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

Acute administration of nicotine into the higher order auditory Te2 cortex specifically decreases the fear-related charge of remote emotional memories

Nicotine elicits several behavioural effects on mood as well as on stress and anxiety processes. Recently, it was found that the higher order components of the sensory cortex, such as the secondary auditory cortex Te2, are essential for the long-term storage of remote fear memories. Therefore, in the present study, we examined the effects of acute nicotine injection into the higher order auditory cortex Te2, on the remote emotional memories of either threat or incentive experiences in rats. We found that intra-Te2 nicotine injection decreased the fear-evoked responses to a tone previously paired with footshock. This effect was cue- and dose-specific and was not due to any interference with auditory stimuli processing, innate anxiety and fear processes, or with motor responses. Nicotine acts acutely in the presence of threat stimuli but it did not determine the permanent degradation of the fear-memory trace, since memories tested one week after nicotine injection were unaffected. Remarkably, nicotine did not affect the memory of a similar tone that was paired to incentive stimuli. We conclude from our results that nicotine, when acting acutely in the auditory cortex, relieves the fear charge embedded by learned stimuli.

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Nicotine reliefs fear memories.

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Nicotine acts on long-term memories.

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Nicotine modulates memory in auditory cortex.

Neurocognitive endophenotypes in schizophrenia: modulation by nicotinic receptor systems

Cigarette smoking is the leading preventable cause of death in the Western world, with a considerably higher prevalence observed in schizophrenia compared to the general population. Despite the negative health consequences of smoking heavily, it has been proposed that individuals with schizophrenia may maintain smoking behaviors to remediate symptoms associated with the disorder. Neurocognitive deficits are a core feature of schizophrenia and are present in approximately 80% of patients. Further, these deficits constitute an endophenotype of schizophrenia, as they are stable across disease phases, and are heritable. The neurocognitive deficits that are present in schizophrenia are especially debilitating, since they are associated with poor clinical and functional outcomes and community integration. Interestingly, these deficits may also constitute a vulnerability factor towards the initiation and maintenance of tobacco use. Contributing to the potential shared vulnerability between schizophrenia and tobacco dependence is a dysregulation of the nicotinic acetylcholine receptor (nAChR) system. Pre-clinical evidence has shown that nicotine affects several neurotransmitter systems, including dopamine (DA), glutamate, and γ-aminobutyric acid (GABA), and certain neuropsychological deficits associated with these neurotransmitters (reaction time, spatial working memory, sustained attention, and sensory gating) are improved after nicotine administration in patients with schizophrenia. These positive effects on neurocognition appear to be more pronounced in smokers with schizophrenia, and may be an important mechanism that explains the co-morbidity of schizophrenia and tobacco dependence.

Working memory- and anxiety-related behavioral effects of repeated nicotine as a stressor: the role of cannabinoid receptors

Background

Like emotional symptoms such as anxiety, modulations in working memory are among the frequently-reported but controversial psychiatric symptoms associated with nicotine (NC) administration. In the present study, repeated NC-induced modulations in working memory, along with concurrently-observed anxiety-related behavioral alterations, were investigated in mice, and compared with the effects of a typical cognition-impairing stressor, immobilization stress (IM). Furthermore, considering the structural and functional contributions of brain cannabinoid (CB) receptors in NC-induced psychiatric symptoms including emotional symptoms, the interactive effects of brain CB receptor ligands (CB ligands) and NC and/or IM on the working memory- and anxiety-related behaviors were examined.

Results

Statistically significant working memory impairment-like behavioral alterations in the Y-maze test and anxiety-like behavioral alterations in the elevated plus-maze (EPM) test were observed in the groups of mice treated with 0.8 mg/kg NC (subcutaneous (s.c.) 0.8 mg/kg treatment, 4 days) and/or IM (10 min treatment, 4 days). In the group of mice treated with NC plus IM (NC-IM group), an enhancement of the behavioral alterations was observed. Among the CB type 1 (CB1) antagonist AM 251 (AM), the non-selective CB agonist CP 55,940 (CP), and the CB1 partial agonist/antagonist virodhamine (VD), significant recovering effects were provided by AM (0.2-2.5 mg/kg) and VD (5 mg/kg) against the working memory impairment-like behaviors, whereas significant anxiolytic-like effects (recoveries from both attenuated percentage of entries into open arms and attenuated percentage of time spent on open arms) were provided by VD (1–10 mg/kg) and CP (2 mg/kg) against the anxiety-like behaviors.

