Chronic cocaine-mediated changes in non-human primate nucleus accumbens gene expression

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

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

Cocaine and Its Abstinence Condition Modulate Striatal and Hippocampal Wnt Signaling in a Male Rat Model of Drug Self-Administration

Recent years have provided more and more evidence confirming the important role of Wnt/β-catenin signaling in the pathophysiology of mental illnesses, including cocaine use disorder. High relapse rates, which is a hallmark of drug addiction, prompt the study of changes in Wnt signaling elements (Wnt5a, Wnt7b, and Ctnnb1) in the motivational aspects of cocaine use and early drug-free period (3 days after the last exposure to cocaine). For this purpose, an animal model of intravenous cocaine self-administration and two types of drug-free period (extinction training and abstinence in the home cage) were used. The studies showed that chronic cocaine self-administration mainly disturbs the expression of Wnt5a and Ctnnb1 (the gene encoding β-catenin) in the examined brain structures (striatum and hippocampus), and the examined types of early abstinence are characterized by a different pattern of changes in the expression of these genes. At the same time, in cocaine self-administrated animals, there were no changes in the level of Wnt5a and β-catenin proteins at the tested time points. Moreover, exposure to cocaine induces a significant reduction in the striatal and hippocampal expression of miR-374 and miR-544, which can regulate Wnt5a levels post-transcriptionally. In summary, previous observations from experimenter-administered cocaine have not been fully validated in the cocaine self-administration model. Yoked cocaine administration appears to disrupt Wnt signaling more than cocaine self-administration. The condition of the cocaine-free period, the routes of drug administration, and the motivational aspect of drug administration play an important role in the type of drug-induced molecular changes observed. Furthermore, in-depth research involving additional brain regions is needed to determine the exact role of Wnt signaling in short-term and long-lasting plasticity as well as in the motivational aspects of cocaine use, and thus to assess its potential as a target for new drug therapy for cocaine use disorder.

Protein kinases in natural versus drug reward

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

Transcriptomics in the nucleus accumbens shell reveal sex- and reinforcer-specific signatures associated with morphine and sucrose craving

Incubation of craving is a well-documented phenomenon referring to the intensification of drug craving over extended abstinence. The neural adaptations that occur during forced abstinence following chronic drug taking have been a topic of intense study. However, little is known about the transcriptomic changes occurring throughout this window of time. To define gene expression changes associated with morphine consumption and extended abstinence, male and female rats underwent 10 days of morphine self-administration. Separate drug-naive rats self-administered sucrose in order to compare opioid-induced changes from those associated with natural, non-drug rewards. After one or 30 days of forced abstinence, rats were tested for craving, or nucleus accumbens shell tissue was dissected for RNA sequencing. Morphine consumption was predictive of drug seeking after extended (30 days) but not brief (1 day) abstinence in both sexes. Extended abstinence was also associated with robust sex- and reinforcer-specific changes in gene expression, suggesting sex differences underlying incubation of morphine and sucrose seeking respectively. Importantly, these changes in gene expression occurred without re-exposure to drug-paired cues, indicating that chronic morphine causes long-lasting changes in gene expression that prime the system for increased craving. These findings lay the groundwork for identifying specific therapeutic targets for curbing opioid craving without impacting the natural reward system in males and females.

MicroRNAs and Synaptic Plasticity: From Their Molecular Roles to Response to Therapy

Synaptic plasticity is the ability of synapses to weaken or strengthen over time, in response to changes in the activity of the neurons. It is orchestrated by a variety of genes, proteins, and external and internal factors, especially epigenetic factors. MicroRNAs (miRNAs) are well-acknowledged epigenetic modulators that regulate the translation and degradation of target genes in the nervous system. Increasing evidence has suggested that a number of miRNAs play important roles in modulating various aspects of synaptic plasticity. The deregulation of miRNAs could be associated with pathological alterations in synaptic plasticity, which could lead to different CNS-related diseases. Herein, we provide an update on the role of miRNAs in governing synaptic plasticity. In addition, we also summarize recent researches on the role of miRNAs in drug addiction, and their targets and mechanism of action. Understanding of the way in which miRNAs contribute to synaptic plasticity provides rational clues in establishing the novel biomarkers and new therapeutic strategies for the diagnosis and treatment of plasticity-related diseases and drug addiction.

Pyk2 Stabilizes Striatal Medium Spiny Neuron Structure and Striatal-Dependent Action

In day-to-day life, we often choose between pursuing familiar behaviors that have been rewarded in the past or adjusting behaviors when new strategies might be more fruitful. The dorsomedial striatum (DMS) is indispensable for flexibly arbitrating between old and new behavioral strategies. The way in which DMS neurons host stable connections necessary for sustained flexibility is still being defined. An entry point to addressing this question may be the structural scaffolds on DMS neurons that house synaptic connections. We find that the non-receptor tyrosine kinase Proline-rich tyrosine kinase 2 (Pyk2) stabilizes both dendrites and spines on striatal medium spiny neurons, such that Pyk2 loss causes dendrite arbor and spine loss. Viral-mediated Pyk2 silencing in the DMS obstructs the ability of mice to arbitrate between rewarded and non-rewarded behaviors. Meanwhile, the overexpression of Pyk2 or the closely related focal adhesion kinase (FAK) enhances this ability. Finally, experiments using combinatorial viral vector strategies suggest that flexible, Pyk2-dependent action involves inputs from the medial prefrontal cortex (mPFC), but not the ventrolateral orbitofrontal cortex (OFC). Thus, Pyk2 stabilizes the striatal medium spiny neuron structure, likely providing substrates for inputs, and supports the capacity of mice to arbitrate between novel and familiar behaviors, including via interactions with the medial-prefrontal cortex.

The Non-receptor Tyrosine Kinase Pyk2 in Brain Function and Neurological and Psychiatric Diseases

Pyk2 is a non-receptor tyrosine kinase highly enriched in forebrain neurons. Pyk2 is closely related to focal adhesion kinase (FAK), which plays an important role in sensing cell contacts with extracellular matrix and other extracellular signals controlling adhesion and survival. Pyk2 shares some of FAK’s characteristics including recruitment of Src-family kinases after autophosphorylation, scaffolding by interacting with multiple partners, and activation of downstream signaling pathways. Pyk2, however, has the unique property to respond to increases in intracellular free Ca²⁺, which triggers its autophosphorylation following stimulation of various receptors including glutamate NMDA receptors. Pyk2 is dephosphorylated by the striatal-enriched phosphatase (STEP) that is highly expressed in the same neuronal populations. Pyk2 localization in neurons is dynamic, and altered following stimulation, with post-synaptic and nuclear enrichment. As a signaling protein Pyk2 is involved in multiple pathways resulting in sometimes opposing functions depending on experimental models. Thus Pyk2 has a dual role on neurites and dendritic spines. With Src family kinases Pyk2 participates in postsynaptic regulations including of NMDA receptors and is necessary for specific types of synaptic plasticity and spatial memory tasks. The diverse functions of Pyk2 are also illustrated by its role in pathology. Pyk2 is activated following epileptic seizures or ischemia-reperfusion and may contribute to the consequences of these insults whereas Pyk2 deficit may contribute to the hippocampal phenotype of Huntington’s disease. Pyk2 gene, PTK2B, is associated with the risk for late-onset Alzheimer’s disease. Studies of underlying mechanisms indicate a complex contribution with involvement in amyloid toxicity and tauopathy, combined with possible functional deficits in neurons and contribution in microglia. A role of Pyk2 has also been proposed in stress-induced depression and cocaine addiction. Pyk2 is also important for the mobility of astrocytes and glioblastoma cells. The implication of Pyk2 in various pathological conditions supports its potential interest for therapeutic interventions. This is possible through molecules inhibiting its activity or increasing it through inhibition of STEP or other means, depending on a precise evaluation of the balance between positive and negative consequences of Pyk2 actions.

