Signs Of Nicotine Withdrawal Research Articles

Nelotanserin, a selective 5-HT2A receptor inverse agonist, attenuates aspects of nicotine withdrawal but not reward in mice

Nicotine smoking contributes to many preventable disabilities, diseases and deaths. Targeting nicotine reward and withdrawal is a basis for the majority of smoking cessation pharmacotherapies. Due to the emergence of interest in 5-HT2A receptor modulators for numerous psychiatric disorders, we investigated the effect of nelotanserin, a 5-HT2A receptor inverse agonist, on nicotine reward and withdrawal in ICR mice. In nicotine-dependent mice, nelotanserin dose-dependently reduced somatic signs of nicotine withdrawal and thermal hyperalgesia as measured in the hot plate test. However, nelotanserin had no effect on anxiety-like behavior and failed to reduce nicotine reward as measured in the conditioned place preference test. Our results suggest that inverse agonism of the 5-HT2A receptor may be a feasible novel mechanism for smoking cessation by reducing both physical withdrawal and thermal hyperalgesia associated with nicotine abstinence but may require complementary pharmacotherapies targeting affective and reward-associated decrements to improve cessation outcomes.

N-oleoyl alanine attenuates nicotine reward and spontaneous nicotine withdrawal in mice

BackgroundAs nicotine dependence represents a longstanding major public health issue, new nicotine cessation pharmacotherapies are needed. Administration of N-oleoyl glycine (OlGly), an endogenous lipid signaling molecule, prevents nicotine-induced conditioned place preference (CPP) through a peroxisome proliferator-activated receptor-alpha (PPARα) dependent mechanism, and also ameliorated withdrawal signs in nicotine-dependent mice. Pharmacological evidence suggests that the methylated analog of OlGly, N-oleoyl alanine (OlAla), has an increased duration of action and may offer translational benefit. Accordingly, OlAla was assessed in nicotine CPP and dependence assays as well as its pharmacokinetics compared to OlGly. MethodsICR female and male mice were tested in nicotine-induced CPP with and without the PPARα antagonist GW6471. OlAla was also assessed in nicotine-dependent mice following removal of nicotine minipumps: somatic withdrawal signs, thermal hyper-nociception and altered affective behavior (i.e., light/dark box). Finally, plasma and brain were collected after administration of OlGly or OlAla and analyzed by high-performance liquid chromatography tandem mass spectrometry. ResultsOlAla prevented nicotine-induced CPP, but this effect was not blocked by GW6471. OlAla attenuated somatic and affective nicotine withdrawal signs, but not thermal hyper-nociception in nicotine-dependent mice undergoing withdrawal. OlAla and OlGly showed similar time-courses in plasma and brain. ConclusionsThe observation that both molecules showed similar pharmacokinetics argues against the notion that OlAla offers increased metabolic stability. Moreover, while these structurally similar lipids show efficacy in mouse models of reward and dependence, they reduce nicotine reward through distinct mechanisms.

Cannabidiol as a potential cessation therapeutic: Effects on intravenous nicotine self-administration and withdrawal symptoms in mice

Cigarette smoking remains a leading cause of preventable disease and death worldwide. Due to the devastating negative health effects of smoking, many users attempt to quit, but few are successful in the long-term. Thus, there is a critical need for novel therapeutic approaches. In these investigations, we sought to examine whether cannabidiol (CBD) has the potential to be repurposed as a nicotine cessation therapeutic. In the first study, male and female mice were trained to respond for intravenous nicotine infusions at either a low or moderate nicotine dose and then were pretreated with CBD prior to their drug-taking session. We found that CBD produced a significant decrease in the number of nicotine rewards earned, and this effect was evidenced across CBD doses and with both the low and moderate levels of nicotine intake. These effects on drug intake were not due to general motor-related effects, since mice self-administering food pellets did not alter their behavior with CBD administration. The potential effects of CBD in mitigating nicotine withdrawal symptoms were then investigated. We found that CBD attenuated the somatic signs of nicotine withdrawal and prevented nicotine's hyperalgesia-inducing effects. Taken together, these results demonstrate that modulation of cannabinoid signaling may be a viable therapeutic option as a smoking cessation aid.

