Neurochemical brain imaging investigations of schizophrenia

Neutrophil/lymphocyte ratio and cognitive performances in first-episode patients with schizophrenia and healthy controls

Abnormal immune and inflammatory responses are considered to contribute to schizophrenia (SZ). The neutrophil/lymphocyte ratio (NLR) is an inexpensive and reproducible marker of systemic inflammatory responses. Accumulating studies have demonstrated that NLR values are increased in SZ compared to healthy controls and closely related to clinical symptoms in antipsychotic-naïve first-episode SZ (ANFES) patients. However, to our knowledge, only one study has examined NLR in relation to neurocognition in 27 first-episode psychosis patients and 27 controls. This study aimed to examine the relationship of NLR values with cognitive performances in ANFES patients with a larger sample size. Whole blood cell counts were measured in ninety-seven ANFES patients and fifty-six control subjects. The neurocognitive functions of all subjects were measured by the repeatable battery for the assessment of neuropsychological status (RBANS). ANFES patients performed worse on cognition and had increased NLR values relative to healthy controls. In addition, increased NLR was negatively associated with cognitive functions in ANFES patients. Lymphocyte count was positively correlated with cognitive functions in patients. These findings suggest that the abnormal immune and inflammation system indicated by NLR may be involved in the cognitive functions in ANFES patients.

Altered circadian activity and sleep/wake rhythms in the stable tubule only polypeptide (STOP) null mouse model of schizophrenia

Sleep and circadian rhythm disruptions commonly occur in individuals with schizophrenia. Stable tubule only polypeptide (STOP) knockout (KO) mice show behavioral impairments resembling symptoms of schizophrenia. We previously reported that STOP KO mice slept less and had more fragmented sleep and waking than wild-type littermates under a light/dark (LD) cycle. Here, we assessed the circadian phenotype of male STOP KO mice by examining wheel-running activity rhythms and EEG/EMG-defined sleep/wake states under both LD and constant darkness (DD) conditions. Wheel-running activity rhythms in KO and wild-type mice were similarly entrained in LD, and had similar free-running periods in DD. The phase delay shift in response to a light pulse given early in the active phase under DD was preserved in KO mice. KO mice had markedly lower activity levels, lower amplitude activity rhythms, less stable activity onsets, and more fragmented activity than wild-type mice in both lighting conditions. KO mice also spent more time awake and less time in rapid eye movement sleep (REMS) and non-REMS (NREMS) in both LD and DD conditions, with the decrease in NREMS concentrated in the active phase. KO mice also showed altered EEG features and higher amplitude rhythms in wake and NREMS (but not REMS) amounts in both lighting conditions, with a longer free-running period in DD, compared to wild-type mice. These results indicate that the STOP null mutation in mice altered the regulation of sleep/wake physiology and activity rhythm expression, but did not grossly disrupt circadian mechanisms.

[PET imaging for better understanding of normal and pathological neurotransmission]

Positron emission tomography imaging is still an expanding field of preclinical and clinical investigations exploring the brain and its normal and pathological functions. In addition to technological improvements in PET scanners, the availability of suitable radiotracers for unexplored pharmacological targets is a key factor in this expansion. Many radiotracers (or radiopharmaceuticals, when administered to humans) have been developed by multidisciplinary teams to visualize and quantify a growing numbers of brain receptors, transporters, enzymes and other targets. The development of new PET radiotracers still represents an exciting challenge, given the large number of neurochemical functions that remain to be explored. In this article, we review the development context of the first preclinical radiotracers and their passage to humans. The main current contributions of PET radiotracers are described in terms of imaging neuronal metabolism, quantification of receptors and transporters, neurodegenerative and neuroinflammatory imaging. The different approaches to functional imaging of neurotransmission are also discussed. Finally, the contributions of PET imaging to the research and development of new brain drugs are described.

Effects of Amisulpride Adjunctive Therapy on Working Memory and Brain Metabolism in the Frontal Cortex of Patients with Schizophrenia: A Preliminary Positron Emission Tomography/Computerized Tomography Investigation

Objective

Dopamine plays a significant role in working memory by acting as a key neuromodulator between brain networks. Additionally, treatment of patients with schizophrenia using amisulpride, a pure dopamine class 2/3 receptor antagonist, improves their clinical symptoms with fewer side effects. We hypothesized that patients with schizophrenia treated with amisulpride and aripiprazole show increased working memory and glucose metabolism compared with those treated with cognitive behavioral therapy (CBT) and aripiprazole instead.

Methods

Sixteen patients with schizophrenia (eight in the amisulpride group [aripiprazole+amisulpride] and eight in the CBT group [aripiprazole+CBT]) and 15 age- and sex-matched healthy control subjects were recruited for a 12-week-long prospective trial. An [18F]-fluorodeoxyglucose-positron emission tomography/computerized tomography scanner was used to acquire the images.

Results

After 12 weeks of treatment, the amisulpride group showed greater improvement in the Letter-Number Span scores than the CBT group. Additionally, although brain metabolism in the left middle frontal gyrus, left occipital lingual gyrus, and right inferior parietal lobe was increased in all patients with schizophrenia, the amisulpride group exhibited a greater increase in metabolism in both the right superior frontal gyrus and right frontal precentral gyrus than the CBT group.

Conclusion

This study suggests that a small dose of amisulpride improves the general psychopathology, working memory performance, and brain glucose metabolism of patients with schizophrenia treated with aripiprazole.

Label-free imaging of neurotransmitters in live brain tissue by multi-photon ultraviolet microscopy

Visualizing small biomolecules in living cells remains a difficult challenge. Neurotransmitters provide one of the most frustrating examples of this difficulty, as our understanding of signaling in the brain critically depends on our ability to follow the neurotransmitter traffic. Last two decades have seen considerable progress in probing some of the neurotransmitters, e.g. by using false neurotransmitter mimics, chemical labeling techniques, or direct fluorescence imaging. Direct imaging harnesses the weak UV fluorescence of monoamines, which are some of the most important neurotransmitters controlling mood, memory, appetite, and learning. Here we describe the progress in imaging of these molecules using the least toxic direct excitation route found so far, namely multi-photon (MP) imaging. MP imaging of serotonin, and more recently that of dopamine, has allowed researchers to determine the location of the vesicles, follow their intracellular dynamics, probe their content, and monitor their release. Recent developments have even allowed ratiometric quantitation of the vesicular content. This review shows that MP ultraviolet (MP-UV) microscopy is an effective but underutilized method for imaging monoamine neurotransmitters in neurones and brain tissue.

