Molecular neurobiology of drug addiction

Memory Reconsolidation Updating in Substance Addiction: Applications, Mechanisms, and Future Prospects for Clinical Therapeutics

Persistent and maladaptive drug-related memories represent a key component in drug addiction. Converging evidence from both preclinical and clinical studies has demonstrated the potential efficacy of the memory reconsolidation updating procedure (MRUP), a non-pharmacological strategy intertwining two distinct memory processes: reconsolidation and extinction-alternatively termed "the memory retrieval-extinction procedure". This procedure presents a promising approach to attenuate, if not erase, entrenched drug memories and prevent relapse. The present review delineates the applications, molecular underpinnings, and operational boundaries of MRUP in the context of various forms of substance dependence. Furthermore, we critically examine the methodological limitations of MRUP, postulating potential refinement to optimize its therapeutic efficacy. In addition, we also look at the potential integration of MRUP and neurostimulation treatments in the domain of substance addiction. Overall, existing studies underscore the significant potential of MRUP, suggesting that interventions predicated on it could herald a promising avenue to enhance clinical outcomes in substance addiction therapy.

Differential Impact of Serotonin Signaling Methylphenidate on Young versus Adult: Insights from Behavioral and Dorsal Raphe Nucleus Neuronal Recordings from Freely Behaving Rats

Methylphenidate (MPD) remains a cornerstone pharmacological intervention for managing ADHD, yet its increasing usage among ordinary youth and adults outside clinical contexts necessitates a thorough investigation into its developmental effects. This study seeks to simultaneously investigate the behavioral and neuronal changes within the dorsal raphe (DR) nucleus, a center of serotonergic neurons in the mammalian brain, before and after the administration of varying doses of acute and chronic MPD in freely behaving young and adult rats implanted with DR recording electrodes. Wireless neuronal and behavioral recording systems were used over 10 consecutive experimental days. Eight groups were examined: saline, 0.6, 2.5, and 10.0 mg/kg MPD for both young and adult rats. Six daily MPD injections were administered on experimental days 1 to 6, followed by a three-day washout period and MPD re-administration on experimental day 10 (ED10). The analysis of neuronal activity recorded from 504 DR neurons (DRNs) in young rats and 356 DRNs in adult rats reveals significant age-dependent differences in acute and chronic MPD responses. This study emphasizes the importance of aligning electrophysiological evaluations with behavioral outcomes following extended MPD exposure, elucidating the critical role of DRNs and serotonin signaling in modulating MPD responses and delineating age-specific variations in young versus adult rat models.

Differential Roles of Key Brain Regions: Ventral Tegmental Area, Locus Coeruleus, Dorsal Raphe, Nucleus Accumbens, Caudate Nucleus, and Prefrontal Cortex in Regulating Response to Methylphenidate: Insights from Neuronal and Behavioral Studies in Freely Behaving Rats

A total of 3102 neurons were recorded before and following acute and chronic methylphenidate (MPD) administration. Acute MPD exposure elicits mainly increases in neuronal and behavioral activity in dose-response characteristics. The response to chronic MPD exposure, as compared to acute 0.6, 2.5, or 10.0 mg/kg MPD administration, elicits electrophysiological and behavioral sensitization in some animals and electrophysiological and behavioral tolerance in others when the neuronal recording evaluations were performed based on the animals' behavioral responses, or amount of locomotor activity, to chronic MPD exposure. The majority of neurons recorded from those expressing behavioral sensitization responded to chronic MPD with further increases in firing rate as compared to the initial MPD responses. The majority of neurons recorded from animals expressing behavioral tolerance responded to chronic MPD with decreases in their firing rate as compared to the initial MPD exposures. Each of the six brain areas studied-the ventral tegmental area, locus coeruleus, dorsal raphe, nucleus accumbens, prefrontal cortex, and caudate nucleus (VTA, LC, DR, NAc, PFC, and CN)-responds significantly (p < 0.001) differently to MPD, suggesting that each one of the above brain areas exhibits different roles in the response to MPD. Moreover, this study demonstrates that it is essential to evaluate neuronal activity responses to psychostimulants based on the animals' behavioral responses to acute and chronic effects of the drug from several brain areas simultaneously to obtain accurate information on each area's role in response to the drug.

Opioid-Induced Hyperalgesia and Tolerance Are Driven by HCN Ion Channels

Prolonged exposure to opioids causes an enhanced sensitivity to painful stimuli (opioid-induced hyperalgesia, OIH) and a need for increased opioid doses to maintain analgesia (opioid-induced tolerance, OIT), but the mechanisms underlying both processes remain obscure. We found that pharmacological block or genetic deletion of HCN2 ion channels in primary nociceptive neurons of male mice completely abolished OIH but had no effect on OIT. Conversely, pharmacological inhibition of central HCN channels alleviated OIT but had no effect on OIH. Expression of C-FOS, a marker of neuronal activity, was increased in second-order neurons of the dorsal spinal cord by induction of OIH, and the increase was prevented by peripheral block or genetic deletion of HCN2, but block of OIT by spinal block of HCN channels had no impact on C-FOS expression in dorsal horn neurons. Collectively, these observations show that OIH is driven by HCN2 ion channels in peripheral nociceptors, while OIT is driven by a member of the HCN family located in the CNS. Induction of OIH increased cAMP in nociceptive neurons, and a consequent shift in the activation curve of HCN2 caused an increase in nociceptor firing. The shift in HCN2 was caused by expression of a constitutively active μ-opioid receptor (MOR) and was reversed by MOR antagonists. We identified the opioid-induced MOR as a six-transmembrane splice variant, and we show that it increases cAMP by coupling constitutively to Gs HCN2 ion channels therefore drive OIH, and likely OIT, and may be a novel therapeutic target for the treatment of addiction.

Discovery of a novel series of potent carbonic anhydrase inhibitors with selective affinity for μ Opioid receptor for Safer and long-lasting analgesia

In this study, we investigated the development of dual-targeted ligands that bind to both μ-opioid receptor (MOR) and carbonic anhydrase (CA) enzymes, using fentanyl structure as a template. We synthesized and evaluated 21 novel compounds with dual-targeted affinity identifying the lead candidate compound 8, showing selective affinity for MOR and potent inhibition of several cytosolic CA isoforms. By means of repeated treatment of 3 daily administrations for 17 days, fentanyl (0.1 mg/kg, subcutaneously) led to tolerance development, pain threshold alterations and withdrawal symptoms in CD-1 mice, as well as astrocyte and microglia activation in the dorsal horn of the lumbar spinal cord. In contrast, compound 8 (0.32 mg/kg s.c.) maintained stable during days its analgesic effect at the higher dose tested with fewer withdrawal symptoms, allodynia development and glial cells activation. Our results suggest that targeting both MOR and CA enzymes can lead to the development of new class of potent analgesic agents with fewer side effects and reduced tolerance development. Further studies are needed to explore the potential mechanisms underlying these effects and to further optimize the therapeutic potential of these compounds.

