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Biomedical subjects

P Clark

Publications and source records attributed to P Clark.

At least 19 recordsLinked to original sources
PubMed1992

Alterations in nuclear envelope invaginations in axotomized fetal and early postnatal hamster facial motoneurons.

In this study, changes in the amount of nuclear envelope invaginations (NEI) were morphometrically assessed after axotomy during late fetal and early postnatal developmental stages in hamster facial motoneurons. These changes were expressed as boundary density or BA (length of nuclear envelope per unit area of nucleus). Axotomy-induced changes in nuclear area and perimeter were also quantitatively determined. At 17 h after axotomy in the fetal operative series, no changes in any of the parameters were seen. At 1 day postoperative (dpo) in newborn, 2 and 4 postnatal day animals, the boundary densities of the total and invaginated portion of the nuclear envelope increased significantly. No corresponding qualitative changes were observed. At 2 dpo in 4 and 7 postnatal day animals, there were significant increases in the boundary densities of both invaginated and total nuclear envelope and a decrease in nuclear area. These changes were not seen at 2 dpo in the 9-day operative series. At 4 dpo in 7 and 9 postnatal day animals, scalloping of the normally smooth nuclear profile, as well as a flattening and elongation in nuclear shape, occurred. These qualitative changes in the 7 and 9 day operated groups were also accompanied by significant changes in all the measured parameters. The boundary density of the invaginated, non-invaginated and total nuclear envelope increased; whereas, nuclear area and perimeter decreased. These results argue against the generally held hypothesis that an increase in nuclear envelope invaginations is indicative of an allied increase in cellular metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Structure of HIV-1 reverse transcriptase/DNA complex at 7 A resolution showing active site locations.

AIDS, caused by human immunodeficiency virus (HIV), is one of the world's most serious health problems, with current protocols being inadequate for either prevention or successful long-term treatment. In retroviruses such as HIV, the enzyme reverse transcriptase copies the single-stranded RNA genome into double-stranded DNA that is then integrated into the chromosomes of infected cells. Reverse transcriptase is the target of the most widely used treatments for AIDS, 3'-azido-3'-deoxythymidine (AZT) and 2',3'-dideoxyinosine (ddI), but resistant strains of HIV-1 arise in patients after a relatively short time. There are several nonnucleoside inhibitors of HIV-1 reverse transcriptase, but resistance to such agents also develops rapidly. We report here the structure at 7 A resolution of a ternary complex of the HIV-1 reverse transcriptase heterodimer, a monoclonal antibody Fab fragment, and a duplex DNA template-primer. The double-stranded DNA binds in a groove on the surface of the enzyme. The electron density near one end of the DNA matches well with the known structure of the HIV-1 reverse transcriptase RNase H domain. At the opposite end of the DNA, a mercurated derivative of UTP has been localized by difference Fourier methods, allowing tentative identification of the polymerase nucleoside triphosphate binding site. We also determined the structure of the reverse transcriptase/Fab complex in the absence of template-primer to compare the bound and free forms of the enzyme. The presence of DNA correlates with movement of protein electron density in the vicinity of the putative template-primer binding groove. These results have important implications for developing improved inhibitors of reverse transcriptase for the treatment of AIDS.

Base Sequence↗
PubMed1992

Dendritic processing: using microstructures to solve a hitherto intractable neurobiological problem.

In vivo, intracellular recordings of mammalian brain stem motoneurones, followed by peroxidase staining and tridimensional reconstruction, suggest that the shape of the dendritic tree plays an important role in the processing of neural information. To test this hypothesis attempts were made to guide, in culture, the growth of neuritic branches of neurones dissociated from the hypoglossal nucleus of rat brain stem. This was performed using topographical and adhesive microstructures which were designed to control the shape of the neuritic tree. Guidance of the neuritic processes can be observed with small grooves engraved on quartz and plastic substrates, and simple shapes with few processes and bifurcations on each neurite could be obtained using adhesive microstructures. These procedures, which allow the shape of a neurone to be controlled, are very promising in the study, by means of classical electrophysiological methods as well as optical recordings, of the involvement of dendritic architecture in the processing of neural information.

