Behavioral characterization of early nicotine withdrawal in the mouse: a potential model of acute dependence

BACKGROUND

Clinical and preclinical research have demonstrated that short-term exposure to nicotine during the initial experimentation stage can lead to early manifestation of withdrawal-like signs, indicating the state of "acute dependence". As drug withdrawal is a major factor driving the progression toward regular drug intake, characterizing and understanding the features of early nicotine withdrawal may be important for the prevention and treatment of drug addiction. In this study, we corroborate the previous studies by showing that withdrawal-like signs can be precipitated after short-term nicotine exposure in mice, providing a potential animal model of acute dependence on nicotine.

RESULTS

To model nicotine exposure from light tobacco use during the initial experimentation stage, mice were treated with 0.5 mg/kg (-)-nicotine ditartrate once daily for 3 days. On the following day, the behavioral tests were conducted after implementing spontaneous or mecamylamine-precipitated withdrawal. In the open field test, precipitated nicotine withdrawal reduced locomotor activity and time spent in the center zone. In the elevated plus maze test, the mecamylamine challenge increased the time spent in the closed arm and reduced the number of entries irrespective of nicotine experience. In the examination of the somatic aspect, precipitated nicotine withdrawal enhanced the number of somatic signs. Finally, nicotine withdrawal did not affect cognitive functioning or social behavior in the passive avoidance, spatial object recognition, or social interaction test.

CONCLUSIONS

Collectively, our data demonstrate that early nicotine withdrawal-like signs could be precipitated by the nicotinic antagonist mecamylamine in mice, and that early withdrawal from nicotine primarily causes physical symptoms.

Synthesis of α3β4 Nicotinic Acetylcholine Receptor Modulators Derived from Aristoquinoline That Reduce Reinstatement of Cocaine-Seeking Behavior

Growing evidence suggests that inhibition of the α3β4 nicotinic acetylcholine receptor (nAChR) represents a promising therapeutic strategy to treat cocaine use disorder. Recently, aristoquinoline (1), an alkaloid from Aristotelia chilensis, was identified as an α3β4-selective nAChR inhibitor. Here, we prepared 22 derivatives of 1 and evaluated their ability to inhibit the α3β4 nAChR. These studies revealed structure-activity trends and several compounds with increased potency compared to 1 with few off-target liabilities. Additional mechanistic studies indicated that these compounds inhibit the α3β4 nAChR noncompetitively, but do not act as channel blockers, suggesting they are negative allosteric modulators. Finally, using a cocaine-primed reinstatement paradigm, we demonstrated that 1 significantly attenuates drug-seeking behavior in an animal model of cocaine relapse. The results from these studies further support a role for the α3β4 nAChR in the addictive properties of cocaine and highlight the possible utility of aristoquinoline derivatives in treating cocaine use disorder.

Anti-smoking drugs cytisine and varenicline reduce cardiac reperfusion injury in rat model of myocardial ischemia

Evidence to date indicates that activation of nicotinic acetylcholine receptors (nAChRs) can reduce cardiac injury from ischemia and subsequent reperfusion. The use of nAChR agonists in various animal models leads to a reduction in reperfusion injury. Earlier this effect was shown for the agonists of α7 nAChR subtype. In this work, we demonstrated the expression of mRNA encoding α4, α6 and β2 nAChR subunits in the left ventricle of rat heart. In a rat model of myocardial ischemia, we studied the effect of α4β2 nAChR agonists cytisine and varenicline, medicines used for the treatment of nicotine addiction, and found them to significantly reduce myocardium ischemia-reperfusion injury, varenicline manifesting a higher protection. Dihydro-β-erythroidine, antagonist of α4β2 nAChR, as well as methyllycaconitine, antagonist of α7 and α6β2-containing nAChR, prevented protective effect of varenicline. This together with the presence of α4, α6 and β2 subunit mRNA in the left ventricule of rat heart raises the possibility that the varenicline effect is mediated by α4β2 as well as by α7 and/or α6β2-containing receptors. Our results point to a new way for the use of cytisine and varenicline as cardioprotective agents.

Addressing Motor Dysfunction by a Selective α6-Containing Nicotinic Receptor Antagonist

In the striatum, presynaptic α6-containig nicotinic receptors are crucially involved in the modulation of dopamine release. CVN417, a novel selective antagonist at this receptor subtype, attenuates motor dysfunction in a Parkinson's disease-relevant animal model, suggesting, for this pathology, a therapeutic strategy that could greatly profit from the restricted localization of α6* nicotinic receptors in the brain.

Mecamylamine inhibits seizure-like activity in CA1-CA3 hippocampus through antagonism to nicotinic receptors

Cholinergic modulation of hippocampal network function is implicated in multiple behavioral and cognitive states. Activation of nicotinic and muscarinic acetylcholine receptors affects neuronal excitability, synaptic transmission and rhythmic oscillations in the hippocampus. In this work, we studied the ability of the cholinergic system to sustain hippocampal epileptiform activity independently from glutamate and GABA transmission. Simultaneous CA3 and CA1 field potential recordings were obtained during the perfusion of hippocampal slices with the aCSF containing AMPA, NMDA and GABA receptor antagonists. Under these conditions, spontaneous epileptiform discharges synchronous between CA3 and CA1 were recorded. Epileptiform discharges were blocked by addition of the calcium-channel blocker Cd²⁺ and disappeared in CA1 after a surgical cut between CA3 and CA1. Cholinergic antagonist mecamylamine abolished CA3-CA1 synchronous epileptiform discharges, while antagonists of α7 and α4β2 nAChRs, MLA and DhβE, had no effect. Our results suggest that activation of nicotinic acetylcholine receptors can sustain CA3-CA1 synchronous epileptiform activity independently from AMPA, NMDA and GABA transmission. In addition, mecamylamine, but not α7 and α4β2 nAChRs antagonists, reduced bicuculline-induced seizure-like activity. The ability of mecamylamine to decrease hippocampal network synchronization might be associated with its therapeutic effects in a wide variety of CNS disorders including addiction, depression and anxiety.