Mice lacking interleukin-18 gene display behavioral changes in animal models of psychiatric disorders: Possible involvement of immunological mechanisms

Preclinical and clinical evidence suggests pro-inflammatory cytokines might play an important role in the neurobiology of schizophrenia and stress-related psychiatric disorders. Interleukin-18 (IL-18) is a member of the IL-1 family of cytokines and it is widely expressed in brain regions involved in emotional regulation. Since IL-18 involvement in the neurobiology of mental illnesses, including schizophrenia, remains unknown, this work aimed at investigating the behavior of IL-18 null mice (KO) in different preclinical models: 1. the prepulse inhibition test (PPI), which provides an operational measure of sensorimotor gating and schizophrenic-like phenotypes; 2. amphetamine-induced hyperlocomotion, a model predictive of antipsychotic activity; 3. resident-intruder test, a model predictive of aggressive behavior. Furthermore, the animals were submitted to models used to assess depressive- and anxiety-like behavior. IL-18KO mice showed impaired baseline PPI response, which was attenuated by d-amphetamine at a dose that did not modify PPI response in wild-type (WT) mice, suggesting a hypodopaminergic prefrontal cortex function in those mice. d-Amphetamine, however, induced hyperlocomotion in IL-18KO mice compared to their WT counterparts, suggesting hyperdopaminergic activity in the midbrain. Moreover, IL-18KO mice presented increased basal levels of IL-1β levels in the hippocampus and TNF-α in the prefrontal cortex, suggesting an overcompensation of IL-18 absence by increased levels of other proinflammatory cytokines. Although no alteration was observed in the forced swimming or in the elevated plus maze tests in naïve IL-18KO mice, these mice presented anxiogenic-like behavior after exposure to repeated forced swimming stress. In conclusion, deletion of the IL-18 gene resembled features similar to symptoms observed in schizophrenia (positive and cognitive symptoms, aggressive behavior), in addition to increased susceptibility to stress. The IL-18KO model, therefore, could provide new insights into how changes in brain immunological homeostasis induce behavioral changes related to psychiatric disorders, such as schizophrenia.

Disruptions of Sleep/Wake Patterns in the Stable Tubule Only Polypeptide (STOP) Null Mouse Model of Schizophrenia

Disruption of sleep/wake cycles is common in patients with schizophrenia and correlates with cognitive and affective abnormalities. Mice deficient in stable tubule only polypeptide (STOP) show cognitive, behavioral, and neurobiological deficits that resemble those seen in patients with schizophrenia, but little is known about their sleep phenotype. We characterized baseline sleep/wake patterns and recovery sleep following sleep deprivation in STOP null mice. Polysomnography was conducted in adult male STOP null and wild-type (WT) mice under a 12:12 hours light:dark cycle before, during, and after 6 hours of sleep deprivation during the light phase. At baseline, STOP null mice spent more time awake and less time in non-rapid eye movement sleep (NREMS) over a 24-hour period, with more frequent transitions between wake and NREMS, compared to WT mice, especially during the dark phase. The distributions of wake, NREMS and REMS across the light and the dark phases differed by genotype, and so did features of the electroencephalogram (EEG). Following sleep deprivation, both genotypes showed homeostatic increases in sleep duration, with no significant genotype differences in the initial compensatory increase in sleep intensity (EEG delta power). These results indicate that STOP null mice sleep less overall, and their sleep and wake periods are more fragmented than those of WT mice. These features in STOP null mice are consistent with the sleep patterns observed in patients with schizophrenia.

Biological mechanisms underlying evolutionary origins of psychotic and mood disorders

Psychotic and mood disorders are brain dysfunctions that are caused by gene environment interactions. Although these disorders are disadvantageous and involve behavioral phenotypes that decrease the reproductive success of afflicted individuals in the modern human society, the prevalence of these disorders have remained constant in the population. Here, we propose several biological mechanisms by which the genes associated with psychotic and mood disorders could be selected for in specific environmental conditions that provide evolutionary bases for explanations of when, why, and where these disorders emerged and have been maintained in humans. We discuss the evolutionary origins of psychotic and mood disorders with specific focuses on the roles of dopamine and serotonin in the conditions of social competitiveness/hierarchy and maternal care and other potential mechanisms, such as social network homophily and symbiosis.

Reelin influences the expression and function of dopamine D2 and serotonin 5-HT2A receptors: a comparative study

Reelin is an extracellular matrix protein that plays a critical role in neuronal guidance during brain neurodevelopment and in synaptic plasticity in adults and has been associated with schizophrenia. Reelin mRNA and protein levels are reduced in various structures of post-mortem schizophrenic brains, in a similar way to those found in heterozygous reeler mice (HRM). Reelin is involved in protein expression in dendritic spines that are the major location where synaptic connections are established. Thus, we hypothesized that a genetic deficit in reelin would affect the expression and function of dopamine D2 and serotonin 5-HT2A receptors that are associated with the action of current antipsychotic drugs. In this study, D2 and 5-HT2A receptor expression and function were quantitated by using radioligand binding studies in the frontal cortex and striatum of HRM and wild-type mice (WTM). We observed increased expression (p<0.05) in striatum membranes and decreased expression (p<0.05) in frontal cortex membranes for both dopamine D2 and serotonin 5-HT2A receptors from HRM compared to WTM. Our results show parallel alterations of D2 and 5-HT2A receptors that are compatible with a possible hetero-oligomeric nature of these receptors. These changes are similar to changes described in schizophrenic patients and provide further support for the suitability of using HRM as a model for studying this disease and the effects of antipsychotic drugs.

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.

Magnetic resonance spectroscopy study of the antioxidant defense system in schizophrenia

Accumulating evidence suggests that oxidative stress associated with impaired metabolism of the antioxidant glutathione (GSH) plays a key role in the pathophysiology of schizophrenia. Magnetic resonance spectroscopy (MRS) is one of the brain-imaging techniques that can quantitatively measure bioactive substances such as GSH in the intact human brain. Four different measurement sequences including double quantum coherence (DQC) filtering, MEscher-GArwood Point-RESolved Spectroscopy (MEGA-PRESS), Stimulated Echo Acquisition Mode (STEAM), and PRESS have been used to evaluate the (1)H-MRS measurement of GSH in the brains of patients with schizophrenia. Although the results of these studies were somewhat diverse, a negative correlation between brain GSH levels and the severity of negative symptoms in schizophrenia patients suggests that increasing the brain GSH levels might be beneficial for schizophrenia patients with negative symptoms. Moreover, a recent double-blind, placebo-controlled study demonstrated that add-on of N-acetyl-l-cysteine (NAC), a precursor of GSH, to antipsychotics improved the negative symptoms and reduced the side effects (akathisia) in patients with chronic schizophrenia. MRS study of the antioxidant defense system in schizophrenia still remains in the infantile stage; future studies are needed to examine the brain GSH level before and after NAC treatment, and thereby to provide direct evidence of the induced production of GSH in the living brain.

