The influence of tobacco smoke and nicotine on antidepressant and memory-improving effects of venlafaxine

Memory deterioration based on the tobacco smoke exposure and methylazoxymethanol acetate administration vs. aripiprazole, olanzapine and enrichment environment conditions

Enrichment environment conditions, as well as tobacco smoke exposure, may affect cognitive function (e.g. spatial memory) in an animal model of schizophrenia and schizophrenic patients. The aim of this study was to find whether spatial memory function impairment is found in methylazoxymethanol acetate treated rats (an animal model of schizophrenia) and whether aripiprazole (1.5 mg/kg) and olanzapine (0.5 mg/kg) modify these functions. We also were able to determine whether tobacco smoke exposure and enrichment environment conditions have an impact on drug efficacy. The effect of methylazoxymethanol acetate, tobacco smoke exposure, enrichment environment and the use of drugs were studied in the Morris Water Maze test (spatial memory). The results of our study clearly show that enriched environment may have a procognitive effect while tobacco smoke and methylazoxymethanol acetate have a contradictory effect. This paper also confirmed that the use of neuroleptics, namely ARI and OLA, reduced the process of spatial memory deterioration tested in the Morris water maze both in terms of the number of escape latencies and crossed quadrants.

Why are Antidepressant Drugs Effective Smoking Cessation Aids?

BACKGROUND

Before the advent of varenicline, antidepressant drugs were reported to exhibit better clinical efficacy than nicotine replacement therapy as smoking cessation aids. The most studied is bupropion, a clinically-effective antidepressant, the first to be marketed throughout Europe for smoking cessation. Since depression and tobacco smoking have a high incidence of cooccurrence, this would implicate an underlying link between these two conditions. If this correlation can be confirmed, then by treating one condition the related state would also be treated.

OBJECTIVES

This review article will evaluate the various theories relating to the use of antidepressant drugs as smoking cessation aids and the underlying mechanisms link tobacco smoking and depression to explain the action of antidepressants in smoking cessation. One plausible theory of self-medication which proposes that people take nicotine to treat their own depressive symptoms and the affective withdrawal symptoms seen with abstinence from the drug. If the depression can instead be treated with antidepressants, then they may stop smoking altogether. Another theory is that the neurobiological pathways underlying smoking and depression may be similar. By targeting the pathways of depression in the brain, antidepressants would also treat the pathways affected by smoking and ease nicotine cravings and withdrawal. The role of genetic variation predisposing an individual to depression and initiation of tobacco smoking has also been discussed as a potential link between the two conditions. Such variation could either occur within the neurobiological pathways involved in both disorders or it could lead to an individual being depressed and selfmedicating with nicotine.

New Pharmacological Agents to Aid Smoking Cessation and Tobacco Harm Reduction: What Has Been Investigated, and What Is in the Pipeline?

A wide range of support is available to help smokers to quit and to aid attempts at harm reduction, including three first-line smoking cessation medications: nicotine replacement therapy, varenicline and bupropion. Despite the efficacy of these, there is a continual need to diversify the range of medications so that the needs of tobacco users are met. This paper compares the first-line smoking cessation medications with (1) two variants of these existing products: new galenic formulations of varenicline and novel nicotine delivery devices; and (2) 24 alternative products: cytisine (novel outside Central and Eastern Europe), nortriptyline, other tricyclic antidepressants, electronic cigarettes, clonidine (an anxiolytic), other anxiolytics (e.g. buspirone), selective serotonin reuptake inhibitors, supplements (e.g. St John's wort), silver acetate, Nicobrevin, modafinil, venlafaxine, monoamine oxidase inhibitors (MAOIs), opioid antagonists, nicotinic acetylcholine receptor (nAChR) antagonists, glucose tablets, selective cannabinoid type 1 receptor antagonists, nicotine vaccines, drugs that affect gamma-aminobutyric acid (GABA) transmission, drugs that affect N-methyl-D-aspartate (NMDA) receptors, dopamine agonists (e.g. levodopa), pioglitazone (Actos; OMS405), noradrenaline reuptake inhibitors and the weight management drug lorcaserin. Six 'ESCUSE' criteria-relative efficacy, relative safety, relative cost, relative use (overall impact of effective medication use), relative scope (ability to serve new groups of patients) and relative ease of use-are used. Many of these products are in the early stages of clinical trials; however, cytisine looks most promising in having established efficacy and safety with low cost. Electronic cigarettes have become very popular, appear to be efficacious and are safer than smoking, but issues of continued dependence and possible harms need to be considered.