Differential roles of diacylglycerol lipase (DAGL) enzymes in nicotine withdrawal

Nicotine and tobacco-related deaths remains a leading cause of preventable death and disease in the United States. Several studies indicate that modulation of the endocannabinoid system, primarily of the endocannabinoid 2-Arachidonoylglycerol (2-AG), alters nicotinic dependence behaviors in rodents. This study, using transgenic knock-out (KO) mice, evaluated the role of the two 2-AG biosynthesis enzymes, (Diacylglycerol lipase-α) DAGL-α and DAGL-β in spontaneous nicotine withdrawal. DAGL-α deletion prevents somatic and affective signs of nicotine withdrawal, while DAGL-β deletion plays a role in hyperalgesia due to nicotine withdrawal. These results suggest a differential role of these enzymes in the various signs of nicotine withdrawal. Our behavioral findings relate to the distribution of these enzymes with DAGL-β being highly expressed in macrophages and DAGL-α in neurons. This study offers new potential targets for smoking cessation therapies.

L-theanine attenuates nicotine reward and withdrawal signs in mice

BackgroundL-theanine, 2-amino-4-(ethylcarbamoyl) butyric acid, an amino acid detected in green tea leaves, is used as a dietary supplement to attenuate stress and enhance mood and cognition. Furthermore, L-theanine induces anxiolytic effects in humans. Recently, L-theanine was reported to reduce morphine physical dependence in primates, suggesting the potential usefulness of L-theanine for drug dependence intervention. ObjectiveThe aim of this study is to determine whether L-theanine attenuates nicotine-withdrawal (somatic and affective signs) and nicotine reward in mice. We also investigated the effects of L-theanine on nicotinic receptors binding and function. MethodsICR male mice rendered dependent to nicotine through implanted subcutaneous osmotic minipumps for 14 days undertook precipitated nicotine withdrawal by mecamylamine on day 15. Anxiety-like behaviors using LDB, somatic signs observation and hot plate latency were assessed consecutively after treatment with L-theanine. Furthermore, we examined the effect of L-theanine on acute nicotine responses and nicotine conditioned reward in mice and on expressed nicotinic receptors in oocytes. Key findingsL-theanine reduced in a dose-dependent manner anxiety-like behavior, hyperalgesia and somatic signs during nicotine withdrawal. Also, L-theanine decreased the nicotine CPP, but it did not affect the acute responses of nicotine. Finally, L-theanine did not alter the binding or the function of expressed α4β2 and α7 nAChRs. ConclusionOur results support the potential of L-theanine as a promising candidate for treating nicotine dependence.

Effects of Dextromethorphan on Nicotine-Induced Reward, Behavioral Sensitization, Withdrawal Signs, and Drug Seeking-Related Behavior in Rats.

Tobacco products are addictive, with nicotine serving as the major addictive ingredient. Chronic tobacco use or chronic administration of nicotine alone results in both physiological and psychological dependence. Our previous studies indicated that dextromethorphan (DM) could effectively attenuate the dependence of morphine and methamphetamine. Thus, we further investigated the possible effects of DM on nicotine dependence. Conditioned place preference (CPP) test was used to examine nicotine-induced rewarding effects as well as the drug-seeking-related behavior in rats. Nicotine dependence was induced by continuous subcutaneous infusion of nicotine via an osmotic minipump for 7 days and abstinence was initiated by removal of the pump. Withdrawal signs were observed and quantified. Locomotor activity was measured to determine the behavioral sensitization induced by nicotine. To investigate the activity of mesolimbic dopaminergic neuronal activity in correlation with the effects of nicotine, the animals were sacrificed and the nucleus accumbens (NAc), dorsal striatum (DS), and medial prefrontal cortex (mPFC) were dissected and used to determine the contents of dopamine (DA) and its metabolites using high-performance liquid chromatography (HPLC). Our results showed that DM could suppress nicotine-induced rewarding effect and drug-seeking-related behavior. In addition, co-administration and post-treatment of DM could both attenuate nicotine withdrawal signs. Moreover, DM could suppress nicotine-induced behavioral sensitization. Neurochemical experiments show that co-administration and post-treatment of DM abolished nicotine-induced increase of the DA turnover rate in the mPFC, but not in the NAc and DS. The results suggest that DM has a great therapeutic potential in the treatment of nicotine dependence. Our results showed that DM could suppress nicotine-induced rewarding effect and drug-seeking-related behavior. In addition, co-administration and post-treatment of DM could both attenuate nicotine withdrawal signs. Moreover, DM could suppress nicotine-induced behavioral sensitization. Neurochemical experiments show that co-administration and post-treatment of DM abolished nicotine-induced increase of the DA turnover rate in the mPFC, but not in the NAc and DS. These results suggest that DM has a great therapeutic potential in the treatment of nicotine dependence.