Animals↗
PubMed1992

Micropatterned substratum adhesiveness: a model for morphogenetic cues controlling cell behavior.

It is generally considered that tracks of cell adhesiveness are important in controlling cell migration during the development and regeneration of many tissues. In order to investigate this experimentally, a number of techniques have in the past been employed to make patterns of differential adhesiveness for in vitro studies. However, practical limitations on patterning resolution and the introduction of residual topography to the experimental substrata have restricted their usefulness. Here we describe a simplified photolithographic technique for patterning cell adhesiveness which allows a high degree of flexibility and precision. We have quantified, using adhesion and spreading characteristics of BHK cells, the differential adhesiveness that can be created on patterned surfaces, how this alters with the duration of exposure to serum proteins, and how this, in turn, relates to the persistence of cell patterning despite increases in cell density. We believe that this technique will prove extremely useful for the detailed in vitro examination of the mechanisms controlling cell behavior as it offers a degree of precision and ease of fabrication that has previously been unavailable.

Adhesiveness↗
PubMed1992

Thyroid screening tests in psychiatric inpatients.

This study reports on a retrospective evaluation of the current practice of screening for thyroid dysfunction in an adult psychiatric inpatient program. Sixty-four percent of 342 admissions were tested during their hospital stay. Although 13.7% of tests yielded abnormal values on one or more of the thyroid indices, only 0.9% resulted in a diagnosis of hypothyroidism. None of the other abnormal test results led to any specific action being taken. The present pattern of use of thyroid function screening as observed in this study does not appear optimal. Issues in the selection of thyroid screening tests, and the value of the results obtained are discussed.

Adult↗
PubMed1992

Dietary calcium as a statistical determinant of spinal trabecular bone density in amenorrhoeic and oestrogen-replete athletes.

A study investigating the relationship between spinal trabecular bone density (measured by QCT), dietary calcium (measured by questionnaire) and menstrual status in 67 elite female athletes was undertaken. Twenty-five athletes were amenorrhoeic, 27 eumenorrhoeic and 15 were taking an oral contraceptive. The mean bone density was significantly lower (P less than 0.0001) in the amenorrhoeics (168 mg/cm3; 95% confidence interval 154-182) than in the eumenorrhoeics (211 mg/cm3; 197-224) and oral contraceptive takers (215 mg/cm3; 197-233). There was also a significant positive linear correlation between trabecular bone density. However, factors with which calcium intake may be linked, such as energy intake and expenditure, were not measured and therefore it is possible that this relationship is indirect. Further studies on the relationship between dietary calcium and bone mineral density in young women are needed.

Adolescent↗
PubMed1992

Assessment of a rapid latex agglutination test for group B streptococcal colonization of the genital tract.

OBJECTIVE: The purpose of this study was to determine the reliability of a rapid enzyme extraction-latex agglutination test in detecting intrapartum colonization of the maternal genital tract by group B streptococci. METHODS: Swabs of vaginal secretions were obtained from 314 patients in labor with either ruptured or intact membranes. Four tests were performed on each specimen: 1) qualitative culture on blood agar, 2) semiquantitative culture on blood agar, 3) culture in selective Todd-Hewitt broth, and 4) latex agglutination preceded by enzyme extraction. RESULTS: The prevalence of positive cultures was 29%. When compared with culture in Todd-Hewitt broth, the latex agglutination test had a sensitivity of 30%, specificity 93%, positive predictive value 64%, and negative predictive value 76%. In patients with heavy colonization the test had a sensitivity of 76%, compared with 17% in patients with light growth (P less than .001). The lower limit of sensitivity of the test was 4 x 10(5) cfu/mL. The performance of the test was not affected by rupture of the membranes. CONCLUSION: Although the latex agglutination test is reasonably sensitive in detecting heavy colonization, low overall performance combined with technical difficulties in assessment of particle agglutination make the test unsuitable for general screening.

