Nicotine Pretreatment Research Articles

Effects and mechanisms of the inflammatory reaction related to NASH and induced by activation of the cholinergic anti-inflammatory pathway

To investigate the effects and mechanisms of the inflammatory reaction related to nonalcoholic steatohepatitis (NASH) and induced by activation of the cholinergic anti-inflammatory pathway. A mouse model of NASH was established by feeding a high-fat and high-sugar diet.Activation of the cholinergic anti-inflammatory pathway was achieved by nicotine administration to the NASH modeled mice and normal controls. Liver biopsies were taken and the concentrations of cytokines were measured. Isolated liver primary Kupffer cells and RAw264.7 cells were cultured, pre-treated or not with lipopolysaccharide (LPS) and exposed to nicotine, after which the supernatant concentrations of IL-6 and TNFa were determined by ELISA. The protein expression levels of phosphorylated (p)-NF-kB and I k B were detected in primary cultured Kupffer cells by western blotting. The mouse model of NASH was successfully established, as evidenced by findings from liver biopsy and serum liver function tests. The degree of liver inflammation in the NASH mice decreased after nicotine administration, and the level of serum TNFa also significantly decreased. The levels of serum TNFa were 21.95+/-0.8 pg/mL in nicotine-treated mice and 38.07+/-1.7 pg/mL in the non-nicotine-treated NASH mice (P less than 0.05). The nicotine treatment also significantly reduced the concentration of TNFa in the culture supernatants of Kupffer cells after LPS stimulation; moreover, the supernatant level of TNFa decreased significantly after the nicotine treatment (Pless than 0.05). LPS stimulation of the RAw264.7 cells led to an increased level ofp-NF-kB and a reduced level ofI-kB, suggesting that the NF-kB pathway had been activated; different doses of nicotine pre-treatment led to down-regulation of the p-NF-kB level and up-regulation of the I-kB level, both in dose-dependent manners. Activating the cholinergic anti-inflammatory pathway inhibits the NASH-related inflammatory reaction, and the mechanism for this inhibition involves the NF-kB signaling pathway.

Monocyte CD40 expression in young healthy female smokers and/or oral contraceptives users without additional risk factors for atherosclerosis

ObjectiveAtherosclerosis, as an inflammatory disease, is characterized by pathologically altered levels of cytokines. We investigated whether smoking and/or oral contraceptives (OCs) affect the CD40/CD40L plasma levels and expression in young females without other risk factors for atherosclerosis. Patients and MethodsA case-control single-center design was used. Expression levels of CD40/CD40L were analyzed in healthy non-pregnant, pre-menopausal, non-smoking women who did not take OCs (n=49), women who currently smoke and take OCs (n=40), and women who are only smokers (n=40) or currently take OCs (n=42). ResultsIn OC users, there was a significant increase in CD40 mRNA expression in circulating monocytes as compared with smokers and control group. However, there were no significant differences in CD40 mRNA expression in monocytes between smokers and non-smokers. Interestingly, CD40 mRNA expression in women taking OCs and currently smoking was significantly decreased compared to only OC users (p<0.001). With regard to plasma CD40 levels there were significant differences between OC-users and control group. However, contrary to our expectations, there were no significant differences in expression levels of CD40L between four groups. In vitro experiments demonstrated enhanced CD40 mRNA and surface expression in human monocyte-derived macrophages stimulated with estrogens. Furthermore, nicotine pretreatment led to a suppression of estrogens stimulated CD40 induction. ConclusionsIn young healthy females without additional risk factors for atherosclerosis, OCs, but not smoking, are associated with dramatic changes in CD40 gene and plasma levels. These findings may be providing an important link between OCs and enhancement of pro-inflammatory and atherothrombotic conditions in healthy women.

