[The concentration of the chosen smoke toxicity biomarkers among smokers suffering from larynx cancer]

INTRODUCTION

An incidence of laryngeal cancer is strongly connected with exposure to tobacco smoke containing dozens of carcinogens. Genotoxic agents such as polycyclic aromatic hydrocarbons present in tobacco smoke are responsible for lesions of structure DNA and formation of DNA adducts by metabolically activated intermediates. Detecting the presence of DNA adducts in human tissues is therefore, a tool for studies of cancer. An evidence demonstrates that DNA adducts are useful markers of carcinogen exposure. The aim of this work was estimation of relationship between cigarette smoke exposure, determined as urinary cotinine and urinary 1-hydroxypyrene concentration, and number of aromatic-DNA adducts in blood lymphocytes.

MATERIAL AND METHODS

The study group consisted of 60 men at the age of 45 up to 65 years - 20 healthy non-smokers, 20 healthy current smokers and 20 current smokers with primary larynx cancer, which was classified histopathologically as squamous cell carcinoma. The cotinine and 1-hydroxypyrene were determined in the urine with high performance liquid chromatography. Analysis of DNA adducts was performed by the 32P - postlabelling method.

RESULTS

Urinary cotinine concentration in healthy smokers and cancer subjects in comparison with non-smokers was significant higher than in non-smokers, respectively, 29- and 31-fold higher but differences between healthy and sicks smokers were insignificant. Concentration of 1-hydroxypyrene in urine of healthy and cancer subjects was significantly higher (9- and 10-fold higher, respectively) compared with non-smokers. The highest level of aromatic-DNA adducts was found in lympfocytes of healthy smokers but differences between number of adducts in healthy smokers compared with non-smokers (+35%) and cancer subjects (+7,1%) were insignificant. The Pearson's coefficient (r) for the correlation between aromatic-DNA level and urinary cotinine or 1-hydroxypyrene concentration were significant only in cancer subjects group (r = 0,676, p = 0,011 and r = 0,465, p = 0,039, respectivelly).

CONCLUSIONS

The results suggest that cotinine and 1-hydroxypyrene concentration in urine are useful biomarkers of the tobacco smoke exposure. In contrast the levels of aromatic-DNA adducts in lymphocytes are not suitable for that purpose. It seems that none of investigated compounds are the risk predictor of larynx cancer.

[Nicotine addiction--diagnosis and treatment]

Smoking consumption prevention is part to the global health strategy of World Health Organisation. Nicotine has important psychotoxic activity but comparing to alcohol and heroin it doesn't determine social disintegrate. Nicotine attaches to specific acetylcholine receptors (nAChR) and their stimulation determines the active substances release. Dopamine release is associated with nicotine-seeking behaviour which provide the passing through "pleasure" to "request". The extent of nicotine dependence is estimated using the Fagestrom test. This is a questionnaire with 6 questions, with a number of points. The highest score is 10, but a score of 7 is associated with high dependence. Nicotine dependence must be regarded as a chronic disease. Practical advice, social support and a safe environment are the main elements of successful therapy.

Association of attentional network function with exon 5 variations of the CHRNA4 gene

Mutational analyses in xenopus oocyte and mice models indicate that the positive effect of nicotine on attention may be modulated by genetic variations within exon 5 of the alpha4 subunit of the nicotinergic acetylcholine receptor gene CHRNA4. The potential relevance of exon 5 is further emphasized by two recent family-based association studies of nicotine dependence because subgroups of nicotine-dependent subjects are thought to 'self-medicate' attentional deficits with nicotine. We investigated a synonymous single nucleotide polymorphisms (SNP): rs1044396, which has recently been associated with nicotine-dependence, plus two adjacent synonymous SNPs rs1044394 and rs1044393 in exon 5 of n = 47 unrelated healthy Caucasian subjects (age: 22.7 +/- 1.7 years; sex: n = 23 males; regular smokers: n = 19). Attentional network function was assessed in supplementary motor area/anterior cingulate (SMA/ACC) and parietal cortex with functional magnetic resonance imaging during an attention-requiring visual oddball task. SNP rs1044396 showed genotype effects on attentional network function both in the SMA/ACC and parietal cortex in the absence of overt behavioral effects. In the parietal cortex, a gene-dosage effect was seen. Comparable genotype effects were also found for the other two SNPs. This investigation provides first evidence that attentional network function may be modulated by genetic variations within CHRNA4 exon 5. If confirmed, future studies need to address what 'functional' polymorphisms are causative for the observed effects.

