Nitric oxide mediates mecamylamine- and naloxone-precipitated nicotine withdrawal

Attenuation by baclofen of nicotine rewarding properties and nicotine withdrawal manifestations

RATIONALE

Nicotine is a major active ingredient in tobacco and plays a major role in tobacco addiction. In rodents, repeated nicotine administration produces behavioral responses related to its addictive properties, such as reinforcing effects and physical dependence.

OBJECTIVES

The aim of the present study was to evaluate the possible role of GABAB receptor in responses induced by repeated nicotine administration in Swiss Webster mice.

RESULTS

Nicotine hydrogen tartrate salt (0.5 mg/kg, s.c.) administration induced rewarding properties in the conditioning place preference test. The GABAB receptor agonist, baclofen (3 mg/kg, i.p.) abolished the rewarding properties induced by nicotine hydrogen tartrate salt (0.5 mg/kg, s.c.). In addition, naloxone-precipitated nicotine withdrawal induced somatic manifestations, anxiety-like effects in the elevated plus maze test and dysphoric manifestations in the conditioned place aversion paradigm. Baclofen (2 and 3 mg/kg, i.p.) prevented the somatic manifestations and the anxiety-like effects associated with naloxone-precipitated nicotine withdrawal but not the dysphoric manifestations.

CONCLUSIONS

These results showed that nicotine rewarding properties and negative aspects of nicotine withdrawal, such as anxiety-like effects and somatic manifestations, can be modulated by the GABAB receptor activity. This study now reveals a novel possible application of baclofen to develop new therapeutic strategies to achieve smoking cessation.

Critical role of nitric oxide on nicotine-induced hyperactivation of dopaminergic nigrostriatal system: Electrophysiological and neurochemical evidence in rats

Nicotine, the main psychoactive ingredient in tobacco, stimulates dopamine (DA) function, increasing DA neuronal activity and DA release. DA is involved in both motor control and in the rewarding and reinforcing effects of nicotine; however, the complete understanding of its molecular mechanisms is yet to be attained. Substantial evidence indicates that the reinforcing properties of drugs of abuse, including nicotine, can be affected by the nitric oxide (NO) system, which may act by modulating central dopaminergic function. In this study, using single cell recordings in vivo coupled with microiontophoresis and microdialysis in freely moving animals, the role of NO signaling on the hyperactivation elicited by nicotine of the nigrostriatal system was investigated in rats. Nicotine induced a dose-dependent increase of the firing activity of the substantia nigra pars compacta (SNc) DA neurons and DA and 3,4-dihydroxyphenylacetic acid (DOPAC) release in the striatum. Pharmacological manipulation of the NO system did not produce any change under basal condition in terms of neuronal discharge and DA release. In contrast, pretreatments with two NO synthase (NOS) inhibitors, N-omega-nitro-l-arginine methyl ester (l-NAME) and 7-nitroindazole (7-NI) were both capable of blocking the nicotine-induced increase of SNc DA neuron activity and DA striatal levels. The effects of nicotine in l-NAME and 7-NI-pretreated rats were partially restored when rats were pretreated with the NO donor molsidomine. These results further support the evidence of an important role played by NO on modulation of dopaminergic function and drug addiction, thus revealing new pharmacological possibilities in the treatment of nicotine dependence and other DA dysfunctions.

Passive immunization against nicotine attenuates somatic nicotine withdrawal syndrome in the rat

INTRODUCTION

Nicotine immunization is under consideration as an intervention for smoking cessation. Therefore, it was of interest to evaluate the effects of nicotine antibodies on the withdrawal syndrome following termination of chronic nicotine administration.

