Varenicline and P50 auditory gating in medicated schizophrenic patients: a pilot study

Cholinergic modulation of sensory perception and plasticity

Sensory systems are highly plastic, but the mechanisms of sensory plasticity remain unclear. People with vision or hearing loss demonstrate significant neural network reorganization that promotes adaptive changes in other sensory modalities as well as in their ability to combine information across the different senses (i.e., multisensory integration. Furthermore, sensory network remodeling is necessary for sensory restoration after a period of sensory deprivation. Acetylcholine is a powerful regulator of sensory plasticity, and studies suggest that cholinergic medications may improve visual and auditory abilities by facilitating sensory network plasticity. There are currently no approved therapeutics for sensory loss that target neuroplasticity. This review explores the systems-level effects of cholinergic signaling on human visual and auditory perception, with a focus on functional performance, sensory disorders, and neural activity. Understanding the role of acetylcholine in sensory plasticity will be essential for developing targeted treatments for sensory restoration.

Selective 5HT3 antagonists and sensory processing: a systematic review

Ondansetron is a selective serotonin (5HT3) receptor antagonist that is under evaluation as an adjunctive treatment for schizophrenia, and a novel treatment for hallucinations in Parkinson's disease. Ondansetron reverses sensory gating deficits and improves visuoperceptual processing in animal models of psychosis, but it is unclear to what extent preclinical findings have been replicated in humans. We systematically reviewed human studies that evaluated the effects of ondansetron and other 5HT3 receptor antagonists on sensory gating deficits or sensory processing. Of 11 eligible studies, eight included patients with schizophrenia who were chronically stable on antipsychotic medication; five measured sensory gating using the P50 suppression response to a repeated auditory stimulus; others included tests of visuoperceptual function. Three studies in healthy participants included tests of visuoperceptual and sensorimotor function. A consistent and robust finding (five studies) was that ondansetron and tropisetron (5HT3 antagonist and α7-nicotinic receptor partial agonist) improved sensory gating in patients with schizophrenia. Tropisetron also improved sustained visual attention in non-smoking patients. There was inconsistent evidence of the effects of 5HT3 antagonists on other measures of sensory processing, but interpretation was limited by the small number of studies, methodological heterogeneity and the potential confounding effects of concomitant medication in patients. Despite these limitations, we found strong evidence that selective 5HT3 antagonists (with or without direct α7-nicotinic partial agonist effects) improved sensory gating. Future studies should investigate how this relates to potential improvement in neurocognitive symptoms in antipsychotic naive patients with prodromal or milder symptoms, in order to understand the clinical implications.

Meta-analysis of auditory P50 sensory gating in schizophrenia and bipolar disorder

The ability of the brain to reduce the amount of trivial or redundant sensory inputs is called gating function. Dysfunction of sensory gating may lead to cognitive fragmentation and poor real-world functioning. The auditory dual-click paradigm is a pertinent neurophysiological measure of sensory gating function. This meta-analysis aimed to examine the subcomponents of abnormal P50 waveforms in bipolar disorder and schizophrenia to assess P50 sensory gating deficits and examine effects of diagnoses, illness states (first-episode psychosis vs. schizophrenia, remission vs. episodes in bipolar disorder), and treatment status (medication-free vs. medicated). Literature search of PubMed between Jan 1st 1980 and March 31st 2019 identified 2091 records for schizophrenia, 362 for bipolar disorder. 115 studies in schizophrenia (4932 patients), 16 in bipolar disorder (975 patients) and 10 in first-degree relatives (848 subjects) met the inclusion criteria. P50 sensory gating ratio (S2/S1) and S1-S2 difference were significantly altered in schizophrenia, bipolar disorder and their first-degree relatives. First-episode psychosis did not differ from schizophrenia, however episodes altered P50 sensory gating in bipolar disorder. Medications improve P50 sensory gating alterations in schizophrenia significantly and at trend level in bipolar disorder. Future studies should examine longitudinal course of P50 sensory gating in schizophrenia and bipolar disorder.

