Effects of nicotine withdrawal on central dopaminergic systems

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.

Increased dopamine D3 receptor expression accompanying behavioral sensitization to nicotine in rats

Behavioral sensitization to nicotine, which appears following repeated nicotine administration, has been suggested to take part in the development of smoking habit in humans. The mesolimbic dopaminergic system plays a role in this process and a hypersensitivity of postsynaptic neurons of the nucleus accumbens as been proposed as a mechanism, but changes in dopamine D(1) or D(2) receptors have not been demonstrated to date. A challenge administration of nicotine (0.5 mg/kg s.c.) produced a strong increase in locomotor activity in rats repeatedly pretreated with nicotine (0.5 mg/kg s.c.), but not saline, once a day for 5 days. This behavioral sensitization was accompanied by an increase in D(3) receptor binding and mRNA in the shell of nucleus accumbens. D(3) receptor expression was unchanged in the core of nucleus accumbens and dorsal striatum, as it was in the shell of nucleus accumbens after an acute administration of nicotine to naive rats. In contrast, no changes were noticed in D(1) and D(2) receptor expressions in any brain region examined after chronic or acute treatment with nicotine. In addition, nicotine challenge decreased preprodynorphin and preprotachykinin mRNA levels in naive rats, but only preprotachykinin mRNA levels in rats pretreated with nicotine. These biochemical changes resemble those occurring during behavioral sensitization to levodopa of dopamine-denervated rats, which had been causally related to the induction of D(3) receptor expression. We propose that a similar mechanism is responsible for behavioral sensitization to nicotine.

A preliminary placebo-controlled trial of selegiline hydrochloride for smoking cessation

BACKGROUND

Since dopaminergic mechanisms appear to be involved in nicotine dependence, we studied the safety and efficacy of the monoamine oxidase B inhibitor selegiline hydrochloride compared with placebo for smoking cessation in nicotine-dependent cigarette smokers.

METHODS

Forty subjects with DSM-IV nicotine dependence were randomized to: 1) selegiline hydrochloride (5 mg p.o. twice daily) or 2) placebo in an 8-week trial. Outcome measures included smoking cessation rates, treatment retention, and medication side effects.

RESULTS

Selegiline hydrochloride increased trial end point (week 8) 7-day point prevalence smoking cessation rates (selegiline hydrochloride, 9/20 [45.0%]; placebo, 3/20 [15.0%], odds ratio = 4.64, 95% CI, 1.02-21.00, p <.05), and smoking cessation rates during the last 4 weeks of the trial (selegiline hydrochloride, 6/20 [30.0%]; placebo, 1/20 [5.0%], odds ratio = 8.14, 95% CI, 0.88-75.48, p =.07) in comparison with placebo. Six-month follow-up 7-day point prevalence smoking cessation rates were reduced compared with trial end point (selegiline hydrochloride, 4/20 [20.0%]; placebo, 1/20 [5.0%], odds ratio = 4.75, 95% CI, 0.48-46.91, p =.18). Treatment retention was similar between drug and placebo groups (p =.13), and selegiline hydrochloride was well tolerated in cigarette smokers.

CONCLUSION

This preliminary study suggests that selegiline (10 mg/day) is safe for use and enhances smoking cessation rates compared with placebo in nicotine-dependent cigarette smokers.

Lasting effects of adolescent nicotine exposure on the electroencephalogram, event related potentials, and locomotor activity in the rat

