Pathway-Specific Dopamine Abnormalities in Schizophrenia

Scopolamine animal model of memory impairment

In this study, we reassessed the suitability of a commonly used pharmacological animal model of Alzheimer's disease (AD) - scopolamine-induced memory impairment. The goal of the study was to explore if this animal model induces other behavioral changes associated with AD. One of the key behavioral features of AD, manifesting already during the early stages of the illness, is apathy-like behavior. We also evaluated how behavioral alterations induced by scopolamine compare to those seen in healthy aging animals. To achieve these goals, locomotor activity and short-term memory of young male Wistar rats were tested in the open field, novel object recognition (NOR) and T-maze spontaneous alternation tests before, during and after 21 daily administrations of scopolamine. Three-, ten- and nineteen-month-old male and female rats were used to measure age-related changes in these behaviors. Our data showed that although both scopolamine treatment and aging reduced the number of approaches to the objects and their exploration time during the NOR test, correlation with impaired object recognition memory was only observed in the scopolamine treated animals. Furthermore, treatment with scopolamine significantly increased the locomotor activity, which could be observed even one week after treatment discontinuation. Contrary, locomotor activity in older rats was significantly lower than that of younger rats. These findings demonstrate that the animal model of scopolamine-induced memory impairment fails to incorporate apathy-like symptoms characteristic to the AD and age-related reduction in physical activity of older rats.

Poly (I:C)-induced maternal immune activation generates impairment of reversal learning performance in offspring

Maternal immune activation (MIA) induces a variety of behavioral and brain abnormalities in offspring of rodent models, compatible with neurodevelopmental disorders, such as schizophrenia or autism. However, it remains controversial whether MIA impairs reversal learning, a basic expression of cognitive flexibility that seems to be altered in schizophrenia. In the present study, MIA was induced by administration of a single dose of polyriboinosinic-polyribocytidylic acid (Poly (I:C) (5 mg/kg i.p.)) or saline to mouse pregnant dams in gestational day (GD) 9.5. Immune activation was monitored through changes in weight and temperature. The offspring were evaluated when they reached adulthood (8 weeks) using a touchscreen-based system to investigate the effects of Poly (I:C) on discrimination and reversal learning performance. After an initial pre-training, mice were trained to discriminate between two different stimuli, of which only one was rewarded (acquisition phase). When the correct response reached above 80% values for two consecutive days, the images were reversed (reversal phase) to assess the adaptation capacity to a changing environment. Maternal Poly (I:C) treatment did not interfere with the learning process but induced deficits in reversal learning compared to control saline animals. Thus, the accuracy in the reversal phase was lower, and Poly (I:C) animals required more sessions to complete it, suggesting impairments in cognitive flexibility. This study advances the knowledge of how MIA affects behavior, especially cognitive domains that are impaired in schizophrenia. The findings support the validity of the Poly (I:C)-based MIA model as a tool to develop pharmacological treatments targeting cognitive deficits associated with neurodevelopmental disorders.

Preventing disease progression in schizophrenia: What are we waiting for

Despite research advances and progress in health care, schizophrenia remains a debilitating and costly disease. Onset occurs typically during youth and can lead to a relapsing and ultimately chronic course with persistent symptoms and functional impairment if not promptly and properly treated. Consequently, over time, schizophrenia causes substantial distress and disability for patients, their families and accrues to a collective burden to society. Recent research has revealed much about the pathophysiology that underlies the progressive nature of schizophrenia. Additionally, treatment strategies for disease management have been developed that have the potential to not just control psychotic symptoms but limit the cumulative morbidity of the illness. Given the evidence for their effectiveness and feasibility for their application, it is perplexing that this model of care has not yet become the standard of care and widely implemented to reduce the burden of illness on patients and society. This begs the question of whether the failure of implementation of a potentially disease-modifying strategy is due to the lack of evidence of efficacy (or belief in it) and readiness for implementation, or whether it's the lack of motivation and political will to support their utilization. To address this question, we reviewed and summarized the literature describing the natural history, pathophysiology and therapeutic strategies that can alleviate symptoms, prevent relapse, and potentially modify the course of schizophrenia. We conclude that, while we await further advances in mental health care from research, we must fully appreciate and take advantage of the effectiveness of existing treatments and overcome the attitudinal, policy, and infrastructural barriers to providing optimal mental health care capable of providing a disease-modifying treatment to patients with schizophrenia.

Synaptotagmin-11 deficiency mediates schizophrenia-like behaviors in mice via dopamine over-transmission

Schizophrenia is a severe neuropsychiatric disease, but the initiation mechanisms are unclear. Although antipsychotics are effective against positive symptoms, therapeutic interventions for negative symptoms are limited due to the lack of pathophysiological mechanisms. Here we identify synaptotagmin-11 (Syt11) as a potential genetic risk factor and dopamine over-transmission as a mechanism in the development of schizophrenia. Syt11 expression is reduced in individuals with schizophrenia but restored following the treatment with antipsychotics. Syt11 deficiency in dopamine neurons in early adolescence, but not in adults, leads to persistent social deficits and other schizophrenia-like behaviors by mediating dopamine over-transmission in mice. Accordingly, dopamine neuron over-excitation before late adolescence induces persistent schizophrenia-associated behavioral deficits, along with the structural and functional alternations in the mPFC. Notably, local intervention of D2R with clinical drugs presynaptically or postsynaptically exhibits both acute and long-lasting therapeutic effects on social deficits in schizophrenia mice models. These findings not only define Syt11 as a risk factor and DA over-transmission as a potential risk factor initiating schizophrenia, but also propose two D2R-targeting strategies for the comprehensive and long-term recovery of schizophrenia-associated social withdrawal.

Antipsychotic-induced prolactin elevation in premenopausal women with schizophrenia: associations with estrogen, disease severity and cognition

PURPOSE

Antipsychotic-induced prolactin elevation may impede protective effects of estrogens in women with schizophrenia-spectrum disorders (SSD). Our study sought to confirm whether the use of prolactin-raising antipsychotics is associated with lower estrogen levels, and to investigate how estrogen and prolactin levels relate to symptom severity and cognition in premenopausal women with SSD.

METHODS

This cross-sectional study included 79 premenopausal women, divided in three groups of women with SSD treated with prolactin-sparing antipsychotics (n = 21) or prolactin-raising antipsychotics (n = 27), and age-matched women without SSD (n = 31). Circulating 17β-estradiol was compared among groups. In patients, we assessed the relationship between prolactin and 17β-estradiol, and the relationships of these hormones to symptom severity and cognition, using correlation analyses and backward regression models.

RESULTS

In women receiving prolactin-raising antipsychotics, 17β-estradiol levels were lower as compared to both other groups (H(2) = 8.34; p = 0.015), and prolactin was inversely correlated with 17β-estradiol (r=-0.42, p = 0.030). In the prolactin-raising group, 17β-estradiol correlated positively with verbal fluency (r = 0.52, p = 0.009), and 17β-estradiol and prolactin together explained 29% of the variation in processing speed (β17β-estradiol = 0.24, βprolactin = -0.45, F(2,25) = 5.98, p = 0.008). In the prolactin-sparing group, 17β-estradiol correlated negatively with depression/anxiety (r = -0.57, p = 0.014), and together with prolactin explained 26% of the variation in total symptoms (β17β-estradiol = -0.41, βprolactin = 0.32, F(2,18) = 4.44, p = 0.027).

CONCLUSIONS

In women with SSD, antipsychotic-induced prolactin elevation was related to lower estrogen levels. Further, estrogens negatively correlated with symptom severity and positively with cognition, whereas prolactin levels correlated negatively with cognition. Our findings stress the clinical importance of maintaining healthy levels of prolactin and estrogens in women with SSD.

Neuromelanin-sensitive MRI for mechanistic research and biomarker development in psychiatry

Neuromelanin-sensitive MRI is a burgeoning non-invasive neuroimaging method with an increasing number of applications in psychiatric research. This MRI modality is sensitive to the concentration of neuromelanin, which is synthesized from intracellular catecholamines and accumulates in catecholaminergic nuclei including the dopaminergic substantia nigra and the noradrenergic locus coeruleus. Emerging data suggest the utility of neuromelanin-sensitive MRI as a proxy measure for variability in catecholamine metabolism and function, even in the absence of catecholaminergic cell loss. Given the importance of catecholamine function to several psychiatric disorders and their treatments, neuromelanin-sensitive MRI is ideally positioned as an informative and easy-to-acquire catecholaminergic index. In this review paper, we examine basic aspects of neuromelanin and neuromelanin-sensitive MRI and focus on its psychiatric applications in the contexts of mechanistic research and biomarker development. We discuss ongoing debates and state-of-the-art research into the mechanisms of the neuromelanin-sensitive MRI contrast, standardized protocols and optimized analytic approaches, and application of cutting-edge methods such as machine learning and artificial intelligence to enhance the feasibility and predictive power of neuromelanin-sensitive-MRI-based tools. We finally lay out important future directions to allow neuromelanin-sensitive-MRI to fulfill its potential as a key component of the research, and ultimately clinical, toolbox in psychiatry.

