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Biomedical subjects

J Knowles

Publications and source records attributed to J Knowles.

67 records · Page 4Linked to original sources
PubMed1980

Genetic interactions in the control of mitochondrial function in Paramecium. II. Interactions between nuclear and mitochondrial genomes.

In an attempt to understand the genetic interactions between nuclear and mitochondrial genomes leading to mitochondrial biogenesis, different combinations of known nuclear and mitochondrial mutations have been constructed by microinjection. Eleven different tetrazolium resistant mutant strains, many clearly affecting mitochondrial function, were injected with mitochondria from four different erythromycin resistant mitochondrial mutants. Cases were found in which mutant mitochondria were unable to replicate in tetrazolium resistant mutants. The successful mitochondrial transfers were characterized for growth rate, temperature and cold sensitivity. Several selected combinations were characterised also for cytochrome spectra and cyanide resistance. Many different phenotypes were produced by the interaction of the different nuclear and mitochondrial mutations. These ranged from a positive interaction in which mutant mitochondria were selected by a nuclear mutant in preference to wild-type, through apparent absence of interaction, to negative interaction in which the mitochondrial-nuclear combination was temperature sensitive even though both 'parents' were thermoresistant. The possible molecular basis of these interactions is discussed.

Animals↗
PubMed1980

Comparison of results following three modalities of periodontal therapy related to tooth type and initial pocket depth.

Results following three modalities of periodontal therapy (subgingival curettage, modified Widman flap surgery, and pocket elimination or reduction surgery) in 78 patients over 8 years were compared for variations in pocket depth and clinical attachment level related to tooth types (maxillary molars, mandibular molars, maxillary biscupids, mandibular biscupids, maxillary anterior teeth, mandibular anterior teeth). The analysis was based on a classification of three severity groups according to initial crevice or pocket depth (Class I, 1-3 mm; Class II, 4-6 mm; and Class III, 7-12 mm) and with patient's means of measurements being the experimental units for the statistical analysis. Reduction in pocket depth and gain of clinical attachment for pockets 4 mm or deeper occurred following all three methods of treatment, and was well sustained over 8 years. No one modality of treatment was consistently superior to any of the other two with regards to sustained reduction of pocket depth and gain of clinical attachment. Surgical pocket elimination or reduction did not enhance the prognosis for maintenance of periodontal support in either moderate or advanced periodontal lesions anywhere in the mouth compared with more conservative modalities of treatment. In spite of prophylaxis and instruction in home care every 3 months, there was a slight progressive loss of attachment over time in areas of shallow crevices (1-3 mm).

Bicuspid↗
PubMed1979

Ultrastructure of intermediate lobe of the pituitary and melanocyte-stimulating hormone secretion in oestrogen-induced kidney tumours in male hamsters.

One group of male Syrian hamsters was killed after various periods of diethylstilboestrol (DES) treatment, ranging from 6 to 36 weeks. All developed renal tumours by 24 weeks. DES also induced hyperplastic and neoplastic changes in the pars intermedia of the pituitary with proliferation of MSH-secreting cells and elevated serum MSH concentration. Another group of male Syrian hamsters was given DES for 36 weeks followed by cessation of hormone treatment. The animals were killed at various intervals from 12 to 36 weeks after DES withdrawal. In these animals the DES-induced renal tumours underwent regression whilst the pituitary changes persisted until the termination of the experiment. The findings suggested that the hormone MSH may be implicated in renal carcinogenesis but plays no role in the maintenance of the established tumours.

Animals↗
PubMed1979

A reappraisal of the effects of ACTH on the response of the central nervous system to injury.

ACTH possesses powerful immuno-suppressive properties and also retards healing by inhibiting fibroblast proliferation and the deposition of collagen. In the present work this hormone was used to test both the 'barrier' and 'immune' hypotheses relating to the failure of CNS regeneration after injury, dosages being administered which had been found to stimulate maximal adrenal production of glucocorticoids in control animals. Although the scarring in the CNS and the systemic humoral and cellular immune responses were significantly depressed, no increase in CNS axon growth was noted, even when large doses of thyroxine were added. We conclude that both 'immune' and 'barrier' hypotheses should be rejected, and that the beneficial effects of thyroxine treatment reported by some workers are not substantiated.

Adrenocorticotropic Hormone↗
PubMed1978

Effect of oestrogen on the pituitary gland of male Syrian hamsters. I. Electron microscope studies of pars intermedia.

The ultrastructure of the pars intermedia of normal and oestrogen-treated male Syrian hamsters is described. 3 types of cell were observed in normal gland, namely, 2 types of "light" cell and a "dark" cell. Light cells were regular in shape with round or oval nuclei and could be divided into type 1 and 2 by the size of their granules 200 to 250 nm in type 1 and 100 to 150 nm in type 2. Dark cells were fewer in number, irregular in outline with highly-indented chromatin-rich nuclei and occasional secretory granules in the Golgi area. Treatment for 6 weeks with diethylstibestrol (DES) 0.6 mg in 0.2 ml distilled water subcutaneously 3 times per week failed to induce recognisable change in the pars intermedia although after 12 weeks treatment cytoplasmic changes were observed. From that time until the experiment ended after 30 weeks of treatment progressive changes indicative of enhanced synthesis of hormone were present, greater cytoplasmic volume, hypertrophy of the Golgi apparatus, marked development of endoplasmic reticulum and ribosomes, increased numbers of secretory granules and the presence of granules within granules.

Animals↗
PubMed1976

Experimental contribution to the pathogenesis of spina bifida.

Reopening of the central canal in 3-day-old chick embryos results in the development of a typical myeloschisis within 5 min. Focal continuity between the ectoderm and neural tissue at the site of experimentally induced spina bifida (SB) may be achieved in 2 hr and increases in consecutive hours. In 24 hr a secondary neuro-ectodermal junction at the site of SB is fully formed and can be misinterpreted as evidence of a failure of the neural tube to close. Therefore the continuity between ectoderm and neural tube to close. The detachment of the notochord from the open portion of the spinal cord is a secondary phenomenon.

Animals↗