Viral-mediated expression of Erk2 in the nucleus accumbens regulates responses to rewarding and aversive stimuli

Second-messenger signaling within the mesolimbic reward circuit is involved in both the long-lived effects of stress and in the underlying mechanisms that promote drug abuse liability. To determine the direct role of kinase signaling within the nucleus accumbens, specifically mitogen-activated protein kinase 1 (ERK2), in mood- and drug-related behavior, we used a herpes-simplex virus to up- or down-regulate ERK2 in adult male rats. We then exposed rats to a battery of behavioral tasks including the elevated plus-maze, open field test, forced-swim test, conditioned place preference, and finally cocaine self-administration. Herein, we show that viral overexpression or knockdown of ERK2 in the nucleus accumbens induces distinct behavioral phenotypes. Specifically, over expression of ERK2 facilitated depression- and anxiety-like behavior while also increasing sensitivity to cocaine. Conversely, down-regulation of ERK2 attenuated behavioral deficits, while blunting sensitivity to cocaine. Taken together, these data implicate ERK2 signaling, within the nucleus accumbens, in the regulation of affective behaviors and modulating sensitivity to the rewarding properties of cocaine.

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.

Signal Transduction and Gene Regulation in the Endothelium

Extracellular signals act on G-protein-coupled receptors (GPCRs) to regulate homeostasis and adapt to stress. This involves rapid intracellular post-translational responses and long-lasting gene-expression changes that ultimately determine cellular phenotype and fate changes. The lipid mediator sphingosine 1-phosphate (S1P) and its receptors (S1PRs) are examples of well-studied GPCR signaling axis essential for vascular development, homeostasis, and diseases. The biochemical cascades involved in rapid S1P signaling are well understood. However, gene-expression regulation by S1PRs are less understood. In this review, we focus our attention to how S1PRs regulate nuclear chromatin changes and gene transcription to modulate vascular and lymphatic endothelial phenotypic changes during embryonic development and adult homeostasis. Because S1PR-targeted drugs approved for use in the treatment of autoimmune diseases cause substantial vascular-related adverse events, these findings are critical not only for general understanding of stimulus-evoked gene regulation in the vascular endothelium, but also for therapeutic development of drugs for autoimmune and perhaps vascular diseases.

Bispecific sigma-1 receptor antagonism and mu-opioid receptor partial agonism: WLB-73502, an analgesic with improved efficacy and safety profile compared to strong opioids

Opioids are the most effective painkillers, but their benefit-risk balance often hinder their therapeutic use. WLB-73502 is a dual, bispecific compound that binds sigma-1 (S1R) and mu-opioid (MOR) receptors. WLB-73502 is an antagonist at the S1R. It behaved as a partial MOR agonist at the G-protein pathway and produced no/unsignificant β-arrestin-2 recruitment, thus demonstrating low intrinsic efficacy on MOR at both signalling pathways. Despite its partial MOR agonism, WLB-73502 exerted full antinociceptive efficacy, with potency superior to morphine and similar to oxycodone against nociceptive, inflammatory and osteoarthritis pain, and superior to both morphine and oxycodone against neuropathic pain. WLB-73502 crosses the blood-brain barrier and binds brain S1R and MOR to an extent consistent with its antinociceptive effect. Contrary to morphine and oxycodone, tolerance to its antinociceptive effect did not develop after repeated 4-week administration. Also, contrary to opioid comparators, WLB-73502 did not inhibit gastrointestinal transit or respiratory function in rats at doses inducing full efficacy, and it was devoid of proemetic effect (retching and vomiting) in ferrets at potentially effective doses. WLB-73502 benefits from its bivalent S1R antagonist and partial MOR agonist nature to provide an improved antinociceptive and safety profile respect to strong opioid therapy.

Claustral MeCP2 Regulates Methamphetamine-induced Conditioned Place Preference in Cynomolgus Monkey

The claustrum, a brain nucleus located between the cortex and the striatum, has recently been highlighted in drug-related reward processing. Methyl CpG-binding protein-2 (MeCP2) is a transcriptional regulator that represses or activates the expression of the target gene and has been known to have an important role in the regulation of drug addiction in the dopaminergic reward system. The claustrum is an important region for regulating reward processing where most neurons receive dopamine input; additionally, in this region, MeCP2 is also abundantly expressed. Therefore, here, we hypothesized that MeCP2 would be involved in drug addiction control in the Claustrum as well and investigated how claustral MeCP2 regulates drug addiction. To better understand the function of human claustral MeCP2, we established a non-human primate model of methamphetamine (METH) - induced conditioned place preference (CPP). After a habituation of two days and conditioning of ten days, the CPP test was conducted for three days. Interestingly, we confirmed that virus-mediated overexpression of MECP2 in the claustrum showed a significant reduction of METH-induced CPP in the three consecutive days during the testing period. Moreover, they showed a decrease in visit scores (frequency for visit) for the METH-paired room compared to the control group although the scores were statistically marginal. Taken together, we suggest that the claustrum is an important brain region associated with drug addiction, in which MeCP2 may function as a mediator in regulating the response to addictive drugs.

Age differences to methylphenidate-NAc neuronal and behavioral recordings from freely behaving animals

Methylphenidate (MPD) is a psychostimulant that is widely prescribed to treat attention deficit-hyperactivity disorder, but it is abused recreationally as well. The nucleus accumbens (NAc) is part of the motivation circuit implicated in drug-seeking behaviors. The NAc neuronal activity was recorded alongside the behavioral activity from young and adult rats to determine if there are significant differences in the response to MPD. The same dose of MPD elicits behavioral sensitization in some animals and behavioral tolerance in others. In adult animals, higher doses of MPD resulted in a greater ratio of tolerance/sensitization. Animals who responded to chronic MPD with behavioral sensitization usually exhibited further increases in their NAc neuronal firing rates as well. Different upregulations of transcription factors (ΔFOSB/CREB), variable proportions of D1/D2 dopamine receptors, and modulation from other brain areas may predispose certain animals to express behavioral and neuronal sensitization versus tolerance to MPD.

Adolescent rats respond differently to methylphenidate as compared to adult rats- concomitant VTA neuronal and behavioral Recordings

Methylphenidate (MPD) is the most widely prescribed psychostimulant used in adolescents and adults to treat attention-deficit/hyperactivity disorder (ADHD). The recreational use of MPD is becoming more prevalent because of its ability to improve cognitive enhancement. The ventral tegmental area (VTA) of the brain is highly associated with reward, cognition and addiction to drugs including psychostimulants like MPD. The VTA neuronal activity was recorded alongside the horizontal behavioral activity from freely behaving non-anesthetized rats. Four adolescent and four adult groups were treated with either saline, 0.6, 2.5 or 10.0 mg/kg MPD. In both adolescent and adult animals, the animals responded to MPD in a dose-dependent manner, such that as the dose of MPD increased, more animals and more VTA unit responded to the drug. The same doses of MPD elicited in some animals behavioral and neuronal sensitization and in other animals behavioral and neuronal tolerance. In the 0.6 and 10.0 mg/kg MPD dose groups there were significant differences between the age groups for how many animals expressed behavioral sensitization and behavioral tolerance to chronic MPD exposure. Additionally, the animal's behavioral response to MPD by excitation or attenuation of activity did not always correlate to the VTA neuronal response, and the age group with significantly higher behavioral responses did not always correlate to the age group with significantly higher VTA neuronal responses for a given MPD dose. These findings differ from similar studies recorded from the prefrontal cortex (PFC), which exhibited behavioral responses continuously directly correlated to PFC responses for increasing MPD doses. This demonstrates that unlike other areas of the brain, there is not a direct relationship between VTA firing and behavioral activity, suggesting that there is input or modulation of this area from elsewhere in the brain. Further investigation is needed to clearly understand the relationship between VTA firing rates and behavioral responses to different MPD doses, especially given the significant differences in response between young and adult animals and the increasing use of the drug in adolescent populations.