Conclusions

Although working memory impairment- and anxiety-like behavioral alterations were commonly induced in the NC, IM, and NC-IM groups and the therapeutic involvement of CB receptors was shown, there were discrepancies in the types of effective CB ligands between the working memory- and anxiety-related behaviors. The differential involvements of CB receptor subtypes and indirectly activated neurotransmitter systems may contribute to these discrepancies.

Adolescent exposure to nicotine alters the aversive effects of cocaine in adult rats

Nicotine is one of the most commonly used drugs in adolescence and has been shown to alter the rewarding effects of cocaine when administered in adulthood. Although the abuse potential of a drug has been suggested to be a balance between its rewarding and aversive effects, the long-term effects of nicotine on the aversive properties of other drugs had not been studied. To that end, in the present study rats exposed to nicotine (0.4 mg/kg) during adolescence (postnatal days 35-44) were tested for the acquisition and extinction of a cocaine-induced conditioned taste aversion (10, 18 or 32 mg/kg) in adulthood. Conditioning consisted of four saccharin-drug pairings followed by six extinction trials. Although cocaine-induced aversions at all doses, no effect of nicotine preexposure was seen during acquisition. During extinction, the nicotine-preexposed groups conditioned with 10 and 18 mg/kg cocaine displayed a decreased rate of extinction compared to their respective controls. These results suggest that while adolescent nicotine exposure does not appear to directly alter the aversive properties of cocaine it may affect other processes related to the response to drugs given in adulthood.

Effects of acute smoking on brain activity vary with abstinence in smokers performing the N-Back task: a preliminary study

We previously reported that compared with a non-deprivation state, overnight abstinence from cigarette smoking was associated with higher brain activity in the left dorsolateral prefrontal cortex (L-DLPFC) during a low demanding working memory challenge, and little increase beyond this activity level during more taxing working memory conditions. In the present study, we aimed to assess how recent smoking (overnight abstinence vs. smoking ad libitum) influenced the effect of smoking a cigarette on brain activity related to a working memory challenge. Six smokers performed the N-Back working memory task during functional magnetic resonance imaging (fMRI) both before and after smoking a cigarette in each of two test sessions: one following overnight abstinence from smoking ( approximately 13 h) and the other following ad libitum smoking. Task-related activity in L-DLPFC showed a significant interaction between the effects of acute smoking, test session, and task load. After overnight abstinence, post-smoking brain activity in L-DLPFC was lower than before smoking at low task load and higher at high task load; corresponding activity on a day of ad libitum smoking was higher at low load and lower at high task load after smoking during the session. These data suggest that the effect of acute smoking on working memory processing depends on recent prior smoking and task load. In particular, they provide preliminary evidence that functional efficiency of working memory is improved by smoking a cigarette during abstinence, while the effect of a cigarette in a non-deprived state varies with the nature and difficulty of the working memory challenge. This interaction merits further examination in larger studies specifically designed to consider this issue.

Effect of prolonged nicotine infusion on response of rat catecholamine biosynthetic enzymes to restraint and cold stress

There is a paradoxical relationship between nicotine and stress. To help elucidate their relationship on catecholamine biosynthesis, rats were infused with nicotine for 7-14 days before exposure to cold or restraint stress. Nicotine (5 mg/kg/day, 14 days) did not alter basal plasma corticosterone or its elevation with 24 h cold stress, but prevented corticosterone elevation following 2 h restraint stress. In adrenal medulla (AM), response of dopamine beta-hydroxylase (DBH), but not tyrosine hydroxylase (TH) mRNA, to both stressors was attenuated in nicotine-infused rats. In locus coeruleus (LC), restraint stress elevated TH and DBH mRNA in saline-, but not in nicotine-infused rats. Cold stress triggered a similar response of TH and DBH mRNAs in LC with and without nicotine infusion. With shorter nicotine infusion (8 mg/kg/day, 7 days), TH mRNA in AM was not induced by restraint stress on one (1x) or two (2x) consecutive days nor was DBH mRNA in AM or LC by 2x. The findings demonstrate that constant release of nicotine can modulate, or even prevent, some stress responses at the level of the HPA axis and gene expression of catecholamine biosynthetic enzymes in LC and AM.

