Cortical regulation of subcortical dopamine systems and its possible relevance to schizophrenia

The Relationship Between Frontostriatal Connectivity and Striatal Dopamine Function in Schizophrenia: An 18F-DOPA PET and Diffusion Tensor Imaging Study in Treatment Responsive and Resistant Patients

OBJECTIVE

Striatal dopamine dysfunction caused by cortical abnormalities is a leading hypothesis of schizophrenia. Although prefrontal cortical pathology is negatively correlated with striatal dopamine synthesis, the relationship between structural frontostriatal connectivity and striatal dopamine synthesis has not been proved in patients with schizophrenia with different treatment response. We therefore investigated the relationship between frontostriatal connectivity and striatal dopamine synthesis in treatment-responsive schizophrenia (non-TRS) and compared them to treatment-resistant schizophrenia (TRS) and healthy controls (HC).

METHODS

Twenty-four patients with schizophrenia and twelve HC underwent [18F] DOPA PET scans to measure dopamine synthesis capacity (the influx rate constant Kicer) and diffusion 3T MRI to measure structural connectivity (fractional anisotropy, FA). Connectivity was assessed in 2 major frontostriatal tracts. Associations between Kicer and FA in each group were evaluated using Spearman's rho correlation coefficients.

RESULTS

Non-TRS showed a negative correlation (r=-0.629, p=0.028) between connectivity of dorsolateral prefrontal cortex-associative striatum (DLPFC-AST) and dopamine synthesis capacity of associative striatum but this was not evident in TRS (r=-0.07, p=0.829) and HC (r=-0.277, p=0.384).

CONCLUSION

Our findings are consistent with the hypothesis of dysregulation of the striatal dopaminergic system being related to prefrontal cortex pathology localized to connectivity of DLPFC-AST in non-TRS, and also extend the hypothesis to suggest that different mechanisms underlie the pathophysiology of non-TRS and TRS.

The relationship between grey matter volume and striatal dopamine function in psychosis: a multimodal 18F-DOPA PET and voxel-based morphometry study

A leading hypothesis for schizophrenia and related psychotic disorders proposes that cortical brain disruption leads to subcortical dopaminergic dysfunction, which underlies psychosis in the majority of patients who respond to treatment. Although supported by preclinical findings that prefrontal cortical lesions lead to striatal dopamine dysregulation, the relationship between prefrontal structural volume and striatal dopamine function has not been tested in people with psychosis. We therefore investigated the in vivo relationship between striatal dopamine synthesis capacity and prefrontal grey matter volume in treatment-responsive patients with psychosis, and compared them to treatment non-responsive patients, where dopaminergic mechanisms are not thought to be central. Forty patients with psychosis across two independent cohorts underwent ¹⁸F-DOPA PET scans to measure dopamine synthesis capacity (indexed as the influx rate constant K_i^cer) and structural 3T MRI. The PET, but not MR, data have been reported previously. Structural images were processed using DARTEL-VBM. GLM analyses were performed in SPM12 to test the relationship between prefrontal grey matter volume and striatal K_i^cer. Treatment responders showed a negative correlation between prefrontal grey matter and striatal dopamine synthesis capacity, but this was not evident in treatment non-responders. Specifically, we found an interaction between treatment response, whole striatal dopamine synthesis capacity and grey matter volume in left (pFWE corr. = 0.017) and right (pFWE corr. = 0.042) prefrontal cortex. We replicated the finding in right prefrontal cortex in the independent sample (pFWE corr. = 0.031). The summary effect size was 0.82. Our findings are consistent with the long-standing hypothesis of dysregulation of the striatal dopaminergic system being related to prefrontal cortex pathology in schizophrenia, but critically also extend the hypothesis to indicate it can be applied to treatment-responsive schizophrenia only. This suggests that different mechanisms underlie the pathophysiology of treatment-responsive and treatment-resistant schizophrenia.

Atypical processing of uncertainty in individuals at risk for psychosis

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Humans at psychosis clinical high risk (CHR) over-estimate environmental volatility.

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Low-level prediction error (PE) signals evoke increased frontal activity in CHR.

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Volatility-related PEs are associated with reduced frontal activity in CHR.

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Frontal cortical activation to low-level PEs reflects impaired clinical functioning.

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Atypical PE learning signal representations may promote delusion formation in CHR.

Current theories of psychosis highlight the role of abnormal learning signals, i.e., prediction errors (PEs) and uncertainty, in the formation of delusional beliefs. We employed computational analyses of behaviour and functional magnetic resonance imaging (fMRI) to examine whether such abnormalities are evident in clinical high risk (CHR) individuals.

Non-medicated CHR individuals (n = 13) and control participants (n = 13) performed a probabilistic learning paradigm during fMRI data acquisition. We used a hierarchical Bayesian model to infer subject-specific computations from behaviour – with a focus on PEs and uncertainty (or its inverse, precision) at different levels, including environmental ‘volatility’ – and used these computational quantities for analyses of fMRI data.

Computational modelling of CHR individuals’ behaviour indicated volatility estimates converged to significantly higher levels than in controls. Model-based fMRI demonstrated increased activity in prefrontal and insular regions of CHR individuals in response to precision-weighted low-level outcome PEs, while activations of prefrontal, orbitofrontal and anterior insula cortex by higher-level PEs (that serve to update volatility estimates) were reduced. Additionally, prefrontal cortical activity in response to outcome PEs in CHR was negatively associated with clinical measures of global functioning.

Our results suggest a multi-faceted learning abnormality in CHR individuals under conditions of environmental uncertainty, comprising higher levels of volatility estimates combined with reduced cortical activation, and abnormally high activations in prefrontal and insular areas by precision-weighted outcome PEs. This atypical representation of high- and low-level learning signals might reflect a predisposition to delusion formation.

Models of persecutory delusions: a mechanistic insight into the early stages of psychosis

Identifying robust markers for predicting the onset of psychosis has been a key challenge for early detection research. Persecutory delusions are core symptoms of psychosis, and social cognition is particularly impaired in first-episode psychosis patients and individuals at risk for developing psychosis. Here, we propose new avenues for translation provided by hierarchical Bayesian models of behaviour and neuroimaging data applied in the context of social learning to target persecutory delusions. As it comprises a mechanistic model embedded in neurophysiology, the findings of this approach may shed light onto inference and neurobiological causes of transition to psychosis.

The Loudness Dependence of Auditory Evoked Potentials (LDAEP) in individuals at risk for developing bipolar disorders and schizophrenia

OBJECTIVES

The Loudness Dependence of Auditory Evoked Potentials (LDAEP) is considered as an indicator of central serotonergic activity. Alteration of serotonergic neurotransmission was reported in bipolar disorders and schizophrenia. In line with previous reports on clinically manifest disorders, we expected a weaker LDAEP in subjects at risk for bipolar disorders and schizophrenia compared to healthy controls.

