Cognitive deficits in schizophrenia: focus on neuronal nicotinic acetylcholine receptors and smoking

An α7 nAChR approach for the baseline-dependent modulation of deviance detection in schizophrenia: A pilot study assessing the combined effect of CDP-choline and galantamine

BACKGROUND

Cognitive operations including pre-attentive sensory processing are markedly impaired in patients with schizophrenia (SCZ) but evidence significant interindividual heterogeneity, which moderates treatment response with nicotinic acetylcholine receptor (nAChR) agonists. Previous studies in healthy volunteers have shown baseline-dependency effects of the α7 nAChR agonist cytidine 5'-diphosphocholine (CDP-choline) administered alone and in combination with a nicotinic allosteric modulator (galantamine) on auditory deviance detection measured with the mismatch negativity (MMN) event-related potential (ERP).

AIM

The objective of this pilot study was to assess the acute effect of this combined α7 nAChR-targeted treatment (CDP-choline/galantamine) on speech MMN in patients with SCZ (N = 24) stratified by baseline MMN responses into low, medium, and high baseline auditory deviance detection subgroups.

METHODS

Patients with a stable diagnosis of SCZ attended two randomized, double-blind, placebo-controlled and counter-balanced testing sessions where they received a placebo or a CDP-choline (500 mg) and galantamine (16 mg) treatment. MMN ERPs were recorded during the presentation of a fast multi-feature speech MMN paradigm including five speech deviants. Clinical measures were acquired before and after treatment administration.

RESULTS

While no main treatment effect was observed, CDP-choline/galantamine significantly increased MMN amplitudes to frequency, duration, and vowel speech deviants in low group individuals. Individuals with higher positive and negative symptom scale negative, general, and total scores expressed the greatest MMN amplitude improvement following CDP-choline/galantamine.

CONCLUSIONS

These baseline-dependent nicotinic effects on early auditory information processing warrant different dosage and repeated administration assessments in patients with low baseline deviance detection levels.

Alternative Therapy of Psychosis: Potential Phytochemicals and Drug Targets in the Management of Schizophrenia

Schizophrenia is a chronic mental and behavioral disorder characterized by clusters of symptoms including hallucinations, delusions, disorganized thoughts and social withdrawal. It is mainly contributed by defects in dopamine, glutamate, cholinergic and serotonergic pathways, genetic and environmental factors, prenatal infections, oxidative stress, immune system activation and inflammation. Management of schizophrenia is usually carried out with typical and atypical antipsychotics, but it yields modest benefits with a diversity of side effects. Therefore, the current study was designed to determine the phytochemicals as new drug candidates for treatment and management of schizophrenia. These phytochemicals alter and affect neurotransmission, cell signaling pathways, endocannabinoid receptors, neuro-inflammation, activation of immune system and status of oxidative stress. Phytochemicals exhibiting anti-schizophrenic activity are mostly flavonoids, polyphenols, alkaloids, terpenoids, terpenes, polypropanoids, lactones and glycosides. However, well-designed clinical trials are consequently required to investigate potential protective effect and therapeutic benefits of these phytochemicals against schizophrenia.

The effects of acute nicotine administration on cognitive and early sensory processes in schizophrenia: a systematic review

Nicotine use, which is mostly done through smoking tobacco, is among the most burdensome comorbidities of schizophrenia. However, the ways in which nicotine affects the cognitive and early sensory alterations found in this illness are still debated. After conducting a systematic literature search, 29 studies were selected. These studies involve individuals with schizophrenia who underwent cognitive and/or early sensory function assessments after acute nicotine administration and include 560 schizophrenia subjects and 346 non-schizophrenia controls. The findings highlight that a single dose of nicotine can improve a range of cognitive functions in schizophrenia subjects, such as attention, working memory, and executive functions, with attention being the most responsive domain. In addition, nicotine can modulate early detection of changes in the sensory environment at both the auditory and visual levels. Nevertheless, effects vary strongly depending on the type of neuropsychological assessment and nicotine intake conditions used in each study. The current findings suggest the need to consider a potential decrease of cognitive and early sensory performance when patients with schizophrenia quit smoking.

The role of nicotinic cholinergic neurotransmission in delusional thinking

Delusions are a difficult-to-treat and intellectually fascinating aspect of many psychiatric illnesses. Although scientific progress on this complex topic has been challenging, some recent advances focus on dysfunction in neural circuits, specifically in those involving dopaminergic and glutamatergic neurotransmission. Here we review the role of cholinergic neurotransmission in delusions, with a focus on nicotinic receptors, which are known to play a part in some illnesses where these symptoms appear, including delirium, schizophrenia spectrum disorders, bipolar disorder, Parkinson, Huntington, and Alzheimer diseases. Beginning with what we know about the emergence of delusions in these illnesses, we advance a hypothesis of cholinergic disturbance in the dorsal striatum where nicotinic receptors are operative. Striosomes are proposed to play a central role in the formation of delusions. This hypothesis is consistent with our current knowledge about the mechanism of action of cholinergic drugs and with our abstract models of basic cognitive mechanisms at the molecular and circuit levels. We conclude by pointing out the need for further research both at the clinical and translational levels.

Pharmacological characterization of JWX-A0108 as a novel type I positive allosteric modulator of α7 nAChR that can reverse acoustic gating deficits in a mouse prepulse inhibition model

The α7 nicotinic acetylcholine receptor (α7 nAChR) is a ligand-gated Ca2+-permeable homopentameric ion channel implicated in cognition and neuropsychiatric disorders. Pharmacological enhancement of α7 nAChR function has been suggested for improvement of cognitive deficits. In the present study, we characterized a thiazolyl heterocyclic derivative, 6-(2-chloro-6-methylphenyl)-2-((3-fluoro-4-methylphenyl)amino)thiazolo[4,5-d]pyrimidin-7(6H)-one (JWX-A0108), as a novel type I α7 nAChR positive allosteric modulator (PAM), and evaluated its ability to reverse auditory gating and spatial working memory deficits in mice. In Xenopus oocytes expressing human nAChR channels, application of JWX-A0108 selectively enhanced α7 nAChR-mediated inward current in the presence of the agonist ACh (EC50 value = 4.35 ± 0.12 µM). In hippocampal slices, co-application of ACh and JWX-A0108 (10 µM for each) markedly increased both the frequency and amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) recorded in pyramidal neurons, but JWX-A0108 did not affect GABA-induced current in oocytes expressing human GABAA receptor α1β3γ2 and α5β3γ2 subtypes. In mice with MK-801-induced deficits in auditory gating, administration of JWX-A0108 (1, 3, and 10 mg/kg, i.p.) dose-dependently attenuates MK-801-induced auditory gating deficits in five prepulse intensities (72, 76, 80, 84, and 88 dB). Furthermore, administration of JWX-A0108 (0.03, 0.1, or 0.3 mg/kg, i.p.) significantly reversed MK-801-induced impaired spatial working memory in mice. Our results demonstrate that JWX-A0108 is a novel type I PAM of α7 nAChR, which may be beneficial for improvement of cognitive deficits commonly found in neuropsychiatric disorders such as schizophrenia and Alzheimer's disease.

