5-HT2A receptor density is decreased in the at-risk mental state

Activity of prefrontal cortex serotonin 2A receptor expressing neurons is necessary for the head-twitch response of mice to psychedelic drug DOI in a sex-dependent manner

Serotonin 2A receptors (5-HT 2A Rs) mediate the effects of psychedelic drugs. 5-HT 2A R agonists, such as (-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI), that produce a psychedelic experience in humans induce a head-twitch response (HTR) behavior in rodents. However, it is unknown whether the activity of 5-HT 2A R expressing neurons is sufficient to produce the HTR in the absence of an agonist, or in which brain region 5-HT 2A Rs control the HTR. Here, we use an optogenetic approach to examine whether activation of 5-HT 2A R expressing neurons in the mouse prefrontal cortex (PFC) is sufficient to induce HTRs alone, or may augment the HTR produced by DOI, and if inhibition of these neurons prevents DOI-induced HTRs in mice. We crossed Htr2a -Cre mice to Cre-dependent optogenetic lines Ai32 (channelrhodopsin) and Ai39 (halorhodopsin) to selectively activate and inhibit (respectively) 5-HT 2A R-expressing neurons in the PFC of adult mice. We found that optogenetic stimulation of PFC 5-HT 2A R expressing neurons in the absence of an agonist does not increase HTRs in mice. In both male and female Ai32 mice that received vehicle, there was no difference in HTRs in mice that expressed Htr2a -Cre compared with control mice, indicating that optogenetic activation of 5-HT 2A R+ cells in the PFC was not sufficient to produce HTRs in the absence of an agonist. In female mice, activation of PFC 5-HT 2A R expressing neurons augmented the HTR produced by DOI. However, this result was not seen in male mice. In contrast, inhibition of 5-HT 2A R expressing neurons in the PFC prevented the increase in HTR produced by DOI in male, but not in female, mice. Together, these findings suggest that activation of 5-HT 2A Rs in the PFC is not sufficient to induce HTRs in the absence of a 5-HT 2A R agonist but is necessary for induction of HTRs by a 5-HT 2A R agonist in a sex-dependent manner.

Reduced Expression of the Htr2a, Grin1, and Bdnf Genes and Cognitive Inflexibility in a Model of High Compulsive Rats

Compulsivity is a core symptom in different psychopathological disorders, characterized by excessive behaviors and behavioral inflexibility. The selection of high drinker (HD) versus low drinker (LD) rats by schedule-induced polydipsia (SIP) is a valid model for studying the compulsive phenotype. The compulsive HD rats showed cognitive inflexibility and reduced serotonin 2A (5-HT2A) receptor binding levels in the frontal cortex (FC). According to that, we hypothesize that compulsive HD rats might have an alteration in the cognitive control domain regarding inflexibility, assessed by spatial memory on the Morris Water Maze (MWM), working and reference memory by the Radial Arm Maze, and behavioral deficits in stimulus processing by the Novel Object Recognition test. The possible underlying mechanisms might be linked to the brain gene expression of 5HT2A, 5HT2C, glutamate NMDA receptors, and brain-derived neurotrophic factor (BDNF) in FC, hippocampus, and amygdala. HD rats confirmed a cognitive inflexibility profile on the reversal condition in the MWM compared to LD rats, while no differences were observed on stimulus processing, spatial, and working memory. Moreover, HD rats showed a reduced expression of the Htr2a, Grin1, and Bdnf genes in FC. Furthermore, there was a negative correlation between the relative expression of the Htr2a, Grin1, and Bdnf genes in FC and the level of compulsive water intake in HD rats on SIP. These data reveal that cognitive inflexibility may not be associated with a memory or stimulus processing deficit in compulsive individuals but may result by a region-specific alteration of the Htr2a, Grin1, and Bdnf gene expression in FC.

Positron Emission Tomography (PET) Imaging Tracers for Serotonin Receptors

Serotonin (5-hydroxytryptamine, 5-HT) and 5-HT receptors (5-HTRs) have crucial roles in various neuropsychiatric disorders and neurodegenerative diseases, making them attractive diagnostic and therapeutic targets. Positron emission tomography (PET) is a noninvasive nuclear molecular imaging technique and is an essential tool in clinical diagnosis and drug discovery. In this context, numerous PET ligands have been developed for "visualizing" 5-HTRs in the brain and translated into human use to study disease mechanisms and/or support drug development. Herein, we present a comprehensive repertoire of 5-HTR PET ligands by focusing on their chemotypes and performance in PET imaging studies. Furthermore, this Perspective summarizes recent 5-HTR-focused drug discovery, including biased agonists and allosteric modulators, which would stimulate the development of more potent and subtype-selective 5-HTR PET ligands and thus further our understanding of 5-HTR biology.

Acute sleep deprivation upregulates serotonin 2A receptors in the frontal cortex of mice via the immediate early gene Egr3

Serotonin 2A receptors (5-HT_2ARs) mediate the hallucinogenic effects of psychedelic drugs and are a key target of the leading class of medications used to treat psychotic disorders. These findings suggest that dysfunction of 5-HT_2ARs may contribute to the symptoms of schizophrenia, a mental illness characterized by perceptual and cognitive disturbances. Indeed, numerous studies have found that 5-HT_2ARs are reduced in the brains of individuals with schizophrenia. However, the mechanisms that regulate 5-HT_2AR expression remain poorly understood. Here, we show that a physiologic environmental stimulus, sleep deprivation, significantly upregulates 5-HT_2AR levels in the mouse frontal cortex in as little as 6-8 h (for mRNA and protein, respectively). This induction requires the activity-dependent immediate early gene transcription factor early growth response 3 (Egr3) as it does not occur in Egr3 deficient (-/-) mice. Using chromatin immunoprecipitation, we show that EGR3 protein binds to the promoter of Htr2a, the gene that encodes the 5-HT_2AR, in the frontal cortex in vivo, and drives expression of in vitro reporter constructs via two EGR3 binding sites in the Htr2a promoter. These results suggest that EGR3 directly regulates Htr2a expression, and 5-HT_2AR levels, in the frontal cortex in response to physiologic stimuli. Analysis of publicly available post-mortem gene expression data revealed that both EGR3 and HTR2A mRNA are reduced in the prefrontal cortex of schizophrenia patients compared to controls. Together these findings suggest a mechanism by which environmental stimuli alter levels of a brain receptor that may mediate the symptoms, and treatment, of mental illness.

5-HT1A and 5-HT2A Signaling, Desensitization, and Downregulation: Serotonergic Dysfunction and Abnormal Receptor Density in Schizophrenia and the Prodrome

The significant role of serotonin (5-hydroxytryptamine [5-HT]) in the pathogenesis and early development of schizophrenia has been established by contemporary research through the assessment of structural and pharmacological neuroimaging, blood metabolites, cerebrospinal fluid, genome polymorphisms, and other valid indicators of abnormal serotonergic activity in prodromal, ultra-high-risk, and schizophrenic patient groups. A modern approach toward understanding the complex psychophysiology behind schizophrenia will be outlined through the demonstration of 5-HT_1A and 5-HT_2A receptors as key modulators within the spectrum of negative symptoms associated with schizoaffective disorders, including a variety of disturbances in cognition, behavior, mood, social function, perception of reality, and hormonal response to stressors. This paper will review the evidence for attributing the risk of schizophrenia onset to early defects in serotonergic neurotransmission and explore the perspective of selective serotonin receptor inhibitor (SSRI) pharmacotherapy as a method of treatment and intervention for prodromal and ultra-high-risk patients by increasing 5-HT_1A receptor sensitivity levels and modifying the transcription of 5-HT_1A receptor-associated gene expression in these groups.

