Importance of the nicotinic acetylcholine receptor system in the prefrontal cortex

Acute Hypobaric Hypoxia Causes Alterations in Acetylcholine-Mediated Signaling Through Varying Expression of Muscarinic Receptors in the Prefrontal Cortex and Cerebellum of Rats' Brain

Sharma, Narendra Kumar, Mansi Srivastava, Tikam Chand Dakal, Vipin Ranga, and Pawan Kumar Maurya. Acute hypobaric hypoxia (HH) causes alterations in acetylcholine-mediated signaling through varying expression of muscarinic receptors in the PFC and cerebellum of rats' brain. High Alt Med Biol. 00:00-00, 2024. Background: Muscarinic receptor (CHRM) proteins are G-protein-associated acetylcholine receptors found in neuronal membranes. Five major subtypes, CHRM1-CHRM5, modulate acetylcholine in central nervous system signaling cascades. CHRM1, CHRM3, and CHRM5 are linked to Gαq/Gα11 proteins, whereas CHRM2 and CHRM4 are linked to Gαi/Gαo proteins. Objective: Limited research has been conducted to explore the impact of HH on CHRM gene expressions. It is caused by low oxygen availability at high altitudes, which impairs neurotransmission, cognitive performance, and physiological functions. Previous studies have shown that exposure to hypoxia leads to a reduction in CHRM receptors, which in turn causes alteration in signal transduction, physiological responses, cognitive deficits, and mood alterations. Method: In the present study, we have used semiquantitative PCR to measure muscarinic receptor gene expression after 6, 12, and 24 hours of HH exposure at 25,000 feet using a decompression chamber in rat brain's PFC and cerebellum. Result: We have found that CHRM1-CHRM5 downregulated after acute exposure to hypoxia until 12 hours, and then, the expression level of these receptors increased to 24 hours when compared with 12 hours in PFC. All subtypes have shown a similar pattern in PFC regions under hypoxia exposure. On the other hand, these receptors have shown altered expression at different time points in the cerebellum. CHRM1 and CHRM4 acutely downregulated, CHRM2 and CHRM5 downregulated, while CHRM3 upregulated after hypoxia exposure. Conclusion: Our study, for the first time, has shown the altered expressions of muscarinic receptors under temporal hypoxia exposure. The altered expression pattern has shown an association with acclimatization and protection against necrosis due to hypoxia. This study may pave further investigations for understanding and addressing the cognitive, behavioral, and physiological impacts of hypoxia and therapeutic development.

Developmental exposure to arsenic reduces anxiety levels and leads to a depressive-like behavior in female offspring rats: Molecular changes in the prefrontal cortex

Exposure to inorganic arsenic (iAs) detrimentally affects the structure and function of the central nervous system. In-utero and postnatal exposure to iAs has been connected to adverse effects on cognitive development. Therefore, this investigation explores neurobehavioral and neurochemical effects of 0.05 and 0.10 mg/L iAs exposure during gestation and lactation periods on 90-day-old female offspring rats. The assessment of anxiety- and depressive-like behaviors was conducted through the application of an elevated plus maze and a forced swim test. The neurochemical changes were evaluated in the prefrontal cortex (PFC) through the determination of enzyme activities and α1 GABAA subunit expression levels. Our findings revealed a notable impact of iAs exposure on anxiety and the induction of depressive-like behavior in 90-day-old female offspring. Furthermore, the antioxidant status within the PFC exhibited discernible alterations in exposed rats. Notably, the activities of acetylcholinesterase and glutamate pyruvate transaminase demonstrated an increase, while glutamate oxaloacetate transaminase activity displayed a decrease within the PFC due to the iAs treatment. Additionally, a distinct downregulation in the mRNA expression of the α1GABAA receptor was observed in this neuronal region. These findings strongly suggest that iAs exposure during early stages of rat development causes significant modifications in brain oxidative stress markers and perturbs the activity of enzymes associated with cholinergic and glutamatergic systems. In parallel, it elicits a discernible reduction in the level of GABA receptors within the PFC. These molecular alterations may play a role in the diminished anxiety levels and the depressive-like behavior outlined in the current investigation.

IGF1R and FLT1 in female endothelial cells and CHD2 in male microglia play important roles in Alzheimer's disease based on gender difference analysis

OBJECTIVE

This study investigated sex-specific pathogenesis mechanisms in Alzheimer's disease (AD) using single-nucleus RNA sequencing (snRNA-seq) data.

METHODS

Data from the Gene Expression Omnibus (GEO) were searched using terms "Alzheimer's Disease", "single cell", and "Homo sapiens". Studies excluding APOE E4 and including comprehensive gender information with 10× sequencing methods were selected, resulting in GSE157827 and GSE174367 datasets from human prefrontal cortex samples. Sex-stratified analyses were conducted on these datasets, and the outcomes of the analysis for GSE157827 were compared with those of GSE174367. The findings were validated using expression profiling from the mouse dataset GSE85162. Furthermore, real-time PCR experiments in mice further confirmed these findings. The Seurat R package was used to identify cell types, and batch effects were mitigated using the Harmony R package. Cell proportions by sex were compared using the Mann-Whitney-Wilcoxon test, and gene expression variability was displayed with an empirical cumulative distribution plot. Differentially expressed genes were identified using the FindMarkers function with the MAST test. Transcription factors were analyzed using the RcisTarget R package.

RESULTS

Seven cell types were identified: astrocytes, endothelial cells, excitatory neurons, inhibitory neurons, microglia, oligodendrocytes, and oligodendrocyte progenitor cells. Additionally, five distinct subpopulations of both endothelial and microglial cells were also identified, respectively. Key findings included: (1) In endothelial cells, genes involved in synapse organization, such as Insulin Like Growth Factor 1 Receptor (IGF1R) and Fms Related Receptor Tyrosine Kinase 1(FLT1), showed higher expression in females with AD. (2) In microglial cells, genes in the ribosome pathway exhibited higher expression in males without AD compared to females (with or without AD) and males with AD. (3) Chromodomain Helicase DNA Binding Protein 2 (CHD2) negatively regulated gene expression in the ribosome pathway in male microglia, suppressing AD, this finding was further validated in mice. (4) Differences between Asians and Caucasians were observed based on sex and disease status stratification.

CONCLUSIONS

IGF1R and FLT1 in endothelial cells contribute to AD in females, while CHD2 negatively regulates ribosome pathway gene expression in male microglia, suppressing AD in humans and mice.

Channelopathies in epilepsy: an overview of clinical presentations, pathogenic mechanisms, and therapeutic insights

Pathogenic variants in genes encoding ion channels are causal for various pediatric and adult neurological conditions. In particular, several epilepsy syndromes have been identified to be caused by specific channelopathies. These encompass a spectrum from self-limited epilepsies to developmental and epileptic encephalopathies spanning genetic and acquired causes. Several of these channelopathies have exquisite responses to specific antiseizure medications (ASMs), while others ASMs may prove ineffective or even worsen seizures. Some channelopathies demonstrate phenotypic pleiotropy and can cause other neurological conditions outside of epilepsy. This review aims to provide a comprehensive exploration of the pathophysiology of seizure generation, ion channels implicated in epilepsy, and several genetic epilepsies due to ion channel dysfunction. We outline the clinical presentation, pathogenesis, and the current state of basic science and clinical research for these channelopathies. In addition, we briefly look at potential precision therapy approaches emerging for these disorders.

A Molecular Framework for Delirium

Over 2.6 million adults over the age of 65 develop delirium each year in the United States (US). Delirium is associated with a significant increase in mortality and the US health care costs associated with delirium are estimated at over $164 billion annually. Despite the prevalence of the condition, the molecular pathophysiology of delirium remains unexplained, limiting the development of pharmacotherapies. Delirious patients can be identified by prominent impairments in attention and working memory (WM), two cognitive domains that localize to the dorsolateral prefrontal cortex (dlPFC). The dlPFC is also a key site for Alzheimer's disease (AD) pathology, and given the high risk of delirium in AD patients, suggests that efforts at understanding delirium might focus on the dlPFC as a final common endpoint for cognitive changes. Preclinical studies of the dlPFC reproduce many of the pharmacological observations made of delirious patients, including sensitivity to anticholinergics and an 'inverted U' pattern of dependence on monoaminergic input, with diminished performance outside a narrow range of signaling. Medications like guanfacine, which influence the dlPFC in the context of attention-deficit/hyperactivity disorder (ADHD), have emerged as therapies for delirium and motivate a detailed understanding of the influence of α-2 agonists on WM. In this review, I will discuss the neural circuitry and molecular mechanisms underlying WM and the function of the dlPFC. Localizing the cognitive deficits that are commonly seen in delirious patients may help identify new molecular targets for this highly prevalent disease.

