Different pharmacokinetics of nicotine following intravenous administration of nicotine base and nicotine hydrogen tartarate in rats

Intermittent nicotine access is as effective as continuous access in promoting nicotine seeking and taking in rats

RATIONALE

Nicotine is a principal psychoactive agent in tobacco, contributing to tobacco's addictive potential. Preclinical studies on the effects of voluntary nicotine intake typically use self-administration procedures that provide continuous nicotine access during each self-administration session. However, many smokers consume cigarettes intermittently rather than continuously throughout each day. For drugs including cocaine and opioids, research in laboratory rats shows that intermittent intake can be more effective than continuous intake in producing patterns of drug use relevant to addiction.

OBJECTIVE

We determined how intermittent versus continuous nicotine self-administration influences nicotine seeking and taking behaviours.

METHODS

Female and male rats had continuous (i.e., Long Access; LgA, 6 h/day) or intermittent (IntA; 12 min ON, 60 min OFF, for 6 h/day) access to intravenous nicotine (15 µg/kg/infusion), for 12 daily sessions. We then assessed intake, responding for nicotine under a progressive ratio schedule of drug reinforcement and cue- and nicotine-induced reinstatement of drug seeking. We also estimated nicotine pharmacokinetic parameters during LgA and IntA self-administration.

RESULTS

Overall, LgA rats took twice more nicotine than did IntA rats, yielding more sustained increases in estimated brain concentrations of the drug. However, the two groups showed similar motivation to seek and take nicotine, as measured using reinstatement and progressive ratio procedures, respectively.

CONCLUSIONS

Intermittent nicotine use is just as effective as continuous use in producing addiction-relevant behaviours, despite significantly less nicotine exposure. This has implications for modeling nicotine self-administration patterns in human smokers and resulting effects on brain and behaviour.

Pharmacokinetic differences in nicotine and nicotine salts mediate reinforcement-related behavior: an animal model study

Since their introduction in the United States and Europe in 2007, electronic cigarettes (E-Cigs) have become increasingly popular among smokers. Nicotine, a key component in both tobacco and e-cigarettes, can exist in two forms: nicotine-freebase (FBN) and nicotine salts (NS). While nicotine salt is becoming more popular in e-cigarettes, the effect of nicotine salts on reinforcement-related behaviors remains poorly understood. This study aimed to compare the reinforcing effects of nicotine and nicotine salts in animal models of drug self-administration and explore potential mechanisms that may contribute to these differences. The results demonstrated that three nicotine salts (nicotine benzoate, nicotine lactate, and nicotine tartrate) resulted in greater reinforcement-related behaviors in rats compared to nicotine-freebase. Moreover, withdrawal-induced anxiety symptoms were lower in the three nicotine salt groups than in the nicotine-freebase group. The study suggested that differences in the pharmacokinetics of nicotine-freebase and nicotine salts in vivo may explain the observed behavioral differences. Overall, this study provides valuable insights into the reinforcing effects of nicotine as well as potential differences between nicotine-freebase and nicotine salts.

Pharmacokinetic and pharmacodynamic studies of nicotine in rat brain: a simultaneous investigation of nicotine metabolites and the release of neurotransmitters in vivo

Introduction: The body's ability to metabolize nicotine and the disposition of nicotine in the brain are important determinants of its exposure. Limited knowledge about the near real-time changes of neurochemicals during the brain nicotine metabolic process hinders the recognition of its multiple neuropharmacological effects. Methods: An online microdialysis coupled with UHPLC-HRMS/MS method for the in vivo multi-analysis of nicotine metabolites and several neurotransmitters in rat brain was developed. Whether the systemic modulation of metabolic enzyme CYP2B would modulate nicotine pharmacokinetics and local neurochemical effects was further investigated. Results: The dynamic profiles of over 10 nicotine metabolites and neurotransmitters were simultaneously obtained after a single injection of nicotine (2 mg·kg-1, i.p.) using the new method. Proadifen pretreatment (50 mg·kg-1·d-1, i.p., 4 days) caused significant inhibition of brain CYP2B1 activity. When exposed to nicotine, the brain C max of nicotine was 1.26 times higher and the levels of nicotine metabolites, nornicotine, and nicotine-N-oxide, were decreased by 85.3% and 34.4% in proadifen-pretreated rats. The higher level of brain nicotine induced a greater release of dopamine, serotonin, glutamate, and γ-amino-butyric acid in the nucleus accumbens. The concentrations of nicotine and dopamine were positively correlated, and the average levels of γ-amino-butyric acid and serotonin were 2.7 and 1.2 times higher, respectively, under the inhibition of nicotine metabolism. Discussion: These results demonstrated that inhibiting nicotine metabolism in rats can enhance the residence of brain nicotine and its local neurotransmitter effects. The metabolic activity of nicotine under different physiological conditions could regulate nicotine's bioavailability and its resulting pharmacology.