Nicotinic acetylcholine receptors: Conventional and unconventional ligands and signaling

Postsynaptic nAChRs in the peripheral nervous system are critical for neuromuscular and autonomic neurotransmission. Pre- and peri-synaptic nAChRs in the brain modulate neurotransmission and are responsible for the addictive effects of nicotine. Subtypes of nAChRs in lymphocytes and non-synaptic locations may modulate inflammation and other cellular functions. All AChRs that function as ligand-gated ion channels are formed from five homologous subunits organized to form a central cation channel whose opening is regulated by ACh bound at extracellular subunit interfaces. nAChR subtype subunit composition can range from α7 homomers to α4β2α6β2β3 heteromers. Subtypes differ in affinities for ACh and other agonists like nicotine and in efficiencies with which their channels are opened and desensitized. Subtypes also differ in affinities for antagonists and for positive and negative allosteric modulators. Some agonists are "silent" with respect to channel opening, and AChRs may be able to signal metabotropic pathways by releasing G-proteins independent of channel opening. Electrophysiological studies that can resolve single-channel openings and molecular genetic approaches have allowed characterization of the structures of ligand binding sites, the cation channel, and the linkages between them, as well as the organization of AChR subunits and their contributions to function. Crystallography and cryo-electron-microscopy are providing increasing insights into the structures and functions of AChRs. However, much remains to be learned about both AChR structure and function, the in vivo functional roles of some AChR subtypes, and the development of better pharmacological tools directed at AChRs to treat addiction, pain, inflammation, and other medically important issues. This article is part of the special issue on 'Contemporary Advances in Nicotine Neuropharmacology'.

Epigenetic pharmacotherapy for substance use disorder

Identifying novel therapeutics for the treatment of substance use disorder (SUD) is an area of intensive investigation. Prior strategies that have attempted to modify one or a few neurotransmitter receptors have had limited success, and currently there are no FDA-approved medications for the treatment of cocaine, methamphetamine, and marijuana use disorders. Because drugs of abuse are known to alter the expression of numerous genes in reward-related brain regions, epigenetic-based therapies have emerged as intriguing targets for therapeutic innovation. Here, I evaluate potential therapeutic approaches and challenges in targeting epigenetic factors for the treatment of SUD and highlight examples of promising strategies and future directions.

Cervical Cancer Correlates with the Differential Expression of Nicotinic Acetylcholine Receptors and Reveals Therapeutic Targets

Nicotinic acetylcholine receptors (nAChRs) are associated with various cancers, but the relation between nAChRs and cervical cancer remains unclear. Therefore, this study investigated the differential expression of nAChR subunits in human cervical cancer cell lines (SiHa, HeLa, and CaSki) and in normal ectocervical cell lines (Ect1/E6E7) at mRNA and protein levels. Two specific nAChR subtype blockers, αO-conotoxin GeXIVA and α-conotoxin TxID, were then selected to treat different human cervical cancer cell lines with specific nAChR subtype overexpression. The results showed that α3, α9, α10, and β4 nAChR subunits were overexpressed in SiHa cells compared with that in normal cells. α9 and α10 nAChR subunits were overexpressed in CaSki cells. α*-conotoxins that targeted either α9α10 or α3β4 nAChR were able to significantly inhibit cervical cancer cell proliferation. These findings may provide a basis for new targets for cervical cancer targeted therapy.

Green tobacco sickness: mecamylamine, varenicline, and nicotine vaccine as clinical research tools and potential therapeutics

INTRODUCTION

Green tobacco sickness occurs from transdermal absorption of chemicals from freshly harvested, green tobacco leaves. Signs and symptoms include nausea, vomiting, headache, and abdominal cramps. Prevalence has shifted from the United States and Europe to China, India, and Brazil. Worldwide 8 million individuals are afflicted, including women and children. Areas covered: Mecamylamine (Inversine®, Vecamyl®), a nicotinic acetylcholine receptor (nAChR) antagonist, should be tested as a remedy for green tobacco sickness. Mecamylamine is approved as an oral tablet for the treatment of hypertension, is safe, and is off-patent. Mecamylamine attenuates many of the effects of nicotine and tobacco including seizures, thereby supporting its use as an effective pharmacotherapy for tobacco dependence. Varenicline (Chantix®) and cytisine (Tabex®) are low efficacy (i.e. intrinsic activity) nAChR agonists, are used as smoking cessation aids, and are viable options to test as remedies against green tobacco sickness. Nicotine immunization strategies may provide further options for future testing. Expert commentary: Efforts to demonstrate reversal and/or prevention of green tobacco sickness by mecamylamine will underscore the importance of nicotine in this illness and highlight a new medication for effective treatment of tobacco poisoning.

Alanine-Scanning Mutagenesis of α-Conotoxin GI Reveals the Residues Crucial for Activity at the Muscle Acetylcholine Receptor

Recently, the muscle-type nicotinic acetylcholine receptors (nAChRs) have been pursued as a potential target of several diseases, including myogenic disorders, muscle dystrophies and myasthenia gravis, etc. α-conotoxin GI isolated from Conus geographus selectively and potently inhibited the muscle-type nAChRs which can be developed as a tool to study them. Herein, alanine scanning mutagenesis was used to reveal the structure–activity relationship (SAR) between GI and mouse α1β1δε nAChRs. The Pro⁵, Gly⁸, Arg⁹, and Tyr¹¹ were proved to be the critical residues for receptor inhibiting as the alanine (Ala) replacement led to a significant potency loss on mouse α1β1δε nAChR. On the contrary, substituting Asn⁴, His¹⁰ and Ser¹² with Ala respectively did not affect its activity. Interestingly, the [E1A] GI analogue exhibited a three-fold potency for mouse α1β1δε nAChR, whereas it obviously decreased potency at rat α9α10 nAChR compared to wildtype GI. Molecular dynamic simulations also suggest that loop2 of GI significantly affects the interaction with α1β1δε nAChR, and Tyr¹¹ of GI is a critical residue binding with three hydrophobic amino acids of the δ subunit, including Leu⁹³, Tyr⁹⁵ and Leu¹⁰³. Our research elucidates the interaction of GI and mouse α1β1δε nAChR in detail that will help to develop the novel analogues of GI.

The contribution of agonist and antagonist activities of α4β2* nAChR ligands to smoking cessation efficacy: a quantitative analysis of literature data

RATIONALE AND OBJECTIVE

Two mechanisms underlie smoking cessation efficacies of α4β2* nicotinic acetylcholine receptor (nAChR) agonists: a "nicotine-like" agonist activity reduces craving by substituting for nicotine during a quit attempt, and a "nicotine-blocking" antagonist activity attenuates reinforcement by competing with inhaled nicotine during a relapse. To evaluate the contribution of each mechanism to clinical efficacy, we estimated the degree of agonist and antagonist activities of nicotine replacement therapy (NRT), varenicline, cytisine, and the discontinued nAChR agonists dianicline, ABT-418, ABT-089, CP-601927, and CP-601932, relative to the functional effects of nicotine from smoking.

METHODS

Functional activities that occur in vivo with clinical doses were predicted from literature data on binding and functional potencies at the target α4β2 nAChR, as well as at α6β2* nAChRs, and from estimates of free drug exposures in human brain. Agonist activity is comprised of nAChR activation and desensitization, which were expressed as percentages of desensitization and activation by nicotine from smoking. Antagonist activity was expressed as the reduction in nAChR occupancy by nicotine during smoking in the presence of an agonist.