Integrated use of biofeedback and neurofeedback techniques in treating pathological conditions and improving performance: a narrative review

In recent years, the scientific community has begun tо explore the efficacy оf an integrated neurofeedback + biofeedback approach іn various conditions, both pathological and non-pathological. Although several studies have contributed valuable insights into its potential benefits, this review aims tо further investigate its effectiveness by synthesizing current findings and identifying areas for future research. Our goal іs tо provide a comprehensive overview that may highlight gaps іn the existing literature and propose directions for subsequent studies. The search for articles was conducted on the digital databases PubMed, Scopus, and Web of Science. Studies to have used the integrated neurofeedback + biofeedback approach published between 2014 and 2023 and reviews to have analyzed the efficacy of neurofeedback and biofeedback, separately, related to the same time interval and topics were selected. The search identified five studies compatible with the objectives of the review, related to several conditions: nicotine addiction, sports performance, Autism Spectrum Disorder (ASD), and Attention Deficit Hyperactivity Disorder (ADHD). The integrated neurofeedback + biofeedback approach has been shown to be effective in improving several aspects of these conditions, such as a reduction in the presence of psychiatric symptoms, anxiety, depression, and withdrawal symptoms and an increase in self-esteem in smokers; improvements in communication, imitation, social/cognitive awareness, and social behavior in ASD subjects; improvements in attention, alertness, and reaction time in sports champions; and improvements in attention and inhibitory control in ADHD subjects. Further research, characterized by greater methodological rigor, is therefore needed to determine the effectiveness of this method and the superiority, if any, of this type of training over the single administration of either. This review іs intended tо serve as a catalyst for future research, signaling promising directions for the advancement оf biofeedback and neurofeedback methodologies.

Nicotinic acetylcholine receptors and learning and memory deficits in Neuroinflammatory diseases

Animal survival depends on cognitive abilities such as learning and memory to adapt to environmental changes. Memory functions require an enhanced activity and connectivity of a particular arrangement of engram neurons, supported by the concerted action of neurons, glia, and vascular cells. The deterioration of the cholinergic system is a common occurrence in neurological conditions exacerbated by aging such as traumatic brain injury (TBI), posttraumatic stress disorder (PTSD), Alzheimer's disease (AD), and Parkinson's disease (PD). Cotinine is a cholinergic modulator with neuroprotective, antidepressant, anti-inflammatory, antioxidant, and memory-enhancing effects. Current evidence suggests Cotinine's beneficial effects on cognition results from the positive modulation of the α7-nicotinic acetylcholine receptors (nAChRs) and the inhibition of the toll-like receptors (TLRs). The α7nAChR affects brain functions by modulating the function of neurons, glia, endothelial, immune, and dendritic cells and regulates inhibitory and excitatory neurotransmission throughout the GABA interneurons. In addition, Cotinine acting on the α7 nAChRs and TLR reduces neuroinflammation by inhibiting the release of pro-inflammatory cytokines by the immune cells. Also, α7nAChRs stimulate signaling pathways supporting structural, biochemical, electrochemical, and cellular changes in the Central nervous system during the cognitive processes, including Neurogenesis. Here, the mechanisms of memory formation as well as potential mechanisms of action of Cotinine on memory preservation in aging and neurological diseases are discussed.

Unanswered questions in the regulation and function of the duplicated α7 nicotinic receptor gene CHRFAM7A

The α7 nicotinic receptor (α7 nAChR) is an important entry point for Ca²⁺ into the cell, which has broad and important effects on gene expression and function. The gene (CHRNA7), mapping to chromosome (15q14), has been genetically linked to a large number of diseases, many of which involve defects in cognition. While numerous mutations in CHRNA7 are associated with mental illness and inflammation, an important control point may be the function of a recently discovered partial duplication CHRNA7, CHRFAM7A, that negatively regulates the function of the α7 receptor, through the formation of heteropentamers; other functions cannot be excluded. The deregulation of this human specific gene (CHRFAM7A) has been linked to neurodevelopmental, neurodegenerative, and inflammatory disorders and has important copy number variations. Much effort is being made to understand its function and regulation both in healthy and pathological conditions. However, many questions remain to be answered regarding its functional role, its regulation, and its role in the etiogenesis of neurological and inflammatory disorders. Missing knowledge on the pharmacology of the heteroreceptor has limited the discovery of new molecules capable of modulating its activity. Here we review the state of the art on the role of CHRFAM7A, highlighting unanswered questions to be addressed. A possible therapeutic approach based on genome editing protocols is also discussed.

Nicotine pretreatment alleviates MK-801-induced behavioral and cognitive deficits in mice by regulating Pdlim5/CRTC1 in the PFC

Increasing evidence shows that smoking-obtained nicotine is indicated to improve cognition and mitigate certain symptoms of schizophrenia. In this study, we investigated whether chronic nicotine treatment alleviated MK-801-induced schizophrenia-like symptoms and cognitive impairment in mice. Mice were injected with MK-801 (0.2 mg/kg, i.p.), and the behavioral deficits were assessed using prepulse inhibition (PPI) and T-maze tests. We showed that MK-801 caused cognitive impairment accompanied by increased expression of PDZ and LIM domain 5 (Pdlim5), an adaptor protein that is critically associated with schizophrenia, in the prefrontal cortex (PFC). Pretreatment with nicotine (0.2 mg · kg-1 · d-1, s.c., for 2 weeks) significantly ameliorated MK-801-induced schizophrenia-like symptoms and cognitive impairment by reversing the increased Pdlim5 expression levels in the PFC. In addition, pretreatment with nicotine prevented the MK-801-induced decrease in CREB-regulated transcription coactivator 1 (CRTC1), a coactivator of CREB that plays an important role in cognition. Furthermore, MK-801 neither induced schizophrenia-like behaviors nor decreased CRTC1 levels in the PFC of Pdlim5-/- mice. Overexpression of Pdlim5 in the PFC through intra-PFC infusion of an adreno-associated virus AAV-Pdlim5 induced significant schizophrenia-like symptoms and cognitive impairment. In conclusion, chronic nicotine treatment alleviates schizophrenia-induced memory deficits in mice by regulating Pdlim5 and CRTC1 expression in the PFC.

Nicotinic acetylcholine receptors and epilepsy

Despite recent advances in understanding the causes of epilepsy, especially the genetic, comprehending the biological mechanisms that lead to the epileptic phenotype remains difficult. A paradigmatic case is constituted by the epilepsies caused by altered neuronal nicotinic acetylcholine receptors (nAChRs), which exert complex physiological functions in mature as well as developing brain. The ascending cholinergic projections exert potent control of forebrain excitability, and wide evidence implicates nAChR dysregulation as both cause and effect of epileptiform activity. First, tonic-clonic seizures are triggered by administration of high doses of nicotinic agonists, whereas non-convulsive doses have kindling effects. Second, sleep-related epilepsy can be caused by mutations on genes encoding nAChR subunits widely expressed in the forebrain (CHRNA4, CHRNB2, CHRNA2). Third, in animal models of acquired epilepsy, complex time-dependent alterations in cholinergic innervation are observed following repeated seizures. Heteromeric nAChRs are central players in epileptogenesis. Evidence is wide for autosomal dominant sleep-related hypermotor epilepsy (ADSHE). Studies of ADSHE-linked nAChR subunits in expression systems suggest that the epileptogenic process is promoted by overactive receptors. Investigation in animal models of ADSHE indicates that expression of mutant nAChRs can lead to lifelong hyperexcitability by altering i) the function of GABAergic populations in the mature neocortex and thalamus, ii) synaptic architecture during synaptogenesis. Understanding the balance of the epileptogenic effects in adult and developing networks is essential to plan rational therapy at different ages. Combining this knowledge with a deeper understanding of the functional and pharmacological properties of individual mutations will advance precision and personalized medicine in nAChR-dependent epilepsy.