Efficacy and Safety of Varenicline for Smoking Cessation in Schizophrenia: A Meta-Analysis

Objective: Smoking represents a major public health problem among patients with schizophrenia. To this end, some studies have investigated the efficacy of varenicline for facilitating smoking cessation in schizophrenia patients. The present review seeks to synthesize the results of these studies as well as document the reported side effects of using this medication. Methods: An electronic search was performed using five major databases: PubMed, Scopus, EMBASE, Web of Science, and Cochrane Library. Included in the current analysis were randomized clinical trials (RCTs) that have investigated the effect of varenicline in promoting smoking cessation in patients with schizophrenia. Risk of bias among included RCTs was assessed using the Cochrane Collaboration's quality assessment tool. Results: Among the 828 screened articles, only four RCTs, which involved 239 participants, were eligible for meta-analysis. In patients with schizophrenia, varenicline treatment when compared to placebo significantly reduced the number of cigarettes consumed per day [SMD (95% CI) = 0.89(0.57-1.22)] and expired carbon monoxide levels [SMD (95% CI) = 0.50 (0.06-0.94)] respectively. Conclusion: Despite a limited number of studies included in the meta-analysis, our results suggest that varenicline is an effective and safe drug to assist smoking cessation in patients with schizophrenia. Future large-scale well-designed RCTs are required to validate these findings.

Translational utility of rodent hippocampal auditory gating in schizophrenia research: a review and evaluation

Impaired gating of the auditory evoked P50 potential is one of the most pharmacologically well-characterized features of schizophrenia. This deficit is most commonly modeled in rodents by implanted electrode recordings from the hippocampus of the rodent analog of the P50, the P20-N40. The validity and effectiveness of this tool, however, has not been systematically reviewed. Here, we summarize findings from studies that have examined the effects of pharmacologic modulation on gating of the rodent hippocampal P20-N40 and the human P50. We show that drug effects on the P20-N40 are highly predictive of human effects across similar dose ranges. Furthermore, mental status (for example, anesthetized vs alert) does not appear to diminish the predictive capacity of these recordings. We then discuss hypothesized neuropharmacologic mechanisms that may underlie gating effects for each drug studied. Overall, this review supports continued use of hippocampal P20-N40 gating as a translational tool for schizophrenia research.

Dementia praecox redux: a systematic review of the nicotinic receptor as a target for cognitive symptoms of schizophrenia

Most individuals with schizophrenia suffer some cognitive dysfunction: such deficits are predictive of longer-term functioning; and current dopamine-blocking antipsychotics have made little impact on this domain. There is a pressing need to develop novel pharmacological agents to tackle this insidious but most disabling of problems. The acetylcholinergic system is involved in cognitive and attentional processing, and its metabotropic and nicotinic receptors are widespread throughout the brain. Deficits in acetylcholinergic functioning occur in schizophrenia, and high rates of tobacco smoking have been posited to represent a form of self-medication. The nicotinic acetylcholine receptor (nAChR) has emerged as a putative target to improve cognitive deficits in schizophrenia, and this study systematically reviewed the emerging data. Nineteen studies were identified, covering three compound classes: agonists at the α7 and α 4β2 nAChRs, and positive allosteric modulators. Overall data are underwhelming: some studies showed significant improvements in cognition but as many studies had negative findings. It remains unclear if this represents drug limitations or nascent study methodology problems. The literature is particularly hindered by variability in inclusion of smokers, generally small sample sizes, and a lack of consensus on cognitive test batteries. Future work should evaluate longer-term outcomes, and, particularly, the effects of concomitant cognitive training.

Acute effects of mecamylamine and varenicline on cognitive performance in non-smokers with and without schizophrenia

RATIONALE

Nicotinic acetylcholine receptors (nAChRs) have been implicated in the pathophysiology of cognitive deficits in the domains of attention and memory in schizophrenia. While nicotinic agonists and antagonists have been proposed as smoking cessation aids, few comparisons have been made of these agents on cognitive performance in individuals with schizophrenia.

OBJECTIVES

This study investigated the acute effects of a nAChR antagonist, mecamylamine, and partial agonist, varenicline, on cognitive function in non-smokers with and without schizophrenia.

METHODS

Single oral doses of mecamylamine 10 mg, varenicline 1 mg, and placebo were administered 1 week apart in random order to adults with schizophrenia (n = 30) and to healthy volunteers (n = 41) in a double-blind, crossover design. The primary outcome of interest was sustained attention as assessed with hit reaction time variability (HRT-SD) on the identical pairs continuous performance test (CPT-IP).

