Cholinergic connectivity: it's implications for psychiatric disorders

EEG-based Signatures of Schizophrenia, Depression, and Aberrant Aging: A Supervised Machine Learning Investigation

BACKGROUND

Electroencephalography (EEG) is a noninvasive, cost-effective, and robust tool, which directly measures in vivo neuronal mass activity with high temporal resolution. Combined with state-of-the-art machine learning (ML) techniques, EEG recordings could potentially yield in silico biomarkers of severe mental disorders.

HYPOTHESIS

Pathological and physiological aging processes influence the electrophysiological signatures of schizophrenia (SCZ) and major depressive disorder (MDD).

STUDY DESIGN

From a single-center cohort (N = 735, 51.6% male) comprising healthy control individuals (HC, N = 245) and inpatients suffering from SCZ (N = 250) or MDD (N = 240), we acquired resting-state 19 channel-EEG recordings. Using repeated nested cross-validation, support vector machine models were trained to (1) classify patients with SCZ or MDD and HC individuals and (2) predict age in HC individuals. The age model was applied to patient groups to calculate Electrophysiological Age Gap Estimation (EphysAGE) as the difference between predicted and chronological age. The links between EphysAGE, diagnosis, and medication were then further explored.

STUDY RESULTS

The classification models robustly discriminated SCZ from HC (balanced accuracy, BAC = 72.7%, P < .001), MDD from HC (BAC = 67.0%, P < .001), and SCZ from MDD individuals (BAC = 63.2%, P < .001). Notably, central alpha (8-11 Hz) power decrease was the most consistently predictive feature for SCZ and MDD. Higher EphysAGE was associated with an increased likelihood of being misclassified as SCZ in HC and MDD (ρHC = 0.23, P < .001; ρMDD = 0.17, P = .01).

CONCLUSIONS

ML models can extract electrophysiological signatures of MDD and SCZ for potential clinical use. However, the impact of aging processes on diagnostic separability calls for timely application of such models, possibly in early recognition settings.

Neurostructural changes in schizophrenia and treatment-resistance: a narrative review

Schizophrenia is a complex disorder characterized by multiple neurochemical abnormalities and structural changes in the brain. These abnormalities may begin before recognizable clinical symptoms appear and continue as a dynamic process throughout the illness. Recent advances in imaging techniques have significantly enriched our comprehension of these structural alterations, particularly focusing on gray and white matter irregularities and prefrontal, temporal, and cingulate cortex alterations. Some of the changes suggest treatment resistance to antipsychotic medications, while treatment nonadherence and relapses may further exacerbate structural abnormalities. This narrative review aims to discuss the literature about alterations and deficits within the brain, which could improve the understanding of schizophrenia and how to interpret neurostructural changes.

The New Horizon of Antipsychotics beyond the Classic Dopaminergic Hypothesis-The Case of the Xanomeline-Trospium Combination: A Systematic Review

Although the dopamine hypothesis of schizophrenia explains the effects of all the available antipsychotics in clinical use, there is an increasing need for developing new drugs for the treatment of the positive, negative, and cognitive symptoms of chronic psychoses. Xanomeline-trospium (KarXT) is a drug combination that is based on the essential role played by acetylcholine in the regulation of cognitive processes and the interactions between this neurotransmitter and other signaling pathways in the central nervous system, with a potential role in the onset of schizophrenia, Alzheimer's disease, and substance use disorders. A systematic literature review that included four electronic databases (PubMed, Cochrane, Clarivate/Web of Science, and Google Scholar) and the US National Library of Medicine database for clinical trials detected twenty-one sources referring to fourteen studies focused on KarXT, out of which only four have available results. Based on the results of these trials, the short-term efficacy and tolerability of xanomeline-trospium are good, but more data are needed before this drug combination may be recommended for clinical use. However, on a theoretical level, the exploration of KarXT is useful for increasing the interest of researchers in finding new, non-dopaminergic, antipsychotics that could be used either as monotherapy or as add-on drugs.

Association of non-essential metals with Chinese schizophrenia: A case-control study

BACKGROUND

The potential link between environmental pollutants, including metals, and schizophrenia development remains debated. This study aimed to explore the association between plasma levels of three non-essential metals-barium (Ba), tungsten (W), and uranium (U)-and schizophrenia risk among Chinese individuals.

METHOD

We recruited a total of 221 patients and 219 healthy controls. Plasma levels of three non-essential metals were measured using inductively coupled plasma mass spectrometry. We employed unconditional logistic regression and Bayesian kernel machine regression (BKMR) to explore the relationship between exposure to multiple metals and the risk of schizophrenia.

RESULTS

Logistic regression analysis revealed that the highest quartile (Q4) of W had an odds ratio (OR) of 1.87 (95% CI: 1.08-3.21) compared to the lowest quartile (Q1), with a significant P-trend of 0.017. For U, the ORs (95% CI) for Q2, Q3, and Q4 were 2.06 (1.19-3.56), 1.99 (1.15-3.44), and 1.74 (1.00-3.00), respectively. BKMR analyses revealed a progressive increase in the risk of schizophrenia with increasing cumulative levels of the three metals at concentrations below 35%, with U playing a major role in this association. U showed a non-linear positive correlation with schizophrenia, particularly at the 75th percentile level. Moreover, potential interactions were observed between W and Ba, as well as between W and U.

CONCLUSION

Higher plasma W and U concentrations were positively associated with the risk of schizophrenia, which was potentially related to the severity of symptoms in schizophrenic patients.

The effect of anticholinergic burden of psychiatric medications on major outcome domains of psychotic disorders: A 21-year prospective cohort study

BACKGROUND

Most medications used to treat psychotic disorders possess anticholinergic properties. This may result in a considerable anticholinergic burden (ACB), which may have deleterious effects on long-term outcomes. The extent to which cumulative ACB over years of treatment with psychotropic medications impacts different outcome domains remains unknown.

METHODS

This was a naturalistic study of 243 subjects with first-episode psychosis aimed at examining the cumulative effect of ACB of psychotropic medications administered over the illness course (ACB-years exposure) on several outcome domains assessed after a mean 21-year follow-up. Associations between ACB and the outcomes were modelled accounting for relevant confounding factors by using hierarchical linear regression analysis.

RESULTS

Over the study period, 81.9 % of the participants were dispensed at least one drug with strong anticholinergic effects for at least 1 year; at the follow-up visit, 60.5 % of the participants continued to take medications with strong ACB. ACB-years exposure was uniquely related to severity of negative symptoms (β = 0.144, p = 0.004), poor psychosocial functioning (β = 0.186, p < 0.001) and poor cognitive performance (β = -0.273, p < 0.001). This association pattern was independent of a schizophrenia diagnosis. Most of the associations between ACB at the follow-up visit and the outcomes were accounted for ACB-years exposure.

CONCLUSION

Lifetime ACB of psychotropic medications has deleterious effects on the outcome of psychotic disorders. Clinicians should avoid prescribing medications with strong ACB, since there are numerous alternatives within each psychotropic drug group for prescribing medications with low ACB.

Muscarinic M1 and M4 receptor agonists for schizophrenia: promising candidates for the therapeutic arsenal

INTRODUCTION

Successful phase 3 trials of KarXT in people with schizophrenia herald a new era of treating the disorder with drugs that do not target the dopamine D2 receptor. The active component of KarXT is xanomeline, a muscarinic (CHRM) M1 and M4 agonist, making muscarinic receptors a viable target for treating schizophrenia.

AREAS COVERED

This review covers the process of taking drugs that activate the muscarinic M1 and M4 receptors from conceptualization to the clinic and details the mechanisms by which activating the CHRM1 and 4 can affect the broad spectrum of symptoms experienced by people with schizophrenia.

EXPERT OPINION

Schizophrenia is a syndrome which means drugs that activate muscarinic M1 and M4 receptors, as was the case for antipsychotic drugs acting on the dopamine D2 receptor, will not give optimal outcomes in everyone within the syndrome. Thus, it would be ideal to identify people who are responsive to drugs activating the CHRM1 and 4. Given knowledge of the actions of these receptors, it is possible treatment non-response could be restricted to sub-groups within the syndrome who have deficits in cortical CHRM1 or those with one of the cognitive endophenotypes that may be identifiable by changes in the blood transcriptome.

