Presynaptic dopaminergic function in the striatum of schizophrenic patients

Imaging the Vesicular Acetylcholine Transporter in Schizophrenia: A Positron Emission Tomography Study Using [18F]-VAT

BACKGROUND

Despite longstanding interest in the central cholinergic system in schizophrenia (SCZ), cholinergic imaging studies with patients have been limited to receptors. Here, we conducted a proof-of-concept positron emission tomography study using [18F]-VAT, a new radiotracer that targets the vesicular acetylcholine transporter as a proxy measure of acetylcholine transmission capacity, in patients with SCZ and explored relationships of vesicular acetylcholine transporter with clinical symptoms and cognition.

METHODS

A total of 18 adult patients with SCZ or schizoaffective disorder (the SCZ group) and 14 healthy control participants underwent a positron emission tomography scan with [18F]-VAT. Distribution volume (VT) for [18F]-VAT was derived for each region of interest, and group differences in VT were assessed with 2-sample t tests. Functional significance was explored through correlations between VT and scores on the Positive and Negative Syndrome Scale and a computerized neurocognitive battery (PennCNB).

RESULTS

No group differences in [18F]-VAT VT were observed. However, within the SCZ group, psychosis symptom severity was positively associated with VT in multiple regions of interest, with the strongest effects in the hippocampus, thalamus, midbrain, cerebellum, and cortex. In addition, in the SCZ group, working memory performance was negatively associated with VT in the substantia innominata and several cortical regions of interest including the dorsolateral prefrontal cortex.

CONCLUSIONS

In this initial study, the severity of 2 important features of SCZ-psychosis and working memory deficit-was strongly associated with [18F]-VAT VT in several cortical and subcortical regions. These correlations provide preliminary evidence of cholinergic activity involvement in SCZ and, if replicated in larger samples, could lead to a more complete mechanistic understanding of psychosis and cognitive deficits in SCZ and the development of therapeutic targets.

Brain mechanisms underlying catatonia: A systematic review

BACKGROUND

Catatonia is a complex psychomotor disorder characterized by motor, affective, and behavioral symptoms. Despite being known for almost 150 years, its pathomechanisms are still largely unknown.

METHODS

A systematic research on PubMed, Web of Science, and Scopus was conducted to identify neuroimaging studies conducted on group or single individuals with catatonia. Overall, 33 studies employing structural magnetic resonance imaging (sMRI, n = 11), functional magnetic resonance imaging (fMRI, n = 10), sMRI and fMRI (n = 2), functional near-infrared spectroscopy (fNIRS, n = 1), single positron emission computer tomography (SPECT, n = 4), positron emission tomography (PET, n = 4), and magnetic resonance spectroscopy (MRS, n = 1), and 171 case reports were retrieved.

RESULTS

Observational sMRI studies showed numerous brain changes in catatonia, including diffuse atrophy and signal hyperintensities, while case-control studies reported alterations in fronto-parietal and limbic regions, the thalamus, and the striatum. Task-based and resting-state fMRI studies found abnormalities located primarily in the orbitofrontal, medial prefrontal, motor cortices, cerebellum, and brainstem. Lastly, metabolic and perfusion changes were observed in the basal ganglia, prefrontal, and motor areas. Most of the case-report studies described widespread white matter lesions and frontal, temporal, or basal ganglia hypoperfusion.

CONCLUSIONS

Catatonia is characterized by structural, functional, perfusion, and metabolic cortico-subcortical abnormalities. However, the majority of studies and case reports included in this systematic review are affected by considerable heterogeneity, both in terms of populations and neuroimaging techniques, which calls for a cautious interpretation. Further elucidation, through future neuroimaging research, could have great potential to improve the description of the neural motor and psychomotor mechanisms underlying catatonia.

Dopamine Synthesis Capacity and GABA and Glutamate Levels Separate Antipsychotic-Naïve Patients With First-Episode Psychosis From Healthy Control Subjects in a Multimodal Prediction Model

Background

Disturbances in presynaptic dopamine activity and levels of GABA (gamma-aminobutyric acid) and glutamate plus glutamine collectively may have a role in the pathophysiology of psychosis, although separately they are poor diagnostic markers. We tested whether these neurotransmitters in combination improve the distinction of antipsychotic-naïve patients with first-episode psychosis from healthy control subjects.

Methods

We included 23 patients (mean age 22.3 years, 9 male) and 20 control subjects (mean age 22.4 years, 8 male). We determined dopamine metabolism in the nucleus accumbens and striatum from 18F-fluorodopa (18F-FDOPA) positron emission tomography. We measured GABA levels in the anterior cingulate cortex (ACC) and glutamate plus glutamine levels in the ACC and left thalamus with 3T proton magnetic resonance spectroscopy. We used binominal logistic regression for unimodal prediction when we modeled neurotransmitters individually and for multimodal prediction when we combined the 3 neurotransmitters. We selected the best combination based on Akaike information criterion.

Results

Individual neurotransmitters failed to predict group. Three triple neurotransmitter combinations significantly predicted group after Benjamini-Hochberg correction. The best model (Akaike information criterion 48.5) carried 93.5% of the cumulative model weight. It reached a classification accuracy of 83.7% (p = .003) and included dopamine synthesis capacity (Ki4p) in the nucleus accumbens (p = .664), GABA levels in the ACC (p = .019), glutamate plus glutamine levels in the thalamus (p = .678), and the interaction term Ki4p × GABA (p = .016).

Conclusions

Our multimodal approach proved superior classification accuracy, implying that the pathophysiology of patients represents a combination of neurotransmitter disturbances rather than aberrations in a single neurotransmitter. Particularly aberrant interrelations between Ki4p in the nucleus accumbens and GABA values in the ACC appeared to contribute diagnostic information.

Striatal dopamine synthesis capacity and its association with negative symptoms upon resolution of positive symptoms in first-episode schizophrenia and delusional disorder

RATIONALE

How striatal dopamine synthesis capacity (DSC) contributes to the pathogenesis of negative symptoms in first-episode schizophrenia (SZ) and delusional disorder (DD) has seldom been explored. As negative symptoms during active psychotic episodes can be complicated by secondary influences, such as positive symptoms, longitudinal investigations may help to clarify the relationship between striatal DSC and negative symptoms and differentiate between primary and secondary negative symptoms.

OBJECTIVE

A longitudinal study was conducted to examine whether baseline striatal DSC would be related to negative symptoms at 3 months in first-episode SZ and DD patients.

METHODS

Twenty-three first-episode age- and gender-matched patients (11 DD and 12 SZ) were consecutively recruited through an early intervention service for psychosis in Hong Kong. Among them, 19 (82.6%) patients (9 DD and 10 SZ) were followed up at 3 months. All patients received an ¹⁸F-DOPA PET/MR scan at baseline.

RESULTS

Baseline striatal DSC (K^occ;30-60) was inversely associated with negative symptoms at 3 months in first-episode SZ patients (r_s =  - 0.80, p = 0.010). This association remained in SZ patients even when controlling for baseline negative, positive, and depressive symptoms, as well as cumulative antipsychotic dosage (β =  - 0.69, p = 0.012). Such associations were not observed in first-episode DD patients. Meanwhile, the severity of negative symptoms at 3 months was associated with more positive symptoms in DD patients (r_s = 0.74, p = 0.010) and not in SZ patients.

CONCLUSIONS

These findings highlight the role of striatal DSC in negative symptoms upon resolution of active psychotic episodes among first-episode SZ patients. Baseline striatal dopamine activity may inform future symptom expression with important treatment implications.

Clinical correlation but no elevation of striatal dopamine synthesis capacity in two independent cohorts of medication-free individuals with schizophrenia

Dysregulation of dopamine systems has been considered a foundational driver of pathophysiological processes in schizophrenia, an illness characterized by diverse domains of symptomatology. Prior work observing elevated presynaptic dopamine synthesis capacity in some patient groups has not always identified consistent symptom correlates, and studies of affected individuals in medication-free states have been challenging to obtain. Here we report on two separate cohorts of individuals with schizophrenia spectrum illness who underwent blinded medication withdrawal and medication-free neuroimaging with [¹⁸F]-FDOPA PET to assess striatal dopamine synthesis capacity. Consistently in both cohorts, we found no significant differences between patient and matched, healthy comparison groups; however, we did identify and replicate robust inverse relationships between negative symptom severity and tracer-specific uptake widely throughout the striatum: [¹⁸F]-FDOPA specific uptake was lower in patients with a greater preponderance of negative symptoms. Complementary voxel-wise and region of interest analyses, both with and without partial volume correction, yielded consistent results. These data suggest that for some individuals, striatal hyperdopaminergia may not be a defining or enduring feature of primary psychotic illness. However, clinical differences across individuals may be significantly linked to variability in striatal dopaminergic tone. These findings call for further experimentation aimed at parsing the heterogeneity of dopaminergic systems function in schizophrenia.

