The striatal dopamine transporter in first-episode, drug-naive schizophrenic patients: evaluation by the new SPECT-ligand[99mTc]TRODAT-1

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

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

Altered levels of dopamine transporter in the frontal pole and dorsal striatum in schizophrenia

The dopamine hypothesis proposes that there is a hypodopaminergic state in the prefrontal cortex and a hyperdopaminergic state in the striatum of patients with schizophrenia. Evidence suggests the hyperdopaminergic state in the striatum is due to synaptic dopamine elevation, particularly in the dorsal striatum. However, the molecular mechanisms causing disrupted dopaminergic function in schizophrenia remains unclear. We postulated that the dopamine transporter (DAT), which regulates intra-synaptic dopamine concentrations by transporting dopamine from the synaptic cleft into the pre-synaptic neuron, could be involved in dopaminergic dysfunction in schizophrenia. Therefore, we measured levels of DAT in the cortex and striatum from patients with schizophrenia and controls using postmortem human brain tissue. Levels of desmethylimipramine-insensitive mazindol-sensitive [³H]mazindol binding to DAT were measured using in situ radioligand binding and autoradiography in gray matter from Brodmann’s area (BA) 10, BA 17, the dorsal striatum, and nucleus accumbens from 15 patients with schizophrenia and 15 controls. Levels of desmethylimipramine-insensitive mazindol-sensitive [³H]mazindol binding were significantly higher in BA 10 from patients with schizophrenia (p = 0.004) and significantly lower in the dorsal striatum (dorsal putamen p = 0.005; dorsal caudate p = 0.007) from those with the disorder. There were no differences in levels of desmethylimipramine-insensitive [³H]mazindol binding in BA 17 or nucleus accumbens. These data raise the possibility that high levels of DAT in BA 10 could be contributing to lower synaptic cortical dopamine, whereas lower levels of DAT could be contributing to a hyperdopaminergic state in the dorsal striatum.

Combination of In Vivo [123I]FP-CIT SPECT and Microdialysis Reveals an Antipsychotic Drug Haloperidol-induced Synaptic Dopamine Availability in the Rat Midbrain and Striatum

Synaptic dopamine (DA) is mainly regulated by the presynaptic DA transporter (DAT). Single-photon emission computerized tomography (SPECT) with the DAT radiotracer [¹²³I]FP-CIT assesses changes in synaptic DA availability when endogenous DA displaces [¹²³I]FP-CIT or competes for DAT. Here, we investigated the effects of haloperidol (HAL) and clozapine (CLZ) on [¹²³I]FP-CIT binding in the rat striatum and midbrain to assess the utility of [¹²³I]FP-CIT SPECT to quantify changes in synaptic DA availability. Rats underwent [¹²³I]FP-CIT SPECT after intraperitoneal administration of normal saline (vehicle), HAL (1 and 7 mg/kg), CLZ (10 and 54 mg/kg) and bupropion (BUP, a DAT blocker, 20 and 100 mg/kg). In the striatum and midbrain, percent differences in the nondisplaceable binding potential (BP_ND) of [¹²³I]FP-CIT compared to the vehicle were calculated for the various drugs and doses. In another experiment, changes in endogenous striatal DA concentration were measured by in vivo microdialysis under the conditions used in the SPECT study. BUP dose-dependently occupied DAT at considerable levels. Compared to the vehicle, HAL decreased [¹²³I]FP-CIT BP_ND in the striatum (−25.29% and −2.27% for 1 and 7 mg/kg, respectively) and to a greater degree in the midbrain (−58.74% and −49.64% for 1 and 7 mg/kg, respectively), whereas the CLZ-treated group showed a decrease in the midbrain (−38.60% and −40.38% for 10 and 54 mg/kg, respectively) but an increase in the striatum (18.85% and 38.64% for 10 and 54 mg/kg, respectively). Antipsychotic-induced changes in endogenous striatal DA concentrations varied across drugs and doses. The data demonstrate that [¹²³I]FP-CIT SPECT may be a useful preclinical technique for detecting increases in synaptic DA availability in the midbrain and striatum in response to HAL, with results comparable to those of in vivo microdialysis.

