Binding of sodium channel inhibitors to hyperpolarized and depolarized conformations of the channel.

Sodium channels are inhibited by a chemically diverse group of compounds. In the last decade entirely new structural classes with superior properties have been discovered, and novel therapeutic uses of sodium channel inhibitors (SCIs) have been suggested. Many promising novel drug candidates have been described and characterized. Published structure-activity relationship studies, pharmacophore models, and mutagenesis studies seem to lag behind, dealing with only a limited group of inhibitor compounds. The abundance of novel compounds requires an organized comparison of drug potencies. The affinity of sodium channel inhibitors can vary typically ten- to thousand-fold depending on the voltage protocol; therefore comparison of electrophysiology data is difficult. In this study we describe a method for standardization of these data with the help of a simple model of state-dependence. We derived hyperpolarized (resting) and depolarized (generally termed "inactivated") state affinities for the studied drugs, which made the measurements comparable. We show a rank order of SCIs based on resting and inactivated affinity values. In an attempt to define basic chemical requirements for sodium channel inhibitor activity we investigated the dependence of both resting and inactivated state affinities on individual chemical descriptors. Lipophilicity (most often expressed by the logP value) is the single most important determinant of SCI potency. We investigated the independent impact of several other calculated chemical properties by standardizing drug potencies for logP values. By combining these two approaches: standardization of affinity values, and standardization of potencies, we concluded that while resting affinity is mostly determined by lipophilicity, inactivated state affinity is determined by a more complex interaction of chemical properties, including hydrogen bond acceptors, aromatic rings, and molecular weight.

Non-synaptic receptors and transporters involved in brain functions and targets of drug treatment.

Beyond direct synaptic communication, neurons are able to talk to each other without making synapses. They are able to send chemical messages by means of diffusion to target cells via the extracellular space, provided that the target neurons are equipped with high-affinity receptors. While synaptic transmission is responsible for the 'what' of brain function, the 'how' of brain function (mood, attention, level of arousal, general excitability, etc.) is mainly controlled non-synaptically using the extracellular space as communication channel. It is principally the 'how' that can be modulated by medicine. In this paper, we discuss different forms of non-synaptic transmission, localized spillover of synaptic transmitters, local presynaptic modulation and tonic influence of ambient transmitter levels on the activity of vast neuronal populations. We consider different aspects of non-synaptic transmission, such as synaptic-extrasynaptic receptor trafficking, neuron-glia communication and retrograde signalling. We review structural and functional aspects of non-synaptic transmission, including (i) anatomical arrangement of non-synaptic release sites, receptors and transporters, (ii) intravesicular, intra- and extracellular concentrations of neurotransmitters, as well as the spatiotemporal pattern of transmitter diffusion. We propose that an effective general strategy for efficient pharmacological intervention could include the identification of specific non-synaptic targets and the subsequent development of selective pharmacological tools to influence them.

Cadherin adhesion, tissue tension, and noncanonical Wnt signaling regulate fibronectin matrix organization.

In this study we demonstrate that planar cell polarity signaling regulates morphogenesis in Xenopus embryos in part through the assembly of the fibronectin (FN) matrix. We outline a regulatory pathway that includes cadherin adhesion and signaling through Rac and Pak, culminating in actin reorganization, myosin contractility, and tissue tension, which, in turn, directs the correct spatiotemporal localization of FN into a fibrillar matrix. Increased mechanical tension promotes FN fibril assembly in the blastocoel roof (BCR), while reduced BCR tension inhibits matrix assembly. These data support a model for matrix assembly in tissues where cell-cell adhesions play an analogous role to the focal adhesions of cultured cells by transferring to integrins the tension required to direct FN fibril formation at cell surfaces.

Reliability and validity of the Gastrointestinal Symptom Rating Scale (GSRS) and Quality of Life in Reflux and Dyspepsia (QOLRAD) questionnaire in dyspepsia: a six-country study.