Development of Dependence in Smokers and Rodents With Voluntary Nicotine Intake: Similarities and Differences

INTRODUCTION

Smoking and vaping throughout adolescence and early adulthood lead to nicotine dependence. Nicotine withdrawal is associated with somatic and affective withdrawal symptoms that contribute to smoking and relapse. Affective nicotine withdrawal symptoms in humans include craving for cigarettes, depression, anxiety, trouble sleeping, and cognitive deficits.

METHODS

Herein, we review clinical studies that investigated nicotine dependence in people who smoke or vape. We also discuss studies that investigated the development of dependence in animals with oral nicotine intake, nicotine aerosol self-administration, and intravenous nicotine self-administration.

RESULTS

Clinical studies report that adolescents who smoke daily develop nicotine dependence before those who smoke infrequently, but ultimately all smokers become dependent in adulthood. Preclinical studies indicate that rats that self-administer nicotine also become dependent. Rats that self-administer nicotine display somatic withdrawal signs and affective withdrawal signs, including increased anxiety and depressive-like behavior, cognitive deficits, and allodynia. Most nicotine withdrawal signs were observed in rodents with daily (7 days/week) or intermittent long access (23-hour) to nicotine. Clinical smoking studies report symptoms of nicotine dependence in adolescents of both sexes, but virtually all preclinical nicotine self-administration studies have been done with adult male rats.

CONCLUSIONS

The role of sex and age in the development of dependence in nicotine self-administration studies remains under-investigated. However, the role of sex and age in nicotine withdrawal has been thoroughly evaluated in studies in which nicotine was administered noncontingently. We discuss the need for volitional nicotine self-administration studies that explore the gradual development of dependence during adolescence and adulthood in rodents of both sexes.

IMPLICATIONS

The reviewed clinical studies investigated the development of nicotine dependence in male and female adolescent and young adult smokers and vapers. These studies indicate that most adolescent smokers and vapers gradually become nicotine dependent. Preclinical studies with rodents show that nicotine intake in widely used self-administration models also leads to dependence. However, almost all animal studies that investigated the development of nicotine dependence have been conducted with adult male rats. To better model smoking and vaping, it is important that nicotine intake in rats or mice starts during adolescence and that both sexes are included.

Study on the interaction between 2,6-dihydroxybenzoic acid nicotine salt and human serum albumin by multi-spectroscopy and molecular dynamics simulation

As a new form of nicotine introduction for novel tobacco products, the interaction of nicotine salt with biological macromolecules may differ from that of free nicotine and thus affect its transport and distribution in vivo. Hence, the mechanism underlying the interaction between 2,6-dihydroxybenzoic acid nicotine salt (DBN) and human serum albumin (HSA) was investigated by multi-spectroscopy, molecular docking, and dynamic simulation. Experiments on steady-state fluorescence and fluorescence lifetime revealed that the quenching mechanism of DBN and HSA was dynamic quenching, and binding constant was in the order of 10^4 L mol^-1. Thermodynamic parameters exhibited that the binding was a spontaneous process with hydrophobic forces as the main driving force. Fluorescence competition experiments revealed that DBN bound to site I of HSA IIA subdomain. According to the results of synchronous fluorescence, 3D fluorescence, FT-IR spectroscopy, circular dichroism (CD) spectroscopy, and molecular dynamics (MD) simulation, DBN did not affect the basic skeleton structure of HSA but changed the microenvironment around the amino acid residues. Computer simulations positively corroborated the experimental results. Moreover, DBN decreased the surface hydrophobicity and weakened the esterase-like activity of HSA, leading to the impaired function of the latter. This work provides important information for studying the interaction between DBN as a nicotine substitute and biological macromolecules and contributes to the further development and application of DBN.