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.

Classics in Chemical Neuroscience: Aripiprazole

Aripiprazole was the first antipsychotic developed to possess agonist properties at dopamine D₂ autoreceptors, a groundbreaking strategy that presented a new vista for schizophrenia drug discovery. The dopamine D₂ receptor is the crucial target of all extant antipsychotics, and all developed prior to aripiprazole were D₂ receptor antagonists. Extensive blockade of these receptors, however, typically produces extrapyramidal (movement) side effects, which plagued first-generation antipsychotics, such as haloperidol. Second-generation antipsychotics, such as clozapine, with unique polypharmacology and D₂ receptor binding kinetics, have significantly lower risk of movement side effects but can cause myriad additional ones, such as severe weight gain and metabolic dysfunction. Aripiprazole's polypharmacology, characterized by its unique agonist activity at dopamine D₂ and D₃ and serotonin 5-HT_1A receptors, as well as antagonist activity at serotonin 5-HT_2A receptors, translates to successful reduction of positive, negative, and cognitive symptoms of schizophrenia, while also mitigating risk of weight gain and movement side effects. New observations, however, link aripiprazole to compulsive behaviors in a small group of patients, an unusual side effect for antipsychotics. In this review, we discuss the chemical synthesis, pharmacology, pharmacogenomics, drug metabolism, and adverse events of aripiprazole, and we present a current understanding of aripiprazole's neurotherapeutic mechanisms, as well as the history and importance of aripiprazole to neuroscience.

In SilicoModel-driven Assessment of the Effects of Brain-derived Neurotrophic Factor Deficiency on Glutamate and Gamma-Aminobutyric Acid: Implications for Understanding Schizophrenia Pathophysiology

Objective

Deficient brain-derived neurotrophic factor (BDNF) is one of the important mechanisms underlying the neuroplasticity abnormalities in schizophrenia. Aberration in BDNF signaling pathways directly or circuitously influences neurotransmitters like glutamate and gamma-aminobutyric acid (GABA). For the first time, this study attempts to construct and simulate the BDNF-neurotransmitter network in order to assess the effects of BDNF deficiency on glutamate and GABA.

Methods

Using CellDesigner, we modeled BDNF interactions with calcium influx via N-methyl-D-aspartate receptor (NMDAR)- Calmodulin activation; synthesis of GABA via cell cycle regulators protein kinase B, glycogen synthase kinase and β-catenin; transportation of glutamate and GABA. Steady state stability, perturbation time-course simulation and sensitivity analysis were performed in COPASI after assigning the kinetic functions, optimizing the unknown parameters using random search and genetic algorithm.

Results

Study observations suggest that increased glutamate in hippocampus, similar to that seen in schizophrenia, could potentially be contributed by indirect pathway originated from BDNF. Deficient BDNF could suppress Glutamate decarboxylase 67-mediated GABA synthesis. Further, deficient BDNF corresponded to impaired transport via vesicular glutamate transporter, thereby further increasing the intracellular glutamate in GABAergic and glutamatergic cells. BDNF also altered calcium dependent neuroplasticity via NMDAR modulation. Sensitivity analysis showed that Calmodulin, cAMP response element-binding protein (CREB) and CREB regulated transcription coactivator-1 played significant role in this network.

Conclusion

The study presents in silicoquantitative model of biochemical network constituting the key signaling molecules implicated in schizophrenia pathogenesis. It provides mechanistic insights into putative contribution of deficient BNDF towards alterations in neurotransmitters and neuroplasticity that are consistent with current understanding of the disorder.

Unaltered Dopamine Transporter Availability in Drug-Naive Patients With Schizophrenia After 6 Months of Antipsychotics Treatment: A Naturalistic Study

BACKGROUND

Dopaminergic dysfunction, namely, dopamine transporter (DAT) availability variations in patients with drug-naive schizophrenia after long-term treatment, is still not well understood. The aims of the study were to explore (i) whether the DAT availability in patients with drug-naive schizophrenia differed after antipsychotic treatment and (ii) whether treatment with different generations of antipsychotics influenced the DAT availability after follow-up for 6 months.

