Modeling spatiotemporal covariance for magnetoencephalography or electroencephalography source analysis.

We propose a new model to approximate spatiotemporal noise covariance for use in neural electromagnetic source analysis, which better captures temporal variability in background activity. As with other existing formalisms, our model employs a Kronecker product of matrices representing temporal and spatial covariance. In our model, spatial components are allowed to have differing temporal covariances. Variability is represented as a series of Kronecker products of spatial component covariances and corresponding temporal covariances. Unlike previous attempts to model covariance through a sum of Kronecker products, our model is designed to have a computationally manageable inverse. Despite increased descriptive power, inversion of the model is fast, making it useful in source analysis. We have explored two versions of the model. One is estimated based on the assumption that spatial components of background noise have uncorrelated time courses. Another version, which gives closer approximation, is based on the assumption that time courses are statistically independent. The accuracy of the structural approximation is compared to an existing model, based on a single Kronecker product, using both Frobenius norm of the difference between spatiotemporal sample covariance and a model, and scatter plots. Performance of ours and previous models is compared in source analysis of a large number of single dipole problems with simulated time courses and with background from authentic magnetoencephalography data.

A generalized spatiotemporal covariance model for stationary background in analysis of MEG data.

Using a noise covariance model based on a single Kronecker product of spatial and temporal covariance in the spatiotemporal analysis of MEG data was demonstrated to provide improvement in the results over that of the commonly used diagonal noise covariance model. In this paper we present a model that is a generalization of all of the above models. It describes models based on a single Kronecker product of spatial and temporal covariance as well as more complicated multi-pair models together with any intermediate form expressed as a sum of Kronecker products of spatial component matrices of reduced rank and their corresponding temporal covariance matrices. The model provides a framework for controlling the tradeoff between the described complexity of the background and computational demand for the analysis using this model. Ways to estimate the value of the parameter controlling this tradeoff are also discussed.

Evolution of enzymatic activities in the enolase superfamily: functional assignment of unknown proteins in Bacillus subtilis and Escherichia coli as L-Ala-D/L-Glu epimerases.

The members of the mechanistically diverse enolase superfamily catalyze different overall reactions by using a common catalytic strategy and structural scaffold. In the muconate lactonizing enzyme (MLE) subgroup of the superfamily, abstraction of a proton adjacent to a carboxylate group initiates reactions, including cycloisomerization (MLE), dehydration [o-succinylbenzoate synthase (OSBS)], and 1,1-proton transfer (catalyzed by an OSBS that also catalyzes a promiscuous N-acylamino acid racemase reaction). The realization that a member of the MLE subgroup could catalyze a 1,1-proton transfer reaction, albeit poorly, led to a search for other enzymes which might catalyze a 1,1-proton transfer as their physiological reaction. YcjG from Escherichia coli and YkfB from Bacillus subtilis, proteins of previously unknown function, were discovered to be L-Ala-D/L-Glu epimerases, although they also catalyze the epimerization of other dipeptides. The values of k(cat)/K(M) for L-Ala-D/L-Glu for both proteins are approximately 10(4) M(-1) s(-1). The genomic context and the substrate specificity of both YcjG and YkfB suggest roles in the metabolism of the murein peptide, of which L-Ala-D-Glu is a component. Homologues possessing L-Ala-D/L-Glu epimerase activity have been identified in at least two other organisms.

Evolution of enzymatic activities in the enolase superfamily: crystal structures of the L-Ala-D/L-Glu epimerases from Escherichia coli and Bacillus subtilis.

The members of the enolase superfamily catalyze different overall reactions, yet share a partial reaction that involves Mg(2+)-assisted enolization of the substrate carboxylate anion. The fate of the resulting enolate intermediate is determined by the active site of each enzyme. Several members of this superfamily have been structurally characterized to permit an understanding of the evolutionary strategy for using a common structural motif to catalyze different overall reactions. In the preceding paper, two new members of the superfamily were identified that catalyze the epimerization of the glutamate residue in L-Ala-D/L-Glu. These enzymes belong to the muconate lactonizing enzyme subgroup of the enolase superfamily, and their sequences are only 31% identical. The structure of YcjG, the epimerase from Escherichia coli, was determined by MAD phasing using both the SeMet-labeled protein and a heavy atom derivative. The structure of YkfB, the epimerase from Bacillus subtilis, was determined by molecular replacement using the muconate lactonizing enzyme as a search model. In this paper, we report the three-dimensional structures of these enzymes and compare them to the structure of o-succinylbenzoate synthase, another member of the muconate lactonizing enzyme subgroup.

Genetic and biochemical analyses of BvgA interaction with the secondary binding region of the fha promoter of Bordetella pertussis.