METHODS

We analyzed LDAEP of individuals at risk for developing bipolar disorders (n=27), with high-risk status (n=74) and ultra-high-risk status for schizophrenia (n=86) and healthy controls (n=47).

RESULTS

The LDAEP did not differ between subjects at risk for schizophrenia or bipolar disorders and controls. Among subjects without medication (n=122), the at-risk-bipolar group showed a trend towards a weaker LDAEP than both the high-risk and the ultra-high-risk groups for schizophrenia.

CONCLUSIONS

The LDAEP did not appear as a vulnerability marker for schizophrenia or bipolar disorders. This suggests that an altered LDAEP may not be measurable until the onset of clinically manifest disorder. However, the hypothesis that pathogenic mechanisms leading to bipolar disorders may differ from those leading to schizophrenia is supported.

SIGNIFICANCE

This is the first study investigating LDAEP in a population at risk for bipolar disorders.

Glutamatergic dysfunction linked to energy and membrane lipid metabolism in frontal and anterior cingulate cortices of never treated first-episode schizophrenia patients

BACKGROUND

Glutamatergic dysfunction and altered membrane lipid and energy metabolism have been repeatedly demonstrated in the frontal/prefrontal and anterior cingulate cortex (ACC) in schizophrenia. Though having been already studied in animals, the presumed link between glutamatergic function and structural plasticity has not been investigated directly in the human brain yet. We measured glutamate (Glu), focal energy metabolism, and membrane phospholipid turnover to investigate main pathologies in those key brain regions of schizophrenia.

METHODS

(1)H- and (31)P-Chemical Shift Imaging (CSI) was combined in a single session to assess Glu and markers of energy (PCr, ATP) and membrane lipid (PME, PDE) metabolism in 31 neuroleptic-naïve first acute onset psychosis patients and 31 matched healthy controls. Multivariate analyses of covariance were used to assess disease effects on Glu and to investigate the impact of Glu alterations on phospholipid and energy metabolites.

RESULTS

Glu levels of patients were increased in the frontal and prefrontal cortex bilaterally and in the ACC. Higher Glu was associated with increased left frontal/prefrontal PME and right frontal/prefrontal PDE in patients, which was not observed in healthy controls. In contrast, higher Glu levels were associated with lower PCr or ATP values in the frontal/prefrontal cortex bilaterally and in the right ACC of controls. This was not observed in the right ACC and left frontal/prefrontal cortex of patients.

CONCLUSION

Frontal glutamatergic hyperactivity is disconnected from physiologically regulated energy metabolism and is associated with increased membrane breakdown in right and increased membrane restoration in left frontal and prefrontal cortical regions. As indicated by previous findings, this pathology is likely dynamic during the course of first acute illness and possibly associated with negative symptoms and cognitive impairment. Our findings underline the importance of further research on neuroprotective treatment options during the early acute or even better for the ultra-high risk state of psychotic illness.

Neurogenetics of depression: a focus on reward processing and stress sensitivity

Major depressive disorder (MDD) is etiologically complex and has a heterogeneous presentation. This heterogeneity hinders the ability of molecular genetic research to reliably detect the small effects conferred by common genetic variation. As a result, significant research efforts have been directed at investigating more homogenous intermediate phenotypes believed to be more proximal to gene function and lie between genes and/or environmental effects and disease processes. In the current review we survey and integrate research on two promising intermediate phenotypes linked to depression: reward processing and stress sensitivity. A synthesis of this burgeoning literature indicates that a molecular genetic approach focused on intermediate phenotypes holds significant promise to fundamentally improve our understanding of the pathophysiology and etiology of depression, which will be required for improved diagnostic definitions and the development of novel and more efficacious treatment and prevention strategies. We conclude by highlighting challenges facing intermediate phenotype research and future development that will be required to propel this pivotal research into new directions.

Neural response to reward as a predictor of increases in depressive symptoms in adolescence

Adolescence is a developmental period characterized by significant increases in the onset of depression, but also by increases in depressive symptoms, even among psychiatrically healthy youth. Disrupted reward function has been postulated as a critical factor in the development of depression, but it is still unclear which adolescents are particularly at risk for rising depressive symptoms. We provide a conceptual stance on gender, pubertal development, and reward type as potential moderators of the association between neural response to reward and rises in depressive symptoms. In addition, we describe preliminary findings that support claims of this conceptual stance. We propose that (1) status-related rewards may be particularly salient for eliciting neural response relevant to depressive symptoms in boys, whereas social rewards may be more salient for eliciting neural response relevant to depressive symptoms in girls and (2) the pattern of reduced striatal response and enhanced medial prefrontal response to reward may be particularly predictive of depressive symptoms in pubertal adolescents. We found that greater vmPFC activation when winning rewards predicted greater increases in depressive symptoms over 2 years, for boys only, and less striatal activation when anticipating rewards predicted greater increases in depressive symptoms over 2 years, for adolescents in mid to late pubertal stages but not those in pre to early puberty. We also propose directions for future studies, including the investigation of social vs. monetary reward directly and the longitudinal assessment of parallel changes in pubertal development, neural response to reward, and depressive symptoms.

Targeting the brain: considerations in 332 consecutive patients treated by deep brain stimulation (DBS) for severe neurological diseases

Deep brain stimulation (DBS) extends the treatment of some severe neurological diseases beyond pharmacological and conservative therapy. Our experience extends the field of DBS beyond the treatment of Parkinson disease and dystonia, including several other diseases such as cluster headache and disruptive behavior. Since 1993, at the Istituto Nazionale Neurologico "Carlo Besta" in Milan, 580 deep brain electrodes were implanted in 332 patients. The DBS targets include Stn, GPi, Voa, Vop, Vim, CM-pf, pHyp, cZi, Nacc, IC, PPN, and Brodmann areas 24 and 25. Three hundred patients are still available for follow-up and therapeutic considerations. DBS gave a new therapeutic chance to these patients affected by severe neurological diseases and in some cases controlled life-threatening pathological conditions, which would otherwise result in the death of the patient such as in status dystonicus, status epilepticus and post-stroke hemiballismus. The balance of DBS in severe neurological disease is strongly positive even if further investigations and studies are needed to search for new applications and refine the selection criteria for the actual indications.