METHODS

Twenty-four first-episode, drug-naive patients with schizophrenia were divided into first- and second-generation antipsychotic groups naturalistically. After 6 months of follow-up, 7 patients who received first-generation antipsychotic treatment and 17 patients who received second-generation antipsychotic treatment completed the study. The patients underwent premedication and 6-month follow-up measurements using single-photon emission computed tomography with technetium Tc 99m (Tc) TRODAT-1. Psychopathological evaluations and adverse effects were recorded using appropriate scales.

RESULTS

Both of the treatment groups significantly improved according to Positive and Negative Symptoms Scale evaluation. However, no significant difference was noticed between the premedication and 6-month follow-up DAT scans. Nonsignificant differences existed even in the groups of different generations of antipsychotics.

CONCLUSIONS

Improvements in psychotic symptoms in patients with schizophrenia may not be influenced by DAT availability, even under treatment with different antipsychotics for a sufficient treatment period.

The neurobiology and treatment of first-episode schizophrenia

It is evident that once psychosis is present in patients with schizophrenia, the underlying biological process of the illness has already been ongoing for many years. At the time of diagnosis, patients with schizophrenia show decreased mean intracranial volume (ICV) as compared with healthy subjects. Since ICV is driven by brain growth, which reaches its maximum size at approximately 13 years of age, this finding suggests that brain development in patients with schizophrenia is stunted before that age. The smaller brain volume is expressed as decrements in both grey and white matter. After diagnosis, it is mainly the grey matter loss that progresses over time whereas white matter deficits are stable or may even improve over the course of the illness. To understand the possible causes of the brain changes in the first phase of schizophrenia, evidence from treatment studies, postmortem and neuroimaging investigations together with animal experiments needs to be incorporated. These data suggest that the pathophysiology of schizophrenia is multifactorial. Increased striatal dopamine synthesis is already evident before the time of diagnosis, starting during the at-risk mental state, and increases during the onset of frank psychosis. Cognitive impairment and negative symptoms may, in turn, result from other abnormalities, such as NMDA receptor hypofunction and low-grade inflammation of the brain. The latter two dysfunctions probably antedate increased dopamine synthesis by many years, reflecting the much earlier presence of cognitive and social dysfunction. Although correction of the hyperdopaminergic state with antipsychotic agents is generally effective in patients with a first-episode psychosis, the effects of treatments to correct NMDA receptor hypofunction or low-grade inflammation are (so far) rather modest at best. Improved efficacy of these interventions can be expected when they are applied at the onset of cognitive and social dysfunction, rather than at the onset of psychosis.

Dopamine transporter dysfunction in Han Chinese people with chronic methamphetamine dependence after a short-term abstinence

Single-photon emission-computed tomography (SPECT) after the administration of (99m)Tc-TRODAT-1 was performed on healthy subjects and subjects with methamphetamine (METH)dependence at time 1 (T1) after 24-48 h of abstinence, time 2 (T2) after 2 weeks of abstinence, and time 3 (T3) after 4 weeks of abstinence. In contrast to values in controls, the values of the striatal DAT specific uptake ratios (SURs) in subjects with METH dependence were significantly lower at T1 (n=25), T2 (n=9), and T3 (n=8); a mild increase in SURs was observed at T2 and T3, but values were still significantly lower than those in controls. In subjects with METH dependence, there was a trend for a negative correlation of striatal DAT SURs and craving for METH at T1. METH craving, anxiety and depression scores significantly decreased from T1 to T2 to T3. We conclude that Han Chinese people with METH dependence experience significant striatal DAT dysfunction, and that these changes may be mildly reversible after 4 weeks of abstinence, but that DAT levels still remain significantly lower than those in healthy subjects. The mild recovery of striatal DAT may parallel improvements in craving, anxiety and depression.