RESULTS

Comparisons with odds ratios at end of treatment suggest that extensive α4β2 and α6β2* nAChR desensitization combined with α6β2* nAChR activation at similar levels as nicotine from smoking is associated with clinical efficacy (NRT, varenicline, cytisine, ABT-418). Effective competition with inhaled nicotine for α4β2 and α6β2* nAChRs further improves clinical efficacy (varenicline). Other discontinued nAChR agonists have lower agonist and antagonist activities at α4β2 nAChRs and are inactive or less efficacious than NRT (dianicline, ABT-089, CP-601927, CP-601932).

CONCLUSION

Three pharmacological effects appear to be key factors underlying smoking cessation efficacy: the degree of activation of α6β2* nAChRs, desensitization of α4β2 and α6β2* nAChRs (agonist activity), and the reduction of nicotine occupancy at α4β2 and α6β2* nAChRs (antagonist activity). No single activity is dominant, and the level of smoking cessation efficacy depends on the profile of these activities achieved at clinical doses. While adequate agonist activity alone seems sufficient for a clinical effect (e.g., NRT, cytisine), clinical efficacy is improved with substantial competitive antagonism of α4β2 nAChRs, i.e., if the drug has a dual agonist-antagonist mechanism of action (e.g., varenicline).

Effects of the nicotinic agonist varenicline, nicotinic antagonist r-bPiDI, and DAT inhibitor (R)-modafinil on co-use of ethanol and nicotine in female P rats

RATIONALE

Co-users of alcohol and nicotine are the largest group of polysubstance users worldwide. Commonalities in mechanisms of action for ethanol (EtOH) and nicotine proposes the possibility of developing a single pharmacotherapeutic to treat co-use.

OBJECTIVES

Toward developing a preclinical model of co-use, female alcohol-preferring (P) rats were trained for voluntary EtOH drinking and i.v. nicotine self-administration in three phases: (1) EtOH alone (0 vs. 15%, two-bottle choice), (2) nicotine alone (0.03 mg/kg/infusion, active vs. inactive lever), and (3) concurrent access to both EtOH and nicotine. Using this model, we examined the effects of (1) varenicline, a nicotinic acetylcholine receptor (nAChR) partial agonist with high affinity for the α4β2* subtype; (2) r-bPiDI, a subtype-selective antagonist at α6β2* nAChRs; and (3) (R)-modafinil, an atypical inhibitor of the dopamine transporter (DAT).

RESULTS

In phases 1 and 2, pharmacologically relevant intake of EtOH and nicotine was achieved. In the concurrent access phase (phase 3), EtOH consumption decreased while nicotine intake increased relative to phases 1 and 2. For drug pretreatments, in the EtOH access phase (phase 1), (R)-modafinil (100 mg/kg) decreased EtOH consumption, with no effect on water consumption. In the concurrent access phase, varenicline (3 mg/kg), r-bPiDI (20 mg/kg), and (R)-modafinil (100 mg/kg) decreased nicotine self-administration but did not alter EtOH consumption, water consumption, or inactive lever pressing.

CONCLUSIONS

These results indicate that therapeutics which may be useful for smoking cessation via selective inhibition of α4β2* or α6β2* nAChRs, or DAT inhibition, may not be sufficient to treat EtOH and nicotine co-use.

Mecamylamine treatment for alcohol dependence: a randomized controlled trial

BACKGROUND AND AIMS

The nicotinic acetylcholine receptor antagonist, mecamylamine, is a potential novel pharmacotherapy for alcohol use disorder. The aims were to compare alcohol consumption between mecamylamine and placebo and test if smoking status modified treatment effects.

DESIGN

Out-patient, randomized, double-blind clinical trial for 12 weeks of treatment with mecamylamine (10 mg) (n = 65) versus placebo (n = 63).

SETTING

Connecticut, USA.

PARTICIPANTS

Individuals had current alcohol dependence (n = 128), had an average age of 48.5 [standard deviation (SD) = 9.4], 110 (85.9%) were men, and included 74 smokers (57.8%) and 54 non-smokers (42.2%). Participants were randomized to mecamylamine 10 mg per day or placebo. All subjects also received medical management therapy administered by trained research personnel.

MEASUREMENTS

Primary outcome was percentage of heavy drinking days during the last month of treatment; other outcomes included drinking days, drinks per drinking days, alcohol craving, smoking, symptoms of nicotine withdrawal and side effects.

FINDINGS

There were no significant differences in the percentage of heavy drinking days at 3 months between the mecamylamine (mean = 18.4, SD = 29.0) and placebo treatment groups (mean = 20.4, SD = 29.2) [F1, 100  = 1.3, P = 0.25; effect size d = 0.07; mean difference = 2.06, 95% confidence interval (CI) = -8.96 to 13.08]. There were no significant differences in percentage of drinking days or in drinks per drinking day at month 3 between the mecamylamine and placebo groups; there were no significant interactions.

CONCLUSIONS

Mecamylamine 10 mg per day did not reduce alcohol consumption significantly in treatment-seeking smokers and non-smokers with alcohol use disorder.

Pathologic role of neuronal nicotinic acetylcholine receptors in epileptic disorders: implication for pharmacological interventions

Accumulating evidence suggests that neuronal nicotinic acetylcholine receptors (nAChRs) may play a key role in the pathophysiology of some neurological diseases such as epilepsy. Based on genetic studies in patients with epileptic disorders worldwide and animal models of seizure, it has been demonstrated that nAChR activity is altered in some specific types of epilepsy, including autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) and juvenile myoclonic epilepsy (JME). Neuronal nAChR antagonists also have antiepileptic effects in pre-clinical studies. There is some evidence that conventional antiepileptic drugs may affect neuronal nAChR function. In this review, we re-examine the evidence for the involvement of nAChRs in the pathophysiology of some epileptic disorders, especially ADNFLE and JME, and provide an overview of nAChR antagonists that have been evaluated in animal models of seizure.

Attenuation in rats of impairments of memory by scopolamine, a muscarinic receptor antagonist, by mecamylamine, a nicotinic receptor antagonist

RATIONALE

Scopolamine, a muscarinic antagonist, impairs learning and memory for many tasks, supporting an important role for the cholinergic system in these cognitive functions. The findings are most often interpreted to indicate that a decrease in postsynaptic muscarinic receptor activation mediates the memory impairments. However, scopolamine also results in increased release of acetylcholine in the brain as a result of blocking presynaptic muscarinic receptors.

OBJECTIVES

The present experiments assess whether scopolamine-induced increases in acetylcholine release may impair memory by overstimulating postsynaptic cholinergic nicotinic receptors, i.e., by reaching the high end of a nicotinic receptor activation inverted-U dose-response function.