Exercise Pills for Drug Addiction: Forced Moderate Endurance Exercise Inhibits Methamphetamine-Induced Hyperactivity through the Striatal Glutamatergic Signaling Pathway in Male Sprague Dawley Rats

Physical exercise reduces the extent, duration, and frequency of drug use in drug addicts during the drug initiation phase, as well as during prolonged addiction, withdrawal, and recurrence. However, information about exercise-induced neurobiological changes is limited. This study aimed to investigate the effects of forced moderate endurance exercise training on methamphetamine (METH)-induced behavior and the associated neurobiological changes. Male Sprague Dawley rats were subjected to the administration of METH (1 mg/kg/day, i.p.) and/or forced moderate endurance exercise (treadmill running, 21 m/min, 60 min/day) for 2 weeks. Over the two weeks, endurance exercise training significantly reduced METH-induced hyperactivity. METH and/or exercise treatment increased striatal dopamine (DA) levels, decreased p(Thr308)-Akt expression, and increased p(Tyr216)-GSK-3β expression. However, the phosphorylation levels of Ser9-GSK-3β were significantly increased in the exercise group. METH administration significantly increased the expression of NMDAr1, CaMKK2, MAPKs, and PP1 in the striatum, and exercise treatment significantly decreased the expression of these molecules. Therefore, it is apparent that endurance exercise inhibited the METH-induced hyperactivity due to the decrease in GSK-3β activation by the regulation of the striatal glutamate signaling pathway.

Involvement of cAMP-Dependent Protein Kinase in the Nucleus Accumbens in Cocaine Versus Social Interaction Reward

Evidence suggests that PKA activity in the nucleus accumbens (NAc) plays an essential role in reward-related learning. In this study, we investigated whether PKA is differentially involved in the expression of learning produced by either natural reinforcers or psychostimulants. For that purpose, we inhibited PKA through a bilateral infusion of Rp-cAMPS, a specific PKA inhibitor, directly into the NAc. The effects of PKA inhibition in the NAc on the expression of concurrent conditioned place preference (CPP) for cocaine (drug) and social interaction (natural reward) in rats were evaluated. We found that PKA inhibition increased the expression of cocaine preference. This effect was not due to altered stress levels or decreased social reward. PKA inhibition did not affect the expression of natural reward as intra-NAc Rp-cAMPS infusion did not affect expression of social preference. When rats were trained to express cocaine or social interaction CPP and tested for eventual persisting preference 7 and 14 days after CPP expression, cocaine preference was persistent, but social preference was abolished after the first test. These results suggest that PKA in the NAc is involved in drug reward learning that might lead to addiction and that only drug, but not natural, reward is persistent.

Sirtuins in Neuroendocrine Regulation and Neurological Diseases

Silent information regulator 1 (SIRT1) is a mammalian homolog of the nicotinamide adenine dinucleotide (NAD)-dependent deacetylase sirtuin family. Sirtuin was originally studied as the lifespan-extending gene, silent information regulator 2 (SIRT2) in budding yeast. There are seven mammalian homologs of sirtuin (SIRT1–7), and SIRT1 is the closest homolog to SIRT2. SIRT1 modulates various key targets via deacetylation. In addition to histones, these targets include transcription factors, such as forkhead box O (FOXO), Ku70, p53, NF-κB, PPAR-gamma co-activator 1-alpha (PGC-1α), and peroxisome proliferator-activated receptor γ (PPARγ). SIRT1 has many biological functions, including aging, cell survival, differentiation, and metabolism. Genetic and physiological analyses in animal models have shown beneficial roles for SIRT1 in the brain during both development and adulthood. Evidence from in vivo and in vitro studies have revealed that SIRT1 regulates the cellular fate of neural progenitors, axon elongation, dendritic branching, synaptic plasticity, and endocrine function. In addition to its importance in physiological processes, SIRT1 has also been implicated in protection of neurons from degeneration in models of neurological diseases, such as traumatic brain injury and Alzheimer’s disease. In this review, we focus on the role of SIRT1 in the neuroendocrine system and neurodegenerative diseases. We also discuss the potential therapeutic implications of targeting the sirtuin pathway.

Environmental, genetic and epigenetic contributions to cocaine addiction

Decades of research on cocaine has produced volumes of data that have answered many important questions about the nature of this highly addictive drug. Sadly, none of this information has translated into the development of effective therapies for the treatment of cocaine addiction. This review endeavors to assess the current state of cocaine research in an attempt to identify novel pathways for therapeutic development. For example, risk of cocaine addiction is highly heritable but genome-wide analyses comparing cocaine-dependent individuals to controls have not resulted in promising targets for drug development. Is this because the genetics of addiction is too complex or because the existing research methodologies are inadequate? Likewise, animal studies have revealed dozens of enduring changes in gene expression following prolonged exposure to cocaine, none of which have translated into therapeutics either because the resulting compounds were ineffective or produced intolerable side-effects. Recently, attention has focused on epigenetic modifications resulting from repeated cocaine intake, some of which appear to be heritable through changes in the germline. While epigenetic changes represent new vistas for therapeutic development, selective manipulation of epigenetic marks is currently challenging even in animals such that translational potential is a distant prospect. This review will reveal that despite the enormous progress made in understanding the molecular and physiological bases of cocaine addiction, there is much that remains a mystery. Continued advances in genetics and molecular biology hold potential for revealing multiple pathways toward the development of treatments for the continuing scourge of cocaine addiction.

Epigenetics of Stress, Addiction, and Resilience: Therapeutic Implications

Substance use disorders (SUDs) are highly prevalent. SUDs involve vicious cycles of binges followed by occasional periods of abstinence with recurrent relapses despite treatment and adverse medical and psychosocial consequences. There is convincing evidence that early and adult stressful life events are risks factors for the development of addiction and serve as cues that trigger relapses. Nevertheless, the fact that not all individuals who face traumatic events develop addiction to licit or illicit drugs suggests the existence of individual and/or familial resilient factors that protect these mentally healthy individuals. Here, I give a brief overview of the epigenetic bases of responses to stressful events and of epigenetic changes associated with the administration of drugs of abuse. I also discuss the psychobiology of resilience and alterations in epigenetic markers that have been observed in models of resilience. Finally, I suggest the possibility that treatment of addiction should involve cognitive and pharmacological approaches that enhance resilience in at risk individuals. Similar approaches should also be used with patients who have already succumbed to the nefarious effects of addictive substances.

Cellular basis of memory for addiction

Despite the importance of numerous psychosocial factors, at its core, drug addiction involves a biological process: the ability of repeated exposure to a drug of abuse to induce changes in a vulnerable brain that drive the compulsive seeking and taking of drugs, and loss of control over drug use, that define a state of addiction. Here, we review the types of molecular and cellular adaptations that occur in specific brain regions to mediate addiction-associated behavioral abnormalities. These include alterations in gene expression achieved in part via epigenetic mechanisms, plasticity in the neurophysiological functioning of neurons and synapses, and associated plasticity in neuronal and synaptic morphology mediated in part by altered neurotrophic factor signaling. Each of these types of drug-induced modifications can be viewed as a form of “cellular or molecular memory.” Moreover, it is striking that most addiction-related forms of plasticity are very similar to the types of plasticity that have been associated with more classic forms of “behavioral memory,” perhaps reflecting the finite repertoire of adaptive mechanisms available to neurons when faced with environmental challenges. Finally, addiction-related molecular and cellular adaptations involve most of the same brain regions that mediate more classic forms of memory, consistent with the view that abnormal memories are important drivers of addiction syndromes. The goal of these studies which aim to explicate the molecular and cellular basis of drug addiction is to eventually develop biologically based diagnostic tests, as well as more effective treatments for addiction disorders.