Dopaminergic Activity in Antipsychotic-Naïve Patients Assessed With Positron Emission Tomography Before and After Partial Dopamine D2 Receptor Agonist Treatment: Association With Psychotic Symptoms and Treatment Response

BACKGROUND

Dopamine activity has been associated with the response to antipsychotic treatment. Our study used a four-parameter model to test the association between the striatal decarboxylation rate of ¹⁸F-DOPA to ¹⁸F-dopamine (k₃) and the effect of treatment on psychotic symptoms in antipsychotic-naïve patients with first-episode psychosis. We further explored the effect of treatment with a partial dopamine D₂ receptor agonist (aripiprazole) on k₃ and dopamine synthesis capacity (DSC) determined by the four-parameter model and by the conventional tissue reference method.

METHODS

Sixty-two individuals (31 patients and 31 control subjects) underwent ¹⁸F-DOPA positron emission tomography at baseline, and 15 patients were re-examined after 6 weeks. Clinical re-examinations were completed after 6 weeks (n = 28) and 6 months (n = 15). Symptoms were evaluated with the Positive and Negative Syndrome Scale.

RESULTS

High baseline decarboxylation rates (k₃) were associated with more positive symptoms at baseline (p < .001) and with symptom improvement after 6 weeks (p = .006). Subregion analyses showed that baseline k₃ for the putamen (p = .003) and nucleus accumbens (p = .013) and DSC values for the nucleus accumbens (p = .003) were associated with psychotic symptoms. The tissue reference method yielded no associations between DSC and symptoms or symptom improvement. Neither method revealed any effects of group or treatment on average magnitudes of k₃ or DSC, whereas changes in dopamine synthesis were correlated with higher baseline values, implying a potential effect of treatment.

CONCLUSIONS

Striatal decarboxylation rate at baseline was associated with psychotic symptoms and treatment response. The strong association between k₃ and treatment effect potentially implicate on new treatment strategies.

Increased Presynaptic Dopamine Synthesis Capacity Is Associated With Aberrant Dopamine Neuron Activity in the Methylazoxymethanol Acetate Rodent Model Used to Study Schizophrenia-Related Pathologies

Aberrant dopamine system function is thought to contribute to the positive symptoms of schizophrenia. Clinical imaging studies have demonstrated that the largest dopamine abnormality in patients appears to be an increase in presynaptic dopamine activity. Indeed, studies utilizing [ 18 F]DOPA positive emission tomography reliably report increases in presynaptic dopamine bioavailability in patients and may serve as a biomarker for treatment response. The mechanisms contributing to this increased presynaptic activity in human patients is not yet fully understood, which necessitates the use of preclinical models. Dopamine system function can be directly examined in experimental animals using in vivo electrophysiology. One consistent finding from preclinical studies in rodent models used to study schizophrenia-like neuropathology is a 2-fold increase in the number of spontaneously active dopamine neurons in the ventral tegmental area (VTA), termed population activity. We posit that increased striatal dopamine synthesis capacity is attributed to an augmented VTA dopamine neuron population activity. Here, we directly test this hypothesis using [3H]DOPA ex vivo autoradiography, to quantify striatal dopamine synthesis capacity, in the methylazoxymethanol acetate (MAM) model, a validated rodent model displaying neurophysiological and behavioral alterations consistent with schizophrenia-like symptomatologies. Consistent with human imaging studies, dopamine synthesis capacity was significantly increased in dorsal and ventral striatal subregionis, including the caudate putamen and nucleus accumbens, of MAM-treated rats and associated with specific increases in dopamine neuron population activity. Taken together, these data provide a link between mechanistic studies in rodent models and clinical studies of increased presynaptic dopamine function in human subjects.

Dopamine dysregulation in psychotic relapse after antipsychotic discontinuation: an [18F]DOPA and [11C]raclopride PET study in first-episode psychosis

Although antipsychotic drugs are effective for relieving the psychotic symptoms of first-episode psychosis (FEP), psychotic relapse is common during the course of the illness. While some FEPs remain remitted even without medication, antipsychotic discontinuation is regarded as the most common risk factor for the relapse. Considering the actions of antipsychotic drugs on presynaptic and postsynaptic dopamine dysregulation, this study evaluated possible mechanisms underlying relapse after antipsychotic discontinuation. Twenty five FEPs who were clinically stable and 14 matched healthy controls were enrolled. Striatal dopamine activity was assessed as K_i^cer value using [¹⁸F]DOPA PET before and 6 weeks after antipsychotic discontinuation. The D2/3 receptor availability was measured as BP_ND using [¹¹C]raclopride PET after antipsychotic discontinuation. Healthy controls also underwent PET scans according to the corresponding schedule of the patients. Patients were monitored for psychotic relapse during 12 weeks after antipsychotic discontinuation. 40% of the patients showed psychotic relapse after antipsychotic discontinuation. The change in K_i^cer value over time significantly differed between relapsed, non-relapsed patients and healthy controls (Week*Group: F = 4.827, df = 2,253.193, p = 0.009). In relapsed patients, a significant correlation was found between baseline striatal K_i^cer values and time to relapse after antipsychotic discontinuation (R² = 0.518, p = 0.018). BP_ND were not significantly different between relapsed, non-relapsed patients and healthy controls (F = 1.402, df = 2,32.000, p = 0.261). These results suggest that dysfunctional dopamine autoregulation might precipitate psychotic relapse after antipsychotic discontinuation in FEP. This finding could be used for developing a strategy for the prevention of psychotic relapse related to antipsychotic discontinuation.

Advances in the Discovery of PDE10A Inhibitors for CNS-Related Disorders. Part 2: Focus on Schizophrenia

Schizophrenia is a debilitating mental disorder with relatively high prevalence (~1%), during which positive manifestations (such as psychotic states) and negative symptoms (e.g., a withdrawal from social life) occur. Moreover, some researchers consider cognitive impairment as a distinct domain of schizophrenia symptoms. The imbalance in dopamine activity, namely an excessive release of this neurotransmitter in the striatum and insufficient amounts in the prefrontal cortex is believed to be partially responsible for the occurrence of these groups of manifestations. Second-generation antipsychotics are currently the standard treatment of schizophrenia. Nevertheless, the existent treatment is sometimes ineffective and burdened with severe adverse effects, such as extrapyramidal symptoms. Thus, there is an urgent need to search for alternative treatment options of this disease. This review summarizes the results of recent preclinical and clinical studies on phosphodiesterase 10A (PDE10A), which is highly expressed in the mammalian striatum, as a potential drug target for the treatment of schizophrenia. Based on the literature data, not only selective PDE10A inhibitors but also dual PDE2A/10A, and PDE4B/10A inhibitors, as well as multifunctional ligands with a PDE10A inhibitory potency are compounds that may combine antipsychotic, precognitive, and antidepressant functions. Thus, designing such compounds may constitute a new direction of research for new potential medications for schizophrenia. Despite failures of previous clinical trials of selective PDE10A inhibitors for the treatment of schizophrenia, new compounds with this mechanism of action are currently investigated clinically, thus, the search for new inhibitors of PDE10A, both selective and multitarget, is still warranted.

Brain imaging in catatonia: systematic review and directions for future research

BACKGROUND

Catatonia is a frequent, complex and severe identifiable syndrome of motor dysregulation. However, its pathophysiology is poorly understood.

METHODS

We aimed to provide a systematic review of all brain imaging studies (both structural and functional) in catatonia.

RESULTS

We identified 137 case reports and 18 group studies representing 186 individual patients with catatonia. Catatonia is often associated with brain imaging abnormalities (in more than 75% of cases). The majority of the case reports show diffuse lesions of white matter, in a wide range of brain regions. Most of the case reports of functional imaging usually show frontal, temporal, or basal ganglia hypoperfusion. These abnormalities appear to be alleviated after successful treatment of clinical symptoms. Structural brain magnetic resonance imaging studies are very scarce in the catatonia literature, mostly showing diffuse cerebral atrophy. Group studies assessing functional brain imaging after catatonic episodes show that emotional dysregulation is related to the GABAergic system, with hypoactivation of orbitofrontal cortex, hyperactivation of median prefrontal cortex, and dysconnectivity between frontal and motor areas.