RESULTS

Rats tested in a spontaneous alternation task showed dose-dependent working memory deficits with systemic injections of mecamylamine and scopolamine. When an amnestic dose of scopolamine (0.15 mg/kg) was co-administered with a subamnestic dose of mecamylamine (0.25 mg/kg), this dose of mecamylamine significantly attenuated the scopolamine-induced memory impairments. We next assessed the levels of acetylcholine release in the hippocampus in the presence of scopolamine and mecamylamine. Mecamylamine injections resulted in decreased release of acetylcholine, while scopolamine administration caused a large increase in acetylcholine release.

CONCLUSIONS

These findings indicate that a nicotinic antagonist can attenuate impairments in memory produced by a muscarinic antagonist. The nicotinic antagonist may block excessive activation of nicotinic receptors postsynaptically or attenuate increases in acetylcholine release presynaptically. Either effect of a nicotinic antagonist-to decrease scopolamine-induced increases in acetylcholine output or to decrease postsynaptic acetylcholine receptor activation-may mediate the negative effects on memory of muscarinic antagonists.

Conotoxin Interactions with α9α10-nAChRs: Is the α9α10-Nicotinic Acetylcholine Receptor an Important Therapeutic Target for Pain Management?

The α9α10-nicotinic acetylcholine receptor (nAChR) has been implicated in pain and has been proposed to be a novel target for analgesics. However, the evidence to support the involvement of the α9α10-nAChR in pain is conflicted. This receptor was first implicated in pain with the characterisation of conotoxin Vc1.1, which is highly selective for α9α10-nAChRs and is an efficacious analgesic in chronic pain models with restorative capacities and no reported side effects. Numerous other analgesic conotoxin and non-conotoxin molecules have been subsequently characterised that also inhibit α9α10-nAChRs. However, there is evidence that α9α10-nAChR inhibition is neither necessary nor sufficient for analgesia. α9α10-nAChR-inhibiting analogues of Vc1.1 have no analgesic effects. Genetically-modified α9-nAChR knockout mice have a phenotype that is markedly different from the analgesic profile of Vc1.1 and similar conotoxins, suggesting that the conotoxin effects are largely independent of α9α10-nAChRs. Furthermore, an alternative mechanism of analgesia by Vc1.1 and other similar conotoxins involving non-canonical coupling of GABAB receptors to voltage-gated calcium channels is known. Additional incongruities regarding α9α10-nAChRs in analgesia are discussed. A more comprehensive characterisation of the role of α9α10-nAChRs in pain is crucial for understanding the analgesic action of conotoxins and for improved drug design.

Potential therapeutic uses of mecamylamine and its stereoisomers

Mecamylamine (3-methylaminoisocamphane hydrochloride) is a nicotinic parasympathetic ganglionic blocker, originally utilized as a therapeutic agent to treat hypertension. Mecamylamine administration produces several deleterious side effects at therapeutically relevant doses. As such, mecamylamine's use as an antihypertensive agent was phased out, except in severe hypertension. Mecamylamine easily traverses the blood-brain barrier to reach the central nervous system (CNS), where it acts as a nicotinic acetylcholine receptor (nAChR) antagonist, inhibiting all known nAChR subtypes. Since nAChRs play a major role in numerous physiological and pathological processes, it is not surprising that mecamylamine has been evaluated for its potential therapeutic effects in a wide variety of CNS disorders, including addiction. Importantly, mecamylamine produces its therapeutic effects on the CNS at doses 3-fold lower than those used to treat hypertension, which diminishes the probability of peripheral side effects. This review focuses on the pharmacological properties of mecamylamine, the differential effects of its stereoisomers, S(+)- and R(-)-mecamylamine, and the potential for effectiveness in treating CNS disorders, including nicotine and alcohol addiction, mood disorders, cognitive impairment and attention deficit hyperactivity disorder.

Review: smoking cessation strategies in patients with lung disease

BACKGROUND

Smoking is related to a great variety of pathological conditions, many of which affect the respiratory system, such as lung cancer and chronic obstructive pulmonary disease (COPD). Smoking cessation should be an integral part of the therapeutic approach to patients with pulmonary disease.

AIM

The objective was to provide a systematic review of the efficacy of the various treatments for smoking cessation in patients with diagnosed pulmonary disease.

MATERIALS AND METHODS

We conducted a search in the PubMed database in order to find studies related to the efficiency of smoking cessation treatments for this group of patients. Studies with confusing or no data on outcome and follow-up, and studies which did not use validated techniques were excluded.

RESULTS

The current treatment options include pharmaceutical therapies (bupropion, varenicline, etc) and counselling techniques. In the few trials that have been conducted, both approaches seem to be effective for treating tobacco dependence, with even higher abstinence rates, when combined.

CONCLUSION

Despite the promising results, more research is necessary, especially in patients with lung cancer, in order to determine the most beneficial smoking cessation treatment for each group of patients.

Lobeline for smoking cessation

BACKGROUND

Lobeline is a partial nicotine agonist, which has been used in a variety of commercially available preparations to help stop smoking.

OBJECTIVES

The objective of this review was to assess the effects of lobeline on long term smoking cessation.

SEARCH METHODS

We searched the Cochrane Tobacco Addiction Group trials register (most recent search December 2011).

SELECTION CRITERIA

Randomized trials comparing lobeline to placebo or an alternative therapeutic control, which reported smoking cessation with at least six months follow-up.

DATA COLLECTION AND ANALYSIS

We extracted data in duplicate on the type of subjects, the dose and form of lobeline, the outcome measures, method of randomisation, and completeness of follow-up.

MAIN RESULTS

We identified no trials meeting the full inclusion criteria including long term follow-up. One large trial failed to detect any effect on short-term abstinence.

AUTHORS' CONCLUSIONS

There is no evidence available from long term trials that lobeline can aid smoking cessation, and the short-term evidence suggests there is no benefit.

[Pharmacotherapeutic treatment strategies for smoking cessation]

Regular tobacco smoking occurs in about 35% of the male and 25% of the female German population. Individual attempts to independently quit smoking and to remain abstinent for 1 year have been shown to be successful in less than 5% of cases. This rate can be doubled by means of individual consulting and cognitive-behavioral interventions and additional pharmacological treatment might increase abstinence rates up to 25%. Apart from nicotine substitution (e.g. transdermal, oral and inhalative applications) and bupropion, recent studies have shown beneficial effects of varenicline for smoking cessation and abstinence. Varenicline, a selective partial nicotinergic agonist, has been specifically developed for the purpose of smoking cessation. Currently available data suggest that varenicline is more effective compared to nicotine substitution therapy and bupropion, increasing the abstinence likelihood by a factor of 2.3 compared to a placebo. Recent data regarding anti-nicotine vaccines suggest that this approach might yield a comparable treatment outcome and probably even better relapse-preventing effects than conventional psychopharmacological strategies. The first anti-nicotine vaccines are expected to be approved by national authorities within the forthcoming 1-2 years.