Does combined training of biofeedback and neurofeedback affect smoking status, behavior, and longitudinal brain plasticity?

Introduction: Investigations of biofeedback (BF) and neurofeedback (NF) training for nicotine addiction have been long documented to lead to positive gains in smoking status, behavior and to changes in brain activity. We aimed to: (a) evaluate a multi-visit combined BF/NF intervention as an alternative smoking cessation approach, (b) validate training-induced feedback learning, and (c) document effects on resting-state functional connectivity networks (rsFCN); considering gender and degree of nicotine dependence in a longitudinal design. Methods: We analyzed clinical, behavioral, and electrophysiological data from 17 smokers who completed five BF and 20 NF sessions and three evaluation stages. Possible neuroplastic effects were explored comparing whole-brain rsFCN by phase-lag index (PLI) for different brain rhythms. PLI connections with significant change across time were investigated according to different resting-state networks (RSNs). Results: Improvements in smoking status were observed as exhaled carbon monoxide levels, Total Oxidative Stress, and Fageström scores decreased while Vitamin E levels increased across time. BF/NF promoted gains in anxiety, self-esteem, and several aspects of cognitive performance. BF learning in temperature enhancement was observed within sessions. NF learning in theta/alpha ratio increase was achieved across baselines and within sessions. PLI network connections significantly changed across time mainly between or within visual, default mode and frontoparietal networks in theta and alpha rhythms, while beta band RSNs mostly changed significantly after BF sessions. Discussion: Combined BF/NF training positively affects the clinical and behavioral status of smokers, displays benefit in smoking harm reduction, plays a neuroprotective role, leads to learning effects and to positive reorganization of RSNs across time. Clinical Trial Registration: https://clinicaltrials.gov/ct2/show/NCT02991781.

Impact of Nicotine on Cognition in Patients With Schizophrenia: A Narrative Review

Nicotine is the psychoactive component given tobacco has several main components and acts as an agonist for nicotinic acetylcholine receptors (nAChRs) in the nervous system. Although the ligand-gated cation channels known as nAChRs are found throughout the nervous system and body, this review focuses on neuronal nAChRs. Individuals with psychiatric diseases such as schizophrenia, comorbid substance use disorders, attention-deficit hyperactivity disorder, major depression, and bipolar disorder have increased rates of smoking. These psychiatric disorders are associated with various cognitive deficits, including working memory, deficits in attention, and response inhibition functions. The cognitive-enhancing effects of nicotine may be particularly relevant predictors of smoking initiation and continuation in this comorbid population. Individuals with schizophrenia make up a significant proportion of smokers. Literature suggests that patients smoke to alleviate cognitive deficiencies due to the stimulating effects of nicotine. This narrative review examines the role of nicotine on cognition in schizophrenia.

Nicotinic acetylcholine receptors in a songbird brain

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that mediate fast synaptic transmission and cell signaling, which contribute to learning, memory, and the execution of motor skills. Birdsong is a complex learned motor skill in songbirds. Although the existence of 15 nAChR subunits has been predicted in the avian genome, their expression patterns and potential contributions to song learning and production have not been comprehensively investigated. Here, we cloned all the 15 nAChR subunits (ChrnA1-10, B2-4, D, and G) from the zebra finch brain and investigated the mRNA expression patterns in the neural pathways responsible for the learning and production of birdsong during a critical period of song learning. Although there were no detectable hybridization signals for ChrnA1, A6, A9, and A10, the other 11 nAChR subunits were uniquely expressed in one or more major subdivisions in the song nuclei of the songbird brain. Of these 11 subunits, ChrnA3-5, A7, and B2 were differentially regulated in the song nuclei compared with the surrounding anatomically related regions. ChrnA5 was upregulated during the critical period of song learning in the lateral magnocellular nucleus of the anterior nidopallium. Furthermore, single-cell RNA sequencing revealed ChrnA7 and B2 to be the major subunits expressed in neurons of the vocal motor nuclei HVC and robust nucleus of the arcopallium, indicating the potential existence of ChrnA7-homomeric and ChrnB2-heteromeric nAChRs in limited cell populations. These results suggest that relatively limited types of nAChR subunits provide functional contributions to song learning and production in songbirds.

Personalized Management and Treatment of Alzheimer's Disease

Alzheimer’s disease (AD) is a priority health problem with a high cost to society and a large consumption of medical and social resources. The management of AD patients is complex and multidisciplinary. Over 90% of patients suffer from concomitant diseases and require personalized therapeutic regimens to reduce adverse drug reactions (ADRs), drug−drug interactions (DDIs), and unnecessary costs. Men and women show substantial differences in their AD-related phenotypes. Genomic, epigenetic, neuroimaging, and biochemical biomarkers are useful for predictive and differential diagnosis. The most frequent concomitant diseases include hypertension (>25%), obesity (>70%), diabetes mellitus type 2 (>25%), hypercholesterolemia (40%), hypertriglyceridemia (20%), metabolic syndrome (20%), hepatobiliary disorder (15%), endocrine/metabolic disorders (>20%), cardiovascular disorder (40%), cerebrovascular disorder (60−90%), neuropsychiatric disorders (60−90%), and cancer (10%). Over 90% of AD patients require multifactorial treatments with risk of ADRs and DDIs. The implementation of pharmacogenetics in clinical practice can help optimize the limited therapeutic resources available to treat AD and personalize the use of anti-dementia drugs, in combination with other medications, for the treatment of concomitant disorders.

Pharmacogenomics of Alzheimer's Disease: Novel Strategies for Drug Utilization and Development

Alzheimer's disease (AD) is a priority health problem in developed countries with a high cost to society. Approximately 20% of direct costs are associated with pharmacological treatment. Over 90% of patients require multifactorial treatments, with risk of adverse drug reactions (ADRs) and drug-drug interactions (DDIs) for the treatment of concomitant diseases such as hypertension (>25%), obesity (>70%), diabetes mellitus type 2 (>25%), hypercholesterolemia (40%), hypertriglyceridemia (20%), metabolic syndrome (20%), hepatobiliary disorder (15%), endocrine/metabolic disorders (>20%), cardiovascular disorder (40%), cerebrovascular disorder (60-90%), neuropsychiatric disorders (60-90%), and cancer (10%).For the past decades, pharmacological studies in search of potential treatments for AD focused on the following categories: neurotransmitter enhancers (11.38%), multitarget drugs (2.45%), anti-amyloid agents (13.30%), anti-tau agents (2.03%), natural products and derivatives (25.58%), novel synthetic drugs (8.13%), novel targets (5.66%), repository drugs (11.77%), anti-inflammatory drugs (1.20%), neuroprotective peptides (1.25%), stem cell therapy (1.85%), nanocarriers/nanotherapeutics (1.52%), and other compounds (<1%).Pharmacogenetic studies have shown that the therapeutic response to drugs in AD is genotype-specific in close association with the gene clusters that constitute the pharmacogenetic machinery (pathogenic, mechanistic, metabolic, transporter, pleiotropic genes) under the regulatory control of epigenetic mechanisms (DNA methylation, histone/chromatin remodeling, microRNA regulation). Most AD patients (>60%) are carriers of over ten pathogenic genes. The genes that most frequently (>50%) accumulate pathogenic variants in the same AD case are A2M (54.38%), ACE (78.94%), BIN1 (57.89%), CLU (63.15%), CPZ (63.15%), LHFPL6 (52.63%), MS4A4E (50.87%), MS4A6A (63.15%), PICALM (54.38%), PRNP (80.7059), and PSEN1 (77.19%). There is also an accumulation of 15 to 26 defective pharmagenes in approximately 85% of AD patients. About 50% of AD patients are carriers of at least 20 mutant pharmagenes, and over 80% are deficient metabolizers for the most common drugs, which are metabolized via the CYP2D6, CYP2C9, CYP2C19, and CYP3A4/5 enzymes.The implementation of pharmacogenetics can help optimize drug development and the limited therapeutic resources available to treat AD, and personalize the use of anti-dementia drugs in combination with other medications for the treatment of concomitant disorders.

Metabolomics Analysis of the Prefrontal Cortex in a Rat Chronic Unpredictable Mild Stress Model of Depression

BACKGROUND

Depressive disorder is the leading cause of disability and suicidality worldwide. Metabolites are considered indicators and regulators of depression. However, the pathophysiology of the prefrontal cortex (PFC) in depression remains unclear.