The four dimensions: a model for the social aetiology of psychosis

Recently, there has been increasing focus on prevention of mental illness, early intervention and the promotion of mental health. The social determinants of health and public health approaches are considered key. Early intervention has focused on psychotic disorders but prevention has not. This may in part reflect the fact that public health planners do not have a clear model for how social determinants influence the risk of developing a psychotic illness. Drawing on biological, genetic and epidemiologic evidence regarding the relationship between social risk factors and psychosis, this paper outlines a conceptual framework for understanding how individual and ecological factors contribute and interact to modulate the risk of developing psychotic illness. The framework asserts that there are four dimensions: individual factors; ecological factors; the interaction between individual and ecological factors; and time. It may help those considering interventions to understand the multilevel and multifactorial effects of social factors on the aetiology of psychotic illness, to develop targeted strategies for the prevention of psychotic illness and serve as a template for the assessment of initiatives.

Plasma homovanillic acid differences in clinical subgroups of first episode schizophrenic patients

This study evaluates the relationship between plasma homovanillic acid (pHVA) levels, which have been used to study the role of central dopamine in schizophrenia, and the positive/negative syndrome in first episode schizophrenic patients before and after antipsychotic treatment. Forty neuroleptic-naive first episode schizophrenic patients were monitored at baseline and on days 7, 14 and 28. Clinical status was evaluated with the Scale for the Assessment of Positive Symptoms (SAPS), the Scale for the Assessment of Negative Symptoms (SANS), and the Brief Psychotic Rating Scale. Plasma HVA levels were also measured. Patients were divided into predominantly positive or negative syndrome groups by subtracting SAPS from SANS scores, at baseline. A healthy control group was also enrolled. Schizophrenic patients as a group had significantly higher pHVA levels than controls at baseline (20.50+/-11.85 vs. 13.04+/-7.22 ng/ml). Moreover, 12 predominantly negative syndrome patients had similar mean baseline pHVA levels (21.30+/-12.36 ng/ml) to those of 28 predominantly positive syndrome patients (19.40+/-11.33 ng/ml). During follow-up, there was a different evolution of pHVA levels in the predominantly positive syndrome group than in the predominantly negative syndrome group, with a significantly greater global reduction of pHVA levels in the former. Although both groups showed clinical improvement following 4 weeks of treatment with risperidone, pHVA levels at endpoint were lower (13.29+/-5.91 ng/ml) than at baseline in patients in the predominantly positive syndrome group, while among those in the predominantly negative syndrome group there was no difference in pHVA levels before and after treatment (21.02+/-13.06 ng/ml). The different pHVA level profiles observed in predominantly positive and negative syndrome first episode patients after 4 weeks of treatment with risperidone suggest that each syndrome may have a different underlying neurobiology.

Regulation of pituitary adenylyl cyclase-activating polypeptide (PACAP, ADCYAP1: adenylyl cyclase-activating polypeptide 1) in the treatment of schizophrenia

BACKGROUND

Deficiency of pituitary adenylyl cyclase-activating polypeptide (PACAP) and its specific receptor, PAC1, causes a schizophrenia-like phenotype in mice. In addition, the relation of the PACAP and PAC1 genes to schizophrenia has been shown by single-nucleotide polymorphism association studies. Furthermore, PACAP is reported to be involved in the function of disrupted-in-schizophrenia 1.

OBJECTIVE

To summarize briefly the recent evidence relating the PACAP system and schizophrenia and discuss the application of PACAP to the treatment of schizophrenia.

RESULTS/CONCLUSION

The regulation of PACAPergic signals is an interesting potential treatment for schizophrenia. Further studies of PACAP signals and the association of PACAP signals with schizophrenia should shed the light on the utility of this approach in the treatment of schizophrenia.

The biochemical womb of schizophrenia: A review

The conclusive identification of specific etiological factors or pathogenic processes in the illness of schizophrenia has remained elusive despite great technological progress. The convergence of state-of-art scientific studies in molecular genetics, molecular neuropathophysiology, in vivo brain imaging and psychopharmacology, however, indicates that we may be coming much closer to understanding the genesis of schizophrenia. In near future, the diagnosis and assessment of schizophrenia using biochemical markers may become a "dream come true" for the medical community as well as for the general population. An understanding of the biochemistry/ visa vis pathophysiology of schizophrenia is essential to the discovery of preventive measures and therapeutic intervention.

Molecular Neuroimaging: From Conventional to Emerging Techniques

The use of molecular imaging techniques in the central nervous system (CNS) has a rich history. Most of the important developments in imaging-such as computed tomography, magnetic resonance imaging, single photon emission computed tomography, and positron emission tomography-began with neuropsychiatric applications. These techniques and modalities were then found to be useful for imaging other organs involved with various disease processes. Molecular imaging of the CNS has enabled scientists and researchers to understand better the basic biology of brain function and the way in which various disease processes affect the brain. Unlike other organs, the brain is not easily accessible, and it has a highly selective barrier at the endothelial cell level known as the blood-brain barrier. Furthermore, the brain is the most complex cellular network known to exist. Various neurotransmitters act in either an excitatory or an inhibitory fashion on adjacent neurons through a multitude of mechanisms. The various neuronal systems and the myriad of neurotransmitter systems become altered in many diseases. Some of the most devastating diseases, including Alzheimer disease, Parkinson disease, brain tumors, psychiatric disease, and numerous degenerative neurologic diseases, affect only the brain. Molecular neuroimaging will be critical to the future understanding and treatment of these diseases. Molecular neuroimaging of the brain shows tremendous promise for clinical application. In this article, the current state and clinical applications of molecular neuroimaging will be reviewed.