Is the antidepressant effect of ketamine separate from its psychotomimetic effect? A review of rodent models

Ketamine is an NMDA (N-methyl-d-aspartate) glutamate receptor antagonist, which has a myriad of dose-dependent pharmacological and behavioral effects, including anesthetic, sedative, amnestic, analgesic, and anti-inflammatory properties. Intriguingly, ketamine at subanesthetic doses displays a relevant profile both in mimicking symptoms of schizophrenia and also as the first fast-acting treatment for depression. Here, we present an overview of the state-of-the-art knowledge about ketamine as an antidepressant as well as a pharmacological model of schizophrenia in animal models and human participants. Ketamine's dual effect appears to arise from its mechanism of action involving NMDA receptors, with both immediate and downstream consequences being triggered as a result. Finally, we discuss the feasibility of a unified approach linking the glutamatergic hypothesis of schizophrenia to the promising preclinical and clinical success of ketamine in the treatment of refractory depression.

Medicinal plants and plant-based traditional medicine: Alternative treatments for depression and their potential mechanisms of action

Background

Clinical depression is a serious public health issue that affects 4.7 % of the world's population and can lead to suicide tendencies. Although drug medications are available, only 60 % of the depressed patients respond positively to the treatments, while the rest experience side effects that resulted in the discontinuation of their medication. Thus, there is an urgent need for developing a new anti-depressant with a distinct mode of action and manageable side effects. One of the options is using medicinal plants or plant-based traditional medicine as alternative therapies for psychiatric disorders.

Objectives

Therefore, the objective of this review was twofold; to identify and critically evaluate anti-depressant properties of medicinal plants or those incorporated in traditional medicine; and to discuss their possible mechanism of action as well as challenges and way forward for this alternative treatment approach.

Methods

Relevant research articles were retrieved from various databases, including Scopus, PubMed, and Web of Science, for the period from 2018 to 2020, and the search was updated in September 2024. The inclusion criterion was relevance to antidepressants, while the exclusion criteria included duplicates, lack of full-text availability, and non-English publications.

Results

Through an extensive literature review, more than 40 medicinal plant species with antidepressant effects were identified, some of which are part of traditional medicine. The list of the said plant species included Albizia zygia (DC.) J.F.Macbr., Calculus bovis Sativus, Celastrus paniculatus Willd., Cinnamomum sp., Erythrina velutina Willd., Ficus platyphylla Delile, Garcinia mangostana Linn., Hyptis martiusii Benth, and Polygonum multiflorum Thunb. Anti-depressant mechanisms associated with those plants were further characterised based on their modes of action such as anti-oxidation system, anti-inflammation action, modulation of various neurotransmitters, neuroprotective effect, the regulation of hypothalamic-pituitary-adrenal (HPA) axis and anti-depressant mechanism. The challenges and future outlook of this alternative and complementary medicine are also explored and discussed.

Conclusion

This pool of identified plant species is hoped to offer health care professionals the best possible alternatives of anti-depressants from natural phytocompounds that are efficacious, safe and affordable for applications in future clinical settings.

Mesostriatal Dopaminergic Circuit Dysfunction in Schizophrenia: A Multimodal Neuromelanin-Sensitive Magnetic Resonance Imaging and [18F]-DOPA Positron Emission Tomography Study

BACKGROUND

Striatal hyperdopaminergia is implicated in the pathoetiology of schizophrenia, but how this relates to dopaminergic midbrain activity is unclear. Neuromelanin (NM)-sensitive magnetic resonance imaging provides a marker of long-term dopamine function. We examined whether midbrain NM-sensitive magnetic resonance imaging contrast-to-noise ratio (NM-CNR) was higher in people with schizophrenia than in healthy control (HC) participants and whether this correlated with dopamine synthesis capacity.

METHODS

One hundred fifty-four participants (schizophrenia group: n = 74, HC group: n = 80) underwent NM-sensitive magnetic resonance imaging of the substantia nigra and ventral tegmental area (SN-VTA). A subset of the schizophrenia group (n = 38) also received [18F]-DOPA positron emission tomography to measure dopamine synthesis capacity (Kicer) in the SN-VTA and striatum.

RESULTS

SN-VTA NM-CNR was significantly higher in patients with schizophrenia than in HC participants (effect size = 0.38, p = .019). This effect was greatest for voxels in the medial and ventral SN-VTA. In patients, SN-VTA Kicer positively correlated with SN-VTA NM-CNR (r = 0.44, p = .005) and striatal Kicer (r = 0.71, p < .001). Voxelwise analysis demonstrated that SN-VTA NM-CNR was positively associated with striatal Kicer (r = 0.53, p = .005) and that this relationship seemed strongest between the ventral SN-VTA and associative striatum in schizophrenia.

CONCLUSIONS

Our results suggest that NM levels are higher in patients with schizophrenia than in HC individuals, particularly in midbrain regions that project to parts of the striatum that receive innervation from the limbic and association cortices. The direct relationship between measures of NM and dopamine synthesis suggests that these aspects of schizophrenia pathophysiology are linked. Our findings highlight specific mesostriatal circuits as the loci of dopamine dysfunction in schizophrenia and thus as potential therapeutic targets.

Inhibition of striatal indirect pathway during second postnatal week leads to long-lasting deficits in motivated behavior

Schizophrenia is a neuropsychiatric disorder with postulated neurodevelopmental etiology. Genetic and imaging studies have shown enhanced dopamine and D2 receptor occupancy in the striatum of patients with schizophrenia. However, whether alterations in postnatal striatal dopamine can lead to long-lasting changes in brain function and behavior is still unclear. Here, we approximated striatal D2R hyperfunction in mice via designer receptor-mediated activation of inhibitory Gi-protein signaling during a defined postnatal time window. We found that Gi-mediated inhibition of the indirect pathway (IP) during postnatal days 8-15 led to long-lasting decreases in locomotor activity and motivated behavior measured in the adult animal. In vivo photometry further showed that the motivational deficit was associated with an attenuated adaptation of outcome-evoked dopamine levels to changes in effort requirements. These data establish a sensitive time window of D2R-regulated striatal development with long-lasting impacts on neuronal function and behavior.

Neuroimaging markers of aberrant brain activity and treatment response in schizophrenia patients based on brain complexity

The complexity of brain activity reflects its ability to process information, adapt to environmental changes, and transition between states. However, it remains unclear how schizophrenia (SZ) affects brain activity complexity, particularly its dynamic changes. This study aimed to investigate the abnormal patterns of brain activity complexity in SZ, their relationship with cognitive deficits, and the impact of antipsychotic medication. Forty-four drug-naive first-episode (DNFE) SZ patients and thirty demographically matched healthy controls (HC) were included. Functional MRI-based sliding window analysis was utilized for the first time to calculate weighted permutation entropy to characterize complex patterns of brain activity in SZ patients before and after 12 weeks of risperidone treatment. Results revealed reduced complexity in the caudate, putamen, and pallidum at baseline in SZ patients compared to HC, with reduced complexity in the left caudate positively correlated with Continuous Performance Test (CPT) and Category Fluency Test scores. After treatment, the complexity of the left caudate increased. Regions with abnormal complexity showed decreased functional connectivity, with complexity positively correlated with connectivity strength. We observed that the dynamic complexity of the brain exhibited the characteristic of spontaneous, recurring "complexity drop", potentially reflecting transient state transitions in the resting brain. Compared to HC, patients exhibited reduced scope, intensity, and duration of complexity drop, all of which improved after treatment. Reduced duration was negatively correlated with CPT scores and positively with clinical symptoms. The results suggest that abnormalities in brain activity complexity and its dynamic changes may underlie cognitive deficits and clinical symptoms in SZ patients. Antipsychotic treatment partially restores these abnormalities, highlighting their potential as indicators of treatment efficacy and biomarkers for personalized therapy.