Systemic nicotine enhances opioid self-administration and modulates the formation of opioid-associated memories partly through actions within the insular cortex

Habitual use of nicotine containing products increases propensity to misuse prescription opioids and its prevalence is substantially increased in individuals currently involved in opioid-treatment programs. Nicotine enhances self-administration of many classes of drugs in rodents, though evidence for direct effects on opioids is lacking. We sought to measure the effects of nicotine pretreatment on the reinforcing efficacy of opioids in both self-administration and contextual conditioning paradigms. First, we measured the effect of systemic nicotine pretreatment on self-administration of two opioids. Additionally, we measured the degree to which systemic nicotine pretreatment impacts the formation of morphine-associated contextual memories in conditioned taste avoidance and place preference paradigms. Given the involvement of the insula in the maintenance of substance abuse, its importance in nicotine addiction, and findings that insular inactivation impairs contextual drug conditioning, we examined whether nicotine administered directly to the insula could recapitulate the effects of systemic nicotine. We demonstrate that systemic nicotine pretreatment significantly enhances opioid self-administration and alters contextual conditioning. Furthermore, intra-insula nicotine similarly altered morphine contextual conditioning by blocking the formation of taste avoidance at all three morphine doses tested (5.0, 10, and 20 mg/kg), while shifting the dose–response curve of morphine in the place preference paradigm rightward. In conclusion, these data demonstrate that nicotine facilitates opioid intake and is partly acting within the insular cortex to obfuscate aversive opiate memories while potentiating approach to morphine-associated stimuli at higher doses.

A mouse model for chronic intermittent electronic cigarette exposure exhibits nicotine pharmacokinetics resembling human vapers

Electronic cigarettes (E-cig) use is increasing rapidly, particularly among youths. Animal models for E-cig exposure with pharmacokinetics resembling human E-cig users are lacking. We developed an E-cig aerosol exposure system for rodents and a chronic intermittent delivery method that simulates E-cig users who vape episodically during wakefulness and abstain during sleep. Mice were exposed to E-cig in a programmed schedule at very low, low, medium, or high doses defined by duration of each puff, number of puffs per delivery episode and frequency of episodes in the dark phase of a 12/12-h circadian cycle for 9 consecutive days. The plasma nicotine/cotinine levels and their time courses were determined using LC/MS-MS. We assessed the body weight, food intake and locomotor activity of Apolipoprotein E null (ApoE-/-) mice exposed to chronic intermittent E-cig aerosol. Plasma nicotine and cotinine levels were positively correlated with exposure doses. Nicotine and cotinine levels showed a circadian variation as they increased with time up to the maximum nicotine level of 21.8 ± 7.1 ng/mL during the daily intermittent E-cig exposure in the 12-h dark phase and then declined during the light phase when there was no E-cig delivery. Chronic E-cig exposure to ApoE-/- mice decreased body weight, food intake and increased locomotion. Our rodent E-cig exposure system and chronic intermittent exposure method yield clinically relevant nicotine pharmacokinetics associated with behavioral and metabolic changes. The methodologies are essential tools for in vivo studies of the health impacts of E-cig exposure on CNS, cardiovascular, pulmonary, hepatic systems, metabolism and carcinogenesis.

Oxidative damage and histopathological changes in lung of rat chronically exposed to nicotine alone or associated to ethanol