Regulation of cerebral CYP2D alters tramadol metabolism in the brain: interactions of tramadol with propranolol and nicotine

1. Cytochrome P450 2D (CYP2D) protein is widely expressed across brain regions in human and rodents. We investigated the interactions between tramadol, a clinically used analgesic, and brain CYP2D regulators, by establishing concentration–time curves of tramadol and O-desmethyltramadol (M1) in rat cerebrospinal fluid (CSF) and plasma, as well as by analyzing the analgesia-time course of tramadol.2. Propranolol (20 μg, intracerebroventricular injection), CYP2D inhibitor, prolonged the elimination t1/2 of tramadol (40 mg/kg, intraperitoneal injection) in the CSF; meanwhile, lower Cmax and AUC0–∞ values of M1 were observed. Nicotine (1 mg base/kg, subcutaneous injection, seven days), brain CYP2D inducer, induced a shorter Tmax and elevated Cmax of M1 in CSF. No differences in the peripheral metabolism of tramadol were observed following propranolol and nicotine pretreatment. Nicotine increased areas under the analgesia-time curve (AUC) for 0–45 min and 0–90 min of tramadol, which was attenuated by propranolol administration. The analgesic actions of tramadol positively correlated with cerebral M1 concentration.3. The results suggest that the regulation of brain CYP2D by xenobiotics may cause drug–drug interactions (DDIs) of tramadol. Brain CYPs may play an important role in DDIs of centrally active substances.

The incentive amplifying effects of nicotine are reduced by selective and non-selective dopamine antagonists in rats

Nicotine is a psychomotor stimulant with ‘reinforcement enhancing’ effects — the actions of nicotine in the brain increase responding for non-nicotine rewards. We hypothesized that this latter effect of nicotine depends on increased incentive properties of anticipatory cues; consistent with this hypothesis, multiple laboratories have reported that nicotine increases sign tracking, i.e. approach to a conditioned stimulus (CS), in Pavlovian conditioned-approach tasks. Incentive motivation and sign tracking are mediated by mesolimbic dopamine (DA) transmission and nicotine facilitates mesolimbic DA release. Therefore, we hypothesized that the incentive-promoting effects of nicotine would be impaired by DA antagonists. To test this hypothesis, separate groups of rats were injected with nicotine (0.4mg/kg base) or saline prior to Pavlovian conditioning sessions in which a CS (30s illumination of a light or presentation of a lever) was immediately followed by a sweet reward delivered in an adjacent location. Both saline and nicotine pretreated rats exhibited similar levels of conditioned approach to the reward location (goal tracking), but nicotine pretreatment significantly increased approach to the CS (sign tracking), regardless of type (lever or light). The DAD1 antagonist SCH-23390 and the DAD2/3 antagonist eticlopride reduced conditioned approach in all rats, but specifically reduced goal tracking in the saline pretreated rats and sign tracking in the nicotine pretreated rats. The non-selective DA antagonist flupenthixol reduced sign-tracking in nicotine rats at all doses tested; however, only the highest dose of flupenthixol reduced goal tracking in both nicotine and saline groups. The reductions in conditioned approach behavior, especially those by SCH-23390, were dissociated from simple motor suppressant effects of the antagonists. These experiments are the first to investigate the effects of dopaminergic drugs on the facilitation of sign-tracking engendered by nicotine and they implicate dopaminergic systems both in conditioned approach as well as the incentive-promoting effects of nicotine.

Chronic nicotine pretreatment is sufficient to upregulate α4* nicotinic receptors and increase oral nicotine self-administration in mice.

BackgroundUnderstanding the underlying causes of nicotine addiction will require a multidisciplinary approach examining the key molecular, cellular and neuronal circuit functional changes that drive escalating levels of nicotine self-administration. In this study, we examined whether mice pretreated with chronic nicotine, at a dosing regimen that results in maximal nicotinic acetylcholine receptor (nAChR) upregulation, would display evidence of nicotine-dependent behaviour during nicotine self-administration.ResultsWe investigated oral self-administration of nicotine using a two-bottle choice paradigm in which one bottle contained the vehicle (saccharine-sweetened water), while the other contained nicotine (200 μg/ml) in vehicle. Knock-in mice with YFP-tagged α4 nAChR subunits (α4YFP) were implanted with osmotic pumps delivering either nicotine (2 mg/kg/hr) or saline for 10 days. After 10 days of pretreatment, mice were exposed to the nicotine self-administration paradigm, consisting of four days of choice followed by three days of nicotine abstinence repeated for five weeks. Mice pre-exposed to nicotine had upregulated α4YFP nAChR subunits in the hippocampal medial perforant path and on ventral tegmental area GABAergic neurons as compared to chronic saline mice. Compared to control saline-pretreated mice, in a two bottle-choice experiment, nicotine-primed mice ingested a significantly larger daily dose of nicotine and also exhibited post-abstinence binge drinking of nicotine.ConclusionsChronic forced pre-exposure of nicotine is sufficient to induce elevated oral nicotine intake and supports the postulate that nAChR upregulation may be a key factor influencing nicotine self-administration.