Erythroxylum cuneatum prevented cellular adaptation in morphine-induced neuroblastoma cells

BACKGROUND

Chronic morphine stimulates prolonged stimulation of opioid receptors, especially µ-opioid subtype (MOR), which in turn signals cellular adaptation. However, the sudden termination of morphine after chronic intake causes withdrawal syndrome.

OBJECTIVES

Hence, this study was designed to find an alternative treatment for the morphine withdrawal using the alkaloid leaf extract of Erythroxylum cuneatum (E. cuneatum), done on morphine-exposed neuroblastoma cell lines.

METHODS

SK-N-SH, a commercialised neuroblastoma cell line, was used in two separate study designs; the antagonistic and pre-treatment of morphine. The antagonistic treatment was conducted through concurrent exposure of the cells to morphine and E. cuneatum or morphine and methadone for 24 h. The pre-treatment design was carried out by exposing the cells to morphine for 24 h, followed by 24 h exposures to E. cuneatum or methadone. The cytosolic fraction was collected and run for protein expression involved in cellular adaptation; mitogen-activated protein (MAP)/extracellular signal-regulated (ERK) kinase 1/2 (MEK 1/2), extracellular signal-regulated kinase 2 (ERK 2), cAMP-dependent protein kinase (PKA) and protein kinases C (PKC).

RESULTS

The antagonistic treatment showed the normal level of MEK 1/2, ERK 2, PKA and PKC by the combination treatment of morphine and E. cuneatum, comparable to the combination of morphine and methadone. Neuroblastoma cells exposed to morphine pre-treatment expressed a high level of MEK 1/2, ERK 2, PKA and PKC, while the treatments with E. cuneatum and methadone normalised the expression of the cellular adaptation proteins.

CONCLUSION

E. cuneatum exerted anti-addiction properties by lowering the levels of cellular adaptation proteins, and its effects are comparable to that of methadone (an established anti-addiction drug).

Receptor-Mediated AKT/PI3K Signalling and Behavioural Alterations in Zebrafish Larvae Reveal Association between Schizophrenia and Opioid Use Disorder

The link between substance abuse and the development of schizophrenia remains elusive. In this study, we assessed the molecular and behavioural alterations associated with schizophrenia, opioid addiction, and opioid withdrawal using zebrafish as a biological model. Larvae of 2 days post fertilization (dpf) were exposed to domperidone (DMP), a dopamine-D2 dopamine D2 receptor antagonist, and morphine for 3 days and 10 days, respectively. MK801, an N-methyl-D-aspartate (NMDA) receptor antagonist, served as a positive control to mimic schizophrenia-like behaviour. The withdrawal syndrome was assessed 5 days after the termination of morphine treatment. The expressions of schizophrenia susceptibility genes, i.e., pi3k, akt1, slc6a4, creb1 and adamts2, in brains were quantified, and the levels of whole-body cyclic adenosine monophosphate (cAMP), serotonin and cortisol were measured. The aggressiveness of larvae was observed using the mirror biting test. After the short-term treatment with DMP and morphine, all studied genes were not differentially expressed. As for the long-term exposure, akt1 was downregulated by DMP and morphine. Downregulation of pi3k and slc6a4 was observed in the morphine-treated larvae, whereas creb1 and adamts2 were upregulated by DMP. The levels of cAMP and cortisol were elevated after 3 days, whereas significant increases were observed in all of the biochemical tests after 10 days. Compared to controls, increased aggression was observed in the DMP-, but not morphine-, treated group. These two groups showed reduction in aggressiveness when drug exposure was prolonged. Both the short- and long-term morphine withdrawal groups showed downregulation in all genes examined except creb1, suggesting dysregulated reward circuitry function. These results suggest that biochemical and behavioural alterations in schizophrenia-like symptoms and opioid dependence could be controlled by common mechanisms.

Cocaine-induced projection-specific and cell type-specific adaptations in the nucleus accumbens

Cocaine craving, seeking, and relapse are mediated, in part, by cocaine-induced adaptive changes in the brain reward circuits. The nucleus accumbens (NAc) integrates and prioritizes different emotional and motivational inputs to the reward system by processing convergent glutamatergic projections from the medial prefrontal cortex, basolateral amygdala, ventral hippocampus, and other limbic and paralimbic brain regions. Medium spiny neurons (MSNs) are the principal projection neurons in the NAc, which can be divided into two major subpopulations, namely dopamine receptor D1- versus D2-expressing MSNs, with complementing roles in reward-associated behaviors. After cocaine experience, NAc MSNs exhibit complex and differential adaptations dependent on cocaine regimen, withdrawal time, cell type, location (NAc core versus shell), and related input and output projections, or any combination of these factors. Detailed characterization of these cellular adaptations has been greatly facilitated by the recent development of optogenetic/chemogenetic techniques combined with transgenic tools. In this review, we discuss such cell type- and projection-specific adaptations induced by cocaine experience. Specifically, (1) D1 and D2 NAc MSNs frequently exhibit differential adaptations in spinogenesis, glutamatergic receptor trafficking, and intrinsic membrane excitability, (2) cocaine experience differentially changes the synaptic transmission at different afferent projections onto NAc MSNs, (3) cocaine-induced NAc adaptations exhibit output specificity, e.g., being different at NAc-ventral pallidum versus NAc-ventral tegmental area synapses, and (4) the input, output, subregion, and D1/D2 cell type may together determine cocaine-induced circuit plasticity in the NAc. In light of the projection- and cell-type specificity, we also briefly discuss ensemble and circuit mechanisms contributing to cocaine craving and relapse after drug withdrawal.

