Cannabinoid receptor ligands suppress memory-related effects of nicotine in the elevated plus maze test in mice

Effects of cannabinoids on ligand-gated ion channels

Phytocannabinoids such as Δ⁹-tetrahydrocannabinol and cannabidiol, endocannabinoids such as N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol, and synthetic cannabinoids such as CP47,497 and JWH-018 constitute major groups of structurally diverse cannabinoids. Along with these cannabinoids, CB1 and CB2 cannabinoid receptors and enzymes involved in synthesis and degradation of endocannabinoids comprise the major components of the cannabinoid system. Although, cannabinoid receptors are known to be involved in anti-convulsant, anti-nociceptive, anti-psychotic, anti-emetic, and anti-oxidant effects of cannabinoids, in recent years, an increasing number of studies suggest that, at pharmacologically relevant concentrations, these compounds interact with several molecular targets including G-protein coupled receptors, ion channels, and enzymes in a cannabinoid-receptor independent manner. In this report, the direct actions of endo-, phyto-, and synthetic cannabinoids on the functional properties of ligand-gated ion channels and the plausible mechanisms mediating these effects were reviewed and discussed.

Avicularin Attenuates Memory Impairment in Rats with Amyloid Beta-Induced Alzheimer's Disease

Amyloid-beta-induced Alzheimer's disease (AD) and its further complications are well-established models in preclinical studies and demonstrated by many researchers. Intracerebroventricular injection of Aβ produces brain malfunction, including neurodegeneration and memory impairment. Avicularin is a bioactive flavonoid that has been found to prevent oxidative stress and proinflammatory cytokines. Alzheimer's disease treatment may benefit from inhibiting amyloid-beta and its related complications. Hence, by considering multiple actions of avicularin, including antioxidant and anti-inflammatory, we demonstrated the neuroprotective action of avicularin against amyloid beta-induced neurotoxicity. Aβ_1-42 (1 µg/µl) was dissolved in phosphate buffer solution (pH7.4) and incubated at 37 °C for 3 days to induce aggregation. A single intracerebroventricular (i.c.v.) injection of the Aβ_1-42 was given to the animals utilizing stereotaxic equipment. Avicularin was dissolved in 0.5% sodium carboxymethyl cellulose (CMC), and treatment was given to the animals for 21 days at a dose of (25, 50, and 100 mg/kg, p.o.) after Aβ_1-42 peptide (i.c.v.) injection. Several behavioral studies, acetylcholinesterase activity, oxidative stress, TNFα, IL-6, IL-1β, and expression of BDNF and amyloid-beta were measured. Avicularin treatment (50 and 100 mg/kg) showed cognition enhancement activity in behavioral studies and could reverse the effects of amyloid beta-induced inflammatory response and excessive oxidative stress. Furthermore, the findings reveal that avicularin can halt AD progression by targeting BDNF and amyloid-beta levels in the brain, suggesting that avicularin could be used for Alzheimer's disease treatment.

Attenuation of spatial memory in 5xFAD mice by targeting cholinesterases, oxidative stress and inflammatory signaling using 2-(hydroxyl-(2-nitrophenyl)methyl)cyclopentanone

Alzheimer's disease (AD) is classified pathologically as a progressive neurological disorder associated with memory decline. The study was designed to assess the underlying molecular signaling involved in the neuroprotective effect of the 2-(hydroxyl-(2-nitrophenyl)methyl)cyclopentanone (2NCP) as a novel therapeutic agent for AD. In this connection, in vitro cholinesterases inhibitory and antioxidant activities were investigated. In vivo studies were carried out on a well-known 5xFAD mice model in different behavioural models such as light/dark box,balance beam, rotarod, elevated plus maze (EPM),novel object recognition (NOR), paddling Y-maze, and Morris water maze (MWM) tests. Hippocampus (HC) and frontal cortex (FC) homogenates were examined for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities, 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radicals, glutathione S-transferase (GST), glutathione (GSH), and catalase. Further, we examined the expression of inflammatory cytokines and Nrf2 in the HC and FC through RT-PCR. Computational studies were conducted to predict the binding mode of the 2NCP with target sites of nuclear factor-κB (NF-κB) and cholinesterases. The findings of in vitro assays revealed that the IC₅₀ values of the 2NCP against AChE and BChE were 17 and 23 µg/ml respectively. DPPH antioxidant assay displayed an IC₅₀ value for the 2NCP was 62 µg/ml. Whereas, theex vivo study depicted that the activities of AChE and BChEwere significantly reduced. Moreover, free radicals load, GSH level, catalase and GST activities were significantly declined. Furthermore, in vivostudies showed that the 2NCP treated animals exhibited gradual memory improvement and improved motor functions. RT-PCR study revealed that mRNA levels of the inflammatory mediators (IL-1β, IL-6, TNF-α) were significantly reduced, while the expression of antioxidant Nrf2 was significantly increased.The molecular docking studies further confirmed that the 2NCP showed excellent binding affinities for NF-κB and cholinesterases. Taken together, the 2NCP improves spatial memory and learning, short- and long-term memory,markedly inhibits cholinesterases, reduced neuroinflammation, and mitigated oxidative stress in the 5xFAD mice; hence the 2NCP may be a potential candidate for the management of AD.