Peripheral nerve stimulation: A neuromodulation-based approach

Recent technological improvements have positioned us at the threshold of innovative discoveries that will assist in new perspectives and avenues of research. Increased attention has been directed towards peripheral nerve stimulation, particularly of the vagus, trigeminal, or greater occipital nerve, due to their unique pathway that engages neural circuits within networks involved in higher cognitive processes. Here, we question whether the effects of transcutaneous electrical stimulation are mediated by synergistic interactions of multiple neuromodulatory networks, considering this pathway is shared by more than one neuromodulatory system. By spotlighting this attractive transcutaneous pathway, this opinion piece aims to acknowledge the contributions of four vital neuromodulators and prompt researchers to consider them in future investigations or explanations.

Associations of common genetic risk variants of the muscarinic acetylcholine receptor M2 with cardiac autonomic dysfunction in patients with schizophrenia

OBJECTIVES

Decreased vagal modulation, which has consistently been observed in schizophrenic patients, might contribute to increased cardiac mortality in schizophrenia. Previously, associations between CHRM2 (Cholinergic Receptor Muscarinic 2) and cardiac autonomic features have been reported. Here, we tested for possible associations between these polymorphisms and heart rate variability in patients with schizophrenia.

METHODS

A total of three single nucleotide polymorphisms (SNPs) in CHRM2 (rs73158705 A>G, rs8191992 T>A and rs2350782 T>C) that achieved significance (p < 5 * 10^-8) in genome-wide association studies for cardiac autonomic features were genotyped in 88 drug-naïve patients, 61 patients receiving antipsychotic medication and 144 healthy controls. Genotypes were analysed for associations with parameters of heart rate variability and complexity, in each diagnostic group.

RESULTS

We observed a significantly altered heart rate variability in unmedicated patients with identified genetic risk status in rs73158705 A>G, rs8191992 T>A and rs2350782 T>C as compared to genotype non-risk status. In patients receiving antipsychotic medication and healthy controls, these associations were not observed.

DISCUSSION

We report novel candidate genetic associations with cardiac autonomic dysfunction in schizophrenia, but larger cohorts are required for replication.

The Difficult Path to the Discovery of Novel Treatments in Psychiatric Disorders

CNS diseases, including psychiatric disorders, represent a significant opportunity for the discovery and development of new drugs and therapeutic treatments with the potential to have a significant impact on human health. CNS diseases, however, present particular challenges to therapeutic discovery efforts, and psychiatric diseases/disorders may be among the most difficult. With specific exceptions such as psychostimulants for ADHD, a large number of psychiatric patients are resistant to existing treatments. In addition, clinicians have no way of knowing which psychiatric patients will respond to which drugs. By definition, psychiatric diagnoses are syndromal in nature; determinations of efficacy are often self-reported, and drug discovery is largely model-based. While such models of psychiatric disease are amenable to screening for new drugs, whether cellular or whole-animal based, they have only modest face validity and, more importantly, predictive validity. Multiple academic, pharmaceutical industry, and government agencies are dedicated to the translation of new findings about the neurobiology of major psychiatric disorders into the discovery and advancement of novel therapies. The collaboration of these agencies provide a pathway for developing new therapeutics. These efforts will be greatly helped by recent advances in understanding the genetic bases of psychiatric disorders, the ongoing search for diagnostic and therapy-responsive biomarkers, and the validation of new animal models.

Dopamine, Immunity, and Disease

The neurotransmitter dopamine is a key factor in central nervous system (CNS) function, regulating many processes including reward, movement, and cognition. Dopamine also regulates critical functions in peripheral organs, such as blood pressure, renal activity, and intestinal motility. Beyond these functions, a growing body of evidence indicates that dopamine is an important immunoregulatory factor. Most types of immune cells express dopamine receptors and other dopaminergic proteins, and many immune cells take up, produce, store, and/or release dopamine, suggesting that dopaminergic immunomodulation is important for immune function. Targeting these pathways could be a promising avenue for the treatment of inflammation and disease, but despite increasing research in this area, data on the specific effects of dopamine on many immune cells and disease processes remain inconsistent and poorly understood. Therefore, this review integrates the current knowledge of the role of dopamine in immune cell function and inflammatory signaling across systems. We also discuss the current understanding of dopaminergic regulation of immune signaling in the CNS and peripheral tissues, highlighting the role of dopaminergic immunomodulation in diseases such as Parkinson's disease, several neuropsychiatric conditions, neurologic human immunodeficiency virus, inflammatory bowel disease, rheumatoid arthritis, and others. Careful consideration is given to the influence of experimental design on results, and we note a number of areas in need of further research. Overall, this review integrates our knowledge of dopaminergic immunology at the cellular, tissue, and disease level and prompts the development of therapeutics and strategies targeted toward ameliorating disease through dopaminergic regulation of immunity. SIGNIFICANCE STATEMENT: Canonically, dopamine is recognized as a neurotransmitter involved in the regulation of movement, cognition, and reward. However, dopamine also acts as an immune modulator in the central nervous system and periphery. This review comprehensively assesses the current knowledge of dopaminergic immunomodulation and the role of dopamine in disease pathogenesis at the cellular and tissue level. This will provide broad access to this information across fields, identify areas in need of further investigation, and drive the development of dopaminergic therapeutic strategies.

Continuous cholinergic-dopaminergic updating in the nucleus accumbens underlies approaches to reward-predicting cues

The ability to learn Pavlovian associations from environmental cues predicting positive outcomes is critical for survival, motivating adaptive behaviours. This cued-motivated behaviour depends on the nucleus accumbens (NAc). NAc output activity mediated by spiny projecting neurons (SPNs) is regulated by dopamine, but also by cholinergic interneurons (CINs), which can release acetylcholine and glutamate via the activity of the vesicular acetylcholine transporter (VAChT) or the vesicular glutamate transporter (VGLUT3), respectively. Here we investigated behavioural and neurochemical changes in mice performing a touchscreen Pavlovian approach task by recording dopamine, acetylcholine, and calcium dynamics from D1- and D2-SPNs using fibre photometry in control, VAChT or VGLUT3 mutant mice to understand how these signals cooperate in the service of approach behaviours toward reward-predicting cues. We reveal that NAc acetylcholine-dopaminergic signalling is continuously updated to regulate striatal output underlying the acquisition of Pavlovian approach learning toward reward-predicting cues.

Development of Benzodioxine-heteroarylpiperazines as Highly Potent and Selective α2c Antagonists

_{Here is reported the design and synthesis of a series of highly potent and selective α2C antagonists using benzodioxine methyl piperazine as a central scaffold by pharmacophoric analysis to improve the pharmacokinetics of suboptimal clinical candidate molecules.}

The Basal Forebrain Cholinergic Nuclei and Their Relevance to Schizophrenia and Other Psychotic Disorders

The basal forebrain cholinergic nuclei (BFCN) provide the main cholinergic input to prefrontal cortices, the hippocampi, and amygdala. These structures are highly relevant for the regulation and maintenance of many cognitive functions, such as attention and memory. In vivo neuroimaging studies reported alterations of the cholinergic system in psychotic disorders. Particularly, a downregulation of nicotinic and muscarinic acetylcholine receptors has been found. Crucially, such alterations in neurotransmission have been associated with cognitive impairments and positive and negative symptoms. Recent pharmacological studies support these findings, as they demonstrated an association between the manipulation of cholinergic transmission and an attenuation in symptom severity. Targeting acetylcholine receptors has therefore become a focus for the development of novel psychopharmacological drugs. However, many open questions remain. For instance, it remains elusive what causes such alterations in neurotransmission. While evidence supports the idea that BFCN structural integrity is altered in schizophrenia, it remains to be determined whether this is also present in other psychotic disorders. Furthermore, it is unclear when throughout the course of the disorder these alterations make their appearance and whether they reflect changes in the BFCN alone or rather aberrant interactions between the BFCN and other brain areas. In this review, the specific role of the BFCN and their projections are discussed from a neuroimaging perspective and with a focus on psychotic disorders alongside future directions. These directions set the stage for the development of new treatment targets for psychotic disorders.