Protection against nerve agent poisoning by a noncompetitive nicotinic antagonist

The acute toxicity of organophosphorus (OP) nerve agents arises from accumulation of acetylcholine (ACh) and overstimulation of ACh receptors. The mainstay of current pharmacotherapy is the competitive muscarinic antagonist, atropine. Nicotinic antagonists have not been used due to the difficulties of administering a dose of a competitive neuromuscular blocker sufficient to antagonise the effects of excessive ACh, but not so much that it paralyses the muscles. An alternative approach would be to use a noncompetitive antagonist whose effects would not be overcome by increasing ACh concentrations. This study demonstrates that the compound 1,1'-(propane-1,3-diyl)bis(4-tert-butylpyridinium), which blocks open nicotinic ion channels noncompetitively, is able to reverse the neuromuscular paralysis after nerve agent poisoning in vitro and to protect guinea pigs against poisoning by nerve agents when used as part of a therapeutic drug combination including a muscarinic antagonist. In contrast to the oxime HI-6, this compound was equally effective in protecting against poisoning by sarin or tabun. Further studies should identify more effective compounds with this action and optimise doses for protection against nerve agent poisoning in vivo.

Nicotine receptors and depression: revisiting and revising the cholinergic hypothesis

There is a well-established connection between smoking and depression. Depressed individuals are over-represented among smokers, and ex-smokers often experience increased depressive symptoms immediately after stopping smoking. Nicotine in tobacco binds, activates and desensitizes nicotinic acetylcholine receptors (nAChRs), but it is not known whether activation or desensitization is more important for the effects of nicotine on depressive symptoms. Here we review, based on clinical and preclinical studies of nicotinic drugs, the hypothesis that blockade (rather than activation) of neuronal nAChRs might be important for the effects of nicotinic agents on depressive symptoms. The endogenous neurotransmitter for nAChRs is acetylcholine, and the effects of nicotine on depression-like behaviors support the idea that dysregulation of the cholinergic system might contribute to the etiology of major depressive disorder. Thus, pharmacological agents that limit acetylcholine signaling through neuronal nAChRs might be promising for the development of novel antidepressant medications.

Investigational medications for treatment of patients with Alzheimer disease

Development of effective treatments for patients with Alzheimer disease has been challenging. Currently approved treatments include acetylcholinesterase inhibitors and the N-methyl-D-aspartate receptor antagonist memantine hydrochloride. To investigate treatments in development for patients with Alzheimer disease, the author conducted a review of the literature. New approaches for treatment or prevention focus on several general areas, including cholinergic receptor agonists, drugs to decrease β-amyloid and tau levels, antiinflammatory agents, drugs to increase nitric oxide and cyclic guanosine monophosphate levels, and substances to reduce cell death or promote cellular regeneration. The author focuses on medications currently in clinical trials. Cholinergic agents include orthostatic and allosteric muscarinic M1 agonists and nicotinic receptor agonists. Investigational agents that target β-amyloid include vaccines, antibodies, and inhibitors of β-amyloid production. Anti-inflammatory agents, including nonsteroidal anti-inflammatory drugs, the natural product curcumin, and the tumor necrosis factor α inhibitor etanercept, have also been studied. Some drugs currently approved for other uses may also show promise for treatment of patients with Alzheimer disease. Results of clinical trials with many of these investigational drugs have been disappointing, perhaps because of their use with patients in advanced stages of Alzheimer disease. Effective treatment may need to begin earlier-before neurodegeneration becomes severe enough for symptoms to appear.

Discovery of novel alpha7 nicotinic receptor antagonists

Two distinct families of small molecules were discovered as novel alpha7 nicotinic acetylcholine receptor (nAChR) antagonists by pharmacophore-based virtual screening. These novel antagonists exhibited selectivity for the neuronal alpha7 subtype over other nAChRs and good brain penetration. Neuroprotection was demonstrated by representative compounds 7i and 8 in a mouse seizure-like behavior model induced by the nerve agent diisopropylfluorophosphate (DFP). These novel nAChR antagonists have potential use as antidote for organophosphorus nerve agent intoxication.

Nicotinic receptor-based therapeutics and candidates for smoking cessation

Tobacco dependence is the most preventable cause of death and is a chronic, relapsing disorder in which compulsive tobacco use persists despite known negative health consequences. All currently available cessation agents (nicotine, varenicline and bupropion) have limited efficacy and are associated with high relapse rates, revealing a need for more efficacious, alternative pharmacotherapies. The major alkaloid in tobacco, nicotine, activates nicotinic receptors (nAChRs) which increase brain extracellular dopamine producing nicotine reward leading to addiction. nAChRs are located primarily presynaptically and modulate synaptic activity by regulating neurotransmitter release. Subtype-selective nAChR antagonists that block reward-relevant mesocorticolimbic and nigrostriatal dopamine release induced by nicotine may offer advantages over current therapies. An innovative approach is to provide pharmacotherapies which are antagonists at nAChR subtypes mediating nicotine evoked dopamine release. In addition, providing multiple medications with a wider array of targets and mechanisms should provide more treatment options for individuals who are not responsive to the currently available pharmacotherapies. This review summarizes the currently available smoking cessation therapies and discusses emerging potential therapeutic approaches employing pharmacological agents which act as antagonists at nicotinic receptors.

Alpha9 nicotinic acetylcholine receptors and the treatment of pain

Chronic pain is a vexing worldwide problem that causes substantial disability and consumes significant medical resources. Although there are numerous analgesic medications, these work through a small set of molecular mechanisms. Even when these medications are used in combination, substantial amounts of pain often remain. It is therefore highly desirable to develop treatments that work through distinct mechanisms of action. While agonists of nicotinic acetylcholine receptors (nAChRs) have been intensively studied, new data suggest a role for selective antagonists of nAChRs. alpha-Conotoxins are small peptides used offensively by carnivorous marine snails known as Conus. A subset of these peptides known as alpha-conotoxins RgIA and Vc1.1 produces both acute and long lasting analgesia. In addition, these peptides appear to accelerate the recovery of function after nerve injury, possibly through immune mediated mechanisms. Pharmacological analysis indicates that RgIA and Vc1.1 are selective antagonists of alpha9alpha10 nAChRs. A recent study also reported that these alpha9alpha10 antagonists are also potent GABA-B agonists. In the current study, we were unable to detect RgIA or Vc1.1 binding to or action on cloned GABA-B receptors expressed in HEK cells or Xenopus oocytes. We review the background, findings and implications of use of compounds that act on alpha9* nAChRs.(1).

Antinociceptive activity of coniine in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Hemlock was used as an analgesic in certain ethnopharmacological traditions and there has been no record about the antinociceptive effect of coniine which is the major alkaloid compound of Hemlock.