Striatal dopamine transporter availability in drug-naive patients with schizophrenia: a case-control SPECT study with [(99m)Tc]-TRODAT-1 and a meta-analysis

Central dopaminergic hyperactivity has been one of the main hypotheses of the pathophysiology of schizophrenia since the 1970s. Excess dopamine (DA) neurotransmission in the striatum is hypothesized to alter the processing of information and result in psychotic symptoms in schizophrenia. Single photon emission computerized tomography (SPECT) provides in vivo indices of DA neurotransmission. Our study aimed to compare dopamine transporter (DAT) availability between drug-naive patients with schizophrenia and controls using SPECT. DAT availability through [(99m)Tc]-TRODAT-1 SPECT was compared between 47 drug-naive patients with recent-onset schizophrenia and 112 healthy controls. We also conducted a random-effects meta-analysis of the available literature synthesizing the results of 6 comparable published articles as well as our current data. The mean specific striatal binding showed a statistical trend for a reduction among the patients compared with controls (estimated difference = 0.071; 95% CI -0.01, 0.15; P = .08). There was an effect of gender, whereby females had a higher ratio of specific striatal binding than males. Age was negatively correlated with the ratio of specific striatal binding, both in patients and controls. The meta-analysis provided a pooled standardized effect size (Cohen's d) of -0.07 (95% CI -0.31, 0.18; P = .60) for the patient vs control comparison in TRODAT binding, with no evidence of heterogeneity between studies or publication bias. Our findings suggest that striatal DAT levels are not altered in the early stages of schizophrenia before medication is introduced. We identified gender differences and aging effects that could have significance for future studies.

Dual-isotope SPECT imaging of striatal dopamine: a comparative study between never-treated and haloperidol-treated first-episode schizophrenic patients

The aim of this dual-isotope SPECT imaging study was to evaluate striatal dopamine transporter (DAT) and D2 receptor availability in first-episode never-treated and haloperidol-treated schizophrenic patients and whether the availability is associated with psychopathology. Twenty-four inpatients with a first acute schizophrenic episode were enrolled in the study; 12 of these patients were treated with haloperidol for 2 weeks before dual-isotope SPECT was performed, whereas the other 12 patients underwent the SPECT evaluation directly after enrollment. Twelve healthy control persons were also recruited and evaluated with the dual-isotope SPECT protocol. Psychopathology was assessed by the Positive and Negative Syndrome Scale and other scales. D2-radioligand binding did not differ between drug-naïve patients and the control group but was significantly lower in the haloperidol-treated group. DAT availability was also significantly lower in the haloperidol patients than in the other two groups and differed significantly between drug-naïve, positive-syndrome-type patients and healthy controls. The data obtained with the new dual-isotope SPECT technique reveal a direct effect of haloperidol at the D2 and DAT receptor level.

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.

A 4-year dopamine transporter (DAT) imaging study in neuroleptic-naive first episode schizophrenia patients

Alterations in the dopaminergic system have long been implicated in schizophrenia. A key component in dopaminergic neurotransmission is the striatal dopamine transporter (DAT). To date, there have been no longitudinal studies evaluating the course of DAT in schizophrenia. A 4-year follow-up study was therefore conducted in which single photon emission computed tomography was used to measure DAT binding in 14 patients and 7 controls. We compared the difference over time in [(123)I] FP-CIT striatal/occipital uptake ratios (SOUR) between patients and controls and the relationship between this difference and both symptomatology and functional outcome at follow-up. We also calculated the relationship between baseline SOUR, symptoms and functional outcome at follow-up. There were no statistically significant differences between patients' SOUR changes over time and those of controls. A significant negative correlation was observed between patients' SOUR changes over time and negative symptomatology at follow-up. A significant negative correlation was also found between baseline SOUR in patients and negative symptomatology, and there was a significant association between lower SOUR at baseline and poor outcome. Although the study found no overall differences in DAT binding during follow-up between schizophrenia patients and controls, it demonstrated that differences in DAT binding relate to patients' characteristics at follow-up.

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.