Opposite alterations of 5-HT2A receptor brain density in subjects with schizophrenia: relevance of radiotracers pharmacological profile

The status of serotonin 5-HT_2A receptors (5-HT_2ARs) in schizophrenia has been controversial. In vivo positron emission tomography neuroimaging and in vitro post-mortem binding studies have reported conflicting results about 5-HT_2AR density. Radiotracers bind different receptor conformations depending on their agonist, antagonist or inverse agonist properties. This study investigates 5-HT_2AR density in the post-mortem prefrontal cortex from subjects with schizophrenia and controls using three radiotracers with a different pharmacological profile. The specific binding parameters of the inverse agonist [¹⁸F]altanserin, the agonist [³H]lysergic acid diethylamide (LSD) and the antagonist [³H]MDL100907 to brain cortex membranes from 20 subjects with schizophrenia and 20 individually matched controls were evaluated under similar methodological conditions. Ten schizophrenia subjects were antipsychotic-free at death. Saturation curve analyses were performed by non-linear regression to obtain a maximal density of binding sites (B_max) and the affinity of the respective radiotracers (K_d). In schizophrenia subjects, 5-HT_2AR density was decreased when quantified by [¹⁸F]altanserin binding, whereas increased when evaluated by [³H]LSD binding. However, [³H]MDL100907 binding was unaltered. A slight loss of affinity (higher K_d) was observed exclusively in [³H]LSD binding. The findings were more evident in antipsychotic-free subjects than in antipsychotic-treated subjects. In conclusion, a higher proportion of the 5-HT_2AR-active functional conformation, which is rather identified by agonist radiotracers, was observed in schizophrenia patients. A consequent reduction of the inactive 5-HT_2AR conformation, which is preferentially identified by inverse agonist radiotracers, was also obtained. Antagonist radiotracers do not distinguish between molecular conformations of the receptor, and accordingly, the absence of changes was shown. These results are compatible with the proposed increased functional activity of brain cortical 5-HT_2ARs in schizophrenia.

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.

Targeting Serotonin 5-HT2A Receptors to Better Treat Schizophrenia: Rationale and Current Approaches

Schizophrenia is a major mental illness associated with profound disability. Current treatments for schizophrenia (antipsychotics) all have a similar mechanism of action and are primarily dopamine type 2 receptor (D₂R) antagonists. Antipsychotics are not fully effective for the majority of schizophrenia patients, suggesting the need for alternative approaches. The primary focus of this review is to assess the evidence for the role of the serotonin type 2A receptor (5-HT_2AR) in schizophrenia. Topics include an overview of 5-HT_2AR physiology and pathophysiology in schizophrenia, 5-HT_2AR interaction with other neurotransmitter systems, including the glutamatergic system, a review of the 5-HT_2AR/d-lysergic acid diethylamide (LSD) model of schizophrenia, a contrast of the 5-HT_2AR and glutamatergic models of schizophrenia, and finally, a review of Food and Drug Administration (FDA)-approved and investigational 5-HT_2AR-modulating compounds. Recent studies with lumeteperone, pimavanserin, and roluperidone are highlighted.

Dopamine D1 receptor availability is not associated with delusional ideation measures of psychosis proneness

The dopamine D1 receptor (D1R) is thought to play a role in psychosis and schizophrenia, however positron emission tomography studies comparing patients and controls have been inconsistent. To circumvent some of the limitations of clinical studies, such as antipsychotic exposure, an alternative approach is to examine subclinical psychotic symptoms within the general population, i.e. psychosis proneness traits. In this study, we investigated whether D1R availability is associated with delusional ideation in healthy controls, in four experiments, using [¹¹C]SCH23390 PET (n = 76) and psychometric questionnaires (n = 217). We performed exploratory analyses, direct self-replication, and confirmatory analyses using Bayesian statistical modelling. Collectively, we found strong evidence that there is little to no linear association between delusional ideation and D1R. If hypothesised changes in D1R in drug-naive psychosis patients can be confirmed, our results suggest that they may either occur at disease onset, or that they are associated with specific aspects of psychosis other than delusional ideation.

Common HTR2A variants and 5-HTTLPR are not associated with human in vivo serotonin 2A receptor levels

The serotonin 2A receptor (5‐HT2AR) is implicated in the pathophysiology and treatment of various psychiatric disorders. [¹⁸F]altanserin and [¹¹C]Cimbi‐36 positron emission tomography (PET) allow for high‐resolution imaging of 5‐HT2AR in the living human brain. Cerebral 5‐HT2AR binding is strongly genetically determined, though the impact of specific variants is poorly understood. Candidate gene studies suggest that HTR2A single nucleotide polymorphisms including rs6311/rs6313, rs6314, and rs7997012 may influence risk for psychiatric disorders and mediate treatment response. Although known to impact in vitro expression of 5‐HT2AR or other serotonin (5‐HT) proteins, their effect on human in vivo brain 5‐HT2AR binding has as of yet been insufficiently studied. We thus assessed the extent to which these variants and the commonly studied 5‐HTTLPR predict neocortex in vivo 5‐HT2AR binding in healthy adult humans. We used linear regression analyses and likelihood ratio tests in 197 subjects scanned with [¹⁸F]altanserin or [¹¹C]Cimbi‐36 PET. Although we observed genotype group differences in 5‐HT2AR binding of up to ~10%, no genetic variants were statistically significantly predictive of 5‐HT2AR binding in what is the largest human in vivo 5‐HT2AR imaging genetics study to date. Thus, in vitro and post mortem results suggesting effects on 5‐HT2AR expression did not carry over to the in vivo setting. To any extent these variants might affect clinical risk, our findings do not support that 5‐HT2AR binding mediates such effects. Our observations indicate that these individual variants do not significantly contribute to genetic load on human in vivo 5‐HT2AR binding.

Kinetic analysis of [18F] altanserin bolus injection in the canine brain using PET imaging

BACKGROUND

Currently, [¹⁸F] altanserin is the most frequently used PET-radioligand for serotonin_2A (5-HT_2A) receptor imaging in the human brain but has never been validated in dogs. In vivo imaging of this receptor in the canine brain could improve diagnosis and therapy of several behavioural disorders in dogs. Furthermore, since dogs are considered as a valuable animal model for human psychiatric disorders, the ability to image this receptor in dogs could help to increase our understanding of the pathophysiology of these diseases. Therefore, five healthy laboratory beagles underwent a 90-min dynamic PET scan with arterial blood sampling after [¹⁸F] altanserin bolus injection. Compartmental modelling using metabolite corrected arterial input functions was compared with reference tissue modelling with the cerebellum as reference region.

RESULTS

The distribution of [¹⁸F] altanserin in the canine brain corresponded well to the distribution of 5-HT_2A receptors in human and rodent studies. The kinetics could be best described by a 2-Tissue compartment (2-TC) model. All reference tissue models were highly correlated with the 2-TC model, indicating compartmental modelling can be replaced by reference tissue models to avoid arterial blood sampling.

CONCLUSIONS

This study demonstrates that [¹⁸F] altanserin PET is a reliable tool to visualize and quantify the 5-HT_2A receptor in the canine brain.

Stress exposure and psychopathology alter methylation of the serotonin receptor 2A (HTR2A) gene in preschoolers

Serotonin signaling pathways play a key role in brain development, stress reactivity, and mental health. Epigenetic alterations in the serotonin system may underlie the effect of early life stress on psychopathology. The current study examined methylation of the serotonin receptor 2A (HTR2A) gene in a sample of 228 children including 119 with child welfare documentation of moderate to severe maltreatment within the last 6 months. Child protection records, semistructured interviews in the home, and parent reports were used to assess child stress exposure, psychiatric symptoms, and behavior. The HTR2A genotype and methylation of HTR2A were measured at two CpG sites (-1420 and -1224) from saliva DNA. HTR2A genotype was associated with HTR2A methylation at both CpG sites. HTR2A genotype also moderated associations of contextual stress exposure and HTR2A methylation at site -1420. Contextual stress was positively associated with -1420 methylation among A homozygotes, but negatively associated with -1420 methylation among G homozygotes. Posttraumatic stress disorder and major depressive disorder symptoms were negatively associated with methylation at -1420, but positively associated with methylation at -1224. Results support the view that the serotonin system is sensitive to stress exposure and psychopathology, and HTR2A methylation may be a mechanism by which early adversity is biologically encoded.