Desensitized nicotinic receptors in brain

Desensitization is an intriguing characteristic of ligand-gated channels, whereby a decrease or loss of biological response occurs following prolonged or repetitive stimulation. Nicotinic acetylcholine receptors (nAChRs), as a member of transmitter gated ion channels family, also can be desensitized by continuous or repeated exposure to agonist. Desensitization of nicotinic receptors can occur as a result of extended nicotine exposure during smoking or prolonged acetylcholine when treatment of Alzheimer's disease (AD) with cholinesterase inhibitors, or anticholinesterase agent poisoning. Studies from our lab have shown that nAChRs desensitization is not a nonfunctional state and we proposed that desensitized nAChRs could increase sensitivity of brain muscarinic receptor to its agonists. Here, we will review the regulation of nicotinic receptor desensitization and discuss the important biological function of desensitized nicotinic receptors in light of our previous studies. These studies provide the critical information for understanding the importance of nicotinic receptors desensitization in both normal physiological processing and in various disease states.

Nicotinic receptor mechanisms and cognition in normal states and neuropsychiatric disorders

Cigarette smoking rates in the American population are approximately 23%, whereas rates of smoking in clinical and population studies of individuals with neuropsychiatric disorders are typically two- to four-fold higher. Studies conducted in a variety of neuropsychiatric populations [e.g. attention-deficit hyperactivity disorder (ADHD), Alzheimer's disease, schizophrenia] have collectively suggested that nicotine may be efficacious in remediating selected cognitive deficits associated with these disorders, thus providing a framework for understanding the specific vulnerability of these patients to smoking initiation and maintenance. However, the specific gain in cognitive performance produced by nicotine administration in healthy subjects with normal cognitive function is less clear. This article reviews our current understanding of central nicotinic acetylcholine receptor (nAChRs) systems in normal and neuropsychiatric disease states and, specifically, their role with respect to cognitive dysfunction and clinical symptoms in several specific neuropsychiatric populations, including ADHD, Alzheimer's disease, Parkinson's disease, Tourette's Disorder, schizophrenia and affective disorders. The potential benefits of nicotinic agents for therapeutic use in neuropsychiatric disorders is discussed, as well as directions for further research in this area.

Co-morbidity of smoking in patients with psychiatric and substance use disorders

This article reviews cigarette smoking in patients with psychiatric disorders (PD) and substance use disorders (SUD). Rates of smoking are approximately 23% in the U.S. population but approximately two- to four-fold higher in patients with PD and SUD. Many remaining smokers have had repeated smoking cessation failures, possibly due to the presence of co-morbid PD and SUDs. There is modest, evidence-based support for effective treatment interventions for nicotine addiction in PD and SUD. Further research is needed to increase our understanding of nicotine addiction in PD and SUD and develop more effective treatment interventions.

Chronic nicotine and smoke treatment modulate dopaminergic activities in ventral tegmental area and nucleus accumbens and the ?-aminobutyric acid type B receptor expression of the rat prefrontal cortex