AIM OF THIS STUDY

The present study was undertaken to evaluate the possible antinociceptive activity of coniine.

MATERIAL AND METHODS

Antinociceptive activity of coniine was tested dose in Hotplate test (thermal pain model) and in Writhing test (chemical pain model) in different nociception models.

RESULTS

Coniine caused a prolongation in reaction time in Hotplate test at 20mg/kg dose. In addition, it was observed that coniine decreased the number of writhes in Writhing test. Both data indicated an antinociceptive effect of coniine. A rotarod test was also conducted in order to clarify, whether this activity was related with a loss of locomotion or with an analgesic activity. None of the chemical agents at those doses used in experiments caused a loss of locomotor activity. It was also shown that antinociceptive effect of morphine was potentialized by coniine which was inhibited by nicotinic receptor blocker mecamylamine (1mg/kg).

CONCLUSION

Coniine has antinociceptive effect via the nicotinic receptors. A pharmacological assessment about the painless death of Socrates due to Hemlock (coniine) toxicity has also been presented by using this data.

Corticotropin-releasing factor within the central nucleus of the amygdala and the nucleus accumbens shell mediates the negative affective state of nicotine withdrawal in rats

Tobacco addiction is a chronic disorder that is characterized by a negative affective state upon smoking cessation and relapse after periods of abstinence. Previous research has shown that an increased central release of corticotropin-releasing factor (CRF) at least partly mediates the deficit in brain reward function associated with nicotine withdrawal in rats. The aim of these studies was to investigate the role of CRF in the central nucleus of the amygdala (CeA), the lateral bed nucleus of the stria terminalis (BNST), and the nucleus accumbens shell (Nacc shell) in the deficit in brain reward function associated with precipitated nicotine withdrawal. The intracranial self-stimulation procedure was used to assess the negative affective aspects of nicotine withdrawal. Elevations in brain reward thresholds are indicative of a deficit in brain reward function. In all experiments, the nicotinic receptor antagonist mecamylamine (3 mg/kg) elevated the brain reward thresholds of the nicotine-dependent rats (9 mg/kg per day of nicotine salt) and did not affect the brain reward thresholds of the saline-treated control rats. The administration of the nonspecific CRF1/2 receptor antagonist D-Phe CRF((12-41)) into the CeA and the Nacc shell prevented the mecamylamine-induced elevations in brain reward thresholds in the nicotine-dependent rats. Blockade of CRF1/2 receptors in the lateral BNST did not prevent the mecamylamine-induced elevations in brain reward thresholds in the nicotine-dependent rats. These studies indicate that the negative emotional state associated with precipitated nicotine withdrawal is at least partly mediated by an increased release of CRF in the CeA and the Nacc shell.

Pharmacotherapy for tobacco dependence

Pharmacotherapy can provide effective treatment of tobacco dependence and withdrawal, and thereby facilitate efforts to achieve and sustain tobacco abstinence. Currently approved medications for smoking cessation are nicotine replacement medications (NRT), including nicotine patch, gum, lozenge, sublingual tablet, inhaler and nasal spray, the antidepressant bupropion, and the nicotinic partial agonist varenicline. This review discusses the pharmacological basis for the use of these medications, and the properties that might contribute to their efficacy, safety, and abuse liability. The review also discusses how pharmacological principles can be used to improve existing medications, as well as assist in the development of new medications.

Disrupting nicotine reinforcement: from cigarette to brain

Cigarette smoking is a tenacious addiction that is maintained to a significant extent by the reinforcing effects of nicotine. An emerging theme in smoking cessation treatment is the development of methods for interfering with these reinforcing effects. By attenuating nicotine reinforcement, treatments may enhance a smoker's chances of successfully remaining abstinent. Several treatment approaches will be described, including the use of denicotinized cigarettes, nicotine vaccines, nicotinic receptor agonists and antagonists, and modulators of brain reinforcement processes. These techniques highlight the numerous sites along the path between the cigarette and the brain that can be targeted for intervention. In addition to unimodal therapies, treatment combinations will be discussed that might more effectively block cigarette reward and thereby further enhance smoking abstinence.

Varenicline for smoking cessation

Varenicline (pronounced va-re-nik-leen) (Champix - Pfizer), a nicotinic receptor partial agonist, is the first medicine of this type licensed for smoking cessation in adults. Launched in the UK in December 2006, the drug accounted for 14% of all prescription items and 22% of total expenditure, for smoking cessation products dispensed in the community in 2007. Marketing materials claim that it has a "unique dual action", a "significantly higher quit rate" than bupropion, and a "favourable safety and tolerability profile". Here we discuss the evidence for varenicline and consider its role in smoking cessation.

Phencyclidine-induced cognitive deficits in mice are improved by subsequent subchronic administration of the novel selective alpha7 nicotinic receptor agonist SSR180711

BACKGROUND

Accumulating evidence suggests that alpha7 nicotinic receptor (alpha7 nAChR) agonists could be potential therapeutic drugs for cognitive deficits in schizophrenia. The present study was undertaken to examine the effects of the novel selective alpha7 nAChR agonist SSR180711 on cognitive deficits in mice after repeated administration of the N-methyl-D-aspartate receptor antagonist phencyclidine (PCP).

METHODS

Saline or PCP (10 mg/kg/day for 10 days) was administered to mice. Subsequently, vehicle, SSR180711 (.3 or 3.0 mg/kg/day), SSR180711 (3.0 mg/kg/day) + the selective alpha7 nAChR antagonist methyllycaconitine (MLA; 3.0 mg/kg/day), or MLA (3.0 mg/kg/day) was administered IP for 2 consecutive weeks. Twenty-four hours after the final administration, a novel object recognition test was performed.

RESULTS

The PCP-induced cognitive deficits were significantly improved by subsequent subchronic (2-week) administration of SSR180711 (3.0 mg/kg). The effects of SSR180711 (3.0 mg/kg) were significantly antagonized by co-administration of MLA (3.0 mg/kg). Furthermore, Western blot analysis and immunohistochemistry revealed that levels of alpha7 nAChRs in the frontal cortex and hippocampus of the PCP (10 mg/kg/day for 10 days)-treated mice were significantly lower than those of saline-treated mice.

CONCLUSIONS

These findings suggest that repeated PCP administration significantly decreased the density of alpha7 nAChRs in the brain and that the alpha7 nAChR agonist SSR180711 could ameliorate cognitive deficits in mice after repeated administration of PCP. Therefore, alpha7 nAChR agonists including SSR180711 are potential therapeutic drugs for treating cognitive deficits in schizophrenic patients.