A systematic review of metabolite biomarkers of schizophrenia

Current diagnosis of schizophrenia relies exclusively on the potentially subjective interpretation of clinical symptoms and social functioning as more objective biological measurement and medical diagnostic tests are not presently available. The use of metabolomics in the discovery of disease biomarkers has grown in recent years. Metabolomic methods could aid in the discovery of diagnostic biomarkers of schizophrenia. This systematic review focuses on biofluid metabolites associated with schizophrenia. A systematic search of Web of Science and Ovid Medline databases was conducted and 63 studies investigating metabolite biomarkers of schizophrenia were included. A review of these studies revealed several potential metabolite signatures of schizophrenia including reduced levels of essential polyunsaturated fatty acids (EPUFAs), vitamin E and creatinine; and elevated levels of lipid peroxidation metabolites and glutamate. Further research is needed to validate these biomarkers and would benefit from large cohort studies and more homogeneous and well-defined subject groups.

Association of Protein Distribution and Gene Expression Revealed by PET and Post-Mortem Quantification in the Serotonergic System of the Human Brain

Regional differences in posttranscriptional mechanisms may influence in vivo protein densities. The association of positron emission tomography (PET) imaging data from 112 healthy controls and gene expression values from the Allen Human Brain Atlas, based on post-mortem brains, was investigated for key serotonergic proteins. PET binding values and gene expression intensities were correlated for the main inhibitory (5-HT1A) and excitatory (5-HT2A) serotonin receptor, the serotonin transporter (SERT) as well as monoamine oxidase-A (MAO-A), using Spearman's correlation coefficients (rs) in a voxel-wise and region-wise analysis. Correlations indicated a strong linear relationship between gene and protein expression for both the 5-HT1A (voxel-wise rs = 0.71; region-wise rs = 0.93) and the 5-HT2A receptor (rs = 0.66; 0.75), but only a weak association for MAO-A (rs = 0.26; 0.66) and no clear correlation for SERT (rs = 0.17; 0.29). Additionally, region-wise correlations were performed using mRNA expression from the HBT, yielding comparable results (5-HT1Ars = 0.82; 5-HT2Ars = 0.88; MAO-A rs = 0.50; SERT rs = -0.01). The SERT and MAO-A appear to be regulated in a region-specific manner across the whole brain. In contrast, the serotonin-1A and -2A receptors are presumably targeted by common posttranscriptional processes similar in all brain areas suggesting the applicability of mRNA expression as surrogate parameter for density of these proteins.

Consensus paper of the WFSBP Task Force on Biological Markers: Criteria for biomarkers and endophenotypes of schizophrenia part II: Cognition, neuroimaging and genetics

OBJECTIVES

Schizophrenia is a group of severe psychiatric disorders with high heritability but only low odds ratios of risk genes. Despite progress in the identification of pathophysiological processes, valid biomarkers of the disease are still lacking.

METHODS

This comprehensive review summarises recent efforts to identify genetic underpinnings, clinical and cognitive endophenotypes and symptom dimensions of schizophrenia and presents findings from neuroimaging studies with structural, functional and spectroscopy magnetic resonance imaging and positron emission tomography. The potential of findings to be biomarkers of schizophrenia is discussed.

RESULTS

Recent findings have not resulted in clear biomarkers for schizophrenia. However, we identified several biomarkers that are potential candidates for future research. Among them, copy number variations and links between genetic polymorphisms derived from genome-wide analysis studies, clinical or cognitive phenotypes, multimodal neuroimaging findings including positron emission tomography and magnetic resonance imaging, and the application of multivariate pattern analyses are promising.

CONCLUSIONS

Future studies should address the effects of treatment and stage of the disease more precisely and apply combinations of biomarker candidates. Although biomarkers for schizophrenia await validation, knowledge on candidate genomic and neuroimaging biomarkers is growing rapidly and research on this topic has the potential to identify psychiatric endophenotypes and in the future increase insight on individual treatment response in schizophrenia.

Hyperactivity of caudate, parahippocampal, and prefrontal regions during working memory in never-medicated persons at clinical high-risk for psychosis

BACKGROUND

Deficits in working memory (WM) are a core feature of schizophrenia (SZ) and other psychotic disorders. We examined brain activity during WM in persons at clinical high risk (CHR) for psychosis.

METHODS

Thirty-seven CHR and 34 healthy control participants underwent functional MRI (fMRI) on a 3.0T scanner while performing an N-back WM task. The sample included a sub-sample of CHR participants who had no lifetime history of treatment with psychotropic medications (n=11). Data were analyzed using SPM8 (2-back>0-back contrast). Pearson correlations between brain activity, symptoms, and WM performance were examined.

RESULTS

The total CHR group and medication-naive CHR sub-sample were comparable to controls in most demographic features and in N-back WM performance, but had significantly lower IQ. Relative to controls, medication-naïve CHR showed hyperactivity in the left parahippocampus (PHP) and the left caudate during performance of the N-back WM task. Relative to medication-exposed CHR, medication naïve CHR exhibited hyperactivity in the left caudate and the right dorsolateral prefrontal cortex (DLPFC). DLPFC activity was significantly negatively correlated with WM performance. PHP, caudate and DLPFC activity correlated strongly with symptoms, but results did not withstand FDR-correction for multiple comparisons. When all CHR participants were combined (regardless of medication status), only trend-level PHP hyperactivity was observed in CHR relative to controls.

CONCLUSIONS

Medication-naïve CHR exhibit hyperactivity in regions that subserve WM. These regions are implicated in studies of schizophrenia and risk for psychosis. Results emphasize the importance of medication status in the interpretation of task - induced brain activity.

Maturation- and sex-sensitive depression of hippocampal excitatory transmission in a rat schizophrenia model

Schizophrenia is associated with behavioral and brain structural abnormalities, of which the hippocampus appears to be one of the most consistent region affected. Previous studies performed on the poly I:C model of schizophrenia suggest that alterations in hippocampal synaptic transmission and plasticity take place in the offspring. However, these investigations yielded conflicting results and the neurophysiological alterations responsible for these deficits are still unclear. Here we performed for the first time a longitudinal study examining the impact of prenatal poly I:C treatment and of gender on hippocampal excitatory neurotransmission. In addition, we examined the potential preventive/curative effects of risperidone (RIS) treatment during the peri-adolescence period. Excitatory synaptic transmission was determined by stimulating Schaffer collaterals and monitoring fiber volley amplitude and slope of field-EPSP (fEPSP) in CA1 pyramidal neurons in male and female offspring hippocampal slices from postnatal days (PNDs) 18-20, 34, 70 and 90. Depression of hippocampal excitatory transmission appeared at juvenile age in male offspring of the poly I:C group, while it expressed with a delay in female, manifesting at adulthood. In addition, a reduced hippocampal size was found in both adult male and female offspring of poly I:C treated dams. Treatment with RIS at the peri-adolescence period fully restored in males but partly repaired in females these deficiencies. A maturation- and sex-dependent decrease in hippocampal excitatory transmission occurs in the offspring of poly I:C treated pregnant mothers. Pharmacological intervention with RIS during peri-adolescence can cure in a gender-sensitive fashion early occurring hippocampal synaptic deficits.

A Review of Biomarkers in Mood and Psychotic Disorders: A Dissection of Clinical vs. Preclinical Correlates

Despite significant research efforts aimed at understanding the neurobiological underpinnings of mood (depression, bipolar disorder) and psychotic disorders, the diagnosis and evaluation of treatment of these disorders are still based solely on relatively subjective assessment of symptoms as well as psychometric evaluations. Therefore, biological markers aimed at improving the current classification of psychotic and mood-related disorders, and that will enable patients to be stratified on a biological basis into more homogeneous clinically distinct subgroups, are urgently needed. The attainment of this goal can be facilitated by identifying biomarkers that accurately reflect pathophysiologic processes in these disorders. This review postulates that the field of psychotic and mood disorder research has advanced sufficiently to develop biochemical hypotheses of the etiopathology of the particular illness and to target the same for more effective disease modifying therapy. This implies that a "one-size fits all" paradigm in the treatment of psychotic and mood disorders is not a viable approach, but that a customized regime based on individual biological abnormalities would pave the way forward to more effective treatment. In reviewing the clinical and preclinical literature, this paper discusses the most highly regarded pathophysiologic processes in mood and psychotic disorders, thereby providing a scaffold for the selection of suitable biomarkers for future studies in this field, to develope biomarker panels, as well as to improve diagnosis and to customize treatment regimens for better therapeutic outcomes.