Intake-dependent effects of cocaine self-administration on impulsive choice in a delay discounting task

Cocaine use is associated with high levels of impulsive choice (greater discounting of delayed rewards) in humans, but the cause/effect relationships between cocaine use and impulsive choice are not fully understood. In previous work, we found that both experimenter- and self-administration of fixed quantities of cocaine caused lasting increases in impulsive choice in rats. The present study extended these findings by taking into account baseline impulsive choice prior to self-administration and by allowing rats free access to cocaine. Male Long-Evans rats were trained in a delay discounting task in which they made discrete-trial choices between small immediate and large delayed food rewards. Half of the rats were then implanted with intravenous catheters and, following recovery, allowed to self-administer cocaine HCl (1.0 mg/kg/infusion) in 6-hr sessions over 14 days. Control rats orally self-administered a sucrose solution under similar conditions. Upon completion of self-administration, rats remained abstinent for 3 weeks before retesting in the delay discounting task. Cocaine and control groups did not differ prior to self-administration, but afterward, the cocaine group showed greater impulsive choice (fewer choices of large, delayed rewards) than controls. Additional analyses revealed that the effects of cocaine on impulsive choice were intake-dependent; rats classified as "low intake" did not differ from controls, whereas rats classified as "high intake" were significantly more impulsive than both controls and their precocaine baseline. These findings are consistent with the idea that cocaine-induced, pharmacologically based neural adaptations promote the development of impulsive decision making.

Drug experience epigenetically primes Fosb gene inducibility in rat nucleus accumbens

ΔFosB, a Fosb gene product, is induced in nucleus accumbens (NAc) and caudate-putamen (CPu) by repeated exposure to drugs of abuse such as cocaine. This induction contributes to aberrant patterns of gene expression and behavioral abnormalities seen with repeated drug exposure. Here, we assessed whether a remote history of cocaine exposure in rats might alter inducibility of the Fosb gene elicited by subsequent drug exposure. We show that prior chronic cocaine administration, followed by extended withdrawal, increases inducibility of Fosb in NAc, as evidenced by greater acute induction of ΔFosB mRNA and faster accumulation of ΔFosB protein after repeated cocaine reexposure. No such primed Fosb induction was observed in CPu; in fact, subsequent acute induction of ΔFosB mRNA was suppressed in CPu. These abnormal patterns of Fosb expression are associated with chromatin modifications at the Fosb gene promoter. Prior chronic cocaine administration induces a long-lasting increase in RNA polymerase II (Pol II) binding at the Fosb promoter in NAc only, suggesting that Pol II "stalling" primes Fosb for induction in this region upon reexposure to cocaine. A cocaine challenge then triggers the release of Pol II from the gene promoter, allowing for more rapid Fosb transcription. A cocaine challenge also decreases repressive histone modifications at the Fosb promoter in NAc, but increases such repressive marks and decreases activating marks in CPu. These results provide new insight into the chromatin dynamics at the Fosb promoter and reveal a novel mechanism for primed Fosb induction in NAc upon reexposure to cocaine.

Methamphetamine and HIV-1 Tat down regulate β-catenin signaling: implications for methampetamine abuse and HIV-1 co-morbidity

Methamphetamine (Meth) abuse exacerbates HIV-1-associated neurocognitive disorders (HAND). The underlying mechanism for this effect is not entirely clear but likely involves cooperation between Meth and HIV-1 virotoxins, such as the transactivator of transcription, Tat. HIV-1 Tat mediates damage in the CNS by inducing inflammatory processes including astrogliosis. Wnt/β-catenin signaling regulates survival processes for both neurons and astrocytes. Here, we evaluated the impact of Meth on the Wnt/β-catenin pathway in astrocytes transfected with Tat. Meth and Tat downregulated Wnt/β-catenin signaling by >50%, as measured by TOPflash reporter activity in both an astrocytoma cell line and primary human fetal astrocytes. Meth and Tat also downregulated LEF-1 transcript by >30%. LEF-1 is a key partner of β-catenin to regulate cognate gene expression. Interestingly, estrogen, which induces β-catenin signaling in a cell-type specific manner, at physiological concentrations of 1.5 and 3 nM normalized individual Meth and Tat effects on β-catenin signaling but not their combined effects. These findings suggest that Meth and Tat likely exert different mechanisms to mediate down regulation of β-catenin signaling. The consequences of which may contribute to the pathophysiologic effects of HIV-1 and Meth co-morbidity in the CNS.

Chronic cocaine exposure induces putamen glutamate and glutamine metabolite abnormalities in squirrel monkeys

RATIONALE

Chronic cocaine exposure has been associated with progressive brain structural and functional changes. Clarifying mechanisms underlying cocaine's progressive brain effects may help in the development of effective cocaine abuse treatments.

OBJECTIVES

We used a controlled squirrel monkey model of chronic cocaine exposure (45 mg/kg/week for 9 months) combined with ultra-high magnetic field (9.4 T) proton magnetic resonance spectroscopy to prospectively measure putamen metabolite changes.

METHODS

Proton metabolites were measured with a STEAM sequence, quantified with LCModel using a simulated basis set, and expressed as metabolite/total creatine (tCr) ratios.

RESULTS

We found cocaine-induced time-dependent changes in putamen glutamate/tCr and glutamine/tCr metabolite ratios suggestive of altered glutamate compartmentalization, neurotransmission, and metabolism. By contrast, saline-treated monkeys exhibited no metabolite changes over time. The time course of cocaine-induced metabolite abnormalities we detected is consistent with the apparent time course of glutamate abnormalities identified in a cross-sectional study in human cocaine users, as well as with microdialysis findings in rodent models of repeated cocaine exposure.

CONCLUSIONS

Together, these findings suggests that this squirrel monkey model may be useful for characterizing glutamatergic changes associated with cocaine exposure and for determining efficacies of treatments designed to mitigate cocaine-induced glutamatergic system dysfunction.

Clinical application for the preservation of phospho-proteins through in-situ tissue stabilization

Background

Protein biomarkers will play a pivotal role in the future of personalized medicine for both diagnosis and treatment decision-making. While the results of several pre-clinical and small-scale clinical studies have demonstrated the value of protein biomarkers, there have been significant challenges to translating these findings into routine clinical care. Challenges to the use of protein biomarkers include inter-sample variability introduced by differences in post-collection handling and ex vivo degradation of proteins and protein modifications.

Results

In this report, we re-create laboratory and clinical scenarios for sample collection and test the utility of a new tissue stabilization technique in preserving proteins and protein modifications. In the laboratory setting, tissue stabilization with the Denator Stabilizor T1 resulted in a significantly higher yield of phospho-protein when compared to standard snap freeze preservation. Furthermore, in a clinical scenario, tissue stabilization at collection resulted in a higher yield of total phospho-protein, total phospho-tyrosine, pErkT202/Y204 and pAktS473 when compared to standard methods. Tissue stabilization did not have a significant effect on other post-translational modifications such as acetylation and glycosylation, which are more stable ex-vivo. Tissue stabilization did decrease total RNA quantity and quality.

Conclusion

Stabilization at the time of collection offers the potential to better preserve tissue protein and protein modification levels, as well as reduce the variability related to tissue processing delays that are often associated with clinical samples.