Schizophrenia genomics: genetic complexity and functional insights

Determining the causes of schizophrenia has been a notoriously intractable problem, resistant to a multitude of investigative approaches over centuries. In recent decades, genomic studies have delivered hundreds of robust findings that implicate nearly 300 common genetic variants (via genome-wide association studies) and more than 20 rare variants (via whole-exome sequencing and copy number variant studies) as risk factors for schizophrenia. In parallel, functional genomic and neurobiological studies have provided exceptionally detailed information about the cellular composition of the brain and its interconnections in neurotypical individuals and, increasingly, in those with schizophrenia. Taken together, these results suggest unexpected complexity in the mechanisms that drive schizophrenia, pointing to the involvement of ensembles of genes (polygenicity) rather than single-gene causation. In this Review, we describe what we now know about the genetics of schizophrenia and consider the neurobiological implications of this information.

Polydopamine functionalized FeTiO3 nanohexagons for selective and simultaneous electrochemical determination of dopamine and uric acid

Herein we report the simultaneous detection of dopamine (DA) and uric acid (UA) using polydopamine (PDA) functionalized FeTiO3 nanohexagons. The nanohexagons were hydrothermally synthesized and subsequently functionalized with PDA in a Tris-buffer solution. The PDA functionalized nanostructure was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR), respectively. The SEM and TEM investigations revealed the presence of FeTiO3 nanohexagons along with a peripheral coating of PDA over the nanostructures. The XRD pattern confirmed the formation of the ilmenite structure, while the chemical structure was investigated through XPS and FTIR respectively. Using cyclic voltammetry (CV) the efficacy of FeTiO3-PDA electrode was evaluated toward DA oxidation. The enhanced activity of the functionalized electrode in DA oxidation, as compared to the untreated FeTiO3, may be attributed to the significant presence of hydroxyl, amine, and imine functional groups over the polymer layer. Differential pulse voltammetry (DPV) was utilized for the detection of DA and UA. With a linear range of 50 μM to 250 μM, the detection limits of 0.30 μM and 4.61 μM were determined for DA and UA, respectively. The peak separation of 263 mV between DA and UA demonstrates the sensor's remarkable selectivity. In addition, the study displayed the ability to detect both DA and UA simultaneously, and the validity of the sensor was evaluated in serum samples, respectively.

Predictive Processing: A Circuit Approach to Psychosis

Predictive processing is a computational framework that aims to explain how the brain processes sensory information by making predictions about the environment and minimizing prediction errors. It can also be used to explain some of the key symptoms of psychotic disorders such as schizophrenia. In recent years, substantial advances have been made in our understanding of the neuronal circuitry that underlies predictive processing in cortex. In this review, we summarize these findings and how they might relate to psychosis and to observed cell type-specific effects of antipsychotic drugs. We argue that quantifying the effects of antipsychotic drugs on specific neuronal circuit elements is a promising approach to understanding not only the mechanism of action of antipsychotic drugs but also psychosis. Finally, we outline some of the key experiments that should be done. The aims of this review are to provide an overview of the current circuit-based approaches to psychosis and to encourage further research in this direction.

Deficit of satellite oligodendrocytes of neurons in the rostral part of the head of the caudate nucleus in schizophrenia

Increasing evidence implicates compromised myelin integrity and oligodendrocyte abnormalities in the dysfunction of neuronal networks in schizophrenia. We previously reported a deficiency of myelinating oligodendrocytes (OL), oligodendrocyte progenitors (OP) and satellite oligodendrocytes of neurons (Sat-OL) in the prefrontal cortex and the inferior parietal cortex - cortical hubs of the frontoparietal cognitive network and default mode network (DMN) altered in schizophrenia. Deficiency of OL and OP was also detected in the head of the caudate nucleus (HCN), which accumulates cortical projections from the associative cortex and is the central node of these networks. However, the number of Sat-Ol per neuron in schizophrenia has not been studied in the HCN. In the current study we estimated the number of Sat-Ol per neuron in the rostral part of the HCN in schizophrenia (n = 18) compared to healthy controls (n = 18) in the same section collection that was previously used to study the number Ol and OP. We found a significant decrease of the number of Sat-Ol per neuron (- 50%, p < 0.001) in schizophrenia as compared to normal controls. Considering that the rostral part of the HCN is an individual network-specific projection zone of the DMN, the deficit of Sat-Ol found in schizophrenia may be related to the dysfunctional DMN-HCN connections, which has been repeatedly described in schizophrenia. The dramatic decrease of the number of Sat-Ol per neuron may be partially related to a pronounced excess of dopamine concentration in the rostral part of the HCN in schizophrenia.

Comparative rhythmic transcriptome profiling of human and mouse striatal subregions

The human striatum can be subdivided into the caudate, putamen, and nucleus accumbens (NAc). In mice, this roughly corresponds to the dorsal medial striatum (DMS), dorsal lateral striatum (DLS), and ventral striatum (NAc). Each of these structures have some overlapping and distinct functions related to motor control, cognitive processing, motivation, and reward. Previously, we used a "time-of-death" approach to identify diurnal rhythms in RNA transcripts in these three human striatal subregions. Here, we identify molecular rhythms across similar striatal subregions collected from C57BL/6J mice across 6 times of day and compare results to the human striatum. Pathway analysis indicates a large degree of overlap between species in rhythmic transcripts involved in processes like cellular stress, energy metabolism, and translation. Notably, a striking finding in humans is that small nucleolar RNAs (snoRNAs) and long non-coding RNAs (lncRNAs) are among the most highly rhythmic transcripts in the NAc and this is not conserved in mice, suggesting the rhythmicity of RNA processing in this region could be uniquely human. Furthermore, the peak timing of overlapping rhythmic genes is altered between species, but not consistently in one direction. Taken together, these studies reveal conserved as well as distinct transcriptome rhythms across the human and mouse striatum and are an important step in understanding the normal function of diurnal rhythms in humans and model organisms in these regions and how disruption could lead to pathology.

Dopaminergic signaling regulates microglial surveillance and adolescent plasticity in the frontal cortex

Adolescence is a sensitive period for frontal cortical development and cognitive maturation. The dopaminergic (DA) mesofrontal circuit is particularly malleable in response to changes in adolescent experience and DA activity. However, the cellular mechanisms engaged in this plasticity remain unexplored. Here, we report that microglia, the innate immune cells of the brain, are uniquely sensitive to adolescent mesofrontal DA signaling. Longitudinal in vivo two-photon imaging in mice shows that frontal cortical microglia respond dynamically to plasticity-inducing behavioral or optogenetic DA axon stimulation with increased parenchymal and DA bouton surveillance. Microglial-axon contact precedes new bouton formation, and both D1 and D2-type DA receptors regulate microglial-bouton interactions and axonal plasticity. Moreover, D2 antagonism in adults reinstates adolescent plasticity, including increased microglial surveillance and new DA bouton formation. Our results reveal that DA signaling regulates microglial surveillance and axonal plasticity uniquely in the adolescent frontal cortex, presenting potential interventions for restoring plasticity in the adult brain.

65 years of research on dopamine's role in classical fear conditioning and extinction: A systematic review

Dopamine, a catecholamine neurotransmitter, has historically been associated with the encoding of reward, whereas its role in aversion has received less attention. Here, we systematically gathered the vast evidence of the role of dopamine in the simplest forms of aversive learning: classical fear conditioning and extinction. In the past, crude methods were used to augment or inhibit dopamine to study its relationship with fear conditioning and extinction. More advanced techniques such as conditional genetic, chemogenic and optogenetic approaches now provide causal evidence for dopamine's role in these learning processes. Dopamine neurons encode conditioned stimuli during fear conditioning and extinction and convey the signal via activation of D1-4 receptor sites particularly in the amygdala, prefrontal cortex and striatum. The coordinated activation of dopamine receptors allows for the continuous formation, consolidation, retrieval and updating of fear and extinction memory in a dynamic and reciprocal manner. Based on the reviewed literature, we conclude that dopamine is crucial for the encoding of classical fear conditioning and extinction and contributes in a way that is comparable to its role in encoding reward.

Generalizability and Out-of-Sample Predictive Ability of Associations Between Neuromelanin-Sensitive Magnetic Resonance Imaging and Psychosis in Antipsychotic-Free Individuals

Importance

The link between psychosis and dopaminergic dysfunction is established, but no generalizable biomarkers with clear potential for clinical adoption exist.