Prefrontal dopamine D1 receptors and working memory in schizotypal personality disorder: a PET study with [¹¹C]NNC112

RATIONALE

Schizotypal personality disorder (SPD) is associated with working memory (WM) impairments that are similar to those observed in schizophrenia. Imaging studies have suggested that schizophrenia is associated with alterations in dopamine D1 receptor availability in the prefrontal cortex (PFC) that may be related to the WM impairments that characterize this disorder.

OBJECTIVES

The aim of this study was to characterize prefrontal D1 receptor availability and its relation to WM performance in SPD.

METHODS

We used positron emission tomography (PET) and the radiotracer [(11)C]NNC112 with 18 unmedicated SPD and 21 healthy control participants; as an index of D1 receptor availability, binding potential (BP) measures (BPF, BPND, and BPP) were calculated for prefrontal and striatal subregions. To assess WM, SPD participants completed the 2-back and Paced Auditory Serial Addition Test (PASAT).

RESULTS

There were no significant group differences in PFC BP. BPF and BPP in the medial PFC were significantly negatively related to PASAT performance (r s  = -0.551, p = .022 and r s  = -0.488, p = .047, respectively), but BP was not related to 2-back performance.

CONCLUSIONS

In contrast to what has been found in schizophrenia, SPD was not associated with significant alterations in prefrontal D1 receptor availability. Similar to previous schizophrenia findings, however, higher prefrontal D1 receptor availability was associated with poorer WM performance (as measured by the PASAT) in SPD. These findings suggest that schizophrenia and SPD may share a common pathophysiological feature related to prefrontal dopamine functioning that contributes to WM dysfunction, but that in SPD, alterations in D1 may occur only in a subset of individuals and/or to an extent that is minor relative to what occurs in schizophrenia.

Alterations in the serotonin system in schizophrenia: a systematic review and meta-analysis of postmortem and molecular imaging studies

Serotonergic dysfunction is thought to contribute to the pathophysiology of schizophrenia but the evidence has not been systematically synthesised before. We therefore systematically reviewed postmortem and in vivo molecular imaging studies of serotonin function in schizophrenia. We identified fifty relevant studies investigating eight different serotonin receptor systems in a total of 684 patients and 675 controls. Meta-analysis of postmortem studies found an elevation in prefrontal 5-HT1A receptors with a moderate to large effect size (N=8, 85 patients and 94 controls, SMD=0.60; CI: 0.17-1.03; p=0.007) and a reduction with a large effect size in prefrontal 5-HT2A receptors (N=8, 168 patients and 163 controls, SMD=-0.73; CI: -1.33, -0.12; p=0.019) in schizophrenia vs healthy controls. The evidence for alterations in serotonin transporter availability or other serotonin receptors (5-HT1B; 5-HT1D; 5-HT3; 5-HT4; 5-HT7) is limited. There are fewer studies investigating 5-HT receptors in schizophrenia with neuroimaging. Findings indicated possible 5-HT alterations at psychosis onset, although due to the limited number it was not possible to combine studies in a meta-analysis. Further in vivo studies, particularly in drug naive patients using radiotracers that can index high affinity states, will help determine if the postmortem findings are primary or secondary to other factors.

DNA hypermethylation of the serotonin receptor type-2A gene is associated with a worse response to a weight loss intervention in subjects with metabolic syndrome

Understanding the regulation of gene activities depending on DNA methylation has been the subject of much recent study. However, although polymorphisms of the HTR2A gene have been associated with both obesity and psychiatric disorders, the role of HTR2A gene methylation in these illnesses remains uncertain. The aim of this study was to evaluate the association of HTR2A gene promoter methylation levels in white blood cells (WBC) with obesity traits and depressive symptoms in individuals with metabolic syndrome (MetS) enrolled in a behavioural weight loss programme. Analyses were based on 41 volunteers (mean age 49 ± 1 year) recruited within the RESMENA study. Depressive symptoms (as determined using the Beck Depression Inventory), anthropometric and biochemical measurements were analysed at the beginning and after six months of weight loss treatment. At baseline, DNA from WBC was isolated and cytosine methylation in the HTR2A gene promoter was quantified by a microarray approach. In the whole-study sample, a positive association of HTR2A gene methylation with waist circumference and insulin levels was detected at baseline. Obesity measures significantly improved after six months of dietary treatment, where a lower mean HTR2A gene methylation at baseline was associated with major reductions in body weight, BMI and fat mass after the treatment. Moreover, mean HTR2A gene methylation at baseline significantly predicted the decrease in depressive symptoms after the weight loss treatment. In conclusion, this study provides newer evidence that hypermethylation of the HTR2A gene in WBC at baseline is significantly associated with a worse response to a weight-loss intervention and with a lower decrease in depressive symptoms after the dietary treatment in subjects with MetS.

Persistent auditory hallucinations and treatment challenges

Despite improved neurotransmitter identification and emergence of novel antipsychotics, treatment of auditory hallucinatory experiences is frustrating. Interest has developed in non-pharmacological approaches to this problem – these do not eliminate the voices but reduce the distress associated with the experience.

Cross sectional PET study of cerebral adenosine A₁ receptors in premanifest and manifest Huntington's disease

PURPOSE

To study cerebral adenosine receptors (AR) in premanifest and manifest stages of Huntington's disease (HD).

METHODS

We quantified the cerebral binding potential (BP ND) of the A₁AR in carriers of the HD CAG trinucleotide repeat expansion using the radioligand [(18) F]CPFPX and PET. Four groups were investigated: (i) premanifest individuals far (preHD-A; n = 7) or (ii) near (preHD-B; n = 6) to the predicted symptom onset, (iii) manifest HD patients (n = 8), and (iv) controls (n = 36).

RESULTS

Cerebral A₁AR values of preHD-A subjects were generally higher than those of controls (by up to 31%, p < .01, in the thalamus on average). Across stages a successive reduction of A₁AR BPND was observed to the levels of controls in preHD-B and undercutting controls in manifest HD by down to 25%, p < .01, in the caudatus and amygdala. There was a strong correlation between A₁AR BP ND and years to onset. Before onset of HD, the assumed annual rates of change of A₁AR density were -1.2% in the caudatus, -1.7% in the thalamus and -3.4% in the amygdala, while the corresponding volume losses amounted to 0.6%, 0.1% and 0.2%, respectively.

CONCLUSIONS

Adenosine receptors switch from supra to subnormal levels during phenoconversion of HD. This differential regulation may play a role in the pathophysiology of altered energy metabolism.

Impaired context processing as a potential marker of psychosis risk state

While structural abnormalities of the dorsolateral prefrontal cortex (DLPFC) may pre-date and predict psychosis onset, the relationships between functional deficits, cognitive and psychosocial impairments has yet to be explored in the at-risk period. An established measure of cognitive control (AXCPT) was administered to demographically matched clinical-high-risk (CHR; n=25), first-episode schizophrenia (FE; n=35), and healthy control (HC; n=35) participants during functional magnetic resonance imaging (fMRI) to investigate these relationships. CHR and FE individuals demonstrated impaired context processing and reduced DLPFC activation relative to HC individuals during increased cognitive control demands. FE and CHR individuals' ability to increase DLPFC activity in response to cognitive control demands was associated with better task performance. Task performance was also associated with severity of disorganization and poverty symptoms in FE participants. These findings support more extensive studies using fMRI to examine the clinical significance of prefrontal cortical functioning in the earliest stages of psychosis.