Relationship of common variants in CHRNA5 with early-onset schizophrenia and executive function

Altered cholinergic neural transmission is hypothesized to increase susceptibility to cognitive deficits in psychotic disorders such as schizophrenia (SCZ). The nicotinic acetylcholine receptor α5 subunit gene (CHRNA5) is reported to be associated with cognitive function in nicotine-dependent populations and SCZ in non-smoking SCZ patients. Nevertheless, it is still not clear whether the CHRNA5 gene contributes to susceptibility to the cognitive deficits of SCZ without smoking. To further clarify the role of CHRNA5, we designed a two-stage, case-control study to examine the association between CHRNA5 and SCZ and its clinical features adjusted for smoking status in early-onset SCZ patients. A total of 15 tag single nucleotide polymorphisms (SNPs) on CHRNA5 were genotyped in the discovery stage, which included 485 early-onset SCZ patients and 1018 controls, and then, we replicated this association in a confirmatory population of 674 patients and 1886 controls. The rs16969968 SNP was identified as significantly associated with SCZ in both datasets. In addition, the severity of psychotic symptoms and cognitive deficits was assessed using the Positive and Negative Syndrome Scale (PANSS) and the Wisconsin Card Sorting Test (WCST). The rs16969968 SNP was associated with psychotic symptoms in patients and with cognitive function in patients and controls. Our results show that rs16969968 on CHRNA5 is tightly linked to genetic susceptibility, psychotic symptoms and cognitive deficits in SCZ in an early-onset Chinese population, suggesting that CHRNA5 may play an important role in the etiology of SCZ.

Effects of Repetitive Transcranial Magnetic Stimulation over Prefrontal Cortex on Attention in Psychiatric Disorders: A Systematic Review

Repetitive transcranial magnetic stimulation (rTMS) may be effective for enhancing cognitive functioning. In this review, we aimed to systematically evaluate the effects of rTMS on attention in psychiatric diseases. In particular, we searched PubMed and Embase to examine the effectiveness of rTMS administered to the dorsolateral prefrontal cortex (DLPFC) on this specific cognitive domain. The search identified 24 articles, 21 of which met inclusion and exclusion criteria. Among them, nine were conducted in patients with depression, four in patients with schizophrenia, three in patients with autism spectrum disorder (ASD), two in patients with attention deficit hyperactivity disorder, one each in patients with Alzheimer's disease and in patients with alcohol or methamphetamine addiction. No evidence for cognitive adverse effects was found in all the included rTMS studies. Several studies showed a significant improvement of attentional function in patients with depression and schizophrenia. The beneficial effects on attention and other executive functions suggest that rTMS has the potential to target core features of ASD. rTMS may influence the attentional networks in alcohol-dependent and other addicted patients. We also reviewed and discussed the studies assessing the effects of rTMS on attention in the healthy population. This review suggests that prefrontal rTMS could exert procognitive effects on attention in patients with many psychiatric disorders.

Smoking does not impact social and non-social cognition in patients with first episode psychosis

BACKGROUND

Many studies having shown significant improvements in non-social and social cognitive performance in smoking FEP patients compared to non-smoking FEP patients. The findings are controversial. This study analyzed the effects of tobacco use on non-social and social cognitive function in a large group of FEP patients and a matched healthy control group.

METHODS

A sample of 335 patients with FEP and 253 healthy controls was divided into four subgroups: control tobacco users (CTU), control non-tobacco users (CNTU), patient tobacco users (PTU) and patient non-tobacco users (PNTU). Demographic variables, tobacco use variables (presence or absence, frequency and duration of tobacco use), neurocognitive (non-social) performance and social cognition were assessed.

RESULTS

Comparison of 4 subgroups in non-social cognitive function revealed significant differences after controlling for covariables in executive functions (F=13.45; p≤0.001) and working memory domains (F=4.30; p=0.005). CTU and CNTU subgroups scored higher in all the domains compared to the PTU and the PNTU subgroups respectively. Social cognitive function was also significantly different within the four subgroups, with control subgroups showing better social cognition than patient subgroups. Significant differences in the executive functions domain were observed when comparing PTU and CTU groups (F=19.60; p≤0.001). No significant differences were revealed in the comparison between the patient groups.

CONCLUSIONS

This large study suggests that tobacco use in FEP patients is not related to better non-social or social cognitive performance.

Nicotinic Acetylcholine Receptors in HIV: Possible Roles During HAND and Inflammation

Infection with the human immunodeficiency virus (HIV) remains a threat to global health. Since its discovery, many efforts have been directed at understanding the mechanisms and consequences of infection. Although there have been substantial advances since the advent of antiretroviral therapy, there are still complications that significantly compromise the health of infected patients, particularly, chronic inflammation and HIV-associated neurocognitive disorders (HAND). In this review, a new perspective is addressed in the field of HIV, where the alpha7 nicotinic acetylcholine receptor (α7-nAChR) is the protagonist. We comprehensively discuss the available evidence implicating α7-nAChRs in the context of HIV and provide possible explanations about its role in HAND and inflammation in both the central nervous system and the periphery.

Enhancing attention in neurodegenerative diseases: current therapies and future directions

We all experience at least occasional lapses in attention but in some neurological conditions, loss of attention is pervasive and debilitating. Treating deficits in attention first requires an understanding of the neurobiology of attention, which we now understand to be a set of different cognitive processes. Cholinesterase inhibitors are already established as effective attentional enhancers used in the treatment of certain dementias. Other stimulant agents such as modafanil, amphetamine and methylphenidate have demonstrated limited success in healthy individuals where attention is already optimal and clinical trials in patients with neurological disease are sparse. Dietary and lifestyle changes are gaining increasing prominence, as are experimental treatments such as deep brain stimulation and transcranial magnetic stimulation. As the therapeutic arsenal widens, clinicians will be able to match specific treatments to selective deficits in attention, giving patients a tailored management plan. Here we review common diseases that impair attention and emphasise how an understanding of attentional processing within the brain might lead to improved therapeutic strategies.

Acute and chronic effects of clozapine on cholinergic transmission in cultured mouse superior cervical ganglion neurons

Cholinergic dysfunction contributes to cognitive deficits in schizophrenia. The atypical antipsychotic clozapine improves cognition in patients with schizophrenia, possibly through modulation of the cholinergic system. However, little is known about specific underlying mechanisms. We investigated the acute and chronic effects of clozapine on cholinergic synaptic transmission in cultured superior cervical ganglion (SCG) neurons. Spontaneous excitatory postsynaptic currents (sEPSCs) were detected and were reversibly inhibited by the nicotinic receptor antagonist d-tubocurarine, confirming that the synaptic responses were primarily mediated by nicotinic receptors. Bath application of clozapine at therapeutic concentrations rapidly and reversely inhibited both the amplitude and frequency of sEPSCs in a concentration-dependent manner, without changing either rise or decay time, suggesting that clozapine effects have both presynaptic and postsynaptic origins. The acute effects of clozapine on sEPSCs were recapitulated by chronic treatment of SCG cultures with similar concentrations of clozapine, as clozapine treatment for 4 d reduced the frequency and amplitude of sEPSCs without affecting their kinetics. Cell survival analysis indicated that SCG neuron cell counts after chronic clozapine treatment were comparable to the control group. These results demonstrate that therapeutic concentrations of clozapine suppress nicotinic synaptic transmission in SCG cholinergic synapses, a simple in vitro preparation of cholinergic transmission.