Changes in hippocampal GABAA receptor subunit composition in bipolar 1 disorder

Postmortem CNS studies have suggested an uncoupling of the gamma-aminobutyric acid (GABA) and benzodiazepine binding sites on the hippocampal GABA(A) receptor in schizophrenia. The GABA(A) receptor is an assembly of discrete subunits that form a ligand-gated ion channel, the binding characteristics of which are defined by receptor subunit composition. Thus, a likely explanation for an uncoupling between the GABA and benzodiazepine binding sites on the GABA(A) receptor would be a change in receptor subunit composition. To test this hypothesis we measured the density of GABA ([(3)H]muscimol) and benzodiazepine ([(3)H]flumazenil) binding sites on the GABA(A) receptor in hippocampi, obtained postmortem, from schizophrenic, bipolar I disorder and control subjects. In addition, we measured the amount of [(3)H]flumazenil binding that could be displaced with zolpidem and clonazepam. Levels of both [(3)H]muscimol and [(3)H]flumazenil binding were significantly decreased in part of the CA2 from subjects with schizophrenia; the decrease in [(3)H]flumazenil being due to decreases in both zolpidem-sensitive and -insensitive radioligand binding. There were complex regionally specific changes in [(3)H]muscimol binding in the hippocampus from subjects with bipolar I disorder but there were no significant changes in the overall levels of [(3)H]flumazenil binding. There were significant decreases in zolpidem-sensitive and increases in zolpidem-insensitive [(3)H]flumazenil binding in most regions of the sections of the hippocampal formation studied in bipolar I disorder. Unlike [(3)H]flumazenil, zolpidem does not bind to the alpha5 subunit of the GABA(A) receptor; therefore, we postulate that there is an increase in GABA(A) receptors containing alpha5 subunit in the hippocampus from subjects with bipolar I disorder.

Quantitative measurement of serotonin synthesis and sequestration in individual live neuronal cells

Synthesis and subsequent sequestration into vesicles are essential steps that precede neurotransmitter exocytosis, but neither the total neurotransmitter content nor the fraction sequestered into vesicles have been measured in individual live neurons. We use multiphoton microscopy to directly observe intracellular and intravesicular serotonin in the serotonergic neuronal cell line RN46A. We focus on how the relationship between synthesis and sequestration changes as synthesis is up-regulated by differentiation or down-regulated by chemical inhibition. Temperature-induced differentiation causes an increase of about 60% in the total serotonin content of individual cells, which goes up to about 10 fmol. However, the number of vesicles per cell increases by a factor of four and the proportion of serotonin sequestered inside the vesicles increases by a factor of five. When serotonin synthesis is inhibited in differentiated cells and the serotonin content goes down to the level present in undifferentiated cells, the sequestered proportion still remains at this high level. The total neurotransmitter content of a cell is, thus, an unreliable indicator of the sequestered amount.

Rethinking models of psychotropic drug action

Theoretical assumptions about how psychotropic drugs 'work' are rarely discussed explicitly. In a 'disease-centred model,' drugs are believed to work by acting on a disease process. In contrast, in a 'drug-centred model,' the characteristic physiological, behavioural and subjective effects of drugs are used to define drug action. The therapeutic value of a drug stems from the usefulness of these effects in clinical situations. The disease-centred model appears dominant but has weaknesses: (1) it cannot logically justify the use of drugs since major pathophysiological hypotheses were derived from selectively observed actions of drugs; (2) comparisons between drugs believed to have specific effects in certain conditions and drugs thought to have non-specific effects fail to support it; (3) outcome measures for various disorders include items responsive to non-specific drug effects; (4) studies with healthy volunteers describe characteristic drug-induced states independently of a psychiatric diagnosis; (5) animal tests show effects with agents not usually thought of as specific treatments for the conditions modelled by tests. This article offers suggestions to develop a drug-centred model and discusses its potential impact on clinical practice.

Processing efficiency of a verbal working memory system is modulated by amphetamine: an fMRI investigation

RATIONALE

Working memory performance may be improved or decreased by amphetamine, depending on baseline working memory capacity and amphetamine dosage. This variable effect suggests an optimal range of monaminergic activity for working memory, either below or above which it is compromised. We directly tested this possibility with human participants by varying amphetamine dosage and measuring the efficiency of cortical processing in brain regions associated with working memory.

OBJECTIVES

The modulation of cortical processing in a verbal working memory network by dextroamphetamine (D-amph) was examined using BOLD functional magnetic resonance imaging (fMRI) with healthy participants. The goal of the study was to test the hypothesis of an inverted U-shaped relationship between D-amph dose and processing efficiency of a verbal working memory system.

METHODS

D-amph dosage was increased cumulatively every 2 h across four scanning sessions collected in a single day. The primary measure used for analyses in this study was the extent of activation in brain regions empirically defined as a working memory network.

RESULTS

An inverted U-shaped relationship was observed between the amount of D-amph administered and working memory processing efficiency. This relationship was specific to brain areas functionally defined as working memory regions and to the encoding/maintenance phase (as opposed to the response phase) of the task.

CONCLUSION

The results are consistent with the hypothesis that the neurochemical effects of amphetamine modulate the efficiency of a verbal working memory system. The effect of amphetamine on working memory in healthy individuals may provide insight regarding the working memory deficits seen in schizophrenia, given the overlap between neurochemical systems affected by amphetamine, and those disordered in schizophrenia.

Interindividual reproducibility of glutamate quantification using 1.5-T proton magnetic resonance spectroscopy

The goal of this study was to measure the interindividual reproducibility of glutamate quantification in 1.5-T (1)H MRS of human brains. To determine the effective echo time (TE) for glutamate quantification, spectra from a phantom and 12 participants were obtained with TE = 30, 35, 40, and 144 ms (repetition time (TR) = 2000 ms and volume of interest = 4 cm(3)). The average Cramer-Rao lower bounds for glutamate quantification using LCModel was lowest in two experiments when TE = 40 ms.Twenty-one subjects participated in experiments that measured interindividual reproducibility of glutamate quantification. Spectra were acquired with TR = 6000 ms and TE = 40 ms. Results showed that the coefficients of variance were 11.0 and 13.1% in the anterior cingulate cortex and insula, respectively. This suggests that glutamate can be reproducibly measured from 1.5-T (1)H MRS with long TR, effective TE, and the LCModel.

Effect of reduction in endogenous dopamine on extrastriatal binding of [11C]FLB 457 in rat brain—An ex vivo study

Carbon-11 labeled FLB 457 has been used successfully as a selective, high affinity PET ligand for the quantification of extrastriatal D2-like receptors in man. This study was carried out in rats to investigate regional values for maximal binding and ED50 (a measure of apparent K(d)) for the radioligand in vivo in control animals and in a group pretreated with the neuronal impulse flow inhibitor, gamma-butyrolactone. The aims were to obtain further information regarding the specific activity needed to ensure tracer kinetics and to investigate baseline occupancy by dopamine (DA), each relevant to optimal clinical use of the radioligand. Regional B(max) values were consistent with the distribution of D2-like receptors in rat brain. Of interest, 60% of the binding in cerebellum, often used as a low-binding "reference region" for PET quantification, was saturable, with B(max) only 2- to 3-fold less than that in neocortex, hippocampus, and thalamus. ED50 values were in the range 2-3 nmol/kg, confirming minimal receptor occupancy by the tracer in human PET, using high but achievable specific activities. In the majority of extrastriatal tissues, reduction in synaptic DA did not significantly decrease the apparent K(d), except in cortical regions, where the extent of the effect suggested a low ( approximately 10%), but measurable baseline receptor occupancy by DA.

