Benefits of lipid lowering on vascular reactivity in patients with coronary artery disease and average cholesterol levels: a mechanism for reducing clinical events?

BACKGROUND

The favorable effects of lowering low-density lipoprotein (LDL)-cholesterol on reducing clinical events in patients with coronary disease have been well established. The mechanisms responsible for this benefit, however, have not been fully understood. This study examined the impact of lipid-lowering therapy on endothelium-dependent vasoreactivity in a subgroup of patients after myocardial infarction with average cholesterol levels who participated in the Cholesterol Recurrent Events (CARE) study to determine whether an effect on endothelial function is a viable mechanism for the observed reduction in clinical events.

METHODS AND RESULTS

Participants were recruited from among volunteers in the CARE trial at 2 university-based outpatient cardiology clinics. Patients were randomly assigned to pravastatin or placebo. Plasma lipids were measured at baseline and semiannually thereafter. During the final 6 months of the trial, vasoreactivity was assessed by change in ultrasound-determined brachial artery diameter in response to blood pressure cuff-induced ischemia (endothelium-dependent) and to nitroglycerin, a direct vasodilator. Differences in response were examined between the 2 randomized groups. The relation between change in LDL-cholesterol from baseline to year 5 and the magnitude of endothelium-dependent vasodilation also was examined. There was significantly greater endothelium-dependent vasodilation observed in the pravastatin group compared with the placebo group (13% vs 8%, P =.0002), with no difference between the groups in their response to the endothelium-independent vasodilator nitroglycerin. The magnitude of the endothelium-dependent vasodilation was significantly correlated with the percent change in LDL-cholesterol from baseline to final visit (r = 0.49, P =.015).

CONCLUSIONS

These findings indicate that the use of pravastatin in patients after myocardial infarction with average cholesterol levels is associated with greater endothelium-dependent vasodilation compared with those who received placebo. The magnitude of this vasodilatory response is correlated to the reduction in LDL-cholesterol. This improvement in endothelium-dependent vasoreactivity may be a likely mechanism, at least in part, for the reduction in recurrent clinical events observed and reported in the CARE study.

The "benefits" of distractibility: mechanisms underlying increased Stroop effects in schizophrenia

Recent studies of selective attention in schizophrenia patients suggest a particular pattern of single-trial Stroop performance: increased facilitation but not interference in reaction times (RTs), combined with increased error interference. Our Stroop task analysis suggests that this pattern can be explained by a selective attention deficit if one accounts for (1) performance in the congruent condition; (2) the nature of the neutral stimulus; (3) the relationship between accuracy and RT; and (4) response set effects. To test these hypotheses, we examined Stroop performance in 40 DSM-IV schizophrenia patients and 20 healthy control subjects, using a range of neutral stimuli (color patches, noncolor words, color words not in the response set). The findings confirmed several of our predictions and the results were consistent with the hypothesis that abnormal Stroop performance in schizophrenia reflects a failure to adequately attend to the task-appropriate stimulus dimension (color). This inattention affects both the congruent and incongruent conditions and multiple points in the information processing pathway.

Parsing executive processes: strategic vs. evaluative functions of the anterior cingulate cortex

Event-related functional MRI and a version of the Stroop color naming task were used to test two conflicting theories of anterior cingulate cortex (ACC) function during executive processes of cognition. A response-related increase in ACC activity was present when strategic processes were less engaged, and conflict high, but not when strategic processes were engaged and conflict reduced. This is inconsistent with the widely held view that the ACC implements strategic processes to reduce cognitive conflicts, such as response competition. Instead, it suggests that the ACC serves an evaluative function, detecting cognitive states such as response competition, which may lead to poor performance, and representing the knowledge that strategic processes need to be engaged.