Tobacco smoking initiated during adolescence is often associated with rapid onset of dependence and difficulty in maintaining abstinence. Animal models have demonstrated that adolescent nicotine exposure causes cell death and altered neurochemistry in the cortex and hippocampus; however, little is known about the neurophysiological consequences of adolescent nicotine exposure in the adult. The primary objective of this study was to assess the consequences of adolescent nicotine exposure on the adult electroencephalogram (EEG) and event-related potentials. Male Sprague-Dawley rats were administered nicotine (5.0 mg/kg per day) for 5 days between postnatal days 35 and 40 using transdermal nicotine patches. Following 6-7 weeks of nicotine withdrawal, EEG activity and event related potentials were assessed. Motor activity and sucrose preference were also examined during the nicotine withdrawal period. Additionally, a set of rats was exposed to multiple doses of nicotine for a single day to assess nicotine and cotinine blood levels. Transdermal nicotine produced nicotine (88+/-21.5 ng/ml) and cotinine (647.6+/-123.2 ng/ml) levels comparable to those previously reported. Reduced motor activity, decreased 1-4 Hz power in the cortical electroencephalogram, and increased cortical N1 amplitude were observed in nicotine-exposed rats compared to controls. These data demonstrate that transdermal nicotine patches provide an effective and non-invasive nicotine delivery system for the adolescent rat. The combined neurophysiological and locomotor activity changes observed in nicotine-exposed rats demonstrate that adolescent nicotine exposure has lasting neurobehavioral consequences. These changes may be indicative of a lasting 'nicotine abstinence syndrome' characterized by increased arousal, anxiety, or emotionality.

The potential of dopamine agonists in drug addiction

The use of dopamine agonists in alcohol, stimulant and nicotine dependence has been examined. The direct agonists, such as bromocriptine and pergolide, have not shown utility in alcohol or cocaine abuse and dependence in larger controlled trials. Indirect agents, such as selegiline, may be helpful in cocaine or nicotine abuse and larger clinical trials are underway. Disulfiram may also raise dopamine levels and has shown promise for cocaine dependence. Other indirect agents, such as mazindol and methylphenidate, have not proven effective for cocaine addiction but have not been tested in alcohol or nicotine abuse. Agents for subtypes of dopamine receptors, such as D3, and the use of partial agonists may be useful future treatment approaches. Animal studies also suggest that tailoring treatment to subgroups of patients based on genotype may improve responses.

Smoking, reward responsiveness, and response inhibition: tests of an incentive motivational model

BACKGROUND

Incentive-motivation models of addiction suggest impairment of functional activity in mesocorticolimbic reward pathways during abstinence. This study tested implications for subjective and behavioral responses to nondrug incentives, cue-elicited craving, and prefrontal cognitive functions, particularly response inhibition.

METHODS

We tested 26 smokers after smoking and after overnight abstinence in counterbalanced order; 26 nonsmokers were also tested twice. Measures included a simple card-sorting test performed with and without financial incentive (the CARROT), the Snaith Hamilton Pleasure Scale as an index of subjective reward responsiveness, ratings of subjective craving and withdrawal before and after exposure to a cigarette, an index of oculomotor response inhibition (saccadic vs. antisaccadic eye movements), verbal fluency, and reversed digit span.

RESULTS

Compared with the smoking condition, and independently of withdrawal severity, abstinence was associated with reduced cue reactivity, pleasure expectancies, responsiveness to financial incentive, and response inhibition (antisaccadic eye movements). Verbal fluency and reversed digit span were unaffected, contrary to findings elsewhere with heavier smokers. Nonsmokers' scores either fell between those of abstainers and recent smokers or approximated those of recent smokers.

CONCLUSIONS

The data were in general consistent with behavioral predictions derived from the incentive-motivational model of addiction and suggest that abstinence may be associated with impairments of motivation and response inhibition, which are independent of other subjectively experienced withdrawal symptoms.

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.

