Cellular basis of memory for addiction

Flying Together: Drosophila as a Tool to Understand the Genetics of Human Alcoholism

Alcohol use disorder (AUD) exacts an immense toll on individuals, families, and society. Genetic factors determine up to 60% of an individual's risk of developing problematic alcohol habits. Effective AUD prevention and treatment requires knowledge of the genes that predispose people to alcoholism, play a role in alcohol responses, and/or contribute to the development of addiction. As a highly tractable and translatable genetic and behavioral model organism, Drosophila melanogaster has proven valuable to uncover important genes and mechanistic pathways that have obvious orthologs in humans and that help explain the complexities of addiction. Vinegar flies exhibit remarkably strong face and mechanistic validity as a model for AUDs, permitting many advancements in the quest to understand human genetic involvement in this disease. These advancements occur via approaches that essentially fall into one of two categories: (1) discovering candidate genes via human genome-wide association studies (GWAS), transcriptomics on post-mortem tissue from AUD patients, or relevant physiological connections, then using reverse genetics in flies to validate candidate genes' roles and investigate their molecular function in the context of alcohol. (2) Utilizing flies to discover candidate genes through unbiased screens, GWAS, quantitative trait locus analyses, transcriptomics, or single-gene studies, then validating their translational role in human genetic surveys. In this review, we highlight the utility of Drosophila as a model for alcoholism by surveying recent advances in our understanding of human AUDs that resulted from these various approaches. We summarize the genes that are conserved in alcohol-related function between humans and flies. We also provide insight into some advantages and limitations of these approaches. Overall, this review demonstrates how Drosophila have and can be used to answer important genetic questions about alcohol addiction.

Impairment of cost-benefit decision making in morphine-dependent rats is partly mediated via the alteration of BDNF and p-CREB levels in the nucleus accumbens

The ability to choose goals based on decision usefulness or the time required to reach the goals chosen are important aspects of decision making. There is considerable evidence in the literature indicating the fact that drug abuse affects different aspects of cognition. In the current study, we assessed the effects of morphine dependence and its withdrawal on cost-benefit decision making and furthermore the involvement of BDNF and p-CREB in the nucleus accumbens, a key brain area involved in decision making was measured. Different groups of male Wistar rats were trained in an effort-based and/or delay-based form of cost-benefit T-maze decision-making task. Thereafter, the animals were morphine dependent and the percentage of the high reward preference was evaluated. After behavioral tests, the BDNF level, and p-CREB/CREB ratio were measured by Western blot analysis. The results showed that during effort-based but not delay-based decision making, BDNF and p-CREB levels increased. During effort-based decision making in morphine dependent rats, BDNF decreased but there was no significant change in p-CREB. Besides, during delay-based decision making in the morphine dependent group, both BDNF and p-CREB did not show any significant change. These findings revealed that BDNF and p-CREB/CREB ratio in the NAc are essential factors for effort-based but not delay-based decision making. In addition, impairment of effort-based decision making in morphine dependent rats is related to the decrease of BDNF level but not p-CREB/CREB ratio in the NAc. However, delay-based decision making defects in morphine dependent rats did not associate with the change in BDNF and p-CREB levels in the NAc.

Cannabis Constituents and Acetylcholinesterase Interaction: Molecular Docking, In Vitro Studies and Association with CNR1 rs806368 and ACHE rs17228602

The study documented here was aimed to find the molecular interactions of some of the cannabinoid constituents of cannabis with acetylcholinesterase (AChE). Molecular docking and LogP determination were performed to predict the AChE inhibitory effect and lipophilicity. AChE enzyme activity was measured in the blood of cannabis addicted human subjects. Further, genetic predisposition to cannabis addiction was investigated by association analysis of cannabinoid receptor 1 (CNR1) single nucleotide polymorphism (SNP) rs806368 and ACHE rs17228602 using restriction fragment length polymorphism (RFLP) method. All the understudied cannabis constituents showed promising binding affinities with AChE and are lipophilic in nature. The AChE activity was observed to be indifferent in cannabis addicted and non-addicted healthy controls. There was no significant association with CNR1 SNP rs806368 and ACHE rs17228602. The study concludes that in silico prediction for individual biomolecules of cannabis is different from in vivo physiological action in human subjects when all are present together. However, for a deeper mechanistic insight into these interactions and association, multi-population studies are suggested. Further studies to explore the inhibitory potential of different cannabis constituents for intended AChE inhibitor-based drug are warranted.

Acute Regulation of the Arousal-Enhancing Drugs Caffeine and Modafinil on Class IIa HDACs In Vivo and In Vitro: Focus on HDAC7

Psychostimulant drugs, such as modafinil and caffeine, induce transcriptional alterations through the dysregulation of epigenetic mechanisms. We have previously demonstrated that acute modafinil administration is accompanied by multiple changes in the expression of histone deacetylases (HDACs) within the mouse medial prefrontal cortex (mPFC). Herein, we compared alterations in class IIa HDACs in the mouse mPFC and dorsal striatum (DS) after a single exposure to each psychostimulant. We treated male C57BL/6 mice with modafinil (90 mg/kg, i.p.), caffeine (10 mg/kg, i.p.), or vehicle and evaluated locomotor activity. Following, we examined hdac4, hdac5, and hdac7 mRNA expression using qRT-PCR and HDAC7, pHDAC7, and pHDACs4/5/7 using Western blot. Last, we explored generalized effects in N2a cell line using modafinil (100 μM and 1 mM) or caffeine (80 μM and 800 μM). Our results indicate that modafinil had greater effects on locomotor activity compared with caffeine. qRT-PCR experiments revealed that modafinil decreased hdac5 and hdac7 mRNA expression in the DS, while caffeine had no effects. In the mPFC, modafinil increased hdac7 mRNA expression, with no effects observed for caffeine. Western blot revealed that within the DS, modafinil induced increases in HDAC7, pHDAC7, and pHDACs4/5/7 protein expression, while, in the mPFC, caffeine induced decreases in HDAC7, pHDAC7, and pHDACs4/5/7 protein levels. In vitro studies revealed that modafinil increased hdac4, hdac5, and hdac7 mRNA levels in N2a, while caffeine only increased hdac5 at a higher dose. These findings support the notion that modafinil and caffeine exert distinct regulation of class IIa HDAC family members and that these transcriptional and translational consequences are region-specific.

Alcohol Causes Lasting Differential Transcription in Drosophila Mushroom Body Neurons

Repeated alcohol experiences can produce long-lasting memories for sensory cues associated with intoxication. These memories can problematically trigger relapse in individuals recovering from alcohol use disorder (AUD). The molecular mechanisms by which ethanol changes memories to become long-lasting and inflexible remain unclear. New methods to analyze gene expression within precise neuronal cell types can provide further insight toward AUD prevention and treatment. Here, we used genetic tools in Drosophila melanogaster to investigate the lasting consequences of ethanol on transcription in memory-encoding neurons. Drosophila rely on mushroom body (MB) neurons to make associative memories, including memories of ethanol-associated sensory cues. Differential expression analyses revealed that distinct transcripts, but not genes, in the MB were associated with experiencing ethanol alone compared to forming a memory of an odor cue associated with ethanol. Adult MB-specific knockdown of spliceosome-associated proteins demonstrated the necessity of RNA-processing in ethanol memory formation. These findings highlight the dynamic, context-specific regulation of transcription in cue-encoding neurons, and the lasting effect of ethanol on transcript usage during memory formation.