BACKGROUND: Symptoms of dyspepsia significantly disrupt patients' lives and reliable methods of assessing symptom status are important for patient management. The aim of the current study was to document the psychometric characteristics of the Gastrointestinal Symptom Rating Scale (GSRS) and the Quality of Life in Reflux and Dyspepsia questionnaire (QOLRAD) in Afrikaans, German, Hungarian, Italian, Polish and Spanish patients with dyspepsia. METHODS: 853 patients with symptoms of dyspepsia completed the GSRS, the QOLRAD, the 36-item Short-Form Health Survey (SF-36) and the Hospital Anxiety and Depression scale. RESULTS: The internal consistency reliability of the GSRS was 0.43-0.87 and of the QOLRAD 0.79-0.95. Test-retest reliability of the GSRS was 0.36-0.75 and of the QOLRAD 0.41-0.82. GSRS Abdominal pain domain correlated significantly with all QOLRAD domains in most language versions, and with SF-36 Bodily pain in all versions. QOLRAD domains correlated significantly with the majority of SF-36 domains in most versions. Both questionnaires were able to differentiate between patients whose health status differed according to symptom frequency and severity. CONCLUSION: The psychometric characteristics of the different language versions of the GSRS and QOLRAD were found to be good, with acceptable reliability and validity. The GSRS and QOLRAD were found to be useful for evaluating dyspeptic symptoms and their impact on patients' daily lives in multinational clinical trials.

The unusual state-dependent affinity of P2X3 receptors can be explained by an allosteric two-open-state model.

High-affinity desensitization (HAD) by nanomolar agonists was described to shape the ability of P2X(3) receptors for mediating pain sensation. These receptors are activated by micromolar ATP, but nanomolar ATP is sufficient to effectively desensitize them. The mechanism behind HAD is still obscure. It has been suggested ( J Neurosci 25: 7359-7365, 2005 ) that HAD can happen only if the receptor has previously been activated and desensitized by high agonist concentrations. It was not clear, however, whether the high-affinity site was different from the conventional binding site and which mechanism led to its exposure during desensitization. A subsequent article ( Mol Pharmacol 70: 373-382, 2006 ) argued that HAD could also occur without preceding desensitization, because even resting receptors expose high-affinity binding sites. To support this hypothesis, a kinetic model was proposed that could reproduce all major phenomena observed experimentally. We attempted to improve this model and used it to simulate the agonist-induced formation of the high-affinity binding site. We collected electrophysiological data using HEK 293 cells expressing human P2X(3) receptors and fitted simulated currents to experimentally acquired currents. A simple allosteric kinetic model in which only triliganded receptors could open failed to reproduce receptor behavior; introduction of an additional diliganded open state was necessary. Simulation with this model gave results that were in good agreement with experimental data. By using simulations and experiments, we analyzed the process of high-affinity binding site formation upon agonist exposure and propose an explanation, which helps to resolve the apparent conflict regarding the mechanism of HAD.

Multiscale computational analysis of Xenopus laevis morphogenesis reveals key insights of systems-level behavior.