A limited access oral oxycodone paradigm produces physical dependence and mesocorticolimbic region-dependent increases in DeltaFosB expression without preference

The abuse of oral formulations of prescription opioids has precipitated the current opioid epidemic. We developed an oral oxycodone consumption model consisting of a limited access (4 h) two-bottle choice drinking in the dark (TBC-DID) paradigm and quantified dependence with naloxone challenge using mice of both sexes. We also assessed neurobiological correlates of withdrawal and dependence elicited via oral oxycodone consumption using immunohistochemistry for DeltaFosB (ΔFosB), a transcription factor described as a molecular marker for drug addiction. Neither sex developed a preference for the oxycodone bottle, irrespective of oxycodone concentration, bottle position or prior water restriction. Mice that volitionally consumed oxycodone exhibited hyperlocomotion in an open field test and supraspinal but not spinally-mediated antinociception. Both sexes also developed robust, dose-dependent levels of opioid withdrawal that was precipitated by the opioid antagonist naloxone. Oral oxycodone consumption followed by naloxone challenge led to mesocorticolimbic region-dependent increases in the number of ΔFosB expressing cells. Naloxone-precipitated withdrawal jumps, but not the oxycodone bottle % preference, was positively correlated with the number of ΔFosB expressing cells specifically in the nucleus accumbens shell. Thus, limited access oral consumption of oxycodone produced physical dependence and increased ΔFosB expression despite the absence of opioid preference. Our TBC-DID paradigm allows for the study of oral opioid consumption in a simple, high-throughput manner and elucidates the underlying neurobiological substrates that accompany opioid-induced physical dependence.

The dopaminergic alterations induced by 4-F-PCP and 4-Keto-PCP may enhance their drug-induced rewarding and reinforcing effects: Implications for abuse

Novel psychoactive substances remain the popular recreational drugs of use over the years. They continue to bypass government restrictions due to their synthesis and modifications. Recent additions to the lists are the 4-F-PCP and 4-Keto-PCP, analogs of the drug phencyclidine (PCP) known to induce adverse effects and abuse potential. However, studies on the abuse potential of 4-F-PCP and 4-Keto-PCP remain scarce. The rewarding and reinforcing effects of the drugs were assessed using conditioned place preference (CPP), self-administration, and locomotor sensitization tests. Dopamine (DA) receptor antagonists (SCH23390 and haloperidol) were administered during CPP to evaluate the involvement of the mesolimbic dopaminergic system. DA-related protein expression in the nucleus accumbens (NAcc) and ventral tegmental area (VTA) was measured. Additionally, phosphorylated cyclic-adenosine monophosphate-activated protein (AMP) response element-binding (p-CREB) protein, deltaFosB (∆FosB), and brain-derived neurotrophic factor (BDNF) protein levels in the NAcc were measured to assess the addiction neural plasticity effect of the drugs. Both 4-F-PCP and 4-Keto-PCP-induced CPP and self-administration; however, only 4-F-PCP elicited locomotor sensitization. Treatment with DA receptor antagonists (SH23390 and haloperidol) inhibited the 4-F- and 4-Keto-induced CPP. Both substances altered the levels of DA receptor D1 (DRD1), thyroxine hydroxylase (TH), DA receptor D2 (DRD2), p-CREB, ∆FosB, and BDNF. The results suggest that 4-F-PCP and 4-Keto-PCP may induce abuse potential in rodents via alterations in dopaminergic system accompanied by addiction neural plasticity.

AddictGene: An integrated knowledge base for differentially expressed genes associated with addictive substance

Addiction, a disorder of maladaptive brain plasticity, is associated with changes in numerous gene expressions. Nowadays, high-throughput sequencing data on addictive substance-induced gene expression have become widely available. A resource for comprehensive annotation of genes that show differential expression in response to commonly abused substances is necessary. So, we developed AddictGene by integrating gene expression, gene-gene interaction, gene-drug interaction and epigenetic regulatory annotation for over 70,156 items of differentially expressed genes associated with 7 commonly abused substances, including alcohol, nicotine, cocaine, morphine, heroin, methamphetamine, and amphetamine, across three species (human, mouse, rat). We also collected 1,141 addiction-related experimentally validated genes by techniques such as RT-PCR, northern blot and in situ hybridization. The easy-to-use web interface of AddictGene (http://159.226.67.237/sun/addictgedb/) allows users to search and browse multidimensional data on DEGs of their interest: 1) detailed gene-specific information extracted from the original studies; 2) basic information about the specific gene extracted from NCBI; 3) SNP associated with substance dependence and other psychiatry disorders; 4) expression alteration of specific gene in other psychiatric disorders; 5) expression patterns of interested gene across 31 primary and 54 secondary human tissues; 6) functional annotation of interested gene; 7) epigenetic regulators involved in the alteration of specific genes, including histone modifications and DNA methylation; 8) protein-protein interaction for functional linkage with interested gene; 9) drug-gene interaction for potential druggability. AddictGene offers a valuable repository for researchers to study the molecular mechanisms underlying addiction, and might provide valuable insights into potential therapies for drug abuse and relapse.

An autophagy-related protein Becn2 regulates cocaine reward behaviors in the dopaminergic system

Drug abuse is a foremost public health problem. Cocaine is a widely abused drug worldwide that produces various reward-related behaviors. The mechanisms that underlie cocaine-induced disorders are unresolved, and effective treatments are lacking. Here, we found that an autophagy-related protein Becn2 is a previously unidentified regulator of cocaine reward behaviors. Becn2 deletion protects mice from cocaine-stimulated locomotion and reward behaviors, as well as cocaine-induced dopamine accumulation and signaling, by increasing presynaptic dopamine receptor 2 (D2R) autoreceptors in dopamine neurons. Becn2 regulates D2R endolysosomal trafficking, degradation, and cocaine-induced behaviors via interacting with a D2R-bound adaptor GASP1. Inactivating Becn2 by upstream autophagy inhibitors stabilizes striatal presynaptic D2R, reduces dopamine release and signaling, and prevents cocaine reward in normal mice. Thus, the autophagy protein Becn2 is essential for cocaine psychomotor stimulation and reward through regulating dopamine neurotransmission, and targeting Becn2 by autophagy inhibitors is a potential strategy to prevent cocaine-induced behaviors.

An Integrated Model of Nature and Nurture Factors that Contribute to Addiction and Recovery

BACKGROUND

In the context of the opioid epidemic and growing awareness of addiction as a public health concern, there are efforts to inform the public, patients, families, and policy makers about the factors that contribute to addiction and facilitate recovery. Several theoretical models provide useful frameworks for this discussion, but each of them has limitations.

OBJECTIVES

This paper presents an accessible yet comprehensive theoretical model that integrates empirical evidence about addiction etiology and recovery using the nature-nurture paradigm.

RESULTS

The model presents substance use along a continuum, and identifies risk and protective factors in multiple domains that have been identified by research. The domains on the nature side of the model include genetic and biological factors, comorbid psychiatric and medical disorders, physiological reinforcement of substance use, and changes to neural mechanisms. The domains on the nurture side of the model include sociocultural factors, environmental factors, personality, emotions, cognitions, psychological reinforcement of substance use, and cognitive and behavioral changes. The progression from increased or decreased substance use to addiction or recovery is mediated by changes in neural mechanisms and cognitive and behavioral changes, which have feedback loops with the physiological and psychological reinforcement.Conclusions/Importance: This model is a useful heuristic, consistent with a public health framework, for discussing addiction and recovery with patients, their families, and the public. This integrated model of nature and nurture factors has the potential to inform clinical practice, consultation, research, prevention programs, educational programs, and public policy.

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.