Overt verbal responding during fMRI scanning: empirical investigations of problems and potential solutions

This paper presents a pair of studies designed to empirically explore the severity of potential artifacts associated with overt verbal responding during fMRI scanning and to examine several different solutions to these artifacts. In Study One, we compared susceptibility artifacts, signal-to-noise ratios, and activation patterns when overt versus covert verbal responses were elicited during fMRI scanning, using both individual and group analyses. The results indicated that different patterns of brain activation were elicited during covert as compared to overt verbal responses. This suggests that covert responses cannot be used as a simple substitute for overt verbal responses. Further, the results suggested that the use of overt verbal responses during fMRI scanning can produce interpretable results if: (1) the primary comparison is between two conditions that both use overt verbal responses, and (2) analyses are conducted on pooled group data rather than individual participant data. In Study Two, we evaluated the feasibility and validity of a method for acquiring participants' overt responses during fMRI scanning. The results indicated that our method was very accurate in acquiring the content of participant's responses. Further, inspection of the responses demonstrated that participants do not always comply with task instructions and highlighted the importance of obtaining behavioral performance measures during fMRI scanning.

Conflict monitoring versus selection-for-action in anterior cingulate cortex

The anterior cingulate cortex (ACC), on the medial surface of the frontal lobes of the brain, is widely believed to be involved in the regulation of attention. Beyond this, however, its specific contribution to cognition remains uncertain. One influential theory has interpreted activation within the ACC as reflecting 'selection-for-action', a set of processes that guide the selection of environmental objects as triggers of or targets for action. We have proposed an alternative hypothesis, in which the ACC serves not to exert top-down attentional control but instead to detect and signal the occurrence of conflicts in information processing. Here, to test this theory against the selection-for-action theory, we used functional magnetic resonance imaging to measure brain activation during performance of a task where, for a particular subset of trials, the strength of selection-for-action is inversely related to the degree of response conflict. Activity within the ACC was greater during trials featuring high levels of conflict (and weak selection-for-action) than during trials with low levels of conflict (and strong selection-for-action), providing evidence in favour of the conflict-monitoring account of ACC function.

Auxin metabolism in mosses and liverworts

The plant hormone auxin (indole-3-acetic acid, IAA) is involved in the control of many phenomena during plant development. By characterizing steady-state free and conjugated IAA levels using a stable isotope dilution method coupled with gas chromatography- selected ion monitoring- mass spectrometry, this paper provides a detailed characterization of IAA metabolism in five liverworts, four mosses, and two tracheophytes. Long-term IAA conjugation patterns were monitored by incubating actively growing tissue with (14)C-IAA and then analyzing the de novo synthesis of IAA conjugates with radioimaging techniques. The liverworts, mosses, and tracheophytes can be differentiated by the total amount of IAA metabolites, the proportion of free and conjugated IAA, the chemical nature of their IAA conjugates, and the rates of IAA conjugation. Our tentative conclusion is that the liverworts appear to employ a biosynthesis-degradation strategy for the regulation of free IAA levels, in contrast to the conjugation-hydrolysis strategy apparently used by the mosses and tracheophytes. Such alternative metabolic strategies may have profound implications for macroevolutionary processes in these plant groups.

Phase I trial of intravenous thymidine and carboplatin in patients with advanced cancer

PURPOSE

To evaluate the biologic interactions and toxicities of carboplatin combined with a 24-hour infusion of thymidine 75 mg/m(2) in a phase I trial.

PATIENTS AND METHODS

Thirty-two patients with cancer refractory to conventional therapy were treated. The first set of patients (n = 7) received thymidine alone 4 weeks before subsequent planned courses of thymidine combined with carboplatin followed (4 weeks) by carboplatin alone. Carboplatin was administered over 20 minutes at hour 20 of the 24-hour thymidine infusion. The carboplatin dose was escalated in patient groups: 200 mg/m(2) (n = 3); 300 mg/m(2) (n = 7); 350 mg/m(2) (n = 4); 400 mg/m(2) (n = 3); 480 mg/m(2) (n = 10); and 576 mg/m(2) (n = 5). At the maximum-tolerated dose (480 mg/m(2)), five patients received combined therapy first and carboplatin alone second, and five patients received carboplatin first and combined therapy second. Maintenance therapy for stable or responding patients was combined therapy.

