Nicotine-induced Changes Research Articles

Morphine Exposure Reduces Nicotine-Induced Upregulation of Nicotinic Receptors and Decreases Volitional Nicotine Intake in a Mouse Model.

IntroductionNicotine addiction remains a primary health concern as tobacco smoking remains the number one cause of preventable death in America. At the same time, America is still facing the threat of the opioid epidemic. While the prevalence of smoking combustible cigarettes or electronic nicotine delivery systems in the United States varies between 12% and 35%, the smoking rates among the opioid use dependent (OUD) population is 74%–97%. We examined changes in brain reward mechanisms in which co-use of nicotine and opioids may result in enhanced reward and reinforcement.Aims and MethodsAdult male and female α4-mCherryα6-GFP mice (C57BL/6J) were used in conditioned place preference (CPP) and microscopy assays to examine reward-related behavior and nicotinic acetylcholine receptor (nAChR) upregulation following treatments with saline, nicotine, morphine, or nicotine plus morphine. Following this, separate mice were trained in e-Vape self-administration assays to examine morphine’s impact on nicotine reinforcement.ResultsWe observed that nicotine and morphine coexposure in a CPP assay did not produce enhanced reward-related behavior when compared with nicotine or morphine alone. In parallel we observed coexposure reduced nicotine-induced upregulation of nAChRs on ventral tegmental area dopamine and GABA neurons. Additionally, we observed that concurrent morphine exposure reduced nicotine (plus menthol) vapor self-administration in male and female mice.ConclusionsWhile nicotine use is high among OUD individuals, our CPP assays suggest coexposure not only fails to enhance reward-related behavior but also reduces nicotine-induced changes in ventral tegmental area neurobiology. Our self-administration assays suggest that morphine exposure during nicotine acquisition reduces nicotine reinforcement-related behavior.ImplicationsWhile some may postulate that the co-use of opioids and nicotine may be driven by reward-related mechanisms, our data indicate that opioid exposure may hinder nicotine intake due to reduced upregulation of nAChRs critical for nicotine reward and reinforcement. Thus, the high co-use in OUD individuals may be a result of other mechanisms and this warrants further investigations into nicotine and opioid co-use.

Nicotine Affects Murine Aortic Stiffness and Fatigue Response During Supraphysiological Cycling.

Nicotine exposure is a major risk factor for several cardiovascular diseases. Although the deleterious effects of nicotine on aortic remodeling processes have been studied to some extent, the biophysical consequences are not fully elucidated. In this investigation, we applied quasi-static and dynamic loading to quantify ways in which exposure to nicotine affects the mechanical behavior of murine arterial tissue. Segments of thoracic aortas from C57BL/6 mice exposed to 25 mg/kg/day of subcutaneous nicotine for 28 days were subjected to uniaxial tensile loading in an open-circumferential configuration. Comparing aorta segments from nicotine-treated mice relative to an equal number of control counterparts, stiffness in the circumferential direction was nearly twofold higher (377 kPa ± 165 kPa versus 191 kPa ± 65 kPa, n = 5, p = 0.03) at 50% strain. Using a degradative power-law fit to fatigue data at supraphysiological loading, we observed that nicotine-treated aortas exhibited significantly higher peak stress, greater loss of tension, and wider oscillation band than control aortas (p ≤ 0.01 for all three variables). Compared to simple stress relaxation tests, fatigue cycling is shown to be more sensitive and versatile in discerning nicotine-induced changes in mechanical behavior over many cycles. Supraphysiological fatigue cycling thus may have broader potential to reveal subtle changes in vascular mechanics caused by other exogenous toxins or pathological conditions.

Exercise Restores The Excitation-inhibition Balance In Vta Dopamine Neurons Disrupted By Nicotine Addiction

