Genes, dopamine and cortical signal-to-noise ratio in schizophrenia

Dysfunctional and compensatory prefrontal cortical systems, genes and the pathogenesis of schizophrenia

Cognitive deficits are critical determinants of schizophrenia morbidity. In this review, we offer a mechanistic perspective regarding schizophrenia-related changes observed in prefrontal cortical networks engaged in working memory. A body of earlier work converges on aberrations in putative macrocircuit stability and functional efficiency as the underlying pathophysiology of the cognitive deficits in schizophrenia. In parsing the dysfunctional prefrontal cortical dynamics of schizophrenia, recent functional magnetic resonance imaging and electoencephalography works suggest that in the context of reduced capacity for executive aspects of working memory, patients engage a larger network of cortical regions consistent with an interplay between reduced signal-to-noise components and the recruitment of compensatory networks. The genetic programming underlying these systems-level cortical interactions has been examined under the lens of certain schizophrenia susceptibility genes, especially catechol-o-methyltransferase (COMT) and GRM3. Variation in COMT, which presumably impacts on cortical dopamine signaling, translates into variable neural strategies for working memory and altering patterns of intracortical functional correlations. GRM3, which impacts on synaptic glutamate, interacts with COMT and exaggerates the genetic dissection of cortical processing strategies. These findings reveal novel insights into the modulation and parcellation of working memory processing in cortical assemblies and provide a mechanistic link between susceptibility genes and cortical pathophysiology related to schizophrenia.

Evidence that the BLOC-1 protein dysbindin modulates dopamine D2 receptor internalization and signaling but not D1 internalization

The schizophrenia susceptibility gene dystrobrevin-binding protein 1 (DTNBP1) encodes dysbindin, which along with its binding partner Muted is an essential component of the biogenesis of lysosome-related organelles complex 1 (BLOC-1). Dysbindin expression is reduced in schizophrenic brain tissue, but the molecular mechanisms by which this contributes to pathogenesis and symptomatology are unknown. We studied the effects of transfection of DTNBP1 siRNA on cell surface levels of dopamine D2 receptor (DRD2) in human SH-SY5Y neuroblastoma cells and in rat primary cortical neurons. DTNBP1 siRNA decreased dysbindin protein, increased cell surface DRD2 and blocked dopamine-induced DRD2 internalization. MUTED siRNA produced similar effects. In contrast, decreased dysbindin did not change dopamine D1 receptor (DRD1) levels, or its basal or dopamine-induced internalization. The DRD2 agonist quinpirole reduced phosphorylation of CREB (cAMP response element-binding protein) in dysbindin downregulated cells, demonstrating enhanced intracellular signaling caused by the upregulation of DRD2. This is the first demonstration of a schizophrenia susceptibility gene exerting a functional effect on DRD2 signaling, a pathway that has long been implicated in the illness. We propose a molecular mechanism for pathogenesis in which risk alleles in DTNBP1, or other factors that also downregulate dysbindin, compromise the ability of BLOC-1 to traffic DRD2 toward degradation, but has little effect on DRD1 trafficking. Impaired trafficking of DRD2 decreases dopamine-induced internalization, and with more receptors retained on the cell surface, dopamine stimulation produces excess intracellular signaling. Such an increase in DRD2 signaling relative to DRD1 would contribute to the imbalances in dopaminergic neurotransmission characteristic of schizophrenia.

Association analysis of exon III and exon I polymorphisms of the dopamine D4 receptor locus in Mexican psychotic patients

In this study, we investigated whether polymorphisms of the dopamine D4 receptor (DRD4) gene were associated with psychotic symptomatology rather than with a unique diagnosis such as schizophrenia. A number of association studies between the DRD4 gene 48 bp-VNTR polymorphism at exon 3 and psychotic disorders have been reported, but the results have been controversial. Both 48 bp-VNTR and the 12 bp-VNTR (at exon 1) polymorphisms of this gene were analyzed in a group of 149 unrelated Mexican subjects with a diagnosis of schizophrenia, schizoaffective disorder, schizophreniform disorder, major depression and bipolar disorder, both with psychotic symptoms, brief psychotic disorder, delusional disorder and non-specific psychotic disorder, and in 169 individuals free of psychiatric illnesses. There were no differences in allele or genotype frequencies between groups for the 12 bp-VNTR polymorphisms. However, a significant excess of "rare" alleles (3-, 5-, 6- and 8-48 bp repeats alleles) was found in the group of psychotics. Moreover, haplotypes 3-A1, 5-A1, 6-A1 and 8-A1 were significantly more frequently associated with cases. This positive association supports a role of this molecule as a genetic risk factor in psychotic disorders.

The neural correlates of implicit sequence learning in schizophrenia

Twenty-seven schizophrenia spectrum patients and 25 healthy controls performed a probabilistic version of the serial reaction time task (SRT) that included sequence trials embedded within random trials. Patients showed diminished, yet measurable, sequence learning. Postexperimental analyses revealed that a group of patients performed above chance when generating short spans of the sequence. This high-generation group showed SRT learning that was similar in magnitude to that of controls. Their learning was evident from the very 1st block; however, unlike controls, learning did not develop further with continued testing. A subset of 12 patients and 11 controls performed the SRT in conjunction with positron emission tomography. High-generation performance, which corresponded to SRT learning in patients, correlated to activity in the premotor cortex and parahippocampus. These areas have been associated with stimulus-driven visuospatial processing. Taken together, these results suggest that a subset of patients who showed moderate success on the SRT used an explicit stimulus-driven strategy to process the sequential stimuli. This adaptive strategy facilitated sequence learning but may have interfered with conventional implicit learning of the overall stimulus pattern.

Neurotech for neuroscience: unifying concepts, organizing principles, and emerging tools

The ability to tackle analysis of the brain at multiple levels simultaneously is emerging from rapid methodological developments. The classical research strategies of "measure," "model," and "make" are being applied to the exploration of nervous system function. These include novel conceptual and theoretical approaches, creative use of mathematical modeling, and attempts to build brain-like devices and systems, as well as other developments including instrumentation and statistical modeling (not covered here). Increasingly, these efforts require teams of scientists from a variety of traditional scientific disciplines to work together. The potential of such efforts for understanding directed motor movement, emergence of cognitive function from neuronal activity, and development of neuromimetic computers are described by a team that includes individuals experienced in behavior and neuroscience, mathematics, and engineering. Funding agencies, including the National Science Foundation, explore the potential of these changing frontiers of research for developing research policies and long-term planning.

Dopamine modulation of hippocampal-prefrontal cortical interaction drives memory-guided behavior

Information gleaned from learning and memory processes is essential in guiding behavior toward a specific goal. However, the neural mechanisms that determine how these processes are effectively utilized to guide goal-directed behavior are unknown. Here, we show that rats utilize retrospective and prospective memory and flexible switching between these 2 memory processes to guide behaviors to obtain rewards. We found that retrospective memory is mainly processed in the hippocampus (HPC) but that this retrospective information must be incorporated within the prefrontal cortex (PFC) to be used to switch to an anticipatory response strategy involving prospective memory. Furthermore, switching between memory processes is regulated by the mesocortical dopamine (DA) system. Thus, DA D1 and D2 receptor activation in the PFC differentially affects retrospective memory processing within the HPC via an indirect feedback pathway. In contrast, D1, but not D2, receptor activation is crucial for incorporation of HPC-based retrospective information into the PFC. However, once this takes place, D2 receptor activation is required for further processing of information to effect preparation of future actions. These results provide a unique perspective on the mechanism of memory-based goal-directed behavior.

On the hypes and falls in neuroprotection: targeting the NMDA receptor

Activation of the NMDA (N-methyl-D-aspartate) responsive subclass of glutamate receptors is an important mechanism of excitatory synaptic transmission. Moreover, NMDA receptors are widely involved in many forms of synaptic plasticity such as long-term potentiation (LTP) and long-term depression (LTD), which are thought to underlie complex tasks, including learning and memory. Dysfunction of these ligand-gated cation channels has been identified as an underlying molecular mechanism in neurological disorders ranging from acute stroke to chronic neurodegeneration in amyotrophic lateral sclerosis. Excessive glutamate levels have been detected following brain trauma and cerebral ischemia, resulting in an unregulated stimulation of NMDA receptors. These conditions are thought to elicit a cascade of excitation-mediated neuronal damage where massive increases in intracellular calcium concentrations finally trigger neuronal damage and apoptosis. Consistent with the hypothesis of NMDA receptors as essential mediators of excitotoxicity, the different functional domains of these ion channels have been identified as potential targets for neuroprotective agents. Following an initial hype on potential NMDA receptor therapeutics, the authors currently see a period of skepticism that, in reverse, appears to neglect the therapeutic potential of this receptor class. This review attempts a reappraisal of this important class of neurotransmitter receptors, with a focus on NMDA receptor heterogeneity, ligand binding domains, and candidate diseases for a potential neuroprotective therapy.