RESULTS

Evaluation demonstrated a trend toward thymidine protection of carboplatin-induced treatment-limiting thrombocytopenia. Neutropenia with carboplatin alone or in combination was negligible. Thymidine alone had no myelosuppressive effects and produced reversible grade 1 or 2 nausea and vomiting (57%), headache (25%), and grade 1 neurotoxicity (22%). Thymidine did not enhance expected carboplatin toxicities. There was no therapy-related infection or bleeding. Analysis of platinum in plasma ultrafiltrate and urine showed no effect by thymidine. Similarly, thymidine pharmacokinetics was not affected by carboplatin. As predicted, nicotinamide adenine dinucleotide levels in peripheral lymphocytes were increased during exposure to carboplatin and/or thymidine but were decreased by carboplatin alone. In three patients with high-grade glioma, responses included one complete remission (21 months) and one partial remission (14 months) at the 480-mg/m(2)-dose level, and disease stabilization (7 months) at the 400-mg/m(2-dose) level. A minor response was observed in a patient with metastatic colon cancer (5 months) at the 480-mg/m(2)-dose level.

CONCLUSION

The combination of carboplatin and thymidine as described is well tolerated. The data presented have resulted in a phase II study by the North American Brain Tumor Consortium.

Increased stroop facilitation effects in schizophrenia are not due to increased automatic spreading activation

Studies using the single trial Stroop task consistently reveal increased reaction time (RT) facilitation effects among schizophrenia patients. One possible mechanism underlying this effect is increased automatic spreading activation in semantic networks. The current study was designed to test this hypothesis. We administered the Stroop task and two semantic priming tasks to the same subjects. Patients showed greater Stroop RT facilitation than controls, no evidence of increased semantic priming at short stimulus onset asynchronies (SOAs), and reduced semantic priming at long SOAs. In addition, abnormal Stroop performance was related to the severity of Disorganization symptoms. These results are inconsistent with the spreading activation hypothesis. Alternative hypotheses regarding the source of Stroop task performance deficits in schizophrenia are discussed.

Cognition and control in schizophrenia: a computational model of dopamine and prefrontal function

Behavioral deficits suffered by patients with schizophrenia in a wide array of cognitive domains can be conceptualized as failures of cognitive control, due to an impaired ability to internally represent, maintain, and update context information. A theory is described that postulates a single neurobiological mechanism for these disturbances, involving dysfunctional interactions between the dopamine neurotransmitter system and the prefrontal cortex. Specifically, it is hypothesized that in schizophrenia, there is increased noise in the activity of the dopamine system, leading to abnormal "gating" of information into prefrontal cortex. The theory is implemented as an explicit connectionist computational model that incorporates the roles of both dopamine and prefrontal cortex in cognitive control. A simulation is presented of behavioral performance in a version of the Continuous Performance Test specifically adapted to measure critical aspects of cognitive control function. Schizophrenia patients exhibit clear behavioral deficits on this task that reflect impairments in both the maintenance and updating of context information. The simulation results suggest that the model can successfully account for these impairments in terms of abnormal dopamine activity. This theory provides a potential point of contact between research on the neurobiological and psychological aspects of schizophrenia, by illustrating how a particular physiological disturbance might lead to precise and quantifiable consequences for behavior.

The contribution of the anterior cingulate cortex to executive processes in cognition

The anterior cingulate cortex (ACC), on the medial surface of the frontal lobes, has frequently been hypothesized to make critical contributions to the function of neural systems involved in the executive control of cognition. Three principal theories have been developed to account for this role. The first, 'motivated attention', emphasizes the limbic identity of the ACC and the effects of lesions to this area of the brain. The second, 'attention allocation', emphasizes the fact that during functional neuroimaging studies activation of the ACC is seen during tasks that elicit incompatible response tendencies that must be resolved for correct performance. The third theory, 'error detection', reflects the observation of a negative scalp potential occurring during incorrect responses which appears to have a medial frontal generator. The first and last theories suggest evaluative functions by the ACC in the service of control, while attention allocation suggests a strategic function. We have proposed that the data supporting all three theories can be reconciled if the ACC were detecting conflicting processes during task performance that might be associated with errors. In support of this hypothesis we describe results using event-related fMRI which confirm that the ACC does show error related activity but that the same region of the brain also shows increased response related activity during correct responses associated with response competition. This suggests a re-conceptualization of the contribution of the ACC to executive processes that support an evaluative role, specifically the on-line detection of processing conflicts that may be associated with deteriorating performance. Unresolved questions related to the contribution of this region to executive processes and potential future directions for research on the function of this region of the brain are discussed.