METHODS

A chronic unpredictable mild stress (CUMS) model and a maturation rodent model of depression was used to investigate metabolic changes in the PFC. Eighteen male Sprague-Dawley rats were randomly divided into CUMS and control groups. The sucrose preference test (SPT) and forced swimming test (FST) were employed to evaluate and record depression-associated behaviors and changes in body weight (BW). High-performance liquid chromatography-tandem mass spectrometry was applied to test metabolites in rat PFC. Furthermore, principal component analysis and orthogonal partial least-squares discriminant analysis were employed to identify differentially abundant metabolites. Metabolic pathways were analyzed using MetaboAnalyst. Finally, a metabolite-protein interaction network was established to illustrate the function of differential metabolites.

RESULTS

SPT and FST results confirmed successful establishment of the CUMS-induced depression-like behavior model in rats. Five metabolites, including 1-methylnicotinamide, 3-methylhistidine, acetylcholine, glycerophospho-N-palmitoyl ethanolamine, α-D-mannose 1-phosphate, were identified as potential biomarkers of depression. Four pathways changed in the CUMS group. Metabolite-protein interaction analysis revealed that 10 pathways play roles in the metabolism of depression.

CONCLUSION

Five potential biomarkers were identified in the PFC and metabolite-protein interactions associated with metabolic pathophysiological processes were explored using the CUMS model. The results of this study will assist physicians and scientists in discovering potential diagnostic markers and novel therapeutic targets for depression.

The molecular mechanism, targets, and novel molecules in the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurological illness that causes dementia mainly in the elderly. The challenging obstacles related to AD has freaked global healthcare system to encourage scientists in developing novel therapeutic startegies to overcome with the fatal disease. The current treatment therapy of AD provides only symptomatic relief and to some extent disease-modifying effects. The current approach for AD treatment involves designing of cholinergic inhibitors, Aβ disaggregation inducing agents, tau inhibitors and several antioxidants. Hence, extensive research on AD therapy urgently requires a deep understanding of its pathophysiology and exploration of various chemical scaffolds to design and develop a potential drug candidate for the treatment. Various issues linked between disease and therapy need to be considered such as BBB penetration capability, clinical failure and multifaceted pathophisiology requires a proper attention to develop a lead candidate. This review article covers all probable mechanisms including one of the recent areas for investigation i.e., lipid dyshomeostasis, pathogenic involvement of P. gingivalis and neurovascular dysfunction, recently reported molecules and drugs under clinical investigations and approved by FDA for AD treatment. Our summarized information on AD will attract the researchers to understand and explore current status and structural modifications of the recently reported heterocyclic derivatives in drug development for AD therapy.

Antagonistic Mechanism of α-Conotoxin BuIA toward the Human α3β2 Nicotinic Acetylcholine Receptor

Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels that are abundantly expressed in the central and peripheral nervous systems, playing an important role in mediating neurotransmitter release and inter-synaptic signaling. Dysfunctional nAChRs are associated with neurological disorders, and studying the structure and function of nAChRs is essential for development of drugs or strategies for treatment of related diseases. α-Conotoxins are selective antagonists of the nAChR and are an important class of drug leads. So far, the antagonistic mechanism of α-conotoxins toward the nAChRs is still unclear. In this study, we built an α3β2 nAChR homology model and investigated its conformational transition mechanism upon binding with a highly potent inhibitor, α-conotoxin BuIA, through μs molecular dynamic simulations and site-directed mutagenesis studies. The results suggested that the α3β2 nAChR underwent global conformational transitions and was stabilized into a closed state with three hydrophobic gates present in the transmembrane domain by BuIA. Finally, the probable antagonistic mechanism of BuIA was proposed. Overall, the closed-state model of the α3β2 nAChR bound with BuIA is not only essential for understanding the antagonistic mechanism of α-conotoxins but also particularly valuable for development of therapeutic inhibitors in future.

Acute effects of inhaled menthol on cognitive effects of intravenous nicotine among young adult cigarette smokers

Basic science studies indicate that menthol can enhance the cognitive effects of nicotine to increase nicotine dependence; however, the effect of menthol and nicotine on cognitive functioning among humans has been understudied. This double-blind, placebo-controlled study examined the dose-dependent effects of inhaled menthol flavoring and intravenous nicotine on cognitive task performance. Twenty menthol (MS) and 18 non-menthol (NMS) cigarette preferring, young-adult smokers (21% female; 7.9% Hispanic, 44.7% Non-Hispanic/White, 47.4% Non-Hispanic/Black) completed three sessions with randomized order of menthol flavoring (between-sessions: 0.0%/tobacco control, 0.5%/low, 3.2%/high) and intravenous nicotine (within-session: 0.0 mg/saline control, 0.25 mg/low, 0.5 mg/high). After each administration, participants completed three cognitive tasks: Continuous Performance Task (CPT), Mathematical Processing Task (MPT), and Stroop Task. Mixed effects models were used to examine interactive effects of cigarette type preference and menthol and nicotine doses. MS vs. NMS had decreased accuracy on CPT and MPT and efficiency during Stroop. No significant effects of cigarette type preference by menthol or nicotine were found for any task. Significant effects of nicotine by menthol were found during Stroop, where participants had greater accuracy for high nicotine compared to saline during the low menthol session. Significant effects of menthol by timepoint were seen during Stroop, where participants improved across timepoints during the low menthol session. Findings did not support significant effects of inhaled menthol, alone or with nicotine, on cognitive performance. Further research clarifying the impact of varying menthol and nicotine levels in nicotine products may help to elucidate menthol's role in smoking sustainment.

Pursuing High-Resolution Structures of Nicotinic Acetylcholine Receptors: Lessons Learned from Five Decades

Since their discovery, nicotinic acetylcholine receptors (nAChRs) have been extensively studied to understand their function, as well as the consequence of alterations leading to disease states. Importantly, these receptors represent pharmacological targets to treat a number of neurological and neurodegenerative disorders. Nevertheless, their therapeutic value has been limited by the absence of high-resolution structures that allow for the design of more specific and effective drugs. This article offers a comprehensive review of five decades of research pursuing high-resolution structures of nAChRs. We provide a historical perspective, from initial structural studies to the most recent X-ray and cryogenic electron microscopy (Cryo-EM) nAChR structures. We also discuss the most relevant structural features that emerged from these studies, as well as perspectives in the field.

Copper, Iron, Selenium and Lipo-Glycemic Dysmetabolism in Alzheimer's Disease

The aim of the present review is to discuss traditional hypotheses on the etiopathogenesis of Alzheimer's disease (AD), as well as the role of metabolic-syndrome-related mechanisms in AD development with a special focus on advanced glycation end-products (AGEs) and their role in metal-induced neurodegeneration in AD. Persistent hyperglycemia along with oxidative stress results in increased protein glycation and formation of AGEs. The latter were shown to possess a wide spectrum of neurotoxic effects including increased Aβ generation and aggregation. In addition, AGE binding to receptor for AGE (RAGE) induces a variety of pathways contributing to neuroinflammation. The existing data also demonstrate that AGE toxicity seems to mediate the involvement of copper (Cu) and potentially other metals in AD pathogenesis. Specifically, Cu promotes AGE formation, AGE-Aβ cross-linking and up-regulation of RAGE expression. Moreover, Aβ glycation was shown to increase prooxidant effects of Cu through Fenton chemistry. Given the role of AGE and RAGE, as well as metal toxicity in AD pathogenesis, it is proposed that metal chelation and/or incretins may slow down oxidative damage. In addition, selenium (Se) compounds seem to attenuate the intracellular toxicity of the deranged tau and Aβ, as well as inhibiting AGE accumulation and metal-induced neurotoxicity.

Differential effects of alkaloids on memory in rodents

Nicotinic acetylcholine receptors (nAChRs) play a critical role in the neuropharmacology of learning and memory. As such, naturally occurring alkaloids that regulate nAChR activity have gained interest for understanding and potentially improving memory function. In this study, we tested the acute effects of three known nicotinic alkaloids, nicotine, cotinine, and anatabine, in suppressing scopolamine-induced memory deficit in rodents by using two classic memory paradigms, Y-maze and novel object recognition (NOR) in mice and rats, respectively. We found that all compounds were able to suppress scopolamine-induced spatial memory deficit in the Y-maze spontaneous alternation paradigm. However, only nicotine was able to suppress the short-term object memory deficit in NOR, despite the higher doses of cotinine and anatabine used to account for their potential differences in nAChR activity. These results indicate that cotinine and anatabine can uniquely regulate short-term spatial memory, while nicotine seems to have more robust and general role in memory regulation in rodents. Thus, nAChR-activating alkaloids may possess distinct procognitive properties in rodents, depending on the memory types examined.

