M Imad Damaj

Virginia Commonwealth University, Richmond, Virginia, United States

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Publications (140)568.45 Total impact

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    ABSTRACT: Diseases associated with tobacco use constitute a major health problem worldwide. Upon cessation of tobacco use, an unpleasant withdrawal syndrome occurs in dependent individuals. Avoidance of the negative state produced by nicotine withdrawal represents a motivational component that promotes continued tobacco use and relapse after smoking cessation. With the modest success rate of currently available smoking cessation therapies, understanding mechanisms involved in the nicotine withdrawal syndrome are crucial for developing successful treatments. Animal models provide a useful tool for examining neuroadaptative mechanisms and factors influencing nicotine withdrawal, including sex, age, and genetic factors. Such research has also identified an important role for nicotinic receptor subtypes in different aspects of the nicotine withdrawal syndrome (e.g., physical vs. affective signs). In addition to nicotinic receptors, the opioid and endocannabinoid systems, various signal transduction pathways, neurotransmitters, and neuropeptides have been implicated in the nicotine withdrawal syndrome. Animal studies have informed human studies of genetic variants and potential targets for smoking cessation therapies. Overall, the available literature indicates that the nicotine withdrawal syndrome is complex, and involves a range of neurobiological mechanisms. As research in nicotine withdrawal progresses, new pharmacological options for smokers attempting to quit can be identified, and treatments with fewer side effects that are better tailored to the unique characteristics of patients may become available. Copyright © 2014. Published by Elsevier Ltd.
    Neuropharmacology 11/2014; · 4.11 Impact Factor
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    ABSTRACT: Background and PurposeAbrupt discontinuation of nicotine, the main psychoactive component in tobacco, induces a withdrawal syndrome in nicotine-dependent animals, consisting of somatic and affective signs, avoidance of which contributes to drug maintenance. While blockade of fatty acid amide hydrolase (FAAH), the primary catabolic enzyme of the endocannabinoid arachidonoylethanolamine (anandamide; AEA), exacerbates withdrawal responses in nicotine-dependent mice, the role of monoacylglycerol lipase (MAGL), the main hydrolytic enzyme of a second endocannabinoid 2-arachidonylglycerol (2-AG), in nicotine withdrawal remains unexplored.Experimental ApproachesTo evaluate the role of MAGL enzyme inhibition in nicotine withdrawal, we initially performed a genetic correlation approach using the BXD recombinant inbred mouse panel. We then assessed nicotine withdrawal intensity in the mouse after treatment with the selective MAGL inhibitor JZL184 and after genetic deletion of the enzyme. Lastly, we assessed the association between genotypes and smoking withdrawal phenotypes in two human data sets.Key ResultsBXD mice displayed significant positive correlations between basal MAGL mRNA expression and nicotine withdrawal responses, consistent with the idea that increased 2-AG brain levels may attenuate withdrawal responses. Strikingly, the MAGL inhibitor JZL184 dose-dependently reduced somatic and aversive withdrawal signs, which was blocked by rimonabant, indicating a CB1 receptor-dependent mechanism. MAGL-knockout mice also showed attenuated nicotine withdrawal. Lastly, genetic analyses in humans revealed associations of the MAGL gene with smoking withdrawal in humans.Conclusion and ImplicationsOverall, our findings suggest that MAGL inhibition maybe a promising target for treatment of nicotine dependence.
    British Journal of Pharmacology 09/2014; · 5.07 Impact Factor
  • Pamela Flood, M Imad Damaj
    Anesthesia and analgesia. 08/2014; 119(2):232-233.
