reduced nicotine-induced increases in phosphorylated CaMKII and cAMP-response element-binding protein (CREB)-positive cells. Importantly, the increase in dopamine D2 receptor (D2R) levels following chronic nicotine exposure was inhibited by MF1 treatment. Moreover, the quinpirole (QNP)-induced increase in the level of CaMKII and ERK phosphorylation was significantly inhibited by MF1 treatment of cultured NAc slices from wild type (WT) mice; however, QNP treatment had no effect on CaMKII and ERK phosphorylation levels in the NAc of D2R null mice. Taken together, these results show that MF1 treatment suppressed D2R/FABP3 signaling, thereby preventing nicotine-induced CPP induction. Hence, MF1 can be used as a novel drug to block addiction to nicotine and other drugs by inhibiting the dopaminergic system.

Novel role of AMPK in cocaine reinforcement via regulating CRTC1

Repeated cocaine exposure causes compensatory neuroadaptations in neurons in the nucleus accumbens (NAc), a region that mediates reinforcing effects of drugs. Previous studies suggested a role for adenosine monophosphate-activated protein kinase (AMPK), a cellular energy sensor, in modulating neuronal morphology and membrane excitability. However, the potential involvement of AMPK in cocaine use disorder is still unclear. The present study employed a cocaine self-administration model in rats to investigate the effect of AMPK and its target cyclic adenosine monophosphate response element binding protein-regulated transcriptional co-activator 1 (CRTC1) on cocaine reinforcement and the motivation for cocaine. We found that intravenous cocaine self-administration significantly decreased AMPK activity in the NAc shell (NAcsh), which persisted for at least 7 days of withdrawal. Cocaine reinforcement, reflected by self-administration behavior, was significantly prevented or enhanced by augmenting or suppressing AMPK activity pharmacologically and genetically, respectively. No difference in sucrose self-administration behavior was found after the same manipulations. The inhibition of AMPK activity in the NAcsh also increased the motivation for cocaine in progressive-ratio schedules of reinforcement, whereas the activation of AMPK had no effect. The knockdown of CRTC1 in the NAcsh significantly impaired cocaine reinforcement, which was rescued by pharmacologically increasing AMPK activity. Altogether, these results indicate that AMPK in the NAcsh is critical for cocaine reinforcement, possibly via the regulation of CRTC1 signaling. These findings may help reveal potential therapeutic targets and have important implications for the treatment of cocaine use disorder and relapse.

Long-lasting BDNF signaling alterations in the amygdala of adolescent female rats exposed to the activity-based anorexia model

Introduction: Anorexia nervosa (AN) is a severe psychiatric disorder characterized by a pathological fear of gaining weight, excessive physical exercise, and emotional instability. Since the amygdala is a key region for emotion processing and BDNF has been shown to play a critical role in this process, we hypothesized that alteration in the amygdalar BDNF system might underline vulnerability traits typical of AN patients. Methods: To this end, adolescent female rats have been exposed to the Activity-Based Anorexia (ABA) protocol, characterized by the combination of caloric restriction and intense physical exercise. Results: The induction of the anorexic phenotype caused hyperactivity and body weight loss in ABA animals. These changes were paralleled by amygdalar hyperactivation, as measured by the up-regulation of cfos mRNA levels. In the acute phase of the pathology, we observed reduced Bdnf exon IX, exon IV, and exon VI gene expression, while mBDNF protein levels were enhanced, an increase that was, instead, uncoupled from its downstream signaling as the phosphorylation of TrkB, Akt, and S6 in ABA rats were reduced. Despite the body weight recovery observed 7 days later, the BDNF-mediated signaling was still downregulated at this time point. Discussion: Our findings indicate that the BDNF system is downregulated in the amygdala of adolescent female rats under these experimental conditions, which mimic the anorexic phenotype in humans, pointing to such dysregulation as a potential contributor to the altered emotional processing observed in AN patients. In addition, since the modulation of BDNF levels is observed in other psychiatric conditions, the persistent AN-induced changes of the BDNF system in the amygdala might contribute to explaining the onset of comorbid psychiatric disorders that persist in patients even beyond recovery from AN.

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.

Protein kinases in natural versus drug reward

Natural and drug rewards act on the same neural pathway, the mesolimbic dopaminergic system. In brain regions such as the nucleus accumbens and ventral tegmental area, drugs of abuse-induced stimulation of signaling pathways can lead to synaptic reshaping within this system. This is believed to be underlying the maladaptive alterations in behaviors associated with addiction. In this review, we discuss animal studies disclosing the implication of several protein kinases, namely protein kinase A (PKA), extracellular signal regulated kinase (ERK) mitogen-activated protein kinases (MAPK), p38 MAPK, and calcium/calmodulin-dependent kinase II (CaMKII), in reward-related brain regions in drug and natural reward. Furthermore, we refer to studies that helped pave the way toward a better understanding of the neurobiology underlying non-drug and drug reward through genetic deletion or brain region-specific pharmacological inhibition of these kinases. Whereas the role of kinases in drug reward has been extensively studied, their implication in natural reward, such as positive social interaction, is less investigated. Discovering molecular candidates, recruited specifically by drug versus natural rewards, can promote the identification of novel targets for the pharmacological treatment of addiction with less off-target effects and being effective when used combined with behavioral-based therapies.

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.

Involvement of the ERK signaling pathways in the NAc in propofol-seeking behavior induced by cues in rats

Propofol, an intravenous short-acting anesthetic, has the potential to induce craving and relapse. Accumulated evidence demonstrates that extracellular signal-regulated kinase (ERK) plays an essential role in drug reward and relapse. In the previous study, we demonstrated that the ERK signaling pathways in the Nucleus accumbens (NAc) were involved in propofol reward. However, the role of the ERK signaling pathways in propofol relapse is still unknown. We first trained rats to self-administer propofol for 14 days, then evaluated propofol-seeking behavior of relapse induced by a contextual cues and conditioned cues after 14-day withdrawal. Meanwhile, MEK inhibitor U0126 was used to investigate the role of the ERK signal pathways in propofol-seeking behavior induced by contextual cues and conditioned cues. Results showed that the number of active nose-poke responses in propofol-seeking behavior induced by conditioned cues was much higher compared to contextual cues. U0126 (5.0 μg/side, Lateral Ventricle (LV)) pretreatment significantly decreased the active responses induced by conditioned cues, which was associated with a large decline in the expression of p-ERK in the NAc. Moreover, microinjectionofU0126 (2.0 μg/side) in the NAc also attenuated the active responses of propofol-seeking behavior. Additionally, microinjections with U0126 in the LV (5.0 μg/side) or NAc (2.0 μg/side) both failed to alter sucrose self-administration or locomotor activity of rats. Therefore, we conclude that ERK phosphorylation in the NAc maybe involved in propofol relapse.