Cytoplasmic Polyadenylation Element Binding Proteins CPEB1 and CPEB3 Regulate the Translation of FosB and Are Required for Maintaining Addiction-Like Behaviors Induced by Cocaine

A recurrent and devastating feature of addiction to a drug of abuse is its persistence, which is mediated by maladaptive long-term memories of the highly pleasurable experience initially associated with the consumption of the drug. We have recently found that members of the CPEB family of proteins (Cytoplasmic Polyadenylation Element-Binding Proteins) are involved in the maintenance of spatial memory. However, their possible role in the maintenance of memories that sustain addictive behavior has yet to be explored. Little is known about any of the mechanisms for maintaining memories for addictive behavior. To address the mechanisms whereby addictive behavior is maintained over time, we utilized a conditional transgenic mouse model expressing a dominant-negative version of CPEB1 that abolishes the activity in the forebrain of two of the four CPEB isoforms (CPEB1 and CPEB3). We found that, following cocaine administration, these dominant-negative (DN) CPEB mice showed a significant decrease, when compared to wild type (WT) mice, in both locomotor sensitizations and conditioned place preference (CPP), two indices of addictive behavior. Supporting these behavioral results, we also found a difference between WT and DN-CPEB1-3 mice in the cocaine-induced synaptic depression in the core of the Nucleus Accumbens (NAc). Finally, we found that (1) CPEB is reduced in transgenic mice following cocaine injections and that (2) FosB, known for its contribution to establishing the addictive phenotype, when its expression in the striatum is increased by drug administration, is a novel target of CPEBs molecules. Thus, our study highlights how CPEB1 and CPEB3 act on target mRNAs to build the neuroadaptative implicit memory responses that lead to the development of the cocaine addictive phenotypes in mammals.

Genetic contributions to the etiology of anorexia nervosa: New perspectives in molecular diagnosis and treatment

Background

Anorexia nervosa is a multifactorial eating disorder that manifests with self‐starvation, extreme anxiety, hyperactivity, and amenorrhea. Long‐term effects include organ failure, disability, and in extreme cases, even death.

Methods

Through a literature search, here we summarize what is known about the molecular etiology of anorexia nervosa and propose genetic testing for this condition.

Results

Anorexia nervosa often has a familial background and shows strong heritability. Various genetic studies along with genome‐wide association studies have identified several genetic loci involved in molecular pathways that might lead to anorexia.

Conclusion

Anorexia nervosa is an eating disorder with a strong genetic component that contributes to its etiology. Various genetic approaches might help in the molecular diagnosis of this disease and in devising novel therapeutic options.

Anorexia nervosa is a multifactorial eating disorder with a strong genetic component that manifests with self‐starvation, extreme anxiety, hyperactivity, and amenorrhea. Through a literature search, here we summarize what is known about the molecular etiology of anorexia nervosa and propose genetic testing for this condition.

4-MeO-PCP and 3-MeO-PCMo, new dissociative drugs, produce rewarding and reinforcing effects through activation of mesolimbic dopamine pathway and alteration of accumbal CREB, deltaFosB, and BDNF levels

RATIONALE

A high number of synthetic dissociative drugs continue to be available through online stores, leading to their misuse. Recent inclusions in this category are 4-MeO-PCP and 3-MeO-PCMo, analogs of phencyclidine. Although the dissociative effects of these drugs and their recreational use have been reported, no studies have investigated their abuse potential.

OBJECTIVES

To examine their rewarding and reinforcing effects and explore the mechanistic correlations.

METHODS

We used conditioned place preference (CPP), self-administration, and locomotor sensitization tests to assess the rewarding and reinforcing effects of the drugs. We explored their mechanism of action by pretreating dopamine receptor (DR) D1 antagonist SCH23390 and DRD2 antagonist haloperidol during CPP test and investigated the effects of 4-MeO-PCP and 3-MeO-PCMo on dopamine-related proteins in the ventral tegmental area and nucleus accumbens. We also measured the levels of dopamine, phosphorylated cyclic-AMP response element-binding (p-CREB) protein, deltaFosB, and brain-derived neurotrophic factor (BDNF) in the nucleus accumbens. Additionally, we examined the effects of both drugs on brain wave activity using electroencephalography.

RESULTS

While both 4-MeO-PCP and 3-MeO-PCMo induced CPP and self-administration, only 4-MeO-PCP elicited locomotor sensitization. SCH23390 and haloperidol inhibited the acquisition of drug CPP. 4-MeO-PCP and 3-MeO-PCMo altered the levels of tyrosine hydroxylase, DRD1, DRD2, and dopamine, as well as that of p-CREB, deltaFosB, and BDNF. All drugs increased the delta and gamma wave activity, whereas pretreatment with SCH23390 and haloperidol inhibited it.

CONCLUSION

Our results indicate that 4-MeO-PCP and 3-MeO-PCMo induce rewarding and reinforcing effects that are probably mediated by the mesolimbic dopamine system, suggesting an abuse liability in humans.

The prefrontal cortex and the caudate nucleus respond conjointly to methylphenidate (Ritalin). Concomitant behavioral and neuronal recording study

Methylphenidate (MPD) is commonly used to treat attention-deficit hyperactivity disorder (ADHD). Recently, it is being abused for cognitive enhancement and recreation leading to concerns regarding its addictive potential. The prefrontal cortex (PFC) and caudate nucleus (CN) are two of the brain structures involved in the motive/reward circuit most affected by MPD and are also thought to be responsible for ADHD phenomena. This study is unique in that it investigated acute and chronic, dose-response MPD exposure on animals' behavior activity concomitantly with PFC and CN neuronal circuitry in freely behaving adult animals without the interference of anesthesia. Further, it compared acute and chronic MPD action on over 1,000 subcortical and cortical neurons simultaneously, allowing for a more accurate interpretation of drug action on corticostriatal neuronal circuitry. For this experiment, four groups of animals were used: saline (control), 0.6, 2.5, and 10.0 mg/kg MPD following acute and repetitive exposure. The data shows that the same MPD dose elicits behavioral sensitization in some animals and tolerance in others and that the PFC and CN neuronal activity correlates with the animals' behavioral responses to MPD. The expression of sensitization and tolerance are experimental biomarkers indicating that a drug has addictive potential. In general, a greater percentage of CN units responded to both acute and chronic MPD exposure as compared to PFC units. Dose response differences between the PFC and the CN units were observed. The dichotomy that some PFC and CN units responded to the same MPD dose by excitation and other units by attenuation in neuronal firing rate is discussed. In conclusion, to understand the mechanism of action of the drug, it is essential to study, simultaneously, on more than one brain site, the electrophysiological and behavioral effects of acute and chronic drug exposure, as sensitization and tolerance are experimental biomarkers indicating that a drug has addictive potential. The behavioral and neuronal data obtained from this study indicates that chronic MPD exposure results in behavioral and biochemical changes consistent with a substance abuse disorder.