Gene expression of conditioned locomotion and context-specific locomotor sensitization controlled by morphine-associated environment

The nucleus accumbens (NAc) is involved in contextual drug associations, which might be particularly important for environmental cue-induced relapse to drug seeking. In the present study, rats were first administered repeated morphine for 5 days (5 mg/kg, i.p.) in a contextually paired and unpaired design. After reexposure to the morphine-associated environment, which induced conditioned locomotor activity in the morphine-paired group, we performed a rat 27k 70-mer oligo array to profile gene expression in the NAc. One hundred fifty-five upregulated and 88 downregulated genes were found in the paired group compared with the unpaired group. Eight gene transcripts were then selected to confirm their alterations by quantitative real-time polymerase chain reaction (qRT-PCR). The identified genes generally play important roles in neuroactive receptor-ligand interactions, synapse plasticity, ion transport, and protein phosphorylation. Furthermore, the expression of the eight selected genes that were identified and confirmed to show significant fold changes in the first microarray experiment were again measured with qRT-PCR after morphine challenge (2 mg/kg, i.p.). As expected, 2 mg/kg morphine-induced context-specific sensitization. Meanwhile, mRNA expression of the selected genes showed marked upregulation in the morphine-paired group compared with the unpaired and acute groups. These results suggest that alterations in the expression of the identified genes in the NAc may contribute to the neuroplasticity underlying contextual cue-induced relapse to drug use.

Cocaine-induced neuroadaptations in glutamate transmission: potential therapeutic targets for craving and addiction

A growing body of evidence indicates that repeated exposure to cocaine leads to profound changes in glutamate transmission in limbic nuclei, particularly the nucleus accumbens. This review focuses on preclinical studies of cocaine-induced behavioral plasticity, including behavioral sensitization, self-administration, and the reinstatement of cocaine seeking. Behavioral, pharmacological, neurochemical, electrophysiological, biochemical, and molecular biological changes associated with cocaine-induced plasticity in glutamate systems are reviewed. The ultimate goal of these lines of research is to identify novel targets for the development of therapies for cocaine craving and addiction. Therefore, we also outline the progress and prospects of glutamate modulators for the treatment of cocaine addiction.

Cocainomics: new insights into the molecular basis of cocaine addiction

Until recently, knowledge of the impact of abused drugs on gene and protein expression in the brain was limited to less than 100 targets. With the advent of high-throughput genomic and proteomic techniques, investigators are now able to evaluate changes across the entire genome and across thousands of proteins in defined brain regions and generate expression profiles of vulnerable neuroanatomical substrates in rodent and nonhuman primate drug abuse models and in human post-mortem brain tissue from drug abuse victims. The availability of gene and protein expression profiles will continue to expand our understanding of the short- and long-term consequences of drug addiction and other addictive disorders and may provide new approaches or new targets for pharmacotherapeutic intervention. This review summarizes several important genomic and proteomic studies of cocaine abuse/addiction from rodent, nonhuman primate, and human postmortem studies of cocaine abuse and explores how these studies have advanced our understanding of addiction.

Chronic cocaine-induced H3 acetylation and transcriptional activation of CaMKIIalpha in the nucleus accumbens is critical for motivation for drug reinforcement

The regulation of gene expression in the brain reward regions is known to contribute to the pathogenesis and persistence of drug addiction. Increasing evidence suggests that the regulation of gene transcription is mediated by epigenetic mechanisms that alter the chromatin structure at specific gene promoters. To better understand the involvement of epigenetic regulation in drug reinforcement properties, rats were subjected to cocaine self-administration paradigm. Daily histone deacetylase (HDAC) inhibitor infusions in the shell of the nucleus accumbens (NAc) caused an upward shift in the dose-response curve under fixed-ratio schedule and increased the break point under progressive-ratio schedule, indicating enhanced motivation for self-administered drug. The effect of the HDAC inhibitor is attributed to the increased elevation of histone acetylation induced by chronic, but not acute, cocaine experience. In contrast, neutralizing the chronic cocaine-induced increase in histone modification by the bilateral overexpression of HDAC4 in the NAc shell reduced drug motivation. The association between the motivation for cocaine and the transcriptional activation of addiction-related genes by H3 acetylation in the NAc shell was analyzed. Among the genes activated by chronic cocaine experiences, the expression of CaMKIIalpha, but not CaMKIIbeta, correlated positively with motivation for the drug. Lentivirus-mediated shRNA knockdown experiments showed that CaMKIIalpha, but not CaMKIIbeta, in the NAc shell is essential for the maintenance of motivation to self-administered cocaine. These findings suggest that chronic drug-use-induced transcriptional activation of genes, such as CaMKIIalpha, modulated by H3 acetylation in the NAc is a critical regulatory mechanism underlying motivation for drug reinforcement.

Gene expression changes in the medial prefrontal cortex and nucleus accumbens following abstinence from cocaine self-administration

Background

Many studies of cocaine-responsive gene expression have focused on changes occurring during cocaine exposure, but few studies have examined the persistence of these changes with cocaine abstinence. Persistent changes in gene expression, as well as alterations induced during abstinence may underlie long-lasting drug craving and relapse liability.

Results

Whole-genome expression analysis was conducted on a rat cocaine binge-abstinence model that has previously been demonstrated to engender increased drug seeking and taking with abstinence. Gene expression changes in two mesolimbic terminal fields (mPFC and NAc) were identified in a comparison of cocaine-naïve rats with rats after 10 days of cocaine self-administration followed by 1, 10, or 100 days of enforced abstinence (n = 6-11 per group). A total of 1,461 genes in the mPFC and 414 genes in the NAc were altered between at least two time points (ANOVA, p < 0.05; ± 1.4 fold-change). These genes can be subdivided into: 1) changes with cocaine self-administration that do not persist into periods of abstinence, 2) changes with cocaine self-administration that persist with abstinence, 3) and those not changed with cocaine self-administration, but changed during enforced abstinence. qPCR analysis was conducted to confirm gene expression changes observed in the microarray analysis.

Conclusions

Together, these changes help to illuminate processes and networks involved in abstinence-induced behaviors, including synaptic plasticity, MAPK signaling, and TNF signaling.

Arginine vasopressin gene expression changes within the nucleus accumbens during environment elicited cocaine-conditioned response in rats

It is known that changes in gene expression within the nucleus accumbens (NAc) occur during cocaine dependence development. However, identification of specific genes involved in cocaine conditioning awaits further investigation. We conducted a high throughput gene expression profile analysis of the NAc, during different stages of the environment-elicited cocaine conditioning. Rats were assigned to two different environmental conditions. Cocaine conditioned group received a cocaine injection (10mg/kg, i.p.) prior to being placed in the activity chambers. Control rats received saline injections before being exposed to their environment. Both groups received a saline injection in their home cage. Conditioning training lasted for 10 days. Animals were then re-exposed to their previously paired environments only on day 12 (test session). We found that the gene for arginine vasopressin (AVP) was differentially expressed on experimental subjects during all stages of environment-elicited cocaine conditioning. To further validate our molecular results, biochemical and immunolocalization experiments were conducted. We found the presence of AVP within accumbal fibers and changes in AVP protein levels following cocaine conditioning. Moreover, we tested the effects of accumbal microinfusions of either AVP receptor V(1A) agonist [pGlu(4), Cyt6, Arg(8)] AVP 4-9 1.0 ng/0.5 microl, or V(1A) antagonist (CH2) 5[Tyr (Me) 2] AVP, 1.0 ng/0.5 microl or vehicle solution (0.9% saline solution) during different stages of the cocaine conditioning. Blockade of V(1A) receptors within the NAc during acquisition interrupted the expression of the conditioned response, while activation leads to an increase in this response. Our findings propose a new role for AVP in cocaine addiction.