Objective

To replicate previous findings relating neuromelanin-sensitive magnetic resonance imaging (NM-MRI), a proxy measure of dopamine function, to psychosis severity in antipsychotic-free individuals in the psychosis spectrum and to evaluate the out-of-sample predictive ability of NM-MRI for psychosis severity.

Design, Setting, and Participants

This cross-sectional study recruited participants from 2019 to 2023 in the New York City area (main samples) and Mexico City area (external validation sample). The main samples consisted of 42 antipsychotic-free patients with schizophrenia, 53 antipsychotic-free individuals at clinical high risk for psychosis (CHR), and 52 matched healthy controls. An external validation sample consisted of 16 antipsychotic-naive patients with schizophrenia.

Main Outcomes and Measures

NM-MRI contrast within a subregion of the substantia nigra previously linked to psychosis severity (a priori psychosis region of interest [ROI]) and psychosis severity measured using the Positive and Negative Syndrome Scale (PANSS) in schizophrenia and the Structured Interview for Psychosis-Risk Syndromes (SIPS) in CHR. The cross-validated performance of linear support vector regression to predict psychosis severity across schizophrenia and CHR was assessed, and a final trained model was tested on the external validation sample.

Results

Of the 163 included participants, 76 (46.6%) were female, and the mean (SD) age was 29.2 (10.4) years. In the schizophrenia sample, higher PANSS positive total scores correlated with higher mean NM-MRI contrast in the psychosis ROI (t37 = 2.24, P = .03; partial r = 0.35; 95% CI, 0.05 to 0.55). In the CHR sample, no significant association was found between higher SIPS positive total score and NM-MRI contrast in the psychosis ROI (t48 = -0.55, P = .68; partial r = -0.08; 95% CI, -0.36 to 0.23). The 10-fold cross-validated prediction accuracy of psychosis severity was above chance in held-out test data (mean r = 0.305, P = .01; mean root-mean-square error [RMSE] = 1.001, P = .005). External validation prediction accuracy was also above chance (r = 0.422, P = .046; RMSE = 0.882, P = .047).

Conclusions and Relevance

This study provided a direct ROI-based replication of the in-sample association between NM-MRI contrast and psychosis severity in antipsychotic-free patients with schizophrenia. In turn, it failed to replicate such association in CHR individuals. Most critically, cross-validated machine-learning analyses provided a proof-of-concept demonstration that NM-MRI patterns can be used to predict psychosis severity in new data, suggesting potential for developing clinically useful tools.

The High-Precision Liquid Chromatography with Electrochemical Detection (HPLC-ECD) for Monoamines Neurotransmitters and Their Metabolites: A Review

This review highlights the advantages of high-precision liquid chromatography with an electrochemical detector (HPLC-ECD) in detecting and quantifying biological samples obtained through intracerebral microdialysis, specifically the serotonergic and dopaminergic systems: Serotonin (5-HT), 5-hydroxyindolacetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC), dopamine (DA), 3-metoxytryptamin (3-MT) and homovanillic acid (HVA). Recognized for its speed and selectivity, HPLC enables direct analysis of intracerebral microdialysis samples without complex derivatization. Various chromatographic methods, including reverse phase (RP), are explored for neurotransmitters (NTs) and metabolites separation. Electrochemical detector (ECD), particularly with glassy carbon (GC) electrodes, is emphasized for its simplicity and sensitivity, aimed at enhancing reproducibility through optimization strategies such as modified electrode materials. This paper underscores the determination of limits of detection (LOD) and quantification (LOQ) and the linear range (L.R.) showcasing the potential for real-time monitoring of compounds concentrations. A non-exhaustive compilation of literature values for LOD, LOQ, and L.R. from recent publications is included.

Fibre density and fibre-bundle cross-section of the corticospinal tract are distinctly linked to psychosis-specific symptoms in antipsychotic-naïve patients with first-episode schizophrenia

Multiple lines of research support the dysconnectivity hypothesis of schizophrenia. However, findings on white matter (WM) alterations in patients with schizophrenia are widespread and non-specific. Confounding factors from magnetic resonance image (MRI) processing, clinical diversity, antipsychotic exposure, and substance use may underlie some of the variability. By application of refined methodology and careful sampling, we rectified common confounders investigating WM and symptom correlates in a sample of strictly antipsychotic-naïve first-episode patients with schizophrenia. Eighty-six patients and 112 matched controls underwent diffusion MRI. Using fixel-based analysis (FBA), we extracted fibre-specific measures such as fibre density and fibre-bundle cross-section. Group differences on fixel-wise measures were examined with multivariate general linear modelling. Psychopathology was assessed with the Positive and Negative Syndrome Scale. We separately tested multivariate correlations between fixel-wise measures and predefined psychosis-specific versus anxio-depressive symptoms. Results were corrected for multiple comparisons. Patients displayed reduced fibre density in the body of corpus callosum and in the middle cerebellar peduncle. Fibre density and fibre-bundle cross-section of the corticospinal tract were positively correlated with suspiciousness/persecution, and negatively correlated with delusions. Fibre-bundle cross-section of isthmus of corpus callosum and hallucinatory behaviour were negatively correlated. Fibre density and fibre-bundle cross-section of genu and splenium of corpus callosum were negative correlated with anxio-depressive symptoms. FBA revealed fibre-specific properties of WM abnormalities in patients and differentiated associations between WM and psychosis-specific versus anxio-depressive symptoms. Our findings encourage an itemised approach to investigate the relationship between WM microstructure and clinical symptoms in patients with schizophrenia.

Cell type specificity for circuit output in the midbrain dopaminergic system

Midbrain dopaminergic neurons are a relatively small group of neurons in the mammalian brain controlling a wide range of behaviors. In recent years, increasingly sophisticated tracing, imaging, transcriptomic, and machine learning approaches have provided substantial insights into the anatomical, molecular, and functional heterogeneity of dopaminergic neurons. Despite this wealth of new knowledge, it remains unclear whether and how the diverse features defining dopaminergic subclasses converge to delineate functional ensembles within the dopaminergic system. Here, we review recent studies investigating various aspects of dopaminergic heterogeneity and discuss how development, behavior, and disease influence subtype characteristics. We then outline what further approaches could be pursued to gain a more inclusive picture of dopaminergic diversity, which could be crucial to understanding the functional architecture of this system.

Adolescent neurostimulation of dopamine circuit reverses genetic deficits in frontal cortex function

Dopamine system dysfunction is implicated in adolescent-onset neuropsychiatric disorders. Although psychosis symptoms can be alleviated by antipsychotics, cognitive symptoms remain unresponsive and novel paradigms investigating the circuit substrates underlying cognitive deficits are critically needed. The frontal cortex and its dopaminergic input from the midbrain are implicated in cognitive functions and undergo maturational changes during adolescence. Here, we used mice carrying mutations in Arc or Disc1 to model mesofrontal dopamine circuit deficiencies and test circuit-based neurostimulation strategies to restore cognitive functions. We found that in a memory-guided spatial navigation task, frontal cortical neurons were activated coordinately at the decision-making point in wild-type but not Arc-/- mice. Chemogenetic stimulation of midbrain dopamine neurons or optogenetic stimulation of frontal cortical dopamine axons in a limited adolescent period consistently reversed genetic defects in mesofrontal innervation, task-coordinated neuronal activity, and memory-guided decision-making at adulthood. Furthermore, adolescent stimulation of dopamine neurons also reversed the same cognitive deficits in Disc1+/- mice. Our findings reveal common mesofrontal circuit alterations underlying the cognitive deficits caused by two different genes and demonstrate the feasibility of adolescent neurostimulation to reverse these circuit and behavioral deficits. These results may suggest developmental windows and circuit targets for treating cognitive deficits in neurodevelopmental disorders.