Serotonergic system in vivo with [11C]DASB PET scans in GTP-cyclohydrolase deficient dopa-responsive dystonia patients

GTP-cyclohydrolase deficiency in dopa-responsive dystonia (DRD) patients impairs the biosynthesis of dopamine, but also of serotonin. The high prevalence of non-motor symptoms suggests involvement of the serotonergic pathway. Our study aimed to investigate the serotonergic system in vivo in the brain of`DRD patients and correlate this to (non-)motor symptoms. Dynamic [¹¹C]DASB PET scans, a marker of serotonin transporter availability, were performed. Ten DRD, 14 cervical dystonia patients and 12 controls were included. Univariate- and network-analysis did not show differences in binding between DRD patients compared to controls. Sleep disturbances were correlated with binding in the dorsal raphe nucleus (all participants: r_s = 0.45, p = 0.04; patients: r_s = 0.64, p = 0.05) and participants with a psychiatric disorder had a lower binding in the hippocampus (all participants: p = 0.00; patients: p = 0.06). Post-hoc analysis with correction for psychiatric co-morbidity showed a significant difference in binding in the hippocampus between DRD patients and controls (p = 0.00). This suggests that psychiatric symptoms might mask the altered serotonergic metabolism in DRD patients, but definite conclusions are difficult as psychiatry is considered part of the phenotype. We hypothesize that an imbalance between different neurotransmitter systems is responsible for the non-motor symptoms, and further research investigating multiple neurotransmitters and psychiatry in DRD is necessary.

The effects of galangin in prepulse inhibition test and experimental schizophrenia models

OBJECTIVE

Acetylcholinesterase inhibitors are the focus of interest in the management of schizophrenia. We aimed to investigate the effects of acute galangin administration, a flavonoid compound with acetylcholinesterase inhibiting activity, on schizophrenia-associated cognitive deficits in rats and schizophrenia models in mice.

METHODS

Apomorphine-induced prepulse inhibition (PPI) disruption for cognitive functions, nicotinic, muscarinic, and serotonergic mechanism involvement, and brain acetylcholine levels were investigated in Wistar rats. Apomorphine-induced climbing, MK-801-induced hyperlocomotion, and catalepsy tests were used as schizophrenia models in Swiss albino mice. The effects of galangin were compared with acetylcholinesterase inhibitor donepezil, and typical and atypical antipsychotics haloperidol and olanzapine, respectively.

RESULTS

Galangin (50,100 mg/kg) enhanced apomorphine-induced PPI disruption similar to donepezil, haloperidol, and olanzapine (p < 0.05). This effect was not altered in the combination of galangin with the nicotinic receptor antagonist mecamylamine (1 mg/kg), the muscarinic receptor antagonist scopolamine (0.05 mg/kg), or the serotonin-1A receptor antagonist WAY-100635 (1 mg/kg) (p > 0.05). Galangin (50,100 mg/kg) alone increased brain acetylcholine concentrations (p < 0.05), but not in apomorphine-injected rats (p > 0.05). Galangin (50 mg/kg) decreased apomorphine-induced climbing and MK-801-induced hyperlocomotion similar to haloperidol and olanzapine (p < 0.05), but did not induce catalepsy, unlike them.

CONCLUSION

We suggest that galangin may help enhance schizophrenia-associated cognitive deficits, and nicotinic, muscarinic cholinergic, and serotonin-1A receptors are not involved in this effect. Galangin also exerted an antipsychotic-like effect without inducing catalepsy and may be considered as an advantageous antipsychotic agent.

Efficacy of a novel proprietary dietary supplement (TRI 360TM) on psychological symptoms and stress-related quality of life in adult subjects: A randomized controlled clinical trial

Nowadays, diet plays an increasingly important role in normal physiology and mental health. Recently, many studies have shown that more use of dietary supplements in mental and psychological disorders. Study objective was to investigate safety and efficacy of proprietary nutraceutical combination (TRI 360^TM) on psychological symptoms in adult human subjects with one or more psychological symptoms in open-label, single-center, parallel-group, randomized controlled trial. Eighty-four participants aged 20-45 years with psychological symptoms were completed this trial. Participants were randomly assigned to placebo and treatment groups. Treatment group received TRI 360^TM capsules twice a day. TRI 360^TM was well-tolerated and didn't show treatment-related adverse-events upto 180 days. All assessed perception scorings on psychological symptoms like fatigue, mental stress, sleep disturbance, anxiety, depression, emotional trauma, mood changes, self-confidence, willpower, and motivation were very significantly (p ≤ 0.0001) improved in TRI 360^TM participants than placebo control group. Furthermore, significantly (p ≤ 0.001) increased levels of functional biomarkers: vitamin C and D₃ metabolites, neurotransmitters, hormones, antiaging protein (klotho) level; and decreased proinflammatory cytokines and oxidative stress marker, malondialdehyde in TRI 360^TM group than placebo. According to these findings, the use of TRI 360^TM supplementation as a potentially safe therapeutic option for reducing psychological symptoms in healthy adults.

PET Imaging of brain muscarinic receptors with 18F-Fluorobenzyl-Dexetimide: A first in human study

M1 and M4 muscarinic receptor (mAChR) agonists are under development for the treatment of schizophrenia, Alzheimer's and Parkinson's disease. We performed first-in-human PET imaging of mAChR with ¹⁸F-Fluorobenzyl-Dexetimide (FDEX) in 10 healthy participants (29.4±4.3yrs). Four underwent dynamic brain scanning for 240 min, and then six underwent static brain scans at 120 and 160-min post injection of 250 MBq of FDEX. Gjedde-Patlak graphical analysis was applied to determine the influx constant (Ki). Regional tissue ratios (SUVR) were calculated using the cerebellar cortex as the reference region. No adverse events were observed. The tracer showed good brain entry (∼4.2% ID at 5 min) but irreversible distribution kinetics over four hours in regions of high mAChR. Binding was consistent with the distribution of mAChR receptors with striatum > cortex > hippocampus >> thalamus >>> cerebellum with low variance in regional binding between subjects. Ki was 0.42±0.04 in the putamen, 0.27±0.01 in frontal cortex, 0.25±0.02 in the hippocampus and 0.10±0.01 in the thalamus. SUVR at 120 and 240 min. were highly correlated with these Ki values with R² of 0.91 and 0.99 respectively. FDEX yields high quality brain images with uptake in the known distribution of mAChR with remarkably little variance between normal subjects.

Galantamine-Memantine Combination and Kynurenine Pathway Enzyme Inhibitors in the Treatment of Neuropsychiatric Disorders

The kynurenine pathway (KP) is a major route for L-tryptophan (L-TRP) metabolism, yielding a variety of bioactive compounds including kynurenic acid (KYNA), 3-hydroxykynurenine (3-HK), quinolinic acid (QUIN), and picolinic acid (PIC). These tryptophan catabolites are involved in the pathogenesis of many neuropsychiatric disorders, particularly when the KP becomes dysregulated. Accordingly, the enzymes that regulate the KP such as indoleamine 2,3-dioxygenase (IDO)/tryptophan 2,3-dioxygenase, kynurenine aminotransferases (KATs), and kynurenine 3-monooxygenase (KMO) represent potential drug targets as enzymatic inhibition can favorably rebalance KP metabolite concentrations. In addition, the galantamine-memantine combination, through its modulatory effects at the alpha7 nicotinic acetylcholine receptors and N-methyl-D-aspartate receptors, may counteract the effects of KYNA. The aim of this review is to highlight the effectiveness of IDO-1, KAT II, and KMO inhibitors, as well as the galantamine-memantine combination in the modulation of different KP metabolites. KAT II inhibitors are capable of decreasing the KYNA levels in the rat brain by a maximum of 80%. KMO inhibitors effectively reduce the central nervous system (CNS) levels of 3-HK, while markedly boosting the brain concentration of KYNA. Emerging data suggest that the galantamine-memantine combination also lowers L-TRP, kynurenine, KYNA, and PIC levels in humans. Presently, there are only 2 pathophysiological mechanisms (cholinergic and glutamatergic) that are FDA approved for the treatment of cognitive dysfunction for which purpose the galantamine-memantine combination has been designed for clinical use against Alzheimer's disease. The alpha7 nicotinic-NMDA hypothesis targeted by the galantamine-memantine combination has been implicated in the pathophysiology of various CNS diseases. Similarly, KYNA is well capable of modulating the neuropathophysiology of these disorders. This is known as the KYNA-centric hypothesis, which may be implicated in the management of certain neuropsychiatric conditions. In line with this hypothesis, KYNA may be considered as the "conductor of the orchestra" for the major pathophysiological mechanisms underlying CNS disorders. Therefore, there is great opportunity to further explore and compare the biological effects of these therapeutic modalities in animal models with a special focus on their effects on KP metabolites in the CNS and with the ultimate goal of progressing to clinical trials for many neuropsychiatric diseases.

