Serotonin transporter availability in thalamic subregions in schizophrenia: a study using 7.0-T MRI with [(11)C]DASB high-resolution PET

Altered brain complexity in first-episode antipsychotic-naïve patients with schizophrenia: A whole-brain voxel-wise study

BACKGROUND

Measures of cortical topology are believed to characterize large-scale cortical networks. Previous studies used region of interest (ROI)-based approaches with predefined templates that limit analyses to linear pair-wise interactions between regions. As cortical topology is inherently complex, a non-linear dynamic model that measures the brain complexity at the voxel level is suggested to characterize topological complexities of brain regions and cortical folding.

METHODS

T1-weighted brain images of 150 first-episode antipsychotic-naïve schizophrenia (FES) patients and 161 healthy comparison participants (HC) were examined. The Chaos analysis approach was applied to detect alterations in brain structural complexity using the largest Lyapunov exponent (Lambda) as the key measure. Then, the Lambda spatial series was mapped in the frequency domain using the correlation of the Morlet wavelet to reflect cortical folding complexity.

RESULTS

A widespread voxel-wise decrease in Lambda values in space and frequency domains was observed in FES, especially in frontal, parietal, temporal, limbic, basal ganglia, thalamic, and cerebellar regions. The widespread decrease indicates a general loss of brain topological complexity and cortical folding. An additional pattern of increased Lambda values in certain regions highlights the redistribution of complexity measures in schizophrenia at an early stage with potential progression as the illness advances. Strong correlations were found between the duration of untreated psychosis and Lambda values related to the cerebellum, temporal, and occipital gyri.

CONCLUSIONS

Our findings support the notion that defining brain complexity by non-linear dynamic analyses offers a novel approach for identifying structural brain alterations related to the early stages of schizophrenia.

Risperidone Decreases Expression of Serotonin Receptor-2A (5-HT2A) and Serotonin Transporter (SERT) but Not Dopamine Receptors and Dopamine Transporter (DAT) in PBMCs from Patients with Schizophrenia

Dopamine and serotonin receptors and transporters play an essential role in the pathophysiology of schizophrenia; changes in their expression have been reported in neurons and leukocytes. Each antipsychotic induces a unique pattern in leukocyte function and phenotype. However, the use of polytherapy to treat schizophrenia makes it challenging to determine the specific effects of risperidone on peripheral blood mononuclear cells (PBMCs). The aim of this study was to evaluate the changes in the expression of D3, D5, DAT, 5-HT2A, and SERT in PBMCs from healthy volunteers (HV), drug-naive patients with schizophrenia (PWS), drug-free PWS, and PWS treated with risperidone for up to 40 weeks using quantitative PCR. Our study revealed elevated mRNA levels of D3, DAT, 5-HT2A, and SERT in unmedicated PWS. Treatment with risperidone led to a reduction only in the expression of 5-HT2A and SERT. Furthermore, we observed a moderate correlation between 5-HT2A expression and the positive and negative syndrome scale (PANSS), as well as SERT expression and PANSS scale. We also found a moderate correlation between 5-HT2A and SERT expression and the positive subscale. The duration of risperidone consumption had a significant negative correlation with the expression of 5-HT2A and SERT. Our study introduces the measurement of 5-HT2A and SERT expression in PBMCs as a useful parameter for assessing the response to risperidone in PWS.

Progress in the application of molecular imaging in psychiatric disorders

Psychiatric disorders have always attracted a lot of attention from researchers due to the difficulties in their diagnoses and treatments. Molecular imaging, as an emerging technology, has played an important role in the researchers of various diseases. In recent years, molecular imaging techniques including magnetic resonance spectroscopy, nuclear medicine imaging, and fluorescence imaging have been widely used in the study of psychiatric disorders. This review will briefly summarize the progression of molecular imaging in psychiatric disorders.

Radiotracers for the Central Serotoninergic System

This review lists the most important radiotracers described so far for imaging the central serotoninergic system. Single-photon emission computed tomography and positron emission tomography radiotracers are reviewed and critically discussed for each receptor.