Nicotine preference and affective behavior of Cd81 knockout mice.

Cd81 -/- (knockout) mice have previously been reported to have reduced cocaine preference and increased striatal dopamine content and dopamine turnover, but normal learning and memory in the Morris water maze. The effects of Cd81 on other behaviors and drugs of abuse have not been investigated. We measured the effects of Cd81 -/- in a modified two-bottle choice test for nicotine, as well as in somatic signs of nicotine withdrawal, four tests of affective behavior, and tyrosine hydroxylase gene expression assays. We found that Cd81 loss-of-function significantly increased voluntary nicotine consumption and somatic signs of nicotine withdrawal. Nicotine consumption of Cd81 -/- female mice increased for 3weeks and then remained relatively stable for the next 5weeks, suggesting that their nicotine consumption continued to be limited by aversion to higher nicotine doses. Cd81 -/- also produced a dramatic and significant increase in struggling in the forced swim test and a significant increase in the time spent in the light chamber of the light/dark box. The elevated plus maze and the tail suspension test did not show a main effect of genotype. Therefore, we conclude that Cd81 did not have an overall effect on anxiety- or depression-like behavior. Tyrosine hydroxylase mRNA levels were unchanged. Cd81 knockouts have a strongly increased nicotine preference, plus a proactive response to specific stressful situations. Together with reports of increased striatal dopamine content and anecdotal reports of increased aggressiveness, these provide intriguing parallels to some aspects of post-traumatic stress disorder.

GABAB receptors blockage modulates somatic and aversive manifestations induced by nicotine withdrawal

There is substantial evidence that GABAB agonist, baclofen, prevents somatic and motivational responses induced by nicotine withdrawal and may target drug cue vulnerabilities in humans. In this context, we explored different aspects associated with the possible mechanisms whereby the GABAB receptors might influence nicotine withdrawal. Male mice received nicotine (2.5 mg/kg, s.c.) 4 times daily, for 7 consecutive days. Nicotine-treated mice received the nicotinic acetylcholine receptor antagonist, mecamylamine (MEC, 2 or 3.5 mg/kg, s.c.), to precipitate the withdrawal state. A second group of dependent mice received 2-hydroxysaclofen (GABAB receptor antagonist, 1 mg/kg, s.c.) before MEC-precipitated abstinence. Somatic signs of nicotine withdrawal were measured for 30 min. Anxiogenic-like response associated to nicotine withdrawal was assessed by the elevated plus maze test. The dysphoric/aversive effect induced by nicotine withdrawal was evaluated using conditioned place aversion paradigm. Dopamine, serotonin and its metabolites concentrations were determined by HPLC in the striatum, cortex and hippocampus. Finally, α4β2 nicotinic acetylcholine receptor density was determined in several brain regions using autoradiography assays. The results showed that MEC-precipitated nicotine withdrawal induced somatic manifestations, anxiogenic-like response and dysphoric/aversive effect, and 2-hydroxysaclofen potentiated these behavioral responses. Additionally, 2-hydroxysaclofen was able to change striatal dopamine levels and α4β2 nicotinic acetylcholine receptor density, both altered by MEC-precipitated nicotine withdrawal. These findings provide important contributions to elucidate neurobiological mechanisms implicated in nicotine withdrawal. We suggest that GABAB receptor activity is necessary to control alterations induced by nicotine withdrawal, which supports the idea of targeting GABAB receptors to treat tobacco addiction in humans.