The Role of G Protein-Coupled Receptors (GPCRs) and Calcium Signaling in Schizophrenia. Focus on GPCRs Activated by Neurotransmitters and Chemokines

Schizophrenia is a common debilitating disease characterized by continuous or relapsing episodes of psychosis. Although the molecular mechanisms underlying this psychiatric illness remain incompletely understood, a growing body of clinical, pharmacological, and genetic evidence suggests that G protein-coupled receptors (GPCRs) play a critical role in disease development, progression, and treatment. This pivotal role is further highlighted by the fact that GPCRs are the most common targets for antipsychotic drugs. The GPCRs activation evokes slow synaptic transmission through several downstream pathways, many of them engaging intracellular Ca²⁺ mobilization. Dysfunctions of the neurotransmitter systems involving the action of GPCRs in the frontal and limbic-related regions are likely to underly the complex picture that includes the whole spectrum of positive and negative schizophrenia symptoms. Therefore, the progress in our understanding of GPCRs function in the control of brain cognitive functions is expected to open new avenues for selective drug development. In this paper, we review and synthesize the recent data regarding the contribution of neurotransmitter-GPCRs signaling to schizophrenia symptomology.

Gauging Working Memory Capacity From Differential Resting Brain Oscillations in Older Individuals With A Wearable Device

Working memory is a core cognitive function and its deficits is one of the most common cognitive impairments. Reduced working memory capacity manifests as reduced accuracy in memory recall and prolonged speed of memory retrieval in older adults. Currently, the relationship between healthy older individuals’ age-related changes in resting brain oscillations and their working memory capacity is not clear. Eyes-closed resting electroencephalogram (rEEG) is gaining momentum as a potential neuromarker of mild cognitive impairments. Wearable and wireless EEG headset measuring key electrophysiological brain signals during rest and a working memory task was utilized. This research’s central hypothesis is that rEEG (e.g., eyes closed for 90 s) frequency and network features are surrogate markers for working memory capacity in healthy older adults. Forty-three older adults’ memory performance (accuracy and reaction times), brain oscillations during rest, and inter-channel magnitude-squared coherence during rest were analyzed. We report that individuals with a lower memory retrieval accuracy showed significantly increased alpha and beta oscillations over the right parietal site. Yet, faster working memory retrieval was significantly correlated with increased delta and theta band powers over the left parietal sites. In addition, significantly increased coherence between the left parietal site and the right frontal area is correlated with the faster speed in memory retrieval. The frontal and parietal dynamics of resting EEG is associated with the “accuracy and speed trade-off” during working memory in healthy older adults. Our results suggest that rEEG brain oscillations at local and distant neural circuits are surrogates of working memory retrieval’s accuracy and processing speed. Our current findings further indicate that rEEG frequency and coherence features recorded by wearable headsets and a brief resting and task protocol are potential biomarkers for working memory capacity. Additionally, wearable headsets are useful for fast screening of cognitive impairment risk.

Neuromodulation of the mind-wandering brain state: the interaction between neuromodulatory tone, sharp wave-ripples and spontaneous thought

Mind-wandering has become a captivating topic for cognitive neuroscientists. By now, it is reasonably well described in terms of its phenomenology and the large-scale neural networks that support it. However, we know very little about what neurobiological mechanisms trigger a mind-wandering episode and sustain the mind-wandering brain state. Here, we focus on the role of ascending neuromodulatory systems (i.e. acetylcholine, noradrenaline, serotonin and dopamine) in shaping mind-wandering. We advance the hypothesis that the hippocampal sharp wave-ripple (SWR) is a compelling candidate for a brain state that can trigger mind-wandering episodes. This hippocampal rhythm, which occurs spontaneously in quiescent behavioural states, is capable of propagating widespread activity in the default network and is functionally associated with recollective, associative, imagination and simulation processes. The occurrence of the SWR is heavily dependent on hippocampal neuromodulatory tone. We describe how the interplay of neuromodulators may promote the hippocampal SWR and trigger mind-wandering episodes. We then identify the global neuromodulatory signatures that shape the evolution of the mind-wandering brain state. Under our proposed framework, mind-wandering emerges due to the interplay between neuromodulatory systems that influence the transitions between brain states, which either facilitate, or impede, a wandering mind. This article is part of the theme issue 'Offline perception: voluntary and spontaneous perceptual experiences without matching external stimulation'.

α7 nicotinic receptor agonist and positive allosteric modulators differently improved schizophrenia-like cognitive deficits in male rats

The majority of schizophrenia patients have cognitive deficits as a separate symptom cluster independent of positive or negative symptoms. Current medicines, unfortunately, cannot provide clear benefits for cognitive symptoms in patients. Recent findings showed decreased α7 nicotinic acetylcholine receptor (nAChR) expressions in subjects with schizophrenia. α7 nAChR full/partial agonists and positive allosteric modulators (PAMs) may be valuable drug candidates to treat cognitive deficits of disease. This study comparatively investigated the effect of α7 nAChR agonist (A-582941), type I PAM (CCMI), type II PAM (PNU-120596), and the antipsychotic drug (clozapine) on behavioral, molecular, and immunohistochemical parameters in a subchronic MK-801 model of schizophrenia in male rats. Novel object recognition (NOR) and Morris water maze (MWM) tests were performed to evaluate recognition and spatial memories, respectively. Gene and protein expressions of parvalbumin, glutamic acid decarboxylase-67 (GAD67), and α7 nAChR were examined in the rats' hippocampal tissue. The subchronic MK-801 administration produced cognitive deficits in the NOR and MWM tests. It also decreased the protein and gene expressions of parvalbumin, GAD67, and α7 nAChR in the hippocampus. Clozapine, A-582941, and PNU-120596 but not CCMI increased the parvalbumin and α7 nAChR expressions and provided benefits in recognition memory. Interestingly, clozapine and CCMI restored the MK-801 induced deficits on GAD1 expression and spatial memory while A-582941 and PNU-120596 were ineffective. These results indicated that α7 nAChR agonist, type I and type II PAMs may provide benefits in different types of cognitive deficits rather than a complete treatment in schizophrenia.

Multiscale neurobiological correlates of human neuroticism

Neuroticism is a heritable personality trait associated with negative emotionality; however, we know little regarding the association between the microscale and macroscale neurobiological substrates of human neuroticism. Cross‐scale correlation analysis may provide such information. In this study, voxel‐wise neuroimaging–neuroticism correlation analyses consistently showed a positive correlation between neuroticism and functional connectivity density (FCD) in the ventral striatum in 274 young Chinese adults. Partial least squares regression analysis showed that the FCD‐neuroticism correlation map was significantly spatially correlated with gene expression profiles in each of six donated human brains. Neuroticism‐related genes derived from the six donors consistently showed significant enrichment in the chemical synaptic transmission, circadian entrainment, long‐term potentiation, inflammatory mediator regulation of transient receptor potential channels, and amphetamine addiction pathways. The protein–protein interaction analysis revealed four hub genes involved in the above pathways, including G protein subunit gamma 10, 5‐hydroxytryptamine receptor 2C, prodynorphin, and calcium/calmodulin‐dependent protein kinase II alpha. By combining multiscale correlation analyses and functional annotations, this study advances our understanding of the genetic and neural substrates of human neuroticism and emphasizes the importance of striatal functional properties in human neuroticism.