CONCLUSION

In catatonia, brain imaging is abnormal in the majority of cases, and abnormalities more frequently diffuse than localised. Brain imaging studies published so far suffer from serious limitations and for now the different models presented in the literature do not explain most of the cases. There is an important need for further studies including a better clinical characterisation of patients with catatonia, functional imaging with concurrent catatonic symptoms and the use of novel brain imaging techniques.

Dysregulation of Midbrain Dopamine System and the Pathophysiology of Schizophrenia

Dysregulation of the dopamine system is central to many models of the pathophysiology of psychosis in schizophrenia. However, emerging evidence suggests that this dysregulation is driven by the disruption of upstream circuits that provide afferent control of midbrain dopamine neurons. Furthermore, stress can profoundly disrupt this regulatory circuit, particularly when it is presented at critical vulnerable prepubertal time points. This review will discuss the dopamine system and the circuits that regulate it, focusing on the hippocampus, medial prefrontal cortex, thalamic nuclei, and medial septum, and the impact of stress. A greater understanding of the regulation of the dopamine system and its disruption in schizophrenia may provide a more complete neurobiological framework to interpret clinical findings and develop novel treatments.

The Topography of Striatal Dopamine and Symptoms in Psychosis: An Integrative Positron Emission Tomography and Magnetic Resonance Imaging Study

Background

Striatal dopamine dysfunction is thought to underlie symptoms in psychosis, yet it remains unclear how a single neurotransmitter could cause the diverse presentations that are observed clinically. One hypothesis is that the consequences of aberrant dopamine signaling vary depending on where within the striatum the dysfunction occurs. Positron emission tomography allows for the quantification of dopamine function across the striatum. In the current study, we used a novel method to investigate the relationship between spatial variability in dopamine synthesis capacity and psychotic symptoms.

Methods

We used a multimodal imaging approach combining ¹⁸F-DOPA positron emission tomography and resting-state magnetic resonance imaging in 29 patients with first-episode psychosis and 21 healthy control subjects. In each participant, resting-state functional connectivity maps were used to quantify the functional connectivity of each striatal voxel to well-established cortical networks. Network-specific striatal dopamine synthesis capacity (Ki^cer) was then calculated for the resulting connectivity-defined parcellations.

Results

The connectivity-defined parcellations generated Ki^cer values with equivalent reliability, and significantly greater orthogonality compared with standard anatomical parcellation methods. As a result, dopamine-symptom associations were significantly different from one another for different subdivisions, whereas no unique subdivision relationships were found when using an anatomical parcellation. In particular, dopamine function within striatal areas connected to the default mode network was strongly associated with negative symptoms (p < .001).

Conclusions

These findings suggest that individual differences in the topography of dopamine dysfunction within the striatum contribute to shaping psychotic symptomatology. Further validation of the novel approach in future studies is necessary.

Acute anxiety disorder, major depressive disorder, bipolar disorder and schizophrenia are related to different patterns of nigrostriatal and mesolimbic dopamine dysfunction

Dopamine (DA) receptor and transporter dysfunctions play a major role in the pathophysiology of neuropsychiatric diseases including anxiety disorder (AD), major depressive disorder (MDD), bipolar disorder (BD) in the manic (BDman) or depressive (BDdep) state and schizophrenia (SZ). We performed a PUBMED search, which provided a total of 239 in vivo imaging studies with either positron emission tomography (PET) or single-proton emission computed tomography (SPECT). In these studies, DA transporter binding, D1 receptor (R) binding, D2R binding, DA synthesis and/or DA release in patients with the primary diagnosis of acute AD (n=310), MDD (n=754), BDman (n=15), BDdep (n=49) or SZ (n=1532) were compared to healthy individuals. A retrospective analysis revealed that AD, MDD, BDman, BDdep and SZ differed as to affected brain region(s), affected synaptic constituent(s) and extent as well as direction of dysfunction in terms of either sensitization or desensitization of transporter and/or receptor binding sites. In contrast to AD and SZ, in MDD, BDman and BDdep, neostriatal DA function was normal, whereas MDD, BDman, and BDdep were characterized by the increased availability of prefrontal and frontal DA. In contrast to AD, MDD, BDman and BDdep, DA function in SZ was impaired throughout the nigrostriatal and mesolimbocortical system with an increased availability of DA in the striatothalamocortical and a decreased availability in the mesolimbocortical pathway.

Defining the Locus of Dopaminergic Dysfunction in Schizophrenia: A Meta-analysis and Test of the Mesolimbic Hypothesis

BACKGROUND

Studies using positron emission tomography to image striatal dopamine function, have demonstrated that individuals with schizophrenia display increases in presynaptic function. Mesolimbic dysfunction specifically, has previously been suggested to underlie psychotic symptoms. This has not been directly tested in vivo, and the precise anatomical locus of dopamine dysfunction within the striatum remains unclear. The current article investigates the magnitude of dopaminergic abnormalities in individuals with schizophrenia, and determines how the magnitude of abnormality varies across functional subdivisions of the striatum.

METHODS

EMBASE, PsychINFO, and MEDLINE were searched from January 1, 1960, to December 1, 2016. Inclusion criteria were molecular imaging studies that had measured presynaptic striatal dopamine functioning. Effects sizes for whole striatum and functional subdivisions were calculated separately. The magnitude of difference between functional subdivisions in patients and controls was meta-analyzed.

RESULTS

Twenty-one eligible studies were identified, including 269 patients and 313 controls. Individuals with schizophrenia (Hedges' g = 0.68, P < .001) demonstrated elevated presynaptic dopamine functioning compared to controls. Seven studies examined functional subdivisions. These demonstrated significant increases in patients compared to controls in associative (g = 0.73, P = .002) and sensorimotor (g = 0.54, P = .005) regions, but not limbic (g = 0.29, P = .09). The magnitude of the difference between associative and limbic subdivisions was significantly greater in patients compared to controls (g = 0.39, P = .003).

CONCLUSION

In individuals with schizophrenia dopaminergic dysfunction is greater in dorsal compared to limbic subdivisions of the striatum. This is inconsistent with the mesolimbic hypothesis and identifies the dorsal striatum as a target for novel treatment development.

Cognitive Function and Monoamine Neurotransmission in Schizophrenia: Evidence From Positron Emission Tomography Studies

Positron emission tomography (PET) is a non-invasive imaging technique used to assess various brain functions, including cerebral blood flow, glucose metabolism, and neurotransmission, in the living human brain. In particular, neurotransmission mediated by the monoamine neurotransmitters dopamine, serotonin, and norepinephrine, has been extensively examined using PET probes, which specifically bind to the monoamine receptors and transporters. This useful tool has revealed the pathophysiology of various psychiatric disorders, including schizophrenia, and the mechanisms of action of psychotropic drugs. Because monoamines are implicated in various cognitive processes such as memory and executive functions, some PET studies have directly investigated the associations between monoamine neurotransmission and cognitive functions in healthy individuals and patients with psychiatric disorders. In this mini review, I discuss the findings of PET studies that investigated monoamine neurotransmission under resting conditions, specifically focusing on cognitive functions in patients with schizophrenia. With regard to the dopaminergic system, some studies have examined the association of dopamine D1 and D2/D3 receptors, dopamine transporters, and dopamine synthesis capacity with various cognitive functions in schizophrenia. With regard to the serotonergic system, 5-HT1A and 5-HT2A receptors have been studied in the context of cognitive functions in schizophrenia. Although relatively few PET studies have examined cognitive functions in patients with psychiatric disorders, these approaches can provide useful information on enhancing cognitive functions by administering drugs that modulate monoamine transmission. Moreover, another paradigm of techniques such as those exploring the release of neurotransmitters and further development of radiotracers for novel targets are warranted.