Dopaminergic afferents from the mesencephalic areas, such as ventral tegmental area (VTA), synapse with the gamma-aminobutyric acid (GABA)-ergic interneurons in the prefrontal cortex (PFC). Pharmacological and electrophysiological data show that the reinforcement, the dependence-producing properties, as well as the psychopharmacologic effects of nicotine depend to a great extent on activation of nicotinic receptors within the mesolimbocortical dopaminergic projection. To explore further the relationship between the mesencephalic dopaminergic neurons and PFC GABAergic neurons, we investigated the effects of nicotine and passive exposure to cigarette smoke on the regulation of tyrosine hydroxylase (TH) in VTA and substantia nigra (SNC) and dopamine (DA) D1 receptor levels in nucleus accumbens (NAc) and caudate-putamen (CPu). Also, the simultaneous changes in GABAB receptors mRNAs in the PFC were studied. The results showed that chronic nicotine and smoking treatment differentially changed the levels of TH protein in VTA and SNC and DA D1 receptor levels in Nac and CPu. GABAB1 and GABAB2 receptor mRNA levels also showed different change patterns. Ten and thirty minutes of smoke exposure increased GABAB1 receptor mRNA to a greater extent than that of GABAB2, whereas GABAB2 was greatly enhanced after 1 hr of smoke exposure. The TH levels in VTA were closely related to DA D1 receptor levels in NAc and with GABAB receptor mRNA changes in PFC. These results suggest that the mesolimbic pathway and GABAB receptor mRNA in PFC are modulated by nicotine and cigarette smoke, implying an important role in nicotine's psychopharmacological effects.

Nicotinic receptor mechanisms and cognition in normal states and neuropsychiatric disorders

Cigarette smoking rates in the American population are approximately 23%, whereas rates of smoking in clinical and population studies of individuals with neuropsychiatric disorders are typically two- to four-fold higher. Studies conducted in a variety of neuropsychiatric populations [e.g. attention-deficit hyperactivity disorder (ADHD), Alzheimer's disease, schizophrenia] have collectively suggested that nicotine may be efficacious in remediating selected cognitive deficits associated with these disorders, thus providing a framework for understanding the specific vulnerability of these patients to smoking initiation and maintenance. However, the specific gain in cognitive performance produced by nicotine administration in healthy subjects with normal cognitive function is less clear. This article reviews our current understanding of central nicotinic acetylcholine receptor (nAChRs) systems in normal and neuropsychiatric disease states and, specifically, their role with respect to cognitive dysfunction and clinical symptoms in several specific neuropsychiatric populations, including ADHD, Alzheimer's disease, Parkinson's disease, Tourette's Disorder, schizophrenia and affective disorders. The potential benefits of nicotinic agents for therapeutic use in neuropsychiatric disorders is discussed, as well as directions for further research in this area.

A distinct neurochemical profile in WKY rats at baseline and in response to acute stress: implications for animal models of anxiety and depression

Wistar-Kyoto (WKY) rats exhibit hyperresponsive neuroendocrine and behavioral responses to stress that exceed normal controls and are especially prone to develop stress-induced depressive disorder. Pharmacological studies indicate altered serotonin (5-HT), norepinephrine (NE) and dopamine (DA) systems functioning in WKY rats, yet no attempt has been made to provide a comprehensive assessment of the neurochemical profile for WKY rats as compared to the outbred progenitor controls, Wistar rats. To this end, male, WKY and Wistar rats (N=6/group) were exposed to an acute forced-swim stress or were left untreated as controls. The prefrontal cortex (PFCtx), striatum, nucleus accumbens (NAS), and amygdala were assayed for levels of NE, DA and 5-HT, as well as major metabolites, by high-pressure liquid chromatography (HPLC) with electrochemical detection. In a separate experiment, designed to assess baseline and stress-induced neuroendocrine activation, male, Wistar and WKY rats (N=6/group) were exposed to an acute forced-swim stress of 15 min or were left untreated as controls. Animals were killed immediately after the test (T=0), 30 min after the test (T=30) or 60 min after the test (T=60), and control animals were killed immediately after weighing. After decapitation, trunk blood was collected and plasma was isolated by centrifugation and analyzed for corticosterone by immunoassay. The neurochemical results demonstrate distinct patterns of baseline and stress-induced monoamine turnover in WKY rats, including alterations to DA and 5-HT turnovers in prefrontal cortex and nucleus accumbens, two critical brain areas implicated in anxiety, depression and drug reward. The neuroendocrine results indicate that WKY rats exhibited a sustained corticosterone response to acute stress, as compared to Wistar controls. Overall, these data are predicted to be useful for understanding the anxiety- and depressive-like behavioral phenotype exhibited by these animals and for increased understanding of the role genetic background in altering neurochemical function.