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    ABSTRACT: Mesolimbic α6* nicotinic acetylcholine receptors (nAChRs) are thought to play an important role in nicotine behavioral effects. However, little is known about the role of the various α6*-nAChRs subtypes in the rewarding effects of nicotine. In this report, we investigated and compared the role of α6*-nAChRs subtypes and their neuro-anatomical locus in nicotine and cocaine reward-like effects in the conditioned place preference (CPP) paradigm, using pharmacological antagonism of α6β2* nAChRs and genetic deletion of the α6 or α4 subunits in mice. We found that α6 KO mice exhibited a rightward shift in the nicotine dose-response curve compared to WT littermates, but that α4 KO failed to show nicotine preference, suggesting that α6α4β2*-nAChRs are involved. Furthermore, α6β2* nAChRs in nucleus accumbens were found to play an important role in nicotine conditioned reward since the intra-accumbal injection of the selective α6β2* α-Conotoxin MII [H9A; L15A], blocked nicotine CPP. In contrast to nicotine, α6 KO failed to condition to cocaine, but cocaine CPP in the α4 KO was preserved. Intriguingly, α-Conotoxin MII [H9A; L15A], blocked cocaine conditioning in α4 KO mice, implicating α6β2* nAChRs in cocaine reward. Importantly, these effects did not generalize as α6 KO showed both a conditioned place aversion to lithium chloride as well as CPP to palatable food. Lastly, dopamine uptake was not different between the α6 KO or WT mice. These data illustrate that the subjective rewarding effects of both nicotine and cocaine may be mediated by mesolimbic α6β2* nAChRs and that antagonists of these receptor subtypes may exhibit therapeutic potential.Neuropsychopharmacology accepted article preview online, 18 July 2014; doi:10.1038/npp.2014.177.
    Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology 07/2014; · 8.68 Impact Factor
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    ABSTRACT: Metabolism of nicotine to inactive cotinine by hepatic enzyme CYP2A6 is the principal pathway by which active nicotine is removed from circulation. We therefore hypothesized that inhibition of mouse CYP2A5, the orthologue of human CYP2A6, by methoxsalen (8-methoxypsoralen) should block nicotine metabolism and decrease its subsequent systemic clearance. Consequently, methoxsalen will alter dependence-related behaviors of nicotine in the mouse. In the first part of the study, a conditioned place preference (CPP) test was used in animals to explore the appetitive reward-like properties of nicotine. In the second part of the study, mice chronically exposed to nicotine were challenged with mecamylamine, a nicotinic antagonist, and tested for physical (somatic and hyperalgesia) and affective (anxiety-related behaviors) precipitated withdrawal signs. The nicotine plasma levels were also measured with or without methoxsalen pretreatment. Methoxsalen (15 and 30 mg/kg, intraperitoneally) pretreatment 15 min before nicotine (0.1 mg/kg, subcutaneously) induced a significant enhancement of nicotine-induced preference in mice (p<0.05). This potentiation was significantly accompanied by an increase in nicotine plasma levels (p<0.05). However, there was a lack of enhancement of nicotine in the CPP test after the highest dose of the CYP-2A5 inhibitor. Similarly to the CPP results, repeated administration of methoxsalen with nicotine increased the intensity of mecamylamine-precipitated withdrawal signs on test day. The potentiation of withdrawal intensity by methoxsalen was accompanied by significant increase in nicotine plasma levels in these mice (p<0.05). Finally, methoxsalen enhanced the ability of nicotine to reverse withdrawal signs in mice undergoing spontaneous withdrawal after chronic nicotine infusion. Spontaneous withdrawal from chronic nicotine administration (36 mg/kg/day in minipumps for 7 days) significantly increased the number of somatic signs and induced hyperalgesia after mini pumps removal (p<0.05). Interestingly, methoxsalen (30 mg/kg, intraperitoneally) pretreatment significantly enhanced the reversal of these withdrawal signs by a very low dose of nicotine (0.05 mg/kg, subcutaneously) (p<0.05). In conclusion, inhibition of nicotine metabolism by methoxsalen apparently enhances nicotine's bioavailability and alters the behavioral effects of nicotine in the mouse. Combining CYP2A6 inhibitors with low dose nicotine replacement therapies may have a beneficial role in smoking cessation because it will decrease the drug elimination rate and maintain plasma and brain nicotine levels.