PURPOSE: The imbalance between excitation and inhibition has been implicated in a variety of neurological disorders including addiction. This study aimed to investigate whether repeated nicotine exposure in vivo altered the excitation-inhibition (E/I) balance of dopamine neurons in the ventral tegmental area (VTA), and if so, whether exercise affects nicotine-induced changes in the E/I balance. METHODS: 2 months old C57BL/6 J mice were randomly divided into sedentary saline group (SS), sedentary nicotine group (SN), exercise saline group (ES) and exercise nicotine group (EN). ES and EN mice were introduced to a treadmill running paradigm (12 m/min for 10 min and 15 m/min for 50 min, 60 min/d, 5 d/w, 8 weeks). The conditioned place preference (CPP) paradigm was used to examine nicotine addiction related behavior. SN and EN mice were given an intraperitoneal injection of nicotine (0.5 mg/kg) while SS and ES mice were given an injection of saline. Patch clamp was used to investigate the excitatory and inhibitory synaptic transmission and E/I ratio in VTA dopamine neurons. RESULTS: Exercise decreased repeated nicotine exposure in vivo induced CPP expression (SS, -27.58 ± 29.72; SN, 123.96 ± 9.74; SE, -21.82 ± 17.23; NE, 65.14 ± 6.58; SS vs. SN, p < 0.001; SN vs. EN, p < 0.001). Exercise restored the reduction of GABAergic inhibition induced by nicotine CPP (IPSC PPR after nicotine acute exposure, SS, 0.53 ± 0.05; SN, 1.23 ± 0.13; SE, 0.71 ± 0.04; NE, 0.81 ± 0.03; SS vs. SN, p < 0.001; SN vs. EN, p < 0.01). Exercise decreases the enhancement of AMPA/NMDA ratio induced by nicotine CPP (SS, 0.58 ± 0.08; SN, 0.96 ± 0.10; SE, 0.62 ± 0.09; NE, 0.59 ± 0.07; SS vs. SN, p < 0.01; SN vs. EN, p < 0.01). Nicotine CPP alters the E/I balance in VTA dopamine neurons, which is reversed by exercise (E/I ratio, SS, 0.74 ± 0.16; SN, 2.09 ± 0.27; SE, 0.86 ± 0.15; NE, 0.96 ± 0.26; SS vs. SN, p < 0.001; SN vs. EN, p < 0.01). CONCLUSIONS: Repeated nicotine exposure in vivo shifts the balance of excitatory and inhibitory synaptic transmission in VTA dopamine neurons. Exercise restores nicotine addiction by reestablishing the balance between excitation and inhibition. Supported by the China Postdoctoral Science Foundation (2018 M641260, 2019 T120067) and the Chinese Universities Scientific Fund (BSU2020038).

Snail/HDAC1/2 mediate skeletal growth retardation in fetuses caused by prenatal nicotine exposure

Previous findings have confirmed that prenatal nicotine exposure (PNE) leads to retarded cartilage development in the fetal growth plate. It is characterized by insufficient matrix synthesis and decreased expression of matrix phenotype genes aggrecan (ACAN) and Col2A1 in the fetal growth plate chondrocytes; however, the specific molecular mechanism is yet unclear. This study intends to clarify the specific molecular mechanism of fetal osteochondral retardation caused by PNE through animal and cellular experiments. The present study demonstrated that in male offspring of the PNE group (the pregnant rats were subcutaneously administered nicotine 1.0 mg/kg twice per day (2.0 mg/kg.d) at GD11–20), the cartilage matrix of the fetal growth plate was lightly stained, the collagen was reduced, and expression of the matrix phenotype genes, ACAN and Col2A1, was significantly decreased. It was further found that PNE decreased histone acetylation (H3K9/H3K14) levels in the ACAN and Col2A1 promoter regions. Moreover, the expression of Snail and HDAC1/2 was increased in the PNE group. in vitro, the nicotine treatment at different concentrations elevated the expression of Snail/HDAC1/2 while decreasing the H3K9/H3K14 levels in the ACAN and Col2A1 promoter regions. Snail-siRNA transfection partially abolished the nicotine-induced increase in HDAC1/2 expression and decreased the histone acetylation levels in the ACAN and Col2A1 promoter regions. Trichostatin A (TSA) treatment partially reversed the nicotine-induced changes in downstream parameters. In summary, PNE-induced decreased cartilage matrix synthesis in the fetal growth plate of male offspring is effectuated by Snail/HDAC1/2-mediated decreased H3K9/H3K14 levels in the ACAN and Col2A1 promoter regions.