REM sleep loss-induced elevated noradrenaline could predispose an individual to psychosomatic disorders: a review focused on proposal for prediction, prevention, and personalized treatment

Historically and traditionally, it is known that sleep helps in maintaining healthy living. Its duration varies not only among individuals but also in the same individual depending on circumstances, suggesting it is a dynamic and personalized physiological process. It has been divided into rapid eye movement sleep (REMS) and non-REMS (NREMS). The former is unique that adult humans spend the least time in this stage, when although one is physically asleep, the brain behaves as if awake, the dream state. As NREMS is a pre-requisite for appearance of REMS, the latter can be considered a predictive readout of sleep quality and health. It plays a protective role against oxidative, stressful, and psychopathological insults. Several modern lifestyle activities compromise quality and quantity of sleep (including REMS) affecting fundamental physiological and psychopathosomatic processes in a personalized manner. REMS loss-induced elevated brain noradrenaline (NA) causes many associated symptoms, which are ameliorated by preventing NA action. Therefore, we propose that awareness about personalized sleep hygiene (including REMS) and maintaining optimum brain NA level should be of paramount significance for leading physical and mental well-being as well as healthy living. As sleep is a dynamic, multifactorial, homeostatically regulated process, for healthy living, we recommend addressing and treating sleep dysfunctions in a personalized manner by the health professionals, caregivers, family, and other supporting members in the society. We also recommend that maintaining sleep profile, optimum level of NA, and/or prevention of elevation of NA or its action in the brain must be seriously considered for ameliorating lifestyle and REMS disturbance-associated dysfunctions.

Higher levels of α7 nicotinic receptors, but not choline acetyltransferase, in the dorsolateral prefrontal cortex from a sub-group of patients with schizophrenia

It has been suggested the study of sub-groups within the syndrome of schizophrenia will assist in elucidating the complex pathophysiology of the syndrome. Hence, we have studied a number of cholinergic markers in the cortex from a sub-group of subjects with schizophrenia that have a marked decrease in levels of muscarinic M1 receptors (MRDS). The displacement of [³H]NMS by cortical extracts was used to measure tissue anticholinergic load, [¹²⁵I]α bungarotoxin binding was used to measure levels of the α7 nicotinic receptor (CHRNA7) and western blotting was used to measure levels of choline acetyltransferase (ChAT) 68 and 82 as well as synaptosome nerve-associated protein 25 (SNAP25). In comparing schizophrenia, MRDS and non-MRDS to controls, there were no differences in levels of ChAT 68 or 82, SNAP 25 or cholinergic load in BA 9. However, levels of CHRNA7 were higher in BA 9, but not BA 6 or 44, from subjects with MRDS. These data argue that there is no change in cholinergic innovation (measured using ChAT), presynaptic neurons (measured using SNAP25) or cholinergic load in schizophrenia, MRDS or non-MRDS. However, increased levels of CHRNA7 may be contributing to a breakdown in cholinergic homeostasis in BA 9, but not BA 6 or 44, in subjects with MRDS.

Anticholinergic medications even in therapeutic range can cause recurrence of psychosis

Anticholinergic drugs are commonly used in psychiatry to attenuate antipsychotic induced extrapyramidal syndrome (EPS). Psychosis as a side effect is generally explained under the rubric of anticholinergic toxicity or induced delirium. Anticholinergic induced worsening of psychosis in patients with normal cognition is extremely rare in literature. Here, we arepresenting a case of young female who was prescribed with multiple anticholinergics to reduce EPS, and each time had worsening of psychosis with intact cognition. We then discussed the possible neurobiological explanation with special reference to muscarinic hypothesis of schizophrenia.

Glutamic acid decarboxylase 67 haplodeficiency in mice: consequences of postweaning social isolation on behavior and changes in brain neurochemical systems

Reductions of glutamate acid decarboxylase (GAD67) and subsequent GABA levels have been consistently observed in neuropsychiatric disorders like schizophrenia and depression, but it has remained unclear how GABAergic dysfunction contributes to different symptoms of the diseases. To address this issue, we investigated male mice haplodeficient for GAD67 (GAD67^+/GFP mice), which showed a reduced social interaction, social dominance and increased immobility in the forced swim test. No differences were found in rotarod performance and sensorimotor gating. We also addressed potential effects of social deprivation, which is known, during early life, to affect GABAergic function and induces behavioral abnormalities similar to the symptoms found in psychiatric disorders. Indeed, social isolation of GAD67^+/GFP mice provoked increased rearing activity in the social interaction test and hyperlocomotion on elevated plus maze. Since GABA closely interacts with the dopaminergic, serotonergic and cholinergic neurotransmitter systems, we investigated GAD67^+/GFP and GAD67^+/+ mice for morphological markers of the latter systems and found increased tyrosine hydroxylase (TH)-IR fiber densities in CA1 of dorsal hippocampus. By contrast, no differences in numbers and densities of TH-positive neurons of the midbrain dopamine regions, serotonin (5-HT) neurons of the raphe nuclei, or choline acetyltransferase (ChAT)-expressing neurons of basal forebrain and their respective terminal fields were observed. Our results indicate that GAD67 haplodeficiency impairs sociability and increases vulnerability to social stress, provokes depressive-like behavior and alters the catecholaminergic innervation in brain areas associated with schizophrenia. GAD67^+/GFP mice may provide a useful model for studying the impact of GABAergic dysfunction as related to neuropsychiatric disorders.

Muscarinic M1 and M4 receptors: Hypothesis driven drug development for schizophrenia

The finding that the drug KarXT, a formulation of xanomeline and tropsium which targets muscarinic receptors, has given a positive result in reducing the positive and negative symptoms of schizophrenia in a phase II trial suggests targeting muscarinic receptors is a new approach to treating the disorder. This review will detail the synergistic interplay between studies to understand the role of muscarinic receptors in the aetiology of schizophrenia and drug development and how this has supported the hypothesis that activating the muscarinic M1 and M4 receptors is critical to the efficacy of KarXT, in schizophrenia. The discovery of an intermediate phenotype within schizophrenia which is characterised by the presence of a marked loss of cortical muscarinic M1 receptors will be reviewed. Highlighted will be progress in understanding the biochemistry of that intermediate phenotype and evidence to suggest that those with the intermediate phenotype may resist treatment with agonist to the orthosteric site on the muscarinic M1 and M4 receptor. Finally, the possibility of using drugs targeting the allosteric binding sites on muscarinic receptors to treat schizophrenia will be discussed. This timely review will therefore highlight how research can influence hypothesis driven drug discovery that should produce new treatments for schizophrenia.

The muscarinic M1 receptor modulates associative learning and memory in psychotic disorders

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Psychosis characterised by different M₁ sensitivity in learning and memory.

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Greater limbic-temporal hyperactivity in response to biperiden in psychosis.

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Hippocampal M₁ binding predicted limbic-temporal hyperactivation underlying learning.

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M₁ agonist may normalise functional response underlying learning & memory in psychosis.

Background

Psychotic disorders are characterized by prominent deficits in associative learning and memory for which there are currently no effective treatments. Functional magnetic resonance imaging (fMRI) studies in psychotic disorders have identified deficits in fronto-temporal activation during associative learning and memory. The underlying pathology of these findings remains unclear. Postmortem data have suggested these deficits may be related to loss of muscarinic M₁ receptor mediated signaling. This is supported by an in-vivo study showing improvements in these symptoms after treatment with the experimental M_1/4 receptor agonist xanomeline. The current study tests whether reported deficits in fronto-temporal activation could be mediated by loss of M₁ receptor signaling in psychotic disorders.

Methods

Twenty-six medication-free subjects diagnosed with a psychotic disorder and 29 age-, gender-, and IQ-matched healthy controls underwent two functional magnetic resonance imaging (fMRI) sessions, one under placebo and one under selective M₁ antagonist biperiden, while performing the paired associated learning task. M₁ binding potentials (BP_ND) were measured in the dorsolateral prefrontal cortex (DLPFC) and hippocampus using ¹²³I-IDEX single photon emission computed tomography.

Results

In the subjects with psychotic disorders DLPFC hypoactivation was only found in the memory phase of the task. In both learning and memory phases of the task, M₁ antagonism by biperiden elicited significantly greater hyperactivation of the parahippocampal gyrus and superior temporal gyrus in subjects with a psychotic disorders compared to controls. Greater hyperactivation of these areas after biperiden was associated with greater hippocampal M₁ receptor binding during learning, with no association found with M₁ receptor binding in the DLPFC. M₁ receptor binding in the DLPFC was related to greater functional sensitivity to biperiden of the cingulate gyrus during the memory phase.

Conclusion

The current study is the first to show differences in M₁ receptor mediated functional sensitivity between subjects with a psychotic disorder and controls during a paired associate learning and memory task. Results point to subjects with psychotic disorders having a loss of M₁ receptor reserve in temporal-limbic areas.