    Neuropharmacology 05/2014; · 4.11 Impact Factor
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    ABSTRACT: Background and PurposeRecent data have indicated that α3β4* neuronal nicotinic acetylcholine receptors (nAChRs) may play a role in morphine dependence. Here we investigated if nAChRs modulate morphine physical withdrawal.Experimental ApproachesTo assess the role of α3β4* neuronal nicotinic acetylcholine receptors in morphine withdrawal, we used a genetic correlation approach using publically available data sets within the GeneNetwork web resource, genetic knockout and pharmacological tools. Lastly, male and female European-American (n=2,772) and African-American (n=1,309) subjects from the SAGE dataset were used to assess the possible association of polymorphisms in the 15q25 gene cluster and opioid dependence.Key ResultsBXD recombinant mouse lines demonstrated an increase in expression of α3, β4, and α5 nAChR mRNA in the forebrain and midbrain, which significantly correlates with an increase in defecation in mice undergoing morphine withdrawal. Indeed, mice with overexpression of the gene cluster CHRNA5/A3/B4 exhibited an increase in somatic signs of withdrawal. Furthermore, α5 and β4 nAChR knockout mice expressed decreased somatic withdrawal signs compared to their wildtype counterparts. Moreover, selective α3β4* nAChR antagonists, α-conotoxin AuIB (AuIB) and AT-1001, attenuated somatic signs of morphine withdrawal in a dose-related manner. In addition, two human datasets revealed a protective role for variants in the CHRNA3 gene, which codes for the α3 nAChR subunit, in opioid dependence and withdrawal. In contrast, we found that the α4β2* nAChR subtype is not involved in morphine somatic withdrawal signs.Conclusion and ImplicationsOverall, our findings suggest an important role for the α3β4* nAChR subtype in morphine physical dependence.
    British Journal of Pharmacology 04/2014; · 5.07 Impact Factor
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    ABSTRACT: 2'-Fluoro-3-(substituted pyridine)epibatidine analogues 7a-e and 8a-e were synthesized and their in vitro and in vivo nAChR properties determined. 2'-Fluoro-3'-(4"-pyridinyl)deschloroepibatidine (7a) and 2'-fluoro-3'-(3"-pyridinyl)deschloroepibatidine (8a) were synthesized as bioisosteres of the 4'-nitrophenyl lead compounds 5a and 5g. Comparison of the in vitro nAChR properties of 7a and 8a to those of 5a and 5g showed that 7a and 8a had in vitro nAChR properties similar to those of 5a and 5g, but both were more selective for the α4β2-nAChR relative to the α3β4- and α7-nAChRs than 5a and 5g. The in vivo nAChR properties in mice of 7a were similar to those of 5a. In contrast, 8a was an agonist in all four mouse acute tests, whereas 5g was active only in a spontaneous activity test. In addition, 5g was a nicotine antagonist in both the tail-flick and hot-plate tests, whereas as 8a was only an antagonist in the tail-flick test.
    Journal of Medicinal Chemistry 01/2014; · 5.61 Impact Factor
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    ABSTRACT: Metabolism of nicotine to inactive cotinine by hepatic enzyme CYP2A6 is the principal pathway by which active nicotine is removed from circulation. We therefore hypothesized that inhibition of mouse CYP2A5, the ortolog of human CYP2A6, by methoxsalen (8-methoxypsoralen) alter dependence-related behaviors of nicotine in the mouse. Conditioned place preference (CPP) test was used to assess the appetitive reward-like properties and precipitated nicotine withdrawal to assess physical (somatic and hyperalgesia) and affective (anxiety-related behaviors) measures. The nicotine plasma levels were also measured with or without methoxsalen pretreatment. Methoxsalen (15 and 30 mg/kg, intraperitoneally) pretreatment enhanced nicotine-induced preference in mice (p < 0.05). However, there was a lack of enhancement of nicotine in the CPP test after the highest dose of the CYP-2A5 inhibitor. Similarly to the CPP results, repeated administration of methoxsalen increased the intensity of mecamylamine-precipitated withdrawal signs. The potentiation of nicotine preference and withdrawal intensity by methoxsalen was accompanied by significant increase in nicotine plasma levels in mice (p < 0.05). Finally, methoxsalen enhanced the ability of a very low dose of nicotine (0.05 mg/kg) to reverse withdrawal signs in mice undergoing spontaneous withdrawal after chronic nicotine infusion (p < 0.05). In conclusion, inhibition of nicotine metabolism by methoxsalen alters the behavioral effects of nicotine in the mouse. Combining CYP2A6 inhibitors with low dose nicotine replacement therapies may have a beneficial role in smoking cessation because it will decrease the drug elimination rate and maintain plasma and brain nicotine levels.