Analysis of the usage and diversity of grey literature in addiction research: a study

Purpose

The purpose of this study is twofold. First, the study shall evaluate the extent of usage of grey literature and its different types of addiction research. The second purpose of the research is to analyze the extent of usage of reports such as research reports, survey reports, data reports, etc. As the reports are produced in general by various organizations and can be accessed by not only academicians but also the general public, they play an important role in the dissemination of research to the people. Therefore, the study endeavored to identify the major organizations that are involved in the publishing of research reports in the field of addiction.

Design/methodology/approach

Scopus database was used for the purpose of collecting the data. References in the reference lists of the articles published in 2018 in the journal Psychology of Addictive Behaviors of the American Psychological Association were collected. Scopus indexes the references of the papers in two different categories, namely, indexed in scopus/scopus references and reference lists. They were then categorized as grey literature and non-grey literature. Further, reports were searched manually so that their producers/authors can be found and categorized according to the organizations.

Findings

The study found that grey literature comprises a very small proportion of citations in addiction research (just approximately 5 per cent). This suggests that the improper indexing and bibliographic control of grey literature may be one of the reasons behind the low numbers. Reports comprised the largest proportion of the grey literature cited in addiction research, followed by software documentation, unpublished manuscripts, guidebooks, handbooks, manuals, websites, government publications, etc. The reports of the US Department of Health and Human Services comprised the maximum citations in the reports category because of the reports produced by organizations like Substance Abuse and Mental Health Services Administration (SAMHSA) which comprised 17.59 per cent of the total reports. National Institute of Health (USA) and Centers for Disease Control and Prevention and others. Other than the reports of the organizations of the USA, the reports published by the organizations of Canada, Australia, UK, New Zealand and one European Body were also cited by the articles of the journal.

Practical implications

The research focuses on the use of grey literature in addiction research. The findings of the study indicate very low citations to grey literature in addiction research. This reinforces the need for a separate worldwide information retrieval system for grey literature for researchers to conduct systematic reviews.

Originality/value

Very few studies have been conducted on the use of grey literature and hardly any research focuses on the use of grey literature in addiction research. The study goes one step further and identifies major organizations that are involved in the production of research reports in the field so that their reports can be properly indexed.

(Don't Fear) the Reefer: Cannabis Worldview Beliefs and the Management of Death-Related Existential Concerns Among High Frequency Cannabis Users

Introduction: The current research employed a terror management framework to understand the cognitive effects of frequent drug use. The study focused specifically on cannabis users and tested the hypothesis that frequent cannabis use is associated with the development of cannabis-related worldview beliefs that take on an existential function for frequent users.

Method: Participants (N = 226) answered questions about their cannabis use and completed a measure of cannabis worldview investment. Thereafter, they were randomly assigned to a cannabis worldview threat (vs. no threat) condition and completed measures of death-thought accessibility (DTA) and cannabis worldview defense.

Results: A positive association between frequency of cannabis use and cannabis worldview investment was observed. Moreover, among high frequency cannabis users, those highly invested in the cannabis worldview evinced significantly more DTA following exposure to the worldview threat than no threat condition. Participants with high investment in the cannabis worldview also showed more derogation of the cannabis worldview threat (vs. no threat) essay-author. However, this relationship was not influenced by DTA or frequency of cannabis use.

Discussion: A terror management perspective on drug use is discussed, including implications for understanding drug abuse, addiction, and treatment.

Heroin exposure and withdrawal differentially influence expression of NMDA receptor NR2 subunits in the prelimbic region of rat medial prefrontal cortex

It is widely reported that drug addiction involves the strengthening of specific reward circuits through N-methyl-d-aspartic acid receptor (NMDAR)-dependent synaptic potentiation, and several lines of evidence strongly implicate NMDA receptor 2 (NR2) subunits in drug abuse. To explore the potential mechanism of heroin dependence, this study examined changes in the expression levels of NR2 subunits NR2A-D in the prelimbic (PL) region of the medial prefrontal cortex (mPFC) after repeated heroin administration and subsequent abstinence. The conditioned place preference (CPP) test confirmed successful induction of heroin dependence and withdrawal. Western blotting and qRT-PCR revealed no differences in NR2A subunit expression among heroin-exposure, heroin-withdrawal, and control group rats; in contrast, expression of NR2B was significantly higher in the heroin-exposure group, whereas expression levels of NR2C and NR2D were significantly higher in the heroin-withdrawal group relative to the controls. Further studies are needed to identify the functional significance based on alterations of NR2 subunits.

Effects of Chronic Ephedrine Toxicity on Functional Connections, Cell Apoptosis, and CREB-Related Proteins in the Prefrontal Cortex of Rhesus Monkeys

Ephedrine abuse has spread in many parts of the world, severely threatening human health. The mechanism of ephedrine toxicity is still unclear. To explore the possible neural mechanisms of ephedrine toxicity, this study established a non-human primate model of ephedrine exposure, analyzed the functional connectivity changes in its prefrontal cortex through resting state BOLD-fMRI, and then inspected the pathophysiological changes as well as the expression of the cyclic adenosine monophosphate response element-binding protein (CREB), phosphorylated CREB (P-CREB), and CREB target proteins (c-fos and fosB) in the prefrontal cortex. After ephedrine toxicity, we found that the prefrontal cortex of monkeys strengthened its functional connectivity with the brain regions that perform motivation, drive, reward, and learning and memory functions and weakened its functional connectivity with the brain regions that perform cognitive control. These results suggest that ephedrine toxicity causes abnormal neural circuits that lead to the amplification and enhancement of drug-related cues and the weakening and damage of cognitive control function. Histology showed that the neurocytotoxicity of ephedrine can cause neuronal degeneration and apoptosis. Real-time PCR and Western blot showed increased expression of CREB mRNA and CREB/P-CREB/c-fos/fosB protein in the prefrontal cortex after ephedrine toxicity. Collectively, the present study indicates that the enhancement of drug-related cues and the weakening of cognitive control caused by abnormal neural circuits after drug exposure may be a major mechanism of brain function changes caused by ephedrine. These histological and molecular changes may be the pathophysiological basis of brain function changes caused by ephedrine.

A specific prelimbic-nucleus accumbens pathway controls resilience versus vulnerability to food addiction

Food addiction is linked to obesity and eating disorders and is characterized by a loss of behavioral control and compulsive food intake. Here, using a food addiction mouse model, we report that the lack of cannabinoid type-1 receptor in dorsal telencephalic glutamatergic neurons prevents the development of food addiction-like behavior, which is associated with enhanced synaptic excitatory transmission in the medial prefrontal cortex (mPFC) and in the nucleus accumbens (NAc). In contrast, chemogenetic inhibition of neuronal activity in the mPFC-NAc pathway induces compulsive food seeking. Transcriptomic analysis and genetic manipulation identified that increased dopamine D2 receptor expression in the mPFC-NAc pathway promotes the addiction-like phenotype. Our study unravels a new neurobiological mechanism underlying resilience and vulnerability to the development of food addiction, which could pave the way towards novel and efficient interventions for this disorder.