Genome-wide analysis of chromatin regulation by cocaine reveals a role for sirtuins

Changes in gene expression contribute to the long-lasting regulation of the brain's reward circuitry seen in drug addiction; however, the specific genes regulated and the transcriptional mechanisms underlying such regulation remain poorly understood. Here, we used chromatin immunoprecipitation coupled with promoter microarray analysis to characterize genome-wide chromatin changes in the mouse nucleus accumbens, a crucial brain reward region, after repeated cocaine administration. Our findings reveal several interesting principles of gene regulation by cocaine and of the role of DeltaFosB and CREB, two prominent cocaine-induced transcription factors, in this brain region. The findings also provide comprehensive insight into the molecular pathways regulated by cocaine-including a new role for sirtuins (Sirt1 and Sirt2)-which are induced in the nucleus accumbens by cocaine and, in turn, dramatically enhance the behavioral effects of the drug.

Phosphorylation of GluR1, ERK, and CREB during spontaneous withdrawal from chronic heroin self-administration

Negative motivational symptoms are observed soon after withdrawal from chronic opiate administration, and are thought to mediate dependence. Examination of brain region-specific signaling changes that accompany early withdrawal may shed light on neural mechanisms underlying negative reinforcement and dependence. Thus, we measured alterations in protein phosphorylation in multiple limbic brain regions in rats undergoing 24 h spontaneous or naltrexone-precipitated withdrawal from chronic (6 h/day) i.v. heroin self-administration. Region-specific increases in cyclic AMP-dependent GluR(1) (S845) phosphorylation were found in the nucleus accumbens shell, basolateral amygdala, hippocampal CA1 and CA3 subregions, and premotor cortex from 12 to 24 h of spontaneous withdrawal, and there were no changes in prefrontal cortex, nucleus accumbens core or caudate-putamen. Increased GluR(1) (S845) phosphorylation was detected earlier (12 h withdrawal) in the central amygdala and ventral tegmental area. In contrast, prominent increases in extracellular signal-regulated kinase phosphorylation were found in both prefrontal and premotor cortex, and CA1 and CA3 between 12 and 24 h withdrawal. Phosphorylation of striatal cyclic AMP response element binding protein increased in the caudate-putamen but not in the nucleus accumbens. Naltrexone administration after 24 h withdrawal increased extracellular signal-regulated kinase phosphorylation in the central amygdala, and nucleus accumbens core and shell. Thus, spontaneous withdrawal from heroin self-administration produces region- and time-dependent changes in cyclic AMP and extracellular signal-regulated kinase activity that could contribute to the behavioral manifestation of opiate dependence.

Transcription factors in long-term memory and synaptic plasticity

Transcription is a molecular requisite for long-term synaptic plasticity and long-term memory formation. Thus, in the last several years, one main interest of molecular neuroscience has been the identification of families of transcription factors that are involved in both of these processes. Transcription is a highly regulated process that involves the combined interaction and function of chromatin and many other proteins, some of which are essential for the basal process of transcription, while others control the selective activation or repression of specific genes. These regulated interactions ultimately allow a sophisticated response to multiple environmental conditions, as well as control of spatial and temporal differences in gene expression. Evidence based on correlative changes in expression, genetic mutations, and targeted molecular inhibition of gene expression have shed light on the function of transcription in both synaptic plasticity and memory formation. This review provides a brief overview of experimental work showing that several families of transcription factors, including CREB, C/EBP, Egr, AP-1, and Rel, have essential functions in both processes. The results of this work suggest that patterns of transcription regulation represent the molecular signatures of long-term synaptic changes and memory formation.

Histone acetylation in drug addiction

Regulation of chromatin structure through post-translational modifications of histones (e.g., acetylation) has emerged as an important mechanism to translate a variety of environmental stimuli, including drugs of abuse, into specific changes in gene expression. Since alterations in gene expression are thought to contribute to the development and maintenance of the addicted state, recent efforts are aimed at identifying how drugs of abuse alter chromatin structure and the enzymes which regulate it. This review discusses how drugs of abuse alter histone acetylation in brain reward regions, through which enzymes this occurs, and ultimately what role histone acetylation plays in addiction-related behaviors.

Correlating human and animal studies of cocaine abuse and gene expression

Gene expression changes resulting from cocaine abuse in both humans and animal models have been studied for several decades. Although human studies have been very useful at illuminating cocaine-related expression changes, there are many factors complicating these studies, including the difficulty of obtaining high-quality postmortem brain tissue and patient comorbidities. Animal models of cocaine abuse have served as valuable additions to human data and allow examination of specific aspects of cocaine abuse, including immediate early gene expression and the molecular effects of abstinence and relapse. In total, human and animal studies of cocaine abuse have uncovered gene expression changes in the brain related to a number of molecular functions, including the extracellular matrix, synaptic communication and neuroplasticity, receptors, ion channels and transporters, oligodendrocytes and myelin, apoptosis and cell death, mitochondrial function, signal transduction, and transcription factors. In addition, the mitogen-activated protein kinase and synaptic long-term potentiation signal transduction pathways are highlighted as pathways in which multiple components are altered by cocaine. Pathways and processes affected by changes in gene expression that overlap among multiple species may be promising pharmacotherapeutic targets for reducing the behavioral effects of cocaine abuse and the relapse potential observed in humans.

The retinal proteome in experimental diabetic retinopathy: up-regulation of crystallins and reversal by systemic and periocular insulin

Diabetic retinopathy is the leading cause of blindness in working age persons. Targeted studies have uncovered several components of the pathophysiology of the disease without unveiling the basic mechanisms. This study describes the use of complementary proteomic and genomic discovery methods that revealed that the proteins of the crystallin superfamily are increased dramatically in early diabetic retinopathy. Orthogonal methods confirmed that the amplitude of the up-regulation is greater than other changes described so far in diabetic retinopathy. A detailed time course study during diabetes showed differential up-regulation of the different isoforms of the crystallins superfamily. alpha- and beta-crystallins were regulated primarily at the translation level, whereas gamma-crystallins were also regulated transcriptionally. We also demonstrated cell-specific patterns of expression of the different crystallins in normal and diabetic rat retinas. In addition, systemic and periocular insulin treatments restored retinal crystallin protein expression during diabetes, indicating effects of phosphoinositide 3-kinase/Akt activity. Altogether this work shows the importance of proteomics discovery methods coupled with targeted approaches to unveil new disease mechanistic details and therapeutic targets.

Protein kinases and addiction

Although drugs of abuse have different chemical structures and interact with different protein targets, all appear to usurp common neuronal systems that regulate reward and motivation. Addiction is a complex disease that is thought to involve drug-induced changes in synaptic plasticity due to alterations in cell signaling, gene transcription, and protein synthesis. Recent evidence suggests that drugs of abuse interact with and change a common network of signaling pathways that include a subset of specific protein kinases. The best studied of these kinases are reviewed here and include extracellular signal-regulated kinase, cAMP-dependent protein kinase, cyclin-dependent protein kinase 5, protein kinase C, calcium/calmodulin-dependent protein kinase II, and Fyn tyrosine kinase. These kinases have been implicated in various aspects of drug addiction including acute drug effects, drug self-administration, withdrawal, reinforcement, sensitization, and tolerance. Identifying protein kinase substrates and signaling pathways that contribute to the addicted state may provide novel approaches for new pharmacotherapies to treat drug addiction.