Density of striatal D2 receptors in untreated first-episode psychosis: an I123-IBZM SPECT study

There is as yet no definite prognostic marker to determine whether a first-episode psychosis will become schizophrenia or not. The aim of the present study is to address whether the mechanism of sensitization of the subcortical dopaminergic pathway - yielding to an increase of the postsynaptic D2 receptors - may serve as a prognostic marker of clinical outcome in drug naïve patients with a first-episode psychosis, by means of a prospective and multicentric study with untreated first-episode psychosis patients (n=37). 123I-IBZM SPECT was performed at the time of the inclusion in the study, before antipsychotic medication was initiated. One year later, patients were assessed again so as to determine their diagnosis. There was a significant group effect at baseline in D2 Striatal/Frontal (S/F) ratios (F=10.2, p<0.001). Bonferroni posthoc comparisons attested significant differences between diagnosis (p=0.006), and between schizophrenia and control groups (p<0.001) but no differences between non-schizophrenia and control groups (p=0.9). The logistic regression model showed that D2R binding (p=0.02) and PAS (Premorbid Adjustment Scale) adulthood score (p=0.03) were predictive of the final diagnosis (schizophrenia/non-schizophrenia; Nagelkerke R(2)=0.59; X(2)=11.08, p=0.001). These findings replicate previous results on the usefulness of D2R binding as an objective prognostic parameter, together with the evaluation of premorbid adjustment, of the evolution of first-episode psychosis. In this regard, the results may provide a new view in the approach of early and personalized treatment in the debut of a psychosis.

Na+,K+-ATPase activity is increased in rats subjected to chronic administration of ketamine

De Luca RD, Fraga DB, Ghedim FV, Kolling J, Ferreira AGK, Cunha AA, Wyse ATS, Zugno AI. Na+,K+-ATPase activity is increased in rats subjected to chronic administration of ketamine.

Objective: Schizophrenia is a devastating psychiatric disorder. Symptoms of schizophrenia can be divided into positive, negative and cognitive, and the physiopathology is still been unknown. Na+,K+-ATPase is a protein in its role as a maintainer of fluid balance in all mammals and alterations in this enzyme could cause brain abnormalities. The aim of our study was to investigate the activity of this enzyme in rats submitted to chronic administration of ketamine.

Methods: Adult male Wistar rats were submitted to sub-anaesthetic doses of the 25 mg/kg ketamine by seven consecutive days and the Na+,K+-ATPase activity was analysed in prefrontal and hippocampus of rats.

Results: We observed an increase in Na+,K+-ATPase activity in prefrontal cortex administration of 25 mg/kg ketamine. However, ketamine has no effect in hippocampus.

Conclusion: This evidence indicates that the alteration in Na+,K+-ATPase may be related with glutamatergic system and consequently could be related to the development of schizophrenia.

Higher levels of glutamate in the associative-striatum of subjects with prodromal symptoms of schizophrenia and patients with first-episode psychosis

The glutamatergic and dopaminergic systems are thought to be involved in the pathophysiology of schizophrenia. Their interaction has been widely documented and may have a role in the neurobiological basis of the disease. The aim of this study was to compare, using proton magnetic resonance spectroscopy ((1)H-MRS), glutamate levels in the precommissural dorsal-caudate (a dopamine-rich region) and the cerebellar cortex (negligible for dopamine) in the following: (1) 18 antipsychotic-naïve subjects with prodromal symptoms and considered to be at ultra high-risk for schizophrenia (UHR), (2) 18 antipsychotic-naïve first- episode psychosis patients (FEP), and (3) 40 age- and sex- matched healthy controls. All subjects underwent a (1)H-MRS study using a 3Tesla scanner. Glutamate levels were quantified and corrected for the proportion of cerebrospinal fluid and percentage of gray matter in the voxel. The UHR and FEP groups showed higher levels of glutamate than controls, without differences between UHR and FEP. In the cerebellum, no differences were seen between the three groups. The higher glutamate level in the precommissural dorsal-caudate and not in the cerebellum of UHR and FEP suggests that a high glutamate level (a) precedes the onset of schizophrenia, and (b) is present in a dopamine-rich region previously implicated in the pathophysiology of schizophrenia.

Cannabis use and striatal D2 receptor density in untreated first-episode psychosis: an in vivo SPECT study

The biological basis of the association between cannabis-induced dopamine dysregulation and psychosis remains poorly understood. This (123)I-IBZM SPECT study assessed striatal dopamine D2 receptor (D2R) binding in 37 untreated first-episode psychosis (FEP) subjects, and 18 healthy controls. The aim was to examine if there were differences between FEP subjects with (n=14) and without (n=23) cannabis use in uptake ratios in the D2R. Striatal/Frontal cortex (S/F) uptake ratios were obtained. Healthy controls showed the lowest D2R binding ratios. No differences were found in S/F ratios between users and non-users, suggesting similar dopaminergic mechanisms underlying psychotic symptoms in both groups.

Tolcapone, COMT polymorphisms and pharmacogenomic treatment of schizophrenia

It is widely accepted that abnormal prefrontal cortex biology resulting in deficient cognition is a primary problem in schizophrenia and that all currently available antipsychotics fail to improve cognitive and negative symptoms originating from this deficit. Evidence from basic science has revealed the importance of prefrontal dopamine signaling for optimal prefrontal function. This article describes succinctly the progress made so far, taking into account the mechanisms involved in catechol-O-methyltransferase (COMT)-induced modulation of prefrontal dopamine signaling, the impact of COMT on cognitive function and the role of COMT gene polymorphisms. The potential role of the COMT inhibitor tolcapone to improve cognitive function in health and disease is also presented here. It will soon be understood if tolcapone represents one of the first hypothesis-driven, biology-based, genotype-specific, targeted treatments of cognitive and negative symptoms of schizophrenia.

Constitutive genetic deletion of the growth regulator Nogo-A induces schizophrenia-related endophenotypes

The membrane protein Nogo-A, which is predominantly expressed by oligodendrocytes in the adult CNS and by neurons mainly during development, is well known for limiting neurite outgrowth and regeneration in the injured mammalian CNS. In addition, it has recently been proposed that abnormal Nogo-A expression or Nogo receptor (NgR) mutations may confer genetic risks for neuropsychiatric disorders of presumed neurodevelopmental origin, such as schizophrenia. We therefore evaluated whether Nogo-A deletion may lead to schizophrenia-like abnormalities in a mouse model of genetic Nogo-A deficiency. Here, we show that systemic, lifelong knock-out of the Nogo-A gene can lead to specific behavioral abnormalities resembling schizophrenia-related endophenotypes: deficient sensorimotor gating, disrupted latent inhibition, perseverative behavior, and increased sensitivity to the locomotor stimulating effects of amphetamine. These behavioral phenotypes were accompanied by altered monoaminergic transmitter levels in specific striatal and limbic structures, as well as changes in dopamine D2 receptor expression in the same brain regions. Nogo-A deletion was further associated with elevated expression of growth-related markers. In contrast, acute antibody-mediated Nogo-A neutralization in adult wild-type mice failed to produce such phenotypes, suggesting that the phenotypes observed in the knock-out mice might be of developmental origin, and that Nogo-A normally subserves critical functions in neurodevelopment. This study provides the first experimental demonstration that Nogo-A bears neuropsychiatric relevance, and alterations in its expression may be one etiological factor in schizophrenia and related disorders.