Implication of Extracellular Signal-Regulated Kinase in the Expression of Natural Reward: Evidence Not Found

Many studies have implicated extracellular signal-regulated kinase (ERK) in drug-rewarding properties. Yet, only few investigated whether ERK also mediates the naturally rewarding stimuli. In this study, we compared ERK activation in the nucleus accumbens (NAc) after cocaine reward and after positive social interaction (SI) with a partner-reward in male rats. With our protocol, ERK phosphorylation in the NAc was not increased after cocaine reward. In addition, the interaction with a social partner did not alter ERK activation in the NAc. These results suggest that ERK in the NAc may not be involved in natural reward learning. SI in an alternative context to the one associated with drugs of abuse can abolish drug preference. Given that intra-NAc core ERK inhibition impaired the expression of cocaine preference, we wanted to investigate whether the protective effects of SI when an individual is allowed to interact with a social partner in an alternative context to the one associated with drugs during the learning phase are enhanced by ERK inhibition. For that, U0126 was bilaterally infused into the NAc core of rats conditioned with cocaine in one context and with SI in the opposite context before assessing the expression of reward-related learning. Intra-NAc core ERK inhibition was ineffective to impair the expression of drug reward as previously demonstrated, when a social partner was available in an alternative context. Thus, the effects of the pharmacological manipulations based on decreasing ERK activity are not cumulative to other treatments for drug addiction based on SI.

Context evoked morphine conditioned effects can be equivalent to morphine induced drug effects in terms of behavioral response and ERK activation in reward associated subcortical brain structures

Conditioned drug cues can evoke brief drug-like responses. In this report we show that using brief test sessions, contextual cues can induce conditioned hyperlocomotion and ERK responses equivalent to morphine induced responses. To assess acute unconditioned effects, rats that received morphine (MOR-1) or vehicle (VEH-1), were immediately placed onto an arena for a 5-min locomotion recording session after which ERK was measured in the ventral tegmental area (VTA) and nucleus accumbens (NAc). There were no differences in locomotion between the groups. However, the MOR-1 group had strong ERK activation in VTA and NAc. To assess MOR-conditioned effects, a chronic phase was carried out according to a Pavlovian conditioning protocol. There were two MOR paired groups (MORP), one MOR unpaired (MOR-UP) group and two VEH groups. The treatments were administered over 5 daily five minute test sessions. The final conditioning test was on day 6, in which one of the MOR-P groups and one of the VEH groups received VEH (MOR-P/VEH-6 and VEH/VEH-6, respectively). The other MOR-P group and VEH group received MOR (MOR-P/MOR; VEH/MOR-6, respectively). The MOR-UP group received VEH (MOR-UP/VEH-6). Rats received the treatments immediately prior to a 5-min arena test, and after the session ERK was measured. No morphine induced locomotor stimulation was observed on day 1 but on days 2 to 5, hyperlocomotion in both MOR-P groups occurred. On test day 6, the MOR-P/VEH-6 and the MOR-P/MOR-6 groups had comparable locomotor stimulant responses and similar ERK activity in the VTA and NAc. The MOR-UP group did not differ from the VEH group. We suggest that ERK activation evoked by acute morphine served as a Pavlovian unconditioned stimulus to enable the contextual cues to acquire morphine conditioned stimulus properties and increase the incentive value of the contextual cues.

Effects of docosanyl ferulate, a constituent of Withania somnifera, on ethanol- and morphine-elicited conditioned place preference and ERK phosphorylation in the accumbens shell of CD1 mice

BACKGROUND

Docosanyl ferulate (DF) is a behaviourally active GABA_A receptor complex (GABA_AR) agonist, recently isolated from the standardized methanolic extract of Withania somnifera Dunal (WSE) root. Previous studies have shown that WSE prevents both ethanol- and morphine-dependent acquisition and expression of conditioned place preference (CPP) and stimulation of dopamine release in the nucleus accumbens shell (AcbSh).

AIMS

The study aimed at determining (a) whether DF contributes to WSE's ability to affect the acquisition and expression of ethanol- and morphine-elicited CPP and, given that phosphorylation of extracellular signal-regulated kinase (pERK) in the AcbSh is involved in associative learning and motivated behaviours, (b) whether WSE and DF may affect ethanol- and morphine-induced ERKs phosphorylation in the AcbSh.

METHODS

In adult male CD1 mice, DF's effects on the acquisition and expression of ethanol- and morphine-elicited CPP were evaluated by a classical place conditioning paradigm, whereas the effects of WSE and DF on ethanol- and morphine-elicited pERK in the AcbSh were evaluated by immunohistochemistry.

RESULTS AND CONCLUSIONS

The study shows that DF, differently from WSE, affects only the acquisition but not the expression of ethanol- and morphine-induced CPP. Moreover, the study shows that both WSE and DF can prevent ethanol- and morphine-elicited pERK expression in the AcbSh. Overall, these results highlight subtle but critical differences for the role of GABA_ARs in the mechanism by which WSE affects these ethanol- and morphine-dependent behavioural and molecular/cellular responses and support the suggestion of WSE and DF for the control of different components of drug addiction.

FACTORS CONTRIBUTING TO THE ESCALATION OF ALCOHOL CONSUMPTION

Understanding factors that contribute to the escalation of alcohol consumption is key to understanding how an individual transitions from non/social drinking to AUD and to providing better treatment. In this review, we discuss how the way ethanol is consumed as well as individual and environmental factors contribute to the escalation of ethanol consumption from intermittent low levels to consistently high levels. Moreover, we discuss how these factors are modelled in animals. It is clear a vast array of complex, interacting factors influence changes in alcohol consumption. Some of these factors act early in the acquisition of ethanol consumption and initial escalation, while others contribute to escalation of ethanol consumption at a later stage and are involved in the development of alcohol dependence. There is considerable need for more studies examining escalation associated with the formation of dependence and other hallmark features of AUD, especially studies examining mechanisms, as it is of considerable relevance to understanding and treating AUD.

Potentiated Response of ERK/MAPK Signaling is Associated with Prolonged Withdrawal from Cocaine Behavioral Sensitization

Among the neuroadaptations underlying the expression of cocaine-induced behaviors are modifications in glutamate-mediated signaling and synaptic plasticity via activation of mitogen-activated protein kinases (MAPKs) within the nucleus accumbens (NAc). We hypothesized that exposure to cocaine leads to alterations in MAPK signaling in NAc neurons, which facilitates changes in the glutamatergic system and thus behavioral changes. We have previously shown that following withdrawal from cocaine-induced behavioral sensitization (BS), an increase in glutamate receptor expression and elevated MAPK signaling was evident. Here, we set out to determine the time course and behavioral consequences of inhibition of extracellular signal-regulated kinase (ERK) or NMDA receptors following withdrawal from BS. We found that inhibiting ERK by microinjection of U0126 into the NAc at 1 or 6 days following withdrawal from BS did not affect the expression of BS when challenged with cocaine at 14 days. However, inhibition of ERK 1 day before the cocaine challenge abolished the expression of BS. We also inhibited NR2B-containing NMDA receptors in the NAc by microinjection of ifenprodil into the NAc following withdrawal from BS, which had no effect on the expression of BS. However, microinjection of ifenprodil to the NAc 1 day before challenge attenuated the expression of BS similar to ERK inhibition. These results suggest that following a prolonged period of withdrawal, NR2B-containing NMDA receptors and ERK activity play a critical role in the expression of cocaine behavioral sensitization.