Serotonin neurons in the median raphe nucleus bidirectionally regulate somatic signs of nicotine withdrawal in mice

In chronic smokers, nicotine withdrawal symptoms during tobacco cessation can lead to smoking relapse. In rodent models, chronic exposure to nicotine elicited physical dependence, whereas acute antagonism of nicotinic acetylcholine receptors (nAChRs) immediately precipitated withdrawal symptoms. Although the central serotonergic system plays an important role in nicotine withdrawal, the exact serotonergic raphe nuclei regulating these symptoms remain unknown. We used transgenic mice expressing archaerhodopsinTP009 or channelrhodopsin-2[C128S] exclusively in the central serotonergic neurons to selectively manipulate serotonergic neurons in each raphe nucleus. Nicotine withdrawal symptoms were precipitated by an acute injection of mecamylamine, a nonspecific nAChR antagonist, following chronic nicotine consumption. Somatic signs were used as measures of nicotine withdrawal symptoms. Acute mecamylamine administration significantly increased ptosis occurrence in nicotine-drinking mice compared with that in control-drinking mice. Optogenetic inhibition of the serotonergic neurons in the median raphe nucleus (MRN), but not of those in the dorsal raphe nucleus (DRN), mimicked the symptoms observed during mecamylamine-precipitated nicotine withdrawal even in nicotine-naïve mice following the administration of acute mecamylamine injection. Optogenetic activation of the serotonergic neurons in the MRN nearly abolished the occurrence of ptosis in nicotine-drinking mice. The serotonergic neurons in the MRN, but not those in the DRN, are necessary for the occurrence of somatic signs, a nicotine withdrawal symptom, and the activation of these neurons may act as a potential therapeutic strategy for preventing the somatic manifestations of nicotine withdrawal.

Chronic Lorcaserin Treatment Reverses the Nicotine Withdrawal-Induced Disruptions to Behavior and Maturation in Developing Neurons in the Hippocampus of Rats.

Preclinical data have shown that treatment with serotonin (5-HT)2C receptor agonists inhibits the behavioral effects of nicotine, including self-administration, reinstatement, and locomotor responses to nicotine. Since the data on the effects of 5-HT2C receptor agonism on nicotine withdrawal signs are limited, we aimed to investigate whether 5-HT2C receptor agonism alleviated the behavioral and neurobiochemical (hippocampal neurogenesis) consequences of nicotine withdrawal in Sprague-Dawley rats. Our data indicate that withdrawal from nicotine self-administration induced locomotor hyperactivity, lengthened immobility time (the forced swim test), induced ‘drug-seeking’ behavior and deficits in cognition-like behavior (the novel object recognition task). A two-week exposure to the 5-HT2C receptor agonist lorcaserin attenuated locomotor hyperactivity and induced recovery from depression-like behavior. Analyses of brain slices from nicotine-withdrawn animals revealed that lorcaserin treatment recovered the reduced number of doublecortin (DCX)-positive cells, but it did not affect the number of Ki-67- or 5-bromo-2’-deoxyuridine (BrdU)-positive cells or the maturation of proliferating neurons in drug-weaned rats. To summarize, we show that lorcaserin alleviated locomotor responses and depression-like state during nicotine withdrawal. We propose that the modulatory effect of lorcaserin on the ‘affective’ aspects of nicotine cessation may be linked to the positive changes caused by the compound in hippocampal neurogenesis during nicotine withdrawal.

The role of pituitary adenylyl cyclase activating polypeptide in affective signs of nicotine withdrawal.