Effect of royal jelly on in vitro fertilization and early embryo development following nicotine treatment in adult female rats

Objective: To scrutinize the protective role of royal jelly as an antioxidant on nicotine-induced changes in malondialdehyde (MDA) level, p53 expression, in vitro fertilization (IVF) rate, and early embryo development in adult female rats. Methods: A total of 56 adult female Wistar rats were divided into 8 groups (n=7 in each group). Group 1 served as an untreated control group, group 2, 3 and 4 received nicotine at a dose of 0.50, 1.00 and 2.00 mg/kg respectively, group 5 received royal jelly at a dose of 100.00 mg/kg, and group 6, 7 and 8 received 0.50, 1.00 and 2.00 mg/kg nicotine, respectively, with 100.00 mg/kg body weight royal jelly. Nicotine and royal jelly were administered daily for 49 days in the experimental groups intra-peritoneally and orally, respectively. At the end of the experimental period, p53 expression, IVF rate and early embryo development as well as MDA concentration were measured. Results: The IVF rate, number of cumulus oocytes, two-cell embryos and blastocysts decreased in the nicotine-treated groups in a dose-dependent manner. In addition, p53 mRNA expression and MDA levels increased in the nicotine-treated groups. Royal jelly co-administration led to partial improvement in the aforementioned parameters. Conclusions: Royal jelly may have a repro-protective effect in nicotine-administered female rats in terms of its anti-oxidant and anti-apoptotic properties.

E-cigarette device power moderates the effects of non-tobacco flavors and nicotine on product appeal in young adults

BackgroundIdentifying e-cigarette product characteristics that moderate the effects of non-tobacco flavors and nicotine on user appeal can inform regulations issued in tandem with e-cigarette nicotine and flavor policies aimed to protect young adult health. An e-cigarette device’s electrical power affects the amount of solution aerosolized per puff, leading to more concentrated or diluted aerosol, which may alter product appeal. This laboratory experiment tested whether e-cigarette device power moderated the independent and interactive effects of non-tobacco flavors and nicotine on appeal in young adults. MethodIn a within-subject design single-visit protocol, young adult e-cigarette users (N = 100) administered standardized doses of e-cigarette solutions varying in flavor (fruit, menthol, tobacco) and nicotine (nicotine-containing [6 mg/mL], nicotine-free). Solutions were administered via a variable-voltage tank-style device at low (7.3 W[3.3 V@1.5 Ω resistance]) and high (12.3 W[4.3 V@1.5 Ω resistance]) power settings. Participants rated each dose’s appeal (0–100 scale). ResultsThe high (vs. low) power setting attenuated the appeal-enhancing effects of menthol (vs. tobacco) flavors (Menthol × Power, estimate = −5.44, P = .03). Power did not moderate the appeal-enhancing effects of fruit flavors. High (vs. low) power amplified the appeal-reducing effects of nicotine-containing (vs. nicotine-free) solutions (Nicotine × Power, estimate = 6.69, P < .001) and augmented the extent to which fruit and menthol flavors suppressed nicotine’s appeal-reducing effects (Flavor × Nicotine × Power, estimates = 9.40–14.85, Ps≤0.03). ConclusionE-cigarette device power appears to moderate flavor- and nicotine-induced changes in product appeal in nuanced ways, including by augmenting the ability of non-tobacco flavors to mask nicotine’s appeal-reducing effects. Regulatory restrictions on high-powered e-cigarette devices warrant consideration in efforts to protect young adult health.

Effect of individual and combined supplementation of phytoene, phytofluene, and lycopene against nicotine-induced pancreatic islet cell dysfunction

To understand the capability of carotenoids phytoene, phytofluene, and lycopene supplementation individually and in combination to counter the effect of nicotine-induced oxidative stress-mediated pancreatic islet dysfunctioning. Thirty male Wistar albino rats were divided into six groups: Group A, control; Group B, treated with intraperitoneal injection of nicotine (3 mg/kg bw); Group C, received nicotine intraperitoneally (3 mg/kg bw) and supplemented with phytoene orally (0.19 mg/kg bw); Group D, treated with nicotine intraperitoneally (3 mg/kg bw) and supplemented with phytofluene orally (0.1 mg/kg bw); Group E, treated with nicotine intraperitoneally (3 mg/kg bw) and supplemented with lycopene orally (10 mg/kg bw); and Group F, treated with nicotine intraperitoneally (3 mg/kg bw) and supplemented with a combined dose of phytoene, phytofluene, and lycopene (0.19 mg/kg + 0.1 mg/kg + 10 mg/kg bw). Then sacrificed on 21st day, pancreatic islet cells were isolated and ROS generation was estimated. Likewise, histology and biochemical assays of oxidative and antioxidative stress parameters, and pro-inflammatory cytokines levels were measured by ELISA. Phytoene, phytofluene, and lycopene individually and in combination decreased the nicotine-induced changes in fasting blood glucose, oral glucose tolerance test, and glycated hemoglobin levels. They also provided protection against the oxidative injury, increase in ROS generation and increase in the pro-inflammatory cytokines, both of which are known to be a major step in nicotine-induced islet injury and impairment of glucose homeostasis. Furthermore, it is very much interesting to note that combined supplementation showed higher degree of protection than the individual supplementation. This study has presented experimental evidences that phytoene, phytofluene, and lycopene supplementation individually provides protection against the nicotine-mediated islet impairment. The degree of protection was further enhanced upon the combined supplementation. Thus, these results suggest that the combined supplementation of phytoene, phytofluene, and lycopene may evolve as a probable approach to blunt the effect of nicotine-induced impairment of pancreatic islets.