A Rational Design of α-Helix-Shaped Peptides Employing the Hydrogen-Bond Surrogate Approach: A Modulation Strategy for Ras-RasGRF1 Interaction in Neuropsychiatric Disorders

In the last two decades, abnormal Ras (rat sarcoma protein)-ERK (extracellular signal-regulated kinase) signalling in the brain has been involved in a variety of neuropsychiatric disorders, including drug addiction, certain forms of intellectual disability, and autism spectrum disorder. Modulation of membrane-receptor-mediated Ras activation has been proposed as a potential target mechanism to attenuate ERK signalling in the brain. Previously, we showed that a cell penetrating peptide, RB3, was able to inhibit downstream signalling by preventing RasGRF1 (Ras guanine nucleotide-releasing factor 1), a neuronal specific GDP/GTP exchange factor, to bind Ras proteins, both in brain slices and in vivo, with an IC₅₀ value in the micromolar range. The aim of this work was to mutate and improve this peptide through computer-aided techniques to increase its inhibitory activity against RasGRF1. The designed peptides were built based on the RB3 peptide structure corresponding to the α-helix of RasGRF1 responsible for Ras binding. For this purpose, the hydrogen-bond surrogate (HBS) approach was exploited to maintain the helical conformation of the designed peptides. Finally, residue scanning, MD simulations, and MM-GBSA calculations were used to identify 18 most promising α-helix-shaped peptides that will be assayed to check their potential activity against Ras-RasGRF1 and prevent downstream molecular events implicated in brain disorders.

RGS14 modulates locomotor behavior and ERK signaling induced by environmental novelty and cocaine within discrete limbic structures

RATIONALE

In rodents, exposure to novel environments or psychostimulants promotes locomotion. Indeed, locomotor reactivity to novelty strongly predicts behavioral responses to psychostimulants in animal models of addiction. RGS14 is a plasticity-restricting protein with unique functional domains that enable it to suppress ERK-dependent signaling as well as regulate G protein activity. Although recent studies show that RGS14 is expressed in multiple limbic regions implicated in psychostimulant- and novelty-induced hyperlocomotion, its function has been examined mostly in the context of hippocampal physiology and memory.

OBJECTIVE

We investigated whether RGS14 modulates novelty- and cocaine-induced locomotion (NIL and CIL, respectively) and neuronal activity.

METHODS

We assessed Rgs14 knockout (RGS14 KO) mice and wild-type (WT) littermate controls using NIL and CIL behavioral tests, followed by quantification of c-fos and phosphorylated ERK (pERK) induction in limbic regions that normally express RGS14.

RESULTS

RGS14 KO mice were less active than WT controls in the NIL test, driven by avoidance of the center of the novel environment. By contrast, RGS14 KO mice demonstrated augmented peripheral locomotion in the CIL test conducted in either a familiar or novel environment. RGS14 KO mice exhibited increased thigmotaxis, as well as greater c-fos and pERK induction in the central amygdala and dorsal hippocampus, when cocaine and novelty were paired.

CONCLUSIONS

RGS14 KO mice exhibited anti-correlated locomotor responses to novelty and cocaine, but displayed increased thigmotaxis in response to either stimuli which was augmented by their combination. Our findings also suggest RGS14 may reduce neuronal activity in limbic subregions by inhibiting ERK-dependent signaling.

The Role of CaMKII and ERK Signaling in Addiction

Nicotine is the predominant addictive compound of tobacco and causes the acquisition of dependence through its interactions with nicotinic acetylcholine receptors and various neurotransmitter releases in the central nervous system. The Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and extracellular signal-regulated kinase (ERK) play a pivotal role in synaptic plasticity in the hippocampus. CaMKII is involved in long-term potentiation induction, which underlies the consolidation of learning and memory; however, the roles of CaMKII in nicotine and other psychostimulant-induced addiction still require further investigation. This article reviews the molecular mechanisms and crucial roles of CaMKII and ERK in nicotine and other stimulant drug-induced addiction. We also discuss dopamine (DA) receptor signaling involved in nicotine-induced addiction in the brain reward circuitry. In the last section, we introduce the association of polyunsaturated fatty acids and cellular chaperones of fatty acid-binding protein 3 in the context of nicotine-induced addiction in the mouse nucleus accumbens and provide a novel target for the treatment of drug abuse affecting dopaminergic systems.

Chronic phenmetrazine treatment promotes D2 dopaminergic and α2-adrenergic receptor desensitization and alters phosphorylation of signaling proteins and local cerebral glucose metabolism in the rat brain

Phenmetrazine (PHEN) is a putative treatment for cocaine and psychostimulant recidivism; however, neurochemical changes underlying its activity have not been fully elucidated. We sought to characterize brain homeostatic adaptations to chronic PHEN, specifically on functional brain activity (local cerebral glucose utilization), G-Protein Coupled Receptor-stimulated G-protein activation, and phosphorylation of ERK1/2Thr202/Tyr204, GSK3βTyr216, and DARPP-32Thr34. Male Sprague-Dawley rats were implanted with sub-cutaneous minipumps delivering either saline (vehicle), acute (2-day) or chronic (14-day) low dose (25 mg/kg/day) or high dose (50 mg/kg/day) PHEN. Acute administration of high dose PHEN increased local cerebral glucose utilization measured by 2-[14C]-deoxyglucose uptake in basal ganglia and motor-related regions of the rat brain. However, chronically treated animals developed tolerance to these effects. To identify the neurochemical changes associated with PHEN's activity, we performed [35S]GTPγS binding assays on unfixed and immunohistochemistry on fixed coronal brain sections. Chronic PHEN treatment dose-dependently attenuated D2 dopamine and α2-adrenergic, but not 5-HT1A, receptor-mediated G-protein activation. Two distinct patterns of effects on pERK1/2 and pDARPP-32 were observed: 1) chronic low dose PHEN decreased pERK1/2, and also significantly increased pDARPP-32 levels in some regions; 2) acute and chronic PHEN increased pERK1/2, but chronic high dose PHEN treatment tended to decrease pDARPP-32. Chronic low dose, but not high dose, PHEN significantly reduced pGSK3β levels in several regions. Our study provides definitive evidence that extended length PHEN dosage schedules elicit distinct modes of neuronal acclimatization in cellular signaling. These pharmacodynamic modifications should be considered in drug development for chronic use.

