Nicotinic receptor mechanisms and cognition in normal states and neuropsychiatric disorders

Vagally Mediated Heart Rate Variability Is Associated With Executive Function Changes in Patients With Treatment-Resistant Depression Following Magnetic Seizure Therapy

OBJECTIVES

Magnetic seizure therapy (MST) is a novel investigational brain stimulation modality for patients with treatment-resistant depression (TRD). MST is a potential alternative seizure-based treatment to electroconvulsive therapy (ECT), given that it may offer equivalent antidepressant efficacy, yet with a relative sparing of cognitive functioning. Heart rate variability (HRV) is a marker of central autonomic functioning. We aimed to explore the relationships among baseline HRV, age, clinical outcome, and executive function following MST, in patients with TRD.

MATERIALS AND METHODS

Eighty-eight TRD patients (55 females; 18-70 years) were enrolled and 48 patients completed a course of MST in an open-label study. Patients received MST treatments two to three times per week, using one of three stimulation frequencies (ie, 100 Hz, 50 Hz, or 25 Hz) at 100% stimulator output. Root mean square of the successive R-R differences (RMSSD), an index of HRV, was computed from a baseline electrocardiogram (ECG) recording. Clinical symptoms were assessed using the Hamilton Depression Rating Scale (HAM-D24) and the Quick Inventory of Depressive Symptomatology (QIDS16). Executive function was assessed using the Trail Making Test and the Mazes Test from the MATRICS battery.

RESULTS

Baseline RMSSD was correlated with baseline HAM-D24 (r = -0.340, p = 0.001) and baseline Mazes Test (r = 0.417, p = 0.0007) but not with baseline Trail Making Test. Furthermore, baseline RMSSD was not correlated with changes on the HAM-D24, QIDS16, or total scores on the Trail Making Test. However, there was a significant correlation between baseline RMSSD and improvement on the Mazes Test following MST (r = 0.502, p = 0.0004).

CONCLUSIONS

Since this is an open-label trial, the influence of the placebo effect cannot be excluded. However, our results suggest that baseline RMSSD may be a state-biomarker of depression and executive function impairment. Additionally, while baseline vagally mediated resting cardiac activity did not predict the outcome of depression, it may mediate executive function improvements following MST.

Active Cigarette Smoking Is Associated With Increased Age-Related Decline on Measures of Visuospatial Learning and Memory and Executive Function in Alcohol Use Disorder

AIMS

The goal of this study was to determine if active cigarette smoking in Veterans with alcohol use disorder (AUD) was associated with greater age-related neurocognitive decline.

METHODS

Veterans with AUD, in residential treatment (n = 125; 47 ± 14 years of age, min = 24, max = 76, 29 ± 26 days of abstinence), completed measures of executive functions, learning and memory, processing speed and working memory. Actively smoking AUD (AsAUD, n = 47) were active daily cigarette smokers; former smoking AUD (FsAUD, n = 45) were predominately daily smokers prior to study but did not smoke at the time of study; non-smoking AUD (NsAUD, n = 33) never used cigarettes or smoked 'only a few times' during lifetime.

RESULTS

AsAUD demonstrated greater age-related decline on measures of visuospatial learning and memory, and response inhibition/cognitive flexibility, primarily relative to NsAUD; there were no age-related differences between FsAUD and NsAUD on any measure. There were few significant mean differences between groups across the 15 neurocognitive measures. In AsAUD, higher scores on indices of smoking severity were associated with poorer performance on measures of auditory-verbal learning and memory, response inhibition, set-shifting and working memory. In FsAUD, longer smoking cessation duration was related to lower PTSD, anxiety and depressive symptomatology.

CONCLUSIONS

Active smoking was associated with accelerated age-related decline on cognitive functions implicated in response to common evidence-based AUD interventions. Results suggest that smoking history contributes to the considerable heterogeneity observed in neurocognitive function in early AUD recovery, and reinforce the clinical movement to offer smoking cessation resources concurrent with treatment for AUD.

Mediational pathways of tobacco use among adult daily smokers with psychiatric symptoms in the Population Assessment of Tobacco and Health (PATH) survey

INTRODUCTION

Individuals with psychiatric conditions suffer disproportionately from tobacco-related morbidity and mortality, but the factors driving this relationship remain unclear. We used data from the Population Assessment of Tobacco and Health (PATH) to investigate whether associations between internalizing psychiatric symptoms and change in smoking heaviness (as measured by cigarettes per day (CPD) were mediated by self-reported respiratory symptoms, smoking risk perceptions, and cigarette dependence.

METHODS

This study used data from PATH Waves 1 through 4 (2013-2017, n = 4,152). Psychiatric symptoms were indexed with the internalizing sub-scale of the Global Appraisal of Individual Needs-Short Screener (GAIN-SS) among daily smokers. We fit auto-regressive structural equation models (SEM) to data from Wave 1-3 and 2-4 to determine the direct and indirect associations between internalizing symptom scores and CPD through each mediator.

RESULTS

The association between internalizing symptoms and CPD was mediated by cigarette dependence (indirect: B = 0.004, SE = 0.041, p = 0.023) and respiratory symptom severity (indirect: B = 0.018, SE = 0.097, p < 0.001). Internalizing symptoms predicted higher harm perceptions (B = 0.056, SE = 0.035, p < 0.001) but the indirect relationship with CPD was non-significant. Findings from Waves 2-4 replicated these results.

CONCLUSION

Our results indicate that cigarette dependence and respiratory symptom severity partially mediate the relationship between internalizing symptoms and CPD but risk perceptions were not significant predictors in our models. This suggests that efforts to reduce smoking among people with internalizing disorders should focus on decreasing nicotine dependence and increasing awareness of respiratory symptoms to encourage a quit attempt or switch to a less harmful source of nicotine.

Sex differences in P50 inhibition defects with psychopathology and cognition in patients with first-episode schizophrenia

BACKGROUND

A large number of studies have shown that the pathophysiology of schizophrenia may be involved in sensory gating that appears to be P50 inhibition. However, few studies have investigated the relationship between clinical symptoms, cognitive impairment and sensory gating disorders in patients with first-episode schizophrenia. The purpose of this study was to explore the sex differences in the relationship between clinical symptoms, cognitive impairment and P50 inhibition defects in patients with first-episode schizophrenia, which has not been reported.

METHODS

130 patients with first-episode schizophrenia (53 males and 77 females) and 189 healthy controls (87 males and 102 females) participated in the study. Positive and Negative Syndrome Scale (PANSS) was used to evaluate the patients' psychopathological symptoms, and the 64-channel electroencephalogram (EEG) system was used to record the P50 inhibition.

RESULTS

Male patients had higher PANSS negative symptom, general psychopathology, cognitive factor and total scores than female patients (all p < 0.01). The S1 amplitude was smaller in male than female patients (all p < 0.05). Multiple regression analysis showed that in male patients, S1 latency was contributor to negative symptoms, while S1 latency, S2 latency, age, and smoking status were contributors to cognitive factor (all p < 0.05). In female patients, no P50 component was found to be an independent contributor to PANSS scores (all p > 0.05).

CONCLUSIONS

Our results indicate that there is a sex difference in the relationship between clinical symptoms, cognitive impairment and P50 inhibition defects in Chinese Han patients with first-episode schizophrenia.

Smoking Affects the Patterns of Metabolic Disorders and Metabolic Syndrome in Patients With First-Episode Drug-Naive Schizophrenia: A Large Sample Study Based on the Chinese Han Population

OBJECTIVE

Although metabolic disorders and smoking are common in schizophrenia, few studies have investigated the effects of smoking on metabolic disorders or metabolic syndrome (MetS) in schizophrenia patients, especially in first-episode drug-naïve (FEDN) patients. We sought to investigate the differences in metabolic disorders and MetS between smoking and nonsmoking FEDN schizophrenia patients.