What is schizophrenia: A neurodevelopmental or neurodegenerative disorder or a combination of both? A critical analysis

The etiology of schizophrenia has been the focus of intensive research for a long time. Perspectives have changed drastically with the development of new investigative techniques. Clinical observations made by Kraepelin, Clouston, Bender, and Watt are now being complemented by neuroimaging and genetic studies to prove the neurodevelopmental hypothesis. At the same time, neuropathological and longitudinal studies of schizophrenia often support a neurodegenerative hypothesis. To provide a theoretical basis to the available evidence, another hypothesis called the progressive neurodevelopmental model has also emerged. This review presents some key evidence supporting each of these theories followed by a critical analysis of each.

Tolcapone effects on gating, working memory, and mood interact with the synonymous catechol-O-methyltransferase rs4818c/g polymorphism

BACKGROUND

The functional catechol-O-methyltransferase (COMT) valine158methionine (val158met) polymorphism determines prepulse inhibition (PPI) levels and working memory performance and the effects of tolcapone on these functions. Here, we explored the effects of the synonymous COMT rs4818 C/G polymorphism and tolcapone on PPI and working memory.

METHODS

Thirteen G/G (low prefrontal cortex [PFC] dopamine [DA]) and 12 C/C (high PFC DA) healthy male subjects entered and completed the study. Subjects participated in two weekly sessions associated with either acute oral tolcapone (200 mg) or placebo according to a balanced, crossover, double-blind design. Prepulse inhibition was assessed with 5 dB and 15 dB above background prepulses at 30-msec, 60-msec, and 120-msec intervals. Subjective mood and working memory performance (n-back and letter-number sequencing) were also assessed.

RESULTS

Prepulse inhibition was lower and reaction time in the n-back was slower in the G/G compared with the C/C group in the placebo condition. Tolcapone increased PPI and improved performance in both working memory tasks in the G/G group only. Baseline startle was greater in the C/C group and was not affected by tolcapone. Mood profile was worse in the C/C group and tended to deteriorate with tolcapone. Status of val158met alone could not explain these results.

CONCLUSIONS

Catechol-O-methyltransferase haplotype analyses are essential in future research. Prepulse inhibition and working memory may both relate to PFC DA levels according to an inverted U-shaped curve function. Tolcapone could be potentially useful in the treatment of conditions with deficient sensorimotor gating and working memory such as schizophrenia and prodromal states but only in a genotype-specific manner.

How have developments in molecular imaging techniques furthered schizophrenia research?

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

Nicotine- and methamphetamine-induced dopamine release evaluated with in-vivo binding of radiolabelled raclopride to dopamine D2 receptors: comparison with in-vivo microdialysis data

The effect of substances which alter extracellular dopamine (DA) concentration has been studied by measuring changes in the binding of radiolabelled raclopride, a DA D2 receptor ligand that is sensitive to endogenous DA. To better characterize the relationship between extracellular DA concentration and DA D2 receptor binding of raclopride, we compared the changes of extracellular DA concentration (measured using in-vivo microdialysis) and in-vivo [3H]raclopride binding induced by different doses of methamphetamine (Meth) and nicotine, drugs that enhance DA release with and without blocking DA transporters (DATs), respectively, in rat striatum. Nicotine elicited a modest increase of striatal extrasynaptic extracellular DA, while Meth produced a marked increase of striatal extrasynaptic DA in a dose-dependent manner. There was a close correlation between the decrease in [3H]raclopride in-vivo binding and the increase in extrasynaptic DA concentration induced by both nicotine (r2=0.95, p<0.001) and Meth (r2=0.98, p=0.001), supporting the usefulness of the radiolabelled raclopride-binding measurement for the non-invasive assessment of DA release following interventions in the living brain. However, the linear regression analysis revealed that the ratio of percent DA increase to percent [3H]raclopride binding reduction was 25-fold higher for Meth (34.8:1) than for nicotine (1.4:1). The apparent discrepancy in the extrasynaptic DA-[3H]raclopride binding relationship between the DA-enhancing drugs with and without DAT-blocking property indicates that the competition between endogenous DA and radiolabelled raclopride takes place at the intrasynaptic rather than extrasynaptic DA D2 receptors and reflects synaptic concentration of DA.

Extracellular dopamine and norepinephrine in the developing rat prefrontal cortex: transient effects of early partial loss of dopamine

Early developmental abnormalities affecting mesocortical dopamine (DA) neurons may result in later functional deficits that play a role in the emergence of psychiatric illness in adolescence/early adulthood. Little is known about the functional maturation of these neurons under either normal or abnormal conditions. In the present study, 6-hydroxydopamine was infused into the rat medial prefrontal cortex (mPFC) on postnatal day (PN) 12-14. On PN30-35, 45-50, and 60-65, mPFC extracellular DA and norepinephrine (NE) concentrations were monitored in intact and lesioned rats using in vivo microdialysis. Extracellular DA and NE concentrations in the intact mPFC remain fairly stable across development; one exception being a trend for acute tailshock-evoked DA concentrations to increase as a function of age. Lesioned rats sustained a persistent (approximately 50%) decrease in mPFC tissue DA concentrations. Tailshock-evoked increases in mPFC extracellular DA were attenuated in lesioned rats tested on PN30-35, but not PN45-50 or 60-65. Basal and evoked extracellular NE was unaffected in lesioned rats tested at any age, despite a persistent (approximately 25%) decrease in tissue NE content. Horizontal locomotor activity was also assessed in the present study. Results of previous studies suggest this behavior is modulated by mesoprefrontal DA neurons. Although not significant, acute tailshock- and acute amphetamine-evoked horizontal locomotor activity tended to be attenuated in lesioned rats tested on PN30-35 and augmented in lesioned rats tested on PN60-65. The present data suggest that early partial loss of mesoprefrontal DA nerve terminals, resulting in a persistent decrease in tissue DA concentrations, is unlikely to result in persistent alterations in local DA release.