Food addiction is linked to obesity and eating disorders. In a mouse model of food addiction, the authors show that a medial prefrontal cortex-nucleus accumbens pathway is involved in vulnerability and resilience against the development of food addiction-like behavior.

Neuroimaging reward, craving, learning, and cognitive control in substance use disorders: review and implications for treatment

Substance use disorder is a leading causes of preventable disease and mortality. Drugs of abuse cause molecular and cellular changes in specific brain regions and these neuroplastic changes are thought to play a role in the transition to uncontrolled drug use. Neuroimaging has identified neural substrates associated with problematic substance use and may offer clues to reduce its burden on the patient and society. Here, we provide a narrative review of neuroimaging studies that have examined the structures and circuits associated with reward, cues and craving, learning, and cognitive control in substance use disorders. Most studies use advanced MRI or positron emission tomography (PET). Many studies have focused on the dopamine neurons of the ventral tegmental area, and the regions where these neurons terminate, such as the striatum and prefrontal cortex. Decreases in dopamine receptors and transmission have been found in chronic users of drugs, alcohol, and nicotine. Recent studies also show evidence of differences in structure and function in substance users relative to controls in brain regions involved in salience evaluation, such as the insula and anterior cingulate cortex. Balancing between reward-related bottom-up and cognitive-control-related top-down processes is discussed in the context of neuromodulation as a potential treatment. Finally, some of the challenges for understanding substance use disorder using neuroimaging methods are discussed.

Persistent Nociception Facilitates the Extinction of Morphine-Induced Conditioned Place Preference

BACKGROUND

As opioid abuse and addiction have developed into a major national health crisis, prescription of opioids for pain management has become more controversial. However, opioids do help some patients by providing pain relief and improving the quality of life. To better understand the addictive properties of opioids under chronic pain conditions, we used a conditioned place preference (CPP) paradigm to examine the rewarding properties of morphine in rats with persistent nociception.

METHODS

Spared nerve injury (SNI) model was used to induce persistent nociception in rats. Nociceptive behavior was assessed by von Frey test. CPP test was used to examine the rewarding properties of morphine.

RESULTS

Our findings are as follows: (1) SNI rats did not show a difference compared with sham rats in magnitude of morphine-induced CPP 1 day after last morphine injection (2-way analysis of variance; for SNI versus sham, F[1,42] = 0.014, P = .91; and 95% confidence intervals for difference of means, -5.9 [-58 to 46], 0.76 [-51 to 53], and 0.90 [-51 to 53] for 2.5, 5, and 10 mg/kg, respectively); (2) increasing morphine dosage (2.5, 5, and 10 mg/kg) did not further increase the magnitude of CPP in both sham and SNI rats (for dosage: F[2,42] = 0.94, P = .40); and (3) morphine-induced CPP persisted in sham rats but extinguished in SNI rats when tested at 8 days after last morphine injection (for sham versus SNI: Bonferroni correction, P < .006 for both 5 and 10 mg/kg doses; and 95% confidence intervals for difference of means, 80.3 [19.7-141] and 87.0 [26.3-148] for 5 and 10 mg/kg, respectively).

CONCLUSIONS

Our data provide new evidence supporting the notion that the brain's reward circuitry changes in the context of persistent pain. This observational study suggests that future investigation into the neurobiology of opioid reward requires consideration of the circumstances in which opioid analgesics are administered.

Nicotine and alcohol: the role of midbrain dopaminergic neurons in drug reinforcement

Nicotine and alcohol addiction are leading causes of preventable death worldwide and continue to constitute a huge socio-economic burden. Both nicotine and alcohol perturb the brain's mesocorticolimbic system. Dopamine (DA) neurons projecting from the ventral tegmental area (VTA) to multiple downstream structures, including the nucleus accumbens, prefrontal cortex, and amygdala, are highly involved in the maintenance of healthy brain function. VTA DA neurons play a crucial role in associative learning and reinforcement. Nicotine and alcohol usurp these functions, promoting reinforcement of drug taking behaviors. In this review, we will first describe how nicotine and alcohol individually affect VTA DA neurons by examining how drug exposure alters the heterogeneous VTA microcircuit and network-wide projections. We will also examine how coadministration or previous exposure to nicotine or alcohol may augment the reinforcing effects of the other. Additionally, this review briefly summarizes the role of VTA DA neurons in nicotine, alcohol, and their synergistic effects in reinforcement and also addresses the remaining questions related to the circuit-function specificity of the dopaminergic system in mediating nicotine/alcohol reinforcement and comorbidity.

μ-Opioid receptor in the CA1 involves in tramadol and morphine cross state-dependent memory

In the present study, the effect of tramadol - an opioid painkiller drug with abuse potential- on amnesia and state-dependent memory and its interaction with the opioidergic system was investigated in male Wistar rats. Intra CA-1 administration of tramadol (0.5, 1, and 2 μg/rat) before training, dose-dependently decreased the learning ability in passive avoidance task. Amnesia induced by pre-train tramadol administration was significantly reversed by pre-test administration of tramadol (1 μg/rat). Pre-test administration of naltrexone (a μ-opioid receptor (MOR) antagonist) inhibited the effect of tramadol on memory retrieval. In addition, the pre-test administration of morphine (1 μg/rat, intra-CA1) also reversed memory impairment induced by pre-train tramadol administration. Although, pre-train morphine administration (1 μg/rat, intra-CA1), induced memory impairment reversed by pre-test tramadol administration (1 μg/rat, intra-CA1). In addition, the level of MOR in the hippocampus decreased in animals with memory impairment due to using tramadol in the training day. However, state-dependent retrieval using tramadol or cross state-dependent retrieval using morphine enhanced the MOR level in the hippocampus. The results of the study suggested that intra-CA1 tramadol administration induced memory impairment, improved by pre-test administration of either tramadol or morphine (MOR agonist). It could be concluded that tramadol is capable to induced state-dependent memory and also, it has a cross state-dependent memory with morphine in the hippocampus, done possibly through MOR.

Association of status of acetylcholinesterase and ACHE gene 3' UTR variants (rs17228602, rs17228616) with drug addiction vulnerability in pakistani population

Substance addiction is a chronic, relapsing mental disorder Characterized by compulsive drug seeking, and loss of control over drug intake and relapse after prolonged abstinence. Genetics has been shown to contribute towards an individual's vulnerability to addiction. Acetylecholine (ACh), a cholinergic neurotransmitter hydrolyzed by acetylcholinesterase (AChE), is an essential neurotransmitter and neuromodulator in central and peripheral nervous system and has regulatory influence on numerous neuronal functions including addiction. The present study was carried out to investigate the role of acetylcholinesterase (AChE) in addiction through measurement of enzyme activity and to find potential association of ACHE gene 3'UTR variants rs17228602 and rs17228616 in heroin, hashish and poly drug addicts. Both SNPs are located within microRNA (miRNA) recognition sites with potential to affect miRNA/transcript interaction. A total of 122 addicts of heroin, hashish and polydrug were recruited from local rehabilitation centers to participate in this study. AChE activity was measured in blood by Ellman's method. SNP genotyping was performed by restriction fragment length polymorphism (PCR-RFLP) and Sanger sequencing. The AChE activity was found significantly higher (p ≤ 0.005) in addicted cohort (mean ± standard error of mean 0.020 ± 0.001 μmol/L/min; 95% confidence interval (CI) 0.018-0.022) in comparison to non-addicted healthy subjects (0.011 ± 0.001 μmol/L/min; 95% confidence interval CI 0.010-0.013). A statistically significant association of ACHE rs17228602 SNP with addiction vulnerability in dominant (DM: Odd's ratio OR = 2.095, 95% CI = 1.157-3.807 p = 0.009) and allelic genetic models (OR = 1.854 95% CI = 1.082-3.187, p = 0.016) was observed. However, no statistically significant association of rs17228616 SNP with substance abuse disorder was found. The data presented here shows that AChE could play significant role in substance addiction. Further studies with larger sample size and other variants of AChE are recommended to identify novel therapeutic approaches for cholinergic based treatment of addiction.