Presynaptic Dopamine Synthesis Capacity in Schizophrenia and Striatal Blood Flow Change During Antipsychotic Treatment and Medication-Free Conditions

Standard-of-care biological treatment of schizophrenia remains dependent upon antipsychotic medications, which demonstrate D₂ receptor affinity and elicit variable, partial clinical responses via neural mechanisms that are not entirely understood. In the striatum, where D₂ receptors are abundant, antipsychotic medications may affect neural function in studies of animals, healthy volunteers, and patients, yet the relevance of this to pharmacotherapeutic actions remains unresolved. In this same brain region, some individuals with schizophrenia may demonstrate phenotypes consistent with exaggerated dopaminergic signaling, including alterations in dopamine synthesis capacity; however, the hypothesis that dopamine system characteristics underlie variance in medication-induced regional blood flow changes has not been directly tested. We therefore studied a cohort of 30 individuals with schizophrenia using longitudinal, multi-session [¹⁵O]-water and [¹⁸F]-FDOPA positron emission tomography to determine striatal blood flow during active atypical antipsychotic medication treatment and after at least 3 weeks of placebo treatment, along with presynaptic dopamine synthesis capacity (ie, DOPA decarboxylase activity). Regional striatal blood flow was significantly higher during active treatment than during the placebo condition. Furthermore, medication-related increases in ventral striatal blood flow were associated with more robust amelioration of excited factor symptoms during active medication and with higher dopamine synthesis capacity. These data indicate that atypical medications enact measureable physiological alterations in limbic striatal circuitry that vary as a function of dopaminergic tone and may have relevance to aspects of therapeutic responses.

Decreased Expression of α-Synuclein, Nogo-A and UCH-L1 in Patients with Schizophrenia: A Preliminary Serum Study

OBJECTIVE

α-synuclein, Nogo-A and Ubiquitin C-terminal hydrolase L1 (UCH-L1) have neuromodulatory roles for human brain. Therefore, abnormalities of these molecules are associated with neuropsychiatric disorders. Although some serum studies in the other disorders have been made, serum study of α-synuclein, Nogo-A and UCH-L1 is not present in patients with schizophrenia and healthy controls. Therefore, our aim was to compare serum levels of α-synuclein, Nogo-A and UCH-L1 of the patients with schizophrenia and healthy controls.

METHODS

Forty-four patients with schizophrenia who is followed by psychotic disorders unit, and 40 healthy control were included in this study. Socio-demographic form and Positive and Negative Syndrome Scale (PANSS) was applied to patients, and sociodemographic form was applied to control group. Fasting bloods were collected and the serum levels of α-synuclein, Nogo-A and UCH-L1 were measured by ELISA method.

RESULTS

Serum α-synuclein [patient: 12.73 (5.18-31.84) ng/mL; control: 41.77 (15.12-66.98) ng/mL], Nogo-A [patient: 33.58 (3.09-77.26) ng/mL; control: 286.05 (136.56-346.82) ng/mL] and UCH-L1 [patient: 5.26 (1.64-10.87) ng/mL; control: 20.48 (11.01-20.81) ng/mL] levels of the patients with schizophrenia were significianly lower than healthy controls (p<0.001).

CONCLUSION

Our study results added new evidence for explaining the etiopathogenesis of schizophrenia on the basis of neurochemical markers.

Dopamine, cognitive biases and assessment of certainty: A neurocognitive model of delusions

This paper examines the evidence that delusions can be explained within the framework of a neurocognitive model of how the brain assesses certainty. Here, 'certainty' refers to both low-level interpretations of one's environment and high-level (conscious) appraisals of one's beliefs and experiences. A model is proposed explaining how the brain systems responsible for assigning certainty might dysfunction, contributing to the cause and maintenance of delusional beliefs. It is suggested that delusions arise through a combination of perturbed striatal dopamine and aberrant salience as well as cognitive biases such as the tendency to jump to conclusions (JTC) and hypersalience of evidence-hypothesis matches. The role of emotion, stress, trauma and sociocultural factors in forming and modifying delusions is also considered. Understanding the mechanisms involved in forming and maintaining delusions has important clinical implications, as interventions that improve cognitive flexibility (e.g. cognitive remediation therapy and mindfulness training) could potentially attenuate neurocognitive processes.

Presynaptic Dopamine Capacity in Patients with Treatment-Resistant Schizophrenia Taking Clozapine: An [18F]DOPA PET Study

Some patients with schizophrenia show poor response to first-line antipsychotic treatments and this is termed treatment-resistant schizophrenia. The differential response to first-line antipsychotic drugs may reflect a different underlying neurobiology. Indeed, a previous study found dopamine synthesis capacity was significantly lower in patients with treatment-resistant schizophrenia. However, in this study, the treatment-resistant patients were highly symptomatic, whereas the responsive patients showed no or minimal symptoms. The study could not distinguish whether this was a trait effect or reflected the difference in symptom levels. Thus, we aimed to test whether dopaminergic function is altered in patients with a history of treatment resistance to first-line drugs relative to treatment responders when both groups are matched for symptom severity levels by recruiting treatment-resistant patients currently showed low symptom severity with the clozapine treatment. Healthy controls (n=12), patients treated with clozapine (n=12) who had not responded to first-line antipsychotics, and patients who had responded to first-line antipsychotics (n=12) were recruited. Participants were matched for age and sex and symptomatic severity level in patient groups. Participants' dopamine synthesis capacity was measured by using [¹⁸F]DOPA PET. We found that patients treated with clozapine show lower dopamine synthesis capacity than patients who have responded to first-line treatment (Cohen's d=0.9191 (whole striatum), 0.7781 (associative striatum), 1.0344 (limbic striatum), and 1.0189 (sensorimotor striatum) in line with the hypothesis that the dopaminergic function is linked to treatment response. This suggests that a different neurobiology may underlie treatment-resistant schizophrenia and that dopamine synthesis capacity may be a useful biomarker to predict treatment responsiveness.

Pathway-Specific Dopamine Abnormalities in Schizophrenia

In light of the clinical evidence implicating dopamine in schizophrenia and the prominent hypotheses put forth regarding alterations in dopaminergic transmission in this disease, molecular imaging has been used to examine multiple aspects of the dopaminergic system. We review the imaging methods used and compare the findings across the different molecular targets. Findings have converged to suggest early dysregulation in the striatum, especially in the rostral caudate, manifesting as excess synthesis and release. Recent data showed deficit extending to most cortical regions and even to other extrastriatal subcortical regions not previously considered to be "hypodopaminergic" in schizophrenia. These findings yield a new topography for the dopaminergic dysregulation in schizophrenia. We discuss the dopaminergic innervation within the individual projection fields to provide a topographical map of this dual dysregulation and explore potential cellular and circuit-based mechanisms for brain region-dependent alterations in dopaminergic parameters. This refined knowledge is essential to better guide translational studies and efforts in early drug development.

Glutamate and dopamine in schizophrenia: an update for the 21st century

The glutamate and dopamine hypotheses are leading theories of the pathoaetiology of schizophrenia. Both were initially based on indirect evidence from pharmacological studies supported by post-mortem findings, but have since been substantially advanced by new lines of evidence from in vivo imaging studies. This review provides an update on the latest findings on dopamine and glutamate abnormalities in schizophrenia, focusing on in vivo neuroimaging studies in patients and clinical high-risk groups, and considers their implications for understanding the biology and treatment of schizophrenia. These findings have refined both the dopamine and glutamate hypotheses, enabling greater anatomical and functional specificity, and have been complemented by preclinical evidence showing how the risk factors for schizophrenia impact on the dopamine and glutamate systems. The implications of this new evidence for understanding the development and treatment of schizophrenia are considered, and the gaps in current knowledge highlighted. Finally, the evidence for an integrated model of the interactions between the glutamate and dopamine systems is reviewed, and future directions discussed.

Imaging-based neurochemistry in schizophrenia: a systematic review and implications for dysfunctional long-term potentiation

Cognitive deficits are commonly observed in patients with schizophrenia. Converging lines of evidence suggest that these deficits are associated with impaired long-term potentiation (LTP). In our systematic review, this hypothesis is evaluated using neuroimaging literature focused on proton magnetic resonance spectroscopy, positron emission tomography, and single-photon emission computed tomography. The review provides evidence for abnormal dopaminergic, GABAergic, and glutamatergic neurotransmission in antipsychotic-naive/free patients with schizophrenia compared with healthy controls. The review concludes with a model illustrating how these abnormalities could lead to impaired LTP in patients with schizophrenia and consequently cognitive deficits.