Sex differences in nicotine-enhanced Pavlovian conditioned approach in rats

BackgroundNicotine exposure enhances Pavlovian conditioned approach (PCA), or the learned approach to reward-predictive cues. While females show elevated approach to conditioned stimuli compared to males, potentially indicating heightened addiction vulnerability, it is unknown how sex may interact with nicotine to influence approach behavior. Additionally, brain-derived neurotrophic factor (BDNF) levels can be altered significantly after repeated nicotine exposure, suggesting a potential mechanism contributing to nicotine-induced behavioral phenotypes. The present study investigated the role of sex on nicotine-induced changes to stimulus-response behavior and associated BDNF protein levels.MethodsMale and female rats were exposed to nicotine (0.4 mg/kg, subcutaneously) or saline 15 min prior to each PCA session. PCA training consisted of 29 sessions of 15 trials, in which a 30-s cue presentation ended concurrently with a sucrose reward (20% w/v in water, 100 μL), and a 120-s variable intertrial interval occurred between trials. Approach behavior to the cue and reward receptacle was recorded. Preference toward the reward receptacle indicated a goal-tracking phenotype, and preference toward the cue indicated a sign-tracking phenotype, demonstrating that the cue had gained incentive salience. Twenty-four hours after the last PCA session, brain tissue was collected and BDNF levels were measured in the basolateral amygdala, orbitofrontal cortex, and nucleus accumbens using Western blot analysis.ResultsNicotine exposure enhanced both sign- and goal-tracking conditioned approach, and females showed elevated sign-tracking compared to males. There were no sex-by-drug interactions on conditioned approach. Day-to-day variability in conditioned approach was similar between sexes. In contrast to prior studies, neither repeated exposure to nicotine nor sex significantly affected BDNF expression.ConclusionsDrug-naïve females exhibited heightened sign-tracking compared to males, and nicotine enhanced conditioned approach similarly in males and females. Further, non-significant changes to BDNF expression in brain regions highly associated with PCA indicate that BDNF is unlikely to drive nicotine-enhanced conditioned behavior.

The Relationship of Varenicline Agonism of α4β2 Nicotinic Acetylcholine Receptors and Nicotine-Induced Dopamine Release in Nicotine-Dependent Humans.

Cigarette smoking continues to be one of the most important behavioral causes of morbidity and mortality in the world. Varenicline, an α4β2 nicotinic acetylcholine receptor (nAChR) partial agonist, has been shown to increase smoking quit rates compared with nicotine-based products. This human laboratory, double-blind, placebo-controlled study examined varenicline and placebo effects on α4β2-nAChRs occupancy, nicotine-induced change in [11C]raclopride non-displaceable binding potential (BPND), and behavioral measures of cigarette smoking, nicotine craving, and withdrawal. Current nicotine dependent daily smokers (N = 17) were randomized to varenicline 1 mg twice daily or placebo for 13 days. Using positron emission tomography), we characterized α4β2-nAChRs occupancy using [18F]AZAN and dopamine receptor binding using [11C]raclopride as well as behavioral measures of cigarettes smoked, craving, and nicotine withdrawal. Varenicline compared with placebo resulted in significant reductions in [18F]AZAN BPND in multiple brain regions including thalamus, midbrain, putamen, and ventral striatum. Following administration of a controlled-dose nicotine cigarette, dopamine release was significantly suppressed in the ventral striatum in the varenicline-treated compared with the placebo group. There was a significant relationship between α4β2-nAChRs BPND measured in thalamus during the [18F]AZAN scan and nicotine-induced change in raclopride BPND in the ventral striatum. This is the first human study to demonstrate a direct relationship between the extent of varenicline occupancy of α4β2-nAChRs and the magnitude of dopamine release following nicotine use. It has remained unclear how nicotinic receptor blockade through partial agonist medications such as varenicline promotes smoking cessation. One hypothesized mechanism is downstream dampening of the mesolimbic reward dopamine system. For the first time in human smokers, we observed a direct relationship between the extent of varenicline blockade of α4β2-nACh nicotinic receptors and the magnitude of dopamine release following smoking. This has mechanistic and therapeutic implications for improving smoking cessation interventions.

