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Relationship Between Nicotine Intake and Reward Function in Rats With Intermittent Short Versus Long Access to Nicotine.

ABSTRACT: INTRODUCTION:Tobacco use improves mood states and smoking cessation leads to anhedonia, which contributes to relapse. Animal studies have shown that noncontingent nicotine administration enhances brain reward function and leads to dependence. However, little is known about the effects of nicotine self-administration on the state of the reward system. METHODS:To investigate the relationship between nicotine self-administration and reward function, rats were prepared with intracranial self-stimulation electrodes and intravenous catheters. The rats were trained on the intracranial self-stimulation procedure and allowed to self-administer 0.03 mg/kg/infusion of nicotine. All rats self-administered nicotine daily for 10 days (1 hour/day) and were then switched to an intermittent short access (ShA, 1 hour/day) or long access (LgA, 23 hour/day) schedule (2 days/week, 5 weeks). RESULTS:During the first 10 daily, 1-hour sessions, nicotine self-administration decreased the reward thresholds, which indicates that nicotine potentiates reward function. After switching to the intermittent LgA or ShA schedule, nicotine intake was lower in the ShA rats than the LgA rats. The LgA rats increased their nicotine intake over time and they gradually consumed a higher percentage of their nicotine during the light phase. The nicotinic acetylcholine receptor (nAChR) antagonist mecamylamine induced a larger increase in reward thresholds (ie, anhedonia) in the LgA rats than the ShA rats. In the LgA rats, nAChR blockade with mecamylamine decreased nicotine intake for 2 hours and this was followed by a rebound increase in nicotine intake. CONCLUSIONS:A brief period of nicotine self-administration enhances reward function and a high level of nicotine intake leads to dependence. IMPLICATIONS:These animal studies indicate that there is a strong relationship between the level of nicotine intake and brain reward function. A high level of nicotine intake was more rewarding than a low level of nicotine intake and nicotine dependence was observed after long, but not short, access to nicotine. This powerful combination of nicotine reward and withdrawal makes it difficult to quit smoking. Blockade of nAChRs temporarily decreased nicotine intake, but this was followed by a large rebound increase in nicotine intake. Therefore, nAChR blockade might not decrease the use of combustible cigarettes or electronic cigarettes.

SUBMITTER: Geste JR

PROVIDER: S-EPMC7297112 | biostudies-literature | 2020 Feb

REPOSITORIES: biostudies-literature

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Relationship Between Nicotine Intake and Reward Function in Rats With Intermittent Short Versus Long Access to Nicotine.

Geste Jean R JR Levin Brandon B Wilks Isaac I Pompilus Marjory M Zhang Xiping X Esser Karyn A KA Febo Marcelo M O'Dell Laura L Bruijnzeel Adriaan W AW

Nicotine & tobacco research : official journal of the Society for Research on Nicotine and Tobacco 20200201 2

<h4>Introduction</h4>Tobacco use improves mood states and smoking cessation leads to anhedonia, which contributes to relapse. Animal studies have shown that noncontingent nicotine administration enhances brain reward function and leads to dependence. However, little is known about the effects of nicotine self-administration on the state of the reward system.<h4>Methods</h4>To investigate the relationship between nicotine self-administration and reward function, rats were prepared with intracrani ...[more]

PMID: 30958557

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Project description:Reward-related disturbances after withdrawal from nicotine are hypothesized to contribute to relapse to tobacco smoking but mechanisms underlying and linking such processes remain largely unknown.To determine whether withdrawal from nicotine affects reward responsiveness (ie, the propensity to modulate behavior as a function of prior reinforcement experience) across species using translational behavioral assessments in humans and rats.Experimental studies used analogous reward responsiveness tasks in both humans and rats to examine whether reward responsiveness varied in (1) an ad libitum smoking condition compared with a 24-hour acute nicotine abstinence condition in 31 human smokers with (n?=?17) or without (n?=?14) a history of depression; (2) rats 24 hours after withdrawal from chronic nicotine (n?=?19) or saline (n?=?20); and (3) rats following acute nicotine exposure after withdrawal from either chronic nicotine or saline administration.Performance on a reward responsiveness task under nicotine and nonnicotine conditions.In both human smokers and nicotine-treated rats, reward responsiveness was significantly reduced after 24-hour withdrawal from nicotine (P?<?.05). In humans, withdrawal-induced deficits in reward responsiveness were greater in those with a history of depression. In rats previously exposed to chronic nicotine, acute nicotine reexposure long after withdrawal potentiated reward responsiveness (P?<?.05).These findings across species converge in suggesting that organisms have diminished ability to modulate behavior as a function of reward during withdrawal of nicotine. This blunting may contribute to relapse to tobacco smoking, particularly in depression-vulnerable individuals, to reinstate responsiveness to natural rewards and to experience potentiated nicotine-induced reward responsiveness. Moreover, demonstration of behavioral homology across humans and rodents provides a strong translational framework for the investigation and development of clinical treatments targeting reward responsiveness deficits during early withdrawal of nicotine.

Project description:IntroductionThe action of nicotine to suppress body weight is often cited as a factor impacting smoking initiation and the failure to quit. Despite the weight-suppressant effects of nicotine, smokers and nonsmokers report equal daily caloric intake. The weight-suppressive effects of nicotine in animal models of smoking are poorly understood. Furthermore, the Food and Drug Administration has authority to implement a policy markedly reducing nicotine levels in cigarettes; such a reduction could reduce smoking behavior, but have detrimental effects on body weight. The aim of this investigation was to examine the effects of self-administered nicotine on body weight and food intake in rats.MethodsIn Experiment 1, rats with ad libitum access to chow responded for intravenous infusions of nicotine (60 µg/kg/infusion) or saline in daily 1-hour sessions; body weight and 24-hour food intake were measured. Experiment 2 tested the effects of subcutaneous injections of nicotine on food intake. In Experiment 3, rats were food restricted and self-administered nicotine across a range of doses (3.75-60 µg/kg/infusion) while body weight was measured. In Experiment 4, rats self-administered 60 µg/kg/infusion nicotine before reduction to one of several doses (1.875-15 µg/kg/infusion) for 50 days.ResultsSelf-administered nicotine suppressed weight gain independent of food intake. In food restricted rats, self-administered nicotine dose-dependently suppressed body weight gain. In rats self-administering 60 µg/kg/infusion nicotine, dose reduction increased body weight.ConclusionsSelf-administered nicotine, even at low doses, suppressed body independent of food intake; this may have important implications for nicotine reduction policy.ImplicationsThe results of the present studies demonstrate that self-administered nicotine suppresses body weight independent of food intake in rats. Further, the present studies establish that self-administered nicotine suppresses body weight even at very low doses and that reduction of nicotine dose results in weight gain. These results have important implications for nicotine reduction policy.

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Relationship Between Nicotine Intake and Reward Function in Rats With Intermittent Short Versus Long Access to Nicotine.

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Relationship Between Nicotine Intake and Reward Function in Rats With Intermittent Short Versus Long Access to Nicotine.

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