METHODS

A total of 428 FEDN schizophrenia patients and 435 controls were recruited. Blood pressure, waist circumference, body mass index (BMI), lipid profiles, and glucose metabolism were measured. The psychopathology was evaluated by Positive and Negative Syndrome Scale.

RESULTS

FEDN schizophrenia patients had a higher smoking rate than controls (23.8% vs 14.0%, P < .001). After adjusting for confounding variables, the prevalence of MetS, overweight, hypertension, hypertriglyceridemia, elevated insulin, and insulin resistance in smoking patients was higher than those in nonsmoking patients, while overweight and hypertension were higher in the smoking controls than in nonsmoking controls (all P < .05). In smoking patients, triglyceridemia, high-density lipoprotein cholesterol, and fasting blood glucose were the main contributing components to MetS, while in nonsmoking patients, waist circumference, systolic blood pressure, triglyceridemia, high-density lipoprotein cholesterol, and fasting blood glucose were the main contributing components to MetS. In smoking patients, BMI and homeostatic model assessment for insulin resistance were associated factors of MetS (both P < .05). In nonsmoking patients, sex, BMI, insulin, and homeostatic model assessment for insulin resistance were associated factors of MetS (all P < .05).

CONCLUSIONS

Our study indicates that smoking schizophrenia patients have a higher prevalence of MetS and metabolic disorders than nonsmoking patients. Moreover, smoking and nonsmoking patients have different contributing components and associated factors for MetS.

Effects of nicotinic antagonists on working memory performance in young rhesus monkeys

Acetylcholine plays a pivotal neuromodulatory role in the brain, influencing neuronal activity and cognitive function. Nicotinic receptors, particularly α7 and α4β2 receptors, modulate firing of dorsolateral prefrontal (dlPFC) excitatory networks that underlie successful working memory function. Minimal work however has been done examining working memory following systemic blockade of nicotinic receptor systems in nonhuman primates, limiting the ability to explore interactions of other neuromodulatory influences with working memory impairment caused by nicotinic antagonism. In this study, we investigated working memory performance after administering three nicotinic antagonists, mecamylamine, methyllycaconitine, and dihydro-β-erythroidine, in rhesus macaques tested in a spatial delayed response task. Surprisingly, we found that no nicotinic antagonist significantly impaired delayed response performance compared to vehicle. In contrast, the muscarinic antagonist scopolamine reliably impaired delayed response performance in all monkeys tested. These findings suggest there are some limitations on using systemic nicotinic antagonists to probe the involvement of nicotinic receptors in aspects of dlPFC-dependent working memory function, necessitating alternative strategies to understand the role of this system in cognitive deficits seen in aging and neurodegenerative disease.

Mechanisms of Nicotine Addiction

Tobacco smoking results in more than five million deaths each year and accounts for ∼90% of all deaths from lung cancer.³ Nicotine, the major reinforcing component of tobacco smoke, acts in the brain through the neuronal nicotinic acetylcholine receptors (nAChRs). The nAChRs are allosterically regulated, ligand-gated ion channels consisting of five membrane-spanning subunits. Twelve mammalian α subunits (α2-α10) and three β subunits (β2-β4) have been cloned. The predominant nAChR subtypes in mammalian brain are those containing α4 and β2 subunits (denoted as α4β2* nAChRs). The α4β2* nAChRs mediate many behaviors related to nicotine addiction and are the primary targets for currently approved smoking cessation agents. Considering the large number of nAChR subunits in the brain, it is likely that nAChRs containing subunits in addition to α4 and β2 also play a role in tobacco smoking. Indeed, genetic variation in the CHRNA5-CHRNA3-CHRNB4 gene cluster, encoding the α5, α3, and β4 nAChR subunits, respectively, has been shown to increase vulnerability to tobacco dependence and smoking-associated diseases including lung cancer. Moreover, mice, in which expression of α5 or β4 subunits has been genetically modified, have profoundly altered patterns of nicotine consumption. In addition to the reinforcing properties of nicotine, the effects of nicotine on appetite, attention, and mood are also thought to contribute to establishment and maintenance of the tobacco smoking habit. Here, we review recent insights into the behavioral actions of nicotine, and the nAChR subtypes involved, which likely contribute to the development of tobacco dependence in smokers.

Role of the purinergic P2Y2 receptor in hippocampal function in mice

OBJECTIVE

The aim of this study is to investigate the role of the purinergic P2Y2 receptor in learning and memory processes.

MATERIALS AND METHODS

Behavioral, electrophysiological, and biochemical tests of memory function were conducted in P2Y2 receptor knockout (P2Y2R-KO) mice, and the findings were compared to those of wild-type mice with the help of unpaired Student's t-test.

RESULTS

The findings of the behavioral Y-maze test showed that the P2Y2R-KO mice had impaired memory and cognitive function. Electrophysiological studies on paired-pulse facilitation showed that glutamate release was higher in the P2Y2R-KO mice than in the WT mice. Furthermore, PCR and Western blot analysis revealed that the mRNA and protein expression of acetylcholinesterase E (AChE) and alpha-7 nicotinic acetylcholine receptors (α7 nAChRs) were increased in the hippocampus of P2Y2R-KO mice.

CONCLUSIONS

The findings of this study indicate that P2Y2 receptors are important regulators of both glutamatergic and cholinergic systems in the hippocampus.

Role of conduct problems in the relation between Attention-Deficit Hyperactivity disorder, substance use, and gaming

Known comorbidities for Attention-Deficit Hyperactivity Disorder (ADHD) include conduct problems, substance use disorder and gaming. Comorbidity with conduct problems may increase the risk for substance use disorder and gaming in individuals with ADHD. The aim of the study was to build a causal model of the relationships between ADHD and comorbid conduct problems, and alcohol, nicotine, and other substance use, and gaming habits, while accounting for age and sex. We used a state-of-the-art causal discovery algorithm to analyze a case-only sample of 362 ADHD-diagnosed individuals in the ages 12-24 years. We found that conduct problem severity mediates between ADHD severity and nicotine use, but not with more severe alcohol or substance use. More severe ADHD-inattentive symptoms lead to more severe gaming habits. Furthermore, our model suggests that ADHD severity has no influence on severity of alcohol or other drug use. Our findings suggest that ADHD severity is a risk factor for nicotine use, and that this effect is fully mediated by conduct problem severity. Finally, ADHD-inattentive severity was a risk factor for gaming, suggesting that gaming dependence has a different causal pathway than substance dependence and should be treated differently. By identifying these intervention points, our model can aid both researchers and clinicians.

NAChR α4β2 Subtype and their Relation with Nicotine Addiction, Cognition, Depression and Hyperactivity Disorder

BACKGROUND

Neuronal α4β2 nAChRs are receptors involved in the role of neurotransmitters regulation and release, and this ionic channel participates in biological process of memory, learning and attention. This work aims to review the structure and functioning of the α4β2 nAChR emphasizing its role in the treatment of associated diseases like nicotine addiction and underlying pathologies such as cognition, depression and attention-deficit hyperactivity disorder.

METHODS

The authors realized extensive bibliographic research using the descriptors "Nicotine Receptor α4β2" and "cognition", "depression", "attention-deficit hyperactivity disorder", besides cross-references of the selected articles and after analysis of references in the specific literature.

RESULTS

As results, it was that found 179 relevant articles presenting the main molecules with affinity to nAChR α4β2 related to the cited diseases. The α4β2 nAChR subtype is a remarkable therapeutic target since this is the most abundant receptor in the central nervous system.

CONCLUSION

In summary, this review presents perspectives on the pharmacology and therapeutic targeting of α4β2 nAChRs for the treatment of cognition and diseases like nicotine dependence, depression and attention-deficit hyperactivity disorder.