The BvgA-BvgS two-component signal transduction system regulates expression of virulence factors in Bordetella pertussis. The BvgA response regulator activates transcription by binding to target promoters, which include those for the genes encoding filamentous hemagglutinin (fha) and pertussis toxin (ptx). We have previously shown that at both promoters the phosphorylated form of BvgA binds multiple high- and low-affinity sites. Specifically, at the fha promoter, we proposed that there may be high- and a low-affinity binding sites for the BvgA dimer. In our present investigation, we used DNA binding analyses and in vitro and in vivo assays of promoters with substitutions and deletions to support and extend this hypothesis. Our observations indicate that (i) binding of BvgA approximately P to a primary (high-affinity) site and a secondary binding region (lower affinity) is cooperative, (ii) although both the primary binding site and the secondary binding region are required for full activity of the wild-type (undeleted) promoter, deletion of two helical turns within the secondary binding region can produce a fully active or hyperactive promoter, and (iii) BvgA binding to the secondary binding region shows limited DNA sequence specificity.

Continuous probability distributions from finite data.

Recent approaches to the problem of inferring a continuous probability distribution from a finite set of data have used a scalar field theory for the form of the prior probability distribution. This paper presents a more general form for the prior distribution that has a geometrical interpretation and can improve the specificity of likely solutions. It is also demonstrated that a numerical sampling of the posterior probability distribution can be used as an alternative to a histogram for visualization and to make probabilistic inferences from the data.

Bayesian inference applied to the electromagnetic inverse problem.

We present a new approach to the electromagnetic inverse problem that explicitly addresses the ambiguity associated with its ill-posed character. Rather than calculating a single "best" solution according to some criterion, our approach produces a large number of likely solutions that both fit the data and any prior information that is used. Whereas the range of the different likely results is representative of the ambiguity in the inverse problem even with prior information present, features that are common across a large number of the different solutions can be identified and are associated with a high degree of probability. This approach is implemented and quantified within the formalism of Bayesian inference, which combines prior information with that of measurement in a common framework using a single measure. To demonstrate this approach, a general neural activation model is constructed that includes a variable number of extended regions of activation and can incorporate a great deal of prior information on neural current such as information on location, orientation, strength, and spatial smoothness. Taken together, this activation model and the Bayesian inferential approach yield estimates of the probability distributions for the number, location, and extent of active regions. Both simulated MEG data and data from a visual evoked response experiment are used to demonstrate the capabilities of this approach.

Clinical course of a fatal ingestion of diquat.

CASE REPORT: A 28-year-old male ingested the herbicide diquat. The patient rapidly developed severe gastrointestinal and metabolic disturbances, airway compromise, respiratory failure, renal failure, hemodynamic collapse, and seizures. We describe multiple metabolic abnormalities, an apparent artifact introduced by diquat in the laboratory assay for serum creatinine, serum diquat levels, and the need for emergency airway management.

Pulmonary complications of HIV infection in Dar es Salaam, Tanzania. Role of bronchoscopy and bronchoalveolar lavage.

To determine the pulmonary complications in HIV-1-infected patients in Dar es Salaam, Tanzania, and to evaluate the diagnostic utility of bronchoscopy and bronchoalveolar lavage, we carried out a prospective study of 237 patients with acute respiratory disease who were hospitalized at Muhimbili Medical Center (MMC). Diagnoses were made using well-defined criteria. Of the total, 127 (54%) were HIV-1-seropositive and 110 (46%) were seronegative. Tuberculosis was the most common diagnosis occurring in 95 (75%) HIV-1-seropositive and 87 (79%) seronegative patients. Bacterial pneumonia was the next most common diagnosis occurring in 18 (14%) HIV-1-seropositive and 17 (15%) seronegative patients. Pneumocystis carinii pneumonia was diagnosed in one and Kaposi's sarcoma was seen in only two HIV-1-seropositive patients. Bronchoscopy with bronchoalveolar lavage was the sole source of a diagnosis in nine (8%) seropositive and six (5%) seronegative patients. We conclude that the HIV seroprevalence rate among patients hospitalized for acute respiratory disease at MMC is extremely high. Tuberculosis was the most common cause of pulmonary disease, regardless of HIV serostatus, and other HIV-associated opportunistic pulmonary infections were unusual. Bronchoscopy with bronchoalveolar lavage added little to the diagnosis and thus should not be high-priority procedures for the routine workup in resource-poor areas where tuberculosis is endemic.

Mapping function in the human brain with magnetoencephalography, anatomical magnetic resonance imaging, and functional magnetic resonance imaging.