Effect of catechol O-methyltransferase val(158)met polymorphism on the p50 gating endophenotype in schizophrenia

BACKGROUND

Studies have implicated prefrontal dopamine in cortical information filtering. Deficit in stimulus filtering, an endophenotype of schizophrenia, can be demonstrated using the auditory P50 paired-click gating paradigm. The role of prefrontal dopamine on P50 gating was investigated, using catechol-O-methyltransferase (COMT) valine (val)(158)methionine (met) polymorphism as a predictor of prefrontal dopamine activity.

METHODS

Twenty-five comparison and 42 schizophrenia subjects underwent P50 gating measurement and COMT genotyping.

RESULTS

In the combined sample, COMT polymorphism accounted for a unique 10% of gating variance (p = .02), after variance due to diagnosis, smoking status, and antipsychotic use was removed. Valine homozygous individuals exhibited the greatest gating deficit.

CONCLUSIONS

Valine homozygous individuals are more likely to have gating deficits, supporting COMT as a genetic determinant of the P50 endophenotype, as well as a role for prefrontal dopamine in auditory filtering.

5-HT6 receptor antagonist reversal of emotional learning and prepulse inhibition deficits induced by apomorphine or scopolamine

5-HT6 receptors have been implicated in consolidation of visuospatial and reward-based learning tasks. Since 5-HT6 receptors may be important in modulation of sensory gating which is often affected in schizophrenic patients, we tested whether Ro 4368554, a 5-HT6 selective antagonist at a dose of 10 mg/kg, could reverse the loss of prepulse inhibition from apomorphine or scopolamine. In addition, we also tested whether Ro 4368554 altered fear conditioning using fear potentiated startle, a model for emotional learning. Prepulse inhibition of startle was disrupted by apomorphine (0.5 mg/kg) when prepulse emissions were 5 dB above background but not above 15 dB, while scopolamine (0.5 mg/kg) caused disruption at both prepulse levels. Scopolamine-mediated disruption was not reversed by Ro 4368854 but apomorphine-mediated disruption was significantly ameliorated by 5-HT6 inhibition. For fear potentiated startle, scopolamine and/or Ro 4368554 were administered before two daily fear conditioning sessions; rats were tested on the following day. Rats that received scopolamine displayed no fear potentiated startle but Ro 4368554 reversed this scopolamine deficit. Additionally, we mapped Fos induction in rats treated with scopolamine and/or Ro 4368554; scopolamine increased Fos expression in the central nucleus of the amygdala and this was attenuated by Ro 4368554. In summary, we have demonstrated the efficacy of 5-HT6 antagonists in modulating sensory gating and fear conditioning, and thus may be of therapeutic use for schizophrenia-related disorders.

Antipsychotic drugs reverse the disruption in prefrontal cortex function produced by NMDA receptor blockade with phencyclidine

NMDA receptor (NMDA-R) antagonists are extensively used as schizophrenia models because of their ability to evoke positive and negative symptoms as well as cognitive deficits similar to those of the illness. Cognitive deficits in schizophrenia are associated with prefrontal cortex (PFC) abnormalities. These deficits are of particular interest because an early improvement in cognitive performance predicts a better long-term clinical outcome. Here, we examined the effect of the noncompetitive NMDA-R antagonist phencyclidine (PCP) on PFC function to understand the cellular and network elements involved in its schizomimetic actions. PCP induces a marked disruption of the activity of the PFC in the rat, increasing and decreasing the activity of 45% and 33% of the pyramidal neurons recorded, respectively (22% of the neurons were unaffected). Concurrently, PCP markedly reduced cortical synchrony in the delta frequency range (0.3-4 Hz) as assessed by recording local field potentials. The subsequent administration of the antipsychotic drugs haloperidol and clozapine reversed PCP effects on pyramidal cell firing and cortical synchronization. PCP increased c-fos expression in PFC pyramidal neurons, an effect prevented by the administration of clozapine. PCP also enhanced c-fos expression in the centromedial and mediodorsal (but not reticular) nuclei of the thalamus, suggesting the participation of enhanced thalamocortical excitatory inputs. These results shed light on the involvement of PFC in the schizomimetic action of NMDA-R antagonists and show that antipsychotic drugs may partly exert their therapeutic effect by normalizing a disrupted PFC activity, an effect that may add to subcortical dopamine receptor blockade.

Treatment of cognitive deficits associated with schizophrenia: potential role of catechol-O-methyltransferase inhibitors

In the last two decades, understanding of the dynamics of dopamine function in the prefrontal cortex and its role in prefrontal cortex physiology has opened up new avenues for therapeutic interventions in conditions in which prefrontal cortex function is compromised. Neuropsychological and imaging studies of prefrontal information processing have confirmed specific cognitive and neurophysiological abnormalities in individuals with schizophrenia. Because such findings are also observed in the healthy siblings of patients with schizophrenia, they may represent intermediate phenotypes related to schizophrenia susceptibility genes.Catechol-O-methyltransferase (COMT) represents an important candidate as a susceptibility gene for cognitive dysfunction in schizophrenia because of the unique role this enzyme plays in regulating prefrontal dopaminergic function. A functional COMT polymorphism (Val158Met) predicts performance in tasks of prefrontal executive function and the neurophysiological response measured with electroencephalography and functional magnetic resonance imaging in tasks assessing working memory. In fact, individuals with the Val/Val genotype, which encodes for the high-activity enzyme resulting in lower dopamine concentrations in the prefrontal cortex, perform less well and are less efficient physiologically than Met/Met individuals. These findings raise the possibility of new pharmacological interventions for the treatment of prefrontal cortex dysfunction and of predicting outcome based on COMT genotype. One strategy consists of the use of CNS-penetrant COMT inhibitors such as tolcapone. A second strategy is to increase extracellular dopamine concentrations in the frontal cortex by blocking the noradrenaline (norepinephrine) reuptake system, a secondary mechanism responsible for the disposal of dopamine from synaptic clefts in the prefrontal cortex. A third possibility involves the use of modafinil, a drug with an unclear mechanism of action but with positive effects on working memory in rodents. The potential of these drugs to improve executive cognitive function by selectively increasing dopamine load in the frontal cortex but not in subcortical territories, and the possibility that response to them may be modified by a COMT polymorphism, provides a novel genotype-based targeted pharmacological approach without abuse potential for the treatment of cognitive disorder in schizophrenia and in other conditions involving prefrontal cortex dysfunction.

Sp1 expression is disrupted in schizophrenia; a possible mechanism for the abnormal expression of mitochondrial complex I genes, NDUFV1 and NDUFV2

BACKGROUND

The prevailing hypothesis regards schizophrenia as a polygenic disease, in which multiple genes combine with each other and with environmental stimuli to produce the variance of its clinical symptoms. We investigated whether the ubiquitous transcription factor Sp1 is abnormally expressed in schizophrenia, and consequently can affect the expression of genes implicated in this disorder.

METHODOLOGY/PRINCIPAL FINDINGS

mRNA of Sp1 and of mitochondrial complex I subunits (NDUFV1, NDUFV2) was analyzed in three postmortem brain regions obtained from the Stanley Foundation Brain Collection, and in lymphocytes of schizophrenic patients and controls. Sp1 role in the transcription of these genes was studied as well. Sp1 was abnormally expressed in schizophrenia in both brain and periphery. Its mRNA alteration pattern paralleled that of NDUFV1 and NDUFV2, decreasing in the prefrontal cortex and the striatum, while increasing in the parieto-occipital cortex and in lymphocytes of schizophrenic patients as compared with controls. Moreover, a high and significant correlation between these genes existed in normal subjects, but was distorted in patients. Sp1 role in the regulation of complex I subunits, was demonstrated by the ability of the Sp1/DNA binding inhibitor, mithramycin, to inhibit the transcription of NDUFV1 and NDUFV2, in neuroblastoma cells. In addition, Sp1 activated NDUFV2 promoter by binding to its three GC-boxes. Both activation and binding were inhibited by mithramycin.