Epigenetic mechanisms in drug addiction

Changes in gene expression in brain reward regions are thought to contribute to the pathogenesis and persistence of drug addiction. Recent studies have begun to focus on the molecular mechanisms by which drugs of abuse and related environmental stimuli, such as drug-associated cues or stress, converge on the genome to alter specific gene programs. Increasing evidence suggests that these stable gene expression changes in neurons are mediated in part by epigenetic mechanisms that alter chromatin structure on specific gene promoters. This review discusses recent findings from behavioral, molecular and bioinformatic approaches being used to understand the complex epigenetic regulation of gene expression by drugs of abuse. This novel mechanistic insight might open new avenues for improved treatments of drug addiction.

Persistent alterations in mesolimbic gene expression with abstinence from cocaine self-administration

Cocaine-responsive gene expression changes have been described after either no drug abstinence or short periods of abstinence. Little data exist on the persistence of these changes after long-term abstinence. Previously, we reported that after discrete-trial cocaine self-administration and 10 days of forced abstinence, incubation of cocaine reinforcement was observable by a progressive ratio schedule. The present study used rat discrete-trial cocaine self-administration and long-term forced abstinence to examine extinction responding, mRNA abundance of known cocaine-responsive genes, and chromatin remodeling. At 30 and 100 days of abstinence, extinction responding increased compared to 3-day abstinent rats. Decreases in both medial prefrontal cortex (mPFC) and nucleus accumbens c-fos, Nr4a1, Arc, and EGR1 mRNA were observed, and in most cases persisted, for 100 days of abstinence. The signaling peptides CART and neuropeptide Y (NPY) transiently increased in the mPFC, but returned to baseline levels following 10 days of abstinence. To investigate a potential regulatory mechanism for these persistent mRNA changes, levels of histone H3 acetylation at promoters for genes with altered mRNA expression were examined. In the mPFC, histone H3 acetylation decreased after 1 and 10 days of abstinence at the promoter for EGR1. H3 acetylation increased for NPY after 1 day of abstinence and returned to control levels by 10 days of abstinence. Behaviorally, these results demonstrate incubation after discrete-trial cocaine self-administration and prolonged forced abstinence. This incubation is accompanied by changes in gene expression that persist long after cessation of drug administration and may be regulated by chromatin remodeling.

Whole genome assessment of the retinal response to diabetes reveals a progressive neurovascular inflammatory response

BACKGROUND

Despite advances in the understanding of diabetic retinopathy, the nature and time course of molecular changes in the retina with diabetes are incompletely described. This study characterized the functional and molecular phenotype of the retina with increasing durations of diabetes.

RESULTS

Using the streptozotocin-induced rat model of diabetes, levels of retinal permeability, caspase activity, and gene expression were examined after 1 and 3 months of diabetes. Gene expression changes were identified by whole genome microarray and confirmed by qPCR in the same set of animals as used in the microarray analyses and subsequently validated in independent sets of animals. Increased levels of vascular permeability and caspase-3 activity were observed at 3 months of diabetes, but not 1 month. Significantly more and larger magnitude gene expression changes were observed after 3 months than after 1 month of diabetes. Quantitative PCR validation of selected genes related to inflammation, microvasculature and neuronal function confirmed gene expression changes in multiple independent sets of animals.

CONCLUSION

These changes in permeability, apoptosis, and gene expression provide further evidence of progressive retinal malfunction with increasing duration of diabetes. The specific gene expression changes confirmed in multiple sets of animals indicate that pro-inflammatory, anti-vascular barrier, and neurodegenerative changes occur in tandem with functional increases in apoptosis and vascular permeability. These responses are shared with the clinically documented inflammatory response in diabetic retinopathy suggesting that this model may be used to test anti-inflammatory therapeutics.

Gene profiling the response to repeated cocaine self-administration in dorsal striatum: a focus on circadian genes

Alterations in gene expression in the dorsal striatum caused by chronic cocaine exposure have been implicated in the long-term behavioral changes associated with cocaine addiction. To gain further insight into the molecular alterations that occur as a result of cocaine self-administration, we conducted a microarray analysis of gene expression followed by bioinformatic gene network analysis that allowed us to identify adaptations at the level of gene expression as well as into interconnected networks. Changes in gene expression were examined in the dorsal striatum of rats 1 day after they had self-administered cocaine for 7 days under a 24-h access, discrete trial paradigm (averaging 98 mg/kg/day). Here we report the regulation of the circadian genes Clock, Bmal1, Cryptochrome1, Period2, as well as several genes that are regulated by/associated with the circadian system (i.e., early growth response 1, dynorphin). We also observed regulation of other relevant genes (i.e., Nur77, beta catenin). These changes were then linked to curated pathways and formulated networks which identified circadian rhythm processes as affected by cocaine self-administration. These data strongly suggest involvement of circadian-associated genes in the brain's response to cocaine and may contribute to an understanding of addictive behavior including disruptions in sleep and circadian rhythmicity.

Upregulation of beta-catenin levels in superior frontal cortex of chronic alcoholics

BACKGROUND

Chronic and excessive alcohol misuse results in neuroadaptive changes in the brain. The complex nature of behavioral, psychological, emotional, and neuropathological characteristics associated with alcoholism is likely a reflection of the network of proteins that are affected by alcohol-induced gene expression patterns in specific brain regions. At the molecular level, however, knowledge remains limited regarding alterations in protein expression levels affected by chronic alcohol abuse. Thus, novel techniques that allow a comprehensive assessment of this complexity will enable the simultaneous assessment of changes across a group of proteins in the relevant neural circuitry.

METHODS

A proteomics analysis was performed using antibody microarrays to determine differential protein levels in superior frontal cortices between chronic alcoholics and age- and gender-matched control subjects. Seventeen proteins related to the catenin signaling pathway were analyzed, including alpha-, beta-, and delta-catenins, their upstream activators cadherin-3 (type I cadherin) and cadherin-5 (type II cadherin), and 5 cytoplasmic regulators c-Src, CK1 epsilon, GSK-3beta, PP2A-C alpha, and APC, as well as the nuclear complex partner of beta-catenin CBP and 2 downstream genes Myc and cyclin D1. ILK, G(alpha1), G(beta1), and G(beta2), which are activity regulators of GSK-3beta, were also analyzed.

RESULTS

Both alpha- and beta-catenin showed significantly increased levels, while delta-catenin did not change significantly, in chronic alcoholics. In addition, the level of the beta-catenin downstream gene product Myc was significantly increased. Average levels of the catenin regulators c-Src, CK1 epsilon, and APC were also increased in chronic alcoholics, but the changes were not statistically significant.

CONCLUSION

Chronic and excessive alcohol consumption leads to an upregulation of alpha- and beta-catenin levels, which in turn increase downstream gene expressions such as Myc that is controlled by beta-catenin signaling. This study showed that the beta-catenin signal transduction pathway was upregulated by chronic alcohol abuse, and prompts further investigation of mechanisms underlying the upregulation of alpha- and beta-catenins in alcoholism, which may have considerable pathogenic and therapeutic relevance.

