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Biomedical subjects

M M Walker

Publications and source records attributed to M M Walker.

At least 73 records · Page 4Linked to original sources
PubMed1989

Conditioning analysis of magnetoreception in honeybees.

A central problem in the study of magnetic sensitivity in animals has been the lack of behavioral techniques sufficiently powerful for the systematic psychophysical work required for an understanding of magnetosensory capacity and of the transduction mechanism. In recent experiments, free-flying honeybees have been conditioned to discriminate the presence and absence of localized magnetic dipole anomalies superimposed on the uniform background field of the earth. The results obtained thus far suggest that movement is necessary for conditioned responding to magnetic field stimuli and support the hypothesis that magnetic field transduction is based on single-domain particles of magnetite found in the anterodorsal abdomen of honeybees.

Animals↗
PubMed1989

Campylobacter pylori in esophagus, antrum, and duodenum. A histological and microbiological study.

Two hundred forty-six patients with a wide range of upper gastrointestinal tract disorders were investigated for the presence of Campylobacter pylori infection in esophagus, gastric antrum, and duodenum. C. pylori was identified in 52% of patients in at least one site, and microbiological and histological techniques were used to exclude the presence of the organism. Esophageal infection was not significant and is probably due to reflux. Antral C. pylori was significantly associated with active gastritis and active duodenitis and is possibly pathogenic.

Adolescent↗
PubMed1989

Hemoglobin induction by Ara-C in human erythroleukemic cells (K562) is cell-cycle dependent.

This study was undertaken to answer the question of whether chemical induction of hemoglobin in the human erythroleukemic line K562 is cell-cycle dependent. Cells were synchronized with respect to the cell cycle by manipulation of culture conditions. S phase was detected microscopically by immunofluorescent staining. Hemin and arabinofuranosylcytosine (Ara-C) were used to induce hemoglobin synthesis in K562 cells. The action of hemin causes induction without specificity in regard to cell cycle phase, while Ara-C is dependent upon cell cycle phase, with cells within late G1 and early S phases being sensitive to the effect of the agent. These studies also confirm the results that the action of hemin is reversible but the induction caused by Ara-C is irreversible. The synergistic effects of these two inducing agents resulted in a sharper rise in the percentage of induced cells.

Cell Cycle↗
PubMed1989

The role of Chlamydia trachomatis in chronic abacterial prostatitis: a study using ultrasound guided biopsy.

We studied 50 patients with chronic abacterial prostatitis as defined by the Stamey procedure via transrectal prostatic ultrasound and subsequent transperineal biopsy of the abnormal areas of the prostate to ascertain the role of Chlamydia trachomatis organisms (chlamydiae) in this condition. Chlamydiae were detected by an immunofluorescence technique in the urethra of 1 patient (2 per cent) but they were not recovered in McCoy cell culture from the prostatic tissue of any patient nor were they detected in the tissue by immunofluorescence. In addition, serum antibody to Chlamydia trachomatis was not found even in moderate titer. The approach in this study has overcome the problem of urethral contamination in the assessment of prostatic specimens from patients with chronic abacterial prostatitis. There is no evidence that chlamydiae are directly implicated in the disease, although the possibility of an earlier active role cannot be excluded.

Adult↗
PubMed1989

Painful bladder syndrome--a clinical and immunopathological study.

Painful bladder syndrome is a clinical diagnosis in patients with symptoms of varying severity which always include frequency and suprapubic pain and occasionally include dysuria, nocturia and urgency persisting for more than 3 months with no loss of bladder capacity and no overt infection. Immunofluorescence studies of biopsy specimens in 38 female patients were assessed and correlated with the duration and severity of symptoms, and also with routine histology (including mast cell infiltration and integrity of the glycosaminoglycans layer), in order to assess the role of immunological mechanisms in this distressing condition. The results indicated that submucosal angiogenesis and persistence of antigen-antibody complex in vessel walls could be responsible for this syndrome.

Adolescent↗
PubMed1989

A search for infectious agents in chronic abacterial prostatitis using ultrasound guided biopsy.

A series of 60 patients with a diagnosis of chronic abacterial prostatitis, as defined by the Stamey procedure, was studied by transrectal prostatic ultrasound and subsequent transperineal biopsy of the abnormal areas of the prostate in order to ascertain the role of micro-organisms in this condition. Histological assessment revealed a chronic inflammatory infiltrate, generally of low grade, in 53 patients (88%). Organisms were isolated from the prostatic tissue of only 9 patients (15%) and were considered to be contaminants from the perineal skin, since treatment with an appropriate antimicrobial agent failed to alter symptoms or affect the leucocyte count in the urine or prostatic fluid. Chronic abacterial prostatitis may be a non-organismal inflammatory process.

Adult↗
PubMed1989

Recognising covert disease in women with chronic vulval symptoms attending an STD clinic: value of detailed examination including colposcopy.