Alpha7 nicotinic acetylcholine receptor agonists and PAMs as adjunctive treatment in schizophrenia. An experimental study

Nicotine has been found to improve cognition and reduce negative symptoms in schizophrenia and a genetic and pathophysiological link between the α7 nicotinic acetylcholine receptors (nAChRs) and schizophrenia has been demonstrated. Therefore, there has been a large interest in developing drugs affecting the α7 nAChRs for schizophrenia. In the present study we investigated, in rats, the effects of a selective α7 agonist (PNU282987) and a α7 positive allosteric modulator (PAM; NS1738) alone and in combination with the atypical antipsychotic drug risperidone for their utility as adjunct treatment in schizophrenia. Moreover we also investigated their utility as adjunct treatment in depression in combination with the SSRI citalopram. We found that NS1738 and to some extent also PNU282987, potentiated a subeffective dose of risperidone in the conditioned avoidance response test. Both drugs also potentiated the effect of a sub-effective concentration of risperidone on NMDA-induced currents in pyramidal cells of the medial prefrontal cortex. Moreover, NS1738 and PNU282987 enhanced recognition memory in the novel object recognition test, when given separately. Both drugs also potentiated accumbal but not prefrontal risperidone-induced dopamine release. Finally, PNU282987 reduced immobility in the forced swim test, indicating an antidepressant-like effect. Taken together, our data support the utility of drugs targeting the α7 nAChRs, perhaps especially α7 PAMs, to potentiate the effect of atypical antipsychotic drugs. Moreover, our data suggest that α7 agonists and PAMs can be used to ameliorate cognitive symptoms in schizophrenia and depression.

Coadministration of tramadol with aripiprazole and venlafaxine--The effect on spatial memory functions in male rats

BACKGROUND

The impairment of memory functions is very common in patients with chronic pain, particularly in patients with existing cognitive disorders. Results of some studies confirmed that tramadol (TRM), a frequently prescribed analgesic drug, improves memory functions in humans. However, there are no studies on the effect of co-administration of TRM with antidepressants or antipsychotics on memory; therefore, the aim of this study was to evaluate the effect of concomitant use of TRM with a second generation antipsychotic-aripiprazole (ARI) and an antidepressant-venlafaxine (VEN) on memory using an animal model.

METHODS

The effect of TRM (5mg/kg)+ARI (1.5mg/kg) and TRM (5mg/kg)+VEN (20mg/kg) on memory in Wistar rats was examined using the Morris water maze test after single and chronic administration (7 and 14 days).

RESULTS

It was observed that a single and chronic administration of TRM, VEN or ARI alone, but not a combination of TRM+VEN or TRM+ARI (except for 14 days of treatment) can improve memory in rats compared to the control group. After 14 days of administration, both combinations achieved improvement similar to each drug individually and improved spatial memory in rats compared to the control animals.

CONCLUSION

It can be assumed that chronic treatment with combinations of TRM+VEN or TRM+ARI is unlikely to cause memory impairment and interfere with either any antidepressant effect of VEN or any antipsychotic effect of ARI in patients suffering from chronic pain using TRM.