Low hot pain threshold predicts shorter time to exercise-induced angina: results from the psychophysiological investigations of myocardial ischemia (PIMI) study

OBJECTIVES

The purpose of this study was to test whether cutaneous thermal pain thresholds are related to anginal pain perception.

BACKGROUND

Few ischemic episodes are associated with angina; symptoms have been related to pain perception thresholds.

METHODS

A total of 196 patients with documented coronary artery disease underwent bicycle exercise testing and thermal pain testing. The Marstock test of cutaneous sensory perception was administered at baseline after 30 min of rest on two days and after exercise and mental stress. Resting hot pain thresholds (HPTs) were averaged for the two baseline visits and divided into two groups: 1) average HPT <41 degrees C, and 2) average HPT > or =41 degrees C, to be clearly indicative of abnormal hypersensitivity to noxious heat.

RESULTS

Patients with HPT <41 degrees C had significantly shorter time to angina onset on exercise testing than patients with HPT > or =41 degrees C (p < 0.04, log-rank test). Heart rates, systolic blood pressure and rate-pressure product at peak exercise were not different for the two groups. Resting plasma beta-endorphin levels were significantly higher in the HPT <41 degrees C group (5.9+/-3.7 pmol/liter vs. 4.7+/-2.8 pmol/liter, p = 0.02). Using a Cox proportional hazards model, patients with HPT <41 degrees C had an increased risk of angina (p = 0.03, rate ratio = 2.0). These differences persisted after adjustment for age, gender, depression, anxiety and history of diabetes or hypertension (p < 0.01).

CONCLUSIONS

Occurrence of angina and timing of angina onset on an exercise test are related to overall hot pain sensory perception. The mechanism of this relationship requires further study.

Modulation of language processing in schizophrenia: effects of context and haloperidol on the event-related potential

BACKGROUND

Disturbances in language associations were among the first clinical symptoms reported for individuals described as schizophrenic (Bleuler 1911/1950). Currently, associative language disturbance is a diagnostic feature of schizophrenia (American Psychiatric Association 1994); however, the mechanisms that produce this symptom remain unknown. In the present study, two candidate psychological functions were examined: sensitivity to semantic context and expectancy (attention).

METHODS

Visual event-related potentials were recorded during a lexical decision task in which semantic relationship and expectancy (relatedness proportions) were varied. Semantic priming processes were compared between 34 male normal control subjects tested once and 37 male schizophrenic inpatients evaluated during their participation in a double-blind haloperidol maintenance therapy and placebo replacement protocol.

RESULTS

Schizophrenic patients failed to discriminate between associated and unassociated words, as measured by the amplitude of the N400 component (i.e., absence of the N400 priming effect); however, the overall mean amplitude of N400 did not differ between patients and control subjects. In addition, patients and control subjects did not differ significantly in the amplitude of N400 elicited to associated words or to unassociated words. Finally, the effect of expectancy-based processing on the magnitude of the N400 priming effect did not differ between patients and control subjects.

CONCLUSIONS

On the basis of these findings, a tentative hypothesis is suggested that schizophrenic patients are characterized by a pattern of indiscriminate or random spread of activation in their semantic network during the processing of single-word semantic contexts.