DRD2 promoter methylation and measures of alcohol reward: functional activation of reward circuits and clinical severity

Studies have identified strong associations between D2 receptor binding potential and neural responses to rewarding stimuli and substance use. Thus, D2 receptor perturbations are central to theoretical models of the pathophysiology of substance dependence, and epigenetic changes may represent one of the fundamental molecular mechanisms impacting the effects of alcohol exposure on the brain. We hypothesized that epigenetic alterations in the promoter region of the dopamine D2 receptor (DRD2) gene would be associated with cue-elicited activation of neural reward regions, as well as severity of alcohol use behavior. The current study leveraged functional neuroimaging (fMRI) during an alcohol reward paradigm (n = 383) to test associations among DRD2 promoter methylation in peripheral tissue, signal change in the striatum during the presentation of alcohol cues, and severity of alcohol use disorder (AUD). Controlling for age, DRD2 promoter methylation was positively associated with responses to alcohol cues in the right accumbens (partial r = 0.144, P = 0.005), left putamen (partial r = 0.133, P = 0.009), right putamen (partial r = 0.106, P = 0.039), left caudate (partial r = 0.117, P = 0.022), and right caudate (partial r = 0.133, P = 0.009), suggesting that DRD2 methylation was positively associated with robust activation in the striatum in response to reward cues. DRD2 methylation was also positively associated with clinical metrics of AUD severity. Specifically, controlling for age, DRD2 methylation was associated with Alcohol Use Disorders Identification Test total (partial r = 0.140, P = 0.002); Impaired Control Scale total (partial r = 0.097, P = 0.044) and Alcohol Dependence Scale total (partial r = 0.152, P = 0.001). Thus, DRD2 methylation may be a critical mechanism linking D2 receptors with functional striatal brain changes and clinical severity among alcohol users.

8-Oxoguanine accumulation in aged female brain impairs neurogenesis in the dentate gyrus and major island of Calleja, causing sexually dimorphic phenotypes

In mammals, including humans, MTH1 with 8-oxo-dGTPase and OGG1 with 8-oxoguanine DNA glycosylase minimize 8-oxoguanine accumulation in genomic DNA. We investigated age-related alterations in behavior, 8-oxoguanine levels, and neurogenesis in the brains of Mth1/Ogg1-double knockout (TO-DKO), Ogg1-knockout, and human MTH1-transgenic (hMTH1-Tg) mice. Spontaneous locomotor activity was significantly decreased in wild-type mice with age, and females consistently exhibited higher locomotor activity than males. This decrease was significantly suppressed in female but not male TO-DKO mice and markedly enhanced in female hMTH1-Tg mice. Long-term memory retrieval was impaired in middle-aged female TO-DKO mice. 8-Oxoguanine accumulation significantly increased in nuclear DNA, particularly in the dentate gyrus (DG), subventricular zone (SVZ) and major island of Calleja (ICjM) in middle-aged female TO-DKO mice. In middle-aged female TO-DKO mice, neurogenesis was severely impaired in SVZ and DG, accompanied by ICjM and DG atrophy. Conversely, expression of hMTH1 efficiently suppressed 8-oxoguanine accumulation in both SVZ and DG with hypertrophy of ICjM. These findings indicate that newborn neurons from SVZ maintain ICjM in the adult brain, and increased accumulation of 8-oxoguanine in nuclear DNA of neural progenitors in females is caused by 8-oxo-dGTP incorporation during proliferation, causing depletion of neural progenitors, altered behavior, and cognitive function changes with age.

Construction and Analysis of Protein-Protein Interaction Network of Heroin Use Disorder

Heroin use disorder (HUD) is a complex disease resulting from interactions among genetic and other factors (e.g., environmental factors). The mechanism of HUD development remains unknown. Newly developed network medicine tools provide a platform for exploring complex diseases at the system level. This study proposes that protein–protein interactions (PPIs), particularly those among proteins encoded by casual or susceptibility genes, are extremely crucial for HUD development. The giant component of our constructed PPI network comprised 111 nodes with 553 edges, including 16 proteins with large degree (k) or high betweenness centrality (BC), which were further identified as the backbone of the network. JUN with the largest degree was suggested to be central to the PPI network associated with HUD. Moreover, PCK1 with the highest BC and MAPK14 with the secondary largest degree and 9^th highest BC might be involved in the development HUD and other substance diseases.

Quantitative Systems Pharmacological Analysis of Drugs of Abuse Reveals the Pleiotropy of Their Targets and the Effector Role of mTORC1

Existing treatments against drug addiction are often ineffective due to the complexity of the networks of protein-drug and protein-protein interactions (PPIs) that mediate the development of drug addiction and related neurobiological disorders. There is an urgent need for understanding the molecular mechanisms that underlie drug addiction toward designing novel preventive or therapeutic strategies. The rapidly accumulating data on addictive drugs and their targets as well as advances in machine learning methods and computing technology now present an opportunity to systematically mine existing data and draw inferences on potential new strategies. To this aim, we carried out a comprehensive analysis of cellular pathways implicated in a diverse set of 50 drugs of abuse using quantitative systems pharmacology methods. The analysis of the drug/ligand-target interactions compiled in DrugBank and STITCH databases revealed 142 known and 48 newly predicted targets, which have been further analyzed to identify the KEGG pathways enriched at different stages of drug addiction cycle, as well as those implicated in cell signaling and regulation events associated with drug abuse. Apart from synaptic neurotransmission pathways detected as upstream signaling modules that “sense” the early effects of drugs of abuse, pathways involved in neuroplasticity are distinguished as determinants of neuronal morphological changes. Notably, many signaling pathways converge on important targets such as mTORC1. The latter emerges as a universal effector of the persistent restructuring of neurons in response to continued use of drugs of abuse.

Acute and chronic neurobehavioral effects of the designer drug and bath salt constituent 3,4-methylenedioxypyrovalerone in the rat

BACKGROUND

The substantial increase in use of 3,4-methylenedioxypyrovalerone (MDPV), a popular recreational synthetic cathinone, has raised legitimate questions about its behavioral consequences and abuse liability.

AIMS

The aim of this study was to study MDPV-induced neurobehavioral effects in the rat, using different paradigms traditionally developed to study drug-attributed addictive properties.

METHODS

Different patterns of intraperitoneal 3 mg/kg MDPV administration were investigated. Consequences on rat horizontal locomotion and behavior of acute, intermittent (once daily dosing over 10 days), and binge (three-time daily dosing for 3 days) MDPV administration as well as challenge after 10 day MDPV withdrawal were studied. The dopamine receptor-D1 antagonist, SCH23390, was bilaterally infused in the nucleus accumbens to determine the role of D1-receptors in MDPV-related effects on the associative memory recall using the conditioned place preference paradigm. In addition, in a separate experience using western blot, we investigated the effects of chronic MDPV administration (four injections during 24 h) on ΔFosB expression in the nucleus accumbens, caudate putamen, and prefrontal cortex.