RESULTS

Mecamylamine worsened performance on CPT-IP HRT-SD, a measure of attention, compared to varenicline in both groups. Performance on mecamylamine was worse than performance on both placebo and varenicline on several additional measures of attention, including CPT-IP hit reaction time (HRT) and random errors at various levels of task difficulty. There was a treatment by diagnosis interaction, such that mecamylamine worsened performance on CPT-IP 2-digit HRT, 3-digit random errors, and 4-digit hit rate compared to placebo and varenicline in participants with schizophrenia; effects not observed in controls.

CONCLUSIONS

These findings support a role for nAChRs in attention and suggest that those with schizophrenia may be particularly sensitive to nAChR blockade.

Long-term improvements in sensory inhibition with gestational choline supplementation linked to α7 nicotinic receptors through studies in Chrna7 null mutation mice

Perinatal choline supplementation has produced several benefits in rodent models, from improved learning and memory to protection from the behavioral effects of fetal alcohol exposure. We have shown that supplemented choline through gestation and lactation produces long-term improvement in deficient sensory inhibition in DBA/2 mice which models a similar deficit in schizophrenia patients. The present study extends that research by feeding normal or supplemented choline diets to DBA/2 mice carrying the null mutation for the α7 nicotinic receptor gene (Chrna7). DBA/2 mice heterozygotic for Chrna7 were bred together. Dams were placed on supplemented (5 gm/kg diet) or normal (1.1 gm/kg diet) choline at mating and remained on the specific diet until offspring weaning. Thereafter, offspring were fed standard rodent chow. Adult offspring were assessed for sensory inhibition. Brains were obtained to ascertain hippocampal α7 nicotinic receptor levels. Choline-supplemented mice heterozygotic or null-mutant for Chrna7 failed to show improvement in sensory inhibition. Only wildtype choline-supplemented mice showed improvement with the effect solely through a decrease in test amplitude. This supports the hypothesis that gestational-choline supplementation is acting through the α7 nicotinic receptor to improve sensory inhibition. Although there was a significant gene-dose-related change in hippocampal α7 receptor numbers, binding studies did not reveal any choline-dose-related change in binding in any hippocampal region, the interaction being driven by a significant genotype main effect (wildtype>heterozygote>null mutant). These data parallel a human study wherein the offspring of pregnant women receiving choline supplementation during gestation, showed better sensory inhibition than offspring of women on placebo.

Muscarinic and nicotinic acetylcholine receptor agonists and allosteric modulators for the treatment of schizophrenia

Muscarinic and nicotinic acetylcholine (ACh) receptors (mAChRs and nAChRs) are emerging as important targets for the development of novel treatments for the symptoms associated with schizophrenia. Preclinical and early proof-of-concept clinical studies have provided strong evidence that activators of specific mAChR (M(1) and M(4)) and nAChR (α(7) and α(2)β(4)) subtypes are effective in animal models of antipsychotic-like activity and/or cognitive enhancement, and in the treatment of positive and cognitive symptoms in patients with schizophrenia. While early attempts to develop selective mAChR and nAChR agonists provided important preliminary findings, these compounds have ultimately failed in clinical development due to a lack of true subtype selectivity and subsequent dose-limiting adverse effects. In recent years, there have been major advances in the discovery of highly selective activators for the different mAChR and nAChR subtypes with suitable properties for optimization as potential candidates for clinical trials. One novel strategy has been to identify ligands that activate a specific receptor subtype through actions at sites that are distinct from the highly conserved ACh-binding site, termed allosteric sites. These allosteric activators, both allosteric agonists and positive allosteric modulators, of mAChR and nAChR subtypes demonstrate unique mechanisms of action and high selectivity in vivo, and may provide innovative treatment strategies for schizophrenia.