Heroin self-administration: II. CNS gene expression following withdrawal and cue-induced drug-seeking behavior

In the accompanying paper, we described incubation of heroin-seeking behavior in rats following 14 days of abstinence. To gain an understanding of genomic changes that accompany this behavioral observation, we measured the expression of genes previously reported to respond to drugs of abuse. Specifically, after 1 or 14 days of abstinence, mRNA expression was measured for 11 genes in the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) immediately following a single 90 min extinction session. Additionally, the role of contingency was examined in control rats that received yoked, response-independent heroin administration. Gene expression was quantified by real-time quantitative PCR. Expression of five genes (Arc, EGR1, EGR2, Fos, and Homer1b/c) was changed in the mPFC. EGR1 and EGR2 expression was increased following the 90 min extinction session in a contingency-specific manner and this increase persisted through the 14 days of abstinence. Fos expression was also increased after 1 and 14 days of abstinence, but at 14 days this increase was response-independent (i.e., it occurred in both the rats with a history of heroin self-administration and in the yoked controls). Arc expression increased following the extinction session only in rats with a history of heroin self-administration and only when tested following 1, but not 14, days of abstinence. Homer 1 b/c decreased after 14 days of enforced abstinence in rats that received non-contingent heroin. Expression of only a single gene (EGR2) was increased in the NAc. These data demonstrate that behavioral incubation is coincident with altered levels of specific transcripts and that this response is contingently-specific. Moreover, EGR1 and EGR2 are specifically upregulated in self-administering rats following extinction and this finding persists through 14 days of abstinence, suggesting that these genes are particularly associated with the incubation phenomenon. These latter observations of persistent changes in gene expression following abstinence may reflect molecular correlates of relapse liability.

Glucocorticoids plus opioids up-regulate genes that influence neuronal function

(1) This study investigated the functional genomics of glucocorticoid and opioid receptor stimulation in cellular adaptations using a cultured neuronal cell model. (2) Human SH-SY5Y neuroblastoma cells grown in hormone-depleted serum were treated for 2-days with the glucocorticoid receptor-II agonist dexamethasone (30 nM); the mu-opioid receptor agonist [D-Ala2, N-Me-Phe4, Gly5-ol]-Enkephalin acetate (DAMGO; 1 nM); or dexamethasone (30 nM) plus DAMGO (1 nM). RNA was extracted; purified, reverse transcribed, and labeled cDNA was hybridized to a 10,000-oliogonucleotide-array human gene chip. Gene expression changes that were significantly different between treatment groups and were of interest due to biological function were verified by real-time reverse transcription polymerase chain reaction (RT-PCR). Five relevant genes were identified for which the combination of dexamethasone plus DAMGO, but neither one alone, significantly up-regulated gene expression (ANOVA, P < 0.05). (3) Proteins coded by the identified genes: FRS2 (fibroblast growth factor receptor substrate-2; CTNNB1 (beta1-catenin); PRCP (prolyl-carboxypeptidase); MPHOSPH9 (M-phase phosphoprotein 9); and ZFP95 (zinc finger protein 95) serve important neuronal functions in signal transduction, synapse formation, neuronal growth and development, or transcription regulation. Neither opioid, glucocorticoid nor combined treatments significantly altered the cell growth rate determined by cell counts and protein. (4) We conclude that sustained mu-opioid receptor stimulation accompanied by glucocorticoids can synergistically regulate genes that influence neuronal function. Future studies are warranted to determine if combined influences of glucocorticoid fluctuations and opioid receptor stimulation in vivo can orchestrate exagerated neuroadaptation to reinforcing drugs under chronic mild stress conditions.

A threshold neurotoxic amphetamine exposure inhibits parietal cortex expression of synaptic plasticity-related genes

Compulsive drug abuse has been conceptualized as a behavioral state where behavioral stimuli override normal decision making. Clinical studies of methamphetamine users have detailed decision making changes and imaging studies have found altered metabolism and activation in the parietal cortex. To examine the molecular effects of amphetamine (AMPH) on the parietal cortex, gene expression responses to amphetamine challenge (7.5 mg/kg) were examined in the parietal cortex of rats pretreated for nine days with either saline, non-neurotoxic amphetamine, or neurotoxic AMPH dosing regimens. The neurotoxic AMPH exposure [three doses of 7.5 mg/kg/day AMPH (6 h between doses), for nine days] produced histological signs of neurotoxicity in the parietal cortex while a non-neurotoxic dosing regimen (2.0 mg/kg/day x 3) did not. Neurotoxic AMPH pretreatment resulted in significantly diminished AMPH challenge-induced mRNA increases of activity-regulated cytoskeletal protein (ARC), nerve growth-factor inducible protein A (NGFI-A), and nerve growth-factor inducible protein B (NGFI-B) in the parietal cortex while neither saline pretreatment nor non-neurotoxic AMPH pretreatment did. This effect was specific to these genes as tissue plasminogen activator (t-PA), neuropeptide Y (NPY) and c-jun expression in response to AMPH challenge was unaltered or enhanced by amphetamine pretreatments. In the striatum, there were no differences between saline, neurotoxic AMPH, and non-neurotoxic AMPH pretreatments on ARC, NGFI-A or NGFI-B expression elicited by the AMPH challenge. These data indicate that the responsiveness of synaptic plasticity-related genes is sensitive to disruption specifically in the parietal cortex by threshold neurotoxic AMPH exposures.

Regulation of mitogen-activated protein kinases by glutamate receptors

Glutamate receptors regulate gene expression in neurons by activating intracellular signaling cascades that phosphorylate transcription factors within the nucleus. The mitogen-activated protein kinase (MAPK) cascade is one of the best characterized cascades in this regulatory process. The Ca(2+)-permeable ionotropic glutamate receptor, mainly the NMDA receptor subtype, activates MAPKs through a biochemical route involving the Ca(2+)-sensitive Ras-guanine nucleotide releasing factor, Ca(2+)/calmodulin-dependent protein kinase II, and phosphoinositide 3-kinase. The metabotropic glutamate receptor (mGluR), however, activates MAPKs primarily through a Ca(2+)-insensitve pathway involving the transactivation of receptor tyrosine kinases. The adaptor protein Homer also plays a role in this process. As an information superhighway between surface glutamate receptors and transcription factors in the nucleus, active MAPKs phosphorylate specific transcription factors (Elk-1 and CREB), and thereby regulate distinct programs of gene expression. The regulated gene expression contributes to the development of multiple forms of synaptic plasticity related to long-lasting changes in memory function and addictive properties of drugs of abuse. This review, by focusing on new data from recent years, discusses the signaling mechanisms by which different types of glutamate receptors activate MAPKs, features of each MAPK cascade in regulating gene expression, and the importance of glutamate/MAPK-dependent synaptic plasticity in memory and addiction.

Altered attention and prefrontal cortex gene expression in rats after binge-like exposure to cocaine during adolescence

Illicit use of drugs frequently begins and escalates during adolescence, with long-term adverse consequences. Because it is increasingly accepted that neural development continues through adolescence, addiction research has become more invested in understanding the behavioral and molecular consequences of early exposure to drugs of abuse. In a novel binge administration paradigm designed to model the pattern of human adolescent drug use, we administered ascending doses of cocaine or saline during a 12-d developmental period [postnatal day 35 (P35) to P46] corresponding to human adolescence. During adulthood (P70), rats treated with this regimen displayed increased responsiveness to the stimulant effects of cocaine. Adult rats also displayed abnormally rapid shifts in attention when performing an attentional set-shifting task, which measures the ability to shift attention between stimuli and whose performance requires an intact prefrontal cortex (PFC). Treatment with cocaine during adolescence also caused acute alterations in the expression of genes encoding cell adhesion molecules and transcription factors within the PFC. Furthermore, we observed decreases in histone methylation, which may indicate a role for chromatin remodeling in the observed changes in gene expression patterns. These findings suggest that exposure to cocaine during adolescence has far-reaching molecular and behavioral consequences in the rat PFC that develop over time and endure long after drug administration has ceased.

