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Biomedical subjects

B R Laurence

Publications and source records attributed to B R Laurence.

At least 19 recordsLinked to original sources
PubMed2003

Comparative pulmonary toxicity assessment of single-wall carbon nanotubes in rats.

The aim of this study was to evaluate the acute lung toxicity of intratracheally instilled single-wall carbon nanotubes (SWCNT) in rats. The lungs of rats were instilled either with 1 or 5 mg/kg of the following control or particle types: (1) SWCNT, (2) quartz particles (positive control), (3) carbonyl iron particles (negative control), (4) phosphate-buffered saline (PBS) + 1% Tween 80, or (5) graphite particles (lung tissue studies only). Following exposures, the lungs of PBS and particle-exposed rats were assessed using bronchoalveolar lavage (BAL) fluid biomarkers and cell proliferation methods, and by histopathological evaluation of lung tissue at 24 h, 1 week, 1 month, and 3 months postinstillation. Exposures to high-dose (5 mg/kg) SWCNT produced mortality in ~15% of the SWCNT-instilled rats within 24 h postinstillation. This mortality resulted from mechanical blockage of the upper airways by the instillate and was not due to inherent pulmonary toxicity of the instilled SWCNT particulate. Exposures to quartz particles produced significant increases versus controls in pulmonary inflammation, cytotoxicity, and lung cell parenchymal cell proliferation indices. Exposures to SWCNT produced transient inflammatory and cell injury effects. Results from the lung histopathology component of the study indicated that pulmonary exposures to quartz particles (5 mg/kg) produced dose-dependent inflammatory responses, concomitant with foamy alveolar macrophage accumulation and lung tissue thickening at the sites of normal particle deposition. Pulmonary exposures to carbonyl iron or graphite particles produced no significant adverse effects. Pulmonary exposures to SWCNT in rats produced a non-dose-dependent series of multifocal granulomas, which were evidence of a foreign tissue body reaction and were nonuniform in distribution and not progressive beyond 1 month postexposure (pe). The observation of SWCNT-induced multifocal granulomas is inconsistent with the following: (1) lack of lung toxicity by assessing lavage parameters, (2) lack of lung toxicity by measuring cell proliferation parameters, (3) an apparent lack of a dose response relationship, (4) nonuniform distribution of lesions, (5) the paradigm of dust-related lung toxicity effects, (6) possible regression of effects over time. In addition, the results of two recent exposure assessment studies indicate very low aerosol SWCNT exposures at the workplace. Thus, the physiological relevance of these findings should ultimately be determined by conducting an inhalation toxicity study.

Alkaline Phosphatase↗
PubMed1988

The tropical African latrine blowfly, Chrysomya putoria (Wiedemann).

The status of the tropical African latrine blowfly Chrysomya putoria (Wiedemann, 1830) is recognized as distinct from the sub-tropical African blowfly C.chloropyga (Wiedemann, 1818) (Diptera: Calliphoridae). The biology of C.putoria in laboratory culture is described briefly with emphasis on the differences in development found in three strains of this species from Tanzania, Liberia and Brazil. All three strains were reproductively compatible and there was no evidence of F1 hybrid sterility or hybrid breakdown in subsequent generations. Larval development was significantly faster in the Brazilian strain than in the strain from Tanzania. Sexual maturity was significantly faster in adults of the Liberian and Brazilian strains compared to that found in the strain from Tanzania. This latter strain was affected by the source of protein available as adult food. These differences between strains did not appear to be due to selection in laboratory culture, but rather evidence of the evolution of physiological divergence within a species occupying different geographical regions.

Animals↗
PubMed1986

Old world blowflies in the new world.

Human activity, particularly migration and the export of live animals, can provide vehicles for the dispersal of many parasites and their vectors. These movements, often overlooked until too late, provide potential for epidemic outbreaks and can profoundly alter accepted ideas on the geographic distribution and epidemiological status of particular species. In this review, Brian Laurence discusses the recent rapid spread of blowflies into the americas; these conspicious green flies transport a variety of gastro-intestinal pathogens between their favoured environments of latrines and exposed food, and some species are important parasites of flesh wounds, causing cutaneous myiasis.

Journal Article↗
PubMed1979

Incorporation of radioactive precursors into filarial larvae of Brugia developing in susceptible and refractory mosquitoes.

The incorporation of tritiated precursors injected into mosquito hosts parasitized by developing filarial larvae of Brugia patei has been studied by autoradiography in 2 species of mosquito, Aedes togoi in which filarial development was normal and Anopheles labranchiae atroparvus in which filarial development was abnormal. In both mosquito hosts there was significant incorporation into 4--5-day-old developing larvae of uridine and amino acids (isoleucine, leucine, valine, arginine, lysine, cystine, methionine, phenylalanine, tyrosine, tryptophan, histidine, and proline), although lower incorporation of methionine, tyrosine, and tryptophan was found during abnormal development. No incorporation of thymidine, hydroxytryptophan, dopa, or carbohydrate was found at this stage of larval development. Some incorporation of glucose and dopa was found in or around earlier stages of development in An. l. atroparvus. Mosquito flight muscle showed lower incorporation of glucose, but not of amino acids, around the site of filarial parasite development. The flight muscle of An. l. atroparvus showed a higher level of incorporation of lysine compared to that in A. togoi and higher levels of lysine and valine were found in the abnormally developing filarial larvae in the refractory mosquito.

Aedes↗
PubMed1978

Development of the calyx and lateral oviduct during oogenesis in Aedes aegypti.

The lateral oviduct and calyx of nulliparous Aedes aegypti on a sucrose diet are both flattened sacs, lacking a well defined lumen. Both are formed of an inner epithelial and an outer muscular layer, each one cell thick. The lateral oviduct is surrounded by a circular muscle sheath which is continuous with the ovarian sheath. Each ovariolar sheath is continuous with the outer layer of the calyx. The structure of both the lateral oviduct and the calyx is greatly modified after the initial blood meal. A distinct lumen develops; there is an extensive development of the outer muscular layers, and the inner epithelial layers become invaginated forming deep crypts lined with extensive microvilli. The follicular stem, which joins the primary follicle to the calyx in each ovariole, is not hollow and does not mark the opening into the calyx through which the mature egg can pass. The eggs gain access to the oviductal system after the calyx extends around the follicular epithelium of the primary follicle, when breaks appear in the calyx wall opposed to the follicular epithelium, until the mature eggs, eventually lie in a highly distended thin-walled sac of calyx from which they have direct and easy access to the lateral oviduct. After oviposition, this sac contrasts to occupy once more a compact axial position in the ovary. Remnants of the follicular epithelium, containing many lysosomes are attached to the calyx at this time.

Aedes↗
PubMed1978

Loss of filarial larvae in a natural mosquito population.

Analysis of log normal parasite densities of Wuchereria bancrofti in the mosquito Culex pipiens fatigans collected in the suburbs of Colombo, Sri Lanka, has shown a decreasing parasite load with age of infection. The median density of microfilarial intake in the natural population was 10.3, but this had decreased to 2.6 by the infective stage. Of the total microfilariae ingested, 51.9% were found in the thorax 12--17 hours after infection of the mosquitoes in the laboratory. Further decrease in parasite density during development could not be attributed to filarial mortality in the mosquito but could be accounted for by increasing mosquito mortality dependent on the density of parasite infection. Dissection of recently blood-fed house-resting mosquitoes gave a prevalence rate of 7% microfilarial carriers in the human population compared to a rate of 4% by routine blood-filming.

Animals↗