Alpha 7 nicotinic receptor agonist and positive allosteric modulators improved social and molecular deficits of MK-801 model of schizophrenia in rats

Schizophrenia is a common psychiatric disease that cannot be fully treated with current antipsychotic drugs. It has shown that glutamatergic NMDA receptor antagonists such as MK-801 cause schizophrenia-like phenotype in rodents. Recent studies indicated that α7 nicotinic acetylcholine receptor (nAChR) deficits contribute to schizophrenia. Enhancing its activity with agonist or positive allosteric modulators (PAMs) may be a valuable approach for treatment. The certain intracellular pathways such as Akt/Glycogen synthase kinase 3 beta (GSK-3β) and phosphodiesterase-4 (PDE-4)/cAMP are associated with the pathogenesis of schizophrenia. In this study, we examined the effect of α7 nAChR agonists and PAMs on the behavioral and molecular phenotype of schizophrenia in the subchronic MK-801 administered rats. Social interaction, the levels of α7 nAChR, and related intracellular pathways (cAMP, PDE4A, PDE4D, p-Akt/Akt, p-GSK-3β/GSK-3β) were measured by behavioral or ELISA and western blot tests. Subchronic MK-801 administration decreased the following behaviors and increased the avoiding behaviors. However, only α7 nAChR agonist (A-582941) increased the following behavior while α7 nAChR agonist, PAMs (CCMI and PNU-120596), and clozapine decreased the avoiding behavior compared to MK-801. For molecular parameters, MK-801 administration decreased the α7 nAChR, p-Akt/Akt, p-GSK-3β/GSK-3β expressions, and cAMP levels while it increased PDE4A, PDE4D expressions in the prefrontal cortex. Besides, MK-801 decreased the α7 nAChR, p-GSK-3β/GSK-3β expressions in the hippocampus. We found clozapine, α7 nAChR agonists, and PAMs reversed the molecular deficits induced by MK-801. Herein, we showed that prefrontal cortex is more sensitive to the devastating effects of subchronic MK-801 administration, especially for PDE4, in rats. In addition to clozapine, α7 nAChR agonists and PAMs found to be beneficial on both social and molecular deficits induced by MK-801 in rats. We suggested that α7 nAChR agonists and PAMs might be valuable approaches to treat negative symptoms of schizophrenia when unmet needs and current limitations considered in this pathology.

Characterization of three-dimensional rat central nervous system culture maturation, with applications to monitor cholinergic integrity

Studying age-related neuropathologies in vitro requires a three-dimensional (3D) culture system presenting mature phenotypes. In this study, we aimed to determine whether aged reaggregate cultures physiologically represent mature brain tissue. Results support that embryo-derived rat central nervous system (CNS) reaggregate cultures develop into mature-like tissues, comparable to in vivo maturation, including the following characteristics: (a) progressive reduction in cell proliferation (reduced anti-Ki-67 immunoreactivity), (b) progressive restriction of long neurite growth potential (as explant cultures), and (c) increased and sustained synaptic enzyme (acetylcholine esterase, AChE) activity. The acquisition of mature-like reaggregate cultures has allowed us to pursue the hypothesis that the physiological integrity of 3D CNS cultures may be monitored by synaptic enzyme activity. To assess this hypothesis, mature-like reaggregates were exposed to H₂ O₂ , glutamate, or amyloid β(1-42); each resulted in diminished AChE activity. H₂ O₂ exposure resulted in nuclear fragmentation. Glutamate and amyloid β(1-42) exposure resulted in acetylcholine content reduction. Simultaneous reduction of AChE activity and acetylcholine content verified diminished cholinergic integrity. This scheme exploiting synapse enzyme activity of mature-like 3D CNS tissue is therefore applicable to age-related neuropathology research including in vitro screening of conditions potentially affecting synapse integrity, including the promotion of dementia.

Pharmacological enrichment of polygenic risk for precision medicine in complex disorders

Individuals with complex disorders typically have a heritable burden of common variation that can be expressed as a polygenic risk score (PRS). While PRS has some predictive utility, it lacks the molecular specificity to be directly informative for clinical interventions. We therefore sought to develop a framework to quantify an individual’s common variant enrichment in clinically actionable systems responsive to existing drugs. This was achieved with a metric designated the pharmagenic enrichment score (PES), which we demonstrate for individual SNP profiles in a cohort of cases with schizophrenia. A large proportion of these had elevated PES in one or more of eight clinically actionable gene-sets enriched with schizophrenia associated common variation. Notable candidates targeting these pathways included vitamins, antioxidants, insulin modulating agents, and cholinergic drugs. Interestingly, elevated PES was also observed in individuals with otherwise low common variant burden. The biological saliency of PES profiles were observed directly through their impact on gene expression in a subset of the cohort with matched transcriptomic data, supporting our assertion that this gene-set orientated approach could integrate an individual’s common variant risk to inform personalised interventions, including drug repositioning, for complex disorders such as schizophrenia.

Alterations in neuromuscular junctions and oxidative stress of the soleus muscle of obese Wistar rats caused by vibratory platform training

OBJECTIVES

evaluate the effects that whole-body vibration (WBV) causes on the neuromuscular junctions and oxidative stress of the soleus muscle of obese Wistar rats.

METHODS

32 male Wistar rats were used, 16 of which were obesity induced by monosodium glutamate, randomized into four groups: control (GC), control with WBV (GCP), obese (GO) and obese with WBV (GOP). At the 70 days old, the training on WBV was started, performed 3 times a week, during 8 consecutive weeks. At the 130 days old, the animals were euthanized and the soleus muscles were collected.

RESULTS

Regarding the analysis of the neuromuscular junctions, the obese groups had lower mean size when compared to the control groups. On the other hand, the WBV presented higher averages when compared to the groups that did not perform the training. Regarding the oxidative stress, for the lipid peroxidation there was a significant difference between obese and non-obese animals, however, there was no difference between the animals WBV and those who did not.

CONCLUSION

WBV promotes beneficial changes such as increased measurements of the structures of the neuromuscular junctions, but is not able to promote changes in the concentration of the cholinesterase enzyme in the synaptic cleft.

Is there a role for antibodies targeting muscarinic acetylcholine receptors in the pathogenesis of schizophrenia?

OBJECTIVE

Muscarinic receptor dysfunction has been suggested to play an important role in the pathophysiology of schizophrenia. Recently, it has also become clear that immune reactivity directed against neurotransmitter receptors may play a pathogenic role in some cases of schizophrenia. The aim of this review is to summarize the case for muscarinic receptor dysfunction in schizophrenia and the evidence supporting the hypothesis that this dysfunction is related to the development of muscarinic receptor-targeting antibodies.

METHOD

The article reviews studies of muscarinic receptors and the presence and potential role(s) of anti-muscarinic acetylcholine receptor antibodies in people with schizophrenia.

RESULTS

There is accumulating evidence that altered or deficient muscarinic signalling underlies some of the key clinical features of schizophrenia. Although the number of studies investigating anti-muscarinic acetylcholine receptor antibodies in schizophrenia is relatively small, they consistently demonstrate that such antibodies are present in a proportion of patients. This evidence suggests that these antibodies could have pathogenic effects or exist as a biomarker to an unknown pathophysiological process in schizophrenia.

CONCLUSION

The presence of elevated levels of anti-muscarinic acetylcholine receptor antibodies may identify a subgroup of people with schizophrenia, potentially informing aetiopathogenesis, clinical presentation and treatment. To date, all studies have examined antibodies in participants with chronic schizophrenia, who have likely received antipsychotic medication for many years. As these medications modulate immune functions and regulate receptor densities, it is recommended that future studies screen for the presence of anti-muscarinic antibodies in people experiencing their first episode of psychosis.

