McClung CA, Nestler EJ, Zachariou V. Regulation of gene expression by chronic morphine and morphine withdrawal in the locus ceruleus and ventral tegmental area. J Neurosci 25: 6005-6015

Department of Psychiatry and Center for Basic Neuroscience, The University of Texas Southwestern Medical Center, Dallas, Texas 75390-9070, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 07/2005; 25(25):6005-15. DOI: 10.1523/JNEUROSCI.0062-05.2005
Source: PubMed


Morphine dependence is associated with long-term adaptive changes in the brain that involve gene expression. Different behavioral effects of morphine are mediated by different brain regions, for example, the locus ceruleus (LC), a noradrenergic nucleus, is implicated in physical dependence and withdrawal, whereas the ventral tegmental area (VTA), a dopaminergic nucleus, contributes to rewarding and locomotor responses to the drug. However, the global changes in gene expression that occur in these brain regions after morphine exposure and during withdrawal remain unknown. Using DNA microarray analysis in both mice and rats, we now characterize gene expression changes that occur in these brain regions with chronic morphine and antagonist-precipitated withdrawal. In the LC, numerous genes display common regulation between mouse and rat, including tyrosine hydroxylase, prodynorphin, and galanin. Furthermore, we identify clusters of genes that are regulated similarly by chronic morphine and by withdrawal, as well as clusters that show opposite regulation under these two conditions. Interestingly, most gene expression changes that occur in the VTA in response to chronic morphine are different from those seen in the LC, but the gene expression patterns in the two brain regions are very similar after withdrawal. In addition, we examined two genes (prodynorphin and FK506 binding protein 5) that are strongly regulated by chronic morphine or morphine withdrawal in the LC for their role in regulating withdrawal-associated behaviors. Inhibition of either protein profoundly affects withdrawal responses, demonstrating that the genes identified in this study have important functional roles in mediating opiate-induced behaviors.

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    • "Several lines of converging evidence suggest that LCderived galanin is at least partially responsible for some of these phenotypes. First, chronic opiate exposure and withdrawal increases galanin and galanin receptor expression in the LC, and withdrawal-induced LC activity is decreased by galanin (Georgescu et al., 2003;Holmes et al., 2012;McClung et al., 2005;Zachariou et al., 1999Zachariou et al., , 2000). Second, given the suppression of LC firing produced by autocrine release of galanin discussed earlier, one might predict that NE depletion would phenocopy increased galanin transmission; indeed, this is the case in many instances. "
    [Show abstract] [Hide abstract] ABSTRACT: Decades of research confirm that noradrenergic locus coeruleus (LC) neurons are essential for arousal, attention, motivation, and stress responses. While most studies on LC transmission focused unsurprisingly on norepinephrine (NE), adrenergic signaling cannot account for all the consequences of LC activation. Galanin coexists with NE in the vast majority of LC neurons, yet the precise function of this neuropeptide has proved to be surprisingly elusive given our solid understanding of the LC system. To elucidate the contribution of galanin to LC physiology, here we briefly summarize the nature of stimuli that drive LC activity from a neuroanatomical perspective. We go on to describe the LC pathways in which galanin most likely exerts its effects on behavior, with a focus on addiction, depression, epilepsy, stress, and Alzheimer's disease. We propose a model in which LC-derived galanin has two distinct functions: as a neuromodulator, primarily acting via the galanin 1 receptor (GAL1), and as a trophic factor, primarily acting via galanin receptor 2 (GAL2). Finally, we discuss how the recent advances in neuropeptide detection, optogenetics and chemical genetics, and galanin receptor pharmacology can be harnessed to identify the roles of LC-derived galanin definitively.
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    • "Many studies have shown that CRF levels are correlated with anxiety in animal models of depression, suggesting a possible link between high level expression of CRF and predisposition to anxiety or morphine withdrawal-induced depression [30]. In addition, previous studies suggested that morphine dependence and withdrawal induce hyperactivity of noradrenergic pathways and an increase in TH modulation in the LC [31]. It has been proposed that clinical anxiety or depression may be the result of alterations in the activity of the LC in central noradrenergic system [32]. "
    [Show abstract] [Hide abstract] ABSTRACT: The purpose of this study was to evaluate whether acupuncture stimulation attenuates withdrawal-induced behaviors in the rats during protracted abstinence following chronic morphine exposure. To do this, male rats were first exposed to morphine gradually from 20 to 100 mg/kg for 5 days, and subsequently naloxone was injected once to extend despair-related withdrawal behaviors for 4 weeks. Acupuncture stimulation was performed once at the SP6 (Sanyinjiao) acupoint on rat's; hind leg for 5 min during protracted abstinence from morphine. The acupuncture stimulation significantly decreased despair-like behavior deficits in the forced swimming test and low sociability in the open-field test as well as increased open-arm exploration in the elevated plus maze test in the last week of 4-week withdrawal period. Also the acupuncture stimulation significantly suppressed the increase in the hypothalamic corticotropin-releasing factor (CRF) expression, the decrease in the tyrosine hydroxylase expression in the locus coeruleus, and the decrease in the hippocampal brain-derived neurotrophic factor mRNA expression, induced by repeated injection of morphine. Taken together, these findings demonstrate that the acupuncture stimulation of SP6 significantly reduces withdrawal-induced behaviors, induced by repeated administration of morphine in rats, possibly through the modulation of hypothalamic CRF and the central noradrenergic system.
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    • "Further, the ability to maintain or restore redox homeostasis might include underlying changes in gene expression mediated via epigeneticmodulation of gene transcription in response to various stimuli, including drugs of abuse (Mao et al., 2002; Xu et al., 2003; McClung et al., 2005; Christie, 2008; Robison and Nestler, 2011; Schwarz et al., 2011). However, we propose that an absence of these stimuli can render the adaptive changes excessive, leading to a plethora of compensatory mechanisms which could potentially result in a switched homeostasis in the opposite direction (Xu et al., 2003Xu et al., , 2006 McClung et al., 2005). Thus, redox-responsive adaptive regulation of epigenetic status might exhibit opposite changes during sustained drug exposure vs. drug withdrawal states and contribute to the observed symptoms (Figure 3). "
    [Show abstract] [Hide abstract] ABSTRACT: Alcohol and other drugs of abuse, including psychostimulants and opioids, can induce epigenetic changes: a contributing factor for drug addiction, tolerance, and associated withdrawal symptoms. DNA methylation is a major epigenetic mechanism and it is one of more than 200 methylation reactions supported by methyl donor S-adenosylmethionine (SAM). Levels of SAM are controlled by cellular redox status via the folate and vitamin B12-dependent enzyme methionine synthase (MS). For example, under oxidative conditions MS is inhibited, diverting its substrate homocysteine (HCY) to the trans sulfuration pathway. Alcohol, dopamine, and morphine, can alter intracellular levels of glutathione (GSH)-based cellular redox status, subsequently affecting SAM levels and DNA methylation status. Here, existing evidence is presented in a coherent manner to propose a novel hypothesis implicating the involvement of redox-based epigenetic changes in drug addiction. Further, we discuss how a "gene priming" phenomenon can contribute to the maintenance of redox and methylation status homeostasis under various stimuli including drugs of abuse. Additionally, a new mechanistic rationale for the use of metabolic interventions/redox-replenishers as symptomatic treatment of alcohol and other drug addiction and associated withdrawal symptoms is also provided. Hence, the current review article strengthens the hypothesis that neuronal metabolism has a critical bidirectional coupling with epigenetic changes in drug addiction exemplified by the link between redox-based metabolic changes and resultant epigenetic consequences under the effect of drugs of abuse.
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