Anger and psychobiological changes during smoking abstinence and in response to acute stress: prediction of smoking relapse

Nicotine may be used to manage negative emotions, and recent research suggests that smokers with high levels of hostility may use cigarettes to cope with anger provoking situations. This study evaluated the extent to which a high level of trait anger is associated with risk for relapse among smokers interested in cessation. Chronic smokers with different levels of trait anger provided reports of withdrawal symptoms, craving, and state anger, and collected saliva samples for cortisol during 24-hour ad libitum smoking and the first 24-hour abstinence period of a quit attempt. They also attended a laboratory session conducted after the 24-hour abstinence during which they performed brief mental and social stress challenges and provided blood samples for adrenocorticotropin (ACTH) and cortisol assays. High trait anger was associated with greater increases in state anger, withdrawal symptoms, and craving during the first 24 h of abstinence. It was also associated with greater ACTH concentrations during the laboratory session. High trait anger was also associated with increased risk for early relapse. The findings support the hypothesis that smokers high in anger trait may have greater mood difficulties during abstinence and may be more vulnerable to early relapse than smokers with low anger trait.

Nicotine increases FosB expression within a subset of reward- and memory-related brain regions during both peri- and post-adolescence

INTRODUCTION

Periadolescent nicotine exposure is associated with increased consumption and rewarding properties of abused drugs. In the case of peri- but not post-adolescent animals, these effects are persistent and last to adulthood, suggesting that early nicotine treatment may alter postnatal CNS development in ways that contribute to long-term problems with drug abuse.

MATERIALS AND METHODS

To begin to identify brain regions that may be altered by developmental nicotine exposure, we have measured expression of a transcription factor, FosB, within a series of reward- and memory-related brain regions of Sprague-Dawley rats.

RESULTS

FosB expression is known to acutely and cumulatively increase within a subset of brain regions, particularly nucleus accumbens, after exposure to many classes of abused drugs. Our results demonstrate that FosB is increased within nucleus accumbens and also the granule cell layer of hippocampal dentate gyrus after both peri- and post-adolescent nicotine exposure (0.4 mg kg(-1) day(-1) from days 34 to 43 and 60 to 69, respectively). In periadolescents, expression increases were detected 2 days after nicotine exposure, and persisted for weeks, through at least early adulthood at 80 days of age. In post-adolescents, expression increases persisted for at least 11 days to postnatal day 80.

DISCUSSION

These findings demonstrate that nicotine treatment during both peri- and post-adolescence persistently alters activity of brain regions involved in reward and memory.

CONCLUSION

Because this altered gene expression occurs after both peri- and post-adolescent treatment, it cannot be directly responsible for increased consumption and rewarding properties of abused drugs previously established to be distinctly associated with periadolescent nicotine exposure.

The role of nicotinic acetylcholine receptors in the primary reinforcing and reinforcement-enhancing effects of nicotine

The primary reinforcing effects of nicotine are mediated by the drugs action at central nervous system nicotinic acetylcholine receptors (nAChRs). Although previous studies have demonstrated that nicotine potently enhances responding for non-pharmacological stimuli, the role of nAChRs in this reinforcement-enhancing effect is not known. The two reinforcement-related effects of nicotine can be dissociated in a paradigm that provides concurrent access to drug infusions and a non-pharmacological visual stimulus (VS). The present study characterized the role of nAChRs in the primary reinforcing effect of nicotine and the reinforcement-enhancing effect of nicotine. For rats with access to VS (VS-Only), nicotine (NIC-Only), both reinforcers contingent upon one response (NIC+VS) or both reinforcers contingent upon separate responses (2-Lever), unit dose-response relationships (0, 30, 60, or 90 microg/kg/infusion, free base) were determined over a 22-day acquisition period. Expression of the two reinforcement-related effects of nicotine was manipulated by pharmacological antagonism of nAChRs (1 mg/kg mecamylamine, subcutaneous, 5-min before the session) or by substituting saline for nicotine infusions (ie extinction) over a series of seven test sessions. Unit dose manipulations yielded an inverse dose-response relationship for active lever responding in the NIC+VS group. The dose-response relationships for rats with independent access to each reinforcer (2-Lever group) were relatively flat. For the 2-Lever group, acute mecamylamine challenge blocked the reinforcement-enhancing effects of nicotine, VS-lever responding decreased to basal levels on the first day of mecamylamine treatment or saline substitution (to the level of the VS-Only group). In contrast, nicotine-lever responding decreased gradually over the 7-day testing period (similar to saline extinction). The two reinforcement-related effects of nicotine are mediated by nAChRs but can be dissociated by acute and chronic profiles.

