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Biomedical subjects

D Brown

Publications and source records attributed to D Brown.

At least 1,009 records · Page 56Linked to original sources
PubMed1981

Stability of poliovirus RNA in cell-free translation systems utilizing two initiation sites.

The stability of purified poliovirus RNA in cell-free translation systems prepared from HeLa cells or rabbit reticulocytes has been examined. Degradation of the RNA occurs with a t1/2 of approximately 35 min at 30 degrees C under conditions used for in vitro translation. Degradation is due in part to activity in the cell lysate, and in part to contaminants in the commercial preparations of creatine phosphokinase used in the energy-regenerating system. Addition of crude preparations of initiation factors significantly slows degradation, presumably as a result of protein-RNA interactions which confer resistance to nuclease action. Prior treatment of RNA with methylmercury hydroxide has no effect on degradation rates. On the other hand, endogenous mRNA, present as a messenger ribonucleoprotein particle in extracts from poliovirus-infected HeLa cells, remains completely intact during in vitro translation. These infected cell extracts synthesize the normal complement of viral proteins and utilize two different initiation sites for translation. Treatment of the infected cell extract with micrococcal nuclease destroys the endogenous mRNA. Subsequent addition of exogenous RNA to the same extract results in the formation of a protein-associated RNA particle with sedimentation properties slightly different from the endogenous messenger ribonucleoprotein, and the added RNA is unstable. We conclude that two initiation sites can be utilized on intact poliovirus mRNA, and fragmentation of the RNA is not prerequisite for generation of a second site in this RNA.

Kinetics↗
PubMed1981

Epidemiology of antibiotic-associated colitis; isolation of Clostridium difficile from the hospital environment.

Clostridium difficile is the most important cause of antibiotic-associated colitis. Using selective media, it was found that contamination with this organism was common in the environment of patients in the hospital with the disease. It was often found on floors, hoppers, toilets, bedding, mops, scales and furniture. This organism was also present on these items, but less often, in areas in which patients known to carry this hardy spore-forming organism had not been detected. Air, food and walls were negative. The organism was isolated from the hands and stools of asymptomatic hospital personnel. It was also found on surfaces in a patient's home. The importance of the various sources of the organism in its spread in the hospital is not known, and further studies are needed. It is suggested that enteric isolation precautions, and careful handwashing and cleansing of potentially contaminated surfaces and objects may be worthwhile when cases of antibiotic-associated colitis are identified.

Anti-Bacterial Agents↗
PubMed1981

The visual evoked response to pattern reversal in 'normal' 6-11-year-old children.

The visual evoked response to a 7 mm (40') check using a pattern reversal stimulus was measured in 73 normal children, aged 6-11. Full pattern displacement for the right and left eye and 1/4 and 1/2 pattern displacement for the right eye were studied. The amplitudes of the N65-P95 and P95-N125 wave, together with the P95 latency, were measured. Analysis of the data showed that there was no clear relationship between the mean amplitude or latency of the evoked response and age. However, significant changes were found between linear displacement and linear age for the N65-P95 wave and there was a complex interaction for the same wave between age, sex and eye. There was a significant difference in latencies between right and left eye between the boys and the girls, with the boys having longer latencies. There are thus both age- and sex-related differences in the amplitude and latency of the N65-P95 wave in 6-11 year-old children.

Brain↗
PubMed1981

Stretch induces granule exocytosis in toad urinary bladder.

Evidence from this sections and freeze-fracture is presented showing that stretch induces a burst of exocytosis in granular cells of the toad urinary bladder epithelium. Since the role of granule exocytosis in hormonally-induced permeability changes in this tissue has not yet been clarified, we propose that the stretch factor is an important parameter to consider and standardise in future physiological and morpho-functional studies using this model transporting system.

Animals↗
PubMed1981

Heterogeneous distribution of filipin--cholesterol complexes across the cisternae of the Golgi apparatus.

The Golgi apparatus is a key element in the ordered movement of secretory polypeptides from the rough endoplasmic reticulum to the plasma membrane during secretion. It has been shown that cisternae that receive membranes from the reticulum are morphologically similar to the latter and that cisternae liberating secretory granules resemble that plasma membrane. By using an ultrastructural probe for membrane cholesterol, filipin, on freeze-fractured and thin-sectioned exocrine and endocrine pancreatic cells, we have shown that an enrichment in filipin-cholesterol complexes takes places across the stacked cisternae of the Golgi apparatus; the reticulum-related (forming) cisternae are poor in such complexes, but the secretory granule-related (maturing) cisternae contain numerous complexes. Secretory granule membrane is also richly labeled with filipin-cholesterol complexes. The heterogeneous cholesterol distribution in the membranes of the Golgi apparatus, as shown by filipin, emphasizes the polarity of this organelle, in agreement with its role in organizing the traffic of the secretory polypeptides from the rough endoplasmic reticulum to the plasma membrane.

Animals↗
PubMed1981

Isolation of Clostridium difficile from the environment and contacts of patients with antibiotic-associated colitis.

Clostridium difficile is the most important cause of antibiotic-associated colitis, but its epidemiology remains unknown. Using a selective medium for the isolation of C. difficile, cultures were obtained from the environment and contacts of hospitalized patients carrying C. difficile in their stools. In areas where carriers had diarrhea, 85 (9.3%) of 910 cultures of floors and other surfaces, especially those subject to fecal contamination, were positive. In areas where there were no known carriers, only 13 (2.6%) of 497 cultures of similar sites were positive (P less than 0.005). C difficile was isolated from hands and stools of asymptomatic hospital personnel, from sewage and soil, and from the home of a patient. Environmental isolates were toxigenic. C. difficile inoculated onto a floor persisted there for five months. Further studies are needed to document how often floor persisted there for five months. Further studies are needed to document how often C. difficile shed by patients with antibiotic-associated colitis is acquired by other persons and whether isolation precautions are capable of limiting the organism's spread.