    Neuropharmacology 01/2014; 85:67–72. · 4.11 Impact Factor
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    ABSTRACT: Bupropion, introduced as an antidepressant in the 1980s, is also effective as a smoking cessation aid and is beneficial in the treatment of methamphetamine addiction, cocaine dependence, addictive behaviors such as pathological gambling, and attention deficit hyperactivity disorder. (2S,3S)-hydroxybupropion is an active metabolite of bupropion produced in humans that contributes to antidepressant and smoking cessation efficacy and perhaps benefits in other CNS disorders. Mechanisms underlying its antidepressant and smoking abstinence remain elusive. However, it seems likely that efficacy is due to a combination of the effects of bupropion and/or its active metabolite (2S,3S)-hydroxybupropion involving the inhibition of reuptake of dopamine (DA) and NE in reward centers of the brain and the noncompetitive antagonism of α4β2- and α3β4*-nAChRs. These combined effects of bupropion and its active metabolite may be responsible for its ability to decrease nicotine reward and withdrawal. Studies directed toward development of a bupropion analog for treatment of cocaine addiction led to compounds, typified by 2-(N-cyclopropylamino)-3'-chloropropiophenone (RTI-6037-39), thought to act as indirect DA agonists. In addition, (2S,3S)-hydroxybupropion analogs were developed, which had varying degrees of DA and NE uptake inhibition and antagonism of nAChRs. These compounds will be valuable tools for animal behavioral studies and as clinical candidates. Here, we review the (1) early studies leading to the development of bupropion, (2) bupropion metabolism and the identification of (2S,3R)-hydroxybupropion as an active metabolite, (3) mechanisms of bupropion and metabolite action, (4) effects in animal behavioral studies, (5) results of clinical studies, and (6) development of bupropion analogs as potential pharmacotherapies for treating nicotine and cocaine addiction.
    Advances in pharmacology (San Diego, Calif.) 01/2014; 69:177-216.
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    ABSTRACT: Mortality from tobacco smoking remains the leading cause of preventable death in the world, yet current cessation therapies are only modestly successful, suggesting new molecular targets are needed. Genetic analysis of gene expression and behavior identified Chrna7 as potentially modulating nicotine place conditioning in the BXD panel of inbred mice. We used gene targeting and pharmacological tools to confirm the role of Chrna7 in nicotine CPP. To identify molecular events downstream of Chrna7 that may modulate nicotine preference, we performed microarray analysis of α7 KO and WT nucleus accumbens tissue, followed by confirmation with quantitative PCR and immunoblotting. In the BXD panel, we found a putative cis eQTL for Chrna7 in nucleus accumbens that correlated inversely to nicotine CPP. We observed that gain-of-function α7 mice did not display nicotine preference at any dose tested, while conversely, α7 KO mice showed nicotine place preference at a dose below that routinely required to produce preference. In B6 mice, the α7 nAChR-selective agonist, PHA-543613, dose-dependently blocked nicotine CPP, which was restored using the α7 nAChR-selective antagonist, MLA. Our genomic studies implicated an mRNA co-expression network regulated by Chrna7 in nucleus accumbens. Mice lacking Chrna7 demonstrate increased insulin signaling in the nucleus accumbens, which may modulate nicotine place preference. Our studies provide novel targets for future work on development of more effective therapeutic approaches to counteract the rewarding properties of nicotine for smoking cessation.
    Genes Brain and Behavior 11/2013; · 3.60 Impact Factor
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    ABSTRACT: A previous characterization of mecamylamine stereoisomers using nicotinic acetylcholine receptors expressed in Xenopus oocytes revealed only small differences between the activity of the R and S forms of mecamylamine. However, that work was limited in the breadth of receptor subtypes tested, especially in regard to the discrimination of high and low sensitivity receptors, which differ in the ratios of alpha and beta subunits. We report new data using subunit concatamers, which produce uniform populations of high-sensitivity or low-sensitivity receptors, as well as alpha2, alpha5, and alpha6-containing receptors, which were not studied previously. Consistent with previous studies, we found that beta4-containing receptors were most sensitive to mecamylamine and that the IC50 values for the inhibition of net charge were lower than for inhibition of peak currents. No large differences were seen between the activities of the mecamylamine isomers. Additionally, a previously reported potentiation of high-sensitivity α4β2 receptors by S-mecamylamine could not be reproduced in the oocyte system, even with mutants that had greatly reduced sensitivity to mecamylamine inhibition or when the selective agonist TC-2559 was used. In vivo studies suggested that the R-isomer might be somewhat more potent than the S isomer at blocking CNS effects of nicotine. Although the potency difference was no more than a factor of two, it is consistent with lower LD50 estimates previously reported for the R isomer. Our results significantly extend knowledge of the nicotinic acetylcholine receptor activity profile of mecamylamine and support the hypothesis that these effects are not strongly stereoisomer selective.