BACKGROUND: Tissue morphogenesis is a complex process whereby tissue structures self-assemble by the aggregate behaviors of independently acting cells responding to both intracellular and extracellular cues in their environment. During embryonic development, morphogenesis is particularly important for organizing cells into tissues, and although key regulatory events of this process are well studied in isolation, a number of important systems-level questions remain unanswered. This is due, in part, to a lack of integrative tools that enable the coupling of biological phenomena across spatial and temporal scales. Here, we present a new computational framework that integrates intracellular signaling information with multi-cell behaviors in the context of a spatially heterogeneous tissue environment. RESULTS: We have developed a computational simulation of mesendoderm migration in the Xenopus laevis explant model, which is a well studied biological model of tissue morphogenesis that recapitulates many features of this process during development in humans. The simulation couples, via a JAVA interface, an ordinary differential equation-based mass action kinetics model to compute intracellular Wnt/beta-catenin signaling with an agent-based model of mesendoderm migration across a fibronectin extracellular matrix substrate. The emergent cell behaviors in the simulation suggest the following properties of the system: maintaining the integrity of cell-to-cell contact signals is necessary for preventing fractionation of cells as they move, contact with the Fn substrate and the existence of a Fn gradient provides an extracellular feedback loop that governs migration speed, the incorporation of polarity signals is required for cells to migrate in the same direction, and a delicate balance of integrin and cadherin interactions is needed to reproduce experimentally observed migratory behaviors. CONCLUSION: Our computational framework couples two different spatial scales in biology: intracellular with multicellular. In our simulation, events at one scale have quantitative and dynamic impact on events at the other scale. This integration enables the testing and identification of key systems-level hypotheses regarding how signaling proteins affect overall tissue-level behavior during morphogenesis in an experimentally verifiable system. Applications of this approach extend to the study of tissue patterning processes that occur during adulthood and disease, such as tumorgenesis and atherogenesis.

The mechanism of activity-dependent sodium channel inhibition by the antidepressants fluoxetine and desipramine.

The effect of monoamine uptake inhibitor-type antidepressants on sodium channels of hippocampal neurons was investigated. Members of the tricyclic group of antidepressants are known to modify multiple targets, including sodium channels, whereas selective serotonin-reuptake inhibitors (SSRIs) are regarded as highly selective compounds, and their effect on sodium channels was not investigated in detail. In this study, a representative member of each group was chosen: the tricyclic antidepressant desipramine and the SSRI fluoxetine. The drugs were roughly equipotent use-dependent inhibitors of sodium channels, with IC(50) values approximately 100 microM at -150 mV holding potential, and approximately 1 microM at -60 mV. We suggest that therapeutic concentrations of antidepressants affect neuronal information processing partly by direct, activity-dependent inhibition of sodium channels. As for the mechanism of inhibition, use-dependent inhibition by antidepressants was believed to be due to a preferential affinity to the fast-inactivated state. Using a voltage and perfusion protocol by which relative affinities to fast-versus slow-inactivated states could be assessed, we challenged this view and found that the affinity of both drugs to slowinactivated state(s) was higher. We propose a different mechanism of action for these antidepressants, in which slow rather than fast inactivation plays the dominant role. This mechanism is similar but not equivalent with the novel mechanism of usedependent sodium channel inhibition previously described by our group (Neuroscience 125:1019-1028, 2004; Neuroreport 14:1945-1949, 2003). Our results suggest that different drugs can produce use-dependent sodium channel inhibition by different mechanisms.

[Psychometric validation of the Polish translation of the Gastrointestinal Symptom Rating Scale (GSRS) and Quality of Life in Reflux and Dyspepsia (QOLRAD) Questionnaire in patients with reflux disease]. / Psychometryczna walidacja polskiego tlumaczenia Skali Ilosciowej Oceny Objawów Zolkdkowo-Jelitowych (GSRS, Gastrointestinal Symptom Rating Scale) oraz Kwestionariusza Oceny Jakosci Zycia w Chorobie Refluksowej i Dyspepsji (QOLRAD, Quality of Life in Reflux and Dyspepsia Questionnaire) u pacjentów z choroba refluksowa.