Dopaminergic function in cannabis users and its relationship to cannabis-induced psychotic symptoms

BACKGROUND

Cannabis is the most widely used illicit drug globally, and users are at increased risk of mental illnesses including psychotic disorders such as schizophrenia. Substance dependence and schizophrenia are both associated with dopaminergic dysfunction. It has been proposed, although never directly tested, that the link between cannabis use and schizophrenia is mediated by altered dopaminergic function.

METHODS

We compared dopamine synthesis capacity in 19 regular cannabis users who experienced psychotic-like symptoms when they consumed cannabis with 19 nonuser sex- and age-matched control subjects. Dopamine synthesis capacity (indexed as the influx rate constant [Formula: see text] ) was measured with positron emission tomography and 3,4-dihydroxy-6-[(18)F]-fluoro-l-phenylalanine ([(18)F]-DOPA).

RESULTS

Cannabis users had reduced dopamine synthesis capacity in the striatum (effect size: .85; t36 = 2.54, p = .016) and its associative (effect size: .85; t36 = 2.54, p = .015) and limbic subdivisions (effect size: .74; t36 = 2.23, p = .032) compared with control subjects. The group difference in dopamine synthesis capacity in cannabis users compared with control subjects was driven by those users meeting cannabis abuse or dependence criteria. Dopamine synthesis capacity was negatively associated with higher levels of cannabis use (r = -.77, p < .001) and positively associated with age of onset of cannabis use (r = .51, p = .027) but was not associated with cannabis-induced psychotic-like symptoms (r = .32, p = .19).

CONCLUSIONS

These findings indicate that chronic cannabis use is associated with reduced dopamine synthesis capacity and question the hypothesis that cannabis increases the risk of psychotic disorders by inducing the same dopaminergic alterations seen in schizophrenia.

Abnormal striatal dopamine transmission in schizophrenia

Despite numerous revisions and reformulations, dopamine (DA) hypothesis of schizophrenia remains a pivotal neurochemical hypothesis of this illness. The aim of this review is to expose and discuss findings from positron emission tomography (PET) or single-photon-emission computed tomography (SPECT) studies investigating DA function in the striatum of medicated, drug-naïve or drug-free patients with schizophrenia and in individuals at risk compared with healthy volunteers.

DA function was studied at several levels: i) at a presynaptic level where neuroimaging studies investigating DOPA uptake capacity clearly show an increase of DA synthesis in patients with schizophrenia; ii) at a synaptic level where neuroimaging studies investigating dopamine transporter availability (DAT) does not bring any evidence of dysfunction; iii) and finally, neuroimaging studies investigating DA receptor density show a mild increase of D2 receptor density in basic condition and, an hyperreactivity of DA system in dynamic condition.

These results are discussed regarding laterality, sub-regions of striatum and implications for the at-risk population. Striatal DA abnormalities are now clearly demonstrated in patients with schizophrenia and at risk population and could constitute an endophenotype of schizophrenia. Subtle sub-clinical striatal DA abnormalities in at risk population could be a biomarker of transition from a vulnerability state to the expression of frank psychosis.

Midbrain dopamine function in schizophrenia and depression: a post-mortem and positron emission tomographic imaging study

Elevated in vivo markers of presynaptic striatal dopamine activity have been a consistent finding in schizophrenia, and include a large effect size elevation in dopamine synthesis capacity. However, it is not known if the dopaminergic dysfunction is limited to the striatal terminals of dopamine neurons, or is also evident in the dopamine neuron cell bodies, which mostly originate in the substantia nigra. The aim of our studies was therefore to determine whether dopamine synthesis capacity is altered in the substantia nigra of people with schizophrenia, and how this relates to symptoms. In a post-mortem study, a semi-quantitative analysis of tyrosine hydroxylase staining was conducted in nigral dopaminergic cells from post-mortem tissue from patients with schizophrenia (n = 12), major depressive disorder (n = 13) and matched control subjects (n = 13). In an in vivo imaging study, nigral and striatal dopaminergic function was measured in patients with schizophrenia (n = 29) and matched healthy control subjects (n = 29) using (18)F-dihydroxyphenyl-L-alanine ((18)F-DOPA) positron emission tomography. In the post-mortem study we found that tyrosine hydroxylase staining was significantly increased in nigral dopaminergic neurons in schizophrenia compared with both control subjects (P < 0.001) and major depressive disorder (P < 0.001). There was no significant difference in tyrosine hydroxylase staining between control subjects and patients with major depressive disorder, indicating that the elevation in schizophrenia is not a non-specific indicator of psychiatric illness. In the in vivo imaging study we found that (18)F-dihydroxyphenyl-L-alanine uptake was elevated in both the substantia nigra and in the striatum of patients with schizophrenia (effect sizes = 0.85, P = 0.003 and 1.14, P < 0.0001, respectively) and, in the voxel-based analysis, was elevated in the right nigra (P < 0.05 corrected for family wise-error). Furthermore, nigral (18)F-dihydroxyphenyl-L-alanine uptake was positively related with the severity of symptoms (r = 0.39, P = 0.035) in patients. However, whereas nigral and striatal (18)F-dihydroxyphenyl-L-alanine uptake were positively related in control subjects (r = 0.63, P < 0.001), this was not the case in patients (r = 0.30, P = 0.11). These findings indicate that elevated dopamine synthesis capacity is seen in the nigral origin of dopamine neurons as well as their striatal terminals in schizophrenia, and is linked to symptom severity in patients.

Ketamine increases striatal dopamine release and hyperlocomotion in adult rats after postnatal functional blockade of the prefrontal cortex

Schizophrenia is a complex psychiatric disorder that may result from defective connectivity, of neurodevelopmental origin, between several integrative brain regions. Different anomalies consistent with brain development failures have been observed in patients' left prefrontal cortex (PFC). A striatal dopaminergic functional disturbance is also commonly acknowledged in schizophrenia and could be related to a dysfunctioning of dopamine-glutamate interactions. Non-competitive NMDA antagonists, such as ketamine, can induce psychotic symptoms in healthy individuals and worsen these symptoms in patients with schizophrenia. Our study set out to investigate the consequences of neonatal functional blockade of the PFC for dopaminergic and behavioral reactivity to ketamine in adult rats. Following tetrodotoxin (TTX) inactivation of the left PFC at postnatal day 8, dopaminergic responses induced by ketamine (5 mg/kg, 10 mg/kg, 20 mg/kg sc) were monitored using in vivo voltammetry in the left part of the dorsal striatum in freely moving adult rats. Dopaminergic responses and locomotor activity were followed in parallel. Compared to PBS animals, in rats microinjected with TTX, ketamine challenge induced a greater release of dopamine in the dorsal striatum for the highest dose (20 mg/kg sc) and the intermediate dose (10mg/kg sc). A higher increase in locomotor activity in TTX animals was observed only for the highest dose of ketamine (20 mg/kg sc). These data suggest transient inactivation of the PFC during early development results in greater behavioral and striatal dopaminergic reactivity to ketamine in adulthood. Our study provides an anatomo-functional framework that may contribute toward a better understanding of the involvement of NMDA glutamatergic receptors in schizophrenia.

Novel nutritional treatment for manic and psychotic disorders: a review of tryptophan and tyrosine depletion studies and the potential of protein-based formulations using glycomacropeptide

RATIONALE

Current amino acid (AA) mixtures used in acute tryptophan (Trp) and tyrosine (Tyr) plus phenylalanine (Phe) depletion and loading tests are unpalatable and lack specificity. Specificity is improved by reducing content of branched-chain amino acids (BCAA) and palatability to a certain extent by dose reduction.

OBJECTIVES

This study aims to identify a palatable naturally occurring alternative(s) to amino acids with the desired BCAA content for use in the above tests.

METHODS

A palatable alternative lacking in Trp, Tyr and Phe has been identified in the whey protein fraction caseino-glycomacropeptide (c-GMP). The absence of these three aromatic amino acids renders GMP suitable as a template for seven formulations for separate and combined depletion or loading and a placebo control. The absence of Phe and Tyr enables GMP to provide a unique nutritional therapy of manic and psychotic disorders by inhibition of cerebral dopamine synthesis and release and possibly also by enhancing glutamatergic function, in general, and in patients resistant to anti-psychotic medication, in particular.

RESULTS

Seven GMP-based formulations for the above tests are proposed, two of which can be used in the above nutritional therapy and a third formulation as a placebo control in clinical trials.