The genetics of schizophrenia

Research on the genetic factors conferring risk for schizophrenia has not provided definitive answers. In the present review, we will discuss potential clinical and genetic limitations intrinsic to the strategies using a diagnostic phenotype. Among clinical factors, uncertainty of the phenotype is certainly a major limitation. Genetic problems include locus heterogeneity and the complex genetic architecture of the phenotype. Given these limiting factors, we will also discuss another hypothesis-driven strategy to uncover genetic risk: the use of quantitative measures (intermediate phenotypes) within more specific neurobiological mechanisms. As a clear example of all these issues and because of the longstanding involvement in the pathophysiology of this disorder, we will review the association of the gene for dopamine D2 receptors (DRD2) with diagnosis of schizophrenia and with specific working memory behavioral and brain activity phenotypes. We conclude by suggesting that hypothesis-free and hypothesis-driven are not mutually exclusive strategies and may provide information at different levels that are both useful and equally valid about genetic risk for a complex diagnostic entity like schizophrenia and for a complex phenotype like psychosis.

The effects of gender and COMT Val158Met polymorphism on fearful facial affect recognition: a fMRI study

The functional catechol-O-methyltransferase (COMT Val108/158Met) polymorphism has been shown to have an impact on tasks of executive function, memory and attention and recently, tasks with an affective component. As oestrogen reduces COMT activity, we focused on the interaction between gender and COMT genotype on brain activations during an affective processing task. We used functional MRI (fMRI) to record brain activations from 74 healthy subjects who engaged in a facial affect recognition task; subjects viewed and identified fearful compared to neutral faces. There was no main effect of the COMT polymorphism, gender or genotypexgender interaction on task performance. We found a significant effect of gender on brain activations in the left amygdala and right temporal pole, where females demonstrated increased activations over males. Within these regions, Val/Val carriers showed greater signal magnitude compared to Met/Met carriers, particularly in females. The COMT Val108/158Met polymorphism impacts on gender-related patterns of activation in limbic and paralimbic regions but the functional significance of any oestrogen-related COMT inhibition appears modest.

Processing of social emotion in patients with schizophrenia and substance use disorder: an fMRI study

The lifetime prevalence of substance use disorders among schizophrenia patients is close to 50%. The negative consequences of substance abuse in schizophrenia are well documented, but the aetiology of this comorbid condition remains unknown. Mounting evidence suggests that dual-diagnosis patients have fewer negative symptoms and better social skills, compared to non-abusing patients. We hypothesized that schizophrenia patients with substance use disorder (SCZ-SUD) would display increased cerebral activations in response to socioemotional stimuli, relative to patients with no SUD (SCZ). Schizophrenia patients (DSM-IV criteria) were divided into two groups: patients with (n=12) and without (n=11) substance use (alcohol and/or cannabis). Using functional magnetic resonance imaging (fMRI), patients were scanned during passive viewing of an emotional film excerpt with social content. Loci of activation were identified in the right mPFC (BA 10) and the right supramarginal gyrus (BA 40) in SCZ-SUD patients, and in the left pons in SCZ patients. Relative to SCZ patients, increased loci of activation were found in the right superior parietal cortex (BA 7) and the left medial prefrontal cortex (BA 10) in SCZ-SUD patients, who reported higher subjective emotional experience on a self-report scale. To our knowledge, this is the first fMRI study to assess social emotions in dual-diagnosis schizophrenia. Our results suggest that socioemotional processing may be less impaired in dual diagnosis, which recruited brain regions seemingly involved in "social cognition." Further studies on the topic are warranted.

Improvement of prepulse inhibition and executive function by the COMT inhibitor tolcapone depends on COMT Val158Met polymorphism

Recent evidence suggests that prepulse inhibition (PPI) levels relate to executive function possibly by a prefrontal cortex (PFC) dopamine (DA) link. We explored the effects of enhanced PFC DA signaling by the nonstimulant catechol-O-methyltransferase (COMT) inhibitor tolcapone, on PPI and working memory of subjects homozygous for the Val (low PFC DA) and the Met (high PFC DA) alleles of the COMT Val158Met polymorphism. Twelve Val/Val and eleven Met/Met healthy male subjects entered the study. Tolcapone 200 mg was administered in two weekly sessions, according to a balanced, crossover, double-blind, placebo-controlled design. PPI was assessed with 5 dB and 15 dB above background prepulses, at 30-, 60-, and 120 ms prepulse-pulse intervals. Subjects also underwent the n-back and the letter-number sequencing (LNS) tasks. PPI was lower in the Val/Val compared to the Met/Met group in the placebo condition. Tolcapone increased PPI significantly in the Val/Val group and tended to have the opposite effect in the Met/Met group. Baseline startle was not affected by tolcapone in the Val/Val group but it was slightly increased in the Met/Met group. Tolcapone improved performance in the n-back and LNS tasks only in the Val/Val group. Enhancement of PFC DA signaling with tolcapone improves both PPI and working memory in a COMT Val158Met genotype-specific manner. These results suggest that early information processing and working memory may both depend on PFC DA signaling, and that they may both relate to PFC DA levels according to an inverted U-shaped curve function.

Tracking the mechanisms of deep brain stimulation for neuropsychiatric disorders

Deep brain stimulation (DBS) has recently emerged as a potential treatment for medically intractable neuropsychiatric disorders. Pilot clinical studies with encouraging results have been performed with DBS of the ventral anterior internal capsule (VAIC) and subgenual cingulate white matter (Cg25WM) for the treatment of obsessive-compulsive disorder and depression. However, little is known about the underlying response of individual neurons, or the networks they are connected to, when DBS is applied to the VAIC or Cg25WM. This review summarizes current understanding of the response of axons to DBS, and discusses the general brain network architectures thought to underlie neuropsychiatric disorders. We also employ diffusion tensor imaging tractography to better understand the axonal trajectories surrounding DBS electrodes implanted in the VAIC or Cg25WM. Finally, we attempt to reconcile various data sets by presenting generalized hypotheses on potential therapeutic mechanisms of DBS for neuropsychiatric disease.

Mechanisms of dopaminergic and serotonergic neurotransmission in Tourette syndrome: clues from an in vivo neurochemistry study with PET

Tourette syndrome (TS) is a neuropsychiatric disorder with childhood onset characterized by motor and phonic tics. Obsessive-compulsive disorder (OCD) is often concomitant with TS. Dysfunctional tonic and phasic dopamine (DA) and serotonin (5-HT) metabolism may play a role in the pathophysiology of TS. We simultaneously measured the density, affinity, and brain distribution of dopamine D2 receptors (D2-R's), dopamine transporter binding potential (BP), and amphetamine-induced dopamine release (DA(rel)) in 14 adults with TS and 10 normal adult controls. We also measured the brain distribution and BP of serotonin 5-HT2A receptors (5-HT2AR), and serotonin transporter (SERT) BP, in 11 subjects with TS and 10 normal control subjects. As compared with controls, DA rel was significantly increased in the ventral striatum among subjects with TS. Adults with TS+OCD exhibited a significant D(2)-R increase in left ventral striatum. SERT BP in midbrain and caudate/putamen was significantly increased in adults with TS (TS+OCD and TS-OCD). In three subjects with TS+OCD, in whom D2-R, 5-HT2AR, and SERT were measured within a 12-month period, there was a weakly significant elevation of DA rel and 5-HT2A BP, when compared with TS-OCD subjects and normal controls. The current study confirms, with a larger sample size and higher resolution PET scanning, our earlier report that elevated DA rel is a primary defect in TS. The finding of decreased SERT BP, and the possible elevation in 5-HT2AR in individuals with TS who had increased DA rel, suggest a condition of increased phasic DA rel modulated by low 5-HT in concomitant OCD.