Tobacco use and dependence in Asian Americans: a review of the literature

This article reports on an integrative review of literature on Asian American tobacco use and dependence, identifies gaps in the literature, and proposes studies needed in the future. Articles were retrieved from electronic health-related databases indexed for permutations of the keywords Asian Americans, smoking, tobacco use, tobacco dependence, and nicotine dependence. A manual search also was done to identify additional literature. A total of 216 articles were identified; the review includes 39 articles reporting gender- and ethnic-specific information on subgroups of Asian Americans in the following areas: Smoking prevalence, correlates of smoking, and tobacco dependence treatment. In addition, 13 articles on tobacco and nicotine metabolism were reviewed. Empirical studies have concentrated on Chinese, Korean, and Vietnamese American men. Smoking prevalence is higher among Asian American men with low acculturation than among their counterparts, but the reverse pattern is observed among Asian American women. Asian Americans tend to smoke fewer cigarettes per day than White Americans, and this difference may be explained by differences between the two groups in nicotine metabolism. More research is needed on this diverse population, especially Asian American women of all ethnic subgroups and Asian Indian, Filipino, Pakistani, and Thai American men. A need also exists for the development of specialized tobacco dependence treatments to address the cultural issues of specific Asian American ethnic subgroups, to enhance access to treatment, and to determine how treatment recommendations should reflect differences in acculturation level and tobacco and nicotine metabolism.

Nornicotine inhibition of dopamine transporter function in striatum via nicotinic receptor activation

Nornicotine, a tobacco alkaloid and N-demethylated nicotine metabolite, releases DA from superfused rat striatal slices in a mecamylamine-sensitive manner, indicating nicotinic receptor (nAChR) modulation of this response. The current study determined the effect of nornicotine on rat striatal dopamine transporter (DAT) function using in vivo voltammetry. In a dose-related and mecamylamine-sensitive manner, nornicotine (0.35-12.0 mg/kg, s.c.) decreased DA clearance, suggesting that nornicotine inhibits striatal DAT function via a nAChR-mediated mechanism. Furthermore, the nAChRs mediating the nornicotine-induced inhibition of DAT function appear to be different from those activated by nicotine which increases DA clearance. Understanding the actions of nornicotine in brain may have significance for emerging therapeutics and for the management of nicotine dependence.

Nicotine and hippocampus-dependent learning: implications for addiction

Addiction is a complex disorder because many factors contribute to the development and maintenance of addiction. One factor is learning. For example, drug-context associations that develop during drug use could facilitate drug craving upon re-exposure to contexts previously associated with drugs. Additionally, deficits in cognitive processes associated with withdrawal could precipitate relapse in attempts to ameliorate those deficits. Because addiction and learning involve common neural areas and cell signaling cascades, addiction-related changes in processes underlying plasticity may contribute to addiction. This article examines similarities between addiction and learning at the behavioral, neural, and cellular levels, with emphasis on the neural substrates underlying the effects of acute nicotine, chronic nicotine, and withdrawal from chronic nicotine on hippocampus-dependent contextual learning.

Clinical laboratory evaluation of potential reduced exposure products for smokers