ERK-Directed Phosphorylation of mGlu5 Gates Methamphetamine Reward and Reinforcement in Mouse

Methamphetamine (MA) is a highly addictive psychomotor stimulant drug. In recent years, MA use has increased exponentially on a global scale, with the number of MA-involved deaths reaching epidemic proportions. There is no approved pharmacotherapy for treating MA use disorder, and we know relatively little regarding the neurobiological determinants of vulnerability to this disease. Extracellular signal-regulated kinase (ERK) is an important signaling molecule implicated in the long-lasting neuroadaptations purported to underlie the development of substance use disorders, but the role for this kinase in the propensity to develop addiction, particularly MA use disorder, is uncharacterized. In a previous MA-induced place-conditioning study of C57BL/6J mice, we characterized mice as MA-preferring, -neutral, or -avoiding and collected tissue from the medial prefrontal cortex (mPFC). Using immunoblotting, we determined that elevated phosphorylated ERK expression within the medial prefrontal cortex (mPFC) is a biochemical correlate of the affective valence of MA in a population of C57BL/6J mice. We confirmed the functional relevance for mPFC ERK activation for MA-induced place-preference via site-directed infusion of the MEK inhibitor U0126. By contrast, ERK inhibition did not have any effect upon MA-induced locomotion or its sensitization upon repeated MA treatment. Through studies of transgenic mice with alanine point mutations on T1123/S1126 of mGlu5 that disrupt ERK-dependent phosphorylation of the receptor, we discovered that ERK-dependent mGlu5 phosphorylation normally suppresses MA-induced conditioned place-preference (MA-CPP), but is necessary for this drug’s reinforcing properties. If relevant to humans, the present results implicate individual differences in the capacity of MA-associated cues/contexts to hyper-activate ERK signaling within mPFC in MA Use Disorder vulnerability and pose mGlu5 as one ERK-directed target contributing to the propensity to seek out and take MA.

Cocaine-Dependent Acquisition of Locomotor Sensitization and Conditioned Place Preference Requires D1 Dopaminergic Signaling through a Cyclic AMP, NCS-Rapgef2, ERK, and Egr-1/Zif268 Pathway

Elucidation of the mechanism of dopamine signaling to ERK that underlies plasticity in dopamine D1 receptor-expressing neurons leading to acquired cocaine preference is incomplete. NCS-Rapgef2 is a novel cAMP effector, expressed in neuronal and endocrine cells in adult mammals, that is required for D1 dopamine receptor-dependent ERK phosphorylation in mouse brain. In this report, we studied the effects of abrogating NCS-Rapgef2 expression on cAMP-dependent ERK→Egr-1/Zif268 signaling in cultured neuroendocrine cells; in D1 medium spiny neurons of NAc slices; and in either male or female mouse brain in a region-specific manner. NCS-Rapgef2 gene deletion in the NAc in adult mice, using adeno-associated virus-mediated expression of cre recombinase, eliminated cocaine-induced ERK phosphorylation and Egr-1/Zif268 upregulation in D1-medium spiny neurons and cocaine-induced behaviors, including locomotor sensitization and conditioned place preference. Abrogation of NCS-Rapgef2 gene expression in mPFC and BLA, by crossing mice bearing a floxed Rapgef2 allele with a cre mouse line driven by calcium/calmodulin-dependent kinase IIα promoter also eliminated cocaine-induced phospho-ERK activation and Egr-1/Zif268 induction, but without effect on the cocaine-induced behaviors. Our results indicate that NCS-Rapgef2 signaling to ERK in dopamine D1 receptor-expressing neurons in the NAc, but not in corticolimbic areas, contributes to cocaine-induced locomotor sensitization and conditioned place preference. Ablation of cocaine-dependent ERK activation by elimination of NCS-Rapgef2 occurred with no effect on phosphorylation of CREB in D1 dopaminoceptive neurons of NAc. This study reveals a new cAMP-dependent signaling pathway for cocaine-induced behavioral adaptations, mediated through NCS-Rapgef2/phospho-ERK activation, independently of PKA/CREB signaling.SIGNIFICANCE STATEMENT ERK phosphorylation in dopamine D1 receptor-expressing neurons exerts a pivotal role in psychostimulant-induced neuronal gene regulation and behavioral adaptation, including locomotor sensitization and drug preference in rodents. In this study, we examined the role of dopamine signaling through the D1 receptor via a novel pathway initiated through the cAMP-activated guanine nucleotide exchange factor NCS-Rapgef2 in mice. NCS-Rapgef2 in the NAc is required for activation of ERK and Egr-1/Zif268 in D1 dopaminoceptive neurons after acute cocaine administration, and subsequent enhanced locomotor response and drug seeking behavior after repeated cocaine administration. This novel component in dopamine signaling provides a potential new target for intervention in psychostimulant-shaped behaviors, and new understanding of how D1-medium spiny neurons encode the experience of psychomotor stimulant exposure.

Psychostimulant-Induced Adaptations in Nucleus Accumbens Glutamatergic Transmission

Carrying different aspects of emotional and motivational signals, glutamatergic synaptic projections from multiple limbic and paralimbic brain regions converge to the nucleus accumbens (NAc), in which these arousing signals are processed and prioritized for behavioral output. In animal models of drug addiction, some key drug-induced alterations at NAc glutamatergic synapses underlie important cellular and circuit mechanisms that promote subsequent drug taking, seeking, and relapse. With the focus of cocaine, we review changes at NAc glutamatergic synapses that occur after different drug procedures and abstinence durations, and the behavioral impact of these changes.

Effects of caffeine on ethanol-elicited place preference, place aversion and ERK phosphorylation in CD-1 mice

BACKGROUND

Epidemiological studies indicate a rise in the combined consumption of caffeinated and alcoholic beverages, which can lead to increased risk of alcoholic-beverage overconsumption. However, the effects of the combination of caffeine and ethanol in animal models related to aspects of drug addiction are still underexplored.

AIMS

To characterize the pharmacological interaction between caffeine and ethanol and establish if caffeine can affect the ability of ethanol (2 g/kg) to elicit conditioned place preference and conditioned place aversion, we administered caffeine (3 or 15 mg/kg) to male CD-1 mice before saline or ethanol. Moreover, we determined if these doses of caffeine could affect ethanol (2 g/kg) elicited extracellular signal-regulated kinase phosphorylation in brain areas, nucleus accumbens, bed nucleus of stria terminalis, central nucleus of the amygdala, and basolateral amygdala, previously associated with this type of associative learning.

RESULTS

In the place-conditioning paradigm, caffeine did not have an effect on its own, whereas ethanol elicited significant conditioned-place preference and conditioned-place aversion. Caffeine (15 mg/kg) significantly prevented the acquisition of ethanol-elicited conditioned-place preference and, at both doses, also prevented the acquisition of ethanol-elicited conditioned-place aversion. Moreover, both doses of caffeine also prevented ethanol-elicited extracellular signal-regulated kinase phosphorylation expression in all brain areas examined.

CONCLUSIONS

The present data indicate a functional antagonistic action of caffeine and ethanol on associative learning and extracellular signal-regulated kinase phosphorylation after an acute interaction. These results could provide exciting grounds for further studies, also in a translational perspective, of their pharmacological interaction modulating other processes involved in drug consumption and addiction.