Alterations of the dopamine transporter in resting lymphocytes of patients with different psychotic disorders

The aim of our study was to investigate and compare the dopamine (DA) transporter (DAT) in resting lymphocytes of 20 psychotic patients and 20 healthy control subjects, by means of both the binding parameters (Bmax and Kd) of 3H-WIN 35,428, and the reuptake parameters (Vmax and Km) of 3H-DA. The results showed that both the Bmax of 3H-WIN 35,428 binding and the Vmax of 3H-DA reuptake of the patients were significantly lower than those of healthy subjects, while the Kd or Km did not show any change. These findings, while indicating a reduced density of the lymphocyte DAT proteins, provide further support of the role of DA in psychoses and suggest that DA alterations may not be limited to brain structures.

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.

Increase in thalamic binding of [(11)C]PE2I in patients with schizophrenia: a positron emission tomography study of dopamine transporter

Previous in vivo imaging studies reported no difference in dopamine transporter (DAT) bindings in the striatum between control subjects and patients with schizophrenia. However, as the signals of radioligands with moderate affinity were insufficient for allowing the evaluation of small amounts of DAT, DAT binding in extrastriatal regions has not been determined. Positron emission tomography scanning using [(11)C]PE2I was performed on eight patients with schizophrenia and twelve normal control subjects. Binding potential (BP(ND)) for DAT in the caudate, putamen, thalamus and substantia nigra was calculated, using the cerebellum as reference region. In patients with schizophrenia, clinical symptoms were evaluated by Positive and Negative Syndrome Scale (PANSS). BP(ND) in the thalamus of patients with schizophrenia was significantly higher than in control subjects (P=0.044). In patients with schizophrenia, there were significantly positive correlations between BP(ND) in the thalamus and total (r=0.75), positive (r=0.78) and negative PANSS scores (r=0.82). Altered DAT in the thalamus might be related to the pathophysiology and clinical symptoms of schizophrenia.

Pretreatment with haloperidol reduces (123)I-FP-CIT binding to the dopamine transporter in the rat striatum: an in vivo imaging study with a dedicated small-animal SPECT camera

Synaptic dopamine is mainly regulated by presynaptic dopamine transporter (DAT) activity. We hypothesized that variations in synaptic dopamine are reflected by variations of DAT radioligand binding. The effect of haloperidol, which increases synaptic dopamine concentrations, was therefore assessed in the rat striatum using (123)I-N-omega-fluoropropyl-2beta-carbomethoxy-3beta-(4-iodophenyl)-nortropane ((123)I-FP-CIT) as a DAT radioligand.

METHODS

Striatal (123)I-FP-CIT binding was measured in 24 rats under baseline conditions (no pretreatment) and at 1 h after injection of haloperidol or a vehicle (1 mg/kg) using a small-animal SPECT camera.

RESULTS

Baseline equilibrium ratios (V(3)'') were 1.32 +/- 0.24 (mean +/- SD). After the haloperidol injection, V(3)'' decreased to 0.99 +/- 0.38 (P(2-tailed) < 0.0001), corresponding to a mean reduction of DAT binding by 25%.

CONCLUSION

Our results are indicative of competition between the DAT ligand (123)I-FP-CIT and synaptic dopamine elevated by haloperidol, suggesting that the assessment of (123)I-FP-CIT binding may be suitable to study variations in synaptic dopamine in vivo.

Regional dopamine synthesis in patients with schizophrenia using L-[beta-11C]DOPA PET

The dopamine hypothesis has been the most widely known theory concerning schizophrenia. However, the exact mechanism including presynaptic dopaminergic activity and its relationship with symptom severity still remains to be revealed. We measured presynaptic dopamine synthesis using positron emission tomography (PET) with L-[beta-(11)C]DOPA in 18 patients with schizophrenia (14 drug-naive and 4 drug-free patients) and 20 control participants. Dopamine synthesis rates, expressed as k(i) values, were obtained using a graphical method, and the occipital cortex was used as reference region. Regions of interest were placed on the prefrontal cortex, temporal cortex, anterior cingulate, parahippocampus, thalamus, caudate nucleus, and putamen. Psychopathology was assessed with the Positive and Negative Symptom Scale (PANSS). We found significantly higher k(i) values in patients than in controls in the left caudate nucleus, but not in the other regions. The k(i) values in the thalamus exhibited a significant positive correlation with the PANSS total scores. Furthermore, a significant positive correlation was observed between the PANSS positive subscale scores and k(i) values in the right temporal cortex. Patients with schizophrenia showed higher dopamine synthesis in the left caudate nucleus, and dopaminergic transmission in the thalamus and right temporal cortex might be implicated in the expression of symptoms in schizophrenia.