Mechanisms of Metabonomic for a Gateway Drug: Nicotine Priming Enhances Behavioral Response to Cocaine with Modification in Energy Metabolism and Neurotransmitter Level

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. 1H 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.

Prolonged nicotine exposure down-regulates presynaptic NMDA receptors in dopaminergic terminals of the rat nucleus accumbens

The presynaptic control of dopamine release in the nucleus accumbens (NAc) by glutamate and acetylcholine has a profound impact on reward signaling. Here we provide immunocytochemical and neurochemical evidence supporting the co-localization and functional interaction between nicotinic acetylcholine receptors (nAChRs) and N-methyl-D-aspartic acid (NMDA) receptors in dopaminergic terminals of the NAc. Most NAc dopaminergic terminals possessed the nAChR α4 subunit and the pre-exposure of synaptosomes to nicotine (30 μM) or to the α4β2-containing nAChR agonist 5IA85380 (10 nM) selectively inhibited the NMDA (100 μM)-evoked, but not the 4-aminopyridine (10 μM)-evoked, [3H] dopamine outflow; this inhibition was blunted by mecamylamine (10 μM). Nicotine and 5IA85380 pretreatment also inhibited the NMDA (100 μM)-evoked increase of calcium levels in single nerve terminals, an effect prevented by dihydro-β-erythroidine (1 μM). This supports a functional interaction between α4β2-containing nAChR and NMDA receptors within the same terminal, as supported by the immunocytochemical co-localization of α4 and GluN1 subunits in individual NAc dopaminergic terminals. The NMDA-evoked [3H]dopamine outflow was blocked by MK801 (1 μM) and inhibited by the selective GluN2B-selective antagonists ifenprodil (1 μM) and RO 25-6981 (1 μM), but not by the GluN2A-preferring antagonists CPP-19755 (1 μM) and ZnCl2 (1 nM). Notably, nicotine pretreatment significantly decreased the density of biotin-tagged GluN2B proteins in NAc synaptosomes. These results show that nAChRs dynamically and negatively regulate NMDA receptors in NAc dopaminergic terminals through the internalization of GluN2B receptors.

Nicotine modulation of adolescent dopamine receptor signaling and hypothalamic peptide response

Adolescence is a sensitive developmental period for limbic and dopamine systems that coincides with the typical age for onset of tobacco use. We have previously shown that a 4-day, low-dose nicotine (0.06 mg/kg) pretreatment enhances locomotor and penile response to the D2-like agonist, quinpirole (0.4 mg/kg), in adolescent but not adult rats. The present study is designed to determine mechanisms underlying this effect. Nicotine enhancement of adolescent quinpirole-induced locomotion was mediated by D2 receptors (D2Rs) since it was blocked by the D2R antagonist, L-741,626, but not by the D3R and D4R antagonists, NGB 2904 and L-745,870. Enhancement of quinpirole-induced erectile response was blocked by both L-741,626 and NGB 2904, indicating involvement of D3Rs. Whereas D2R binding was unaffected by adolescent nicotine pretreatment, effector coupling in the striatum was increased, as determined by GTPγS binding. Nicotine pretreatment enhanced quinpirole-induced c-fos mRNA expression in the hypothalamic paraventricular and supraoptic nuclei in adolescents only. Adolescent nicotine pretreatment enhanced c-fos mRNA expression in corticotropin releasing factor (CRF) cells of the paraventricular nucleus, and enhancement of penile erection was blocked by the CRF-1 receptor antagonist, CP 376,396. These findings suggest that adolescent dopamine and CRF systems are vulnerable to alteration by nicotine. This is the first evidence for a role of CRF in adolescent erectile response.