Cortical surface-based analysis reduces bias and variance in kinetic modeling of brain PET data

Exploratory (i.e., voxelwise) spatial methods are commonly used in neuroimaging to identify areas that show an effect when a region-of-interest (ROI) analysis cannot be performed because no strong a priori anatomical hypothesis exists. However, noise at a single voxel is much higher than noise in a ROI making noise management critical to successful exploratory analysis. This work explores how preprocessing choices affect the bias and variability of voxelwise kinetic modeling analysis of brain positron emission tomography (PET) data. These choices include the use of volume- or cortical surface-based smoothing, level of smoothing, use of voxelwise partial volume correction (PVC), and PVC masking threshold. PVC was implemented using the Muller-Gartner method with the masking out of voxels with low gray matter (GM) partial volume fraction. Dynamic PET scans of an antagonist serotonin-4 receptor radioligand ([(11)C]SB207145) were collected on sixteen healthy subjects using a Siemens HRRT PET scanner. Kinetic modeling was used to compute maps of non-displaceable binding potential (BPND) after preprocessing. The results showed a complicated interaction between smoothing, PVC, and masking on BPND estimates. Volume-based smoothing resulted in large bias and intersubject variance because it smears signal across tissue types. In some cases, PVC with volume smoothing paradoxically caused the estimated BPND to be less than when no PVC was used at all. When applied in the absence of PVC, cortical surface-based smoothing resulted in dramatically less bias and the least variance of the methods tested for smoothing levels 5mm and higher. When used in combination with PVC, surface-based smoothing minimized the bias without significantly increasing the variance. Surface-based smoothing resulted in 2-4 times less intersubject variance than when volume smoothing was used. This translates into more than 4 times fewer subjects needed in a group analysis to achieve similarly powered statistical tests. Surface-based smoothing has less bias and variance because it respects cortical geometry by smoothing the PET data only along the cortical ribbon and so does not contaminate the GM signal with that of white matter and cerebrospinal fluid. The use of surface-based analysis in PET should result in substantial improvements in the reliability and detectability of effects in exploratory PET analysis, with or without PVC.

[¹⁸F]Altanserin and small animal PET: impact of multidrug efflux transporters on ligand brain uptake and subsequent quantification of 5-HT₂A receptor densities in the rat brain

INTRODUCTION

The selective 5-hydroxytryptamine type 2a receptor (5-HT(2A)R) radiotracer [(18)F]altanserin is a promising ligand for in vivo brain imaging in rodents. However, [(18)F]altanserin is a substrate of P-glycoprotein (P-gp) in rats. Its applicability might therefore be constrained by both a differential expression of P-gp under pathological conditions, e.g. epilepsy, and its relatively low cerebral uptake. The aim of the present study was therefore twofold: (i) to investigate whether inhibition of multidrug transporters (MDT) is suitable to enhance the cerebral uptake of [(18)F]altanserin in vivo and (ii) to test different pharmacokinetic, particularly reference tissue-based models for exact quantification of 5-HT(2A)R densities in the rat brain.

METHODS

Eighteen Sprague-Dawley rats, either treated with the MDT inhibitor cyclosporine A (CsA, 50 mg/kg, n=8) or vehicle (n=10) underwent 180-min PET scans with arterial blood sampling. Kinetic analyses of tissue time-activity curves (TACs) were performed to validate invasive and non-invasive pharmacokinetic models.

RESULTS

CsA application lead to a two- to threefold increase of [(18)F]altanserin uptake in different brain regions and showed a trend toward higher binding potentials (BP(ND)) of the radioligand.

CONCLUSIONS

MDT inhibition led to an increased cerebral uptake of [(18)F]altanserin but did not improve the reliability of BP(ND) as a non-invasive estimate of 5-HT(2A)R. This finding is most probable caused by the heterogeneous distribution of P-gp in the rat brain and its incomplete blockade in the reference region (cerebellum). Differential MDT expressions in experimental animal models or pathological conditions are therefore likely to influence the applicability of imaging protocols and have to be carefully evaluated.

Biomarker investigations related to pathophysiological pathways in schizophrenia and psychosis

Post-mortem brain investigations of schizophrenia have generated swathes of data in the last few decades implicating candidate genes and protein. However, the relation of these findings to peripheral biomarker indicators and symptomatology remain to be elucidated. While biomarkers for disease do not have to be involved with underlying pathophysiology and may be largely indicative of diagnosis or prognosis, the ideal may be a biomarker that is involved in underlying disease processes and which is therefore more likely to change with progression of the illness as well as potentially being more responsive to treatment. One of the main difficulties in conducting biomarker investigations for major psychiatric disorders is the relative inconsistency in clinical diagnoses between disorders such as bipolar and schizophrenia. This has led some researchers to investigate biomarkers associated with core symptoms of these disorders, such as psychosis. The aim of this review is to evaluate the contribution of post-mortem brain investigations to elucidating the pathophysiology pathways involved in schizophrenia and psychosis, with an emphasis on major neurotransmitter systems that have been implicated. This data will then be compared to functional neuroimaging findings as well as findings from blood based gene expression investigations in schizophrenia in order to highlight the relative overlap in pathological processes between these different modalities used to elucidate pathogenesis of schizophrenia. In addition we will cover some recent and exciting findings demonstrating microRNA (miRNA) dysregulation in both the blood and the brain in patients with schizophrenia. These changes are pertinent to the topic due to their known role in post-transcriptional modification of gene expression with the potential to contribute or underlie gene expression changes observed in schizophrenia. Finally, we will discuss how post-mortem studies may aid future biomarker investigations.

Suitability of [18F]altanserin and PET to determine 5-HT2A receptor availability in the rat brain: in vivo and in vitro validation of invasive and non-invasive kinetic models

PURPOSE

While the selective 5-hydroxytryptamine type 2a receptor (5-HT2AR) radiotracer [18F]altanserin is well established in humans, the present study evaluated its suitability for quantifying cerebral 5-HT2ARs with positron emission tomography (PET) in albino rats.

PROCEDURES

Ten Sprague Dawley rats underwent 180 min PET scans with arterial blood sampling. Reference tissue methods were evaluated on the basis of invasive kinetic models with metabolite-corrected arterial input functions. In vivo 5-HT2AR quantification with PET was validated by in vitro autoradiographic saturation experiments in the same animals.

RESULT

Overall brain uptake of [18F]altanserin was reliably quantified by invasive and non-invasive models with the cerebellum as reference region shown by linear correlation of outcome parameters. Unlike in humans, no lipophilic metabolites occurred so that brain activity derived solely from parent compound. PET data correlated very well with in vitro autoradiographic data of the same animals.

CONCLUSION

[18F]Altanserin PET is a reliable tool for in vivo quantification of 5-HT2AR availability in albino rats. Models based on both blood input and reference tissue describe radiotracer kinetics adequately. Low cerebral tracer uptake might, however, cause restrictions in experimental usage.

T102C polymorphism of serotonin 2A type receptor gene confers susceptibility to (early onset) schizophrenia in Han Chinese: an association study and meta-analysis

INTRODUCTION

Several lines of evidence have indicated that serotonin 2A receptor (HTR2A) may be involved in the pathophysiology of schizophrenia. One functional polymorphism in HTR2A (T102C) has been widely investigated; however, the results have been inconsistent. The purpose of this study was to evaluate the association between HTR2A T02C polymorphism and schizophrenia in a Chinese Han population.

METHODS

We performed a case-control study, using an early onset sample, which may be an attractive subgroup for genetic studies. In addition, we performed a meta-analysis of the combined sample groups in Han Chinese.

RESULTS

Our study, based on 385 schizophrenic patients and 399 controls, found a significant genotype-wise association of T102C and schizophrenia (P = 0.02). After applying stratified analyses, the dominant model for T allele produced significant association (OR = 1.60, 95%CI = 1.11-2.30, P = 0.01). In the meta-analysis including all of the published population-based association studies in Han Chinese and the present association study, the pooled genotype-wise result in a dominant model was statistically significant with a summary OR of 1.25 (95%CI = 1.04-1.50, P = 0.02).

DISCUSSION

Our results suggest that the HTR2A T102C polymorphism may confer susceptibility to schizophrenia in Han Chinese.