Clinically relevant deoxycytidine levels are high enough to profoundly alter 9-beta-D-arabinofuranosylguanine cytotoxicity for human T-cell acute leukemia cells in vitro

Plasma deoxycytidine levels can vary markedly during chemotherapy, from < 0.05 microM to at least 10.3 microM in T-cell acute lymphoblastic leukemia (T-ALL). This study demonstrates that clinically relevant deoxycytidine levels can dramatically protect human T-ALL cells against 9-beta-D-arabinofuranosylguanine (araG), a promising drug in this leukemia. At 0.4, 1.2, 3.6, and 10.8 microM deoxycytidine, the dose of araG required to kill 50% of MOLT3 T-ALL cells increased 4.23 +/- 1.95-(mean +/- SEM), 23.1 +/- 5.42-, 39.3 +/- 19.3-, and 67.0 +/- 11.5-fold compared to araG without deoxycytidine. Such deoxycytidine concentrations sharply reduced intracellular araG levels and blocked inhibition of DNA synthesis even in the presence of 160 and 640 microM araG. These data offer the first evidence that clinically relevant deoxycytidine levels could profoundly modulate araG toxicity in T-ALL.

Indole glucosinolate and auxin biosynthesis in Arabidopsis thaliana (L.) Heynh. glucosinolate mutants and the development of clubroot disease

Mutants and wild type plants of Arabidopsis thaliana were analysed for differences in glucosinolate accumulation patterns, indole-3-acetic acid (IAA) biosynthesis and phenotype. A previously identified series of mutants, termed TU, with altered glucosinolate patterns was used in this study. Only the line TU8 was affected in shoot phenotype (shorter stems, altered branching pattern). Synthesis of IAA and metabolism were not much affected in the TU8 mutant during seedling development, although the content of free IAA peaked earlier in TU8 during plant development than in the wild type. Indole glucosinolates and IAA may, however, be involved in the development of clubroot disease caused by the obligate biotrophic fungus Plasmodiophora brassicae since the TU3 line had a lower infection rate than the wild type, and lines TU3 and TU8 showed decreased symptom development. The decline in clubroot formation was accompanied by a reduced number of fungal structures within the root cortex and slower development of the fungus. Indole glucosinolates were lower in infected roots of TU3 and TU8 than in control roots of these lines, whereas in wild-type plants the differences were not as prominent. Free IAA and indole-3-acetonitrile (IAN) were increased in infected roots of the wild type and mutants with normal clubroot symptoms, whereas they were reduced in infected roots of mutants TU3 and TU8. These results indicate a role for indole glucosinolates and IAN/IAA in relation to symptom development in clubroot disease.

Relationship among mental stress-induced ischemia and ischemia during daily life and during exercise: the Psychophysiologic Investigations of Myocardial Ischemia (PIMI) study

OBJECTIVES

The purposes of this database study were to determine: 1) the relationship between mental stress-induced ischemia and ischemia during daily life and during exercise; 2) whether patients who exhibited daily life ischemia experienced greater hemodynamic and catecholamine responses to mental or physical stress than patients who did not exhibit daily life ischemia, and 3) whether patients who experienced daily life ischemia could be identified on the basis of laboratory-induced ischemia using mental or exercise stress testing.

BACKGROUND

The relationships between mental stress-induced ischemia in the laboratory and ischemia during daily life and during exercise are unclear.

METHODS

One hundred ninety-six stable patients with documented coronary disease and a positive exercise test underwent mental stress testing and bicycle exercise testing. Radionuclide ventriculography and electrocardiographic (ECG) monitoring were performed during the mental stress and bicycle tests. Patients underwent 48 h of ambulatory ECG monitoring. Hemodynamic and catecholamine responses were obtained during mental stress and bicycle tests.

RESULTS

Ischemia (reversible left ventricular dysfunction or ST segment depression > or = 1 mm) developed in 106 of 183 patients (58%) during the mental stress test. There were no significant differences in clinical characteristics of patients with, compared with those without, mental stress-induced ischemia. Patients with mental stress ischemia more often had daily life ischemia than patients without mental stress ischemia, but their exercise tests were similar. Patients with daily life ischemia had higher ejection fraction and cardiac output, and lower systemic vascular resistance during mental stress than patients without daily life ischemia. Blood pressure and catecholamine levels at rest and during the mental stress tests were not different in patients with, compared with those without, daily life ischemia. Patients with daily life ischemia had a higher ejection fraction at rest and at peak bicycle exercise compared with patients without daily life ischemia, but there were no other differences in peak hemodynamic or catecholamine responses to exercise. The presence of ST segment depression during routine daily activities was best predicted by ST segment depression during mental or bicycle exercise stress, although ST segment depression was rare during mental stress.