Abnormalities in the dopamine system in schizophrenia may lie in altered levels of dopamine receptor-interacting proteins

BACKGROUND

Dopamine receptor-interacting proteins constitute a part of the dopamine system that is involved in regulation of dopamine receptor-associated intracellular signaling. Previously, we demonstrated that two such proteins, the D1 receptor-interacting protein calcyon and the D2 receptor-interacting protein neuronal calcium sensor-1 (NCS-1), were elevated in the prefrontal cortex of schizophrenia cases from the Stanley Foundation Neuropathology Consortium.

METHODS

The aim of this study was to confirm and expand these findings. We employed Western blot and real-time reverse transcriptase polymerase chain reaction analyses to compare prefrontal (area 46) and occipital (area 17) cortical levels of calcyon and NCS-1 proteins and mRNAs between schizophrenia (n = 37) and control (n = 30) cohorts from the Brain Collection of the Mount Sinai Medical School/Bronx Veterans Administration Medical Center.

RESULTS

The schizophrenia cohort showed significant up-regulation of calcyon protein and message levels in both prefrontal and occipital cortical regions, both of which also displayed schizophrenia-associated up-regulation of NCS-1 message. Protein levels of NCS-1 were elevated only in the prefrontal cortex. All increases in protein levels were correlated with those of corresponding messages. Furthermore, schizophrenia-associated alterations in the levels of calcyon and NCS-1 messages were correlated.

CONCLUSIONS

Up-regulation of calcyon and NCS-1 in the second schizophrenia cohort strengthens the proposition that abnormalities of the dopamine system in this disease may lie in altered levels of dopamine receptor-interacting proteins. Also, up-regulation of both calcyon and NCS-1 in the cortex of schizophrenia patients can be attributed largely to an enhanced transcription or reduced degradation of their messages. Finally, our findings suggest that elevations in the expressions of calcyon and NCS-1 in schizophrenia may have the same underlying cause.

Regulation of central dopamine-2 receptor sensitivity by a proportional control thermostat in humans

Central dopamine-2 (D2) receptors are importantly involved in the pathogenesis and treatment of schizophrenia. Central D2 receptors are also involved in thermoregulation. Recently, a type of central nervous system proportional control thermostat was described that governs the magnitude of several serotonin receptor-mediated core body thermoregulatory responses in proportion to both the amount of nocturnal melatonin secreted and the minimum level of nocturnal core body temperature (Tmin). The present study investigated whether the magnitude of D2 receptor-mediated hypothermia--a putative index of central D2 receptor sensitivity--is also regulated by this proportional control thermostat in humans. Twenty healthy subjects had their 02:00 h melatonin concentrations (MT2am) and Tmin measured during consecutive sleep episodes and their core body temperature responses (TAUC) measured the next two mornings after oral ingestion of either the D2 receptor agonist bromocriptine 3.125 mg or placebo. We found that the bromocriptine-induced TAUC was significantly and independently correlated with both Tmin and MT2am. In conclusion, D2 receptor-mediated hypothermia, an index of central D2 receptor sensitivity, is regulated by a proportional control thermostat in humans. The abnormal D2 receptor function in schizophrenia could be related to dysfunction of this thermostat.

Schizophrenia: etiology and course

Decades of research on schizophrenia have not produced major breakthroughs, but gradual progress has been made in identifying risk factors and clarifying the nature of the etiologic process. This article provides an overview of trends in research findings as well as current assumptions about the interplay between environmental and genetic factors in the etiology of schizophrenia. Based on the cumulative findings, it appears that both genetic and prenatal factors can give rise to constitutional vulnerability. Subsequent neuromaturational processes, especially those that occur during adolescence, and exposure to stressful events can trigger the behavioral expression of this vulnerability.

Striatal dopamine D2 receptor density in neuroleptic-naive and in neuroleptic-free schizophrenic patients: an 123I-IBZM-SPECT study

Most post-mortem autoradiographic studies have described striatal dopamine D(2) receptor up-regulation due to chronic neuroleptic exposure. The aim of our study was to compare in-vivo striatal D(2) receptor density in neuroleptic-naive and neuroleptic-free schizophrenic patients. We included 28 young (mean age: 28+/-8 years) acute psychotic patients meeting DSM-IV criteria for schizophrenia or schizophreniform disorder. Enrolled patients were either first-episode neuroleptic-naive (n=12) or neuroleptic-free (n=16) after a minimum washout period of 7 days. All neuroleptic-free subjects had previously received neuroleptic treatment for a median period of 3.5 years. Both groups were evaluated using standard clinical scales. In-vivo striatal D(2) receptor binding was assessed by basal ganglia/frontal cortex ratios using (123)I-IBZM SPECT. No statistically significant differences were found in age or clinical assessment between neuroleptic-naive and neuroleptic-free schizophrenic patients. No differences were found in the basal ganglia/frontal cortex ratios of neuroleptic-naive (1.78+/-0.11) and neuroleptic-free (1.81+/-0.15) patients. No striatal uptake laterality was observed in either group. No correlation was demonstrated between BG/FC ratios and duration of illness, period of neuroleptic exposure or time of drug washout. We conclude that our neuroleptic-naive and neuroleptic-free schizophrenic patients did not show differences in striatal D(2) receptor binding, suggesting that IBZM-SPECT fails to detect D(2) receptor up-regulation induced by chronic exposure to neuroleptic drugs.

Proton magnetic resonance spectroscopy of the frontal lobe in schizophrenics: a critical review of the methodology

Schizophrenic patients undergoing proton magnetic resonance spectroscopy show alterations in N-acetyl aspartate levels in several brain regions, indicating neuronal dysfunction. The present review focuses on the main proton magnetic resonance spectroscopy studies in the frontal lobe of schizophrenics. A MEDLINE search, from 1991 to March 2004, was carried out using the key-words spectroscopy and schizophrenia and proton and frontal. In addition, articles cited in the reference list of the studies obtained through MEDLINE were included. As a result, 27 articles were selected. The results were inconsistent, 19 papers reporting changes in the N-acetyl aspartate levels, while 8 reported no change. Methodological analysis led to the conclusion that the discrepancy may be due the following factors: (i) number of participants; (ii) variation in the clinical and demographic characteristics of the groups; (iii) little standardization of the acquisition parameters of spectroscopy. Overall, studies that fulfill strict methodological criteria show N-acetyl aspartate decrease in the frontal lobe of male schizophrenics.