RESULTS

Acute MDPV administration increased stereotypies and open arm entries in the elevated plus maze while SCH23390 abolished MDPV-induced enhancing effects on memory consolidation. Intermittent MDPV administration resulted in sensitization of MDPV-induced locomotor effects and tolerance during the following challenge. With binge MDPV administration, locomotor activity was not altered despite tolerance onset after challenge. SCH23390 abolished MDPV-induced conditioned place preference. Chronic MDPV administration induced ΔFosB accumulation in the nucleus accumbens, caudate putamen, and prefrontal cortex.

CONCLUSIONS

Our findings clearly show that MDPV produces profound behavioral alterations mediated by the activation of the dopaminergic system similarly to other amphetamines.

Biochemical Analysis and Association of Butyrylcholinesterase SNPs rs3495 and rs1803274 with Substance Abuse Disorder

Addiction is a complex mental and behavioral disorder that changes the neurochemistry and physiology of the brain. Genetics also plays a significant role in the pathophysiology of addiction. Butyrylcholinesterase (BChE), a cholinergic enzyme, has been implicated in the metabolism of various drugs, including cocaine, and an association between single-nucleotide polymorphisms (SNPs) of the butyrylcholinesterase gene (BCHE) and neuronal disorders has been reported. We report here the first investigation to be conducted on the status of BChE activity and the potential association of two BCHE gene SNPs, rs3495 (c.*189G > A) and rs1803274 (c.1699G>A, p.Ala567Thr, K-variant), with addiction vulnerability in heroin, hashish and polydrug users. Seventy-five individuals with an addiction to heroin, hashish and/or polydrug use were recruited to this study. BChE levels in the plasma were determined by Ellman's principle. SNPs were genotyped by standard procedures, followed by Sanger sequencing. Plasma BChE levels were found to be significantly higher (p ≤ 0.05) in addicts (mean ± standard error of the mean 0.031 ± 0.004 μmol/L/min; 95% confidence interval [CI] 0.024-0.038) than in non-addicts (controls) (0.014 ± 0.001 μmol/L/min; 95% CI 0.012-0.017). Statistical significant differences were also observed between the addicted cohorts. A statistically significant association for both SNPs (rs3495 and rs1803274) was not observed in addicted subjects tested in the dominant, recessive and allele genetic models, but trends of variations of the rs3495 risk G allele were noted. The authors conclude that BChE plays significant roles in addiction pathophysiology as increased BChE activity in blood samples obtained from the cohorts with addiction was evident. Further studies in this direction may provide novel approaches for the treatment of addiction, but studies with a larger sample size and different ethnic groups are warranted for broader conclusions to be drawn.

Activity-Dependent Epigenetic Remodeling in Cocaine Use Disorder

Substance use disorder (SUD) is a behavioral disorder characterized by cycles of abstinence, drug seeking, and relapse. SUD is characterized by aberrant learning processes which develop after repeated exposure to drugs of abuse. At the core of this phenotype is the persistence of symptoms, such as craving and relapse to drug seeking, long after the cessation of drug use. The neural basis of these behavioral changes has been linked to dysfunction in neural circuits across the brain; however, the molecular drivers that allow for these changes to persist beyond the lifespan of any individual protein remain opaque. Epigenetic adaptations - where DNA is modified to increase or decrease the probability of gene expression at key genes - have been identified as a mechanism underlying the long-lasting nature of drug-seeking behavior. Thus, to understand SUD, it is critical to define the interplay between neuronal activation and longer-term changes in transcription and epigenetic remodeling and define their role in addictive behaviors. In this review, we discuss the current understanding of drug-induced changes to circuit function, recent discoveries in epigenetic mechanisms that mediate these changes, and, ultimately, how these adaptations drive the persistent nature of relapse, with emphasis on adaptations in models of cocaine use disorder. Understanding the complex interplay between epigenetic gene regulation and circuit activity will be critical in elucidating the neural mechanisms underlying SUD. This, with the advent of novel genetic-based techniques, will allow for the generation of novel therapeutic avenues to improve treatment outcomes in SUD.

Interaction Between Stress and Addiction: Contributions From Latin-American Neuroscience

Drug addiction is a chronic neuropsychiatric disorder that escalates from an initial exposure to drugs of abuse, such as cocaine, cannabis, or heroin, to compulsive drug-seeking and intake, reduced ability to inhibit craving-induced behaviors, and repeated cycles of abstinence and relapse. It is well-known that chronic changes in the brain’s reward system play an important role in the neurobiology of addiction. Notably, environmental factors such as acute or chronic stress affect this system, and increase the risk for drug consumption and relapse. Indeed, the HPA axis, the autonomic nervous system, and the extended amygdala, among other brain stress systems, interact with the brain’s reward circuit involved in addictive behaviors. There has been a growing interest in studying the molecular, cellular, and behavioral mechanisms of stress and addiction in Latin-America over the last decade. Nonetheless, these contributions may not be as strongly acknowledged by the broad scientific audience as studies coming from developed countries. In this review, we compile for the first time a series of studies conducted by Latin American-based neuroscientists, who have devoted their careers to studying the interaction between stress and addiction, from a neurobiological and clinical perspective. Specific contributions about this interaction include the study of CRF receptors in the lateral septum, investigations on the neural mechanisms of cross-sensitization for psychostimulants and ethanol, the identification of the Wnt/β-catenin pathway as a critical neural substrate for stress and addiction, and the emergence of the cannabinoid system as a promising therapeutic target. We highlight animal and human studies, including for instance, reports coming from Latin American laboratories on single nucleotide polymorphisms in stress-related genes and potential biomarkers of vulnerability to addiction, that aim to bridge the knowledge from basic science to clinical research.

Activation of GABAergic Neurons in the Nucleus Accumbens Mediates the Expression of Cocaine-Associated Memory

Cocaine-associated environmental cues elicit craving and relapse to cocaine use by recalling the rewarding memory of cocaine. However, the neuronal mechanisms underlying the expression of cocaine-associated memory are not fully understood. Here, we investigated the possible contribution of γ-aminobutyrate (GABA)ergic neurons in the nucleus accumbens (NAc), a key brain region associated with the rewarding and reinforcing effects of cocaine, to the expression of cocaine-associated memory using the conditioned place preference (CPP) paradigm combined with designer receptors exclusively activated by designer drugs (DREADD) technology. The inhibitory DREADD hM4Di was selectively expressed in NAc GABAergic neurons of vesicular GABA transporter-Cre (vGAT-Cre) mice by infusing adeno-associated virus (AAV) vectors. Ex vivo electrophysiological recordings revealed that bath application of clozapine-N-oxide (CNO) significantly hyperpolarized membrane potentials and reduced the number of spikes induced by depolarizing current injections in hM4Di-positive NAc neurons. Additionally, systemic CNO injections into cocaine-conditioned mice 30 min before posttest session significantly reduced CPP scores compared to saline-injected mice. These results indicate that chemogenetic inhibition of NAc GABAergic neurons attenuated the expression of cocaine CPP, suggesting that NAc GABAergic neuronal activation is required for the environmental context-induced expression of cocaine-associated memory.