CONCLUSIONS

Patients with daily life ischemia exhibit a heightened generalized response to mental stress. ST segment depression in response to mental or exercise stress is more predictive of ST segment depression during routine daily activities than other laboratory-based ischemic markers. Therapeutic management strategies might therefore focus on patients with these physiologic responses to stress and on whether lessening such responses reduces ischemia.

Cardiovascular disease: tomorrow is the reason for today's therapeutics. An interview with Jerome D. Chen

The prevalence and magnitude of cardiovascular disease in the United States make it the leading cause of mortality, far surpassing deaths from all cancers. More than 900,000 Americans die each year from cardiovascular causes, including stroke, hypertension, congestive heart failure, atherosclerosis, and congenital heart defects, according to American Heart Association estimates. Coronary heart disease alone accounts for 50% of all cardiovascular deaths. A host of agents designed to help manage cardiovascular disorders and related conditions (eg, hypertension, diabetes, and hypercholesterolemia) are available to physicians who treat patients at high risk. In this interview, Jerome D. Cohen, MD, explains why more aggressive use of these drug treatments today could significantly improve older patients' quality of life and reduce the risk of a disabling or fatal cardiovascular event in the next millennium.

Gastric emptying after elective abdominal aortic aneurysm surgery: the case for early postoperative enteral feeding

OBJECTIVE

To assess gastric emptying with a view to early postoperative enteral nutrition after elective abdominal aortic aneurysm (AAA) surgery.

METHODS

The paracetamol absorption test was used to assess gastric emptying in 13 consecutive patients at 6, 18 and 32 h following elective AAA surgery. All patients received postoperative analgesia with marcaine given via an epidural catheter during the first 48 postoperative hours. Normal emptying was defined as an area under the plasma paracetamol concentration curve at 60 min (AUC-60) of > 600 mg/min/l.

RESULTS

The median time to normal gastric emptying was 18 +/- 7.7 h. One patient (7.6%) had normal emptying at 6 h, nine (69%) at 18 h and 12 (92%) at 32 h. The nasogastric tubes were removed at a median of 3.2 days after surgery, and enteral feeding was commenced on day 4.

CONCLUSIONS

Gastric emptying was normal 18 h post-AAA surgery as assessed by the paracetamol absorption test. In view of the importance of maintaining an intact gastrointestinal mucosa, enteral nutrition may be commenced on the second postoperative day.

Context-processing deficits in schizophrenia: converging evidence from three theoretically motivated cognitive tasks

To test the hypothesis that the ability to actively represent and maintain context information in a central function of working memory and that a disturbance in this function contributes to cognitive deficits in schizophrenia, the authors modified 3 tasks--the AX version of the Continuous Performance Test, Stroop, and a lexical disambiguation task--and administered them to patients with schizophrenia as well as to depressed and healthy controls. The results suggest an accentuation of deficits in patients with schizophrenia in context-sensitive conditions and cross-task correlations of performance in these conditions. However, the results do not definitively eliminate the possibility of a generalized deficit. The significance of these findings is discussed with regard to the specificity of deficits in schizophrenia and the hypothesis concerning the neural and cognitive mechanisms that underlie these deficits.

The role of locus coeruleus in the regulation of cognitive performance

Noradrenergic locus coeruleus (LC) neurons were recorded in monkeys performing a visual discrimination task, and a computational model was developed addressing the role of the LC brain system in cognitive performance. Changes in spontaneous and stimulus-induced patterns of LC activity correlated closely with fluctuations in behavioral performance. The model explains these fluctuations in terms of changes in electrotonic coupling among LC neurons and predicts improved performance during epochs of high coupling and synchronized LC firing. Cross correlations of simultaneously recorded LC neurons confirmed this prediction, indicating that electrotonic coupling in LC may play an important role in attentional modulation and the regulation of goal-directed versus exploratory behaviors.