Genetic, Epigenetic, and Environmental Factors Influencing Neurovisceral Integration of Cardiovascular Modulation: Focus on Multiple Sclerosis

Thought to be an autoimmune inflammatory CNS disease, multiple sclerosis (MS) involves multiple pathologies with heterogeneous clinical presentations. An impaired neurovisceral integration of cardiovascular modulation, indicated by sympathetic and parasympathetic autonomic nervous system (ANS) dysfunction, is among common MS clinical presentations. ANS dysfunction could not only enhance MS inflammatory and neurodegenerative processes, but can also lead to clinical symptoms such as depression, fatigue, sleep disorder, migraine, osteoporosis, and cerebral hemodynamic impairments. Therefore, factors influencing ANS functional activities, in one way or another, will have a significant impact on MS disease course. This review describes the genetic and epigenetic factors, and their interactions with a number of environmental factors contributing to the neurovisceral integration of cardiovascular modulation, with a focus on MS. Future studies should investigate the improvement in cardiovascular ANS function, as a strategy for preventing and minimizing MS-related morbidities, and improving patients' quality of life.

Oxidative stress in the brain of cigarette smoke-induced noxiousness: neuroprotective role of Sesbania grandiflora

Cigarette smoking is concerned as a major risk factor in the development of various neurological disorders. Oxidative stress is suggested as a possible contributing factor in the pathogenesis of cigarette smoking-induced toxicity. Therefore, the present study was intended to evaluate the neuroprotective role of Sesbania grandiflora (S. grandiflora) against chronic cigarette smoke induced oxidative damage in rat brain. Adult male Wistar-Kyoto rats were exposed to cigarette smoke for a period of 90 days and consecutively treated with S. grandiflora aqueous suspension (SGAS, 1,000 mg/kg body weight per day by oral gavage) for a period of 3 weeks. Lipid peroxidation and antioxidants status were analyzed in the brain. Rats exposed to cigarette smoke showed significant increase in conjugated diens (CD), hydroperoxides (HP) and malendialdehyde (MDA) levels with concomitant decrease in superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione-S-transferase (GST) and glucose-6-phosphate dehydrogenase (G6PDH) activities and the levels of reduced glutathione (GSH), vitamin C and vitamin E. Also cigarette smoke-exposure resulted in a marked increase in copper and decrease in zinc, manganese and selenium levels in brain. Administration of SGAS attenuates lipid peroxidation, enhanced the antioxidant status, restored the levels of micronutrients and retained the brain histology. The results of our study indicate that chronic cigarette smoke-exposure accelerates oxidative stress, thereby disquieting the brain defensive mechanism and S. grandiflora protects the brain from the oxidative damage through its biopotency.

Drug-, dose- and sex-dependent effects of chronic fluoxetine, reboxetine and venlafaxine on open-field behavior and spatial memory in rats

In an effort to address the need to include both sexes in studies of effects of the SSRI fluoxetine, the NRI reboxetine and the SNRI venlafaxine on anxiety-related behavior and memory along with the use of chronic drug administration, male and female PVG/c rats were fed diets containing two doses of each drug for 21 days. The rats' anxiety level was then assessed in an open field. Short-term spatial memory for a brightness change in a Y maze was also measured. While there was little evidence of anxiolytic effects of any of the drugs, both fluoxetine and, to a lesser extent, venlafaxine appeared to be mainly anxiogenic in their action depending on both dose and sex. Reboxetine was relatively ineffective in this respect. Ability to locate the Y-maze arm that had changed (from white to black) seemed to be impaired for male (but not female) rats by both fluoxetine and venlafaxine and, to a much lesser extent, by reboxetine. Given the relative ineffectiveness of reboxetine in either test, it is possible that the effects of the other two drugs on both anxiety and memory were mainly due to their serotonin reuptake inhibiting properties. The differences that occurred between males and females in responsiveness to all three drugs supported the long-held view that both sexes should be investigated in studies of this sort, especially in view of reports of sex differences in effects of clinically prescribed antidepressants.