Neuropharmacological and Neurogenetic Correlates of Opioid Use Disorder (OUD) As a Function of Ethnicity: Relevance to Precision Addiction Medicine

BACKGROUND

Over 100 people die daily from opioid overdose and $78.5B per year is spent on treatment efforts, however, the real societal cost is multifold greater. Alternative strategies to eradicate/manage drug misuse and addiction need consideration. The perception of opioid addiction as a social/criminal problem has evolved to evidence-based considerations of them as clinical disorders with a genetic basis. We present evaluations of the genetics of addiction with ancestryspecific risk profiles for consideration.

OBJECTIVE

Studies of gene variants associated with predisposition to substance use disorders (SUDs) are monolithic, and exclude many ethnic groups, especially Hispanics and African Americans. We evaluate gene polymorphisms that impact brain reward and predispose individuals to opioid addictions, with a focus on the disparity of research which includes individuals of African and Hispanic descent.

METHODOLOGY

PubMed and Google Scholar were searched for: Opioid Use Disorder (OUD), Genome- wide association studies (GWAS); genetic variants; polymorphisms, restriction fragment length polymorphisms (RFLP); genomics, epigenetics, race, ethnic group, ethnicity, ancestry, Caucasian/ White, African American/Black, Hispanic, Asian, addictive behaviors, reward deficiency syndrome (RDS), mutation, insertion/deletion, and promotor region.

RESULTS

Many studies exclude non-White individuals. Studies that include diverse populations report ethnicity-specific frequencies of risk genes, with certain polymorphisms specifically associated with Caucasian and not African-American or Hispanic susceptibility to OUD or SUDs, and vice versa.

CONCLUSION

To adapt precision medicine-based addiction management in a blended society, we propose that ethnicity/ancestry-informed genetic variations must be analyzed to provide real precision- guided therapeutics with the intent to attenuate this uncontrollable fatal epidemic.

Role of RGS12 in the differential regulation of kappa opioid receptor-dependent signaling and behavior

Kappa opioid receptor (KOR) agonists show promise in ameliorating disorders, such as addiction and chronic pain, but are limited by dysphoric and aversive side effects. Clinically beneficial effects of KOR agonists (e.g., analgesia) are predominantly mediated by heterotrimeric G protein signaling, whereas β-arrestin signaling is considered central to their detrimental side effects (e.g., dysphoria/aversion). Here we show that Regulator of G protein Signaling-12 (RGS12), via independent signaling mechanisms, simultaneously attenuates G protein signaling and augments β-arrestin signaling downstream of KOR, exhibiting considerable selectivity in its actions for KOR over other opioid receptors. We previously reported that RGS12-null mice exhibit increased dopamine transporter-mediated dopamine (DA) uptake in the ventral (vSTR), but not dorsal striatum (dSTR), as well as reduced psychostimulant-induced hyperlocomotion; in the current study, we found that these phenotypes are reversed following KOR antagonism. Fast-scan cyclic voltammetry studies of dopamine (DA) release and reuptake suggest that striatal disruptions to KOR-dependent DAergic neurotransmission in RGS12-null mice are restricted to the nucleus accumbens. In both ventral striatal tissue and transfected cells, RGS12 and KOR are seen to interact within a protein complex. Ventral striatal-specific increases in KOR levels and KOR-induced G protein activation are seen in RGS12-null mice, as well as enhanced sensitivity to KOR agonist-induced hypolocomotion and analgesia-G protein signaling-dependent behaviors; a ventral striatal-specific increase in KOR levels was also observed in β-arrestin-2-deficient mice, highlighting the importance of β-arrestin signaling to establishing steady-state KOR levels in this particular brain region. Conversely, RGS12-null mice exhibited attenuated KOR-induced conditioned place aversion (considered a β-arrestin signaling-dependent behavior), consistent with the augmented KOR-mediated β-arrestin signaling seen upon RGS12 over-expression. Collectively, our findings highlight a role for RGS12 as a novel, differential regulator of both G protein-dependent and -independent signaling downstream of KOR activation.

Neuroimmune mechanisms of psychostimulant and opioid use disorders

Substance use disorders are global health problems with few effective treatment options. Unfortunately, most potential pharmacological treatments are hindered by abuse potential of their own, limited efficacy, or adverse side effects. As a consequence, there is a pressing need for the development of addiction treatments with limited abuse potential and fewer off target effects. Given the difficulties in developing new pharmacotherapies for substance use disorders, there has been growing interest in medications that act on non-traditional targets. Recent evidence suggests a role for dysregulated immune signaling in the pathophysiology of multiple psychiatric diseases. While there is evidence that immune responses in the periphery and the central nervous system are altered by exposure to drugs of abuse, the contributions of neuroimmune interactions to addictive behaviors are just beginning to be appreciated. In this review, we discuss the data on immunological changes seen in clinical populations with substance use disorders, as well as in translational animal models of addiction. Importantly, we highlight those mechanistic findings showing causal roles for central or peripheral immune mediators in substance use disorder and appropriate animal models. Based on the literature reviewed here, it is clear that brain-immune system interactions in substance use disorders are much more complex and important than previously understood. While much work remains to be done, there are tremendous potential therapeutic implications for immunomodulatory treatments in substance use disorders.

Emerging roles of microRNAs in morphine tolerance

Morphine is commonly used in clinical management to alleviate moderate-to-severe pain. However, prolonged and repeated use of morphine leads to tolerance. Morphine tolerance is a challenging clinical problem that limits its clinical application in pain treatment. The mechanisms underlying morphine tolerance are still not completely understood. MicroRNAs (miRNAs) are small noncoding RNAs containing 18~22 nucleotides that modulate gene expression in a post-transcriptional manner, and their dysregulation causes various diseases. miRNAs bind to the 3ʹ-UTR (untranslated region) of target gene mRNA, inhibiting or destabilizing translation of the transcripts. Morphine causes differential miRNA upregulation or downregulation. This review will present evidence for the contribution of miRNAs to tolerance of the antinociception effect of opioids.

Characterization of locomotor response to psychostimulants in the parthenogenetic marbled crayfish (Procambarus fallax forma virginalis): A promising model for studying the neural and molecular mechanisms of drug addiction

Although scientific research using mammalian models has made great strides in uncovering the enigmatic neural and molecular mechanisms orchestrating the state of drug addiction, a complete understanding has thus far eluded researchers. The complexity of the task has led to the use of invertebrate model systems to complement the research of drug-induced reward in mammalian systems. Invertebrates, such as crayfish, offer excellent model systems to help reveal the underlying mechanisms of drug addiction as they retain the ancestral neural reward circuit that is evolutionarily conserved across taxa, and they possess relatively few, large neurons, laid out in an accessible, modularly organized nervous system. Crayfish offer the benefits of delineated developmental life stages, a large body size suitable for a variety of experimental methods, and stereotyped behaviors. Unique among crayfish is the parthenogenetic marbled crayfish (Procambarus fallax forma virginalis), a species of asexually reproducing, genetically identical clones. With the benefits of reduced individual variation, high fecundity, and easy lab husbandry, the marbled crayfish would make a particularly powerful addition to the animal model repertoire. Here we characterize the locomotor response of juvenile P. f. f. virginalis exposed to the psychostimulant, d-amphetamine sulfate. Custom video-tracking software was used to record the movement patterns of juveniles exposed to water infused with varying concentrations of d-amphetamine sulfate. ANOVA demonstrated that crayfish locomotion was significantly impacted by drug concentration. These psychostimulant effects provide the foundation of P. f. f. virginalis as a model for parsing the neural and molecular mechanisms of drug addiction.