Smoking, stress, and negative affect: correlation, causation, and context across stages of smoking

This transdisciplinary review of the literature addresses the questions, Do stress and negative affect (NA) promote smoking? and Does smoking genuinely relieve stress and NA? Drawing on both human and animal literatures, the authors examine these questions across three developmental stages of smoking--initiation, maintenance, and relapse. Methodological and conceptual distinctions relating to within- and between-subjects levels of analyses are emphasized throughout the review. Potential mechanisms underlying links between stress and NA and smoking are also reviewed. Relative to direct-effect explanations, the authors argue that contextual mediator-moderator approaches hold greater potential for elucidating complex associations between NA and stress and smoking. The authors conclude with recommendations for research initiatives that draw on more sophisticated theories and methodologies.

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.

Effects of dopamine receptor antagonists on nicotine-induced attentional enhancement

An understanding of the neuropharmacological mechanisms mediating attentional enhancement by nicotine would indicate whether these effects could be dissociated pharmacologically from other behavioural effects of nicotine. The aim of the present study was to examine the involvement of dopamine neurotransmission in the effects of nicotine on different response indices of an attentional paradigm. The effects of the D2-type dopamine receptor antagonist raclopride (0.025-0.1 mg/kg) and the D1-type receptor antagonist SCH23390 (0.006-0.024 mg/kg) were tested, in both the presence and absence of nicotine (0.1 mg/kg), in rats trained in a modified version of the five-choice serial reaction time task (5-CSRTT). Nicotine robustly enhanced the accuracy of signal detection, reduced omission errors and shortened response latencies. Neither raclopride nor SCH23390 altered the effects of nicotine on accuracy and omissions, but raclopride augmented accuracy and SCH23390 increased omissions when given alone. By contrast, raclopride, but not SCH23390, reversed the nicotine-induced reductions in response latencies, at doses that had no effect on their own. In the presence of nicotine, both antagonists had rate-disruptive effects at the highest dose. Both antagonists also reduced responding in the intertrial interval, and this effect was additive to the nicotine-induced decrease in this measure. The data indicate that D2-type dopamine receptors may be involved in the effects of nicotine on response speed. Neither the D1- nor the D2-type dopamine receptor antagonist affected nicotine-induced improvements in signal detection, at doses that reversed dependence-related behavioural effects of nicotine in previous studies. Thus these effects may be pharmacologically dissociable.

Effect of nicotine and nicotinic receptors on anxiety and depression

Nicotine has been shown to have effects on anxiety and depression in both human and animal studies. These studies suggest that nicotinic acetylcholine receptors (nAChRs) can modulate the function of pathways involved in stress response, anxiety and depression in the normal brain, and that smoking can result in alterations of anxiety level and mood. The effects of nicotine are complex however, and nicotine treatment can be either anxiolytic or anxiogenic depending on the anxiety model tested, the route of nicotine administration and the time course of administration. The paradoxical effects of nicotine on emotionality are likely due to the broad expression of nAChRs throughout the brain, the large number of nAChR subtypes that have been identified and the ability of nicotine treatment to both activate and desensitize nAChRs. Activation of nAChRs has been shown to modulate many systems associated with stress response including stress hormone pathways, monoaminergic transmission and release of classical neurotransmitters throughout the brain. Local administration studies in animals have identified brain areas that may be involved in the anxiogenic and anxiolytic actions of nicotine including the lateral septum, the dorsal raphe nuclei, the mesolimbic dopamine system and the hippocampus. The ensemble of studies to date suggest that under certain conditions nicotine can act as an anxiolytic and an antidepressant, but that following chronic use, adaptations to nicotine can occur resulting in increased anxiety and depression following withdrawal.

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.