Mechanisms and Functions of Activity-Regulated Cytoskeleton-Associated Protein in Synaptic Plasticity

Activity-regulated cytoskeleton-associated protein (Arc) is one of the most important regulators of cognitive functions in the brain regions. As a hub protein, Arc plays different roles in modulating synaptic plasticity. Arc supports the maintenance of long-term potentiation (LTP) by regulating actin cytoskeletal dynamics, while it guides the endocytosis of AMPAR in long-term depression (LTD). Moreover, Arc can self-assemble into capsids, leading to a new way of communicating among neurons. The transcription and translation of the immediate early gene Arc are rigorous procedures guided by numerous factors, and RNA polymerase II (Pol II) is considered to regulate the precise timing dynamics of gene expression. Since astrocytes can secrete brain-derived neurotrophic factor (BDNF) and L-lactate, their unique roles in Arc expression are emphasized. Here, we review the entire process of Arc expression and summarize the factors that can affect Arc expression and function, including noncoding RNAs, transcription factors, and posttranscriptional regulations. We also attempt to review the functional states and mechanisms of Arc in modulating synaptic plasticity. Furthermore, we discuss the recent progress in understanding the roles of Arc in the occurrence of major neurological disorders and provide new thoughts for future research on Arc.

Dopaminergic signalling and behavioural alterations by Comt-Dtnbp1 genetic interaction and their clinical relevance

BACKGROUND AND PURPOSE

Cognitive and motor functions are modulated by dopaminergic signalling, which is shaped by several genetic factors. The biological effects of single genetic variants might differ depending on epistatic interactions that can be functionally multi-directional and non-linear.

EXPERIMENTAL APPROACH

We performed behavioural and neurochemical assessments in genetically modified mice and behavioural assessments and genetic screening in human patients with 22q11.2 deletion syndrome (22q11.2DS).

KEY RESULTS

Here, we confirm a genetic interaction between the Comt (catechol-O-methyltransferase, human orthologue: COMT) and Dtnbp1 (dystrobrevin binding protein 1, alias dysbindin, human orthologue: DTNBP1) genes that modulate cortical and striatal dopaminergic signalling in a manner not predictable by the effects of each single gene. In mice, Comt-by-Dtnbp1 concomitant reduction leads to a hypoactive mesocortical and a hyperactive mesostriatal dopamine pathway, associated with specific cognitive abnormalities. Like mice, in subjects with the 22q11.2DS (characterized by COMT hemideletion and dopamine alterations), COMT-by-DTNBP1 concomitant reduction was associated with analogous cognitive disturbances. We then developed an easy and inexpensive colourimetric kit for the genetic screening of common COMT and DTNBP1 functional genetic variants for clinical application.

CONCLUSIONS AND IMPLICATIONS

These findings illustrate an epistatic interaction of two dopamine-related genes and their functional effects, supporting the need to address genetic interaction mechanisms at the base of complex behavioural traits.

Deficiency of Cullin 3, a Protein Encoded by a Schizophrenia and Autism Risk Gene, Impairs Behaviors by Enhancing the Excitability of Ventral Tegmental Area (VTA) DA Neurons

The dopaminergic neuromodulator system is fundamental to brain functions. Abnormal dopamine (DA) pathway is implicated in psychiatric disorders, including schizophrenia (SZ) and autism spectrum disorder (ASD). Mutations in Cullin 3 (CUL3), a core component of the Cullin-RING ubiquitin E3 ligase complex, have been associated with SZ and ASD. However, little is known about the function and mechanism of CUL3 in the DA system. Here, we show that CUL3 is critical for the function of DA neurons and DA-relevant behaviors in male mice. CUL3-deficient mice exhibited hyperactive locomotion, deficits in working memory and sensorimotor gating, and increased sensitivity to psychostimulants. In addition, enhanced DA signaling and elevated excitability of the VTA DA neurons were observed in CUL3-deficient animals. Behavioral impairments were attenuated by dopamine D2 receptor antagonist haloperidol and chemogenetic inhibition of DA neurons. Furthermore, we identified HCN2, a hyperpolarization-activated and cyclic nucleotide-gated channel, as a potential target of CUL3 in DA neurons. Our study indicates that CUL3 controls DA neuronal activity by maintaining ion channel homeostasis and provides insight into the role of CUL3 in the pathogenesis of psychiatric disorders.SIGNIFICANCE STATEMENT This study provides evidence that Cullin 3 (CUL3), a core component of the Cullin-RING ubiquitin E3 ligase complex that has been associated with autism spectrum disorder and schizophrenia, controls the excitability of dopamine (DA) neurons in mice. Its DA-specific heterozygous deficiency increased spontaneous locomotion, impaired working memory and sensorimotor gating, and elevated response to psychostimulants. We showed that CUL3 deficiency increased the excitability of VTA DA neurons, and inhibiting D2 receptor or DA neuronal activity attenuated behavioral deficits of CUL3-deficient mice. We found HCN2, a hyperpolarization-activated channel, as a target of CUL3 in DA neurons. Our findings reveal CUL3's role in DA neurons and offer insights into the pathogenic mechanisms of autism spectrum disorder and schizophrenia.

Possible involvement of Interleukin-17A in the deterioration of prepulse inhibition on acoustic startle response in mice

AIM

Proinflammatory cytokines such as interleukin-6 (IL-6) and IL-17A have been implicated in the pathophysiology of schizophrenia which often shows sensorimotor gating abnormalities. This study aimed to examine whether a proinflammatory cytokine, IL-17A, induces impairment in sensorimotor gating in mice. We also examined whether IL-17A administration affects GSK3α/β protein level or phosphorylation in the striatum.

METHODS

Recombinant mouse IL-17A (low-dose: 0.5 ng/mL and high-dose: 50 ng/mL with 10 μL/g mouse body weight, respectively) or vehicle was intraperitoneally administered into C57BL/6 male mice 10 times in 3 weeks (sub-chronic administration). Prepulse inhibition test using acoustic startle stimulus was conducted 4 weeks after the final IL-17A administration. We evaluated the effect of IL-17A administration on protein level or phosphorylation of GSK3α/β in the striatum by using Western blot analysis.

RESULTS

Administration of IL-17A induced significant PPI deterioration. Low-dose of IL-17A administration significantly decreased both GSK3α (Ser21) and GSK3β (Ser9) phosphorylation in mouse striatum. There was no significant alteration of GSK3α/β protein levels except for GSK3α in low-dose IL-17A administration group.

CONCLUSION

We demonstrated for the first time that sub-chronic IL-17A administration induced PPI disruption and that IL-17A administration resulted in decreased phosphorylation of GSKα/β at the striatum. These results suggest that IL-17A could be a target molecule in the prevention and treatment of sensorimotor gating abnormalities observed in schizophrenia.

Mechanisms of NURR1 Regulation: Consequences for Its Biological Activity and Involvement in Pathology

NURR1 (Nuclear receptor-related 1 protein or NR4A2) is a nuclear protein receptor transcription factor with an essential role in the development, regulation, and maintenance of dopaminergic neurons and mediates the response to stressful stimuli during the perinatal period in mammalian brain development. The dysregulation of NURR1 activity may play a role in various diseases, including the onset and progression of neurodegenerative diseases, and several other pathologies. NURR1 is regulated by multiple mechanisms, among which phosphorylation by kinases or SUMOylation are the best characterized. Both post-translational modifications can regulate the activity of NURR1, affecting its stability and transcriptional activity. Other non-post-translational regulatory mechanisms include changes in its subcellular distribution or interaction with other protein partners by heterodimerization, also affecting its transcription activity. Here, we summarize the currently known regulatory mechanisms of NURR1 and provide a brief overview of its participation in pathological alterations.

Inflammation, Dopaminergic Brain and Bilirubin

Dopamine is a well-known neurotransmitter due to its involvement in Parkinson's disease (PD). Dopamine is not only involved in PD but also controls multiple mental and physical activities, such as the pleasure of food, friends and loved ones, music, art, mood, cognition, motivation, fear, affective disorders, addiction, attention deficit disorder, depression, and schizophrenia. Dopaminergic neurons (DOPAn) are susceptible to stressors, and inflammation is a recognized risk for neuronal malfunctioning and cell death in major neurodegenerative diseases. Less is known for non-neurodegenerative conditions. Among the endogenous defenses, bilirubin, a heme metabolite, has been shown to possess important anti-inflammatory activity and, most importantly, to prevent DOPAn demise in an ex vivo model of PD by acting on the tumor necrosis factor-alpha (TNFα). This review summarizes the evidence linking DOPAn, inflammation (when possible, specifically TNFα), and bilirubin as an anti-inflammatory in order to understand what is known, the gaps that need filling, and the hypotheses of anti-inflammatory strategies to preserve dopamine homeostasis with bilirubin included.