UNLABELLED: Symptoms of heartburn and their impact on health-related quality of life (HRQL) are often evaluated in clinical trials. When a questionnaire is translated into a new language, a linguistic validation is necessary but not sufficient unless the psychometric characteristics have been verified. The aim of the study is to document the psychometric characteristics of the Polish translation of the Gastrointestinal Symptom Rating Scale (GSRS) and quality of life in reflux and dyspepsia (QOLRAD) questionnaire. One hundred and thirty-five patients with symptoms of heartburn (mean age: 44, SD = 14.6; females % = 60.7) completed the Polish translation of GSRS, the heartburn version of QOLRAD, the Short-Form-36 (SF-36) and the Hospital Anxiety and Depression (HAD) scale. Seventy patients were scheduled for a second visit a week later to complete the GSRS and QOLRAD again. The internal consistency reliability of GSRS ranged from 0.58 to 0.88 and of QOLRAD from 0.84 to 0.95, and the test-retest reliability of GSRS ranged from 0.34 to 0.63 and of QOLRAD from 0.51 to 0.74. The relevant domains of the GSRS, "reflux", "abdominal pain" and "indigestion", and all QOLRAD domain scores significantly correlated. GSRS domains "abdominal pain" and "indigestion" were related to all SF-36 domains. All QOLRAD domains significantly correlated with all SF-36 domains. CONCLUSIONS: the psychometric characteristics of the Polish translations of GSRS and QOLRAD were found to be good, with satisfactory reliability and validity. The test-retest reliability of the GSRS "reflux" domain was however not optimal.

[Burden of illness in Polish patients with reflux disease]. / Obciazenie polskich pacjentów zwiazane z choroba refluksowa przelyku.

The clinical and socioeconomic burden of gastro-esophageal reflux disease (GERD) is considerable. The primary symptom of GERD is heartburn, but it may also be associated with extraesophageal manifestations, such as asthma, chest pain and otolaryngologic disorders. The objective of the study was to describe the impact of heartburn on patients' Health-Related Quality of Life (HRQL) in Poland, using validated generic and disease-specific instruments to measure patient-reported outcomes. Patients with symptoms of heartburn completed the Polish versions of the Gastrointestinal Symptom Rating Scale (GSRS), the Quality of Life in Reflux and Dyspepsia questionnaire (QOLRAD), the Short Form-36 (SF-36) and the Hospital Anxiety and Depression (HAD) scale. Frequency and severity of heartburn during the previous 7 days were also recorded. 135 patients completed the assessments (mean age of 44 years, SD = 15; 61% female). 55% of patients had moderate symptoms and nearly two thirds (64%) had symptoms on 5 or more days in the previous week. Patients were most bothered by symptoms of reflux (mean GSRS score of 4.1, on a scale of 1 [not bothered] to 7 [very bothered]), indigestion (3.5) and abdominal pain (3.2). As a result of their symptoms, patients experienced impaired vitality (mean QOLRAD score of 3.8, on a scale of 1 to 7, where 1 represents the most severe impact on daily functioning), problems with food and drink (3.9), emotional distress (4.1) and sleep disturbance (4.7). Using HAD, 32% of heartburn patients were anxious and 10% were depressed. In conclusion it should be stated that there is consistent evidence that GERD substantially impairs all aspects of health-related quality of life.

Impact of irritable bowel syndrome on patients' lives: development and psychometric documentation of a disease-specific measure for use in clinical trials.

OBJECTIVE: To develop a disease-specific questionnaire to capture the impact of irritable bowel syndrome (IBS) and its treatment on patients' lives, the Irritable Bowel Syndrome Impact Scale (IBS-IS). PATIENTS AND METHODS: One hundred and fifty-five IBS patients participated (126 (81%) female; age (mean+/-SD) 45.5+/-12.4 years). We developed the initial 39 items from the literature, available IBS-specific instruments and input from physicians, nurses and patients. We deleted IBS-IS items with a high ceiling effect, items that measured a different construct and items showing a high correlation (r>0.90) with another item and with Rasch analysis, leaving 26 items. We then applied exploratory factor analysis to examine domain groupings. Subjects completed the IBS-IS instrument, the Gastrointestinal Symptom Rating Scale for IBS (GSRS-IBS), Short Form-36 (SF-36), Visceral Sensitivity Index (VSI), and Hospital Anxiety and Depression (HAD) scale. Internal consistency, construct validity and discriminate validity were assessed. RESULTS: The 26 items represented five domains: fatigue, impact on daily activities, sleep disturbance, emotional distress and eating habits. The internal consistency reliability for the domains was 0.87 to 0.96. Most associations between similar constructs in the IBS-IS, GSRS-IBS, SF-36, VSI, and HAD were >0.40. Each IBS-IS domain score decreased with increasing IBS symptom severity (P<0.05), and the patients scored >5 score units lower than a US general population scored on all eight SF-36 dimensions. CONCLUSION: The IBS-IS is a short, user-friendly instrument with excellent psychometric properties that has potential usefulness for clinical trials.