It is a complex issue: emerging connections between epigenetic regulators in drug addiction

Drug use leads to addiction in some individuals, but the underlying brain mechanisms that control the transition from casual drug use to an intractable substance use disorder (SUD) are not well understood. Gene x environment interactions such as the frequency of drug use and the type of substance used likely to promote maladaptive plastic changes in brain regions that are critical for controlling addiction-related behavior. Epigenetics encompasses a broad spectrum of mechanisms important for regulating gene transcription that are not dependent on changes in DNA base pair sequences. This review focuses on the proteins and complexes contributing to epigenetic modifications in the nucleus accumbens (NAc) following drug experience. We discuss in detail the three major mechanisms: histone acetylation and deacetylation, histone methylation, and DNA methylation. We discuss how drug use alters the regulation of the associated proteins regulating these processes and highlight how experimental manipulations of these proteins in the NAc can alter drug-related behaviors. Finally, we discuss the ways that histone modifications and DNA methylation coordinate actions by recruiting large epigenetic enzyme complexes to aid in transcriptional repression. Targeting these multiprotein epigenetic enzyme complexes - and the individual proteins that comprise them - might lead to effective therapeutics to reverse or treat SUDs in patients.

Association of CamK2A genetic variants with transition time from occasional to regular heroin use in a sample of heroin-dependent individuals

OBJECTIVES

Susceptibility to heroin dependence is strongly influenced by genetic factors with heritability estimates as high as 0.7. A number of genes, as well as environmental factors, are likely to contribute to its etiology. Not all individuals who have ever tried heroin at some stage during their lifetime become dependent on heroin. It has been suggested that genetic factors might be more important in the transition stage to heroin dependence rather than in environmental exposures and experimenting with heroin. As the features of substance dependence and memory formation have been found to be strikingly similar, we have focused on a key enzyme involved in long-term potentiation and synaptic plasticity, namely the calcium-dependent/calmodulin-dependent protein kinase IIα (CAMKIIa). We hypothesized, that CamK2A genetic variation may play a role in the transition from occasional to regular heroin use.

MATERIALS AND METHODS

Using quantitative trait association analysis, we addressed this hypothesis by correlating the self-reported time interval between occasional and regular heroin use with the frequency of 12 single nucleotide polymorphisms located within the genomic region of the CamK2A gene. A sample of 570 Caucasian patients was available for analysis.

RESULTS

Single marker association analysis (rs10066581, P=0.007), as well as haplotype analysis (global P=0.005), suggested an association with the quantitative trait 'time interval from occasional to regular heroin use.'

CONCLUSION

Our results propose that genetic variants located in the genomic region of the CamK2A gene may be involved in transition time from occasional to regular heroin use.

Synaptic Plasticity in the Nucleus Accumbens: Lessons Learned from Experience

Synaptic plasticity contributes to behavioral adaptations. As a key node in the reward pathway, the nucleus accumbens (NAc) is important for determining motivation-to-action outcomes. Across animal models of motivation including addiction, depression, anxiety, and hedonic feeding, selective recruitment of neuromodulatory signals and plasticity mechanisms have been a focus of physiologists and behaviorists alike. Experience-dependent plasticity mechanisms within the NAc vary depending on the distinct afferents and cell-types over time. A greater understanding of molecular mechanisms determining how these changes in synaptic strength track with behavioral adaptations will provide insight into the process of learning and memory along with identifying maladaptations underlying pathological behavior. Here, we summarize recent findings detailing how changes in NAc synaptic strength and mechanisms of plasticity manifest in various models of motivational disorders.

Exposure to environmental enrichment attenuates addiction-like behavior and alters molecular effects of heroin self-administration in rats

Environmental factors profoundly affect the addictive potential of drugs of abuse and may also modulate the neuro-anatomical/neuro-chemical impacts of uncontrolled drug use and relapse propensity. This study examined the impact of environmental enrichment on heroin self-administration, addiction-related behaviors, and molecular processes proposed to underlie these behaviors. Male Sprague-Dawley rats in standard and enriched housing conditions intravenously self-administered similar amounts of heroin over 14 days. However, environmental enrichment attenuated progressive ratio, extinction, and reinstatement session responding after 14 days of enforced abstinence. Molecular mechanisms, namely DNA methylation and gene expression, are proposed to underlie abstinence-persistent behaviors. A global reduction in methylation is reported to coincide with addiction, but no differences in total genomic methylation or repeat element methylation were observed in CpG or non-CpG (CH) contexts across the mesolimbic circuitry as assessed by multiple methods including whole genome bisulfite sequencing. Immediate early gene expression associated with drug seeking, taking, and abstinence also were examined. EGR1 and EGR2 were suppressed in mesolimbic regions with heroin-taking and environmental enrichment. Site-specific methylation analysis of EGR1 and EGR2 promoter regions using bisulfite amplicon sequencing (BSAS) revealed hypo-methylation in the EGR2 promoter region and EGR1 intragenic CpG sites with heroin-taking and environmental enrichment that was associated with decreased mRNA expression. Taken together, these findings illuminate the impact of drug taking and environment on the epigenome in a locus and gene-specific manner and highlight the need for positive, alternative rewards in the treatment and prevention of drug addiction.

Formation of Opioid-Induced Memory and Its Prevention: A Computational Study

There are several experimental studies which suggest opioids consumption forms pathological memories in different brain regions. For example it has been empirically demonstrated that the theta rhythm which appears during chronic opioid consumption is correlated with the addiction memory formation. In this paper, we present a minimal computational model that shows how opioids can change firing patterns of the neurons during acute and chronic opioid consumption and also during withdrawal periods. The model consists of a pre- and post-synaptic neuronal circuits and the astrocyte that monitors the synapses. The output circuitry consists of inhibitory interneurons and excitatory pyramidal neurons. Our simulation results demonstrate that acute opioid consumption induces synchronous patterns in the beta frequency range, while, chronic opioid consumption provokes theta frequency oscillations. This allows us to infer that the theta rhythm appeared during chronic treatment can be an indication of brain engagement in opioid-induced memory formation. Our results also suggest that changing the inputs of the interneurons and the inhibitory neuronal network is not an appropriate method for preventing the formation of pathological memory. However, the same results suggest that prevention of pathological memory formation is possible by manipulating the input of the stimulatory network and the excitatory connections in the neuronal network. They also show that during withdrawal periods, firing rate is reduced and random fluctuations are generated in the modeled neural network. The random fluctuations disappear and synchronized patterns emerge when the activities of the astrocytic transporters are decreased. These results suggest that formation of the synchronized activities can be correlated with the relapse. Our model also predicts that reduction in gliotransmitter release can eliminate the synchrony and thereby it can reduce the likelihood of the relapse occurrence.