A fractionated analysis of hot and cool self-regulation in cigarette smokers from different socioeconomic backgrounds

Smoking cigarettes and low socioeconomic status (SES) are both related to impaired cognition. However, it is unknown whether people of lower SES, who comprise most tobacco smokers worldwide, are more susceptible to cognitive impairment associated with smoking. In this non-randomized, cross-sectional study we investigated the effects of cigarette smoking, SES and their interaction on dissociable executive or “cool” and “hot” measures of behavioural self-regulation. Participants (n = 80) were selected among young physically and mentally healthy smokers and non-smokers who had graduated high school and were from different SES backgrounds. Cool self-regulation was measured by executive function tasks that tap inhibition, updating, shifting, dual tasking, planning, access to long-term memory (semantic fluency), and working memory capacity. Hot measures assessed self-reported impulsivity, delay discounting and risk taking. Exposure to tobacco (cotinine, exhaled carbon monoxide, tobacco dependence, cigarette consumption) was assessed to determine to what extent it mediated the cognitive effects of smoking. Nicotine abstinence and its acute effects were controlled, as were sex, age, schooling, and psychiatric symptoms despite the fact that smokers and non-smokers were selected as being as similar as possible in these demographic characteristics. Lower SES (less years of parental schooling) was associated with worse performance on tasks that measured all cool domains except dual tasking and fluency, while smoking status was related to impaired delayed discounting and impulsivity (hot domains), effects that were not mediated by tobacco exposure. Smoking and SES, however, did not interact. In short, impaired performance in measures of most cool skills was associated with SES irrespective of smoking status; in contrast, regardless of SES, smokers showed specific impairment in hot self-regulation domains (more difficulty resisting immediate temptations and weighing future consequences of actions). Possible explanations for the lack of mediation of tobacco exposure on hot skills of smokers are discussed.

Effects of nicotine on smooth pursuit eye movements in healthy non-smokers

RATIONALE

The non-selective nicotinic acetylcholine receptor (nAChR) agonist nicotine has been argued to improve attention via enhanced filtering of irrelevant stimuli. Here, we tested this hypothesis in the context of smooth pursuit eye movements (SPEMs), an oculomotor function previously shown to improve with nicotine in some but not all studies.

OBJECTIVES

In order to test whether nicotine improves performance particularly when the inhibition of distracting stimuli is required, SPEM was elicited in conditions with or without peripheral distractors. Additionally, different target frequencies were employed in order to parametrically vary general processing demands on the SPEM system.

METHODS

Healthy adult non-smokers (N = 18 females, N = 13 males) completed a horizontal sinusoidal SPEM task at different target frequencies (0.2 Hz, 0.4 Hz, 0.6 Hz) in the presence or absence of peripheral distractors in a double-blind, placebo-controlled, cross-over design using a 2 mg nicotine gum.

RESULTS

Nicotine increased peak pursuit gain relative to placebo (p < .001), but an interaction with distractor condition (p = .001) indicated that this effect was most pronounced in the presence of distractors. Catch-up saccade frequency was reduced by nicotine (p = .01), particularly at higher target frequencies (two-way interaction, p = .04). However, a three-way interaction (p = .006) indicated that the reduction with nicotine was strongest at the highest target frequency (0.6 Hz) only without distractors, whereas in the presence of distractors, it was strongest at 0.4-Hz target frequency. There were no effects of nicotine on subjective state measures.

CONCLUSIONS

Together, these findings support a role of both distractor inhibition and general processing load in the effects of nicotine on smooth pursuit.

Neuromodulatory Influences on Integration and Segregation in the Brain

Cognitive function relies on the dynamic cooperation of specialized regions of the brain; however, the elements of the system responsible for coordinating this interaction remain poorly understood. In this Opinion article I argue that this capacity is mediated in part by competitive and cooperative dynamic interactions between two prominent metabotropic neuromodulatory systems - the cholinergic basal forebrain and the noradrenergic locus coeruleus (LC). I assert that activity in these projection nuclei regulates the amount of segregation and integration within the whole brain network by modulating the activity of a diverse set of specialized regions of the brain on a timescale relevant for cognition and attention.

Neurobiological Determinants of Tobacco Smoking in Schizophrenia

Purpose of review: To provide an overview of the underlying neurobiology of tobacco smoking in schizophrenia, and implications for treatment of this comorbidity. Recent findings: Explanations for heavy tobacco smoking in schizophrenia include pro-cognitive effects of nicotine, and remediation of the underlying pathophysiology of schizophrenia. Nicotine may ameliorate neurochemical deficits through nicotine acetylcholine receptors (nAChRs) located on the dopamine, glutamate, and GABA neurons. Neurophysiological indices including electroencephalography, electromyography, and smooth pursuit eye movement (SPEM) paradigms may be biomarkers for underlying neuronal imbalances that contribute to the specific risk of tobacco smoking initiation, maintenance, and difficulty quitting within schizophrenia. Moreover, several social factors including socioeconomic factors and permissive smoking culture in mental health facilities, may contribute to the smoking behaviors (initiation, maintenance, and inability to quit smoking) within this disorder. Summary: Tobacco smoking may alleviate specific symptoms associated with schizophrenia. Understanding the neurobiological underpinnings and psychosocial determinants of this comorbidity may better explain these potential beneficial effects, while also providing important insights into effective treatments for smoking cessation.

A case report SPECT study and theoretical rationale for the sequential administration of ibogaine and 5-MeO-DMT in the treatment of alcohol use disorder

Ibogaine is a plant-derived alkaloid and dissociative psychedelic that demonstrates anti-addictive properties with several substances of abuse, including alcohol. 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) is a naturally occurring psychedelic known to occasion potent mystical-type experiences and also demonstrates anti-addictive properties. The potential therapeutic effects of both compounds in treating alcohol use disorder require further investigation and there are no published human neuroimaging findings of either treatment to date. We present the case of a 31-year-old male military veteran with moderate alcohol use disorder who sought treatment at an inpatient clinic in Mexico that utilized a sequential protocol with ibogaine hydrochloride (1550mg, 17.9mg/kg) on day 1, followed by vaporized 5-MeO-DMT (bufotoxin source 50mg, estimated 5-MeO-DMT content, 5-7mg) on day 3. The patient received SPECT neuroimaging that included a resting-state protocol before, and 3 days after completion of the program. During the patient's ibogaine treatment, he experienced dream-like visions that included content pertaining to his alcohol use and resolution of past developmental traumas. He described his treatment with 5-MeO-DMT as a peak transformational and spiritual breakthrough. On post-treatment SPECT neuroimaging, increases in brain perfusion were noted in bilateral caudate nuclei, left putamen, right insula, as well as temporal, occipital, and cerebellar regions compared to the patient's baseline scan. The patient reported improvement in mood, cessation of alcohol use, and reduced cravings at 5 days post-treatment, effects which were sustained at 1 month, with a partial return to mild alcohol use at 2 months. In this case, serial administration of ibogaine and 5-MeO-DMT resulted in increased perfusion in multiple brain regions broadly associated with alcohol use disorders and known pharmacology of both compounds, which coincided with a short-term therapeutic outcome. We present theoretical considerations regarding the potential of both psychedelic medicines in treating alcohol use disorders in the context of these isolated findings, and areas for future investigation.