Cyclopentanone Derivative Attenuates Memory Impairment by Inhibiting Amyloid Plaques Formation in the 5xFAD Mice

Alzheimer's disease (AD) is a chronic neurodegenerative disorder. This study was designed to investigate the effects of cyclopentanone derivative i.e., 2-(hydroxyl-(3-nitrophenyl)methyl)cyclopentanone (3NCP) on behavior, amyloid β (Aβ) plaque deposition, and βAPP cleaving enzyme-1 (BACE-1) expression in the 5xFAD mouse brain. In this study, computational studies were conducted to predict the binding mode of the 3NCP with target sites of the β-secretase. In vivo studies were performed on the 5xFAD mice model of AD using different behavioral test models like light/dark box, elevated plus maze (EPM), and the Barnes maze tests for the assessment of anxiety, spatial learning and memory. The thioflavin-S staining, immunohistochemistry (IHC), and RT-PCR studies were carried out to find the effect of the 3NCP on the β-amyloid plaques formation and BACE-1 expression. The results of the computational studies showed that the 3NCP has excellent binding affinities for beta-secretase. The light/dark box study depicted that the 3NCP does not cause anxiety. The 3NCP treatment effects in the EPM and Barnes maze tests showed a significant effect on learning and memory. Furthermore, the results of the thioflavin staining and IHC revealed that the 3NCP significantly reduced the formation of the beta-amyloid plaques in brain tissues. Moreover, the RT-PCR study showed that 3NCP significantly reduced the BACE-1 expression in the brain. Conclusively, the results of the current study demonstrate that the 3NCP may be a potential candidate for AD treatment in the future.

Antidepressant-like effects of β-caryophyllene on restraint plus stress-induced depression

Chronic stress is depressogenic by altering neurotrophic and neuroinflammatory environments of the organism. The endocannabinoid system controls cognitive and emotional responses related with stress through the interaction with endocannabinoid receptors. β-Caryophyllene (BCP) is a CB2 agonist that exhibited anti-inflammatory, analgesic effects but minimal psychoactive effects. To test if BCP exhibits antidepressant-like action, animals were chronically restrained with additional stressors for 28 days, and BCP (25, 50, 100 mg/kg) was intraperitoneally injected once a day during the stress inflicting period. Then despair related behaviors and hippocampal expression of neurotrophic, inflammatory and cannabinoid receptor levels were measured. To test the effect of BCP on long-term depression, field potentials were measured during the application of lipopolysaccharide and low frequency stimulation. In the tail suspension test and forced swim test, chronic stress-induced despair behaviors were reduced by BCP. Also BCP improved the stress-related changes in the hippocampal expression of COX-2, BDNF, and CB2 receptor expression. In organotypic hippocampal slices, BCP reduced the lipopolysaccharide-induced intensification of the long-term depression. In conclusion, BCP improved chronic stress related behavioral and biochemical changes. These results suggest that BCP may be effective in treating depression and stress related mental illnesses.

Protective effect of Centella asiatica against D-galactose and aluminium chloride induced rats: Behavioral and ultrastructural approaches

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder and the commonest cause of dementia among the aged people. _D-galactose (D-gal) is a senescence agent, while aluminium is a known neurotoxin linked to pathogenesis of AD. The combined administration of rats with d-gal and aluminium chloride (AlCl₃) is considered to be an easy and a cheap method to obtain an animal model of AD. The plant Centella asiatica (CA) is reported to exert neuroprotective effects both in vitro and in vivo. Therefore, this study explored the protective effects of CA on cognition and brain ultrastructure in d-gal and AlCl₃ induced rats.