A Review of Varenicline's Efficacy and Tolerability in Smoking Cessation Studies in Subjects with Schizophrenia

Schizophrenia is a severe psychiatric disorder affecting 1% of the world's population. Nicotine addiction is one of the most important health concerns for patients with schizophrenia. An extensive body of evidence points to a high prevalence rate of comorbid nicotine addiction in people with schizophrenia (70-90%), which contributes to significant cardiovascular and cancer risks in this vulnerable population. Therefore, effective smoking cessation strategies could play a major role in preventing significant morbidity and mortality in this population. Two of the most common pharmacological approaches to smoking cessation, bupropion and nicotine replacement therapy (NRT), have been used in psychiatric patients to reduce their smoking. In 2006, varenicline, a partial agonist of α4β2 acetylcholine receptor, was approved for smoking cessation by the FDA. This drug not only has the beneficial effects on withdrawal symptoms, but also reduces craving and rewarding effects of smoking. While varenicline has been shown to be an effective, safe medication for the general population, its efficacy and safety for subjects with schizophrenia is less well characterized. A number of case studies have prompted FDA warnings about the potential exacerbation of psychiatric symptoms. However, other case studies and pilot studies have shown varenicline to be a safe and effective treatment for smoking cessation in subjects with schizophrenia. Varenicline has the potential to reduce smoking in subjects with schizophrenia, however, clinicians should carefully monitor patients receiving varenicline for potential exacerbation of psychiatric symptoms.

Varenicline prevents affective and cognitive exacerbation during smoking abstinence in male patients with schizophrenia

To explore the effects of varenicline on the psychopathology and cognition of chronic inpatients with schizophrenia, we conducted a non-randomized control group time series investigation between March 2009 and April 2010. In a mandatory smoking cessation intervention, 41 male inpatient smokers were scheduled to undergo either a 5-week varenicline treatment (varenicline group) or the use of no drugs (non-treatment group). Depression (HAM-D), anxiety (HAM-A), and psychosis (PANSS) were evaluated at baseline, and at the 2nd, 4th, 8th and 12th week after abstinence; four neuropsychological tests, including Digit Span Forward and Backward (DSF and DSB), and Trail Making Test-A and -B, were evaluated at baseline and at the 4th, 8th and 12th week. .Thirty patients completed the study. Among 15 patients in the non-treatment group, the HAM-D, HAM-A, DSF, and DSB scores were exacerbated during the 2-8 weeks of abstinence, but there were no changes in psychotic symptoms and the other two neuropsychological tests. Compared with the non-treatment group, varenicline users experienced less impairment in HAM-D and HAM-A scores at the 2nd and 4th weeks, and in DSF tasks at the 4th week after abstinence. In conclusions, varenicline can attenuate abstinence-induced adverse outcomes and appears to be well-tolerated in smokers with schizophrenia.

Effects of moderate-dose treatment with varenicline on neurobiological and cognitive biomarkers in smokers and nonsmokers with schizophrenia or schizoaffective disorder

CONTEXT

The administration of nicotine transiently improves many neurobiological and cognitive functions in schizophrenia and schizoaffective disorder. It is not yet clear which nicotinic acetylcholine receptor (nAChR) subtype or subtypes are responsible for these seemingly pervasive nicotinic effects in schizophrenia and schizoaffective disorder.

OBJECTIVE

Because α4β2 is a key nAChR subtype for nicotinic actions, we investigated the effect of varenicline tartrate, a relatively specific α4β2 partial agonist and antagonist, on key biomarkers that are associated with schizophrenia and are previously shown to be responsive to nicotinic challenge in humans.

DESIGN

A double-blind, parallel, randomized, placebo-controlled trial of patients with schizophrenia or schizoaffective disorder to examine the effects of varenicline on biomarkers at 2 weeks (short-term treatment) and 8 weeks (long-term treatment), using a slow titration and moderate dosing strategy for retaining α4β2-specific effects while minimizing adverse effects.

SETTING

Outpatient clinics.

PARTICIPANTS

A total of 69 smoking and nonsmoking patients; 64 patients completed week 2, and 59 patients completed week 8. Intervention Varenicline.

MAIN OUTCOME MEASURES

Prepulse inhibition, sensory gating, antisaccade, spatial working memory, eye tracking, processing speed, and sustained attention.