CONCLUSIONS/SIGNIFICANCE

These findings suggest that abnormality in Sp1, which can be the main activator/repressor or act in combination with additional transcription factors and is subjected to environmental stimuli, can contribute to the polygenic and clinically heterogeneous nature of schizophrenia.

Disrupted prediction-error signal in psychosis: evidence for an associative account of delusions

Delusions are maladaptive beliefs about the world. Based upon experimental evidence that prediction error-a mismatch between expectancy and outcome--drives belief formation, this study examined the possibility that delusions form because of disrupted prediction--error processing. We used fMRI to determine prediction-error-related brain responses in 12 healthy subjects and 12 individuals (7 males) with delusional beliefs. Frontal cortex responses in the patient group were suggestive of disrupted prediction-error processing. Furthermore, across subjects, the extent of disruption was significantly related to an individual's propensity to delusion formation. Our results support a neurobiological theory of delusion formation that implicates aberrant prediction-error signalling, disrupted attentional allocation and associative learning in the formation of delusional beliefs.

Allelic variation in GAD1 (GAD67) is associated with schizophrenia and influences cortical function and gene expression

Cortical GABAergic dysfunction has been implicated as a key component of the pathophysiology of schizophrenia and decreased expression of the gamma-aminobutyric acid (GABA) synthetic enzyme glutamic acid decarboxylase 67 (GAD(67)), encoded by GAD1, is found in schizophrenic post-mortem brain. We report evidence of distorted transmission of single-nucleotide polymorphism (SNP) alleles in two independent schizophrenia family-based samples. In both samples, allelic association was dependent on the gender of the affected offspring, and in the Clinical Brain Disorders Branch/National Institute of Mental Health (CBDB/NIMH) sample it was also dependent on catechol-O-methyltransferase (COMT) Val158Met genotype. Quantitative transmission disequilibrium test analyses revealed that variation in GAD1 influenced multiple domains of cognition, including declarative memory, attention and working memory. A 5' flanking SNP affecting cognition in the families was also associated in unrelated healthy individuals with inefficient BOLD functional magnetic resonance imaging activation of dorsal prefrontal cortex (PFC) during a working memory task, a physiologic phenotype associated with schizophrenia and altered cortical inhibition. In addition, a SNP in the 5' untranslated (and predicted promoter) region that also influenced cognition was associated with decreased expression of GAD1 mRNA in the PFC of schizophrenic brain. Finally, we observed evidence of statistical epistasis between two SNPs in COMT and SNPs in GAD1, suggesting a potential biological synergism leading to increased risk. These coincident results implicate GAD1 in the etiology of schizophrenia and suggest that the mechanism involves altered cortical GABA inhibitory activity, perhaps modulated by dopaminergic function.

Dopamine modulation of prefrontal cortex interneurons occurs independently of DARPP-32

Dopamine (DA) exerts a strong influence on inhibition in prefrontal cortex. The main cortical interneuron subtype targeted by DA are fast-spiking gamma-aminobutyric acidergic (GABAergic) cells that express the calcium-binding protein parvalbumin. D1 stimulation depolarizes these interneurons and increases excitability evoked by current injection. The present study examined whether this direct DA-dependent modulation of fast-spiking interneurons involves DARPP-32. Whole-cell patch-clamp recordings were made from fast-spiking interneurons in brain slices from DARPP-32 knockout (KO) mice, wild-type mice, and rats. Low concentrations of DA (100 nM) increased interneuron excitability via D1 receptors, protein kinase A, and cyclic adenosine 3',5'-monophosphate in slices from both normal and DARPP-32 KO mice. Immunohistochemical staining of slices from normal animals revealed a lack of colocalization of DARPP-32 with calcium-binding proteins selective for fast-spiking interneurons, indicating that these interneurons do not express DARPP-32. Therefore, although DARPP-32 impacts cortical inhibition through a previously demonstrated D2-dependent regulation of GABAergic currents in pyramidal cells, it is not involved in the direct D1-mediated regulation of fast-spiking interneurons.

Reduction of corticostriatal glutamatergic fibers in basic fibroblast growth factor deficient mice is associated with hyperactivity and enhanced dopaminergic transmission

BACKGROUND

Basic fibroblast growth factor (FGF2) plays a crucial role during the development of the cerebral cortex. Mice with a knockout of the FGF2 gene have a reduced number of glutamatergic neurons within the deep layers of the cerebral cortex.

METHODS

We used molecular and behavioral analyses to investigate possible alterations in corticostriatal function in FGF2 -/- mice.

RESULTS

We found that FGF2 deficiency leads to decreased expression of presynaptic markers of integrity for glutamatergic fibers in the striatum, namely the membrane excitatory amino acid transporter 3 (EAAT3) and the vesicular glutamate transporter 1 (VGLUT1). The reduction of corticostriatal glutamatergic function in FGF2 -/- mice is associated with enhanced locomotor activity in a novel environment and increased responsiveness to dopaminergic drugs, such as cocaine or amphetamine. The behavioral alterations of FGF2 -/- can be normalized by injection of a low dose of the dopaminergic agonist apomorphine (.1 mg/kg) that reduces dopamine release by acting on presynaptic receptors.

CONCLUSIONS

Our data demonstrate that FGF2 -/- mice have an increased tone and responsiveness of the dopaminergic system and suggest that these animals might represent a model to study disorders that are characterized by an imbalance between glutamatergic and dopaminergic neurotransmission.

EphB1 null mice exhibit neuronal loss in substantia nigra pars reticulata and spontaneous locomotor hyperactivity

The molecular mechanisms that regulate basal ganglia development are largely unknown. Eph receptor tyrosine kinases are potential participants in this process as they regulate development of other CNS regions and are expressed in basal ganglia nuclei, such as the substantia nigra (SN) and striatum. To address the role of Eph receptors in the development of these nuclei, we analysed anatomical changes in the SN and striatum of mice with null mutations for EphB1. These mice express beta-galactosidase as a marker for cells normally expressing EphB1. In situ hybridization data and a direct comparison of SN neurons expressing tyrosine hydroxylase (TH) and/or the beta-gal marker for EphB1 revealed that EphB1 is not expressed in TH+ neurons of pars compacta (SNc), but is restricted to neurons in pars reticulata (SNr). Consistent with this, we find that EphB1 null mice exhibit a significant decrease in the volume and number of neurons (40% decrease) in SNr, whereas the volume and number of TH+ neurons in SNc is not significantly affected nor are there changes in the distribution of nigrostriatal dopamine neurons. Although EphB1 is expressed in the striatum, EphB1-/- mice exhibit no significant changes in striatal volume and TH fiber density, and have no obvious alterations in striatal patch/matrix organization. Behavioral evaluation of EphB1 null mice in an open-field environment revealed that these mice exhibited spontaneous locomotor hyperactivity. These results suggest that EphB1 is necessary for the proper formation of SNr, and that neuronal loss in SNr is associated with altered locomotor functions.

Epistasis between catechol-O-methyltransferase and type II metabotropic glutamate receptor 3 genes on working memory brain function

Dopaminergic and glutamatergic systems are critical components responsible for prefrontal signal-to-noise tuning in working memory. Recent functional MRI (fMRI) studies of genetic variation in these systems in catechol-O-methyltransferase (COMT) and in metabotropic glutamate receptor mgluR3 (GRM3), respectively, suggest that these genes influence prefrontal physiological signal-to-noise in humans. Here, using fMRI, we extend these individual gene findings to examine the combined effects of COMT and GRM3 on dissociable components of the frontoparietal working memory network. We observed an apparent epistatic interaction of these two genes on the engagement of prefrontal cortex during working memory. Specifically, the GRM3 genotype putatively associated with suboptimal glutamatergic signaling was significantly associated with inefficient prefrontal engagement and altered prefrontal-parietal coupling on the background of COMT Val-homozygous genotype. Conversely, COMT Met-homozygous background mediated against the effect of GRM3 genotype. These findings extend putative brain dopaminergic and glutamatergic relationships indexed by COMT and GRM3 to a systems-level interaction in human cortical circuits implicated in working memory dysfunction such as in schizophrenia.