Nicotinic Acetylcholine Receptor α7 Subunit Is an Essential Regulator of Seizure Susceptibility

A large body of data has confirmed that α7 nicotinic acetylcholine receptors (nAChRs) play a pivotal role in cognition, memory, and other neuropsychiatric diseases, but their effect on seizure susceptibility in C57BL/6 wild-type mice is not fully understood. Here, we showed that decreased activity of α7 nAChRs could increase the excitability of CA1 pyramidal neurons and shorten the onset time of epilepsy in pilocarpine-induced mouse models. However, compared with the control group, there was no apparent effect of increasing the activity of α7 nAChRs. Moreover, the expression of α7 nAChRs is downregulated in human epileptogenic tissues. Taken together, our findings indicate that α7 nAChR is an essential regulator of seizure susceptibility.

The Potential Role of miRNAs as Predictive Biomarkers in Neurodevelopmental Disorders

Neurodevelopmental disorders are defined as a set of abnormal brain developmental conditions marked by the early childhood onset of cognitive, behavioral, and functional deficits leading to memory and learning problems, emotional instability, and impulsivity. Autism spectrum disorder, attention-deficit/hyperactivity disorder, Tourette syndrome, fragile X syndrome, and Down's syndrome are a few known examples of neurodevelopmental disorders. Although they are relatively common in both developed and developing countries, very little is currently known about their underlying molecular mechanisms. Both genetic and environmental factors are known to increase the risk of neurodevelopmental disorders. Current diagnostic and screening tests for neurodevelopmental disorders are not reliable; hence, individuals with neurodevelopmental disorders are often diagnosed in the later stages. This negatively affects their prognosis and quality of life, prompting the need for a better diagnostic biomarker. Recent studies on microRNAs and their altered regulation in diseases have shed some light on the possible role they could play in the development of the central nervous system. This review attempts to elucidate our current understanding of the role that microRNAs play in neurodevelopmental disorders with the hope of utilizing them as potential biomarkers in the future.

Neuromodulation of Persistent Activity and Working Memory Circuitry in Primate Prefrontal Cortex by Muscarinic Receptors

Neuromodulation by acetylcholine plays a vital role in shaping the physiology and functions of cerebral cortex. Cholinergic neuromodulation influences brain-state transitions, controls the gating of cortical sensory stimulus responses, and has been shown to influence the generation and maintenance of persistent activity in prefrontal cortex. Here we review our current understanding of the role of muscarinic cholinergic receptors in primate prefrontal cortex during its engagement in the performance of working memory tasks. We summarize the localization of muscarinic receptors in prefrontal cortex, review the effects of muscarinic neuromodulation on arousal, working memory and cognitive control tasks, and describe the effects of muscarinic M1 receptor stimulation and blockade on the generation and maintenance of persistent activity of prefrontal neurons encoding working memory representations. Recent studies describing the pharmacological effects of M1 receptors on prefrontal persistent activity demonstrate the heterogeneity of muscarinic actions and delineate unexpected modulatory effects discovered in primate prefrontal cortex when compared with studies in rodents. Understanding the underlying mechanisms by which muscarinic receptors regulate prefrontal cognitive control circuitry will inform the search of muscarinic-based therapeutic targets in the treatment of neuropsychiatric disorders.

Efficacy of nicotine administration on obsessions and compulsions in OCD: a systematic review

BACKGROUND

Preliminary studies have tested nicotine as a novel treatment for OCD patients who respond partially/incompletely or not at all to first and second-line treatment strategies, with the former represented by SSRIs or clomipramine, and the latter by switching to another SSRI, or augmentation with atypical antipsychotics, and/or combination with/switching to cognitive-behavioural therapy. Some studies found nicotine-induced reduction of obsessive thoughts and/or compulsive behaviour in OCD patients. We aimed to evaluate the efficacy of nicotine administration in OCD patients.

METHODS

We searched the PubMed, ScienceDirect Scopus, CINHAL, Cochrane, PsycINFO/PsycARTICLES, and EMBASE databases from inception to the present for relevant papers. The 'Preferred Reporting Items for Systematic Review and Meta-Analyses' (PRISMA) standards were used. We included all studies focusing on the effects of nicotine administration on OCD patients' obsessions or compulsions. Studies could be open-label, cross-sectional, randomized controlled trials, case series or case reports.

RESULTS

A total of five studies could be included. Nicotine administration may ameliorate behavioural features and recurrent thoughts of severe, treatment-resistant OCD patients; however, in one study it was not associated with OC symptom improvement or cognitive enhancement across various executive function subdomains.

CONCLUSIONS

Although encouraging, the initial positive response from the use of nicotine in OCD needs testing in large controlled studies. This, however, raises ethical issues related to nicotine administration, due to its addiction potential, which were not addressed in the limited literature we examined. As an alternative, novel treatments with drugs able to mimic only the positive effects of nicotine could be implemented.

Nicotinic Acetylcholine Receptor Signaling in the Hypothalamus: Mechanisms Related to Nicotine's Effects on Food Intake

Despite health risks associated with smoking, up to 20% of the US population persist in this behavior; many smoke to control body weight or appetite, and fear of post-cessation weight gain can motivate continued smoking. Nicotine and tobacco use is associated with lower body weight, and cessation yields an average weight gain of about 4 kg, which is thought to reflect a return to the body weight of a typical nonsmoker. Nicotine replacement therapies can delay this weight gain but do not prevent it altogether, and the underlying mechanism for how nicotine is able to reduce weight is not fully understood. In rodent models, nicotine reduces weight gain, reduces food consumption, and alters energy expenditure, but these effects vary with duration and route of nicotine administration. Nicotine, acting through nicotinic acetylcholine receptors (nAChRs), increases the firing rate of both orexigenic agouti-related peptide and anorexigenic proopiomelanocortin neurons in the arcuate nucleus of the hypothalamus (ARC). Manipulation of nAChR subunit expression within the ARC can block the ability of nicotine and the nicotinic agonist cytisine from decreasing food intake; however, it is unknown exactly how this reduces food intake. This review summarizes the clinical and preclinical work on nicotine, food intake, and weight gain, then explores the feeding circuitry of the ARC and how it is regulated by nicotine. Finally, we propose a novel hypothesis for how nicotine acts on this hypothalamic circuit to reduce food intake. Implications: This review provides a comprehensive and updated summary of the clinical and preclinical work examining nicotine and food intake, as well as a summary of recent work examining feeding circuits of the hypothalamus. Synthesis of these two topics has led to new understanding of how nAChR signaling regulates food intake circuits in the hypothalamus.

Cigarette smoking and cognitive function among older adults living in the community

Background. The present study aimed to examine the long-term impact of CS on Executive Function (EF) and memory among older adults living in the community. Methods. Clock Drawing Test (CDT) and Delayed Word Recall Test (DWRT) were used to examine EF and memory, respectively, using four waves of National Health and Aging Trend Study. The respondents were asked whether they have ever smoked, length of smoking, and age of start and quit smoking. Results. CS can have a long-term impact on both EF and memory. However, current smoking can increase the risk of EF impairment compared to former smokers. Lung disease and current smoking can have a synergic effect of impairment in EF. Conclusion. In the long-term, smoking can negatively affect cognitive. Lung diseases and smoking can synergize their impacts on EF. The impact of smoking on cognition varies across ethnic groups; hence, educational programs targeting minorities can reduce discrepancies.