Molecular imaging of schizophrenia: Neurochemical findings in a heterogeneous and evolving disorder

The past four decades have seen enormous efforts placed on a search for molecular markers of schizophrenia using positron emission tomography (PET) and single photon emission computed tomography (SPECT). In this narrative review, we cast a broad net to define and summarize what researchers have learned about schizophrenia from molecular imaging studies. Some PET studies of brain energy metabolism with the glucose analogue FDGhave have shown a hypofrontality defect in patients with schizophrenia, but more generally indicate a loss of metabolic coherence between different brain regions. An early finding of significantly increased striatal trapping of the dopamine synthesis tracer FDOPA has survived a meta-analysis of many replications, but the increase is not pathognomonic of the disorder, since one half of patients have entirely normal dopamine synthesis capacity. Similarly, competition SPECT studies show greater basal and amphetamine-evoked dopamine occupancy at post-synaptic dopamine D_2/3 receptors in patients with schizophrenia, but the difference is likewise not pathognomonic. We thus propose that molecular imaging studies of brain dopamine indicate neurochemical heterogeneity within the diagnostic entity of schizophrenia. Occupancy studies have established the relevant target engagement by antipsychotic medications at dopamine D_2/3 receptors in living brain. There is evidence for elevated frontal cortical dopamine D₁ receptors, especially in relation to cognitive deficits in schizophrenia. There is a general lack of consistent findings of abnormalities in serotonin markers, but some evidence for decreased levels of nicotinic receptors in patients. There are sparse and somewhat inconsistent findings of reduced binding of muscarinic, glutamate, and opioid receptors ligands, inconsistent findings of microglial activation, and very recently, evidence of globally reduced levels of synaptic proteins in brain of patients. One study reports a decline in histone acetylase binding that is confined to the dorsolateral prefrontal cortex. In most contexts, the phase of the disease and effects of past or present medication can obscure or confound PET and SPECT findings in schizophrenia.

Risperidone administered during adolescence induced metabolic, anatomical and inflammatory/oxidative changes in adult brain: A PET and MRI study in the maternal immune stimulation animal model

Inflammation and oxidative stress (IOS) are considered key pathophysiological elements in the development of mental disorders. Recent studies demonstrated that the antipsychotic risperidone elicits an antiinflammatory effect in the brain. We administered risperidone for 2-weeks at adolescence to assess its role in preventing brain-related IOS changes in the maternal immune stimulation (MIS) model at adulthood. We also investigated the development of volumetric and neurotrophic abnormalities in areas related to the HPA-axis. Poly I:C (MIS) or saline (Sal) were injected into pregnant Wistar rats on GD15. Male offspring received risperidone or vehicle daily from PND35-PND49. We studied 4 groups (8-15 animals/group): Sal-vehicle, MIS-vehicle, Sal-risperidone and MIS-risperidone. [¹⁸F]FDG-PET and MRI studies were performed at adulthood and analyzed using SPM12 software. IOS and neurotrophic markers were measured using WB and ELISA assays in brain tissue. Risperidone elicited a protective function of schizophrenia-related IOS deficits. In particular, risperidone elicited the following effects: reduced volume in the ventricles and the pituitary gland; reduced glucose metabolism in the cerebellum, periaqueductal gray matter, and parietal cortex; higher FDG uptake in the cingulate cortex, hippocampus, thalamus, and brainstem; reduced NFκB activity and iNOS expression; and increased enzymatic activity of CAT and SOD in some brain areas. Our study suggests that some schizophrenia-related IOS changes can be prevented in the MIS model. It also stresses the need to search for novel strategies based on anti-inflammatory compounds in risk populations at early stages in order to alter the course of the disease.

Cerebral serotonin transporter measurements with [11C]DASB: A review on acquisition and preprocessing across 21 PET centres

Positron Emission Tomography (PET) imaging has become a prominent tool to capture the spatiotemporal distribution of neurotransmitters and receptors in the brain. The outcome of a PET study can, however, potentially be obscured by suboptimal and/or inconsistent choices made in complex processing pipelines required to reach a quantitative estimate of radioligand binding. Variations in subject selection, experimental design, data acquisition, preprocessing, and statistical analysis may lead to different outcomes and neurobiological interpretations. We here review the approaches used in 105 original research articles published by 21 different PET centres, using the tracer [¹¹C]DASB for quantification of cerebral serotonin transporter binding, as an exemplary case. We highlight and quantify the impact of the remarkable variety of ways in which researchers are currently conducting their studies, while implicitly expecting generalizable results across research groups. Our review provides evidence that the foundation for a given choice of a preprocessing pipeline seems to be an overlooked aspect in modern PET neuroscience. Furthermore, we believe that a thorough testing of pipeline performance is necessary to produce reproducible research outcomes, avoiding biased results and allowing for better understanding of human brain function.