Developmental profile of neuregulin receptor ErbB4 in postnatal rat cerebral cortex and hippocampus

We investigated the cellular and subcellular distributions of neuregulin tyrosine kinase receptor ErbB4 in the postnatal rat frontal cortex and hippocampus by light-, confocal- and electron-microscopic immunocytochemistry. At birth, ErbB4-immunoreactivity (ErbB4-IR) was prominent in the apical cytoplasm and dendrites of cortical plate neurons and hippocampal pyramidal cells. Throughout postnatal development and in adulthood, ErbB4-IR in both regions remained confined to the somatodendritic compartment of neurons, which increased in number to reach the adult pattern by the end of the first postnatal month (P30). At all ages examined, double-labeling experiments revealed that ErbB4-IR always co-localized with the neuronal marker neuronal nuclei (NeuN) and never with glial markers Nestin or glial fibrillary acidic protein (GFAP). Immunoperoxidase labeling at the ultrastructural level confirmed the exclusive localization of ErbB4-IR in somatodendrites, and notably in dendritic spines. Immunogold labeling showed preponderant ErbB4-IR in the cytoplasm, where it was associated with microtubules. Furthermore, ErbB4-IR was abundant in the nucleus of adult cortical and hippocampal neurons, suggesting a role for ErbB4 nuclear signaling in the brain beyond embryonic development. Taken together, these results show that ErbB4 is expressed by neuronal somatodendrites in cerebral cortex and hippocampus from birth to adulthood, and support a role for neuregulins in dendritic growth and plasticity.

The met(158) allele of catechol-O-methyltransferase (COMT) is associated with obsessive-compulsive disorder in men: case-control study and meta-analysis

Existing data suggest a genetic association between the met(158) allele of catechol-O-methyltransferase (COMT) and obsessive-compulsive disorder (OCD). However, the results are inconclusive and complicated by possible gender differences. We sought to resolve the question in two ways. First, we carried out a new case-control study in 87 adults with OCD and 327 healthy comparison subjects. The study replicated reports of an increased met(158) allele frequency in men with OCD (odds ratio (OR)=1.91, 95% confidence interval (CI) 1.07-3.40, P=0.026), with no effect in women (OR=1.13, 95% CI 0.74-1.72, P=0.56). Second, we performed a meta-analysis of all published case-control data (n=1908 subjects). This revealed an association of COMT met(158) with OCD (OR=1.23, 95% CI 1.06-1.42, P=0.005) and an interaction with gender (z=4.27, P<0.0001). The association between COMT met(158) and OCD was present in men (OR=1.88, 95% CI 1.45-2.44, P<0.001) but not in women (OR=0.98, 95% CI 0.78-1.22, P=0.83). We conclude that COMT may play a role in the genetic aetiology of OCD in men. The biological plausibility of the association is increased by the functionality of the val(158)met polymorphism in terms of its effect on COMT enzyme activity, and by the role of COMT in cortical dopamine signalling and information processing. The finding also extends the evidence for sexual dimorphism in COMT and in OCD.

Which perspectives can endophenotypes and biological markers offer in the early recognition of schizophrenia?

The early recognition of schizophrenia seems crucial; various studies relate a longer duration-of-untreated-psychosis to a worse prognosis. We give an overview over common psychopathological early recognition instruments (BSABS, CAARMS, SIPS, IRAOS, ERIraos). However, many clinical symptoms of prodromal schizophrenia stages are not sufficiently specific. Thus we review recent contributions of neuroimaging and electrophysiological as well as genetic studies: which new diagnostic perspectives offer endophenotypes (such as P300, P50 sensory gating, MMN, smooth pursuit eye movements; indicating a specific genetic vulnerability) together with a better understanding of schizophrenic pathophysiology (state-dependent biological markers, e.g. aggravated motor neurological soft signs during psychosis) in prodromal schizophrenia when still ambiguous clinical symptoms are present. Several examples (e.g. from COMT polymorphisms to working memory deficits) illustrate more specific underlying neuronal mechanisms behind behavioural symptoms. This way, a characteristic pattern of disturbed cerebral maturation might be distinguished in order to complement clinical instruments of early schizophrenia detection.

Do NMDA receptor antagonist models of schizophrenia predict the clinical efficacy of antipsychotic drugs?

N-methyl-D-aspartate (NMDA) receptor antagonists, such as ketamine and phencyclidine, induce perceptual abnormalities, psychosis-like symptoms, and mood changes in healthy humans and patients with schizophrenia. The similarity between NMDA receptor antagonist-induced psychosis and schizophrenia has led to the widespread use of the drugs to provide models to aid the development of novel treatments for the disorder. This review investigates the predictive validity of NMDA receptor antagonist models based on a range of novel treatments that have now reached clinical trials. Furthermore, it considers the extent to which the different hypotheses that have been proposed to account for the psychotomimetic effects of NMDA receptor antagonist have been validated by the results of these trials. Finally, the review discusses some of the caveats associated with use of the models and some suggestions as to how a greater use of translational markers might ensure progress in understanding the relationship between the models and schizophrenia.

Response inhibition and cognitive flexibility in schizophrenia with and without comorbid substance use disorder

Addiction is a frequent comorbid disorder in schizophrenia related to dopaminergic dysfunction in fronto-subcortical circuits. These brain networks are relevant for both (executive) cognition and the neuropathology of schizophrenia. The aim of the present study was to elucidate whether response inhibition and cognitive flexibility - executive abilities relevant for achieving and maintaining abstinence - are differentially impaired in schizophrenia patients with or without comorbid substance use disorder. Patients suffering from major depression or alcoholism as well as healthy controls served as comparison groups. The ability to inhibit predominant response tendencies during response conflict and to efficiently shift the focus of attention between different task requirements was assessed by verbal and non-verbal cognitive tasks. Contrary to expectation, non-addicted schizophrenia patients showed the most pronounced executive function impairments relative to the control groups, affecting both response suppression and cognitive flexibility. Dual diagnosis patients did not differ significantly from non-addicted schizophrenia patients or from the alcoholic group, but were impaired at cognitive flexibility relative to the depression subgroup and healthy controls. Whether the relative preservation of response inhibition and cognitive flexibility in the dual disorder patients is due to high premorbid functioning, beneficial self-medication effects or compensatory brain activation remains to be elucidated. The relatively intact executive abilities in young, addicted schizophrenia patients might represent a beneficial resource for treatment strategies.

Distribution of serotonin 5-HT2C receptors in the ventral tegmental area

Serotonin 2C receptors (5-HT2CR) appear to exert tonic inhibitory influence over dopamine (DA) neurotransmission in the ventral tegmental area (VTA), the origin of the mesolimbic DA system, thought to be important in psychiatric disorders including addiction and schizophrenia. Current literature suggests that the inhibitory influence of 5-HT2CR on DA neurotransmission occurs via indirect activation of GABA inhibitory neurons, rather than via a direct action of 5-HT2CR on DA neurons. The present experiments were performed to establish the distribution of 5-HT2CR protein on DA and GABA neurons in the VTA of male rats via double-label immunofluorescence techniques. The 5-HT2CR protein was found to be co-localized with the GABA synthetic enzyme glutamic acid decarboxylase (GAD), confirming the presence of the 5-HT2CR on GABA neurons within the VTA. The 5-HT2CR immunoreactivity was also present in cells that contained immunoreactivity for tyrosine hydroxylase (TH), the DA synthetic enzyme, validating the localization of 5-HT2CR to DA neurons in the VTA. While the degree of 5-HT2CR+GAD co-localization was similar across the rostro-caudal levels of VTA subnuclei, 5-HT2CR+TH co-localization was highest in the middle relative to rostral and caudal levels of the VTA, particularly in the paranigral, parabrachial, and interfascicular subnuclei. The present results suggest that the inhibitory influence of the 5-HT2CR over DA neurotransmission in the VTA is a multifaceted and complex interplay of 5-HT2CR control of the output of both GABA and DA neurons within this region.

Association between the DTNBP1 gene and intelligence: a case-control study in young patients with schizophrenia and related disorders and unaffected siblings

BACKGROUND

The dystrobrevin-binding protein 1 (DTNBP1) gene is a susceptibility gene for schizophrenia. There is growing evidence that DTNPB1 contributes to intelligence and cognition. In this study, we investigated association between single nucleotide polymorphisms (SNPs) in the DTNBP1 gene and intellectual functioning in patients with a first episode of schizophrenia or related psychotic disorder (first-episode psychosis, FEP), their healthy siblings, and unrelated controls.

METHODS

From all subjects IQ measurements were obtained (verbal IQ [VIQ], performance IQ [PIQ], and full scale IQ [FSIQ]). Seven SNPs in the DTNBP1 gene were genotyped using single base primer extension and analyzed by matrix-assisted laser deionization mass spectrometry (MALDI-TOF).