Reduced dopamine D1 receptor binding in the ventral striatum of cigarette smokers

Several drugs of abuse, including nicotine, are thought to exert their reinforcing effects through actions on the mesolimbic dopamine system. Animal and human studies suggest that chronic administration of addictive drugs may lead to impaired dopamine neurotransmission in the nucleus accumbens. We measured D1 receptor density in 11 smokers and 18 nonsmokers using positron emission tomography and the D1 receptor ligand [11C]SCH 23390. Ten of the smokers were scanned twice, once after overnight abstinence from cigarettes, and once while smoking at their usual rate, to account for possible acute effects of cigarette smoking on D1 receptor binding. In addition, eight control subjects were scanned twice to assess the reproducibility of the method. We used compartmental modeling to measure [11C]SCH 23390 binding potential, a measure of D1 receptor density. There were no differences in binding between abstinent and nonabstinent scans in smokers or in the two scans in controls. However, there was a significant reduction in [11C]SCH 23390 binding potential in smokers compared to nonsmokers in the striatum, most prominently in the ventral striatum. This suggests that there is a reduction in dopamine D1 receptor density in the ventral striatum of human cigarette smokers relative to nonsmokers, which implies that the postsynaptic mesolimbic dopamine system may be chronically underactive in smokers, either as an antecedent or consequence of addiction to cigarettes. Such a hypodopaminergic state may play an important role in sustaining nicotine-seeking behavior. Alternatively, an inherited reduction in dopamine receptors in the striatum may be associated with an increased risk of addictive behavior.

Changes in the glutamate release and uptake of cerebellar cells in perinatally nicotine-exposed rat pups

Cerebellar granule and glial cells were cultured from 7 day-old rat pups after pre- and post-natal nicotine treatment. Ten days later, the basal release of glutamate in the granule cells prepared from the pre- and post-natally nicotine-exposed pups was higher and lower than the controls, respectively. The N-methyl-D-aspartate-induced release of glutamate was higher in the granule cells of post-natal nicotine exposed rats. However, the nicotine-induced glutamate release was either unchanged or was lower in the granule cells of all nicotine-treated pups. The basal glutamate uptake was higher in the glial cells from those exposed pre-natally and lower in the continuously nicotine-exposed pups. The sensitivities of L-trans-pyrrolidine-2,4-dicarboxylic acid on glutamate uptake were higher in all nicotine treated groups. There was a higher number of specific [3H]dizocilpine binding sites in the pre- or continuously nicotine-exposed group. These results suggest that the cerebellar cell properties are altered after perinatal nicotine exposure and that the development of an excitatory amino acid system might be affected differently depending on the nicotine exposure time.

Nicotine as an Addictive Substance: A Critical Examination of the Basic Concepts and Empirical Evidence

The present review is a critical analysis of the concepts behind and the empirical data supporting the view that tobacco use represents an addiction to nicotine. It deals with general aspects of the notion of addiction, while concentrating on specific problems associated with incorporating nicotine into current frameworks. The notion of addiction suffers from unprecedented definitional difficulties. The definitions offered by various authorities are very different, even contradictory. Definitions that reasonably include nicotine are so broad and vague that they allow many trivial things, such as salt, sugar, and watching television, to be considered addictive. Definitions that exclude the trivia also exclude nicotine. The addiction hypothesis, in general, is strongly shaped by views that certain drugs bring about a molecular level subversion of rationality. The main human evidence for this is verbal reports of smokers who say that they can't quit. On the other hand, the existence of many millions of successful quitters suggests that most people can quit. Some smokers don't quit, but whether they can't is another matter. The addiction hypothesis would be greatly strengthened by the demonstration that any drug of abuse produces special changes in the brain. It has yet to be shown that any drug produces changes in the brain different from those produced by many innocuous substances and events. The effects of nicotine on the brain are similar to those of sugar, salt, exercise, and other harmless substances and events. Apart from numerous conceptual and definitional inadequacies with the addiction concept in general, the notion that nicotine is addictive lacks reasonable empirical support. Nicotine does not have the properties of reference drugs of abuse. There are so many findings that conflict so starkly with the view that nicotine is addictive that it increasingly appears that adhering to the nicotine addiction thesis is only defensible on extra-scientific grounds.