Subchronic and chronic PCP treatment produces temporally distinct deficits in attentional set shifting and prepulse inhibition in rats

RATIONALE

We have previously demonstrated that subchronic (five daily administrations of 2.6 mg/kg PCP) and chronic intermittent administration of 2.6 mg/kg PCP to rats produces hypofrontality and other neurochemical changes akin to schizophrenia pathology (Cochran et al., Neuropsychopharmacology, 28:265-275, 2003).

OBJECTIVES

We sought to determine whether behavioral alterations related to discrete aspects of schizophrenia are also induced by these PCP treatment regimes.

MATERIALS AND METHODS

Following administration of vehicle or PCP according to the protocols described above, rats were assessed for attentional set shifting ability, prepulse inhibition (PPI), or social interaction and the locomotor response to a challenge dose of amphetamine.

RESULTS

Ability to shift attentional set was impaired 72 h after the last PCP administration following the subchronic and chronic intermittent treatment regimes. PPI was disrupted after each acute administration of PCP in animals under the subchronic treatment regime. However, PPI deficits were not sustained 72 h after the last of five daily administrations. In subchronic and chronic PCP treated animals, no change was found in social interaction behavior, and there was little change in baseline or amphetamine-stimulated locomotor activity, employed as an indicator of dopaminergic hyperfunction.

CONCLUSIONS

The temporally distinct behavioral effects of these PCP treatment regimes suggest that PPI deficits relate directly to acute NMDA receptor antagonism, whereas the more enduring set shifting deficits relate to the longer term consequences of NMDA receptor blockade. Therefore, these subchronic and chronic PCP treatment regimes produce hypofrontality (Cochran et al., Neuropsychopharmacology, 28:265-275, 2003) and associated prefrontal cortex-dependent deficits in behavioral flexibility which mirror core deficits in schizophrenia.

Behavioral functions of the mesolimbic dopaminergic system: an affective neuroethological perspective

The mesolimbic dopaminergic (ML-DA) system has been recognized for its central role in motivated behaviors, various types of reward, and, more recently, in cognitive processes. Functional theories have emphasized DA's involvement in the orchestration of goal-directed behaviors and in the promotion and reinforcement of learning. The affective neuroethological perspective presented here views the ML-DA system in terms of its ability to activate an instinctual emotional appetitive state (SEEKING) evolved to induce organisms to search for all varieties of life-supporting stimuli and to avoid harms. A description of the anatomical framework in which the ML system is embedded is followed by the argument that the SEEKING disposition emerges through functional integration of ventral basal ganglia (BG) into thalamocortical activities. Filtering cortical and limbic input that spreads into BG, DA transmission promotes the "release" of neural activity patterns that induce active SEEKING behaviors when expressed at the motor level. Reverberation of these patterns constitutes a neurodynamic process for the inclusion of cognitive and perceptual representations within the extended networks of the SEEKING urge. In this way, the SEEKING disposition influences attention, incentive salience, associative learning, and anticipatory predictions. In our view, the rewarding properties of drugs of abuse are, in part, caused by the activation of the SEEKING disposition, ranging from appetitive drive to persistent craving depending on the intensity of the affect. The implications of such a view for understanding addiction are considered, with particular emphasis on factors predisposing individuals to develop compulsive drug seeking behaviors.

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.

Frontal dopaminergic abnormality in Tourette syndrome: a postmortem analysis

Frontal-subcortical abnormalities have been implicated in the pathophysiology of Tourette syndrome (TS). The goal of this study was to more extensively evaluate a possible underlying neurochemical abnormality in frontal cortex. Postmortem brain tissue from frontal and occipital regions (Brodmann's areas 4, 6, 9, 10, 11, 12, and 17) from three TS patients and three age-and sex-matched controls were analyzed by semiquantitative immunoblotting. Relative densities were measured for a variety of neurochemical markers including dopamine (D1, D2), serotonin (5HT-1A), and alpha-adrenergic (alpha-2A) receptors, the dopamine transporter (DAT), a monoamine terminal marker (vesicular monoamine transporter type 2, VMAT-2), and vesicular docking and release proteins (VAMP-2, synaptotagmin, SNAP-25, syntaxin, synaptophysin). Data from each TS sample, corrected for actin content, was expressed as a percentage value of its control. Results identified consistent increases of DAT and D2 receptor density in five of six frontal regions in all three TS subjects. D1 and alpha-2A receptor density were increased in a few frontal regions. These results support the hypothesis of a dopaminergic dysfunction in the frontal lobe and a likely role in the pathophysiology of TS.

Alterations of serotonin transmission in schizophrenia

A role for serotonin alterations in the pathophysiology of schizophrenia has long been suspected because of the psychotogenic effects of serotonergic agonists and the therapeutic effects of 5-HT(2) antagonism. This chapter is a review of the evidence derived from pharmacological studies, postmortem, and imaging studies that have assessed the role of serotonin transmission in schizophrenia. While a clear picture of specific serotonergic alterations in schizophrenia has not emerged despite much research, this review reinforces a modulatory role of serotonergic agents on dopamine transmission in schizophrenia, which may contribute to the therapeutic effects of atypical antipsychotics.

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.

On feeling in control: A biological theory for individual differences in control perception

This review aims to create a cross-disciplinary framework for understanding the perception of control. Although, the personality trait locus of control, the most common measure of control perception, has traditionally been regarded as a product of social learning, it may have biological antecedents as well. It is suggested that control perception follows from the brain's capacity for self regulation, leading to flexible and goal directed behaviours. To this account, a model is presented which spans several levels of analyses. On a behavioural level, control perception may be a corollary of emotion regulation, executive functions, and social cognition. On a neural level, these self-regulatory functions are substantiated in part by the dorsolateral and ventral prefrontal cortex and the anterior cingulate cortex. In addition, a possible role of subcortical-cortical dopamine pathways underlying control perception is discussed.