Integrated analyses of human anatomical and functional measurements offer a powerful paradigm for human brain mapping. Magnetoencephalography (MEG) and EEG provide excellent temporal resolution of neural population dynamics as well as capabilities for source localization. Anatomical magnetic resonance imaging (MRI) provides excellent spatial resolution of head and brain anatomy, whereas functional MRI (fMRI) techniques provide an alternative measure of neural activation based on associated hemodynamic changes. These methodologies constrain and complement each other and can thereby improve our interpretation of functional neural organization. We have developed a number of computational tools and techniques for the visualization, comparison, and integrated analysis of multiple neuroimaging techniques. Construction of geometric anatomical models from volumetric MRI data allows improved models of the head volume conductor and can provide powerful constraints for neural electromagnetic source modeling. These approaches, coupled to enhanced algorithmic strategies for the inverse problem, can significantly enhance the accuracy of source-localization procedures. We have begun to apply these techniques for studies of the functional organization of the human visual system. Such studies have demonstrated multiple, functionally distinct visual areas that can be resolved on the basis of their locations, temporal dynamics, and differential sensitivity to stimulus parameters. Our studies have also produced evidence of internal retinotopic organization in both striate and extrastriate visual areas but have disclosed organizational departures from classical models. Comparative studies of MEG and fMRI suggest a reasonable but imperfect correlation between electrophysiological and hemodynamic responses. We have demonstrated a method for the integrated analysis of fMRI and MEG, and we outline strategies for improvement of these methods. By combining multiple measurement techniques, we can exploit the complementary strengths and transcend the limitations of the individual neuro-imaging methods.

Cryptococcosis presenting as a neck mass.

A rare case of cryptococcal infection presenting as a neck mass in an otherwise healthy individual is reported. The mass resulted in lytic destruction of portions of the cervical vertebrae and produced a focal neurologic deficit in one of the upper extremities. Although other lesions in the skull, femur, and humerus were identified, no involvement of the lungs or central nervous system could be detected. The patient was initially treated with amphotericin B and flucytosine, but eventually also required fluconazole and surgical debridement for complete resolution of the infection. The diagnosis, treatment, and manifestations of cryptococcosis in the head and neck are discussed.

The C-terminus of the succinate dehydrogenase IP peptide of Saccharomyces cerevisiae is significant for assembly of complex II.

Site-directed mutagenesis was used to introduce mutations into the gene for the iron protein (IP) of succinate dehydrogenase (SDH) of Saccharomyces cerevisiae. Specifically, three mutations were examined which caused the synthesis of truncated IP peptides missing four, seven, or 17 amino acids from the C-terminus, respectively. The deletion of seven or more amino acids includes the loss of two lysine residues, which appear to have been highly conserved in evolution. While the deletion of four amino acids had no effect on the assembly of complex II and on its activity, the deletion including the two lysines abolished SDS activity completely and led to the failure of the imported IP peptide to be incorporated into a stable complex II or SDH complex. Replacement of one of the lysines by threonine had no effect, but replacement of both by threonine affected the specific activity of complex II but not its assembly and stability.

The tethered spinal cord. Etiology and clinical manifestations.

Tethering of the spinal cord is frequently associated with myelomeningocele. However, orthopaedic surgeons must be familiar with the primary tethered cord, which is associated not with an overt myelomeningocele but with more subtle clinical findings, particularly in the pediatric patient. The charts of patients with tethered spinal cords from the Honolulu Unit of the Shriners Hospital for Crippled Children are reviewed to highlight potential diagnostic and treatment problems. Tethered spinal cord should be considered in the differential diagnosis of patients who present with isolated lower extremity deformities and/or subtle neurologic findings. Appropriate evaluation may require magnetic resonance imaging, ultrasonography, or metrizamide computed tomography. Urologic function must also be evaluated and monitored. The literature supports an aggressive diagnostic and, where indicated, surgical approach to the tethered spinal cord. Diagnosis and treatment at a young age has been shown to correlate with optimal results.

Microvascular anastomoses in replanted fingers: do they stay open?

Replantation of fingers is a well established procedure following traumatic amputation. Several studies have documented the functional results of replanted digits. Studies have not documented the long-term (greater than 5 yrs) patency of the microvascular anastomosis in the replanted digit. Duplex imaging, a combination of B-mode ultrasound and bidirectional Doppler ultrasound has been shown to visualize vessels 1 mm in diameter. Color enhancement of the ultrasound image is now possible. We evaluated 18 patients with 24 replanted fingers to assess vascular patency. A minimum of five years follow-up was required for inclusion in the study group. Examination showed a patent anastomosis in every case and a Digital-Brachial Index within normal limits in 71% of the digits. Microvascular anastomoses in vessels as small as 1 mm in diameter remain open as long as 11 years following completion. The sophisticated techniques of color enhanced Duplex imaging makes long-term evaluation of these procedures possible in a non-invasive and accurate fashion. The use of such imaging modalities will have an important role in the evaluation of replanted digits and microvascular procedures in general.