Tolerance to nicotine's effects in the elevated plus-maze and increased anxiety during withdrawal

In the elevated plus-maze test of anxiety, nicotine (0.1 mg/kg sc; 30 min after injection) had a significant anxiogenic effect, shown by specific decreases in the percentage of time spent on the open arms and in the percentage of open-arm entries. Tolerance developed to this anxiogenic effect after 7 days of nicotine treatment (0.1 mg/kg/day). Five minutes after an acute injection, nicotine (0.1 mg/kg) was ineffective, but after 7 days of treatment a significant anxiolytic effect, shown by specific increases in the percentage of time spent on the open arms and in the percentage of open-arm entries, emerged. After 14 days of nicotine treatment, tolerance developed to this anxiolytic effect. There was a complete dissociation between the effects of nicotine on the measures of anxiety, and on the locomotor activity as measured by closed-arm entries. No changes in closed-arm entries were found after acute administration of nicotine, but rats tested 30 min after their 7th injection made significantly fewer, and those tested 5 min after their 14th injection made significantly more, entries than their respective controls. Rats that were tested after 24 h withdrawal from six daily nicotine injections showed a significant anxiogenic effect. A low dose of nicotine (5 ng) injected into the dorsal hippocampus was without effect in vehicle pretreated rats, but it was able to reverse the anxiogenic effect found after 24 h of withdrawal from 6 days of nicotine treatment.

Subacute nicotine exposure in cultured cerebellar cells increased the release and uptake of glutamate

Cerebellar granule and glial cells prepared from 7 day-old rat pups were used to investigate the effects of sub-acute nicotine exposure on the glutamatergic nervous system. These cells were exposed to nicotine in various concentrations for 2 to 10 days in situ. Nicotine-exposure did not result in any changes in cerebellar granule and glial cell viability at concentrations of up to 500 microM. In cerebellar granule cells, the basal extracellular levels of glutamate, aspartate and glycine were enhanced in the nicotine-exposed granule cells. In addition, the responses of N-methyl-D-aspartate (NMDA)-induced glutamate release were enhanced at low NMDA concentrations in the nicotine-exposed granule cells. However, this decreased at higher NMDA concentrations. The glutaminase activity was increased after nicotine exposure. In cerebellar glial cells, glutamate uptake in the nicotine-exposed glial cells were either increased at low nicotine exposure levels or decreased at higher levels. The inhibition of glutamate uptake by L-trans-pyrollidine-2,4-dicarboxylic acid (PDC) was lower in glial cells exposed to 50 microM nicotine. Glutamine synthetase activity was lower in glial cells exposed to 100 or 500 microM of nicotine. These results indicate that the properties of cerebellar granule and glial cells may alter after subacute nicotine exposure. Furthermore, they suggest that nicotine exposure during development may modulate glutamatergic nervous activity.

Influence of various drugs on the voluntary intake of nicotine by rats

The effects of the dopaminergic agonists (L-dopa, pergolide) and antagonists (haloperidol, clozapin) and a cholinergic agonist (tacrine) and antagonist (mecamylamine) on the voluntary intake of nicotine were investigated with the 2-bottle paradigm with the test drugs being dissolved directly in the drinking fluid of the animals. This method was found to be a reliable procedure to quickly screen compounds with specific sites of action in the brain for their effects on the voluntary intake of nicotine or perhaps other substances of abuse as well. L-dopa, pergolide and haloperidol did not affect the intake of nicotine, whereas tacrine increased it slightly and clozapine and mecamylamine markedly. These results indicate that blockade of nicotinic and dopaminergic D4 receptors partially reduce the desired effect of nicotine by forcing the animals to consume more of this substance.