    European journal of pharmacology 10/2013; · 2.59 Impact Factor
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    ABSTRACT: A growing body of evidence indicates that α7 nicotinic receptor subtypes play an important role in chronic inflammatory and neuropathic pain signaling. In the present study, we investigated the role of the endogenous α7 nicotinic receptors (nAChRs) signaling in pain and inflammation using transgenic mice. For that we evaluated pain-related behaviors in the α7 mutant mice (KO) and its complementary α7 hypersensitive mice (KI) expressing expressing the L250T α7 nAChRs and their respective WT mice in acute, chronic inflammatory and neuropathic mouse models. α7 KO and KI mice showed no signficant changes in pain responses evoked by acute noxious thermal and mechanical stimuli as compared with WT litermates. While α7 KO mice showed no alterations in thermal and mechanical allodynia comapred to WT mice after chronic nerve injury in the CCI test, α7 KI mice showed a signficant reduction in these pain-related responses. However, marked increase in edema, hyperalgesia, and allodynia associated with intraplantar CFA injection was observed in the α7 KO mice compared with the WT littermates. In contrast, α7 KI mice displayed lesser degree of hyperalgesia and allodynia after CFA injection. Finally, the ability of systemic nicotine to reverse already-developed mechanical allodynia produced by intraplantar CFA seen in WT mice was lost in the α7 KO animals. Overall, our results demonstrate that endogenous α7 nAChRs mechanisms play an important role in chronic inflammatory and neuropathic pain models. This provides an additional rationale for the utility of α7 nAChR agonists in the treatment of inflammatory and chronic pain.
    Biochemical pharmacology 06/2013; · 4.25 Impact Factor
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    ABSTRACT: Smoking rates among individuals with schizophrenia are significantly higher than the general population. One possible explanation for this comorbidity is that there are shared genes and biological pathways between smoking and schizophrenia. The histidine triad nucleotide binding protein 1 (HINT1) is a potential candidate, as genetic association and expression studies implicate the gene in both schizophrenia and nicotine dependence; however, the behavioral role of HINT1 in nicotine dependence is unknown. Thus, the goal of the current study was to determine the behavioral role of HINT1 in nicotine dependence. We tested male HINT1 wild-type (+/+) and knockout (-/-) mice in the nicotine conditioned place preference (CPP) test of reward, a nicotine withdrawal model assessing both physical and affective signs, and the nicotine withdrawal conditioned place aversion (CPA) test. HINT1 -/- mice failed to develop a significant nicotine CPP and physical withdrawal signs (hyperalgesia and somatic signs) were attenuated in HINT1 -/- mice. Conversely, HINT1 -/- mice developed a significant nicotine withdrawal CPA similar to their++ counterparts. Overall, our data support a role for the HINT1 gene in mediating behaviors associated with nicotine reward and physical nicotine withdrawal, and provide insight into the role of HINT1 in nicotine dependence-like behaviors.