Negative Allosteric Modulation of Nicotinic Acetylcholine Receptors Blocks Nicotine Self-Administration in Rats

Drugs that antagonize nicotinic acetylcholine receptors (nAChRs) can be used to inhibit nicotine-induced behavior in both humans and animals. The aim of our experiments is to establish a proof-of-principle that antagonism of nAChRs by negative allosteric modulation can alter behavior in a relevant animal model of addiction, nicotine self-administration. We have identified a novel, negative allosteric modulator of nAChRs, UCI-30002 [N-(1,2,3,4-tetrahydro-1-naphthyl)-4-nitroaniline], with selectivity for the major neuronal nAChR subtypes over muscle-type nAChRs. After systemic administration, UCI-30002 significantly reduces nicotine self-administration in rats on both fixed ratio and progressive ratio schedules of reinforcement. The minimum effective dose that significantly alters nicotine self-administration corresponds to brain concentrations of UCI-30002 that produce at least 30% inhibition of the major neuronal nAChR subtypes measured in vitro. UCI-30002 has no effect on responding for food reinforcement in rats on either type of schedule, indicating that there is no effect on general responding or natural reward. UCI-30002 represents validation of the concept that negative allosteric modulators may have significant benefits as a strategy for treating nicotine addiction and encourages the development of subtype-selective modulators.

Targeting the alpha9alpha10 nicotinic acetylcholine receptor to treat severe pain

The alpha9alpha10 nicotinic acetylcholine receptors (nAChRs) are recognized for their function in the hair cells of the inner ear; transcripts for a9 and/or a10 subunits have also been identified in a diverse range of other tissues , including immune cells. The functioning of alpha9alpha10 nAChRs in these latter tissues is unknown. However, a recent series of studies has provided evidence that blockade of the alpha9alpha10 nAChR can alleviate chronic pain resulting from overt peripheral nerve injury or inflammation and increase the functional recovery of damaged neurons. Systemic administration of alpha9alpha10 antagonists produces an acute analgesia; repeated daily administrations produces sustained and cumulative levels of analgesia across 7 days without the development of tolerance. Although the exact mechanism of action is unknown, antagonism of the alpha9alpha10 nAChRs reduces the number of immune cells present at the site of injury.

Discovery of a novel nicotinic receptor antagonist for the treatment of nicotine addiction: 1-(3-Picolinium)-12-triethylammonium-dodecane dibromide (TMPD)

Limitations in efficacy and high relapse rates of currently available smoking cessation agents reveal the need for more efficacious pharmacotherapies. One strategy is to develop subtype-selective nicotinic receptor (nAChR) antagonists that inhibit nicotine-evoked dopamine (DA) release, the primary neurotransmitter involved in nicotine reward. Simple alkylation of the pyridino N-atom converts nicotine from a potent agonist into a potent antagonist. The classical antagonists, hexamethonium and decamethonium, differentiate between peripheral nAChR subtypes. Using a similar approach, we interconnected varying quaternary ammonium moieties with a lipophilic linker to provide N,N'-bis-nicotinium analogs, affording a lead compound, N,N'-dodecyl-1,12-diyl-bis-3-picolinium dibromide (bPiDDB), which inhibited nicotine-evoked DA release and decreased nicotine self-administration. The current work describes a novel compound, 1-(3-picolinium)-12-triethylammonium-dodecane dibromide (TMPD), a hybrid of bPiDDB and decamethonium. TMPD completely inhibited (IC(50)=500 nM) nicotine-evoked DA release from superfused rat striatal slices, suggesting that TMPD acts as a nAChR antagonist at more than one subtype. TMPD (1 microM) inhibited the response to acetylcholine at alpha3beta4, alpha4beta4, alpha4beta2, and alpha1beta1varepsilondelta receptors expressed in Xenopus oocytes. TMPD had a 2-fold higher affinity than choline for the blood-brain barrier choline transporter, suggesting brain bioavailability. TMPD did not inhibit hyperactivity in nicotine sensitized rats, but significantly and specifically decreased nicotine self-administration. Together, the results suggest that TMPD may have the ability to reduce the rewarding effect of nicotine with minimal side effects, a pharmacological profile indicative of potential clinical utility for the treatment of tobacco dependence.

The neurobiological bases for the pharmacotherapy of nicotine addiction

Nicotine, the major psychoactive agent present in tobacco, acts as a potent addictive drug both in humans and laboratory animals, whose locomotor activity is also stimulated. A large body of evidence indicates that the locomotor activation and the reinforcing effects of nicotine may be related to its stimulatory effects on the mesolimbic dopaminergic function. Thus, it is now well established that nicotine can increase in vivo DA outflow in the nucleus accumbens and the corpus striatum. The stimulatory effect of nicotine on DA release most probably results from its ability to excite the neuronal firing rate and to increase the bursting activity of DA neurons in the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA), and from its stimulatory action on DA terminals in the corpus striatum and the nucleus accumbens. The neurochemical data are consistent with neuroanatomical findings showing the presence of nicotinic acetylcholine receptors (nAChRs) in the SNc, the VTA, and in projection areas of the central dopaminergic system such as the corpus striatum and the nucleus accumbens. Several lines of evidence indicate that the reinforcing properties of drugs of abuse, including nicotine, can be affected by a number of transmitter systems which may act by modulating central dopaminergic function. In this paper, the neurobiological mechanisms underlying nicotine addiction will be reviewed, and the possible strategies for new pharmacological treatments of nicotine dependence will be examined.

Nicotinic alpha 7 receptors as a new target for treatment of cannabis abuse

Increasing use of cannabis makes the search for medications to reduce cannabis abuse extremely important. Here, we show that homomeric alpha7 nicotinic receptors are novel molecular entities that could be targeted in the development of new drugs for the treatment of cannabis dependence. In rats, systemic administration of the selective alpha7 nicotinic acetylcholine receptor antagonist methyllycaconitine (MLA), but not the selective heteromeric non-alpha7 nicotinic acetylcholine receptor antagonist dihydrobetaerythroidine, (1) antagonized the discriminative effects of delta-9-tetrahydrocannabinol (THC), the main active ingredient in cannabis, (2) reduced intravenous self-administration of the synthetic cannabinoid CB1 receptor agonist WIN55,212-2 [(R)-(+)-[2,3-dihydro-5-methyl-3[(4-morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl)methanone, mesylate salt], and (3) decreased THC-induced dopamine elevations in the shell of the nucleus accumbens. Altogether, our results indicate that blockade of alpha7 nicotinic receptors reverses abuse-related behavioral and neurochemical effects of cannabinoids. Importantly, MLA reversed the effects of cannabinoids at doses that did not produce depressant or toxic effects, further pointing to alpha7 nicotinic antagonists as potentially useful agents in the treatment of cannabis abuse in humans.