Determinants of the voluntary consumption of nicotine by rats

The 2-bottle free-choice method was used to study the voluntary consumption of nicotine by rats. Rats consumed nicotine voluntarily at different, albeit quite consistent, amounts. Voluntary intakes were higher in younger than older rats, but were not affected by gender. A previously forced nicotine intake had no effect on a subsequent voluntary intake of nicotine in older but increased it in younger rats. Forced exposure to nicotine of pregnant and lactating rats did not increase the voluntary intake by their offsprings. Established free-choice drinking patterns of nicotine were not affected by a temporary forced intake of this substance. The 2-bottle choice proved to be a reliable method to study the voluntary intake of nicotine, and results suggest that nicotine is not 'addictive' per se, but that its use is apparently determined by the response of an individual rat to this substance.

Effects of chronic oral nicotine treatment and its withdrawal on locomotor activity and brain monoamines in mice

The effects of chronic nicotine and its withdrawal on locomotor activity and brain monoamines were studied using a new animal model of administering nicotine in the drinking water to male NMRI mice as the sole source of fluid. Locomotor activity as well as cerebral concentrations of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), noradrenaline (NA) and 3-methoxy-4-hydroxyphenylethyleneglycol (MOPEG) were measured post mortem on the 50th day of nicotine administration or at 12-14 or 23-25 h after withdrawal. On the 50th day of drug administration the chronically nicotine-treated mice were more active than the control mice drinking tap water and after withdrawal from nicotine the locomotor activity dropped to the level of the controls. In chronically nicotine-treated mice the striatal concentrations of DOPAC, HVA and 5-HIAA, hypothalamic 5-HIAA and NA as well as cortical NA were elevated. The concentrations of DOPAC, HVA and 5-HIAA reversed to control levels within 23-25 h after withdrawal from nicotine. The nicotine-induced elevation of the hypothalamic NA concentration was still significant at 23-25 h after withdrawal. At 12-14 h after withdrawal the hypothalamic concentration of MOPEG was increased. In conclusion, our findings on locomotor activity suggest that administration of nicotine in the drinking water to mice for several weeks seems to be a relevant method to study nicotine dependence. Furthermore, the alterations found in cerebral DA, NA and 5-HT metabolism during chronic nicotine administration indicate that all three cerebral transmitter monoamines might be involved in nicotine dependence and withdrawal.

A within-subject comparison of three different schedules of reinforcement of drug abstinence using cigarette smoking as an exemplar

In this experiment we compared three different schedules of reinforcement for promoting and sustaining short-term drug abstinence. For pragmatic reasons, cigarette smoking was studied as an exemplar of drug self-administration. The three schedules studied were a fixed magnitude of reinforcement for abstinence, a progressive increase in magnitude of reinforcement for abstinence with a reset contingency for drug use, and a progressive increase in magnitude of reinforcement for abstinence without a reset contingency. Eighteen cigarette smokers experienced the three schedules in a counterbalanced order. Each schedule was in effect for 5 consecutive days (M-F), during which time abstinence was reinforced according to the different schedules of reinforcement. The total amount of reinforcement (money) available was the same during each condition. The progressive magnitude with a reset schedule was more effective than the other two schedules in sustaining an initial period of abstinence. These results systematically replicate and extend those from prior studies demonstrating the efficacy of schedules incorporating a progressively increasing magnitude of reinforcement with a reset contingency for sustaining initial drug abstinence, and demonstrate the importance of the reset contingency to that effect.

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.

Mecamylamine-precipitated nicotine-withdrawal aversion in Lewis and Fischer 344 inbred rat strains

Many studies have indicated that Lewis and Fischer 344 inbred rat strains show marked differences in behavioral responses to abused drugs. In the present study, we sought to determine whether these two strains of rats show different responses in mecamylamine-precipitated nicotine-withdrawal aversion using the conditioned place preference paradigm. Rats were treated subcutaneously with 10 mg/kg/day nicotine for 7 days using an osmotic minipump. After chronic nicotine infusion, the nicotinic receptor antagonist mecamylamine produced a significant place aversion in Lewis, but not in Fischer 344 rats. These results suggest that mecamylamine-precipitated nicotine-withdrawal aversion is strongly regulated by genetic factors.