The separate and combined effects of monoamine oxidase A inhibition and nicotine on the mismatch negativity event related potential

The mismatch negativity (MMN) auditory event-related potential (ERP) has been extensively studied as a potential biomarker for abnormal auditory processing in schizophrenia (SZ), a population which exhibits abnormally high smoking rates. The relationship between nicotinic activation and cognition in SZ may be related to underlying nicotinic and NMDA receptor dysfunction within the disease. However, transient cognitive improvements via smoking in patients may also result from monoamine oxidase (MAO) inhibition, achieved through tobacco smoke. In 24 healthy non-smoking males, we investigated the separate and combined effects of nicotine and MAO-A inhibition via moclobemide (75mg) on the optimal-5 variation of the MMN paradigm. No significant drug effects were observed in our total sample, however, stratification of individuals into low (N=12) and high (N=12) baseline MMN amplitude groups revealed increases in duration MMN amplitude relative to placebo by nicotine, as well as moclobemide, but not after the combination of the two. Because previous research has shown there was no effect of monoamine modulation on MMN, this study shows an unexpected effect of moclobemide on duration MMN.

Neurocognitive effects of acute choline supplementation in low, medium and high performer healthy volunteers

Novel pharmacological treatments targeting alpha 7 nicotinic acetylcholine receptor (α7 nAChR) hypofunction in schizophrenia have shown mixed success in ameliorating cognitive impairments associated with this disorder. Choline, a selective agonist at α7 receptors is increased with oral administration of cytidine 5'-diphosphocholine (CDP-choline), the cognitive effects of which were assessed in healthy volunteers. Using the CogState test battery, behavioral performance in schizophrenia-relevant cognitive domains was assessed in 24 male participants following a single low (500mg) and moderate (1000mg) dose of CDP-choline. Relative to placebo, CDP-choline improved processing speed, working memory, verbal learning, verbal memory, and executive function in low baseline performers, while exerting no effects in medium baseline performers, and diminishing cognition in high baseline performers. Dose effects varied with cognitive domain but were evident with both the 500mg and 1000mg doses. These preliminary findings of cognitive enhancement in relatively impaired performers are consistent with the α7 receptor mechanism and support further trials with CDP-choline as a potential pro-cognitive strategy for cognitive impairment in schizophrenia.

The effects of varenicline on sensory gating and exploratory behavior with pretreatment with nicotinic or 5-HT3A receptor antagonists

Individuals with schizophrenia smoke at high frequency relative to the general population. Despite the harmful effects of cigarette smoking, smoking among schizophrenic patients improves cognitive impairments not addressed or worsened by common neuroleptics. Varenicline, a nonselective neuronal nicotinic receptor (NNR) agonist and full agonist of 5-HT3A receptors, helps reduce smoking among schizophrenic patients. To determine whether varenicline also improves a cognitive symptom of schizophrenia, namely, impaired sensory gating, a transgenic mouse with schizophrenia, th-fgfr1(tk-), was used. Varenicline dose-dependently increased prepulse inhibition (PPI) of the startle response, a measure of sensory gating, in th-fgfr1(tk-) mice and normalized PPI deficits relative to nontransgenic controls. With the highest dose (10 mg/kg), however, there was a robust elevation of PPI and startle response, as well as reduced exploratory behavior in the open field and elevated plus maze. Pretreatment with the nonspecific NNR antagonist mecamylamine attenuated the exaggerated PPI response and, similar to the 5-HT3A receptor antagonist ondansetron, it prevented the reduction in exploratory behavior. Collectively, these results indicate that varenicline at low-to-moderate doses may be beneficial against impaired sensory gating in schizophrenia; however, higher doses may induce anxiogenic effects, which can be prevented with antagonists of NNRs or 5-HT3A receptors.

Nicotine exposure during adolescence: cognitive performance and brain gene expression in adult heterozygous reeler mice

RATIONALE

We have recently reported nicotine-induced stimulation of reelin and glutamic acid decarboxylase 67 (GAD67) mRNA expression levels in the brain of heterozygous reeler mice (HRM), a putative animal model for the study of symptoms relevant to major behavioral disorders.

OBJECTIVES

We aimed to evaluate long-term behavioral effects and brain molecular changes as a result of adaptations to nicotine exposure in the developing HRM males.

METHODS

Adolescent mice (pnd 37-42) were exposed to oral nicotine (10 mg/l) in a 6-day free-choice drinking schedule. As expected, no differences in total nicotine intake between WT (wild-type) mice and HRM were found.

RESULTS

Long-term behavioral effects and brain molecular changes, as a consequence of nicotine exposure during adolescence, were only evidenced in HRM. Indeed, HRM perseverative exploratory behavior and poor cognitive performance were modulated to WT levels by subchronic exposure to nicotine during development. Furthermore, the expected reduction in the expression of mRNA of reelin and GAD67 in behaviorally relevant brain areas of HRM appeared persistently restored by nicotine. For brain-derived neurotrophic factor (BDNF) mRNA expression, no genotype-dependent changes appeared. However, expression levels were increased by previous nicotine in brains from both genotypes. The mRNA encoding for nicotine receptor subunits (α7, β2 and α4) did not differ between genotypes and as a result of previous nicotine exposure.

CONCLUSION

These findings support the hypothesis of pre-existing vulnerability (based on haploinsufficiency of reelin) to brain and behavioral disorders and regulative short- and long-term effects associated with nicotine modulation.

Smoking cessation and reduction in schizophrenia (SCARIS) with e-cigarette: study protocol for a randomized control trial

Background

It is well established in studies across several countries that tobacco smoking is more prevalent among schizophrenic patients than the general population. Electronic cigarettes are becoming increasingly popular with smokers worldwide. To date there are no large randomized trials of electronic cigarettes in schizophrenic smokers. A well-designed trial is needed to compare efficacy and safety of these products in this special population.

Methods/Design

Intervention: We have designed a randomized controlled trial investigating the efficacy and safety of electronic cigarette. The trial will take the form of a prospective 12-month randomized clinical study to evaluate smoking reduction, smoking abstinence and adverse events in schizophrenic smokers not intending to quit. We will also monitor quality of life, neurocognitive functioning and measure participants’ perception and satisfaction of the product.

Outcome measures: A ≥50% reduction in the number of cigarettes/day from baseline, will be calculated at each study visit (“reducers”). Abstinence from smoking will be calculated at each study visit (“quitters”). Smokers who leave the study protocol before its completion and will carry out the Early Termination Visit or who will not satisfy the criteria of “reducers” and “quitters” will be defined “non responders”.

Statistical analysis: The differences of continuous variables between the three groups will be evaluated with the Kruskal-Wallis Test, followed by the Dunn multiple comparison test. The differences between the three groups for normally distributed data will be evaluated with ANOVA test one way, followed by the Newman-Keuls multiple comparison test. The normality of the distribution will be evaluated with the Kolmogorov-Smirnov test. Any correlations between the variables under evaluation will be assessed by Spearman r correlation. To compare qualitative data will be used the Chi-square test.

Discussion

The main strengths of the SCARIS study are the following: it’s the first large RCT on schizophrenic patient, involving in and outpatient, evaluating the effect of a three-arm study design, and a long term of follow-up (52-weeks).

The goal is to propose an effective intervention to reduce the risk of tobacco smoking, as a complementary tool to treat tobacco addiction in schizophrenia.

Trial registration

ClinicalTrials.gov, NCT01979796.

