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Biomedical subjects

H F Thomas

Publications and source records attributed to H F Thomas.

11 recordsLinked to original sources
PubMed1992

Investigation of the role of Von Korff fibers during murine dentinogenesis.

The existence and significance of Von Korff fibers during early dentinogenesis are still very controversial. The purpose of the present study was to re-examine the questions of the existence, nature and significance of Von Korff's fibers using light microscopy and immunohistochemistry. Specimens were obtained from 3 days-old CD-I mice and mandibles were carefully dissected under constant irrigation and immediately fixed in 10% neutral buffered formalin for light microscopy. Sections were treated or not with collagenase prior to silver staining. For immunohistochemistry, specimens were fixed in 95% ethanol and embedded in paraffin. Sections were reacted with goat anti-human-bovine type I or type III collagen and a rhodamine (RITC) labelled rabbit anti-goat IgG was then reacted as a secondary antibody. Slides were then examined under a Zeiss II photomicroscope equipped with epifluorescence. Our results have confirmed the presence of argyrophilic material concentrated at the periphery of the dental papilla and stretching from the subodontoblastic layer to the future dentino enamel junction. The distribution of type III collagen was very similar to the distribution of the silver staining at the cervical loop area. Type I collagen distribution was different and concentrated in areas where odontoblasts were fully differentiated. Our study showed that Von Korff fibers are not artefactual. We have established the presence of an apical compartment containing type I collagen fibers and a basal compartment containing type III collagen to explain the image of continuous silver staining crossing the entire thickness of the odontoblast layer.

Animals↗
PubMed1979

Nitrous acid mutagenesis of duplex DNA as a three-component system.

Purified native Hemophilus influenzae DNA is relatively insusceptible to nitrous acid (NA) mutagenesis in vitro, but is readily mutated following denaturation. NA mutagenicity for duplex DNA is significantly increased in the presence of various alcohols, glycols, phenols or primary amines. Phenol-extracted DNA contains dissociable contaminants of low molecular weight that enhance NA mutagenesis. Enhancement of NA mutagenesis by phenol and by spermine is due to the formation of unstable molecular species. We propose that reactive organic nitroso compounds are formed which then serve as delivery vehicles to promote mutagenicity of native DNA, perhaps via transnitrosation reactions. Similar reactions probably occur in vivo to promote NA-induced base substitution (but not frameshift) mutations in Salmonella typhimurium and in Escherichia coli. The possible significance of these observations to carcinogenesis is discussed.

DNA, Bacterial↗
PubMed1979

Aryl-monoalkyl and cyclic triazenes: direct-acting mutagens.

An aryl-monoalkyl triazene, methyl-p-tolyl triazene (MTT) and a cyclic triazene (delta2-triazoline) are direct-acting mutagens for Salmonella typhimurium bacteria and for cell-free Hemophilus influenzae DNA. MTT causes reversion of the hisG46 base-substitution mutation, but no reversion of the hisD3052 frameshift mutation. Induced mutation frequency is not strongly influenced by modifications in the genetic background of the S. typhimurium Ames tester strains, but is mildly enhanced by the addition of a pool of amino acids to the plating medium and is strongly enhanced by liquid preincubation before plating.

Base Sequence↗
PubMed1979

The extent of the odontoblast process in human dentin.

Impacted human third molar teeth were examined, both with the light and electron microscope, to determine the extent of the odontoblast process. The odontoblast process was found to be limited to the inner third of coronal dentin and inner half of mid-root dentin.

Adult↗
PubMed1977

The hazard of old lead mines in Wales.

Two population surveys were conducted near old lead workings in Wales. The first, at Y Fan in the middle of Wales, gave evidence suggestive of a gradient in blood lead level, highest in subjects resident close to the contaminated spoil heaps, and lowest in those who lived in farms some distance away. However, the gradient was significant (P less than 0.05) only in males, and all but one of the blood lead levels were below 2.0 mumol/l. In the second survey, at Halkyn in North Wales, levels in subjects living in the area contaminated by spoil were compared with those in subjects living in a nearby industrial area, and with subjects in a market town some distance away. Mean blood lead in people living in the three areas were homogeneous. These studies give no evidence that old lead workings in Wales are a serious hazard to health.

Adult↗