Smoking-related cancer and other disease account for more than 400,000 U.S. deaths annually. Smoking cessation reduces smoking-related disease rates, but relapse rates are high. Thus, interest in reducing the harm of continued smoking is growing. Potential reduced exposure products (PREPs) are marketed to reduce smokers' exposure to smoke toxicants such as carbon monoxide (CO) and carcinogens and may be harm reduction tools. New PREPs are proliferating, but past experience with "low-yield" cigarettes that failed to reduce smokers' toxicant exposure suggests that comprehensive evaluation is necessary to predict if these new products are likely to alter the harm caused by smoking. The purpose of the study was to develop clinical laboratory methods for PREP evaluation. Smokers (N = 35) completed four, 5-day conditions that differed by product used: Advance, Eclipse, own brand cigarettes, or no cigarettes. Carcinogen (as assessed by one nitrosamine and one polycyclic aromatic hydrocarbon biomarker) and nicotine exposure were assessed via thrice-weekly urine sampling. Withdrawal symptoms were measured daily, and smoking behavior was assessed on the first and last day of each condition. Relative to own brand, Advance reduced exposure to the nitrosamine NNK and CO, and Eclipse reduced exposure to nicotine and the nitrosamine NNK, increased exposure to CO, and resulted in larger, longer, and more frequent puffs. No smoking reduced exposure to the nitrosamine NNK, CO, and nicotine, whereas withdrawal was elevated (all p values <.05). Clinical laboratory evaluation of PREPs for smokers is valuable for measuring users' smoke toxicant exposure, withdrawal, and smoking behavior and should be incorporated into a comprehensive PREP evaluation strategy.

Effects of the selective dopamine D3 receptor antagonist SB-277011A on the reinforcing effects of nicotine as measured by a progressive-ratio schedule in rats

The dopamine D3 receptor is primarily localized within the mesocorticolimbic system, and may therefore have potential as a pharmacotherapeutic target for the treatment of drug dependence. Studies have shown that the selective dopamine D3 receptor antagonist SB-277011A reduces a variety of dependence-related behavioral effects of cocaine, alcohol and heroin. A previous study examining SB-277011A on nicotine self-administration using relatively low doses of the antagonist and a low response requirement for nicotine found no effect on drug-taking behavior per se, whereas reinstatement of nicotine-seeking was reduced. The purpose of the present study was to further examine the effects of higher doses of SB-277011A on nicotine self-administration in rats under a progressive-ratio (PR) schedule, which imposes relatively high response requirements for nicotine. Rats were trained to respond under a PR schedule of either nicotine or food reinforcement. Once responding was stable, SB-277011A (3-56 mg/kg) or vehicle was administered i.p. 1 h prior to the operant session. The highest dose tested significantly decreased the mean number of reinforcers and mean response rates in the nicotine self-administration group, but had no effect on either the mean number of reinforcers or response rate in the food group. In a separate set of experiments, the effects of SB-277011A on locomotor activity were measured. At the dose that significantly decreased nicotine self-administration, total distance traveled was also significantly decreased, suggesting that the effect on operant responding at the high dose of SB-277011A is at a threshold for motor effects and may not be directly mediated by an action at dopamine D3 receptors.

Smoking modulation of mu-opioid and dopamine D2 receptor-mediated neurotransmission in humans

This is a pilot examination of the hypothesis that some of the effects of smoking cigarettes in humans are mediated through nicotine activation of opioid and dopamine (DA) neurotransmission. Neuroimaging was performed using positron emission tomography and the radiotracers [11C]carfentanil and [11C]raclopride, labeling mu-opioid and DA D2 receptors, respectively. Six healthy male smokers were abstinent overnight. After radiotracer administration, subjects smoked two denicotinized cigarettes, followed 45 min later by two average nicotine cigarettes. Dynamic data were acquired over 90 min, and transformed into parametric maps of receptor availability in vivo (binding potential, BP), corresponding to low and high nicotine smoking periods and analyzed on a voxel-by-voxel basis using SPM'99 and correction for multiple comparisons. Significant activation of mu-opioid receptor-mediated neurotransmission from denicotinized to average nicotine conditions was observed in the right anterior cingulate cortex. DA D2 neurotransmission was activated in the ventral basal ganglia, correlating with Fagerström scale nicotine dependence scores. Lower mu-opioid receptor BP was also detected during the denicotinized smoking condition in the smoker group, compared to baseline scans in non-smokers, in the cingulate cortex, thalamus, ventral basal ganglia, and amygdala. These reductions were reversed during the average nicotine condition in the thalamus, ventral basal ganglia and amygdala. These data point to both the feasibility of simultaneously examining opioid and DA neurotransmission responses to smoking in humans, as well as to the need to examine non-nicotine aspects of smoking to more fully understand the behavioral effects of this drug.