Chronopharmacological effects on nicotine repeated administration on heart rate, body temperature and locomotor activity circadian rhythms in rats

The aim of this study was to compare morning and evening repeated nicotine administration on the circadian rhythms of heart rate (H), body temperature (T) and locomotor activity (A) in unrestrained rats by using implanted radio-telemetry transmitters. The study was divided into three 7-day periods: a control period (P1), a treatment period (P2) and a recovery period (P3). During P2, four rats received nicotine (1mg.kg(-1)) subcutaneously at 09.00 h and four rats received nicotine in the same conditions at 21.00 h. For P1, P2 and P3, a power spectrum analysis was applied in order to determine the dominant period of rhythmicity. If H, T and A circadian rhythms were detected, the characteristics of these rhythms were determined by cosinor analysis, expressed as means+/-SEM and compared by ANOVA. Our results indicated: (1) a lack of detection of A circadian rhythm during P2 for the morning group while H and T circadian rhythms were detected for the morning and evening group whatever the period. (2) alterations of mesors, amplitudes and acrophases of H and T circadian rhythms for the morning and evening group during P2 and alterations of mesor, amplitude and acrophase of A circadian rhythm for the evening group. Furthermore these alterations were significantly different for the morning and evening group during P2. These results showed that the time of administration of nicotine differently affect H, T and A rhythms. The authors suggest that these effects can be mediated by central cholinergic and/or monoaminergic mechanisms.

Effects of repeated nicotine pre-treatment on mesoprefrontal dopaminergic and behavioral responses to acute footshock stress

The effects of acute and repeated nicotine administration on the stress response of rat mesoprefrontal dopaminergic pathways were examined. Rats were given daily injections of nicotine (0.15 or 0.60 mg/kg, s.c., freebase) or saline for 4 days, then challenged with either nicotine or saline. A regimen of inescapable electrical footshocks or no footshocks was then administered. Thirty minutes after final injection, rats were sacrificed, brains removed and dopamine (DA) and its metabolite dihydroxy-O-phenylacetic acid (DOPAC) were extracted from medial prefrontal cortex (mPFC), nucleus accumbens septi (NAS) and dorsolateral striatum and quantified by high performance liquid chromatography with electrochemical detection. Acute administration of low dose nicotine (0.15 mg/kg) produced an increase in DA utilization (increased DOPAC/DA ratio) in mPFC and NAS, but not striatum. High dose nicotine (0.60 mg/kg) produced activation in NAS, but not mPFC or striatum. Repeated low dose nicotine pre-treatment produced tolerance to the effects of nicotine challenge in the mPFC, and reduced its effects in NAS. Footshock stress preferentially increased DA utilization in mPFC and associated footshock stress-induced immobility responses, and these were reduced by low, but not high, dose repeated nicotine pre-treatment. Further, a single dose of the nicotinic acetylcholine receptor (nAChR) antagonist mecamylamine (MCA) 30 min prior to nicotine challenge dose-dependently blocked the reduction of mesoprefrontal DA stress responsivity and immobility responses produced by repeated nicotine pre-treatment. These results indicate that: (1) there are dose-dependent differential effects of acute and repeated nicotine pre-exposure on regional DA utilization; (2) low, but not high, dose repeated nicotine reduces both the mesoprefrontal DA and behavioral effects of acute footshock stress; and (3) these effects of repeated nicotine may depend on mecamylamine-sensitive nAChR stimulation. These results may have relevance to acute stress and nicotine dependence, particularly in schizophrenic disorders, which have high prevalence rates of co-morbid nicotine dependence, stress-induced symptom exacerbation and prefrontal cortical dysfunction.