Genetic deletion of the adenosine A(2A) receptor prevents nicotine-induced upregulation of α7, but not α4β2* nicotinic acetylcholine receptor binding in the brain

Considerable evidence indicates that adenosine A(2A) receptors (A(2A)Rs) modulate cholinergic neurotransmission, nicotinic acetylcholine receptor (nAChR) function, and nicotine-induced behavioural effects. To explore the interaction between A(2A) and nAChRs, we examined if the complete genetic deletion of adenosine A(2A)Rs in mice induces compensatory alterations in the binding of different nAChR subtypes, and whether the long-term effects of nicotine on nAChR regulation are altered in the absence of the A(2A)R gene. Quantitative autoradiography was used to measure cytisine-sensitive [¹²⁵I]epibatidine and [¹²⁵I]α-bungarotoxin binding to α4β2* and α7 nAChRs, respectively, in brain sections of drug-naïve (n = 6) or nicotine treated (n = 5-7), wild-type and adenosine A(2A)R knockout mice. Saline or nicotine (7.8 mg/kg/day; free-base weight) were administered to male CD1 mice via subcutaneous osmotic minipumps for a period of 14 days. Blood plasma levels of nicotine and cotinine were measured at the end of treatment. There were no compensatory developmental alterations in nAChR subtype distribution or density in drug-naïve A(2A)R knockout mice. In nicotine treated wild-type mice, both α4β2* and α7 nAChR binding sites were increased compared with saline treated controls. The genetic ablation of adenosine A(2A)Rs prevented nicotine-induced upregulation of α7 nAChRs, without affecting α4β2* receptor upregulation. This selective effect was observed at plasma levels of nicotine that were within the range reported for smokers (10-50 ng ml⁻¹). Our data highlight the involvement of adenosine A(2A)Rs in the mechanisms of nicotine-induced α7 nAChR upregulation, and identify A(2A)Rs as novel pharmacological targets for modulating the long-term effects of nicotine on α7 receptors.

Newer antipsychotics and upcoming molecules for schizophrenia

BACKGROUND

The management of schizophrenia has seen significant strides over the last few decades, due to the increasing availability of a number of antipsychotics. Yet, the diminished efficacy in relation to the negative and cognitive symptoms of schizophrenia, and the disturbing adverse reactions associated with the current antipsychotics, reflect the need for better molecules targeting unexplored pathways.

PURPOSE

To review the salient features of the recently approved antipsychotics; namely, iloperidone, asenapine, lurasidone and blonanserin.

METHODS

We discuss the advantages, limitations and place in modern pharmacotherapy of each of these drugs. In addition, we briefly highlight the new targets that are being explored.

RESULTS

Promising strategies include modulation of the glutamatergic and GABAergic pathways, as well as cholinergic systems.

CONCLUSIONS

Although regulatory bodies have approved only a handful of antipsychotics in recent years, the wide spectrum of targets that are being explored could eventually bring out antipsychotics with improved efficacy and acceptability, as well as the potential to revolutionize psychiatric practice.

Nicotine restores Wt-like levels of reelin and GAD67 gene expression in brain of heterozygous reeler mice

Important reduction of reelin, a neural development- and plasticity-associated protein, and glutamic acid decarboxylase (GAD67) are reported in brains of schizophrenic patients. These individuals are consistently engaged in tobacco smoking and nicotine is thought to alleviate negative behavioral symptoms or cognitive alterations. In mouse brain, nicotine has been shown to reduce GAD67 promoter methylation and increase its transcription. We assessed the effects of administration of nicotine (1 mg/kg s.c.) for 6 days, in male mice heterozygous for reelin (HRM), a putative model for symptoms related to schizophrenia. Expression of reelin, GAD67 and brain-derived neurotrophic factor (BDNF) was measured in different brain areas. RNA expression analysis evidenced genotype-related changes, with a marked reduction in reelin and GAD67 gene expression in prefrontal cortex, hippocampus, cerebellum, and striatum from HRM. Nicotine treatment selectively reversed the HRM-related phenotype in most brain areas and increased BDNF gene expression in cortex and hippocampus of both genotypes. Locomotor performance in their home cage revealed that HRM subjects were characterized by general hyperactivity; with nicotine administration restoring WT-like levels of locomotion. These findings are interpreted within the hypothesis of pre-existing vulnerability (based on haploinsufficiency of reelin) to brain and behavioral disorders and regulative effects associated with nicotine exposure.

Exploring the relationships between tobacco smoking and schizophrenia in first-degree relatives

Up to 90% of individuals with schizophrenia suffer from nicotine dependence. Both schizophrenia and nicotine consumption have strong genetic components, which may overlap. The relationship between schizophrenia and nicotine dependence remains unclear, due in part to confounding factors. Studies of the relationship between nicotine consumption and milder schizophrenia-related phenotypes, such as schizotypy, in first-degree relatives of individuals with schizophrenia could help to better understand the relationship between smoking and schizophrenia while avoiding such confounders. We assessed the proportion of smokers, their level of nicotine dependence and their level of schizotypy in a sample of 98 first-degree relatives of schizophrenic subjects and 110 healthy controls. Partial correlation analysis was used to assess the relationship between schizotypal dimensions and smoking dependence. The prevalence of smoking and nicotine dependence levels were higher in the relatives than in the healthy control group. We found no relationship between nicotine dependence and the magnitude of schizotypal features in either group. Our results support the hypothesis that the relationship between schizophrenia and smoking is largely mediated by common familial factors, which may be genetic.

Are cardiovascular risk factors associated with verbal learning and memory impairment in patients with schizophrenia? A cross-sectional study

Objective. The aim of this study is to assess the relationships of cardiovascular risk factors with verbal learning and memory in patients with schizophrenia. Methods and Design. cross-sectional study. Inclusion Criteria. Diagnosis of schizophrenia according to the DSM-IV-TR criteria. Data Collection. Sociodemographic information, clinical characteristics, anthropometric measurements, blood tests, and episodic memory using the California Verbal Learning Test (CVLT). Analysis. A multivariate analysis using multiple linear regressions was performed to determine variables that are potentially associated with verbal learning and memory. Results. One hundred and sixty-eight outpatients participated in our study. An association was found between the metabolic syndrome (MetS) and memory impairment on measures of verbal learning, and short- and long-term memory. Among the different components of MeTS, hypertriglycerides, abdominal obesity, and low HDL cholesterol were the only factors associated with memory impairment. Alcohol dependence or abuse was associated with a higher rate of forgetting. Conclusion. Our findings suggest that MetS and alcohol use may be linked with memory impairment in schizophrenia. These findings provide important insights into the interdependencies of cardiovascular risk factors and cognitive disorders and support novel strategies for treating and preventing cognitive disorders in patients with schizophrenia.

Nicotine, Auditory Sensory Memory, and sustained Attention in a Human Ketamine Model of Schizophrenia: Moderating Influence of a Hallucinatory Trait

BACKGROUND

The procognitive actions of the nicotinic acetylcholine receptor (nAChR) agonist nicotine are believed, in part, to motivate the excessive cigarette smoking in schizophrenia, a disorder associated with deficits in multiple cognitive domains, including low-level auditory sensory processes and higher-order attention-dependent operations.

OBJECTIVES

As N-methyl-d-aspartate receptor (NMDAR) hypofunction has been shown to contribute to these cognitive impairments, the primary aims of this healthy volunteer study were to: (a) to shed light on the separate and interactive roles of nAChR and NMDAR systems in the modulation of auditory sensory memory (and sustained attention), as indexed by the auditory event-related brain potential - mismatch negativity (MMN), and (b) to examine how these effects are moderated by a predisposition to auditory hallucinations/delusions (HD).