CONCLUSIONS

Development of these formulations should advance the above research and diagnostic tests, open new avenues for neuroscience research on monoamine function, and improve the therapy of bipolar and psychotic disorders and enhance the quality of life of sufferers.

Proton magnetic resonance spectroscopy of the substantia nigra in schizophrenia

BACKGROUND

Converging evidence in schizophrenia points to disruption of the dopamine and glutamate neurotransmitter systems in the pathophysiology of the disorder. Dopamine is produced in the substantia nigra, but few neuroimaging studies have specifically targeted this structure. In fact, no studies of the substantia nigra in schizophrenia have used proton magnetic resonance spectroscopy (MRS). We sought to demonstrate the feasibility of acquiring single-voxel MRS measurements at 3T from the substantia nigra and to determine which metabolites could be reliably quantified in schizophrenia patients and healthy controls.

METHODS

We used a turbo spin echo sequence with magnetization transfer contrast to visualize the substantia nigra and single-voxel proton MRS to quantify levels of N-acetylaspartate, glutamate and glutamine (Glx), and choline in the left substantia nigra of 35 people with schizophrenia and 22 healthy controls.

RESULTS

We obtained spectra from the substantia nigra and quantified neurometabolites in both groups. We found no differences in levels of N-acetylaspartate/creatine, Glx/creatine, or choline/creatine between the groups. We found a significant correlation between Glx/creatine and overall cognitive performance, measured with the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), in controls but not patients, a difference that was statistically significant.

CONCLUSIONS

Our study demonstrates the feasibility of obtaining single-voxel MRS data from the substantia nigra in schizophrenia. Such measurements may prove useful in understanding the biochemistry underlying cellular function in a region implicated in the pathophysiology of schizophrenia.

Dopamine D2 and D3 binding in people at clinical high risk for schizophrenia, antipsychotic-naive patients and healthy controls while performing a cognitive task

BACKGROUND

The dopamine (DA) D2 receptors exist in 2 states: a high-affinity state (D2 high) that is linked to second messenger systems, responsible for functional effects, exhibits high affinity for agonists (e.g., DA), and a low-affinity state that is functionally inert exhibits lower affinity for agonists. The DA D3 receptor subtype exhibits high agonist affinity, whereas the existence of the multiple affinity states is controversial. Preclinical studies in animal models of psychosis have shown a selective increase of D2 high as the common factor in psychosis, and the D3 receptor has been suggested to be involved in the pathophysiology of schizophrenia.

METHODS

We studied D2 high and D3 in people at clinical high risk (CHR) for schizophrenia and in antipsychotic-naive patients with schizophrenia using the novel positron emission tomography radiotracer, [11C]-(+)-PHNO. The binding potential nondisplaceable (BP(ND)) was examined in the regions of interest (ROI; caudate, putamen, ventral striatum, globus pallidus, substantia nigra and thalamus) using an ROI and a voxel-wise approach while participants performed a cognitive task.

RESULTS

We recruited 12 CHR individuals and 13 antipsychotic-naive patients with schizophrenia-spectrum disorder, whom we compared with 12 age- and sex-matched healthy controls. The BP(ND) between patients and controls did not differ in any of the ROIs, consistent with the voxel-wise analysis. Correlations between the BP(ND) in D3-rich regions and psychopathology warrant further investigation.

LIMITATIONS

In the absence of resting-state (baseline) BP(ND) data, or following a depletion paradigm (i.e., α-methyl partyrosine), it is not possible to ascertain whether the lack of difference among the groups is owing to different levels of baseline DA or to release during the cognitive task.

CONCLUSION

To our knowledge, the present study represents the first effort to measure the D2 and D3 receptors under a cognitive challenge in individuals putative/prodromal for schizophrenia using [11C]-(+)-PHNO.

Striatal presynaptic dopamine in schizophrenia, part II: meta-analysis of [(18)F/(11)C]-DOPA PET studies

BACKGROUND

Alterations in striatal dopamine neurotransmission are central to the emergence of psychotic symptoms and to the mechanism of action of antipsychotics. Although the functional integrity of the presynaptic system can be assessed by measuring striatal dopamine synthesis capacity (DSC), no quantitative meta-analysis is available.

METHODS

Eleven striatal (caudate and putamen) [(11)C/(18)F]-DOPA positron emission tomography studies comparing 113 patients with schizophrenia and 131 healthy controls were included in a quantitative meta-analysis of DSC. Demographic, clinical, and methodological variables were extracted from each study or obtained from the authors and tested as covariates. Hedges' g was used as a measure of effect size in Comprehensive Meta-Analysis. Publication bias was assessed with funnel plots and Egger's intercept. Heterogeneity was addressed with the Q statistic and I(2) index.

RESULTS

Patients and controls were well matched in sociodemographic variables (P > .05). Quantitative evaluation of publication bias was nonsignificant (P = .276). Heterogeneity across study was modest in magnitude and statistically nonsignificant (Q = 19.19; P = .078; I (2) = 39.17). Patients with schizophrenia showed increased striatal DSC as compared with controls (Hedges' g = 0.867, CI 95% from 0.594 to 1.140, Z = 6.222, P < .001). The DSC schizophrenia/control ratio showed a relatively homogenous elevation of around 14% in schizophrenic patients as compared with controls. DSC elevation was regionally confirmed in both caudate and putamen. Controlling for potential confounders such as age, illness duration, gender, psychotic symptoms, and exposure to antipsychotics had no impact on the results. Sensitivity analysis confirmed robustness of meta-analytic findings.

CONCLUSIONS

The present meta-analysis showed consistently increased striatal DSC in schizophrenia, with a 14% elevation in patients as compared with healthy controls.

Lack of association between the G-660C polymorphism in the dopamine transporter gene (SLC6A3) and schizophrenia in the Iranian population

BACKGROUND:

Dopaminergenic system plays an essential role in the plasticity of the human brain. The dopamine transporter gene (SLC6A3) mediates active reuptake of dopamine from synapsis, terminates dopamine signals, and therefore, is implicated in a number of dopamine-related disorders like psychosis. Variations in the form of single nucleotide polymorphisms in the core promoter of the SLC6A3 gene are reported to be involved in the pathogenesis of schizophrenia. In this study, we also attempted to establish the possible role of the polymorphism G-660C in the SLC6A3 gene promoter in schizophrenia in a case-control study.

MATERIALS AND METHODS:

The allele and genotype frequency were analyzed in an Iranian cohort of 200 unrelated patients and 200 controls using polymerase chain reaction and restriction fragment length polymorphism.

RESULTS:

The genotype frequency for case and control groups was GG 100%, GC 0%, CC 0%, and GG 100%, GC 0%, CC 0%, respectively. The C allele was failed in both groups.

CONCLUSION:

Our data suggest clearly that there is no association between the -660G/C polymorphism and outcome of schizophrenia in the Iranian population.

Abnormal relationship between medial temporal lobe and subcortical dopamine function in people with an ultra high risk for psychosis

BACKGROUND

Neuroimaging studies in humans have implicated both dysfunction of the medial temporal lobe (MTL) and the dopamine system in psychosis, but the relationship between them is unclear. We addressed this issue by measuring MTL activation and striatal dopaminergic function in individuals with an At Risk Mental State (ARMS) for psychosis, using functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), respectively.

METHODS

Thirty-four subjects (20 ARMS and 14 Controls), matched for age, gender, digit span performance, and premorbid IQ, were scanned using fMRI, while performing a verbal encoding and recognition task, and using 18F-DOPA PET. All participants were naïve to antipsychotic medication.

RESULTS

ARMS subjects showed reduced MTL activation when encoding words and made more false alarm responses for Novel words than controls. The relationship between striatal dopamine function and MTL activation during both verbal encoding and verbal recognition was significantly different in ARMS subjects compared with controls.

CONCLUSION

An altered relationship between MTL function and dopamine storage/synthesis capacity exists in the ARMS and may be related to psychosis vulnerability.

Alterations of the brain reward system in antipsychotic naïve schizophrenia patients

BACKGROUND

Various schizophrenic symptoms are suggested to be linked to a dysfunction of the brain reward system. Several studies have found alterations in the reward processing in patients with schizophrenia; however, most previous findings might be confounded by medication effects.