Recent evidence implicates endogenous pituitary adenylyl cyclase activating polypeptide (PACAP) in the aversive effect of nicotine. In the present study, we assessed if nicotine-induced conditioned place preference (CPP) or affective signs of nicotine withdrawal would be altered in the absence of PACAP and if there were any sex-related differences in these responses. Male and female mice lacking PACAP and their wild-type controls were tested for baseline place preference on day 1, received conditioning with saline or nicotine (1mg/kg) on alternate days for 6days and were then tested for CPP the next day. Mice were then exposed to four additional conditioning and were tested again for nicotine-induced CPP 24hr later. Controls were conditioned with saline in both chambers and tested similarly. All mice were then, 96hr later, challenged with mecamylamine (3mg/kg), and tested for anxiety-like behaviors 30min later. Mice were then, 2hr later, forced to swim for 15min and then tested for depression-like behaviors 24hr later. Our results showed that male but not female mice lacking PACAP expressed a significant CPP that was comparable to their wild-type controls. In contrast, male but not female mice lacking PACAP exhibited reduced anxiety- and depression-like behaviors compared to their wild-type controls following the mecamylamine challenge. These results suggest that endogenous PACAP is involved in affective signs of nicotine withdrawal, but there is a sex-related difference in this response.

Differential Effects of Nicotine and Nicotine Withdrawal on Fear Conditioning in Male Rats.

BackgroundTobacco use is prevalent in individuals who are routinely exposed to stress. However, little is known about how nicotine affects responses to trauma. We examined in rats how nicotine exposure affects fear conditioning, a procedure often used to study stress-related psychiatric illness.MethodsWe examined 2 methods of nicotine exposure: self-administration, modeling voluntary use, and experimenter-programmed subcutaneous administration, modeling medicinal administration (nicotine patch). For self-administered nicotine, rats trained to self-administer nicotine i.v. were fear conditioned (via light cue preceding foot-shock) either immediately after a 12-hour self-administration session or 12 hours later during a period with somatic signs of nicotine withdrawal. For experimenter-delivered nicotine, rats were conditioned after 1–21 days of nicotine delivered by programmable (12 hours on) subcutaneous mini-pumps. Tests to evaluate acoustic startle responses to the conditioning environment (context-potentiated startle) and in the presence or absence of the light cue (fear-potentiated startle) occurred after a 10-day period.ResultsRats fear conditioned immediately after nicotine self-administration showed reduced responses to the shock-associated context, whereas those trained during nicotine withdrawal showed exaggerated responses. Experimenter-programmed nicotine produced effects qualitatively similar to those seen with self-administered nicotine.ConclusionsSelf-administration or experimenter-programmed delivery of nicotine immediately before exposure to aversive events can reduce conditioned fear responses. In contrast, exposure to aversive events during nicotine withdrawal exacerbates fear responses. These studies raise the possibility of developing safe and effective methods to deliver nicotine or related drugs to mitigate the effects of stress while also highlighting the importance of preventing withdrawal in nicotine-dependent individuals.

Activation of PPARγ Attenuates the Expression of Physical and Affective Nicotine Withdrawal Symptoms through Mechanisms Involving Amygdala and Hippocampus Neurotransmission.

An isoform of peroxisome proliferator-activated receptors (PPARs), PPARγ, is the receptor for the thiazolidinedione class of anti-diabetic medications including pioglitazone. Neuroanatomical data indicate PPARγ localization in brain areas involved in drug addiction. Preclinical and clinical data have shown that pioglitazone reduces alcohol and opioid self-administration, relapse to drug seeking, and plays a role in emotional responses. Here, we investigated the behavioral effect of PPARγ manipulation on nicotine withdrawal in male Wistar rats and in male mice with neuron-specific PPARγ deletion (PPARγ(-/-)) and their littermate wild-type (PPARγ(+/+)) controls. Real-time quantitative RT-PCR and RNAscope in situ hybridization assays were used for assessing the levels of expression and cell-type localization of PPARγ during nicotine withdrawal. Brain site-specific microinjections of the PPARγ agonist pioglitazone were performed to explore the role of this system on nicotine withdrawal at a neurocircuitry level. Results showed that activation of PPARγ by pioglitazone abolished the expression of somatic and affective nicotine withdrawal signs in rats and in (PPARγ(+/+)) mice. This effect was blocked by the PPARγ antagonist GW9662. During early withdrawal and protracted abstinence, the expression of PPARγ increased in GABAergic and glutamatergic cells of the amygdala and hippocampus, respectively. Hippocampal microinjections of pioglitazone reduced the expression of the physical signs of withdrawal, whereas excessive anxiety associated with protracted abstinence was prevented by pioglitazone microinjection into the amygdala. Our results demonstrate the implication of the neuronal PPARγ in nicotine withdrawal and indicates that activation of PPARγ may offer an interesting strategy for smoking cessation.SIGNIFICANCE STATEMENT Smoking cessation leads the occurrence of physical and affective withdrawal symptoms representing a major burden to quit tobacco use. Here, we show that activation of PPARγ prevents the expression of both somatic and affective signs of nicotine withdrawal. At molecular levels results show that PPARγ expression increases in GABAergic cells in the hippocampus and in GABA- and glutamate-positive cells in the basolateral amygdala. Hippocampal microinjections of pioglitazone reduce the insurgence of the physical withdrawal signs, whereas anxiety linked to protracted abstinence is attenuated by pioglitazone injected into the amygdala. Our results demonstrate the implication of neuronal PPARγ in nicotine withdrawal and suggest that PPARγ agonism may represent a promising treatment to aid smoking cessation.