Dopamine receptors in emesis: Molecular mechanisms and potential therapeutic function

Dopamine is a member of the catecholamine family and is associated with multiple physiological functions. Together with its five receptor subtypes, dopamine is closely linked to neurological disorders such as schizophrenia, Parkinson's disease, depression, attention deficit-hyperactivity, and restless leg syndrome. Unfortunately, several dopamine receptor-based agonists used to treat some of these diseases cause nausea and vomiting as impending side-effects. The high degree of cross interactions of dopamine receptor ligands with many other targets including G-protein coupled receptors, transporters, enzymes, and ion-channels, add to the complexity of discovering new targets for the treatment of nausea and vomiting. Using activation status of signaling cascades as mechanism-based biomarkers to foresee drug sensitivity combined with the development of dopamine receptor-based biased agonists may hold great promise and seems as the next step in drug development for the treatment of such multifactorial diseases. In this review, we update the present knowledge on dopamine and dopamine receptors and their potential roles in nausea and vomiting. The pre- and clinical evidence provided in this review supports the implication of both dopamine and dopamine receptor agonists in the incidence of emesis. Besides the conventional dopaminergic antiemetic drugs, potential novel antiemetic targeting emetic protein signaling cascades may offer superior selectivity profile and potency.

Environmental enrichment during forced abstinence from cocaine self-administration opposes gene network expression changes associated with the incubation effect

Environmental enrichment (EE) is a robust intervention for reducing cocaine-seeking behaviors in animals when given during forced abstinence. However, the mechanisms that underlie these effects are not well-established. We investigated the adult male rat transcriptome using RNA-sequencing (RNA-seq) following differential housing during forced abstinence from cocaine self-administration for either 1 or 21 days. Enriched, 21-day forced abstinence rats displayed a significant reduction in cocaine-seeking behavior compared to rats housed in isolation. RNA-seq of the nucleus accumbens shell revealed hundreds of differentially regulated transcripts between rats of different forced abstinence length and housing environment, as well as within specific contrasts such as enrichment (isolated 21 days vs. enriched 21 days) or incubation (isolated 1 day vs. isolated 21 days). Ingenuity Pathway Analysis affirmed several pathways as differentially enriched based on housing condition and forced abstinence length including RELN, the Eif2 signaling pathway, synaptogenesis and neurogenesis pathways. Numerous pathways showed upregulation with incubation, but downregulation with EE, suggesting that EE may prevent or reverse changes in gene expression associated with protracted forced abstinence. The findings reveal novel candidate mechanisms involved in the protective effects of EE against cocaine seeking, which may inform efforts to develop pharmacological and gene therapies for treating cocaine use disorders. Furthermore, the finding that EE opposes multiple pathway changes associated with incubation of cocaine seeking strongly supports EE as a therapeutic intervention and suggests EE is capable of preventing or reversing the widespread dysregulation of signaling pathways that occurs during cocaine forced abstinence.

The Efficacy of Lidocaine in Disrupting Cocaine Cue-Induced Memory Reconsolidation

RATIONAL

Cue-induced craving memories, linked to drug-seeking behaviors, require key molecular processes for memory reconsolidation. Lidocaine, a sodium channel blocker, inhibits NMDA receptor activation and suppresses nitric oxide and ERK production. These processes are required for memory re-consolidation; inhibiting them may reduce cue-related craving memories in cocaine dependent subjects.

OBJECTIVES

To assess the efficacy of lidocaine in decreasing cue-induced cocaine craving and cocaine use.

METHODS

Treatment-seeking cocaine-dependent participants (n = 33, 25 men) were recruited. Personalized craving and relaxation scripts were developed. Participants were then randomly assigned in a double-blind design to either receive intravenous lidocaine immediately following a cocaine craving script (lidocaine/craving), saline following a craving script (saline/craving), or lidocaine following a relaxation script (lidocaine/relax). One week following the infusion, cue-induced craving was assessed in the same paradigm without an infusion. Cocaine use and craving were assessed for 4 weeks following infusion.

RESULTS

The administration of lidocaine during craving induction (lidocaine/craving) did not decrease cue-induced craving during craving reactivation one week later or craving and cocaine use over the 4-week follow-up period compared to the saline/craving group. There were no significant differences in craving and cocaine use between the lidocaine/relax and saline/craving groups.

CONCLUSION

Lidocaine administered following craving induction did not decrease subsequent cue-induced craving or cocaine use. Blocking the reconsolidation of craving-related memories with pharmacological agents remains an important area of investigation.

Phosphorylation barcode-dependent signal bias of the dopamine D1 receptor

Agonist-activated G protein-coupled receptors (GPCRs) must correctly select from hundreds of potential downstream signaling cascades and effectors. To accomplish this, GPCRs first bind to an intermediary signaling protein, such as G protein or arrestin. These intermediaries initiate signaling cascades that promote the activity of different effectors, including several protein kinases. The relative roles of G proteins versus arrestins in initiating and directing signaling is hotly debated, and it remains unclear how the correct final signaling pathway is chosen given the ready availability of protein partners. Here, we begin to deconvolute the process of signal bias from the dopamine D1 receptor (D1R) by exploring factors that promote the activation of ERK1/2 or Src, the kinases that lead to cell growth and proliferation. We found that ERK1/2 activation involves both arrestin and Gαs, while Src activation depends solely on arrestin. Interestingly, we found that the phosphorylation pattern influences both arrestin and Gαs coupling, suggesting an additional way the cells regulate G protein signaling. The phosphorylation sites in the D1R intracellular loop 3 are particularly important for directing the binding of G protein versus arrestin and for selecting between the activation of ERK1/2 and Src. Collectively, these studies correlate functional outcomes with a physical basis for signaling bias and provide fundamental information on how GPCR signaling is directed.

Long-term Changes in the Central Amygdala Proteome in Rats with a History of Chronic Cocaine Self-administration

The central nucleus of the amygdala (CeA) is a striatum-like structure that contains mainly inhibitory circuits controlling a repertoire of (mal)adaptive behaviors related to pain, anxiety, motivation, and addiction. Neural activity in the CeA is also necessary for the expression of persistent and robust drug seeking, also termed 'incubation of drug craving.' However, neuroadaptations within this brain region supporting incubated drug craving have not been characterized. Here, we conducted a comprehensive analysis of protein expression in the CeA of male rats after prolonged (45-day) abstinence from extended-access cocaine self-administration using a quantitative proteomic approach. The proteomic analysis identified 228 unique proteins altered in cocaine rats relative to animals that received saline. Out of the identified proteins, 160 were downregulated, while 68 upregulated. Upregulation of tyrosine hydroxylase and downregulation of neural cell-adhesion protein contactin-1 were validated by immunoblotting. Follow-up analysis by the Ingenuity Pathway Analysis tool revealed alterations in protein networks associated with several neurobehavioral disorders, cellular function and morphology, as well as axogenesis, long-term potentiation, and receptor signaling pathways. This study suggests that chronic cocaine self-administration, followed by a prolonged abstinence results in reorganization of specific protein signaling networks within the CeA that may underlie incubated cocaine craving and identifies potential novel 'druggable' targets for the treatment of cocaine use disorder (CUD).