Regulation of microRNA-29c in the nucleus accumbens modulates methamphetamine -induced locomotor sensitization in mice

Changes in microRNA (miRNA)-mediated gene expression in the nucleus accumbens (NAc) may play important roles in regulating drug addiction. MiR-29c is a highly expressed miRNA in the human and rodent nervous systems where it plays a broad regulatory role. As the first step towards investigating potential functions of miR-29c in methamphetamine (METH) addiction, we used C57BL/6 mice in a model of METH-induced locomotor sensitization. We measured miR-29c expression changes in the NAc of the mice after repeated-intermittent METH exposure and acute METH administration respectively by using quantitative real-time PCR (qPCR). We found that miR-29c expression was significantly down-regulated in the NAc of METH-sensitized mice but not in the acute METH-treated mice. Then, we tested the respective effects of miR-29c over-expression and inhibition in the NAc on METH-induced locomotor sensitization. To reach this goal, we constructed adeno-associated virus (AAV)-expressing miR-29c (AAV-miR-29c) and its corresponding inhibitor - tough decoy (AAV-anti-miR-29c TuD) to over-express and inhibit miR-29c, respectively. We found that AAV-miR-29c over-expression in the NAc enhanced METH-induced locomotor sensitization, whereas AAV inhibition of miR-29c expression in the NAc attenuated the effects of METH. Moreover, we observed the participation of Dnmt3a, Dnmt3b, and Meg3 in the effects of miR-29c on METH sensitization. Our results suggest that miR-29c is an important epigenetic regulator of METH-induced behavioural sensitization and changes in gene expression. These data further suggest a potential role of miR-29c in regulating long-term METH-induced adaptation in the brain.

Methylphenidate dose-response behavioral and neurophysiological study of the ventral tegmental area and nucleus accumbens in adolescent rats

The psychostimulant methylphenidate (MPD) is the most common medication used in treating ADHD in children. Studies have shown an increasing prevalence among adolescents without ADHD to take MPD as a cognitive booster and recreational drug, even though it is a Schedule II drug and has a high potential for abuse. The objective of this study is to explore if there is an association between the animals' behavioral and neurophysiological responses to acute and/or chronic methylphenidate exposure within the ventral tegmental area and the nucleus accumbens, and to compare how these two brain structures fire in response to methylphenidate. Freely moving adolescent rats implanted with semimicroelectrodes within the VTA and NAc were divided into three MPD dosing groups: 0.6, 2.5, and 10 mg/kg i.p., as well as a saline control group. The animals were divided into two groups based on their behavioral responses to chronic MPD, behavioral sensitization and tolerance, and the neuronal responses of the two groups were compared for each MPD dosing. Significant differences in the proportion of neuronal units in the VTA and NAc responding to MPD were observed at the 0.6 and 10.0 mg/kg MPD dosing groups. Moreover, the same doses of 0.6, 2.5, and 10.0 mg/kg MPD elicited behavioral sensitization in some animals and behavioral tolerance in others. This specific study shows that the VTA and NAc neurons respond differently to the same doses of MPD. MPD has different neuronal and behavioral effects depending on the individual, the dosage of MPD, and the brain structure studied.

Common neurocircuitry mediating drug and fear relapse in preclinical models

BACKGROUND

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

OBJECTIVES

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

KEY FINDINGS

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

CONCLUSIONS

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

Concomitant behavioral and prefrontal cortex neuronal responses following acute and chronic methylphenidate exposure in adolescent and adult rats

There is growing concern that the psychostimulant Methylphenidate (MPD) is being abused for cognitive enhancement and recreation by healthy adults and adolescents seeking to improve their work or academic performance. This study concomitantly recorded the behavioral and prefrontal cortex (PFC) neuronal activity in freely behaving animals exposed to acute and chronic MPD doses (0.6, 2.5, and 10.0 mg/kg MPD) in order to compare MPD effects on adult and adolescent rats. The PFC is one of the primary brain areas affected by MPD and the drug of choice for treating ADHD. Moreover, the PFC is one of the last brain areas to complete development, suggesting that the behavioral and neurophysiological response to MPD may differ in adolescents and adults. In both adult and adolescent animals, it was observed that the same repetitive (chronic) dose of either 0.6, 2.5, or 10.0 mg/kg MPD elicited behavioral sensitization in some animals and tolerance in others, experimental biomarkers indicating drug of abuse symptoms, and the majority of PFC units recorded in animals expressing behavioral sensitization or tolerance to chronic MPD exposure responded by increasing and decreasing their neuronal firing rate, respectively. Further, it was shown that high doses of 10.0 mg/kg MPD significantly modified adolescent behavioral activity but did not impact adults suggesting that adolescents may be more receptive to chronic MPD exposure. These findings raise concerns regarding the use and abuse of MPD in normal, healthy individuals and support the notion that the adolescent PFC is more susceptible than the adult PFC to neuromodulation from chronic MPD use.

Cardiovascular complications and related risk factors underlying opium consumption

Opium is considered as the second most abused addictive compound in worldwide. It seems that one of the causes for common consumption of opium in many countries is a traditional belief, even among medical personnel, through which opium might have advantageous influences on cardiovascular events and be beneficial in controlling hypertension, dyslipidemia, and diabetes. According to several investigations, it is thought that opium not only has no beneficial effects on cardiovascular events, but it might have deleterious influences on these settings. As a result, people need to be trained with regard to the adverse effects of opium on cardiovascular events. In this review, we try to go through the understanding of the effects of opium cardiovascular disorders and related complications such as blood pressure, blood sugar, lipid circumstances, and finally atherosclerosis.

tDCS in Addiction and Impulse Control Disorders

The study of addiction and impulsion control disorders has shown that behaviors of seeking and consumption of addictive substances are subserved by neurobiological alterations specifically related to brain networks for reward, stress, and executive control, representing the brain's adaptation to the continued use of an addictive substance. In parallel, studies using neuromodulation techniques such as transcranial direct current stimulation (tDCS) have demonstrated promising effects in modulating cognitive and motor functions. This review aims to describe the neurobiology of addiction and some of the most relevant cognitive models of addictive behavior and to clarify how tDCS application modulates the intake and craving for several addictive substances, such as food, alcohol, nicotine, cocaine, crack, methamphetamine, and cannabis. We also discuss the positive and null outcomes of the use of this neuromodulatory technique in the treatment of addiction disorders resulting from the use of these substances. The reviewed findings lead us to conclude that tDCS interventions hold several promising clinical avenues in addiction and impulsive control. However, methodological investigations are necessary for undercover optimal parameters before implementing its clinical application.