Adolescent neurostimulation of dopamine circuit reverses genetic deficits in frontal cortex function

Dopamine system dysfunction is commonly implicated in adolescent-onset neuropsychiatric disorders. Although psychosis symptoms can be alleviated by antipsychotics, cognitive symptoms remain unresponsive to such pharmacological treatments and novel research paradigms investigating the circuit substrates underlying cognitive deficits are critically needed. The frontal cortex and its dopaminergic input from the midbrain are implicated in cognitive functions and undergo maturational changes during adolescence. Here, we used mice carrying mutations in the Arc or DISC1 genes to model mesofrontal dopamine circuit deficiencies and test circuit-based neurostimulation strategies to restore cognitive functions. We found that in a memory-guided spatial navigation task, frontal cortical neurons were activated coordinately at the decision-making point in wild-type but not Arc mutant mice. Chemogenetic stimulation of midbrain dopamine neurons or optogenetic stimulation of frontal cortical dopamine axons in a limited adolescent period consistently reversed genetic defects in mesofrontal innervation, task-coordinated neuronal activity, and memory-guided decision-making at adulthood. Furthermore, adolescent stimulation of dopamine neurons also reversed the same cognitive deficits in DISC1 mutant mice. Our findings reveal common mesofrontal circuit alterations underlying the cognitive deficits caused by two different genes and demonstrate the feasibility of adolescent neurostimulation to reverse these circuit and behavioral deficits. These results may suggest developmental windows and circuit targets for treating cognitive deficits in neurodevelopmental disorders.

Antipsychotic-induced bone loss: the role of dopamine, serotonin and adrenergic receptor signalling

Antipsychotics are commonly used in treating psychiatric disorders. These medications primarily target dopamine the serotonin receptors, they have some affinity to adrenergic, histamine, glutamate and muscarinic receptors. There is clinical evidence that antipsychotic use decreases BMD and increases fracture risk, with dopamine, serotonin and adrenergic receptor-signalling becoming an increasing area of focus where the presence of these receptors in osteoclasts and osteoblasts have been demonstrated. Osteoclasts and osteoblasts are the most important cells in the bone remodelling and the bone regeneration process where the activity of these cells determine the bone resorption and formation process in order to maintain healthy bone. However, an imbalance in osteoclast and osteoblast activity can lead to decreased BMD and increased fracture risk, which is also believed to be exacerbated by antipsychotics use. Therefore, the aim of this review is to provide an overview of the mechanisms of action of first, second and third generation antipsychotics and the expression profiles of dopamine, serotonin and adrenergic receptors during osteoclastogenesis and osteoblastogenesis.

Perturbed iron biology in the prefrontal cortex of people with schizophrenia

Despite loss of grey matter volume and emergence of distinct cognitive deficits in young adults diagnosed with schizophrenia, current treatments for schizophrenia do not target disruptions in late maturational reshaping of the prefrontal cortex. Iron, the most abundant transition metal in the brain, is essential to brain development and function, but in excess, it can impair major neurotransmission systems and lead to lipid peroxidation, neuroinflammation and accelerated aging. However, analysis of cortical iron biology in schizophrenia has not been reported in modern literature. Using a combination of inductively coupled plasma-mass spectrometry and western blots, we quantified iron and its major-storage protein, ferritin, in post-mortem prefrontal cortex specimens obtained from three independent, well-characterised brain tissue resources. Compared to matched controls (n = 85), among schizophrenia cases (n = 86) we found elevated tissue iron, unlikely to be confounded by demographic and lifestyle variables, by duration, dose and type of antipsychotic medications used or by copper and zinc levels. We further observed a loss of physiologic age-dependent iron accumulation among people with schizophrenia, in that the iron level among cases was already high in young adulthood. Ferritin, which stores iron in a redox-inactive form, was paradoxically decreased in individuals with the disorder. Such iron-ferritin uncoupling could alter free, chemically reactive, tissue iron in key reasoning and planning areas of the young-adult schizophrenia cortex. Using a prediction model based on iron and ferritin, our data provide a pathophysiologic link between perturbed cortical iron biology and schizophrenia and indicate that achievement of optimal cortical iron homeostasis could offer a new therapeutic target.

Histological Analysis of a Mouse Model of the 22q11.2 Microdeletion Syndrome

22q11.2 deletion syndrome (22q11.2DS) is associated with a high risk of developing various psychiatric and developmental disorders, including schizophrenia and early-onset Parkinson's disease. Recently, a mouse model of this disease, Del(3.0Mb)/+, mimicking the 3.0 Mb deletion which is most frequently found in patients with 22q11.2DS, was generated. The behavior of this mouse model was extensively studied and several abnormalities related to the symptoms of 22q11.2DS were found. However, the histological features of their brains have been little addressed. Here we describe the cytoarchitectures of the brains of Del(3.0Mb)/+ mice. First, we investigated the overall histology of the embryonic and adult cerebral cortices, but they were indistinguishable from the wild type. However, the morphologies of individual neurons were slightly but significantly changed from the wild type counterparts in a region-specific manner. The dendritic branches and/or dendritic spine densities of neurons in the medial prefrontal cortex, nucleus accumbens, and primary somatosensory cortex were reduced. We also observed reduced axon innervation of dopaminergic neurons into the prefrontal cortex. Given these affected neurons function together as the dopamine system to control animal behaviors, the impairment we observed may explain a part of the abnormal behaviors of Del(3.0Mb)/+ mice and the psychiatric symptoms of 22q11.2DS.

Schizophrenia Synaptic Pathology and Antipsychotic Treatment in the Framework of Oxidative and Mitochondrial Dysfunction: Translational Highlights for the Clinics and Treatment

Schizophrenia is a worldwide mental illness characterized by alterations at dopaminergic and glutamatergic synapses resulting in global dysconnectivity within and between brain networks. Impairments in inflammatory processes, mitochondrial functions, energy expenditure, and oxidative stress have been extensively associated with schizophrenia pathophysiology. Antipsychotics, the mainstay of schizophrenia pharmacological treatment and all sharing the common feature of dopamine D2 receptor occupancy, may affect antioxidant pathways as well as mitochondrial protein levels and gene expression. Here, we systematically reviewed the available evidence on antioxidants' mechanisms in antipsychotic action and the impact of first- and second-generation compounds on mitochondrial functions and oxidative stress. We further focused on clinical trials addressing the efficacy and tolerability of antioxidants as an augmentation strategy of antipsychotic treatment. EMBASE, Scopus, and Medline/PubMed databases were interrogated. The selection process was conducted in respect of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria. Several mitochondrial proteins involved in cell viability, energy metabolism, and regulation of oxidative systems were reported to be significantly modified by antipsychotic treatment with differences between first- and second-generation drugs. Finally, antioxidants may affect cognitive and psychotic symptoms in patients with schizophrenia, and although the evidence is only preliminary, the results indicate that further studies are warranted.

Gradients of striatal function in antipsychotic-free first-episode psychosis and schizotypy

Both psychotic illness and subclinical psychosis-like experiences (PLEs) have been associated with cortico-striatal dysfunction. This work has largely relied on a discrete parcellation of the striatum into distinct functional areas, but recent evidence suggests that the striatum comprises multiple overlapping and smoothly varying gradients (i.e., modes) of functional organization. Here, we investigated two of these functional connectivity modes, previously associated with variations in the topographic patterning of cortico-striatal connectivity (first-order gradient), and dopaminergic innervation of the striatum (second-order gradient), and assessed continuities in striatal function from subclinical to clinical domains. We applied connectopic mapping to resting-state fMRI data to obtain the first-order and second-order striatal connectivity modes in two distinct samples: (1) 56 antipsychotic-free patients (26 females) with first-episode psychosis (FEP) and 27 healthy controls (17 females); and (2) a community-based cohort of 377 healthy individuals (213 females) comprehensively assessed for subclinical PLEs and schizotypy. The first-order "cortico-striatal" and second-order "dopaminergic" connectivity gradients were significantly different in FEP patients compared to controls bilaterally. In the independent sample of healthy individuals, variations in the left first-order "cortico-striatal" connectivity gradient were associated with inter-individual differences in a factor capturing general schizotypy and PLE severity. The presumed cortico-striatal connectivity gradient was implicated in both subclinical and clinical cohorts, suggesting that variations in its organization may represent a neurobiological trait marker across the psychosis continuum. Disruption of the presumed dopaminergic gradient was only noticeable in patients, suggesting that neurotransmitter dysfunction may be more apparent to clinical illness.