An in vitro system from maize seedlings for tryptophan-independent indole-3-acetic acid biosynthesis

The enzymatic synthesis of indole-3-acetic acid (IAA) from indole by an in vitro preparation from maize (Zea mays L.) that does not use tryptophan (Trp) as an intermediate is described. Light-grown seedlings of normal maize and the maize mutant orange pericarp were shown to contain the necessary enzymes to convert [14C]indole to IAA. The reaction was not inhibited by unlabeled Trp and neither [14C]Trp nor [14C]serine substituted for [14C]indole in this in vitro system. The reaction had a pH optimum greater than 8.0, required a reducing environment, and had an oxidation potential near that of ascorbate. The results obtained with this in vitro enzyme preparation provide strong, additional evidence for the presence of a Trp-independent IAA biosynthesis pathway in plants.

Reproducibility of fMRI results across four institutions using a spatial working memory task

Four U.S. sites formed a consortium to conduct a multisite study of fMRI methods. The primary purpose of this consortium was to examine the reliability and reproducibility of fMRI results. FMRI data were collected on healthy adults during performance of a spatial working memory task at four different institutions. Two sets of data from each institution were made available. First, data from two subjects were made available from each site and were processed and analyzed as a pooled data set. Second, statistical maps from five to eight subjects per site were made available. These images were aligned in stereotactic space and common regions of activation were examined to address the reproducibility of fMRI results when both image acquisition and analysis vary as a function of site. Our grouped and individual data analyses showed reliable patterns of activation in dorsolateral prefrontal cortex and posterior parietal cortex during performance of the working memory task across all four sites. This multisite study, the first of its kind using fMRI data, demonstrates highly consistent findings across sites.

Functional hypofrontality and working memory dysfunction in schizophrenia

OBJECTIVE

Hypofrontality is a common but not invariable finding in schizophrenia. Inconsistencies in the literature may reflect, in part, the fact that abnormal physiological responses in the prefrontal cortex are best identified under conditions that place well-specified functional demands on this region.

METHOD

The authors studied eight patients with schizophrenia and eight matched comparison subjects using [(15)O]H2O positron emission tomography and the "N-back" task, which activates the prefrontal cortex as a function of working memory load in normal subjects.

RESULTS

Under low-working-memory-load conditions, the accuracy of both groups in the N-back task was equal, but when the memory load increased, the patients' performance deteriorated more than did that of the comparison subjects. The regional cerebral blood flow response to increased working memory load was significantly reduced in the patients' right dorsolateral prefrontal cortex.

CONCLUSIONS

These results confirm the importance of using tasks that tap specific cognitive functions, linked to specific neural systems, in studies of brain-behavior relationships in schizophrenia. Hypofrontality is reliably demonstrated in schizophrenia during tasks that engage working memory functions of the prefrontal cortex.

The gene for indole-3-acetyl-L-aspartic acid hydrolase from Enterobacter agglomerans: molecular cloning, nucleotide sequence, and expression in Escherichia coli

A 5.5-kb DNA fragment containing the indole-3-acetyl-aspartic acid (IAA-asp) hydrolase gene (iaaspH) was isolated from Enterobacter agglomerans strain GK12 using a hybridization probe based on the N-terminal amino acid sequence of the protein. The DNA sequence of a 2.4-kb region of this fragment was determined and revealed a 1311-nucleotide ORF large enough to encode the 45-kDa IAA-asp hydrolase. A 1.5-kb DNA fragment containing iaaspH was subcloned into the Escherichia coli expression plasmid pTTQ8 to yield plasmid pJCC2. Extracts of IPTG-induced E. coli cultures containing the pJCC2 recombinant plasmid showed IAA-asp hydrolase levels 5 to 10-fold higher than those in E. agglomerans extracts. Homology searches revealed that the IAA-asp hydrolase was similar to a variety of amidohydrolases. In addition, IAA-asp hydrolase showed 70% sequence identity to a putative thermostable carboxypeptidase of E. coli.