    Neuroscience Letters 06/2013; · 2.03 Impact Factor
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    ABSTRACT: Background and PurposeThe α7 nicotinic ACh receptor subtype is abundantly expressed in the CNS and in the periphery. Recent evidence suggests that α7 nicotinic ACh receptor (nAChR) subtypes, which can be activated by an endogenous cholinergic tone comprising ACh and the α7 agonist choline, play an important role in chronic pain and inflammation. In this study, we evaluated whether type II α7 positive allosteric modulator PNU-120596 induces antinociception on its own and in combination with choline in the formalin pain model. Experimental ApproachWe assessed the effects of PNU-120596 and choline and the nature of their interactions in the formalin test using an isobolographic analysis. In addition, we evaluated the interaction of PNU-120596 with PHA-54613, an exogenous selective α7 nAChR agonist, in the formalin test. Finally, we assessed the interaction between PNU-120596 and nicotine using acute thermal pain, locomotor activity, body temperature and convulsing activity tests in mice. Key ResultsWe found that PNU-120596 dose-dependently attenuated nociceptive behaviour in the formalin test after systemic administration in mice. In addition, mixtures of PNU-120596 and choline synergistically reduced formalin-induced pain. PNU-120596 enhanced the effects of nicotine and α7 agonist PHA-543613 in the same test. In contrast, PNU-120596 failed to enhance nicotine-induced convulsions, hypomotility and antinociception in acute pain models. Surprisingly, it enhanced nicotine-induced hypothermia via activation of α7 nAChRs. Conclusions and ImplicationsOur results demonstrate that type II α7 positive allosteric modulators produce antinociceptive effects in the formalin test through a synergistic interaction with the endogenous α7 agonist choline.
    British Journal of Pharmacology 06/2013; 169(3). · 5.07 Impact Factor
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    ABSTRACT: RATIONALE: Whereas cannabinoid CB1 receptors have long been known to contribute to the rewarding effects and dependence liability of many drugs of abuse, recent studies have implicated the involvement of cannabinoid CB2 receptors. OBJECTIVE: Here, we evaluated the role of CB2 receptors in the rewarding properties of nicotine, as assessed in the conditioned place preference (CPP) paradigm and mecamylamine-precipitated withdrawal in nicotine dependent mice. METHODS: Using complementary pharmacological and genetic approaches, we investigated the involvement of CB2 receptors in nicotine- and cocaine-induced CPP in mice and mecamylamine-precipitated withdrawal in nicotine-dependent mice. We also determined whether deletion of CB2 receptors affects nicotine-induced hypothermia and hypoalgesia. RESULTS: Nicotine-induced (0.5 mg/kg) CPP was completely blocked by selective CB2 antagonist, SR144528 (3 mg/kg) in wild-type mice, and was absent in CB2 (-/-) mice. Conversely, the CB2 receptor agonist, O-1966 (1, 3, 5, 10, 20 mg/kg) given in combination with a subthreshold dose of nicotine (0.1 mg/kg) elicited a place preference. In contrast, O-1966 (20 mg/kg) blocked cocaine (10 mg/kg)-induced CPP in wild type mice, while CB2 (-/-) mice showed unaltered cocaine CPP. CB2 (+/+) and (-/-) nicotine-dependent mice showed almost identical precipitated withdrawal responses and deletion of CB2 receptor did not alter acute somatic effects of nicotine. CONCLUSIONS: Collectively, these results indicate that CB2 receptors are required for nicotine-induced CPP in the mouse, while it is not involved in nicotine withdrawal or acute effects of nicotine. Moreover, these results suggest that CB2 receptors play opposing roles in nicotine- and cocaine-induced CPP.
    Psychopharmacology 05/2013; · 4.06 Impact Factor
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    ABSTRACT: RATIONALE: Several studies suggest that repeated nicotine administration causes alterations in glutaminergic transmission that may play an important role in developing and maintaining nicotine addiction. Chronic nicotine administration in rats decreases the expression of the glutamate transporter-1 (GLT-1) and cysteine-glutamate exchanger (system xC-) in the nucleus accumbens. We hypothesized that ceftriaxone, a GLT-1 and system xC- activator, would decrease murine behavioral aspects of nicotine dependence. OBJECTIVE: This study aimed to investigate the effect of repeated ceftriaxone administration on the behavioral effects of nicotine using mouse models of conditioned reward and withdrawal. METHOD: Using male ICR mice, the ability of repeated ceftriaxone injections to modulate the development and reinstatement of a nicotine-conditioned place preference (CPP) was evaluated. Additionally, nicotine withdrawal-associated signs were assessed. These included both physical (somatic signs and hyperalgesia) and affective (anxiety-related behaviors) withdrawal signs in mice. Finally, the effects of ceftriaxone on nicotine-induced antinociception and hypothermia after acute nicotine injection were measured. RESULT: Ceftriaxone had no effect on the development of nicotine preference but significantly attenuated nicotine-induced reinstatement of CPP. Furthermore, ceftriaxone reversed all nicotine withdrawal signs measured in mice. CONCLUSION: Altogether, these findings show that a β-lactam antibiotic reduces nicotine withdrawal and nicotine-seeking behavior. Our results suggest that the documented efficacy of ceftriaxone against cocaine and morphine dependence-related behaviors effects extends to nicotine.