Dopamine transporter change in drug-naive schizophrenia: an imaging study with 99mTc-TRODAT-1

The aim of this study was to use a specific dopamine transporter (DAT) ligand, 99mTc-TRODAT-1 with single photon emission computed tomography (SPECT) to investigate the densities of DAT in the striatal dopaminergic system in patients with schizophrenia. Striatal DAT uptakes were measured in 12 drug-nai;ve schizophrenic patients and 12 age- and sex-matched healthy volunteers. The psychometric tools included the Standardized Clinical Assessment for Neuropsychiatry (SCAN) and the Positive and Negative Syndrome Scale (PANSS). Semiquantitative analyses using the ratio of uptake in caudate, putamen, and striatum to occipital lobe, and left-right asymmetry were performed. Decreased TRODAT uptake in the right striatum and increased uptake in the left striatum were found in the schizophrenics. However, there is no overall difference in the average striatum uptake. The right-left asymmetry of the caudate and putamen DAT binding seen in the healthy control group disappeared in the schizophrenia group. The decreased right uptake and increased left uptake in the striatum might lead to the lack of right-left asymmetry in neuroleptic-nai;ve schizophrenia patients, confirming that the disorder could be due to a disruption in brain lateralization. This is the first report on the use TRODAT to evaluate the DAT density in schizophrenia patients and shows lack of asymmetry in striatal uptake of TRODAT in schizophrenics. The findings also suggest that TRODAT SPECT may be a useful technique to measure dopamine transmission in the human brain and for understanding the pathophysiology of neuropsychiatric disorders.

Signal transduction and genes-to-behaviors pathways in psychiatric diseases

Although psychiatric diseases are among the most common and destructive of all human illnesses, the molecular and cellular mechanisms underlying their complex origins remain to be elucidated. Dysfunction of critical intracellular signaling pathways is very likely to be involved. This conclusion is based on a number of observations, including the short- and long-term cellular effects of psychiatric drugs; the critical role signaling pathways play in neurotransmitter, neuropeptide, and neurohormone communication; and the fact that signaling pathways are principle regulators of the diverse array of behavioral symptoms experienced by patients. The genomics era has brought to psychiatry an abundance of genetic linkage and candidate gene findings. The difficult task--now under way--is to discern the functional relevance of these results. Recent evidence suggests the involvement of the ubiquitous protein phosphatase 2B (calcineurin), a critical regulator of many signal transduction pathways, as a schizophrenia susceptibility gene. It is likely that genetic findings in severe psychiatric disorders will continue to implicate direct and indirect modulation of critical intracellular signaling pathways.

Half a century of antipsychotics and still a central role for dopamine D2 receptors

A review of the history of antipsychotics reveals that while the therapeutic effects of chlorpromazine and reserpine were discovered and actively researched almost concurrently, subsequent drug development has been restricted to drugs acting on postsynaptic receptors rather than modulation of dopamine release. The fundamental property of atypical antipsychotics is their ability to produce an antipsychotic effect in the absence of extrapyramidal side effects (EPS) or prolactin elevation. Modulation of the dopamine D2 receptor remains both necessary and sufficient for antipsychotic drug action, with affinity to the D2-receptor being the single most important discriminator between a typical and atypical drug profile. Most antipsychotics, including atypical antipsychotics, show a dose-dependent threshold of D2 receptor occupancy for their therapeutic effects, although the precise threshold is different for different drugs. Some atypical antipsychotics do not appear to reach the threshold for EPS and prolactin elevation, possibly accounting for their atypical nature. To link the biological theories of antipsychotics to their psychological effects, a hypothesis is proposed wherein psychosis is a state of aberrant salience of stimuli and ideas, and antipsychotics, via modulation of the mesolimbic dopamine system, dampen the salience of these symptoms. Thus, antipsychotics do not excise psychosis: they provide the neurochemical platform for the resolution of symptoms. Future generations of antipsychotics may need to move away from a "one-size-fits-all polypharmacy-in-a-pill" approach to treat all the different aspects of schizophrenia. At least in theory a preferred approach would be the development of specific treatments for the different dimensions of schizophrenia (e.g., positive, negative, cognitive, and affective) that can be flexibly used and titrated in the service of patients' presenting psychopathology.

Predicting EEG responses using MEG sources in superior temporal gyrus reveals source asynchrony in patients with schizophrenia

OBJECTIVE

An integrated analysis using Electroencephalography (EEG) and magnetoencephalography (MEG) is introduced to study abnormalities in early cortical responses to auditory stimuli in schizophrenia.

METHODS

Auditory responses were recorded simultaneously using EEG and MEG from 20 patients with schizophrenia and 19 control subjects. Bilateral superior temporal gyrus (STG) sources and their time courses were obtained using MEG for the 30-100 ms post-stimulus interval. The MEG STG source time courses were used to predict the EEG signal at electrode Cz.

RESULTS

In control subjects, the STG sources predicted the EEG Cz recording very well (97% variance explained). In schizophrenia patients, the STG sources accounted for substantially (86%) and significantly (P<0.0002) less variance. After MEG-derived STG activity was removed from the EEG Cz signal, the residual signal was dominated by 40 Hz activity, an indication that the remaining variance in EEG is probably contributed by other brain generators, rather than by random noise.

CONCLUSIONS

Integrated MEG and EEG analysis can differentiate patients and controls, and suggests a basis for a well established abnormality in the cortical auditory response in schizophrenia, implicating a disorder of functional connectivity in the relationship between STG sources and other brain generators.

Evolutionary perspectives on schizophrenia

The theory of evolution may be relevant to psychiatric disorders. Evolution reflects changes in genes throughout time. Thus, evolutionary forces can shape any phenotype that is genetically rooted and that possesses a long history. Schizophrenia is likely an ancient condition with a substantial genetic component. Since the 1960s, several researchers have applied evolutionary principles to the study of schizophrenia. In general, schizophrenia is either viewed as an evolutionary advantageous condition or as a disadvantageous byproduct of normal brain evolution. This paper reviews major evolutionary explanations--historical and current--that speculate on the possible origins of schizophrenia.