α-Conotoxin as Potential to α7-nAChR Recombinant Expressed in Escherichia coli

α7 nicotinic acetylcholine receptors (nAChR) is an important nicotinic acetylcholine receptors subtype and closely associated with cognitive disorders, such as Alzheimer’s and schizophrenia disease. The mutant ArIB (V11L, V16A) of α-conotoxin ArIB with 17-amino acid residues specifically targets α7 nAChR with no obvious effect on other nAChR subtypes. In the study, the synthetic gene encoding mature peptide of ArIB and mutant ArIB (V11L, V16A) carried a fusion protein Trx and 6 × His-tag was separately inserted in pET-32a (+) vector and transformed into Escherichia coli strain BL21(DE3) pLysS for expression. The expressions of Trx-ArIB-His₆ and Trx-ArIB (V11L, V16A)-His₆ were soluble in Escherichia coli, which were purified by Ni-NTA affinity chromatography column and cleaved by enterokinase to release rArIB and rArIB (V11L, V16A). Then, rArIB and rArIB (V11L, V16A) were purified by high-performance liquid chromatography (HPLC) and identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Bioactivity of rArIB and rArIB (V11L, V16A) was assessed by two-electrode voltage-clamp electrophysiology in Xenopus laevis oocytes expressing human nAChR subtypes. The results indicated that the yield of the fusion proteins was approximately 50 mg/L and rArIB (V11L, V16A) antagonized the α7 nAChR subtype selectively with 8-nM IC₅₀. In summary, this study provides an efficient method to biosynthesize α-conotoxin ArIB and rArIB (V11L, V16A) in Escherichia coli, which could be economical to obtain massively bioactive disulfide-rich polypeptides at fast speed.

Pharmacogenetic considerations when prescribing cholinesterase inhibitors for the treatment of Alzheimer's disease

INTRODUCTION

Cholinergic dysfunction, demonstrated in the late 1970s and early 1980s, led to the introduction of acetylcholinesterase inhibitors (AChEIs) in 1993 (Tacrine) to enhance cholinergic neurotransmission as the first line of treatment against Alzheimer's disease (AD). The new generation of AChEIs, represented by Donepezil (1996), Galantamine (2001) and Rivastigmine (2002), is the only treatment for AD to date, together with Memantine (2003). AChEIs are not devoid of side-effects and their cost-effectiveness is limited. An option to optimize the correct use of AChEIs is the implementation of pharmacogenetics (PGx) in the clinical practice.

AREAS COVERED

(i) The cholinergic system in AD, (ii) principles of AD PGx, (iii) PGx of Donepezil, Galantamine, Rivastigmine, Huperzine and other treatments, and (iv) practical recommendations.

EXPERT OPINION

The most relevant genes influencing AChEI efficacy and safety are APOE and CYPs. APOE-4 carriers are the worst responders to AChEIs. With the exception of Rivastigmine (UGT2B7, BCHE-K), the other AChEIs are primarily metabolized via CYP2D6, CYP3A4, and UGT enzymes, with involvement of ABC transporters and cholinergic genes (CHAT, ACHE, BCHE, SLC5A7, SLC18A3, CHRNA7) in most ethnic groups. Defective variants may affect the clinical response to AChEIs. PGx geno-phenotyping is highly recommended prior to treatment.

Increased dopamine availability magnifies nicotine effects on cognitive control: A pilot study

INTRODUCTION AND OBJECTIVES

The ability to adapt to new task demands flexibly and to stabilise performance in the presence of distractors is termed cognitive control and is mediated by dopaminergic and cholinergic neurotransmission. We aimed to test the hypothesis that the effect of the cholinergic agonist nicotine on cognitive control depends on baseline dopamine levels.

METHODS

Thirty-eight healthy non-smokers (16 males; M_age=24.05 years) performed a cognitive control task including distractor and switch trials twice. Subjects were split into two parallel groups. One group received 2 g of L-tyrosine two hours prior to testing to manipulate dopamine availability experimentally, while the other group received placebo on both days. One hour later, both groups received in a within-subject design: on one day, a 7 mg nicotine patch; on the other day, a matched placebo. Response time costs for distractor and switch trials served as measures of cognitive stability and flexibility.

RESULTS

Nicotinic modulation reduced response time costs in switch trials and increased costs in distractor trials (nicotine×condition, p=0.027) with a trend-wise interaction between nicotine, L-tyrosine and trial type (nicotine×L-tyrosine×condition, p=0.068), which was due to stronger nicotine effects under L-tyrosine.

CONCLUSIONS

Our data provide preliminary evidence that nicotine has opponent effects on cognitive stability and flexibility. Subjects who received the dopamine precursor L-tyrosine were more prone to nicotine effects on behaviours, which are improvements in cognitive flexibility at the cost of decreased cognitive stability.

Dissociation of nicotinic α7 and α4/β2 sub-receptor agonists for enhancing learning and attentional filtering in nonhuman primates

RATIONALE

Nicotinic acetylcholine receptors (nAChRs) modulate attention, memory, and higher executive functioning, but it is unclear how nACh sub-receptors mediate different mechanisms supporting these functions.

OBJECTIVES

We investigated whether selective agonists for the alpha-7 nAChR versus the alpha-4/beta-2 nAChR have unique functional contributions for value learning and attentional filtering of distractors in the nonhuman primate.

METHODS

Two adult rhesus macaque monkeys performed reversal learning following systemic administration of either the alpha-7 nAChR agonist PHA-543613 or the alpha-4/beta-2 nAChR agonist ABT-089 or a vehicle control. Behavioral analysis quantified performance accuracy, speed of processing, reversal learning speed, the control of distractor interference, perseveration tendencies, and motivation.

RESULTS

We found that the alpha-7 nAChR agonist PHA-543613 enhanced the learning speed of feature values but did not modulate how salient distracting information was filtered from ongoing choice processes. In contrast, the selective alpha-4/beta-2 nAChR agonist ABT-089 did not affect learning speed but reduced distractibility. This dissociation was dose-dependent and evident in the absence of systematic changes in overall performance, reward intake, motivation to perform the task, perseveration tendencies, or reaction times.

CONCLUSIONS

These results suggest nicotinic sub-receptor specific mechanisms consistent with (1) alpha-4/beta-2 nAChR specific amplification of cholinergic transients in prefrontal cortex linked to enhanced cue detection in light of interferences, and (2) alpha-7 nAChR specific activation prolonging cholinergic transients, which could facilitate subjects to follow-through with newly established attentional strategies when outcome contingencies change. These insights will be critical for developing function-specific drugs alleviating attention and learning deficits in neuro-psychiatric diseases.

A Review of the Cholinergic System and Therapeutic Approaches to Treat Brain Disorders

Since its identification over a hundred years ago, the neurotransmitter acetylcholine (ACh) has proven to play an essential role in supporting many diverse functions. Some well-characterized functions include: chemical transmission at the neuromuscular junction; autonomic function in the peripheral nervous system; and, sustained attention, sleep/wake regulation, and learning and memory within the central nervous system. Within the brain, major cholinergic projection pathways from the basal forebrain and the brainstem support these centrally mediated processes, and dysregulation of the cholinergic system is implicated in cognitive decline associated with aging and dementias including Alzheimer's disease. ACh exerts its effects by binding to two different membrane-bound receptor classes: (1) G‑protein coupled muscarinic acetylcholine receptors (mAChRs), and (2) ligand-gated nicotinic acetylcholine receptors (nAChRs). These receptor systems are described in detail within this chapter along with discussion on the successes and failures of synthetic ligands designed to selectively target receptor subtypes for treating brain disorders. New molecular approaches and advances in our understanding of the target biology combined with opportunities to re-purpose existing cholinergic drugs for new indications continue to highlight the exciting opportunities for modulating this system for therapeutic purposes.