Evaluation Studies as Topic↗
PubMed1992

Cell guidance by micropatterned adhesiveness in vitro.

Tracks of adhesiveness are believed to be involved in guiding morphogenetic cell migrations. Here, electronics microfabrication technology was used to manufacture patterns of alternating tracks of adhesive and non-adhesive substratum (untreated fused quartz and adjacent parallel tracks of hydrophobic treatment) of varying period (4, 6, 12, 24 and 50 microns). These experimental substrata were used to model, in vitro, possible differentially adhesive guidance cues. The effect of such patterned substrata was assessed using fibroblastic BHK cells and epithelial MDCK cells. Cells were oriented and elongated by these surfaces. Their responsiveness was dependent on cell type, cell-cell interactions, and the geometry of the patterns. Alignment of BHK cells increased with increasing pattern period. Single MDCK cells aligned to all pattern periods, their elongation being period-dependent, whereas colonies were mainly unaffected. These in vitro data have important implications, which are discussed with regard to in vivo guidance cues. The ability of cells to bridge over non-adhesive regions will influence the effectiveness of linear cues, and will be important for guideposting. The geometry of patterns of differential adhesion is here shown to be an important factor in determining the precision with which local guidance of cells may be controlled.

Animals↗
PubMed1992

The importance of combining xylene clearance and immunohistochemistry in the accurate staging of colorectal carcinoma.

The prognosis of colorectal carcinoma relies heavily on pathological staging which includes the metastatic state of lymph nodes. Colorectal resectates from 47 patients (41 with colorectal carcinoma and six with non-malignant disease) were entered into a study to assess the best method for detecting metastases in lymph nodes. The maximum number of lymph nodes was harvested at an initial careful examination of the specimen. Subsequently, the pericolic and perirectal fat was dissected out, dehydrated in alcohol, cleared in xylene and further lymph nodes were recovered. Both sets of lymph nodes were examined by the standard histological method and subsequently stained immunohistochemically for cytokeratins (CK). The mean number of lymph nodes recovered at the initial dissection from all 47 cases was 6.7, this was raised to 58.2 after xylene clearance, ie an average of 51.5 lymph nodes were not recovered by traditional methods. At the initial dissection no epithelial cells were detected in any of the lymph nodes from the nonmalignant cases or 25 of the malignant cases. In the other 16 cases, epithelial cells were detected by H&E in 38 lymph nodes. Thus the initial staging was 3 Dukes A, 22 Dukes B and 16 Dukes C. After immunohistochemistry, eight additional cases (originally staged Dukes B) showed epithelial cells in the lymph nodes, these were chiefly occult invasion, raising the involved lymph nodes number to 70. After xylene clearance and applying the CK staining, an additional 135 lymph nodes were found to be involved, thus the overall number of involved lymph nodes was increased to 205. The combined technique changed the Dukes staging in 12 out of 41 cases of colorectal carcinoma, resulting finally in 3 Dukes A, 10 Dukes B and 28 Dukes C, ie 55% of Dukes B become Dukes C.

Antibodies, Monoclonal↗
PubMed1992

Aztreonam.

Aztreonam is a synthetic monobactam antibiotic that has excellent activity against aerobic gram-negative bacilli. It can be used as a single agent for the treatment of upper urinary tract infections caused by organisms resistant to the cephalosporins and ampicillin. It also can be administered in combination with a drug such as clindamycin for treatment of pelvic inflammatory disease or postoperative pelvic infections.

Aztreonam↗
PubMed1992

Assessment of rapid identification tests for genital carriage of group B streptococci.