Dehydroepiandrosterone and Addiction

Drug addiction has a great negative influence on society, both social and economic burden. It was widely thought that addicts could choose to stop using drugs if only they had some self-control and principles. Nowadays, science has changed this view, defining drug addiction as a complex brain disease that affects behavior in many ways, both biological and psychological. Currently there is no ground-breaking reliable treatment for drug addiction. For more than a decade we are researching an alternative approach for intervention with drug craving and relapse to its usage, using DHEA, a well-being and antiaging food supplement. In this chapter we navigate through the significant therapeutic effect of DHEA on the brain circuits that control addiction and on behavioral performance both in animal models and addicts. We suggest that an integrative program of add-on DHEA treatment may further enable to dynamically evaluate the progress of rehabilitation of an individual patient, in a comprehensive assessment. Such a program may boost and support the detoxification and rehabilitation process, and help patients regain a normal life in a shorter amount of time.

Cyclic nucleotide phosphodiesterases: potential therapeutic targets for alcohol use disorder

Alcohol use disorder (AUD), which combines the criteria of both alcohol abuse and dependence, contributes as an important causal factor to multiple health and social problems. Given the limitation of current treatments, novel medications for AUD are needed to better control alcohol consumption and maintain abstinence. It has been well established that the intracellular signal transduction mediated by the second messengers cyclic AMP (cAMP) and cyclic GMP (cGMP) crucially underlies the genetic predisposition, rewarding properties, relapsing features, and systemic toxicity of compulsive alcohol consumption. On this basis, the upstream modulators phosphodiesterases (PDEs), which critically control intracellular levels of cyclic nucleotides by catalyzing their degradation, are proposed to play a role in modulating alcohol abuse and dependent process. Here, we highlight existing evidence that correlates cAMP and cGMP signal cascades with the regulation of alcohol-drinking behavior and discuss the possibility that PDEs may become a novel class of therapeutic targets for AUD.

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.

Targeting Phosphodiesterases in Pharmacotherapy for Substance Dependence

Substance dependence is a chronic relapsing brain disorder associated with adaptational changes in synaptic plasticity and neuronal functions. The high levels of substance consumption and relapse rate suggest more reliable medications are in need to better address the underlying causes of this disease. It has been well established that the intracellular second messengers cyclic AMP (cAMP) and cyclic GMP (cGMP) and their signaling systems play an important role in the molecular mechanisms of substance taking behaviors. On this basis, the phosphodiesterase (PDE) superfamily, which crucially controls cyclic nucleotide levels by catalyzing their hydrolysis, has been proposed as a novel class of therapeutic targets for substance use disorders. This chapter reviews the expression patterns of PDEs in the brain with regard to neural structures underlying the dependent process and highlights available evidence for a modulatory role of PDEs in substance dependence.

Depletion of D3 dopamine receptor affects methamphetamine-induced expression patterns of Pde4b and Atf3

The role of the D3 dopamine receptor (D3R) and the specific molecular mechanisms underlying the regulation of D3R via the cAMP signaling pathway in methamphetamine (METH) addiction are still unclear. Here, we measured changes in Pde4b and Atf3 in the cAMP signaling pathway of dopaminergic system components, including the nucleus accumbens (NAc), caudate putamen (CPu) and hippocampus (Hip), in D3R knockout mice(D3R-/-) 1h and 24h after METH-induced behavioral sensitization. We found that knocking out D3R attenuated METH-induced behavioral sensitization, and Pde4b and Atf3 exhibited different expression patterns in brain regions in response to METH. Knocking out D3R suppressed the METH-induced increase in Pde4b in the Hip of mice 24h after the final METH injection and augmented the METH-induced increase in Atf3 in the CPu of mice 1h after the final METH injection. Our study suggests that D3R knockout controls METH-induced behavioral sensitization via regulation of Pde4b and Atf3 in different brain regions. Furthermore, the responses of Pde4b and Atf3 to METH exposure depend on the specific region of the brain involved.

GABAB receptors within the central nucleus of amygdala may involve in the morphine-induced incentive tolerance in female rats

Objective(s):

Central nucleus of amygdala (CeA) is the most important region for morphine-induced reward, and GABAergic system plays an important role on morphine reinforcement. The influence of CeA administration of GABA_B receptor agonist and antagonist on the expression and acquisition of morphine-induced incentive tolerance using conditioned place preference (CPP) paradigm was investigated in the present study. Our purpose was to evaluate the role of CeA GABA_B receptors in morphine tolerance.

Materials and Methods:

Seven days after surgery and cannulation, the experiments were begun. Subcutaneous (SC) injections of morphine induced CPP. Administration of one daily dose of morphine (12.5 mg/kg) for 3 days in order to develop tolerance to the drug reduced the conditioning induced by morphine (7.5 mg/kg, SC). GABA_B receptor agonist, baclofen (1.5, 6 and 12 µg/rat) or GABA_B receptor antagonist, CGP35348 (1.5, 6 and 12 µg/rat) were injected into the CeA 5 min before the experiments in the test day (expression of tolerance) or 5 min before each injection of morphine (12.5 mg/kg) (acquisition of tolerance).

Results:

It was shown that injections of baclofen (1.5 and 12 µg/rat) reduced acquisition, whereas the dose of 6 µg/rat of the drug exacerbated the acquisition of morphine tolerance. Baclofen at all doses significantly increased the expression of tolerance to morphine. Administration of CGP35348 (1.5, 6 and 12 µg/rat) reduced the acquisition and expression of morphine tolerance.

Conclusion:

These results confirmed the importance of GABA_B receptors with in the CeA in morphine tolerance in female rats.

Poly (ADP-Ribose) Polymerase-1 (PARP-1) Induction by Cocaine Is Post-Transcriptionally Regulated by miR-125b

Cocaine exposure alters gene expression in the brain via methylation and acetylation of histones along with methylation of DNA. Recently, poly (ADP-ribose) polymerase-1 (PARP-1) catalyzed PARylation has been reported as an important regulator of cocaine-mediated gene expression. In this study, we report that the cellular microRNA “miR-125b” plays a key role for cocaine-induced PARP-1 expression. Acute and chronic cocaine exposure resulted in the downregulation of miR-125b concurrent with upregulation of PARP-1 in dopaminergic neuronal cells and nucleus accumbens (NAc) of mice but not in the medial prefrontal cortex (PFC) or ventral tegmental area (VTA). In silico analysis predicted a binding site of miR-125b in a conserved 3’-untranslated region (3’UTR) of the PARP-1 mRNA. Knockdown and overexpression studies showed that miR-125b levels negatively correlate with PARP-1 protein expression. Luciferase reporter assay using a vector containing the 3’UTR of PARP-1 mRNA confirmed regulation of PARP-1 by miR-125b. Specific nucleotide mutations within the binding site abrogated miR-125b’s regulatory effect on PARP-1 3’UTR. Finally, we established that downregulation of miR-125b and concurrent upregulation of PARP-1 is dependent on binding of cocaine to the dopamine transporter (DAT). Collectively, these results identify miR-125b as a post-transcriptional regulator of PARP-1 expression and establish a novel mechanism underlying the molecular effects of cocaine action.