Visualizing the Human Subcortex Using Ultra-high Field Magnetic Resonance Imaging

With the recent increased availability of ultra-high field (UHF) magnetic resonance imaging (MRI), substantial progress has been made in visualizing the human brain, which can now be done in extraordinary detail. This review provides an extensive overview of the use of UHF MRI in visualizing the human subcortex for both healthy and patient populations. The high inter-subject variability in size and location of subcortical structures limits the usability of atlases in the midbrain. Fortunately, the combined results of this review indicate that a large number of subcortical areas can be visualized in individual space using UHF MRI. Current limitations and potential solutions of UHF MRI for visualizing the subcortex are also discussed.

Penalized PET Reconstruction Using Deep Learning Prior and Local Linear Fitting

Motivated by the great potential of deep learning in medical imaging, we propose an iterative positron emission tomography reconstruction framework using a deep learning-based prior. We utilized the denoising convolutional neural network (DnCNN) method and trained the network using full-dose images as the ground truth and low dose images reconstructed from downsampled data by Poisson thinning as input. Since most published deep networks are trained at a predetermined noise level, the noise level disparity of training and testing data is a major problem for their applicability as a generalized prior. In particular, the noise level significantly changes in each iteration, which can potentially degrade the overall performance of iterative reconstruction. Due to insufficient existing studies, we conducted simulations and evaluated the degradation of performance at various noise conditions. Our findings indicated that DnCNN produces additional bias induced by the disparity of noise levels. To address this issue, we propose a local linear fitting function incorporated with the DnCNN prior to improve the image quality by preventing unwanted bias. We demonstrate that the resultant method is robust against noise level disparities despite the network being trained at a predetermined noise level. By means of bias and standard deviation studies via both simulations and clinical experiments, we show that the proposed method outperforms conventional methods based on total variation and non-local means penalties. We thereby confirm that the proposed method improves the reconstruction result both quantitatively and qualitatively.

Altered interregional correlations between serotonin transporter availability and cerebral glucose metabolism in schizophrenia: A high-resolution PET study using [11C]DASB and [18F]FDG

The purpose of the present study was to investigate the patterns of interregional correlations of serotonin transporter (SERT) availability with glucose metabolism using 7-Tesla magnetic resonance imaging (MRI) and high-resolution positron emission tomography (PET) with ¹¹C-3-amino-4-(2-dimethylaminomethylphenylthio)benzonitrile ([¹¹C]DASB) and [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) in antipsychotic-free patients with schizophrenia in order to shed new light on the disrupted functional connectivity in schizophrenia. Nineteen patients with schizophrenia and 18 healthy controls underwent high-resolution PET and MRI. The binding potential (BP_ND) of [¹¹C]DASB and standardized uptake value ratio (SUVR) of [¹⁸F]FDG were obtained. In SERT availability, the region of interest (ROI)-based analyses showed no significant group differences in any region, except for the anterior hippocampus where the SERT availability was lower in patients with schizophrenia than in controls. The ROI- and voxel-based analyses revealed that the [¹⁸F]FDG SUVR values were significantly lower in patients than in controls in the right superior frontal gyrus and medial part of the left superior frontal gyrus. Regarding the interregional correlations of [¹¹C]DASB BP_ND with [¹⁸F]FDG SUVR, more widespread positive correlations across the brain regions were observed in control subjects than in patients with schizophrenia. Notably, the patients and control subjects showed statistically significant differences in correlations between the SERT availability in the parietal and temporal cortices and the glucose metabolism in the posterior cingulate cortex. These results suggest abnormal functional connectivity between the higher-order cortical regions in schizophrenia and a possible important role of the posterior cingulate gyrus and its related circuitry in the pathophysiology of schizophrenia.

Self-perceived cognitive deficits and their relationship with internalized stigma and quality of life in patients with schizophrenia

BACKGROUND

We investigated self-perceived cognitive deficits and their relationship with internalized stigma and quality of life in patients with schizophrenia in order to shed light on the clinical correlates of subjective cognitive deficits in schizophrenia.

METHODS

Seventy outpatients with schizophrenia were evaluated. Patients' self-perceived cognitive deficits, internalized stigma, and subjective quality of life were assessed using the Scale to Investigate Cognition in Schizophrenia (SSTICS), the Internalized Stigma of Mental Illness Scale (ISMI), and the Schizophrenia Quality of Life Scale Revision 4 (SQLS-R4), respectively. Correlation and regression analyses controlling for the severity of symptoms of schizophrenia were performed, and a mediation analysis was conducted to examine the hypothesis that internalized stigma mediates the relationship between self-perceived cognitive deficits and subjective quality of life.