Anti-Bacterial Agents↗
PubMed1981

Polyvinyl alcohol coating: an improvement of the freeze-fracture technique.

A modification of the freeze-fracture technique, involving the coating of tissues with polyvinyl alcohol (Vinol) prior to freezing, is described. This results in substantial improvements over the more conventional method in which material is cryoprotected and frozen in buffered glycerol alone. The high vacuum is produced more rapidly and can be better than in the absence of vinol and the speed of replica recuperation is greatly increased.

Erythrocyte Membrane↗
PubMed1981

Comparison of the cardiovascular effects of amitriptyline and zimelidine using thoracic impedance cardiography.

Twelve depressed patients were allocated to amitriptyline (7 days 75 mg nocte, increasing to 150 mg nocte) or zimelidine (100 mg nocte increasing to 200 mg nocte) in a randomized double-blind design. Cardiovascular assessment was made at pre-drug, 7 and 14 days using thoracic impedance cardiography, a non-invasive technique for measurement of both cardiac output (CO) and systolic time intervals. Neither drug significantly changed systolic time intervals. Amitriptyline 75 mg significantly reduced stroke volume (SV) (sitting P less than 0.02, standing P less than 0.01) with a similar trend at 150 mg. Zimelidine tended to increase SV. Heart rate (HR) was increased by amitriptyline 75 mg (P less than 0.02) but zimelidine induced no consistent changes in HR. Amitriptyline 75 mg in the standing data reduced CO (P less than 0.005). In contrast zimelidine 100 mg increased sitting CO (P less than 0.05) and this trend was seen at 200 mg in both sitting and standing data. The results suggest that zimelidine has low cardiotoxicity and may have a role in the treatment of depressed patients with cardiovascular disease.

Amitriptyline↗
PubMed1981

Characterization of a Nuclear Polyhedrosis Virus Isolated from Diseased Gonometa podocarpi (Lepidoptera:Lasiocampidae).

Gonometa podocarpi is an important pest of several species of pine in East Africa, and large numbers of trees in plantations in Kenya were partially or completely defoliated by the larval stage of this insect. After the infestation in the Mt. Elgon region, large numbers of dead and moribund larvae were found on the ground. Examination of extracts of these larvae demonstrated the presence of an occluded virus. Electron microscopy of purified sectioned polyhedra demonstrated the presence of virus particles containing from 1 to 12 nucleocapsids. Purification of virus particles from polyhedra was accomplished by using alkali solubilization and sucrose gradient centrifugation. Virus particles contained 15 proteins as determined by polyacrylamide gel electrophoresis. Detergent solubilization of the virus particles released polyhedra containing one major structural protein. Electron microscopy of purified virus particles and nucleocapsids demonstrated them to be similar in structure to previously recorded nuclear polyhedrosis viruses. The viral deoxyribonucleic acid was extracted and spread for electron microscopy and was determined to have a size of approximately 80 x 10 daltons.

Journal Article↗
PubMed1981

The amphibian epidermis: distribution of mitochondria-rich cells and the effect of oxytocin.

It is known that the ion-transporting capacity and the permeability to water of amphibian skins vary greatly both between and within species. Furthermore, the extent to which different skins respond to hormonal stimulation of these parameters also shows considerable inter- and intra-specific variation. As a first step towards defining a possible morphological basis for this physiological heterogeneity, we examined different regions of skins from 3 anurans, Bufo bufo, Rana ridibunda and Xenopus laevis, that are species with widely differing habitats. The mitochondria-rich cell population of the epidermis was counted and the epidermal thickness was measured. There were large differences in the mitochondria-rich cell content and in the epidermal thickness of the skins from different species and from different regions of skin from the same animal. In a second set of studies, the same morphological features were examined and, in addition, routine functional parameters were measured to monitor some transport properties of the skins used. The skins also varied considerably with respect to short-circuit current, potential difference, water permeability and sensitivity to oxytocin. Although no apparent relationship was noted between either basal or hormone-stimulated physiological parameters and the morphological features of the individual skins, the striking variation in the density of mitochondria-rich cells in amphibian epidermis merits further studies, including the use of techniques or experimental designs that allow the movement of individual species of ion across the skin to be followed.

Animals↗
PubMed1981

Testicular function in strains of mice selected for differences in gonadotrophin-induced ovulation.

Mice were selected on the basis of ovulatory responses to injections of pregnant mare serum gonadotrophin (PMSG) and human chorionic gonadotrophin (hCG). Various parameters of pituitary and gonadal function as well as responsiveness to exogenous gonadotrophins were examined in males from high induced-ovulation rate (HIOV) and low induced-ovulation rate (LIOV) lines. Testicular weight, seminal vesicle weight and plasma LH levels were lower in HIOV than in LIOV males, while plasma concentrations of FSH and testosterone did not differ. Binding of FSH, but not of LH, in the testes was significantly higher in HIOV mice. Twenty-four hours after administration of hCG, plasma testosterone levels were higher and testicular LH binding sites appeared more depleted in HIOV than in LIOV males. Production of testosterone by decapsulated testes in vitro was significantly higher in HIOV than in LIOV mice under basal conditions, as well as in the presence of LH, FSH, hCG or PMSG. It was concluded that selection for differences in gonadotrophin-induced ovulation rate produced correlated differences in the steroidogenic response of the testes to gonadotrophins and that these differences may be due to divergence in the number of gonadal FSH binding sites.

Animals↗