METHODS

Experiment 1 determined whether passive immunization following continuous nicotine infusion would alter the intensity of nicotine withdrawal syndrome in the rat. Fourteen rats were rendered nicotine dependent by 7 days of subcutaneous nicotine bitartrate infusion. On the final day, seven rats received 150 mg intraperitoneal (i.p.) of immune gamma globulin (IgG) raised against 3'-aminomethylnicotine-recombinant Pseudomonas aeruginosa exoprotein A (NicVAX, Nabi Biopharmaceuticals, Rockville, MD) and seven rats received normal IgG. Rats were observed under blind conditions for somatically expressed nicotine abstinence signs immediately prior to drug termination and at 12, 24, and 36 hr afterward. In Experiment 2, similarly treated rats were observed at 6- and 72-hr postwithdrawal, to test the possibility that immunization altered the time course rather than the intensity of withdrawal syndrome. Experiment 3 tested whether immunized rats were still nicotine dependent. Without pump removal, each rat was challenged by 1/mg/kg mecamylamine HCl and observed for precipitated withdrawal syndrome.

RESULTS

In Experiment 1, there was no premature withdrawal syndrome during nicotine infusion. After termination, the immunized group had significantly fewer withdrawal signs than controls. Experiment 2 showed that immunization did not simply alter the timing of the nicotine abstinence syndrome since immunization did not increase signs before or after the usual withdrawal timeframe. In Experiment 3, rats immunized on the final day of infusion were still nicotine dependent since they exhibited a vigorous mecamylamine-precipitated withdrawal syndrome.

DISCUSSION

Nicotine antibodies did not precipitate a withdrawal syndrome, and they markedly reduced the severity of spontaneous nicotine withdrawal. The present data suggests that this may be most readily explained by their reported delay of nicotine clearance.

Nicotine anxiogenic and rewarding effects are decreased in mice lacking beta-endorphin

The endogenous opioid system plays an important role in the behavioral effects of nicotine. Thus, micro-opioid receptor and the endogenous opioids derived from proenkephalin are involved in the central effects of nicotine. However, the role played by the different endogenous opioid peptides in the acute and chronic effects of nicotine remains to be fully established. Mice lacking beta-endorphin were acutely injected with nicotine at different doses to evaluate locomotor, anxiogenic and antinociceptive responses. The rewarding properties of nicotine were evaluated by using the conditioned place-preference paradigm. Mice chronically treated with nicotine were acutely injected with mecamylamine to study the behavioral expression of nicotine withdrawal. Mice lacking beta-endorphin exhibited a spontaneous hypoalgesia and hyperlocomotion and a reduction on the anxiogenic and rewarding effects induced by nicotine. Nicotine induced similar antinociception and hypolocomotion in both genotypes and no differences were found in the development of physical dependence. The dissociation between nicotine rewarding properties and physical dependence suggests a differential implication of beta-endorphin in these addictive related responses.

Rodent models of nicotine withdrawal syndrome

Simple, rapid and inexpensive rodent models of nicotine physical dependence and withdrawal syndrome have proved useful for preliminary screening of smoking cessation treatments. They have led to an exponential increase of knowledge regarding the underlying neurobiological mechanisms of dependence and withdrawal syndrome. The human nicotine withdrawal syndrome in smoking cessation is variable and multidimensional, involving irritability, anxiety, depression, cognitive and attentional impairments, weight gain, sleep disturbances, and craving for nicotine. Aside from sleep disturbances, analogous phenomena have been seen in rodent models using different measures of withdrawal intensity. It appears likely that different withdrawal phenomena may involve some partially divergent mechanisms. For example, depression-like phenomena may involve alterations in mechanisms such as the mesolimbic dopamine pathway from the ventral tegmental area to the nucleus accumbens. Irritability and anxiety may involve alterations in endogenous opioid systems and other regions, such as the amygdala. This chapter reviews many additional anatomical, neurochemical, and developmental elements that impact nicotine physical dependence.