Loss of Lypd6 leads to reduced anxiety-like behaviour and enhanced responses to nicotine

Nicotine consumption through smoking affects anxious states in humans. However, the precise role of nicotinic acetylcholine receptor (nAChR) circuitry in the regulation of anxiety remains elusive. The Lynx protein Lypd6 is highly enriched in synaptic loci and has been previously identified as an endogenous inhibitor of neuronal nAChR function in vitro. Here, we investigate the effect of Lypd6 in anxiety-related behaviour and examine the molecular underpinnings of its function in the brain. We employ the marble burying (MB) and elevated zero maze (EZM) tests in Lypd6 knock-out (KO) and wild-type (WT) mice and find that loss of Lypd6 leads to decreased digging behaviour in the MB test and increased time spent in the open area in the EZM test. Moreover, we demonstrate that acute nicotine administration reduces digging in the MB test in both KO and WT mice and further accentuates the inherent genotype difference. Using in vitro electrophysiology in dorsal raphe nuclei (DRN) neurons from Lypd6 KO mice, we show that nicotine-evoked whole-cell currents are enhanced in the absence of Lypd6. Collectively, these data are the first to indicate the involvement of Lypd6 in circuits associated with anxiety and suggest that a possible underlying neurobiological mechanism is the modulation of cholinergic responses in the DRN.

Tobacco retail environment near housing programmes for patients with mental health conditions in New York City

OBJECTIVES

The current study sought to characterise the tobacco retail environment of supportive housing facilities for persons with mental health (MH) conditions in New York City (NYC) and to estimate the potential impact of a tobacco retail ban near public schools on the retail environment of MH housing in NYC.

METHODS

Texas A&M Geocoding Services was used to geocode the addresses of housing programmes for patients with MH conditions, non-MH residences, public schools and tobacco retailers in NYC. ESRI ArcMap was used to calculate the number of tobacco retailers within a 500-foot radius around each housing programme and school address point, and the Euclidean distance to the nearest retailer. Generalised linear models were used to compare retail counts and distance between MH and non-MH residences.

RESULTS

The mean number of tobacco retailers within 500 feet of an MH housing programme was 2.9 (SD=2.3) and the mean distance to nearest tobacco retailer was 370.6 feet (SD=350.7). MH residences had more retailers within 500 feet and a shorter distance to the nearest retailer compared with non-MH residences in Brooklyn, the Bronx and Staten Island (p<0.001). Banning tobacco licences within 350, 500 or 1000 feet of a school would significantly improve the tobacco retail environment of MH housing programmes and reduce disparities between MH and non-MH residences in some boroughs.

CONCLUSIONS

People with MH conditions residing in supportive housing in NYC encounter a heavy tobacco retail environment in close proximity to their home, and in some boroughs, one worse than non-MH residences. Implementing a ban on tobacco retail near public schools would improve the tobacco retail environment of MH housing programmes in NYC.

Compromised neuroplasticity in cigarette smokers under nicotine withdrawal is restituted by the nicotinic α4β2-receptor partial agonist varenicline

Nicotine modulates neuroplasticity and improves cognitive functions in animals and humans. In the brain of smoking individuals, calcium-dependent plasticity induced by non-invasive brain stimulation methods such as transcranial direct current stimulation (tDCS) and paired associative stimulation (PAS) is impaired by nicotine withdrawal, but partially re-established after nicotine re-administration. In order to investigate the underlying mechanism further, we tested the impact of the α₄β₂-nicotinic receptor partial agonist varenicline on focal and non-focal plasticity in smokers during nicotine withdrawal, induced by PAS and tDCS, respectively. We administered low (0.3 mg) and high (1.0 mg) single doses of varenicline or placebo medication before stimulation over the left motor cortex of 20 healthy smokers under nicotine withdrawal. Motor cortex excitability was monitored by single-pulse transcranial magnetic stimulation-induced motor evoked potential amplitudes for 36 hours after plasticity induction. Stimulation-induced plasticity was absent under placebo medication, whereas it was present in all conditions under high dose. Low dose restituted only tDCS-induced non-focal plasticity, producing no significant impact on focal plasticity. High dose varenicline also prolonged inhibitory plasticity. These results are comparable to the impact of nicotine on withdrawal-related impaired plasticity in smokers and suggest that α₄β₂ nicotinic receptors are relevantly involved in plasticity deficits and restitution in smokers.

Secondhand Smoke Exposure and Low Blood Lead Levels in Association With Attention-Deficit Hyperactivity Disorder and Its Symptom Domain in Children: A Community-Based Case-Control Study

AIM

Secondhand smoke (SHS) is a major indoor pollutant. We examined the possible association between exposure to both SHS and low levels of lead and attention-deficit-hyperactivity disorder (ADHD) and its symptom domain in children.

METHODS

This case-control study was based on the results of a community survey using the ADHD rating scale conducted in 49 elementary schools. Both cases and control subjects were confirmed by a child psychiatrist. Each case was matched with one control subject according to gender, school, and grade in school. Using a multivariate conditional logistic regression model, we analyzed 214 case-control pairs of children who ranged in age from 6 to 10 years. Urine and blood levels of cotinine and of lead were determined, and information pertaining to SHS exposure was obtained by means of a questionnaire.

RESULTS

Exposure to low levels of lead (geometric mean = 1.65 µg/dL) was related to ADHD, particularly inattention (odds ratio [OR] = 1.67, 95% confidence interval [CI] = 1.07-2.59), whereas SHS exposure was associated mainly with hyperactivity/impulsivity (OR = 3.85, 95% CI = 1.55-9.56). In the pathway from blood lead to hyperactivity/impulsivity, children's SHS exposure mediated and indirectly accounted for about 73% of this relationship. The combined exposure to lead and SHS synergistically increased the risk of ADHD, evident as both inattention and hyperactivity/impulsivity.

CONCLUSION

SHS, which is associated with hyperactivity/impulsivity in particular, combined with exposure to low blood levels of lead synergistically increased the risk of ADHD. Therefore, the exposure of children to both SHS and lead needs to be reduced.

IMPLICATIONS

Although exposure to low levels of lead has been shown to be associated with ADHD, there is little evidence of symptom domain specificity. In our study, low blood lead levels were related to inattention. In addition, prenatal or postnatal exposure to SHS increased the risk of ADHD, particularly hyperactivity/impulsivity. Combined exposure to lead and SHS synergistically increased the risk for both these ADHD symptom domains. To protect children from environmental risk factors related to ADHD, it is necessary to further reduce children's exposure to SHS and lead, even in those with low blood lead levels.

Not All Differences between Patients with Schizophrenia and Healthy Subjects Are Pathological: Performance on the Conners' Continuous Performance Test

OBJECTIVE

This study analyzed attentional performance in patients with schizophrenia during a continuous performance task requiring a high response rate.

METHOD

The Conners' Continuous Performance Test-II (CPT-II) was administered to 64 patients with schizophrenia and 64 healthy comparison subjects. A cross-sectional design was used in order to allow analysis of the means between patients and healthy subjects. Differences in performance were assessed for significance using ANCOVA. Percentiles were also analyzed in order to determine whether a participant showed normal or pathological performance. Pearson's correlation was used to detect possible relationships between attentional performance and psychopathology.

RESULTS

Of the 12 CPT-II measures, response style and slowing of reaction time (RT) between targets increased to similar extents between patients and healthy comparison subjects. Patients performed significantly less well than non-patient group on all other measures. Nevertheless, patient's performance on four of these measures remained within the normal range, and patient's performance on the remaining measures qualified as pathological only in the case of variability in hit RT. No significant correlations between attention performance and symptoms were found.

CONCLUSIONS

These results suggest that although patients may show lower attentional functioning than non-patients on tasks requiring a high response rate, their attentional performance remains within the normal range on most dimensions.

Executive Functions in Tobacco Dependence: Importance of Inhibitory Capacities

BACKGROUND

Executive functions are linked to tobacco dependence and craving. In this cross-sectional study, we assessed the impact of three executive functions: updating, inhibition and shifting processes on tobacco craving and dependence.