Transmembrane domain Nrg1 mutant mice show altered susceptibility to the neurobehavioural actions of repeated THC exposure in adolescence

Heavy cannabis abuse increases the risk of developing schizophrenia. Adolescents appear particularly vulnerable to the development of psychosis-like symptoms after cannabis use. To test whether the schizophrenia candidate gene neuregulin 1 (NRG1) modulates the effects of cannabinoids in adolescence, we tested male adolescent heterozygous transmembrane domain Nrg1 mutant (Nrg1 TM HET) mice and wild type-like littermates (WT) for their neurobehavioural response to repeated Δ(9)-tetrahydrocannabinol (THC, 10 mg/kg i.p. for 21 d starting on post-natal day 31). During treatment and 48 h after treatment withdrawal, we assessed several behavioural parameters relevant to schizophrenia. After behavioural testing we measured autoradiographic CB(1), 5-HT(2A) and NMDA receptor binding. The hyperlocomotor phenotype typical of Nrg1 mutants emerged after drug withdrawal and was more pronounced in vehicle than THC-treated Nrg1 TM HET mice. All mice were equally sensitive to THC-induced suppression of locomotion. However, mutant mice appeared protected against inhibiting effects of repeated THC on investigative social behaviours. Neither THC nor Nrg1 genotype altered prepulse inhibition. Repeated adolescent THC promoted differential effects on CB(1) and 5-HT(2A) receptor binding in the substantia nigra and insular cortex respectively, decreasing binding in WT while increasing it in Nrg1 TM HET mice. THC also selectively affected 5-HT(2A) receptor binding in several other regions in WT mice, whereas NMDA receptor binding was only affected in mutant mice. Overall, Nrg1 mutation does not appear to increase the induction of psychotomimetic symptoms by repeated adolescent THC exposure but may attenuate some of its actions on social behaviour and schizophrenia-relevant neurotransmitter receptor profiles.

Sleep deprivation increases cerebral serotonin 2A receptor binding in humans

STUDY OBJECTIVES

Serotonin and its cerebral receptors play an important role in sleep-wake regulation. The aim of the current study is to investigate the effect of 24-h total sleep deprivation on the apparent serotonin 2A receptor (5-HT(2A)R) binding capacity in the human brain to test the hypothesis that sleep deprivation induces global molecular alterations in the cortical serotonergic receptor system.

DESIGN

Volunteers were tested twice with the subtype-selective radiotracer [(18)F]altanserin and positron emission tomography (PET) for imaging of 5-HT(2A)Rs at baseline and after 24 h of sleep deprivation. [(18)F]Altanserin binding potentials were analyzed in 13 neocortical regions of interest. The efficacy of sleep deprivation was assessed by questionnaires, waking electroencephalography, and cognitive performance measurements.

SETTING

Sleep laboratory and neuroimaging center.

PATIENTS OR PARTICIPANTS

Eighteen healthy volunteers.

INTERVENTIONS

Sleep deprivation.

MEASUREMENTS AND RESULTS

A total of 24 hours of sleep deprivation led to a 9.6% increase of [(18)F]altanserin binding on neocortical 5-HT(2A) receptors. Significant region-specific increases were found in the medial inferior frontal gyrus, insula, and anterior cingulate, parietal, sensomotoric, and ventrolateral prefrontal cortices.

CONCLUSIONS

This study demonstrates that a single night of total sleep deprivation causes significant increases of 5-HT(2A)R binding potentials in a variety of cortical regions although the increase declines as sleep deprivation continued. It provides in vivo evidence that total sleep deprivation induces adaptive processes in the serotonergic system of the human brain.

From the prodrome to chronic schizophrenia: the neurobiology underlying psychotic symptoms and cognitive impairments

Schizophrenia is a chronic psychotic disorder that remains a considerable cause of global disease burden. Cognitive impairments are common and contribute significantly to the morbidity of the disorder. Over the last two decades or so molecular imaging studies have refined understanding of the pathophysiology underlying the development of psychosis and cognitive impairments. Firstly they have consistently implicated presynaptic dopaminergic dysfunction in the disorder, finding that dopamine synthesis capacity, dopamine release and baseline dopamine levels are increased in the illness. Secondly recent findings show that dopamine synthesis capacity is elevated in those that go on to develop psychosis in the following year, but not in those that do not, and appears to increase further with the development of psychosis. Thirdly evidence links greater dopamine synthesis capacity to poorer cognitive performance and altered frontal cortical function measured using functional imaging during cognitive tasks. Finally they have provided data on the nature of other neurofunctional alterations in the disorder, in particular in the serotonergic system and neuroinflammation. We review these findings and discuss their implications for understanding the neurobiology of psychosis and cognitive impairments in schizophrenia.

Normative database of the serotonergic system in healthy subjects using multi-tracer PET

The highly diverse serotonergic system with at least 16 different receptor subtypes is implicated in the pathophysiology of most neuropsychiatric disorders including affective and anxiety disorders, obsessive compulsive disorder, post-traumatic stress disorder, eating disorders, sleep disturbance, attention deficit/hyperactivity disorder, drug addiction, suicidal behavior, schizophrenia, Alzheimer, etc. Alterations of the interplay between various pre- and postsynaptic receptor subtypes might be involved in the pathogenesis of these disorders. However, there is a lack of comprehensive in vivo values using standardized procedures. In the current PET study we quantified 3 receptor subtypes, including the major inhibitory (5-HT(1A) and 5-HT(1B)) and excitatory (5-HT(2A)) receptors, and the transporter (5-HTT) in the brain of healthy human subjects to provide a database of standard values. PET scans were performed on 95 healthy subjects (age=28.0 ± 6.9 years; 59% males) using the selective radioligands [carbonyl-(11)C]WAY-100635, [(11)C]P943, [(18)F]altanserin and [(11)C]DASB, respectively. A standard template in MNI stereotactic space served for region of interest delineation. This template follows two anatomical parcellation schemes: 1) Brodmann areas including 41 regions and 2) AAL (automated anatomical labeling) including 52 regions. Standard values (mean, SD, and range) for each receptor and region are presented. Mean cortical and subcortical binding potential (BP) values were in good agreement with previously published human in vivo and post-mortem data. By means of linear equations, PET binding potentials were translated to post-mortem binding (provided in pmol/g), yielding 5.89 pmol/g (5-HT(1A)), 23.5 pmol/g (5-HT(1B)), 31.44 pmol/g (5-HT(2A)), and 11.33 pmol/g (5-HTT) being equivalent to the BP of 1, respectively. Furthermore, we computed individual voxel-wise maps with BP values and generated average tracer-specific whole-brain binding maps. This knowledge might improve our interpretation of the alterations taking place in the serotonergic system during neuropsychiatric disorders.

Reduced levels of serotonin 2A receptors underlie resistance of Egr3-deficient mice to locomotor suppression by clozapine

The immediate-early gene early growth response 3 (Egr3) is associated with schizophrenia and expressed at reduced levels in postmortem patients' brains. We have previously reported that Egr3-deficient (Egr3(-/-)) mice display reduced sensitivity to the sedating effects of clozapine compared with wild-type (WT) littermates, paralleling the heightened tolerance of schizophrenia patients to antipsychotic side effects. In this study, we have used a pharmacological dissection approach to identify a neurotransmitter receptor defect in Egr3(-/-) mice that may mediate their resistance to the locomotor suppressive effects of clozapine. We report that this response is specific to second-generation antipsychotic agents (SGAs), as first-generation medications suppress the locomotor activity of Egr3(-/-) and WT mice to a similar degree. Further, in contrast to the leading theory that sedation by clozapine results from anti-histaminergic effects, we show that H1 histamine receptors are not responsible for this effect in C57BL/6 mice. Instead, selective serotonin 2A receptor (5HT(2A)R) antagonists ketanserin and MDL-11939 replicate the effect of SGAs, repressing the activity in WT mice at a dosage that fails to suppress the activity of Egr3(-/-) mice. Radioligand binding revealed nearly 70% reduction in 5HT(2A)R expression in the prefrontal cortex of Egr3(-/-) mice compared with controls. Egr3(-/-) mice also exhibit a decreased head-twitch response to 5HT(2A)R agonist 1-(2,5-dimethoxy 4-iodophenyl)-2-amino propane (DOI). These findings provide a mechanism to explain the reduced sensitivity of Egr3(-/-) mice to the locomotor suppressive effects of SGAs, and suggest that 5HT(2A)Rs may also contribute to the sedating properties of these medications in humans. Moreover, as the deficit in cortical 5HT(2A)R in Egr3(-/-) mice aligns with numerous studies reporting decreased 5HT(2A)R levels in the brains of schizophrenia patients, and the gene encoding the 5HT(2A)R is itself a leading schizophrenia candidate gene, these findings suggest a potential mechanism by which putative dysfunction in EGR3 in humans may influence risk for schizophrenia.

Insular volume abnormalities associated with different transition probabilities to psychosis

BACKGROUND

Although individuals vulnerable to psychosis show brain volumetric abnormalities, structural alterations underlying different probabilities for later transition are unknown. The present study addresses this issue by means of voxel-based morphometry (VBM).