Inverse agonists of the 5-HT2A receptor reduce nicotine withdrawal signs in rats

Previous work has shown that chronic nicotine administration causes adaptive changes in 5-HT2A receptor expression. Based on this relationship, it was hypothesized that inactivating 5-HT2A receptors with the inverse agonists pimavanserin and volinanserin (MDL100907), would reduce the symptoms of nicotine withdrawal syndrome. Sprague-Dawley rats were rendered nicotine-dependent by subcutaneous infusion of nicotine bitartrate, 9 mg/kg/day for seven days. The infusions were then terminated, and 22 h later, rats were observed under “blind” conditions for somatically expressed behavioral nicotine withdrawal signs. One hour before observations, the nicotine dependent rats were injected i.p. with saline alone, or either 0.3 or 1.0 mg/kg pimavanserin in saline. Total withdrawal signs were reduced in a dose-dependent manner. A one-way ANOVA (total withdrawal signs as a function of dose) was highly significant, as was the descending linear trend of withdrawal signs as a function of dose. The 1.0 mg/kg dose reduced withdrawal signs nearly to the level exhibited by a comparison group of non-dependent rats injected with saline. A second experiment was conducted in a similar manner, which showed that volinanserin at 1.0 mg/kg but not 0.25 mg/kg also reduced nicotine withdrawal signs to nearly the level of non-dependent rats. In vitro experiments demonstrated that both pimavanserin and volinanserin potently antagonize 5-HT2A receptors, with approximately 25-fold, and 300-fold selectivity over 5-HT2C receptors, respectively. The results suggest that the 5-HT2A receptor contributes to mediating nicotine withdrawal syndrome, and thus represents a potential target for interventions to aid smoking cessation.

The β3 subunit of the nicotinic acetylcholine receptor is required for nicotine withdrawal-induced affective but not physical signs or nicotine reward in mice

Nicotinic acetylcholine receptors (nAChRs) are the primary target for nicotine, the addictive component in tobacco products. These pentameric receptors are made up of various subunits which contribute to the diverse functions of nAChR subtypes. The β3 subunit of the nAChR has been understudied in nicotine dependence, even though it is expressed in brain regions important for drug reward. Therefore, we assessed nicotine dependence behaviors in β3 wildtype (WT) and knockout (KO) male and female mice. We evaluated nicotine reward in the conditioned place preference (CPP) test and then measured nicotine withdrawal signs after chronic exposure to the drug. For the withdrawal studies, mice were continuously infused with 24 mg/kg/day of nicotine using surgically implanted osmotic mini-pumps for 14 days. Mini-pumps were removed at day 15, and withdrawal signs (somatic signs, hyperalgesia, anhedonia-like measure using the sucrose preference test and anxiety-like behaviors using the light dark boxes) were collected at 24 h intervals for three days following spontaneous withdrawal of nicotine. Nicotine-induced CPP did not differ between β3 KO and WT mice. β3 KO mice displayed similar somatic symptoms and hyperalgesia compared to WT mice but showed significant absence in affective (anhedonia and anxiety-like behaviors) withdrawal signs in nicotine-dependent mice. These observations suggest that the β3 nicotinic subunits do not seem to influence nicotine reward but plays an important role in affective nicotine withdrawal signs. Given the health burden of tobacco use disorder and the modest effect of smoking cessation aids, it is important to understand underlying factor contributing to nicotine dependence. The results of this study will further our knowledge of the role of the β3 nAChR subunit in nicotine reward and withdrawal behaviors in hopes of finding new molecular targets for smoking cessation aids.