Assessments of the effects of nicotine and ketamine using tyrosine hydroxylase-green fluorescent protein transgenic zebrafish as biosensors

Transgenic zebrafish are a common vertebrate model system for the study of addictive behavior. In the present study, plasmid constructs containing green fluorescent protein (GFP) and the promoter of tyrosine hydroxylase (TH), a key synthetic enzyme for catecholamines, were produced. The TH-GFP constructs were microinjected into zebrafish embryonic cells. Three days post-fertilization, GFP began expressing in distinct catecholaminergic areas. The TH-GFP transgenic zebrafish were employed as live biosensors to test the effects of the commonly abused drugs nicotine and ketamine. First, locomotion assays were used to study the general excitatory effects of the drugs. Maximal locomotor activity was obtained after treatment with a high concentration of nicotine (10 μM), but with a much lower concentration of ketamine (0.1 μM). Second, TH protein levels in zebrafish brains were assessed by Western blot. TH protein levels were significantly increased, with maximal protein levels found after treatment with the same drug concentrations that gave maximal locomotor activity. Importantly, analysis of GFP in the zebrafish catecholaminergic areas revealed the same expression patterns as was obtained by Western blot. The present results indicate that increased locomotor activity can be correlated to TH protein expression, as indicated by Western blot and expression of TH-GFP. We have shown that TH-GFP expression is a reliable method to show the effects of drugs on TH expression that may be employed as a novel high-throughput live biosensor for screening drugs of abuse.

Cigarette smoke exposure greatly increases alcohol consumption in adolescent C57BL/6 mice

BACKGROUND

Alcohol and tobacco are often used together, and alcoholism is much more common among smokers compared with nonsmokers. Studies in humans suggest that nicotine (an active ingredient in cigarette smoke) can increase the consumption of alcohol. Research on rats and mice demonstrated mixed results; some studies report that nicotine increases alcohol consumption, while others show a decrease in drinking. Because cigarette smoke includes many other chemicals, these also may play a significant role in alcohol consumption. For example, 2 of these other constituents, monoamine oxidase inhibitors and acetaldehyde, increase alcohol tolerance and/or alcohol consumption in rodents. This study was designed to investigate how cigarette smoke from tobacco may modify self-administration of alcohol in adolescent C57BL/6 mice, a critical time when adolescent humans begin abusing drugs.

METHODS

C57BL/6 male mice (4 to 5 weeks old) were acclimated for 3 weeks to consume a 10% (w/v) alcohol solution during a 2-hour daily access in the dark. Subsequently, half the animals were exposed to cigarette smoke for 6 h/d for 16 days. The remaining animals (control) were placed in a smoke-free adjacent chamber. Immediately following the 6-hour period in the chambers, the control and smoke-exposed mice were given access to the 10% alcohol solution for 2 hours.

RESULTS

Animals exposed to cigarette smoke for 6 h/d consumed approximately 3- to 5-fold more alcohol than the mice in the control group throughout the 16-day study. The mice in the smoke group had a blood alcohol concentration that was nearly 4-fold that of the control mice.

CONCLUSIONS

Cigarette smoke increases alcohol consumption several fold higher than reported studies using nicotine treatment alone in adolescent rodents. Thus, this model should be useful to determine the roles of other bioactive components in cigarette smoke that may be important in the high co-abuse of smoking and alcohol consumption.

Curcumin protects against cigarette smoke-induced cognitive impairment and increased acetylcholinesterase activity in rats

Cigarette smoke, a widely spread habit, is associated with a decline in cognitive function and studies have demonstrated that curcumin (Cur), an Indian spice, possesses a strong neuroprotective potential. Considering the relevance of investigating dietary compounds this study aimed to investigate the effect of Cur on memory and acetylcholinesterase (AChE) activity in brain structures and blood of cigarette smoke-exposed rats. Male Wistar rats were treated with curcumin and cigarette smoke, once a day, 5 days each week, for 30 days. The experimental procedures were divided in two sets of experiments. In the first, the animals were divided into 4 groups: Vehicle (corn oil), Cur 12.5 mg/kg, Cur 25 mg/kg and Cur 50 mg/kg. In the second, the animals were divided into 5 groups: Vehicle (corn oil), Smoke, Smoke plus Cur 12.5 mg/kg, Smoke plus Cur 25 mg/kg and Smoke plus Cur 50 mg/kg. Treatment with Cur significantly prevented the decreased latency and cholinergic alterations in cigarette smoke-exposed rats. These AChE alterations could suggest a role in the memory impairment promoted by cigarette smoke-exposure and point toward the potential of Cur to modulate cholinergic neurotransmission and, consequently, improve cognition deficits induced by smoke. This study suggests that the dietary compound Cur may be involved in cholinergic system modulation and as a consequence exert an effect on learning and memory.