METHOD

134 tobacco consumers were included in this study: 81 moderately (Fagerström score <7) and 53 heavily dependent (Fagerström score >7). Dependence was assessed with the Fagerström test and craving with the tobacco craving questionnaire (TCQ 12). We used the Stroop test and the Hayling test to measure inhibition, the Trail Making Test to measure shifting processes and the n-back test to measure updating processes. A multivariate logistic model was used to assess which variables explained best the level of nicotine dependence.

RESULTS

Inhibition (p = 0.002) and updating (p = 0.014) processes, but not shifting processes, were associated with higher tobacco dependence. Inhibition capacity had a significant effect on the nicotine dependence level independently of age, education, time since last cigarette, intellectual quotient, craving, updating and shifting process.

CONCLUSIONS

Nicotine dependence level seems better explained by inhibition capacities than by craving and updating effects. The capacity to inhibit our behaviours is a good predictor of the severity of tobacco dependence. Our results suggest a prefrontal cortex dysfunction affecting the inhibitory capacities of heavy tobacco dependent smokers. Further studies are needed to investigate the application of these findings in the treatment of tobacco dependence.

nAChR dysfunction as a common substrate for schizophrenia and comorbid nicotine addiction: Current trends and perspectives

INTRODUCTION

The prevalence of tobacco use in the population with schizophrenia is enormously high. Moreover, nicotine dependence is found to be associated with symptom severity and poor outcome in patients with schizophrenia. The neurobiological mechanisms that explain schizophrenia-nicotine dependence comorbidity are not known. This study systematically reviews the evidence highlighting the contribution of nicotinic acetylcholine receptors (nAChRs) to nicotine abuse in schizophrenia.

METHODS

Electronic data bases (Medline, Google Scholar, and Web of Science) were searched using the selected key words that match the aims set forth for this review. A total of 276 articles were used for the qualitative synthesis of this review.

RESULTS

Substantial evidence from preclinical and clinical studies indicated that dysregulation of α7 and β2-subunit containing nAChRs account for the cognitive and affective symptoms of schizophrenia and nicotine use may represent a strategy to remediate these symptoms. Additionally, recent meta-analyses proposed that early tobacco use may itself increase the risk of developing schizophrenia. Genetic studies demonstrating that nAChR dysfunction that may act as a shared vulnerability factor for comorbid tobacco dependence and schizophrenia were found to support this view. The development of nAChR modulators was considered an effective therapeutic strategy to ameliorate psychiatric symptoms and to promote smoking cessation in schizophrenia patients.

CONCLUSIONS

The relationship between schizophrenia and smoking is complex. While the debate for the self-medication versus addiction vulnerability hypothesis continues, it is widely accepted that a dysfunction in the central nAChRs represent a common substrate for various symptoms of schizophrenia and comorbid nicotine dependence.

Effects of cigarette smoking and alcohol use on neurocognition and BDNF levels in a Chinese population

OBJECTIVE

Few studies have examined the potential interactive effect of both smoking and drinking on cognition. Brain-derived neurotrophic factor (BDNF) plays a critical role in cognition. This is the first study to examine the neurocognitive consequences of cigarette smoking combined with chronic alcohol consumption and their relationship to serum BDNF levels in a Chinese Han population.

MATERIALS AND METHODS

We recruited 191 healthy male subjects, including 47 isolated smokers, 31 isolated chronic alcohol users, 58 combined smokers and chronic alcohol users, and 55 non-smokers and non-alcohol users. We then compared the repeatable battery for the assessment of neuropsychological status (RBANS) scores and serum BDNF levels in these four groups.

RESULTS

When compared to the non-smoking + non-alcohol-using group, the smoking group performed worse on immediate memory, attention, language, and RBANS total score. There were no significant differences in the RBANS scores between the alcohol-using group and non-smoking + non-alcohol-using group, or between the smoking group and smoking + alcohol-using group. We did not find an association between BDNF and smoking or drinking status or between BDNF and cognitive performance. In the smoking group, there was a significant correlation between BDNF and carbon monoxide concentration, and between BDNF and the Fagerstrom Test for Nicotine Dependence (FTND) total score.

CONCLUSIONS

Our results suggest that smoking is associated with cognitive decline, but not with BDNF levels in a normal population. However, smoking severity is positively associated with BDNF levels. Concomitant alcohol use does not worsen the cognitive decline caused by smoking.

Subtype-selective nicotinic acetylcholine receptor agonists can improve cognitive flexibility in an attentional set shifting task

Nicotinic acetylcholine receptors (nAChRs) are considered to be viable targets to enhance cognition in patients diagnosed with schizophrenia. Activation of nAChRs with selective nicotinic receptor agonists may provide effective means to pharmacologically treat cognitive deficits observed in schizophrenia. Cognitive flexibility is one aspect of cognition, which can be assessed in a rodent model of the attentional set-shifting task (ASST). The aim of the present study was two-fold, firstly, to evaluate the efficacy of a series of subtype selective nAChR agonists, such as those that target α7 and α4β2 nAChR subtypes in non-compromised rodents. Secondly, nicotine as a prototypic agonist was evaluated for its effects to restore attentional deficits produced by sub-chronic ketamine exposure in the ASST. Male hooded Lister rats underwent habituation, consisting of a simple odour and medium discrimination with subsequent assessment 24 h later. In experimentally naïve rats, α7 subtype selective agonists, compound-A and SSR180711 along with PNU-120596, an α7 positive allosteric modulator (PAM), were compared against the β2* selective agonist, 5IA-85380. All compounds except for PNU-120596 were observed to significantly improve extra-dimensional (ED) shift performance, nicotine, 5IA-85380 and SSR180711 further enhanced the final reversal (REV3) stage of the task. In another experiment, sub-chronic ketamine treatment produced robust deficits during the ED and the REV3 stages of the discriminations; rodents required significantly more trials to reach criterion during these discriminations. These deficits were attenuated in rodents treated acutely with nicotine (0.1 mg/kg SC) 10 min prior to the ED shift. These results highlight the potential utility of targeting nAChRs to enhance cognitive flexibility, particularly the α7 and β2* receptor subtypes. The improvement with nicotine was much greater in rodents that were impaired following the sub-chronic ketamine exposure suggesting a greater therapeutic opportunity to target nicotinic receptors for patients diagnosed with schizophrenia.

Nicotinic receptors as targets for therapeutic discovery

Nicotinic acetylcholine receptors (nAChRs) represent a class of therapeutic targets with the potential to impact numerous diseases and disorders where significant unmet medical needs remain. The latter include cognitive and neurodegenerative diseases; psychotic disorders, such as schizophrenia; acute nociceptive, neuropathic and inflammatory pain; affective disorders, such as depression and inflammation, where nAChR subtypes modulate key cellular pathways involved in anti-inflammatory processes as well as cell survival. Our increased understanding of the heterogeneity of nAChR targets is defining the relationship of biologic effects to specific receptor subtypes, which in turn, will allow further refinement of desired therapeutic activities. Both preclinical and clinical evidence support the notion that novel compounds targeting specific nAChR subtypes will offer increased potency and efficacy, longer lasting effects, fewer side effects and a more rapid onset of action and less dependence, compared with existing therapies. Clinical proof-of-concept is rapidly emerging and will solidify the position of this new therapeutic approach.

Smoking in schizophrenic patients: A critique of the self-medication hypothesis

A common remark among laypeople, and notably also among mental health workers, is that individuals with mental illnesses use drugs as self-medication to allay clinical symptoms and the side effects of drug treatments. Roots of the self-medication concept in psychiatry date back at least to the 1980s. Observations that rates of smokers in schizophrenic patients are multiple times the rates for regular smoking in the general population, as well as those with other disorders, proved particularly tempting for a self-medication explanation. Additional evidence came from experiments with animal models exposed to nicotine and the identification of neurobiological mechanisms suggesting self-medication with smoking is a plausible idea. More recently, results from studies comparing smoking and non-smoking schizophrenic patients have led to the questioning of the self-medication hypothesis. Closer examination of the literature points to the possibility that smoking is less beneficial on schizophrenic symptomology than generally assumed while clearly increasing the risk of cancer and other smoking-related diseases responsible for early mortality. It is a good time to examine the evidence for the self-medication concept as it relates to smoking. Our approach is to focus on data addressing direct or implied predictions of the hypothesis in schizophrenic smokers.