OBJECTIVE: The purpose of this study was to assess the relative value of reported methods for rapid identification of group B streptococcal colonization of the female genital tract. DATA SOURCES: Trials of group B streptococcal identification techniques published in peer-reviewed journals were located using a computerized literature search and cited references from relevant articles or text chapters. METHODS OF STUDY SELECTION: Reports were included in the analysis if the methodology fulfilled the following criteria: 1) A reference culture method was used for comparison; 2) performance characteristics were presented or could be calculated; 3) the method could be performed in a standard laboratory on a 24-hour-a-day basis; and 4) results could be routinely available within 12 hours. DATA EXTRACTION AND SYNTHESIS: Performance characteristics such as sensitivity, specificity, and predictive values for the various methods were evaluated and compared. Factors such as colonization rates and methods for identifying carriers were included in the overall assessment of test performance. CONCLUSIONS: The overall sensitivity of current methods for the rapid detection of group B streptococcal colonization is low. However, some rapid antigen detection tests are highly sensitive in identifying heavily colonized patients, and therefore may be useful for selecting high-risk patients for intrapartum antibiotic prophylaxis.

Cervix Uteri↗
PubMed1991

Crystals of a ternary complex of human immunodeficiency virus type 1 reverse transcriptase with a monoclonal antibody Fab fragment and double-stranded DNA diffract x-rays to 3.5-A resolution.

Two crystal forms of complexes have been grown that contain human immunodeficiency virus type 1 reverse transcriptase and a monoclonal antibody Fab fragment. One of the crystal forms (form II, space group P3112, a = 168.7 A, c = 220.3 A) diffracts x-rays to 3.5-A resolution and appears suitable for moderate-resolution structure determination. The form II crystals have the unusual property that their maximum resolution of diffraction and resistance to radiation damage are enhanced by either crystallization in the presence of or soaking with double-stranded DNA primer-template mimics. These crystals may permit structural studies of catalytically relevant complexes and eventually enable us to experimentally observe successive steps in the reverse transcription process.

Antibodies, Monoclonal↗
PubMed1991

Ultrastructural changes in the nucleolus of facial motor neurons following axotomy during an early critical period in development.

In this study, the effects of axotomy on the ultrastructure of the nucleolus and associated organelles were examined in fetal, newborn, and early postnatal facial motoneurons of the hamster. Golden hamsters used for this study were the 14-day fetus, newborn (0 days; less than 6 hr) and 2, 4, 7, and 9 days postnatal ages, with 3 animals per group. For prenatal surgeries, pregnant hamsters were anesthetized and the facial nerves severed in the fetuses via electrocautery through the uterine wall and amniotic membrane. For postnatal surgeries, the animals were anesthetized and the right facial nerve exposed and severed at its exit from the stylomastoid foramen. At the appropriate postoperative times, the animals were reanesthetized and perfused-fixed. The facial nuclear groups were dissected and processed for routine electron microscopy. Microbody and coiled body frequencies were determined from the number of neurons containing these structures per number of neurons sampled per animal in each experimental or control group and subjected to statistical analysis. Nucleolar reactive changes that occurred during this developmental sequence fell into two major categories. The first category displayed by most injured cells consisted of an initial compacting of fibrillar material and reduction in vacuolar space. The second category appeared to represent a progression from this first stage of nucleolar reactivity into degenerative changes involving a striking segregation of nucleolar components into five distinct regions. The incidence of microbodies increased as a result of axotomy, whereas the presence of coiled bodies decreased at the later postoperative stages in the older animals. With increasing age and nucleolar maturation, the nucleolar reactive pattern became less pronounced and severe, and neuronal survival predominated. It appears, therefore, that the two categories of nucleolar changes following axotomy during early development correlate with changes observed in nucleoli under conditions of rRNA downregulation. It is hypothesized from these results that a key step in the ability of neurons to survive axotomy and successfully regenerate at these early developmental stages occurs at some point in ribosomal RNA transcription and/or processing. Complementary information at the molecular level concerning changes in nucleolar synthetic activity and ribosome production will be necessary to test this hypothesis.

Animals↗
PubMed1991

Phase I immunotoxin trial in patients with B-cell lymphoma.