Mecamylamine attenuates cue-induced reinstatement of nicotine-seeking behavior in rats

Mecamylamine, a noncompetitive nicotinic cholinergic antagonist, inhibits nicotine self-administration in animals and may attenuate tobacco smoking in humans trying to quit. Our preliminary data suggested that this agent, at a dose of 2 mg/kg (subcutaneous (s.c.)), also attenuates cue-induced relapse to nicotine-seeking behavior in rats. This study determined whether mecamylamine-induced attenuation can be obtained at doses lower than the high 2 mg/kg dose used in the first study, and whether it is specific to nicotine-associated cues. Male Sprague-Dawley rats were trained to intravenously self-administer nicotine (0.03 mg/kg/infusion) on a fixed-ratio 5 schedule. Each infusion was accompanied by a visual cue (1 s onset of a lever light followed by offset of a house light for 20 s during which time no infusions could be obtained). After the nicotine-maintained responding was extinguished by withholding the delivery of nicotine (saline substitution) and its associated cue, reinstatement tests were conducted. Response-contingent re-presentation of the cue without further availability of nicotine significantly reinstated extinguished responding at the previously nicotine-reinforced lever. Pretreatment with mecamylamine (0.5, 1, and 2 mg/kg, s.c.) dose-dependently attenuated the cue-induced reinstatement of lever responding. Mecamylamine did not change food-taking and -seeking responses, whereas the highest dose (2 mg/kg) decreased nicotine self-administration behavior. The results confirm previous findings that stimuli conditioned to nicotine self-administration effectively elicit reinstatement of nicotine-seeking behavior after extinction and demonstrate that mecamylamine, besides suppressing self-administration of nicotine, effectively attenuates cue-induced nicotine-seeking behavior. These findings suggest that the response-reinstatement procedures used in this study may be useful for studying neurobiological mechanisms of nicotine-seeking behavior and that mecamylamine-like drugs may be potential candidates for pharmacological treatment and prevention of relapse to tobacco smoking in abstinent smokers.

Lack of effect ofNω-nitro-L-arginine methyl ester on bromocriptine-induced locomotor sensitization in mice

The present study was designed to investigate the effects of Nomega-nitro-L-arginine methyl ester (L-NAME), a nitric oxide (NO) synthase inhibitory agent, on bromocriptine-induced locomotor sensitization in mice. Adult male Swiss-Webster mice (26-32 g) were the subjects. Saline or L-NAME (15-60 mg/kg) was injected to mice intraperitoneally 30 min before bromocriptine (5 mg/kg), and locomotor activity was recorded for 240 min in an open field activity monitoring system. This procedure lasted for 2 weeks, once in 2 days from Monday to Friday, six sessions in total. After a 2-day drug-free period, a challenge injection of bromocriptine (5 mg/kg) or vehicle was administered by all groups of mice. Other groups of mice treated with bromocriptine according to the aforementioned procedure except L-NAME pretreatments were challenged with saline or L-NAME (15-60 mg/kg) plus bromocriptine (5 mg/kg) after a 2-day drug-free period. Bromocriptine produced a significant locomotor sensitization. L-NAME (15-60 mg/kg) did not have any significant effect on the development and expression of bromocriptine-induced locomotor sensitization in mice. Meanwhile, the data also imply that NO-related mechanisms may not be responsible for bromocriptine-induced locomotor sensitization in mice.

Mu-opioid receptors are involved in the tolerance to nicotine antinociception

Several studies have shown the participation of the endogenous opioid system on the antinociceptive effects and addictive properties of nicotine. The aim of the present study was to explore the involvement of the mu-opioid receptors in the development of tolerance to nicotine antinociception. Chronic treatment of C57BL/6 mice with nicotine (5 mg/kg s.c., three times daily during 12 days) resulted in tolerance to its antinociceptive responses in the tail-immersion test. We investigated the possible existence of adaptive changes in the expression and/or functional activity of mu-opioid receptors in these tolerant mice by using autoradiography of [(3)H]D-Ala(2)-MePhe(4)-Gly-ol(5) enkephalin ([(3)H]DAMGO) binding and DAMGO-stimulated guanosine [(35)S]5'-(gamma-thio)-triphosphate ([(35)S]GTPgammaS) binding. The density of mu-opioid receptors in the spinal cord was not modified in nicotine-tolerant mice, whereas a decrease was found in the caudate-putamen, as well as in the core and the shell of the nucleus accumbens. However, the functional activity of these receptors was significantly increased in the spinal cord as a consequence of nicotine treatment. To further investigate the role of mu-opioid receptors in the tolerance to nicotine-induced antinociception, we evaluated this response in C57BL/6 mu-opioid receptor knockout mice. Chronic nicotine treatment produced tolerance in both wild-type and knockout animals, but tolerance developed faster in mice lacking mu-opioid receptors. These results indicate that mu-opioid receptors play an important role in the development of tolerance to nicotine antinociceptive effects.