An instrument for measuring health-related quality of life in patients with Deep Venous Thrombosis (DVT): development and validation of Deep Venous Thrombosis Quality of Life (DVTQOL) questionnaire.

BACKGROUND: Few studies have evaluated patient-reported outcomes in connection with a primary event of deep venous thrombosis, partly due to a lack of disease-specific measures. The aim here was to develop a disease-specific health-related quality of life (HRQL) measure, the deep venous thrombosis quality of life questionnaire (DVTQOL), for patients with recent exposition and treatment of proximal deep venous thrombosis. METHODS: A total of 121 consecutive outpatients (50 % males; mean age 61.2 +/- 14 years) treated with warfarin (Waran) for symptomatic proximal deep venous thrombosis were included in the study. Patients completed the SF-36, EQ-5D and the pilot version of the DVTQOL. RESULTS: Items having: high ceiling and floor effect, items with lower factor loadings than 0.50 and items loading in several factors were removed from the pilot version of DVTQOL. In addition, overlapping and redundant items identified by the Rasch analysis were excluded. The final DVTQOL questionnaire consists of 29 items composing six dimensions depicting problems with: emotional distress; symptoms (e.g. pain, swollen ankles, cramp, bruising); limitation in physical activity; hassle with coagulation monitoring; sleep disturbance; and dietary problems. The internal consistency reliability was high (alpha value ranged from 0.79 to 0.93). The relevant domains of the SF-36 and EQ-5D significantly correlated with DVTQOL, thereby confirming its construct validity. CONCLUSIONS: The DVTQOL is a short and user-friendly instrument with good reliability and validity. Its test-retest reliability and responsiveness to change in clinical trials, however, must be explored.

A novel modulatory mechanism of sodium currents: frequency-dependence without state-dependent binding.

We have previously found that the dopamine uptake inhibitor 1-(2-[bis(4-fluorophenyl)methoxy]ethyl)-4-(3-phenylpropyl)piperazine dihydrochloride (GBR 12909) inhibits neuronal sodium channels. The inhibition was profoundly dependent on the voltage protocol, suggesting that the effect is determined by the activity pattern of individual neurons. Our present study was aimed to understand more thoroughly the mechanism of this inhibition. The effect of GBR 12909 on sodium currents was investigated using whole-cell patch clamp recordings on cultured hippocampal neurons. Repetitive trains of depolarizations revealed two distinct components of inhibition: a frequency-dependent, transient and a frequency-independent, sustained component. Frequency-dependent inhibition can reflect dynamic equilibrium of binding or gating. In order to decide which is the dominant mechanism in the case of GBR 12909, we studied the rates of association and dissociation. We found an unexpectedly fast rate of association (tau=819.2 ms) to resting ion channels kept at hyperpolarized membrane potential (-150 mV), while the rate of dissociation was too slow to explain recovery between trains of stimulation (tau=248 s). These data suggest that frequency-dependent inhibition cannot be explained by binding and unbinding, but rather it is due to conformational transitions of the liganded channel, which can only be explained if ligand binding is assumed to enhance slow inactivation. We studied, therefore, the rate of slow inactivation in the presence of different concentrations of GBR 12909. We have found that GBR 12909 accelerates slow inactivation substantially (time constants more than hundredfold lower at concentrations above 10 microM), causing the time range of slow inactivation to overlap with the time range of fast inactivation. Slow inactivation can even be the dominant process, especially during subthreshold depolarizations in the presence of >10 microM of GBR 12909. This mechanism of inhibition could provide a selective inhibition of neurons not only with high frequency bursting activity but also with moderately depolarized membrane potential.