Fifteen patients with refractory B-cell lymphoma were treated in a Phase I dose escalation clinical trial with a highly potent immunotoxin consisting of the Fab' fragment of a monoclonal anti-CD22 antibody (RFB4) coupled to chemically deglycosylated ricin A chain. All patients had low, intermediate, or high grade non-Hodgkin's lymphoma. The immunotoxin was administered i.v. in two to six doses at 48-h intervals. The peak serum concentration and the t1/2 were not dose dependent among patients and averaged 1.3 micrograms/ml and 86 min, respectively. Three patients made antibody against A chain, and a fourth made antibody against both A chain and mouse immunoglobulin. Antibody responses were low (less than or equal to 85 micrograms/ml) in three patients and were not detected until 1 mo after treatment. The maximum tolerated dose of the immunotoxin was 75 mg/m2. Dose-related toxicities included vascular leak syndrome, fever, anorexia, and myalgia. Dose-limiting toxicities included pulmonary edema and/or effusion, expressive aphasia, and rhabdomyolysis (resulting in reversible kidney failure). There was no evidence of liver dysfunction. Partial responses were achieved in 38% of evaluable patients, and in those patients who had greater than 50% CD22+ tumor cells, 50% of the patients achieved a partial response. Clinical responses were not related to tumor grade and were generally transient, lasting between 1 and 4 mo.

Adult↗
PubMed1991

Myeloablative therapy with autologous bone marrow transplantation as consolidation of remission in patients with follicular lymphoma.

A study has been in progress since June 1985 to evaluate the use of myeloablative therapy (cyclophosphamide [60 mg/kg x 2] and total body irradiation [200 cGy x 6]) followed by reinfusion of autologous bone marrow in patients in second or subsequent remission of B-cell non-Hodgkin's lymphoma. The marrow mononuclear cell fraction is being treated in vitro with three cycles of the monoclonal antibody anti-CD20 (anti-B1, Coulter Immunology) and baby rabbit complement (Pel-Freez). Thirty-eight patients with follicular lymphoma (age range 29-61 years, median 43) have been treated to date. At the time of treatment, 28 patients were in second remission, 7 were in third, and 3 were in more than third remission. Twenty-three patients were in complete remission, 15 had residual disease (7 had lymph nodes less than 2 cm diameter, 4 had less than 10% bone marrow infiltration, 1 had involvement of lymph nodes and bone marrow, and 3 had involvement at other sites). Of the 38 study patients, 32 are alive; 6 have died, 4 in remission. Two of the deaths were treatment related: 1 resulted from cerebral haemorrhage at 29 days; 1 resulted from systemic fungal infection at three months). One patient died from secondary acute myelogenous leukaemia at four years, and another from an unrelated cause. Two patients died following relapse. The median time to engraftment was 28 days (range 15-45 days) for neutrophils greater than 0.5 x 10(9)/L and 28 days (range 15-46 days) for platelets greater than 20 x 10(9)/L.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Location of abnormalities in panoramic radiographs of edentulous patients.

A series of 308 panoramic radiographs of edentulous patients was examined for the presence of pathoses to determine whether any predictive basis could be found for occurrence of abnormalities by sex, age, or location. Radiolucencies, radiopacities, and retained roots and teeth were recorded by size and by anterior or posterior location in edentulous jaws. Radiopacities were the most frequently found abnormality (18% of subjects), followed by retained roots (8%), radiolucencies (3%), and retained teeth (3%). No significant correlation was found by chi-square test between type or location of abnormality and sex of the patient. There was, however, a significant relationship between location and type of abnormality. Radiopaque and radiolucent lesions were more frequently found in the mandible, and unerupted teeth and retained roots were more frequently seen in the posterior maxilla. Selective radiographs to detect retained roots and unerupted teeth in the posterior maxilla may be most productive in terms of prosthodontic treatment outcome. Otherwise, this study finds no basis for selection of intraoral sites for specific intraoral radiographs of asymptomatic edentulous patients.

Aged↗