Nicotine-induced perturbations on heart rate, body temperature and locomotor activity daily rhythms in rats

The aim of this study was to evaluate the influence of nicotine on the daily rhythms of heart rate, body temperature and locomotor activity in unrestrained rats by use of implanted radiotelemetry transmitters. The study was divided into three seven-day periods: a control period, a treatment period and a recovery period. The control period was used for baseline measurement of heart rate, body temperature and locomotor activity. During the treatment period three rats received nicotine (1 mg kg(-1), s.c.) at 0900 h. Three rats received saline under the same experimental conditions. Heart rate, body temperature and locomotor activity were continuously monitored and plotted every 10 min. During the three periods a power spectrum analysis was used to determine the dominant period of rhythmicity. If daily rhythms of heart rate, body temperature and locomotor activity were detected, the characteristics of these rhythms, i.e. the mesors, amplitudes and acrophases, were determined by cosinor analysis, expressed as means +/- s.e.m. and compared by analysis of variance. Nicotine did not suppress daily rhythmicity but induced decreases of amplitudes and phase-advances of acrophases for heart rate, body temperature and locomotor activity. These perturbations might result from the effects of nicotine on the suprachiasmatic nucleus, the hypothalamic clock that co-ordinates biological rhythms.

Short-term effects of nicotine on bone and calciotropic hormones in adult female rats

This study assessed the effects of two months nicotine treatment on bone formation and resorption end-points in adult, female rats. In addition, the concentrations of calciotropic hormones which included parathyroid hormone, calcitonin, 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D in rats (7 months old) were determined. All animals received either saline (n = 7/group), nicotine (3.0 mg/kg/day) (n = 7/group) or nicotine (4.5 mg/kg/day) (n = 7/group) via subcutaneous implantation of osmotic minipumps containing either saline or nicotine for a period of two months. Serum, right tibia, left femur and lumbar vertebra (3-5) were collected for determination of hormonal concentrations as well as various parameters, including histomorphometry, bone mineral density, bone mineral content and vertebral strength. Although nicotine-treated rats showed a lower level of 25-hydroxyvitamin D [54.4 +/- 3.1 ng/ml for the 3.0 mg/kg/day and 55.8 +/- 2.8 for the 4.5 mg/kg/day group] (mean +/- S.E.M.) as compared to controls (74.8 +/- 2.8 ng/ml) (P < 0.01, Newman-Keuls test), no significant difference could be detected for the levels of the remaining hormones. Similarly, no statistical differences were detected on histomorphometric end-points, bone mineral density, bone mineral content and vertebral strength of rats. We conclude that, in spite of lowering serum 25-hydroxyvitamin D by about 30%, nicotine administration of two months duration does not alter bone mass, strength or formation and resorption end-points.

Reduced dopamine output in the nucleus accumbens but not in the medial prefrontal cortex in rats displaying a mecamylamine-precipitated nicotine withdrawal syndrome

Mesolimbocortical dopamine (DA) neurotransmission is important in the mediation of the dependence-producing actions of nicotine and other drugs of abuse. Withdrawal from chronic treatment with various types of addictive drugs, including amphetamine, cocaine, ethanol and morphine is associated with a decrease in dopaminergic output in the nucleus accumbens (NAC), whereas the effects of withdrawal from these drugs on dopaminergic output in the medial prefrontal cortex (PFC), as yet, remain largely unknown. This study examined putative changes in the extracellular levels of dopamine and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the NAC and in the PFC of rats displaying behavioral signs of nicotine withdrawal. Rats were infused for 7 days with nicotine via subcutaneously implanted minipumps, whereas control animals carried saline-containing pumps. On the fifth day of infusion a microdialysis probe was implanted in the NAC or the PFC of the rats. Forty-eight hours later the levels of DA and the monoamine metabolites were assessed in the dialysate. The behavioral and biochemical effects of a saline injection and a subsequent challenge with the nicotinic receptor antagonist mecamylamine (1 mg/kg s.c.) were determined. Following mecamylamine challenge in nicotine-treated animals, the levels of DA, DOPAC and HVA in the NAC, but not in the PFC, decreased below pre-injection levels and in relation to control animals. The score of abstinence signs increased in the nicotine-treated rats, as compared both to the score after saline and to that in control animals. The decreased DA output in the NAC in animals displaying nicotine withdrawal signs is similar to that seen after withdrawal of several other drugs of abuse, and may have bearing on motivational deficits associated with the abstinence reactions.