Nicotine consumption during the prodromal phase of schizophrenia - a review of the literature

Recent research has fueled a debate concerning the role of nicotine in the emergence of schizophrenia. The three main hypotheses are: (a) the self-medication effect, (b) the causal relationship hypothesis, or (c) the shared diathesis hypothesis. To explore this role, the study of nicotine consumption during the initial prodromal phase of schizophrenia offers important opportunities. In the present work, 10 relevant studies are reviewed, out of 727 retrieved citations, in order to address questions regarding the prevalence of smoking in the prodromal period, the time of smoking initiation, existing patterns of tobacco use in relation with the escalation of prodromal symptoms into first psychotic episode, and potential differences in symptomatology between smokers and nonsmokers. Even though there was considerable heterogeneity among studies, relevant findings are discussed. Prevalence of nicotine use during the prodromal period was reported to be 16.6-46%. Tobacco use was found to be taken up most often before or during the prodromal period of schizophrenia. Even though a protective role of smoking has been reported by one study, other studies report an increased risk for psychosis, with hazard ratios 2.77 (95% CI: 2.34-3.43) and 2.21 (95% CI: 1.11-4.42) for female and male heavy smokers (11-20 and >20 cigarettes/day), respectively. In a different study, the risk of onset was associated with the progressive use of cannabis and tobacco prior to onset, particularly with rapid escalation to the highest levels of use. Also, nicotine use in ultra high risk (UHR) for developing psychosis subjects is associated with elevated cognitive performance, namely better processing speed, visual learning, and spatial working memory. As a conclusion, it appears that evidence accumulates supporting a possible etiologic role of smoking, in the emergence of schizophrenia along with diverse effects on patients' symptomatology, already demonstrable at the prodromal phase. Future research employing better-defined criteria should further explore the patterns of use and effects of nicotine during the schizophrenia prodrome.

Effects of Euterpe oleracea to Enhance Learning and Memory in a Conditioned Nicotinic and Muscarinic Receptor Response Paradigm by Modulation of Cholinergic Mechanisms in Rats

Euterpe oleracea (EO) includes a large number of polyphenolic compounds such as phenolics, flavonoids, and anthocyanins that have antioxidant activities. E. oleracea was suggested to ease the oxidative stress and inflammation in brain cells. Our aim was to analyze the effects of E. oleracea on learning and memory. Seventy-two (250 ± 25 g) male Wistar albino rats were used for this study. The groups consisted of control, EO100 mg/kg, EO300 mg/kg, scopolamine 1.5 mg/kg, mecamylamine 7.5 mg/kg, combinations of scopolamine with EO100 mg/kg, EO300 mg/kg, and rivastigmine 1.5 mg/kg; and mecamylamine combined with EO100 mg/kg. Before the start of the study, E. oleracea doses were provided once a day for a period of 15 days and for a 6-day experimental period. Thirty minutes after intraperitoneal scopolamine and mecamylamine injections, gastrogavage was applied to each group. Ninety minutes after the drug treatments, locomotor activity and Morris water maze tests were performed. Rats were killed and each hippocampus was used for the quantification of acetylcholine (Ach). Statistical analyses were calculated using one-way and two-way analyses of variance (ANOVA), and a value of P < .05 was considered significant. In groups EO100 mg/kg and EO300 mg/kg the results did not show any significant changes on learning and memory compared with the control group. Mecamylamine and scopolamine enhanced the latency for the escape platform, and decreased the time spent in escape platform quadrant when the memory tests were applied in reference to the control value of P < .05. Scopolamine and mecamylamine combinations of EO100 mg/kg, EO300 mg/kg, and rivastigmine were proven to improve the memory. There was significant difference between the first and fifth days of the learning tests in all the groups, but no significant difference occurred between the groups. Ach levels in hippocampi supported all memory tests. We suggest that E. oleracea made no alterations on learning and memory, but still improved nicotinic and muscarinic receptor-mediated and impaired memory just as rivastigmine.

Nucleus Accumbens Cholinergic Interneurons Oppose Cue-Motivated Behavior

BACKGROUND

Environmental reward-predictive stimuli provide a major source of motivation for adaptive reward pursuit behavior. This cue-motivated behavior is known to be mediated by the nucleus accumbens (NAc) core. The cholinergic interneurons in the NAc are tonically active and densely arborized and thus well suited to modulate NAc function. However, their causal contribution to adaptive behavior remains unknown. Here we investigated the function of NAc cholinergic interneurons in cue-motivated behavior.

METHODS

We used chemogenetics, optogenetics, pharmacology, and a translationally analogous Pavlovian-to-instrumental transfer behavioral task designed to assess the motivating influence of a reward-predictive cue over reward-seeking actions in male and female rats.

RESULTS

The data show that NAc cholinergic interneuron activity critically opposes the motivating influence of appetitive cues. Chemogenetic inhibition of NAc cholinergic interneurons augmented cue-motivated behavior. Optical stimulation of acetylcholine release from NAc cholinergic interneurons prevented cues from invigorating reward-seeking behavior, an effect that was mediated by activation of β2-containing nicotinic acetylcholine receptors.

CONCLUSIONS

NAc cholinergic interneurons provide a critical regulatory influence over adaptive cue-motivated behavior and therefore are a potential therapeutic target for the maladaptive cue-motivated behavior that marks many psychiatric conditions, including addiction and depression.

New Insights Into Cholinergic Neuron Diversity

Cholinergic neurons comprise a small population of cells in the striatum but have fundamental roles in fine tuning brain function, and in the etiology of neurological and psychiatric disorders such as Parkinson’s disease (PD) or schizophrenia. The process of developmental cell specification underlying neuronal identity and function is an area of great current interest. There has been significant progress in identifying the developmental origins, commonalities in molecular markers, and physiological properties of the cholinergic neurons. Currently, we are aware of a number of key factors that promote cholinergic fate during development. However, the extent of cholinergic cell diversity is still largely underestimated. New insights into the biological basis of their specification indicate that cholinergic neurons may be far more diverse than previously thought. This review article, highlights the physiological features and the synaptic properties that segregate cholinergic cell subtypes. It provides an accurate picture of cholinergic cell diversity underlying their organization and function in neuronal networks. This review article, also discusses current challenges in deciphering the logic of the cholinergic cell heterogeneity that plays a fundamental role in the control of neural processes in health and disease.

Cholinergic Neurons of the Medial Septum Are Crucial for Sensorimotor Gating

Hypofunction of NMDA receptors has been considered a possible cause for the pathophysiology of schizophrenia. More recently, indirect ways to regulate NMDA that would be less disruptive have been proposed and metabotropic glutamate receptor subtype 5 (mGluR5) represents one such candidate. To characterize the cell populations involved, we demonstrated here that knock-out (KO) of mGluR5 in cholinergic, but not glutamatergic or parvalbumin (PV)-positive GABAergic, neurons reduced prepulse inhibition of the startle response (PPI) and enhanced sensitivity to MK801-induced locomotor activity. Inhibition of cholinergic neurons in the medial septum by DREADD (designer receptors exclusively activated by designer drugs) resulted in reduced PPI further demonstrating the importance of these neurons in sensorimotor gating. Volume imaging and quantification were used to compare PV and cholinergic cell distribution, density, and total cell counts in the different cell-type-specific KO lines. Electrophysiological studies showed reduced NMDA receptor-mediated currents in cholinergic neurons of the medial septum in mGluR5 KO mice. These results obtained from male and female mice indicate that cholinergic neurons in the medial septum represent a key cell type involved in sensorimotor gating and are relevant to pathologies associated with disrupted sensorimotor gating such as schizophrenia.SIGNIFICANCE STATEMENT The mechanistic complexity underlying psychiatric disorders remains a major challenge that is hindering the drug discovery process. Here, we generated genetically modified mouse lines to better characterize the involvement of the receptor mGluR5 in the fine-tuning of NMDA receptors, specifically in the context of sensorimotor gating. We evaluated the importance of knocking-out mGluR5 in three different cell types in two brain regions and performed different sets of experiments including behavioral testing and electrophysiological recordings. We demonstrated that cholinergic neurons in the medial septum represent a key cell-type involved in sensorimotor gating. We are proposing that pathologies associated with disrupted sensorimotor gating, such as with schizophrenia, could benefit from further evaluating strategies to modulate specifically cholinergic neurons in the medial septum.