Cannabinoid exposure in rat adolescence reprograms the initial behavioral, molecular, and epigenetic response to cocaine

The endocannabinoid system has a modulatory role in brain reward and cognitive processes. It has been hypothesized that repeated interference with endocannabinoid signaling (e.g., through abuse of cannabis or synthetic cannabinoids) can remodel the adolescent brain and make it respond differently to more addictive substances, such as cocaine. In the present study, we demonstrate that a history of synthetic cannabinoid exposure in adolescent animals results in distinct molecular and epigenetic changes following initial exposure to cocaine. These changes were pronounced in the prefrontal cortex and associated with an enhanced response to cocaine’s stimulatory effects. The prefrontal cortex is a brain region that still undergoes maturation in adolescence and its dysfunction contributes to the development of addictions.

The initial response to an addictive substance can facilitate repeated use: That is, individuals experiencing more positive effects are more likely to use that drug again. Increasing evidence suggests that psychoactive cannabinoid use in adolescence enhances the behavioral effects of cocaine. However, despite the behavioral data, there is no neurobiological evidence demonstrating that cannabinoids can also alter the brain’s initial molecular and epigenetic response to cocaine. Here, we utilized a multiomics approach (epigenomics, transcriptomics, proteomics, and phosphoproteomics) to characterize how the rat brain responds to its first encounter with cocaine, with or without preexposure to the synthetic cannabinoid WIN 55,212-2 (WIN). We find that in adolescent (but not in adult) rats, preexposure to WIN results in cross-sensitization to cocaine, which correlates with histone hyperacetylation and decreased levels of HDAC6 in the prefrontal cortex (PFC). In the PFC, we also find that WIN preexposure blunts the typical mRNA response to cocaine and instead results in alternative splicing and chromatin accessibility events, involving genes such as Npas2. Moreover, preexposure to WIN enhances the effects of cocaine on protein phosphorylation, including ERK/MAPK-targets like gephyrin, and modulates the synaptic AMPAR/GluR composition both in the PFC and the nucleus accumbens (NAcc). PFC–NAcc gene network topological analyses, following cocaine exposure, reveal distinct top nodes in the WIN preexposed group, which include PACAP/ADCYAP1. These preclinical data demonstrate that adolescent cannabinoid exposure reprograms the initial behavioral, molecular, and epigenetic response to cocaine.

Quetiapine Abuse Fourteen Years Later: Where Are We Now? A Systematic Review

Background: Quetiapine, an atypical antipsychotic endowed with weak dopamine antagonist, potent 5-HT_2A-blocking, partial 5-HT_1A-agonist, anti-H₁ histamine, adrenolytic, and sigma₁ receptor agonist activities, since an original 2004 report is increasingly misused. Although some of its pharmacodynamics might explain some motives for voluptuary use, most of its actions are directed at setting-off those motives. Hence, it is possible that its popularity in special populations is due to the fact that the unpleasant or unwanted effects of addiction substances are somehow soothed by quetiapine. Currently, quetiapine is tested in substance use disorders, showing some promise, but it is likely to be misused in certain contexts. Objectives: To review the evidence for the use of quetiapine as addiction substance and investigate the characteristics of populations involved in such addiction. Methods: A systematic review of literature on various databases retrieved on September 7, 2018 87 records to comment. Results. We reviewed the evidence for quetiapine's addictive potential in the light of its pharmacodynamics properties and presented two cases of recreational quetiapine use, by a 35-year old male patient with past addictive behavior and by a 50-year-old woman with major depressive disorder and conversion disorder. We found quetiapine to be abused mainly by addict populations and people with law involvement. Conclusions/Importance: There is no reason to include quetiapine among regulated substances, but monitoring of its use in selected populations is warranted. Psychiatrists and physicians working in the penitentiary system should be aware of the addictive potential of quetiapine and adopt measures restricting its use.

Therapeutic efficacy of environmental enrichment for substance use disorders

Addiction to drug and alcohol is regarded as a major health problem worldwide for which available treatments show limited effectiveness. The biggest challenge remains to enhance the capacities of interventions to reduce craving, prevent relapse and promote long-term recovery. New strategies to meet these challenges are being explored. Findings from preclinical work suggest that environmental enrichment (EE) holds therapeutic potential for the treatment of substance use disorders, as demonstrated in a number of animal models of drug abuse. The EE intervention introduced after drug exposure leads to attenuation of compulsive drug taking, attenuation of the rewarding (and reinforcing) effects of drugs, reductions in control of behavior by drug cues, and, very importantly, relapse prevention. Clinical work also suggests that multidimensional EE interventions (involving physical activity, social interaction, vocational training, recreational and community involvement) might produce similar therapeutic effects, if implemented continuously and rigorously. In this review we survey preclinical and clinical studies assessing the efficacy of EE as a behavioral intervention for substance use disorders and address related challenges. We also review work providing empirical evidence for EE-induced neuroplasticity within the mesocorticolimbic system that is believed to contribute to the seemingly therapeutic effects of EE on drug and alcohol-related behaviors.

Accumbens brain-derived neurotrophic factor (BDNF) transmission inhibits cocaine seeking

Brain-derived neurotrophic factor (BDNF) regulates a variety of physiological processes, and several studies have explored the role of BDNF in addiction-related brain regions like the nucleus accumbens core (NAcore). We sought to understand the rapid effects of endogenous BDNF on cocaine seeking. Rats were trained to self-administer cocaine and extinguished. We then microinjected two inhibitors of BDNF stimulation of tropomyosin receptor kinase B (TrkB), the non-competitive receptor antagonist ANA-12 and TrkB/Fc, a fusion protein that binds BDNF and prevents TrkB stimulation. Blocking TrkB or inactivating BDNF in NAcore potentiated active lever pressing, showing that endogenous BDNF tone was present and supplying inhibitory tone on cue-induced reinstatement. To determine if exogenous BDNF also negatively regulated reinstatement, BDNF was microinjected into NAcore 15 minutes before cue-induced reinstatement. BDNF decreased cocaine seeking through TrkB receptor binding, but had no effect on inactive lever pressing, spontaneous or cocaine-induced locomotion, or on reinstated sucrose seeking. BDNF-infusion potentiated within trial extinction when microinjected in the NAcore during cue- and context + cue induced reinstatement, and the inhibition of lever pressing lasted at least 3 days post injection. Although decreased reinstatement endured for 3 days when BDNF was administered prior to a reinstatement session, when microinjected before an extinction session or in the home cage, BDNF did not alter subsequent cued-reinstatement. Together, these data show that endogenous BDNF acts on TrKB to provide inhibitory tone on reinstated cocaine seeking, and this effect was recapitulated by exogenous BDNF.