Age-dependent alterations in reward-seeking behavior after brief nicotine exposure

Adolescence is a developmental period that coincides with the onset of tobacco use. Teen smokers are also more likely to abuse other drugs compared to nonsmokers. Previous studies with rats have shown that low-dose nicotine pretreatment enhances initial acquisition of cocaine self-administration when given during early adolescence, but not at later ages. The aim of the present study was to determine whether these nicotine pretreatment effects extend to extinction and reinstatement of reward-seeking behavior. Adolescent [postnatal day (P)28] and adult rats (P86) were pretreated for 4 days with nicotine (60 μg/kg, i.v.) or saline. Following pretreatment, rats were allowed to nose poke for cocaine (500 μg/kg/infusion) or sucrose pellets for at least 12 days or until meeting acquisition criterion. Responding was then extinguished for at least 7 days or until extinction criterion was met. The following day, the rats were reinstated with either a priming injection of cocaine (10 mg/kg, i.p.) or sucrose pellets. Nicotine markedly enhanced extinction of cocaine self-administration in adolescent rats, but not adults. Pretreatment also enhanced the acquisition of cocaine self-administration in adolescents, while reducing discrimination for the reinforced hole in adults. There were no pretreatment or age effects on cocaine-induced reinstatement. In contrast, nicotine induced only minor enhancement of sucrose-taking behavior in adolescents, with no significant impact on extinction or reinstatement at either age. Nicotine pretreatment affects reward-related behavior in both an age- and reward-dependent manner. These findings show that brief nicotine exposure during early adolescence enhances drug-related learning.

Nicotine increases lifespan and rescues olfactory and motor deficits in a Drosophila model of Parkinson's disease

Drosophila melanogaster is an attractive model of familial Parkinson's disease, as flies with loss-of-function mutations of the parkin gene exhibit many pathologies observed in PD patients. Progressive motor deficits found in homozygous parkin mutants seem to result from mitochondrial pathology that causes indirect flight muscle and dopaminergic neuronal degeneration [1,2]. We have found that heterozygous parkin mutants have decreased lifespan, generally progressive motor dysfunction and olfactory deficits compared to control flies, suggesting that mutation of this gene produces a dominant phenotype. Tobacco smokers are dose-dependently less likely to develop PD [3,4]; subsequent in vitro and in vivo studies show that nicotine is protective in models of sporadic PD [6]. Literature addressing the potential protection by nicotine in Parkin loss-of-function models spans limited concentrations and selected time points in the organism's lifespan. We have found that parkin heterozygotes have late-onset climbing and flying deficits as well as decreased viability and olfactory deficits that precede motor defects. While chronic nicotine exposure decreases lifespan and climbing and flying abilities in control flies, it can improve viability and flying capability as well as rescue climbing and olfactory deficits in parkin heterozygotes. Dopaminergic neurons are spared in the parkin heterozygote, perhaps because this phenotype is less severe than in the homozygous parkin mutants. Nicotine pretreatment may be protective in sporadic PD patients and models; however, timely diagnosis remains to be an obstacle. Our results suggest that nicotine also may be protective in familial PD patients, who can be easily identified before motor symptoms occur.

Nicotine reduces established levodopa‐induced dyskinesias in a monkey model of Parkinson's disease