The anxiolytic-like effect of nicotine undergoes rapid tolerance in a model of contextual fear conditioning in rats

The effects of repeated administration of nicotine on contextual fear conditioning, locomotor activity, and pain threshold, were examined in rats. It was found that a single injection of nicotine prior to the training session (three 0.7-mA footshocks, each 0.5 s long), decreased the freezing reaction during the retest 24 h later. The locomotor activity was moderately enhanced, and the pain threshold remained unchanged. The baseline freezing measured immediately after administration of a single dose of nicotine was not significantly different from the saline-treated group. The anxiolytic-like effect of nicotine was as potent as that of midazolam, a benzodiazepine derivative. After five day-by-day injections, the anxiolytic-like effect of nicotine (0.6 mg/kg, sc) was no longer present, independently whether the last drug injection was given 24 h or 5 min (i.e., the sixth, additional, nicotine injection), prior to the training session. Thus, it appeared that the expression of tolerance to the nicotine-induced anxiolytic-like action did not require a direct stimulation of nicotinic receptors. Simultaneously, in this group of animals, nicotine caused a potent stimulation of locomotor activity in the open field test. The applied dosage and regimen of nicotine administration did not change rat pain threshold (flinch-jump test). Collectively, the present data showed for the first time, that short-term, intermittent, administration of nicotine was sufficient to induce tolerance to the anxiolytic-like effect of this drug, in the model of fear conditioning to context. Importantly, a clear dissociation between the locomotor and anxiolytic-like effects of nicotine was present. This effect appeared independent also of changes in rat pain threshold. The possible mechanisms of this phenomenon are discussed.

Effects of nicotine pretreatment on dopaminergic and behavioral responses to conditioned fear stress in rats: dissociation of biochemical and behavioral effects

BACKGROUND

We have examined the effects of nicotine pretreatment on dopaminergic and behavioral responses to conditioned fear stress in the rat.

METHODS

Rats were pretreated daily with saline or nicotine for 20 days then challenged with nicotine or saline on day 21. Animals were trained in a classical conditioned fear paradigm. Dopamine utilization in the medial prefrontal cortex and nucleus accumbens shell and conditioned fear stress-induced immobility responses were assessed.

RESULTS

Saline pretreated animals rapidly acquired the conditioned fear stress response as assessed by preferential activation of mesoprefrontal dopamine metabolism and tone-elicited immobility responses. Repeated, but not acute, nicotine pretreatment significantly reduced conditioned fear stress-induced dopamine metabolism in the medial prefrontal cortex and nucleus accumbens shell. Repeated nicotine pretreatment did not modify the acquisition or expression of conditioned fear stress responses, however.

CONCLUSIONS

The dissimilar effects of repeated nicotine exposure on the cortical dopamine and behavioral responses to conditioned fear stress suggest that nicotine differs from other agents with anxiolytic activity that produce coordinated changes in conditioned fear stress-induced cortical dopaminergic and behavioral responses. Furthermore, compared with results of acute footshock stress, repeated nicotine pretreatment appears to have differential effects on physical versus psychological stressors. Results are discussed within the clinical context of stress-related psychopathology syndromes and comorbid nicotine dependence.

Nicotine attenuates stress-induced changes in plasma amino acid concentrations and locomotor activity in rats

It is known that stressor stimuli (both systemic and processive) and nicotine activate central nervous system. Surprisingly, numerous studies have demonstrated an increase in nicotine self-administration among smokers when exposed to stress in order to reduce the stress-related tension. Therefore, in the present study, we decided to investigate the influence of nicotine on both behavioral (i.e., on locomotor activity) and metabolic (i.e., on the level of amino acids in the plasma) changes following water immersion restraint stress in rats. As expected, the stress produced evident decline in locomotor activity of the rats (p < 0.001) and in the levels of all plasma amino acids studied (p < 0.05). Nicotine alone also significantly reduced locomotor activity (p < 0.05) and the levels of some plasma amino acids. However, when administered to rats subjected to water immersion and restraint, nicotine attenuated both stress-induced decrease in locomotor activity (p < 0.05) and in some plasma amino acids. Thus, this study demonstrated that the mode of action of nicotine is strongly dependent on the level of initial brain activity, which provide new evidence for arousal-modulation model of nicotine action.