Perinatal nicotine exposure impairs learning of a skilled forelimb reaching task in male but not female adult mice

Developmental tobacco or nicotine exposure is associated with various adverse outcomes in human and preclinical studies, respectively. For example, perinatal nicotine exposure in mice causes morphologic changes in neurons across sensory and motor cortices and results in impairments in sensory learning. However, the effects of developmental nicotine exposure on motor learning have not been reported. To determine whether nicotine-induced changes in behavior extend to motor tasks, we provided female C57Bl/6 dams with nicotine drinking water (200 μg/ml in 2% saccharin), or vehicle (2% saccharin), a standard paradigm to expose pups to nicotine in utero and postnatally through lactation. Male and female pups were subsequently tested in adulthood in a single-pellet reaching task with millet seeds, and also tested for gross motor function and feeding behavior. We found that male, but not female, mice exposed to nicotine throughout early development demonstrated impaired learning of single-seed reaching. Nicotine-treated animals did not differ from control animals in gross motor performance or millet seed intake, although female mice consumed more millet seeds than male mice when reaching was not required. These studies show that nicotine exposure during development can impair behavior in a skilled motor task that depends on cortical synaptic plasticity, and that this effect is sex-dependent.

Nicotine exposure of male mice produces behavioral impairment in multiple generations of descendants.

Use of tobacco products is injurious to health in men and women. However, tobacco use by pregnant women receives greater scrutiny because it can also compromise the health of future generations. More men smoke cigarettes than women. Yet the impact of nicotine use by men upon their descendants has not been as widely scrutinized. We exposed male C57BL/6 mice to nicotine (200 μg/mL in drinking water) for 12 wk and bred the mice with drug-naïve females to produce the F1 generation. Male and female F1 mice were bred with drug-naïve partners to produce the F2 generation. We analyzed spontaneous locomotor activity, working memory, attention, and reversal learning in male and female F1 and F2 mice. Both male and female F1 mice derived from the nicotine-exposed males showed significant increases in spontaneous locomotor activity and significant deficits in reversal learning. The male F1 mice also showed significant deficits in attention, brain monoamine content, and dopamine receptor mRNA expression. Examination of the F2 generation showed that male F2 mice derived from paternally nicotine-exposed female F1 mice had significant deficits in reversal learning. Analysis of epigenetic changes in the spermatozoa of the nicotine-exposed male founders (F0) showed significant changes in global DNA methylation and DNA methylation at promoter regions of the dopamine D2 receptor gene. Our findings show that nicotine exposure of male mice produces behavioral changes in multiple generations of descendants. Nicotine-induced changes in spermatozoal DNA methylation are a plausible mechanism for the transgenerational transmission of the phenotypes. These findings underscore the need to enlarge the current focus of research and public policy targeting nicotine exposure of pregnant mothers by a more equitable focus on nicotine exposure of the mother and the father.

Testing environment shape differentially modulates baseline and nicotine-induced changes in behavior: Sex differences, hypoactivity, and behavioral sensitization