Recent Updates in Animal Models of Nicotine Withdrawal: Intracranial Self-Stimulation and Somatic Signs.

Tobacco use is one of the leading causes of disease, disability, and death in the world. Despite the negative health consequences of smoking and the fact that most people would like to quit, very few people are able to maintain abstinence. Nicotine, the main psychoactive component of tobacco, is mildly rewarding and plays a role in the initiation and maintenance of smoking. Cessation of nicotine intake induces mild somatic withdrawal symptoms that may contribute to the maintenance of smoking. However, it has been hypothesized that negative affective nicotine withdrawal signs are of greater motivational significance in contributing to relapse and continued smoking (Markou and Koob (eds) Intracranial self-stimulation thresholds as a measure of reward, vol 2. Oxford University Press, New York, 1993; Koob et al., Semin Neurosci 5:351-358, 1993). Intracranial self-stimulation (ICSS) has been established as a method to assess the acute rewarding properties of nicotine and the dysphoria associated with nicotine withdrawal. The ICSS method provides a means to measure the negative affective aspects of nicotine withdrawal in animal models and may contribute to the understanding of the neurobiological bases of nicotine dependence.

New insights on the effects of varenicline on nicotine reward, withdrawal and hyperalgesia in mice

Varenicline, a partial agonist for α4β2* nicotinic acetylcholine receptors (nAChRs) and a full agonist for α3β4 and α7 nAChRs, is approved for smoking cessation treatment. Although, partial agonism at α4β2* nAChRs is believed to be the mechanism underlying the effects of varenicline on nicotine reward, the contribution of other nicotinic subtypes to varenicline's effects on nicotine reward is currently unknown. Therefore, we examined the role of α5 and α7 nAChR subunits in the effects of varenicline on nicotine reward using the conditioned place preference (CPP) test in mice. Moreover, the effects of varenicline on nicotine withdrawal-induced hyperalgesia and aversion are unknown. We also examined the reversal of nicotine withdrawal in mouse models of dependence by varenicline.Varenicline dose-dependently blocked the development and expression of nicotine reward in the CPP test. The blockade of nicotine reward by varenicline (0.1 mg/kg) was preserved in α7 knockout mice but reduced in α5 knockout mice. Administration of varenicline at high dose of 2.5 mg/kg resulted in a place aversion that was dependent on α5 nAChRs but not β2 nAChRs. Furthermore, varenicline (0.1 and 0.5 mg/kg) reversed nicotine withdrawal signs such as hyperalgesia and somatic signs and withdrawal-induced aversion in a dose-related manner.Our results indicate that the α5 nAChR subunit plays a role in the effects of varenicline on nicotine reward in mice. Moreover, the mediation of α5 nAChRs, but not β2 nAChRs are probably needed for aversive properties of varenicline at high dose. Varenicline was also shown to reduce several nicotine withdrawal signs.

Pharmacological modulation of the α7 nicotinic acetylcholine receptor in a mouse model of mecamylamine-precipitated nicotine withdrawal.

Recent preclinical data has implicated the α7 nicotinic acetylcholine receptor (nAChR) as a target in modulating nicotine reward. However, the role of the channel properties of the α7 nAChR in nicotine withdrawal is unknown. This study aimed to investigate the impact of α7 nAChR pharmacological modulation on mecamylamine-precipitated nicotine withdrawal behaviors in mice by using positive allosteric modulators (PAMs). The effect of the orthosteric α7 nAChR full agonist PNU282987 (1, 3, 9mg/kg, s.c.), type I α7 PAM NS1738 (1 and 10mg/kg; i.p.) and the type II α7 PAM PNU120596 (3 and 9mg/kg, i.p.) on anxiety-like behavior, somatic signs, and hyperalgesia was measured in mice undergoing mecamylamine-precipitated nicotine withdrawal. Mice were infused with 24mg/kg/day nicotine or saline for 14days using s.c. osmotic minipumps. Nicotine withdrawal signs were precipitated upon administration of the non-selective nAChR antagonist mecamylamine (3.5mg/kg, i.p.). Anxiety-like behavior in nicotine withdrawn mice was only attenuated by PNU282987 in a dose-related fashion. Somatic signs were reduced by PNU282987 and NS1738. PNU120596 was the only compound that reversed precipitated nicotine withdrawal-induced hyperalgesia. Taken together, our results suggest that modulation of the α7 nAChR can play important roles in mecamylamine-precipitated nicotine withdrawal behaviors in mice. In addition, the effects of PAMs in this study suggest that endogenous acetylcholine/choline tone is sufficient to attenuate some aspects of precipitated nicotine withdrawal. These findings highlight a beneficial effect of using α7 nAChR PAMs in some aspects of precipitated nicotine withdrawal.