A neurobehavioral systems analysis of adult rats exposed to methylazoxymethanol acetate on E17: implications for the neuropathology of schizophrenia

BACKGROUND

As a test of plausibility for the hypothesis that schizophrenia can result from abnormal brain, especially cerebral cortical, development, these studies examined whether, in the rat, disruption of brain development initiated on embryonic day (E) 17, using the methylating agent methylazoxymethanol acetate (MAM), leads to a schizophrenia-relevant pattern of neural and behavioral pathology. Specifically, we tested whether this manipulation leads to disruptions of frontal and limbic corticostriatal circuit function, while producing schizophrenia-like, region-dependent reductions in gray matter in cortex and thalamus.

METHODS

In offspring of rats administered MAM (22 mg/kg) on E17 or earlier (E15), regional size, neuron number and neuron density were determined in multiple brain regions. Spontaneous synaptic activity at prefrontal cortical (PFC) and ventral striatal (vSTR) neurons was recorded in vivio. Finally, cognitive and sensorimotor processes mediated by frontal and limbic corticostriatal circuits were assessed.

RESULTS

Adult MAM-E17-exposed offspring showed selective histopathology: size reductions in mediodorsal thalamus, hippocampus, and parahippocampal, prefrontal, and occipital cortices, but not in sensory midbrain, cerebellum, or sensorimotor cortex. The prefrontal, perirhinal, and occipital cortices showed increased neuron density with no neuron loss. The histopathology was accompanied by a disruption of synaptically-driven "bistable membrane states" in PFC and vSTR neurons, and, at the behavioral level, cognitive inflexibility, orofacial dyskinesias, sensorimotor gating deficits and a post-pubertal-emerging hyper-responsiveness to amphetamine. Earlier embryonic MAM exposure led to microcephaly and a motor phenotype.

CONCLUSIONS

The "MAM-E17" rodent models key aspects of neuropathology in circuits that are highly relevant to schizophrenia.

Catechol-o-methyltransferase, cognition, and psychosis: Val158Met and beyond

This review summarizes our current understanding of catechol-o-methyltransferase (COMT) and how it relates to brain function and schizophrenia. We begin by considering the COMT gene, its transcripts and proteins, and its relevance for central catecholamine function. We then describe how variation in COMT activity affects the function of the prefrontal cortex (PFC) and associated areas, reviewing evidence that COMT modulates executive function and working memory and highlighting recent data that also implicate it in emotional processing. Finally, we discuss briefly the genetic association between COMT and schizophrenia, focusing in particular on the complex interaction of functional loci within the gene that may underlie the mixed results of studies to date. We conclude by outlining preliminary data indicating that COMT is a promising therapeutic target for ameliorating the cognitive deficits associated with schizophrenia.

Influence of methylphenidate on brain development--an update of recent animal experiments

Methylphenidate (MPH) is the most commonly used drug to treat attention deficit/hyperactivity disorder (ADHD) in children effectively and safely. In spite of its widespread application throughout one of the most plastic and sensitive phases of brain development, very little is known to date about its long-term effects on brain structure and function. Hence, this short review updates the influence of MPH on brain development, since recent human and animal studies suggest that MPH alters the dopaminergic system with long-term effects beyond the termination of treatment.

Animal studies imply that the effects of MPH may depend on the neural responder system: Whereas structural and functional parameters are improved by MPH in animals with psychomotor impairments, they remain unaltered or get worse in healthy controls. While recent behavioural studies do not fully support such a differential effect of MPH in ADHD, the animal studies certainly prompt for further investigation of this issue. Furthermore, the abuse of MPH, when (rarely) intravenously applied, may even impair the maturation of dopaminergic fibres in subcortical brain areas. This argues for careful clinical assessment and diagnostics of ADHD symptomatology not only in conjunction with the prescription of MPH. Hence, one should be assured that MPH is only given to children with clear ADHD symptomatology leading to psychosocial impairment. The animal data suggest that under these conditions MPH is supportive for brain development and the related behaviour in children with ADHD.

How antipsychotics work-from receptors to reality

How does a small molecule blocking a few receptors change a patients' passionately held paranoid belief that the FBI is out to get him? To address this central puzzle of antipsychotic action, we review a framework linking dopamine neurochemistry to psychosis, and then link this framework to the mechanism of action of antipsychotics. Normal dopamine transmission has a role in predicting novel rewards and in marking and responding to motivationally salient stimuli. Abnormal dopamine transmission alters these processes and results in an aberrant sense of novelty and inappropriate assignment of salience leading to the experience of psychosis. Antipsychotics improve psychosis by diminishing this abnormal transmission by blocking the dopamine D2/3 receptor (not D1 or D4), and although several brain regions may be involved, it is suggested that the ventral striatal regions (analog of the nucleus accumbens in animals) may have a particularly critical role. Contrary to popular belief, the antipsychotic effect is not delayed in its onset, but starts within the first few days. There is more improvement in the first 2 weeks, than in any subsequent 2-week period thereafter. However, a simple organic molecule cannot target the complex phenomenology of the individual psychotic experience. Antipsychotics diminish dopamine transmission and thereby dampen the salience of the pre-occupying symptoms. Therefore, in the initial stage of an antipsychotic response, the patients experience a detachment from symptoms, a relegation of the delusions and hallucinations to the back of their minds, rather than a complete erasure of the symptoms. Only with time, and only in some, via the mediation of new learning and plasticity, is there a complete resolution of symptoms. The implications of these findings for clinical care, animal models, future target discovery and drug development are discussed.

Targeting prefrontal cortical dopamine D1 and N-methyl-D-aspartate receptor interactions in schizophrenia treatment

The prefrontal cortex plays a principal role in higher cognition and particularly in the fast online manipulation of appropriate information to guide forthcoming behavior. Dysfunction of this process represents a main feature in the pathophysiology of schizophrenia. Both dopamine D1 and N-methyl-D-aspartate (NMDA) receptors in the prefrontal cortex play a critical role in synaptic plasticity, memory mechanisms, and cognition. Recent data have shown that D1 and NMDA receptors interact bidirectionally and may greatly influence the output of the prefrontal cortex. Hypofunction of these receptor systems in the prefrontal cortex is found in schizophrenia. This review attempts to summarize some of the latest findings on the cellular mechanisms that underlie D1-NMDA receptor interactions. These findings have provided potential therapeutic strategies that aim to functionally up-regulate D1 and/or NMDA receptor safely via selective activation of D1 receptors or coagonist activation of NMDA receptors through blockade of the glycine transporter-1.