RESULTS

A moderate dose of varenicline (1) significantly reduced the P50 sensory gating deficit in nonsmokers after long-term treatment (P = .006), (2) reduced startle reactivity (P = .02) regardless of baseline smoking status, and (3) improved executive function by reducing the antisaccadic error rate (P = .03) regardless of smoking status. A moderate dose of varenicline had no significant effect on spatial working memory, predictive and maintenance pursuit measures, processing speed, or sustained attention by Conners' Continuous Performance Test. Clinically, there was no evidence of exacerbation of psychiatric symptoms, psychosis, depression, or suicidality using a gradual titration (1-mg daily dose).

CONCLUSIONS

Moderate-dose treatment with varenicline has a unique treatment profile on core schizophrenia-related biomarkers. Further development is warranted for specific nAChR compounds and dosing and duration strategies to target subgroups of schizophrenic patients with specific biological deficits.

Alterations in the expression of neuronal chloride transporters may contribute to schizophrenia

During brain development, neuronal stem cells and immature neurons express high and low levels of, respectively, the Cl(-) transporters NKCC1 and KCC2, which results in high intracellular Cl(-) concentrations. Under these circumstances chloride-flux through the GABA-A channel is from intracellular to extracellular and consequently GABA depolarizes rather than hyperpolarizes immature cells. This excitatory response is essential for neurodevelopment since it affects proliferation of the neuronal progenitor pool, neuronal differentiation, dendrite and synapse formation and integration into the existing neuronal network. In animal experiments, seizures were found to increase NKCC1 expression, lower the KCC2 expression and accelerate neuronal differentiation. An increased expression of NKCC1 and mutations of the gene have been associated with schizophrenia. Stimulation of nicotinic α-7 receptors on mouse hippocampal neurons increases the expression of KCC2. A microdeletion in the genomic area 15q13-14 containing the nicotine α7 receptor has been described in patients with mental retardation, schizophrenia and juvenile epilepsy. It is conceivable that haplotype-insufficiency of the nicotinic α7 receptor might lead to a reduction in KCC2 protein levels. The data indicate that all three schizophrenia risk factors, i.e. seizures, mutations in NKCC1 and nicotinic α-7 receptors haplotype-insufficiency contribute to higher intracellular Cl(-) concentrations, increased neuronal excitability and accelerated neuronal differentiation. Since also several other genetic risk factors for schizophrenia seem to accelerate neuronal maturation, it is hypothesized that the structural, cognitive and behavioral deficits of schizophrenia are caused be a too fast brain maturation process.

A randomised, double-blind, placebo-controlled trial of tropisetron in patients with schizophrenia

BACKGROUND

Cognitive deficits in schizophrenia are associated with psychosocial deficits that are primarily responsible for the poor long-term outcome of this disease. Auditory sensory gating P50 deficits are correlated with neuropsychological deficits in attention, one of the principal cognitive disturbances in schizophrenia. Our studies suggest that the alpha7 nicotinic acetylcholine receptor (alpha7 nAChR) agonist tropisetron might be a potential therapeutic drug for cognitive deficits in schizophrenia. Therefore, it is of particular interest to investigate the effects of tropisetron on the cognitive deficits in patients with schizophrenia.

METHODS

A randomised, placebo-controlled trial of tropisetron in patients with schizophrenia was performed. A total of 40 patients with chronic schizophrenia who had taken risperidone (2 to 6 mg/day) were enrolled. Subjects were randomly assigned to a fixed titration of tropisetron (n = 20, 10 mg/day) or placebo (n = 20) in an 8-week double-blind trial. Auditory sensory gating P50 deficits and Quality of Life Scale (QLS), Cambridge Neuropsychological Test Automated Battery (CANTAB), and Positive and Negative Syndrome Scale (PANSS) scores were measured.

RESULTS

In all, 33 patients completed the trial. Tropisetron was well tolerated. Administration of tropisetron, but not placebo, significantly improved auditory sensory gating P50 deficits in non-smoking patients with schizophrenia. The score on the rapid visual information processing (sustained visual attention) task of CANTAB was significantly improved by tropisetron treatment. Total and subscale scores of PANSS were not changed by this trial. QLS scores in the all patients, but not non-smoking patients, were significantly improved by tropisetron trial.

CONCLUSIONS

This first randomised, double-blind, placebo-controlled trial supports the safety and efficacy of adjunctive tropisetron for treatment of cognitive deficits in schizophrenia.