Although 3,4-dihydroxyphenylalanine (levodopa) is the gold-standard treatment for Parkinson's disease, it can lead to disabling dyskinesias. Previous work demonstrated that nicotine reduces levodopa-induced dyskinesias (LIDs) in several parkinsonian animal models. The goal of this study was to determine whether the duration of nicotine administration affects its ability to reduce LIDs in levodopa-primed and levodopa-naíve monkeys and also to test whether tolerance develops to the beneficial effects of nicotine. Monkeys were injected with MPTP (1.9-2.0 mg/kg subcutaneously) over 3 to 5 months until parkinsonism developed. Nicotine (300 μg/mL) was administered in drinking water (over 4-6 months) to levodopa-primed or levodopa-naíve monkeys, with levodopa/carbidopa (10/2.5 mg/kg) gavaged twice daily. One set of MPTP-lesioned monkeys (n = 23) was first gavaged with levodopa and subsequently received nicotine 4 weeks later, when dyskinesias plateaued, or 8 weeks later, when dyskinesias were established. A 60% to 70% decrease in LIDs was observed after several weeks of nicotine treatment in both groups. A second set of monkeys (n = 26) received nicotine 8 or 2 weeks before levodopa. In the 8-week nicotine pretreatment group, there was an immediate reduction in LIDs, which plateaued at 60% to 70%. In the 2-week nicotine pretreatment group, there were initial small decreases in LIDs, which plateaued at 60% to 70% several weeks later. Thus, nicotine pretreatment and nicotine post-treatment were similarly efficacious in reducing LIDs. The beneficial effect of nicotine persisted throughout the study (17-23 weeks). Nicotine did not worsen parkinsonism. These data suggest that nicotine treatment has potential as a successful antidyskinetic therapy for patients with Parkinson's disease.

Effect of nicotine pretreatment on cardiac function following myocardial ischemia-reperfusion in rats

Objective To evaluate the effect of nicotine pretreatment on cardiac function following myocardial ischemia-reperfusion (I/R) in rats.Methods Sixty male Sprague-Dawley rats,weighing 200-250 g,were randomly divided into 3 groups (n =20 each):sham operation group (group S),group I/R and nicotine pretreatment group (group N).The rats were anesthetized with intraperitoneal 20％ urethane 1 g/kg,tracheostomized and mechanically ventilated.Myocardial ischemia was induced by occlusion of the left anterior descending branch of coronary artery for 30 min followed by 120 min of reperfusion.The left anterior descending branch of coronary artery was only exposed,but not occluded in group S.Nicotine 400 μg/kg was injected intravenously via the right jugular vein at 30 min before myocardial ischemia in group N.The equal volume of normal saline was injected instead in groups S and I/R.Before ischemia,at 30 min of ischemia and at 30 and 120 min of reperfusion,10 rats from each group were chosen for record of left ventricular systolic pressure (LVSP),left ventricular diastolic pressure (LVDP),± dp/dtmax,HR and mean arterial pressure (MAP).Blood samples were collected from the right carotid artery of the left 10 rats in each group at 60 min of reperfusion to measure plasma CK-MB activity and cTnI and TNF-α concentrations.Results Compared with group S,MAP and LVSP at T2,3 and HR,LVDP and ± dp/dtmax at T1-3 were significantly decreased,and the plasma CK-MB activity and cTnI and TNF-α concentrations were increased in group I/R,and LVDP at T1,2 and HR and ± dp/dtmax at T1-3 were significantly decreased,and the plasma CK-MB activity and cTnI and TNF-α concentrations were increased in group N (P ＜ 0.05).Compared with group I/R,MAP,HR,LVSP,LVDP and ± dp/dtmax were significantly increased at T3,and the plasma CK-MB activity and cTnI and TNF-α concentrations were decreased in group N (P ＜ 0.05).Conclusion Nicotine pretreatment can reduce myocardial I/R injury through activating cholinergic anti-inflammatory pathway,thus improving cardiac function in rats. Key words: Cholinergic Agents; Myocardial reperfusion injury; Heart function tests

Effect of nicotine pretreatment on arsenic-induced oxidative stress in male Wistar rats

Humans are commonly exposed to nicotine, one of the most important lifestyle chemicals. The occurrence of high levels of arsenic in the groundwater of the southeast region of Asia has received much attention in the past decade and has become a global health concern. Predominant occurrence of both these chemicals and ease of their human exposure led us to investigate the effect of nicotine, a major tobacco alkaloid, on arsenic toxicity. Adult male rats were pre-exposed to two different doses of nicotine (0.75 and 3 mg/kg, intraperitoneally) for 7 days followed by 30 days of arsenic exposure (50 ppm sodium arsenite in drinking water). Nicotine pre-exposure resulted in an increased brain arsenic accumulation and a decreased liver arsenic concentration. Arsenic also caused a significant oxidative stress in the blood, brain and liver of the exposed rats. Glutathione-S-transferase, a phase II enzyme, was inhibited by both arsenic and nicotine but no such inhibition was noted in arsenic-treated animals pre-exposed to nicotine. Upon nicotine pre-exposure, brain acetylcholinesterase increased, while monoamine oxidase (MAO) decreased. The toxic effects of MAO significantly attenuated with nicotine pre-exposure. The present study suggests that nicotine may not be the major contributing factor for the previously reported synergistic toxic interaction between tobacco and arsenic. Nicotine pre-exposure in arsenic-exposed animals revealed interesting toxicokinetics and oxidative stress modulating interactions in the brain and liver of rats, which requires further exploration.