Evidence for upregulation of excitatory synaptic transmission in the substantia nigra in Schizophrenia: a postmortem ultrastructural study

The dopamine hypothesis of schizophrenia suggests that psychotic symptoms originate from dysregulation of dopaminergic activity, which may be controlled by upstream innervation. We hypothesized that we would find anatomical evidence for the hyperexcitability seen in the SN. We examined and quantified synaptic morphology, which correlates with function, in the postmortem substantia nigra (SN) from 15 schizophrenia and 12 normal subjects. Synapses were counted using stereological techniques and classified based on the morphology of the post-synaptic density (PSD) and the presence or absence of a presynaptic density. The density and proportion of excitatory synapses was higher in the schizophrenia group than in controls, while the proportion (but not density) of inhibitory synapses was lower. We also detected in the schizophrenia group an increase in density of synapses with a PSD of intermediate thickness, which may represent excitatory synapses. The density of synapses with presynaptic densities was similar in both groups. The density of synapses with mixed morphologies was higher in the schizophrenia group than in controls. The human SN contains atypical synaptic morphology. We found an excess amount and proportion of excitatory synapses in the SN in schizophrenia that could result in hyperactivity and drive the psychotic symptoms of schizophrenia. The sources of afferent excitatory inputs to the SN arise from the subthalamic nucleus, the pedunculopontine nucleus, and the ventral tegmental area (VTA), areas that could be the source of excess excitation. Synapses with mixed morphologies may represent inputs from the VTA, which release multiple transmitters.

Dyadic Interactions of Treatment-Resistant Schizophrenia Patients Having Followed Virtual Reality Therapy: A Content Analysis

(1) Background: Very little is known about the inner therapeutic processes of psychotherapy interventions for patients suffering from treatment-resistant schizophrenia. Avatar therapy (AT) is one such modalities in which the patient is undergoing immersive sessions in which they interact with an Avatar representing their main persistent auditory verbal hallucination. The aim of this study is to identify the most prevalent dyadic interactions between the patient and the Avatar in AT for patient’s suffering from TRS. (2) Methods: A content analysis of 256 verbatims originating from 32 patients who completed AT between 2017 and 2022 at the Institut universitaire en santé mentale de Montréal was conducted to identify dyadic interactions between the patients and their Avatar. (3) Results: Five key dyads were identified to occur on average more than 10 times for each participant during the immersive sessions across their AT: (Avatar: Reinforcement, Patient: Self-affirmation), (Avatar: Provocation, Patient: Self-affirmation), (Avatar: Coping mechanisms, Patient: Prevention), (Patient: Self-affirmation, Avatar: Reinforcement), and (Patient: Self-appraisal, Avatar: Reinforcement). (4) Conclusion: These dyads offer a first qualitative insight to the interpersonal dynamics and patient-avatar relationships taking place during AT. Future studies on the implication of such dyadic interactions with the therapeutic outcome of AT should be conducted considering the importance of dyadic relationships in psychotherapy.

Urinary exosomal microRNAs as predictive biomarkers for persistent psychotic-like experiences

Psychotic-like experiences (PLEs) occur occasionally in adolescence and mostly disappear with increasing age. Their presence, if persistent, is considered a robust risk factor for subsequent psychiatric disorders. To date, only a few biological markers have been investigated for persistent PLE prediction. This study identified urinary exosomal microRNAs that can serve as predictive biomarkers for persistent PLEs. This study was part of a population-based biomarker subsample study of the Tokyo Teen Cohort Study. A total of 345 participants aged 13 (baseline) and 14 (follow-up) years underwent PLE assessments by experienced psychiatrists using semi-structured interviews. We defined remitted and persistent PLEs based on longitudinal profiles. We obtained urine at baseline and the expression levels of urinary exosomal miRNAs were compared between 15 individuals with persistent PLEs and 15 age- and sex-matched individuals with remitted PLEs. We constructed a logistic regression model to examine whether miRNA expression levels could predict persistent PLEs. We identified six significant differentially expressed microRNAs, namely hsa-miR-486-5p, hsa-miR-199a-3p, hsa-miR-144-5p, hsa-miR-451a, hsa-miR-143-3p, and hsa-miR-142-3p. The predictive model showed an area under the curve of 0.860 (95% confidence interval: 0.713-0.993) for five-fold cross-validation. We found a subset of urinary exosomal microRNAs that were differentially expressed in persistent PLEs and presented the likelihood that a microRNA-based statistical model could predict them with high accuracy. Therefore, urine exosomal miRNAs may serve as novel biomarkers for the risk of psychiatric disorders.

Treatment-Resistant Schizophrenia, Clozapine Resistance, Genetic Associations, and Implications for Precision Psychiatry: A Scoping Review

Treatment-resistant schizophrenia (TRS) is often associated with severe burden of disease, poor quality of life and functional impairment. Clozapine is the gold standard for the treatment of TRS, although it is also known to cause significant side effects in some patients. In view of the burgeoning interest in the role of genetic factors in precision psychiatry, we conducted a scoping review to narratively summarize the current genetic factors associated with TRS, clozapine resistance and side effects to clozapine treatment. We searched PubMed from inception to December 2022 and included 104 relevant studies in this review. Extant evidence comprised associations between TRS and clozapine resistance with genetic factors related to mainly dopaminergic and serotoninergic neurotransmitter systems, specifically, TRS and rs4680, rs4818 within COMT, and rs1799978 within DRD2; clozapine resistance and DRD3 polymorphisms, CYP1A2 polymorphisms; weight gain with LEP and SNAP-25 genes; and agranulocytosis risk with HLA-related polymorphisms. Future studies, including replication in larger multi-site samples, are still needed to elucidate putative risk genes and the interactions between different genes and their correlations with relevant clinical factors such as psychopathology, psychosocial functioning, cognition and progressive changes with treatment over time in TRS and clozapine resistance.

Mendelian Randomization Study Using Dopaminergic Neuron-Specific eQTL Identifies Novel Risk Genes for Schizophrenia

Multiple integrative studies have been performed to identify the potential target genes of the non-coding schizophrenia (SCZ) risk variants. However, all the integrative studies used expression quantitative trait loci (eQTL) data from bulk tissues. Considering the cell type-specific regulatory effect of many genetic variants, it is important to conduct integrative studies using cell type-specific eQTL data. Here, we conduct a Mendelian randomization (MR) study by integrating genome-wide associations of SCZ (74,776 cases and 101,023 controls) and eQTL data (N = 215) from dopaminergic neurons, which were differentiated from human-induced pluripotent stem cell (iPSC) lines. For eQTL from young post-mitotic dopaminergic neurons (differentiation of iPSC for 30 days, D30), we identified 34 genes whose genetically regulated expression in dopaminergic neurons may have a causal role in SCZ. Among which, ARL3 showed the most significant associations with SCZ. For eQTL from more mature dopaminergic neurons (D52), we identified 37 potential SCZ causal genes, and ARL3 and GNL3 showed the most significant associations. Only 12 genes showed significant associations with SCZ in both D30 and D52 eQTL datasets, indicating the time point-specific genetic regulatory effects in young post-mitotic dopaminergic neurons and more mature dopaminergic neurons. Comparing the results from dopaminergic neurons with bulk brain tissues prioritized 2 high-confidence risk genes, including DDHD2 and GALNT10. Our study identifies multiple risk genes whose genetically regulated expression in dopaminergic neurons may have a causal role in SCZ. Further mechanistic investigation will provide pivotal insights into SCZ pathophysiology.

Negative symptoms, striatal dopamine and model-free reward decision-making in schizophrenia

Negative symptoms, such as lack of motivation or social withdrawal, are highly prevalent and debilitating in patients with schizophrenia. Underlying mechanisms of negative symptoms are incompletely understood, thereby preventing the development of targeted treatments. We hypothesized that in patients with schizophrenia during psychotic remission, impaired influences of both model-based and model-free reward predictions on decision-making ('reward prediction influence', RPI) underlie negative symptoms. We focused on psychotic remission, because psychotic symptoms might confound reward-based decision-making. Moreover, we hypothesized that impaired model-based/model-free RPIs depend on alterations of both associative striatum dopamine synthesis and storage (DSS) and executive functioning. Both factors influence RPI in healthy subjects and are typically impaired in schizophrenia. Twenty-five patients with schizophrenia with pronounced negative symptoms during psychotic remission and 24 healthy controls were included in the study. Negative symptom severity was measured by the Positive and Negative Syndrome Scale negative subscale, model-based/model-free RPI by the two-stage decision task, associative striatum DSS by 18F-DOPA positron emission tomography and executive functioning by the symbol coding task. Model-free RPI was selectively reduced in patients and associated with negative symptom severity as well as with reduced associative striatum DSS (in patients only) and executive functions (both in patients and controls). In contrast, model-based RPI was not altered in patients. Results provide evidence for impaired model-free reward prediction influence as a mechanism for negative symptoms in schizophrenia as well as for reduced associative striatum dopamine and executive dysfunction as relevant factors. Data suggest potential treatment targets for patients with schizophrenia and pronounced negative symptoms.