Smoking is the most important preventable risk factor of chronic obstructive pulmonary disease and lung cancer. This study was designed to investigate oxidative damage and histopathological changes in lung tissue of rats chronically exposed to nicotine alone or supplemented with ethanol. Twenty-four male Wistar rats divided into three groups were used for the study. The nicotine group received nicotine (2.5mg/kg/day); the nicotine-ethanol group was given simultaneously same dose of nicotine plus ethanol (0.2g/kg/day), while the control group was administered only normal saline (1 ml/kg/day). The treatment was administered by subcutaneous injection once daily for a period of 18 weeks. Chronic nicotine administration alone or combined to ethanol caused a significant increase in malondialdehyde (MDA) level, superoxide dismutase (SOD) activity and catalase (CAT) activity in lung tissue compared to control rats suggesting an oxidative damage. However, these increases were mostly prominent in nicotine group. The histopathological examination of lung tissue of rats in both treated groups revealed many alterations in the pulmonary structures such as emphysema change (disappearance of the alveolar septa, increased irregularity and size of air sacs) and marked lymphocytic infiltration in perivascular and interstitial areas. However, the changes characterized in the nicotine group (pulmonary congestion, hemorrhage into alveoli and interstitial areas, edema) were more drastic than those observed in the nicotine-ethanol group, and they can be attributed to a significant degree of capillary endothelial permeability and microvascular leak. Conversely, the ethanol supplementation caused an appearance of fatty change and fibrosis in pulmonary tissue essentially due to a metabolism of ethanol. Finally, the lung damage illustrated in nicotine group was more severe than that observed in the nicotine-ethanol group. We conclude that the combined administration of nicotine and ethanol may moderate the effect of nicotine administered independently by counteractive interactions between these two drugs.

Antioxidative effect of folate-modified chitosan nanoparticles

OBJECTIVE

To evaluate the potency of carboxymethyl chitosan-2, 2' ethylenedioxy bis-ethylamine-folate (CMC-EDBE-FA) on tissue injury, antioxidant status and glutathione system in tissue mitochondria and serum against nicotine-induced oxidative stress in mice.

METHODS

CMC-EDBE-FA was prepared on basis of carboxymethyl chitosan tagged with folic acid by covalently linkage through 2, 2' ethylenedioxy bis-ethylamine. Animals were divided into four groups, i.e., control, nicotine (1 mg/kg bw/day), CMC-EDBE-FA (1 mg/kg bw/day) and nicotine (1 mg/kg bw/day) and CMC-EDBE-FA (1 mg/kg bw/day) for 7 days. Levels of lipid peroxidation, oxidized glutathione level, antioxidant enzyme status and DNA damage were observed and compared.

RESULTS

The significantly increase of lipid peroxidation, oxidized glutathione levels and DNA damage was observed in nicotine treated group as compared with control group; those were significantly reduced in CMC-EDBE-FA supplemented group. Moreover, significantly reduced antioxidant status in nicotine treated group was effectively ameliorated by the supplementation of CMC-EDBE-FA. Only CMC-EDBE-FA treated groups showed no significant change as compared with control group; rather than it repairs the tissue damage of nicotine treated group.

CONCLUSIONS

These findings suggest that CMC-EDBE-FA is non-toxic and ameliorates nicotine-induced toxicity.

Prenatal exposure to nicotine in pregnant rat increased inflammatory marker in newborn rat

This study aimed to investigate any inflammatory effect of nicotine on rat embryo by exposing their mothers to different dosages of nicotine during pregnancy. During this experimental study, 32 pregnant healthy Wistar rats were divided into 4 equal groups, including a control and 3 nicotine exposure groups. Injections were performed subcutaneously starting at the first day of pregnancy until parturition. As the dosages of nicotine were increased, the weight gain by pregnant rats and the mean weight of their newborns were significantly reduced. Mean ± SD of hs-CRP was significantly higher among groups exposed to various dosages of nicotine (2, 4, and 6 mg/kg) compared to the control group (P < 0.0001) and its increasing rate was also dose dependent. Mean ± SD serum level of IL-6 and TNF-α among all groups exposed to nicotine, except for 2 mg/kg nicotine injected group, was increased significantly (P < 0.0001). Mean ± SD of serum level of TGF-β and nitrite oxide among exposure groups showed significant differences compared to the control group only at the dosage of 6 mg/kg (P < 0.0001). The current study showed that exposing pregnant rats to nicotine causes a dose dependent increase in the rate of all the studied inflammatory serum markers among their newborns.