In those who use nicotine, the likelihood of dependence, negative health consequences, and failed treatment outcomes differ as a function of gender. Women may be more sensitive to learning processes driven by repeated nicotine exposure that influence conditioned approach and craving. Sex differences in nicotine's influence over overt behaviors (i.e. hypoactivity or behavioral sensitization) can be examined using passive drug administration models in male and female rats. Following repeated intravenous (IV) nicotine injections, behavioral sensitization is enhanced in female rats compared to males. Nonetheless, characteristics of the testing environment also mediate rodent behavior following drug administration. The current experiment used a within-subjects design to determine if nicotine-induced changes in horizontal activity, center entries, and rearing displayed by male and female rats is detected when behavior was recorded in round vs. square chambers. Behaviors were recorded from each group (males-round: n=19; males-square: n=18; females-square: n=19; and females-round: n=19) immediately following IV injection of saline, acute nicotine, and repeated nicotine (0.05mg/kg/injection). Prior to nicotine treatment, sex differences were apparent only in round chambers. Following nicotine administration, the order of magnitude for the chamber that provided enhanced detection of hypoactivity or sensitization was contingent upon both the dependent measure under examination and the animal's biological sex. As such, round and square testing chambers provide different, and sometimes contradictory, accounts of how male and female rats respond to nicotine treatment. It is possible that a central mechanism such as stress or cue sensitivity is impacted by both drug exposure and environment to drive the sex differences observed in the current experiment. Until these complex relations are better understood, experiments considering sex differences in drug responses should balance characteristics of the testing environment to provide a complete interpretation of drug-induced changes to behavior.

Fatty acid amide hydrolase (FAAH) inactivation confers enhanced sensitivity to nicotine-induced dopamine release in the mouse nucleus accumbens.

Nicotine exerts its rewarding effects by promoting an increase in dopamine (DA) release in the nucleus accumbens (NAc), and this process is influenced by the endocannabinoid system. Fatty acid amide hydrolase (FAAH) is the main enzyme responsible for the degradation of the endocannabinoid anandamide and other non-cannabinoid N-acylethanolamines. Previous research has reported that both genetic deletion and pharmacological inhibition of FAAH enhance nicotine-induced conditioned place preference at low doses. We conducted a microdialysis study to characterize nicotine-induced changes in DA and serotonin (5-HT) levels in the NAc of FAAH knockout (KO) mice using a conditioned place preference-like paradigm with three nicotine doses (0.1, 1 and 10mg/kg, s.c.). Additionally, the effects of the selective FAAH inhibitor PF-3845 (10mg/kg, i.p.) were also examined. Our data indicated that compared with wild-type mice, genetic deletion of FAAH selectively enhanced the effect of low-dose nicotine on DA release (p<0.001) and resulted in a strong post-nicotine elevation in DA levels (p<0.01). However, there were no differences between the genotypes at higher doses. Furthermore, FAAH KO mice displayed a moderate enhancement of the effect of low-dose nicotine on NAc 5-HT release (p<0.05), with no differences between the genotypes at higher doses. Compared with vehicle-pretreated mice, mice pretreated with PF-3845 displayed an enhancement of the effect of low-dose nicotine on NAc DA release (p<0.001), which resulted in a sustained increase in DA levels (p<0.05). Similar to FAAH KO mice, PF-3845-pretreated mice displayed a moderate enhancement of the effect of low-dose nicotine on NAc 5-HT release (p<0.01). These observations in mice suggest that enhanced nicotine-induced NAc DA release might contribute to increased sensitivity to the conditioned rewarding effects of low-dose nicotine following FAAH inhibition, which has been previously reported. Future studies combining behavioral and neurochemical approaches are needed to elucidate the precise mechanism of these effects.

Nicotine effects on exercise performance and physiological responses in nicotine-naïve individuals: a systematic review.

The purpose of this systematic review was to evaluate the effects of smokeless forms of nicotine on physiological responses and exercise performance. Methodology and reporting were based on the PRISMA statement. The intervention was defined as any product containing nicotine that did not require smoking. Searches were conducted across two electronic databases with supplementary approaches utilized. Studies were selected following set inclusion and exclusion criteria and checked by two independent authors. A modified PEDro scale was utilized to rate study quality with studies averaging 9·3/13. Six studies assessed exercise performance with endurance-based parameters reported as significantly improved with nicotine in one study, while anaerobic parameters were unaffected or decreased compared to placebo except in one study which reported enhanced leg extensor torque but no effect on countermovement jump or Wingate anaerobic capacity. Sixteen of 28 studies investigating physiological responses reported that nicotine significantly increased heart rate compared to placebo or control. Blood pressure and blood flow were also reported as significantly increased in multiple studies. While there is strong evidence of nicotine-induced changes in physiological function that would benefit physical performance, beneficial effects have only been reported on leg extensor torque and endurance performance by one study each. Subsequently, there is need for more research with strong methodological quality to definitively evaluate nicotine's potential as an ergogenic aid.

Chronic nicotine-induced changes in gene expression of delta and kappa-opioid receptors and their endogenous ligands in the mesocorticolimbic system of the rat.