    Psychopharmacology 03/2013; · 4.06 Impact Factor
  • Anton Dawson, Micheal F Miles, M Imad Damaj
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    ABSTRACT: The high co-morbidity between alcohol (ethanol) and nicotine abuse suggests that nicotinic acetylcholine receptors (nAChRs), thought to underlie nicotine dependence, may also be involved in alcohol dependence. The β2* nAChR subtype serves as a potential interface for these interactions since they are the principle mediators of nicotine dependence and have recently been shown to modulate some acute responses to ethanol. Therefore, the aim of this study was to more fully characterize the role of β2* nAChRs in ethanol-responsive behaviors in mice after acute exposure to the drug. We conducted a battery of tests in mice lacking the β2* coding gene (Chrnb2) or pretreated with a selective β2* nAChR antagonist for a range of ethanol-induced behaviors including locomotor depression, hypothermia, hypnosis, and anxiolysis. We also tested the effect of deletion on voluntary escalated ethanol consumption in an intermittent access two-bottle choice paradigm to determine the extent of these effects on drinking behavior. Our results showed that antagonism of β2* nAChRs modulated some acute behaviors, namely by reducing recovery time from hypnosis and enhancing the anxiolytic-like response produced by acute ethanol in mice. Chrnb2 deletion had no effect on ethanol drinking behavior, however. We provide further evidence that β2* nAChRs have a measurable role in mediating specific behavioral effects induced by acute ethanol exposure without affecting drinking behavior directly. We conclude that these receptors, along with being key components in nicotine dependence, may also present viable candidates in the discovery of the molecular underpinnings of alcohol dependence.
    Alcohol (Fayetteville, N.Y.) 03/2013; 47(2):85-94. · 2.41 Impact Factor
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    ABSTRACT: The 15q25 gene cluster contains genes that code for the α5, α3, and β4 nicotinic acetylcholine receptor (nAChRs) subunits, and in human genetic studies, has shown the most robust association with smoking behavior and nicotine dependence to date. The limited available animal studies implicate a role for the α5 and β4 nAChR subunits in nicotine dependence and withdrawal; however studies focusing on the behavioral role of the α3β4* nAChR receptor subtype in nicotine dependence are lacking. Because of the apparent role of the α3β4* nAChR subtype in nicotine dependence, the goal of the current study was to better evaluate the involvement of this subtype in nicotine mediated behavioral responses. Using the selective α3β4* nAChR antagonist, α-conotoxin AuIB, we assessed the role of α3β4* nAChRs in acute nicotine, nicotine reward, and physical and affective nicotine withdrawal. Because α5 has also been implicated in nicotine dependence behaviors in mice and can form functional receptors with α3β4*, we also evaluated the role of the α3β4α5* nAChR subtype in nicotine reward and somatic nicotine withdrawal signs by blocking the α3β4* nAChR subtype in α5 nAChR knockout mice with AuIB. AuIB had no significant effect on acute nicotine behaviors, but dose-dependently attenuated nicotine reward and physical withdrawal signs, with no significant effect in affective withdrawal measures. Interestingly, AuIB also attenuated nicotine reward and somatic signs in α5 nAChR knockout mice. This study shows that α3β4* nAChRs mediate nicotine reward and physical nicotine withdrawal, but not acute nicotine behaviors or affective nicotine withdrawal signs in mice. The α5 subunit is not required in the receptor assembly to mediate these effects. Our findings suggest an important role for the α3β4* nAChR subtype in nicotine reward and physical aspects of the nicotine withdrawal syndrome.