Heteromeric nicotinic receptors are involved in the sensitization and addictive properties of MDMA in mice

We have investigated the effect of nicotinic receptor ligands in the behavioral sensitization (hyperlocomotion) and rewarding properties (conditioned place preference paradigm, CPP) of 3,4-methylenedioxy-methamphetamine (MDMA) in mice. Each animal received intraperitoneal pretreatment with either saline, dihydro-β-erythroidine (DHβE, 1 mg/kg) or varenicline (VAR, 0.3 mg/kg), 15 min prior to subcutaneous saline or MDMA (5 mg/kg), for 10 consecutive days. On day 1, both DHβE and VAR inhibited the MDMA-induced hyperlocomotion. After 10 days of treatment, MDMA induced a hyperlocomotion that was not reduced (rather enhanced) in antagonist-pretreated animals. This early hyperlocomotion was accompanied by a significant increase in heteromeric nicotinic receptors in cortex that was not blocked by DHβE or VAR. Behavioral sensitization to MDMA was highest 2 weeks after the discontinuation of MDMA treatment. This additional increase in sensitivity was prevented in animals pretreated with DHβE or VAR. At this time, MDMA-treated mice showed a significant increase in heteromeric receptors in cortex that was prevented by DHβE and VAR. An involvement of α7 nicotinic receptors in this effect is ruled out. MDMA (10 mg/kg) induced positive CPP that was abolished by DHβE (2 mg/kg) and VAR (2 mg/kg). Moreover, chronic nicotine pretreatment (2 mg/kg, ip, b.i.d., for 14 days) caused MDMA, administered at a low dose (3 mg/kg), to induce CPP, which would otherwise not occur. Finally, present results point out that heteromeric nicotinic receptors are involved in locomotor sensitization and addictive potential induced by MDMA. Thus, varenicline might be a useful drug to treat both tobacco and MDMA abuse at once.

Effects of nicotine on olfactogustatory incentives: preference, palatability, and operant choice tests.

The use of additives in tobacco may capitalize on the incentive motivational properties of tastes and scents such as mint (menthol), vanilla, and strawberry. These incentives are intended to increase tobacco experimentation, but their salience may also be enhanced by the incentive amplifying effects of nicotine (NIC). The goal of the present studies was to investigate the potential interaction between the incentive amplifying effects of NIC and gustatory incentives. One of two discriminable tastes (grape or cherry Kool-Aid®; 0.05% wt/vol; unsweetened) was paired with sucrose (20% wt/vol; conditioned stimulus [CS+]) in deionized water, whereas the other taste (CS-) was presented in deionized water. Experiment 1 investigated the effects of NIC pretreatment on preference for the CS+ versus CS- in 2-bottle choice tests. Experiment 2 investigated the effects of NIC on palatability of the CS+ and CS- using orofacial taste reactions. Experiment 3 investigated the effects of NIC on reinforcement by the CS+ and CS- using a concurrent choice operant task. NIC pretreatment robustly increased operant responding for the CS+ but did not alter responding for the CS- in the operant choice task (Experiment 3). However, NIC pretreatment did not alter intake or palatability of the CS+ or CS- (Experiments 1 and 2). NIC increases the reinforcing effects of gustatory incentive stimuli, even though these stimuli were not paired with NIC administration. The findings suggest that adding taste incentives to tobacco products may increase the attractiveness of these products to consumers and the probability of repeated use.