RESULTS

Mean VIQ, PIQ, and FSIQ scores differed significantly (p < 0.001) between patients, siblings, and controls. Using a family-based and a case-control design, several single SNPs were significantly associated with IQ scores in patients, siblings, and controls.

CONCLUSION

Although preliminary, our results provide evidence for association between the DTNBP1 gene and intelligence in patients with FEP and their unaffected siblings. Genetic variation in the DTNBP1 gene may increase schizophrenia susceptibility by affecting intellectual functioning.

The ability of the mesocortical dopamine system to operate in distinct temporal modes

BACKGROUND

This review discusses evidence that cells in the mesocortical dopamine (DA) system influence information processing in target areas across three distinct temporal domains.

DISCUSSIONS

Phasic bursting of midbrain DA neurons may provide temporally precise information about the mismatch between expected and actual rewards (prediction errors) that has been hypothesized to serve as a learning signal in efferent regions. However, because DA acts as a relatively slow modulator of cortical neurotransmission, it is unclear whether DA can indeed act to precisely transmit prediction errors to prefrontal cortex (PFC). In light of recent physiological and anatomical evidence, we propose that corelease of glutamate from DA and/or non-DA neurons in the VTA could serve to transmit this temporally precise signal. In contrast, DA acts in a protracted manner to provide spatially and temporally diffuse modulation of PFC pyramidal neurons and interneurons. This modulation occurs first via a relatively rapid depolarization of fast-spiking interneurons that acts on the order of seconds. This is followed by a more protracted modulation of a variety of other ionic currents on timescales of minutes to hours, which may bias the manner in which cortical networks process information. However, the prolonged actions of DA may be curtailed by counteracting influences, which likely include opposing actions at D1 and D2-like receptors that have been shown to be time- and concentration-dependent. In this way, the mesocortical DA system optimizes the characteristics of glutamate, GABA, and DA neurotransmission both within the midbrain and cortex to communicate temporally precise information and to modulate network activity patterns on prolonged timescales.

Dopaminergic modulation of local network activity in rat prefrontal cortex

Dopamine modulates prefrontal cortex excitability in complex ways. Dopamine's net effect on local neuronal networks is therefore difficult to predict based on studies on pharmacologically isolated excitatory or inhibitory connections. In the present work, we have studied the effects of dopamine on evoked activity in acute rat brain slices when both excitation and inhibition are intact. Whole cell recordings from layer II/III pyramidal cells under conditions of normal synaptic transmission showed that bath-applied dopamine (30 microM) increased the outward inhibitory component of composite postsynaptic currents, whereas inward excitatory currents were not significantly affected. Optical imaging with the voltage-sensitive dye N-(3-(triethylammonium)propyl)-4-(4-(p-diethylaminophenyl)buta-dienyl)pyridinium dibromide revealed that bath application of dopamine significantly decreased the amplitude, duration, and lateral spread of activity in local cortical networks. This effect of dopamine was observed both with single and train (5 at 20 Hz) stimuli. The effect was mimicked by the D1-like receptor agonistR(+)-6-chloro-7,8-dihydroxy-1-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (1 microM) and was blocked by R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (10 microM), a selective antagonist for D1-like receptors. The D2-like receptor agonist quinpirole (10 microM) had no significant effect on evoked dye signals. Our results suggest that dopamine's effect on inhibition dominates over that on excitation under conditions of normal synaptic transmission. Such neuromodulation by dopamine may be important for maintenance of stability in local neuronal networks in the prefrontal cortex.

Potential clinical targets of repetitive transcranial magnetic stimulation treatment in schizophrenia

Despite the introduction of atypical antipsychotic drugs, treatment-resistant symptoms still represent a serious problem in schizophrenia. Currently, there is evidence from clinical studies suggesting that treatment with repetitive transcranial magnetic stimulation (rTMS) may improve schizophrenia symptoms. Our review provides an overview of clinical rTMS studies in schizophrenic patients. A systematic search of the literature (Cochrane and Medline databases up to December 2005) was conducted. Most studies showed methodological problems due to their explorative character and small sample sizes. In some studies, a treatment effect of high-frequency rTMS applied over the prefrontal cortex was seen with respect to negative symptoms. On the other hand, low-frequency rTMS in the temporal lobe area might lead to a suppression of auditory hallucinations. It is concluded that larger sham-controlled studies are required to allow an adequate assessment of the clinical and neurobiological effects of rTMS in schizophrenic patients. The currently available data provide insufficient evidence to support the use of rTMS as an adjuvant treatment for schizophrenic psychopathology, but encourage further investigation of rTMS as a novel treatment approach.

Clinical involvement of catechol-O-methyltransferase polymorphisms in schizophrenia spectrum disorders: influence on the severity of psychotic symptoms and on the response to neuroleptic treatment

Genetic variation in the catechol-O-methyltransferase (COMT) gene may influence the susceptibility to schizophrenia and the response to neuroleptic treatment. The authors tested for an association between a COMT haplotype and schizophrenia-spectrum disorders and for an eventual influence of a specific COMT genotype in the clinical outcome and in the response to treatment. The genotypes for single nucleotide polymorphisms rs737865, rs4633, rs6267, rs4680 (Val 158 Met) and rs165599 were determined in 207 patients with schizophrenia-spectrum disorders and 204 paired controls. Statistical tests for linkage disequilibrium and for case-control differences in haplotype frequencies were performed using log-linear modelling embedded within the expectation-maximization algorithm. P-values based on permutations were calculated using the software UNPHASED, and odds ratios were estimated using the SHEsis platform. The response to neuroleptic treatment was assessed by the Global Assessment of Functioning scale and the severity of psychotic symptoms by the positive and negative syndrome scale (PANSS) scale. The overall disease status was significantly associated with the T-G (Val) diplotype for rs4633-rs4680 (P=0.0049). A significant association was observed between schizophrenia, but not other related disorders, and genotypes GG (Val/Val) for rs4680 and TT for rs4633. Val/Val patients with schizophrenia showed a higher severity of the psychotic symptoms and a worse response to the neuroleptic treatment. COMT genetic variation seems to be involved in the psychotic symptomatology of the schizophrenia-spectrum disorders and specifically in the narrow schizophrenia phenotype. Our results show an influence of the Val 158 Met polymorphism on the severity of psychotic symptoms and on the response to treatment.

Involvement of a dysfunctional dopamine-D1/N-methyl-d-aspartate-NR1 and Ca2+/calmodulin-dependent protein kinase II pathway in the impairment of latent learning in a model of schizophrenia induced by phencyclidine

Continuous ingestion of phencyclidine (PCP) in humans produces long-lasting schizophrenic-like cognitive dysfunction. Although a malfunction of dopaminergic and/or glutamatergic neurotransmission is implicated in the etiology of schizophrenia, involvement of the dopaminergic-glutamatergic neurotransmission in the cognitive dysfunction induced by repeated PCP treatment is minor. We demonstrated that mice treated with PCP (10 mg/kg/day s.c.) for 14 days displayed an impairment of latent learning in a water-finding task and of learning-associated phosphorylation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and NR1 in the prefrontal cortex even after drug withdrawal. The infusion of a CaMKII inhibitor and NR1 antisense oligonucleotide into the prefrontal cortex produced an impairment of latent learning and decrease of learning-associated phosphorylation of CaMKII, which were observed in the PCP-treated mice. Exogenous NMDA-induced CaMKII activation was not observed in slices of the prefrontal cortex prepared from mice treated repeatedly with PCP. The potentiation of NMDA receptor function by the infusion of glycine into the prefrontal cortex ameliorated these impairments in mice treated repeatedly with PCP. The high potassium-stimulated release of dopamine from the prefrontal cortex was less extensive in the PCP-treated than saline-treated mice. The infusion of a dopamine-D1 receptor agonist into the prefrontal cortex attenuated the impairment of latent learning and decrease of learning-associated NR1 phosphorylation in the PCP-treated mice, suggesting a functional linkage between glutamatergic and dopaminergic signaling. These findings indicate that repeated PCP treatment impairs latent learning through a prefrontal cortical dysfunction of NMDA-CaMKII signaling, which is associated with dopaminergic hypofunction.

Fine-tuning of awake prefrontal cortex neurons by clozapine: comparison with haloperidol and N-desmethylclozapine

BACKGROUND

Mechanisms underlying clozapine's better clinical efficacy in schizophrenia remain poorly understood. The prefrontal cortex (PFC) has been implicated as a primary site for the therapeutic effects of clozapine; however, evidence for how clozapine influences the activity of PFC neurons in behaviorally relevant contexts is lacking.