Psychometric validation of the italian translation of the gastrointestinal symptom-rating scale and quality of life in reflux and dyspepsia questionnaire in patients with gastro-oesophageal reflux disease.

BACKGROUND: Symptoms of heartburn and their impact on health-related quality of life (HR-QOL) are often evaluated in clinical trials. When a questionnaire is translated into a new language, a linguistic validation is necessary but not sufficient unless the psychometric characteristics have been verified. OBJECTIVE: To document the psychometric characteristics of the Italian translation of the Gastrointestinal Symptom-Rating Scale (GSRS) and Quality of Life in Reflux and Dyspepsia (QOLRAD) questionnaire. PATIENTS AND METHODS: 152 consecutive patients with symptoms of heartburn (mean +/- SD age 46.5 +/- 16.2 years; 40.1% males) completed the Italian translation of GSRS, the heartburn version of QOLRAD, the 36-item Short-Form health survey (SF-36), and the Hospital Anxiety and Depression (HAD) scale. RESULTS: The internal consistency reliability of GSRS ranged from 0.62 to 0.76 and of QOLRAD from 0.77 to 0.89. The relevant domains of the GSRS ('Reflux', 'Abdominal Pain' and 'Indigestion') and QOLRAD domain scores significantly correlated. GSRS domains 'Reflux' and 'Abdominal Pain' strongly correlated (negatively) with most of the domains of the SF-36. Similarly, all QOLRAD domains significantly correlated with all SF-36 domains. CONCLUSION: The psychometric characteristics of the Italian translations of GSRS and QOLRAD were found to be good, with satisfactory reliability and validity.

Psychometric validation of the German translation of the Gastrointestinal Symptom Rating Scale (GSRS) and Quality of Life in Reflux and Dyspepsia (QOLRAD) questionnaire in patients with reflux disease.

BACKGROUND: Symptoms of heartburn has an impact on health-related quality of life (HRQL). When a questionnaire is translated into a new language, a linguistic validation is necessary but not sufficient unless the psychometric characteristics have been verified. The aim is to document the psychometric characteristics of the German translation of the Gastrointestinal Symptom Rating Scale (GSRS) and Quality of Life in Reflux and Dyspepsia (QOLRAD) questionnaire. METHODS: 142 patients with symptoms of heartburn (Age: M = 47.5, +/- 14.6; Males = 44.4%) completed the German translation of GSRS, the QOLRAD, the Short-Form-36 (SF-36) and the Hospital Anxiety and Depression (HAD) scale. RESULTS: The internal consistency reliability of GSRS ranged from 0.53-0.91 and of QOLRAD from 0.90-0.94, respectively. The test-retest reliability of GSRS ranged from 0.49-0.73 and of QOLRAD from 0.70-0.84. The relevant domains of the GSRS and QOLRAD domain scores significantly correlated. GSRS domains of Abdominal Pain and Constipation correlated (negatively) with most of the domains of the SF-36. The relevant QOLRAD domains significantly correlated with all SF-36 domains. CONCLUSIONS: The psychometric characteristics of the German translation of GSRS and QOLRAD were found to be good, with satisfactory reliability and validity. The reliability of the GSRS Abdominal Pain domain was moderate.

Factor structure of the Quality of Life in Reflux and Dyspepsia (QOLRAD) questionnaire evaluated in patients with heartburn predominant reflux disease.