METHODS

Thirty-one antipsychotic-naïve schizophrenia patients and 31 age- and gender-matched healthy control subjects were examined with functional magnetic resonance imaging while playing a variant of the monetary incentive delay task. The task variant made it possible to separate overall salience (defined as arousing events) into behavioral salience (events where a predicted reward requires performance) and valence anticipation (the anticipation of a monetarily significant outcome). Furthermore, the evaluation of monetary gain and loss was assessed.

RESULTS

During reward anticipation, patients had a significant attenuation of the activation in ventral tegmentum, ventral striatum, and anterior cingulate cortex during presentation of salient cues. This signal attenuation in ventral striatum was correlated with the degree of positive symptoms. Signal attenuation was most pronounced for behavioral salience and nonsignificant for value anticipation. Furthermore, patients showed a changed activation pattern during outcome evaluation in right prefrontal cortex.

CONCLUSION

Our results suggest that changes during reward anticipation in schizophrenia are present from the beginning of the disease. This supports a possible involvement of reward disturbances in the pathophysiology of schizophrenia. The most pronounced changes were seen in relation to overall salience. In ventral striatum these changes were associated with the degree of positive symptoms.

Adversity and psychosis: a 10-year prospective study investigating synergism between early and recent adversity in psychosis

OBJECTIVE

Recent studies have suggested that early adverse events, such as childhood trauma, may promote enduring liability for psychosis whereas more recent adverse events may act as precipitants. Examination of these environmental dynamics, however, requires prospective studies in large samples. This study examines whether the association between recent adverse events and psychosis is moderated by exposure to early adversity.

METHOD

A random regional representative population sample of 3021 adolescents and young adults in Munich, Germany, was assessed three times over a period of up to 10 years, collecting information on sociodemographic factors, environmental exposures, and measures of psychopathology and associated clinical relevance. Evidence of statistical non-additivity between early adversity (two levels) and more recent adversity (four levels) was assessed in models of psychotic symptoms. Analyses were a priori corrected for age, gender, cannabis use, and urbanicity.

RESULTS

Early and recent adversity were associated with each other (RR = 1.32, 95% CI 1.06-1.66; P = 0.014) and displayed statistical non-additivity at the highest level of exposure to recent adversity (χ(2) = 4.59; P = 0.032).

CONCLUSION

The findings suggest that early adversity may impact on later expression of psychosis either by increasing exposure to later adversity and/or by rendering individuals more sensitive to later adversity if it is severe.

Role of dopamine D(2) receptors for antipsychotic activity

This review summarizes the current state of knowledge regarding the proposed mechanisms by which antipsychotic agents reduce the symptoms of schizophrenia while giving rise to adverse side effects. The first part summarizes the contribution of neuroimaging studies to our understanding of the neurochemical substrates of schizophrenia, putting emphasis on direct evidence suggestive of a presynaptic rather than a postsynaptic dysregulation of dopaminergic neurotransmission in this disorder. The second part addresses the role of D(2) and non-D(2) receptor blockade in the treatment of schizophrenia and highlights a preponderant role of D(2) receptors in the mechanism of antipsychotic action. Neuroimaging studies have defined a narrow, but optimal, therapeutic window of 65-78 % D(2) receptor blockade within which most antipsychotics achieve optimal clinical efficacy with minimal side effects. Some antipsychotics though do not conform to that therapeutic window, notably clozapine. The reasons for its unexcelled clinical efficacy despite subthreshold levels of D(2) blockade are unclear and current theories on clozapine's mechanisms of action are discussed, including transiency of its D(2) receptor blocking effects or preferential blockade of limbic D(2) receptors. Evidence is also highlighted to consider the use of extended antipsychotic dosing to achieve transiency of D(2) blockade as a way to optimize functional outcomes in patients. We also present some critical clinical considerations regarding the mechanisms linking dopamine disturbance to the expression of psychosis and its blockade to the progressive resolution of psychosis, keeping in perspective the speed and onset of antipsychotic action. Finally, we discuss potential novel therapeutic strategies for schizophrenia.

The dopamine dysfunction in schizophrenia revisited: new insights into topography and course

Schizophrenia has long been associated with an imbalance in dopamine (DA) neurotransmission, and brain imaging has played an important role in advancing our knowledge and providing evidence for the dopaminergic abnormalities. This chapter reviews the evidence for DA dysfunction in different brain regions in schizophrenia, in particular striatal, extrastriatal, and prefrontal regions, with emphasis on recently published findings. As opposed to the traditional view that most striatal dopaminergic excess, associated with the positive symptoms of schizophrenia, involves the dopaminergic mesolimbic pathway, recent evidence points to the nigrostriatal pathway as the area of highest dysregulation. Furthermore, evidence from translational research suggests that dopaminergic excess may be present in the prodromal phase, and may by itself, as suggested by the phenotype observed in transgenic mice with developmental overexpression of dorso-striatal D(2) receptors, be an early pathogenic condition, leading to irreversible cortical dysfunction.

Imaging as tool to investigate psychoses and antipsychotics

The results of imaging studies have played an important role in the formulation of hypotheses regarding the etiology of psychosis and schizophrenia, as well as in our understanding of the mechanisms of action of antipsychotics. Since this volume is primarily directed to molecular aspects of psychosis and antipsychotics, only the results of molecular imaging techniques addressing these topics will be discussed here.One of the most consistent findings of molecular imaging studies in schizophrenia is an increased uptake of DOPA in the striatum, which may be interpreted as an increased synthesis of L-DOPA. Also, several studies reported an increased release of dopamine induced by amphetamine in schizophrenia patients. These findings played an important role in reformulating the dopamine hypothesis of schizophrenia. To study the roles of the neurotransmitters γ-aminobutyric acid (GABA) and glutamate in schizophrenia, SPECT as well as MR spectroscopy have been used. The results of preliminary SPECT studies are consistent with the hypothesis of NMDA receptor dysfunction in schizophrenia. Regarding the GABA deficit hypothesis of schizophrenia, imaging results are inconsistent. No changes in serotonin transporters were demonstrated in imaging studies in schizophrenia, but studies of several serotonin receptors showed conflicting results. The lack of selective radiotracers for muscarinic receptors may have hampered examination of this system in schizophrenia as well as its role in the induction of side effects of antipsychotics. Interestingly, preliminary molecular imaging studies on the cannabinoid-1 receptor and on neuroinflammatory processes in schizophrenia have recently been published. Finally, a substantial number of PET/SPECT studies have examined the occupancy of receptors by antipsychotics and an increasing number of studies is now focusing on the effects of these drugs using techniques like spectroscopy and pharmacological MRI.

Striatal dopamine synthesis capacity in twins discordant for schizophrenia

BACKGROUND

Elevated striatal dopamine synthesis capacity is thought to be fundamental to the pathophysiology of schizophrenia and has also been reported in people at risk of psychosis. It is therefore unclear if striatal hyperdopaminergia is a vulnerability marker for schizophrenia, or a state feature related to the psychosis itself. Relatives of patients with schizophrenia are themselves at increased risk of developing the condition. In this study we examined striatal dopamine synthesis capacity in both members of twin pairs discordant for schizophrenia.

METHOD

In vivo striatal dopamine synthesis capacity was examined using fluorine-18-l-dihydroxyphenylalanine (18F-DOPA) positron emission tomography (PET) scans in seven twin pairs discordant for schizophrenia and in a control sample of 10 healthy control twin pairs.

RESULTS

Striatal 18F-DOPA uptake was not elevated in the unaffected co-twins of patients with schizophrenia (p=0.65) or indeed in the twins with schizophrenia (p=0.89) compared to the control group. Levels of psychotic symptoms were low in the patients with schizophrenia who were in general stable [mean (s.d.) Positive and Negative Syndrome Scale (PANSS) total=56.8 (25.5)] whereas the unaffected co-twins were largely asymptomatic.

CONCLUSIONS

Striatal dopamine synthesis capacity is not elevated in symptom-free individuals at genetic risk of schizophrenia, or in well-treated stable patients with chronic schizophrenia. These findings suggest that striatal hyperdopaminergia is not a vulnerability marker for schizophrenia.