Venlafaxine facilitates between-session extinction and prevents reinstatement of auditory-cue conditioned fear

Anxiety disorders, characterized by anxiety and fearfulness, are found to be able to cause abnormal emotional responses' associated with memories of negative events, which implicate pressure on society with an increasingly large burden. Better treatment has been of concern to the community. Venlafaxine (VEN), a nonclassical antidepressant agent, is applied in the treatment of social phobia, major depression (MD) and general anxiety disorder (GAD) and, to a certain extent, posttraumatic stress disorder (PTSD), which improves working memory and spatial memory as well as ameliorates emotion by affecting specified brain regions. In this study, we committed to seek a new way for using VEN on treatment of anxiety disorders. To investigate the effect of VEN on extinction of auditory-cue conditioned fear, conditioned rats received a treatment with VEN before extinction training and tests for freezing level of within-session and between-session extinction. To investigate the effect of VEN on reinstatement, all conditioned rats received a treatment with VEN over a period for 21 days. After a rest for 7 days, two tests for freezing level were conducted. We found that: (1) VEN (40mg/kg) treatment at 30min prior to extinction training significantly facilitated the between-session extinction, but not the within-session extinction; (2) chronic administration with VEN (40mg/kg) prevented the return of extinguished auditory-cue fear. These data elucidate the critical role of VEN in auditory-cue fear memory, suggesting that VEN may be an ideal choice for the exposure-based drug treatment and maintenance treatment in patients with GAD, SAD and PTSD.

Combined α7 nicotinic acetylcholine receptor agonism and partial serotonin transporter inhibition produce antidepressant-like effects in the mouse forced swim and tail suspension tests: a comparison of SSR180711 and PNU-282987

Emerging evidence points to an involvement of nicotinic acetylcholine receptors (nAChRs) in major depression. Nicotine improves symptoms of depression in humans and shows antidepressant-like effects in rodents. Monoamine release is facilitated by nAChR stimulation, and nicotine-evoked serotonin (5-HT) release has been shown to depend on α7 nAChR activation. The α7 nAChR agonist PNU-282987 shows no antidepressant-like activity when tested alone in the mouse forced swim (mFST) or tail suspension tests (mTST). However, in combination with a sub-active dose of the selective 5-HT reuptake inhibitor citalopram, inducing ~50% 5-HT reuptake inhibition, PNU-282987 has shown marked antidepressant-like effects in the mFST. SSR180711 is a recently described α7 nAChR agonist that has shown antidepressant-like activity in the rat forced swim test. To address the possibility that 5-HT reuptake inhibition contributes to the antidepressant-like profile of SSR180711, we compared the behavioural and biochemical profiles of PNU-282987 and SSR180711. In the mFST and mTST, SSR180711 (3-30 mg/kg, s.c.) showed dose-dependent antidepressant-like activity, while PNU-282987 (3-30 mg/kg, s.c.) showed no significant effect. The ED(50) to displace [³H]α-bungarotoxin binding was 1.7 and 5.5 mg/kg for SSR180711 and PNU-282987, respectively, suggesting that both compounds produce near-maximal α7 nAChR occupancy at the highest dose. While PNU-282987 did not affect ex vivo [³H]5-HT uptake, SSR180711 inhibited [³H]5-HT uptake with an ED₅₀ of 30 mg/kg. This degree of inhibition is similar to that observed with a citalopram dose of ~2.4 mg/kg, a dose that is normally not active in the mFST or mTST. This suggests that the antidepressant-like activity of SSR180711 may involve partial 5-HT reuptake inhibition. SSR180711 therefore represents a compound displaying the synergistic effect of α7 nAChR agonism combined with partial 5-HT reuptake inhibition previously described. The addition of α7 nAChR agonism to classical monoamine-based mechanisms may represent a novel option for the improved treatment of major depression.