METHODS

In a randomized, double-blind, placebo-controlled design involving a low intravenous dose of ketamine (0.04 mg/kg) and a 4 mg dose of nicotine gum, MMN, and performance on a rapid visual information processing (RVIP) task of sustained attention were examined in 24 healthy controls psychometrically stratified as being lower (L-HD, n = 12) or higher (H-HD) for HD propensity.

RESULTS

Ketamine significantly slowed MMN, and reduced MMN in H-HD, with amplitude attenuation being blocked by the co-administration of nicotine. Nicotine significantly enhanced response speed [reaction time (RT)] and accuracy (increased % hits and d' and reduced false alarms) on the RVIP, with improved performance accuracy being prevented when nicotine was administered with ketamine. Both % hits and d', as well as RT were poorer in H-HD (vs. L-HD) and while hit rate and d' was increased by nicotine in H-HD, RT was slowed by ketamine in L-HD.

CONCLUSIONS

Nicotine alleviated ketamine-induced sensory memory impairment and improved attention, particularly in individuals prone to HD.

Cigarette smoking and cognitive function in Chinese male schizophrenia: a case-control study

Schizophrenic patients have higher smoking rates than the general population. Studies show that smoking may be a form of self-medication in an attempt to alleviate cognitive deficits in schizophrenic patients of European background. This study examined the relationships between smoking and cognitive deficits in Chinese schizophrenic patients, which have previously received little systemic study. We recruited 580 male chronic patients meeting DSM-IV criteria for schizophrenia and 175 male control subjects who were matched on age and education. The subjects completed a detailed cigarette smoking questionnaire, the Fagerstrom Test for Nicotine Dependence (FTND), and the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). Patients also were rated on the Positive and Negative Symptom Scale (PANSS), the Simpson and Angus Extrapyramidal Symptom Rating Scale (SAES), and the Abnormal Involuntary Movement Scale (AIMS). All five RBANS subscales except for the Visuospatial/Constructional index showed significantly lower cognitive performance for schizophrenics than normal controls. The schizophrenic smokers scored lower than the schizophrenic non-smokers on the RBANS total score and the Visuospatial/Constructional and Immediate Memory indices. Similarly, the control smokers scored lower than the control non-smokers on the RBANS total score and the Immediate Memory index . Also, the schizophrenic smokers consistently performed the poorest on the cognitive domains of the RBANS. Among the schizophrenic patients, smokers displayed significantly fewer negative symptoms than non-smokers. Using multivariate regression analysis the following variables were independently associated with the RBANS total score: years of education, PANSS negative symptom score, age at schizophrenia onset, and number of hospitalizations. Our results show that smoking is associated with significant cognitive impairment in both schizophrenic patients and normal controls, but the smokers with schizophrenia had a reduced level of negative symptoms, suggesting that the benefits of smoking for those with schizophrenia may be limited to certain aspects of a given clinical phenotype.

The nicotinic acetylcholine receptor as a target for antidepressant drug development

An important new area of antidepressant drug development involves targeting the nicotinic acetylcholine receptor (nAChR). This receptor, which is distributed widely in regions of the brain associated with depression, is also implicated in other important processes that are relevant to depression, such as stress and inflammation. The two classes of drugs that target nAChRs can be broadly divided into mecamylamine- and cytisine-based compounds. These drugs probably exert their effects via antagonism at α4β2 nAChRs, and strong preclinical data support the antidepressant efficacy of both classes when used in conjunction with other primary antidepressants (e.g., monoamine reuptake inhibitors). Although clinical data remain limited, preliminary results in this area constitute a compelling argument for further evaluation of the nAChR as a target for future antidepressant drug development.

The Relationship between Attention/Vigilance and Symptom Severity in Schizophrenic Patients

OBJECTIVE

In schizophrenia, neurocognitive functions are one to two standard deviations below the normal controls and these deficits have a significant relationship with overall functioning and poor outcome. According to this fact, it is important to investigate the factors that effect neurocognition in schizophrenic patients. This study was carried out to demonstrate the relationship between attention/vigilance and some demographic and clinical variables in Iranian schizophrenic patients.

METHODS

This was a cross-sectional study; the participants were 60 Iranian schizophrenic patients. They were assessed using the Positive and Negative Syndrome Scale, and the Continuous Performance Test.

RESULTS

No significant relationship was found between gender, age, education, Positive and Negative Syndrome Scale scores and CPS scores.

CONCLUSIONS

Our findings suggest that contrary to some domains of cognitive functions, in schizophrenia, attention/vigilance is not influenced by severity of symptoms.

Separate and combined effects of low dose ketamine and nicotine on behavioural and neural correlates of sustained attention

Given the cognitive-promoting properties of the nicotinic acetylcholinergic receptor (nAChR) agonist, nicotine, the increased prevalence of smoke-inhaled nicotine in schizophrenia has been interpreted as an attempt to self-correct cognitive deficits, which have been particularly pronounced in the attentional domain. As glutamatergic abnormalities have been implicated in these attentional deficiencies, this study attempted to shed light on the separate and interactive roles of the N-methyl-d-aspartate receptor (NMDAR) and nAChR systems in the modulation of attention by investigating, in healthy volunteers, the separate and combined effects of nicotine and the NMDAR antagonist ketamine on neural and behavioural responses in a sustained attention task. In a randomized, double-blind, placebo controlled study, performance and the P300 event-related brain potential (ERP) in a visual information processing (RVIP) task were examined in 20 smokers and 20 non-smokers (both male and female). Assessment involved intravenous injection of a low subperceptual bolus dose (.04mg/kg) of ketamine or placebo, which was accompanied by acute treatment with nicotine (4mg) or placebo gum. Nicotine-enhanced attentional processing was most evident in nonsmokers, with both performance accuracy and P300 amplitude measures. Ketamine's detrimental effects on these behavioural and electrophysiologic measures were negatively moderated by acute nicotine, the synergistic effects being expressed differently in smokers and nonsmokers. These findings support the view that acute alterations and individual differences in nAChR function can moderate even subtle glutamatergic-driven cognitive deficiencies in schizophrenia and can be important therapeutic targets for treating cognitive impairments in schizophrenia.

Selective α4β2 nicotinic acetylcholine receptor agonists target epigenetic mechanisms in cortical GABAergic neurons

Nicotine improves cognitive performance and attention in both experimental animals and in human subjects, including patients affected by neuropsychiatric disorders. However, the specific molecular mechanisms underlying nicotine-induced behavioral changes remain unclear. We have recently shown in mice that repeated injections of nicotine, which achieve plasma concentrations comparable to those reported in high cigarette smokers, result in an epigenetically induced increase of glutamic acid decarboxylase 67 (GAD(67)) expression. Here we explored the impact of synthetic α(4)β(2) and α(7) nAChR agonists on GABAergic epigenetic parameters. Varenicline (VAR), a high-affinity partial agonist at α(4)β(2) and a lower affinity full agonist at α(7) neuronal nAChR, injected in doses of 1-5 mg/kg/s.c. twice daily for 5 days, elicited a 30-40% decrease of cortical DNA methyltransferase (DNMT)1 mRNA and an increased expression of GAD(67) mRNA and protein. This upregulation of GAD(67) was abolished by the nAChR antagonist mecamylamine. Furthermore, the level of MeCP(2) binding to GAD(67) promoters was significantly reduced following VAR administration. This effect was abolished when VAR was administered with mecamylamine. Similar effects on cortical DNMT1 and GAD(67) expression were obtained after administration of A-85380, an agonist that binds to α(4)β(2) but has negligible affinity for α(3)β(4) or α(7) subtypes containing nAChR. In contrast, PNU-282987, an agonist of the homomeric α(7) nAChR, failed to decrease cortical DNMT1 mRNA or to induce GAD(67) expression. The present study suggests that the α(4)β(2) nAChR agonists may be better suited to control the epigenetic alterations of GABAergic neurons in schizophrenia than the α(7) nAChR agonists.