Delta and kappa opioid receptors (DOR and KOR, respectively) and their endogenous ligands, proenkephalin (PENK) and prodynorphin (PDYN)-derived opioid peptides are proposed as important mediators of nicotine reward. This study investigated the regulatory effect of chronic nicotine treatment on the gene expression of DOR, KOR, PENK and PDYN in the mesocorticolimbic system. Three groups of rats were injected subcutaneously with nicotine at doses of 0.2, 0.4, or 0.6 mg/kg/day for 6 days. Rats were decapitated 1 hr after the last dose on day six, as this timing coincides with increased dopamine release in the mesocorticolimbic system. mRNA levels in the ventral tegmental area (VTA), lateral hypothalamic area (LHA), amygdala (AMG), dorsal striatum (DST), nucleus accumbens, and medial prefrontal cortex were measured by quantitative real-time PCR. Our results showed that nicotine upregulated DOR mRNA in the VTA at all of the doses employed, in the AMG at the 0.4 and 0.6 mg/kg doses, and in the DST at the 0.4 mg/kg dose. Conversely, PDYN mRNA was reduced in the LHA with 0.6 mg/kg nicotine and in the AMG with 0.4 mg/kg nicotine. KOR mRNA was also decreased in the DST with 0.6 mg/kg nicotine. Nicotine did not regulate PENK mRNA in any brain region studied.

Menthol Enhances Nicotine Reward-Related Behavior by Potentiating Nicotine-Induced Changes in nAChR Function, nAChR Upregulation, and DA Neuron Excitability

Understanding why the quit rate among smokers of menthol cigarettes is lower than non-menthol smokers requires identifying the neurons that are altered by nicotine, menthol, and acetylcholine. Dopaminergic (DA) neurons in the ventral tegmental area (VTA) mediate the positive reinforcing effects of nicotine. Using mouse models, we show that menthol enhances nicotine-induced changes in nicotinic acetylcholine receptors (nAChRs) expressed on midbrain DA neurons. Menthol plus nicotine upregulates nAChR number and function on midbrain DA neurons more than nicotine alone. Menthol also enhances nicotine-induced changes in DA neuron excitability. In a conditioned place preference (CPP) assay, we observed that menthol plus nicotine produces greater reward-related behavior than nicotine alone. Our results connect changes in midbrain DA neurons to menthol-induced enhancements of nicotine reward-related behavior and may help explain how smokers of menthol cigarettes exhibit reduced cessation rates.

Temporal Rewiring of Striatal Circuits Initiated by Nicotine.

Drug addiction has been conceptualized as maladaptive recruitment of integrative circuits coursing through the striatum, facilitating drug-seeking and drug-taking behavior. The aim of this study was to define temporal neuroadaptations in striatal subregions initiated by 3 weeks of intermittent nicotine exposure followed by protracted abstinence. Enhanced rearing activity was assessed in motor activity boxes as a measurement of behavioral change induced by nicotine (0.36 mg/kg), whereas electrophysiological field potential recordings were performed to evaluate treatment effects on neuronal activity. Dopamine receptor mRNA expression was quantified by qPCR, and nicotine-induced dopamine release was measured in striatal subregions using in vivo microdialysis. Golgi staining was performed to assess nicotine-induced changes in spine density of medium spiny neurons. The data presented here show that a brief period of nicotine exposure followed by abstinence leads to temporal changes in synaptic efficacy, dopamine receptor expression, and spine density in a subregion-specific manner. Nicotine may thus initiate a reorganization of striatal circuits that continues to develop despite protracted abstinence. We also show that the response to nicotine is modulated in previously exposed rats even after 6 months of abstinence. The data presented here suggests that, even though not self-administered, nicotine may produce progressive neuronal alterations in brain regions associated with goal-directed and habitual performance, which might contribute to the development of compulsive drug seeking and the increased vulnerability to relapse, which are hallmarks of drug addiction.

Effect of Maternal Electroacupuncture on Perinatal Nicotine Exposure-Induced Lung Phenotype in Offspring.