Proton magnetic resonance spectroscopy of the inferior frontal gyrus and thalamus and its relationship to verbal learning task performance in patients with schizophrenia: a preliminary report

Previous research has found frontal lobe involvement in memory impairment in schizophrenia. In the present study, proton magnetic resonance spectroscopy was performed in 13 young patients with schizophrenia and 13 normal control subjects. Spectra were obtained from a voxel of 2 x 2 x 1.5 cm(3) in the bilateral inferior frontal gyrus and thalamus. Subjects were given a verbal learning task and stimulus category repetition (SCR) was calculated from the performance of the task. Significantly reduced N-acetylaspartate (NAA)/choline-containing compounds ratios were found in the left inferior frontal cortex of patients compared with controls. The total number of words recalled by patients was significantly lower than that recalled by controls. In all subjects, SCR scores were positively correlated with NAA/phosphocreatine ratios of the left inferior frontal cortex, which showed a trend towards a decrease in patients. These results support the notion of metabolic abnormalities in the left inferior frontal region related to verbal memory deficits in patients with schizophrenia.

Can brain-imaging studies provide a 'mood stabilizer signature?'

Brain-imaging investigations have attempted to characterize the neurobiological basis of bipolar disorder. Preliminary studies have also focused on in vivo brain correlates of treatment response with antidepressants, mood stabilizers and other psychotropic medications. A MEDLINE literature search was conducted dating back to 1966. Selected in vivo brain-imaging studies that examined neurobiological correlates of treatment response in mood disorder patients were identified. Discrete anatomical abnormalities in subregions of the prefrontal cortex, medial temporal lobe and cerebellum have been identified in bipolar patients. Functional imaging studies suggested abnormalities in particular brain circuits encompassing these same brain regions and the striatum. However, functional imaging correlates of treatment response with lithium or other mood stabilizers have not yet been characterized. Neurochemical studies suggested a reduction in N-acetyl aspartate levels in prefrontal cortex and abnormalities in membrane phospholipids in frontal and temporal lobes. Preliminary findings suggest that lithium may increase the gray matter content and N-acetyl aspartate levels in various cortical regions, which could reflect its putative neurotrophic effects. Few in vivo receptor-imaging studies have examined brain correlates of treatment response in bipolar patients. The available studies suggest anatomical, neurochemical and functional brain abnormalities in bipolar patients. However, in vivo brain correlates of treatment response with mood stabilizers in bipolar patients have not yet been well characterized.

Functional brain mapping of psychopathology

In this paper, we consider the impact that the novel functional neuroimaging techniques may have upon psychiatric illness. Functional neuroimaging has rapidly developed as a powerful tool in cognitive neuroscience and, in recent years, has seen widespread application in psychiatry. Although such studies have produced evidence for abnormal patterns of brain response in association with some pathological conditions, the core pathophysiologies remain unresolved. Although imaging techniques provide an unprecedented opportunity for investigation of physiological function of the living human brain, there are fundamental questions and assumptions which remain to be addressed. In this review we examine these conceptual issues under three broad sections: (1) characterising the clinical population of interest, (2) defining appropriate levels of description of normal brain function, and (3) relating these models to pathophysiological conditions. Parallel advances in each of these questions will be required before imaging techniques can impact on clinical decisions in psychiatry.

Could stress cause psychosis in individuals vulnerable to schizophrenia?

It has long been considered that psychosocial stress plays a role in the expression of symptoms in schizophrenia (SZ), as it interacts with latent neural vulnerability that stems from genetic liability and early environmental insult. Advances in the understanding of the neurobiology of the stress cascade in both animal and human studies lead to a plausible model by which this interaction may occur: through neurotoxic effects on the hippocampus that may involve synaptic remodeling. Of late, the neurodevelopmental model of SZ etiology has been favored. But an elaboration of this schema that credits the impact of postnatal events and considers a role for neurodegenerative changes may be more plausible, given the evidence for gene-environment interaction in SZ expression and progressive structural changes observed with magnetic resonance imaging. Furthermore, new insights into nongliotic neurotoxic effects such as apoptosis, failure of neurogenesis, and changes in circuitry lead to an expansion of the time frame in which environmental effects may mediate expression of SZ symptoms.

Diffusion tensor imaging (DTI) and proton magnetic resonance spectroscopy (1H MRS) in schizophrenic subjects and normal controls

Several proton magnetic resonance spectroscopy (1H MRS) studies in schizophrenia have found reduced N-acetyl aspartate (NAA) concentrations in pre-frontal and temporal regions of the brain. Reductions in NAA may reflect abnormalities of neuronal structure (e.g. reduced neuronal density or viability) or abnormalities of neuronal function. Diffusion tensor imaging (DTI) measures diffusion anisotropy, an indicator of the structural integrity of a neuronal tract. Both techniques were used to examine the anatomical basis of pre-frontal dysfunction in schizophrenia. Ten patients with DSM-IV schizophrenia were compared with 10 healthy controls. 1H MRS and DTI were performed on a clinical MR system and analysed with a region of interest approach. NAA concentrations and diffusion anisotropy were measured in the same pre-frontal white matter region. Diffusion anisotropy was also measured in a control region (occipital white matter). 1H MRS revealed non-significant but consistently reduced NAA concentrations (by 10-15%) in the pre-frontal white matter in schizophrenic subjects. Diffusion anisotropy measures revealed no such differences between schizophrenics and controls. It is concluded that the abnormalities of 'connectivity' reported in brain-imaging studies of schizophrenia may not be attributable to structural abnormalities of white matter and that reduced NAA in the pre-frontal white matter may reflect abnormal function of structurally intact neurons.

Reproducibility of in vivo brain measures of 5-HT2A receptors with PET and

The test/retest reproducibility of brain measures of 5-HT2A receptors with positron emission tomography (PET) and [18F]deuteroaltanserin was examined in a group of eight healthy human subjects. PET measures of 5-HT2A receptors were obtained under an equilibrium paradigm, with a 40-min PET acquisition starting approximately at 300 min (308+/-11 min) after bolus plus constant infusion of the radiotracer. Three brain outcome measures were obtained at equilibrium, V(3) (ratio of specific brain uptake to free parent plasma concentration of radiotracer), V(3)' (ratio of specific brain uptake to total parent plasma concentration) and RT (ratio of specific to non-displaceable brain uptakes). V(3)' and RT had high test/retest reproducibility, as measured by mean intra-subject% change for cortical brain areas of 14.1 and 11.0%, respectively. They also had high reliability, as measured by mean intra-class correlation coefficients (ICC) for cortical brain areas of 0.86 and 0.88, respectively. V(3) had low test/retest reproducibility, due to high variability in the measures of free parent tracer in plasma. This study supports the feasibility of equilibrium imaging of 5-HT2A receptors with PET and [18F]deuteroaltanserin. The equilibrium imaging method with [18F]deuteroaltanserin allows a single acquisition and blood measurement to provide an image whose pixel values equal a receptor volume of distribution. Since the single image pixel values are proportional to receptor densities, the images can be used in pixel-by-pixel statistical methods, such as SPM, to assess the distribution and density of 5-HT2A receptors in neuropsychiatric disorders.