The effect of nicotine on sign-tracking and goal-tracking in a Pavlovian conditioned approach paradigm in rats

Nicotine (NIC) potently increases operant responding for non-NIC reinforcers, and this effect may depend on drug-mediated increases in incentive motivation. According to this hypothesis, NIC should also potently increase approach to Pavlovian-conditioned stimuli associated with rewards. The present studies explored the effects of NIC on Pavlovian-conditioned approach responses. To do so, liquid dippers were used to deliver an unconditioned stimulus (US; 0.1ml sucrose) after presentation of a conditioned stimulus (CS; 30s illumination of a stimulus light)-both the CS and US were presented in receptacles equipped to monitor head entries. In experiment 1, the CS and US were presented in the same receptacle, but NIC pretreatment (0.4mg/kg base) did not increase conditioned approach responses. Delivery of the sucrose US was then shifted to receptacle in a different location. All rats learned to approach the new US location (goal-tracking) at similar rates. Approach to the CS receptacle (sign-tracking) declined for saline-pretreated rats, but NIC pretreatment increased sign-tracking. In experiment 2, NIC pretreatment increased sign-tracking when the CS and US were spatially separated during acquisition. In experiment 3, NIC pretreatments were replaced with saline, but the effect of NIC persisted for an additional 24 test sessions. The findings suggest that NIC increases incentive motivation and that this effect is long-lasting, persisting beyond the pharmacological effects of NIC.

Nicotine-mediated improvement in l-dopa-induced dyskinesias in MPTP-lesioned monkeys is dependent on dopamine nerve terminal function

l-Dopa-induced dyskinesias (LIDs) are abnormal involuntary movements that develop with long term l-dopa therapy for Parkinson's disease. Studies show that nicotine administration reduced LIDs in several parkinsonian animal models. The present work was done to understand the factors that regulate the nicotine-mediated reduction in LIDs in MPTP-lesioned nonhuman primates. To approach this, we used two groups of monkeys, one with mild-moderate and the other with more severe parkinsonism rendered dyskinetic using l-dopa. In mild-moderately parkinsonian monkeys, nicotine pretreatment (300μg/ml via drinking water) prevented the development of LIDs by ~75%. This improvement was maintained when the nicotine dose was lowered to 50μg/ml but was lost with nicotine removal. Nicotine re-exposure again decreased LIDs. By contrast, nicotine treatment did not reduce LIDs in monkeys with more severe parkinsonism. We next determined how nicotine's ability to reduce LIDs correlated with lesion-induced changes in the striatal dopamine transporter and 3H-dopamine release in these two groups of monkeys. The striatal dopamine transporter was reduced to 54% and 28% of control in mild-moderately and more severely parkinsonian monkeys, respectively. However, basal, K+, α4β2* and α6β2* nAChR-evoked 3H-dopamine release were near control levels in striatum of mild-moderately parkinsonian monkeys. By contrast, these same release measures were reduced to a significantly greater extent in striatum of more severely parkinsonian monkeys. Thus, nicotine best improves LIDs in lesioned monkeys in which striatal dopamine transmission is still relatively intact. These data suggest that nicotine treatment would most effectively reduce LIDs in patients with mild to moderate Parkinson's disease.

Combined Effects of Ephedrine-Containing Dietary Supplements, Caffeine, and Nicotine on Morphology and Ultrastructure of Rat Hearts.

Cigarette smokers have an increased risk for coronary artery disease. Nicotine present in cigarettes can adversely affect the cardiovascular system via stimulation of both sympathetic and parasympathetic neurons. Caffeine, another cardiovascular and central nervous system (CNS) stimulant, is commonly found in Ephedra and Ephedra-free dietary supplements. These caffeine-containing supplements also have been linked to cardiovascular toxicities. Although no longer on the U.S market, Ephedra-containing supplements are another source of cardiovascular and CNS stimulants, namely the ephedrine alkaloids. Together caffeine, nicotine, and ephedrine can individually stress the cardiovascular system, and an overlap of these agents is predicted in smokers and dieters. To understand the collective effects of these stimulants on the heart morphology and ultrastructure, rats were exposed to synthetic combinations of nicotine (0.2 mg/kg/day), ephedrine (0-30 mg/kg/day), and/or caffeine (0-24 mg/kg/day) as well as an extract from a caffeine-containing Ephedra supplement (Metabolife 356). After exposure for 3 days, the hearts were removed and examined for hypersensitivity myocarditis and myocardial necrosis. None of the drugs tested alone affected heart tissue morphology, nor were atypical cardiac cells observed. However, in combination, significant interactions were found between caffeine and ephedrine; the interventricular septum was most susceptible, with a significant increase in atypical cardiac cells observed. Nicotine pretreatment caused greater susceptibility to cardiotoxicity associated with combinations of caffeine + ephedrine or Metabolife, particularly in the left ventricle wall. These results indicate that sympathomimetic combinations present in Ephedra supplements may have produced cardiotoxicity reported in consumers of these products. Moreover, the presence of nicotine exacerbates these toxic effects.