METHODS

Ensemble single unit recording in awake rats was used to measure the activity of PFC neurons in response to clozapine, its main metabolite N-desmethylclozapine (DMClz), and the typical antipsychotic drug haloperidol during baseline conditions and after treatment with the N-methyl-D-aspartate antagonist MK801. Behavioral stereotypy was scored during recording.

RESULTS

Clozapine and DMClz but not haloperidol had an activity-dependent influence on spontaneous firing rate of PFC cells: they increased the activity of neurons with low baseline firing rates and decreased the activity of neurons with higher firing rates. Clozapine and DMClz but not haloperidol also reversed the effect of MK801 on PFC neuronal firing. This reversal was strongly correlated with blockade of MK801-induced behavioral stereotypy.

CONCLUSIONS

These findings indicate that clozapine has the capacity to fine-tune spontaneous and disrupted activity of PFC neurons. This effect might contribute, in part, to the therapeutic efficacy of clozapine in schizophrenia.

Motion-perception deficits and reading impairment: it's the noise, not the motion

We tested the hypothesis that deficits on sensory-processing tasks frequently associated with poor reading and dyslexia are the result of impairments in external-noise exclusion, rather than motion perception or magnocellular processing. We compared the motion-direction discrimination thresholds of adults and children with good or poor reading performance, using coherent-motion displays embedded in external noise. Both adults and children who were poor readers had higher thresholds than their respective peers in the presence of high external noise, but not in the presence of low external noise or when the signal was clearly demarcated. Adults' performance in high external noise correlated with their general reading ability, whereas children's performance correlated with their language and verbal abilities. The results support the hypothesis that noise-exclusion deficits impair reading and language development and suggest that the impact of such deficits on the development of reading skills changes with age.

Volume, neuron density and total neuron number in five subcortical regions in schizophrenia

Several studies have pointed to alterations in mean volumes, neuron densities and total neuron numbers in the caudate nucleus (CN), putamen, nucleus accumbens (NA), mediodorsal nucleus of the thalamus (MDNT) and lateral nucleus of the amygdala (LNA) in schizophrenia. However, the results of these studies are conflicting and no clear pattern of alterations has yet been established in these subcortical regions, possibly due to differences in quantitative histological methods used as well as differences in the investigated case series. The present study investigates these subcortical regions in both hemispheres of the same post-mortem brains for volume, neuron density and total neuron number with high-precision design-based stereology. The analysed case series consisted of 13 post-mortem brains from male schizophrenic patients [age range: 22-64 years; mean age 51.5 +/- 3.3 years (mean +/- SEM)] and 13 age-matched male controls (age range: 25-65 years; mean age 51.9 +/- 3.1 years). A general linear model multivariate analysis of variance with diagnosis and hemisphere as fixed factors and illness duration (schizophrenic patients) or age (controls), post-mortem interval and fixation time as covariates showed a number of statistically significant alterations in the brains from schizophrenic patients compared with the controls. There was a reduced mean volume of the putamen [-5.0% on the left side (l) and -4.1% on the right side (r)] and the LNA (l: -12.1%, r: -17.6%), and a reduced mean total neuron number in the CN (l: -10.4%, r: -10.2%), putamen (l: -8.1%, r: -11.6%) and the LNA (l: -15.9%, r: -16.2%). These data show a previously unreported, distinct pattern of alterations in mean total neuron numbers in identified subcortical brain regions in a carefully selected sample of brains from schizophrenic patients. The rigorous quantitative analysis of several regions in brains from schizophrenic patients and matched controls is crucial to provide reliable information on the neuropathology of schizophrenia as well as insights about its pathogenesis.

Prefrontal cortical network activity: Opposite effects of psychedelic hallucinogens and D1/D5 dopamine receptor activation

The fine-tuning of network activity provides a modulating influence on how information is processed and interpreted in the brain. Here, we use brain slices of rat prefrontal cortex to study how recurrent network activity is affected by neuromodulators known to alter normal cortical function. We previously determined that glutamate spillover and stimulation of extrasynaptic N-methyl-d-aspartic acid (NMDA) receptors are required to support hallucinogen-induced cortical network activity. Since microdialysis studies suggest that psychedelic hallucinogens and dopamine D1/D5 receptor agonists have opposite effects on extracellular glutamate in prefrontal cortex, we hypothesized that these two families of psychoactive drugs would have opposite effects on cortical network activity. We found that network activity can be enhanced by 2,5-dimethoxy-4-iodoamphetamine (DOI) (a psychedelic hallucinogen that is a partial agonist of 5-HT(2A/2C) receptors) and suppressed by the selective D1/D5 agonist SKF 38393. This suppression could be mimicked by direct activation of adenylyl cyclase with forskolin or by addition of a cAMP analog. These findings are consistent with previous work showing that activation of adenylyl cyclase can upregulate neuronal glutamate transporters, thereby decreasing synaptic spillover of glutamate. Consistent with this hypothesis, a low concentration of the glutamate transporter inhibitor threo-beta-benzoylaspartic acid (TBOA) restored electrically-evoked recurrent activity in the presence of a selective D1/D5 agonist, whereas recurrent activity in the presence of a low level of the GABA(A) antagonist bicuculline was not resistant to suppression by the D1/D5 agonist. The tempering of network UP states by D1/D5 receptor activation may have implications for the proposed use of D1/D5 agonists in the treatment of schizophrenia.

Within-person trial-to-trial variability precedes and predicts cognitive decline in old and very old age: Longitudinal data from the Berlin Aging Study

Neurocomputational modeling and empirical evidence suggest that losses in neuronal signaling fidelity cause senescent changes in behavior. We applied structural equation modeling to five-occasion 13-year longitudinal data from the Berlin Aging Study (n=447; age range at t1=70-102 years) to test whether trial-to-trial reaction time variability in perceptual speed (identical pictures) antecedes and signals longitudinal decline in levels of performance on perceptual speed (digit letter and identical pictures) and ideational fluency (category fluency). Higher trial-to-trial variability preceded and predicted greater cognitive decline in perceptual speed and ideational fluency. We conclude that trial-to-trial variability signals impending decline in cognitive performance, and that theories of neurocognitive aging need to postulate developmental cascades between senescent changes in variability and central tendency.

Serotonin and Dopamine Interactions in Rodents and Primates: Implications for Psychosis and Antipsychotic Drug Development

Since the late 1950s, appreciation of dopamine receptor blockade has played a primary role in understanding the mechanism underlying the therapeutic effects of antipsychotic drugs in schizophrenic patients in treating the positive symptoms of schizophrenia (e.g., delusions and hallucinations). Development of the second generation of antipsychotic drugs, otherwise known as atypical antipsychotic drugs, has resulted in treatments with improved subjective tolerability but relatively modest improvements in the negative symptoms of schizophrenia such as avolition, flat affect, and anhedonia. The major current challenge is to develop medications which can further improve negative symptoms treatment and also tackle the intractable clinical problems of cognitive impairment associated with schizophrenia. Further advances along these lines with respect to the dopaminergic and serotonergic neurostransmitter systems will be aided by an appreciation of the interaction between dopamine and serotonin receptor subtypes in a range of key brain structures, such as the prefrontal cortex, thalamus, striatum, amygdala, hippocampus, and the brain stem nuclei, from which the cell bodies of monoaminergic-containing neurons originate. Increasing emphasis on the use of animal models which are homologous to critical aspects of the pathophysiology in the brains of schizophrenic patients will also be required, especially as negative symptoms and cognitive impairment become an important focus for generating novel therapeutics.

Circuits formultisensory integration and attentional modulation through the prefrontal cortex and the thalamic reticular nucleus in primates

Converging evidence from anatomic and physiological studies suggests that the interaction of high-order association cortices with the thalamus is necessary to focus attention on a task in a complex environment with multiple distractions. Interposed between the thalamus and cortex, the inhibitory thalamic reticular nucleus intercepts and regulates communication between the two structures. Recent findings demonstrate that a unique circuitry links the prefrontal cortex with the reticular nucleus and may underlie the process of selective attention to enhance salient stimuli and suppress irrelevant stimuli in behavior. Unlike other cortices, some prefrontal areas issue widespread projections to the reticular nucleus, extending beyond the frontal sector to the sensory sectors of the nucleus, and may influence the flow of sensory information from the thalamus to the cortex. Unlike other thalamic nuclei, the mediodorsal nucleus, which is the principal thalamic nucleus for the prefrontal cortex, has similarly widespread connections with the reticular nucleus. Unlike sensory association cortices, some terminations from prefrontal areas to the reticular nucleus are large, suggesting efficient transfer of information. We propose a model showing that the specialized features of prefrontal pathways in the reticular nucleus may allow selection of relevant information and override distractors, in processes that are deranged in schizophrenia.