Alzheimer's Disease Therapeutic Approaches

Alzheimer's disease (AD) was first described and diagnosed by Dr. Alois Alzheimer in 1906 (Hippius and Neundorfer, Dialogues Clin Neurosc 5:101-108, 2003). According to World Health Organization (WHO), AD is the most common cause of dementia, accounting for as many as 60-70% of senile dementia cases and affecting 47.5 million people worldwide (data from 2015) (Dementia Fact Sheet No 362. http://who.int/mediacentre/factsheets/fs362/en/ ). The median survival time after the onset of dementia ranges from 3.3 to 11.7 years (Todd et al. Int J Geriatr Psychiatry 28:1109-1124, 2013). AD is characterized as a severe, chronic, incurable, and progressive neurodegenerative disorder, associated with memory loss and cognition impairment accompanied by abnormal behavior and personality changes (Godyn et al. Pharmacol Rep 68:127-138, 2016). AD is characterized by neuronal death, which usually correlates with the appearance of key neuropathological changes, including acetylcholine deficiency, glutamate excitotoxicity, extracellular deposition of β-amyloid (Aβ plaques), intracellular neurofibrillary tangles by hyperphosphorylated tau protein deposits, neuroinflammation, and widespread neuronal loss (Godyn et al. Pharmacol Rep 68:127-138, 2016; Graham et al. Annu Rev. Med 68:413-430, 2017). The discovery of the degeneration of cholinergic neurons and the reduction of acetylcholine levels in postmortem studies of patients resulted in the use of drugs that leads to the increase of acetylcholine levels in brain (Dubois et al. Lacet Neurol 13:614-629, 2014). At present there is no preventative or curative treatment that interferes with the development of the disease. However, in recent years progress was made in the development of cholinergic drugs which have a positive effect on disease progression. Nowadays, specific drugs that can inhibit the enzyme that degrades acetylcholine are used. The development of new effective drugs involves a difficult and time-consuming process, accompanied by a very high failure rate. In the absence of effective therapies, the estimated number of people with dementia will reach 115 to 131, five million by 2050 (Dubois et al. Lacet Neurol 13:614-629, 2014; Cummings et al. Alzheimers Res Ther 6:37, 2014). Novel therapies and new targets required for developing more effective drugs for the treatment of AD patients are urgently needed.

Nicotinic Acetylcholine Receptors Control Encoding and Retrieval of Associative Recognition Memory through Plasticity in the Medial Prefrontal Cortex

Nicotinic acetylcholine receptors (nAChRs) expressed in the medial prefrontal cortex have critical roles in cognitive function. However, whether nAChRs are required for associative recognition memory and the mechanisms by which nAChRs may contribute to mnemonic processing are not known. We demonstrate that nAChRs in the prefrontal cortex exhibit subtype-specific roles in associative memory encoding and retrieval. We present evidence that these separate roles of nAChRs may rely on bidirectional modulation of plasticity at synaptic inputs to the prefrontal cortex that are essential for associative recognition memory.

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Prefrontal α7 nAChRs are critical for encoding of associative recognition memory

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Prefrontal α4β2 nAChRs are required for retrieval of associative recognition memory

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α7 and α4β2 nAChRs gate bidirectional plasticity at hippocampal-prefrontal synapses

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Bidirectional plasticity underlies the role of nAChR in associative recognition

Vitamin D3 favorable outcome on recognition memory and prefrontal cortex expression of choline acetyltransferase and acetylcholinesterase in experimental model of chronic high-fat feeding

Aim of the study: High-fat diet (HFD) consumption and insufficient vitamin D levels are globally increasing phenomena. The present study assessed the effect of chronic HFD feeding with and without vitamin D supplementation on recognition memory and prefrontal cortex expression of choline acetyltransferase (CAT) and acetylcholinesterase (Achase).Materials and methods: Forty male Wistar rats were subjected to four dietary regimens (n = 10); control diet (10% fat), control + vitamin D3, high-fat diet (HFD 45% fat) and HFD + vitamin D3 for 6 months. Rats were tested for the novel object recognition test, and their prefrontal cortices were assessed for expression of CAT and Achase.Results: Recognition memory was impaired in HFD-fed rats compared to control rats as evidenced by significantly decreased discrimination index in the novel object recognition test. Moreover, CAT expression was significantly decreased while Achase expression was significantly increased in the prefrontal cortex of HFD-fed rats. Vitamin D3 supplementation with HFD significantly increased the exploration of the novel object and the discrimination index and attenuated the alterations in the prefrontal cortex CAT and Achase expression.Conclusions: The present findings support the potential effect of vitamin D on recognition memory and cholinergic transmission in the prefrontal cortex and add to the pathophysiology of HFD consumption.

Verbal learning deficits associated with increased anticholinergic burden are attenuated with targeted cognitive training in treatment refractory schizophrenia patients

Targeted cognitive training (TCT) has been reported to improve verbal learning deficits in patients with schizophrenia (SZ). Despite positive findings, it is not clear whether demographic factors and clinical characteristics contribute to the success of TCT on an individual basis. Medication-associated anticholinergic burden has been shown to impact TCT-associated verbal learning gains in SZ outpatients, but the role of anticholinergic medication burden on TCT gains in treatment refractory SZ patients has not been described. In this study, SZ patients mandated to a locked residential rehabilitation center were randomized to treatment as usual (TAU; n=22) or a course of TAU augmented with TCT (n=24). Anticholinergic medication burden was calculated from medication data at baseline and follow-up using the Anticholinergic Cognitive Burden (ACB) Scale. MATRICS Consensus Cognitive Battery Verbal Learning domain scores were used as the primary outcome variable. The TAU and TCT groups were matched in ACB at baseline and follow-up. While baseline ACB was not associated with verbal learning in either group, increases in ACB over the course of the study were significantly associated with deterioration of verbal learning in the TAU group (r=-0.51, p=0.02). This was not seen in subjects randomized to TCT (r=-0.13, p=0.62). Our results suggest that TCT may blunt anticholinergic medication burden associated reduction in verbal learning in severely disabled SZ inpatients.

Not all smokers appear to seek nicotine for the same reasons: implications for preclinical research in nicotine dependence

Tobacco use leads to 6 million deaths every year due to severe long-lasting diseases. The main component of tobacco, nicotine, is recognized as one of the most addictive drugs, making smoking cessation difficult, even when 70 percent of smokers wish to do so. Clinical and preclinical studies have demonstrated consistently that nicotine seeking is a complex behavior involving various psychopharmacological mechanisms. Evidence supports that the population of smokers is heterogeneous, particularly as regards the breadth of motives that determine the urge to smoke. Here, we review converging psychological, genetic and neurobiological data from clinical and preclinical studies supporting that the mechanisms controlling nicotine seeking may vary from individual to individual. It appears timely that basic neuroscience integrates this heterogeneity to refine our understanding of the neurobiology of nicotine seeking, as tremendous progress has been made in modeling the various psychopharmacological mechanisms driving nicotine seeking in rodents. For a better understanding of the mechanisms that drive nicotine seeking, we emphasize the need for individual-based research strategies in which nicotine seeking, and eventually treatment efficacy, are determined while taking into account individual variations in the mechanisms of nicotine seeking.

Insights into the Potential Role of Mercury in Alzheimer's Disease

Mercury (Hg), which is a non-essential element, is considered a highly toxic pollutant for biological systems even when present at trace levels. Elevated Hg exposure with the growing release of atmospheric pollutant Hg and rising accumulations of mono-methylmercury (highly neurotoxic) in seafood products have increased its toxic potential for humans. This review aims to highlight the potential relationship between Hg exposure and Alzheimer's disease (AD), based on the existing literature in the field. Recent reports have hypothesized that Hg exposure could increase the potential risk of developing AD. Also, AD is known as a complex neurological disorder with increased amounts of both extracellular neuritic plaques and intracellular neurofibrillary tangles, which may also be related to lifestyle and genetic variables. Research reports on AD and relationships between Hg and AD indicate that neurotransmitters such as serotonin, acetylcholine, dopamine, norepinephrine, and glutamate are dysregulated in patients with AD. Many researchers have suggested that AD patients should be evaluated for Hg exposure and toxicity. Some authors suggest further exploration of the Hg concentrations in AD patients. Dysfunctional signaling pathways in AD and Hg exposure appear to be interlinked with some driving factors such as arachidonic acid, homocysteine, dehydroepiandrosterone (DHEA) sulfate, hydrogen peroxide, glucosamine glycans, glutathione, acetyl-L carnitine, melatonin, and HDL. This evidence suggests the need for a better understanding of the relationship between AD and Hg exposure, and potential mechanisms underlying the effects of Hg exposure on regional brain functions. Also, further studies evaluating brain functions are needed to explore the long-term effects of subclinical and untreated Hg toxicity on the brain function of AD patients.