Emerging concepts: novel integration of in vivo approaches to localize the function of nicotinic receptors

Nicotinic acetylcholine receptors (nAChRs) are important targets of the neuromodulator acetylcholine (ACh) and the drug nicotine. The role of their different subunits has been analysed for a decade by the creation of knock-out (KO) mice using homologous recombination. This technique shows that a given subunit is necessary for a given function. However, for ubiquitously expressed genes, it cannot demonstrate the localization for a given subunit in which its expression is sufficient, especially for behavioural phenotypes. Sufficient in this context means that the brain region requiring the expression of the gene product has been localized. Novel strategies have therefore been developed to re-express, region specifically, nAChR subunits on a KO background using lentiviral vectors. Localized regeneration of fully functional high-affinity nAChRs in defined brain regions has proven that these receptors are sufficient to restore a variety of functions: nicotine-induced dopamine release, nicotine self-administration in mice, dopamine neuron firing patterns, and exploratory and locomotor behaviours in a sequential locomotor task testing executive function were thus defined as depending exclusively on the 'knock-back' of beta2*-nAChRs into the ventral tegmental area. These analyses highlight the important role of endogenous cholinergic regulation of a variety of functions. The novel integrated use of restricted re-expressed nAChR subunits with in vivo electrophysiology and automated quantitative behavioural analysis enables the further analysis of defined neuronal circuits in nicotine addiction and higher cognitive function.

Differential effects of acute and chronic nicotine on Elk-1 in rat hippocampus

Transcriptional regulation is central to the long-term effects of drugs of abuse. Activation of the extracellular signal-regulated kinase (ERK1/2) pathway underlies plasticity changes that accompany drug use. One target of ERK1/2 activation is the Ets-like transcription factor Elk-1. We show here that nicotine modulates Elk-1 in the rat hippocampus in a spatially and temporally specific manner. In-vitro nicotine (1 muM) activated Elk-1 in hippocampal slices. In-vivo acute nicotine (0.4 mg/kg) activated Elk-1 in the CA1 area but not in the dentate gyrus. Chronic nicotine for 14 days changed the level of total Elk-1 but not its phosphorylation state. Thus, Elk-1 regulation of transcriptional events may contribute to nicotine-induced changes in the hippocampus.

The endocannabinoid system: Association with metabolic disorders and tobacco dependence

RACKGROUND: Obesity and smoking are major health problems globally as they are risk factors for cardiovascular disease. There appears to be a link between obesity and smoking which is manifested in the endocannabiniod system. This review aims to highlight the physiologic role of the endocannabinoid system and its possible therapeutic applications.

METHODS

Literature on the endocannabiniod system was reviewed using MEDLINE/PUBMED and bibliographic searches for English language studies.

RESULT

The endocannabiniod system is a physiological system that plays a significant role in the regulation of body metabolism, especially glucose and fat metabolism in addition to nicotine dependence with promising therapeutic application.

CONCLUSION

The discovery and insights into the functioning of the endocannabiniod system have made a way for new and effective therapeutic approaches. These therapies may provide an effective treatment for obesity and related risk factors for diabetes and cardiovascular disease as well as help people to stop smoking.

The pharmacological activity of nicotine and nornicotine on nAChRs subtypes: relevance to nicotine dependence and drug discovery

Cigarette smoking and other forms of tobacco use deliver an array of pharmacologically active alkaloids, including nicotine and ultimately various metabolites of these substances. While nornicotine is a significant component in tobacco as well as a minor systemic metabolite of nicotine, nornicotine appears to be N-demethylated locally in the brain where it accumulates at relatively high levels after chronic nicotine administration. We have now examined the effects of nornicotine on specific combinations of neuronal nicotinic acetylcholine receptor (nAChR) subunits expressed in Xenopus oocytes and compared these responses to those evoked by acetylcholine and nicotine. Of the nAChR subtypes studied, we have found that alpha7 receptors are very responsive to nornicotine (EC50 approximately 17 micromol/L I(max) 50%, compared with acetylcholine (ACh)). nAChRs containing the ligand-binding domain of the alpha6 subunits (in the form of an alpha6/alpha3 chimera) are also strongly responsive to nornicotine (EC50 approximately 4 micromol/L I(max) 50%, compared with ACh). Alpha7-type nAChRs have been suggested to be potential therapeutic targets for Alzheimer's disease, schizophrenia and possibly other pathologies. nAChRs containing alpha6 subunits have been suggested to have a role in nicotine-evoked dopamine release. Thus, understanding the actions of nornicotine in the brain may have significance for both emerging therapeutics and the management of nicotine dependence.