Smoking in schizophrenia: cognitive impact of nicotine and relationship to smoking motivators

Smoking prevalence in schizophrenia is significantly elevated relative to other clinical and to non-clinical groups. The cognitive self-medication hypothesis attributes this to the beneficial effects of nicotine on illness-related cognitive deficits. Significant effects of nicotine have been observed on visual spatial working memory (VSWM), sustained attention (Continuous Performance Test - Identical Pairs; CPT-IP) and prepulse inhibition (PPI). It remains unclear whether these neurophysiological and neurocognitive effects of nicotine influence self-reported smoking motivation. To explore the relationship between nicotine effects on cognition and self-reported smoking motivation in schizophrenia and non-psychiatric control smokers, the impact of smoking abstinence and reinstatement was examined across three cognitive indices (VSWM, CPT-IP, PPI) and compared to self-reported smoking motivation (Modified Reasons for Smoking Scale revised to include 'cognitive motivators'). Cognitive function was assessed after 'typical' smoking and overnight abstinence. Schizophrenia smokers (but not controls) demonstrated significantly less error on the VSWM task in the smoking relative to abstinent condition. Control (but not schizophrenia) smokers, showed evidence of CPT-IP improvement in the smoking relative to abstinent condition. The overall profile of smoking motivation was comparable between groups. However, significant relationships between subjective and objective indices of smoking related cognitive change were observed for controls. Differential effects of nicotine on cognition have been hypothesised to influence the pattern and persistence of smoking in schizophrenia. These preliminary findings indicate that evidence for such effects is apparent even in small samples - particularly for VSWM. This is the first study to show that neurocognitive effects of smoking may influence self-reported smoking motivation.

Chronic nicotine administration does not alter cognitive or mood associated behavioural parameters

Nicotine, the major specific alkaloid in tobacco smoke, exhibits widespread pharmacological effects and may contribute to deterioration in behaviour. The present study thus examined the effects of its chronic administration on some cognitive and mood associated behaviours. Adult rats weighing between 150 and 200g were randomly divided into 4 groups each of 5 females and 5 males. Three groups were administered graded doses of nicotine at 0.25, 2 and 4mg/kg body weight via subcutaneous injections. One group served as control and received normal saline (vehicle for nicotine). Behavioural tests were performed using the Y-maze, elevated-plus maze (EPM) and tail suspension tests (TST) at various time points. Nicotine produced no significant effect in spontaneous alternation on Y-maze, nor on six parameters scored on EPM (open arm entries, time spent in open arms, time per open arm entries, open/closed arm quotient, closed arm entries, and total arm entries), and also no significant effect on immobility time in TST. This lack of effects was observed to be independent of sex and dose administered. The study shows that nicotine does not produce long-term changes in some cognitive and mood associated behaviours, thus suggesting it could be well tolerated even following chronic administration.

Genetic and behavioral determinants of hippocampal volume recovery during abstinence from alcohol

Alcohol-dependent individuals (ALC) have smaller hippocampi and poorer neurocognition than healthy controls. Results from studies on the association between alcohol consumption and hippocampal volume have been mixed, suggesting that comorbid or premorbid factors (i.e., those present prior to the initiation of alcohol dependence) determine hippocampal volume in ALC. We aimed to characterize the effects of select comorbid (i.e., cigarette smoking) and premorbid factors (brain-derived neurotrophic factor [BDNF] genotype [Val66Met rs6265]) on hippocampal volume in an ALC cohort followed longitudinally into extended abstinence. One hundred twenty-one adult ALC in treatment (76 smokers, 45 non-smokers) and 35 non-smoking light-drinking controls underwent quantitative magnetic resonance imaging, BDNF genotyping, and neurocognitive assessments. Representative subgroups were studied at 1 week, 1 month, and at an average of 7 months of abstinence. ALC had smaller hippocampi than healthy controls at all time points. Hippocampal volume at 1 month of abstinence correlated with lower visuospatial function. Smoking status did not influence hippocampal volume or hippocampal volume recovery during abstinence. However, only BDNF Val homozygotes tended to have hippocampal volume increases over 7 months of abstinence, and Val homozygotes had significantly larger hippocampi than Met carriers at 7 months of abstinence. These findings suggest that BDNF genotype, but not smoking status or measures of drinking severity, regulate functionally relevant hippocampal volume recovery in abstinent ALC. Future studies aimed at exploring genetic determinants of brain morphometry in ALC may need to evaluate individuals during extended abstinence after the acute environmental effects of chronic alcohol consumption have waned.

Effects of cigarette smoking history on neurocognitive recovery over 8 months of abstinence in alcohol-dependent individuals

BACKGROUND

This study compared the rate and extent of recovery on measures of learning and memory, processing speed, and working memory in treatment-seeking alcohol-dependent individuals (ALC) who were never smokers (nvsALC), former smokers (fsALC), and active smokers (asALC) over the first 8 months of sustained abstinence from alcohol. Assessments after 1 week, 1 month, and 8 months of abstinence in ALC enabled a comparison of the rates of neurocognitive changes from 1 week to 1 month versus 1 to 8 months of abstinence.

METHODS

ALC and never-smoking controls were administered standardized measures of auditory-verbal and visuospatial learning and memory, processing speed, and working memory. Controls completed a baseline assessment and a follow-up approximately 9 months later.

RESULTS

Over 8 months of abstinence, asALC showed poorer recovery than nvsALC on visuospatial learning, and both fsALC and asALC recovered less than nvsALC on processing speed measures. The corresponding recovery rates for the ALC group, as a whole, were greater from 1 week to 1 month than from 1 to 8 months of abstinence; these findings were largely driven by improvements in nvsALC. The recovery levels for fsALC on most measures were similar to those in asALC. Additionally, over 8 months, asALC showed significantly less improvement with increasing age than nvsALC on measures of processing speed and learning and memory. At 8 months of abstinence, asALC were inferior to controls and nvsALC on multiple measures, fsALC performed worse than nvsALC on several tests, but nvsALC were not different from controls on any measure.

CONCLUSIONS

Overall, ALC showed rapid improvement on measures of visuospatial learning and processing speed during the first month of abstinence from alcohol. Results also provide robust evidence that smoking status influenced the rate and level of neurocognitive recovery over 8 months of abstinence in this ALC cohort.

In vivo evidence for β2 nicotinic acetylcholine receptor subunit upregulation in smokers as compared with nonsmokers with schizophrenia

BACKGROUND

Schizophrenia is associated with very high rates of tobacco smoking. The latter may be related to an attempt to self-medicate symptoms and/or to alterations in function of high-affinity β2-subunit-containing nicotinic acetylcholine receptors (β2*-nAChRs).

METHODS

Smoking and nonsmoking subjects with schizophrenia (n=31) and age-, smoking-, and sex-matched comparison subjects (n=31) participated in one [123I]5-IA-85380 single photon emission computed tomography scan to quantify β2*-nAChR availability. Psychiatric, cognitive, nicotine craving, and mood assessments were obtained during active smoking, as well as smoking abstinence.

RESULTS

There were no differences in smoking characteristics between smokers with and without schizophrenia. Subjects with schizophrenia had lower β2*-nAChR availability relative to comparison group, and nonsmokers had lower β2*-nAChR availability relative to smokers. However, there was no smoking by diagnosis interaction. Relative to nonsmokers with schizophrenia, smokers with schizophrenia had higher β2*-nAChR availability in limited brain regions. In smokers with schizophrenia, higher β2*-nAChR availability was associated with lower negative symptoms of schizophrenia and better performance on tests of executive control. Chronic exposure to antipsychotic drugs was not associated with changes in β2*-nAChR availability in schizophrenia.

