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Background The nucleus accumbens in the midbrain dopamine limbic system plays a key role in cocaine addiction. Toll-like receptors (TLRs) are important pattern-recognition receptors (PPRs) in the innate immune system that are also involved in drug dependence; however, the detailed mechanism is largely unknown. Methods The present study was designed to investigate the potential role of TLR3 in cocaine addiction. Cocaine-induced conditioned place preference (CPP), locomotor activity, and self-administration were used to determine the effects of TLR3 in the rewarding properties of cocaine. Lentivirus-mediated re-expression of Tlr3 (LV-TLR3) was applied to determine if restoration of TLR3 expression in the NAc is sufficient to restore the cocaine effect in TLR3−/− mice. The protein levels of phospho-NF-κB p65, IKKβ, and p-IκBα both in the cytoplasm and nucleus of cocaine-induced CPP mice were detected by Western blot. Results We showed that both TLR3 deficiency and intra-NAc injection of TLR3 inhibitors significantly attenuated cocaine-induced CPP, locomotor activity, and self-administration in mice. Importantly, the TLR3−/− mice that received intra-NAc injection of LV-TLR3 displayed significant increases in cocaine-induced CPP and locomotor activity. Finally, we found that TLR3 inhibitor reverted cocaine-induced upregulation of phospho-NF-κB p65, IKKβ, and p-IκBα. Conclusions Taken together, our results describe that TLR3 modulates cocaine-induced behaviors and provide further evidence supporting a role for central pro-inflammatory immune signaling in drug reward. We propose that TLR3 blockade could be a novel approach to treat cocaine addiction. Electronic supplementary material The online version of this article (10.1186/s12974-018-1130-8) contains supplementary material, which is available to authorized users.

Supplementary material for ORF of LV-TLR3. (DOCX 14Â kb)

Nicotinamide phosphoribosyltransferase (NAMPT), a rate-limiting enzyme in nicotinamide adenine dinucleotide (NAD) biosynthesis in mammals, converts nicotinamide into nicotinamide mononucleotide (NMN). NMN is subsequently converted to NAD, a component that is critical for cell energy metabolism and survival. Sirtuin 1 (SIRT1), an NAD-dependent histone deacetylase, plays an important role in mediating memory and synaptic plasticity. Here, we found that NAMPT was significantly upregulated in the ventral tegmental area (VTA) of cocaine-conditioned mice. Intraperitoneal or intra-VTA injection of FK866, a specific inhibitor of NAMPT, significantly attenuated cocaine reward. However, such effects were clearly repressed by intra-VTA expression of NAMPT or supplementation with NMN. Using 1H-nuclear magnetic resonance metabolomic analysis, we found that the content of NAD and NMN were increased in the VTA of cocaine-conditioned mice; moreover, the expression of SIRT1 was also upregulated. Interestingly, the inhibitory effect of FK866 on cocaine reward was significantly weakened in Sirt1 midbrain conditional knockout mice. Our results suggest that NAMPT-mediated NAD biosynthesis may modify cocaine behavioral effects through SIRT1. Moreover, our findings reveal that the interplay between NAD biosynthesis and SIRT1 regulation may comprise a novel regulatory pathway that responds to chronic cocaine stimuli.

Recent evidence suggests that histone modifications play a role in the behavioral effects of cocaine in rodent models. Histone arginine is known to be methylated by protein arginineN-methyltransferases (PRMTs). Evidence shows that PRMT1 contributes to >90% of cellular PRMT activity, which regulates histone H4 arginine 3 asymmetric dimethylation (H4R3me2a). Though histone arginine methylation represents a chemical modification that is relatively stable compared with other histone alterations, it is less well studied in the setting of addiction. Here, we demonstrate that repeated noncontingent cocaine injections increase PRMT1 activity in the nucleus accumbens (NAc) of C57BL/6 mice. We, subsequently, identify a selective inhibitor of PRMT1, SKLB-639, and show that systemic injections of the drug decrease cocaine-induced conditioned place preference to levels observed with genetic knockdown of PRMT1. NAc-specific downregulation of PRMT1 leads to hypomethylation of H4R3me2a, and hypoacetylation of histone H3 lysine 9 and 14. We also found that H4R3me2a is upregulated in NAc after repeated cocaine administration, and that H4R3me2a upregulation in turn controls the expression ofCdk5andCaMKII. Additionally, the suppression of PRMT1 in NAc with lentiviral-short hairpin PMRT1 decreases levels ofCaMKIIandCdk5in the cocaine-treated group, demonstrating that PRMT1 affects the ability of cocaine to induceCaMKIIandCdk5in NAc. Notably, increased H4R3me2a by repeated cocaine injections is relatively long-lived, as increased expression was observed for up to 7 d after the last cocaine injection. These results show the role of PRMT1 in the behavioral effects of cocaine.SIGNIFICANCE STATEMENTThis work demonstrated that repeated cocaine injections led to an increase of protein arginineN-methyltransferase (PRMT1) in nucleus accumbens (NAc). We then identified a selective inhibitor of PRMT1 (SKLB-639), which inhibited cocaine-induced conditioned place preference (CPP). Additionally, genetic downregulation of PRMT1 in NAc also attenuated cocaine-caused CPP and locomotion activity, which was associated with decreased expression of histone H4 arginine 3 asymmetric demethylation (H4R3me2a) and hypoacetylation of histone H3 lysine 9 and 14 (acH3K9/K14). This study also showed that H4R3me2a controlled transcriptions of Cdk5 and CaMKII, and that PRMT1 negatively affected the ability of cocaine to induce CaMKII and Cdk5 in NAc. Notably, increased H4R3me2a by repeated cocaine injection was relatively long-lived as increased expression was observed up to 7 d after withdrawal from cocaine. Together, this study suggests that PRMT1 inhibition may serve as a potential therapeutic strategy for cocaine addiction.