Dopamine D3receptor ligands for the treatment of tobacco dependence

This review considers the potential use of the dopamine D(3) receptor (DRD3) as a novel therapeutic target for the treatment of tobacco dependence. Among the 5 dopamine receptors identified, the DRD3 is located in the nucleus accumbens, ventral tegmental area and amygdala: 3 brain structures that are implicated in the motivational control of drug-seeking behaviour and drug-conditioning processes. Although it has been proposed that modulating dopamine transmission would be effective in the treatment of drug dependence, no validation has been provided in humans so far. Several highly selective DRD3 ligands have recently been evaluated in preclinical models of drug dependence. These ligands act as DRD3 antagonists in vivo and are able to decrease the motivation to take various drugs of abuse and reduce the influence of associated drug-conditioned behaviour. Of note is that these effects have been found with nicotine-seeking behaviour and nicotine relapse in rodents, suggesting a potential use of these ligands for the treatment of tobacco smokers. In contrast to nicotine replacement therapy, varenicline and bupropion (which are currently used for the treatment of smokers), DRD3 antagonists do not seem to produce nicotine-like effects in experimental animals and, therefore, may not substitute for nicotine or alleviate nicotine withdrawal symptoms in human smokers. This behavioural profile, which was also reported recently with cannabinoid CB(1) receptor antagonists, may result from effects on specific brain pathways that express DRD3 receptors and are involved in relapse and conditioning processes. These preclinical studies suggest that the clinical evaluation of DRD3 ligands should be performed with clinical trials designed specifically to evaluate the relapse phenomena.

Salivary cotinine concentration versus self-reported cigarette smoking: Three patterns of inconsistency in adolescence

The present study examined the extent and sources of discrepancies between self-reported cigarette smoking and salivary cotinine concentration among adolescents. The data are from household interviews with a cohort of 1,024 adolescents from an urban school system. Histories of tobacco use in the last 7 days and saliva samples were obtained. Logistic regressions identified correlates of three inconsistent patterns: (a) Pattern 1-self-reported nonsmoking among adolescents with cotinine concentration above the 11.4 ng/mg cutpoint (n = 176), (b) Pattern 2-low cotinine concentration (below cutpoint) among adolescents reporting having smoked within the last 3 days (n = 155), and (c) Pattern 3-high cotinine concentration (above cutpoint) among adolescents reporting not having smoked within the last 3 days (n = 869). Rates of inconsistency were high among smokers defined by cotinine levels or self-reports (Pattern 1 = 49.1%; Pattern 2 = 42.0%). Controlling for other covariates, we found that reports of nonsmoking among those with high cotinine (Pattern 1) were associated with younger age, having few friends smoking, little recent exposure to smokers, and being interviewed by the same interviewer as the parent and on the same day. Low cotinine concentration among self-reported smokers (Pattern 2) was negatively associated with older age, being African American, number of cigarettes smoked, depth of inhalation, and exposure to passive smoke but positively associated with less recent smoking and depressive symptoms. High cotinine concentrations among self-reported nonsmokers was positively associated with exposure to passive smoke (Pattern 3). The data are consonant with laboratory findings regarding ethnic differences in nicotine metabolism rate. The inverse relationship of cotinine concentration with depressive symptoms has not previously been reported. Depressed adolescent smokers may take in smaller doses of nicotine than nondepressed smokers; alternatively, depressed adolescents may metabolize nicotine more rapidly.

Memantine fails to facilitate partial cigarette deprivation in smokers – no role of Memantine in the treatment of nicotine dependency?

The efficacy of Memantine in the treatment of nicotine dependency in humans remained to be evaluated. The aims of our pilot study were to investigate (1) the effectiveness of Memantine in facilitating smoking reduction and (2) the influence of Memantine on the perception of nicotine. In order to achieve these aims we conducted a placebo controlled double-blind parallel group study in smokers (n = 20 per group). Before the beginning of the treatment-phase (10/20 mg Memantine per day) all participants were instructed to reduce smoking (partial deprivation). Before and during partial deprivation we registered the daily cigarette consumption and craving estimates. Following nasal stimulation with nicotine enantiomers hedonic and intensity estimates and the discrimination ability were assessed. Memantine failed to facilitate smoking reduction and did not influence the perception of nicotine with the exception of a weak reduction of olfactory intensity estimates reaching statistical significance for one nicotine enantiomer only.