Prefrontal-hippocampal coupling during memory processing is modulated by COMT val158met genotype

BACKGROUND

Studies in humans and in animals have demonstrated that a network of brain regions is involved in performance of declarative and recognition memory tasks. This network includes the hippocampal formation (HF) as well as the ventrolateral prefrontal cortex (VLPFC). Studies in animals have suggested that the relationship between these brain regions is strongly modulated by dopamine.

METHODS

Using fMRI in healthy humans matched for a series of demographic and genetic variables, we studied the effect of the COMT val158met polymorphism on function of HF and VLPFC as well as on their functional coupling during recognition memory.

RESULTS

The COMT Val allele was associated with: relatively poorer performance at retrieval; reduced recruitment of neuronal resources in HF and increased recruitment in VLPFC during both encoding and retrieval; and unfavorable functional coupling between these two regions at retrieval. Moreover, functional coupling during retrieval was predictive of behavioral accuracy.

CONCLUSIONS

These results shed new light on individual differences in responsivity and connectivity between HF and VLPFC related to genetic modulation of dopamine, a mechanism accounting at least in part for individual differences in recognition memory performance.

D2 antidopaminergic modulation of frontal lobe function in healthy human subjects

BACKGROUND

Although the major principles of dopamine (DA) signaling have been well described previously, its precise modulatory impact on the prefrontal cortex (PFC) in humans is poorly understood. Two major neurophysiological models propose segregated functional circuits on the systems level as well as D(1) and D(2) receptor-dependent processing states on the cellular level (two-state model).

METHODS

We examined the predictive validity of these models in 10 healthy male volunteers with a haloperidol challenge (HLP). Cortico-striatal-thalamo-cortical (CSTC) motor loop functions were examined during functional magnetic resonance imaging (fMRI) with a sequential finger opposition task. Neuropsychological implications of the two-state model were evaluated with a test battery of D(1)- or D(2)-sensitive prefrontal measures.

RESULTS

Analysis of fMRI data revealed a significant HLP-induced blood oxygen level dependent-signal decrease in the sensorimotor striatum and a lateralized activation loss of ipsilateral higher order motor cortices and contralateral cerebellum. Neuropsychological evaluation demonstrated a preferential impairment of D(2)-sensitive functions, whereas D(1) or non-dopaminergic domains were unaffected.

CONCLUSIONS

Our data support the hypothesis that mesocortical D(1) and D(2) receptors exert differential influences in the PFC for cognitive function, but the nigrostriatal CSTC network model for the motor domain could not be confirmed.

Social brain dysfunctions in schizophrenia: a review of neuroimaging studies

Several studies have indicated that schizophrenic patients show impaired performance in various aspects of social cognition, including theory of mind, emotion processing, and agency judgments. Neuroimaging studies that have compared patients and healthy subjects during such mental activity indicate an abnormal hemodynamic response in the medial prefrontal cortex, the prefrontal cortex, the amygdala, the inferior parietal lobe, i.e., a set of regions known to be critically involved in social cognition. This paper addresses a number of issues raised by schizophrenia research into theory of mind, emotion perception and self-agency with regards to the neural systems that mediate social cognition. In healthy subjects, typical brain patterns are associated with theory of mind, emotion perception and self-agency; some activated clusters overlap, while others are distinct. For instance, activations in the paracingulate gyrus are almost systematically associated with theory of mind tasks, while the amygdala is mainly involved in emotion perception tasks. Additional foci are frequently found activated during those tasks: superior temporal sulcus, inferior frontal area. Moreover, the inferior parietal lobe is thought to contribute to agency judgments. In the light of the data on brain abnormalities and neurochemical dysfunctions in schizophrenia, we discuss the interaction of social cognitive dysfunction with the supposed information processing abnormalities caused by dopamine dysregulation.

Gamma band oscillations reveal neural network cortical coherence dysfunction in schizophrenia patients

BACKGROUND

Gamma band activity has been associated with many sensory and cognitive functions, and is important for cortico-cortical transmission and the integration of information across neural networks. The aims of the present study were to determine if schizophrenia patients have deficits in the generation and maintenance of coherent, synchronized oscillations in response to steady-state stimulation, and to examine the clinical and cognitive correlates of the electroencephalography (EEG) oscillatory dynamics.

METHODS

Schizophrenia patients (n = 100) and nonpsychiatric subjects (n = 80) underwent auditory steady-state event-related potential testing. Click trains varying in rate of stimulation (20, 30, and 40 Hz) were presented; EEG-evoked power and intertrial phase synchronization were obtained in response to each stimulation frequency. Subjects also underwent clinical and neurocognitive assessments.

RESULTS

Patients had reductions in both evoked power and phase synchronization in response to 30- and 40-Hz stimulation but normal responsivity to 20-Hz stimulation. Maximal deficits were detected in response to 40-Hz stimulation. A modest association of reduced working memory performance and 40-Hz intertrial phase synchronization was present in schizophrenia patients (r = .32, p <.01).

CONCLUSIONS

Schizophrenia patients have frequency-specific deficits in the generation and maintenance of coherent gamma-range oscillations, reflecting a fundamental degradation of basic integrated neural network activity.

Involvement of hyperprolinemia in cognitive and psychiatric features of the 22q11 deletion syndrome

Microdeletions of the 22q11 region, responsible for the velo-cardio-facial syndrome (VCFS), are associated with an increased risk for psychosis and mental retardation. Recently, it has been shown in a hyperprolinemic mouse model that an interaction between two genes localized in the hemideleted region, proline dehydrogenase (PRODH) and catechol-o-methyl-transferase (COMT), could be involved in this phenotype. Here, we further characterize in eight children the molecular basis of type I hyperprolinemia (HPI), a recessive disorder resulting from reduced activity of proline dehydrogenase (POX). We show that these patients present with mental retardation, epilepsy and, in some cases, psychiatric features. We next report that, among 92 adult or adolescent VCFS subjects, a subset of patients with severe hyperprolinemia has a phenotype distinguishable from that of other VCFS patients and reminiscent of HPI. Forward stepwise multiple regression analysis selected hyperprolinemia, psychosis and COMT genotype as independent variables influencing IQ in the whole VCFS sample. An inverse correlation between plasma proline level and IQ was found. In addition, as predicted from the mouse model, hyperprolinemic VCFS subjects bearing the Met-COMT low activity allele are at risk for psychosis (OR = 2.8, 95% CI = 1.04-7.4). Finally, from the extensive analysis of the PRODH gene coding sequence variations, it is predicted that POX residual activity in the 0-30% range results into HPI, whereas residual activity in the 30-50% range is associated either with normal plasma proline levels or with mild-to-moderate hyperprolinemia.

Nur77 and retinoid X receptors: crucial factors in dopamine-related neuroadaptation

Dopaminergic systems in the brain adapt in response to various stimuli from the internal and external world, but the mechanisms underlying this process are incompletely understood. Here, we review recent evidence that certain types of transcription factor of the nuclear receptor family, specifically Nur77 and retinoid X receptors, have important roles in adaptation and homeostatic regulation of dopaminergic systems. These findings call for a reassessment of our fundamental understanding of the molecular and cellular basis of dopamine-mediated transmission. Given that diseases such as Parkinson's disease and schizophrenia are thought to involve adaptation of dopamine signalling, these findings might provide new insight into these pathologies and offer new avenues for drug development.

Glutamate-dopamine cotransmission and reward processing in addiction

While Dale's principle of "one neuron, one neurotransmitter" has undergone revisions to incorporate evidence of the corelease of atypical neurotransmitters such as neuropeptides, the corelease of classical neurotransmitters has only recently been realized. Surprisingly, numerous studies now indicate that the corelease of neurotransmitters in the mammalian central nervous system is not an obscure and rare phenomenon but is widespread and involves most classical neurotransmitters systems. However, the suggestion that glutamate can be coreleased with dopamine (DA) has remained controversial. Furthermore, glutamate-DA cotransmission has not yet been seriously considered in the context of the neurocircuitry of addiction. If glutamate is in fact coreleased with DA as some evidence now suggests, this may have significant implications for advancing our understanding of the interactive role that these 2 neurotransmitters play in cognitive and reward processes. In this commentary, we review the evidence for and against glutamate as a cotransmitter and discuss the potential role of glutamate-DA corelease in addiction. In particular, we describe a recently proposed model in which coreleased glutamate transmits a temporally precise prediction error signal of reward described by Schultz et al., whereas the function of coreleased DA is to exert prolonged modulatory influences on neuronal activity. In addition, we suggest that as alcohol consumption transitions from recreational use to addiction, there is a corresponding transition in the reward valence signal from better than predicted to worse than predicted.