Assessment of nicotine withdrawal-induced changes in sucrose preference in mice

Anhedonia, induced by nicotine withdrawal, may serve as an important affective sign that reinforces tobacco use and smoking relapse rates in humans. Animal models provide a way to investigate the underlying neurobiological factors involved in the decrease in responding for positive affective stimuli during nicotine withdrawal and may aid in drug development for nicotine dependence. Thus, we explored the use of the sucrose preference test to measure nicotine withdrawal-induced reduction in response for positive affective stimuli in mice. C57BL/6J and knockout (KO) mice were chronically exposed to different doses of nicotine through surgically implanted subcutaneous osmotic minipumps for 14days and underwent spontaneous nicotine withdrawal on day 15. A sucrose preference time course was performed and the results were compared to another well-established affective sign of nicotine withdrawal, the reduction in time spent in light side, using the Light Dark Box test. Subsequently, our results demonstrated a time-dependent and dose-related reduction in sucrose preference in nicotine withdrawn male C57BL/6J mice, indicative of a decrease in responding for positive affective stimuli. Furthermore, the sucrose preference reduction during nicotine withdrawal was consistent with decrease in time spent in the light side of the Light Dark Box test. We also found the reduction for positive affective stimuli and time spent in the light side was not present in nicotine withdrawn β2 and α6 KO mice, suggesting that these nicotinic subunits are involved in the affective signs of nicotine withdrawal. Thus, this report highlights the potential utility of the sucrose preference test as a useful measure of the decrease in responding for positive affective stimuli during spontaneous nicotine withdrawal.

Reversal of Nicotine Withdrawal Signs Through Positive Allosteric Modulation of α4β2 Nicotinic Acetylcholine Receptors in Male Mice.

Nicotine withdrawal symptoms are important factors in determining the relapse rate to tobacco smoking and drugs that diminish these symptoms would potentially have a higher success rate as smoking cessation aids. Unlike US Food and Drug administration approved smoke cessation aids (nicotine and varenicline) which act as nicotinic acetylcholine receptors (nAChRs) agonists, desformylflustrabromine (dFBr) acts as a nAChR positive allosteric modulator with higher selectivity to the α4β2 nAChR. In animal studies, dFBr was well tolerated and reduced intravenous nicotine self-administration. In this study, we use behavioral test in mouse model of spontaneous nicotine withdrawal to assess the effect of dFBr on nicotine withdrawal symptoms. Spontaneous nicotine withdrawal in nicotine-dependent ICR male mice was established 18-24 h after termination (minipump removal) of 14 days infusion of nicotine. After that (day 15), spontaneous signs of nicotine withdrawal were examined in the following order: anxiety-like behaviors, somatic signs, and then hyperalgesia using previously published behavioral protocols. Fifteen minutes before withdrawal signs testing, mice received a subcutaneous acute injection of vehicle or dFBr at the doses of 0.02, 0.1, and 1 mg/kg to determine the effect of dFBr on nicotine withdrawal symptoms. dFBr produced dose-dependent reversal of nicotine withdrawal signs in mouse model of spontaneous nicotine withdrawal. Positive allosteric modulators of nAChR such as dFBr reduce nicotine withdrawal symptoms supporting the potential clinical use of this novel class of nAChR-based therapeutics as smoking cessation aid.