Central Nicotinic Receptors: Structure, Function, Ligands, and Therapeutic Potential

The growing interest in nicotinic receptors, because of their wide expression in neuronal and non-neuronal tissues and their involvement in several important CNS pathologies, has stimulated the synthesis of a high number of ligands able to modulate their function. These membrane proteins appear to be highly heterogeneous, and still only incomplete information is available on their structure, subunit composition, and stoichiometry. This is due to the lack of selective ligands to study the role of nAChR under physiological or pathological conditions; so far, only compounds showing selectivity between alpha4beta2 and alpha7 receptors have been obtained. The nicotinic receptor ligands have been designed starting from lead compounds from natural sources such as nicotine, cytisine, or epibatidine, and, more recently, through the high-throughput screening of chemical libraries. This review focuses on the structure of the new agonists, antagonists, and allosteric ligands of nicotinic receptors, it highlights the current knowledge on the binding site models as a molecular modeling approach to design new compounds, and it discusses the nAChR modulators which have entered clinical trials.

Emerging drugs in neuropathic pain

Neuropathic pain is a personally devastating and costly condition affecting 3-8% of the population. Existing treatments have limited effectiveness and produce relatively frequent adverse effects. Preclinical research has identified many promising pharmacological targets; however, reliable predictors of success in humans remain elusive. At least 50 new molecular entities have reached clinical development including: glutamate antagonists, cytokine inhibitors, vanilloid-receptor agonists, catecholamine modulators, ion-channel blockers, anticonvulsants, opioids, cannabinoids, COX inhibitors, acteylcholine modulators, adenosine receptor agonists and several miscellaneous drugs. Eight drugs are in Phase III trials at present. Strategies that may show promise over existing treatments include topical therapies, analgesic combinations and, in future, gene-related therapies. Recent years have heralded an explosion of pharmaceutical development in neuropathic pain, reflecting advanced knowledge of neurobiology and a heightened perception of the commercial value of neuropathic pain therapeutics. In the interest of improving patient care, the authors recommend implementing comparative studies throughout the development process in order to demonstrate the increased value of novel agents.

Effects of acute abstinence, reinstatement, and mecamylamine on biochemical and behavioral measures of cigarette smoking in schizophrenia

BACKGROUND

Schizophrenics have higher rates of smoking than the general population, and more difficulty with smoking cessation. However, there has been little study of differences between schizophrenics and controls with respect to biochemical and behavioral indices of smoking. We compared smokers with schizophrenia (SS; n=27) and control smokers (CS; n=26) on smoking and psychiatric outcomes at baseline, during acute smoking abstinence and reinstatement, and with pre-treatment using the nicotinic acetylcholine receptor (nAChR) antagonist mecamylamine (MEC) in a human laboratory setting.

METHODS

Biochemical (e.g., plasma nicotine) and behavioral (e.g., craving, withdrawal) outcomes were assessed at baseline, after overnight abstinence, and after smoking reinstatement during three consecutive test weeks. Each week, participants received one of three doses of MEC (0.0, 5.0, or 10.0 mg/dayx3 days) in a randomized, counterbalanced manner.

RESULTS

Compared to CS, SS displayed similar levels of craving and withdrawal, but higher plasma nicotine and cotinine levels, and cotinine/CPD ratio. During reinstatement, SS consumed significantly more cigarettes than CS, but MEC did not significantly alter indices of smoking, psychiatric symptoms, or cigarette consumption during reinstatement.

CONCLUSIONS

1) The reinforcing effects of smoking may be increased in SS versus CS after overnight abstinence; 2) the lack of effects of nAChR antagonism may suggest that non-nicotinic components of cigarettes may contribute to the behavioral effects of smoking in both SS and CS; and 3) consistent with previous studies, SS may exhibit higher baseline levels of nicotine and cotinine, and greater extraction of nicotine per cigarette than CS.

5alpha-cardenolides from Kanahia laniflora inhibit ionotropic acetylcholine receptors

5alpha-cardenolides isolated from Kanahia laniflora are inhibitors of muscle-type nicotinic acetylcholine receptors expressed in TE671 cells with IC (50) values in the range of 27 - 60 microM, as determined by whole-cell patch-clamp electrophysiological experiments.

Molecular mechanism for analgesia involving specific antagonism of alpha9alpha10 nicotinic acetylcholine receptors

alpha9alpha10 nicotinic acetylcholine receptors (nAChRs) have been identified in a variety of tissues including lymphocytes and dorsal root ganglia; except in the case of the auditory system, the function of alpha9alpha10 nAChRs is not known. Here we show that selective block (rather than stimulation) of alpha9alpha10 nAChRs is analgesic in an animal model of nerve injury pain. In addition, blockade of this nAChR subtype reduces the number of choline acetyltransferase-positive cells, macrophages, and lymphocytes at the site of injury. Chronic neuropathic pain is estimated to affect up to 8% of the world's population; the numerous analgesic compounds currently available are largely ineffective and act through a small number of pharmacological mechanisms. Our findings not only suggest a molecular mechanism for the treatment of neuropathic pain but also demonstrate the involvement of alpha9alpha10 nAChRs in the pathophysiology of peripheral nerve injury.

Mechanism of action of agents used in attention-deficit/hyperactivity disorder

Several medications have been demonstrated effective in treating individuals with attention-deficit/hyperactivity disorder (ADHD). There appears to be some commonality in the physiologic mechanisms of action of these agents relevant to the treatment of ADHD. Either direct or indirect attenuation of dopamine and norepinephrine neurotransmission appears related to both the stimulant and nonstimulant medications efficacious in ADHD. However, important differences exist both between and within the specific classes of agents. Elucidating the various mechanisms of action of ADHD medications may lead to better choices in matching potential response to the characteristics (e.g., genotype) of individuals.

Partial agonists as therapeutic agents at neuronal nicotinic acetylcholine receptors

Improved understanding of how brain function is altered in neurodegenerative disease states, pain and conditions, such as schizophrenia and attention deficit disorder, has highlighted the role of nicotinic acetylcholine receptors (nAChRs) in these conditions and identified them as promising therapeutic targets. nAChRs are widely expressed throughout the peripheral and central nervous system, and this widespread nature underlines the need for new ligands with different selectivities and pharmacological profiles if we are to avoid the adverse side effects associated with many of the nAChR modulators currently identified. Partial agonists have the unique property of being able to act both as agonists or antagonists depending on the concentration of endogenous neurotransmitter. Moreover, the agonist action of partial agonists has a 'ceiling' effect, giving them a large safety margin and making them an attractive proposition for therapeutic molecules. Partial agonists of nAChRs are currently being developed as a nicotine replacement therapy for smoking cessation and for the treatment of a number of neurological diseases associated with a loss of cholinergic function. This commentary will discuss the pharmacological properties of partial agonists and review recent research developments in the field of partial agonists acting at nicotinic receptors.