MATERIALS AND METHODS

Rats were exposed to d-gal 60 mg/kg/b.wt/day + AlCl₃ 200 mg/kg/b.wt/day and CA (200, 400 and 800 mg/kg/b.wt/day) and 1 mg/kg/b.wt/day of donepezil for 70 days. Different cognitive paradigms viz. T maze spontaneous alternation, modified elevated plus maze and novel object recognition test, were used to evaluate full lesions of the hippocampus, spatial learning and memory and non-spatial learning and memory respectively. Nissl's staining was used to determine the survival of hippocampus CA1 pyramidal cells, while transmission electron microscopy was used to check the ultrastructural changes.

RESULTS

The results revealed that d-gal and AlCl₃ could significantly impair behavior and cognitive functions, besides causing damage to the hippocampal CA1 pyramidal neurons in rats. In addition, it also caused ultrastructural morphological alterations in rat hippocampus. Conversely, co-administration o;f CA, irrespective of the dosage used, alleviated the cognitive impairments and pathological changes in the rats comparable to donepezil.

CONCLUSION

In conclusion the results suggest that CA could protect cognitive impairments and morphological alterations caused by d-gal and AlCl₃ toxicity in rats. Biochemical and molecular studies are ongoing to elucidate the probable pharmacodynamics of CA.

Interactive effects of morphine and nicotine on memory function depend on the central amygdala cannabinoid CB1 receptor function in rats

The present study investigated the possible involvement of the central amygdala (CeA) cannabinoid receptors type-1 (CB1Rs) in the interactive effects of morphine and nicotine on memory formation in a passive avoidance learning task. Our results showed that systemic administration of morphine (3 and 6mg/kg, s.c.) immediately after training phase impaired memory consolidation and induced amnesia. Administration of nicotine (0.3 and 0.6mg/kg, s.c.) before testing phase significantly restored morphine-induced amnesia, suggesting a cross state-dependent learning between morphine and nicotine. The results showed that while the administration of the lower dose of nicotine (0.1mg/kg, s.c.) per se did not induce a significant effect on morphine-induced amnesia, intra-CeA injection of arachidonylcyclopropylamide (ACPA), a cannabinoid CB1 receptor agonist (3 and 4ng/rat), significantly potentiated the nicotine response. Furthermore, the blockade of the CeA cannabinoid CB1 receptors by the injection of AM251 (0.75 and 1ng/rat) reversed the potentiative effect of nicotine (0.6mg/kg, s.c.) on morphine-induced amnesia. It should be considered that bilateral injection of the same doses of ACPA or AM251 (0.5-1ng/rat) into the CeA by itself had no effect on morphine response in a passive avoidance learning task. Confirmed by the cubic interpolation planes, the dose-response data revealed a cross-state-dependent learning between morphine and nicotine which may be mediated by the CeA endocannabinoid system via CB1 receptors.

The Influence of the CB1 Receptor Ligands on the Schizophrenia-Like Effects in Mice Induced by MK-801

A growing body of psychiatric research has emerged, focusing on the role of endocannabinoid system in psychiatric disorders. For example, the endocannabinoid system, via cannabinoid CB (CB1 and CB2) receptors, is able to control the function of many receptors, such as N-methyl-d-aspartate (NMDA) receptors connected strictly with psychosis or other schizophrenia-associated symptoms. The aim of the present research was to investigate the impact of the CB1 receptor ligands on the symptoms typical for schizophrenia. We provoked psychosis-like effects in mice by an acute administration of NMDA receptor antagonist, MK-801 (0.1–0.6 mg/kg). An acute administration of MK-801 induced psychotic symptoms, manifested in the increase in locomotor activity (hyperactivity), measured in actimeters, as well as the memory impairment, assessed in the passive avoidance task. We revealed that an acute injection of CB1 receptor agonist, oleamide (5–20 mg/kg), had no influence on the short- and long-term memory-related disturbances, as well as on the hyperlocomotion in mice, provoking by an acute MK-801. In turn, an amnestic effects or hyperactivity induced by an acute MK-801 was attenuated by an acute administration of AM 251 (0.25–3 mg/kg), a CB1 receptor antagonist. The present findings confirm that endocannabinoid system is able to modify a variety of schizophrenia-like responses, including the cognitive disturbances and hyperlocomotion in mice. Antipsychotic-like effects induced by CB1 receptor antagonist, obtained in our research, confirm the potential effect of CB1 receptor blockade and could have important therapeutic implications on clinical settings, in the future.