Nicotine reverses anhedonic-like response and cognitive impairment in the rat chronic mild stress model of depression: comparison with sertraline

Smoking rates among depressed individuals are higher than is observed in the background population, and nicotine alleviates depressive symptoms. In rodents, nicotine shows antidepressant-like effects in the forced swim and learned helplessness paradigms. Clinical depression is associated with both anhedonia and cognitive impairments. In rats, chronic mild stress (CMS) decreases voluntary sucrose intake, reflecting an anhedonic-like state, and impairs performance in the spontaneous alternation behaviour (SAB) test, suggesting impaired cognitive function. Here, we examine the effect of chronic treatment of nicotine (0.4 mg/kg/day) and sertraline (5 mg/kg/day) on CMS-induced anhedonic-like behaviour and impairment in the SAB test. Nicotine and sertraline administered individually or in combination show significant and equally efficacious reversal of the CMS-induced decrease in sucrose intake, implying there is no additive or synergistic effect of the nicotine + sertraline combination. In the SAB test, nicotine, but not sertraline or nicotine + sertraline, reversed the CMS-induced impairment. The present results show that the effect of nicotine on a CMS-induced anhedonic-like state in rats is similar to that of a standard antidepressant drug. Moreover, the data suggest that nicotine alleviates CMS-induced cognitive disturbance. A treatment strategy involving the targeting of nicotinic acetylcholine receptors may prove beneficial for emotional and cognitive disturbances associated with depression.

Comparison of the behavioral effects of cigarette smoke and pure nicotine in rats

Animal models of tobacco dependence typically rely on parenteral administration of pure nicotine. Models using cigarette smoke inhalation might more accurately simulate nicotine exposure in smokers. The primary goal of this study was to validate methods for administering cigarette smoke to rats using exposure conditions that were clinically relevant and also produced brain nicotine levels similar to those produced by behaviorally active doses of pure nicotine. A secondary goal was to begin examining the behavioral effects of smoke. Nose-only exposure (NOE) to smoke for 10-45min or whole-body exposure (WBE) to smoke for 1-4h produced serum nicotine concentrations similar to those in smokers (14-55ng/ml), without excessive carbon monoxide exposure. Daily nicotine (0.1mg/kg, s.c.) induced locomotor sensitization whereas 45-min NOE producing brain nicotine levels within the same range did not. Nicotine 0.125mg/kg s.c. reversed withdrawal from a chronic nicotine infusion as measured by elevations in intracranial self-stimulation thresholds whereas 4-h WBE producing similar brain nicotine levels did not. These data demonstrate the feasibility of delivering cigarette smoke to rats at clinically relevant doses, and provide preliminary evidence that the behavioral effects of nicotine delivered in smoke may differ from those of pure nicotine.

Influences of chronic venlafaxine, olanzapine and nicotine on the hippocampal and cortical concentrations of brain-derived neurotrophic factor (BDNF)