DRD3, but not COMT or DRD2, genotype affects executive functions in healthy and first-episode psychosis adolescents

Catechol-O-methyltransferase (COMT) and dopamine receptors 2 (DRD2) and 3 (DRD3) have been associated with a higher risk of developing psychosis and with dopaminergic system (DAS) regulation. Frontal cognitive functioning has been proven to be a useful endophenotype for psychosis and it is partially controlled by the DAS. Val158Met (rs4680, COMT), Taq IA (rs1800497, DRD2) and Ser9Gly (rs6280; DRD3) polymorphisms were analyzed in a sample of 84 adolescent Caucasian patients with first-episode psychosis (ages 11-17) and 85 healthy Caucasian controls (ages 10-17). A comprehensive neuropsychological battery, assessing attention, working memory, memory, and executive functions, was administered to the entire sample. The relationship between neuropsychological scores and genotype was determined. Subjects with the DRD3 Gly/Gly genotype showed significantly poorer performance than Ser/Ser subjects in executive functioning tasks (P = 0.002; adjusted R(2) = 0.031), with no significant differences in the other cognitive paradigms. Neither COMT nor DRD2 polymorphisms significantly contributed to variance in cognition in our adolescent sample. The DRD3 Ser9Gly polymorphism seems to be involved with prefrontal cognition. This effect seems to be heterogeneous in terms of cognitive paradigms. The lack of association between COMT and DRD2 genotypes and cognition in our sample may be partially explained by the young age of the sample and the clinical heterogeneity of the patients.

Dual-isotope SPECT imaging of striatal dopamine: first episode, drug naïve schizophrenic patients

OBJECTIVE

The aim of this investigation was to evaluate the usefulness of a dual-isotope SPECT technique to assess simultaneously striatal dopamine binding structures - presynaptic dopamine transporter (DAT) and postsynaptic dopamine D(2) receptor - in first-episode, drug-naive schizophrenic patients compared to healthy control persons. Additionally, relations between radioligand binding to DAT and D(2) and positive symptoms were assessed.

METHODS

Twenty acutely ill inpatients suffering from a first acute schizophrenic episode and 12 healthy control persons participated in the study. Patients were naïve with respect to neuroleptic or antidepressant medication. A dual-isotope SPECT protocol was performed using combined application of [99mTc]TRODAT-1 and [123I]IBZM. On the day of SPECT, psychopathology was assessed in the patient group by PANSS rating.

RESULTS

In the patient but not in the healthy control group there was a significant correlation between DAT and D(2) receptor availability. Patients with predominant positive symptoms (n=12) had a significantly higher DAT availability compared to the healthy control group. An inverse correlation between DAT and D(2) availability and the extent of "delusions", "conceptual disorganization", and "hallucinatory behaviour" could be demonstrated.

DISCUSSION

The data obtained with this dual-isotope SPECT technique show a change in interaction between striatal DAT and D(2) receptor in first-episode, never-treated schizophrenic patients. Additionally, an association between dopamine transmission and the core symptoms of the acute psychotic syndrome was found.

Neuroreceptor imaging studies in schizophrenia

The ability of SPECT and PET to image specific biomolecules in the living brain provides a unique tool for clinical researchers. It is therefore not surprising that the use of neuroreceptor-imaging techniques has become more widespread over the past decade. This article reviews the application of these techniques to the study of schizophrenia. The design of neuroreceptor-imaging studies performed in the field of schizophrenia research can be broadly divided into two categories: (1) studies of pathophysiology and (2) studies of pharmacology. The former examines neuroreceptor and neurotransmitter parameters in individuals with schizophrenia compared to control subjects in order to provide a better understanding of the disease process. Studies of pharmacology seek to elucidate the mechanism of action for the treatments utilized in schizophrenia. This review will consider both studies of pathophysiology and pharmacology, with a discussion of the application of these techniques to drug development.