Behavioral evidence for the interaction between cannabinoids and Catha edulis F. (Khat) in mice

Several studies have shown the existence of an interaction between the endocannabinoid system and some drugs of abuse, such as opioids, nicotine, alcohol, and cocaine. For instance, the endocannabinoid system has long been known to play a role in the underlying mechanisms of drug reward and dependence. The aim of this study was to evaluate the possible existence of an interaction between the endocannabinoid system and khat after acute administration. Behavioral interactions of khat extract with cannabinoids were assessed. To this effect, mice were randomly divided into different groups (vehicle, khat extract, khat and WIN55,212-2, a cannabinoid agonist, khat extract and cannabinoid antagonists, AM251 & AM630) and their behavioral responses were evaluated in activity monitor, elevated plus maze and Y-maze tests. These tests were used to determine changes in locomotor activity, anxiety-like behavior, and working memory. Khat and WIN55,212-2 demonstrated differential responses in these tests, but co-administration of these agents invariably increased the measured parameters, which were reversed by the cannabinoid receptor antagonists used. The data collectively indicate that there is an interaction between khat and the endocannabinoid system, which most likely involves the cannabinoid receptors or a common mechanism separately activated by the two agents.

Khat (Catha edulis F.) and cannabinoids: Parallel and contrasting behavioral effects in preclinical and clinical studies

After a brief outline of Catha edulis F. (khat) and the cannabinoid systems, the interactions between the pharmacological effects of khat and cannabinoids will be reviewed. Khat chewing is a widespread habit that has a deep-rooted sociocultural tradition in Africa and the Middle East. Experimental studies conducted to investigate khat's central and peripheral effects have revealed an amphetamine-like mechanism of action mediated through the dopaminergic system. The endocannabinoid system comprises the receptors, the endogenous agonists and the related biochemical machinery responsible for synthesizing these substances and terminating their actions. Endocannabinoids are synthesized "on demand" from membrane phospholipids and then rapidly cleared by cellular uptake and enzymatic degradation. Khat and cannabinoids produce a body of parallel and contrasting behavioral effects. Concurrent consumption of khat and cannabinoids may increase the risk of getting or precipitating psychosis, has rewarding and motivational effect, increases the threshold of pain perception and impairs learning and memory. On the other hand, the action of cannabis to enhance food intake is likely to reduce khat's appetite suppressant effects.

Negative affective states and cognitive impairments in nicotine dependence

Smokers have substantial individual differences in quit success in response to current treatments for nicotine dependence. This observation may suggest that different underlying motivations for continued tobacco use across individuals and nicotine cessation may require different treatments in different individuals. Although most animal models of nicotine dependence emphasize the positive reinforcing effects of nicotine as the major motivational force behind nicotine use, smokers generally report that other consequences of nicotine use, including the ability of nicotine to alleviate negative affective states or cognitive impairments, as reasons for continued smoking. These states could result from nicotine withdrawal, but also may be associated with premorbid differences in affective and/or cognitive function. Effects of nicotine on cognition and affect may alleviate these impairments regardless of their premorbid or postmorbid origin (e.g., before or after the development of nicotine dependence). The ability of nicotine to alleviate these symptoms would thus negatively reinforce behavior, and thus maintain subsequent nicotine use, contributing to the initiation of smoking, the progression to dependence and relapse during quit attempts. The human and animal studies reviewed here support the idea that self-medication for pre-morbid and withdrawal-induced impairments may be more important factors in nicotine addiction and relapse than has been previously appreciated in preclinical research into nicotine dependence. Given the diverse beneficial effects of nicotine under these conditions, individuals might smoke for quite different reasons. This review suggests that inter-individual differences in the diverse effects of nicotine associated with self-medication and negative reinforcement are an important consideration in studies attempting to understand the causes of nicotine addiction, as well as in the development of effective, individualized nicotine cessation treatments.