Brain-derived neurotrophic factor (BDNF) is a key neurotrophic factor in the brain. It plays an important role in the etiopathogenesis and pharmacotherapy of mental disorders, such as depression or schizophrenia. In recent years, studies have shown that cognitive processes, which are impaired in the course of mental disorders, significantly change BDNF levels in the brain. Administered to rats at a dose of 20 mg/kg (b.d. for 5 weeks), venlafaxine (VEN) increases BDNF levels in the hippocampus and cortex, compared to controls. Administered at a dose of 0.5 mg/kg (b.d. for 5 weeks), olanzapine (OLA) significantly increases BDNF levels in both the cortex and the hippocampus. Similarly, nicotine (NIC) administered at a dose of 0.2 mg/kg (b.d. for 5 weeks) increases BDNF concentrations in both the hippocampus and the cortex. Combined administration of NIC with VEN or OLA does not increase BDNF levels in the hippocampus or the cortex. Based on our study, it can be claimed that BDNF mediates behavioral responses only to drugs used individually and participates in the antidepressant and procognitive effects of the study compounds. BDNF also initiates plastic changes and modulation of synaptic activity in rat brains.

Antidepressants are a rational complementary therapy for the treatment of Alzheimer's disease

There is a high prevalence rate (30-50%) of Alzheimer's disease (AD) and depression comorbidity. Depression can be a risk factor for the development of AD or it can be developed secondary to the neurodegenerative process. There are numerous documented diagnosis and treatment challenges for the patients who suffer comorbidity between these two diseases. Meta analysis studies have provided evidence for the safety and efficacy of antidepressants in treatment of depression in AD patients. Preclinical and clinical studies show the positive role of chronic administration of selective serotonin reuptake inhibitor (SSRI) antidepressants in hindering the progression of the AD and improving patient performance. A number of clinical studies suggest a beneficial role of combinatorial therapies that pair antidepressants with FDA approved AD drugs. Preclinical studies also demonstrate a favorable effect of natural antidepressants for AD patients. Based on the preclinical studies there are a number of plausible antidepressants effects that may modulate the progression of AD. These effects include an increase in neurogenesis, improvement in learning and memory, elevation in the levels of neurotrophic factors and pCREB and a reduction of amyloid peptide burden. Based on this preclinical and clinical evidence, antidepressants represent a rational complimentary strategy for the treatment of AD patients with depression comorbidity.

Chronic oral nicotine increases brain [3H]epibatidine binding and responsiveness to antidepressant drugs, but not nicotine, in the mouse forced swim test

INTRODUCTION

Smoking rates among depressed individuals is higher than among healthy subjects, and nicotine alleviates depressive symptoms. Nicotine increases serotonergic and noradrenergic neuronal activity and facilitates serotonin and noradrenaline release. In mice, acute nicotine administration enhances the activity of antidepressants in the mouse forced swim (mFST) and tail suspension tests. Here, we investigated if this action of nicotine is also reflected in a chronic treatment regimen.

MATERIALS AND METHODS

After chronic treatment with nicotine in the drinking water, mice were challenged with nicotine, duloxetine, citalopram, and reboxetine in the mFST. Additionally, 8-OH-DPAT- and clonidine-induced hypothermia was tested in vehicle- and nicotine-pretreated mice, as a measure of 5-HT(1A) and alpha(2)-adrenoceptor function, respectively. Finally, the effects on the brain expression levels of high- and low-affinity nicotinic acetylcholine receptors (nAChRs) and the transporters for serotonin (SERT) and noradrenaline (NET) were assessed using [(3)H]epibatidine, [(3)H]alpha-bungarotoxin, [(3)H]citalopram, and [(3)H]nisoxetine binding, respectively.

RESULTS

In the mFST, nicotine-pretreated mice did not show altered response to the nicotine challenge, but increased responses to all three antidepressants tested were observed when compared to mice that had been administered drinking water without nicotine. There was no change in hypothermic responses to 8-OH-DPAT or clonidine. [(3)H]epibatidine binding was significantly increased in all brain regions investigated; whereas, [(3)H]alpha-bungarotoxin, [(3)H]citalopram, and [(3)H]nisoxetine binding were not altered, indicating that chronic oral nicotine increases the expression and/or affinity of high-affinity nAChRs, but not low-affinity nAChRs, SERT, or NET.

DISCUSSION

It is suggested that the increased sensitivity to antidepressants after chronic nicotine exposure involves increased high-affinity nAChR-mediated neurotransmission.