Bupropion attenuates nicotine abstinence syndrome in the rat

RATIONALE

Bupropion reduces discomfort and craving associated with smoking cessation. This study determined whether a rat model of nicotine dependence could detect such nicotine abstinence-alleviating effects.

OBJECTIVES

Experiments determined whether the abstinence-alleviating effects of bupropion were detectable by (1) behavioral abstinence signs precipitated by the nicotinic antagonist mecamylamine, (2) place aversion conditioned to mecamylamine-precipitated nicotine abstinence, and (3) spontaneous behavioral abstinence signs after abrupt nicotine withdrawal.

METHODS

In experiments 1 and 2, nicotine-dependent rats were coinfused for 7 days with 3.15 mg/kg/day nicotine and 20 mg/kg/day bupropion or with nicotine alone. They were then challenged with 1 mg/kg mecamylamine and observed for behavioral abstinence signs (experiment 1) or place aversion conditioned to precipitated abstinence (experiment 2). In experiment 3, rats were nicotine-infused for 7 days as above. A day after termination of nicotine infusion, rats were observed for spontaneous nicotine abstinence signs before and after injection with saline or bupropion.

RESULTS

In experiment 1, rats coinfused with nicotine and bupropion had significantly fewer mecamylamine-precipitated abstinence signs than rats infused with nicotine alone but similar numbers to rats infused with saline alone. In experiment 2, bupropion pretreatment significantly reduced the aversiveness of mecamylamine-precipitated nicotine abstinence. In experiment 3, a single bupropion injection dose-dependently alleviated spontaneous nicotine abstinence syndrome.

CONCLUSIONS

These results suggest that these rat models of nicotine dependence and abstinence syndrome may be useful in detecting nicotine abstinence-alleviating effects of potential medications for smoking cessation. The effects of acute bupropion administration raise interesting questions regarding bupropion's mechanism of action.

Nicotine-induced antinociception, rewarding effects, and physical dependence are decreased in mice lacking the preproenkephalin gene

It has been shown previously that the endogenous opioid system may be involved in the behavioral effects of nicotine. In the present study, the participation of endogenous enkephalins on nicotine responses has been investigated by using preproenkephalin knock-out mice. Acute nicotine-induced hypolocomotion remained unaffected in these mice. In contrast, antinociception elicited in the tail-immersion and hot-plate tests by acute nicotine administration was reduced in mutant animals. The rewarding properties of nicotine were then investigated using the place-conditioning paradigm. Nicotine induced a conditioned place preference in wild-type animals, but this effect was absent in knock-out mice. Accordingly, in vivo microdialysis studies revealed that the enhancement in dopamine extracellular levels in the nucleus accumbens induced by nicotine was also reduced in preproenkephalin-deficient mice. Finally, the somatic expression of the nicotine withdrawal syndrome precipitated in nicotine-dependent mice by mecamylamine was significantly attenuated in mutant animals. In summary, the present results indicate that endogenous opioid peptides derived from preproenkephalin are involved in the antinociceptive and rewarding properties of nicotine and participate in the expression of physical nicotine dependence.