Biological hypotheses, risk factors, and biomarkers of schizophrenia

Both the discovery of biomarkers of schizophrenia and the verification of biological hypotheses of schizophrenia are an essential part of the process of understanding the etiology of this mental disorder. Schizophrenia has long been considered a neurodevelopmental disease whose symptoms are caused by impaired synaptic signal transduction and brain neuroplasticity. Both the onset and chronic course of schizophrenia are associated with risk factors-induced disruption of brain function and the establishment of a new homeostatic setpoint characterized by biomarkers. Different risk factors and biomarkers can converge to the same symptoms of schizophrenia, suggesting that the primary cause of the disease can be highly individual. Schizophrenia-related biomarkers include measurable biochemical changes induced by stress (elevated allostatic load), mitochondrial dysfunction, neuroinflammation, oxidative and nitrosative stress, and circadian rhythm disturbances. Here is a summary of selected valid biological hypotheses of schizophrenia formulated based on risk factors and biomarkers, neurodevelopment, neuroplasticity, brain chemistry, and antipsychotic medication. The integrative neurodevelopmental-vulnerability-neurochemical model is based on current knowledge of the neurobiology of the onset and progression of the disease and the effects of antipsychotics and psychotomimetics and reflects the complex and multifactorial nature of schizophrenia.

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.

Accelerated atrophy in dopaminergic targets and medial temporo-parietal regions precedes the onset of delusions in patients with Alzheimer's disease

People with Alzheimer's disease (AD) and delusions have worse quality of life and prognosis. However, early markers of delusions have not been identified yet. The present study investigated whether there are any detectable differences in grey matter (GM) volume and cognitive changes in the year before symptom onset between patients with AD who did and did not develop delusions. Two matched samples of AD patients, 63 who did (PT-D) and 63 who did not develop delusions (PT-ND) over 1 year, were identified from the Alzheimer's Disease Neuroimaging Initiative database. The Neuropsychiatric Inventory (NPI) was used to assess the presence of delusions. Sixty-three additional matched healthy controls (HC) were selected. Repeated-measures ANCOVA models were used to investigate group-by-time effects on the volume of selected GM regions of interest and on cognitive performance. No neurocognitive differences were observed between patient groups prior to symptom onset. Greater episodic memory decline and GM loss in bilateral caudate nuclei, medio-temporal and midline cingulo-parietal regions were found in the PT-D compared with the PT-ND group. A pattern of faster GM loss in brain areas typically affected by AD and in cortical and subcortical targets of dopaminergic pathways, paralleled by worsening of episodic memory and behavioural symptoms, may explain the emergence of delusions in patients with AD.

On predictability of individual functional connectivity networks from clinical characteristics

In recent years, understanding functional brain connectivity has become increasingly important as a scientific tool with potential clinical implications. Statistical methods, such as graphical models and network analysis, have been adopted to construct functional connectivity networks for single subjects. Here we focus on studying the association between functional connectivity networks and clinical characteristics such as psychiatric symptoms and diagnoses. Utilizing machine learning algorithms, we propose a method to examine predictability of functional connectivity networks from clinical characteristics. Our methods can identify salient clinical characteristics predictive of the whole brain network or specific subnetworks. We illustrate our methods on the analysis of fMRI data in the Philadelphia Neurodevelopmental Cohort study, demonstrating clinically meaningful results.

Ultrastructural evidence for glutamatergic dysregulation in schizophrenia

The aim of this paper is to summarize ultrastructural evidence for glutamatergic dysregulation in several linked regions in postmortem schizophrenia brain. Following a brief summary of glutamate circuitry and how synapses are identified at the electron microscopic (EM) level, we will review EM pathology in the cortex and basal ganglia. We will include the effects of antipsychotic drugs and the relation of treatment response. We will discuss how these findings support or confirm other postmortem findings as well as imaging results. Briefly, synaptic and mitochondrial density in anterior cingulate cortex was decreased in schizophrenia, versus normal controls (NCs), in a selective layer specific pattern. In dorsal striatum, increases in excitatory synaptic density were detected in caudate matrix, a compartment associated with cognitive and motor function, and in the putamen patches, a region associated with limbic function and in the core of the nucleus accumbens. Patients who were treatment resistant or untreated had significantly elevated numbers of excitatory synapses in limbic striatal areas in comparison to NCs and responders. Protein levels of vGLUT2, found in subcortical glutamatergic neurons, were increased in the nucleus accumbens in schizophrenia. At the EM level, schizophrenia subjects had an increase in density of excitatory synapses in several areas of the basal ganglia. In the substantia nigra, the protein levels of vGLUT2 were elevated in untreated patients compared to NCs. The density of inhibitory synapses was decreased in schizophrenia versus NCs. In schizophrenia, glutamatergic synapses are differentially affected depending on the brain region, treatment status, and treatment response.

Unraveling schizophrenia replicable functional connectivity disruption patterns across sites

Functional connectivity (FC) disruption is a remarkable characteristic of schizophrenia. However, heterogeneous patterns reported across sites severely hindered its clinical generalization. Based on qualified nodal-based FC of 340 schizophrenia patients (SZ) and 348 normal controls (NC) acquired from seven different scanners, this study compared four commonly used site-effect correction methods in removing the site-related heterogeneities, and then tried to cluster the abnormal FCs into several replicable and independent disrupted subnets across sites, related them to clinical symptoms, and evaluated their potentials in schizophrenia classification. Among the four site-related heterogeneity correction methods, ComBat harmonization (F1 score: 0.806 ± 0.145) achieved the overall best balance between sensitivity and false discovery rate in unraveling the aberrant FCs of schizophrenia in the local and public data sets. Hierarchical clustering analysis identified three replicable FC disruption subnets across the local and public data sets: hypo-connectivity within sensory areas (Net1), hypo-connectivity within thalamus, striatum, and ventral attention network (Net2), and hyper-connectivity between thalamus and sensory processing system (Net3). Notably, the derived composite FC within Net1 was negatively correlated with hostility and disorientation in the public validation set (p < .05). Finally, the three subnet-specific composite FCs (Best area under the receiver operating characteristic curve [AUC] = 0.728) can robustly and meaningfully discriminate the SZ from NC with comparable performance with the full identified FCs features (best AUC = 0.765) in the out-of-sample public data set (Z = -1.583, p = .114). In conclusion, ComBat harmonization was most robust in detecting aberrant connectivity for schizophrenia. Besides, the three subnet-specific composite FC measures might be replicable neuroimaging markers for schizophrenia.

Dysbindin-1A modulation of astrocytic dopamine and basal ganglia dependent behaviors relevant to schizophrenia

The mechanisms underlying the dichotomic cortical/basal ganglia dopaminergic abnormalities in schizophrenia are unclear. Astrocytes are important non-neuronal modulators of brain circuits, but their role in dopaminergic system remains poorly explored. Microarray analyses, immunohistochemistry, and two-photon laser scanning microscopy revealed that Dys1 hypofunction increases the reactivity of astrocytes, which express only the Dys1A isoform. Notably, behavioral and electrochemical assessments in mice selectively lacking the Dys1A isoform unraveled a more prominent impact of Dys1A in behavioral and dopaminergic/D2 alterations related to basal ganglia, but not cortical functioning. Ex vivo electron microscopy and protein expression analyses indicated that selective Dys1A disruption might alter intracellular trafficking in astrocytes, but not in neurons. In agreement, Dys1A disruption only in astrocytes resulted in decreased motivation and sensorimotor gating deficits, increased astrocytic dopamine D2 receptors and decreased dopaminergic tone within basal ganglia. These processes might have clinical relevance because the caudate, but not the cortex, of patients with schizophrenia shows a reduction of the Dys1A isoform. Therefore, we started to show a hitherto unknown role for the Dys1A isoform in astrocytic-related modulation of basal ganglia behavioral and dopaminergic phenotypes, with relevance to schizophrenia.