Influence of acute or chronic calcium channel antagonists on the acquisition and consolidation of memory and nicotine-induced cognitive effects in mice

Nicotinic cholinergic receptors (nAChRs) form a heterogeneous family of ligand-gated ion channels found in the nervous system. The main objective of our research was to investigate the interaction between cholinergic nicotinic system and calcium homeostasis in cognitive processes using the modified elevated plus maze memory model in mice. The time each mouse took to move from the open arm to either of the enclosed arms on the retention trial (transfer latency, TL2) was used as an index of memory. Our results showed that a single injection of nicotine (0.035 and 0.175 mg/kg) shortened TL2 values, improving memory-related processes. Similarly, L-type calcium channel antagonists (CCAs), i.e., flunarizine, verapamil, amlodipine, nimodipine, nifedipine, and nicardipine (at the range of dose 5–20 mg/kg) administered before or after training, decreased TL2 value improving memory acquisition and/or consolidation. Interestingly, at the subthresold doses, flunarizine, nicardipine, amlodipine, verapamil, and bupropion, a nAChR antagonist, significantly reversed the nicotine improvement of memory acquisition, while flunarizine, verapamil, and bupropion attenuated the improvement of memory consolidation provoked by an acute injection of nicotine (0.035 mg/kg, s.c.). After subchronic administration (14 days, i.p.) of verapamil and amlodipine, two CCAs with the highest affinity for nAChRs, only verapamil (5 mg/kg) impaired memory acquisition and consolidation while both verapamil and amlodipine, at the subthresold, ineffective dose (2.5 mg/kg), significantly reversed the improvement of memory provoked by an acute injection of nicotine (0.035 mg/kg, s.c.). Our findings can be useful to better understand the interaction between cholinergic nicotinic receptors and calcium-related mechanisms in memory-related processes.

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.

Effects of NOS inhibitors on the benzodiazepines-induced memory impairment of mice in the modified elevated plus-maze task

The aim of the present study was to examine the effects of nitric oxide synthase (NOS) inhibitors on responses, elicited by benzodiazepines (BZs) in a modified elevated plus-maze task in mice. It was shown that acute doses of diazepam (DZ; 1 and 2 mg/kg) and flunitrazepam (FNZ; 0.05, 0.1 and 0.2 mg/kg) significantly increased the time of transfer latency (TL2) in a retention trial, thus confirming memory impairing effects of BZs. l-NAME (N(G)-nitro-l-arginine methyl ester; 200 mg/kg), a non-selective inhibitor of NOS, and 7-NI (7-nitroindazole; 40 mg/kg), a selective inhibitor of NOS, further intensified DZ-induced memory impairment. On the other hand, L-NAME (50, 100 and 200 mg/kg) and 7-NI (10, 20 and 40 mg/kg) prevented FNZ-induced memory compromising process. The results of this study indicated that suppressed NO synthesis enhanced DZ-induced but prevented FNZ-induced memory impairment. Taken together, these findings could suggest NO involvement in BZs-induced impairment of memory processes. The precise mechanism of these controversial effects, however, remains elusive.

Evaluation of standardized Bacopa monniera extract in sodium fluoride-induced behavioural, biochemical, and histopathological alterations in mice

Effect of standardized Bacopa monniera (BM; family: Scrophulariaceae) extract (100 and 300 mg/kg) against sodium fluoride (NaF; 100 and 200 ppm)-induced behavioural, biochemical, and neuropathological alterations in mice was evaluated. Akinesia, rotarod (motor coordination), forced swim test (depression), open field test (anxiety), transfer latency (memory), cholinesterase (ChE), and oxidative stress (superoxide dismutase, catalase, glutathione peroxidase, and lipid peroxidation) were determined in mice treated with NaF for 30 days alone and in combination with BM. NaF induced motor incoordination, depression, and memory impairment, and these were prevented by coadministration of BM in mice. However, NaF did not alter the weight gain, feed/water consumption, and anxiety profile. Suppression of ChE levels and increased oxidative stress were observed in mice treated with NaF. Coadministration of BM significantly improved the memory, ChE levels, and antioxidant enzymes but failed to alter the fluoride levels in NaF-treated mice. Histopathological studies revealed that BM protected the neuropathological alterations induced by NaF.