Tobacco smoke influence on heart rate, body temperature, and locomotor activity daily rhythms as assessed by radiotelemetry in rats

Using radiotelemetry, this study aimed to evaluate the influence of tobacco smoke on heart rate (H), body temperature (T) and locomotor activity (A) daily rhythms in rats. The tobacco smoke intoxication was produced with a smoking apparatus. H, T, and A data were captured by radiotelemetry. The study was divided into three periods: a 1-week control period (P1), a 1-week stress period (P2), in order to evaluate the stress induced by the animals' restraint in the smoking apparatus, and a 1-week daily tobacco smoke intoxication period (P3). For P1, P2, and P3, a power spectrum analysis was applied in order to determine the dominant period of rhythmicity. Then, characteristics of the rhythms were determined by cosinor analysis. Statistical comparisons were done by ANOVA. Power spectrum analysis showed that neither stress nor tobacco suppressed the daily rhythmicity. Cosinor revealed some modifications: H amplitude was decreased during P2 and P3 with a greater reduction during P3, while T and A amplitudes were decreased during P2 and P3 without difference between P2 and P3. T acrophase was delayed during P2, while A acrophase was delayed during P2 and P3 without any difference between P2 and P3. These perturbations may reflect the effects of stress and tobacco on the suprachiasmatic nucleus by a dopaminergic mechanism.

Attenuation of mecamylamine-precipitated nicotine-withdrawal aversion by the 5-HT3 receptor antagonist ondansetron

The effect of ondansetron (0.01-0.1 mg/kg, s.c.), a selective 5-HT3 receptor antagonist, on mecamylamine-precipitated nicotine-withdrawal aversion was examined in the conditioned place preference paradigm. Male Sprague-Dawley rats were chronically treated subcutaneously with 9 mg/kg/day (-)-nicotine tartrate using an osmotic minipump. After nicotine treatment for 7 days, mecamylamine (1 mg/kg, s.c.), a nicotinic receptor antagonist, produced place aversion in nicotine-dependent rats. This aversive effect was dose-dependently antagonized by pretreatment with ondansetron 30 min prior to the conditioning. These results suggest that ondansetron may attenuate the place aversion associated with nicotine withdrawal, and may be useful for the treatment of nicotine dependence.

Mecamylamine-precipitated nicotine-withdrawal aversion in rats

The present study examined a rapid and convenient model for evaluating nicotine dependence using the conditioned place preference paradigm. Rats were chronically infused subcutaneously with 9 mg/kg per day nicotine using an osmotic minipump. After nicotine infusion for 7 days, the nicotinic receptor antagonist mecamylamine produced a place aversion in nicotine-dependent rats, but not in acute nicotine-treated rats or sham-operated rats. These results suggest that the mecamylamine-precipitated withdrawal aversion in rats chronically treated with nicotine may result from physical dependence on nicotine, and may be useful for studying the physical dependence on nicotine.

An experimental comparison of three different schedules of reinforcement of drug abstinence using cigarette smoking as an exemplar

The efficacy of three different schedules of reinforcement for promoting and sustaining drug abstinence was compared in this study. Cigarette smoking was studied as an exemplar of stimulant drug self-administration. Sixty cigarette smokers were assigned to one of three groups (progressive rate of reinforcement, fixed rate of reinforcement, and yoked control). Participants in all three groups were asked to refrain from smoking for 1 week. Participants in the progressive and fixed groups achieved greater mean levels of abstinence than those in the control group. Participants in the progressive group were significantly less likely to resume smoking when they became abstinent than participants in the other groups.