Effect of gabapentin on cognitive processes in rats not exposed and exposed to tobacco smoke during fetal life

Cognitive deficits, including memory deficiencies, are currently deemed one of key symptoms of psychopathologic mental disorders or epilepsy. The impairment of neurocognitive processes could be due to the administered therapy, in particular combined therapy or therapy using antiepileptics of older type. Gabapentin (GBP) is one of new antiepileptics with normothymic properties. It is known that epileptic patients run a significant risk of developing depression and mood changes. Smoking may also have a negative effect on memory processes and efficacy of administered drugs. Note that smoking in pregnant women also leads to neurobehavioral changes in their children. The objective of our research was to evaluate the effect of GBP on memory functions and antidepressant effect in rats not exposed and exposed to tobacco smoke in fetal life. We were also intent on finding whether GBP has an anticonvulsant effect in contact and without contact with tobacco smoke, and whether it affects motor coordination in animals if administered in the dose of 25 mg/kg. Spatial memory of the animals was assessed in the Morris test and the antidepressant effect in the Porsolt test. The ED(50) value was determined in the Swinyard maximum electric shock test, and the effect on motor coordination was assessed in the chimney test. GBP administered in the dose of 25 mg/kg intraperitoneal (i.p.) significantly reduced the immobility time on days 1 and 7 of the test in animals exposed to tobacco smoke, and on days 7 and 14 of the test in rats not exposed to tobacco smoke. Upon single and multiple administration of GBP to animals not exposed to tobacco smoke, the spatial memory improved, whereas in animals exposed to tobacco smoke in fetal life tolerance for procognitive effect was observed on day 21 of the test. It has been found that in rats not exposed to tobacco smoke, ED(50) of GBP was 28.73 mg/kg, whereas in animals exposed to tobacco smoke in fetal life, ED(50) was 46.2 mg/kg. Upon 14 and 21 days of drug administration, motor coordination was impaired in both GBP receiving animal groups. In conclusion, GBP beside its anticonvulsant efficacy also improves memory processes and has antidepressant effect. We also proved that GBP may reverse cognitive deficits concerning working memory induced by prenatal exposure to tobacco smoke and may have antidepressant effect in rats exposed to tobacco smoke.

Antidepressant drugs and memory: insights from animal studies

This is a selective review of the literature concerning the effects of antidepressant drugs on animal memory, which was performed with the aid of the PubMed database. Monoamine oxidase inhibitors tend to either have no effect on memory or result in its improvement. Studies with cyclic antidepressants have reported no effect or, more often, memory impairments. Pre-training administration of selective serotonin reuptake inhibitors (SSRIs) has been shown to have either no effect on memory or undermine it (with some isolated exceptions, in which improvements have been recorded), while post-training administration of SSRIs has been demonstrated to improve memory or have no effect. A small group formed by the remaining antidepressants has been shown to improve memory, with the exception of trazodone, which impairs memory. These findings are discussed in the light of knowledge regarding the actions of antidepressants on several neurotransmission systems. The possibility that the effects of antidepressants on memory are the core of the therapeutic effects of these drugs is also considered.

Stress, depression, and neuroplasticity: a convergence of mechanisms

Increasing evidence demonstrates that neuroplasticity, a fundamental mechanism of neuronal adaptation, is disrupted in mood disorders and in animal models of stress. Here we provide an overview of the evidence that chronic stress, which can precipitate or exacerbate depression, disrupts neuroplasticity, while antidepressant treatment produces opposing effects and can enhance neuroplasticity. We discuss neuroplasticity at different levels: structural plasticity (such as plastic changes in spine and dendrite morphology as well as adult neurogenesis), functional synaptic plasticity, and the molecular and cellular mechanisms accompanying such changes. Together, these studies elucidate mechanisms that may contribute to the pathophysiology of depression. Greater appreciation of the convergence of mechanisms between stress, depression, and neuroplasticity is likely to lead to the identification of novel targets for more efficacious treatments.