Combined D1/D2 receptor stimulation under conditions of dopamine depletion impairs spatial working memory performance in humans

RATIONALE

The mesocortical dopamine system is regarded as an important modulator of working memory. While it has been established that stimulation of the D1/D2 receptor in primates can improve spatial working memory performance, findings in humans are less consistent. Recent studies in humans suggest that global depletion of dopamine via tyrosine/phenylalanine depletion may impair spatial working memory performance, although these results are also inconsistent, and it has been suggested that task differences may partly underlie the inconsistent findings.

OBJECTIVES

This study had two aims: (1) to investigate the effects of acute tyrosine depletion (TPD) on a number of working memory tasks and (2) to examine whether stimulation of D1/D2 receptors under conditions of TPD can attenuate or "reverse" TPD-induced working memory impairments.

METHODS

Eighteen healthy male participants performed a spatial working memory delayed-recognition task, non-spatial working memory task and spatial n-back task on three separate occasions, after TPD, TPD and pergolide (D1/D2 agonist), and placebo.

RESULTS

TPD did not impair working memory performance on any of the tasks administered. However, stimulation of D1/D2 receptors under TPD conditions caused a subtle impairment in spatial working memory performance.

CONCLUSIONS

The finding that D1/D2 stimulation under TPD conditions impairs working memory highlights the complexity of functional effects of augmenting dopaminergic transmission within a dopamine-depleted state. The lack of TPD-related effects on a range of working memory tasks questions the reliability of TPD as a modulator of dopamine function and working memory performance in humans.

Striatal D2 receptor binding as a marker of prognosis and outcome in untreated first-episode psychosis

In a preliminary 123I-IBZM SPECT study in first-episode psychosis, a relationship between striatal dopaminergic D2 receptor (D2R) binding and premorbid adjustment was suggested. These results were replicated in the present study (n = 18), and D2R binding at diagnosis predicted a high probability for schizophrenia outcome by 2-year follow-up. The present findings contribute to the evidence of abnormal D2R binding in schizophrenia and suggest that SPECT might be useful for outcome prediction in first-episode psychosis.

Prenatal disruption of neocortical development alters prefrontal cortical neuron responses to dopamine in adult rats

A growing body of evidence suggests that structural changes in the cortex may disrupt dopaminergic transmission in circuits involving the prefrontal cortex (PFC) and may contribute to the etiology of schizophrenia. In this study, we utilize a rodent model of neonatal disruption of cortical development using prenatal administration of the mitotoxin methylazoxymethanol acetate (MAM). Using intracellular recordings in vivo, we compare the physiology of prefrontal cortical neurons and their responses to topical administration of dopamine (DA) in intact animals and adult rats treated prenatally with MAM. Topical administration of DA hyperpolarized the membrane potential (MP) and decreased the firing rate of neurons recorded in deep layers of the PFC in intact animals. Furthermore, electrical stimulation of the VTA evoked fast onset epsps or long-lasting depolarizations in PFC neurons. In comparison, PFC neurons recorded in MAM-treated animals had significantly faster baseline firing rates. Moreover, topical administration of DA did not affect the MP or firing rate of the neurons in MAM-treated animals. However, MAM-treated animals exhibited an increase in the percentage of neurons responding with long-lasting depolarizations to stimulation of the VTA. The results of this study indicate that PFC neurons in the MAM-treated rats are not responsive to DA administered superficially, while at the same time exhibit greater responsiveness to VTA stimulation. These results are consistent with a rewiring of the corticolimbic system in response to neurodevelopmental insults.

Isolation rearing or methamphetamine traumatisation induce a "dysconnection" of prefrontal efferents in gerbils: implications for schizophrenia

A miswiring of prefrontal efferents is generally discussed by the name of "dysconnection" as the anatomical substrate of schizophrenia. Since direct histological confirmation of this hypothesis can hardly be obtained in humans, we used an animal model of schizophrenia to trace prefrontal efferents to distal cortical fields. Mongolian gerbils were intoxicated with a single high dose of methamphetamine on postnatal day 14 and reared in isolation after weaning (day 30). Controls received a saline injection and/or were reared under enriched conditions. Upon reaching adulthood (day 90), biocytin was injected into the medial prefrontal cortex into either deep or superficial laminae. The density of passing fibres and terminal fields in the frontal, parietal and insular cortices was assessed by digital image analysis. Isolation rearing or methamphetamine treatment alone reduced the projections from lamina V/VI to the frontal and from lamina III to the insular cortex, and from both laminae to the parietal cortex. In contrast, isolation rearing of methamphetamine-intoxicated gerbils significantly increased the projections from the deep laminae to the frontal and parietal cortices, compared to isolation-reared controls, with no difference in the efferents from superficial laminae. These results are the first to demonstrate a miswiring of prefrontal efferents in response to adverse systemic influences. They might give a hint at the anatomical basis of "dysconnection" in schizophrenia.

Neonatal depletion of cortical dopamine: effects on dopamine turnover and motor behavior in juvenile and adult rats

Abnormal development of mesoprefrontal dopamine (DA) neurons may contribute to the pathophysiology of schizophrenia. Consistent with this hypothesis, DA nerve terminal density is decreased in the cortex of schizophrenic subjects [M. Akil, J.N. Pierri, R.E. Whitehead, C.L. Edgar, C. Mohila, A.R. Sampson, and D.A. Lewis, Lamina-specific alterations in the dopamine innervation of the prefrontal cortex in schizophrenic subjects, Am. J. Psychiatry, 156 (1999) 1580-1589]. This abnormality may be present early in development, giving rise to dysfunction as an individual matures. The present studies examined the effects of early partial loss of medial prefrontal cortex (mPFC) DA on DA turnover and locomotor behavior in juvenile, pubertal, and adult rats (30, 45, and 60 days of age, respectively). Local infusions of 6-hydroxydopamine on postnatal day (PN) 12-14 produced persistent decreases in basal tissue DA concentrations and increases in 3,4-dihydroxyphenylacetic acid (DOPAC):DA ratios in the mPFC. In the nucleus accumbens of lesioned rats, basal DA concentrations were decreased and DOPAC:DA ratios were increased on PN30, but not PN45 or 60. Footshock (30 min at 0.6 mA) increased DOPAC and DOPAC:DA ratios in the mPFC of PN30 and 60 control rats. These effects were attenuated in age-matched rats previously sustaining approximately 50% loss of mPFC DA on PN12-14. Footshock did not affect DOPAC:DA ratios in the nucleus accumbens of control or lesioned rats. The lesion also failed to alter basal or stress-evoked motor activity. The present data suggest that a decreased density of mPFC DA nerve terminals occurring early in development results in persistent alterations in basal and stress-evoked activity of mesoprefrontal DA neurons, but not mesoaccumbens DA neurons.