    Neuropharmacology 02/2013; 70C:228-235. · 4.11 Impact Factor
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    ABSTRACT: OBJECTIVE Early onset of regular smoking is associated with an elevated risk for later nicotine dependence. Whether or not this association is causal is unknown and has substantial public policy implications. METHOD The authors used a monozygotic co-twin control study design. Pairs were selected from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders for discordance in age at onset of regular smoking. Nicotine dependence was measured by the Fagerström Test for Nicotine Dependence and level of craving. RESULTS The authors identified 175 male-male and 69 female-female monozygotic twin pairs who differed by at least 2 years in age at onset of regular smoking. During their period of heaviest smoking, the twin who began smoking earlier had significantly higher Fagerström Test scores in both the male-male (Cohen's d=0.20) and female-female twin pairs (d=0.26). Craving for cigarettes when unable to smoke was also higher in the early-onset member in both groups (male pairs, d=0.38; female pairs, d=0.25). The early-onset smoking twin did not differ from the later-onset twin in symptoms of alcohol or cannabis abuse or dependence, current alcohol use, or maximal level of cannabis, sedative, stimulant, or cocaine use. CONCLUSIONS Controlling for genetic and familial-environmental effects, age at onset of regular smoking predicted level of nicotine dependence. Consistent with the animal literature, these findings suggest that in humans, early nicotine exposure directly increases level of later nicotine dependence. These results should be interpreted in the context of the methodological strengths and limitations of the monozygotic co-twin design.
    American Journal of Psychiatry 01/2013; · 14.72 Impact Factor
  • Kia J Jackson, M Imad Damaj
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    ABSTRACT: Nicotinic acetylcholine receptors are calcium-permeable and the initial targets for nicotine. Studies suggest that calcium-dependent mechanisms mediate some behavioral responses to nicotine; however, the post-receptor calcium-dependent mechanisms associated with chronic nicotine and nicotine withdrawal remain unclear. The proteins calcium/calmodulin-dependent protein kinase II (CaMKII) and synapsin I are essential for neurotransmitter release and were shown to be involved in drug dependence. In the current study, using pharmacological techniques, we sought to (a) complement previously published behavioral findings from our lab indicating a role for calcium-dependent signaling in nicotine dependence and (b) expand on previously published acute biochemical and pharmacological findings indicating the relevance of calcium-dependent mechanisms in acute nicotine responses by evaluating the function of CaMKII and synapsin I after chronic nicotine and withdrawal in the nucleus accumbens, a brain region implicated in drug dependence. Male mice were chronically infused with nicotine for 14 days, and treated with the β2 -selective antagonist dihydro-β-erythroidine (DHβE), or the α7 antagonist, methyllycaconitine citrate (MLA) 20minutes prior to dissection of the nucleus accumbens. Results show that phosphorylated and total CaMKII and synapsin I protein levels were significantly increased in the nucleus accumbens after chronic nicotine infusion, and reduced after treatment with DHβE, but not MLA. A spontaneous nicotine withdrawal assessment also revealed significant reductions in phosphorylated CaMKII and synapsin I levels 24h after cessation of nicotine treatment. Our findings suggest that post-receptor calcium-dependent mechanisms associated with nicotine withdrawal are mediated through β2-containing nicotinic receptors.
    European journal of pharmacology 01/2013; · 2.59 Impact Factor

Publication Stats

3k Citations
568.45 Total Impact Points

Institutions

  • 1993–2014
    • Virginia Commonwealth University
      • • Department of Pharmacology and Toxicology
      • • Department of Psychiatry
      • • Department of Medicinal Chemistry
      Richmond, Virginia, United States
  • 2013
    • King Saud University
      • College of Pharmacy
      Riyadh, Mintaqat ar Riyad, Saudi Arabia
  • 2001–2012
    • Research Triangle Park Laboratories, Inc.
      Raleigh, North Carolina, United States
  • 2010
    • Barrow Neurological Institute
      • Division of Neurobiology
      Phoenix, AZ, United States
    • RTI International
      • Division of Organic and Medicinal Chemistry
      Durham, North Carolina, United States
    • University of Richmond
      Richmond, Virginia, United States
  • 2000–2002
    • University of Camerino
      • Dipartimento di Scienze Chimiche
      Matelica, The Marches, Italy
  • 1999
    • Duke University Medical Center
      Durham, North Carolina, United States