AIM: To test whether the original factor structure of the Quality of Life in Reflux and Dyspepsia (QOLRAD) can be replicated in Nordic patients and English speaking patients. PATIENTS AND METHODS: Clinical trial patients with heartburn without esophagitis completed the Swedish, Norwegian, Finnish and Danish versions (n = 634) and the English version (n = 1185). The factor structure was examined using models generated by exploratory and confirmatory factor analysis. RESULTS: The exploratory factor analysis suggested that the original five-factor structure solution was the most optimal. The Nordic versions explained 67% and the English version 72% of the variance. The factor loading of 22 out of 25 items was >0.55. In the confirmatory factor analysis, because of the sample size, only the Swedish and Norwegian data were used. Confirmatory factor analysis indicated an acceptable goodness of fit of the five-factor solution to the data with a goodness of fit index of 0.85 in the Swedish, 0.77 in the Norwegian and 0.91 in the English speaking population. The internal consistency reliability ranged from 0.70 to 0.94 (in the Nordic translations) and from 0.85 to 0.92 (in the English version), supporting the homogeneity of the items within the factors and thus their construct validity. The QOLRAD distinguished severity and frequency of heartburn, thereby documenting its known-group validity to distinguish between groups of patients. CONCLUSIONS: The factor structure and dimensionality of the English version and the Swedish and Norwegian translations of the QOLRAD could be replicated by the exploratory and confirmed by the confirmatory factor analysis. The QOLRAD is a valid and reliable instrument for use in clinical trials.

A qualitative analysis of patient-centered dentistry in consultations with dental phobic patients.

Dental phobia is regarded as one of the greatest obstructions to adequate dental care. It has long been established that fearful dental patients are particularly sensitive to dentists' behavior and performance of dental care. There is a need for the establishment of a systematic theory of dentist-patient communication and new methods analyzing how dentists interact with their patients. In this qualitative study, thirty semi-structured interviews were conducted in 1998 and 1999 with five dentists (three male and two female). Dentists consulted on two occasions with 15 newly enrolled, consecutive dental phobic patients (2 male and 13 female) in a Swedish clinic specializing in the treatment of odontophobia. The time interval between consultation one and two was approximately 2-3 weeks. Analysis of the transcribed interviews was based by the principles of Grounded Theory. The study identified one core category, "Holistic perception and understanding of the patient", two categories, "The dentist's positive outlook on people" and "The dentist's positive view of patient contact", and six further subcategories. Findings support previous models of patient-centered medicine and contribute to a better understanding of how patient-centered dentists interact with dental phobic patients.

Spurious precision: procedural validity of diagnostic assessment in psychotic disorders.

OBJECTIVE: Very few studies have quantified the level of agreement among alternative diagnostic procedures that use a common set of fixed operational criteria. The authors examined the procedural validity of four independent methods of assigning DSM-III-R diagnoses of psychotic disorders. METHOD: The research was conducted as a satellite study to the DSM-IV Field Trial for Schizophrenia and Related Psychotic Disorders. The setting was the National Health and Medical Research Council Schizophrenia Research Unit's Early Psychosis Prevention and Intervention Centre, which focuses on first-episode psychosis. Consecutively admitted patients (N = 50) were assessed by independent raters who used four different procedures to determine a DSM-III-R diagnosis. These procedures were 1) the diagnostic instrument developed for the DSM-IV field trial, 2) the Royal Park Multidiagnostic Instrument for Psychosis, 3) the Munich Diagnostic Checklists, and 4) a consensus DSM-III-R diagnosis assigned by a team of clinician researchers who were expert in the use of diagnostic criteria. RESULTS: Concordance between pairs of diagnostic procedures was only moderate. Corresponding levels of percent agreement, however, ranged from 66% to 76%, with converse misclassification rates of 24%-34% (assuming one procedure to be "correct"). CONCLUSIONS: These findings have significant research and clinical implications. Despite the introduction of operationally defined diagnoses, there remained an appreciable level of differential classification or misclassification arising from variability in the method of assigning the diagnostic criteria rather than the criteria themselves. Such misclassification may impede neurobiological research and have harmful clinical effects on patients with first-episode psychosis.