Chemistry and pharmacological characterization of novel nitrogen analogues of AMOP-H-OH (Sazetidine-A, 6-[5-(azetidin-2-ylmethoxy)pyridin-3-yl]hex-5-yn-1-ol) as α4β2-nicotinic acetylcholine receptor-selective partial agonists

In order to advance therapeutic applications of nicotinic ligands, continuing research efforts are being directed toward the identification and characterization of novel nicotinic acetylcholine receptor (nAChR) ligands that are both potent and subtype selective. Herein we report the synthesis and pharmacological evaluation of members of a new series of 3-alkoxy-5-aminopyridine derivatives that display good selectivity for the α4β2-nAChR subtype based on ligand binding and functional evaluations. The most potent ligand in this series, compound 64, showed high radioligand binding affinity and selectivity for rat α4β2-nAChR with a K(i) value of 1.2 nM and 4700-fold selectivity for α4β2- over α3β4-nAChR, and ∼100-fold selectivity for functional, high-sensitivity, human α4β2-nAChR over α3β4*-nAChR. In the mouse forced swim test, compound 64 exhibited antidepressant-like effects. Structure-activity relationship (SAR) analyses suggest that the introduction of additional substituents to the amino group present on the pyridine ring of the N-demethylated analogue of compound 17 can provide potent α4β2-nAChR-selective ligands for possible use in treatment of neurological and psychiatric disorders including depression.

Detection of SNP-SNP interactions in trios of parents with schizophrenic children

Schizophrenia (SZ) is a heritable and complex psychiatric disorder with an estimated worldwide prevalence of about 1%. Research on the risk factors for SZ has thus far yielded few clues to causes, but has pointed to a heterogeneous etiology that likely involves multiple genes and gene-environment interactions. In this manuscript, we apply a novel method (trio logic regression, Li et al., 2009) to case-parent trio data from a SZ candidate gene study conducted on families of Ashkenazi Jewish descent, and demonstrate the method's ability to detect multi-gene models for SZ risk in the family-based design. In particular, we demonstrate how this method revealed a genotype-phenotype association that includes an allele without marginal effect.

Acute nicotine alteration of sensory memory impairment in smokers with schizophrenia

CONTEXT

Patients with schizophrenia have a high rate of cigarette smoking and also exhibit profound deficits in sensory processing, which may in part be ameliorated by the acute actions of smoke-inhaled nicotine. The mismatch negativity (MMN), a preattentive event-related potential index of auditory sensory memory, is diminished in schizophrenia. The MMN is increased in healthy controls with acute nicotine.

OBJECTIVE

To utilize the MMN to compare auditory sensory memory in minimally tobacco-deprived (3 hours) patients and matched tobacco-deprived smoking controls and to assess the effects of acute nicotine on MMN-indexed sensory memory processing in the patients.

DESIGN

Event-related potentials were recorded in 2 auditory oddball paradigms, one involving tone frequency changes (frequency MMN) and one involving tone duration changes (duration MMN). Controls were assessed once under nontreatment conditions, and patients were assessed twice under randomized double-blind treatment conditions involving placebo and nicotine (8 mg) gum.

SETTING

Outpatient mental health center.

PATIENTS

Twelve smokers with schizophrenia and twelve control smokers.

RESULTS

Compared with the controls, the patients showed reduced frequency-MMN (P < 0.001) and duration-MMN (P < 0.04) amplitudes. In addition to prolonging peak latency in duration MMN (P < 0.01), nicotine, relative to placebo, increased the amplitude of the patients' duration MMN (P < 0.01), but not their frequency MMN, to a level comparable with that seen in the controls.

CONCLUSIONS

These preliminary findings demonstrate for the first time that acute nicotine can normalize temporal aspects of sensory memory processing in patients with schizophrenia, an effect that may be mediated by activation of α7 nicotinic acetylcholine receptors, the function of which is diminished in schizophrenia. These ameliorating actions of nicotine may have implications for understanding the close relationship between tobacco smoking and schizophrenia and for developing nicotinic pharmacotherapies to alleviate sensory memory impairments in schizophrenia.

Nicotinic acetylcholine receptors and depression: a review of the preclinical and clinical literature

Many patients with depression fail to derive sufficient benefit from available treatment options, with up to a third never reaching remission despite multiple trials of appropriate treatment. Novel antidepressant agents are needed, and drugs targeting nicotinic acetylcholine receptors (nAChRs) appear to hold promise in this regard. nAChRs are involved in a variety of neurobiological systems implicated in the pathophysiology of depression. In addition to their role in cholinergic neurotransmission, they modulate dopamine function and influence inflammation and hypothalamic-pituitary-adrenal axis activity. Preclinical studies have suggested antidepressant-like effects of drugs targeting nAChRs, with the most consistent results observed with alpha4beta2 nAChR modulators such as varenicline and nonspecific nAChR antagonists such as mecamylamine. These agents appear to offer the most potential antidepressant-like efficacy when used in conjunction with other established antidepressant treatments. nAChR modulators also influence neural processes that appear to mediate the behavioral effects of antidepressants, such as hippocampal cell proliferation. Clinical evidence, while limited, shows preliminary efficacy for mecamylamine and varenicline. Taken together, the preclinical and clinical evidence suggests that drugs targeting nAChRs may represent an important new approach to the treatment of depression.

Cognitive effects of nicotine: genetic moderators

Cigarette smoking is the main preventable cause of death in developed countries, and the development of more effective treatments is necessary. Cumulating evidence suggests that cognitive enhancement may contribute to the addictive actions of nicotine. Several studies have demonstrated that nicotine enhances cognitive performance in both smokers and non-smokers. Genetic studies support the role of both dopamine (DA) and nicotinic acetylcholine receptors (nAChRs) associated with nicotine-induced cognitive enhancement. Based on knockout mice studies, beta2 nAChRs are thought to be essential in mediating the cognitive effects of nicotine. alpha7nAChRs are associated with attentional and sensory filtering response, especially in schizophrenic individuals. Genetic variation in D2 type DA receptors and the catechol-O-methyltransferase enzyme appears to moderate cognitive deficits induced by smoking abstinence. Serotonin transporter (5-HTT) gene variation also moderates nicotine-induced improvement in spatial working memory. Less is known about the contribution of genetic variation in DA transporter and D4 type DA receptor genetic variation on the cognitive effects of nicotine. Future research will provide a clearer understanding of the mechanism underlying the cognitive-enhancing actions of nicotine.