Effects of isoarecolone, a nicotinic receptor agonist in rodent models of nicotine dependence

RATIONALE

The nicotinic receptor agonist, isoarecolone, has 'nicotine-like' subjective properties as detected by rats in a discrimination paradigm. However, isoarecolone lacks the intra-accumbens dopamine-releasing effects, a feature akin to most abused substances. In the five-choice serial reaction time task, isoarecolone can enhance attention and thus may be developed as a cognitive enhancer.

OBJECTIVE

The present experiments assess the dependence profile of isoarecolone in rodent models of nicotine dependence.

METHOD AND RESULTS

Tests for cross-substitution in which isoarecolone is substituted for nicotine [0.3 mg/kg/infusion (inf)] self-administration suggest isoarecolone to have nominal reinforcing properties (0.3 or 1.0 mg/kg/inf); intake of isoarecolone declined over three test sessions in which responding was no different from saline extinction, and behaviour was reinstated by re-presenting nicotine. In a model of nicotine-seeking behaviour, rats having been extinguished by removal of nicotine (0.03 mg/kg/inf) and associated cues, the presentation of priming doses of nicotine (0.1-0.4 mg/kg s.c.) with the cues robustly reinstated responding of nicotine-seeking behaviour. Tests with priming doses of isoarecolone (1-20 mg/kg s.c.) shown previously to generalise to nicotine in discrimination tests produced significant levels of reinstatement but the responses were significantly less compared to nicotine-induced reinstatement.

CONCLUSION

Overall, these results suggest that isoarecolone with its unique profile of behavioural activity should be further examined for treating chronic diseases that are characterised by attentional dysfunction.

Neurochemical and behavioral effects of bupropion and mecamylamine in the presence of nicotine

The primary mechanism of action of bupropion, a smoking cessation drug, is commonly believed to involve the dopaminergic system although evidence exists that bupropion also has effects at nicotinic acetylcholine receptors (nAChRs). This study evaluated the disruptive effects of nicotine on response rates in the presence of bupropion and the nAChR antagonist, mecamylamine, as well as the ability of these drugs to alter nicotine-stimulated nAChR function in various brain areas. Rats were trained to respond on a single lever under a variable interval 15 (VI15) schedule for food reinforcement. Initially, dose effect curves were generated for nicotine, bupropion and mecamylamine. Upon determining the dose of nicotine (1.2 mg/kg) effective in completely disrupting rates of responding, it was established that both mecamylamine and bupropion block nicotine's rate-reducing effects. This result suggests that bupropion shares behavioral effects with mecamylamine when administered in the presence of nicotine. To explore this relationship further, the effect of in vivo administration of bupropion or mecamylamine on nicotine-stimulated (86)Rb(+) efflux was studied in synaptosomes prepared from the frontal cortex, hippocampus, striatum and thalamus. Nicotine-stimulated (86)Rb(+) efflux from all brain regions was significantly reduced in rats administered 3.0 mg/kg mecamylamine (s.c.) 15 min prior to dissection compared to control rats. In contrast, a significant increase in nicotine-stimulated (86)Rb(+) efflux was observed in all brain regions from rats administered 30.0 mg/kg bupropion (s.c.) 15 min prior to dissection compared to control rats. Taken together these results demonstrate that when administered in the presence of nicotine, bupropion elicits unique pharmacological differences such that it exhibits both nAChR agonist- and antagonistic-like effects.

Nicotine-induced changes of glutamate and arginine in naive and chronically alcoholized rats: An in vivo microdialysis study

The effects of nicotine, when administered either acutely or chronically, at doses of 0.15, 0.3 or 0.6 mg/kg, on the release of glutamate and arginine in the rat nucleus accumbens have been studied in microdialysis experiments. Glutamate release significantly increased after acute nicotine injection, 0.3 mg/kg, which was accentuated if there was a priming regime of saline for the previous 27 days. This is possibly related to the rewarding effects of nicotine. Five hours after cessation of chronic oral nicotine administration, there were significant increases in glutamate content, which was possibly reflective of a withdrawal process. Significant decreases in nucleus accumbens arginine release were evident, between 1 and 2 h, after chronic nicotine administration. When nicotine was co-administered to rats during chronic ethanol intoxication, at either 0.15 mg/kg or 0.3 mg/kg doses, glutamate release did not increase during the first 12 h of withdrawal. However, a decrease in arginine microdialysate content was still observed with all nicotine doses. The nicotine-induced changes in glutamate and arginine release in nucleus accumbens highlights the complex neuropharmacological interactions evoked by this compound and also identified its possible modulating effect on glutamate release during the initial stages of chronic ethanol withdrawal.