Palatable Food Affects HPA Axis Responsivity and Forebrain Neurocircuitry in an Estrous Cycle-specific Manner in Female Rats

Eating palatable foods can provide stress relief, but the mechanisms by which this occurs are unclear. We previously characterized a limited sucrose intake (LSI) paradigm in which twice-daily access to a small amount of 30% sucrose (vs. water as a control) reduces hypothalamic-pituitary-adrenocortical (HPA) axis responses to stress and alters neuronal activation in stress-regulatory brain regions in male rats. However, women may be more prone to 'comfort feeding' behaviors than men, and stress-related eating may vary across the menstrual cycle. This suggests that LSI effects may be sex- and estrous cycle-dependent. The present study therefore investigated the effects of LSI on HPA axis stress responsivity, as well as markers of neuronal activation/plasticity in stress- and reward-related neurocircuitry in female rats across the estrous cycle. We found that LSI reduced post-restraint stress plasma ACTH in female rats specifically during proestrus/estrus (P/E). LSI also increased basal (non-stress) FosB/deltaFosB- and pCREB-immunolabeling in the basolateral amygdala (BLA) and central amygdala specifically during P/E. Finally, Bayesian network modeling of the FosB/deltaFosB and pCREB expression data identified a neurocircuit that includes the BLA, nucleus accumbens, prefrontal cortex, and bed nucleus of the stria terminalis as likely being modified by LSI during P/E. When considered in the context of our prior results, the present findings suggest that palatable food reduces stress responses in female rats similar to males, but in an estrous cycle-dependent manner. Further, the BLA may contribute to the LSI effects in both sexes, whereas the involvement of other brain regions appears to be sex-dependent.

Transcriptome profiling of whisker follicles in methamphetamine self-administered rats

Methamphetamine (MA) is a highly addictive psychostimulant that disturbs the central nervous system; therefore, diagnosis of MA addiction is important in clinical and forensic toxicology. In this study, a MA self-administration rat model was used to illustrate the gene expression profiling of the rewarding effect caused by MA. RNA-sequencing was performed to examine changes in gene expression in rat whisker follicles collected before self-administration, after MA self-administration, and after withdrawal sessions. We identified six distinct groups of genes, with statistically significant expression patterns. By constructing the functional association network of these genes and performing the subsequent topological analysis, we identified 43 genes, which have the potential to regulate MA reward and addiction. The gene pathways were then analysed using the Reactome and Knowledgebase for Addiction-Related Gene database, and it was found that genes and pathways associated with Alzheimer's disease and the heparan sulfate biosynthesis were enriched in MA self-administration rats. The findings suggest that changes of the genes identified in rat whisker follicles may be useful indicators of the rewarding effect of MA. Further studies are needed to provide a comprehensive understanding of MA addiction.

Cocaine-induced epigenetic DNA modification in mouse addiction-specific and non-specific tissues

Cocaine-related DNA methylation studies have primarily focused on the specific brain regions associated with drug addiction (e.g., the nucleus accumbens, NAc). To date, no studies have focused on the complex role of both DNA methylation and demethylation in the mechanisms of psychostimulant-induced addiction in the brain and peripheral tissues. Therefore, in this study, we evaluated cocaine treatment and withdrawal (animals were withdrawn from seven days of repeated injections of cocaine that caused behavioral sensitization) effects on epigenetic DNA modifiers (i.e., DNA methyltransferases, [DNMTs] and ten-eleven translocation enzymes [TETs]) in an addiction-specific brain region (NAc), a structure outside the mesolimbic dopaminergic system (cerebellum, Cer), and in peripheral blood cells (PBCs). Using a mouse behavioral sensitization model, we demonstrated that acute cocaine (AC; 0.5 h) treatment significantly decreased Dnmt1, Dnmt3a, Tet1, and Tet2 mRNA levels in the NAc and PBC, whereas at 24 h after AC treatment, Dnmt mRNA expression and enzyme activity levels were significantly increased. Acute procaine treatment caused the opposite effect on the Dnmt3a mRNA level in PBCs; this outcome suggests that the inhibition of voltage-gated sodium channels may be the mechanism that alters Dnmt expression in PBCs. Cocaine withdrawal is associated with increased expression of Dnmts in the NAc, Cer and PBCs and the decreased expression of Tet1 and Tet3 in the NAc. Additionally, cocaine withdrawal increased DNMT but decreased TET activity levels, and these changes were associated with enhanced global and selected candidate gene promoter-region DNA methylation and hydroxymethylation levels in the NAc and PBCs. Together, these data indicate that cocaine treatment and withdrawal affect the expression of epigenetic DNA modifiers in both addiction-specific brain structures and structures outside of the mesolimbic dopaminergic system and PBCs.

Extinction and Reinstatement of Cocaine-seeking in Self-administering Mice is Associated with Bidirectional AMPAR-mediated Plasticity in the Nucleus Accumbens Shell

Experience-dependent synaptic plasticity is an important component of both learning and motivational disturbances found in addicted individuals. Here, we investigated the role of cocaine experience-dependent plasticity at excitatory synapses in the nucleus accumbens shell (NAcSh) in relapse-related behavior in mice with a history of volitional cocaine self-administration. Using an extinction/reinstatement paradigm of cocaine-seeking behavior, we demonstrate that cocaine-experienced mice with extinguished cocaine-seeking behavior show potentiation of synaptic strength at excitatory inputs onto NAcSh medium spiny neurons (MSNs). Conversely, we found that exposure to various distinct types of reinstating stimuli (cocaine, cocaine-associated cues, yohimbine "stress") after extinction can produce a relative depotentiation of NAcSh synapses that is strongly associated with the magnitude of cocaine-seeking behavior exhibited in response to these challenges. Furthermore, we show that these effects are due to α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-specific mechanisms that differ depending on the nature and context of the reinstatement-inducing stimuli. Together, our findings identify common themes as well as differential mechanisms that are likely important for the ability of diverse environmental stimuli to drive relapse to addictive-like cocaine-seeking behavior.

Ethanol actions on the ventral tegmental area: novel potential targets on reward pathway neurons

The ventral tegmental area (VTA) evaluates salience of environmental stimuli and provides dopaminergic innervation to many brain areas affected by acute and chronic ethanol exposure. While primarily associated with rewarding and reinforcing stimuli, recent evidence indicates a role for the VTA in aversion as well. Ethanol actions in the VTA may trigger neuroadaptation resulting in reduction of the aversive responses to alcohol and a relative increase in the rewarding responses. In searching for effective pharmacotherapies for the treatment of alcohol abuse and alcoholism, recognition of this imbalance may reveal novel strategies. In addition to conventional receptor/ion channel pharmacotherapies, epigenetic factors that control neuroadaptation to chronic ethanol treatment can be targeted as an avenue for development of therapeutic approaches to restore the balance. Furthermore, when exploring therapies to address reward/aversion imbalance in the action of alcohol in the VTA, sex differences have to be taken into account to ensure effective treatment for both men and women. These principles apply to a VTA-centric approach to therapies, but should hold true when thinking about the overall approach in the development of neuroactive drugs to treat alcohol use disorders. Although the functions of the VTA itself are complex, it is a useful model system to evaluate the reward/aversion imbalance that occurs with ethanol exposure and could be used to provide new leads in the efforts to develop novel drugs to treat alcoholism.

Persistent effects of obesity: a neuroplasticity hypothesis

The obesity epidemic is a leading cause of health problems in the United States, increasing the risk of cardiovascular, endocrine, and psychiatric diseases. Although many people lose weight through changes in diet and lifestyle, keeping the weight off remains a challenge. Here, we discuss a hypothesis that seeks to explain why obesity is so persistent. There is a great degree of overlap in the circuits implicated in substance use disorder and obesity, and neural plasticity of these circuits in response to drugs of abuse is well documented. We hypothesize that obesity is also associated with neural plasticity in these circuits, and this may underlie persistent changes in behavior, energy balance, and body weight. Here, we discuss how obesity-associated reductions in motivation and physical activity may be rooted in neurophysiological alterations in these circuits. Such plasticity may alter how humans and animals use, expend, and store energy, even after weight loss.