Reduced nNOS expression induced by repeated nicotine treatment in μ-opioid receptor knockout mice

To determine whether neuronal nitric oxide synthase (nNOS) is involved in nicotine-induced behavioral sensitization in mu-opioid receptor knockout mice we adopted an immunohistochemical approach. Our results confirm that repeated nicotine administration increased locomotor activity in wild-type mice, but failed to increase locomotor activity in mu-opioid receptor knockout mice, thus suggesting that the mu-opioid receptor is involved in behavioral sensitization. Higher numbers of nNOS-positive cells were observed in the striatum of wild-type mice repeatedly treated with nicotine than in saline-treated wild-type mice. However, mu-opioid receptor knockout mice showed significantly lower nicotine-induced nNOS expression in the striatum versus wild-type mice. No differences were found in the hilus of the dentate gyrus between wild-type and mu-opioid receptor knockout mice. These findings demonstrate that the absence of mu-opioid receptors can cause a significant reduction in the expression of nNOS in the striatum, as induced by repeated nicotine treatment.

The effects of nitric oxide on the acquisition and expression of nicotine-induced conditioned place preference in mice

In the present study, the possible role of nitric oxide on the conditioned place preference (CPP) induced by nicotine in mice was investigated. Intraperitoneal (i.p.) injections of nicotine (1 mg/kg) and the nitric oxide (NO) precursor, L-arginine (200 and 500 mg/kg), produced significant place preference. However, injection of mecamylamine (0.05 and 0.1 mg/kg; i.p.) or the NO synthase (NOS) inhibitor, L-Nitro-amino-methyl-ester, L-NAME (5-20 mg/kg; i.p.), had no effect. Ineffective doses of nicotine in combination with ineffective doses of L-arginine produced significant place preference. Administration of L-arginine (50, 100 and 150 mg/kg; i.p.) on the test day reduced the expression of nicotine-induced place preference. Nicotine injection (0.25, 0.5 and 0.75 mg/kg) on the test day reduced the expression of place preference induced by L-arginine, while both mecamylamine (0.05 and 0.1 mg/kg) and L-NAME (5, 10 and 20 mg/kg) inhibited the acquisition of place preference induced by nicotine (1 mg/kg) and L-arginine (200 mg/kg). Moreover, neither of the antagonists reduced the expression of nicotine- or L-arginine-induced place preference. It is suggested that nitric oxide may play an important role in nicotine-induced place preference.

Bases genéticas del hábito tabáquico

Dependence on tobacco is one of the most important health problems in our society due to the direct relationship with lung cancer. Early studies in twins revealed that genetic factors modify the susceptibility to develop tobacco dependence. Different studies are underway to try to find an association between polymorphisms of genes involved either in nicotine metabolization or in neural transmission and the initiation and maintenance of the dependence on tobacco. Here we review the studies performed so far and discuss new perspectives for future studies.

Impact of nicotine withdrawal on novelty reward and related behaviors

The authors tested the decreased reward function hypothesis of nicotine withdrawal using a novel-object place conditioning task. A conditioned place preference was evident in controls and in rats that had experienced 4 nicotine withdrawal days, but not in rats that had experienced 1-3 withdrawal days. This implies that the rewarding properties of interacting with novel objects were not readily associated with the environment in which they were paired. Follow-up experiments eliminated other explanations based on withdrawal-induced failures to process object or environment information. Also, expression of conditioning was not affected, indicating that withdrawal likely altered acquisition. Further investigation into the neurochemical and behavioral changes that accompany nicotine withdrawal will lead to a better understanding of the withdrawal syndrome.

Modulation of kappa-opioidergic systems on mecamylamine-precipitated nicotine-withdrawal aversion in rats

The present study was designed to examine the modulation of the kappa-opioidergic system on mecamylamine-precipitated nicotine-withdrawal aversion. The nicotinic receptor antagonist mecamylamine, which is known to pass the blood-brain barrier, produced a place aversion in rats chronically treated with nicotine using an osmotic mini-pump. This effect was significantly attenuated by pretreatment with -opioid receptor agonists U50,488H (1.0 mg/kg, s.c.) and TRK-820 (0.03 mg/kg, s.c.). The attenuation of mecamylamine-precipitated nicotine-withdrawal aversion by U50,488H was completely reversed by the combination with a selective -opioid receptor antagonist nor-binaltorphimine (10.0 mg/kg, i.p.). These results suggest that the activation of endogenous -opioidergic systems can suppress the mecamylamine-precipitated nicotine-withdrawal aversion.