Cigarette smoking saturates brain alpha 4 beta 2 nicotinic acetylcholine receptors

CONTEXT

2-[18F]fluoro-3-(2(S)-azetidinylmethoxy) pyridine (2-F-A-85380, abbreviated as 2-FA) is a recently developed radioligand that allows for visualization of brain alpha 4 beta 2* nicotinic acetylcholine receptors (nAChRs) with positron emission tomography (PET) scanning in humans.

OBJECTIVE

To determine the effect of cigarette smoking on alpha 4 beta 2* nAChR occupancy in tobacco-dependent smokers.

DESIGN

Fourteen 2-FA PET scanning sessions were performed. During the PET scanning sessions, subjects smoked 1 of 5 amounts (none, 1 puff, 3 puffs, 1 full cigarette, or to satiety [2(1/2) to 3 cigarettes]).

SETTING

Academic brain imaging center.

PARTICIPANTS

Eleven tobacco-dependent smokers (paid volunteers). Main Outcome Measure Dose-dependent effect of smoking on occupancy of alpha 4 beta 2* nAChRs, as measured with 2-FA and PET in nAChR-rich brain regions.

RESULTS

Smoking 0.13 (1 to 2 puffs) of a cigarette resulted in 50% occupancy of alpha 4 beta 2* nAChRs for 3.1 hours after smoking. Smoking a full cigarette (or more) resulted in more than 88% receptor occupancy and was accompanied by a reduction in cigarette craving. A venous plasma nicotine concentration of 0.87 ng/mL (roughly 1/25th of the level achieved in typical daily smokers) was associated with 50% occupancy of alpha 4 beta 2* nAChRs.

CONCLUSIONS

Cigarette smoking in amounts used by typical daily smokers leads to nearly complete occupancy of alpha 4 beta 2* nAChRs, indicating that tobacco-dependent smokers maintain alpha 4 beta 2* nAChR saturation throughout the day. Because prolonged binding of nicotine to alpha 4 beta 2* nAChRs is associated with desensitization of these receptors, the extent of receptor occupancy found herein suggests that smoking may lead to withdrawal alleviation by maintaining nAChRs in the desensitized state.

Nicotinic receptor agonists as neuroprotective/neurotrophic drugs. Progress in molecular mechanisms

In the present work we reviewed recent advances concerning neuroprotective/neurotrophic effects of acute or chronic nicotine exposure, and the signalling pathways mediating these effects, including mechanisms implicated in nicotine addiction and nAChR desensitization. Experimental and clinical data largely indicate long-lasting effects of nicotine and nicotinic agonists that imply a neuroprotective/neurotrophic role of nAChR activation, involving mainly alpha7 and alpha4beta2 nAChR subtypes, as evidenced using selective nAChR agonists. Compounds interacting with neuronal nAChRs have the potential to be neuroprotective and treatment with nAChR agonists elicits long-lasting neurotrophic effects, e.g. improvement of cognitive performance in a variety of behavioural tests in rats, monkeys and humans. Nicotine addiction, which is mediated by interaction with nACh receptors, is believed to involve the modification of signalling cascades that modulate synaptic plasticity and gene expression. Desensitization, in addition to protecting cells from uncontrolled excitation, is recently considered as a form of signal plasticity. nAChR can generate these longe-lasting effects by elaboration of complex intracellular signals that mediate medium to long-term events crucial for neuronal maintenance, survival and regeneration. Although a comprehensive survey of the gene-based molecular mechanisms that underlie nicotine effects has yet not been performed a growing amount of data is beginning to improve our understanding of signalling mechanisms that lead to neurotrophic/neuroprotective responses. Evidence for an involvement of the fibroblast growth factor-2 gene in nAChR mechanisms mediating neuronal survival, trophism and plasticity has been obtained. However, more work is needed to establish the mechanisms involved in the effects of nicotinic receptor subtype activation from cognition-enhancing and neurotrophic effects to smoking behaviour and to determine more precisely the therapeutic objectives in potential nicotinic drug treatments of neurodegenerative diseases.