Signaling pathways in schizophrenia: emerging targets and therapeutic strategies

Dopamine D(2) receptor antagonism is a unifying property of all antipsychotic drugs in use for schizophrenia. While often effective at ameliorating psychosis, these drugs are largely ineffective at treating negative and cognitive symptoms. Increasing attention is being focused on the complex genetics of the illness and the signaling pathways implicated in its pathophysiology. We review targeted approaches for pharmacotherapy involving the glutamatergic, GABAergic and cholinergic pathways. We also describe several of the major genetic findings that identify signaling pathways representing potential targets for novel pharmacological intervention. These include genes in the 22q11 locus, DISC1, Neuregulin 1/ErbB4, and components of the Akt/GSK-3 pathway.

Neuronal nicotinic acetylcholine receptors as pharmacotherapeutic targets for the treatment of alcohol use disorders

Alcohol use disorders (AUDs) are complex, and developing effective treatments will require the combination of novel medications and cognitive behavioral therapy approaches. Epidemiological studies have shown there is a high correlation between alcohol consumption and tobacco use, and the prevalence of smoking in alcoholics is as high as 80% compared to about 30% for the general population. Both preclinical and clinical data provide evidence that nicotine administration increases alcohol intake and non-specific nicotinic receptor antagonists reduce alcohol-mediated behaviors. As nicotine interacts specifically with the neuronal nicotinic acetylcholine receptor (nAChR) system, this suggests that nAChRs play an important role in the behavioral effects of alcohol. In this review, we discuss the importance of nAChRs for the treatment of AUDs and argue that the use of FDA approved nAChR ligands, such as varenicline and mecamylamine, approved as smoking cessation aids may prove to be valuable treatments for AUDs. We also address the importance of combining effective medications with behavioral therapy for the treatment of alcohol dependent individuals.

The relationship of DSM-IV personality disorders to nicotine dependence-results from a national survey

This study examined the prevalence of nicotine dependence (ND) and its associations with DSM-IV personality disorders (PDs) among current smokers (n=7078), controlling for sociodemographic characteristics and comorbid Axis I and II disorders. Data were derived from a nationally representative sample of the U.S. population. Although all PDs were significantly associated with ND when sociodemographic factors were controlled, only schizotypal, borderline, narcissistic and obsessive-compulsive PDs were associated with ND after adding controls for Axis I and other Axis II disorders. These associations remained significant after controlling for degree of smoking exposure. The results suggest that both shared and PD-specific pathogenetic factors underlie these PD-ND associations. Implications are also discussed in terms of the relationship between personality features of schizotypal, borderline, narcissistic and obsessive-compulsive PDs and the self-medication hypothesis and the role of neurotransmission.

Why do young women smoke? VI. A controlled study of nicotine effects on attention: pharmacogenetic interactions

In prior studies we found that young, female smokers manifest poorer performance than non-smokers on attention-related tasks and that these findings can be moderated by variation in nicotinic acetylcholine receptor (nAChR) genes. We predicted that under controlled conditions (1) nicotine would improve functioning on attentional tasks in smokers who previously manifested relatively poor performance, and that (2) smokers who carry genetic variations associated with poorer attention performance would derive greater benefit from nicotine. To test these hypotheses, 31 young female smokers, who participated in our previous study, performed the Matching Familiar Figures Test (MFFT), Tower of London Test and Continuous Performance Task (CPT) in a double-blind, within-between subject design, placebo or nicotine (4 mg as gum) serving as the within factor and genetic profile as the between factor. Repeated measures ANCOVA controlling for attention deficit symptomatology, substance abuse and nicotine dependence showed better performance under nicotine among participants with higher levels of attention deficit symptoms (MFFT errors: P=0.04; CPT commissions: P=0.01) and nicotine dependence (CPT stability of response: P=0.04) and greater consumption of caffeine (CPT stability of response: P=0.04). An interactive effect of genetic profile was demonstrated for SNP rs2337980 in CHRNA7. These findings suggest that nicotine may have stronger short-term facilitating effects on attention in women who have more attention deficit symptoms and consume more nicotine and caffeine. This effect may be modified by a specific genetic make-up. Such individuals may be at increased risk for nicotine addiction and for greater difficulties in smoking cessation.

Why do patients with schizophrenia smoke?

PURPOSE OF REVIEW

Among the mentally ill, smoking prevalence is highest in patients with schizophrenia ( approximately 70-80%). This can impose a significant financial burden on patients, not to speak of increased smoking-related morbidity and mortality. Therefore, it is critical for clinicians to understand why patients with schizophrenia smoke in order to adapt treatment schemes. Understanding the reasons may also help to develop new drugs that target the nicotinic system in the brain as well as smoking cessation programs that are specifically designed for this particular patient population.

RECENT FINDINGS

So far, several reasons have been identified which are believed to explain tobacco consumption in patients with schizophrenia. Originally, it was widely believed that patients with schizophrenia smoke to increase hepatic clearance and to restore the dopamine blockade of certain antipsychotic drugs to diminish their side effects. However, more recently it became obvious that cigarette smoking may also be reinforcing for patients because it improves psychiatric symptoms, most notably negative and cognitive symptoms. The underlying molecular mechanisms of these nicotine effects are currently under intensive investigation.

SUMMARY

Heavy smoking in schizophrenia cannot simply be viewed as a 'bad habit'. Rather, self-medication of clinical symptoms and side effects of antipsychotic drugs appear to play a major role.

Investigation of clinical factors influencing cognitive function in Japanese schizophrenia

Several investigators have reported cognitive dysfunction in chronic schizophrenia that was associated with insight and social skills. Such cognitive dysfunction seriously hinders an immediate return to normal life. Recently, Kaneda et al. reported that the Brief Assessment of Cognition in Schizophrenia, Japanese-language version (BACS-J) was superior in the evaluation of the cognitive function. We investigated which clinical factors (age, sex, duration of illness, level of education, smoking status, the Positive and Negative Syndrome Scale (PANSS) score and medication dosage) affected cognitive dysfunction in 115 Japanese schizophrenic patients, with the use of multiple regression analysis. We detected an association between composite score, verbal memory, working memory and executive function and PANSS total score. Moreover, most cognitive tasks were associated with a negative PANSS score but not a positive PANSS score or general score. We also showed an association between age and verbal fluency and attention in schizophrenia. In addition, anxiolytics/hypnotics (diazepam-equivalent) were associated with composite score, working memory and motor speed. In conclusion, cognitive function was associated with PANSS score, especially negative PANSS score. Because anxiolytics/hypnotics might have a detrimental influence on cognitive function, we strongly suggest that the use of anxiolytics/hypnotics be reduced in schizophrenics as much as possible.

Muscarinic antagonist effects on executive control of attention

Acetylcholine plays a major role in mediating attention processes. We investigated the muscarinic antagonist effect of scopolamine on functional neuro-anatomy of attention and cognition. We assessed 12 healthy volunteers while performing the Attention Network Task on 0.4 mg scopolamine and placebo in a single-blind randomized trial in a 1.5 T magnetic resonance scanner. Neurocognitive measures included verbal learning, verbal memory, verbal fluency, trail making, digit span, a continuous performance task and a planning task (Tower of London). When compared to placebo, scopolamine increased reaction times for conflicting stimulus processing, together with decreasing brain activation in the anterior cingulate cortex (a brain region involved in conflict processing) suggestive of a muscarinic antagonist effect on executive control of attention. Contrary to the notion of a predominantly right-hemispheric lateralization of cognitive processes associated with orienting attention, scopolamine reduced brain activity in left superior and left middle frontal brain areas. Our neuropsychological test data revealed a selective effect of scopolamine on verbal learning and memory while other cognitive domains, such as planning and working memory, were unaffected. These findings are consistent with muscarinic modulation of dopaminergic neurotransmission in frontal attention networks when processing conflicting information.