Age dependent changes in arsenic and nicotine induced oxidative stress in male rat

The present study was planned to compare the differential toxicity of arsenic and nicotine among three different age groups of rats. In this study blood and tissue oxidative stress was determined in different age group of rats exposed to arsenic (2 mg/kg, i.p.) and nicotine (6 mg/kg, i.p.) for 2 weeks. Arsenic inhibited blood δ-aminolevulinic acid dehydratase activity in all age groups of rats while, a moderate inhibition was noted following nicotine exposure in young and old rats. Arsenic caused an increase in blood reactive oxygen species in young and old rats while glutathione level increased only in young rats unlike nicotine. A significant increase in thiobarbituric acid reactive substance was noted in liver of young and old rats while, hepatic GSH showed an increase in young and a decrease in old rats. Catalase activity decreased significantly in arsenic exposed young and old rats. At the given dose and duration both toxicants did not induce oxidative stress in rat brain. Blood arsenic concentration increased with age whereas its level brain and liver was independent of age. Conclusively, young and old animals were found to be most sensitive to both toxicants; with arsenic being more toxic than nicotine targeting liver.

Combined α7 nicotinic acetylcholine receptor agonism and partial serotonin transporter inhibition produce antidepressant-like effects in the mouse forced swim and tail suspension tests: a comparison of SSR180711 and PNU-282987

Emerging evidence points to an involvement of nicotinic acetylcholine receptors (nAChRs) in major depression. Nicotine improves symptoms of depression in humans and shows antidepressant-like effects in rodents. Monoamine release is facilitated by nAChR stimulation, and nicotine-evoked serotonin (5-HT) release has been shown to depend on α7 nAChR activation. The α7 nAChR agonist PNU-282987 shows no antidepressant-like activity when tested alone in the mouse forced swim (mFST) or tail suspension tests (mTST). However, in combination with a sub-active dose of the selective 5-HT reuptake inhibitor citalopram, inducing ~50% 5-HT reuptake inhibition, PNU-282987 has shown marked antidepressant-like effects in the mFST. SSR180711 is a recently described α7 nAChR agonist that has shown antidepressant-like activity in the rat forced swim test. To address the possibility that 5-HT reuptake inhibition contributes to the antidepressant-like profile of SSR180711, we compared the behavioural and biochemical profiles of PNU-282987 and SSR180711. In the mFST and mTST, SSR180711 (3-30 mg/kg, s.c.) showed dose-dependent antidepressant-like activity, while PNU-282987 (3-30 mg/kg, s.c.) showed no significant effect. The ED(50) to displace [³H]α-bungarotoxin binding was 1.7 and 5.5 mg/kg for SSR180711 and PNU-282987, respectively, suggesting that both compounds produce near-maximal α7 nAChR occupancy at the highest dose. While PNU-282987 did not affect ex vivo [³H]5-HT uptake, SSR180711 inhibited [³H]5-HT uptake with an ED₅₀ of 30 mg/kg. This degree of inhibition is similar to that observed with a citalopram dose of ~2.4 mg/kg, a dose that is normally not active in the mFST or mTST. This suggests that the antidepressant-like activity of SSR180711 may involve partial 5-HT reuptake inhibition. SSR180711 therefore represents a compound displaying the synergistic effect of α7 nAChR agonism combined with partial 5-HT reuptake inhibition previously described. The addition of α7 nAChR agonism to classical monoamine-based mechanisms may represent a novel option for the improved treatment of major depression.

Nicotine and cotinine increases the brain penetration of saquinavir in rat

Endothelial tight junctions and efflux transporters of the blood-brain barrier (BBB) significantly limit brain accumulation of many drugs, including protease inhibitors such as saquinavir. The cholinergic agonist nicotine is one of the most commonly used drugs in the world and the incidence is even higher in the human immune deficiency virus population (∼ 70%). We examined the ability of nicotine and its primary metabolite cotinine to modify brain uptake of saquinavir in rats. Both nicotine and cotinine at pharmacological concentrations matching those in smokers, increased brain saquinavir uptake by two fold. Co-perfusion with nicotinic receptor antagonists and passive permeability markers showed that the effect was not caused by receptor activation or BBB permeability disruption. Transport inhibition studies demonstrated that brain saquinavir uptake is limited by multiple efflux transporters, P-glycoprotein (P-gp), breast cancer resistance protein and multidrug resistance-associated protein. In situ perfusion and in vitro experiments using a classical P-gp substrate rhodamine 123 linked the effect of nicotine to inhibition of BBB P-gp transport. The effect was confirmed in vivo in chronic 14 day nicotine administration animals. These data suggest nicotine increases antiretroviral drug exposure to brain and may represent a significant in vivo drug-drug interaction at the BBB. Although this may slightly benefit CNS antiretroviral efficacy, it may also expose the brain to potential serious neurotoxicity.