Striatal cholinergic interneurons regulate cognitive and affective dysfunction in partially dopamine-depleted mice

Early non-motor symptoms such as mood disorders and cognitive deficits are increasingly recognised in Parkinson's disease (PD). They may precede the characteristic motor symptomatology caused by dopamine (DA) neuronal loss in the substantia nigra pars compacta (SNc). It is well known that striatal cholinergic interneurons (ChIs) are emerging as key regulators of PD motor symptom, however, their involvement in the cognitive and affective alterations occurring in the premotor phase of PD is poorly understood. We used optogenetic photoinhibition of striatal ChIs in mice with mild nigrostriatal 6-hydroxydopamine (6-OHDA) lesions and assessed their role in anxiety-like behaviour in the elevated plus maze, social memory recognition of a congener and visuospatial object recognition. In transgenic mice specifically expressing halorhodopsin (eNpHR) in cholinergic neurons, striatal ChIs photoinhibition reduced the anxiety-like behaviour and reversed social and spatial short-term memory impairment induced by moderate DA depletion (e.g., 50% loss of tyrosine hydroxylase TH-positive neurons in the SNc). Systemic injection of telenzepine (0.3 mg/kg), a preferential M1 muscarinic cholinergic receptors antagonist, improved anxiety-like behaviour, social memory recognition but not spatial memory deficits. Our results suggest that dysfunction of the striatal cholinergic system may play a role in the short-term cognitive and emotional deficits of partially DA-depleted mice. Blocking cholinergic activity with M1 muscarinic receptor antagonists may represent a possible therapeutic target, although not exclusive, to modulate these early non-motor deficits.

Muscarinic M1 Receptor Modulation of Synaptic Plasticity in Nucleus Accumbens of Wild-Type and Fragile X Mice

We investigated how metabotropic acetylcholine receptors control excitatory synaptic plasticity in the mouse nucleus accumbens core. Pharmacological and genetic approaches revealed that M₁ mAChRs (muscarinic acetylcholine receptors) trigger multiple and interacting forms of synaptic plasticity. As previously described in the dorsal striatum, moderate pharmacological activation of M₁ mAChR potentiated postsynaptic NMDARs. The M₁-potentiation of NMDAR masked a previously unknown coincident TRPV1-mediated long-term depression (LTD). In addition, strong pharmacological activation of M₁ mAChR induced canonical retrograde LTD, mediated by presynaptic CB1R. In the fmr1-/y mouse model of Fragile X, we found that CB1R but not TRPV1 M₁-LTD was impaired. Finally, pharmacological blockade of the degradation of anandamide and 2-arachidonylglycerol, the two principal endocannabinoids restored fmr1-/y LTD to wild-type levels. These findings shed new light on the complex influence of acetylcholine on excitatory synapses in the nucleus accumbens core and identify new substrates of the synaptic deficits of Fragile X.

A gender dimorphism in up-regulation of BACE1 gene expression in schizophrenia

Schizophrenia has long been considered as a devastating brain disorder in which both genetic and environmental factors are involved. The BACE1 gene is one of the most important susceptibility genes for this disorder. However, the changes in BACE1 expression in schizophrenic patients compared with healthy subjects have not been evaluated yet. In this case-control study, we examined BACE1 expression in a group of 50 patients with schizophrenia and 50 healthy controls. The level of BACE1 gene expression was measured using Real-Time PCR. Substantial increase in gene expression was detected in the patients compared with normal individuals (P = 0.001). Furthermore, a gender dimorphism was observed in BACE1 gene expression in the patients in a way that the male patients manifested a statistically significant higher levels of BACE1 expression (P = 0.002). BACE1 might be implicated in the pathogenesis of schizophrenia. Besides, BACE1 physiology may be gender -based at some levels. Our findings warrant an investigation of BACE1 gene in a larger number of cases and controls.

Differential inputs to striatal cholinergic and parvalbumin interneurons imply functional distinctions

Striatal cholinergic (ChAT) and parvalbumin (PV) interneurons exert powerful influences on striatal function in health and disease, yet little is known about the organization of their inputs. Here using rabies tracing, electrophysiology and genetic tools, we compare the whole-brain inputs to these two types of striatal interneurons and dissect their functional connectivity in mice. ChAT interneurons receive a substantial cortical input from associative regions of cortex, such as the orbitofrontal cortex. Amongst subcortical inputs, a previously unknown inhibitory thalamic reticular nucleus input to striatal PV interneurons is identified. Additionally, the external segment of the globus pallidus targets striatal ChAT interneurons, which is sufficient to inhibit tonic ChAT interneuron firing. Finally, we describe a novel excitatory pathway from the pedunculopontine nucleus that innervates ChAT interneurons. These results establish the brain-wide direct inputs of two major types of striatal interneurons and allude to distinct roles in regulating striatal activity and controlling behavior.

The role of catecholamines in HIV neuropathogenesis

The success of anti-retroviral therapy has improved the quality of life and lifespan of HIV + individuals, transforming HIV infection into a chronic condition. These improvements have come with a cost, as chronic HIV infection and long-term therapy have resulted in the emergence of a number of new pathologies. This includes a variety of the neuropathological and neurocognitive effects collectively known as HIVassociated neurocognitive disorders (HAND) or NeuroHIV. These effects persist even in the absence of viral replication, suggesting that they are mediated the long-term changes in the CNS induced by HIV infection rather than by active replication. Among these effects are significant changes in catecholaminergic neurotransmission, especially in dopaminergic brain regions. In HIV-infected individuals not treated with ARV show prominent neuropathology is common in dopamine-rich brain regions and altered autonomic nervous system activity. Even infected individuals on therapy, there is significant dopaminergic neuropathology, and elevated stress and norepinephrine levels correlate with a decreased effectiveness of antiretroviral drugs. As catecholamines function as immunomodulatory factors, the resultant dysregulation of catecholaminergic tone could substantially alter the development of HIVassociated neuroinflammation and neuropathology. In this review, we discuss the role of catecholamines in the etiology of HIV neuropathogenesis. Providing a comprehensive examination of what is known about these molecules in the context of HIV-associated disease demonstrates the importance of further studies in this area, and may open the door to new therapeutic strategies that specifically ameliorate the effects of catecholaminergic dysregulation on NeuroHIV.

Changed frontal pole gene expression suggest altered interplay between neurotransmitter, developmental, and inflammatory pathways in schizophrenia

Schizophrenia (Sz) probably occurs after genetically susceptible individuals encounter a deleterious environmental factor that triggers epigenetic mechanisms to change CNS gene expression. To determine if omnibus changes in CNS gene expression are present in Sz, we compared mRNA levels in the frontal pole (Brodmann’s area (BA) 10), the dorsolateral prefrontal cortex (BA 9) and cingulate cortex (BA 33) from 15 subjects with Sz and 15 controls using the Affymetrix™ Human Exon 1.0 ST Array. Differences in mRNA levels (±≥20%; p < 0.01) were identified (JMP Genomics 5.1) and used to predict pathways and gene x gene interactions that would be affected by the changes in gene expression using Ingenuity Pathway Analysis. There was significant variation in mRNA levels with diagnoses for 566 genes in BA 10, 65 genes in BA 9 and 40 genes in BA 33. In Sz, there was an over-representation of genes with changed expression involved in inflammation and development in BA 10, cell morphology in BA 9 and amino acid metabolism and small molecule biochemistry in BA 33. Using 94 genes with altered levels of expression in BA 10 from subjects with Sz, it was possible to construct an interactome of proven direct gene x gene interactions that was enriched for genes in inflammatory, developmental, oestrogen, serotonergic, cholinergic and NRG1 regulated pathways. Our data shows complex, regionally specific changes in cortical gene expression in Sz that are predicted to affect homeostasis between biochemical pathways already proposed to be important in the pathophysiology of the disorder.

Anterior brain regions exhibit significant amounts of differentially-expressed genes which might cause dysfunction in schizophrenia. It’s thought that schizophrenia occurs when environmental factors trigger gene expression changes and downstream effects in the human brain, though this is not fully understood. An Australian research group led by Brian Dean, from the Florey Institute of Neuroscience and Mental Health, conducted a post-mortem human brain study in which they compared gene expression between 15 schizophrenia patients and 15 controls. They found 566 instances of altered gene expression in the most frontal part of the brain, Brodmann Area 10, and fewer changes in proximal regions. These are brain areas known to mediate schizophrenia-related traits and the changes in gene expression in these areas will affect a range of essential biological pathways. The group also found 97 differentially-expressed genes that have been shown to directly interact with each. This study paints a complex picture of the causes of schizophrenia but suggests modern technologies can help unravel these complexities.