Nicotine-induced neuroprotection against ischemic injury involves activation of endocannabinoid system in rats

Nicotine has been reported to exert certain protective effect in the Parkinson's and Alzheimer's diseases. Whether it has a similar action in focal cerebral ischemia was unclear. In the present study, rats received either an injection of (-)-nicotine hydrogen tartrate salt (1.2 mg/kg, i.p.) or the vehicle 2 h before the 120 min middle cerebral artery occlusion. Neurological deficits and histological injury were assessed at 24 h after reperfusion. The content of endocannabinoids and the expression of cannabinoid receptor CB1 in brain tissues were determined at different time points after nicotine administration. Results showed that nicotine administration ameliorated neurological deficits and reduced infarct volume induced by cerebral ischemia in the rats. The neuroprotective effect was partially reversed by CB1 blockage. The content of the endocannabinoids N-arachidonylethanolamine and 2-arachidonoylglycerol, as well as the expression of cannabinoid receptor CB1 were up-regulated in brain tissues after nicotine delivery. These results suggest that endogenous cannabinoid system is involved in the nicotine-induced neuroprotection against transient focal cerebral ischemia.

Memory-related effects of cholinergic receptor ligands in mice as measured by the elevated plus maze test

The purpose of our experiments was to examine the influence of cholinergic receptor ligands on memory-related behavior in mice using the elevated plus maze (EPM) test. The EPM test allows the exploration of different memory processes (acquisition and consolidation), depending on the time of drug treatment. The time necessary for mice to move from the opened arm to the enclosed arm (i.e., transfer latency, TL) was used as an index of memory. Our findings reveal that for both the processes of acquisition and consolidation, treatment with nicotine (0.035 or 0.175 mg/kg, free base, sc) shortened TL on the second day of the experiments (TL2), thus improving memory processes. Treatment with scopolamine (0.3 or 1.0 mg/kg, ip) significantly increased TL2 values, thus impairing cognitive processes. Moreover, we found that treatment with nicotine, at the non-effective doses used during testing, prevented scopolamine-induced memory impairment by inducing a decrease in TL2 values. Next, we evaluated the influence of bupropion (10 or 20 mg/kg, ip), a drug currently used for smoking cessation in humans, on memory-related behavior induced by treatment with nicotine and scopolamine. An acute injection of bupropion (10 or 20 mg/kg) prior to injection with either nicotine (0.035 mg/kg) or scopolamine (1.0 mg/kg) significantly prevented nicotine-induced memory improvement or scopolamine-induced memory impairment. Bupropion treatment can diminish the rewarding (dependence-producing) effects of nicotine and also the cognitive effects that are related to addiction. Our studies further indicate the great involvement of the cholinergic system in memory processes and the potential for the development of more effective pharmacotherapies for memory impairment-like human disorders in which the cholinergic pathways have been implicated.

Mouse models for studying genetic influences on factors determining smoking cessation success in humans

Humans differ in their ability to quit using addictive substances, including nicotine, the major psychoactive ingredient in tobacco. For tobacco smoking, a substantial body of evidence, largely derived from twin studies, indicates that approximately half of these individual differences in ability to quit are heritable genetic influences that likely overlap with those for other addictive substances. Both twin and molecular genetic studies support overlapping influences on nicotine addiction vulnerability and smoking cessation success, although there is little formal analysis of the twin data that support this important point. None of the current datasets provides clarity concerning which heritable factors might provide robust dimensions around which individuals differ in ability to quit smoking. One approach to this problem is to test mice with genetic variations in genes that contain human variants that alter quit success. This review considers which features of quit success should be included in a comprehensive approach to elucidate the genetics of quit success, and how those features may be modeled in mice.

Nicotine-induced memory impairment by increasing brain oxidative stress

Male Wistar rats were subjected to chronic nicotine treatment (0.3 mg/kg; 7 continuous days) and their memory performance was studied by means of Y-maze and multi-trial passive avoidance tasks. Nicotine significantly decreased spontaneous alternation in Y-maze task and step-through-latency in the multi-trial passive avoidance task, suggesting effects on both short-term memory and long-term memory, respectively. In addition, nicotine induced neuronal apoptosis, DNA fragmentation, reduced antioxidant enzymes activity, and increased production of lipid peroxidation and reactive oxygen species, suggesting pro-oxidant activity. Our results provide further support that nicotine-induced memory impairment is due to an increase in brain oxidative stress in rats.