Abnormal plasma monoamine metabolism in schizophrenia and its correlation with clinical responses to risperidone treatment

Abnormalities in plasma monoamine metabolism reflect partly the illness of schizophrenia and sometimes the symptoms. Such studies have been repeatedly reported but have rarely taken both metabolites and parent amines or inter-amine activity ratios into account. In this study, the monoamines, their metabolites, turnovers and between-metabolite ratios in plasma were measured longitudinally in 32 schizophrenic patients treated with risperidone for 6 weeks, to examine possible biochemical alterations in schizophrenia, and to examine the association between treatment responses and psychopathology assessed according to the Positive and Negative Syndrome Scale (PANSS). The results showed lower level of plasma 3,4-dihydroxyphenylacetic acid (DOPAC) in relapsed versus first-episode schizophrenic patients, higher norepinephrine (NE) turnover rate (TR) in undifferentiated in comparison to paranoid schizophrenic patients and relatively higher metabolic activity of dopamine (DA) to serotonin (5-HT) in first-episode versus relapsed schizophrenic patients. Risperidone treatment induced a decrement of plasma DA levels and increments of plasma DOPAC and DA TR in the total group of schizophrenic patients. The turnover rate of 5-HT was was reduced in undifferentiated and relapsed subgroups of schizophrenic patients. The linkages between 5-HT TR, DA/NE relative activity and clinical symptomatology were also identified. These findings are consistent with an involvement of these systems in the pathogenesis of schizophrenia as well as in the responses to treatment, and the usefulness of certain biochemical indices as markers for subgrouping.

Presynaptic regulation of dopamine transmission in schizophrenia

A role for dopamine (DA) release in the hallucinations and other positive symptoms associated with schizophrenia has long been inferred from the antipsychotic response to D2 DA receptor antagonists and because the DA releaser amphetamine can be psychotogenic. Recent studies suggest that patients with schizophrenia, including those never exposed to antipsychotic drugs, maintain high presynaptic DA accumulation in the striatum. New laboratory approaches are elucidating mechanisms that control the level of presynaptic DA stores, thus contributing to fundamental understanding of the basic pathophysiologic mechanism in schizophrenia.

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.

Motor behavior abnormalities in drug-naïve patients with schizophrenia spectrum disorders

Prevalence and correlates of primary motor abnormalities in schizophrenia are presently ill defined. This study was aimed at examining the prevalence, syndromic structure, external correlates, and response to antipsychotic medication of a broad array of primary motor abnormalities. Two-hundred antipsychotic-naive patients with schizophrenia spectrum disorders were examined for motor abnormalities using the Modified Rogers Scale. Thirty-one motor signs were subjected to factor analysis, and the resulting factors examined for association with a number of risk factors, clinical and psychopathological variables. One-hundred and eighty-nine patients were reassessed for motor abnormalities after completing a 4-week trial with antipsychotic medication. Prevalence rates for at least one motor sign and syndrome at baseline were 66% and 40%, respectively. Motor signs clustered together into seven clinically interpretable factors: abnormal involuntary movements, hypokinesia, retarded catatonia, echo-phenomena, excited catatonia, catalepsy, and parkinsonism. All motor domains but parkinsonism were inter-related. Abnormal involuntary movements were associated with variables indicating both neurodevelopmental dysfunction and illness severity, and most motor domains were closely related to negative or disorganization symptoms. Change scores in motor domains after treatment with antipsychotic medication indicated improvement for abnormal involuntary movements, hypokinesia, retarded catatonia, excited catatonia and echophenomena, and worsening for parkinsonism. It is concluded that primary motor dysfunction is a prevalent and heterogeneous condition of schizophrenia. Motor abnormalities segregate into various syndromes, which have different clinical correlates and a differential response pattern to antipsychotic medication. It is hypothesized that the existence of a differential dopaminergic dysfunction in the nigroestriatal circuitry is responsible for the generation of those motor domains that improve and worsen with antipsychotic drugs.

Neurochemical imaging in schizophrenia

Recent advances in the development and applications of neurochemical brain imaging methods have improved the ability to study the neurochemistry of the living brain in normal processes as well as psychiatric disorders. In particular, positron emission tomography (PET) and single photon emission computed tomography (SPECT) have been used to determine neurochemical substrates of schizophrenia and to uncover the mechanism of action of antipsychotic medications. The growing availability of radiotracers for monoaminergic neurotransmitter synthesis, transporters and receptors, has enabled the evaluation of hypotheses regarding neurotransmitter function in schizophrenia derived from preclinical and clinical observations. This chapter reviews the studies using neurochemical brain imaging methods for (1) detection of abnormalities in indices of dopamine and serotonin transmission in patients with schizophrenia compared to controls, (2) development of new tools to study other neurotransmitters systems, such as gamma-aminobutyric acid (GABA) and glutamate, and (3) characterization of target occupancy by antipsychotic drugs, as well as its relationship to efficacy and side effects. As more imaging tools become available, this knowledge will expand and will lead to better detection of disease, as well as better therapeutic approaches.

Executive function, neural circuitry, and genetic mechanisms in schizophrenia

After decades of research aimed at elucidating the pathophysiology and etiology of schizophrenia, it has become increasingly apparent that it is an illness knowing few boundaries. Psychopathological manifestations extend across several domains, impacting multiple facets of real-world functioning for the affected individual. Even within one such domain, arguably the most enduring, difficult to treat, and devastating to long-term functioning-executive impairment-there are not only a host of disrupted component processes, but also a complex underlying dysfunctional neural architecture. Further, just as implicated brain structures (eg, dorsolateral prefrontal cortex) through postmortem and neuroimaging techniques continue to show alterations in multiple, interacting signaling pathways, so too does evolving understanding of genetic risk factors suggest multiple molecular entry points to illness liability. With this expansive network of interactions in mind, the present chapter takes a systems-level approach to executive dysfunction in schizophrenia, by identifying key regions both within and outside of the frontal lobes that show changes in schizophrenia and are important in cognitive control neural circuitry, summarizing current knowledge of their relevant functional interactions, and reviewing emerging links between schizophrenia risk genetics and characteristic executive circuit aberrancies observed with neuroimaging methods.

How have developments in molecular imaging techniques furthered schizophrenia research?

Molecular imaging techniques have led to significant advances in understanding the pathophysiology of schizophrenia and contributed to knowledge regarding potential mechanisms of action of the drugs used to treat this illness. The aim of this article is to provide a review of the major findings related to the application of molecular imaging techniques that have furthered schizophrenia research. This article focuses specifically on neuroreceptor imaging studies with PET and SPECT. After providing a brief overview of neuroreceptor imaging methodology, we consider relevant findings from studies of receptor availability, and dopamine synthesis and release. Results are discussed in the context of current hypotheses regarding neurochemical alterations in the illness. We then selectively review pharmacological occupancy studies and the role of neuroreceptor imaging in drug development for schizophrenia.

Neurobiology of dopamine in schizophrenia

This chapter is an update on the dopamine (DA) imbalance in schizophrenia, including the evidence for subcortical hyperstimulation of D2 receptors underlying positive symptoms and cortical hypodopaminergia-mediating cognitive disturbances and negative symptoms. After a brief review of the anatomical neurocircuitry of this transmitter system as a background, we summarize the evidence for dopaminergic alterations deriving from pharmacological, postmortem, and imaging studies. This evidence supports a prominent role for D2 antagonism in the treatment of positive symptoms of schizophrenia and strongly suggests the need for alternative approaches to address the more challenging problem of negative symptoms and cognitive disturbances.

A critique of the dopamine hypothesis of schizophrenia and psychosis

The dopamine hypothesis of schizophrenia and psychosis originated from observations of the dopamine-blocking actions of early neuroleptic drugs. These results support the dopamine hypothesis, however, only on the assumption that the drugs act by reversing an underlying disease mechanism (or part of it). An alternative explanation is that the drugs work by inducing a state of neurological suppression that reduces the intensity of symptoms. Although stimulant drugs are known to induce episodes of psychosis, the mechanism for stimulant-induced psychosis has not been clarified, and stimulants are known to affect many neurotransmitters other than dopamine. Recent imaging studies suggest that there may be increased dopamine release in response to amphetamine administration compared to controls. Some studies indicate increased uptake of L-dopa in parts of the striatum, but some do not. The potential confounding effects of factors associated with dopamine release--such as movement, arousal, attention, stress, and smoking--have rarely been examined, and prior medication use may also have influenced results in some studies. Comparable research on other psychiatric conditions associated with increased arousal, stress, and physical activity is sparse. Research on dopamine concentrations in postmortem brain tissue, on homovanillic acid concentrations, and on dopamine receptors has been negative or inconclusive. Therefore, the idea that the symptoms of psychosis or schizophrenia are caused by the overactivity of dopamine is not supported by current evidence.