CONCLUSIONS

Although subjects with schizophrenia have lower β2*-nAChR availability relative to comparison group, smokers with schizophrenia appear to upregulate in the cortical regions. Lower receptor availability in smokers with schizophrenia in the cortical regions is associated with a greater number of negative symptoms and worse performance on tests of executive function, suggesting smoking subjects with schizophrenia who upregulate to a lesser degree may be at risk for poorer outcomes.

Discovery of a new subclass of α-conotoxins in the venom of Conus australis

Cone snails (Conus sp.) are poisonous animals that can be found in all oceans where they developed a venomous strategy to prey or to defend. The venom of these species contains an undeniable source of unique and potent pharmacologically active compounds. Their peptide compounds, called conotoxins, are not only interesting for the development of new pharmaceutical ligands, but they are also useful for studying their broad spectrum of targets. One conotoxin family in particular, the α-conotoxins, acts on nicotinic acetylcholine receptors (nAChRs) which dysfunctions play important roles in pathologies such as epilepsy, myasthenic syndromes, schizophrenia, Parkinson's disease and Alzheimer's disease. Here we define a new subclass of the α-conotoxin family. We purified the venom of a yet unexplored cone snail species, i.e. Conus australis, and we isolated a 16-amino acid peptide named α-conotoxin AusIA. The peptide has the typical α-conotoxin CC-Xm-C-Xn-C framework, but both loops (m/n) contain 5 amino acids, which has never been described before. Using conventional electrophysiology we investigated the response of synthetically made globular (I-III, II-IV) and ribbon (I-IV, II-III) AusIA to different nicotinic acetylcholine receptors. The α7 nAChR was the only receptor found to be blocked with a similar potency by both peptide-configurations. This suggests that both α5/5 conotoxin isomers might be present in the venom gland of C. australis. NMR spectroscopy showed that no secondary structures define the peptides' three-dimensional topology. Moreover, the ribbon configuration, which is generally considered to be non-native, is more stable than the globular isomer. Accordingly, our findings show relevancy concerning the α-conotoxin classification which might be helpful in the design of novel therapeutic compounds.

Effects of tobacco smoking on neuropsychological function in schizophrenia in comparison to other psychiatric disorders and non-psychiatric controls

BACKGROUND AND OBJECTIVES

Compared to the general population cigarette smoking prevalence is elevated in psychiatric disorders such as schizophrenia (SZ), bipolar disorder (BD), and major depressive disorder (MDD). These disorders are also associated with neurocognitive impairments. Cigarette smoking is associated with improved cognition in SZ. The effects of smoking on cognition in BD and MDD are less well studied.

METHODS

We used a cross-sectional design to study neuropsychological performance in these disorders as a function of smoking status. Subjects (N = 108) were SZ smokers (n = 32), SZ non-smokers (n = 15), BD smokers (n = 10), BD non-smokers (n = 6), MDD smokers (n = 6), MDD non-smokers (n = 10), control smokers (n = 12), and control non-smokers (n = 17). Participants completed a neuropsychological battery; smokers were non-deprived.

RESULTS

SZ subjects performed significantly worse than controls in select domains, while BD and MDD subjects did not differ from controls. Three verbal memory outcomes were improved in SZ smokers compared with non-smokers; smoking status did not alter performance in BD or MDD.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

These data suggest that smoking is associated with neurocognitive improvements in SZ, but not BD or MDD. Our data may suggest specificity of cigarette-smoking modulation of neurocognitive deficits in SZ.

Neurocognitive endophenotypes in schizophrenia: modulation by nicotinic receptor systems

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

Conotoxins targeting nicotinic acetylcholine receptors: an overview

Marine snails of the genus Conus are a large family of predatory gastropods with an unparalleled molecular diversity of pharmacologically active compounds in their venom. Cone snail venom comprises of a rich and diverse cocktail of peptide toxins which act on a wide variety of ion channels such as voltage-gated sodium- (Na_V), potassium- (K_V), and calcium- (Ca_V) channels as well as nicotinic acetylcholine receptors (nAChRs) which are classified as ligand-gated ion channels. The mode of action of several conotoxins has been the subject of investigation, while for many others this remains unknown. This review aims to give an overview of the knowledge we have today on the molecular pharmacology of conotoxins specifically interacting with nAChRs along with the structure–function relationship data.

Adult attention-deficit/hyperactivity disorder and nicotine use: a qualitative study of patient perceptions

BACKGROUND

Adult Attention-Deficit/Hyperactivity Disorder (ADHD) is associated with high rates of comorbid substance use disorders, and cigarette smoking has a particularly high prevalence in this population. However, there is an ongoing debate as to whether this tobacco use is an attempt at "self-medication" or due to behavioral disinhibition. There is a surprising lack of qualitative studies that investigate the subjective perceptions of adults with ADHD regarding cigarette smoking. The present study was designed to fill this gap in the literature.

METHODS

We recruited twelve adult patients with ADHD and comorbid tobacco use from our ADHD consultation service, an outpatient facility of the Zurich University Psychiatric Hospital. Subjects were interviewed using qualitative methodology, and Mayring's qualitative content analysis was used to evaluate findings.

RESULTS

We identified two explanatory models linking ADHD and tobacco use: smoking as an attempt at self-medication and "smoking as a social behavior". On one hand, subjects considered tobacco a therapeutic aid, reporting positive effects on "inner tension" and cognitive function, and noted possible antidepressant properties as well. On the other hand, subjects considered smoking to enhance social functioning and to have a positive impact on interpersonal relationships. The majority believed that stimulant medications offered only a transient decrease in patterns of tobacco use because their ability to reduce nicotine cravings wore off quickly. Others believed that stimulants had no effect or even reinforced cigarette use.

CONCLUSIONS

Participants had different views about the link between cigarette smoking and ADHD. While the majority thought of nicotine as a sort of therapy, viewing smoking as a way to self-medicate symptoms of ADHD, motivations for nicotine use were also related to self-image, desire to belong to a peer-group, and a drive to undermine perceived social norms. Ultimately, these findings can be used by clinicians to improve treatment alliance and collaboration.

Altered acetylcholine release in the hippocampus of dystrophin-deficient mice

Mild cognitive impairments have been described in one-third of patients with Duchenne muscle dystrophy (DMD). DMD is characterized by progressive and irreversible muscle degeneration caused by mutations in the dystrophin gene and lack of the protein expression. Previously, we have reported altered concentrations of α7- and β2-containing nicotinic acetylcholine receptors (nAChRs) in hippocampal membranes of dystrophic (mdx) mice. This suggests that alterations in the central cholinergic synapses are associated with dystrophin deficiency. In this study, we examined the release of acetylcholine (ACh) and the level of the vesicular ACh transporter (VAChT) using synaptosomes isolated from brain regions that normally have a high density of dystrophin (cortex, hippocampus and cerebellum), in control and mdx mice at 4 and 12months of age. ACh release evoked by nicotinic stimulation or K(+) depolarization was measured as the tritium outflow from superfused synaptosomes preloaded with [(3)H]-choline. The results showed that the evoked tritium release was Ca(2+)-dependent and mostly formed by [(3)H]-ACh. β2-containing nAChRs were involved in agonist-evoked [(3)H]-ACh release in control and mdx preparations. In hippocampal synaptosomes from 12-month-old mdx mice, nAChR-evoked [(3)H]-ACh release increased by 57% compared to age-matched controls. Moreover, there was a 98% increase in [(3)H]-ACh release compared to 4-month-old mdx mice. [(3)H]-ACh release evoked by K(+) depolarization was not altered, while the VAChT protein level was decreased (19%) compared to that of age-matched controls. In cortical and cerebellar preparations, there was no difference in nAChR-evoked [(3)H]-ACh release and VAChT levels between mdx and age-matched control groups. Our previous findings and the presynaptic alterations observed in the hippocampi of 12-month-old mdx mice indicate possible dysfunction of nicotinic cholinergic synapses associated with dystrophin deficiency. These changes may contribute to the cognitive and behavioral abnormalities described in dystrophic mice and patients with DMD.