Sorafenib, an active multi-kinase inhibitor, has been widely used as a chemotherapy drug to treat advanced clear-cell renal cell carcinoma patients. In spite of the relative safety, sorafenib has been shown to exert a negative impact on cognitive functioning in cancer patients, specifically on learning and memory; however, the underlying mechanism remains unclear. In this study, an NMR-based metabolomics approach was applied to investigate the neurochemical effects of sorafenib in rats. Male rats were once daily administrated with 120 mg/kg sorafenib by gavage for 3, 7, and 28 days, respectively. NMR-based metabolomics coupled with histopathology examinations for hippocampus, prefrontal cortex (PFC), and striatum were performed. The (1)H NMR spectra data were analyzed by using multivariate pattern recognition techniques to show the time-dependent biochemical variations induced by sorafenib. Excellent separation was obtained and distinguishing metabolites were observed between sorafenib-treated and control rats. A total of 36 differential metabolites in hippocampus of rats treated with sorafenib were identified, some of which were significantly changed. Furthermore, these modified metabolites mainly reflected the disturbances in neurotransmitters, energy metabolism, membrane, and amino acids. However, only a few metabolites in PFC and striatum were altered by sorafenib. Additionally, no apparent histological changes in these three brain regions were observed in sorafenib-treated rats. Together, our findings demonstrate the disturbed metabonomics pathways, especially, in hippocampus, which may underlie the sorafenib-induced cognitive deficits in patients. This work also shows the advantage of NMR-based metabolomics over traditional approach on the study of biochemical effects of drugs.

Background Nicotine is rapidly absorbed from cigarette smoke and therefore induces a number of chronic illnesses with the widespread use of tobacco products. Studies have shown a few cerebral metabolites modified by nicotine; however, endogenous metabolic profiling in brain has not been well explored. Results H NMR-based on metabonomics was applied to investigate the endogenous metabolic profiling of brain hippocampus, nucleus acumens (NAc), prefrontal cortex (PFC) and striatum. We found that nicotine significantly increased CPP in mice, and some specific cerebral metabolites differentially changed in nicotine-treated mice. These modified metabolites included glutamate, acetylcholine, tryptamine, glucose, lactate, creatine, 3-hydroxybutyrate and nicotinamide-adenine dinucleotide (NAD), which was closely associated with neurotransmitter and energy source. Additionally, glutathione and taurine in hippocampus and striatum, phosphocholine in PFC and glycerol in NAc were significantly modified by nicotine, implying the dysregulation of anti-oxidative stress response and membrane metabolism. Conclusions Nicotine induces significant metabonomic alterations in brain, which are involved in neurotransmitter disturbance, energy metabolism dysregulation, anti-oxidation and membrane function disruptions, as well as amino acid metabolism imbalance. These findings provide a new insight into rewarding effects of nicotine and the underlying mechanism.

Nicotine, one of the most commonly used drugs, has become a major concern because tobacco serves as a gateway drug and is linked to illicit drug abuse, such as cocaine and marijuana. However, previous studies mainly focused on certain genes or neurotransmitters which have already been known to participate in drug addiction, lacking endogenous metabolic profiling in a global view. To further explore the mechanism by which nicotine modifies the response to cocaine, we developed two conditioned place preference (CPP) models in mice. In threshold dose model, mice were pretreated with nicotine, followed by cocaine treatment at the dose of 2 mg/kg, a threshold dose of cocaine to induce CPP in mice. In high-dose model, mice were only treated with 20 mg/kg cocaine, which induced a significant CPP. (1)H nuclear magnetic resonance based on metabonomics was used to investigate metabolic profiles of the nucleus accumbens (NAc) and striatum. We found that nicotine pretreatment dramatically increased CPP induced by 2 mg/kg cocaine, which was similar to 20 mg/kg cocaine-induced CPP. Interestingly, metabolic profiles showed considerable overlap between these two models. These overlapped metabolites mainly included neurotransmitters as well as the molecules participating in energy homeostasis and cellular metabolism. Our results show that the reinforcing effect of nicotine on behavioral response to cocaine may attribute to the modification of some specific metabolites in NAc and striatum, thus creating a favorable metabolic environment for enhancing conditioned rewarding effect of cocaine. Our findings provide an insight into the effect of cigarette smoking on cocaine dependence and the underlying mechanism.