Methamphetamine causes alterations in the MAP kinase-related pathways in the brains of mice that display increased aggressiveness

Aggressive behaviors have been reported in patients who suffer from some psychiatric disorders, and are common in methamphetamine (METH) abusers. Herein, we report that multiple (but not single) injections of METH significantly increased aggressiveness in male CD-1 mice. This increase in aggressiveness was not secondary to METH-induced hyperactivity. Analysis of protein expression using antibody microarrays and Western blotting revealed differential changes in MAP kinase-related pathways after multiple and single METH injections. There were statistically significant (p<0.05) decreases in MEK1, Erk2p, GSK3alpha, 14-3-3e, and MEK7 in the striata of mice after multiple injections of METH. MEK1 was significantly decreased also after a single injection of METH, but to a much lesser degree than after multiple injections of METH. In the frontal cortex, there was a statistically significant decrease in GSK3alpha after multiple (but not single) injections of METH. These findings suggest that alterations in MAP kinase-related pathways in the prefronto-striatal circuitries might be involved in the manifestation of aggressive behaviors in mice.

Persistent changes in motivation to self-administer cocaine following modulation of cyclic AMP-dependent protein kinase A (PKA) activity in the nucleus accumbens

Drug-induced neuroadaptations within the nucleus accumbens, including activation of cAMP-dependent protein kinase A (PKA), may contribute to the synaptic plasticity and behavioural changes that underlie drug addiction. As a direct test of this hypothesis, we examined the effects in rats of PKA activation (Sp-cAMPS infusions of 10 and 20 nmol/side) and inhibition (Rp-cAMPS infusions of 10 and 20 nmol/side) in the nucleus accumbens on motivation to obtain cocaine as measured by responding under the progressive-ratio schedule. Bilateral infusions of Sp-cAMPS (20 nmol/side) resulted in an increase in progressive-ratio responding for cocaine and this effect persisted for several days. In contrast, Rp-cAMPS (20 nmol/side) produced persistent decreases in progressive-ratio responding for cocaine beginning on the day of administration and lasting for several days. These data suggest that alternations in PKA activity within the nucleus accumbens as a consequence of repeated cocaine exposure may contribute to addiction by producing persistent increases in motivation to obtain cocaine.

Assessment of genome and proteome profiles in cocaine abuse

Until recently, knowledge of the impact of abuse drugs on gene and protein expression in the brain was limited to less than 100 targets. With the advent of high-throughput genomic and proteomic techniques investigators are now able to evaluate changes across the entire genome and across thousands of proteins in defined brain regions and generate expression profiles of vulnerable neuroanatomical substrates in rodent and non-human primate drug abuse models and in human post-mortem brain tissue from drug abuse victims. The availability of gene and protein expression profiles will continue to expand our understanding of the short- and long-term consequences of drug addiction and other addictive disorders and may provide new approaches or new targets for pharmacotherapeutic intervention. This chapter will review gene expression data from rodent, non-human primate and human post-mortem studies of cocaine abuse and will provide a preliminary proteomic profile of human cocaine abuse and explore how these studies have advanced our understanding of addiction.

Antisense-induced reduction in nucleus accumbens cyclic AMP response element binding protein attenuates cocaine reinforcement

Repeated cocaine exposure up-regulates cyclic AMP signaling and increases the transcriptional activity of cyclic AMP response element binding protein (CREB) in the nucleus accumbens. To study the possibility that nucleus accumbens CREB activity regulates self-administration behavior, we tested the effects of a single, bilateral infusion of CREB antisense oligonucleotide into nucleus accumbens core and shell sub-regions on cocaine self-administration in rats. Nucleus accumbens core infusions of CREB antisense reduced CREB and the CREB-regulated immediate early gene brain-derived neurotrophic factor by 31 and 27%, respectively, but failed to alter levels of the homologous CREB family proteins cyclic AMP response element modulator and activating transcription factor 1, and had no effect on CREB levels in adjacent nucleus accumbens shell tissue. Similar infusions of CREB antisense in either core or shell produced a transient downward shift in cocaine self-administration dose-response curves on a fixed ratio 5 (five responses/injection) reinforcement schedule, indicating a reduction in cocaine reinforcement that fully recovered 3 days after treatment. CREB antisense also increased the threshold dose of cocaine required for reinstating cocaine self-administration, indicating that nucleus accumbens CREB levels regulate the incentive properties of cocaine. When access to cocaine was less restricted on a fixed ratio 1 schedule, infusion of CREB antisense in the core, but not shell, caused a transient (1-2 days) reduction in stabilized cocaine self-administration, but had no effect on responding maintained by sucrose pellets, indicating that basal CREB levels in the nucleus accumbens core regulate drug intake. None of these effects were produced by nucleus accumbens infusions of complementary sense oligonucleotide. These results suggest a necessary role for nucleus accumbens CREB activity in cocaine reinforcement, and, by converse analogy, up-regulation in CREB activity after chronic cocaine use could contribute to addiction-related increases in cocaine self-administration.

Extended cocaine self-administration and deprivation produces region-specific and time-dependent changes in connexin36 expression in rat brain

Cocaine addiction is a disease that develops over time, and it is thought that drug-induced neuro-adaptations underlie the changes in behavior seen across the addictive process. While a number of alterations in synaptic transmission have been identified, little is currently known regarding cocaine's effects on gap junctional communication between neurons. Here we examine the effects of a cocaine self-administration regimen, previously shown to increase the reinforcing efficacy of cocaine, on the expression of the neuron-specific gap junction-forming protein connexin36 (C x 36). Using real-time RT-PCR and immunoblotting, we show that binge cocaine self-administration produces region-specific and time-dependent changes in C x 36 mRNA and protein expression in the nucleus accumbens, prefrontal cortex, and hippocampus. A number of changes in C x 36 were present 1 day and 7 days following self-administration, and C x 36 mRNA and protein appeared to be differentially regulated in a region-specific manner. C x 36 protein was significantly decreased in the prefrontal cortex 7 days following self-administration, a time point when behavioral sensitization to the reinforcing effects of cocaine is observed. These results suggest that changes in neuronal gap junction expression may be one mechanism by which cocaine self-administration produces enduring changes in behavior.

Long versus short oligonucleotide microarrays for the study of gene expression in nonhuman primates

The high degree of sequence similarity between human and nonhuman primate (NHP) genomic DNA suggests that human genome sequence-based DNA microarrays may be used effectively to study gene expression in NHP disease models. In the present study, two distinct commercially available human genome microarray platforms, the Affymetrix HG U133A GeneChip System utilizing Human Genome U133A GeneChips and the Applied Biosystems Expression Array System utilizing the Human Genome Survey Microarray, were used to identify and characterize gene expression changes in the anterior cerebellum of a macaque monkey model of human alcoholism. The Affymetrix microarray consists of eleven short oligonucleotide probe sets for each gene while the Applied Biosystems Microarray uses a single long oligonucleotide per gene. Cross-mapping of probes revealed a total of 11,542 genes that are represented on both microarray platforms. Absolute measures of gene expression ("present calls") from the cerebellum RNA samples were 65-70% (Applied Biosystems Expression Array System) and 27-30% (AffymetrixGeneChip System) among these common gene targets. Analysis of variance (ANOVA; p<0.05; >1.2 fold change; detected on at least 50% of the arrays) indicated 932 and 515 differentially expressed genes for the Applied Biosystems and Affymetrix microarrays, respectively. Significance analysis of microarrays (SAM) identified 255 significant genes at 5% false discovery rate (FDR) for the Applied Biosystems data set and five significant genes at 60% FDR (minimum FDR) for the Affymetrix data set. TaqMan assay-based real-time PCR validation of a number of differentially-expressed genes yielded results that agreed well with the array data in the majority of comparisons. This study demonstrates that human sequence-based DNA arrays can be used effectively to detect differential gene expression in an NHP disease model and provides evidence that the use of this long oligonucleotide-based microarray platform may be more suitable for cross-species gene expression studies than a short oligonucleotide-based system.