Structure-function elucidation of a new α-conotoxin, Lo1a, from Conus longurionis

α-Conotoxins are peptide toxins found in the venom of marine cone snails and potent antagonists of various subtypes of nicotinic acetylcholine receptors (nAChRs). nAChRs are cholinergic receptors forming ligand-gated ion channels in the plasma membranes of certain neurons and the neuromuscular junction. Because nAChRs have an important role in regulating transmitter release, cell excitability, and neuronal integration, nAChR dysfunctions have been implicated in a variety of severe pathologies such as epilepsy, myasthenic syndromes, schizophrenia, Parkinson disease, and Alzheimer disease. To expand the knowledge concerning cone snail toxins, we examined the venom of Conus longurionis. We isolated an 18-amino acid peptide named α-conotoxin Lo1a, which is active on nAChRs. To the best of our knowledge, this is the first characterization of a conotoxin from this species. The peptide was characterized by electrophysiological screening against several types of cloned nAChRs expressed in Xenopus laevis oocytes. The three-dimensional solution structure of the α-conotoxin Lo1a was determined by NMR spectroscopy. Lo1a, a member of the α4/7 family, blocks the response to acetylcholine in oocytes expressing α7 nAChRs with an IC50 of 3.24 ± 0.7 μM. Furthermore, Lo1a shows a high selectivity for neuronal versus muscle subtype nAChRs. Because Lo1a has an unusual C terminus, we designed two mutants, Lo1a-ΔD and Lo1a-RRR, to investigate the influence of the C-terminal residue. Lo1a-ΔD has a C-terminal Asp deletion, whereas in Lo1a-RRR, a triple-Arg tail replaces the Asp. They blocked the neuronal nAChR α7 with a lower IC50 value, but remarkably, both adopted affinity for the muscle subtype α1β1δε.

AZD3480, a novel nicotinic receptor agonist, for the treatment of attention-deficit/hyperactivity disorder in adults

BACKGROUND

Laboratory studies have found that acute stimulation of nicotinic acetylcholine receptors improves cognition in adult attention-deficit/hyperactivity disorder (ADHD). Clinical trials of nicotinic agonists have been mixed, underscoring the need to understand the mechanisms for individual differences in clinical response. Using cognitive models within a clinical trial framework may provide insight into these differences.

METHODS

This was a within-subjects, randomized, placebo-controlled double-blind trial of the nicotinic agonist AZD3480 (also termed TC-1734) at doses of 5 mg and 50 mg and placebo in adults with ADHD. The order of the 2-week treatment periods was randomized, and a 3-week wash out separated each drug treatment period. Response inhibition (Stop Signal Task [SST]) and clinical efficacy (Investigator Rated Conners Adult ADHD Rating Scale [CAARS-INV]) were the a priori primary outcome measures of cognitive and clinical effects. We hypothesized that AZD3480 treatment would improve SST performance and clinical symptoms (CAARS-INV Total ADHD Symptoms Score).

RESULTS

Thirty subjects were randomized, with 24 included in the intent-to-treat analyses. SST performance and total ADHD symptoms were significantly improved with 50 mg of AZD3480. CAARS-INV ratings of inattention, memory problems, and emotional lability/impulsivity were significantly improved with 50 mg of AZD3480.

CONCLUSIONS

These results support previous work suggesting that nicotinic agonists are viable as treatments for adult ADHD. Measuring cognitive endophenotypes related to both the disorder and mechanism of treatment may help further rational drug development for dimensional features that cross-cut psychiatric disorders.

Acetylcholinergic neurotransmission and the β-amyloid cascade: implications for Alzheimer’s disease

Alzheimer's disease is characterized by both decreases in acetylcholinergic neurotransmission and increases in beta-amyloid accumulation. Currently, available clinical psychopharmacologic treatment is focused on increasing acetylcholinergic neurotransmission, whereas no clinical treatments to directly reduce beta-amyloid accumulation are available. Cholinesterase inhibitors improve cognition, certain neuropsychiatric symptoms and functional impairment in patients with mild-to-moderate Alzheimer's disease, and it is believed that this is mainly symptomatic treatment. However, this review discusses various levels of interaction between acetylcholinergic neurotransmission and the beta-amyloid cascade, which suggest that some specific acetylcholinergic treatments may reduce beta-amyloid accumulation, and therefore may slow disease progression over the long term. Various suggestions are made on how such potential disease-modifying effects could be studied in the future.

The efficiency of functional brain networks does not differ between smokers and non-smokers

Acute nicotine consumption in smokers impacts on functional brain network topology indicating an increase in the efficiency of information transfer and attentional task performance. The effects of chronic nicotine consumption on functional brain network topology are unknown. We here investigated the effects of chronic smoking-behaviour on functional brain network topology. Minimally-deprived smokers (N=18) and non-smokers (N=17) were measured within an fMRI scanner during a resting state condition. Graph-theoretical metrics of functional network integration (global efficiency and clustering) that have been shown to be affected by acute nicotine administration were compared between both groups. Our results revealed that smoking status did not significantly change functional network integration. Additional tests for non-inferiority confirmed the similarity of regional or nodal network properties. Brain regions such as the left insular and middle frontal gyrus, in which acute nicotine consumption affected network topology, did not reveal any decrease in functional network efficiency following chronic nicotine consumption. Within the limitation of the investigated sample size, our data suggest that the integration of functional brain networks is not altered in minimally-deprived smokers. Our findings are of relevance for clinical studies showing changes in network topology between psychiatric patients with high prevalence of smoking and healthy control subjects.

Top-down beta rhythms support selective attention via interlaminar interaction: a model

Cortical rhythms have been thought to play crucial roles in our cognitive abilities. Rhythmic activity in the beta frequency band, around 20 Hz, has been reported in recent studies that focused on neural correlates of attention, indicating that top-down beta rhythms, generated in higher cognitive areas and delivered to earlier sensory areas, can support attentional gain modulation. To elucidate functional roles of beta rhythms and underlying mechanisms, we built a computational model of sensory cortical areas. Our simulation results show that top-down beta rhythms can activate ascending synaptic projections from L5 to L4 and L2/3, responsible for biased competition in superficial layers. In the simulation, slow-inhibitory interneurons are shown to resonate to the 20 Hz input and modulate the activity in superficial layers in an attention-related manner. The predicted critical roles of these cells in attentional gain provide a potential mechanism by which cholinergic drive can support selective attention.

Top-down signals originate from higher cognitive areas such as parietal and prefrontal cortex and propagate to earlier stages of the brain. They have been thought to be associated with selective attention, and recent physiological studies suggest that top-down signals in the beta frequency band can support selective attention. In this study, we employ a computational model to investigate potential mechanisms by which top-down beta rhythms can influence neural responses induced by presentation of stimuli. The model includes several cell types, reportedly crucial for generating cortical rhythmic activity in the gamma and beta frequency bands, and the simulation results show that top-down beta rhythms are capable of reproducing experimentally observed attentional effects on neural responses to visual stimuli. These modulatory effects of top-down beta rhythms are mainly induced via activation of ascending inhibition originating from deep layer slow inhibitory interneurons. Since the excitability of slow interneurons can be increased by cholinergic neuromodulators, these interneurons may mediate the effects of cholinergic tone on attention.