Role of reduced glutathione in the amelioration of nicotine-induced oxidative stress

Nicotine, a major toxic component of cigarette smoke has been identified as a major risk factor for different diseases. This study investigates the role of reduce glutathione (GSH) against nicotine treated liver and kidney toxicity. Results showed that the application of 80 mg GSH per kg body weight per day exert protective effect against nicotine-induced liver and kidney toxicity by modulating the biochemical marker enzyme LDH, lipid peroxidation and augmenting antioxidant defense system. To our knowledge, this is the first finding of this sort.

Oxidative stress in the brain of nicotine-induced toxicity: protective role of Andrographis paniculata Nees and vitamin E

Mitochondria are the crossroads of several crucial cellular activities; they produce considerable quantities of superoxide radical and hydrogen peroxide, which can damage important macromolecules. Nicotine affects a variety of cellular processes, from induction of gene expression to modulation of enzymatic activities. The aim of this study was to elucidate the protective effects of andrographolide (ANDRO) aqueous extract (AE-Ap) of Andrographis paniculata, and vitamin E on nicotine-induced brain mitochondria. In this investigation, nicotine (1 mg.kg body mass-1.day-1) was treated, for the period of 7 days, simultaneously with 2 A. paniculata products, ANDRO and AE-Ap (250 mg.kg body mass-1.day-1); and vitamin E (50 mg.kg body mass-1.day-1) was supplemented in different group of male Wistar rats. The activities of mitochondrial electron transport chain (Mito-ETC) complexes (I, II, III), nitric oxide production, superoxide anion, catalase, glutathione reductase, glutathione peroxidase, glutathione-S-transferase, and concentrations of reduced glutathione and oxidized glutathione were measured in discrete regions of brain (the cerebral hemisphere, cerebellum, diencephalons, and brain stem). The study revealed that nicotine inhibits the Mito-ETC complexes and produces nitric oxide, which suppressed the mitochondrial oxidative stress scavenger system in different brain regions. In these circumstances, lipid peroxidation and protein oxidation were noted in different discrete regions of brain mitochondria. ANDRO, AE-Ap, and vitamin E showed the protective potentiality against nicotine toxicity. The analysis of such alterations is important in determining the basis of normal dysfunction in the brain associated with nicotine toxicity, which could be ameliorated by A. paniculata and vitamin E, and may help to develop therapeutic means against nicotine-induced disorders.

Amelioratory effect of Andrographis paniculata Nees on liver, kidney, heart, lung and spleen during nicotine induced oxidative stress

The ameliorative properties of bioactive compound andrographolide (ANDRO), aqueous extract of Andrographis paniculata (AE-AP) and vitamin E (vit.E) were tested against nicotine induced liver, kidney, heart, lung and spleen toxicity. A group of male Wistar rats were intraperitoneally administered vehicle, nicotine (1mg/kg body weight/day), nicotine+ANDRO (250mg/kg body weight/day), nicotine+AE-AP (250mg/kg body weight/day) and nicotine+vit.E (50mg/kg body weight/day) for the period of 7 days. The significantly increased levels of lipid peroxidation, protein oxidation and the decreased antioxidant enzyme status were noted in nicotine treated group as compared to vehicle treated group. ANDRO, AE-AP and vit.E significantly reduced the lipid peroxidation, protein oxidation and increased the antioxidant enzyme status. This indicates A. paniculata and vit.E may act as putative protective agent against nicotine induced tissue injury and may pave a new path to develop suitable drug therapy.