Signaling Properties of Structurally Diverse Kappa Opioid Receptor Ligands: Toward in Vitro Models of in Vivo Responses

Biased ligands preferentially activate certain signaling pathways downstream of their target receptor, leading to differential physiological or behavioral responses downstream. The kappa opioid receptor (KOR) is a drug target for diseases involving mood and reward, such as depression and addiction. Biased KOR ligands offer the potential to overcome negative side effects that have previously hampered the therapeutic development of KOR agonists by preferentially activating certain signaling pathways. Understanding relationships between ligand bias and behavior is difficult, however, because differences in cellular context and bias quantification methods lead to variation between studies. Here, a set of 21 structurally diverse KOR ligands were tested in parallel, to systematically quantify ligand bias at the KOR. Compounds included the endogenous peptide ligand Dynorphin A(1-17), two novel compounds synthesized for our research, and 18 additional compounds of different structural classes, including morphinans and the natural product Salvinorin A. Compounds were tested for their activity in early KOR signaling pathways (G-protein and β-arrestin recruitment) in KOR-expressing U2OS cells, and ligand bias was calculated. A subset of compounds was tested for sedative properties in the rotarod assay in mice. We found that rotarod sedation significantly correlated with β-arrestin signaling in this system, indicating that this in vitro system can be used to accurately describe this in vivo behavior caused by KOR agonists. Additionally, downstream signaling pathways ERK1/2 and mTOR were evaluated, and we determined that signaling via both of these pathways could diverge from KOR-mediated G-protein and arrestin signaling in this system.

Relevance of ERK1/2 Post-retrieval Participation on Memory Processes: Insights in Their Particular Role on Reconsolidation and Persistence of Memories

Back in 1968, Misanin and his group posited that reactivation of consolidated memories could support changes in that trace, similar to what might happen during the consolidation process. Not until 2000, when Nader et al. (2000) studied the behavioral effect of a protein synthesis inhibitor on retrieved memories, could this previous statement be taken under consideration once again; suggesting that consolidated memories can become labile after reactivation. The process of strengthening after memory labilization was named memory reconsolidation. In recent years, many studies pointed towards a critical participation of the extracellular signal-regulated kinase (ERK)/mitogen activated protein kinases (MAPKs) pathway in different memory processes (e.g., consolidation, extinction, reconsolidation, among others). In this review article, we will focus on how this system might be modulating the processes triggered after retrieval of well-consolidated memories in mice.

Commonly Used Anesthesia/Euthanasia Methods for Brain Collection Differentially Impact MAPK Activity in Male and Female C57BL/6 Mice

The mitogen-activated protein kinases (MAPKs) are a family of protein kinases that regulate crucial neuronal functions such as neuronal differentiation, proliferation, and apoptosis through phosphorylation of subsequent protein kinases. The three classical MAPK subfamilies, extracellular signal-regulated kinase 1 and 2 (ERK1/2), c-Jun N-terminal kinase (JNK), and p38 kinase have been linked to various neurological disorders often in conjunction with activation of a wide range of G protein-coupled receptors and receptor tyrosine kinases. Many studies investigating MAPK function in these disorders rely on histochemistry or immunoblotting that require brain isolation following euthanasia. Here, we evaluated to what degree different modes of anesthesia/euthanasia impact MAPK activity in adult male and female C57BL/6 mice. Mice were decapitated following ketamine/xylazine or isoflurane anesthesia, carbon dioxide asphyxiation, or without anesthesia. We selectively chose five brain regions (the prefrontal cortex, the dorsal hippocampus, the dorsal striatum, the nucleus accumbens, and the amygdala) that are heavily implicated in neuropsychiatric disorders. We found that relative to carbon dioxide asphyxiation, the other methods displayed significantly stronger ERK1/2 phosphorylation in select brain regions of male and female mice, with no pronounced sex difference. A similar, yet, less pronounced trend was observed for JNK activity, whereas the choice of euthanasia method did not differentially impact p38 phosphorylation. Our study results reveal how small differences in experimental design may impact whether one will be able to detect drug- or disease-related changes in MAPK activity. These findings are timely in a period where experimental rigor is emphasized to increase reproducibility of research.

ERK/MAPK signaling and autism spectrum disorders

The MAPK pathway is a prominent intracellular signaling pathway regulating various intracellular functions. Components of this pathway are mutated in a related collection of congenital syndromes collectively referred to as neuro-cardio-facio-cutaneous syndromes (NCFC) or Rasopathies. Recently, it has been appreciated that these disorders are associated with autism spectrum disorders (ASD). In addition, idiopathic ASD has also implicated the MAPK signaling cascade as a common pathway that is affected by many of the genetic variants that have been found to be linked to ASDs. This chapter describes the components of the MAPK pathway and how it is regulated. Furthermore, this chapter will highlight the various functions of the MAPK pathway during both embryonic development of the central nervous system (CNS) and its roles in neuronal physiology and ultimately, behavior. Finally, we will summarize the perturbations to MAPK signaling in various models of autism spectrum disorders and Rasopathies to highlight how dysregulation of this pivotal pathway may contribute to the pathogenesis of autism.

TAAR1 in Addiction: Looking Beyond the Tip of the Iceberg

Trace-amine associated receptor 1 (TAAR1) is the best-characterized member of the family of TAARs. TAAR1 is broadly expressed in the brain, especially within the monoaminergic systems. Evidence from electrophysiological and neurochemical studies evaluating the effects of genetic and pharmacological interventions on TAAR1 revealed that TAAR1 modulates transmission of monoamines, especially dopamine. TAAR1 agonists dampened drugs of abuse-induced dopamine accumulation. In general, TAAR1 agonists specifically inhibited the rewarding and reinforcing effects of drugs of abuse and drug-abuse related behaviors. Details of the mechanism of TAAR1 remain elusive; however, it is thought to be regulated by its interactions with D2 receptors. In addition, the alternative cellular mechanism such as an interaction between TAAR1 and D3 may also participate in the action of TAAR1 agonists. Further studies are required to investigate the role of TAAR1 in other drugs of abuse-related behaviors and the underlying neural mechanisms. Collectively, TAAR1 negatively modulates dopaminergic systems and dopamine-related behaviors and TAAR1 agonists are promising pharmacotherapy to treat drug addiction and relapse.

Transcriptome Sequencing Reveals Candidate NF-κB Target Genes Involved in Repeated Cocaine Administration

BACKGROUND

Drug-induced alterations in gene expression play an important role in the development of addictive behavior. Numerous transcription factors have been implicated in mediating the gene expression changes that occur in drug addiction. Nuclear factor kappa B is an inducible transcription factor complex that is rapidly activated by diverse stimuli.

METHODS

We performed next-generation high-throughput sequencing of the prefrontal cortex in a mouse model of repeated cocaine administration combined with pharmacological nuclear factor kappa B inhibition to identify nuclear factor kappa B target genes that participate in the cocaine addiction process.

RESULTS

We found that the nuclear factor kappa B antagonist sodium diethyldithiocarbamate trihydrate significantly reversed the cocaine-induced expression changes of the amphetamine addiction pathway. Genes that demonstrated differential expression in response to cocaine treatment that was also reversed by sodium diethyldithiocarbamate trihydrate were enriched for the axon guidance pathway. Furthermore, the nuclear factor kappa B homo-dimer motif could be mapped to 86 of these sodium diethyldithiocarbamate trihydrate-reversed genes, which were also enriched for axon guidance.

CONCLUSIONS

We suggest that nuclear factor kappa B directly modifies the expression of axon guidance pathway members, leading to cocaine sensitization. Our findings reveal the role of prefrontal cortex nuclear factor kappa B activity in addiction and uncover the molecular mechanisms by which nuclear factor kappa B drives changes in the addicted brain.