Functional connectivity and working memory in schizophrenia: an EEG study

A leading hypothesis suggests that schizophrenic patients suffer from a disconnection syndrome. A failure in functional connectivity curtails the cortical integration and network activation needed to perform working memory tasks. Simulations with neural network models also indicate that connectivity is crucial for simulation of working memory asks. Multichannel EEG correlation-coefficient estimations are considered as a reliable measurement of connectivity patterns among cortical regions. In this study EEG samples are obtained selectively at the delay epochs of a delayed response working memory task. Results of correlation-coefficient estimations indicate a lack of statistically significant changes between non-task and task conditions in frontal, certain parietal, temporal and central channels. These findings propose that schizophrenics probably "fail" to activate the neural networks of the fronto-temporal regions. These are the networks involved in computation of the working memory task. Interestingly also good performers schizophrenics failed to activate these networks suggesting that the connectivity function is more relevant to the disorder than to task performance. If distinct deficits in cortical network activations would correlate with mental disorders it would be relevant to diagnosis and treatment of psychiatric disorders.

Reduction of latent inhibition by D-amphetamine in a conditioned suppression paradigm in humans

The sensitivity of latent inhibition (LI) to amphetamine has been tested in humans with a paradigm close to the conditioned emotional response suppression currently used in experimental animals. The conditioned stimulus (CS) was a tone, the unconditioned stimulus (US) a strong white noise, and the response a transient delay in a regular sequence of hand movements in the resolution of the Tower of Toronto puzzle. The aim of this study was to verify whether the previously reported, disruptive effect of CS preexposure on conditioning really represents LI, by examining its sensitivity to amphetamine. Three groups of healthy volunteers received placebo, 5 or 10 mg of dexamphetamine sulphate, respectively, in a double-blind experimental design. The preexposure, conditioning and test phases were carried out under either amphetamine or placebo. The non preexposed groups treated with amphetamine were not different from the non preexposed placebo group, indicating that amphetamine did not affect conditioning. Among the preexposed groups, those receiving 10 mg of amphetamine showed normal rates of conditioning, whereas those treated with either 5 mg of amphetamine or placebo showed LI. Similar results have been reported in experimental animals. This sensitivity to amphetamine suggests that the present paradigm may be used to study LI in humans.

Postmortem studies in schizophrenia

For over a century, postmortem studies have played a central part in the search for the structural and biochemical pathology of schizophrenia. However, for most of this time, little progress has been made. Recently, the situation has begun to change, helped by the emergence of more powerful methodologies and research designs, and by the availability of brain imaging to provide complementary information. As a result, it can now be clearly concluded that there are structural cerebral abnormalities in schizophrenia that are intrinsic to the disorder. The neuropathological process is not primarily degenerative, but involves a change in the normal cytoarchitecture of the brain, probably originating in development. Neurochemically, there is postmortem evidence for alterations in several transmitter systems including dopamine, glutamate, serotonin, and γ-aminobutyric acid (GABA). The cardinal findings are reviewed here, together with a consideration of the conceptual and methodological issues that face postmortem studies of schizophrenia.

Quantitation of striatal and extrastriatal D-2 dopamine receptors using PET imaging of [(18)F]fallypride in nonhuman primates

[(18)F]Fallypride is a highly selective, high-affinity dopamine D-2 receptor ligand. The high affinity, K(D) = 30 pM, makes it a suitable candidate for visualizing both striatal and extrastriatal binding in the brain. In this work, dynamic PET studies of two macaque monkeys were acquired along with arterial plasma samples. Compartmental analysis and Logan plots were used to analyze the striatum, thalamus, frontal, and temporal cortices and to validate a reference region of analysis which yields a distribution volume ratio (DVR). The cerebellum was used as the reference region. The results indicate that all methods of analysis are in close agreement over all the analyzed regions in the brain. The average DVRs for the two monkeys was found to be: caudate = 26, putamen = 29, thalamus = 3.8, frontal ctx = 1.7, and temporal ctx = 1.7 on a high-resolution PET scanner. It was found that a scan time of 2 h is needed to accurately estimate the DVR for all regions of the brain. The striatal regions require the longest to linearize and are the most sensitive to variations in the average tissue-to-plasma efflux constant, k(2). For the extrastriatal regions, the effect of the k(2) term on DVR calculation is negligible. Repeatability measurements for all regions were found to be within 10% using the DVR parameter.

Dopamine and serotonin transporters in patients with schizophrenia: an imaging study with [(123)I]beta-CIT

BACKGROUND

Several lines of evidence derived from imaging and postmortem studies suggest that schizophrenia is associated with hyperactivity of dopamine function and deficiency in serotonin (5-HT) function. The aim of this study was to investigate potential alterations of striatal dopamine transporters (DAT) and brainstem serotonin transporters (SERT) density in schizophrenia.

METHODS

Striatal DAT and brainstem SERT were measured in 24 patients with schizophrenia and 22 matched healthy control subjects using single photon emission computed tomography and [(123)I]beta-CIT. In this cohort of subjects, we previously reported an increase in striatal amphetamine-induced dopamine release, measured as the displacement of the D(2) receptor radiotracer [(123)I]IBZM.

RESULTS

No differences were observed between patients and control subjects in the equilibrium uptake ratio (V(3)") of [(123)I]beta-CIT in the striatum, indicating that schizophrenia is not generally associated with an alteration of striatal DAT density; however, a trend level association (p =.07) was observed in patients with schizophrenia between low striatal [(123)I]beta-CIT V(3)" and severity of negative symptoms. After controlling for age, striatal [(123)I]beta-CIT V(3)" in patients was not associated with duration of illness, suggesting that this relative deficit was not secondary to a neurodegenerative process. No correlation was observed between DAT density and amphetamine-induced dopamine release, either in the patients or in the controls. Brainstem [(123)I]beta-CIT V(3)" was unaffected in patients with schizophrenia, and was unrelated to symptomatology.

CONCLUSIONS

Schizophrenia is generally not associated with alterations of DAT in the striatum or SERT in the brainstem. In some patients, a relative deficit in dopamine nerve terminals might play a role in the pathophysiology of negative symptoms.