Retroviral protein P15E and tumorigenesis. Expression is neither required nor sufficient for tumor development.

Murine tumor cells frequently express retroviral protein p15E, a protein with antiinflammatory activity. This has led to the hypothesis that p15E expression allows nascent tumor cells to escape host immunologic defenses. To evaluate the role of p15E expression in tumorigenesis, NIH3T3 cells transformed by various oncogenes and BALB/c lines transformed by carcinogens or SV40 were examined for p15E expression and tumorigenicity. All of the NIH3T3 transformants and most of the BALB/c transformants did not express p15E, indicating that transformation per se does not inevitably induce the expression of p15E. Although not expressing p15E, some of these transformants were capable of forming tumors in immune competent hosts, indicating that p15E is not universally required for tumor growth. Four of the transformed cell lines negative for p15E expression and deficient in tumor-forming capacity were transfected with a gene coding for Moloney retroviral p15E. Despite the expression of p15E, there was no augmentation of their tumorigenic capacity, showing that p15E is not sufficient to ensure tumor formation by a transformed cell. These results argue against a general role for retroviral p15E expression in tumorigenesis.

Atraumatic avascular necrosis of the head of the talus: a case report.

Avascular necrosis of the talus has frequently been reported following trauma. The incidence of avascular necrosis has been reported to be as high as 50% for Hawkins Type II talar fractures and to range from 75-100% for Type III fracture-dislocations. The resultant avascular necrosis has been reported to occur primarily in the body and dome of the talus with apparent sparing of the head of the talus. The close association of trauma to avascular necrosis of the talus has been alluded to by Cobey and others. Reports of avascular necrosis of the talus, without an antecedent history of trauma, have been rare. This paper presents a case of atraumatic avascular necrosis of the talar head.

Recombinant hydrophilic region of murine retroviral protein p15E inhibits stimulated T-lymphocyte proliferation.

Retroviral envelope protein p15E and antigenically related proteins have been implicated as potential mediators of immune dysfunction associated with retroviral infections and with neoplasia. Due to its extreme hydrophobicity, purified p15E has not been available in a nondenatured form or in sufficient quantities for detailed studies on the mechanisms of its immunosuppressive effects. Therefore, a plasmid was constructed to direct the synthesis in Escherichia coli of the major hydrophilic region of murine p15E. The purified recombinant p15E derivative, soluble under physiological conditions, inhibited by up to 60% (EC50 = 7.5 nM) the anti-CD3-driven proliferation of human T lymphocytes but had no effect on the proliferation of the transformed T-cell line Jurkat. The recombinant protein also inhibited, by up to an average of 92% (EC50 = 2.1 microM), the proliferation of the murine T-cell line CTLL-2. These data (i) provide direct evidence that a retroviral envelope protein can itself inhibit lymphoproliferative function and (ii) map the inhibitory activity to a specific region of p15E. The availability of soluble, recombinant p15E should facilitate studies of the pathogenesis of the immunosuppression accompanying retroviral infections and neoplastic diseases.

The immunohistology of the persistent generalized lymphadenopathy syndrome (PGL).

The authors employed a large panel of monoclonal antibodies to characterize and quantitate lymphoid subpopulations within the paracortex, mantle, and germinal centers of frozen sections of lymph nodes from 18 patients with the persistent generalized lymphadenopathy (PGL) syndrome and five heterosexual controls. The authors' data indicate that Leu-3+ phenotypic T-helper cells (TH) are reduced within all three compartments, while T-cytotoxic-suppressor cells (Tcs) are increased. Using the antibody 9.3, which allows dissection of the Leu-2+ Tcs subset into 9.3+ cytotoxic cells (Tc) and 9.3- suppressor cells (Ts), the authors found that the Ts subset is increased in the lymph nodes of these patients. In contrast to acquired immune deficiency syndrome (AIDS) patients, paracortical total T-cells and Leu-8+ cells appear to be preserved in patients with PGL. Study of TH and Tcs subpopulations in peripheral blood in 12 of these patients revealed inverted ratios (mean, 0.59), which did not correlate with those seen in the lymph nodes. Although the paracortical TH/Tcs ratios were significantly reduced (mean, 1.44) they were not inverted, in contrast to some other reported series. In aggregate, these data suggest that, relative to AIDS, there is preservation of the paracortical T-cell microenvironment in PGL. Clinically, this correlates with more intact cell-mediated immunity and the absence of opportunistic infections and Kaposi's sarcoma in this patient group. Follicle lysis was present in 11 patients. Increased HLA-DR+ paracortical cells, aggregates of Leu-6+ dendritic cells, decreased TAC+ cells, increased OKT-10+ plasma cells, and increased interstitial immunoglobulin were among the other features observed in these patients.