Protein Translation in the Nucleus Accumbens Is Dysregulated during Cocaine Withdrawal and Required for Expression of Incubation of Cocaine Craving

Exposure to drug-associated cues can induce drug craving and relapse in abstinent addicts. Cue-induced craving that progressively intensifies ("incubates") during withdrawal from cocaine has been observed in both rats and humans. Building on recent evidence that aberrant protein translation underlies incubation-related adaptations in the NAc, we used male rats to test the hypothesis that translation is dysregulated during cocaine withdrawal and/or when rats express incubated cocaine craving. We found that intra-NAc infusion of anisomycin, a general protein translation inhibitor, or rapamycin, an inhibitor of mammalian target of rapamycin, reduced the expression of incubated cocaine craving, consistent with previous results showing that inhibition of translation in slices normalized the adaptations that maintain incubation. We then examined signaling pathways involved in protein translation using NAc synaptoneurosomes prepared after >47 d of withdrawal from cocaine or saline self-administration, or after withdrawal plus a cue-induced seeking test. The most robust changes were observed following seeking tests. Most notably, we found that eukaryotic elongation factor 2 (eEF2) and eukaryotic initiation factor 2α (eIF2α) are dephosphorylated when cocaine rats undergo a cue-induced seeking test; both effects are consistent with increased translation during the test. Blocking eIF2α dephosphorylation and thereby restoring its inhibitory influence on translation, via intra-NAc injection of Sal003 just before the test, substantially reduced cocaine seeking. These results are consistent with dysregulation of protein translation in the NAc during cocaine withdrawal, enabling cocaine cues to elicit an aberrant increase in translation that is required for the expression of incubated cocaine craving.SIGNIFICANCE STATEMENT Cue-induced cocaine craving progressively intensifies (incubates) during withdrawal in both humans and rats. This may contribute to persistent vulnerability to relapse. We previously demonstrated a role for protein translation in synaptic adaptations in the NAc closely linked to incubation. Here, we tested the hypothesis that translation is dysregulated during cocaine withdrawal, and this contributes to incubated craving. Analysis of signaling pathways regulating translation suggested that translation is enhanced when "incubated" rats undergo a cue-induced seeking test. Furthermore, intra-NAc infusions of drugs that inhibit protein translation through different mechanisms reduced expression of incubated cue-induced cocaine seeking. These results demonstrate that the expression of incubation depends on an acute increase in translation that may result from dysregulation of several pathways.

Neuronal RNA-binding protein HuD regulates addiction-related gene expression and behavior

The neuronal RNA-binding protein HuD is involved in synaptic plasticity and learning and memory mechanisms. These effects are thought to be due to HuD-mediated stabilization and translation of target mRNAs associated with plasticity. To investigate the potential role of HuD in drug addiction, we first used bioinformatics prediction algorithms together with microarray analyses to search for specific genes and functional networks upregulated within the forebrain of HuD overexpressing mice (HuD_OE ). When this set was further limited to genes in the knowledgebase of addiction-related genes database (KARG) that contains predicted HuD-binding sites in their 3' untranslated regions (3'UTRs), we found that HuD regulates networks that have been associated with addiction-like behavior. These genes included Bdnf and Camk2a, 2 previously validated HuD targets. Since addiction is hypothesized to be a disorder stemming from altered gene expression causing aberrant plasticity, we sought to test the role of HuD in cocaine conditioned placed preference (CPP), a model of addiction-related behaviors. HuD mRNA and protein were upregulated by CPP within the nucleus accumbens of wild-type C57BL/6J mice. These changes were associated with increased expression of Bdnf and Camk2a mRNA and protein. To test this further, we trained HuD_OE and wild-type mice in CPP and found that HuD_OE mice showed increased cocaine CPP compared with controls. This was also associated with elevated expression of HuD target mRNAs and proteins, CaMKIIα and BDNF. These findings suggest HuD involvement in addiction-related behaviors such as cocaine conditioning and seeking, through increased plasticity-related gene expression.

Intra-prelimbic cortical inhibition of striatal-enriched tyrosine phosphatase suppresses cocaine seeking in rats

Cocaine self-administration in rats results in dysfunctional neuroadaptations in the prelimbic (PrL) cortex during early abstinence. Central to these adaptations is decreased phospho-extracellular signal-regulated kinase (p-ERK), which plays a key role in cocaine seeking. Normalizing ERK phosphorylation in the PrL cortex immediately after cocaine self-administration decreases subsequent cocaine seeking. The disturbance in ERK phosphorylation is accompanied by decreased phosphorylation of striatal-enriched protein tyrosine phosphatase (STEP), indicating increased STEP activity. STEP is a well-recognized ERK phosphatase but whether STEP activation during early abstinence mediates the decrease in p-ERK and is involved in relapse is unknown. Here, we show that a single intra-PrL cortical microinfusion of the selective STEP inhibitor, TC-2153, immediately after self-administration suppressed post-abstinence context-induced relapse under extinction conditions and cue-induced reinstatement, but not cocaine prime-induced drug seeking or sucrose seeking. Moreover, an intra-PrL cortical TC-2153 microinfusion immediately after self-administration prevented the cocaine-induced decrease in p-ERK within the PrL cortex during early abstinence. Interestingly, a systemic TC-2153 injection at the same timepoint failed to suppress post-abstinence context-induced relapse or cue-induced reinstatement, but did suppress cocaine prime-induced reinstatement. These data indicate that the STEP-induced ERK dephosphorylation in the PrL cortex during early abstinence is a critical neuroadaptation that promotes relapse to cocaine seeking and that systemic versus intra-PrL cortical inhibition of STEP during early abstinence differentially suppresses cocaine seeking.

The genetic epidemiology of substance use disorder: A review

BACKGROUND

Substance use disorder (SUD) remains a significant public health issue. A greater understanding of how genes and environment interact to regulate phenotypes comprising SUD will facilitate directed treatments and prevention.

METHODS

The literature studying the neurobiological correlates of SUD with a focus on the genetic and environmental influences underlying these mechanisms was reviewed. Results from twin/family, human genetic association, gene-environment interaction, epigenetic literature, phenome-wide association studies are summarized for alcohol, nicotine, cannabinoids, cocaine, and opioids.

RESULTS

There are substantial genetic influences on SUD that are expected to influence multiple neurotransmission pathways, and these influences are particularly important within the dopaminergic system. Genetic influences involved in other aspects of SUD etiology including drug processing and metabolism are also identified. Studies of gene-environment interaction emphasize the importance of environmental context in SUD. Epigenetic studies indicate drug-specific changes in gene expression as well as differences in gene expression related to the use of multiple substances. Further, gene expression is expected to differ by stage of SUD such as substance initiation versus chronic substance use. While a substantial literature has developed for alcohol and nicotine use disorders, there is comparatively less information for other commonly abused substances.

CONCLUSIONS

A better understanding of genetically-mediated mechanisms involved in the neurobiology of SUD provides increased opportunity to develop behavioral and biologically based treatment and prevention of SUD.

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

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