A vulval colposcopy clinic was established in the sexually transmitted diseases (STD) clinic of St Mary's Hospital, London, to investigate patients with chronic symptoms (mean duration 3 1/2 years). Fifty patients with a mean age of 33 were studied for 12 months, and a specific diagnosis was established for many of them. Forty complained of pruritus vulvae, 33 of dyspareunia, and 30 of vulvodynia. One or more macroscopic abnormality was seen in 29 of the women, the most common being erythema, papules, plaques, and fissures. Colposcopic abnormalities, however, were identified in 45 of the women, the most common being acetowhite epithelium in a flat, papillary, or cobblestone pattern. Biopsy specimens were obtained from 33 of the patients, and all had abnormal histological features. Those of human papillomavirus (HPV) infection were the most common, and were found in 27 specimens; evidence of vulval intraepithelial neoplasia was seen in seven and that of dermatoses in 10. Further work is required, however, before concluding that HPV was necessarily responsible for the chronic symptoms.

Adult↗
PubMed1988

Ultrastructure, morphology and organization of biogenic magnetite from sockeye salmon, Oncorhynchus nerka: implications for magnetoreception.

Although ferromagnetic material has been detected in the tissues of a variety of animals that are known or suspected to respond to magnetic fields, in only a few cases has the material been identified and its suitability for use in magnetoreception been determined. Using high-resolution transmission electron microscopy (HRTEM), we have studied magnetic particles isolated from ethmoid tissue of the sockeye salmon, Oncorhynchus nerka. Low-magnification electron micrographs showed chains containing up to 58 (median = 21-25) electron-dense particles that were held together by intimately attached organic material. The particle size range was 25-60 nm with a mean of 48 nm and a standard deviation of 8.5 nm. Elemental analysis, by energy-dispersive X-ray analysis (EDXA), electron diffraction patterns and HRTEM lattice images, showed that many of the particles were structurally well-ordered and crystallographically single-domain magnetite. These results imply that the production of the biomineral is under precise biological control. The crystal morphology was cubo-octahedral with the (111) faces of adjacent crystals lying perpendicular to the chain axis. The magnetic moments of the particles will therefore be aligned along the chain axis and will sum to produce a total moment dependent on the number of particles present in each chain. In the presence of the geomagnetic field, the mean moment for the particles will give a magnetic to thermal energy ratio of about 0.2. The corresponding calculations for individual chains gave two clusters of ratios ranging between 2.7 and 5.3 and between 6.6 and 9.5. The implications of these results in the possible use of the particles in magnetoreception are discussed.

Animals↗
PubMed1988

Production of single-domain magnetite throughout life by sockeye salmon, Oncorhynchus nerka.

Although single-domain particles of biogenic magnetite have been found in different species of pelagic fishes, nothing is known about when it is synthesized, or about whether the time during life when it is produced is correlated with the development of responses to magnetic field stimuli. We have investigated production of biogenic magnetite suitable for use in magnetoreception in different life stages of the sockeye salmon, Oncorhynchus nerka (Walbaum). Sockeye salmon were chosen because responses in orientation arenas to magnetic field stimuli have been demonstrated in both fry and smolt stages of this species. We found significant quantities of single-domain magnetite in connective tissue from the ethmoid region of the skull of adult (4-year-old) sockeye salmon. The ontogenetic study revealed an orderly increase in the amount of magnetic material in the same region of the skull but not in other tissues of sockeye salmon fry, yearlings and smolts. The physical properties of this material closely matched those of magnetite particles extracted from the ethmoid tissue of the adult fish. We suggest that single-domain magnetite particles suitable for use in magnetoreception are produced throughout life in the ethmoid region of the skull in sockeye salmon. Based on theoretical calculations, we conclude that there are enough particles present in the skulls of the fry to mediate their responses to magnetic field direction. By the smolt stage, the amount of magnetite present in the front of the skull is sufficient to provide the fish with a magnetoreceptor capable of detecting small changes in the intensity of the geomagnetic field. Other tissues of the salmon, such as the eye and skin, often contained ferromagnetic material, although the magnetizations of these tissues were usually more variable than in the ethmoid tissue. These deposits of unidentified magnetic material, some of which may be magnetite, appear almost exclusively in adults and so would not be useful in magnetoreception by young fish. We suggest that tissue from within the ethmoid region of the skull in pelagic fishes is the only site yet identified where magnetite suitable for use in magnetoreception is concentrated.

Aging↗
PubMed1987

Immunochemical detection of cell cycle synchronization in a human erythroleukemia cell line, K562.

Cells of the human erythroleukemic line K562 can be induced by manipulation of culture conditions to arrest within the G1 phase of the cell cycle, and subsequently to enter S phase synchronously after release from G1. Cell cultures subjected to serum deprivation and hydroxyurea (HU) treatment demonstrated less than 5% of the cells to be in S phase. Four hours after release from HU, 63% of the cells were in S phase, as detected by immunofluorescent staining. This protocol offers a method for synchronization of K562 cells at the G1/S border and a technique for detection of S-phase cells without the use of radioisotopes or flow cytometry instrumentation.

Cell Cycle↗