RESULTS

Pearson's partial correlation analysis showed significant correlations among the SSTICS, ISMI, and SQLS-R4 scores (P<0.01). Multiple regression analysis showed that the SSTICS and ISMI scores significantly predicted the SQLS-R4 score (P<0.01). Mediation analysis revealed that the strength of the association between the SSTICS and SQLS-R4 scores decreased from β=0.74 (P<0.01) to β=0.56 (P<0.01), when the ISMI score was statistically controlled. The Sobel test revealed that this difference was significant (P<0.01), indicating that internalized stigma partially mediated the relationship between self-perceived cognitive deficits and quality of life.

CONCLUSION

The present study indicates that self-perceived cognitive deficits are significantly associated with internalized stigma and quality of life. Furthermore, internalized stigma was identified as a partial mediator of the relationship between self-perceived cognitive deficits and quality of life. These findings suggest that clinicians should be aware that patients with schizophrenia experience significantly greater self-stigma when they suffer subjective cognitive deficits, and that this may further compromise their quality of life.

The serotonin transporter in psychiatric disorders: insights from PET imaging

Over the past 20 years, psychotropics affecting the serotonergic system have been used extensively in the treatment of psychiatric disorders. Molecular imaging, in particular PET, has allowed for elucidation of the essential contribution of the serotonin transporter to the pathophysiology of various psychiatric disorders and their treatment. We review studies that use PET to measure cerebral serotonin transporter activity in psychiatric disorders, focusing on major depressive disorder and antidepressant treatment. We also discuss opportunities and limitations in the application of this neuroimaging method in clinical practice. Although results from individual studies diverge, meta-analysis indicates a trend towards reduced serotonin transporter availability in patients with major depressive disorder. Inconsistencies in results might suggest symptom heterogeneity in major depressive disorder and might therefore be relevant for stratification of patients into clinical subsets. PET has enabled the elucidation of mechanisms of response to selective serotonin reuptake inhibitors (SSRIs) and hence provides a basis for rational pharmacological treatment of major depressive disorder. Such imaging studies have also suggested that the pattern of serotonin transporter binding before treatment might predict response to antidepressant treatment, which could potentially be clinically useful in the future. Additionally, this Review discusses PET studies investigating the serotonin transporter in anxiety, obsessive-compulsive disorder, and eating disorders. Few studies have shown changes in serotonin transporter activity in schizophrenia and attention deficit hyperactivity disorder. By showing the scarcity of data in these psychiatric disorders, we highlight the potential for further investigation in this field.

Relationship between cognitive insight and subjective quality of life in outpatients with schizophrenia

BACKGROUND

The concept of cognitive insight refers to the cognitive processes involved in patients' re-evaluation of their anomalous experiences and of their misinterpretations. The purpose of the present study was to examine the relationship between cognitive insight and subjective quality of life in patients with schizophrenia to further shed light on the nature of cognitive insight and its functional correlates in schizophrenia.

METHODS

Seventy-one stable outpatients with schizophrenia were evaluated for cognitive insight and subjective quality of life using the Beck Cognitive Insight Scale (BCIS) and the Schizophrenia Quality of Life Scale Revision 4 (SQLS-R4). The symptoms of schizophrenia were also assessed. Pearson's correlation analysis and partial correlation analysis that controlled for the severity of symptoms were performed to adjust for the possible effects of symptoms.

RESULTS

The self-reflectiveness subscale score of the BCIS had significant positive correlations with the SQLS-R4 psychosocial domain and total SQLS-R4 scores, indicating that the higher the level of cognitive insight, the lower the subjective quality of life. In partial correlation analysis controlling for symptoms, the BCIS self-reflectiveness subscale score still had a significant correlation with the SQLS-R4 psychosocial domain score. The correlation coefficient between the BCIS self-reflectiveness and total SQLS-R4 scores was reduced to a nonsignificant statistical tendency.

CONCLUSION

The results of our study suggest that cognitive insight, particularly the level of self-reflectiveness, is negatively associated with the level of subjective quality of life in outpatients with schizophrenia and that this relationship is not wholly due to the confounding effect of symptoms. Future studies are necessary to explore possible mediating and moderating factors and to evaluate the effects of therapeutic interventions on the relationship.