MR spectroscopy: its potential role for drug development for the treatment of psychiatric diseases

Magnetic resonance spectroscopy (MRS) is likely in the near future to play a key role in the process of drug discovery and evaluation. As the pharmaceutical industry seeks biochemical markers of drug delivery, efficacy and toxicity, this non-invasive technique offers numerous ways to study adults and children repeatedly and without ionizing radiation. In this article, we survey an array of the information that MRS offers about neurochemistry in general and psychiatric disorders and their treatment in particular. We also present growing evidence of glial abnormalities in neuropsychiatric disorders and discuss what MRS is contributing to that line of investigation. The third major direction of this article is the discussion of where MRS techniques are headed and how those new techniques can contribute to studies of mechanisms of psychiatric disease and drug discovery.

COMT genotype predicts BOLD signal and noise characteristics in prefrontal circuits

OBJECTIVE

Prefrontal dopamine (DA) is catabolized by the COMT (catechol-O-methyltransferase) enzyme. Literature suggests that the Val/Met single nucleotide polymorphism (SNP) in the COMT gene predicts executive cognition in humans with Val carriers showing poorer performance due to less available synaptic DA. Recent fMRI studies are thought to agree with these studies having demonstrated prefrontal hyperactivation during n-back and attention-requiring tasks. This was interpreted as "less efficient" processing due to impaired signal-to-noise ratio (SNR) of neuronal activity. However, electrophysiological studies of neuronal SNR in primates and humans imply that prefrontal cortex should show a diminished prefrontal BOLD response in Val carriers. In the present study, we addressed the question of whether the prefrontal SNR of the BOLD response is decreased in Val carriers using a visual oddball task and an approach to analysis of fMRI data that maximizes noise characterization.

METHODS

We investigated N=17 homozygous Met carriers compared with N=24 Val carriers matched for age, sex, education, IQ, reaction time (variability) and head motion. Event-related fMRI was conducted presenting 160 visual stimuli (40 targets, checkerboard reversal). Subjects had to respond as quickly as possible to targets by button press. In the fMRI GLM [y(t)=beta*x(t)+c+e(t)] analysis, voxel-by-voxel 'activation' [y(t)] as well as residual noise variance [e(t)=sigma2] were calculated using a conservative full-width half maximum (FWHM=6 mm).

RESULTS

As compared to Val carriers, we observed a stronger and more extended BOLD responses in homozygous Met carriers in left supplementary motor area (SMA) extending to ACC and dorsolateral prefrontal cortex. Vice versa, increased levels of noise were seen in Val carriers surrounding the peak activation maximum.

DISCUSSION

In line with our expectations from prior electrophysiological studies, we observed a diminished BOLD response and increased noise in Val carriers. This suggests that the DA stabilizes cortical microcircuits by sharpening the signal and suppressing surrounding noise.

Evidence for statistical epistasis between catechol-O-methyltransferase (COMT) and polymorphisms in RGS4, G72 (DAOA), GRM3, and DISC1: influence on risk of schizophrenia

Catechol-O-methyltransferase (COMT) regulates dopamine degradation and is located in a genomic region that is deleted in a syndrome associated with psychosis, making it a promising candidate gene for schizophrenia. COMT also has been shown to influence prefrontal cortex processing efficiency. Prefrontal processing dysfunction is a common finding in schizophrenia, and a background of inefficient processing may modulate the effect of other candidate genes. Using the NIMH sibling study (SS), a non-independent case-control set, and an independent German (G) case-control set, we performed conditional/unconditional logistic regression to test for epistasis between SNPs in COMT (rs2097603, Val158Met (rs4680), rs165599) and polymorphisms in other schizophrenia susceptibility genes. Evidence for interaction was evaluated using a likelihood ratio test (LRT) between nested models. SNPs in RGS4, G72, GRM3, and DISC1 showed evidence for significant statistical epistasis with COMT. A striking result was found in RGS4: three of five SNPs showed a significant increase in risk [LRT P-values: 90387 = 0.05 (SS); SNP4 = 0.02 (SS), 0.02 (G); SNP18 = 0.04 (SS), 0.008 (G)] in interaction with COMT; main effects for RGS4 SNPs were null. Significant results for SNP4 and SNP18 were also found in the German study. We were able to detect statistical interaction between COMT and polymorphisms in candidate genes for schizophrenia, many of which had no significant main effect. In addition, we were able to replicate other studies, including allelic directionality. The use of epistatic models may improve replication of psychiatric candidate gene studies.

Psychosis pathways converge via D2high dopamine receptors

The objective of this review is to identify a target or biomarker of altered neurochemical sensitivity that is common to the many animal models of human psychoses associated with street drugs, brain injury, steroid use, birth injury, and gene alterations. Psychosis in humans can be caused by amphetamine, phencyclidine, steroids, ethanol, and brain lesions such as hippocampal, cortical, and entorhinal lesions. Strikingly, all of these drugs and lesions in rats lead to dopamine supersensitivity and increase the high-affinity states of dopamine D2 receptors, or D2High, by 200-400% in striata. Similar supersensitivity and D2High elevations occur in rats born by Caesarian section and in rats treated with corticosterone or antipsychotics such as reserpine, risperidone, haloperidol, olanzapine, quetiapine, and clozapine, with the latter two inducing elevated D2High states less than that caused by haloperidol or olanzapine. Mice born with gene knockouts of some possible schizophrenia susceptibility genes are dopamine supersensitive, and their striata reveal markedly elevated D2High states; suchgenes include dopamine-beta-hydroxylase, dopamine D4 receptors, G protein receptor kinase 6, tyrosine hydroxylase, catechol-O-methyltransferase, the trace amine-1 receptor, regulator of G protein signaling RGS9, and the RIIbeta form of cAMP-dependent protein kinase (PKA). Striata from mice that are not dopamine supersensitive did not reveal elevated D2High states; these include mice with knockouts of adenosine A2A receptors, glycogen synthase kinase GSK3beta, metabotropic glutamate receptor 5, dopamine D1 or D3 receptors, histamine H1, H2, or H3 receptors, and rats treated with ketanserin or aD1 antagonist. The evidence suggests that there are multiple pathways that convergetoelevate the D2High state in brain regions and that this elevation may elicit psychosis. This proposition is supported by the dopamine supersensitivity that is a common feature of schizophrenia and that also occurs in many types of genetically altered, drug-altered, and lesion-altered animals. Dopamine supersensitivity, in turn, correlates with D2High states. The finding that all antipsychotics, traditional and recent ones, act on D2High dopamine receptors further supports the proposition.

Frontal dopamine D(2/3) receptor binding in drug-naive first-episode schizophrenic patients correlates with positive psychotic symptoms and gender

BACKGROUND

The aim of the study was to examine extrastriatal dopamine D(2/3) receptor binding and psychopathology in schizophrenic patients, and to relate binding potential (BP) values to psychopathology.

METHODS

Twenty-five drug-naive schizophrenic patients and 20 healthy controls were examined with single-photon emission computerized tomography (SPECT) using the D(2/3)-receptor ligand [123I]epidepride.

RESULTS

In the hitherto largest study on extrastriatal D(2/3) receptors we detected a significant correlation between frontal D(2/3) BP values and positive schizophrenic symptoms in the larger group of male schizophrenic patients, higher frontal BP values in male (n = 17) compared to female (n = 8) patients, and - in accordance with this - significantly fewer positive schizophrenic symptoms in the female patients. No significant differences in BP values were observed between patients and controls; the patients, however, had significantly higher BP in the right compared to the left thalamus, whereas no significant hemispheric imbalances were observed in the healthy subjects.

CONCLUSIONS

The present data are the first to confirm a significant correlation between frontal D(2/3) receptor BP values and positive symptoms in male schizophrenic patients. They are in agreement with the hypothesis that frontal D(2/3) receptor activity is significant for positive psychotic symptoms. Additionally, the data support a thalamic hemispheric imbalance in schizophrenia.