METHOD

We investigated grey matter volume (GMV) abnormalities by comparing four neuroleptic-free groups: individuals with first episode of psychosis (FEP) and with at-risk mental state (ARMS), with either long-term (ARMS-LT) or short-term ARMS (ARMS-ST), compared to the healthy control (HC) group. Using three-dimensional (3D) magnetic resonance imaging (MRI), we examined 16 FEP, 31 ARMS, clinically followed up for on average 3 months (ARMS-ST, n=18) and 4.5 years (ARMS-LT, n=13), and 19 HC.

RESULTS

The ARMS-ST group showed less GMV in the right and left insula compared to the ARMS-LT (Cohen's d 1.67) and FEP groups (Cohen's d 1.81) respectively. These GMV differences were correlated positively with global functioning in the whole ARMS group. Insular alterations were associated with negative symptomatology in the whole ARMS group, and also with hallucinations in the ARMS-ST and ARMS-LT subgroups. We found a significant effect of previous antipsychotic medication use on GMV abnormalities in the FEP group.

CONCLUSIONS

GMV abnormalities in subjects at high clinical risk for psychosis are associated with negative and positive psychotic symptoms, and global functioning. Alterations in the right insula are associated with a higher risk for transition to psychosis, and thus may be related to different transition probabilities.

Epigenetics of psychoactive drugs

Objectives

Epigenetics refers to the heritable, but reversible regulation of various biological functions. Changes in DNA methylation and chromatin structure derived from histone modifications are involved in the brain development, pathogenesis and pharmacotherapy of brain disorders.

Key findings

Evidence suggests that epigenetic modulations play key roles in psychiatric diseases such as schizophrenia and bipolar disorder. The analysis of epigenetic aberrations in the mechanisms of psychoactive drugs helps to determine dysfunctional genes and pathways in the brain, to predict side effects of drugs on human genome and identify new pharmaceutical targets for treatment of psychiatric diseases.

Summary

Although numerous studies have concentrated on epigenetics of psychosis, the epigenetic studies of antipsychotics are limited. Here we present epigenetic mechanisms of various psychoactive drugs and review the current literature on psychiatric epigenomics. Furthermore, we discuss various epigenetic modulations in the pharmacology and toxicology of typical and atypical antipsychotics, methionine, lithium and valproic acid.

Fluoxetine and aripiprazole treatment following prenatal immune activation exert longstanding effects on rat locomotor response

AIM

Studies characterizing treatment interventions in a naturalistic setting suggest that antidepressant and antipsychotic medications may be equally effective in improving clinical outcome in individuals at high risk for first-episode psychosis. Of interest, both beneficial as well as potentially adverse effects have been observed following fluoxetine treatment in a mouse prenatal immune activation model of relevance to psychosis prevention. We sought to extend those findings by examining the effects of fluoxetine, as well as the antipsychotic medication aripiprazole, in a rat prenatal immune activation model.

METHODS

Pregnant Sprague-Dawley rats were injected with poly I:C or saline on gestational day 14. Offspring of poly I:C and saline-treated dams received fluoxetine (10.0 mg/kg/d), aripiprazole (0.66 mg/kg/d), or vehicle from postnatal days 35 to 70. Locomotor responses to novelty, saline injection, and amphetamine (1 and 5 mg/kg) were determined at three months, i.e., 21 days following drug discontinuation.

RESULTS

Both fluoxetine and aripiprazole had beneficial effects on behavioral response to amphetamine (1 mg/kg) at 3 months, ameliorating the impact of prenatal immune activation on offspring of poly I:C-treated dams. Significantly, both drugs also exerted effects in offspring of control (saline-treated) dams on locomotor response to injection.

CONCLUSIONS

Fluoxetine and aripiprazole pretreatment of poly I:C offspring from postnatal days 35 to 70 stabilized response to amphetamine exposure persisting through 3 months of age, similar to earlier findings in mice that fluoxetine treatment following prenatal immune activation prevented altered locomotor response to amphetamine. The current data also confirm earlier findings of potential adverse behavioral effects in offspring of control dams following treatment with fluoxetine and antipsychotic medications, highlighting the potential for both therapeutic as well as safety concerns with exposure to preventive pharmacological treatments over the course of adolescent development. Further study is needed to determine clinical and epidemiological consequences of these pre-clinical findings.

Serotonergic mechanisms as targets for existing and novel antipsychotics

A variety of serotonin (5-HT) receptors, especially 5-HT(2A), 5-HT(1A), 5-HT(6), 5-HT(7), and 5-HT(2C), have been postulated to contribute to the mechanism of action of atypical antipsychotic drugs (APDs), i.e., APDs which cause fewer extrapyramidal side effects (EPS) at clinically optimal doses, in contrast with typical APDs, which are more likely to cause EPS. This advantage, rarely disputed, has made such drugs the preferred treatment for schizophrenia and other indications for APDs. These 5-HT receptors are still of interest as components of novel multireceptor or stand-alone APDs, and potentially to remediate cognitive deficits in schizophrenia. Almost all currently available atypical APDs are 5-HT(2A) receptor inverse agonists, as well as dopamine (DA) D(2) receptor antagonists or partial agonists. Amisulpride, an exceptional atypical APD, has 5-HT(7) antagonism to complement its DA D(2/3) antagonism. Some atypical APDs are also 5-HT(1A) partial agonists, 5-HT(6), or 5-HT(7) antagonists, or some combination of the above. 5-HT(2C) antagonism has been found to contribute to the metabolic side effects of some atypical APDs, whereas 5-HT(2C) agonists have potential as stand-alone APDs and/or cognitive enhancers. This review will provide an update of current preclinical and clinical evidence for the role of these five 5-HT receptors in the actions of current APDs and for the development of novel psychotropic drugs.

Epigenetic dysregulation of HTR2A in the brain of patients with schizophrenia and bipolar disorder

INTRODUCTION

HTR2A gene has been the subject of numerous studies in psychiatric genetics because LSD, which resembles serotonin causes psychosis and atypical antipsychotic drugs target the HTR2A receptor. However, evidence for the role of HTR2A polymorphism(s) in schizophrenia (SCZ) and bipolar disorder (BD) has been elusive. We hypothesized that epigenetic dysregulation of HTR2A may be involved in psycho-pathogenesis and analyzed promoter DNA methylome and expression of HTR2A in SCZ, BD and control subjects.

METHOD

DNA derived from post-mortem brains of patients with SCZ and BD and matched control subjects (each 35) were obtained from the Stanley Medical Research Institute. While bisulfite DNA sequencing was used to screen and quantify cytosine methylation in the HTR2A promoter, corresponding gene expression was analyzed by qRT-PCR.

RESULTS

We found strong evidence for epigenetic fine-tuning of HTR2A expression. In general, the expression of HTR2A in individuals carrying the C allele of T102C (or G allele of -1438A/G polymorphism) was higher than TT genotype. Interestingly, promoter DNA of HTR2A was hypermethylated at and around the -1438A/G polymorphic site, but was hypomethylated at and around T102C polymorphic site in SCZ and BD compared to the controls. Furthermore, epigenetic down-regulation of HTR2A was associated with early age of disease onset in SCZ and BD.

CONCLUSION

Epigenetic dysregulation of HTR2A may contribute to SCZ, BD and earlier age of disease onset. Further research is required to delineate the dysregulation of other components of serotoninergic pathway to design new therapeutics based on the downstream effects of serotonin.

5-HT radioligands for human brain imaging with PET and SPECT

The serotonergic system plays a key modulatory role in the brain and is the target for many drug treatments for brain disorders either through reuptake blockade or via interactions at the 14 subtypes of 5-HT receptors. This review provides the history and current status of radioligands used for positron emission tomography (PET) and single photon emission computerized tomography (SPECT) imaging of human brain serotonin (5-HT) receptors, the 5-HT transporter (SERT), and 5-HT synthesis rate. Currently available radioligands for in vivo brain imaging of the 5-HT system in humans include antagonists for the 5-HT(1A), 5-HT(1B), 5-HT(2A), and 5-HT(4) receptors, and for SERT. Here we describe the evolution of these radioligands, along with the attempts made to develop radioligands for additional serotonergic targets. We describe the properties needed for a radioligand to become successful and the main caveats. The success of a PET or SPECT radioligand can ultimately be assessed by its frequency of use, its utility in humans, and the number of research sites using it relative to its invention date, and so these aspects are also covered. In conclusion, the development of PET and SPECT radioligands to image serotonergic targets is of high interest, and successful evaluation in humans is leading to invaluable insight into normal and abnormal brain function, emphasizing the need for continued development of both SPECT and PET radioligands for human brain imaging.