The role of dopamine for the pathophysiology of schizophrenia

Since decades, experimental approaches and clinical experience have suggested a dopaminergic system's dysregulation playing an important role within the pathophysiology of schizophrenia. This paper summarizes the actual standard of knowledge of the physiological fundamentals and hypothesized dysbalances of the dopamine (DA) system with respect to schizophrenia including interaction with other neurotransmitter systems (glutamate, GABA). The assumed functional role of DA with respect to physiological and illness-associated cognitive performance, especially working memory, reward, and motivation, as it was assessed by fMRI studies, is presented. A third focus concentrates on giving a short survey of SPECT and PET studies measuring the amount of the striatal and extrastriatal DA, the striatal and extrastriatal dopamine D2 receptor, and the dopamine transporter (DAT) comparing first-episode, drug-naïve, treated, and relapsing schizophrenic patients and healthy control persons.

Study of childhood onset schizophrenia (COS) using SPECT and neuropsychological assessment

BACKGROUND

In recent years, the development of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging has enhanced our understanding of the physiological functioning of the intact brain.

AIM

To study cerebral cortical perfusion defects in patients with childhood onset schizophrenia (COS) and to assess their neuropsychological functioning.

METHODS

This cross-sectional study comprised 14 patients with COS with onset at or before 14 years of age, diagnosed as per ICD-10 DCR criteria, attending a tertiary care centre in North India. All the patients were assessed on sociodemographic, clinical profile sheet, Positive and Negative Symptom Scale (PANSS) and Edinburgh Handedness Inventory (EHI). The Wisconsin Card Sorting Test (WCST) was used to assess their neuropsychological functioning. All patients underwent SPECT. A control group of 10 healthy subjects was studied with SPECT for comparison.

RESULTS

Nine patients (64.3%) showed perfusion anomaly on SPECT scan specifically in the left temporal and frontal areas of the brain. On WCST score these 9 patients showed a higher percentage of total errors (64.49%+/-9.42%) as compared to the other 5 patients (48.54%+/-12.70%) who showed no abnormality on SPECT scan. All normal control subjects showed no abnormality on SPECT.

CONCLUSION

The results from WCST show that COS patients have difficulty in executive functioning. Also, patients had perfusion anomaly in the left temporal, frontal and parietal areas. Deficits found in COS are similar to those found in adult onset schizophrenia (AOS). In view of the findings, the nature of COS and its relationship with AOS are discussed.

Striatal dopamine transporter availability is associated with the productive psychotic state in first episode, drug-naive schizophrenic patients

OBJECTIVE

Supposing a "hyperdopaminergic State" associated at least with acute psychotic illness phases in schizophrenia, a direct relationship between striatal dopamine metabolism and the core psychopathological symptoms rarely can be provided. Recently, a new SPECT ligand to the presynaptic dopamine transporter (DAT) was introduced. Association of DAT availability and the acute psychotic syndrome is now demonstrated in a large cohort of first episode, never treated schizophrenic patients.

METHODS

Twenty-eight inpatients suffering from a first acute exacerbation of schizophrenia and 12 healthy control subjects underwent SPECT scanning with the new radioligand [(99m)Tc]TRODAT-1. On the day of SPECT, psychopathology was assessed using specific scales including PANSS.

RESULTS

There was no significant difference in [(99m)Tc]TRODAT-1 specific binding to the striatal DAT comparing both groups. The extend of hallucinations was significantly inversely correlated with DAT availability in patients with a predominantly positive syndrome type.

DISCUSSION

Our data support evidence that differences in presynaptic dopaminergic activity in schizophrenic patients are associated with the extend of the acute psychotic syndrome. [(99m)Tc]TRODAT-1 seems to be a useful agent for in vivo assessment of a psychopathological association with dopamine metabolism.