Chronic treatment with galantamine rescues reversal learning in an attentional set-shifting test after experimental brain trauma

Approximately 10 million new cases of traumatic brain injury (TBI) are reported each year worldwide with many of these injuries resulting in higher order cognitive impairments. Galantamine (GAL), an acetylcholine esterase inhibitor (AChEI) and positive allosteric modulator of nicotinic acetylcholine receptors (nAChRs), has been reported to ameliorate cognitive deficits after clinical TBI. Previously, we demonstrated that controlled cortical impact (CCI) injury to rats resulted in significant executive function impairments as measured by the attentional set-shifting test (AST), a complex cognitive task analogous to the Wisconsin Card Sorting Test (WCST). We hypothesized that chronic administration of GAL would normalize performance on the AST post-TBI. Isoflurane-anesthetized adult male rats were subjected to moderate CCI (2.8 mm tissue deformation at 4 m/s) or sham injury. Rats were then randomized into one of three treatment groups (i.e., 1 mg/kg GAL, 2 mg/kg GAL, or 1 mL/kg saline vehicle; VEH) or their respective sham controls. GAL or VEH was administered intraperitoneally daily commencing 24 hours post-surgery and until AST testing at 4 weeks post-injury. The AST data revealed significant impairments in the first reversal stage after TBI, seen as increased trials to reach criterion and elevated total errors (p < 0.05). These behavioral flexibility deficits were equally normalized by the administration of both doses of GAL (p < 0.05). Additionally, the higher dose of GAL (2 mg/kg) also significantly reduced cortical lesion volume compared to TBI + VEH controls (p < 0.05). In summary, daily GAL administration provides an efficacious treatment for cognitive deficits and histological recovery after experimental brain trauma. Clinically, these findings are promising considering robust results were attained using a pharmacotherapy already used in the clinic to treat mild dementia.

Sleep Related Epilepsy and Pharmacotherapy: An Insight

In the last several decades, sleep-related epilepsy has drawn considerable attention among epileptologists and neuroscientists in the interest of new paradigms of the disease etiology, pathogenesis and management. Sleep-related epilepsy is nocturnal seizures that manifest solely during the sleep state. Sleep comprises two distinct stages i.e., non-rapid eye movement (NREM) and rapid eye movement (REM) that alternate every 90 min with NREM preceding REM. Current findings indicate that the sleep-related epilepsy manifests predominantly during the synchronized stages of sleep; NREM over REM stage. Sleep related hypermotor epilepsy (SHE), benign partial epilepsy with centrotemporal spikes or benign rolandic epilepsy (BECTS), and Panayiotopoulos Syndrome (PS) are three of the most frequently implicated epilepsies occurring during the sleep state. Although some familial types are described, others are seemingly sporadic occurrences. In the present review, we aim to discuss the predominance of sleep-related epilepsy during NREM, established familial links to the pathogenesis of SHE, BECTS and PS, and highlight the present available pharmacotherapy options.

Cholinergic basal forebrain neurons regulate fear extinction consolidation through p75 neurotrophin receptor signaling

Cholinergic basal forebrain (cBF)-derived neurotransmission plays a crucial role in regulating neuronal function throughout the cortex, yet the mechanisms controlling cholinergic innervation to downstream targets have not been elucidated. Here we report that removing the p75 neurotrophin receptor (p75NTR) from cBF neurons induces a significant impairment in fear extinction consolidation. We demonstrate that this is achieved through alterations in synaptic connectivity and functional activity within the medial prefrontal cortex. These deficits revert back to wild-type levels upon re-expression of the active domain of p75NTR in adult animals. These findings demonstrate a novel role for cholinergic neurons in fear extinction consolidation and suggest that neurotrophic signaling is a key regulator of cholinergic-cortical innervation and function.

Opposing Cholinergic and Serotonergic Modulation of Layer 6 in Prefrontal Cortex

Prefrontal cortex is a hub for attention processing and receives abundant innervation from cholinergic and serotonergic afferents. A growing body of evidence suggests that acetylcholine (ACh) and serotonin (5-HT) have opposing influences on tasks requiring attention, but the underlying neurophysiology of their opposition is unclear. One candidate target population is medial prefrontal layer 6 pyramidal neurons, which provide feedback modulation of the thalamus, as well as feed-forward excitation of cortical interneurons. Here, we assess the response of these neurons to ACh and 5-HT using whole cell recordings in acute brain slices from mouse cortex. With application of exogenous agonists, we show that individual layer 6 pyramidal neurons are bidirectionally-modulated, with ACh and 5-HT exerting opposite effects on excitability across a number of concentrations. Next, we tested the responses of layer 6 pyramidal neurons to optogenetic release of endogenous ACh or 5-HT. These experiments were performed in brain slices from transgenic mice expressing channelrhodopsin in either ChAT-expressing cholinergic neurons or Pet1-expressing serotonergic neurons. Light-evoked endogenous neuromodulation recapitulated the effects of exogenous neurotransmitters, showing opposing modulation of layer 6 pyramidal neurons by ACh and 5-HT. Lastly, the addition of 5-HT to either endogenous or exogenous ACh significantly suppressed the excitation of pyramidal neurons in prefrontal layer 6. Taken together, this work suggests that the major corticothalamic layer of prefrontal cortex is a substrate for opposing modulatory influences on neuronal activity that could have implications for regulation of attention.

Cognitive Effects of Nicotine: Recent Progress

BACKGROUND

Cigarette smoking is the main cause of preventable death in developed countries. While the direct positive behavioral reinforcing effect of nicotine has historically been considered the primary mechanism driving the development of TUD, accumulating contemporary research suggests that the cognitive-enhancing effects of nicotine may also significantly contribute to the initiation and maintenance of TUD, especially in individuals with pre-existing cognitive deficits.

METHODS

We provide a selective overview of recent advances in understanding nicotine's effects on cognitive function, a discussion of the role of cognitive function in vulnerability to TUD, followed by an overview of the neurobiological mechanisms underlying the cognitive effects of nicotine.

RESULTS

Preclinical models and human studies have demonstrated that nicotine has cognitiveenhancing effects. Attention, working memory, fine motor skills and episodic memory functions are particularly sensitive to nicotine's effects. Recent studies have demonstrated that the α4, β2, and α7 subunits of the nicotinic acetylcholine receptor (nAChR) participate in the cognitive-enhancing effects of nicotine. Imaging studies have been instrumental in identifying brain regions where nicotine is active, and research on the dynamics of large-scale networks after activation by, or withdrawal from, nicotine hold promise for improved understanding of the complex actions of nicotine on human cognition.

CONCLUSION

Because poor cognitive performance at baseline predicts relapse among smokers who are attempting to quit smoking, studies examining the potential efficacy of cognitive-enhancement as strategy for the treatment of TUD may lead to the development of more efficacious interventions.

A Complex Interplay of Vitamin B1 and B6 Metabolism with Cognition, Brain Structure, and Functional Connectivity in Older Adults

Aging is associated with brain atrophy, functional brain network reorganization and decline of cognitive performance, albeit characterized by high interindividual variability. Among environmental influencing factors accounting for this variability, nutrition and particularly vitamin supply is thought to play an important role. While evidence exists that supplementation of vitamins B6 and B1 might be beneficial for cognition and brain structure, at least in deficient states and neurodegenerative diseases, little is known about this relation during healthy aging and in relation to reorganization of functional brain networks. We thus assessed the relation between blood levels of vitamins B1 and B6 and cognitive performance, cortical folding, and functional resting-state connectivity in a large sample of older adults (N > 600; age: 55-85 years), drawn from the population-based 1000BRAINS study. In addition to blood sampling, subjects underwent structural and functional resting-state neuroimaging as well as extensive neuropsychological testing in the domains of executive functions, (working) memory, attention, and language. Brain regions showing changes in the local gyrification index as calculated using FreeSurfer in relation to vitamin levels were used for subsequent seed-based resting-state functional connectivity analysis. For B6, a positive correlation with local cortical folding was found throughout the brain, while only slight changes in functional connectivity were observed. Contrarily, for B1, a negative correlation with cortical folding as well as problem solving and visuo-spatial working memory performance was found, which was accompanied by pronounced increases of interhemispheric and decreases of intrahemispheric functional connectivity. While the effects for B6 expand previous knowledge on beneficial effects of B6 supplementation on brain structure, they also showed that additional effects on cognition might not be recognizable in healthy older subjects with normal B6 blood levels. The cortical atrophy and pronounced functional reorganization associated with B1, contrarily, was more in line with the theory of a disturbed B1 metabolism in older adults, leading to B1 utilization deficits, and thus, an effective B1 deficiency in the brain, despite normal to high-normal blood levels.