Nicotinic antagonist effects on functional attention networks

Cholinergic neurotransmission has been implicated in memory and attention. We investigated the effect of the non-competitive nicotinic antagonist mecamylamine on three components of attention processes (i.e. alerting, orienting and executive control) in 12 healthy male subjects whilst performing the Attention Network Task (ANT) in a magnetic resonance imaging (MRI) scanner. Participants received 15 mg mecamylamine in a single blind and placebo- controlled randomized procedure 90 min prior to obtaining functional MRI data. Our results confirm previous reports of beneficial effects of cueing (alerting and orienting) and detrimental effects of conflict (executive control) on reaction times when performing the ANT. The functional MRI data confirmed distinct neural networks associated with each of the three attention components. Alerting was associated with increased left temporal lobe activation while orienting increased bilateral prefrontal, right precuneus and left caudate activation. Executive control activated anterior cingulate and precuneus. Mecamylamine slowed overall response time and down-regulated brain activation associated with orienting and to some extent brain activation associated with executive control when compared to placebo. These findings are consistent with nicotinic modulation of orienting attention by cueing and executive control when responding to conflicting information. The latter nicotine antagonist effect may be mediated via cholinergic modulation of dopamine neurotransmission in mesolimbic pathways.

Differential contribution of genetic variation in multiple brain nicotinic cholinergic receptors to nicotine dependence: recent progress and emerging open questions

Nicotine dependence (ND), a major public health challenge, is a complex, multifactorial behavior, in which both genetic and environmental factors have a role. Brain nicotinic acetylcholine receptor (nAChR)-encoding genes are among the most prominent candidate genes studied in the context of ND, because of their biological relevance as binding sites for nicotine. Until recently, most research on the role of nAChRs in ND has focused on two of these genes (encoding the alpha4- and beta2-subunits) and not much attention has been paid to the possible contribution of the other nine brain nAChR subunit genes (alpha2-alpha3, alpha5-alpha7, alpha9-alpha10, beta3-beta4) to the pathophysiology and genetics of ND. This situation has changed dramatically in the last 2 years during which intensive research had addressed the issue, mainly from the genetics perspective, and has shown the importance of the CHRNA5-CHRNA3-CHRNB4 and CHRNA6-CHRNB3 loci in ND-related phenotypes. In this review, we highlight recent findings regarding the contribution of non-alpha4/beta2-subunit containing nAChRs to ND, based on several lines of evidence: (1) human genetics studies (including linkage analysis, candidate-gene association studies and whole-genome association studies) of several ND-related phenotypes; (2) differential pharmacological and biochemical properties of receptors containing these subunits; (3) evidence from genetically manipulated mice; and (4) the contribution of nAChR genes to ND-related personality traits and neurocognitive profiles. Combining neurobiological genetic and behavioral perspectives, we suggest that genetic susceptibility to ND is not linked to one or two specific nAChR subtype genes but to several. In particular, the alpha3, alpha5-6 and beta3-4 nAChR subunit-encoding genes may play a much more pivotal role in the neurobiology and genetics of ND than was appreciated earlier. At the functional level, variants in these subunit genes (most likely regulatory) may have independent as well as interactive contributions to the ND phenotype spectrum. We address methodological challenges in the field, highlight open questions and suggest possible pathways for future research.

Smoking, nicotine and neuropsychiatric disorders

Tobacco smoking is an extremely addictive and harmful form of nicotine (NIC) consumption, but unfortunately also the most prevalent. Although disproportionately high frequencies of smoking and its health consequences among psychiatric patients are widely known, the neurobiological background of this epidemiological association is still obscure. The diverse neuroactive effects of NIC and some other major tobacco smoke constituents in the central nervous system may underlie this association. This present paper summarizes the pharmacology of NIC and its receptors (nAChR) based on a systematic review of the literature. The role of the brain's reward system(s) in NIC addiction and the results of functional and structural neuroimaging studies on smoking-related states and behaviors (i.e. dependence, craving, withdrawal) are also discussed. In addition, the epidemiological, neurobiological, and genetic aspects of smoking in several specific neuropsychiatric disorders are reviewed and the clinical relevance of smoking in these disease states addressed.

Prenatal nicotine exposure alters medullary nicotinic and AMPA-mediated control of respiratory frequency in vitro

Prenatal nicotine exposure (PNE) is correlated with breathing abnormalities in humans and other animals. Despite evidence that this relationship results from alterations in nicotinic acetylcholine receptors (nAChRs), the mechanisms are poorly understood. Here, we hypothesize that PNE blunts nAChR-mediated respiratory-related motor output. We also hypothesize that the PNE-induced changes in nAChRs leads to secondary alterations in glutamatergic neurotransmission. To test these hypotheses, we used an in vitro brainstem-spinal cord preparation and recorded C4 ventral root (C4 VR) nerve bursts from 0 to 4-day-old rats that were exposed to either nicotine (6mgkg(-1)day(-1)) or saline (control) in utero. Nicotine bitartrate, nAChR antagonists, NMDA and AMPA were applied to the brainstem compartment of a "split-bath" configuration, which physically separated the medulla from the spinal cord. Nicotine (0.2 or 0.5microM) increased peak C4 VR burst frequency by over 230% in control pups, but only 140% in PNE animals. The application of nAChR antagonists showed that these effects were mediated by the alpha4beta2 nAChR subtype with no effect on alpha7 nAChRs in either group. We also show that AMPA-mediated excitatory neurotransmission is enhanced by PNE, but NMDA-mediated neurotransmission is unaltered. These data and the work of others suggest that the PNE may functionally desensitize alpha4beta2 nAChRs located on the presynaptic terminals of glutamatergic neurons leading to less neurotransmitter release, which in turn up-regulates AMPA receptors on rhythm generating neurons.

Approaches to measuring the effects of wake-promoting drugs: a focus on cognitive function

OBJECTIVES

In clinical drug development, wakefulness and wake-promotion may be assessed by a large number of scales and questionnaires. Objective assessment of wakefulness is most commonly made using sleep latency/maintenance of wakefulness tests, polysomnography and/or behavioral measures. The purpose of the present review is to highlight the degree of overlap in the assessment of wakefulness and cognition, with consideration of assessment techniques and the underlying neurobiology of both concepts.

DESIGN

Reviews of four key areas were conducted: commonly used techniques in the assessment of wakefulness; neurobiology of sleep/wake and cognition; targets of wake promoting and/or cognition enhancing drugs; and ongoing clinical trials investigating wake promoting effects.

RESULTS

There is clear overlap between the assessment of wakefulness and cognition. There are common techniques which may be used to assess both concepts; aspects of the neurobiology of both concepts may be closely related; and wake-promoting drugs may have nootropic properties (and vice versa). Clinical trials of wake-promoting drugs often, though not routinely, assess aspects of cognition.

CONCLUSIONS

Routine and broad assessment of cognition in the development of wake-promoting drugs may reveal important nootropic effects, which are not secondary to alertness/wakefulness, whilst existing cognitive enhancers may have underexplored or unknown wake promoting properties.