Inhibition of nicotine metabolism by methoxysalen: Pharmacokinetic and pharmacological studies in mice

Studies were undertaken to examine whether methoxsalen (9-methoxyfuro[3,2-g][1]benzopyran-7-one), a specific and relatively selective inhibitor of human CYP2A6, inhibited CYP2A5-mediated nicotine metabolism in vitro. Furthermore, studies were performed in vivo to determine whether methoxsalen would modulate acute nicotine pharmacokinetics and pharmacological effects (antinociception and hypothermia) in the ICR mouse. Our results demonstrated that methoxsalen competitively inhibits in vitro nicotine metabolism in mice. The inhibition was potent, as seen in human inhibition studies, with a Ki of 0.32 microM. In addition, we found that administration of methoxsalen significantly increased the plasma half-life of nicotine (approximately doubled) and increased its area under the curve compared with saline treatment. There was a dose-dependent enhancement in the pharmacological effects of nicotine (body temperature and analgesia) after methoxsalen treatment. Methoxsalen prolonged the duration of nicotine-induced antinociception and hypothermia (2.5 mg/kg) for periods up to 180 min postnicotine administration. Furthermore, this prolongation in nicotine's effects after methoxsalen was associated with a parallel prolongation of nicotine plasma levels in mice. These data strongly suggest that variation in the rates of nicotine metabolic inactivation substantially alter nicotine's pharmacological effects. In conclusion, these results confirmed that methoxsalen did indeed inhibit the conversion of nicotine to cotinine both in vitro and in vivo. They also suggest that mice may represent a suitable model for studying variation in nicotine metabolism and its impact on mechanisms of nicotine dependence, including the use of inhibitors to reduce nicotine metabolism.

Repeated nicotine exposure in rats: effects on memory function, cholinergic markers and nerve growth factor

A decrease in the number of nicotinic-acetylcholine receptors (nAChRs) in the brain is thought to contribute to the cognitive dysfunction associated with diseases as diverse as Alzheimer's disease and schizophrenia. Interestingly, nicotine and similar compounds have been shown to enhance memory function and increase the expression of nAChRs and therefore, could have a therapeutic role in the aforementioned diseases. Nicotine has also been shown to exert positive effects on certain neurotrophins such as nerve growth factor (NGF), and therefore could play a role beyond mere symptomatic therapy. However, to date, comprehensive studies of nicotine's effects on the expression of specific acetylcholine (ACh) receptor subtypes, key cholinergic proteins (that are regulated by NGF) such as choline acetyltransferase (ChAT) and the vesicular ACh transporter (VAChT) are lacking. Studies to further investigate the effects of nicotine on NGF especially its high- and low-affinity receptors are also needed. In the present study, male Wistar rats exposed a relatively low dosage of nicotine (0.35 mg/kg every 12 h) for 14 days demonstrated improved memory performance (assessed in two separate water maze testing methods) when compared with controls. Autoradiographic experiments indicated that nicotine increased [3H]-epibatidine, [125I]-alpha-bungarotoxin and [3H]-AFDX384, but not [3H]-pirenzepine binding sites in several learning- and memory-related brain areas. The expression of ChAT, VAChT, as well as tropomyosin-receptor kinase A (TrkA) NGF receptors and phospho-TrK receptors was increased by nicotine in the hippocampus. No changes were observed in the levels of the NGF peptide or low affinity p75 neurotrophin receptors (p75NTR), however. These results suggest that repeated exposure to nicotine results in positive effects on central cholinergic markers and memory function, which may be mediated via effects on high-affinity NGF receptors.

Involvement of specific transport system of renal basolateral membranes in distribution of nicotine in rats

We measured the nicotine concentrations in tissues after a bolus i.v. administration of [(3)H]nicotine to rats to characterize the distribution profile of nicotine. The kidney showed the greatest distribution of nicotine compared to other tissues including liver, lung, heart, brain, and intestine. We also performed an HPLC assay for the determination of nicotine and its major metabolite, cotinine, and found that cotinine was negligible in the distribution of almost all tissues, except for the kidney and lung. In the kidney, cotinine was detected at a lower level than nicotine, while cotinine tended to be distributed in the lung compared to nicotine. [(3)H]Nicotine was accumulated in renal slices in a concentration dependent fashion, suggesting that the nicotine uptake in the renal tubules could be mediated by a specific transport system. Unlabeled nicotine, cotinine, and quinidine showed potent inhibitory effects on [(3)H]nicotine uptake by renal slices. In contrast, tetraethylammonium (TEA), cimetidine, and N(1)-methylnicotinamide (NMN), which were substrates of renal organic cation transporters, had no effects on the uptake. These findings suggested that a specific transporter was involved in nicotine transport at the basolateral membranes of rat renal tubules, which could mediate the high accumulation of nicotine from blood into the kidney.