Nicotine reduces mortality of developing rats exposed to high-altitude hypoxia and partially suppresses the duration of cortical epileptic afterdischarges

Nicotine has been repeatedly reported as substance possessing neuroprotective properties. This study focused on the possible beneficial effects of nicotine against the high-altitude hypoxia (9000 m for one hour). 15 min prior to hypoxia exposition rats (12- and 35-day-old) were treated with nicotine. Next day electrodes have been implanted and the effects of nicotine and hypoxia (or both factors) on duration of afterdischarges (ADs) were tested. Administration of nicotine declined the hypoxia-induced mortality in 35-day-old animals. Nicotine pretreatment had no effect on ADs duration in 12-day-old pups, therefore brought about suppression of ADs in 35-day-old animals. Taken together, our data show that nicotine exhibits an anticonvulsant effect that is age-dependent. The mechanisms of nicotine neuroprotective properties include probably the influence of calcium homeostasis, increase synthesis of variety of growth factors, inhibition of the caspase cascades and antioxidant capability of nicotine.

Impact of Repeated Nicotine and Alcohol Coexposure on in Vitro and in Vivo Chlorpyrifos Dosimetry and Cholinesterase Inhibition

Chlorpyrifos (CPF) is an organophosphorus insecticide, and neurotoxicity results from inhibition of acetylcholinesterase (AChE) by its metabolite, chlorpyrifos-oxon. Routine consumption of alcohol and tobacco modifies metabolic and physiological processes impacting the metabolism and pharmacokinetics of other xenobiotics, including pesticides. This study evaluated the influence of repeated ethanol and nicotine coexposure on in vivo CPF dosimetry and cholinesterase (ChE) response (ChE- includes AChE and/or butyrylcholinesterase (BuChE)). Hepatic microsomes were prepared from groups of naive, ethanol-only (1 g/kg/d, 7 d, po), and ethanol + nicotine (1 mg/kg/d 7 d, sc)-treated rats, and the in vitro metabolism of CPF was evaluated. For in vivo studies, rats were treated with saline or ethanol (1 g/kg/d, po) + nicotine (1 mg/kg/d, sc) in addition to CPF (1 or 5 mg/kg/d, po) for 7 d. The major CPF metabolite, 3,5,6-trichloro-2-pyridinol (TCPy), in blood and urine and the plasma ChE and brain acetylcholinesterase (AChE) activities were measured in rats. There were differences in pharmacokinetics, with higher TCPy peak concentrations and increased blood TCPy AUC in ethanol + nicotine groups compared to CPF only (approximately 1.8- and 3.8-fold at 1 and 5 mg CPF doses, respectively). Brain AChE activities after ethanol + nicotine treatments showed significantly less inhibition following repeated 5 mg CPF/kg dosing compared to CPF only (96 ± 13 and 66 ± 7% of naive at 4 h post last CPF dosing, respectively). Although brain AChE activity was minimal inhibited for the 1-mg CPF/kg/d groups, the ethanol + nicotine pretreatment resulted in a similar trend (i.e., slightly less inhibition). No marked differences were observed in plasma ChE activities due to the alcohol + nicotine treatments. In vitro, CPF metabolism was not markedly affected by repeated ethanol or both ethanol + nicotine exposures. Compared with a previous study of nicotine and CPF exposure, there were no apparent additional exacerbating effects due to ethanol coexposure.