Cognitive control deficits in schizophrenia: mechanisms and meaning

Although schizophrenia is an illness that has been historically characterized by the presence of positive symptomatology, decades of research highlight the importance of cognitive deficits in this disorder. This review proposes that the theoretical model of cognitive control, which is based on contemporary cognitive neuroscience, provides a unifying theory for the cognitive and neural abnormalities underlying higher cognitive dysfunction in schizophrenia. To support this model, we outline converging evidence from multiple modalities (eg, structural and functional neuroimaging, pharmacological data, and animal models) and samples (eg, clinical high risk, genetic high risk, first episode, and chronic subjects) to emphasize how dysfunction in cognitive control mechanisms supported by the prefrontal cortex contribute to the pathophysiology of higher cognitive deficits in schizophrenia. Our model provides a theoretical link between cellular abnormalities (eg, reductions in dentritic spines, interneuronal dysfunction), functional disturbances in local circuit function (eg, gamma abnormalities), altered inter-regional cortical connectivity, a range of higher cognitive deficits, and symptom presentation (eg, disorganization) in the disorder. Finally, we discuss recent advances in the neuropharmacology of cognition and how they can inform a targeted approach to the development of effective therapies for this disabling aspect of schizophrenia.

Gray matter in first-episode schizophrenia before and after antipsychotic drug treatment. Anatomical likelihood estimation meta-analyses with sample size weighting

BACKGROUND

Cerebral morphological abnormalities in schizophrenia may be modulated by treatment, chronicity, and duration of illness. Comparing brain imaging studies of individuals with first-episode schizophrenia and neuroleptic naive (NN-FES) with that of their neuroleptic-treated counterparts (NT-FES) can help to dissect out the effect of these potential confounders.

METHODS

We used the anatomical likelihood estimation method to compare voxel-based morphometric studies of NN-FES (n = 162 patients) and NT-FES (n = 336 patients) studies. The analysis included a sample size weighting step based on the Liptak-Stouffer method to reflect the greater power of larger studies.

RESULTS

Patient samples were matched for age, gender, and duration of illness. An extensive network of gray matter deficits in frontal, temporal, insular, striatal, posterior cingulate, and cerebellar regions was detected in the NN-FES samples as compared with healthy controls. Major deficits were detected in the frontal, superior temporal, insular, and parahippocampal regions for the NT-FES group compared with the NN-FES group. In addition, the NT-FES group showed minor deficits in the caudate, cingulate, and inferior temporal regions compared with the NN-FES group. There were no regions with gray matter volumetric excess in the NT-FES group.

CONCLUSION

Frontal, striato-limbic, and temporal morphological abnormalities are present in the early stage of schizophrenia and are unrelated to the effects of neuroleptic treatment, chronicity, and duration of illness. There may be dynamic effects of treatment on striato-limbic and temporal, but not frontal, regional gray matter volumes of the brain.

Dysfunctional brain networks and genetic risk for schizophrenia: specific neurotransmitter systems

Multiple neurotransmitter circuits are disturbed in schizophrenia, and the dopamine hypothesis of schizophrenia prevails as the hypothesis with most empirical support. On the other hand, schizophrenia is highly heritable with a pattern consistent with both common and rare allelic variants and gene × environment interaction. Advances in the field of neuroimaging have expanded our knowledge of intermediate phenotypes, the neurobiological processes that convey the risk from the genes to the complex phenotype. In this article, we review the recent and continuously accumulating evidence from in vivo imaging studies aiming at characterizing neurochemical intermediate phenotypes of schizophrenia. Dopaminergic alterations in schizophrenia are shared by individuals at genetic risk who do not express the illness, suggesting a "dopamine hypothesis of schizophrenia vulnerability." This hypothesis has the potential to help us better understand the dopaminergic dysfunction in the context of the complex pathophysiological process leading to schizophrenia. In the future, neurotransmitter imaging studies should investigate the gene × environment interaction in schizophrenia, and try to identify neurobiological correlates of heightened sensitivity to environmental stressors (e.g., cannabis, childhood trauma, and other psychosocial stress) in genetically vulnerable individuals.

Are Bipolar Disorder and Schizophrenia Neuroanatomically Distinct? An Anatomical Likelihood Meta-analysis

Objective: There is renewed debate on whether modern diagnostic classification should adopt a dichotomous or dimensional approach to schizophrenia and bipolar disorder. This study synthesizes data from voxel-based studies of schizophrenia and bipolar disorder to estimate the extent to which these conditions have a common neuroanatomical phenotype. Methods: A post-hoc meta-analytic estimation of the extent to which bipolar disorder, schizophrenia, or both conditions contribute to brain gray matter differences compared to controls was achieved using a novel application of the conventional anatomical likelihood estimation (ALE) method. 19 schizophrenia studies (651 patients and 693 controls) were matched as closely as possible to 19 bipolar studies (540 patients and 745 controls). Result: Substantial overlaps in the regions affected by schizophrenia and bipolar disorder included regions in prefrontal cortex, thalamus, left caudate, left medial temporal lobe, and right insula. Bipolar disorder and schizophrenia jointly contributed to clusters in the right hemisphere, but schizophrenia was almost exclusively associated with additional gray matter deficits (left insula and amygdala) in the left hemisphere. Limitation: The current meta-analytic method has a number of constraints. Importantly, only studies identifying differences between controls and patient groups could be included in this analysis. Conclusion: Bipolar disorder shares many of the same brain regions as schizophrenia. However, relative to neurotypical controls, lower gray matter volume in schizophrenia is more extensive and includes the amygdala. This fresh application of ALE accommodates multiple studies in a relatively unbiased comparison. Common biological mechanisms may explain the neuroanatomical overlap between these major disorders, but explaining why brain differences are more extensive in schizophrenia remains challenging.

Research in people with psychosis risk syndrome: a review of the current evidence and future directions

After decades of research, schizophrenia and related psychotic disorders are still among the most debilitating disorders in medicine. The chronic illness course in most individuals, greater treatment responsiveness during the first episode, progressive gray matter decline during early disease stages, and retrospective accounts of 'prodromal' or early illness signs and symptoms formed the basis for research on the psychosis risk syndrome (PRS), known variably as 'clinical high risk' (CHR), or 'ultra-high risk' (UHR), or 'prodromal'. The pioneering era of research on PRS focused on the development and validation of specific assessment tools and the delineation of high risk criteria. This was followed by the examination of conversion rates in psychosis risk cohorts followed naturalistically, identification of predictors of conversion to psychosis, and investigation of interventions able to abort or delay the development of full psychosis. Despite initially encouraging results concerning the predictive validity of PRS criteria, recent findings of declining conversion rates demonstrate the need for further investigations. Results from intervention studies, mostly involving second-generation antipsychotics and cognitive behavioral therapy, are encouraging, but are currently still insufficient to make treatment recommendations for this early, relatively non-specific illness phase. The next phase of research on PRS, just now beginning, has moved to larger, 'multisite' projects to increase generalizability and to ensure that sufficiently large samples at true risk for psychosis are included. Emphasis in these emerging studies is on: 1) identification of biomarkers for conversion to psychosis; 2) examination of non-antipsychotic, neuroprotective and low-risk pharmacologic and non-pharmacologic interventions; 3) testing of potentially phase-specific interventions; 4) examination of the relationship between treatment response during PRS and prognosis for the course of illness; 5) follow-up of patients who developed schizophrenia despite early interventions and comparison of illness trajectories with patients who did not receive early interventions; 6) characterization of individuals with outcomes other than schizophrenia-spectrum disorders, such as bipolar disorder and remission from PRS, including false positive cases; and 7) assessment of meaningful social and role functioning outcomes. While the research conducted to date has already yielded crucial information, the translation of the concept of a clinically identifiable PRS into clinical practice does not seem justified at this point.