Nicotine dependence: studies with a laboratory model

Simple, rapid preclinical models of nicotine physical dependence and abstinence syndrome are needed to identify underlying neurobiological mechanisms and screen potential therapies. One such model induces dependence by 7 days of continuous subcutaneous nicotine infusion in the rat. Abstinence is initiated through termination of infusion or injection of nicotinic antagonist drugs. The result is an abstinence syndrome involving a pattern of behaviors somewhat resembling opiate abstinence in the rat as well as weight gain and depressed locomotor activity. The model has met a number of validity criteria and its essential features have been replicated in several laboratories. Several research groups have modified or extended the model by measuring emotional/motivational changes associated with nicotine abstinence such as conditioned aversion, intracranial self-stimulation (ICSS) thresholds and the startle response. Dependence models have been used to identify neurobiological systems that contribute to nicotine dependence, particularly endogenous opiate systems and the mesolimbic dopamine pathway. It is hypothesized that these different systems contribute to different behavioral aspects of nicotine abstinence syndrome. Increasingly used as a preclinical screening tool, the model has proved sensitive to various abstinence-alleviating therapeutic approaches, including some with already demonstrated clinical effectiveness.

Nitric oxide and substance dependence

The free-radical gas nitric oxide (NO) plays an important role in a diverse range of physiological processes. It is synthesized from the precursor L-arginine by the enzyme NO synthase (NOS), which transforms L-arginine into NO and citrulline. This synthetic pathway exists in the central nervous system (CNS), and NO appears to be a messenger molecule in the CNS, fulfilling most of the criteria of a neurotransmitter. Recent studies indicate that NO may play an important role in dependence on drugs of abuse. The purpose of this review is to address the role of NO in dependence on substances such as opioids, ethanol, psychostimulants and nicotine. Inhibitors of NOS modulate withdrawal from opioids and ethanol, diminishing many signs of withdrawal. In addition, NOS inhibitors suppress signs of withdrawal from nicotine. These data suggest that NO may be involved in the expression of withdrawal signs, and they leave open the possibility that NO may mediate the development of many of these signs. Although preliminary, data to date suggest that glutamate neurotransmission may be related to these beneficial effects of NOS inhibitors on signs of withdrawal. Emerging data further suggest that NO may have a general role in the dependence potential of various classes of drugs of abuse. Thus, modulation of NO systems may be a potential therapeutic target for treatment of substance abuse.

Nicotine abstinence in the mouse

We present evidence that intermittent administration of nicotine, 2 mg/kg s.c., four times daily to mice for 14 days produces a somatic abstinence syndrome after discontinuing treatment. The nicotine abstinence was mild and protracted, lasting more than 92 h. The constellation of abstinence signs was characterized by rearing, jumping, shakes, abdominal constrictions, chewing, facial tremor and scratching. No autonomic symptomatology was observed. Nicotine abstinence was attenuated with a single dose of nicotine administered at 24 or 48 h into withdrawal. The nicotinic antagonist mecamylamine, 3 mg/kg, induced a small increase in the total abstinence score when given 60 min after the last nicotine injection. Nicotine-abstinent mice displayed reduced locomotor activity. Finally, mice lost weight during the nicotine treatment which was not recovered during the withdrawal. Along with the rat nicotine abstinence model, the mouse model of intermittent nicotine administration and abstinence might be useful for studying the pharmacological and biochemical mechanisms of nicotine addiction and tobacco use.

Endogenous opiates: 1998

This paper is the twenty-first installment of our annual review of research concerning the opiate system. It summarizes papers published during 1998 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; eating and drinking; alcohol; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunologic responses; and other behaviors.