Pregnant women exposed to tobacco smoke predispose the offspring to many adverse consequences including an altered lung development and function. There is no effective therapeutic intervention to block the effects of smoke exposure on the developing lung. Clinical and animal studies demonstrate that acupuncture can modulate a variety of pathophysiological processes, including those involving the respiratory system; however, whether acupuncture affects the lung damage caused by perinatal smoke exposure is not known. To determine the effect of acupuncture on perinatal nicotine exposure on the developing lung, pregnant rat dams were administered (1) saline, (2) nicotine, or (3) nicotine+electroacupuncture (EA). Nicotine was administered (1mg/kg subcutaneously) once a day and EA was applied to both "Zusanli" (ST 36) points. Both interventions were administered from gestational day 6 to postnatal day 21 (PND21), following which pups were sacrificed. Lungs, blood, and brain were collected to examine markers of lung injury, repair, and hypothalamic pituitary adrenal (HPA) axis. Concomitant EA application blocked nicotine-induced changes in lung morphology, lung peroxisome proliferator-activated receptor γ and wingless-int signaling, two key lung developmental signaling pathways, hypothalamic pituitary adrenal axis (hypothalamic corticotropic releasing hormone and lung glucocorticoid receptor levels), and plasma β-endorphin levels. Electroacupuncture blocks the nicotine-induced changes in lung developmental signaling pathways and the resultant myogenic lung phenotype, known to be present in the affected offspring. We conclude that EA is a promising novel intervention against the smoke exposed lung damage to the developing lung.

Protective effects of melatonin against nicotine-induced oxidative damage of kidney

Several studies demonstrated that melatonin treatment prevents tissue damage in various models of oxidative stress (1). Experiments have shown that chronic nicotine administration caused oxidant damage in various organs by increasing lipid peroxidation products and decreasing the activity of endogenous antioxidants (2). The aim of this study was to investigate the effects of melatonin treatment on nicotine-induced oxidative changes in rat kidney and to explore the possible mechanisms of action. Three groups of rats were used as controls (the first without treatment, the second with melatonin alone and the third with nicotine alone). The last group of rats was orally treated with nicotine and melatonin for 28 days. Morphological changes in kidney were evaluated by histological procedures and immunohistochemical analysis using inflammation (NFkB and IL-6) and oxidative stress (SOD, CAT and iNOS) markers. Experiments performed demonstrated that nicotine administration increases inflammation and oxidative stress. Melatonin has a protective effect against nicotine kidney toxicity through an inhibition of inflammation and consequent oxidative damage. These data suggest that melatonin supplementation effectively counteracts the deleterious effect of chronic nicotine administration on kidney and attenuates oxidative damage possibly by its anti-inflammatory and antioxidant effects.This work was supported by grants from University of Brescia (EX 60%).

Synergistic protective effect of folic acid and vitamin B12 against nicotine-induced oxidative stress and apoptosis in pancreatic islets of the rat

Context: Nicotine is an abundant and most significant component of cigarette smoke. Epidemiological evidence strongly suggests an association between cigarette smoking and pancreatic injury, although effects of smoking on endocrine pancreas are still controversial.Objective: We examined the impact and underlying mechanisms of action of folic acid and vitamin B12 on nicotine-induced damage in pancreatic islets of rats.Materials and methods: Male Wistar rats were treated with nicotine (3 mg/kg body weight/d, intraperitonealy) with or without folic acid (36 µg/kg body weight/d, orally) and vitamin B12 (0.63 µg/kg body weight/d, orally) for 21 d. Fasting blood glucose, oral glucose tolerance test, HBA1c, insulin, oxidative stress parameters, proinflammatory cytokines, and CRP level were measured. Histological evaluation, TUNEL assay, and immunohistochemical staining of NF-κB and caspase-3 were also performed.Results: Folic acid and vitamin B12 blunted the nicotine-induced impairment in fasting blood glucose (51–56% recovery), HbA1c (64–76% recovery), oral glucose tolerance, insulin level (23–40% recovery), and islet cell counts (26–74% recovery) in rats. Moreover, folic acid in combination with vitamin B12 also attenuated the nicotine-induced changes in markers of oxidative stress (17–88% recovery), TNF-α (40–99% recovery), and IL-6 level (47–65% recovery), CRP level (59–73% recovery), expression of NF-κB and caspase-3, and apoptosis in pancreatic islet cells.Discussion and conclusion: The present study shows that folic acid and vitamin B12 supplementation can reduce nicotine-induced impairment in glucose homeostasis and apoptosis and damage of pancreatic islet cells by modulating oxidative stress, levels of proinflammatory cytokines, and expression of NF-κB.