VTA mTOR Signaling Regulates Dopamine Dynamics, Cocaine-Induced Synaptic Alterations, and Reward

Mechanistic target of rapamycin (mTOR) regulates long-term synaptic plasticity, learning, and memory by controlling dendritic protein synthesis. The mTOR inhibitor rapamycin has been shown to attenuate the behavioral effects of drugs of abuse, including cocaine. Using viral vectors to selectively delete mTOR in the ventral tegmental area (VTA) in adult male mTOR^loxP/loxP mice, we investigated the role of mTOR in regulating neuronal morphology, basal synaptic transmission, dopamine dynamics, and cocaine-induced synaptic plasticity and rewarding effects. We find that targeted deletion of mTOR in the VTA had no significant effects on soma size and dendritic morphology of VTA neurons but significantly decreased dopamine release and reuptake in the nucleus accumbens (NAc) shell, a major target region. Western blot analysis revealed that mTOR deletion led to decreases in phosphorylated tyrosine hydroxylase (pTH-Ser40) levels in the VTA and dopamine transporter expression in the NAc. mTOR deletion had no significant effects on basal excitatory transmission in VTA dopamine neurons but caused an increase in GABAergic inhibition because of an increase in VTA GABAergic neuron firing. Furthermore, mTOR deletion attenuated conditioned place preference to cocaine and cocaine-induced potentiation of excitation and reduction of GABAergic inhibition in VTA dopamine neurons. Taken together, these results suggest that loss of mTOR in the VTA shifts the balance of excitatory and inhibitory synaptic transmission and decreases dopamine release and reuptake in the NAc. In addition, VTA mTOR signaling regulates cocaine-cue associative learning and cocaine-induced synaptic plasticity in VTA dopamine neurons.

The antipsychotic landscape: dopamine and beyond

Until recently, the actions of antipsychotic and pro-psychotic drugs have largely been evaluated in the framework of neuronal doctrine - namely, that neurons communicate by releasing transmitters, and that psychiatric disorders are caused by neurotransmitter imbalances. Moreover, the majority of studies have focused on single transmitter systems - neglecting the fact that in the nervous system, different transmitter systems work in concert and impact on not only their immediate receptors but also downstream pathways that shape structural plasticity. In this review, we discuss the history of understanding the antipsychotic and pro-psychotic actions of drugs, recent developments and future perspectives.

Computational modeling of opioid-induced synaptic plasticity in hippocampus

According to a broad range of research, opioids consumption can lead to pathological memory formation. Experimental observations suggested that hippocampal glutamatergic synapses play an indispensable role in forming such a pathological memory. It has been suggested that memory formation at the synaptic level is developed through LTP induction. Here, we attempt to computationally indicate how morphine induces pathological LTP at hippocampal CA3-CA1 synapses. Then, based on simulations, we will suggest how one can prevent this type of pathological LTP. To this purpose, a detailed computational model is presented, which consists of one pyramidal neuron and one interneuron both from CA3, one CA1 pyramidal neuron, and one astrocyte. Based on experimental findings morphine affects the hippocampal neurons in three primary ways: 1) disinhibitory mechanism of interneurons in CA3, 2) enhancement of NMDARs current by μ Opioid Receptor (μOR) activation and 3) by attenuation of astrocytic glutamate reuptake ability. By utilizing these effects, simulations were implemented. Our results indicate that morphine can induce LTP by all aforementioned possible mechanisms. Based on our simulation results, attenuation of pathologic LTP achieved mainly by stimulation of astrocytic glutamate transporters, down-regulation of the astrocytic metabotropic glutamate receptors (mGlurs) or by applying NMDAR’s antagonist. Based on our observations, we suggest that astrocyte has a dominant role in forming addiction-related memories. This finding may help researchers in exploring drug actions for preventing relapse.

Nicotine-induced CREB and DeltaFosB activity is modified by caffeine in the brain reward system of the rat

Coffee and nicotine consumption are frequently combined, indicating possible intensifying effect of caffeine on smoking behavior, although neurobiological background of this phenomenon remains unknown. We aimed at determining the effect of caffeine and nicotine, applied separately or simultaneously, on activation of six structures of the brain reward system: nucleus accumbens (NAc), ventral tegmental area (VTA), amygdala (Amg), hippocampus (Hip), medial prefrontal cortex (mPfr) and dorsal striatum (CdP) in the adult male Wistar rats. Activation of two transcription factors, the phosphorylated form of cyclic AMP-response element binding protein (pCREB) and DeltaFosB (ΔFosB) was assessed by immunohistochemistry after multiple-dose five-days psychostimulants administration followed by 20min and 24h survival, respectively. Nicotine evoked the highest increase of pCREB-immunoreactivity (-ir) in NAc, while caffeine exerted the weakest effect in mPfr and CdP. Nicotine/caffeine co-administration resulted in decrease of pCREB-ir in NAc and increase in Amg, compared with the effect of each psychostimulant used separately. Nicotine was the strongest psychostimulant activating ΔFosB-ir in Amg, whereas caffeine - in Hip. Nicotine/caffeine-exerted effect upon ΔFosB-ir in Amg was weaker, whereas in mPfr stronger, than nicotine-evoked effect in these structures. In summary, pCREB and ΔFosB activation is dependent on the type of stimulus, brain structure and functional context. Activation of both transcription factors is responsible for caffeine's modifying effect upon nicotine-related behaviors and must be taken into account while quitting cigarette smoking.

Muscarinic receptors in the nucleus accumbens shell play different roles in context-induced or morphine-challenged expression of behavioral sensitization in rats

Both drug-related cues and drug priming are the main factors that induce relapse of drug addiction. Previous research has reported that blockade of the muscarinic receptors could significantly depress addictive behavior, suggesting that the muscarinic receptors might be involved in drug use and relapse behavior. The nucleus accumbens (NAc), especially the shell of the NAc, where the muscarinic receptors are expressed, is critical for craving and relapse. This study investigated the effects of microinfusion of the muscarinic receptor antagonist scopolamine into the NAc shell on context- and morphine-induced expression of behavioral sensitization. Behavioral sensitization was established by exposure to 5mg/kg morphine once daily for five consecutive days. Expression of behavioral sensitization was induced by saline challenge or 5mg/kg morphine challenge. The results showed that: (a) the muscarinic receptor antagonist scopolamine (10.8μg/rat) microinjected into the NAc shell blocked expression of conditional sensitization; (b) acetylcholinesterase inhibitor huperzine-A (0.5 and 0.1μg/rat), but not scopolamine (10.8μg/rat), microinjected into the NAc shell blocked morphine-induced expression of sensitization; and (c) pre-infusion of scopolamine (10.8μg/rat) reversed the inhibitory effect of huperzine-A (0.5μg/rat) on morphine-induced sensitization. Our findings suggest that muscarinic receptors in the NAc shell play different roles in context-induced and morphine-challenged expression of behavioral sensitization.